WO2001003170A1

WO2001003170A1 - Exposure method and device

Info

Publication number: WO2001003170A1
Application number: PCT/JP1999/003534
Authority: WO
Inventors: Taro Ogata
Original assignee: Nikon Corporation
Priority date: 1999-06-30
Filing date: 1999-06-30
Publication date: 2001-01-11
Also published as: AU4395099A

Abstract

An exposure method and device capable of restricting illuminance variations on a wafer to be caused by the transmittance variations of optical members such as a projection optical system on receiving an illuminating light and controlling a luminous exposure with high accuracy, wherein variations in transmittance with respect to an ultraviolet pulse beam (IL) of a projection optical system (PL) is predicted before an exposure operation based on exposure conditions (such as intensity of ultraviolet pulse beam (IL)), whether or not a luminous exposure with respect to a wafer (W) falls within an allowable range is judged, and, if not, an ND filter (41) for reducing the intensity of the ultraviolet pulse beam (IL) is inserted in an optical path between an ArF eximer laser light source (1) and a variable radiation attenuator (6) in an illumination optical system so that the luminous exposure is within the allowable range during an exposure operation.

Description

Description Exposure method and apparatus

The present invention relates to a lithographic apparatus for manufacturing a device such as a semiconductor device, an image pickup device (CCD or the like), a liquid crystal display device, a plasma display device or a thin film magnetic head. The present invention relates to an exposure method for transferring onto a substrate, an exposure apparatus, and a device manufacturing method. Background art

In recent years, in order to respond to the improvement in the integration and fineness of semiconductor devices, the lithography process (typically consisting of a resist coating process, an exposure process, and a resist development process) for manufacturing semiconductor devices has been performed. In the apparatus, it is required to further improve the resolution, transfer accuracy, and the like. In order to increase the resolution and transfer accuracy of the exposure apparatus, it is necessary to perform high-precision exposure dose control for exposing the resist applied on the wafer as a substrate with an appropriate exposure dose.

Conventionally, for example, the amount of illumination light branched in the illumination optical system immediately before exposure and the optical system (part of the illumination optical system and the projection optical system) arranged in the optical path from the branched position to the wafer surface The amount of exposure on the surface of jehachi was calculated from the transmittance, and the amount of exposure was controlled based on the calculation result. In a step-and-repeat type exposure apparatus (stepper), the exposure time is controlled so that the calculated integrated value of the exposure amount becomes a predetermined value, and a step-and-scan type exposure apparatus is provided. So, its calculated The output of the light source or the scanning speed was controlled so that the exposure amount became a constant value.

In addition, since the resolution of an exposure apparatus increases as the wavelength of the exposure light decreases, the wavelength of the exposure light used in the exposure apparatus has been decreasing year by year. The mainstream exposure wavelength is the KrF excimer laser at 248 nm, and the shorter wavelength ArF excimer laser at 193 nm is being put into practical use. Therefore, when ultraviolet pulse light (wavelength of about 250 nm or less) from these excimer laser light sources is used as exposure light, the glass material of the illumination optical system or projection optical system is used for the exposure. A glass material having a relatively high transmittance, for example, synthetic quartz glass (Si ₂ ) is used. As described above, in the conventional exposure apparatus, it is assumed that the transmittance and reflectivity of the optical system arranged in the optical path from the position where the illumination light is branched to the wafer surface in the illumination optical system do not fluctuate in a short time. Exposure amount control is performed based on the exposure amount on the wafer surface calculated from the amount of illumination light branched in the illumination optical system and the transmittance of the optical system measured in advance. .

However, in an exposure apparatus such as an ArF excimer laser beam, which uses ultraviolet pulsed light in a substantially vacuum ultraviolet region as exposure light, solar irradiation is generated by irradiation of the ultraviolet pulsed light. As a result, the optical constant of the synthetic quartz glass used as a glass material in the optical system or the like changes, and the transmittance may gradually decrease with the irradiation of the ultraviolet pulse light. The decrease in transmittance due to this solarization is a reversible change. When irradiation with ultraviolet pulse light is stopped, damage to the synthetic quartz glass due to the solarization is gradually recovered, and the transmittance is gradually recovered. The change rate and time constant of transmittance due to solarization vary depending on the type of glass material, and the higher the pulse energy, peak power, average power, or duty ratio of the ultraviolet pulse light, the higher the transmittance due to solarization. Rate change The change rate of becomes large and the time constant becomes short.

In addition to the solarization, for example, a trace amount of an organic substance in the atmosphere around the optical member causes a chemical reaction by ultraviolet light to produce a cloudy substance, thereby causing the transmittance or the reflectance of the optical member to change. May change.

When the transmittance or reflectance of the optical member changes over time due to the irradiation of the ultraviolet pulse light (exposure light), the amount of the illumination light branched in the illumination optical system and the transmittance of the optical system before the exposure are changed. Since the exposure light amount on the wafer surface calculated from the above is different from the actual exposure amount on the wafer surface, accurate exposure amount control becomes difficult.

In view of the above, the present invention provides an exposure method capable of preventing deterioration of exposure amount control accuracy due to a change in transmittance or reflectance of an optical member such as an illumination optical system or a projection optical system due to irradiation of exposure light. The purpose is to: Another object of the present invention is to provide an exposure apparatus capable of performing such an exposure method. Another object of the present invention is to provide a device manufacturing method capable of manufacturing a highly accurate device using such an exposure apparatus.

Disclosure of the invention

A first exposure method according to the present invention illuminates a first object (R) with illumination light from an illumination optical system (1, 6, 7A, 7B, 11 to 19), and In an exposure method for transferring a pattern onto a second object (W) via a projection optical system (PL), the transmittance or reflectance of the illumination optical system and at least a part of the optical members in the projection optical system is determined. The intensity of the illumination light is controlled so as to suppress the fluctuation amount.

According to the first exposure method of the present invention, the irradiation of the illumination light causes, for example, solarization ゃ the adhesion of a cloudy substance, and the illumination optical system or If the transmittance or reflectance of a predetermined optical member in the projection optical system fluctuates, the intensity of the illumination light and the transmittance or reflection of the optical member due to the irradiation of the illumination light are determined in advance. Measure the relationship with the rate variation. Then, for example, when exposing a layer having a high exposure amount control accuracy, the intensity of the illumination light is reduced so as to reduce the fluctuation of the transmittance or the reflectance of the optical member based on the above relationship. By controlling the illuminance, the illuminance fluctuation on the second object can be suppressed within an allowable range, and the exposure amount can be controlled with high accuracy.

Next, the second exposure method according to the present invention illuminates the first object (R) with illumination light from the illumination optical system (1, 6, 7A, 7B, 11 to 19). 1 In an exposure method for transferring a pattern of an object onto a second object (W) via a projection optical system (PL), the transmittance or transmittance of at least some of the optical members in the illumination optical system and the projection optical system The amount of change in reflectance is predicted according to the exposure process, and the intensity of the illumination light is controlled so as to suppress the predicted amount of change.

According to the second exposure method of the present invention, in the initial exposure process, the intensity of the illuminating light is large, and the variation of the transmittance or the reflectance of the predetermined optical member is expected to exceed the allowable range. In such a case, for example, the intensity of the illumination light is reduced even if the throughput is slightly reduced, so that the amount of change in the transmittance or reflectance of the optical member during exposure is reduced. Thereby, required exposure amount control accuracy on the second object can be obtained.

Next, in the third exposure method of the present invention, the first object (R) is illuminated with the illumination light from the light source (1), and the pattern of the first object is transferred onto the second object (W). In the exposure method described above, the intensity of the illuminating light is controlled so as to suppress the variation of the transmittance or the reflectance of at least some of the optical members arranged in the optical path of the illuminating light. According to the third exposure method of the present invention, for example, by the irradiation of the illumination light, the transmittance or the reflectance of the optical member arranged in the optical path of the illumination light fluctuates beyond the allowable range. In such a case, by reducing the intensity of the illuminating light, the amount of change in the transmittance or the like of the optical member can be reduced, and highly accurate exposure amount control can be performed on the second object.

Further, in the first, second, and third exposure methods of the present invention, when the illumination light is ultraviolet pulse light having a wavelength of 300 nm or less, such as ArF excimer laser light, When controlling the intensity of the illumination light, it is preferable to control the peak power or the oscillation frequency of the illumination light. The control of the peak power includes a method of indirectly controlling the power by inserting or removing an optical filter having a predetermined transmittance.

Next, the exposure apparatus according to the present invention includes an illumination optical system (1, 6, 7A, 7B, 11 to: L9) for illuminating a first object with illumination light, and the first object (R). An exposure system having a projection optical system (PL) for transferring the above pattern onto a second object (W), an intensity control system (40, 41) for controlling the intensity of the illumination light, An arithmetic control system (3) that controls the intensity of the illumination light via the intensity control system so as to suppress the amount of change in the transmittance or the reflectance of at least some of the optical members in the optical system and the projection optical system. 0) and.

According to such an exposure apparatus of the present invention, the intensity control system is provided through the intensity control system so as to suppress the variation of the transmittance or the reflectance of at least some of the optical members in the illumination optical system and the projection optical system. By controlling the illuminance of the illumination light, the first, second and third exposure methods of the present invention can be performed.

Next, in the device manufacturing method of the present invention, an exposure light from the exposure light source (1) is used to transfer an image of a predetermined circuit pattern to a substrate (W) via an optical system, and to divide the device. In a device manufacturing method for manufacturing a semiconductor device, an image of the predetermined circuit pattern is formed while controlling the intensity of the exposure light so as to suppress a variation in transmittance or reflectance of the optical system with respect to the exposure light. It is transferred onto the substrate.

According to such a device manufacturing method of the present invention, high-precision exposure amount control is performed by controlling the intensity of the exposure light so as to suppress the fluctuation amount of the transmittance or the reflectance of the optical system. As a result, high-performance devices can be obtained. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic configuration diagram showing a projection exposure apparatus used in an example of an embodiment of the present invention, with a part cut away. FIG. 2 is a diagram showing an example of a measurement result of the transmittance of the projection optical system by irradiation of the ultraviolet pulse light. Fig. 3 (a) is a diagram showing the ND filter 41 of Fig. 1, Fig. 3 (b) is a diagram showing another example of an optical filter that can be used in place of the ND filter 41, and Fig. 3 (c) is It is a figure which shows another example of the optical filter. FIG. 4 is a diagram illustrating an example of a semiconductor device manufacturing process. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an example of a preferred embodiment of the present invention will be described with reference to the drawings. In this example, the present invention is applied to the case where exposure is performed by a projection exposure apparatus of a step and scan type.

FIG. 1 shows a schematic configuration of the projection exposure apparatus of the present example.

Ultraviolet pulse light IL as the illumination light (exposure light) for exposure narrowed at a wavelength of 193 nm from the ArF excimer laser light source 1 is used to positionally match the optical path with the exposure apparatus body. Beam including a movable mirror etc. The light passes through a matching unit (BMU) 3 and enters a sub-chamber 35 containing a predetermined optical system via a cylindrical pipe 5 made of a light-shielding material. In the vicinity of the entrance in the sub-chamber 35, an ND filter for reducing the illuminance (an example of the intensity) of the ultraviolet pulse light IL is provided so that it can be inserted into and removed from the optical path by the drive mode. I have. ND Filler 41 has a stable transmittance even for ultraviolet pulsed light.

This is a filter in which a light-shielding film such as a fine metal film of several m square is distributed almost evenly so that a predetermined transmittance can be obtained with respect to the (C a F ₂ ) substrate. The transmittance of the ND filter 41 is set to be very small, for example, about 0.5 (50).

By the ND filter 41 and the drive motor 40 of this example, the transmittance for the ultraviolet pulse light IL can be largely switched between two stages of 100% and, for example, about 50%. The ND filter 41 and the drive mode 40 correspond to the optical filter and the drive member of the present invention, respectively, and both correspond to the intensity control system. In the following, the value of “1—transmittance”, ie, the value of “100—transmittance (%)” in%, is referred to as “dimming rate”.

When the ND filter 41 is retracted from the optical path, the ultraviolet pulse light IL that has passed near the ND filter 41, or when the ND filter 41 is installed on the optical path, the ultraviolet pulse light IL that has passed through the ND filter 41 Enters the variable attenuator 6 as a light athens overnight. When a pulsed laser light source is used as the exposure light source as in this example, since there is energy variation for each pulsed light, a certain number (hereinafter referred to as “minimum exposure pulse number”) for each point on the wafer Exposure with a plurality of pulsed light beams as described above provides desired reproducibility of exposure amount control accuracy. For example, when exposing a high-sensitivity resist, the target integrated exposure amount is small, so if the laser light from the pulse laser light source is used as it is, the minimum exposure Exposure with more than the pulse number becomes impossible. Therefore, in this example, a certain degree of control of the output of the laser light source itself is combined with a control of the dimming rate for the pulsed light by the variable dimmer 6 as a dimming mechanism installed on the optical path. Exposure is performed with a pulse number equal to or greater than the minimum exposure pulse number.

The variable dimmer 6 of the present example is composed of two rotatable variable dimmers 6 c and 6 b and drive motors 6 d and 6 a for respectively rotating these dimmers. On the light plates 6b and 6c, a plurality (for example, five) of ND filters having different dimming rates (= 1 one transmittance) with respect to the ultraviolet pulse light IL are arranged. These ND filters are formed of a fluorite substrate whose transmittance is stable, for example, even for ultraviolet pulsed light. Each of the variable neutral density plates 6c and 6b includes a transparent portion having a light attenuation rate of 0. For example, if the number of ND filters is set to 5, the light attenuation rate for the ultraviolet pulse light IL is 0. Thus, for example, switching can be performed over 25 steps with a step amount of about 1 to 3%. As described above, the variable dimmer 6 of the present example can switch the dimming rate for the ultraviolet pulse light IL within a predetermined range and in several steps with a step amount of about several percent. At present, it is not always easy to control the output (= pulse energy X oscillation frequency) of the ArF excimer laser light source 1 with high accuracy within a wide range of, for example, about 10%. However, the output can be controlled relatively easily and continuously as long as the output is within a range of about several%, which is the step amount of the change of the dimming rate in the variable dimmer 6. Therefore, in this example, by switching the dimming rate in the variable attenuator 6 and controlling the output of the ArF excimer laser light source 1, the ultraviolet pulse light IL after passing through the variable attenuator 6 The average output is controlled almost continuously within the range of several 10%, for example. The exposure control unit 30 for controlling the exposure amount of the resist on the wafer controls the start and stop of the light emission of the ArF excimer laser light source 1, and the output determined by the oscillation frequency and the pulse energy. The extinction ratio for the ultraviolet pulse light in the variator 6 is adjusted stepwise. The operation of the exposure control unit 30 is controlled by a main control system 30 composed of a combination unit that supervises and controls the operation of the entire apparatus. Instead of controlling the output of the ArF excimer laser light source 1, for example, a pair of glass substrates with variable tilt angles is arranged on the output side of the variable dimmer 6, and the tilt angles of these glass substrates are adjusted. By controlling symmetrically, the output of the ultraviolet pulse light IL may be continuously controlled within a range of about several percent.

As the exposure light, wavelength 2 4 8 nm of K r F excimer laser light, or a wavelength 1 5 7 nm of fluorine laser (F ₂ laser), etc. or a YAG laser harmonic, wavelength 3 0 0 nm approximately The present invention is also applied to the case where the following ultraviolet pulse light is used.

In FIG. 1, the ultraviolet pulse light IL that has passed through the variable dimmer 6 passes through an optical integrator through a beam shaping optical system composed of lens systems 7A and 7B arranged along the optical axis of the illumination optical system. (Homogenizer) The fly-eye lens 11 is incident on the lens. In this example, the fly-eye lens 1 1

Although it is one stage, in order to improve the uniformity of the illuminance distribution, for example, as disclosed in Japanese Patent Application Laid-Open No. 1-25392 / 89, _two stages of optical 'integers are arranged in series. You may do so. Also, a rod-type optical integrator may be used instead of the fly-eye lens, or a fly-eye lens and a rod-type optical integrator may be used in combination. An aperture stop system 12 of an illumination system is arranged on the exit surface of the fly-eye lens 11. The aperture stop system 12 includes a circular aperture stop for normal illumination and an aperture stop for deformed illumination consisting of multiple eccentric small apertures. In addition, an aperture stop for orbicular illumination and the like are arranged to be switchable. The ultraviolet pulse light IL emitted from the fly-eye lens 11 and passing through a predetermined aperture stop in the aperture stop system 12 is a fluorite having a high transmittance, a low reflectance, and a stable transmittance (reflectance). It is incident on beam splitter 8 consisting of The ultraviolet pulse light reflected by the beam splitter 8 enters an integral sensor 9 composed of a photoelectric detector, and a detection signal of the integral sensor 9 is supplied to an exposure control unit 30.

The transmittance and the reflectance of the beam splitter 8 are measured with high precision in advance and stored in a memory in the exposure control unit 30. Further, the measured values of the transmittance of the illumination system and the projection optical system PL after the beam splitter 8 before the start of exposure are also stored in the memory of the exposure control unit 30, and the exposure control unit 30 The projection optical system PL and, consequently, the incident light amount of the ultraviolet pulse light IL to the wafer W to be exposed and the integrated value thereof can be monitored indirectly from the detection signal of the integer sensor 9. In order to monitor the amount of light incident on the projection optical system PL and, consequently, the wafer W, for example, a beam splitter is arranged in front of the lens system 7A (on the side of the ArF excimer laser light source 1 than the lens system 7A). Alternatively, the reflected light from the beam splitter may be received by a photoelectric detector, and the detection signal may be supplied to the exposure control unit 30.

In this example, since the output of the ultraviolet pulse light IL at the output side of the fly-eye lens 11 is monitored by the integrator sensor 9, the transmittance of the variable dimmer 6 and the ND filter 41 is limited. Even if it fluctuates to the extent, the amount of the fluctuation can be monitored. Therefore, quartz glass or the like may be used as a substrate for the variable dimmers 6 c and 6 b of the variable dimmer 6 and the ND filter 41.

The ultraviolet pulse light IL transmitted through the beam splitter 8 passes through the reflection mirror 13 and the condenser lens system 14 and is fixed in the reticle blind mechanism 16. Constant blind (fixed illumination field stop) 15 A is incident on an opening formed to extend in a straight slit or rectangular shape (hereinafter collectively referred to as “slit shape”) at 15A. Further, in the reticle blind mechanism 16, a movable blind 15 B for changing the width of the illumination visual field in the scanning exposure direction is provided separately from the fixed blind 15 A. The movable blind 15 B reduces the scanning stroke of the reticle stage and the width of the reticle scale light-shielding band. The value obtained by multiplying the incident light amount obtained from the detection signal of the integrate sensor 9 by the aperture ratio of the fixed blind 15A and the movable blind 15B is the actual incident light amount to the projection optical system PL.

The ultraviolet pulse light IL shaped into a slit with the fixed blind 15 A of the reticle blind mechanism 16 is passed through the reticle through the imaging lens system 17, the reflection mirror 18, and the main condenser lens system 19. A slit-shaped illumination area on the R circuit pattern area is illuminated with a uniform illuminance distribution. That is, the arrangement surface of the opening of the fixed blind 15A and the opening of the movable blind 15B is almost conjugate with the pattern surface of the reticle R. A r F excimer laser light source 1, beam matching unit (BMU) 3, variable dimmer 6, beam shaping optics (lens systems 7A, 7B), fly-eye lens 11, aperture stop system 12, The illumination optical system is composed of the mirror 13 to the main condenser lens system 19, etc., and the optical components (also called the “illumination system”) from the variable dimmer 6 to the main condenser lens system 19 are the illumination sub-chamber 3. 5 is stored inside. Further, in the illumination optical system of this example, immediately before the variable dimmer 6 in the sub-chamber 35, which is a position close to the ArF excimer laser light source 1, the ND filter can be inserted into and removed from the optical path. 4 1 are arranged.

Under the ultraviolet pulse light IL, the image of the circuit pattern in the illumination area of the reticle R is on both sides (or one side on the wafer side) Telecentric projection optical system PL At a predetermined projection magnification j3 (/ 3 is, for example, 1Z4, 1Z5, etc.), the slit-like exposure area of the resist layer on the wafer W placed on the image plane of the projection optical system PL Transcribed. Reticle R and wafer W correspond to the first object and the second object of the present invention, respectively. The exposure area on the wafer W is located on one of the plurality of shot areas on the wafer. The projection optical system PL of this example is a dioptric system (refractive system), but it is needless to say that a power dioptric system (catadioptric system) can also be used. Hereinafter, the Z axis is taken in parallel with the optical axis AX of the projection optical system PL, and the X axis is set in the scanning direction 4 2 (here, the direction parallel to the plane of FIG. 1) indicated by an arrow in a plane perpendicular to the Z axis. And the Y-axis in the non-scanning direction orthogonal to the scanning direction 42 (here, the direction perpendicular to the plane of FIG. 1).

The reticle R is held by suction on the reticle stage 2OA, and the reticle stage 20A can move at a constant speed in the X direction on the reticle base 20B, and can move slightly in the X, Y, and rotation directions. It is placed in. The two-dimensional position and rotation angle of the reticle stage 2 O A (reticle R) are measured in real time by a laser interferometer in the drive control unit 22. Based on the measurement results and the control information from the main control system 27, the driving modes (linear mode, voice coil mode, etc.) in the drive control unit 22 are controlled by the scanning speed of the reticle stage 20A, and Control the position.

On the other hand, the wafer W is suction-held on the Z tilt stage 24 Z via the wafer holder WH, and the Z tilt stage 24 Z moves two-dimensionally along an XY plane parallel to the image plane of the projection optical system PL. The XY stage 24 is fixed on the XY, and the Z tilt stage 24 Z and the XY stage 24 XY constitute a wafer stage 24. The Z tilt stage 2 4 Z controls the focus position (position in the Z direction) and the tilt angle of the wafer W to control the wafer W. The surface of the wafer W is aligned with the image plane of the projection optical system PL by an autofocus method, and the XY stage 24 XY performs constant-speed movement of the wafer W in the X direction and stepping in the X and Y directions. The two-dimensional position and rotation angle of the Z tilt stage 24 Z (wafer W) are measured in real time by a laser interferometer in the drive control unit 25. Based on the measurement results and the control information from the main control system 27, the drive motor (linear motor, etc.) in the drive control unit 25 controls the scanning speed and position of the XY stage 24 XY. . The rotation error of the wafer W is corrected, for example, by rotating the reticle stage 20A via the main control system 27 and the drive control unit 22.

The main control system 27 sends various information such as the moving position, moving speed, moving acceleration, and position offset of each of the reticle stage 20 A and the XY stage 24 XY to the drive control units 22 and 25. At the time of scanning exposure, the reticle R is scanned in the + X direction (or one X direction) at a speed Vr with respect to the illumination area of the ultraviolet pulse light IL via the reticle stage 20A. The wafer W moves in the −X direction (or + X direction) to the exposure area of the pattern image of the reticle R via the XY stage 24 XY 3 Vr (3 is the projection from the reticle R to the wafer W) (Magnification). The reason that the scanning directions of the reticle R and the wafer W are opposite is that the projection optical system PL performs reverse projection, and when the projection optical system PL projects an erect image, the scanning directions of both are the same. Turn.

The main control system 27 is provided for synchronizing the movement of each blade of the movable blind 15 B provided in the reticle blind mechanism 16 with the movement of the reticle stage 20 A during scanning exposure. Perform control. Further, the main control system 27 sets various exposure conditions for scanning and exposing the resist in each shot area on the wafer W with an appropriate exposure amount in cooperation with the exposure control unit 30. And execute the optimal exposure sequence. Then, at the end of the scanning exposure on the shot area, the emission of the ArF excimer laser light source 1 is stopped.

In addition, an irradiation amount monitor 32 composed of a photoelectric detector is installed near the wafer holder WH on the Z tilt stage 24 Z in this example, and a detection signal of the irradiation amount monitor 32 is also supplied to the exposure control unit 30. ing. The irradiation dose monitor 32 has a light receiving surface large enough to cover the entire slit-shaped exposure area by the projection optical system PL. The XY stage 24 drives the XY stage to cover the light receiving surface with the exposed area. By setting to, the amount of ultraviolet pulse light IL that has passed through the projection optical system PL can be measured. In this example, the transmittance of the projection optical system PL is measured using the detection signals of the integrator sensor 9 and the irradiation amount monitor 32. Instead of the irradiation amount monitor 32, an uneven illuminance sensor having a pinhole-shaped light receiving portion for measuring the light amount distribution in the exposure area may be used. When an uneven illuminance sensor is used, it is preferable to arrange a large number of pinhole-shaped light receiving units in a two-dimensional direction so that uneven illuminance of the entire exposure area can be measured at a time.

In this example, an ArF excimer laser beam (wavelength: 193 nm) is used as the exposure light. In this manner, light in the vacuum ultraviolet region having a wavelength of about 200 nm or less has an absorption amount by oxygen. As the size increases, the illuminance on the wafer W drops significantly in the air. Therefore, the sub-chamber 35 in which most of the optical path of the illumination optical system of this example is housed blocks the internal optical path from the outside air, and the entire inside of the sub-chamber 35 has an acid through a pipe 36. Dry nitrogen gas (N ₂ ) with extremely low element content is supplied. Similarly, dry nitrogen gas is supplied to the entire space inside the lens barrel of the projection optical system PL (space between multiple lens elements) via the pipe 37, and the ultraviolet pulse light IL is attenuated on the optical path. The amount has become extremely small. In addition, dry nitrogen gas May be provided by providing a pipe between each lens element constituting the illumination optical system and the projection optical system.

In addition, a reticle chamber is formed between the sub-chamber 35 and the projection optical system PL, that is, around the reticle stage from outside air, and a reticle chamber is formed between the projection optical system PL and the wafer, that is, around the wafer stage. The wafer chamber may be configured to shut off from outside air, and dry nitrogen gas may be supplied to each chamber. In addition, the reticle chamber and the wafer chamber are not configured, and the sub-chamber 35 and the projection optics are simply provided. Dry nitrogen gas may always be supplied (flow) between the system PL and between the projection optical system PL and the wafer.

If the sub-chamber 35 and the lens barrel of the projection optical system PL have high airtightness, the supply of the dry nitrogen gas does not need to be performed so frequently after the air has been completely replaced once. However, transmittance fluctuations caused by water molecules and hydrocarbon molecules generated from various substances (glass materials, coating materials, adhesives, paints, metals, ceramics, etc.) existing in the optical path adhere to the surface of the optical element. In view of this, it is necessary to remove these impurity molecules by using a chemical filter and an electrostatic filter while forcing the temperature-controlled nitrogen gas to flow in the optical path.

The supply pipe for supplying the dry nitrogen gas is made of a material that generates less impurity gas (and degassed), such as stainless steel, tetrafluoroethylene, tetrafluoroethylene-terfluoro (alkyl vinyl ether), or tetrafluoroethylene. It is desirable to form with various fluorine polymers such as hexafluoropropene copolymer. Further, in place of the dry nitrogen gas, an inert gas such as helium (He), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn) may be used.

Furthermore, the glass material having a sufficient transmittance practical in to light of up to about 1 6 0 nm wavelength vacuum ultraviolet region, synthetic quartz (S i 〇 _2), fluorine-doped Most of the glass material of the refractive optical member in the illumination optical system and the projection optical system PL of this example is made of synthetic quartz because it is limited to synthetic quartz and fluorite, etc., and fluorite is expensive. . However, when synthetic quartz is continuously irradiated with ultraviolet pulse light, the transmittance tends to reversibly decrease due to solarization.

Here, the synthetic quartz used in the projection exposure apparatus will be described in detail.

And an optical member of a projection exposure apparatus that the exposure light source A r F excimer laser light source, synthetic quartz or calcium fluoride (C a F ₂₎ single crystal of fluoride and the like are generally used. The image forming optical system of the projection exposure apparatus is composed of a large number of large-diameter thick lenses (optical members) of, for example, Φ 200 mm x t 20 mm, so that the optical path length becomes extremely long. Therefore, in order to increase the transmittance of the entire optical system, it is necessary to increase the transmittance of each optical member.

In addition, when an optical member having a low transmittance is used, the temperature of the optical member rises due to absorption of the illumination light, causing a non-uniform refractive index distribution. Deformation causes a decrease in optical performance.

That is, it is desirable that the optical member has an internal transmittance of 99.5% / cm or more. Further, if there is uneven or distortion of the refractive index distribution in the optical element (secondary refraction), since the imaging performance (resolution) is reduced, uniformity Δη refractive index distribution 4 X 1 0- ⁶ or less, distortion Desirably, it is 4 nmZcm or less.

In addition, the ArF excimer laser is a high-energy pulsed laser, and even if synthetic quartz is stable compared to other optical materials, the transmittance and the structure due to the generation of defects due to the irradiation of the ArF excimer laser are increased. Changes, so-called laser damage.

Therefore, as little synthetic silica of such laser damage, OH group concentration of from 800 to 1 000 p pm, the hydrogen molecule concentration is 2 X ¹ 0 1 'molecules / cm ³ or more is used. Doping with fluorine or hydrogen has also been proposed as a method for improving the durability of synthetic quartz to laser light.

Further, optical thin films of various configurations are formed on optical members of the projection exposure apparatus to maintain desired optical characteristics, and the film materials are also formed by absorption of exposure light, such as ArF excimer laser light. It is necessary to use a material that is unlikely to cause a change in the substrate surface or film destruction due to loss of light amount or absorption heat generation, that is, a material having high transmittance and high durability to ArF excimer laser light.

Further, a cloudy substance may gradually adhere to the surface of the refractive optical member and the reflective optical member (mirror or the like) due to a chemical reaction or the like due to ultraviolet pulse light, and the transmittance or the reflectance may fluctuate. In some cases, such a cloudy substance can be removed by, for example, light washing in which an ultraviolet pulse light whose output is larger than usual is irradiated. However, in this example, as described above, since dry nitrogen gas from which impurities have been removed is supplied to the inside of the sub-chamber 35 and the projection optical system PL, the transmittance and reflectance of such a cloudy substance are reduced. Fluctuations are kept very small.

In addition, since the number of refractive optical members in the projection optical system PL is considerably larger than that in the illumination optical system, most of the variation in transmittance on the optical path from the beam splitter 8 to the wafer W Can be regarded as the transmittance variation of the projection optical system PL. Therefore, a method for preventing a decrease in exposure amount control accuracy due to a change in transmittance of the projection optical system PL caused by irradiation with the ultraviolet pulse light IL will be described below. First, a method of measuring the relationship between the integrated value of the irradiation energy of the ultraviolet pulse light IL and the amount of change with time in the transmittance of the projection optical system PL will be described.

When measuring the transmittance of the projection optical system PL, the dose monitor The light receiving surface of evening 32 is set in the exposure area of projection optical system PL, and the total aperture ratio of fixed blind 15A and movable blind 15B is set to 100%. Here, since the purpose is to find the relationship between the incident energy and the transmittance with respect to the projection optical system PL, the reticle R is removed from the reticle stage 2OA, and the reticle stage 20A is not scanned. Then, the extinction rate of the variable dimmer 6 is set to a reference value, for example, 0% (transmittance is 100%), and the ND filter 41 is retracted from the optical path, and A r The pulse emission of the F excimer laser light source 1 starts at an average output. Subsequently, the exposure control unit 30 takes in the photoelectric conversion signals of the integrator sensor 9 and the irradiation amount monitor 32 in parallel to form a detection signal S i corresponding to the actual incident energy E i to the projection optical system PL. , And a detection signal S o corresponding to the transmitted energy E o actually passing through the projection optical system PL. In order to detect the ultraviolet pulse light IL, a peak hold circuit and an AZD converter are connected to the outputs of the integrator sensor 9 and the dose monitor 32, respectively. S i and S 0 are captured as digital data. The exposure control unit 30 calculates the incident energy Ei and the transmitted energy Eo by multiplying the detection signals S i and S o by a coefficient obtained in advance.

Then, for each pulse emission, the exposure control unit 30 calculates the transmittance T (= Eo / Ei) by dividing the transmitted energy Eo by the incident energy Ei, and calculates the incident energy Ei. Integrate and calculate the total incident energy-e up to that point. This operation is continuously performed until the end of the measurement. When a continuous light of almost the same wavelength is used instead of the ArF excimer laser light (pulse light) as the exposure light, a sample-and-hold circuit is used instead of the peak-and-hold circuit to detect the detection signal. E o and E i are The transmittance T is calculated by sequentially detecting at the pulling rate, and the incident energy Ei may be integrated.

When the ultraviolet pulse light IL is detected for each pulse emission, each point on the wafer W is exposed with a pulse number equal to or more than the minimum exposure pulse number, that is, a certain fixed number or more of a plurality of pulse lights. The transmittance T and the total incident energy e are calculated at measurement intervals sufficiently short with respect to the exposure time of the shot. The measurement time is set so that the total incident energy e at the end of the measurement is sufficiently larger than the total incident energy accumulated during the normal one-shot exposure. The measurement time is, for example, several seconds to ten seconds. After the measurement is completed, the transmittance T of the projection optical system PL is approximated by a function of the quadratic or higher order of the total incident energy e or an exponential function of the incident energy e, and the transmittance T of the transmittance T is calculated from the approximated function. The saturated value and the time constant of the change amount are obtained (details will be described later), and the obtained saturated value and the time constant are stored in the memory in the exposure control unit 30. In this case, since the emission frequency of the ultraviolet pulse light IL is almost uniform and the average value of the pulse energy is also almost uniform, the total incident energy e is almost proportional to the elapsed time t from the start of the measurement. Therefore, the transmittance T can be regarded as a function T (q, t) of the illuminance q of the ultraviolet pulse light and the elapsed time t, for example. Accordingly, the saturation value and the time constant of the change amount of the transmittance T can be expressed by a primary or secondary function of the illuminance Q, respectively.

The transmittance change due to the solarization is a reversible change, and when the irradiation of the ultraviolet pulse light is stopped, the transmittance T of the projection optical system PL gradually recovers. It also measures the transmittance T of the projection optical system PL. Specifically, after stopping the emission of the ArF excimer laser light source 1, the ArF excimer laser light source 1 emits as few pulses as possible at predetermined time intervals, and the exposure control unit. In 30, ト The transmissivity T (= E o ZE i) of the projection optical system PL is calculated from the over energy E o and the incident energy E i. The total incident energy at this time can be regarded as almost zero. The measurement of the transmittance T is repeated a predetermined number of times, and after the measurement is completed, the transmittance T of the projection optical system PL is, for example, a function T (Tst , t '), and the time constant at which the transmittance T recovers from this function T (Tst, t') is calculated as a first-order or second-order function of the transmittance Tst, and the time constant is calculated as It is stored in the memory in the exposure control unit 30.

Fig. 2 shows an example of the change in the transmittance T of the projection optical system PL due to the irradiation of the ArF excimer laser light. In Fig. 2, the horizontal axis indicates the progress from the start of the irradiation of the ArF excimer laser light. The time t [min], and the vertical axis is the value obtained by dividing the transmittance T of the projection optical system PL by the initial transmittance Ta before the start of the irradiation of the ArF excimer laser beam, that is, the relative value of the transmittance T (= TZT a). In FIG. 1, the ND filter 41 is retracted from the optical path, the extinction ratio of the variable dimmer 6 is set to 0, and the illuminance of the ultraviolet pulse light IL is almost maximized. The measurement result of the relative value of the transmittance T of the projection optical system PL when the ultraviolet pulse light IL is emitted until the value of the curve is 43 A. In the curve 43A, the characteristic after the time t1 indicates a change in the transmittance T after the irradiation of the ultraviolet pulse light IL is stopped. In addition, the time t1 is set to a time (time constant) until the transmittance T saturates to a substantially predetermined value when the variation of the transmittance T becomes small.

As can be seen from the curve 43A, when the irradiation of the ultraviolet pulsed light IL is started, the transmittance T of the projection optical system PL decreases rapidly at first due to the transmittance fluctuation of the synthetic quartz, and gradually becomes the initial value. It is saturated to a value that is about 2% lower than. After stopping irradiation of the ultraviolet pulse light IL at time t1, the damage of the synthetic quartz glass due to the solarization is gradually repaired, and the projection light The transmittance T of the academic PL gradually recovers toward the initial value.

The saturation value and time constant of the change in the transmittance による due to this solarization vary depending on the illuminance of the ultraviolet pulse light IL and the type of glass material, etc., but when the illuminance of the ultraviolet pulse light IL is close to the maximum, the average The saturation value of the change in the transmittance Τ is about 2 to 3% of the initial value TO, and the time constant of the change in the transmittance T is about 2 to 3 for the decrease in the transmittance during irradiation with ultraviolet pulse light. The recovery of the transmittance after stopping irradiation of the UV pulse light for 3 min is about 10 to 20 min.

Next, in Fig. 1, measurement of the transmittance T of the projection optical system PL was performed in the same manner as above, with the ND filter 4 having a transmittance of approximately 50% installed in the optical path of the ultraviolet pulsed light IL. The result is the dotted curve 43B in FIG. In the case of the curve 43B, the time t2 until the transmittance T is substantially saturated is longer than the time t1, and the transmittance T is a value that is reduced by about 1% from the initial value. Saturated. From this, the illuminance of the irradiated ultraviolet pulse light IL (pulse energy, peak power, average power, or the duty ratio during the period when the light energy is at a high level, etc.) can be reduced. It can be seen that the saturation value of the change in the transmittance T decreases and the time constant of the change in the transmittance T increases. In this example, this is used to increase the control accuracy of the exposure amount as needed.

Actually, in FIG. 1, for example, even when the ND filter 41 is retracted from the optical path and the dimming rate of the variable dimmer 6 is variously set, the ND filter 41 is further placed on the optical path. Even when the variable extinction device 6 is arranged and the extinction ratio of the variable extinction device 6 is variously set, the transmittance T of the projection optical system PL is measured during emission of the ultraviolet pulse light IL and emission stop thereof.

In a projection exposure apparatus, the integrated exposure amount for one shot, illumination conditions (such as the size of the aperture stop and the type of deformed illumination), and the exposure such as the numerical aperture of the projection optical system Since the light conditions are changed as appropriate, the transmittance T of the projection optical system PL is measured for each exposure condition. A configuration for measuring the transmittance (time change of optical characteristics) for each exposure condition is described in Japanese Patent Application No. 9-19710. Therefore, the transmittance T of the projection optical system PL is measured in advance for each exposure condition, or the transmittance T of the projection optical system PL is measured immediately after the change of the exposure condition.

Then, for example, the projection optical system PL when irradiating the ultraviolet pulse light IL as a function of the average illuminance Q of the ultraviolet pulse light IL measured by the integration sensor 9 or in the form of a table corresponding to the illuminance Q. The measurement results of the saturation value of the change amount of the transmittance T and the time constant of the change are stored in the memory in the exposure control unit 30. In the case where the data is stored in the form of a table, in a region where there is no measured value of the illuminance Q of the ultraviolet pulse light IL, for example, by interpolating the measurement data in the vicinity thereof, the change amount of the transmittance T can be calculated. The saturation value and time constant can be obtained.

Next, for example, in the exposure step of actually exposing one lot of wafers, first, the illumination conditions, the resist sensitivity (dose) on the wafer, the tolerance for the integrated exposure amount, and the reticle R used for exposure are used. The exposure conditions such as the illuminance of the ultraviolet pulse light IL at the time of scanning exposure, the number of exposure pulses, and the scanning speed are determined based on the conditions such as the pattern abundance ratio.

Here, the output per unit time of the ArF excimer laser light source 1 (= oscillation frequency X pulse energy) is Ea [W]. Further, hereinafter, the output Ea is a value obtained by multiplying the transmittance of the ND filter 41 and the variable dimmer 6 by the transmittance calculated from the known pattern existence ratio of the reticle R. You. The initial transmittance of the projection optical system PL is Ta, the area of the slit-shaped exposure area is S [cm ² ], the width of the exposure area in the scanning direction is L [cm], and the resist sensitivity is I [JZ]. cm ² ], the wafer stay during scanning exposure The initial value Vwa [cm / sec] of the scanning speed of di 24 is as follows. Vw a = (L-E a-T a) / (I-S) (1)

Also, assuming that the number of exposure pulses for each point on page 8 is N (≥ minimum exposure pulse number Nmin) and the average oscillation frequency of ultraviolet pulse light IL is fa [1 sec], the average pulse of ultraviolet pulse light IL Since the energy is E a / fa, the following relationship holds.

N = (L / Vw a) f a≥Nmin (2)

E a / f a = I / N (3)

In practice, substituting equation (2) into equation (3) yields equation (1), so equations (3) and (1) are equivalent. In equation (1), since E aZ S is the illuminance of the ultraviolet pulse light IL on the wafer, controlling the output E a is equivalent to controlling the illuminance. In this example, first, the scanning speed Vwa and the oscillation frequency f a are determined based on the equation (2), and then the output Ea of the ultraviolet pulse light IL is determined based on the equation (1). In this case, the output E a is multiplied by the transmittance of the ND filter 41 and the variable dimmer 6. Normally, the ND filter 41 is retracted from the optical path, and the variable dimmer is After the transmittance at 6 (= 1 extinction) is selected, the output of the ArF excimer laser light source 1 is fine-tuned. These values are set for the variable dimmer 6 and the ArF excimer laser light source 1 from the exposure control unit 30.

Then, the transmittance fluctuation of the projection optical system P, which occurs when the exposure is performed under these exposure conditions, is determined by the illuminance of the ultraviolet pulse light IL stored in the memory in the exposure control unit 30 and the projection optical system PL. Predict from the relationship with the change in transmittance (saturation value and time constant). Then, it is determined whether or not the fluctuation amount of the transmittance of the projection optical system PL becomes larger than a predetermined allowable value during the exposure of each wafer according to the predicted change amount of the transmittance. The amount of change in transmittance If the allowable value is exceeded, adjust the intensity of the ultraviolet pulse light IL. That is, during exposure of each wafer, it is determined whether the integrated exposure amount for each shot area on the wafer falls within the allowable range defined by the resist and the exposure process, and the integrated exposure amount falls within the allowable range. In this example, if it is determined that the laser beam does not fall within the range, the ND filter 41 is installed on the optical path of the ultraviolet pulse light IL via the driving mode 40 in FIG. Output (and thus illuminance) to about 50%. After that, the dimming rate of the variable dimmer 6 is selected again and the output of the ArF excimer laser light source 1 is finely adjusted from the equations (2) and (1). As a result, as shown in FIG. 2, the amount of change in the transmittance of the projection optical system PL during the exposure is approximately 1 to 2, so that the integrated exposure amount falls within the allowable range. In this case, although the illuminance of the ultraviolet pulse light IL is reduced and the throughput is reduced, the control accuracy of the exposure amount is improved.

In this regard, when manufacturing semiconductor devices, etc., a low-sensitivity (high value of the resist sensitivity I) resist is used in a plurality of layers on a wafer, for example, in a critical layer including a pattern with an extremely narrow line width. In some cases, the tolerance of the error of the integrated exposure amount is quite narrow. Specifically, the resist sensitivity I (the target value of the integrated exposure amount) is about l OmJZ cm ² in a normal layer, but the resist sensitivity I force is about 10 Om J Zcm ^{2 in} a critical layer. There is a special layer that becomes In such a special layer, the allowable range of the error of the integrated exposure amount is, for example, about 1/2 or less of that of a normal layer in order to increase the control accuracy of the line width. Therefore, in the resist sensitivity is 1 Om JZcm ² about normal Layer, exposure is performed is retracted the ND fill evening 4 1 from the optical path, the light of the ND fill evening 41 is a layer Regis Bok sensitivity is 1 0 OmJZcm ² about By setting the exposure on the road and performing exposure, the throughput of the entire exposure process is almost reduced. Thus, the required control accuracy can be obtained for a layer having a high control accuracy of the integrated exposure amount.

Further, in this example, the fluctuation of the transmittance of the projection optical system PL after stopping the irradiation of the ultraviolet pulse light IL is considered in controlling the exposure amount. Depending on the recovery rate of the transmittance after stopping the irradiation of the ultraviolet pulse light I L, the transmittance may not be sufficiently restored to the initial state after the exposure of one shot is completed and before the exposure of the next shot is started. In addition, even when the stepping time between shots is shortened in order to improve the throughput of the exposure apparatus, the recovery of the transmittance between shots may be insufficient. For this reason, the variation of the transmittance of the projection optical system PL when the irradiation of the ultraviolet pulse light IL is interrupted between shots

By taking into account (recovery), the exposure amount can be controlled with higher accuracy.

Next, an example of a manufacturing process of a semiconductor device using the exposure apparatus of the present embodiment will be described with reference to FIG.

FIG. 4 shows an example of a semiconductor device manufacturing process. In FIG. 4, when manufacturing a semiconductor device, first, for example, a single crystal silicon ingot SI is sliced and polished to manufacture a wafer W. (Step ST1). At this time, a notch (a notch or the like) serving as a reference for wafer alignment is provided on the outer periphery of the wafer W. Next, in step ST2, for example, a metal film, an insulating film, or the like is deposited on the wafer W, and a photoresist PR1 is applied. Then, in step ST3, a change in the transmittance of the projection optical system PL or the like is predicted from the exposure conditions. Here, if the layer to be exposed is a normal layer and the value of the register sensitivity is not so large and the control accuracy of the integrated exposure amount is normal, the ND filter 41 in FIG. 1 is retracted from the optical path. The exposure condition is set, and the image of the pattern PA 1 (represented by the symbol A) of the reticle R 1 is irradiated with the ultraviolet pulse light IL 1 to each shot area S on the wafer W. Expose to C. Then, in step ST4, a pattern PW1 is formed in each shot area on the wafer W by performing development, etching, and the like.

When exposing the next layer, first, in step ST5, for example, a metal film, an insulating film, or the like is deposited on the wafer W and a photoresist PR 2 is applied. Predict the transmittance fluctuation of the system PL etc. This layer is assumed to be a layer with low registration sensitivity and high control accuracy of the integrated exposure, and the ND filter 41 in Fig. 1 is arranged on the optical path to reduce the illuminance of the ultraviolet pulse light. Set the exposure conditions. Then, the pattern P A 2 of the reticle R 2 by the ultraviolet pulse light I L 2

The image (represented by the symbol B) is exposed to each shot area SC on the wafer W. Then, in step ST7, a pattern P W2 is formed in each shot area on the wafer W by performing development and etching of the wafer W.

The above-described photoresist coating process to power forming process (step ST2 to step ST4 or step ST5 to step ST7) are repeated as many times as necessary to manufacture a desired semiconductor device. Then, a semiconductor device SP as a product is manufactured through a dicing process (step ST8) for separating each chip CP on the wafer W, a bonding process, a packaging process, and the like (step ST9). . At this time, in this example, in the layer having high control accuracy of the integrated exposure amount, the illuminance of the ultraviolet pulse light is reduced to suppress the fluctuation of the transmittance of the projection optical system PL. Thus, a desired circuit pattern can be formed on the wafer W with high transfer fidelity. Therefore, the yield of high-performance semiconductor devices can be improved without substantially lowering the throughput. In this example, as shown in Fig. 3 (a), the ND filter 41 is set on the optical path of the ultraviolet pulse light IL by the drive motor 40, and the illuminance as the intensity of the ultraviolet pulse light is adjusted. It is carried out. In addition, as shown in FIG. 3 (b), a glass substrate 41A made of synthetic quartz or the like is used as an optical filter, and this glass substrate 41A is moved with respect to the optical path of the ultraviolet pulse light IL by, for example, 5 mm. The intensity of the ultraviolet pulse light IL may be adjusted by arranging it at an angle such that a reflectance of about 0% is obtained. As shown in Fig. 3 (c), a metal mesh plate 41B with a light shielding area of about 50% was used as an optical filter, and this metal mesh plate 41B was inserted into the optical path of the ultraviolet pulse light. You may come off.

In the above embodiment, the transmittance of the ND filter 41 or the like as the optical filter is about 50%, but the transmittance may be about 30% to 70%. If the transmittance is less than 30%, the throughput will be too low, and if the transmittance is more than 70%, the variable dimmer 6 can be used instead of switching the dimming rate, so the equipment tends to overlap. Because. Further, the ND filter 41 has a simple device configuration because the UV pulse light is substantially switched in two steps, but for example, in three or four steps within a range of about 30 to 70%. The transmittance may be roughly switched.

In addition, the insertion position of the ND filter 41 in Fig. 1 is set to the Ar F excimer laser light source as much as possible in order to reduce the variation of the transmittance or reflectance of the optical member in the illumination optical system due to the irradiation of the ultraviolet pulse light IL. It is desirable to place it near 1.

Further, in the above embodiment, the transmittance variation of the projection optical system PL is considered as a problem. However, when the intensity of the ultraviolet pulse light is reduced by the ND filter 41, the amount of cloudy substance generated is reduced. Since the amount of change in the reflectance of the reflecting member also decreases, the amount of change in the transmittance of the entire optical system (reflectance (Including the fluctuations of).

Further, the method of adjusting the intensity of the ultraviolet pulse light IL is not limited to the method of inserting an optical filter such as the ND filter 41 on the optical path, but the oscillation of the ultraviolet pulse light IL in the ArF excimer laser light source 1 is described. The frequency may be reduced, or the output itself may be significantly reduced. At present, it is not always easy to change the output of the ArF excimer laser light source 1 stably over a wide range, but if the output can be easily controlled over a wide range in the future, Since the ND filter 41 and the like are not required, the device configuration is simplified.

In the above embodiment, the output of the ArF excimer laser light source 1 may be finely adjusted according to the transmittance of the projection optical system P for each pulse emission.

In this embodiment, the illumination optical system from the power beam splitter 8 to the reticle R has been described in which the transmittance variation of the projection optical system PL is described as the transmittance variation on the optical path from the beam splitter 8 to the wafer W. In the case where the transmittance fluctuation amount greatly contributes, it is desirable to consider the transmittance fluctuation of the illumination optical system and the projection optical system disposed between the beam splitter 8 and the wafer W.

In the above embodiment, synthetic quartz or synthetic quartz doped with a predetermined impurity is used in the projection optical system PL. However, fluorite or the like is mainly used as a refractive member of the projection optical system PL. Even in the case of use, if the degree of integration of semiconductor devices and the like increases in the future and higher exposure control accuracy is required, slight fluctuations in the refractive index will deteriorate the exposure control accuracy. Cases may arise. In such a case, the required exposure amount control accuracy can be obtained by applying the present invention.

When measuring the change in transmittance of the projection optical system PL, etc., A reticle R that emits light may be used to scan it in the same manner as in actual exposure. In this case, the total amount of light incident on the projection optical system PL while scanning the reticle R to a certain arbitrary position from the start of scanning is the same between the time of measurement and the time of scanning exposure. The amount of light that is actually incident on the projection optical system PL is calculated by adding the incident energy E i measured by the integrator sensor 9 to the pattern transmittance of the reticle R (= the area of the transmission part in the illumination area, the area of the illumination area on the reticle R) ) Is multiplied by. Since the pattern transmittance is also a value obtained by subtracting the pattern existence rate from 1, this pattern existence rate may be used. The transmitted energy E o measured via the irradiation amount monitor 32 is obtained by multiplying the incident light amount by the transmittance of the pattern of the reticle R and the transmittance of the projection optical system PL. Also, the pattern existence rate is known as a function of the position of the reticle R from the design data of the reticle R.

Thus, by taking into account the pattern transmittance of the reticle R, it is possible to more accurately detect the variation in the transmittance of the projection optical system PL during the actual scanning exposure, and to perform highly accurate exposure control. There are advantages that can be. Since the shape of the function representing the transmittance T of the projection optical system PL may slightly change depending on the scanning direction, the function is obtained for each scanning direction, and the function is determined according to the scanning direction during scanning exposure. May be used properly. Accordingly, even when the reticle pattern transmittance is not symmetric or the reticle substrate itself has a non-symmetric transmittance, exposure amount control is performed with high accuracy.

Also, the function representing the variation of the transmittance T of the projection optical system P L due to solarization may change depending on the irradiation time of the ultraviolet pulse light and the like. Therefore, it is desirable to measure the transmittance T of the projection optical system PL periodically (for example, every three months or every six months).

In the above embodiment, the present invention is applied to a step-and-scan method. Although the present invention is applied to an exposure apparatus of a type, the present invention can also be applied to a case where exposure is performed by an exposure apparatus (stepper) of a step-and-repeat method. In the case of a stepper, for example, the exposure time is controlled so that the integrated exposure amount to the shot area on the wafer becomes a predetermined value.

Further, the exposure apparatus of the present embodiment can be applied to a proximity exposure apparatus that exposes a mask pattern by bringing a mask and a substrate into close contact with each other without using a projection optical system. The application of the exposure apparatus is not limited to an exposure apparatus for manufacturing semiconductors. For example, an exposure apparatus for a liquid crystal that exposes a liquid crystal display element pattern to a square glass plate, a thin film magnetic head Can also be widely applied to an exposure apparatus for manufacturing a semiconductor device.

INDUSTRIAL APPLICABILITY The present invention can be applied to a case where the transmittance of at least some of the optical members (lenses, reflection mirrors, and the like) constituting the illumination optical system and the projection optical system changes. For example, g-ray (4 3 6 nm), i-rays (3 6 5 nm), K r F excimer one The (2 4 8 nm), or by using the F ₂ laser (1 5 7 nm), the transmission It can also be applied when the rate changes.

Further, the magnification of the projection optical system may be not only a reduction system but also any of an equal magnification and an enlargement system.

As the projection optical system, if using a far ultraviolet ray such as an excimer laser using a material which transmits far ultraviolet quartz and fluorite as glass material, F ₂ Les - if used The or X-ray catadioptric Or a refraction type optical system. As described above, the projection exposure apparatus according to the present embodiment includes the components shown in FIG. 1 (illumination optical system, projection optical system, reticle stage, wafer stage, light source, and other elements shown in FIG. 1). It is manufactured by assembling to maintain the prescribed mechanical, electrical, and optical accuracy. Before and after this assembly, adjustments to achieve optical accuracy for various optical systems, and mechanical accuracy for various mechanical systems are performed before and after this assembly to ensure these various accuracies. Adjustments to achieve, and various electrical systems are adjusted to achieve electrical accuracy. The process of assembling the exposure apparatus from various subsystems includes mechanical connection between various subsystems, wiring connection of electric circuits, and connection of pneumatic circuits. It goes without saying that there is an assembly process for each of the various subsystems before the assembly process from these various subsystems to the exposure apparatus. When the assembly process for the various subsystems to the exposure apparatus is completed, comprehensive adjustment is performed. Therefore, various precisions of the entire exposure apparatus are ensured. It is desirable to manufacture the exposure apparatus in a clean room where the temperature and cleanliness are controlled.

It should be noted that the present invention is not limited to the above-described embodiment, and it is needless to say that various configurations can be adopted without departing from the gist of the present invention. Industrial applicability

According to the first exposure method of the present invention, for example, due to the irradiation of the illumination light, the transmittance or the reflectance of the illumination optical system and a predetermined optical member in the projection optical system fluctuates beyond an allowable range. In such a case, by reducing the intensity of the illumination light, the amount of change in the transmittance or the like of the optical member can be reduced, and highly accurate exposure amount control can be performed on the second object.

Next, according to the second exposure method of the present invention, the intensity of the illuminating light is controlled based on the amount of change in the transmittance or the like of the predetermined optical member that is predicted in advance. Thus, the exposure amount can be controlled with high accuracy.

Further, according to the third exposure method of the present invention, it is possible to perform high-precision exposure control on the second object by reducing the amount of change in the transmittance or the like of the optical member.

Next, according to the exposure apparatus of the present invention, the first, second, and third exposure methods of the present invention can be performed, and the exposure amount can be controlled with high precision as necessary. Therefore, for example, high-performance semiconductor devices can be mass-produced with high throughput and high yield as a whole.

Further, according to the device manufacturing method of the present invention, high-precision exposure amount control is performed by controlling the intensity of the exposure light so as to suppress the variation amount of the transmittance or the reflectance of the optical system. As a result, high-performance devices can be obtained.

Claims

The scope of the claims

1. An exposure method for illuminating a first object with illumination light from an illumination optical system and transferring a pattern of the first object onto a second object via a projection optical system, wherein the illumination optical system and the projection optical An exposure method, comprising: controlling the intensity of the illumination light so as to suppress a variation in transmittance or reflectance of at least some of the optical members in the system.

2. Before the exposure operation, the amount of change in transmittance or reflectance of at least some of the optical members in the illumination optical system and the projection optical system with respect to the intensity of the illumination light based on the intensity of the illumination light. Predict

It is determined whether or not the exposure amount for the second object falls within an allowable range based on the prediction result,

When it is determined that the exposure amount does not fall within the allowable range, the intensity of the illumination light is adjusted so that the exposure amount falls within the allowable range during the exposure operation. The exposure method according to claim 1.

3. The exposure method according to claim 2, wherein the intensity of the illumination light is adjusted by an optical filter that is inserted and removed in an optical path of the illumination optical system.

4. The exposure method according to claim 2, wherein, when adjusting the intensity of the illumination light, at least one of a peak power and an oscillation frequency of the illumination light is controlled.

5. The method according to claim 2, wherein the estimation of the variation of the transmittance or the reflectance is performed based on the variation of the transmittance or the reflectance when the illumination light is measured in advance. Exposure method.

6. The estimation of the variation of the transmittance or the reflectance is performed based on the variation of the transmittance or the reflectance after stopping the irradiation of the illumination light measured in advance. 3. The exposure method according to claim 2, wherein the exposure method is performed.

7. The illumination light is ultraviolet pulse light having a wavelength of 300 nm or less, and the measurement of the amount of change in the transmittance or the reflectance of the optical member after the irradiation of the illumination light is stopped is performed during transfer. 7. The exposure method according to claim 6, wherein the number of pulses is smaller than the number of pulses of the illumination light.

8. The exposure method according to claim 1, wherein the optical member is a refractive optical element whose main material is synthetic quartz.

9. An exposure method for illuminating a first object with illumination light from an illumination optical system and transferring a pattern of the first object onto a second object via a projection optical system, wherein the illumination optical system and the projection optical Predict the amount of change in transmittance or reflectance of at least some optical members in the system according to the exposure process,

An exposure method, comprising: controlling the intensity of the illumination light so as to suppress the predicted fluctuation amount.

10. The second object is a photosensitive substrate coated with a photosensitive material,

The exposure method according to claim 9, wherein the exposure process is a sensitivity of the photosensitive material.

11. The exposure method according to claim 9, wherein the exposure process is a transfer condition for transferring a pattern of the first object onto the second object.

12. The projection optical system includes a refractive member mainly composed of synthetic quartz, and the illumination light is ultraviolet pulsed light having a wavelength of 300 nm or less.

10. The exposure method according to claim 9, wherein when changing the intensity of the illumination light, at least one of a peak power and an oscillation frequency of the illumination light is controlled.

13. An exposure method for illuminating a first object with illumination light from a light source and transferring a pattern of the first object onto a second object. An exposure method, comprising: controlling the intensity of the illumination light so as to suppress a variation in transmittance or reflectance of at least a part of the optical members arranged in an optical path of the illumination light.

14. In the optical path of the illumination light, at least an illumination optical system that illuminates the first object with the illumination light, and a projection optical system that transfers a pattern of the first object onto the second object. 14. The exposure method according to claim 13, comprising one of them.

15. An exposure apparatus comprising: an illumination optical system that illuminates a first object with illumination light; and a projection optical system that transfers a pattern of the first object onto a second object. An intensity control system for controlling,

An arithmetic and control system for controlling the intensity of the illumination light via the intensity control system so as to suppress a variation in transmittance or reflectance of at least some of the optical members in the illumination optical system and the projection optical system. When,

An exposure apparatus comprising:

16. The illumination optical system includes: an exposure light source that supplies the illumination light; and an optical system that guides the illumination light to the first object.

The intensity control system includes: an optical filter that adjusts the intensity of the illumination light; and a driving member that moves the optical filter into and out of an optical path between the exposure light source and the optical system. The exposure apparatus according to claim 15, wherein:

17. The illumination optical system has an exposure light source for supplying the illumination light, and the intensity control system controls at least one of a peak power and an oscillation frequency of the illumination light. Exposure apparatus according to the above item 15.

18. A device manufacturing method for manufacturing a device by transferring an image of a predetermined circuit pattern to a substrate via an optical system with exposure light from an exposure light source, wherein the transmittance or reflection of the optical system with respect to the exposure light The predetermined circuit pattern is controlled while controlling the intensity of the exposure light so as to suppress the variation of the rate. Transferring the image of (1) onto the substrate.

19. The device according to claim 18, wherein the optical system is an illumination optical system that illuminates a mask on which the predetermined circuit pattern is formed with exposure light from the exposure light source. Production method.

20. The device manufacturing method according to claim 18, wherein the optical system is a projection optical system that transfers an image of the predetermined circuit pattern onto the substrate.