WO2014016163A1

WO2014016163A1 - Lithographic apparatus and device manufacturing method

Info

Publication number: WO2014016163A1
Application number: PCT/EP2013/064973
Authority: WO
Inventors: Hans Butler
Original assignee: Asml Netherlands B.V.
Priority date: 2012-07-23
Filing date: 2013-07-16
Publication date: 2014-01-30
Also published as: NL2011172A

Abstract

A masking device (200) for use in an immersion lithographic apparatus. The masking device comprising a blade assembly (250.1, 250.2) configured to limit a width (260) of a cross-section (270) of a radiation beam in a direction substantially perpendicular to a scanning direction. The blade assembly is further configured to adjust, during exposure of a target portion comprising a substrate edge, the width of the cross-section of the radiation beam, thereby reducing a radiation dose of the substrate edge to a value less than a nominal radiation dose of the target portion.

Description

LITHOGRAPHIC APPARATUS AND DEVICE MANUFACTURING METHOD

BACKGROUND

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of US provisional application 61/674,476, which filed on July 23, 2012, and which is incorporated herein in its entirety by reference.

Field of the present invention

[0002] The present invention relates to a masking device, a lithographic apparatus and a method for manufacturing a device.

Description of the Related Art

[0003] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., including part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the "scanning" -direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. During such scanning, only part of the pattern is irradiated at the same time. Typically, a masking device is used to limit the cross-sectional dimensions of the radiation beam (e.g., to a rectangular cross-section). Such masking device can e.g., comprise a pair of blades obscuring part of the radiation such that the width of the radiation beam cross-section substantially corresponds to the width of the pattern to be irradiated. Such blades thus limiting the size of the radiation beam in a direction substantially perpendicular to the scanning direction. Typically, the masking device can comprise a second pair of blades arranged to limit the length of the radiation beam cross-section in the scanning direction.

[0004] In conventional lithographical apparatuses, substantially the entire area of the substrate is exposed. Even target portions that comprise part of the substrate edge are typically exposed in the same manner as target portions that are entirely within the substrate border.

[0005] It has been observed that the conventional exposure of target areas that overlap with the substrate edge may cause contamination inside the apparatus. Such contamination is e.g., caused by an out-of focus exposure of the resist on the substrate edge, which can cause structures being generated on the edge that are easily separated from the substrate. Such separated structures may cause image defects, in particular in an immersion type lithographic apparatus. With respect to such type of apparatus, the following can be mentioned. It has been proposed to immerse the substrate (or part thereof) in the lithographic apparatus in a liquid having a relatively high refractive index, e.g., water, so as to fill a space between the final element of the projection system, i.e., the bottom of the projection system, and the substrate. This enables more accurate projections and imaging of smaller features since the exposure radiation will have a shorter wavelength in the liquid. The effect of the immersion liquid may also be regarded as increasing the effective numerical aperture number NA of the system and also increasing the depth of focus. Other immersion liquids have been proposed, including water with solid particles (e.g., quartz) suspended therein. Thus, a lithographic apparatus may be provided with a fluid provider which is arranged to provide the immersion liquid, or to keep the liquid in its place.

SUMMARY

[0006] It is desirable to provide in an improved exposure of a substrate in an immersion type lithographic apparatus thereby mitigating contamination due to the exposure of a substrate edge. [0007] According to an embodiment of the present invention, there is provided a masking device for use in an immersion lithographic apparatus, the masking device comprising a blade assembly configured to limit a width of a cross-section of a radiation beam in a direction substantially perpendicular to a scanning direction. The blade assembly is further configured to adjust, during exposure of a target portion comprising a substrate edge, the width of the cross-section of the radiation beam, thereby reducing a radiation dose of the substrate edge to a value less than a nominal radiation dose of the target portion.

[0008] In another embodiment of the present invention, there is provided an immersion lithographic apparatus comprising an illumination system configured to condition a radiation beam, a support constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate table constructed to hold a substrate, and a projection system configured to project the patterned radiation beam onto a target portion of the substrate. The apparatus further comprises a masking device according to the present invention.

[0009] According to an embodiment of the present invention, there is provided a device manufacturing method comprising projecting a patterned beam of radiation onto a substrate, wherein a cross-section of the patterned beam of radiation is adjusted using a masking device according to the present invention.

[0010] Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings. It is noted that the present invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

[0011] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the present invention and to enable a person skilled in the relevant art(s) to make and use the present invention. [0012] Figure 1 depicts a lithographic apparatus according to an embodiment of the present invention.

[0013] Figure 2 depicts a first embodiment of a masking device according to the present invention.

[0014] Figure 3A depicts an exposure sequence using a conventional masking device.

[0015] Figure 3B depicts an exposure sequence using a masking device according to an embodiment of the present invention.

[0016] Figure 4 depicts the first embodiment of a masking device including a drive arrangement.

[0017] Figure 5 depicts a second embodiment of a masking device according to the present invention including a drive arrangement.

[0018] Figure 6 depicts a blade assembly as can be applied in a third embodiment of a masking device according to the present invention.

[0019] Figures 7 and 8 depict the third embodiment of a masking device according to the present invention in two different operating positions.

[0020] The features and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the corresponding reference number.

DETAILED DESCRIPTION

[0021] This specification discloses one or more embodiments that incorporate the features of this invention. The disclosed embodiment(s) merely exemplify the present invention. The scope of the present invention is not limited to the disclosed embodiment(s). The present invention is defined by the claims appended hereto.

[0022] The embodiment(s) described, and references in the specification to "one embodiment", "an embodiment", "an example embodiment", etc., indicate that the embodiment(s) described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is understood that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0023] Embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, instructions may be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions in fact result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc.

[0024] Before describing such embodiments in more detail, however, it is instructive to present an example environment in which embodiments of the present invention may be implemented.

[0025] Figure 1 schematically depicts a lithographic apparatus according to one embodiment of the present invention. The apparatus includes an illumination system (illuminator) IL configured to condition a radiation beam B (e.g., UV radiation or any other suitable radiation), a mask support structure (e.g., a mask table) MT constructed to support a patterning device (e.g., a mask) MA and connected to a first positioning device PM configured to accurately position the patterning device in accordance with certain parameters. The apparatus also includes a substrate table (e.g., a wafer table) WT or "substrate support" constructed to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioning device PW configured to accurately position the substrate in accordance with certain parameters. The apparatus further includes a projection system (e.g., a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g., including one or more dies) of the substrate W.

[0026] The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation.

[0027] The mask support structure supports, i.e., bears the weight of, the patterning device.

It holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The mask support structure can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The mask support structure may be a frame or a table, for example, which may be fixed or movable as required. The mask support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms "reticle" or "mask" herein may be considered synonymous with the more general term "patterning device."

[0028] The term "patterning device" used herein should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section so as to create a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase- shifting features or so called assist features. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit.

[0029] The patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam which is reflected by the mirror matrix. [0030] The term "projection system" used herein should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term "projection lens" herein may be considered as synonymous with the more general term "projection system".

[0031] As here depicted, the apparatus is of a transmissive type (e.g., employing a transmissive mask). Alternatively, the apparatus may be of a reflective type (e.g., employing a programmable mirror array of a type as referred to above, or employing a reflective mask).

[0032] The lithographic apparatus may be of a type having two (dual stage) or more substrate tables or "substrate supports" (and/or two or more mask tables or "mask supports"). In such "multiple stage" machines the additional tables or supports may be used in parallel, or preparatory steps may be carried out on one or more tables or supports while one or more other tables or supports are being used for exposure.

[0033] The lithographic apparatus may also be of a type wherein at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, e.g., water, so as to fill a space between the projection system and the substrate. An immersion liquid may also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques can be used to increase the numerical aperture of projection systems. The term "immersion" as used herein does not mean that a structure, such as a substrate, must be submerged in liquid, but rather only means that a liquid is located between the projection system and the substrate during exposure.

[0034] Referring to figure 1, the illuminator IL receives a radiation beam from a radiation source SO. The source and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In such cases, the source is not considered to form part of the lithographic apparatus and the radiation beam is passed from the source SO to the illuminator IL with the aid of a beam delivery system BD including, for example, suitable directing mirrors and/or a beam expander. In other cases the source may be an integral part of the lithographic apparatus, for example when the source is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD if required, may be referred to as a radiation system.

[0035] The illuminator IL may include an adjuster AD configured to adjust the angular intensity distribution of the radiation beam. Generally, at least the outer and/or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL may include various other components, such as an integrator IN and a condenser CO. The illuminator may be used to condition the radiation beam, to have a desired uniformity and intensity distribution in its cross-section. In accordance with the present invention, the lithographic apparatus further comprises a masking device (which, in the embodiment shown, is arranged in the illuminator IL) for adjusting a size of the cross-section of the radiation beam to match the size of a target portion on the substrate. The masking device as applied in the present invention is discussed in more detail below. It is however important to note that the masking device can be positioned at various locations along the radiation beam. As an example, shown in Figure 1, the masking device can be integrated in the illuminator, e.g., in a focal plane. As an alternative, the masking device (or part thereof) can be positioned in a focal plane of the projection system PS.

[0036] The radiation beam B is incident on the patterning device (e.g., mask MA), which is held on the mask support structure (e.g., mask table MT), and is patterned by the patterning device. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioning device PW and position sensor IF (e.g., an interferometric device, linear encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g., so as to position different target portions C in the path of the radiation beam B. Similarly, the first positioning device PM and another position sensor (which is not explicitly depicted in Figure 1) can be used to accurately position the mask MA with respect to the path of the radiation beam B, e.g., after mechanical retrieval from a mask library, or during a scan. In general, movement of the mask table MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioning device PM. Similarly, movement of the substrate table WT or "substrate support" may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner) the mask table MT may be connected to a short-stroke actuator only, or may be fixed. Mask MA and substrate W may be aligned using mask alignment marks Ml, M2 and substrate alignment marks PI, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the mask MA, the mask alignment marks may be located between the dies. The substrate, or the substrate and the substrate table, may be immersed in a bath of immersion liquid. An example of such an arrangement is disclosed in U.S. Patent No. 4,509,852 which hereby is incorporated by reference in its entirety. Alternatively, the immersion liquid may be provided by a liquid supply system only on a localized area of the substrate and in between the final element of the projection system and the substrate using a liquid confinement system, the substrate generally having a larger surface area than the final element of the projection system. An example of such an arrangement is disclosed in International Patent Application No. 99/49,504 which hereby is incorporated by reference in its entirety. The liquid is supplied by at least one inlet on the substrate, preferably along a direction of movement of the substrate relative to the final element of the projection system, and the liquid is discharged by at least one outlet which may be connected to a low pressure source. Various orientations and numbers of inlets and outlets positioned near the periphery of the final element are possible. Further, a liquid supply system may be provided with a seal member which extends along at least a part of a boundary of the space between the final element of the projection system and the substrate table. The seal member is substantially stationary relative to the projection system in the XY plane though there may be some relative movement in the Z direction (the direction of the optical axis of the projection system). A seal is formed between the seal member and the surface of the substrate. Preferably the seal is a contactless seal such as a gas seal, which may further function as a gas bearing. An example of such an arrangement is disclosed in European Patent Application No. 03252955.4 which hereby is incorporated by reference in its entirety.

European Patent Application No. 03257072.3, which hereby is incorporated by reference in its entirety, discloses a twin or dual stage immersion lithography apparatus. Such an apparatus is provided with two stages for supporting the substrate. Leveling measurements are carried out with a stage at a first position, without the presence of an immersion liquid, and exposure is carried out with a stage at a second position, where an immersion liquid is present. Alternatively, the apparatus has only one stage.

[0038] The depicted apparatus could be used in at least one of the following modes:

[0039] 1. In step mode, the mask table MT or "mask support" and the substrate table

WT or "substrate support" are kept essentially stationary, while an entire pattern imparted to the radiation beam is projected onto a target portion C at one time (i.e., a single static exposure). The substrate table WT or "substrate support" is then shifted in the X and/or Y direction so that a different target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure.

[0040] 2. In scan mode, the mask table MT or "mask support" and the substrate table

WT or "substrate support" are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e., a single dynamic exposure). The velocity and direction of the substrate table WT or "substrate support" relative to the mask table MT or "mask support" may be determined by the (de-)magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width (in the non-scanning direction) of the target portion in a single dynamic exposure, whereas the length of the scanning motion determines the height (in the scanning direction) of the target portion.

[0041] 3. In another mode, the mask table MT or "mask support" is kept essentially stationary holding a programmable patterning device, and the substrate table WT or "substrate support" is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, generally a pulsed radiation source is employed and the programmable patterning device is updated as required after each movement of the substrate table WT or "substrate support" or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array of a type as referred to above.

[0042] Combinations and/or variations on the above described modes of use or entirely different modes of use may also be employed.

[0043] In accordance with the present invention, the immersion lithographic apparatus comprises a masking device for modifying a cross-sectional shape of the radiation beam. [0044] Typically, a masking device comprises one or more blades for generating a slit shaped radiation beam suitable for scanning a particular pattern on a patterning device.

[0045] In general, the width of such a slit is defined by a pair of blades (further on also referred to as X-blades), whereby the width of the slit refers to the length of the slit in the X-direction, the X-direction being perpendicular to the Y-direction or scanning direction. The height of the slit (i.e., the length of the slit in the Y- or scanning direction) can e.g., be defined by a plate provided with a rectangular aperture (also known as a field stop), preferably combined with a pair of blades (referred to as Y-blades) for opening and closing the slit at the beginning and end of an exposure of a target portion.

[0046] In general, the X-blades of a masking device are set at a fixed distance (defining the width of the slit) which is maintained throughout the exposure of an entire substrate or set of substrates.

[0047] Typically, along the edge of a substrate, there are a number of target portions which do not fit entirely onto the substrate. Such target portions, which are further on also referred to as edge portions or edge dies, thus include part of the substrate edge. Such dies or target portions are conventionally exposed in the same manner as target portions that are entirely within the substrate. Though such edge dies will not result in properly operating electronic circuits, these edge dies are exposed in order to obtain a substrate surface that is entirely processed in substantially the same manner. As a result, subsequent processing steps such as performed in a track apparatus are facilitated because of the uniform exposure of the substrate.

[0048] The exposure of the substrate edge may however have adverse consequences, in particular in an immersion lithographic apparatus. Typically, an important height (or thickness) variation can be noticed on a substrate in the edge region; the edge region of a substrate being referred to as the outer 2 - 5 mm of the outer border of the substrate. In this region, a phenomenon known as "edge roll off can be noticed; i.e., an important decrease in thickness of the substrate towards the outer edge of the substrate. The thickness variation in this edge region can e.g., amount up to several tenths of a mm. As will be appreciated by the skilled person, due to this height variation, the exposure of the edge region cannot properly be performed in a focal plane of the projection system of the lithographic apparatus. [0049] It has been devised by the inventor that, as a result of such out-of-focus exposure of the edge region, structures can be generated in the resist layer of the edge region that are easily detached from the resist layer. Such detached structures or particles can be a source of contamination in that these structures or particles can be absorbed by the immersion fluid. As a consequence, the immersion fluid can become contaminated, resulting in an increased level of defects on the exposed target portions; the structures or particles can e.g., adhere to the substrate and/or partly block the patterned radiation beam. In order to at least mitigate the effect as described, the present invention provides in a masking device enabling a reduced exposure of an edge region of a substrate. In order to realize this, the masking device according to the present invention comprises a blade assembly configured to adjust, during exposure of a target portion comprising a substrate edge, the width of the cross-section of the radiation beam, thereby reducing a radiation dose of the substrate edge to a value less than a nominal radiation dose of the target portion. In accordance with the present invention, the width of the cross-section of the radiation beam; i.e., the length of the radiation beam in a direction substantially perpendicular to the scanning direction, is thus adjusted during the exposure of an edge die, i.e., a target portion comprising a substrate edge. By doing so, the radiation dose on the substrate edge can be reduced, thus reducing the generation of the aforementioned detachable structures.

[0050] In Figure 2, a first embodiment of a masking device according to the present invention is schematically shown. In Figure 2, a top view of a masking device 200 is shown, together with a patterning device 210 comprising a pattern 220 to be projected onto a substrate. In the embodiment shown, the masking device 200 comprises a blade assembly comprising two blades 250.1 and 250.2 for limiting a width 260 of the cross-section 270 of the radiation beam; i.e., the length of the cross-section of the radiation beam in a direction substantially perpendicular to the scanning direction. In the embodiment as shown, the scanning direction is indicated as the Y-direction. As shown, the blades 250.1 and 250.2 are positioned to limit the width of the cross-section of the radiation beam to substantially match the width of the pattern 220 provided on the patterning device 210. Note that, in general, a comparatively small border (e.g., a chrome border 225) is provided surrounding the pattern to be exposed. [0051] In accordance with the present invention, the feature blade or blade assembly is used to denote a structure that can be positioned (e.g., using an actuator) to partly obscure or block a radiation beam.

[0052] In general, the masking device can comprise a further masking structure (not shown) for limiting a length 280 of the cross-section of the radiation beam in the scanning direction.

[0053] In accordance with the present invention, the blade assembly is further configured to adjust, during exposure of a target portion comprising a substrate edge, the width of the cross-section of the radiation beam, thereby reducing a radiation dose of the substrate edge to a value less than a nominal radiation dose of the target portion.

[0054] This is illustrated in Figure 3B. In Figure 3, the cross-section 300 of the radiation beam is shown (at substrate level) relative to a substrate 310 and a target portion 320 overlapping the edge 330 of the substrate. Conventionally, as shown in Figure 3A, the entire target portion 320 is exposed to the radiation beam by scanning the substrate relative to the radiation beam. During such exposure, starting with a relative position as shown in the upper graph and ending with a relative position as shown in the lower graph of Figure 3 A, the width 340 of the cross-section is substantially maintained at a constant value, e.g., by maintaining a pair or blades at a substantially constant distance apart; in Figure 3A, the dotted lines 370.1 and 370.2 denote the contour (at substrate level) of a blade or blade assembly enabling limiting the width of the cross-section 300 of the radiation beam. Note that, as a result of maintaining the width 340 substantially constant, the exposure dose (i.e., the amount of radiation received) is substantially the same for each position of the target portion; the exposure dose e.g., depending on the intensity of the radiation beam, the length of the cross-section of the radiation beam in the scanning direction and the scanning speed. In accordance with the present invention, the width 340 of the cross-section of the radiation beam is adjusted during exposure of a target portion 320 comprising a substrate edge 330, as illustrated in Figure 3B. Figure 3B shows different positions of the cross-section of the radiation beam 300 relative to the substrate 310 and target portion 320 during an exposure sequence (starting with a relative position as shown in the upper graph and ending with a relative position as shown in the lower graph of Figure 3B. As can be seen, the shape of the cross-section 300, in particular the width 340 of the cross-section 300 is adjusted, i.e., reduced. In Figure 3B, the dotted lines 380.1 and 380.2 denote the contour (at substrate level) of a blade or blade assembly enabling the width adjustment. As such, the contours 380.1 and 380.2 can e.g., correspond to areas that are covered by blades 250.1 and 250.2 as shown in Figure 2. In the arrangement as shown, the width of the cross-section is adjusted (reduced) to such extent that the substrate edge 330 is substantially obscured from radiation. As can be seen from the contours 380.1 and 380.2 indicating the blade positions, this obscuring is, in the embodiment shown, obtained by displacing a blade of the blade assembly in the X-direction, i.e., in the direction substantially perpendicular to the scanning or Y- direction. Referring to the embodiment of the masking device shown in Figure 2, this may thus be realized by displacing the blade 250.2 towards blade 250.1 during the exposure of the target portion. In the embodiment as shown, the reduction of the width of the cross-section is initiated when the substrate edge 330 approaches the cross-section 300. By reduction the width of the cross-section, the radiation dose of the substrate edge 330 can be to a value less than a nominal radiation dose of the target portion; in the embodiment shown, the exposure dose on the substrate edge is substantially reduced to zero. Note, in order to reduce the adverse effects as mentioned above, it may be sufficient to reduce the exposure dose on the substrate edge by e.g., 50% compared to the nominal dose. In such a situation, the reduction of the width of the cross-section may thus commence at a later instance.

[0055] In the embodiment as shown in Figure 3B, the reduction of the width of the cross-section 300 is established by a mere displacement of a blade (of the blade assembly of the masking device) in a direction perpendicular to the scanning direction. The displacement of the blade as a function of time is not linear, i.e., the blade velocity is not constant, during this motion. Because of the curved wafer edge, the blade velocity in the sequence in Figure 3B needs to increase during the exposure scan. In other scans, for example in the opposite direction, the blade speed may need to decrease during the scan.

[0056] It has been devised by the inventor that other arrangements are feasible as well to reduce the exposure dose on the substrate edge. Such arrangement e.g., include a rotation of one or more blades of the blade assembly, combining both a translation and a rotation, applying particularly shaped blades enabling and adjustment of the width by a displacement in the scanning direction or any combination thereof. [0057] The following Figures show some possible, non-limiting, configurations of blades or blade assemblies enabling the required width adjustment for reducing the exposure dose on the substrate edge.

[0058] In Figure 4, a blade assembly comprising two blades 420 is schematically shown.

The blades are displaceably mounted on a frame 400. The blades can be moved in the X-direction by a driving arrangement e.g., comprising actuators 430. Such actuators can e.g., include linear motors whereby a coil of the motors is mounted to the frame 400 and a permanent magnet co-operating with the coils is mounted to the blades. An air or gas bearing can be provided enabling a non-contact relative displacement of the blades relative to the frame.

[0059] The arrangement as shown thus enables the width of the cross-section of the radiation beam (the cross-section being indicated by reference number 410) to the altered. An exposure process as schematically shown in Figure 3B can thus be realized.

[0060] In Figure 5, another possible X-blade assembly is schematically shown; the

X-blades 420 being mounted to a frame 410 and displaceable relative to each other in the X-direction by one or more actuators (not shown). In the arrangement of Figure 5, the blades are rotatably mounted on the frame 410. In Figure 5, 440 and 445 indicate the rotation axis about which the blades can be rotated, e.g., using a rotary actuator (not shown). By enabling the blades to rotate, the cross-section 410 of the radiation beam can varied in such manner that the width of the cross-section varies over the height of the cross-section. By doing so, the shape of the cross-section corresponds more accurately to the shape of the target portion that includes the substrate edge (e.g., edge 330 in Figure 3B). The substrate edge can thus be obscured more easily.

[0061] In Figure 6, a pair of X-blades 420 of a masking device according to an embodiment of the present invention are shown. The blades comprise a concave curvature or edge 425. In Figure 7, the blades 420 are shown in an assembled, overlapping state, thus forming an aperture wherein the cross-section of the radiation beam 410 is indicated. The blades 420 are mounted to a frame 400 and are displaceable relative to this frame (in the Y-direction) by actuators 430, which can be linear actuators or motors such as Lorentz actuators. In Figure 8, the right hand blade of the blade assembly is moved downwardly, relative to the cross-section of the radiation. Due to the concave curvature of the blade, the width of the cross-section 410 can be reduced. In such arrangement, a reduction of the width of the cross-section (i.e., a reduction of the length in the X-direction) can be realized by a displacement of the X-blades in the Y-direction.

[0062] Using a blade having a concave curvature enables, by an appropriate positioning of the blade, an adjustment of the cross-section of the radiation beam that substantially mimics the shape of the target portion (on substrate level) having the substrate edge.

[0063] Figures 4-8 have shown various ways of providing a blade assembly enabling an adjustment of the width of a cross-section of a radiation beam, in order to reduce, during an exposure of the target portion having a substrate edge, an exposure dose on this edge. Note that a combination of the various features of these embodiments can be made as well. As an example, the blades as shown in Figures 4 and 5 can be equipped with a concave edge as well. As a further example, the blade assembly of Figures 6-8 can be equipped with a drive arrangement for rotating the blades about the Z-axis (perpendicular to the XY-plane).

[0064] The blade assembly as applied in the masking device according to the present invention and e.g., described in above Figures can be complemented with so-called Y-blades or a field stop for limiting the cross-sectional height of the radiation beam. Such Y-blades or a field stop can be mounted independently of the X-blades. Further, in an embodiment, the blade assembly as applied in the masking device according to the present invention can be equipped with a first blade (or pair of blades) for limiting a width of the cross-section of the radiation beam to a nominal value and a second blade (or pair of blades) for adjusting the width of the cross-section of the radiation. In such arrangement the second blade (or blades) can thus be constructed as an add-on to conventional masking devices. More details on possible blade arrangements that include Y-blades can e.g., be found in US Pub. Appl. No. 2005-0012913, incorporated herein by reference in its entirety.

[0065] In an embodiment, the masking device further comprises a control unit for controlling the drive arrangement of the blade assembly. Such control unit can e.g., comprise an input terminal for receiving a signal representing a position of the substrate relative to the radiation beam, enabling the control unit to control the drive arrangement to make the appropriate adjustment to the position of the blade arrangement in order to cover or obscure the substrate edge.

[0066] Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms "wafer" or "die" herein may be considered as synonymous with the more general terms "substrate" or "target portion", respectively. The substrate referred to herein may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool and/or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers.

[0067] Although specific reference may have been made above to the use of embodiments of the present invention in the context of optical lithography, it will be appreciated that the present invention may be used in other applications, for example imprint lithography, and where the context allows, is not limited to optical lithography. In imprint lithography a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device may be pressed into a layer of resist supplied to the substrate whereupon the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is moved out of the resist leaving a pattern in it after the resist is cured.

[0068] The terms "radiation" and "beam" used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g., having a wavelength of or about 365, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV) radiation (e.g., having a wavelength in the range of 5-20 nm), as well as particle beams, such as ion beams or electron beams.

[0069] The term "lens", where the context allows, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic and electrostatic optical components.

[0070] While specific embodiments of the present invention have been described above, it will be appreciated that the present invention may be practiced otherwise than as described. For example, the present invention may take the form of a computer program containing one or more sequences of machine-readable instructions describing a method as disclosed above, or a data storage medium (e.g., semiconductor memory, magnetic or optical disk) having such a computer program stored therein.

[0071] The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the present invention as described without departing from the scope of the claims set out below.

[0072] It is to be appreciated that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections may set forth one or more but not all exemplary embodiments of the present invention as contemplated by the inventor(s), and thus, are not intended to limit the present invention and the appended claims in any way.

[0073] The present invention has been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed.

[0074] The foregoing description of the specific embodiments will so fully reveal the general nature of the present invention that others can, by applying knowledge within the skill of the art, readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, without departing from the general concept of the present invention. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance.

[0075] The breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims

WHAT IS CLAIMED IS:

1. A masking device for use in an immersion lithographic apparatus, the masking device comprising a blade assembly configured to limit a width of a cross-section of a radiation beam in a direction substantially perpendicular to a scanning direction, wherein the blade assembly is further configured to adjust, during exposure of a target portion comprising a substrate edge, the width of the cross-section of the radiation beam, thereby reducing a radiation dose of the substrate edge to a value less than a nominal radiation dose of the target portion.

2. The masking device according to claim 1, wherein the blade assembly comprises a first blade for limiting a width of the cross-section of the radiation beam to a nominal width corresponding to a width of the target portion and a second blade for adjusting, during exposure of the target portion comprising the substrate edge, the width of the cross-section of the radiation beam.

3. The masking device according to claim 1, wherein the blade assembly comprises a blade extending in the scanning direction and having a variable width in the scanning direction, and wherein the width of the cross-section of the radiation beam is adjusted, during exposure of a target portion comprising a substrate edge, by displacing the blade in the scanning direction.

4. The masking device according to claim 1, wherein the blade assembly is configured to adjust the width of the cross-section of the radiation beam, during exposure of a target portion comprising a substrate edge, by displacing a blade of the blade assembly in a direction substantially perpendicular to the scanning direction.

5. The masking device according to claim 1, wherein the blade assembly is configured to adjust the width of the cross-section of the radiation beam, during exposure of a target portion comprising a substrate edge, by rotating a blade of the blade assembly about an axis substantially parallel to the radiation beam.

6. The masking device according to claim 1, wherein the blade assembly comprises a pair of blades having a concave curvature, the concave curvatures of the blades facing each other.

7. The masking device according to any of the claims 3-6, further comprising a drive arrangement for displacing the blade or blades.

8. The masking device according to any of the preceding claims, wherein the width of the cross-section of the radiation beam is adjusted, during exposure of a target portion comprising a substrate edge, such that the radiation dose of the substrate edge is substantially zero.

9. The masking device according to any of the preceding claims, further comprising a masking arrangement for limiting a height of the cross-section of the radiation beam.

10. An immersion lithographic apparatus comprising:

an illumination system configured to condition a radiation beam; a support constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam;

a substrate table constructed to hold a substrate; and a projection system configured to project the patterned radiation beam onto a target portion of the substrate, wherein the apparatus further comprises a masking device according to any of the claims 1 to 9.

11. The lithographic apparatus according to claim 10, wherein the blade assembly of the masking device is incorporated in the illuminator.

12. The lithographic apparatus according to claim 10, wherein the blade assembly of the masking device is provided in a focal plane of the projection system.

13. The lithographic apparatus according to any of the claims 10 to 12, further comprising a control unit for controlling a position of the blade assembly of the masking device, the control unit being arranged to receive an input signal representing a position of the substrate relative to the patterned radiation beam.

14. A device manufacturing method comprising projecting a patterned beam of radiation onto a substrate, wherein a cross-section of the patterned beam of radiation is adjusted using a masking device according to any of the claims 1 to 9.

15. A masking device comprising: a blade assembly configured to limit a width of a cross-section of a radiation beam in a direction substantially perpendicular to a scanning direction, wherein the blade assembly is further configured to adjust, during exposure of a target portion comprising a substrate edge, the width of the cross-section of the radiation beam, thereby reducing a radiation dose of the substrate edge to a value less than a nominal radiation dose of the target portion.

16. The masking device according to claim 15, wherein the blade assembly comprises: a first blade configured to limit a width of the cross-section of the radiation beam to a nominal width corresponding to a width of the target portion; and a second blade configured to adjust, during exposure of the target portion comprising the substrate edge, the width of the cross-section of the radiation beam.

17. The masking device according to claim 15, wherein: the blade assembly comprises a blade extending in the scanning direction and having a variable width in the scanning direction, and the width of the cross-section of the radiation beam is adjusted, during exposure of a target portion comprising a substrate edge, by displacing the blade in the scanning direction.

18. The masking device according to claim 17, further comprising a drive arrangement for displacing the blade or blades.

19. The masking device according to claim 15, wherein the blade assembly is configured to adjust the width of the cross-section of the radiation beam, during exposure of a target portion comprising a substrate edge, by displacing a blade of the blade assembly in a direction substantially perpendicular to the scanning direction.

20. The masking device according to claim 15, wherein the blade assembly is configured to adjust the width of the cross-section of the radiation beam, during exposure of a target portion comprising a substrate edge, by rotating a blade of the blade assembly about an axis substantially parallel to the radiation beam.

21. The masking device according to claim 15, wherein the blade assembly comprises a pair of blades having a concave curvature, the concave curvatures of the blades facing each other.

22. The masking device according to claim 15, wherein the width of the cross-section of the radiation beam is adjusted, during exposure of a target portion comprising a substrate edge, such that the radiation dose of the substrate edge is substantially zero.

23. The masking device according to claim 15, further comprising a masking arrangement for limiting a height of the cross-section of the radiation beam.

24. An immersion lithographic apparatus comprising:

an illumination system configured to condition a radiation beam;

a support constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam;

a substrate table constructed to hold a substrate; and a projection system configured to project the patterned radiation beam onto a target portion of the substrate; and a masking device comprising: a blade assembly configured to limit a width of a cross-section of a radiation beam in a direction substantially perpendicular to a scanning direction,

wherein the blade assembly is further configured to adjust, during exposure of a target portion comprising a substrate edge, the width of the cross-section of the radiation beam, thereby reducing a radiation dose of the substrate edge to a value less than a nominal radiation dose of the target portion.

25. The lithographic apparatus according to claim 24, wherein the blade assembly of the masking device is incorporated in the illuminator.

26. The lithographic apparatus according to claim 24, wherein the blade assembly of the masking device is provided in a focal plane of the projection system.

27. The lithographic apparatus according to claim 24, further comprising a control unit configured to control a position of the blade assembly of the masking device, the control unit being arranged to receive an input signal representing a position of the substrate relative to the patterned radiation beam.

28. A device manufacturing method comprising: projecting a patterned beam of radiation onto a substrate, adjusting a cross-section of the patterned beam of radiation using a masking device comprising: a blade assembly configured to limit a width of a cross-section of a radiation beam in a direction substantially perpendicular to a scanning direction, wherein the blade assembly is further configured to adjust, during exposure of a target portion comprising a substrate edge, the width of the cross-section of the radiation beam, thereby reducing a radiation dose of the substrate edge to a value less than a nominal radiation dose of the target portion.