CN100488729C - Polishing state monitoring apparatus and polishing apparatus and method - Google Patents

Abstract

A polishing state monitoring apparatus measures characteristic values of a surface, being polished, of a workpiece to determine the timing of a polishing end point. The polishing state monitoring apparatus includes a light-emitting unit for applying light from a light source to a surface of a workpiece being polished, a light-receiving unit for receiving reflected light from the surface of the workpiece, a spectroscope unit for dividing the reflected light received by the light-receiving unit into a plurality of light rays having respective wavelengths, and light-receiving elements for accumulating the detected light rays as electrical information. The polishing state monitoring apparatus further includes a spectral data generator for reading the electrical information accumulated by the light-receiving elements and generating spectral data of the reflected light, and a processor for calculating a predetermined characteristic value on the surface of the workpiece based on the spectral data generated by the spectral data generator.

Description

Polishing state monitoring apparatus and burnishing device and method

Technical field

The present invention relates to be used for the device of the polishing condition of monitoring workpiece, and more specifically, relate to and be used to measure for example characteristic value on the polished surface of the workpiece of semiconductor wafer (polished object), with the polishing state monitoring apparatus of the timing of determining polish end point (polishing stops or the change of polishing condition).The present invention also relates to burnishing device in conjunction with this polishing state monitoring apparatus, and finishing method.

Background technology

Along with the semiconductor devices Highgrade integration more that become in recent years, it is thinner that circuit interconnection has become, and treat that integrated device has become sandwich construction.Therefore, must throw the surface of flat semiconductor wafer.Dispel surface irregularity by chemically mechanical polishing (CMP) processing from the surface of semiconductor wafer, the surface of throwing flat semiconductor wafer has thus become common way.

According to chemical mechanical polish process, after the polished specific period of semiconductor wafer, this polishing is finished in the position that need expect on semiconductor wafer.For example, can preferably on the metal interconnect structure of Cu (copper) or Al (aluminium), keep for example SiO ₂Insulating barrier (this insulating barrier is called as the interlayer film, because will form metal level on this insulating barrier in processing subsequently).If polished more of semiconductor wafer than what need, metal film that so will be below expose on the surface.Therefore, keep predetermined thickness, need to finish polishing in order to make the interlayer film.

Handle according to another kind, form the predetermined pattern of interconnection groove at semiconductor wafer surface.Utilizing after Cu (copper) or Cu alloy be filled in the interconnection groove, handling by chemically mechanical polishing (CMP) unnecessary portions is dispeled from the surface of semiconductor wafer.When handling polishing Cu layer by CMP, must dispel the Cu layer from semiconductor wafer selectively, only keep the Cu layer that forms in the interconnection groove simultaneously.Specifically, need in the zone except that the interconnection groove, the Cu layer be dispeled, to expose SiO ₂Deng dielectric film.

In this case, if the Cu layer in the groove that exceedingly will interconnect polishes with insulating barrier, then circuitous resistance will increase, and the discarded whole semiconductor wafer of will having to, thereby causes very big loss.Otherwise if the Cu layer is not fully polished and is retained on the insulating barrier, then partitioning circuitry well can cause short circuit like this.As a result, the Cu layer needs polished once more, causes manufacturing cost to increase.

Like this, there is known polishing state monitoring apparatus, is used to the end point of utilizing optical pickocff to measure catoptrical intensity and detect the CMP processing based on catoptrical measured intensity.Specifically, polishing state monitoring apparatus has optical pickocff, it comprises light-emitting component and photodetector, and light is applied to the polished surface of semiconductor wafer from optical pickocff, the variation of reflection of light rate in the polished surface of detection semiconductor wafer is to detect the end point that CMP handles.

The processing that below is used for measuring the optical characteristics that CMP handles is being well-known in the art:

(1) is applied to the polished surface of semiconductor wafer from for example light of semiconductor laser, light emitting diode monochromatic sources such as (LED), and the Strength Changes of reverberation is detected.

(2) white light is applied to the polished surface of semiconductor wafer, and with its spectral reflectivity with compare at the prerecorded spectral reflectivity of polish end point.

In this manual, spectral reflectivity is defined as comprising the term of " spectral reflectivity " and " spectrum specific reflectance (spectral specific reflectance) ".Spectral reflectivity is defined as " ratio of the energy of catoptrical energy and incident light ".The spectrum specific reflectance is defined as " from the energy of the reverberation of object to be monitored and ratio from the catoptrical energy of references object (for example, naked silicon wafer) ".

Recently, developed a kind of polishing state monitoring apparatus, laser beam has been applied on the wafer, and used sinusoidal wave pattern function to estimate over time, to calculate the initial film thickness of wafer from the measured value of the intensity of the reverberation of wafer.

But, in traditional polishing state monitoring apparatus, do not control the position of the polished lip-deep sampled point of wafer conductor, and, change described sampled point according to position, rotary acceleration and the stable state rotary speed of the initial angle of polishing block and the time that starts sampling processing.Therefore, for example characteristic value of desired locations on wafer surface, for example film thickness of center line on the wafer or the circumferential section on the wafer of energy measurement not.Especially, if the sampling period is very long, then be difficult to estimate remaining film profile.

Utilize in the polishing state monitoring apparatus that pattern function measures film thickness above-mentioned, change according to time of the measured value of the initial film thickness of expectation and reflected intensity and come calculating film thicknesses.Thereby, if polishing speed changes,,, then can not determine the precise analytic model function if perhaps initial film thickness is very little if perhaps be difficult to estimate initial film thickness during polishing, be difficult to measure film thickness like this.

If the sampling period is very long and a sampled point (sample area) is in the scope very wide on the surface of wafer, then the various film thicknesses that depend on isomorphic graphs and remove quantity are not measured simultaneously.Thereby, can not determine the precise analytic model function, and therefore be difficult to measure film thickness.

In CMP handled, the influence owing to mud (polishing fluid), bubble or mechanical oscillation changed from the intensity of reflected light on the polished surface of wafer.Specifically, if use monochromatic source, then the fluctuation of intensity of reflected light directly causes measure error.If the use white light, then the fluctuation of spectral reflectivity also directly causes error, has reduced the accuracy of end point detection like this.

Summary of the invention

In view of the problems referred to above of the prior art, make the present invention.An object of the present invention is to provide a kind of polishing state monitoring apparatus and in conjunction with the burnishing device of this polishing state monitoring apparatus, it can be exactly and measuring workpieces cheaply, the membrane stage of for example polished semiconductor wafer, and the timing of the definite polish end point change of polishing condition (stop to polish or).

In order to solve these traditional problems, according to a first aspect of the invention, provide a kind of polishing state monitoring apparatus, it comprises: light source; Luminescence unit is arranged in the polishing block with polished surface, is used for the light from light source is applied to the polished surface of workpiece; Light receiving unit is arranged in the polishing block, is used to receive the reverberation from the surface of workpiece; Spectroscope unit, the reverberation that is used for being received by light receiving unit are split up into has many light of wavelength separately; A plurality of light receiving elements are used to detect the light that is separated by the spectroscope unit, and accumulate detected light and cease as telecommunications; The spectroscopic data generator is used to read the telecommunications breath by a plurality of light receiving element accumulations, and produces catoptrical spectroscopic data; Control module is used to control a plurality of light receiving elements, with in the polishing block rotation, carries out sampling processing at preset time; And processor, be used for calculating the lip-deep predetermined characteristic value of workpiece based on spectroscopic data by described spectroscopic data generator generation.

By this setting, because can reasonably adjust the timing of the sampling processing of carrying out by a plurality of light receiving elements, so the desired locations on measurement point and luminescence unit and the light receiving unit process path (light that is applied and catoptrical path) of surface of the work can be aligned.Like this, whenever polishing block revolves when turning around, repeatedly the characteristic value of predetermined radial position is gone up on the surface of measuring workpieces.If the sampling period is constant, then the radial position of lip-deep each sampled point of workpiece is constant in each rotation of polishing block.Therefore, even spended time reads and calculates the telecommunications breath that is accumulated in a plurality of light receiving elements, increased the sampling period like this, but because can duplicate measurements in the characteristic value of lip-deep a plurality of radial positions of workpiece, so can find the residue film profile and the polishing progress on the polished surface of workpiece at an easy rate.Because the sampling period may be very long, so for example the general light receiving element of photodiode array can be used as light receiving element, and therefore polishing state monitoring apparatus can use cheap optical system.

In addition, have many light of wavelength separately, can determine for example characteristic value of film thickness exactly, and not be subjected to the variation of polishing speed and the influence of initial film thickness by being split up into from the reverberation on the polished surface of workpiece.Many light of wavelength increase even the sampling period is owing to use has separately, but because the characteristic value of lip-deep a plurality of radial positions that can the duplicate measurements workpiece, just as described above, so can easily control the residue film profile and the polishing progress on the polished surface of workpiece.

According to a preferred aspect of the present invention, the timing of the sampling processing that control module control is carried out by light receiving element makes sampled point be positioned on the interconnected line in center with the center of polishing block and workpiece.

According to a preferred aspect of the present invention, luminescence unit and light receiving unit are through the center of workpiece.By allowing light receiving element to pass through the center of workpiece and as mentioned above the timing of sampling processing being controlled, whenever polishing block revolves when turning around, the center of workpiece can be measured as fixing point when needing, the time that can control the residue film of workpiece so exactly changes.

According to a preferred aspect of the present invention, control module can be based on the rotary speed of polishing block to being adjusted by the sampling period of the performed sampling processing of light receiving element.Because the sampling period can be adjusted based on the rotary speed of polishing block, the radial position of lip-deep two or more expectations of workpiece can be as sampled point.Therefore, can see of the transformation of residue film, and therefore can measure the surface of workpiece with degree of precision at the specified point of peripheral part of the center of for example wafer and wafer.

According to a second aspect of the invention, provide a kind of polishing state monitoring apparatus, comprising: light source; Luminescence unit is arranged in the polishing block with polished surface, is used for the light from light source is applied to the polished surface of workpiece; Light receiving unit is arranged in the polishing block, is used to receive the reverberation from the surface of workpiece; Spectroscope unit, the reverberation that is used for being received by light receiving unit are split up into has many light of wavelength separately; A plurality of light receiving elements are used to detect many light that separated by the spectroscope unit, and accumulate detected light and cease as telecommunications; The spectroscopic data generator is used to read the telecommunications breath by the light receiving element accumulation, and produces catoptrical spectroscopic data; Control module is used to control light receiving element, with in the polishing block rotation, carries out sampling processing in predetermined timing; And processor, predetermined characteristic value is gone up on the surface that is used for calculating according to the calculating that includes multiplication workpiece, and described multiplication is multiply by predetermined weight coefficient by the wavelength component of the spectroscopic data of spectroscopic data generator generation.

By come computation of characteristic values (index) based on spectroscopic data, even initial film thickness is very little, perhaps the light transmission capacity of film is very little so that do not produce interference signal, also can monitor polishing condition based on calculated feature values.For example, can be converted into digital value as characteristic value, and therefore can detect owing to dispeling specific film and make the change point of color change with the color in the corresponding zone of sampled point.When along with polishing is carried out and the upper layer film attenuation, when causing the shape of spectral waveform to change, can measure color over time, and, can determine polish end point (stop polishing or change polishing condition) based on the characteristic value of expression color.Because characteristic value can be by standardization, so can eliminate the influence of fluctuating in the spectroscopic data.

According to a preferred aspect of the present invention, characteristic value comprises from the chromaticity coordinate value of spectroscopic data conversion.By using the standardization chromaticity coordinate value, can eliminate the influence of fluctuating in the spectroscopic data by standardization as characteristic value.Thereby, can eliminate the influence of the spectroscopic data fluctuation that the unstability by measuring system causes.

According to a preferred aspect of the present invention, light source sends the light with wave band.For example white light has broadband light from light emitted, and reverberation is separated, to obtain reflectance spectrum.Therefore, the measured value that can not rely on before each time calculates film thickness, and this is different from monochromatic sources such as for example employed semiconductor laser, LED.Thereby, can accurately determine for example characteristic value of film thickness, and not influenced by the variation in polishing speed and the initial film thickness.

According to a preferred aspect of the present invention, light source comprises light-pulse generator.By using light-pulse generator, can reduce and the corresponding scope of measuring the surface of each sampled point as light source.Like this, can calculate characteristic value more accurately, seldom be subjected to the influence of different polishing compositions and polishing speed simultaneously.

According to a preferred aspect of the present invention, light source comprises continuous light source, and this continuous light source is opened when described light receiving element is detecting reverberation from the described surface of described workpiece at least continuously.By using continuous light source as light source, can homogenizing and the reverberation that reads in the specific region, the wherein surface of light receiving element scanning workpiece in this specific region.Therefore, can discern the general variation in the color in described zone, produce the very little time dependent waveform of high-frequency fluctuation.

According to a third aspect of the invention we, provide the method for the film that a kind of polishing forms on workpiece, comprising: will be applied to the polished surface of workpiece from the light of light source; Detection is from the light of the surface reflection of workpiece; The light of separate detection and produce its spectroscopic data; Spectroscopic data and the weight function of being scheduled to are multiplied each other, and product is carried out integration, to produce scalar value; Utilize described scalar value to calculate the characteristic value on the polished surface of workpiece; And utilize the progress of described characteristic value monitoring to the surface finish of workpiece.

Preferably, the characteristic point that the time of detected characteristics value changes, and after the scheduled time that begins through the feature point detection of associating, stop polishing or change polishing condition.In addition, preferably, utilize time of characteristic value to change and adjust weight function.Weight function can move along wavelength axis.Can be used to increase the accuracy of determining polish end point according to the position of required adjustment extreme value (peak value) like this.Spectroscopic data can multiply by second weight function that is different from above-mentioned weight function, and can carry out integration to product, to produce second scalar value, utilize second scalar value to calculate second characteristic value on the polished surface of workpiece, and utilize the polishing progress that described characteristic value and second characteristic value can the monitoring workpiece surface.Thereby when the polishing to the surface of workpiece detected, (that is, minimum and maximum value) quantity was used to increase the precision (resolution ratio) that monitoring is handled can to increase extreme value.

According to a forth aspect of the invention, provide a kind of device that is used to polish the film that forms on workpiece, comprising: light source is used for light is applied to the polished surface of workpiece; Light receiving unit is used to receive the reverberation from the surface of workpiece; The spectroscope unit is used for the reverberation that is separately received by light receiving unit; The spectroscopic data generator is used for producing spectroscopic data according to the light that separates; And processor, be used for weight function with spectroscopic data and expectation and multiply each other and product is carried out integration, producing scalar value, and utilize scalar value to calculate the characteristic value on the polished surface of workpiece.

According to a preferred aspect of the present invention, device also comprises input block, is used to set weight function; And display unit, be used for the monitoring feature value.

According to a preferred aspect of the present invention, provide a kind of device, also comprise: polished surface; The top steel ring, polished surface is pressed on the surface that is used to keep workpiece and make workpiece; Detector is used to detect the characteristic point of time dependent characteristic value; And control module, be used for beginning through after the preset time in detection from characteristic point, stop polishing or change polishing condition.Described processor multiply by the second desired weight function that is different from described weight function with spectroscopic data, and product is carried out integration, producing second scalar value, and utilizes this second scalar value to calculate second characteristic value on the described surface of workpiece.Thereby when the polishing to the surface of workpiece detected, (that is, minimum and maximum value) quantity was used to improve the precision (resolution ratio) that monitoring is handled can to increase extreme value.

According to a fifth aspect of the invention, provide a kind of polishing state monitoring apparatus, comprising: light source is used for light is applied to the polished surface of workpiece; Light receiving unit is used to receive the reverberation from the surface of workpiece; The spectroscope unit is used for the reverberation that is separately received by light receiving unit; The spectroscopic data generator is used for producing spectroscopic data according to the light that separates; And processor, be used for spectroscopic data be multiply by desired weight function and product is carried out integration, with the generation scalar value, and utilize described scalar value to calculate the characteristic value on the polished surface of workpiece.

According to a preferred aspect of the present invention, device also comprises input block, is used to set weight function; And display unit, be used for the monitoring feature value.

According to the present invention, because can reasonably adjust the timing of the sampling processing of carrying out by light receiving element, so can be with measurement point with the desired locations on the path (light that is applied and catoptrical path) of process on the surface of the work aligns along luminescence unit and light receiving unit.Like this, whenever polishing block revolves when turning around, repeatedly the characteristic value of predetermined radial position is gone up on the surface of measuring workpieces.If the sampling period is constant, then the radial position of lip-deep each sampled point of workpiece is constant when polishing block rotates at every turn.Therefore, even spended time reads and calculates the telecommunications breath that is accumulated in the light receiving element, increased the sampling period, but because can be repeated to measure, so can easily understand the residue film profile and the polishing progress of surface of the work in the characteristic value of lip-deep a plurality of radial positions of workpiece.Because the sampling period may be very long, so for example the general light receiving element of photodiode array can be used as light receiving element, and therefore described polishing state monitoring apparatus can use cheap optical system.

Therefore, have many light of wavelength separately, can determine for example characteristic value of film thickness exactly, and not be subjected to the variation of polishing speed and the influence of initial film thickness by being split up into from the reverberation on the polished surface of workpiece.Even many light of wavelength increase the sampling period owing to use has separately, but because can duplicate measurements in the characteristic value of lip-deep a plurality of radial positions of workpiece, just as described above, so can easily understand the residue film profile and the polishing progress on the polished surface of workpiece.

According to the present invention, by come computation of characteristic values (index) based on spectroscopic data, even initial film thickness is very little, perhaps the light transmission capacity of film is very little so that do not produce interference signal, also can come the polishing condition of monitoring workpiece based on calculated feature values.For example, digital value can be converted into as characteristic value, and therefore the change point that makes color change owing to dispeling of film can be detected with the color in the corresponding zone of sampled point.When along with polishing is carried out and the upper layer film attenuation, when causing the shape of spectral waveform to change, can measure color over time, and, can determine polish end point (stop polishing or change polishing condition) based on the characteristic value of expression color.Because characteristic value can be by standardization, so can eliminate the influence of the fluctuation in the spectroscopic data.

Description of drawings

Fig. 1 is the schematic diagram of overall arrangement that shows the burnishing device with polishing state monitoring apparatus of the embodiment according to the present invention;

Fig. 2 is the schematic diagram that is presented at the operation of the light receiving element in the spectroscope unit under the situation of using light-pulse generator in the polishing state monitoring apparatus shown in Figure 1;

Fig. 3 is the schematic diagram that is presented at the operation of the light receiving element in the spectroscope unit under the situation of using continuous light source in the polishing state monitoring apparatus shown in Figure 1;

Fig. 4 is a plane of describing the sampling timing of polishing state monitoring apparatus shown in Figure 1:

Fig. 5 is the curve map that shows the spectroscopic data that is produced by polishing state monitoring apparatus according to the present invention;

Fig. 6 shows the curve map that concerns between the minimum variance that is used in according to film thickness in the polishing state monitoring apparatus of the present invention and spectrum approximation;

Fig. 7 is the plane that is presented at according to the measurement point under the situation of using light-pulse generator in the polishing state monitoring apparatus of the present invention;

Fig. 8 is a curve map of describing the weight function of using in the polishing state monitoring apparatus shown in Figure 1;

Fig. 9 describes the curve map of time dependent relative reflectance when oxidation film is polished be used for according to polishing state monitoring apparatus of the present invention;

Figure 10 is the curve map of variation of describing the cycle of the characteristic value that causes owing to different weight function wave-length coverages, and it is used for according to polishing state monitoring apparatus of the present invention;

Figure 11 is the schematic diagram of describing according to many groups weight function of short wavelength who uses in the polishing state monitoring apparatus of the present invention and long wavelength;

Figure 12 is the curve map of time dependent relative reflectance when oxidation film is polished that is used for according to polishing state monitoring apparatus of the present invention; This curve map has shown the variation of the spectral waveform that the variation owing to film thickness causes;

Figure 13 describes to be used for according to the characteristic value of polishing state monitoring apparatus of the present invention curve map with respect to the variation of the wave-length coverage of weight function;

Figure 14 is the plane that is presented at according to the sampled point under the situation of using continuous light source in the polishing state monitoring apparatus of the present invention;

Figure 15 is the flow chart that is used for adjusting according to the processing in sampling period of polishing state monitoring apparatus of the present invention; And

Figure 16 is the plane that is presented at according to the mode of in the polishing state monitoring apparatus of the present invention the sampling period being adjusted.

The specific embodiment

By referring to figs. 1 to 16, below will describe embodiment in detail according to burnishing device of the present invention.In Fig. 1 to 16, identical or corresponding element is represented by identical reference marker, and will no longer be repeated in this description it.

Fig. 1 is the schematic diagram of overall arrangement of the burnishing device of the embodiment according to the present invention.As shown in Figure 1, the polishing pad 10 and the top steel ring 14 that have polishing block 12, surface fixed thereon according to the burnishing device of present embodiment, top steel ring 14 is used for the semiconductor wafer W of maintenance as workpiece (polished object), and the upper surface that semiconductor wafer W is pressed on polishing pad 10.The upper surface of polishing pad 10 is as polished surface, itself and semiconductor wafer W sliding-contact as polished object.Comprise tiny abrasive particle by adhesive such as resins (by CeO ₂Deng manufacturing) fixedly abrasive sheet on the surface can be used as polished surface.

Polishing block 12 is connected to setting motor (not shown) thereunder, and the axle rotation that can center on himself as shown by arrows.Polishing liquid supply nozzle 16 is arranged on the top of polishing block 12, and provides polishing fluid Q on the polishing pad 10.

Top steel ring 14 is connected to top steel ring axle 18, and top steel ring axle 18 is connected with motor, rising and decline cylinder (not shown).Top steel ring 14 can vertically move as shown by arrows like this, and round 18 rotations of top steel ring axle.To be attracted to the lower surface of top steel ring 14 as the semiconductor wafer W of polished object and by its maintenance by vacuum etc.Utilize this configuration, the semiconductor wafer W that top steel ring 14 can will be kept by the lower surface of himself under desired pressure is pressed to polishing pad 10, and top steel ring 14 is around the axle rotation of himself simultaneously.

In the burnishing device of said structure, the semiconductor wafer W that is kept by surface under the top steel ring 14 is forced at the upper surface that rotates the polishing pad 10 on the polishing block 12.At this moment, by polishing liquid supply nozzle 16 polishing fluid Q is provided on the polishing pad 10.Utilize the polishing fluid Q that provides between surface of semiconductor wafer W (lower surface) and the polishing pad 10 that semiconductor wafer W is polished.

According to present embodiment, polishing block 12 has the polishing state monitoring apparatus 20 that is embedded in wherein, be used to measure the film thickness that for example is formed on lip-deep dielectric film of semiconductor wafer W or metal film and the characteristic value of color, and when semiconductor wafer W is polished the monitoring polishing condition.When semiconductor wafer W was polished, polishing state monitoring apparatus 20 was used for the polishing situation (thickness and the state of residue film) on the polished surface of real-time continuous ground monitoring semiconductor wafer W.Light transmissive element 22 is connected on the polishing pad 10, is used to make the light transmission from polishing state monitoring apparatus 20 to pass through.Light transmissive element 22 is made by the high-transmission rate material, for example, and non-foam polyurethane etc.Alternatively, light transmissive element 22 can be the form of transparency liquid, and described transparency liquid upwards entered in this through hole when wherein the through hole that forms on polishing pad 10 was sealed by semiconductor wafer W.Light transmissive element 22 can be positioned at the optional position on the polishing block 12, as long as it can pass through the polished surface of the semiconductor wafer W that is kept by top steel ring 14.Yet preferably, light transmissive element 22 should be positioned at its position through the semiconductor wafer W center.

As shown in Figure 1, polishing state monitoring apparatus 20 comprises: light source 30; As the light launching fiber 32 of luminescence unit, be used for the light from light source 30 be applied to semiconductor wafer W it.Polished surface; Light-receiving optical fiber 34 as light receiving unit is used to receive the reverberation from the polished surface of semiconductor wafer; Spectroscope unit 36 is used for separately the light that received by light-receiving optical fiber 34 and a plurality of photodetector and is used to store the light that is separated by spectroscope and ceases as telecommunications; Control module 40 is used to control the reading the time of handling beginning of photodetector of light source 30 energisings and dead electricity and spectroscope unit 36; And power supply 42, be used to provide electrical power to control module 40.Light source 30 and spectroscope unit 36 all are provided electrical power via control module 40.

Light launching fiber 32 and light-receiving optical fiber 34 have light transmitting terminal and optical receiving end respectively, and it is set to the polished surface perpendicular to semiconductor wafer W basically.Consider the replacement work of polishing pad 10 and the light quantity that is received by light-receiving optical fiber 34, light launching fiber 32 and light-receiving optical fiber 34 are arranged so that not from the polished surface of polishing block 12 and protrude upward.A plurality of photodetectors of spectroscope unit 36 are used as light receiving element, and comprise the array of 512 photodiodes.

Spectroscope unit 36 is connected to control module 40 via cable 44.Information from the photodetector (light receiving element) of spectroscope unit 36 is sent to control module 40 by cable 44.Based on the information of this transmission, control module 40 produces catoptrical spectroscopic data.Specifically,, be used for reading the telecommunications breath that photodetector is stored, and produce catoptrical spectroscopic data as the spectroscopic data generator according to the control module 40 of present embodiment.The cable 46 that stretches out from control module 40 extends through polishing block 12 and is connected to the processor 48 that for example includes personal computer.The spectroscopic data that is produced by the spectroscopic data generator of control module 40 is sent to processor 48 via cable 46.

Based on the spectroscopic data that receives from control module 40, processor 48 calculates the characteristic value on the polished surface of semiconductor wafer W, for example film thickness and color.Processor 48 also has from the controller (not shown) of control burnishing device and receives function about the information of polishing condition, and changes based on time of calculated feature values and to determine polish end point (stop polishing or change polishing condition) and the function that sends order to the controller of burnishing device.

As shown in Figure 1, range sensor (proximity sensor) 50 is arranged on the lower end of polishing block 12 near its outer, circumferential edge, and tracker (dog) 52 is arranged on the outside of polishing block 12, and aims at range sensor 50.Whenever polishing block 12 revolves when turning around, 50 pairs of trackers 52 of range sensor detect, to detect the anglec of rotation of polishing block 12.

Light source 30 comprises the light source that is used to launch the light with the wave-length coverage that comprises white light.For example, light source 30 can comprise for example light-pulse generator of xenon lamp etc.If light source 30 comprises light-pulse generator, then light source 30 is switched at each measurement point with the form of pulse by triggering signal during polishing.Alternatively, light source 30 can comprise tengsten lamp, and the light-receiving end of terminal in the emission of the light of light launching fiber 32 at least and light-receiving optical fiber 34 all can be switched on when semiconductor wafer W polished surperficial continuously.

Pass the terminal and light transmissive element 22 of light emission of light launching fiber 32 from the light of light source 30, and be applied to the polished surface of semiconductor wafer W.Light is passed light transmissive element 22 by the polished surface reflection of semiconductor wafer W, and the light-receiving optical fiber 34 of polished state monitoring apparatus receives.The light that is received by light-receiving optical fiber 34 is sent to spectroscope unit 36, and wherein spectroscope unit 36 is separated into light and has many light of wavelength separately.Have separately that the light that separates of wavelength is applied to and the corresponding photodetector of wavelength, and photodetector comes stored charge according to the amount of the light that is applied.The telecommunications breath of storing in the photodetector is read (release) in the predetermined moment, and is converted into data signal.This data signal is sent to the spectroscopic data generator of control module 40, and control module 40 produces and the corresponding spectroscopic data of each measurement point.

The operation of the photodetector of spectroscope unit 36 below will be described.Fig. 2 and 3 is presented at the schematic diagram that spectroscope unit 36 comprises the photodetector mode of operation of N photodetector 60-1 under the situation of 60-N.Fig. 2 has shown the operator scheme when light source 30 comprises light-pulse generator, and Fig. 3 has shown the operator scheme when light source 30 comprises continuous light source.In Fig. 2 and 3, transverse axis is represented the time.In the line of each photodetector of expression, rising part represents that the telecommunications breath is stored in the photodetector, and sloping portion is represented the telecommunications breath is read (release) from photodetector.In Fig. 2, the time that solid circles (●) indicating impulse light source is energized.

In a sampling period, photodetector 60-1 is switched continuously to 60-N, to cease from wherein reading (release) telecommunications.Just as described above, photodetector 60-1 ceases as telecommunications to the amount of the light of 60-N storage respective wavelength, and the sampling period T that phase place is different betwixt reads the telecommunications breath of (release) storage repeatedly from photodetector 60-1 to 60-N.Sampling period T is set to less relatively value, ceases as telecommunications in 60-N as long as there are enough light quantities to be stored in photodetector 60-1, and can handle the data that read from photodetector 60-1 to 60-N fully in real time.If photodetector comprises the array of 512 photodiodes, sampling period T is at 10 milliseconds of orders of magnitude so.In Fig. 2 and Fig. 3, to the last a photodetector 60-N is read after first photodetector 60-1 is read, elapsed time S, wherein S＜T.In Fig. 2, the time that light-pulse generator is energized (among Fig. 2 by ● the expression) as the sampling time.In Fig. 3, first photodetector 60-1 be read and begin to store new telecommunications breath to the last half time (among Fig. 3 by * expression) of time of being read of photodetector 60-N as sampling time of corresponding measured zone.Be called as sampled point in the sampling time in the face of the point of light transmissive element 22 on the semiconductor wafer W.

In Fig. 2, all photodetector 60-1 to 60-N all when light source 30 was switched on by moment (about several microseconds) storage light.Suppose that the telecommunications breath of storing among last photodetector 60-N is read (release) and is represented by Q up to the time that light source 30 is energized afterwards, if the telecommunications that light source 30 is stored in first photodetector 60-1 breath is read (release) and is energized before, then 0＜Q＜T-S.Q can be the arbitrary value in the scope of being represented by above-mentioned inequality.Yet, below suppose Q=(T-S)/2.The first photodetector 60-1 is than Zao S+Q of sampling time, i.e. the timing of (T+S)/2 is read and begins to store new telecommunications breath.In Fig. 3, the first photodetector 60-1 also is read in the time than Zao (T+S)/2 of sampling time.For continuous light source shown in Figure 3, because photodetector 60-1 begins store electricity information in the different time respectively to 60-N, and read the telecommunications breath of storage respectively from photodetector 60-1 to 60-N in the different time, so the actual measurement zone is slightly different according to wavelength.

Then, below will describe and utilize polishing state monitoring apparatus 20 to determine the processing in sampling times.At first, below will be described in the processing of determining the sampling time under the situation that adopts light-pulse generator.Fig. 4 is a schematic diagram of describing the sampling time of polishing state monitoring apparatus 20.Whenever polishing block 12 revolves when turning around, the 50 pairs of trackers 52 as the reference position of triggering range sensor 50 of range sensor that are arranged on the outer, circumferential edge of turntable 12 detect.Specifically, as shown in Figure 4, the anglec of rotation is defined as along the direction opposite with polishing block 12 direction of rotation from line L _T-WThe angle of (after this be called and be the center wafer line) beginning, wherein L _T-WThe pivot C that connects polishing block 12 _TCenter C with semiconductor wafer W _WWhen the anglec of rotation was θ, range sensor 50 detected tracker 52.The center C of semiconductor wafer W _WCan specify by the position of control top steel ring 14.

As shown in Figure 4, if the center C of supposition polishing block 12 _TCenter C with light transmissive element 22 _LBetween lateral separation represent the center C of polishing block 12 by L _TCenter C with semiconductor wafer W _WBetween lateral separation represent by M, the radius on the measured surface of semiconductor wafer W (equaling the polished surface of semiconductor wafer W except that its zone, cut edge) is represented by R, and the angle that the measured surface of 22 pairs of semiconductor wafer W of light transmissive element is scanned is represented by 2 α, then, satisfy following equation (1) according to the cosine law that is used for determining angle α:

$\mathrm{\α}={\cos }^{-1}\left(\frac{L^2+M^2-R^2}{2\mathrm{LM}}\right)---\left(1\right)$

According to present embodiment, the sampling time is adjusted, make center wafer line L _T-WThe point P of last light transmissive element 22 processes must be sampled point.If center wafer line L _T-WThe quantity of the sampled point of one side is n (integer), and when the measured surface of 22 pairs of semiconductor wafer W of light transmissive element was scanned, the quantity of all sampled points was represented by 2n+1, comprises center wafer line L so _T-WOn sampled point P.

If the outer circumferential area of top steel ring 14 is positioned at the outside of semiconductor wafer so that stop bias light, the condition that is present in the measured surface in semiconductor wafer W in first sampling time of light transmissive element 22 can be represented by the inequality (2) of following demonstration so, wherein ω _TThe angular speed of expression polishing block 12.Can determine to satisfy the Integer n of this condition according to inequality (2).

α-ω _TT≤nω _TT<α

Promptly

$\frac{\mathrm{\&alpha;}}{{\mathrm{\&omega;}}_{T}T}-1\&le;n<\frac{\mathrm{\&alpha;}}{{\mathrm{\&omega;}}_{T}T}---\left(2\right)$

If light transmissive element 22 and range sensor 50 are all with respect to the center C of polishing block 12 _TBe positioned at identical angle, do when once rotating when polishing block 12 so, can determine that range sensor 50 detects the time t that begins store electricity information after the trackers 52 up to the first photodetector 60-1 in first sampling period according to following equation (3) _s, that is, and sampling time started t _s:

$t_s=\frac{\mathrm{\&theta;}}{{\mathrm{\&omega;}}_T}-(\mathrm{nT}+\frac{T+S}{2})$

$=\frac{\mathrm{\&theta;}}{{\mathrm{\&omega;}}_T}-(n+\frac{1}{2})T-\frac{S}{2}---\left(3\right)$

When light transmissive element 22 appears at outside the polished surface of semiconductor wafer W,, can be discarded in the data that obtain in first sampling period in order to remove the light quantity of storing in the photodetector reliably.In this case, can determine the time started t that samples according to following equation (4) _s:

$t_s=\frac{\mathrm{\&theta;}}{{\mathrm{\&omega;}}_T}-(\mathrm{nT}+\frac{T+S}{2}+T)$

$=\frac{\mathrm{\&theta;}}{{\mathrm{\&omega;}}_T}-(n+\frac{3}{2})T-\frac{S}{2}---\left(4\right)$

Polishing state monitoring apparatus 20 is based on the sampling time started t that determines thus _sBegin its sampling processing.Specifically, detecting beginning elapsed time t by 50 pairs of trackers 52 of range sensor _sAfterwards, the pulsing light of control module 40 beginning light sources 30, and the operation timing of the photodetector of control spectroscope unit 36 are with in each sampling period T repeated sampling cycle.Be created in the spectrum of reflected light data of each sampled point by the spectroscopic data generator of control module 40, and send it to processor 48.Based on spectroscopic data, processor 48 is determined the characteristic value on the polished surface of semiconductor wafer W, for example, and film thickness.

According to present embodiment, because the center wafer line L of 22 processes of light transmissive element _T-WOn some P must be sampled point, so whenever polishing block 12 revolve when turning around can the duplicate measurements object surface on the characteristic value at specified radial position place.If the sampling period is constant, then the radial position of the measurement point on the object surface all is constant when each rotation of polishing block 12.Therefore, and compare in the situation of uncertain position measurement characteristic value, this measures the situation that more helps discerning the residue film on the semiconductor wafer W of handling.Especially, if light transmissive element 22 is set to pass the center C of semiconductor wafer W _W, then polishing block 12 whenever revolves and turns around, must be with the center C of semiconductor wafer W _WMeasure as fixing point, thereby discern the situation of time dependent residue film on the semiconductor wafer W more accurately.

If light source 30 comprises continuous light source, so because each photodetector store electricity information and begin store electricity information continuously, so Integer n is to determine in the mode that is different from light-pulse generator in the different time.Specifically, when the first photodetector 60-1 began store electricity information, light transmissive element 22 need be present in the measured surface of semiconductor wafer W.Therefore, provide the following inequality that is used for determining Integer n:

$\mathrm{\&alpha;}-{\mathrm{\&omega;}}_{T}T\&le;n{\mathrm{\&omega;}}_{T}T+{\mathrm{\&omega;}}_I\frac{T+S}{2}<\mathrm{\&alpha;}$

That is,

$\frac{(\frac{\mathrm{\&alpha;}}{{\mathrm{\&omega;}}_T}-\frac{S}{2})}{T}-\frac{3}{2}\&le;n<\frac{(\frac{\mathrm{\&alpha;}}{{\mathrm{\&omega;}}_T}-\frac{S}{2})}{T}-\frac{1}{2}---\left(5\right)$

Integer n can be according to determining with upper inequality (5), and sampling time started t _sCan determine according to equation (3) or (4).As using light-pulse generator, polishing state monitoring apparatus 20 is based on the sampling time started t that determines _sBegin its sampling processing, and from determine the characteristic value on the polished surface of semiconductor wafer W at the spectroscopic data of each sampled point, for example, film thickness.In above-mentioned example,, set up certain conditions with respect to the timing and the relation of the position between light transmissive element 22 and the range sensor 50 of paired pulses light source energising.Even these conditions do not satisfy, n and t ₂Can be determined equally.

Then, below will describe from the processing of the spectroscopic data calculating film thicknesses of each sampled point as characteristic value.In the present embodiment, if express spectroscopic data, come calculating film thicknesses based on cycle (quantity of the ripple between the peak value) with the proportional fact of this film thickness so about the spectroscopic data of layer film thickness according to the wave number (quantity of per unit length ripple) of the spectroscopic data of representing by transverse axis that is obtained with by the light intensity that the longitudinal axis is represented.

For example, suppose that the spectroscopic data that obtains has the waveform as showing among Fig. 5.Spectral waveform shown in Figure 5 has illustrated the following fact:

(1) existence has the interference wave pattern of constant cycle.

(2) there is skew.

(3) there is the linear drift that is essentially that increases to the right.

(4) owing to interfere efficient,, interfere wave amplitude more little along with wave number is big more.

Because the above-mentioned fact, if interference ω wave period is known, expectation can be estimated spectral waveform by following function f (x) so:

$f\left(x\right)={\mathrm{\&alpha;}}_0+{\mathrm{\&alpha;}}_{1}x+{\mathrm{\&alpha;}}_2\left(\frac{1}{x}\right)\sin (\mathrm{\&omega;x}+\mathrm{\&delta;})---\left(6\right)$

Right side in equation (6), the skew of first reflection spectral waveform, the drift of second reflection spectral waveform, and the periodic waveform of the 3rd reflection spectroscopic data.More particularly, in the 3rd, (1/x) reflection is reduced by the amplitude that the wave number increase causes, and δ reflection phase shift, if film thickness is very big, it is very remarkable that phase shift just becomes.

According to addition theorem, satisfy following equation (7):

sin(ωx+δ)＝sinωx·cosδ+cosωx·sinδ (7)

Therefore, equation (6) can be amended as follows:

$f\left(x\right)={\mathrm{\&alpha;}}_0+{\mathrm{\&alpha;}}_{1}x+{\mathrm{\&alpha;}}_2\left(\frac{1}{x}\right)\sin \mathrm{\&omega;x}+{\mathrm{\&alpha;}}_3\left(\frac{1}{x}\right)\cos \mathrm{\&omega;x}---\left(8\right)$

If f ₀(x)=1, f ₁(x)=and x, f ₂(x)=(1/x) sin ω x, and f ₃(x)=(1/x) cos ω x can estimate the spectrum of measuring by function f (x) according to following equation (9) so, as the linear summation of these four functions:

f(X)＝α ₀f ₀(x)+α ₁f ₁(x)+α ₂f ₂(x)+α ₃f ₃(x) (9)

If evaluation function f (x) is estimated best that with respect to the spectrum of measuring it is minimum that variance so therebetween becomes.Like this, defined the evaluation function f (x) of hypothesis certain films thickness, the factor alpha of function f (x) ₀, α ₁, α ₂And α ₃Be determined, make evaluation function f (x) and the spectrum measured between the variance minimum, and determine the minimum variance of this moment.Aforementioned calculation is carried out when changing film thickness, and the result is plotted in the curve map of the transverse axis with expression film thickness value and the longitudinal axis of representing minimum variance.As a result, produced the curve map that shows among Fig. 6.As shown in Figure 6, curve map has the minimum point (summit) of minimum variance, and the shape that has at the evaluation function f of minimum point (x) spectrum of approaching measurement.Therefore, to calculating, as the film thickness that will determine with the corresponding film thickness of this evaluation function f (x) (the film thickness d among Fig. 6).

In the time of in measuring processing, polishing block 12 and light transmissive element 22 move on the polished surface of semiconductor eyeglass W.If the rotary speed of polishing block or top steel ring 14 and sampling period T are very big, the sweep limits of each sampled point is very big so.Therefore, if not simultaneously, light source 30 switch on continuously according to the polished lip-deep position of semiconductor eyeglass W when composition and polishing speed, so various film thicknesses are all measured a sampled point while.Therefore, do not obtain tangible interference spectrum, and therefore, can not produce tangible summit shown in Figure 6.In view of this shortcoming, preferably, use light-pulse generator as light source 30, it is switched in several microseconds.If use this light-pulse generator, so can be with the polished lip-deep little discrete point P of semiconductor wafer W _S1Measure as measurement point, and can measure the film thickness in each measurement point exactly.

In above-mentioned example, film thickness is calculated as characteristic value.Will calculated feature values be not limited to film thickness.According to the material of workpiece (polished object), when removing upper layer film from object, the color of object may have very big variation.For example, when the copper film on the workpiece was removed, the color that has red gloss may be from disappearing at workpiece.Therefore, the change color on the polished surface of workpiece can be used as the index of the state that is used to discern polished surface.In view of above-mentioned characteristic, below will be described in each sampled point and calculate the processing of color as characteristic value according to spectroscopic data.

As shown in Figure 8, before and spectroscopic data g afterwards with polish end point (stop polishing or change polishing condition) ₁(λ), g ₂(λ) compare mutually, and defined the weight function w (λ) that has higher value for the bigger variation in wave-length coverage in advance.Measured value ρ (λ) at the spectroscopic data of the reverberation of each wavelength X multiply by weight function w (λ), and the result is added, that is, integration is a scalar value.The scalar value that produces is used as characteristic value X.Specifically, according to following equation (10) defined feature value X:

$X_i=\underset{\mathrm{\&lambda;}}{\mathrm{\&Sigma;}}w\left(\mathrm{\&lambda;}\right)\mathrm{\&rho;}\left(\mathrm{\&lambda;}\right)\mathrm{\&Delta;\&lambda;}---\left(10\right)$

Alternatively, can define a plurality of weight function w _i(λ) (i=1,2 ...), and can defined feature value X according to following equation (11) _i:

$X_i=\frac{\underset{\mathrm{\&lambda;}}{\mathrm{\&Sigma;}}{w}_i\left(\mathrm{\&lambda;}\right)\mathrm{\&rho;}\left(\mathrm{\&lambda;}\right)\mathrm{\&Delta;\&lambda;}}{\underset{i}{\mathrm{\&Sigma;}}\underset{\mathrm{\&lambda;}}{\mathrm{\&Sigma;}}w\left(\mathrm{\&lambda;}\right)\mathrm{\&rho;}\left(\mathrm{\&lambda;}\right)\mathrm{\&Delta;\&lambda;}}---\left(11\right)$

According to above-mentioned processing, even along with polishing is carried out and become thin and spectral waveform of upper layer film changes its shape, also can measure the variation in the color at any time, and can determine polish end point (stop polishing or change polishing condition) based on the characteristic value of color.

In equation (10), if weight function w (λ) is defined as w (λ ₀)=1, w (λ)=0 (λ ≠ λ ₀), Δ λ=1 can obtain to be illustrated in wavelength X so ₀The characteristic value X of representative spectral value.If weight function w (λ) is defined as w (λ ₁)=1, w (λ ₂)=-1, w (λ)=0 (λ ≠ λ ₁, λ ₂), Δ λ=1/ (λ ₁-λ ₂), can obtain characteristic value X so, it is illustrated in and is connected to each other wavelength X in the spectrogram ₁, λ ₂The slope of straight line.The measured value ρ (λ) of spectroscopic data can be in advance near wavelength separately by homogenizing, to reduce the influence of noise.

The spectroscopic data ρ (λ) that measures can be the spectrum of a large amount of reverberation at each wavelength, perhaps by the spectrum of reference reflecting plate, or and then measures the standardized relative spectral reflectivity of handling after the beginning of spectrum.

Weight function w (λ) can be defined as mating with JIS-8701.Specifically, the spectroscopic data (reflectivity of spectrum) that has been switched to chromaticity coordinate (x, y) also can be used as characteristic value.Below will describe spectroscopic data is transformed into chromaticity coordinate (x, y) and uses the processing of the chromaticity coordinate (x, y) of conversion as characteristic value.To (14), can calculate tristimulus values X, Y, the Z of the color of reflective object according to following equation (12):

$Y=k{\&Integral;}_{380}^{780}P\left(\mathrm{\&lambda;}\right)\stackrel{\&OverBar;}{x}\left(\mathrm{\&lambda;}\right)\mathrm{\&rho;}\left(\mathrm{\&lambda;}\right)\mathrm{d\&lambda;}---\left(12\right)$

$Y=k{\&Integral;}_{380}^{780}P\left(\mathrm{\&lambda;}\right)\stackrel{\&OverBar;}{y}\left(\mathrm{\&lambda;}\right)\mathrm{\&rho;}\left(\mathrm{\&lambda;}\right)\mathrm{d\&lambda;}---\left(13\right)$

$Z=k{\&Integral;}_{380}^{780}P\left(\mathrm{\&lambda;}\right)\stackrel{\&OverBar;}{z}\left(\mathrm{\&lambda;}\right)\mathrm{\&rho;}\left(\mathrm{\&lambda;}\right)\mathrm{d\&lambda;}---\left(14\right)$

X (λ), y (λ), z (λ): based on the color matching functions of 2 dimension visual field XYZ systems, wherein λ represents wavelength, the spatial distribution of the light source of P (λ) expression supposition, k represents to make look excitation value Y to equate coefficient to be determined with light quantity, and the spatial distribution that ρ (λ) expression is measured.Can define the spatial distribution ρ (λ) that measures according to following equation (15), for example:

$\mathrm{\&rho;}\left(\mathrm{\&lambda;}\right)=\frac{{\mathrm{\&rho;}}_M\left(\mathrm{\&lambda;}\right)}{{\mathrm{\&rho;}}_B\left(\mathrm{\&lambda;}\right)}---\left(15\right)$

ρ wherein _M(λ) spatial distribution of expression measurement, and ρ _B(λ) reflectance spectrum of the naked silicon of expression distributes.

Ratio x, the y of X component, Y component and Z component, z arrive (18) according to following equation (16) and determine from look excitation value X, Y, Z:

$x=\frac{X}{X+Y+Z}---\left(16\right)$

$y=\frac{Y}{X+Y+Z}---\left(17\right)$

$z=\frac{Z}{X+Y+Z}---\left(18\right)$

The ratio x of Que Dinging, y, z are called chromaticity coordinate thus.Among ratio x, y, the z, have only two to be independently.Therefore, the combination of x, y be often used as chromaticity coordinate value (x, y).

By this way, spectroscopic data can be converted into chromaticity coordinate value (x, y), and based on chromaticity coordinate value (x, y) any one or two come together to determine polish end point (stop polishing or change polishing condition).Chromaticity coordinate value can be considered to the special case of equation (11).As utilizing equation (11), chromaticity coordinate value as equation (16) to (18) represented by standardization.Thereby, can eliminate the influence of the fluctuation of spectral reflectivity by standardization.By this way, by using chromaticity coordinate value, can eliminate the influence of the fluctuation of the spectral reflectivity that the unstability by measuring system causes as characteristic value.

By the color matching functions in the equation (12) to (14) and the spatial distribution of light source are being set at parameter, can be the weight of each wafer optimized wave-length coverage, it has a plurality of variations on spectral reflectivity owing to polish.Therefore, can measure the state on the polished surface of wafer more accurately.

Then, a specific example below will be described, wherein by comprising that the calculating with multiplication calculates on the polished surface of workpiece predetermined characteristic value, described multiplication multiplies each other the wavelength component of the spectroscopic data that is produced by the spectroscopic data generator and the weight function of being scheduled to, with monitoring polishing progress.

For according to definite characteristic values such as equation (10), (11), importantly how to define weight function w (λ).Preferably, can adjust weight function w (λ) according to purpose.

For example,, and will discern the time of dispeling this film on color if polished film is the metal film that a great difference is arranged with basalis, so with the corresponding wave band of color of film to be dispeled in definition have the weight function of big weight.For example, if polished film is a copper film, because copper film has red color and luster and is approximately λ=800nm at wavelength and has bigger reflected intensity, weight function w (λ) has bigger weight near being defined in λ=800nm so.According to the following definite characteristic value X of equation (10):

$X=\underset{\mathrm{\&lambda;}}{\mathrm{\&Sigma;}}w\left(\mathrm{\&lambda;}\right)\mathrm{\&rho;}\left(\mathrm{\&lambda;}\right)\mathrm{\&Delta;\&lambda;}$

The value of characteristic value X depends on it whether is copper film to be arranged and great changes will take place.Even the specific wavelength of the first spectroscopic data ρ (λ) occur to disturb, owing to carried out integration operation, so compare with the reflected intensity at the λ=800nm place of direct monitoring, the influence of interference is littler.

Use equation (11), i is set at i=1,2, and weight function w ₁(λ) have bigger weight near being defined in λ=800nm, and weight function w ₂(λ) be defined in no matter whether be to have copper film all in the wave band of reflected intensity, to have big weight with substantial constant.At this moment, characteristic value:

${\mathrm{<figure-callout\; id="1"\; label="X"\; filenames="C200380101631E00371.png"\; state="\{\{state\}\}">X</figure-callout>}}_1=1/\{1+\underset{\mathrm{\&lambda;}}{\mathrm{\&Sigma;}}{w}_2\left(\mathrm{\&lambda;}\right)\mathrm{\&rho;}\left(\mathrm{\&lambda;}\right)\mathrm{\&Delta;\&lambda;}/\underset{\mathrm{\&lambda;}}{\mathrm{\&Sigma;}}{w}_1\left(\mathrm{\&lambda;}\right)\mathrm{\&rho;}\left(\mathrm{\&lambda;}\right)\mathrm{\&Delta;\&lambda;}\}$

Have whether its basis is the value that copper film alters a great deal.In addition, even the amount of reflection ray increases or reduces according to interference, also can obtain the waveform of time vary stable.

In order to detect polish end point (polish stop stop or for example be applied to pressure in a plurality of pressurized zone that are provided with in the steel ring of top respectively or the polishing condition of mud (polishing fluid) type changes), the characteristic point that time of the characteristic value that occurs is in the above described manner changed (predetermined threshold value, increase or the beginning that reduces or end, extreme value or the like) detects, and at the fixed time film is carried out excessive polishing, and switch polishing operation then.The excessive polishing time can be zero.

Then, below will be described in polished film is under the situation of for example light transmissive films of oxidation film etc., the specific examples of the processing that weight function is adjusted.

If polished film is the light transmissive films of oxidation film etc. for example, and has uniform thickness and be in interference-free perfect condition, so because the polished caused interference of film, relative reflectance changed just as shown in Figure 9 in the time of each wavelength.If polished film has refractive index n and film thickness d, and light has wavelength X (in a vacuum), and the corresponding film thickness difference of one-period that changes with the time is represented by Δ d=λ/2n so.Therefore, if film thickness is along with the polishing time linearity reduces, then relative reflectance changes in time, makes its minimum and maximum value periodically occur, and is just as shown in Figure 9.In Fig. 9, block curve is represented the relative reflectance at wavelength X=500nm place, and dashed curve is represented the relative reflectance at wavelength X=700nm place.

Fig. 9 studies show that: along with light wavelength shortens, the time dependent cycle of relative reflectance also shortens, and extreme value occurs more continually.Therefore, calculating for the multiplication that is multiplied each other by the wavelength component and the weight function that comprise spectroscopic data comes the time of calculated feature values to change, along with the wavelength in the weight function of discussing becomes shorter, the cycle that this time changes is supposed to become shorter, and has more multipole value.

Figure 10 has shown when the oxidation film in interconnection composition (interconnection pattern) is polished and has come monitoring feature value X according to equation (11) ₃An example.Characteristic value is to utilize three weight function w shown in Figure 11 ₁(λ), w ₂(λ), w ₃Set (λ) (sets) L, S calculate.Characteristic value repeatedly increases or reduces, and up to about 70 seconds, and changes the state of characteristic value then.Because characteristic value is considered to increase and reduce owing to the light that reduces based on the thickness of polished film disturbs basically,, prevents the increase of characteristic value and reduce so the part of the supposition interconnection composition or the composition that interconnects was exposed about 70 seconds.

For the monitoring feature value, the minimum and maximum value that time of characteristic value is changed detects, with explanation polishing progress.If the polishing progress stops when detecting extreme value and measures film thickness as a reference, the progress of polishing can be relevant with the thickness of polished film so.Therefore, the cycle that changes along with time of characteristic value shortens, and resolution ratio improves and can carry out meticulous monitoring.

In the example that Figure 10 shows, the characteristic value of L has 10 extreme values, and the characteristic value of S has 15 extreme values.According to the characteristic value of L, can in 11 zones that separate, discern polishing.According to the characteristic value of S, can in 16 zones that separate, discern polishing.

For polish end point (polishing stops or the change of polishing condition), detect being close to the film thickness extreme value (characteristic point) before that reaches expectation, and film at a time between by excessive polishing, this time is corresponding to the difference between the film thickness of the film thickness at extreme value place and expectation.Therefore, the cycle that changes along with time of characteristic value shortens, and the excessive polishing time also shortens, and like this, has increased the accuracy of end point detection.Just as described above, by weight function is set to short-wave band, can improve the accuracy of monitoring polishing and the accuracy of detection end point.

Usually, light source has effective energy in the wave band that limits.Along with light wavelength shortens, light is by a large amount of scatterings such as the light transmissive element in mud, the polishing pad, thereby reduced signal to noise ratio (S/N).Consider the cycle and the signal to noise ratio of the time variation of characteristic value, determine to set the wave band of weight function.

The processing that two or more characteristic values in the set that derives from a plurality of different weight functions are followed the tracks of simultaneously below will be described.

As understandable according to Figure 10, by using the characteristic value of determining respectively from set L, the S of weight function shown in Figure 11 simultaneously, can in 26 zones that separate, discern polishing, be used for further increasing the accuracy (resolution ratio) that monitoring is handled.In fact, because occur simultaneously basically,, polishing is less than 26 zones so can being divided into about two some extreme values of gathering the characteristic value of L, S.

The example that weight function moves and adjusts in wave-length coverage below will be described.If polished film is the light transmissive films of oxidation film etc. for example, and have homogeneous thickness and be in interference-free perfect condition, owing to the interference that is caused by polished film, spectral waveform is (corresponding to by wave number being changed into the curve map that wavelength is drawn on the transverse axis shown in Figure 5) as shown in figure 12 so.If film has refractive index n and film thickness d, and for the wavelength that closes on maximum point (or smallest point) by λ ₁, λ ₂Expression, and supposition is very little in the influence of the phase place variation of reflex time light wave, satisfies following equation so:

That is,

When film thickness carried out along with polishing and reduces, represented to the film thickness of 980nm as changing to 990nm from 1000nm among Figure 12, the minimum and maximum of spectrogram shifted to the short wavelength from the long wavelength.Therefore, expectation is: when weight function was shifted to long wavelength side, the extreme value of characteristic value occurred more early.

Figure 13 shown when the oxidation film of as shown in figure 10 same patterned is polished, utilize the set L of weight function of Figure 11 and weight function L1, L2, L3 according to equation (11) to characteristic value X ₃An example of monitoring, wherein weight function L1, L2, L3 be by on wavelength axis, will gathering L weight function respectively to long wavelength side move 10nm, 20nm, 30nm obtains.Can see from Figure 13: along with weight function is all shifted to the long wavelength, the phase place that the time of characteristic value changes is offset more forward.

Therefore, the waveform of the characteristic value that changes based on time about the sample wafer of having been polished in advance, by move and adjust weight function on wavelength axis, the extreme value (summit or end point) that the time of characteristic value changes can be adjusted to the timing of expectation.Like this, the excessive polishing time can be minimized, to increase the accuracy of end point detection.

Specifically, the excessive polishing time is based on that the peak value of characteristic value establishes.Because the polishing of excessive polishing in the time is to carry out under the situation that supposition is not observed truly to film, implement under uniform films thickness speed yet polish, so preferably make the excessive polishing time shorter, obtain polish end point accurately thus.Thereby preferably, the peak value of characteristic value and polish end point are close as far as possible mutually.According to above-mentioned processing, by the flexible strategy of weight function being shifted to long wavelength (or short wavelength), peak value can be brought into the timing of expectation.In order to determine above-mentioned weight function, preferably, the wafer as polished object is polished, from wherein obtaining spectroscopic data, carry out simulation when adjusting weight function, with computation of characteristic values, and the time change list of employing characteristic value reveals the weight function of the trend of expectation.

The situation of continuous light source as light source 30 of using here will be described.The time of considering the characteristic value of determining according to above-mentioned processing (color) changes, if light-pulse generator is used as light source 30, so owing to semiconductor wafer W on the difference of the corresponding composition of measurement point make change color, the time that trends towards changing characteristic value like this under high frequency changes.In this case, be difficult to the general trend of the time variation of grasp characteristic value.If carry out the smoothing processing that for example rolling average is handled, to suppress high-frequency fluctuation, phase delay takes place so, and the detection of polish end point is delayed.

Preferably, use continuous light source, be used to suppress this high-frequency fluctuation as light source 30.Figure 14 has shown at the situation down-sampling point P of continuous light source as light source 30 _S2With with sampled point P _S2Relation between the corresponding measured zone X.As shown in figure 14, each sampled point P _S2Before and after reverberation all be accumulated in continuously in each photodetector, and by homogenizing physically.Therefore, reduce the fluctuation that the influence owing to composition causes, reduced high-frequency fluctuation described above like this.

In order to measure the polished surface of semiconductor wafer W, importantly watch the transition of residue film at the specified point of the circumferential section of the center of for example semiconductor wafer W and semiconductor wafer W.If the sampling period is fixed, still, according to the rotary speed of polishing block 12, sampled point is fixed on the position on the line that scans along the polished surface of 22 pairs of semiconductor wafer W of light transmissive element.For example, the circumferential section of energy measurement semiconductor wafer W not.According to present embodiment, in the sampling period, promptly the accumulated time of photodetector can be adjusted based on the rotary speed of polishing block 12.

The flow chart of the processing that the rotary speed that Figure 15 is based on polishing block 12 was adjusted the sampling period.At first, as shown in figure 16, being included in should be as the desired point P of sampled point _VThe radius R at place _V, polishing block 12 center C _TCenter C with semiconductor wafer W _WBetween lateral separation M, the center C of polishing block 12 _TCenter C with light transmissive element 22 _LBetween lateral separation L, the angular velocity of rotation ω of polishing block 12 _T, and minimum sampling period T all be transfused to (step 1) in interior condition.These conditions can perhaps can be stored in the memory in advance by the operator via the keyboard input as the personal computer of processor 48, perhaps can transmit from the controller of burnishing device.

Then, according to equation (1), determine center C at polishing block 12 _TThe place is from wafer center line L _T-WThe angle α of beginning _V(step 2).Determine from a P according to inequality (2) _VTo center wafer line L _T-WThe quantity n of sampled point _V(step 3).No matter whether light source 30 comprises light-pulse generator, as fruit dot P _VBe positioned at the measured interior surface of semiconductor wafer W fully, then use the inequality (2) relevant with light-pulse generator, then, based on the angle α that calculates thus _VQuantity n with sampled point _V, come the calculating sampling period T according to following equation (19) _V(step 4):

$T_V=\frac{{\mathrm{\&alpha;}}_V}{n_V{\mathrm{\&omega;}}_T}---\left(19\right)$

According to the sampling period T that determines thus _V, can measure at the expectation radius R _VThe point P at place _VTherefore, by adjusting expectation radius R as condition entry _V, except center wafer line L _T-WOn point beyond, for example the desired radial position of wafer circumferential position can be used as sampled point, as shown in Figure 16.

Although show in detail and described certain preferred embodiment of the present invention, be appreciated that at this and can make various variations and modification, and do not deviate from the scope of claims.

Industrial applicability

The present invention can be applied to for for example workpiece of semiconductor wafer and be polished to flat stone mill The burnishing device of light, and preferably be used in the semiconductor devices manufacturing.

Claims (7)

1, a kind of polishing state monitoring apparatus comprises:

Light source;

Luminescence unit is arranged in the polishing block with polished surface, is used for light is applied to from described light source the polished surface of workpiece;

Light receiving unit is arranged in the described polishing block, is used to receive the reverberation from the described surface of described workpiece;

The spectroscope unit, the reverberation that is used for being received by described light receiving unit is separated into has many light of wavelength separately;

A plurality of light receiving elements are used to detect many light that separated by described spectroscope unit, and many light that accumulation detects cease as telecommunications;

The spectroscopic data generator is used to read the telecommunications breath by described a plurality of light receiving element accumulations, and produces described catoptrical spectroscopic data;

Control module is used to control described a plurality of light receiving element, with in described polishing block rotation, carries out sampling processing in predetermined timing; And

Processor is used for calculating the characteristic value of being scheduled on the described surface of described workpiece based on the spectroscopic data that is produced by described spectroscopic data generator; Wherein,

The timing of the sampling processing that the control of described control module is carried out by described a plurality of light receiving elements makes sampled point be positioned on the interconnected line in center with the center of described polishing block and described workpiece.

2, according to the polishing state monitoring apparatus of claim 1, wherein, described luminescence unit and described light receiving unit are through the center of described workpiece.

3, according to any one polishing state monitoring apparatus in the claim 1 to 2, wherein, described control module can be adjusted the sampling period of the sampling processing of being carried out by described a plurality of light receiving elements based on the rotary speed of described polishing block.

4, according to any one polishing state monitoring apparatus in the claim 1 to 2, wherein, described light emitted has the light of a wave band.

5, according to any one polishing state monitoring apparatus in the claim 1 to 2, wherein, described light source comprises light-pulse generator.

6, according to any one polishing state monitoring apparatus in the claim 1 to 2, wherein, described light source comprises continuous light source, and this continuous light source is opened when described a plurality of light receiving elements detect the reverberation from the described surface of described workpiece at least continuously.

7, a kind of burnishing device comprises:

The top steel ring is used to keep workpiece;

Polishing block has the polished surface with described workpiece sliding-contact;

According to any one polishing state monitoring apparatus in the claim 1 to 6; And

Light transmissive element is arranged on the described polishing block, be used to make the light that applies from the described luminescence unit of described polishing state monitoring apparatus and from the reverberation on the described surface of described workpiece from wherein seeing through.

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