JP7494096B2 - Method and apparatus for monitoring polishing of a workpiece - Google Patents

Description

The present invention relates to a method and apparatus for polishing workpieces such as wafers, substrates, and panels, and in particular to a technique for monitoring the polishing of a workpiece based on optical information contained in reflected light from the workpiece.

In the manufacturing process of semiconductor devices, various materials are repeatedly formed in the form of films on a silicon wafer to form a layered structure. In order to form this layered structure, technology that flattens the surface of the top layer is important. One method of flattening the surface is chemical mechanical polishing (CMP).

Chemical mechanical polishing (CMP) is performed by a polishing apparatus. This type of polishing apparatus generally includes a polishing table that supports a polishing pad, a polishing head that holds a workpiece (e.g., a wafer having a film), and a polishing liquid supply nozzle that supplies a polishing liquid (e.g., a slurry) onto the polishing pad. When polishing a workpiece, the polishing head presses the surface of the workpiece against the polishing pad while supplying a polishing liquid from the polishing liquid supply nozzle onto the polishing pad. The polishing head and polishing table are each rotated to move the workpiece and polishing pad relative to each other, thereby polishing the layer to be polished that forms the surface of the workpiece.

To measure the thickness of the layer being polished, such as an insulating film or a silicon layer, the polishing machine is generally equipped with an optical film thickness measuring device. This optical film thickness measuring device is configured to direct light emitted from a light source to the surface of the workpiece and determine the thickness of the layer being polished on the workpiece by analyzing the spectrum of the light reflected from the workpiece.

Patent Document 1 discloses a technique for determining film thickness based on the amount of change in the spectrum of reflected light. Figure 8 is a graph showing the relationship between the amount of change in the spectrum and polishing time. The amount of change in the spectrum is the amount of change in the shape of the spectrum per unit time. The spectrum of the reflected light changes according to the thickness of the layer being polished. Therefore, the amount of change in the spectrum of the reflected light corresponds to the amount of the layer being polished removed per unit time.

Figure 9 is a graph showing the cumulative spectral change obtained by integrating the amount of change in the spectrum over the polishing time. As can be seen from Figure 9, the cumulative spectral change increases almost monotonically with polishing time. Therefore, the amount of polishing of the layer being polished (i.e., the current thickness or the current amount removed) can be determined from the cumulative spectral change.

JP 2015-156503 A

However, as shown in FIG. 10, local noise may be added to the amount of change in the spectrum due to the influence of the pattern formed on the surface of the workpiece, the influence of the polishing environment (e.g., slurry), etc. For this reason, as shown in FIG. 11, the cumulative amount of change in the spectrum may not increase monotonically, which may result in an erroneous estimation of the amount of polishing of the layer being polished.

Therefore, the present invention provides a method and apparatus that can accurately monitor the polishing of a workpiece while eliminating the influence of patterns formed on the surface of the workpiece and the polishing environment (e.g., slurry), etc.

In one aspect, a method for monitoring polishing of a workpiece is provided, which includes irradiating the workpiece with light while the workpiece is being polished, generating a spectrum of reflected light from the workpiece, calculating an amount of change in the spectrum per predetermined time, correcting the amount of change in the spectrum when the amount of change in the spectrum satisfies a predetermined exclusion condition, and integrating the amount of change in the spectrum that does not satisfy the exclusion condition and the corrected amount of change in the spectrum over the polishing time to calculate an accumulated amount of change in the spectrum.

In one embodiment, the exclusion condition is any one of the following: the amount of change in the spectrum is greater than a threshold value; the difference between the current amount of change in the spectrum and the average value of multiple amounts of change in the spectrum already obtained during polishing of the workpiece is greater than a threshold value; the amount of change in the spectrum is outside the range of ±Xσ from the average value of the normal distribution of multiple amounts of change in the spectrum obtained in the past (X is a predetermined coefficient); and the amount of change in the spectrum is determined to be an outlier by the Smirnoff-Grubbs test.

In one embodiment, the step of correcting the amount of change in the spectrum is a step of correcting the amount of change in the spectrum by extrapolation or interpolation.
In one aspect, the extrapolation correction uses multiple amounts of change in the spectrum aligned along the polishing time, and the interpolation correction uses multiple amounts of change in the spectrum obtained at multiple measurement points aligned on the workpiece.

In one aspect, a polishing monitoring device for a workpiece is provided, the polishing monitoring device comprising: an optical sensor head that irradiates light onto the workpiece while the workpiece is being polished and receives reflected light from the workpiece; a spectrometer that measures the intensity of the reflected light for each wavelength; and a data processing unit having a storage device in which a program is stored and an arithmetic unit that executes calculations according to instructions included in the program, the data processing unit being configured to generate a spectrum of the reflected light from measurement data of the intensity of the reflected light, calculate a change in the spectrum per predetermined time, correct the change in the spectrum when the change in the spectrum satisfies a predetermined exclusion condition, and calculate an accumulated change in the spectrum by integrating the change in the spectrum that does not satisfy the exclusion condition and the corrected change in the spectrum over the polishing time.

In one embodiment, the exclusion condition is any one of the following: the amount of change in the spectrum is greater than a threshold value; the difference between the current amount of change in the spectrum and the average value of multiple amounts of change in the spectrum already obtained during polishing of the workpiece is greater than a threshold value; the amount of change in the spectrum is outside the range of ±Xσ from the average value of the normal distribution of multiple amounts of change in the spectrum obtained in the past (X is a predetermined coefficient); and the amount of change in the spectrum is determined to be an outlier by the Smirnoff-Grubbs test.

In one embodiment, the data processing unit is configured to correct the amount of change in the spectrum by extrapolation or interpolation.
In one aspect, the data processing unit is configured to perform the extrapolation correction using multiple amounts of change in the spectrum aligned along the polishing time, and to perform the interpolation correction using multiple amounts of change in the spectrum acquired at multiple measurement points aligned on the workpiece.

According to the present invention, the amount of change in the spectrum that satisfies the exclusion criteria (i.e., contains noise) is corrected, allowing accurate monitoring of the polishing of the workpiece.

FIG. 1 is a schematic diagram illustrating an embodiment of a polishing apparatus. FIG. 4 is a diagram showing an example of a spectrum generated by a data processing unit. FIG. 1 is a diagram showing a spectrum that changes over a unit time. 1 is a graph showing the change in spectral change over polishing time while polishing a workpiece. 1 is a graph showing an accumulated amount of change in the spectrum obtained by integrating the amount of change in the spectrum over the polishing time. FIG. 6( a ) is a graph in which the amount of change in the spectrum containing noise has been removed, and FIG. 6 ( b ) is a graph in which the amount of change in the spectrum missing due to the removal has been replaced with the amount of change in the spectrum not containing noise. FIG. 1 shows an approximation generated from multiple variations in the spectrum obtained during polishing of a workpiece. 11 is a graph showing the relationship between the amount of change in spectrum and polishing time. 1 is a graph showing an accumulated amount of change in the spectrum obtained by integrating the amount of change in the spectrum over the polishing time. 11 is a graph showing the relationship between the amount of change in a spectrum including local noise and polishing time. 11 is a graph showing the relationship between the polishing time and the cumulative amount of change in the spectrum obtained by integrating the amount of change in the spectrum shown in FIG. 10 .

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
Fig. 1 is a schematic diagram showing one embodiment of a polishing apparatus. As shown in Fig. 1, the polishing apparatus includes a polishing table 3 that supports a polishing pad 2, a polishing head 1 that presses a workpiece W, such as a wafer, a substrate, or a panel having a layer to be polished, against the polishing pad 2, a table motor 6 that rotates the polishing table 3, and a polishing liquid supply nozzle 5 for supplying a polishing liquid, such as a slurry, onto the polishing pad 2. The upper surface of the polishing pad 2 constitutes a polishing surface 2a that polishes the workpiece W.

The polishing head 1 is connected to a head shaft 10, which is connected to a polishing head motor (not shown). The polishing head motor rotates the polishing head 1 together with the head shaft 10 in the direction indicated by the arrow. The polishing table 3 is connected to a table motor 6, which is configured to rotate the polishing table 3 and polishing pad 2 in the direction indicated by the arrow.

The workpiece W is polished as follows. While rotating the polishing table 3 and polishing head 1 in the direction indicated by the arrow in FIG. 1, polishing liquid is supplied from the polishing liquid supply nozzle 5 to the polishing surface 2a of the polishing pad 2 on the polishing table 3. While rotating the workpiece W by the polishing head 1, the workpiece W is pressed against the polishing surface 2a of the polishing pad 2 by the polishing head 1 with the polishing liquid present on the polishing pad 2. The layer to be polished that constitutes the exposed surface of the workpiece W is polished by the chemical action of the polishing liquid and the mechanical action of the abrasive grains contained in the polishing liquid and the polishing pad 2. Examples of the layer to be polished of the workpiece W include, but are not limited to, an insulating film and a silicon layer.

The polishing apparatus is equipped with an optical polishing monitoring device 40 that monitors the polishing of the workpiece W. The optical polishing monitoring device 40 is equipped with a light source 44 that emits light, a spectrometer 47, an optical sensor head 7 optically connected to the light source 44 and the spectrometer 47, and a data processing unit 49 connected to the spectrometer 47. The optical sensor head 7, the light source 44, and the spectrometer 47 are attached to the polishing table 3 and rotate together with the polishing table 3 and the polishing pad 2. The position of the optical sensor head 7 is a position where it crosses the workpiece W on the polishing pad 2 every time the polishing table 3 and the polishing pad 2 rotate once.

The data processing unit 49 includes a storage device 49a that stores a program for generating a spectrum and monitoring the polishing of the workpiece W, which will be described later, and a calculation device 49b that performs calculations according to instructions included in the program. The data processing unit 49 is composed of at least one computer. The storage device 49a includes a main storage device such as a RAM, and an auxiliary storage device such as a hard disk drive (HDD) or a solid state drive (SSD). Examples of the calculation device 49b include a CPU (central processing unit) and a GPU (graphic processing unit). However, the specific configuration of the data processing unit 49 is not limited to these examples.

Light emitted from the light source 44 is transmitted to the optical sensor head 7 and guided from the optical sensor head 7 to the workpiece W. The light is reflected by the workpiece W, and the reflected light from the workpiece W is received by the optical sensor head 7 and sent to the spectrometer 47. The spectrometer 47 breaks down the reflected light according to wavelength and measures the intensity of the reflected light at each wavelength. The reflected light intensity measurement data is sent to the data processing unit 49.

The data processing unit 49 is configured to generate a spectrum of the reflected light from the reflected light intensity measurement data. The spectrum of the reflected light is represented as a line graph (i.e., a spectral waveform) showing the relationship between the wavelength and intensity of the reflected light. The intensity of the reflected light can also be represented as a relative value such as reflectance or relative reflectance.

Figure 2 shows an example of a spectrum generated by the data processing unit 49. The spectrum is represented as a line graph (i.e., a spectral waveform) showing the relationship between the wavelength and intensity of light. In Figure 2, the horizontal axis represents the wavelength of the light reflected from the workpiece W, and the vertical axis represents the relative reflectance derived from the intensity of the reflected light. Relative reflectance is an index indicating the intensity of the reflected light, and is the ratio of the light intensity to a predetermined reference intensity. By dividing the light intensity (actual intensity) at each wavelength by the predetermined reference intensity, unnecessary noise such as variations in intensity inherent to the optical system of the device and the light source can be removed from the actual intensity.

The reference intensity is the intensity of light measured in advance for each wavelength, and the relative reflectance is calculated for each wavelength. Specifically, the relative reflectance is calculated by dividing the light intensity (actual intensity) at each wavelength by the corresponding reference intensity. The reference intensity can be obtained, for example, by directly measuring the intensity of light emitted from the optical sensor head 7, or by irradiating a mirror with light from the optical sensor head 7 and measuring the intensity of the reflected light from the mirror. Alternatively, the reference intensity can be the intensity of reflected light from a silicon substrate measured by the spectroscope 47 when a silicon substrate (bare substrate) on which no film is formed is being polished in the presence of water on the polishing pad 2, or when the silicon substrate (bare substrate) is placed on the polishing pad 2.

ここで、λはワークピースＷからの反射光の波長であり、Ｅ（λ）は波長λでの強度であり、Ｂ（λ）は波長λでの基準強度であり、Ｄ（λ）は光を遮断した条件下で測定された波長λでの背景強度（ダークレベル）である。 In actual polishing, the corrected actual intensity is obtained by subtracting the dark level (background intensity obtained under conditions where light is blocked) from the actual intensity, and the corrected standard intensity is obtained by subtracting the dark level from the standard intensity, and the corrected actual intensity is divided by the corrected standard intensity to obtain the relative reflectance. Specifically, the relative reflectance R(λ) can be obtained using the following formula (1).

where λ is the wavelength of reflected light from the workpiece W, E(λ) is the intensity at wavelength λ, B(λ) is the reference intensity at wavelength λ, and D(λ) is the background intensity (dark level) at wavelength λ measured under light-blocking conditions.

The optical sensor head 7 guides light to multiple measurement points on the workpiece W while crossing the workpiece W each time the polishing table 3 rotates, and receives reflected light from these multiple measurement points. The reflected light is sent to a spectroscope 47. The spectroscope 47 resolves the reflected light from each measurement point according to wavelength, and measures the intensity of the reflected light at each wavelength. The reflected light intensity measurement data is sent to a data processing unit 49, which generates a spectrum as shown in FIG. 2 from the reflected light intensity measurement data. In the example shown in FIG. 2, the spectrum of the reflected light is a spectral waveform that indicates the relationship between the relative reflectance and the wavelength of the reflected light, but the spectrum of the reflected light may also be a spectral waveform that indicates the relationship between the intensity of the reflected light itself and the wavelength of the reflected light.

ここで、λは反射光の波長であり、λ１，λ２は監視対象とするスペクトルの波長範囲を指定する最小波長および最大波長であり、ｔは研磨時間であり、Δｔは所定の単位時間であり、Ｒ（λ，ｔ）は、波長λ、時間ｔのときの相対反射率（反射光の強度）である。Δｔとしては、例えば、研磨テーブルがｐ回転（ｐは小さな自然数（例えば１））するのに要する時間とすることができる。 The spectrum of the reflected light changes according to the thickness of the layer being polished of the workpiece W. Therefore, the data processing unit 49 monitors the polishing of the workpiece W from the spectrum of the reflected light as follows: The data processing unit 49 calculates the amount of spectrum change ΔS(t) per unit time using the following equation (2).

Here, λ is the wavelength of the reflected light, λ1 and λ2 are the minimum and maximum wavelengths that specify the wavelength range of the spectrum to be monitored, t is the polishing time, Δt is a predetermined unit time, and R(λ, t) is the relative reflectance (intensity of the reflected light) at the wavelength λ and time t. Δt can be, for example, the time required for the polishing table to make p rotations (p is a small natural number (e.g., 1)).

Figure 3 shows the spectrum that has changed over a unit time Δt. The amount of spectral change ΔS(t) calculated by the above formula (2) corresponds to the area (shown by hatching) surrounded by the two spectra acquired at two different times. The area of this area corresponds to the change in thickness of the polished layer per unit time Δt. Therefore, it is expected that the change in thickness of the polished layer can be captured by integrating the amount of spectral change ΔS(t) during polishing.

ここで、ｔ０は膜厚変化の監視を開始する時間である。 Fig. 4 is a graph showing the change in the amount of spectral change ΔS(t) along the polishing time while polishing the workpiece W. As shown in Fig. 4, the amount of spectral change ΔS(t) varies periodically, but the average level of the amount of spectral change ΔS(t) is approximately constant. The data processing unit 49 calculates the amount of accumulated spectral change, which is the accumulated value of the amount of spectral change ΔS(t) along the polishing time, using the following equation (3).

Here, t0 is the time when monitoring of the film thickness change starts.

Figure 5 is a graph showing the amount of accumulated spectral change A(t) calculated using the above formula (3). As described above, since the amount of accumulated spectral change fluctuates periodically, the error from the average level due to the fluctuation is hardly accumulated. Therefore, as shown in Figure 5, the amount of accumulated spectral change A(t) increases almost linearly with the polishing time. The amount of accumulated spectral change A(t) corresponds to the amount of polishing of the workpiece W (i.e., the amount of removed layer to be polished). The above-mentioned data processing unit 49 calculates the amount of accumulated spectral change during polishing of the workpiece W and monitors the progress of polishing of the workpiece W based on the amount of accumulated spectral change. Furthermore, the data processing unit 49 may determine the polishing end point of the workpiece W from the amount of accumulated spectral change. The polishing end point can be the point at which the amount of accumulated spectral change reaches a predetermined target value.

As described with reference to FIG. 10, local noise may be added to the amount of change in the spectrum due to the influence of the pattern formed on the surface of the workpiece W, the polishing environment (e.g., slurry), etc. Such noise may prevent accurate monitoring of the polishing of the workpiece W.

The data processing unit 49 is configured to correct the amount of change in the spectrum to which noise has been added. That is, the data processing unit 49 is configured to remove the amount of change in the spectrum containing noise as shown in FIG. 6(a), and to replace the amount of change in the spectrum missing due to the removal with the amount of change in the spectrum not containing noise as shown in FIG. 6(b). More specifically, the data processing unit 49 is configured to correct the amount of change in the spectrum when the amount of change in the spectrum satisfies a predetermined exclusion condition, and to calculate the cumulative amount of change in the spectrum by integrating the amount of change in the spectrum that does not satisfy the exclusion condition and the above-mentioned corrected amount of change in the spectrum over the polishing time.

The predetermined exclusion condition is a condition for determining that the calculated amount of change in the spectrum contains noise. Specific examples of the predetermined exclusion condition include the following:
(i) the amount of change in the spectrum is greater than a threshold value; (ii) the difference between the current amount of change in the spectrum and the average value of a plurality of amounts of change in the spectrum already obtained during polishing of the workpiece W is greater than a threshold value; and (iii) the amount of change in the spectrum is outside a range of ±Xσ from the average value of a normal distribution of a plurality of amounts of change in the spectrum previously obtained (X being a predetermined coefficient).
(iv) The amount of change in the spectrum is judged to be an outlier by the Smirnoff-Grubbs test.

Regarding (i) above, the threshold is a preset fixed value, and is determined based on previously obtained data on the amount of change in the spectrum. For example, the threshold is a value that can meaningfully separate previously obtained data on the amount of change in the spectrum into a group of amounts of change in the spectrum that does not contain noise and a group of amounts of change in the spectrum that contains noise.

With regard to (ii) above, the multiple amounts of change in the spectrum already obtained during polishing of the workpiece W are, for example, the most recent N amounts of change in the spectrum excluding the amount of change in the current spectrum. The number N is a preset value. When the difference between the amount of change in the current spectrum and the average value of the multiple amounts of change in the spectra already obtained is greater than a threshold value, the amount of change in the current spectrum is likely to include noise. This threshold value may be a fixed value. Alternatively, the threshold value may be a value that varies according to the average value. For example, the threshold value may be a value that deviates from the average value by a predetermined percentage (%).

Regarding (iii) above, the multiple amounts of change in the spectrum previously obtained may be multiple amounts of change in the spectrum obtained while polishing at least one workpiece having the same structure as the workpiece W, or multiple amounts of change in the spectrum already obtained during polishing of the workpiece W.

Regarding (iv) above, the sample data used in the Smirnoff-Grubbs test may be multiple amounts of change in the spectrum obtained while polishing at least one workpiece having the same structure as workpiece W, or multiple amounts of change in the spectrum already obtained during polishing of workpiece W.

A spectral change amount that satisfies any of the above-mentioned exclusion conditions (i) to (iv) is presumed to include noise. Therefore, the data processing unit 49 corrects the spectral change amount calculated during polishing of the workpiece W when the spectral change amount satisfies any of the above-mentioned multiple exclusion conditions. This correction of the spectral change amount is a process for removing noise. The exclusion condition may be one pre-selected from the above-mentioned exclusion conditions (i) to (iv).

In one embodiment, the data processing unit 49 corrects the amount of change in the spectrum that satisfies the exclusion condition by extrapolation or interpolation. More specifically, the data processing unit 49 excludes the amount of change in the spectrum that satisfies the exclusion condition (i.e., contains noise), and obtains the amount of change in the spectrum that does not satisfy the exclusion condition (i.e., does not contain noise) that corresponds to the amount of change in the excluded spectrum by extrapolation or interpolation. Correction by extrapolation uses multiple amounts of change in the spectrum that are aligned along the polishing time, and correction by interpolation uses multiple amounts of change in the spectrum acquired at multiple measurement points that are aligned on the workpiece W.

The data processing unit 49 is configured to correct the amount of change in the spectrum that satisfies the exclusion condition by performing any one of the following operations.
(I) an operation of replacing the amount of change in a spectrum that satisfies the exclusion condition (i.e., contains noise) with the amount of change in a spectrum that does not satisfy the exclusion condition (i.e., does not contain noise); (II) an operation of replacing the amount of change in a spectrum that satisfies the exclusion condition with an average value of multiple amounts of change in a spectrum already obtained during polishing of the workpiece W; (III) an operation of replacing the amount of change in a spectrum that satisfies the exclusion condition with an average value of multiple amounts of change in a spectrum obtained at multiple adjacent measurement points on the workpiece W; (IV) an operation of generating an approximation formula from multiple amounts of change in a spectrum already obtained during polishing of the workpiece W, and replacing the amount of change in a spectrum that satisfies the exclusion condition with a value obtained by the approximation formula.

With regard to (I) above, the amount of change in the spectrum that does not satisfy the exclusion condition (i.e., does not contain noise) is the amount of change in the spectrum that has already been obtained during polishing of the workpiece W. In one embodiment, the amount of change in the spectrum that does not satisfy the exclusion condition (i.e., does not contain noise) is the amount of change in the most recent spectrum obtained immediately before the amount of change in the spectrum that satisfies the exclusion condition is obtained.

Regarding (II) above, the multiple amounts of change in the spectrum already obtained during polishing of the workpiece W are multiple amounts of change in the spectrum that do not satisfy the exclusion condition (i.e., do not contain noise). In one embodiment, the multiple amounts of change in the spectrum already obtained during polishing of the workpiece W are the most recent M amounts of change in the spectrum, not including the amount of change in the current spectrum. The number M is a preset value.

With regard to (III) above, the adjacent measurement points on the workpiece W are multiple measurement points adjacent to the measurement point on the workpiece W at which a spectral change amount satisfying the exclusion condition was obtained. As described above, the optical sensor head 7 guides light to multiple measurement points on the workpiece W while crossing the workpiece W each time the polishing table 3 rotates once, and receives reflected light from these multiple measurement points. The adjacent measurement points on the workpiece W may be, for example, multiple measurement points located on both sides of the measurement point at which a spectral change amount satisfying the exclusion condition (i.e., including noise) was obtained. The spectral change amount obtained at each adjacent measurement point is a spectral change amount that does not satisfy the exclusion condition (i.e., does not include noise).

Regarding (IV) above, the approximation formula is an equation in a coordinate system having coordinate axes representing the amount of change in the spectrum and the polishing time, as shown in FIG. 7. The approximation formula has the polishing time as a variable. The approximation formula is determined from a plurality of data points in the coordinate system identified by a plurality of amounts of change in the spectrum that do not satisfy the exclusion condition (i.e., do not contain noise) and a plurality of corresponding polishing times. The approximation formula may be expressed by a polynomial. There is no particular limit to the method of obtaining the approximation formula. The data processing unit 49 generates the approximation formula during polishing of the workpiece W, and can correct the amount of change in the spectrum by inputting the polishing time at which the amount of change in the spectrum that satisfies the exclusion condition (i.e., contains noise) is obtained into the approximation formula.

The data processing unit 49 calculates the cumulative spectral change by integrating the amount of change in the spectrum that does not satisfy the exclusion condition (i.e., does not contain noise) and the above-mentioned corrected amount of change in the spectrum over the polishing time, and monitors the amount of polishing of the workpiece W based on the cumulative spectral change. Since the cumulative spectral change is the cumulative value of the amount of change in the spectrum that does not contain noise, the data processing unit 49 can accurately monitor the amount of polishing of the workpiece W.

The above-described embodiments have been described for the purpose of enabling a person having ordinary knowledge in the technical field to which the present invention pertains to practice the present invention. Various modifications of the above-described embodiments would naturally be possible for a person skilled in the art, and the technical ideas of the present invention may also be applied to other embodiments. Therefore, the present invention is not limited to the described embodiments, but is to be interpreted in the broadest scope in accordance with the technical ideas defined by the scope of the claims.

REFERENCE SIGNS LIST 1 polishing head 2 polishing pad 2a polishing surface 3 polishing table 5 polishing liquid supply nozzle 6 table motor 7 optical sensor head 10 head shaft 40 optical polishing monitor device 44 light source 47 spectroscope 49 data processing unit 49a storage device 49b arithmetic unit

Claims (10)

1. A method for monitoring polishing of a workpiece, comprising:
irradiating the workpiece with light while the workpiece is being polished;
generating a spectrum of reflected light from the workpiece;
Calculating the amount of change in the spectrum per predetermined time;
correcting the amount of change in the spectrum when the amount of change in the spectrum satisfies a predetermined exclusion condition;
and calculating an accumulated amount of change in the spectrum by integrating the amount of change in the spectrum that does not satisfy the exclusion condition and the amount of change in the corrected spectrum over a polishing time ,
The exclusion conditions are:
the amount of change in the spectrum is greater than a fixed threshold;
a difference between the change in the current spectrum and an average of a plurality of changes in the spectra already obtained during polishing of the workpiece is greater than a variation threshold;
The amount of change in the spectrum is outside the range of ±Xσ from the average value of a normal distribution of a plurality of amounts of change in the spectrum obtained in the past (X is a predetermined coefficient); and
the amount of change in the spectrum is determined to be an outlier by the Smirnoff-Grubbs test;
is one of
the fixed threshold is a fixed value determined based on data of the amount of change in the spectrum obtained in the past,
the fluctuation threshold value is a value that is shifted from the average value by a predetermined percentage,
the plurality of variation amounts of the previously obtained spectrum used to calculate the mean value of the normal distribution are a plurality of variation amounts of the spectrum obtained while polishing at least one workpiece having the same structure as the workpiece, or a plurality of variation amounts of the spectrum already obtained during polishing of the workpiece;
A method in which the sample data used in the Smirnoff-Grubbs test are multiple variations in spectra obtained while polishing at least one workpiece having the same structure as the workpiece, or multiple variations in spectra already obtained during polishing of the workpiece. The method according to claim 1 , wherein the step of correcting the amount of change in the spectrum is a step of correcting the amount of change in the spectrum by extrapolation or interpolation. 3. The method of claim 2, wherein the correction by extrapolation uses a plurality of changes in the spectrum aligned along the polishing time, and the correction by interpolation uses a plurality of changes in the spectrum obtained at a plurality of measurement points aligned on the workpiece. The step of correcting the amount of change in the spectrum includes:
(I) replacing the amount of change in the spectrum satisfying the exclusion condition with the amount of change in the spectrum not satisfying the exclusion condition;
(II) replacing the change in the spectrum that satisfies the exclusion condition with an average value of a plurality of changes in the spectrum already obtained during polishing of the workpiece;
(III) replacing the change amount of the spectrum that satisfies the exclusion condition with an average value of a plurality of change amounts of the spectrum obtained at a plurality of adjacent measurement points on the workpiece;
(IV) generating an approximation formula from a plurality of changes in the spectrum already obtained during polishing of the workpiece, and replacing the change in the spectrum that satisfies the exclusion condition with a value obtained by the approximation formula;
The method according to claim 1, wherein In the above (I), the amount of change in the spectrum not satisfying the exclusion condition is an amount of change in the most recent spectrum acquired immediately before an amount of change in the spectrum satisfying the exclusion condition is acquired during polishing of the workpiece,
In the above (II), the plurality of change amounts of the spectrum already obtained during polishing of the workpiece are a plurality of change amounts of the spectrum that do not satisfy the exclusion condition,
In the above (III), the adjacent measurement points on the workpiece are adjacent measurement points on the workpiece at which a change in the spectrum that satisfies the exclusion condition is obtained,
5. The method according to claim 4, wherein in (IV), the approximation formula is an equation determined from a plurality of data points on a coordinate system specified by a plurality of amounts of change in the spectrum not satisfying the exclusion condition and a plurality of corresponding polishing times. 1. An apparatus for monitoring polishing of a workpiece, comprising:
an optical sensor head that irradiates light onto a workpiece and receives light reflected from the workpiece while the workpiece is being polished;
a spectroscope for measuring the intensity of the reflected light for each wavelength;
a data processing unit having a storage device storing a program and a calculation device that executes calculations according to instructions included in the program;
The data processing unit includes:
generating a spectrum of the reflected light from the measured data of the intensity of the reflected light;
Calculating the amount of change in the spectrum per predetermined time;
correcting the amount of change in the spectrum when the amount of change in the spectrum satisfies a predetermined exclusion condition;
a spectrum change amount that does not satisfy the exclusion condition and a spectrum change amount that is corrected are integrated over a polishing time to calculate a spectrum cumulative change amount,
The exclusion conditions are:
the amount of change in the spectrum is greater than a fixed threshold;
a difference between the change in the current spectrum and an average of a plurality of changes in the spectra already obtained during polishing of the workpiece is greater than a variation threshold;
The amount of change in the spectrum is outside the range of ±Xσ from the average value of a normal distribution of a plurality of amounts of change in the spectrum obtained in the past (X is a predetermined coefficient); and
the amount of change in the spectrum is determined to be an outlier by the Smirnoff-Grubbs test;
is one of
the fixed threshold is a fixed value determined based on data of the amount of change in the spectrum obtained in the past,
the fluctuation threshold value is a value that is shifted from the average value by a predetermined percentage,
the plurality of variation amounts of the previously obtained spectrum used to calculate the mean value of the normal distribution are a plurality of variation amounts of the spectrum obtained while polishing at least one workpiece having the same structure as the workpiece, or a plurality of variation amounts of the spectrum already obtained during polishing of the workpiece;
A polishing monitoring device in which the sample data used in the Smirnoff-Grubbs test are multiple changes in spectra obtained while polishing at least one workpiece having the same structure as the workpiece, or multiple changes in spectra already obtained during polishing of the workpiece. 7. The polishing monitoring apparatus according to claim 6 , wherein the data processing unit is configured to correct the amount of change in the spectrum by extrapolation or interpolation. The polishing monitoring device according to claim 7, wherein the data processing unit is configured to perform the extrapolation correction using multiple amounts of change in the spectrum aligned along the polishing time, and to perform the interpolation correction using multiple amounts of change in the spectrum acquired at multiple measurement points aligned on the workpiece. The data processing unit includes:
(I) replacing the amount of change in the spectrum that satisfies the exclusion condition with the amount of change in the spectrum that does not satisfy the exclusion condition;
(II) replacing the change in the spectrum that satisfies the exclusion condition with an average value of a plurality of change in the spectrum already obtained during polishing of the workpiece;
(III) replacing the amount of change in the spectrum that satisfies the exclusion condition with an average value of a plurality of amounts of change in the spectrum obtained at a plurality of adjacent measurement points on the workpiece;
(IV) generating an approximation formula from a plurality of changes in the spectrum already obtained during polishing of the workpiece, and replacing the changes in the spectrum that satisfy the exclusion condition with a value obtained by the approximation formula;
7. The polishing monitoring apparatus according to claim 6, wherein the amount of change in the spectrum that satisfies the exclusion condition is corrected by executing any one of the operations above. In the above (I), the amount of change in the spectrum not satisfying the exclusion condition is an amount of change in the most recent spectrum acquired immediately before an amount of change in the spectrum satisfying the exclusion condition is acquired during polishing of the workpiece,
In the above (II), the plurality of change amounts of the spectrum already obtained during polishing of the workpiece are a plurality of change amounts of the spectrum that do not satisfy the exclusion condition,
In the above (III), the adjacent measurement points on the workpiece are adjacent measurement points on the workpiece at which a change in the spectrum that satisfies the exclusion condition is obtained,
The polishing monitoring device of claim 9, wherein in (IV), the approximation equation is an equation determined from a plurality of data points on a coordinate system identified by a plurality of change amounts of the spectrum that does not satisfy the exclusion condition and a plurality of corresponding polishing times.

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