JP2022082902A - Polishing method - Google Patents

Abstract

To provide a polishing method enabling accurate thickness of a polishing object layer to be determined, without receiving influence of noise.SOLUTION: The method is a polishing method for polishing a polishing object layer of a workpiece W, and includes the steps of: rotating a polishing table 3 supporting a polishing pad 2; polishing the polishing object layer by pressing the workpiece W against the polishing pad 2; irradiating the workpiece W with light; receiving reflected light from the workpiece W; measuring intensity of the reflected light for each wavelength; generating a spectral waveform showing a relationship between the intensity and the wavelength of the reflected light; performing Fourier transformation processing on the spectra waveform thereby generating a frequency spectrum; moving a peak search range of the frequency spectrum in accordance with a polishing time; determining peak of the frequency spectrum in the peak search range; and determining thickness of the polishing object layer corresponding to the determined peak.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for polishing a workpiece such as a wafer, a substrate, and a panel, and more particularly to a technique for determining the thickness of a layer to be polished based on the spectrum of reflected light from the workpiece.

The manufacturing process of a semiconductor device includes various steps such as a step of polishing an insulating film such as SiO ₂ and a step of polishing a metal film such as copper and tungsten. The back-illuminated CMOS sensor manufacturing process includes a process of polishing a silicon layer (silicon wafer) in addition to a process of polishing an insulating film or a metal film.

Polishing of the polishing target layer (insulating film, metal film, silicon layer, etc.) constituting the exposed surface of the workpiece is terminated when the thickness of the polishing target layer reaches a predetermined target value. As an example of the method of measuring the thickness of the layer to be polished during polishing, the surface of the workpiece was irradiated with light, and the spectral waveform of the light reflected from the workpiece was subjected to the Fourier transform to obtain the obtained result. There is an optical monitoring method that determines the thickness based on the peak of the frequency spectrum (see, for example, Patent Document 1). The peak of the frequency spectrum changes depending on the thickness of the layer to be polished. Therefore, the thickness of the layer to be polished can be monitored by tracking the peak of the frequency spectrum during polishing of the workpiece.

Japanese Unexamined Patent Publication No. 2013-11390

However, a pseudo peak may appear in the frequency spectrum due to the polishing environment such as slurry or the underlying layer existing under the polishing target layer. Conventional optical monitoring methods may erroneously track such pseudopeaks, resulting in inability to determine accurate thickness.

Further, the conventional optical monitoring method may fail to determine the thickness of the layer to be polished when the pseudo-peak caused by noise overlaps the target peak corresponding to the thickness of the layer to be polished. ..

Therefore, an object of the present invention is to provide a polishing method capable of accurately determining the thickness of the polishing target layer without being affected by noise.

In one aspect, it is a polishing method for polishing the polishing target layer of the workpiece, in which the polishing table supporting the polishing pad is rotated and the workpiece is pressed against the polishing pad to polish the polishing target layer. The workpiece is irradiated with light, the reflected light from the workpiece is received, the intensity of the reflected light is measured for each frequency, and a spectral waveform showing the relationship between the intensity and the frequency of the reflected light is generated. The spectral waveform is subjected to Fourier transform processing to generate a frequency spectrum, the peak search range of the frequency spectrum is moved according to the polishing time, the peak of the frequency spectrum within the peak search range is determined, and the determination is made. A polishing method for determining the thickness of the layer to be polished corresponding to the peak is provided.

In one aspect, the peak search range is a range including a value calculated based on the previously determined thickness of the polishing target layer and the polishing rate of the workpiece.
In one aspect, the polishing rate is a preset polishing rate.
In one aspect, the polishing rate is a polishing rate calculated during polishing of the workpiece.

In one aspect, it is a polishing method for polishing the polishing target layer of the work piece, in which the polishing table supporting the polishing pad is rotated, the work piece is pressed against the polishing pad, and the polishing target layer is polished. The work piece is irradiated with light, the reflected light from the work piece is received, the intensity of the reflected light is measured for each wavelength, and a spectral waveform showing the relationship between the intensity and the wavelength of the reflected light is generated. Noise is removed from the spectral waveform using a filter, and the spectral waveform from which the noise has been removed is subjected to Fourier transform processing to generate a frequency spectrum, and the thickness of the polishing target layer is based on the peak of the frequency spectrum. The thickness of the polishing target layer corresponding to the peak of the frequency spectrum disappeared by the removal of the noise is determined, and a plurality of values of the polishing target layer obtained during polishing of the workpiece are used. Polishing methods are provided that are complemented by the extrapolation used.

In one aspect, the filter is configured to remove from the spectral waveform noise having a frequency at the peak of the frequency spectrum that does not move with the polishing time of the workpiece.
In one aspect, the noise is noise caused by light reflected from the underlying layer of the polishing target layer.
In one aspect, the filter is a band stop filter.
In one aspect, the polishing method polishes another work piece having the same pattern as the work piece before polishing the work piece, and noise contained in the spectral waveform of the reflected light from the other work piece. Further includes the step of creating the filter for removing the above.
In one aspect, the polishing method further comprises the step of creating the filter for removing noise contained in the spectral waveform of the reflected light from the workpiece during polishing of the workpiece.

In one reference example, a polishing device for polishing a layer to be polished of a workpiece, a rotatable polishing table that supports the polishing pad, and a polishing head that presses the workpiece against the polishing pad on the polishing table. An optical sensor head that irradiates the work piece held by the polishing head with light and receives the reflected light from the work piece, a spectroscope that measures the intensity of the reflected light for each wavelength, and the reflection. A polishing control unit that determines the thickness of the layer to be polished from the intensity of light is provided, and the polishing control unit generates a spectral waveform showing the relationship between the intensity and the wavelength of the reflected light, and Fouriers the spectral waveform. The conversion process is performed to generate a frequency spectrum, the peak search range of the frequency spectrum is moved according to the polishing time, the peak of the frequency spectrum within the peak search range is determined, and the peak of the determined peak corresponds to the determined peak. A polishing apparatus is provided that is configured to determine the thickness of the layer to be polished.

In one reference example, a polishing device for polishing a layer to be polished of a workpiece, a rotatable polishing table that supports the polishing pad, and a polishing head that presses the workpiece against the polishing pad on the polishing table. An optical sensor head that irradiates the work piece held by the polishing head with light and receives the reflected light from the work piece, a spectroscope that measures the intensity of the reflected light for each wavelength, and the reflection. A polishing control unit that determines the thickness of the layer to be polished from the intensity of light is provided, and the polishing control unit generates a spectral waveform showing the relationship between the intensity and the wavelength of the reflected light, and uses a filter to generate the spectral waveform. Noise is removed from the spectral waveform, the spectral waveform from which the noise has been removed is subjected to Fourier transform processing to generate a frequency spectrum, and the thickness of the polishing target layer is determined based on the peak of the frequency spectrum. The thickness of the layer to be polished corresponding to the peak of the frequency spectrum disappeared by the removal of the noise is obtained by extrapolation using a plurality of values of the thickness of the layer to be polished acquired during polishing of the workpiece. Polishing equipment is provided that is configured to complement.

In one reference example, a command is issued to the table motor to rotate the polishing table supporting the polishing pad, and a command is issued to the polishing head to press the workpiece against the polishing pad to press the workpiece against the polishing pad to be a layer to be polished. A step of irradiating the workpiece with light by issuing a command to the light source, and a step of generating a spectral waveform showing the relationship between the intensity of the reflected light from the workpiece and the wavelength of the reflected light. A step of generating a frequency spectrum by performing a Fourier conversion process on the spectral waveform, a step of moving the peak search range of the frequency spectrum according to the polishing time, and a peak of the frequency spectrum within the peak search range. A computer-readable recording medium on which a program is recorded is provided for causing a computer to perform a step of determining and a step of determining the thickness of the layer to be polished corresponding to the determined peak.

In one reference example, a command is issued to the table motor to rotate the polishing table supporting the polishing pad, and a command is issued to the polishing head to press the workpiece against the polishing pad to press the workpiece against the polishing pad to be a layer to be polished. A step of irradiating the workpiece with light by issuing a command to the light source, and a step of generating a spectral waveform showing the relationship between the intensity of the reflected light from the workpiece and the frequency of the reflected light. Based on the step of removing noise from the spectral waveform using a filter, the step of performing a Fourier conversion process on the spectral waveform from which the noise has been removed to generate a frequency spectrum, and the peak of the frequency spectrum. The polishing target layer obtained during the polishing of the workpiece was obtained from the steps of determining the thickness of the polishing target layer and the thickness of the polishing target layer corresponding to the peak of the frequency spectrum disappeared by removing the noise. A computer-readable recording medium on which the program is recorded is provided to allow the computer to perform steps complemented by extrapolation with multiple values of thickness.

According to the present invention, the polishing method determines the exact thickness of the layer to be polished by moving the search range of the peak of the frequency spectrum according to the polishing time without tracking the pseudo peak caused by noise. Can be done.
Further, the polishing method can determine the exact thickness of the layer to be polished by removing noise from the spectral waveform generated from the reflected light from the workpiece using a filter.

It is a schematic diagram which shows one Embodiment of a polishing apparatus. It is a schematic diagram for demonstrating the principle of an optical film thickness measuring apparatus. It is a top view which shows the positional relationship between a work piece and a polishing table. It is a figure which shows an example of the spectral waveform generated by a polishing control part. It is a figure which shows an example of the frequency spectrum generated by a polishing control part. It is a figure explaining the peak search range in the Nth measurement. It is a figure explaining the peak search range in N + 1th measurement. It is a figure explaining how the peak search range is moved according to a polishing time. It is a flowchart explaining an example of the process of moving a peak search range and determining the thickness of a layer to be polished. It is a figure which shows the frequency spectrum before the filter processing. It is a figure which shows the frequency spectrum after a filter process. It is a figure explaining the state of extrapolating the disappeared peak. It is a flowchart explaining an example of the process of removing noise by using a filter.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic view showing an embodiment of a polishing device. As shown in FIG. 1, the polishing apparatus includes a polishing table 3 that supports the polishing pad 2, a polishing head 1 that presses a workpiece W having a polishing target layer against the polishing pad 2, and a table motor 6 that rotates the polishing table 3. A polishing liquid supply nozzle 5 for supplying a polishing liquid such as a slurry and a polishing control unit 49 for controlling the operation of the polishing device are provided on the polishing pad 2. The upper surface of the polishing pad 2 constitutes a polishing surface 2a for polishing the workpiece W. Examples of the workpiece W include wafers, substrates, panels and the like.

The polishing head 1 is connected to a head shaft 10, and the head shaft 10 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 the table motor 6, and the table motor 6 is configured to rotate the polishing table 3 and the polishing pad 2 in the direction indicated by the arrow. The polishing head 1, the polishing head motor, and the table motor 6 are connected to the polishing control unit 49.

The workpiece W is polished as follows. While rotating the polishing table 3 and the polishing head 1 in the direction indicated by the arrow in FIG. 1, the 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 the work piece W is rotated by the polishing head 1, the work piece W is pressed against the polishing surface 2a of the polishing pad 2 by the polishing head 1 in a state where the polishing liquid is present on the polishing pad 2. The surface of the workpiece W is polished by the chemical action of the polishing liquid and the mechanical action of the abrasive grains and the polishing pad 2 contained in the polishing liquid.

The polishing device includes an optical film thickness measuring device 40 that measures the thickness of the layer to be polished of the workpiece W. The optical film thickness measuring device 40 includes a light source 44 that emits light, a spectroscope 47, and an optical sensor head 7 connected to the light source 44 and the spectroscope 47. The light source 44 and the spectroscope 47 are connected to the polishing control unit 49. The optical sensor head 7, the light source 44, and the spectroscope 47 are attached to the polishing table 3 and rotate integrally with the polishing table 3 and the polishing pad 2. The position of the optical sensor head 7 is a position that crosses the surface of the workpiece W on the polishing pad 2 each time the polishing table 3 and the polishing pad 2 make one rotation.

The light emitted from the light source 44 is transmitted to the optical sensor head 7 and irradiates the surface of the workpiece W from the optical sensor head 7. 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 spectroscope 47. The spectroscope 47 decomposes the reflected light according to the wavelength and measures the intensity of the reflected light at each wavelength. The intensity measurement data of the reflected light is sent to the polishing control unit 49.

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

FIG. 2 is a schematic view for explaining the principle of the optical film thickness measuring device 40, and FIG. 3 is a plan view showing the positional relationship between the workpiece W and the polishing table 3. In the example shown in FIG. 2, the workpiece W has a base layer and a polishing target layer formed on the base layer. The layer to be polished is, for example, a silicon layer or an insulating film.

The optical sensor head 7 is composed of the tips of the light emitting optical fiber cable 31 and the light receiving optical fiber cable 32, and is arranged so as to face the surface of the workpiece W. The optical sensor head 7 irradiates the workpiece W with light each time the polishing table 3 rotates once, and receives the reflected light from the workpiece W.

The light radiated to the workpiece W is reflected at the interface between the medium (water in the example of FIG. 2) and the layer to be polished, and the interface between the layer to be polished and the base layer, and the light wave reflected at these interfaces. Interfere with each other. The way of interference of this light wave changes depending on the thickness of the layer to be polished (that is, the optical path length). Therefore, the spectrum generated from the reflected light from the workpiece W changes according to the thickness of the layer to be polished. The polishing control unit 49 performs a Fourier transform process (or a fast Fourier transform process) on the spectral waveform to generate a frequency spectrum, and determines the thickness of the layer to be polished based on the peak of the frequency spectrum. When the polishing target layer is a silicon layer and the medium is water as shown in FIG. 2, it is preferable to use light having a wavelength of 1100 nm or less in order to prevent the light from being absorbed by water.

During the polishing of the workpiece W, the optical sensor head 7 moves across the workpiece W each time the polishing table 3 makes one rotation. When the optical sensor head 7 is below the workpiece W, the light source 44 emits light. The light is transmitted through the light projecting optical fiber cable 31 and irradiates the surface (polished surface) of the workpiece W from the optical sensor head 7. The reflected light from the workpiece W is received by the optical sensor head 7 and sent to the spectroscope 47 through the light receiving optical fiber cable 32. The spectroscope 47 measures the intensity of the reflected light at each wavelength over a predetermined wavelength range, and sends the intensity measurement data of the reflected light to the polishing control unit 49. The polishing control unit 49 generates a spectrum of reflected light (that is, a spectral waveform) representing the intensity of light for each wavelength from the intensity measurement data.

FIG. 4 is a diagram showing an example of a spectral waveform generated by the polishing control unit 49. In FIG. 4, the horizontal axis represents the wavelength of the reflected light from the workpiece W, and the vertical axis represents the relative reflectance derived from the intensity of the reflected light. The relative reflectance is an index showing the intensity of the reflected light, and is a ratio of the intensity of the light to a predetermined reference intensity. By dividing the light intensity (measured intensity) at each wavelength by a predetermined reference intensity, unnecessary noise such as variation in the intensity peculiar to the optical system of the device or the light source can be removed from the measured 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 obtained by dividing the light intensity (measured intensity) at each wavelength by the corresponding reference intensity. The reference intensity is obtained, for example, by directly measuring the intensity of the light emitted from the optical sensor head 7, or by irradiating the mirror with light from the optical sensor head 7 and measuring the intensity of the reflected light from the mirror. .. Alternatively, the reference strength is when the silicon substrate (bare substrate) on which the film is not formed is water-polished on the polishing pad 2 in the presence of water, or the silicon substrate (bare substrate) is on the polishing pad 2. It may be the intensity of the reflected light from the silicon substrate measured by the spectroscope 47 when placed.

ここで、λはワークピースＷから反射した光の波長であり、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 dark level (background strength obtained under the condition of blocking light) is subtracted from the measured strength to obtain the corrected measured strength, and the dark level is subtracted from the standard strength to obtain the corrected reference strength. Then, the relative reflectance is obtained by dividing the corrected actual measurement intensity by the correction reference intensity. Specifically, the relative reflectance R (λ) can be obtained by using the following equation (1).

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

The polishing control unit 49 issues a command to the light source 44 to generate light each time the polishing table 3 rotates once. The optical sensor head 7 optically connected to the light source 44 irradiates the surface (polished surface) of the workpiece W with light, and the optical sensor head 7 further receives the reflected light from the workpiece W. The reflected light is sent to the spectroscope 47 optically connected to the optical sensor head 7. The spectroscope 47 decomposes the reflected light according to the wavelength and measures the intensity of the reflected light at each wavelength. The reflected light intensity measurement data is sent to the polishing control unit 49, and the polishing control unit 49 generates a spectrum as shown in FIG. 4 from the reflected light intensity measurement data. In the example shown in FIG. 4, the spectrum of the reflected light is a spectral waveform showing the relationship between the relative reflectance and the wavelength of the reflected light, but the spectrum of the reflected light is the intensity of the reflected light itself and the wavelength of the reflected light. It may be a spectral waveform showing the relationship between.

The polishing control unit 49 performs a Fourier transform process (typically, a fast Fourier transform process) on the obtained spectral waveform to analyze the spectral waveform. More specifically, the polishing control unit 49 performs a Fourier transform process (or a fast Fourier transform process) on the spectral waveform to extract the frequency component and its intensity contained in the spectral waveform, and obtains the frequency component. Is transformed into the thickness of the layer to be polished using a predetermined relational expression, and a frequency spectrum showing the relationship between the thickness of the layer to be polished and the intensity of the frequency component is generated. The above-mentioned predetermined relational expression is a function representing the thickness of the layer to be polished with the frequency component as a variable, and can be obtained from the actual measurement result, the optical film thickness measurement simulation, the theoretical expression, and the like.

FIG. 5 is a diagram showing a frequency spectrum generated by the polishing control unit 49. In FIG. 5, the vertical axis represents the intensity of the frequency component included in the spectral waveform, and the horizontal axis represents the thickness of the layer to be polished. As can be seen from FIG. 5, the frequency spectrum has a peak at thickness t1. That is, this frequency spectrum indicates that the thickness of the polishing target layer is t1. In this way, the thickness of the layer to be polished is determined from the peak of the frequency spectrum.

The polishing control unit 49 includes a storage device 49a in which a program for executing a determination of the thickness of the polishing target layer is stored, and a processing device 49b for executing an operation according to an instruction included in the program. The polishing control 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) and a solid state drive (SSD). Examples of the processing device 49b include a CPU (central processing unit) and a GPU (graphic processing unit). However, the specific configuration of the polishing control unit 49 is not limited to these examples.

The polishing control unit 49 determines the polishing end point based on the determined thickness of the polishing target layer, and controls the operation of the polishing device. For example, the polishing control unit 49 determines the polishing end point at the time when the determined thickness of the polishing target layer reaches the target value. In one embodiment, the polishing end point may be determined by measuring the thickness of the layer to be polished and the thickness of the underlying layer. The polishing control unit for determining the thickness of the layer to be polished and the control unit for controlling the polishing operation of the workpiece W may be configured separately.

FIG. 6 is a diagram illustrating a peak search range R1 in the Nth measurement. In FIG. 6, the vertical axis represents the intensity of the frequency component included in the spectral waveform, and the horizontal axis represents the thickness of the layer to be polished. Each of the plurality of frequency spectra shown in FIG. 6 is generated by the polishing control unit 49 each time the polishing table 3 makes one rotation during polishing of the workpiece W. The peak P1 is the peak that appears at the Nth measurement (when the polishing table 3 is at the Nth rotation), and the peak P2 is the peak that appears at the N + 1th measurement (when the polishing table 3 is at the N + 1th rotation). Yes, the peak P3 is the peak that appeared in the N + 2nd measurement (when the polishing table 3 is N + 2nd rotation), and the peak P4 is the peak that appeared in the N + 3rd measurement (when the polishing table 3 is N + 3rd rotation). It is a peak. In FIG. 6, peaks having a small frequency component intensity are omitted. The reference numeral N is a natural number, for example, 1.

As shown in FIG. 6, the peak of the frequency spectrum moves as the polishing of the workpiece W progresses. The polishing target layer of the workpiece W is polished even while the polishing table 3 makes one rotation. Therefore, the thickness of the polishing target layer becomes smaller each time the polishing table 3 rotates once. The relationship between the thickness t1 corresponding to the peak P1, the thickness t2 corresponding to the peak P2, the thickness t3 corresponding to the peak P3, and the thickness t4 corresponding to the peak P4 is t1> t2> t3> t4.

The thickness of the layer to be polished is determined by the optical film thickness measuring device 40 based on the peak of the frequency spectrum each time the polishing table 3 rotates once. However, the polishing control unit 49 erroneously determines the thickness of the layer to be polished due to the pseudo peak caused by noise during polishing of the workpiece W (those caused by the polishing environment such as slurry, those caused by the underlying layer, etc.). I may end up doing it. In FIG. 6, the pseudo peak Pf1 is a peak caused by noise generated during polishing of the workpiece W, and is a pseudo peak appearing in the Nth measurement. In this case, in the Nth measurement, the thickness tf1 corresponding to the pseudo peak Pf1 having a higher intensity than the peak P1 is erroneously determined as the thickness of the polishing target layer.

Therefore, the polishing control unit 49 is configured to search for the peak of the frequency spectrum within the peak search range R1. In the example shown in FIG. 6, the polishing control unit 49 determines the peak P1 within the peak search range R1, and sets the thickness t1 (that is, the exact thickness) corresponding to the determined peak P1 to the thickness of the polishing target layer. To decide. At this time, since the pseudo peak Pf1 is not within the peak search range R1, the pseudo peak Pf1 is not erroneously determined.

In FIG. 6, the peak search range R1 represents the peak search range in the Nth measurement. In one embodiment, the polishing control unit 49 determines the peak search range R1 based on the value of the initial thickness of the polishing target layer. For example, the peak search range R1 may be a range including the value of the initial thickness of the layer to be polished of the workpiece W. The initial thickness of the layer to be polished is the thickness of the layer to be polished before the start of polishing of the workpiece W, and is measured in advance by a stand-alone film thickness measuring device (not shown) or the workpiece W. It is given as basic information.

FIG. 7 is a diagram illustrating a peak search range R2 in the N + 1th measurement. In FIG. 7, the peaks P1 to P4 are the same as the peaks described with reference to FIG. The pseudo peak Pf2 represents a peak caused by noise generated during polishing of the workpiece W, and is a pseudo peak that appears at the time of N + 1th measurement. Since this pseudo peak Pf2 is within the peak search range R1 in the previous Nth measurement, the polishing control unit 49 erroneously determines the thickness tf2 corresponding to the pseudo peak Pf2 as the thickness of the polishing target layer. It ends up.

Therefore, in the present embodiment, the peak search range of the frequency spectrum is configured to move according to the polishing time. As described above, as the polishing of the workpiece W progresses, the thickness of the layer to be polished becomes smaller, that is, the peak of the frequency spectrum moves. The polishing control unit 49 can accurately determine the thickness of the polishing target layer even if a pseudo peak exists by moving the peak search range so as to follow the change in the thickness of the polishing target layer.

In FIG. 7, the peak search range R2 represents the peak search range in the N + 1th measurement. The polishing control unit 49 moves the peak search range so as to follow the thickness of the polishing target layer that changes with the polishing time. In the N + 1th measurement, the peak search range is moved from the peak search range R1 in FIG. 6 to the peak search range R2. For example, the peak search range R2 may be calculated based on the previously determined thickness t1 of the polishing target layer and the polishing rate of the workpiece W, as will be described later.

The polishing control unit 49 determines the peak P2 within the peak search range R2, and determines t2 (that is, an accurate thickness) corresponding to the determined peak P2 as the thickness of the polishing target layer. At this time, since the pseudo peak Pf2 is not within the peak search range R2, the pseudo peak Pf2 is not erroneously determined. Similarly, in the N + second and subsequent measurements, the exact thickness of the layer to be polished can be determined by moving the peak search range according to the polishing time.

FIG. 8 is a diagram illustrating how the peak search range is moved according to the polishing time. In FIG. 8, the peaks P1 to P4, the pseudo peaks Pf1 and Pf2, and the peak search ranges R1 and R2 correspond to the same reference numerals shown in FIGS. 6 and 7. The graph of FIG. 8 shows the relationship between the polishing time and the thickness corresponding to each peak. The pseudo peak Pf3 represents the pseudo peak that appeared at the time of N + 2nd measurement. The pseudo peak Pf4 represents the pseudo peak that appeared at the time of N + 3rd measurement. The peak search range R3 represents the peak search range moved during the N + second measurement. The peak search range R4 represents the peak search range moved during the N + 3rd measurement.

In FIG. 8, the initial value t0 represents the thickness of the polishing target layer of the workpiece W before polishing. The initial value t0 is the initial thickness of the layer to be polished measured in advance before polishing the workpiece W, or a value given by the user. In one embodiment, the peak search range R1 at the time of the Nth measurement is set based on the initial value t0. Specifically, the peak search range R1 is determined by using the following equation (2).
Peak search range R1 = initial value t0 ± first set value X (2)
Here, the first set value X can be freely set by the user.

In one embodiment, the peak search range R2 is set to a range including values calculated based on the previously determined thickness t1 of the polishing target layer and the polishing rate PR of the workpiece W. Specifically, the peak search range R2 is set using the following equation (3).
Peak search range R2 =
(Thickness t1-determined last time (polishing rate PR x time interval dT))
± 2nd set value Y (3)
Here, the polishing rate is also referred to as a removal rate. The time interval dT corresponds to the time required for the polishing table 3 to make one rotation. Normally, the time interval dT is constant during polishing of the workpiece W. The polishing rate PR may be a preset polishing rate. The second set value Y can be freely set by the user. The second set value Y may be smaller than or the same as the first set value X.

The peak search range R3 and R4 are calculated using the equation (3) in the same manner as the peak search range R2. At this time, in the formula (3), the polishing rate PR may be a preset polishing rate or a polishing rate calculated during the polishing of the workpiece W. The polishing rate can be calculated from a plurality of values of the thickness of the layer to be polished acquired during polishing of the workpiece W and the polishing time required for these plurality of values to be acquired.

FIG. 9 is a flowchart illustrating an example of a process of moving the peak search range to determine the thickness of the layer to be polished.
In step S101, the table motor 6 rotates the polishing table 3 that supports the polishing pad 2.
In step S102, the polishing head 1 presses the work piece W against the polishing surface 2a of the polishing pad 2 to start polishing the work piece W. At this time, as described with reference to FIG. 1, while the workpiece W is rotated by the polishing head 1, the workpiece W is moved by the polishing head 1 to the polishing pad 2 in a state where the polishing liquid is present on the polishing pad 2. It is pressed against the polished surface 2a.

Next, during the polishing of the workpiece W, the thickness of the layer to be polished is measured by the optical film thickness measuring device 40.
In step S103, the light source 44 emits light, and the light is emitted from the optical sensor head 7 onto the surface of the workpiece W.
In step S104, the optical sensor head 7 receives the reflected light from the workpiece W.
In step S105, the spectroscope 47 measures the intensity of the reflected light from the workpiece W for each wavelength.
In step S106, the polishing control unit 49 generates a spectral waveform from the intensity measurement data of the reflected light.
In step S107, the polishing control unit 49 performs a Fourier transform process on the spectral waveform to generate a frequency spectrum.

In step S108, the polishing control unit 49 moves the peak search range according to the polishing time. The peak search range is moved by calculating the peak search range by the method described with reference to FIG.
In step S109, the polishing control unit 49 determines the peak of the frequency spectrum within the peak search range.
In step S110, the polishing control unit 49 determines the thickness of the polishing target layer corresponding to the determined peak.

The polishing control unit 49 operates according to an instruction included in the program electrically stored in the storage device 49a. That is, the polishing control unit 49 issues a command to the table motor 6 to rotate the polishing table 3 supporting the polishing pad 2 (see step S101), and issues a command to the polishing head 1 to cause the workpiece W to rotate. Spectral waveform from the step of starting polishing (see step S102), the step of issuing a command to the light source 44 to irradiate the workpiece W with light (see step S103), and the intensity measurement data of the reflected light from the workpiece W. (See step S106), a step of performing a Fourier conversion process on the spectral waveform to generate a frequency spectrum (see step S107), and a step of moving the peak search range according to the polishing time (see step S108). , A step of determining the peak of the frequency spectrum within the peak search range (see step S109) and a step of determining the thickness of the layer to be polished corresponding to the determined peak (see step S110) are executed.

The program for causing the polishing control unit 49 to execute these steps is recorded on a computer-readable recording medium which is a non-temporary tangible object, and is provided to the polishing control unit 49 via the recording medium. Alternatively, the program may be input to the polishing control unit 49 via a communication network such as the Internet or a local area network.

Next, an embodiment in which the thickness of the layer to be polished is accurately determined by removing noise using a filter will be described.
FIG. 10 is a diagram showing a frequency spectrum before filtering. In FIG. 10, the vertical axis represents the intensity of the frequency component included in the spectral waveform, and the horizontal axis represents the thickness of the layer to be polished. Each of the plurality of frequency spectra shown in FIG. 10 is generated by the polishing control unit 49 each time the polishing table 3 makes one rotation during polishing of the workpiece W. The peak P1 is the peak that appears at the Nth measurement (when the polishing table 3 is at the Nth rotation), and the peak P2 is the peak that appears at the N + 1th measurement (when the polishing table 3 is at the N + 1th rotation). Yes, the peak P3 is the peak that appeared in the N + 2nd measurement (when the polishing table 3 is N + 2nd rotation), and the peak P4 is the peak that appeared in the N + 3rd measurement (when the polishing table 3 is N + 3rd rotation). It is a peak. In FIG. 10, peaks having a low frequency component intensity are omitted. The reference numeral N is a natural number, for example, 1.

The thickness of the layer to be polished is determined by the optical film thickness measuring device 40 based on the peak of the frequency component each time the polishing table 3 rotates once. However, due to the influence of noise caused by the underlying layer existing under the polishing target layer, it may not be possible to accurately determine the thickness of the polishing target layer. In FIG. 10, the lower peak Pu is a peak due to the reflected light from the underlying layer of the polishing target layer, and is noise unnecessary for determining the thickness of the polishing target layer. Since the base layer is not polished during the polishing of the workpiece W, the position of the lower peak Pu does not change even if the polishing target layer is polished. In the example shown in FIG. 10, since the lower layer peak Pu appears at a position overlapping the peak P3, the polishing control unit 49 cannot correctly determine the thickness of the polishing target layer corresponding to the peak P3.

Therefore, in the present embodiment, the polishing control unit 49 uses a filter to remove noise caused by the underlying layer from the spectral waveform of the reflected light from the workpiece W, and further, the peak of the frequency spectrum disappeared by removing the noise. The thickness of the layer to be polished is determined by supplementing the thickness of the layer to be polished corresponding to the above by externalization.

The filter for removing noise from the spectral waveform of the reflected light is preliminarily created as follows. Before polishing the workpiece W, another workpiece W'having the same pattern as the workpiece W is polished. During polishing of another workpiece W', the thickness of the layer to be polished is measured by the optical film thickness measuring device 40. The polishing control unit 49 identifies the lower peak, which is noise, based on the frequency spectrum generated from the spectral waveform of the reflected light from another workpiece W', and creates a filter for removing the identified noise. Specifically, the polishing control unit 49 identifies the peak of the frequency spectrum that does not move with the polishing time of another workpiece W', and the component (noise) having the frequency of the specified peak is extracted from the spectral waveform of the reflected light. Create a filter to remove. This filter is a digital filter, for example, a band stop filter.

In one embodiment, without using another workpiece W'having the same pattern as the workpiece W, the polishing control unit 49 identifies the lower peak, which is noise, in the initial stage of polishing the workpiece W. You may create a filter. Specifically, during polishing of the workpiece W, the polishing control unit 49 identifies a peak of a frequency spectrum that does not move with the polishing time, and a component (noise) having a frequency of the specified peak is converted into a spectral waveform of reflected light. Create a filter to remove from.

FIG. 11 is a diagram showing a frequency spectrum after filtering. The polishing control unit 49 applies a filter created in advance to the spectral waveform of the reflected light from the workpiece W to remove noise. The plurality of frequency spectra shown in FIG. 11 are frequency spectra generated by the polishing control unit 49 by performing a Fourier transform process (or a fast Fourier transform process) on the spectral waveform after removing noise. By removing the noise from the spectral waveform of the reflected light, the peak P3 at the position overlapping with the lower peak Pu disappears together with the lower peak Pu. Therefore, the polishing control unit 49 cannot accurately determine the thickness of the polishing target layer corresponding to the peak P3.

Therefore, the polishing control unit 49 is configured to supplement the thickness of the polishing target layer corresponding to the peak P3 by extrapolation. FIG. 12 is a diagram illustrating how the disappeared peak P3 is extrapolated. In FIG. 12, peaks P1 to P4 correspond to the same reference numerals shown in FIGS. 10 and 11, and the graph shown in FIG. 12 shows the relationship between the polishing time and the thickness corresponding to each peak. Is. As described with reference to FIG. 11, when the peak P3 disappears by removing the lower layer peak Pu which is noise, the polishing control unit 49 determines the thickness of the polishing target layer corresponding to the peak P1 and the peak P2. From the above value, the thickness of the layer to be polished corresponding to the disappeared portion of the peak P3 is supplemented by extrapolation. 10 to 12 have described the case where the peak P3 disappears, but the present invention is not limited to this. If a plurality of values of the thickness of the layer to be polished are acquired during polishing of the workpiece W, the thickness of the layer to be polished can be complemented by extrapolation using the acquired plurality of values.

In the above-described embodiment, the peak (noise) that does not change with the polishing time is caused by the underlying layer of the polishing target layer, but the present invention is not limited to the present embodiment. For example, the peak (noise) that does not change with polishing time may be noise inherent in a device such as a light source 44 or a spectroscope 47.

FIG. 13 is a flowchart illustrating an example of a process of removing noise by using a filter.
In step S201, the polishing device grinds another workpiece W'having the same pattern as the workpiece W to be polished.
In step S202, the polishing control unit 49 measures the thickness of the layer to be polished by the optical film thickness measuring device 40 during polishing of another workpiece W'. The polishing control unit 49 Fourier transforms the spectral waveform obtained from the reflected light from another workpiece W'to generate a frequency spectrum. The steps of steps S201 to S202 are the same as the steps of steps S101 to S107 of FIG.
In step S203, the polishing control unit 49 identifies a peak in the frequency spectrum that does not change with polishing time.
In step S204, the polishing control unit 49 creates a filter that removes noise having a specified peak frequency from the spectral waveform of the reflected light from another workpiece W'.

In step S205, the polishing device starts polishing the workpiece W to be polished.
In step S206, the thickness of the layer to be polished is measured by the optical film thickness measuring device 40 while the workpiece W is being polished. The polishing control unit 49 removes noise from the spectral waveform of the reflected light from the workpiece W by using the filter created in step S204. The steps from step S205 to the generation of the spectral waveforms in S206 are the same as the steps in steps S101 to S106 of FIG.
In step S207, the polishing control unit 49 performs a Fourier transform process on the spectral waveform from which noise has been removed to generate a frequency spectrum.
In step S208, the polishing control unit 49 determines the thickness of the polishing target layer based on the peak of the frequency spectrum.
In step S209, the polishing control unit 49 supplements the thickness of the polishing target layer corresponding to the peak of the frequency spectrum disappeared by removing noise by extrapolation.

The polishing control unit 49 operates according to an instruction included in the program electrically stored in the storage device 49a. That is, the polishing control unit 49 issues a command to the table motor 6 to rotate the polishing table 3 supporting the polishing pad 2, and issues a command to the polishing head 1 to start polishing the workpiece W. (See step S205), a step of issuing a command to the light source 44 to irradiate the workpiece W with light, a step of generating a spectral waveform from the intensity measurement data of the reflected light from the workpiece W, and a filter. A step of removing noise from the spectral waveform (see step S206), a step of performing Fourier conversion processing on the spectral waveform from which noise has been removed to generate a frequency spectrum (see step S207), and a polishing target from the peak of the frequency spectrum. A step of determining the layer thickness (see step S208) and a step of complementing the thickness of the layer to be polished corresponding to the peak of the frequency spectrum disappeared by the noise removal by extrapolation (see step S209) are performed. ..

The program for causing the polishing control unit 49 to execute these steps is recorded on a computer-readable recording medium which is a non-temporary tangible object, and is provided to the polishing control unit 49 via the recording medium. Alternatively, the program may be input to the polishing control unit 49 via a communication network such as the Internet or a local area network.

The embodiments described in FIGS. 6 to 9 and the embodiments described in FIGS. 10 to 13 may be implemented in combination. That is, noise may be removed from the spectral waveform using a filter to generate a frequency spectrum, and the peak search range of the frequency spectrum may be moved to determine the thickness of the layer to be polished.

The above-described embodiments have been described for the purpose of allowing a person having ordinary knowledge in the technical field to which the present invention belongs to carry out the present invention. Various modifications of the above embodiment can be naturally made by those skilled in the art, and the technical idea of the present invention can be applied to other embodiments. Accordingly, the invention is not limited to the described embodiments, but is to be construed in the broadest range according to the technical ideas defined by the claims.

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 31 Optical fiber cable for floodlight 32 Optical fiber cable for light reception 40 Optical film thickness measuring device 44 Light source 47 Spectrometer 49 Polishing control unit 49a Storage device 49b Processing device P1, P2, P3, P4 Peak Pf1, Pf2, Pf3, Pf4 Pseudo-peak Pu Lower layer peak R1, R2, R3, R4 Peak search range

Claims (10)

It is a polishing method for polishing the polishing target layer of the workpiece.
Rotate the polishing table that supports the polishing pad and
The work piece is pressed against the polishing pad to polish the polishing target layer, and the polishing target layer is polished.
Irradiate the workpiece with light to
Receiving the reflected light from the workpiece
The intensity of the reflected light is measured for each wavelength,
A spectral waveform showing the relationship between the intensity and the wavelength of the reflected light is generated.
The spectral waveform is subjected to a Fourier transform process to generate a frequency spectrum.
The peak search range of the frequency spectrum is moved according to the polishing time.
The peak of the frequency spectrum within the peak search range is determined, and the peak is determined.
A polishing method for determining the thickness of the layer to be polished corresponding to the determined peak. The polishing method according to claim 1, wherein the peak search range includes a value calculated based on the thickness of the polishing target layer and the polishing rate of the workpiece determined last time. The polishing method according to claim 2, wherein the polishing rate is a preset polishing rate. The polishing method according to claim 2, wherein the polishing rate is a polishing rate calculated during polishing of the workpiece. It is a polishing method for polishing the polishing target layer of the workpiece.
Rotate the polishing table that supports the polishing pad and
The work piece is pressed against the polishing pad to polish the polishing target layer, and the polishing target layer is polished.
Irradiate the workpiece with light to
Receiving the reflected light from the workpiece
The intensity of the reflected light is measured for each wavelength,
A spectral waveform showing the relationship between the intensity and the wavelength of the reflected light is generated.
A filter is used to remove noise from the spectral waveform.
The spectral waveform from which the noise has been removed is subjected to a Fourier transform process to generate a frequency spectrum.
The thickness of the polishing target layer is determined based on the peak of the frequency spectrum, and the thickness is determined.
The thickness of the polishing target layer corresponding to the peak of the frequency spectrum disappeared by the noise removal is extrapolated using a plurality of values of the polishing target layer thickness acquired during polishing of the workpiece. Complementary polishing method. The polishing method according to claim 5, wherein the filter is configured to remove noise having a peak frequency of the frequency spectrum that does not move with the polishing time of the workpiece from the spectral waveform. The polishing method according to claim 5 or 6, wherein the noise is noise caused by light reflected from the underlying layer of the polishing target layer. The polishing method according to any one of claims 5 to 7, wherein the filter is a band stop filter. Before polishing the work piece, another work piece having the same pattern as the work piece is polished.
The polishing method according to any one of claims 5 to 8, further comprising the step of creating the filter for removing noise contained in the spectral waveform of the reflected light from the other workpiece. The invention according to any one of claims 5 to 8, further comprising the step of creating the filter for removing noise contained in the spectral waveform of the reflected light from the workpiece during polishing of the workpiece. Polishing method.

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