JP2015053349A - Polishing method and polishing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polishing method and a polishing device capable of accurately determining a polishing end point even in a state of an exceedingly thin film.SOLUTION: The polishing method includes: polishing a substrate while measuring the film thickness of the substrate by an optical film thickness measuring instrument; calculating a polishing rate of the substrate during polishing of the substrate; calculating an additional polishing time by dividing a difference between a predetermined detection threshold and a predetermined target film thickness by the polishing rate; and completing polishing of the substrate when the additional polishing time elapses from a time point at which the film thickness reaches the predetermined detection threshold.

Description

  The present invention relates to a method and an apparatus for polishing a substrate having an exposed surface made of a film such as a silicon layer, and more particularly to a method and an apparatus for polishing a substrate while measuring the film thickness based on optical information contained in reflected light from the substrate. Relates to the device.

The semiconductor device manufacturing process 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 manufacturing process of the back-illuminated CMOS sensor and the silicon through electrode (TSV) includes a process of polishing a silicon layer (silicon wafer) in addition to a process of polishing an insulating film and a metal film.

  The polishing of the wafer is terminated when the thickness of a film (insulating film, metal film, silicon layer, etc.) constituting the surface reaches a predetermined target value. A CMP (Chemical Mechanical Polishing) apparatus is used for polishing the wafer. The CMP apparatus includes a film thickness measuring device for measuring the film thickness of a wafer being polished. For example, an optical film thickness measuring instrument is used for measuring the thickness of the insulating layer or silicon layer. The optical film thickness measuring device is configured to irradiate the surface of the wafer with light and determine the current film thickness of the wafer from optical information included in the reflected light from the wafer.

  However, when wafer polishing approaches its end point, an accurate film thickness value may not be obtained even though the wafer is being polished normally. Specifically, when the film becomes extremely thin, the S / N of the optical information contained in the reflected light from the wafer deteriorates, and as a result, an accurate polishing end point may not be detected.

Japanese Patent Laid-Open No. 2004-154928 JP-A-10-125634

  The present invention has been made to solve the above-described conventional problems, and an object thereof is to provide a polishing method and a polishing apparatus capable of accurately determining the polishing end point even when the film is extremely thin. To do.

  In order to achieve the above-described object, one embodiment of the present invention is to polish a substrate while measuring the film thickness of the substrate with an optical film thickness measuring device, and calculate the polishing rate of the substrate during polishing of the substrate. Then, an additional polishing time is calculated by dividing a difference between a predetermined detection threshold value and a predetermined target film thickness by the polishing rate, and the additional time is reached when the film thickness reaches the predetermined detection threshold value. The polishing method is characterized in that the polishing of the substrate is terminated when a polishing time has elapsed.

In a preferred aspect of the present invention, the polishing rate is calculated on condition that a fluctuation range of the change amount of the film thickness per unit time is within a predetermined range.
In a preferred aspect of the present invention, an alarm signal is generated when the fluctuation range of the change amount of the film thickness per unit time exceeds a predetermined range.
In a preferred aspect of the present invention, the additional polishing time is calculated on the condition that the polishing rate is within a predetermined range.
In a preferred aspect of the present invention, an alarm signal is generated when the polishing rate exceeds a predetermined range.

In a preferred aspect of the present invention, the polishing rate is obtained by calculating a difference between the first monitoring value and the second monitoring value of the film thickness from the time when the film thickness reaches the first monitoring value. It is calculated by dividing by the time until the thickness reaches the second monitoring value.
In a preferred aspect of the present invention, an alarm signal is generated when the film thickness reaches a preset upper limit value of the polishing time before reaching the first monitoring value or the second monitoring value. It is characterized by that.
In a preferred aspect of the present invention, the step of calculating the polishing rate is such that the polishing rate of the substrate is repeatedly calculated during polishing of the substrate to obtain a plurality of polishing rates, and the most frequent of the plurality of polishing rates is obtained. This is a step of determining a polishing rate having a large value.

  Another aspect of the present invention includes a polishing table that supports a polishing pad, a top ring that presses the substrate against the polishing pad, an optical film thickness measuring device that measures the film thickness of the substrate being polished, and the substrate A polishing control unit that controls the polishing of the substrate, the polishing control unit calculates a polishing rate of the substrate during polishing of the substrate, and calculates a difference between a predetermined detection threshold and a predetermined target film thickness An additional polishing time is calculated by dividing by a polishing rate, and polishing of the substrate is terminated when the additional polishing time has elapsed from the time when the film thickness reaches the predetermined detection threshold value. It is a polishing apparatus.

In a preferred aspect of the present invention, the polishing control unit calculates the polishing rate on the condition that a fluctuation range of the change amount of the film thickness per unit time is within a predetermined range.
In a preferred aspect of the present invention, the polishing control unit generates an alarm signal when the fluctuation range of the change amount of the film thickness per unit time exceeds a predetermined range.
In a preferred aspect of the present invention, the polishing control unit calculates the additional polishing time on the condition that the polishing rate is within a predetermined range.
In a preferred aspect of the present invention, the polishing control unit generates an alarm signal when the polishing rate exceeds a predetermined range.

In a preferred aspect of the present invention, the polishing control unit calculates the difference between the first monitoring value and the second monitoring value of the film thickness from the time when the film thickness reaches the first monitoring value. The polishing rate is calculated by dividing by the time until the film thickness reaches the second monitoring value.
In a preferred aspect of the present invention, when the film thickness reaches the upper limit value of a preset polishing time before reaching the first monitoring value or the second monitoring value, the polishing control unit An alarm signal is generated.
In a preferred aspect of the present invention, the polishing control unit repeatedly calculates the polishing rate of the substrate during polishing of the substrate to obtain a plurality of polishing rates, and the polishing having the highest frequency among the plurality of polishing rates. It is characterized by determining a rate.

  According to the present invention, the polishing end point is determined based on the additional polishing time calculated from the polishing rate, not the measured value of the film thickness. Therefore, an accurate polishing end point can be determined even if the measured value of the film thickness obtained from the optical film thickness measuring instrument is unstable.

FIG. 1 is a diagram showing a polishing apparatus according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing a polishing apparatus equipped with an optical film thickness measuring device. FIG. 3 is a schematic diagram for explaining the principle of the optical film thickness measuring instrument. FIG. 4 is a plan view showing the positional relationship between the wafer and the polishing table. FIG. 5 is a diagram illustrating a spectrum generated by the processing unit. FIG. 6 is a diagram illustrating a frequency spectrum generated by the processing unit. FIG. 7 is a diagram illustrating a process for determining the current film thickness from a comparison between the obtained spectrum and a plurality of reference spectra. FIG. 8 is a diagram showing a change in film thickness during polishing of the wafer. FIG. 9 is a diagram illustrating a case where the fluctuation range of the change amount of the film thickness per unit time is within a predetermined range. FIG. 10 is a diagram illustrating a case where the fluctuation range of the change amount of the film thickness per unit time exceeds a predetermined range.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a polishing apparatus according to an embodiment of the present invention. As shown in FIG. 1, the polishing apparatus holds a polishing table 3 to which a polishing pad 1 having a polishing surface 1 a is attached, and holds a wafer as a substrate and presses the wafer against the polishing pad 1 on the polishing table 3. A top ring 5 for polishing, a polishing liquid supply nozzle 10 for supplying a polishing liquid (for example, slurry) to the polishing pad 1, and a polishing controller 12 for controlling the polishing of the wafer are provided.

  The polishing table 3 is connected to a table motor 19 arranged below the table shaft 3a, and the table motor 19 rotates the polishing table 3 in the direction indicated by the arrow. A polishing pad 1 is attached to the upper surface of the polishing table 3, and the upper surface of the polishing pad 1 constitutes a polishing surface 1 a for polishing the wafer W. The top ring 5 is connected to the lower end of the top ring shaft 16. The top ring 5 is configured to hold the wafer W on the lower surface thereof by vacuum suction. The top ring shaft 16 is moved up and down by a vertical movement mechanism (not shown).

  The polishing apparatus includes an optical film thickness measuring device 25 for monitoring the film thickness of the wafer W. The optical film thickness measuring instrument 25 includes a film thickness sensor 31 that acquires a film thickness signal that changes according to the film thickness of the wafer W, and a processing unit 32 that determines the film thickness from the film thickness signal. The film thickness sensor 31 is disposed inside the polishing table 3, and the processing unit 32 is connected to the polishing control unit 12. The film thickness sensor 31 rotates integrally with the polishing table 3 as indicated by symbol A, and acquires a film thickness signal of the wafer W held on the top ring 5. The film thickness sensor 31 is connected to the processing unit 32, and the film thickness signal acquired by the film thickness sensor 31 is sent to the processing unit 32.

  FIG. 2 is a schematic cross-sectional view showing a polishing apparatus provided with an optical film thickness measuring device 25. The top ring shaft 16 is connected to a top ring motor 18 via a connecting means 17 such as a belt and is rotated. As the top ring shaft 16 rotates, the top ring 5 rotates in the direction indicated by the arrow.

  As described above, the optical film thickness measuring instrument 25 includes the film thickness sensor 31 and the processing unit 32. The film thickness sensor 31 is configured to irradiate the surface of the wafer W with light, receive reflected light from the wafer W, and decompose the reflected light according to the wavelength. The film thickness sensor 31 includes a light projecting unit 42 that irradiates a surface to be polished of the wafer W, an optical fiber 43 that receives reflected light returning from the wafer W, and a wavelength of the reflected light from the wafer W. And a spectroscope 44 that measures the intensity of reflected light over a predetermined wavelength range.

  The polishing table 3 is formed with a first hole 50A and a second hole 50B that open on the upper surface thereof. The polishing pad 1 has through holes 51 at positions corresponding to the holes 50A and 50B. The holes 50A, 50B and the through hole 51 communicate with each other, and the through hole 51 is opened at the polishing surface 1a. The first hole 50A is connected to a liquid supply source 55 via a liquid supply path 53 and a rotary joint (not shown), and the second hole 50B is connected to a liquid discharge path 54.

  The light projecting unit 42 includes a light source 47 that emits multi-wavelength light, and an optical fiber 48 connected to the light source 47. The optical fiber 48 is an optical transmission unit that guides light emitted from the light source 47 to the surface of the wafer W. The tips of the optical fiber 48 and the optical fiber 43 are located in the first hole 50A and are located in the vicinity of the surface to be polished of the wafer W. The tips of the optical fiber 48 and the optical fiber 43 are arranged to face the wafer W held on the top ring 5. Each time the polishing table 3 rotates, a plurality of regions of the wafer W are irradiated with light. Preferably, the distal ends of the optical fiber 48 and the optical fiber 43 are arranged to face the center of the wafer W held by the top ring 5.

  During polishing of the wafer W, water (preferably pure water) is supplied as a transparent liquid from the liquid supply source 55 to the first hole 50A via the liquid supply path 53, and the lower surface of the wafer W and the optical fiber 48, Fill the space between 43 tips. The water further flows into the second hole 50 </ b> B and is discharged through the liquid discharge path 54. The polishing liquid is discharged together with water, thereby securing an optical path. The liquid supply path 53 is provided with a valve (not shown) that operates in synchronization with the rotation of the polishing table 3. This valve operates to stop the flow of water or reduce the flow rate of water when the wafer W is not positioned over the through hole 51.

  The optical fiber 48 and the optical fiber 43 are arranged in parallel with each other. The tips of the optical fiber 48 and the optical fiber 43 are arranged perpendicular to the surface of the wafer W, and the optical fiber 48 irradiates light to the surface of the wafer W perpendicularly.

  During polishing of the wafer W, light is irradiated from the light projecting unit 42 to the wafer W, and reflected light from the wafer W is received by the optical fiber (light receiving unit) 43. The spectroscope 44 measures the intensity at each wavelength of the reflected light over a predetermined wavelength range, and sends the obtained light intensity data to the processing unit 32. This light intensity data is a film thickness signal reflecting the film thickness of the wafer W, and changes according to the film thickness. The processing unit 32 generates a spectrum representing the light intensity for each wavelength from the light intensity data, and further determines the film thickness of the wafer W from the spectrum.

  FIG. 3 is a schematic diagram for explaining the principle of the optical film thickness measuring instrument 25, and FIG. 4 is a plan view showing the positional relationship between the wafer W and the polishing table 3. In the example shown in FIG. 3, the wafer W has a lower layer film and an upper layer film formed thereon. The upper layer film is, for example, a silicon layer or an insulating film. The light projecting unit 42 and the light receiving unit 43 are arranged to face the surface of the wafer W. The light projecting unit 42 irradiates light to a plurality of regions including the center of the wafer W every time the polishing table 3 rotates once.

  The light irradiated on the wafer W is reflected at the interface between the medium (water in the example of FIG. 3) and the upper film and the interface between the upper film and the lower film, and the waves of light reflected at these interfaces interfere with each other. To do. The way of interference of the light wave changes according to the thickness of the upper layer film (that is, the optical path length). For this reason, the spectrum generated from the reflected light from the wafer W changes according to the thickness of the upper layer film. The spectroscope 44 decomposes the reflected light according to the wavelength, and measures the intensity of the reflected light for each wavelength. The processing unit 32 generates a spectrum from the intensity data (film thickness signal) of the reflected light obtained from the spectroscope 44. This spectrum is represented as a line graph (that is, a spectral waveform) indicating the relationship between the wavelength and intensity of light. The intensity of light can also be expressed as a relative value such as reflectance or relative reflectance.

  FIG. 5 is a diagram illustrating a spectrum generated by the processing unit 32. In FIG. 5, the horizontal axis represents the wavelength of the reflected light, and the vertical axis represents the relative reflectance derived from the intensity of the reflected light. The relative reflectance is one index representing the intensity of the reflected light, and specifically is a ratio between the intensity of the reflected light and a predetermined reference intensity. The reference intensity is acquired in advance for each wavelength. By dividing the intensity of the reflected light (measured intensity) at each wavelength by the corresponding reference intensity, unnecessary elements such as variations in the intensity of the optical system of the apparatus and the light source are removed from the measured intensity. A spectrum reflecting only thickness information can be obtained.

ここで、λは波長であり、Ｅ（λ）はウェハからの反射光の波長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）は波長λでのダークレベル（光を遮断した条件下で測定された光の強度）である。 The predetermined reference intensity can be, for example, the intensity of reflected light obtained when a silicon wafer (bare wafer) on which no film is formed is polished in the presence of water. In actual polishing, subtract the dark level (background intensity obtained under light-shielded conditions) from the measured intensity to obtain the corrected measured intensity, and further subtract the dark level from the reference intensity to obtain the corrected reference intensity. Then, the relative reflectance is obtained by dividing the corrected actually measured intensity by the corrected reference intensity. Specifically, the relative reflectance R (λ) can be obtained using the following equation (1).

Here, λ is the wavelength, E (λ) is the intensity of the reflected light from the wafer at the wavelength λ, B (λ) is the reference intensity at the wavelength λ, and D (λ) is the wavelength λ. The dark level (light intensity measured under light blocking conditions).

  The processing unit 32 analyzes the spectral waveform by performing fast Fourier transform (or Fourier transform) processing on the obtained spectrum (spectral waveform). More specifically, the processing unit 32 extracts a frequency component and its intensity included in the spectral waveform, converts the obtained frequency component into a film thickness using a predetermined relational expression, and the film A frequency spectrum indicating the relationship between the thickness of the signal and the intensity of the frequency component is generated. The predetermined relational expression described above is a linear function representing the thickness of the film with the frequency component as a variable, and can be obtained from an actual measurement result.

  FIG. 6 is a diagram illustrating a frequency spectrum generated by the processing unit 32. 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 film. As can be seen from FIG. 6, when the thickness is t1, the intensity value is the largest. That is, this frequency spectrum indicates that the thickness of the film is t1. In this way, the film thickness is determined from the peak of the frequency spectrum.

  As another example, the processing unit 32 can determine the current film thickness from a comparison between the obtained spectrum and a plurality of reference spectra. FIG. 7 is a diagram illustrating a process for determining the current film thickness from a comparison between the obtained spectrum and a plurality of reference spectra. The processing unit 32 determines a reference spectrum closest to the generated spectrum by comparing the spectrum generated during polishing with a plurality of reference spectra, and determines the film thickness associated with the determined reference spectrum. Determine the current film thickness. The reference spectrum closest to the current spectrum is the spectrum with the smallest relative reflectance difference between the reference spectrum and the current spectrum.

  The plurality of reference spectra are acquired in advance by polishing a wafer of the same type as the wafer to be polished, and each reference spectrum is associated with the film thickness when the reference spectrum is acquired. That is, each reference spectrum is acquired at a different film thickness, and a plurality of reference spectra correspond to a plurality of different film thicknesses. Therefore, the current film thickness can be estimated by specifying the reference spectrum closest to the current spectrum.

  The polishing of the wafer W is performed as follows. The top ring 5 and the polishing table 3 are rotated in directions indicated by arrows, respectively, and a polishing liquid (slurry) is supplied onto the polishing pad 1 from the polishing liquid supply nozzle 10. In this state, the top ring 5 holding the wafer W on the lower surface presses the wafer W against the polishing surface 1 a of the polishing pad 1. The surface of the wafer W is polished by the mechanical action of abrasive grains contained in the polishing liquid and the chemical action of the polishing liquid.

  The optical film thickness measuring device 25 measures the film thickness during polishing of the wafer and transmits the measured value to the polishing control unit 12. FIG. 8 is a diagram showing a change in film thickness during polishing of the wafer. In the graph shown in FIG. 8, the vertical axis represents the measured value of the film thickness, and the horizontal axis represents time. At the initial stage of wafer polishing, as shown in FIG. 8, the measured value of the film thickness is not stable due to the presence of foreign matter on the wafer or the unevenness of the film surface. The measured value of becomes stable and decreases with time.

  The polishing control unit 12 calculates the polishing rate of the wafer when the initial stage of polishing has passed and the measured value of the film thickness is stable, that is, when the measured value decreases with the lapse of the polishing time. More specifically, the polishing controller 12 uses the difference ΔT between the predetermined first monitoring value T1 and the predetermined second monitoring value T2 as the film thickness, and the measured value of the film thickness as the first monitoring value T1. The polishing rate is calculated by dividing by the time (polishing rate calculation period) Δt from the time t1 when the measured value reaches the time t2 when the measured value of the film thickness reaches the second monitoring value T2. The polishing rate refers to the thickness of a film that is polished (that is, removed by polishing) per predetermined time. For example, the polishing rate is expressed as the thickness of the film polished per minute [μm / min].

  In the polishing controller 12, a predetermined detection threshold T3 and a predetermined target film thickness T4 are stored in advance. The polishing controller 12 calculates the additional polishing time OP by dividing the difference ΔT ′ between the detection threshold value T3 and the target film thickness T4 by the polishing rate. Then, the polishing controller 12 ends the polishing of the wafer when the additional polishing time OP elapses from the time when the measured value of the film thickness reaches the detection threshold value T3.

  From the start of polishing of the wafer to the end of polishing, polishing conditions such as the rotation speed of the polishing table 3 and the top ring 5, the supply flow rate of the polishing liquid, and the polishing pressure for the wafer are kept constant. Under constant polishing conditions, the polishing rate is also constant. Therefore, the target film thickness T4 can be achieved by determining the polishing end point based on the additional polishing time OP calculated from the polishing rate and the film thickness difference ΔT ′.

  As described above, after the measured value of the film thickness reaches the detection threshold value T3, the polishing control unit 12 monitors the polishing time instead of monitoring the film thickness, and determines the polishing end point based on the polishing time. To do. Therefore, even if the measured value of the film thickness is unstable, the polishing end point can be determined accurately.

  In order to accurately determine the polishing end point, it is preferable to calculate the polishing rate when the film thickness decreases according to the polishing time, that is, when the polishing rate is substantially constant. For example, it is preferable to calculate the polishing rate on the condition that the fluctuation range of the change amount of the film thickness per unit time is within a predetermined range. FIG. 9 shows a case where the fluctuation range of the change amount of the film thickness per unit time is within the predetermined range R, and FIG. 10 shows that the fluctuation range of the change amount of the film thickness per unit time falls within the predetermined range R. Indicates the case where the number is exceeded. In the case of FIG. 9, it is estimated that the polishing rate is stable. On the other hand, in the case of FIG. 10, it is estimated that the polishing rate is unstable. In such a case, it is preferable that the polishing control unit 12 generates an alarm signal and issues an alarm according to the alarm signal or transmits the alarm signal to an external alarm device.

  Instead of the fluctuation range of the change amount of the film thickness per unit time, it may be determined whether the polishing rate is stable based on the calculated value of the polishing rate itself. Specifically, the polishing control unit 12 is added on the condition that the polishing rate calculated when the film thickness decreases from the first monitoring value T1 to the second monitoring value T2 is within a predetermined range. The polishing time OP may be calculated. When the calculated polishing rate is not within the predetermined range, the polishing controller 12 preferably generates an alarm signal.

  In order to acquire an accurate polishing rate, the polishing control unit 12 repeatedly calculates the wafer polishing rate during polishing of the wafer to acquire a plurality of polishing rates, and the polishing having the highest frequency among the plurality of polishing rates. The rate may be determined. More specifically, the polishing control unit 12 creates a frequency distribution from a plurality of polishing rates acquired during a predetermined polishing rate calculation period, and determines the polishing rate with the highest frequency. The polishing rate calculation period in this case is not limited to the period defined by the times t1 and t2 corresponding to the first monitoring value T1 and the second monitoring value T2 described above, and may be arbitrarily determined by the user. it can. According to this method, the most probable polishing rate can be obtained from a plurality of polishing rates.

  It is also conceivable that the polishing rate is not stable for some reason from the start of polishing to the end of polishing. For example, when the film thickness reaches the upper limit value of the preset polishing time before reaching the first monitoring value T1 or the second monitoring value T2, the polishing control unit 12 generates an alarm signal. It is preferable.

  The above-described polishing method and polishing apparatus can be applied to polishing a wafer having a surface formed from a film such as an insulating film or a silicon layer.

  The embodiment described above is described for the purpose of enabling the person having ordinary knowledge in the technical field to which the present invention belongs to implement 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 present invention is not limited to the described embodiments, but is to be construed in the widest scope according to the technical idea defined by the claims.

DESCRIPTION OF SYMBOLS 1 Polishing pad 3 Polishing table 5 Top ring 10 Polishing liquid supply nozzle 12 Polishing control part 16 Top ring shaft 17 Connection means 18 Top ring motor 19 Table motor 25 Optical film thickness measuring device 31 Film thickness sensor 32 Processing part 42 Light projection part 43 Light-receiving part (optical fiber)
44 Spectrometer 47 Light source 48 Optical fiber 50A First hole 50B Second hole 51 Through hole 53 Liquid supply path 54 Liquid discharge path 55 Liquid supply source

Claims (16)

Polishing the substrate while measuring the thickness of the substrate with an optical film thickness measuring instrument,
Calculating the polishing rate of the substrate during polishing of the substrate;
Calculate the additional polishing time by dividing the difference between the predetermined detection threshold and the predetermined target film thickness by the polishing rate,
A polishing method, comprising: polishing the substrate when the additional polishing time has elapsed since the film thickness reached the predetermined detection threshold.   The polishing method according to claim 1, wherein the polishing rate is calculated on condition that a fluctuation range of the change amount of the film thickness per unit time is within a predetermined range.   The polishing method according to claim 1, wherein an alarm signal is generated when a fluctuation range of the change amount of the film thickness per unit time exceeds a predetermined range.   The polishing method according to claim 1, wherein the additional polishing time is calculated on condition that the polishing rate is within a predetermined range.   The polishing method according to claim 1, wherein an alarm signal is generated when the polishing rate exceeds a predetermined range.   The polishing rate is the difference between the first monitor value and the second monitor value of the film thickness, and the film thickness is the second monitor value from the time when the film thickness reaches the first monitor value. The polishing method according to claim 1, wherein the polishing method is calculated by dividing by a time until reaching a point of time.   The alarm signal is generated when the film thickness reaches an upper limit value of a preset polishing time before the film thickness reaches the first monitoring value or the second monitoring value. 6. The polishing method according to 6.   In the step of calculating the polishing rate, the polishing rate of the substrate is repeatedly calculated during polishing of the substrate to obtain a plurality of polishing rates, and the polishing rate having the highest frequency among the plurality of polishing rates is determined. The polishing method according to claim 1, wherein the polishing method is a process. A polishing table that supports the polishing pad;
A top ring that presses the substrate against the polishing pad;
An optical film thickness measuring instrument for measuring the film thickness of the substrate being polished;
A polishing control unit for controlling the polishing of the substrate,
The polishing controller is
Calculating the polishing rate of the substrate during polishing of the substrate;
Calculate the additional polishing time by dividing the difference between the predetermined detection threshold and the predetermined target film thickness by the polishing rate,
The polishing apparatus, wherein the polishing of the substrate is terminated when the additional polishing time elapses from the time when the film thickness reaches the predetermined detection threshold value.   The polishing apparatus according to claim 9, wherein the polishing control unit calculates the polishing rate on condition that a variation range of the change amount of the film thickness per unit time is within a predetermined range. .   The polishing apparatus according to claim 9, wherein the polishing control unit generates an alarm signal when a fluctuation range of the change amount of the film thickness per unit time exceeds a predetermined range.   The polishing apparatus according to claim 9, wherein the polishing control unit calculates the additional polishing time on condition that the polishing rate is within a predetermined range.   The polishing apparatus according to claim 9, wherein the polishing control unit generates an alarm signal when the polishing rate exceeds a predetermined range.   The polishing control unit calculates a difference between the first monitoring value and the second monitoring value of the film thickness from the time when the film thickness reaches the first monitoring value. The polishing apparatus according to claim 9, wherein the polishing rate is calculated by dividing by a time until a value is reached.   If the film thickness reaches the upper limit value of the preset polishing time before reaching the first monitoring value or the second monitoring value, the polishing control unit generates an alarm signal. The polishing apparatus according to claim 14.   The polishing control unit repeatedly calculates a polishing rate of the substrate during polishing of the substrate to obtain a plurality of polishing rates, and determines a polishing rate having the highest frequency among the plurality of polishing rates. The polishing apparatus according to claim 9.

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