POLISHING METHOD, POLISHING APPARATUS, AND NON-TRANSITORY COMPUTER-READABLE RECORDING MEDIUM

Info

Publication number: 20240424635
Type: Application
Filed: Jun 26, 2024
Publication Date: Dec 26, 2024
Applicant: EBARA CORPORATION (Tokyo)
Inventors: HIROKI NAKAMURA (Tokyo), YUTA SUZUKI (Tokyo), TARO TAKAHASHI (Tokyo)
Application Number: 18/754,174

Abstract

A polishing method includes: detecting, by an acoustic sensor, an environmental sound including a sound arising from a polishing environment of a substrate to output an environmental sound signal representing the environmental sound from the acoustic sensor; generating an environmental sound spectrum indicating a relationship between a frequency and a sound pressure level from the environmental sound signal; detecting, by the acoustic sensor, a polishing sound of the substrate while pressing the substrate against a polishing pad to polish the substrate, to output a polishing sound signal representing the polishing sound from the acoustic sensor; generating a polishing sound spectrum indicating a relationship between a frequency and a sound pressure level from the polishing sound signal; calculating a difference between the polishing sound spectrum and the environmental sound spectrum to generate a differential spectrum; and monitoring a polishing progress of the substrate based on the differential spectrum.

Description

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Japan application serial no. 2023-104125, filed on Jun. 26, 2023. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND Technical Field

The disclosure relates to a polishing method and a polishing apparatus for polishing a substrate such as a wafer. Further, the disclosure relates to a program for executing such a polishing method.

Related Art

In a fabrication process of a semiconductor device, a chemical mechanical polishing (CMP) apparatus is used to polish a surface of a substrate such as a semiconductor substrate. The CMP apparatus includes a polishing pad attached onto a polishing table, and a polishing head for pressing the substrate against a polishing surface of the polishing pad. While supplying a polishing liquid containing abrasive grains onto the polishing pad, the CMP apparatus presses the substrate against the polishing surface of the polishing pad by the polishing head to cause sliding contact between the surface of the substrate and the polishing surface of the polishing pad. The surface of the substrate is planarized by a chemical action of the polishing liquid and a mechanical action of the abrasive grains contained in the polishing liquid and/or the polishing pad.

To end polishing of the substrate at a time point at which the substrate is polished to a targeted polishing amount (film thickness), the polishing of the substrate requires accurate monitoring. So far, various techniques have been proposed to monitor the polishing of the substrate (e.g., Japanese Patent No. 5511600 and Japanese Patent No. 7182653).

One method of monitoring the polishing of the substrate is to detect a change in a polishing sound of the substrate using an acoustic sensor. This method is based on a change in the polishing sound that occurs when an upper layer (e.g., an insulating film, a metal film, a silicon layer, etc.) constituting the surface of the substrate is polished and a lower layer (e.g., a stopper layer) present under the upper layer appears, or when a surface status of the substrate changes. However, the polishing sound detected by the acoustic sensor during polishing of the substrate may include various environmental sounds such as a vibration and a noise caused by the operation of the polishing apparatus. Such environmental sounds may affect the accurate monitoring of the polishing of the substrate.

SUMMARY

An aspect provides a polishing method including steps below. An environmental sound including a sound arising from a polishing environment of a substrate is detected by an acoustic sensor to output an environmental sound signal representing the environmental sound from the acoustic sensor. An environmental sound spectrum indicating a relationship between a frequency and a sound pressure level is generated from the environmental sound signal. A polishing sound of the substrate is detected by the acoustic sensor while pressing the substrate against a polishing surface of a polishing pad to polish the substrate, to output a polishing sound signal representing the polishing sound from the acoustic sensor. A polishing sound spectrum indicating a relationship between a frequency and a sound pressure level is generated from the polishing sound signal. A difference between the polishing sound spectrum and the environmental sound spectrum is calculated to generate a differential spectrum. A polishing progress of the substrate is monitored based on the differential spectrum.

In an aspect, the polishing method further includes steps below. A differential spectrum map indicating over-time changes in the differential spectrum is generated by arranging the differential spectrum along a time axis. The monitoring the polishing progress includes monitoring the polishing progress based on a change in the sound pressure level in the differential spectrum map.

In an aspect, the monitoring the polishing progress includes detecting a polishing endpoint of the substrate. The polishing method further includes ending polishing of the substrate based on the polishing endpoint.

In an aspect, the environmental sound spectrum is generated by performing a Fourier transform on the environmental sound signal. The polishing sound spectrum is generated by performing a Fourier transform on the polishing sound signal.

In an aspect, the environmental sound is a sound detected after start of polishing of the substrate.

In an aspect, the environmental sound is a sound detected when a polishing apparatus performing polishing of the substrate is operated before polishing the substrate.

In an aspect, the generating the environmental sound spectrum includes: generating a plurality of environmental sound spectra from the environmental sound signals outputted from the acoustic sensor in a predetermined period, calculating a representative value of a sound pressure level for each frequency from the plurality of environmental sound spectra, and generating the environmental sound spectrum indicating a relationship between the frequency and the representative value of the sound pressure level.

In an aspect, the polishing method further includes monitoring the polishing environment based on the environmental sound spectrum.

An aspect provides a polishing apparatus including a polishing table, a polishing head, an acoustic sensor, and a processing system. The polishing table supports a polishing pad. The polishing head serves to press a substrate against a polishing surface of the polishing pad. The acoustic sensor is attached to the polishing table or the polishing head and detects a sound to output a signal representing the sound. The processing system generates a frequency spectrum from the signal outputted from the acoustic sensor. The acoustic sensor is configured to: detect an environmental sound including a sound arising from a polishing environment of the substrate to output an environmental sound signal representing the environmental sound, and detect a polishing sound of the substrate to output a polishing sound signal representing the polishing sound. The processing system is configured to: generate an environmental sound spectrum indicating a relationship between a frequency and a sound pressure level from the environmental sound signal, generate a polishing sound spectrum indicating a relationship between a frequency and a sound pressure level from the polishing sound signal, calculate a difference between the polishing sound spectrum and the environmental sound spectrum to generate a differential spectrum, and monitor a polishing progress based on the differential spectrum.

In an aspect, the processing system is configured to: arrange the differential spectrum along a time axis to generate a differential spectrum map indicating over-time changes in the differential spectrum, and monitor the polishing progress based on a change in the sound pressure level in the differential spectrum map.

In an aspect, the processing system is configured to: monitor the polishing progress to detect a polishing endpoint of the substrate, and end polishing of the substrate based on the polishing endpoint.

In an aspect, the processing system is configured to: generate the environmental sound spectrum by performing a Fourier transform on the environmental sound signal, and generate the polishing sound spectrum by performing a Fourier transform on the polishing sound signal.

In an aspect, the processing system is configured to issue a command to the acoustic sensor to detect the environmental sound after start of polishing of the substrate.

In an aspect, the processing system is configured to issue a command to the acoustic sensor to detect the environmental sound when the polishing apparatus is operated before polishing the substrate.

In an aspect, the processing system is configured to: generate a plurality of environmental sound spectra from the environmental sound signals outputted from the acoustic sensor in a predetermined period, calculate a representative value of a sound pressure level for each frequency from the plurality of environmental sound spectra, and generate the environmental sound spectrum indicating a relationship between the frequency and the representative value of the sound pressure level.

In an aspect, the processing system is configured to monitor the polishing environment based on the environmental sound spectrum.

An aspect provides a program causing a computer to execute steps below. An environmental sound including a sound arising from a polishing environment of a substrate is detected by an acoustic sensor to output an environmental sound signal representing the environmental sound from the acoustic sensor. An environmental sound spectrum indicating a relationship between a frequency and a sound pressure level is generated from the environmental sound signal. A polishing sound of the substrate is detected by the acoustic sensor while pressing the substrate against a polishing surface of a polishing pad to polish the substrate, to output a polishing sound signal representing the polishing sound from the acoustic sensor. A polishing sound spectrum indicating a relationship between a frequency and a sound pressure level is generated from the polishing sound signal. A difference between the polishing sound spectrum and the environmental sound spectrum is calculated to generate a differential spectrum. A polishing progress of the substrate is monitored based on the differential spectrum.

In an aspect, the program is configured to cause the computer to further execute: generating a differential spectrum map indicating over-time changes in the differential spectrum by arranging the differential spectrum along a time axis. The monitoring the polishing progress includes monitoring the polishing progress based on a change in the sound pressure level in the differential spectrum map.

According to embodiments of the disclosure, an environmental sound spectrum is generated based on an environmental sound including a sound arising from a polishing environment of a substrate, and a difference from a polishing sound spectrum generated based on a polishing sound detected during polishing is calculated to generate a differential spectrum. Since the differential spectrum is obtained by removing noise arising from the polishing environment, a polishing progress of the substrate can be monitored with high precision based on the differential spectrum.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view showing an embodiment of a polishing apparatus.

FIG. 2 is a side view schematically showing the polishing apparatus shown in FIG. 1.

FIG. 3 is a graph showing an example of over-time changes in a polishing sound signal outputted by an acoustic sensor.

FIG. 4 is a graph showing an example of a polishing sound spectrum generated by a processing system.

FIG. 5 is a diagram for describing an embodiment of detecting an environmental sound after start of polishing of a substrate.

FIG. 6 is a graph showing an example of a polishing sound spectrum, an environmental sound spectrum, and a differential spectrum generated by the processing system.

FIG. 7 is a graph showing an example of a differential spectrum map generated by the processing system.

FIG. 8 is a flowchart showing an embodiment of a polishing method of the substrate.

FIG. 9 is a flowchart showing another embodiment of the polishing method of the substrate.

FIG. 10 is a flowchart showing still another embodiment of the polishing method of the substrate.

DESCRIPTION OF EMBODIMENTS

Embodiments of the disclosure provide a polishing method and a polishing apparatus capable of accurately monitoring polishing of a substrate using an acoustic sensor. Furthermore, embodiments of the disclosure provide a program for executing such a polishing method.

Hereinafter, embodiments of the disclosure will be described with reference to the drawings.

FIG. 1 is a schematic view showing an embodiment of a polishing apparatus 1, and FIG. 2 is a side view schematically showing the polishing apparatus 1 shown in FIG. 1. The polishing apparatus 1 is an apparatus that chemically and mechanically polishes a substrate W such as a wafer and a panel. As shown in FIG. 1, the polishing apparatus 1 includes a polishing table 3 that supports a polishing pad 2, a polishing head 5 that presses the substrate W against a polishing surface 2a of the polishing pad 2, and a polishing liquid supply nozzle 10 for supplying a polishing liquid (e.g., a slurry) to the polishing pad 2. The polishing pad 2 is attached to an upper surface of the polishing table 3. An exposed surface of the polishing pad 2 constitutes the polishing surface 2a for polishing the substrate W.

The polishing apparatus 1 further includes a support shaft 14, a polishing head arm 16 connected to an upper end of the support shaft 14, a polishing head shaft 18 rotatably supported at a free end of the polishing head arm 16, and a polishing head rotating device 20 that rotates the polishing head 5 together with the polishing head shaft 18. The polishing head 5 is fixed to a lower end of the polishing head shaft 18. The polishing head 5 is configured to be capable of holding the substrate W by vacuum suction on a lower surface of the polishing head 5. The substrate W is held by the polishing head 5 such that a surface to be polished faces downward.

The polishing head rotating device 20 is arranged in the polishing head arm 16. The polishing head rotating device 20 is connected to the polishing head shaft 18 and is configured to rotate the polishing head shaft 18 and the polishing head 5 in a direction indicated by an arrow. The polishing head rotating device 20 is composed of, for example, a combination of a motor, a timing pulley, and a belt. In FIG. 1 and FIG. 2, the polishing head rotating device 20 is depicted schematically.

The polishing apparatus 1 further includes a table motor 6 that rotates the polishing table 3. The table motor 6 is arranged below the polishing table 3, and the polishing table 3 is connected to the table motor 6 via a table shaft 3a. The table motor 6 is configured to rotate the polishing table 3 and the polishing pad 2 in a direction indicated by an arrow around the table shaft 3a.

The polishing apparatus 1 further includes a processing system 40. The polishing head 5, the table motor 6, the polishing liquid supply nozzle 10, and the polishing head rotating device 20 are electrically connected to the processing system 40, and actions of the polishing head 5, the table motor 6, the polishing liquid supply nozzle 10, and the polishing head rotating device 20 are controlled by the processing system 40.

The processing system 40 is composed of at least one computer. The processing system 40 includes a storage device 40a in which programs are stored, and a calculation device 40b that executes calculations according to commands included in the programs. The storage device 40a includes a main storage device such as a random access memory (RAM), and an auxiliary storage devices such as a hard disk drive (HDD) and a solid state drive (SSD). Examples of the calculation device 40b include a central processing unit (CPU) and a graphics processing unit (GPU). However, the specific configuration of the processing system 40 is not limited to these examples.

In an embodiment, the processing system 40 may be composed of a plurality of computers, or may be a plurality of servers connected by a communication network such as the Internet or a local area network. For example, the processing system 40 may be a combination of an edge server and a cloud server. In an embodiment, the storage device 40a may be provided at a location away from the calculation device 40b.

Polishing of the substrate W is performed as follows. The polishing head 5 and the polishing table 3 are respectively rotated in directions indicated by arrows, and a polishing liquid is supplied from the polishing liquid supply nozzle 10 onto the polishing surface 2a of the polishing pad 2. In this state, the polishing head 5 presses the substrate W against the polishing surface 2a of the polishing pad 2. The surface of the substrate W is polished by a combination of a chemical action of the polishing liquid and a mechanical action of abrasive grains included in the polishing liquid and/or the polishing pad 2.

The polishing apparatus 1 further includes an acoustic sensor 30 attached to the polishing table 3 or the polishing head 5. In this embodiment, the acoustic sensor 30 is installed in the polishing table 3. The acoustic sensor 30 is configured to detect a sound at a predetermined time interval (e.g., an interval of 1×10⁻⁶seconds) to output (generate) a signal representing the sound. The acoustic sensor 30 is electrically connected to the processing system 40, and an action of the acoustic sensor 30 is controlled by the processing system 40.

During the polishing of the substrate W, the acoustic sensor 30 detects a polishing sound of the substrate W to output (generate) a polishing sound signal representing the polishing sound. Specifically, the processing system 40 issues a command to the acoustic sensor 30 to detect a polishing sound during the polishing of the substrate W and output a polishing sound signal representing the polishing sound from the acoustic sensor 30. The arrangement of the acoustic sensor 30 may be configured in any manner as long as the acoustic sensor 30 is capable of detecting the polishing sound of the substrate W, and is not limited to this embodiment. For example, the acoustic sensor 30 may also be attached to the polishing head 5. Although the polishing apparatus 1 includes one acoustic sensor 30 in this embodiment, in another embodiment, the polishing apparatus 1 may include two or more acoustic sensors.

The polishing sound of the substrate W changes according to a surface status of the substrate W. For example, when polishing of an upper layer (e.g., an insulating film, a metal film, a silicon layer, etc.) constituting a surface of the substrate W progresses and a lower layer (e.g., a stopper layer) present under the upper layer is exposed, the polishing sound of the substrate W changes. This is because materials constituting the upper layer and the lower layer of the substrate W are different, and a coefficient of friction of the upper layer and a coefficient of friction of the lower layer are different. In another example, when the polishing of the substrate W progresses and a surface roughness of the substrate W changes, the polishing sound of the substrate W changes. This is because a friction (frictional resistance) of the substrate W changes according to the surface roughness of the substrate W. The processing system 40 in this embodiment monitors a polishing progress of the substrate W based on changes in the polishing sound detected by the acoustic sensor 30. “Monitoring the polishing progress of the substrate W” includes detecting a polishing endpoint of the substrate W.

FIG. 3 is a graph showing an example of over-time changes in the polishing sound signal outputted by the acoustic sensor 30. In FIG. 3, the horizontal axis represents a polishing time, and the vertical axis represents an intensity of the polishing sound signal. In this embodiment, the acoustic sensor 30 starts detection of the polishing sound from a predetermined detection start time T1. The detection start time T1 is a time before a polishing endpoint of the substrate W and determined in advance based on a polishing data and the like of polishing the substrate in the past. In an embodiment, the acoustic sensor 30 may also start the detection of the polishing sound along with start of the polishing of the substrate W. The acoustic sensor 30 detects the polishing sound at a predetermined time interval (e.g., an interval of 1×10⁻⁶seconds) to output (generate) a polishing sound signal representing the polishing sound. The polishing sound signal outputted by the acoustic sensor 30 is sent to the processing system 40.

The processing system 40 is configured to generate a polishing sound spectrum indicating a relationship between a frequency and a sound pressure level from the polishing sound signal sent from the acoustic sensor 30. More specifically, the processing system 40 performs a Fourier transform on the polishing sound signal sent from the acoustic sensor 30 to analyze a frequency component and its intensity and generate a polishing sound spectrum. In an embodiment, the processing system 40 performs a Fast Fourier transform (FFT) on the polishing sound signal to generate a polishing sound spectrum.

Polishing sound signals of a predetermined data quantity are used in the generation of a polishing sound spectrum. In the example shown in FIG. 3, the acoustic sensor 30 outputs polishing sound signals of a predetermined data quantity to be used in the generation of one polishing sound spectrum in a predetermined duration dt (e.g., 10 seconds). Thus, the processing system 40 generates a polishing sound spectrum each time the processing system 40 acquires polishing sound signals of the predetermined data quantity outputted from the acoustic sensor 30 in the predetermined duration dt.

FIG. 4 is a graph showing an example of a polishing sound spectrum generated by the processing system 40. In FIG. 4, the horizontal axis represents a frequency, and the vertical axis represents a sound pressure level. As described above, when the polishing sound of the substrate W changes together with a change in the surface status of the substrate W, a peak (i.e., a peak position, a peak height, and a peak width) appearing in the polishing sound spectrum changes. Thus, during the polishing of the substrate W, the processing system 40 is capable of monitoring the polishing progress of the substrate W based on the polishing sound spectrum.

The polishing sound detected by the acoustic sensor 30 during the polishing of the substrate W includes an environmental sound that contains a sound arising from a polishing environment of the substrate W, such as a vibration and a noise caused by the operation of the polishing apparatus 1. In a polishing sound spectrum generated based on a polishing sound including such an environmental sound, it is likely that the polishing progress of the substrate W cannot be accurately monitored. Thus, the processing system 40 generates a differential spectrum obtained by removing a component of the environmental sound from the polishing sound spectrum, and monitors the polishing progress of the substrate W based on the differential spectrum.

The acoustic sensor 30 detects an environmental sound including a sound arising from the polishing environment of the substrate W at a predetermined time interval (e.g., an interval of 1×10⁻⁶seconds) to output (generate) an environmental sound signal representing the environmental sound. In this embodiment, the environmental sound is a sound detected after the start of the polishing of the substrate W. Specifically, the processing system 40 issues a command to the acoustic sensor 30 to detect an environmental sound after the start of the polishing of the substrate W and output an environmental sound signal representing the environmental sound from the acoustic sensor 30.

FIG. 5 is a diagram for describing an embodiment in which an environmental sound is detected after the start of the polishing of the substrate W. The graph shown in FIG. 5 is the same as the graph showing an example of over-time changes in the polishing sound signal outputted by the acoustic sensor 30 shown in FIG. 3. In the embodiment shown in FIG. 5, the acoustic sensor 30 detects an environmental sound in a predetermined period from a time T2 to a time T3 after the start of the polishing of the substrate W to output an environmental sound signal representing the environmental sound. The predetermined period of detecting the environmental sound is a predetermined period immediately after the start of the polishing of the substrate W or before the surface status of the substrate W changes in an initial polishing stage. The environmental sound detected after the start of the polishing of the substrate W may also include a polishing sound of the substrate W that does not affect the monitoring of the polishing progress of the substrate W.

The environmental sound signal outputted from the acoustic sensor 30 is sent to the processing system 40. The processing system 40 is configured to generate an environmental sound spectrum indicating a relationship between a frequency and a sound pressure level from the environmental sound signal sent from the acoustic sensor 30. More specifically, the processing system 40 performs a Fourier transform on the environmental sound signal sent from the acoustic sensor 30 to analyze a frequency component and its intensity and generate an environmental sound spectrum. In an embodiment, the processing system 40 may perform a Fast Fourier transform (FFT) on the environmental sound signal to generate an environmental sound spectrum. The generated environmental sound spectrum is stored to the storage device 40a of the processing system 40.

Environmental sound signals of a predetermined data quantity are used in the generation of an environmental sound spectrum. In the embodiment shown in FIG. 5, the acoustic sensor 30 outputs environmental sound signals of a predetermined data quantity to be used in the generation of one environmental sound spectrum in a predetermined duration dt (e.g., 10 seconds). Thus, the processing system 40 generates an environmental sound spectrum each time the processing system 40 acquires environmental sound signals of the predetermined data quantity outputted from the acoustic sensor 30 in the predetermined duration dt. In the embodiment shown in FIG. 5, a predetermined period from a time T2 to a time T3 is three times the predetermined duration dt, and the processing system 40 generates three environmental sound spectra. Thus, the processing system 40 may generate a plurality of environmental sound spectra from the environmental sound signals outputted from the acoustic sensor 30 in the predetermined period.

In an embodiment, the processing system 40 may calculate a representative value of the sound pressure level for each frequency from a plurality of environmental sound spectra, and generate an environmental sound spectrum indicating a relationship between the frequency and the representative value of the sound pressure level. Examples of the representative value include a mean, a median, a maximum value, a minimum value, etc.

In an embodiment, the environmental sound may be a sound detected when the polishing apparatus 1 is operated before polishing the substrate W. Specifically, the processing system 40 issues a command to the acoustic sensor 30 to detect an environmental sound during the operation of the polishing apparatus 1 before the polishing of the substrate W, to output an environmental sound signal representing the environmental sound from the acoustic sensor 30. For example, the detection of an environmental sound is performed when the polishing head 5 and the polishing table 3 are rotated, and a polishing liquid is supplied from the polishing liquid supply nozzle 10 onto the polishing pad 2, in a state in which the substrate W held by the polishing head 5 is separated from the polishing pad 2. In this case as well, the processing system 40 may generate a plurality of environmental sound spectra from the environmental sound signals outputted from the acoustic sensor 30 in the predetermined period, and calculate a representative value of the sound pressure level for each frequency from the plurality of environmental sound spectra to generate an environmental sound spectrum indicating a relationship between the frequency and the representative value of the sound pressure level.

The processing system 40 is configured to calculate a difference between the polishing sound spectrum and the environmental sound spectrum to generate a differential spectrum. FIG. 6 is a graph showing an example of a polishing sound spectrum, an environmental sound spectrum, and a differential spectrum generated by the processing system 40. In FIG. 6, the horizontal axis represents a frequency, and the vertical axis represents a sound pressure level. The graph indicated by a broken line is an example of the polishing sound spectrum generated by the processing system 40, the graph indicated by a thin line is an example of the environmental sound spectrum generated by the processing system 40, and the graph indicated by a thick line is an example of the differential spectrum generated by the processing system 40. The processing system 40 calculates the difference between the sound pressure level of the polishing sound spectrum and the sound pressure level of the environmental sound spectrum for each frequency to generate the differential spectrum from the calculated difference in the sound pressure level for each frequency.

As described above, the processing system 40 generates a polishing sound spectrum each time the processing system 40 acquires polishing sound signals of the predetermined data quantity from the acoustic sensor 30. Each time the processing system 40 generates a polishing sound spectrum, the processing system 40 calculates a difference between the polishing sound spectrum and the environmental sound spectrum stored in the storage device 40a to generate a differential spectrum. The processing system 40 is configured to monitor the polishing progress of the substrate W based on the generated differential spectrum. Since the differential spectrum is obtained by removing the component of the environmental sound from the polishing sound spectrum, the processing system 40 can monitor changes in the polishing sound arising from a change in the surface status of the substrate W with high precision.

In an embodiment, the processing system 40 is configured to detect a polishing endpoint of the substrate W based on the differential spectrum. As described above, when the polishing of the upper layer (e.g., an insulating film, a metal film, a silicon layer, etc.) constituting the surface of the substrate W progresses and the lower layer (e.g., a stopper layer) present under the upper layer is exposed, the polishing sound of the substrate W changes. Based on such a change in the polishing sound, the processing system 40 can detect the polishing endpoint of the substrate W. For example, the processing system 40 detects the polishing endpoint of the substrate W when the sound pressure level at a predetermined frequency in the differential spectrum reaches a target value. The target value of the sound pressure level at the predetermined frequency is determined in advance based on a polishing data and the like of polishing the substrate in the past.

The processing system 40 is configured to end the polishing of the substrate W based on the detected polishing endpoint of the substrate W. Specifically, based on the polishing endpoint of the substrate W, the processing system 40 issues commands to the polishing head rotating device 20 and the table motor 6 to stop the rotation of the polishing head 5 and the polishing table 3 and end the polishing of the substrate W. In an embodiment, the processing system 40 may end the polishing of the substrate W after a predetermined transition time elapses from the polishing endpoint of the substrate W.

In an embodiment, the processing system 40 is configured to detect a change point in a polishing condition of the substrate W based on the differential spectrum. When the polishing of the upper layer constituting the surface of the substrate W progresses and the lower layer present under the upper layer is exposed, a polishing condition of the substrate W (e.g., a rotational speed of the polishing head 5, a pressing force on the substrate W by the polishing head 5, a rotational speed of the polishing table 3, a type of the polishing liquid supplied onto the polishing pad 2, etc.) may be changed. For example, the processing system 40 detects a change point in the polishing condition of the substrate W when the sound pressure level at a predetermined frequency in the differential spectrum reaches a reference value. The reference value is determined in advance based on a polishing data and the like of polishing the substrate in the past.

The processing system 40 is configured to change the polishing condition of the substrate W based on the detected change point in the polishing condition of the substrate W. Specifically, based on the change point in the polishing condition of the substrate W, the processing system 40 issues commands to the table motor 6, the polishing liquid supply nozzle 10, and/or the polishing head rotating device 20 to change actions thereof according to the polishing condition to be changed. In an embodiment, the processing system 40 may change the polishing condition of the substrate W when a predetermined transition time elapses from the change point in the polishing condition of the substrate W.

In an embodiment, the processing system 40 is configured to monitor the surface roughness of the substrate W based on the differential spectrum. As described above, the surface roughness of the substrate W may be monitored based on a change in the polishing sound of the substrate W that occurs when the surface roughness of the substrate W changes. For example, the processing system 40 may monitor the surface roughness of the substrate W based on a peak position, a peak height, and a peak width of the differential spectrum. In another example, the processing system 40 detects that the surface roughness of the substrate W changes when the sound pressure level at a predetermined frequency in the differential spectrum exceeds a threshold value or drops below a threshold value. The processing system 40 may detect a change in the surface roughness of the substrate W to detect a polishing endpoint of the substrate W. The threshold value is determined in advance based on a polishing data and the like of polishing the substrate in the past.

In an embodiment, the processing system 40 is configured to generate a differential spectrum map showing over-time changes in the differential spectrum by arranging the differential spectrum along a time axis. FIG. 7 is a graph showing an example of a differential spectrum map generated by the processing system 40. In FIG. 7, the X-axis represents a frequency, the Y-axis represents a time, and the Z-axis represents a sound pressure level. The processing system 40 generates a differential spectrum map each time the processing system 40 generates a differential spectrum. More specifically, the processing system 40 adds newly generated differential spectra along the time axis of the differential spectrum map to generate (update) the differential spectrum map.

The processing system 40 is configured to monitor the polishing progress of the substrate W based on changes in the sound pressure level in the differential spectrum map. For example, the processing system 40 detects a polishing endpoint of the substrate W, which is a time point at which a change amount in the sound pressure level in a predetermined monitor frequency domain of the differential spectrum map exceeds a reference value. The monitor frequency domain is determined in advance based on a polishing data and the like of polishing the substrate in the past. The monitoring of the polishing progress of the substrate W based on the differential spectrum map may be applied to any of the detection of a polishing endpoint of the substrate W described above, the detection of a change point in the polishing condition of the substrate W, and the monitoring of the surface roughness of the substrate W.

FIG. 8 is a flowchart showing an embodiment of a polishing method of the substrate W.

In step S101, the processing system 40 issues commands to the polishing head 5, the table motor 6, the polishing liquid supply nozzle 10, and the polishing head rotating device 20 to supply a polishing liquid (slurry) from the polishing liquid supply nozzle 10 onto the polishing pad 2 while rotating the polishing head 5 and the polishing table 3. In this state, the substrate W is pressed against the polishing surface 2a of the polishing pad 2 by the polishing head 5 to start polishing of the substrate W.

In step S102, the processing system 40 issues a command to the acoustic sensor 30 to detect an environmental sound after start of the polishing of the substrate W and output an environmental sound signal representing the environmental sound from the acoustic sensor 30. The outputted environmental sound signal is sent to the processing system 40. The detection of the environmental sound is performed immediately after the start of the polishing of the substrate W or before the surface status of the substrate W changes in an initial polishing stage.

In step S103, the processing system 40 generates an environmental sound spectrum indicating a relationship between a frequency and a sound pressure level from the environmental sound signal sent from the acoustic sensor 30. More specifically, the processing system 40 performs a Fourier transform (e.g., a Fast Fourier transform) on the environmental sound signal sent from the acoustic sensor 30 to generate an environmental sound spectrum. In an embodiment, a plurality of environmental sound spectra may be generated from environmental sound signals outputted from the acoustic sensor 30 in a predetermined period after the start of the polishing of the substrate W, and a representative value of the sound pressure level may be calculated for each frequency from the plurality of environmental sound spectra to generate an environmental sound spectrum indicating a relationship between the frequency and the representative value of the sound pressure level. The generated environmental sound spectrum is stored to the storage device 40a of the processing system 40.

In step S104, the processing system 40 issues a command to the acoustic sensor 30 to detect a polishing sound during the polishing of the substrate W and output a polishing sound signal representing the polishing sound from the acoustic sensor 30. The detection of the polishing sound by the acoustic sensor 30 may be performed from a detection start time T1 (see FIG. 3) determined in advance, or may be performed with the start of the polishing of the substrate W.

In step S105, the processing system 40 generates a polishing sound spectrum indicating a relationship between a frequency and a sound pressure level from the polishing sound signal sent from the acoustic sensor 30. More specifically, the processing system 40 performs a Fourier transform (e.g., a Fast Fourier transform) on the polishing sound signal sent from the acoustic sensor 30 to generate a polishing sound spectrum.

In step S106, the processing system 40 calculates a difference between the generated polishing sound spectrum and the environmental sound spectrum stored in the storage device 40a to generate a differential spectrum. More specifically, the processing system 40 calculates a difference between the sound pressure level of the polishing sound spectrum and the sound pressure level of the environmental sound spectrum for each frequency to generate a differential spectrum from the calculated difference in the sound pressure level for each frequency.

In step S107, the processing system 40 monitors a polishing progress of the substrate W based on the differential spectrum. More specifically, in the embodiment shown in FIG. 8, the processing system 40 determines whether a polishing endpoint of the substrate W has been reached based on the differential spectrum. For example, the processing system 40 detects the polishing endpoint of the substrate W, which is a time point at which the sound pressure level at a predetermined frequency in the differential spectrum reaches a target value. If the processing system 40 does not detect the polishing endpoint of the substrate W (“NO” in step S107), the processing system 40 continues the polishing of the substrate W and repeats steps S105 to S107. If the processing system 40 detects the polishing endpoint of the substrate W (“YES” in step S107), the processing system 40 ends the polishing of the substrate W (step S108). Specifically, based on the polishing endpoint of the substrate W, the processing system 40 issues commands to the polishing head rotating device 20 and the table motor 6 to stop the rotation of the polishing head 5 and the polishing table 3 and end the polishing of the substrate W.

In this embodiment, in step S107, the processing system 40 detects the polishing endpoint of the substrate W. However, in an embodiment, in step S107, the processing system 40 may also detect a change point in a polishing condition of the substrate W, or may also detect a change point in the surface roughness of the substrate W.

FIG. 9 is a flowchart showing another embodiment of the polishing method of the substrate W.

In step S201, the processing system 40 operates the polishing apparatus 1 before polishing the substrate W. For example, the processing system 40 issues commands to the table motor 6, the polishing liquid supply nozzle 10, and the polishing head rotating device 20 to supply a polishing liquid from the polishing liquid supply nozzle 10 onto the polishing pad 2 while rotating the polishing head 5 and the polishing table 3, in a state in which the substrate W held by the polishing head 5 is separated from the polishing pad 2.

In step S202, the processing system 40 issues a command to the acoustic sensor 30 to detect an environmental sound during the operation of the polishing apparatus 1 before polishing of the substrate W and output an environmental sound signal representing the environmental sound from the acoustic sensor 30. The outputted environmental sound signal is sent to the processing system 40.

In step S203, the processing system 40 generates an environmental sound spectrum indicating a relationship between a frequency and a sound pressure level from the environmental sound signal sent from the acoustic sensor 30. More specifically, the processing system 40 performs a Fourier transform (e.g., a Fast Fourier transform) on the environmental sound signal sent from the acoustic sensor 30 to generate an environmental sound spectrum. In an embodiment, a plurality of environmental sound spectra may be generated from environmental sound signals outputted from the acoustic sensor 30 in a predetermined period, and a representative value of the sound pressure level may be calculated for each frequency from the plurality of environmental sound spectra to generate an environmental sound spectrum indicating a relationship between the frequency and the representative value of the sound pressure level. The generated environmental sound spectrum is stored to the storage device 40a of the processing system 40.

In step S204, the processing system 40 issues commands to the polishing head 5, the table motor 6, the polishing liquid supply nozzle 10, and the polishing head rotating device 20 to supply a polishing liquid (slurry) from the polishing liquid supply nozzle 10 onto the polishing pad 2 while rotating the polishing head 5 and the polishing table 3. In this state, the substrate W is pressed against the polishing surface 2a of the polishing pad 2 by the polishing head 5 to start polishing of the substrate W.

Steps S205 to S209 are the same as steps S104 to S108 of the embodiment described with reference to FIG. 8, so repeated descriptions thereof will be omitted.

FIG. 10 is a flowchart showing still another embodiment of the polishing method of the substrate W.

Steps S301 to S306 are the same as steps S101 to S106 of the embodiment described with reference to FIG. 8, so repeated descriptions thereof will be omitted. In an embodiment, the process of generating an environmental sound spectrum in steps S201 to S203 of the embodiment described with reference to FIG. 9 may also be applied to the process of generating an environmental sound spectrum in the embodiment of FIG. 10.

In step S307, the processing system 40 generates a differential spectrum map indicating over-time changes in the differential spectrum by arranging the differential spectrum along a time axis. More specifically, the processing system 40 adds newly generated differential spectra along the time axis of the differential spectrum map to generate (update) the differential spectrum map.

In step S308, the processing system 40 monitors a polishing progress of the substrate W based on changes in the sound pressure level in the differential spectrum map. More specifically, in the embodiment shown in FIG. 10, the processing system 40 determines whether the polishing endpoint of the substrate W has been reached based on changes in the sound pressure level in the differential spectrum map. For example, the processing system 40 detects the polishing endpoint of the substrate W, which is a time point at which a change amount in the sound pressure level in a predetermined monitor frequency domain of the differential spectrum map exceeds a reference value. If the processing system 40 does not detect the polishing endpoint of the substrate W (“NO” in step S308), the processing system 40 continues the polishing of the substrate W and repeats steps S305 to S308. If the processing system 40 detects the polishing endpoint of the substrate W (“YES” in step S308), the processing system 40 ends the polishing of the substrate W (step S309). Specifically, based on the polishing endpoint of the substrate W, the processing system 40 issues commands to the polishing head rotating device 20 and the table motor 6 to stop the rotation of the polishing head 5 and the polishing table 3 and end the polishing of the substrate W.

The processing system 40 acts according to commands included in a program electronically stored in the storage device 40a thereof. The processing system 40 executes each action step in each of the above embodiments according to the commands included in the program. The program for causing the processing system 40 to execute these steps is recorded on a non-transitory tangible computer-readable recording medium and is provided to the processing system 40 via the recording medium. Alternatively, the program may also be inputted to the processing system 40 via a communication network such as the Internet or a local area network.

In an embodiment, the processing system 40 may be configured to monitor a polishing environment of the substrate based on the environmental sound spectrum. An environmental sound spectrum generated based on an environmental sound detected under the same conditions basically has a same peak (i.e., a peak position, a peak height, and a peak width). However, for example, in the case where an abnormality occurs in the polishing environment of the substrate, such as a malfunction occurring in the polishing apparatus 1, the vibration and sound arising from the operation of the polishing apparatus 1 change, and the peak of the generated environmental sound spectrum also changes. Thus, the polishing environment of the substrate can be monitored based on the environmental sound spectrum.

The processing system 40 generates an environmental sound spectrum by the method described above each time a substrate is polished, and monitors the polishing environment of the substrate based on the environmental sound spectrum. In an embodiment, the processing system 40 may also generate an environmental sound spectrum each time a plurality of substrates are polished, and may monitor the polishing environment of the substrate based on the environmental sound spectrum. For example, the processing system 40 detects that an abnormality occurs in the polishing environment of the substrate when the sound pressure level at a predetermined frequency in the environmental sound spectrum reaches an abnormality threshold value. The abnormality threshold value of the sound pressure level at the predetermined frequency is determined in advance based on an environmental sound spectrum or the like generated based on an environmental sound detected by the acoustic sensor 30 when an abnormality occurs in the polishing environment of the substrate. When it is detected that an abnormality occurs in the polishing environment of the substrate, an operator performs maintenance as necessary.

In an embodiment, the processing system 40 may generate an environmental sound spectrum by the method described above based on an environmental sound detected by the acoustic sensor 30 in a state in which an abnormality does not occur in the polishing environment of the substrate (i.e., a state in which the polishing environment of the substrate is normal), and may store this environmental sound spectrum as a reference environmental sound spectrum to the storage device 40a. In that case, the processing system 40 monitors the polishing environment of the substrate based on a comparison between the reference environmental sound spectrum stored in the storage device 40a and the environmental sound spectrum. Specifically, the processing system 40 detects that an abnormality occurs in the polishing environment of the substrate when the environmental sound spectrum changes with respect to the reference environmental sound spectrum.

As described above, the environmental sound spectrum may be generated based on the environmental sound detected after the start of the polishing of the substrate, or may be generated based on the environmental sound detected during the operation of the polishing apparatus 1 before the polishing of the substrate. Thus, the monitoring of the polishing environment of the substrate based on the environmental sound spectrum may be performed when an environmental sound spectrum is generated based on the environmental sound detected after the start of the polishing of the substrate, or may be performed when an environmental sound spectrum is generated based on the environmental sound detected during the operation of the polishing apparatus 1 before the polishing of the substrate.

The embodiments described above are intended to enable those skilled in the art of the disclosure to implement the disclosure. Various modification examples of the above embodiments may naturally be made by those skilled in the art, and the technical concept of the disclosure may also be applied to other embodiments. Thus, the disclosure is not limited to the described embodiments, but is interpreted in the broadest range according to the technical concept defined by the scope of the patent claims.

Claims

1. A polishing method comprising:

detecting, by an acoustic sensor, an environmental sound comprising a sound arising from a polishing environment of a substrate to output an environmental sound signal representing the environmental sound from the acoustic sensor;

generating an environmental sound spectrum indicating a relationship between a frequency and a sound pressure level from the environmental sound signal;

detecting, by the acoustic sensor, a polishing sound of the substrate while pressing the substrate against a polishing surface of a polishing pad to polish the substrate, to output a polishing sound signal representing the polishing sound from the acoustic sensor;

generating a polishing sound spectrum indicating a relationship between a frequency and a sound pressure level from the polishing sound signal;

calculating a difference between the polishing sound spectrum and the environmental sound spectrum to generate a differential spectrum; and

monitoring a polishing progress of the substrate based on the differential spectrum.

2. The polishing method according to claim 1, further comprising:

generating a differential spectrum map indicating over-time changes in the differential spectrum by arranging the differential spectrum along a time axis, wherein

the monitoring the polishing progress comprises monitoring the polishing progress based on a change in the sound pressure level in the differential spectrum map.

3. The polishing method according to claim 1, wherein

the monitoring the polishing progress comprises detecting a polishing endpoint of the substrate, and

the polishing method further comprises ending polishing of the substrate based on the polishing endpoint.

4. The polishing method according to claim 1, wherein

the environmental sound spectrum is generated by performing a Fourier transform on the environmental sound signal, and

the polishing sound spectrum is generated by performing a Fourier transform on the polishing sound signal.

5. The polishing method according to claim 1, wherein

the environmental sound is a sound detected after start of polishing of the substrate.

6. The polishing method according to claim 1, wherein

the environmental sound is a sound detected when a polishing apparatus performing polishing of the substrate is operated before polishing the substrate.

7. The polishing method according to claim 1, wherein

the generating the environmental sound spectrum comprises: generating a plurality of environmental sound spectra from the environmental sound signals outputted from the acoustic sensor in a predetermined period, calculating a representative value of a sound pressure level for each frequency from the plurality of environmental sound spectra, and generating the environmental sound spectrum indicating a relationship between the frequency and the representative value of the sound pressure level.

8. The polishing method according to claim 1, further comprising:

monitoring the polishing environment based on the environmental sound spectrum.

9. A polishing apparatus comprising:

a polishing table supporting a polishing pad;

a polishing head for pressing a substrate against a polishing surface of the polishing pad;

an acoustic sensor attached to the polishing table or the polishing head and detecting a sound to output a signal representing the sound; and

a processing system generating a frequency spectrum from the signal outputted from the acoustic sensor, wherein

the acoustic sensor is configured to: detect an environmental sound comprising a sound arising from a polishing environment of the substrate to output an environmental sound signal representing the environmental sound, and detect a polishing sound of the substrate to output a polishing sound signal representing the polishing sound, and

the processing system is configured to: generate an environmental sound spectrum indicating a relationship between a frequency and a sound pressure level from the environmental sound signal, generate a polishing sound spectrum indicating a relationship between a frequency and a sound pressure level from the polishing sound signal, calculate a difference between the polishing sound spectrum and the environmental sound spectrum to generate a differential spectrum, and monitor a polishing progress based on the differential spectrum.

10. The polishing apparatus according to claim 9, wherein

the processing system is configured to: arrange the differential spectrum along a time axis to generate a differential spectrum map indicating over-time changes in the differential spectrum, and monitor the polishing progress based on a change in the sound pressure level in the differential spectrum map.

11. The polishing apparatus according to claim 9, wherein the processing system is configured to:

monitor the polishing progress to detect a polishing endpoint of the substrate, and

end polishing of the substrate based on the polishing endpoint.

12. The polishing apparatus according to claim 9, wherein the processing system is configured to:

generate the environmental sound spectrum by performing a Fourier transform on the environmental sound signal, and

generate the polishing sound spectrum by performing a Fourier transform on the polishing sound signal.

13. The polishing apparatus according to claim 9, wherein the processing system is configured to issue a command to the acoustic sensor to detect the environmental sound after start of polishing of the substrate.

14. The polishing apparatus according to claim 9, wherein the processing system is configured to issue a command to the acoustic sensor to detect the environmental sound when the polishing apparatus is operated before polishing the substrate.

15. The polishing apparatus according to claim 9, wherein

the processing system is configured to:

generate a plurality of environmental sound spectra from the environmental sound signals outputted from the acoustic sensor in a predetermined period,

calculate a representative value of a sound pressure level for each frequency from the plurality of environmental sound spectra, and

generate the environmental sound spectrum indicating a relationship between the frequency and the representative value of the sound pressure level.

16. The polishing apparatus according to claim 9, wherein the processing system is configured to monitor the polishing environment based on the environmental sound spectrum.

17. A non-transitory computer-readable recording medium recording a program causing a computer to execute: