METHOD OF DETECTING POLISHING ENDPOINT, AND PROGRAM FOR DETECTING POLISHING ENDPOINT

Description

CROSS REFERENCE TO RELATED APPLICATION

This document claims priority to Japanese Patent Application No. 2023-051685 filed Mar. 28, 2023, the entire contents of which are hereby incorporated by reference.

BACKGROUND

In a manufacturing process of the semiconductor devices, a planarization technique of a surface of the semiconductor device is becoming more important. The most important technique in this planarization technique is chemical mechanical polishing. This chemical mechanical polishing (which will be hereinafter called CMP) is a process of polishing a substrate, such as a wafer, by placing the substrate in sliding contact with a polishing pad while supplying a polishing liquid containing abrasive grains, such as silica (SiO₂), onto the polishing pad.

A polishing apparatus for performing CMP includes a polishing table that supports a polishing pad having a polishing surface, and a polishing head for holding a substrate. Such polishing apparatus is configured to move the polishing table and the polishing head relative to each other, and to press the substrate against the polishing surface of the polishing pad by use of the polishing head while supplying a polishing liquid onto the polishing pad disposed on the polishing table. The surface of the substrate is brought into sliding contact with the polishing surface in the presence of the polishing liquid, so that the surface of the substrate is polished to a flat and mirror finish.

In order to polish the substrate more flatly, a thickness of a film formed on the top layer of the substrate (hereinafter simply referred to as “film thickness” or “thickness of film”) is conventionally measured by a film-thickness sensor during polishing the substrate, and a distribution of a remaining film thickness within the substrate surface is controlled based on the measurement values of the film thickness sensor, or a polishing endpoint in the substrate is detected based on the measurement values of the film thickness (see Japanese laid-open patent publication No. 2007-331108, for example). The polishing apparatus is configured to determine the polishing endpoint, which is a time point when the film has been removed to a target film thickness, based on the measurement values of the film thickness sensor.

In the polishing of the substrate, if the film to be removed remains in the surface of the substrate (i.e., insufficient polishing), or if the film that is to be left with a desired film thickness is excessively polished (i.e., over-polished), performance of the devices formed in the substrate may be adversely affected. For this reason, the polishing apparatus is required to detect an optimal polishing endpoint.

However, it is difficult to detect this polishing endpoint with high accuracy. This is because, depending on properties, such as a type of film formed in the top layer of the substrate, and/or an initial film-thickness profile, the film at a peripheral portion of the substrate may be polished faster than the film in a center portion of the substrate, and vice versa.

SUMMARY

Therefore, there are provided a polishing endpoint detecting method and a polishing endpoint detecting program capable of detecting a polishing endpoint of a substrate with high accuracy.

Embodiments, which will be described below, relate to a polishing endpoint detecting method and a polishing endpoint detecting program capable of detecting a polishing endpoint of a substrate with high accuracy.

In one embodiment, there is provided a polishing endpoint detecting method, comprising: polishing a substrate by rotating a polishing table which supports a polishing pad and pressing the substrate against a polishing surface of the polishing pad by use of a polishing head; sequentially acquiring signals, corresponding to the film thickness of the substrate, at a plurality of measurement points in the substrate when a film-thickness sensor mounted to the polishing table moves across the substrate, thereby creating a film-thickness profile of the substrate each time the polishing table is rotated a predetermined number of times; dividing the film-thickness profile into a plurality of measurement zones and selecting a monitoring zone from the plurality of measurement zones for determining a polishing endpoint of the substrate; determining whether or not the monitoring zone is changed to another measurement zone based on changes in the film-thickness profile obtained from start to end of polishing of the substrate; and determining a polishing endpoint of the substrate based on the signals in the monitoring zone.

In one embodiment, selecting the monitoring zone is calculating differences in film thickness between each of the measurement zones and selecting the measurement zone with the smallest amount of remaining film as the monitoring zone when any of the differences exceeds a predetermined threshold value.

In one embodiment, selecting the monitoring zone is calculating differences in film thickness between each of the measurement zones and selecting the measurement zone with the largest amount of remaining film as the monitoring zone when any of the differences exceeds a predetermined threshold value.

In one embodiment, the polishing endpoint detecting method further comprises: constructing a learned model that is constructed to output the monitoring zone to be changed when state variables, including at least the film-thickness profile, are input, wherein selecting the monitoring zone is performed based on an output when the created film-thickness profile is input to the learned model

In one embodiment, there is provided a polishing endpoint detecting method, comprising: polishing a substrate by rotating a polishing table which supports a polishing pad and pressing the substrate against a polishing surface of the polishing pad by use of a polishing head; sequentially acquiring signals, corresponding to the film thickness of the substrate, at a plurality of measurement points in the substrate when a film-thickness sensor mounted to the polishing table moves across the substrate, thereby creating a film-thickness profile of the substrate each time the polishing table is rotated a predetermined number of times; dividing the film-thickness profile into a plurality of measurement zones; determining whether or not ranges of each of the measurement zones are changed based on changes in the film-thickness profile obtained from start to end of polishing of the substrate; and determining a polishing endpoint of the substrate based on the signals in the plurality of the measurement zones.

In one embodiment, changing the ranges of each of the measurement zones is obtaining an inflection point of the film-thickness profile between adjacent measurement zones, and shifting a border of the adjacent measurement zones to the inflection point.

In one embodiment, changing the ranges of each of the measurement zones is calculating differences between measurement values of film thickness at adjacent measurement points, and shifting a border of adjacent measurement zones between two excess measurement points when the two excess measurement points appear where the difference exceeds a threshold value.

In one embodiment, changing the ranges of each of the measurement zones is calculating variations of a plurality of measurement values of the film thickness for each of the measurement zones, and shifting a border between adjacent measurement zones such that the variations are less than or equal to an allowable value.

In one embodiment, the polishing endpoint detecting method further comprises: constructing a learned model that is constructed so as to output the ranges of measurement zones to be changed when state variables, including at least the film-thickness profile, are inputted, wherein changing the ranges of each of the measurement zones is performed based on the output when the created film-thickness profiles are input to the learned model.

In one embodiment, there is provided a polishing endpoint detecting program for causing a computer to execute: polishing a substrate by rotating a polishing table which supports a polishing pad and pressing the substrate against a polishing surface of the polishing pad by use of a polishing head; sequentially acquiring signals, corresponding to the film thickness of the substrate, at a plurality of measurement points in the substrate when a film-thickness sensor mounted to the polishing table moves across the substrate, thereby creating a film-thickness profile of the substrate each time the polishing table is rotated a predetermined number of times; dividing the film-thickness profile into a plurality of measurement zones and selecting a monitoring zone from the plurality of measurement zones for determining a polishing endpoint of the substrate; determining whether or not the monitoring zone is changed to another measurement zone based on changes in the film-thickness profile obtained from start to end of polishing of the substrate; and determining a polishing endpoint of the substrate based on the signals in the monitoring zone.

In one embodiment, selecting the monitoring zone is calculating differences in film thickness between each of the measurement zones and selecting the measurement zone with the largest amount of remaining film as the monitoring zone when any of the differences exceeds a predetermined threshold value.

In one embodiment, selecting the monitoring zone is performed based on an output when the created film-thickness profile is input to a learned model, and the learned model is constructed so as to output the monitoring zone to be changed when state variables, including at least the film-thickness profile, are input.

In one embodiment, there is provided a polishing endpoint detecting program for causing a computer to execute: polishing a substrate by rotating a polishing table which supports a polishing pad and pressing the substrate against a polishing surface of the polishing pad by use of a polishing head; sequentially acquiring signals, corresponding to the film thickness of the substrate, at a plurality of measurement points in the substrate when a film-thickness sensor mounted to the polishing table moves across the substrate, thereby creating a film-thickness profile of the substrate each time the polishing table is rotated a predetermined number of times; dividing the film-thickness profile into a plurality of measurement zones; determining whether or not ranges of each of the measurement zones are changed based on changes in the film-thickness profile obtained from start to end of polishing of the substrate; and determining a polishing endpoint of the substrate based on the signals in the plurality of the measurement zones.

In one embodiment, changing the ranges of each of the measurement zones is performed based on an output when the created film-thickness profiles are input to a learned model, and the learned model is constructed so as to output the ranges of measurement zones to be changed when state variables, including at least the film-thickness profile, are inputted.

The polishing apparatus changes the monitoring zone or the ranges of the measurement zones based on the film-thickness profile acquired by the film-thickness sensor. Therefore, the optimal monitoring zone or the optimal ranges of measurement zones are automatically selected based on the actual film-thickness profile, so that the polishing endpoint of the substrate can be determined with high accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a polishing apparatus according to an embodiment;

FIG. 2 is a schematic view showing one path of a film-thickness sensor when moving across a surface of a substrate (wafer W);

FIG. 3 is a schematic view showing a plurality of paths of the film-thickness sensor when moving across the surface of the substrate;

FIG. 4 is a schematic view showing a relationship between an example of the film-thickness profile of the substrate and a plurality of measurement zones set for that film-thickness profile;

FIG. 5 is a flowchart showing a polishing endpoint detecting method according to an embodiment;

FIG. 6 is a schematic view showing one example of the film-thickness profile that changes with polishing of the wafer W;

FIG. 7 is a schematic view showing another example of the film-thickness profile that changes with polishing of the wafer W;

FIG. 8 is a flowchart showing the polishing endpoint detecting method according to another embodiment;

FIG. 9 is a schematic view showing a state in which the border between the adjacent measurement zones is changed to the inflection point of the film-thickness profile;

FIG. 10 is a schematic view showing a state in which the border between adjacent measurement zones is changed between the two excess measurement points;

FIG. 11 is a schematic view showing an example of machine learning; and

FIG. 12 is a schematic view showing an example of structure of a neural network.

DESCRIPTION OF EMBODIMENTS

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

FIG. 1 is a schematic view showing a polishing apparatus (CMP apparatus) according to an embodiment. As shown in FIG. 1, the polishing apparatus includes a polishing head 1 for holding and rotating a wafer W, which is an example of a substrate, a polishing table 2 that supports a polishing pad 3, and a polishing-liquid supply nozzle 4 for supplying a polishing liquid (e.g. a slurry) onto a surface of the polishing pad 3. A surface (upper surface) of the polishing pad 3 provides a polishing surface for polishing the wafer W. Although not shown, the polishing apparatus may further include a pad-temperature regulating apparatus for regulating a surface temperature of the polishing pad 3 at an optimal polishing temperature.

The polishing head 1 is vertically movable, and is rotatable about its axis in a direction indicated by arrow. The wafer W is held on a lower surface of the polishing head 1 by vacuum suction, for example. A table motor 6 is coupled to the polishing table 2, so that the polishing table 2 can rotate in a direction indicated by arrow. As shown in FIG. 1, the polishing head 1 and the polishing table 2 rotate in the same direction. The polishing pad 3 is attached to an upper surface of the polishing table 2.

The polishing apparatus has a controller 40 that controls operations of at least the polishing head 1, the table motor 6, and the polishing-liquid supply nozzles 4. The controller 40 is composed of at least one computer. The controller 40 includes a memory 110 storing programs, and an arithmetic device 120 configured to perform arithmetic operations according to instructions included in the programs. The arithmetic device 120 includes a CPU (Central Processing Unit) or GPU (Graphic Processing Module) configured to perform arithmetic operations according to instructions included in programs. The memory 110 includes a main memory (e.g., random access memory) to which the arithmetic device 120 is accessible, and an auxiliary memory (e.g., hard disk drive or solid state drive) for storing data and the programs.

The polishing apparatus further includes a film-thickness sensor (film-thickness measuring device) 7 configured to measure a thickness of a film in the wafer W (i.e., a film in a top layer of the wafer W). The film-thickness sensor 7 is fixed to the polishing table 2, and rotates together with the polishing table 2. The film-thickness sensor 7 is electrically coupled to the controller 40, and is configured to generate a film-thickness signal that changes according to the film thickness of the wafer W and output the film-thickness signal to the controller 40. The film-thickness sensor 7 is arranged in the polishing table 2, and generates film-thickness signals at a plurality of measurement points, including a center portion of the wafer W, each time the polishing table 2 makes one rotation.

Examples of the film-thickness sensor 7 may include an optical sensor and an eddy current sensor. The eddy-current sensor has a sensor coil configured to pass a magnetic flux through a conductive film of the wafer W to generate an eddy current. The eddy-current sensor detects the eddy current that varies according to the film thickness of the wafer W, and outputs an eddy current signal. The eddy current signal is the film-thickness signal that varies according to the film thickness of the wafer W. The optical sensor is a sensor that detects the film thickness in the top layer of the wafer W by irradiating the wafer W with light and measuring an interference wave reflected from the wafer W. The optical sensor is configured to irradiate the surface of the wafer W with light, measure intensities of reflected light from the wafer W at respective wavelengths, and output the intensities of the reflected light in relation to the wavelengths. The intensity data of the reflected light in relation to the wavelengths is the film-thickness signal which varies according to the film thickness of the wafer W.

During polishing of the wafer W, the film-thickness sensor 7 rotates together with the polishing table 2, and generates the film-thickness signals while sweeping across the surface of the wafer W. This film-thickness signal comprises an index value that directly or indirectly indicates the film thickness of the wafer W, and thus is a signal corresponding to the film thickness of the wafer W. More specifically, the film-thickness signal varies as the film thickness of the wafer W decreases. The controller 40 determines that the polishing endpoint has been reached when the film thickness of wafer W, indicated by the film-thickness signal sent from the film-thickness sensor 7, reaches a predetermined target thickness. Detailed polishing endpoint detecting method will be described later. When the polishing endpoint is reached, the controller 40 instructs the polishing head 1 and the polishing table 2 to stop the operations of these polishing head 1 and polishing table 2 (i.e., to terminate the polishing of wafer W).

FIG. 2 is a schematic view showing one path of a film-thickness sensor when moving across a surface of a wafer (substrate) W, and FIG. 3 is a schematic view showing a plurality of paths of the film-thickness sensor when moving across the surface of the wafer W. As shown in FIG. 2, during polishing of the wafer W, each time the polishing table 2 makes one rotation, the film-thickness sensor 7 measures the film thickness in the top layer of the wafer W at a plurality of measurement points MP on the wafer W while moving across the surface of the wafer W on the polishing pad 3.

During polishing of the wafer W, the polishing table 2 and the polishing head 1 rotate at different speeds. Under such conditions, as shown in FIG. 3, the film-thickness sensor 7 moves across the wafer W in different paths each time the polishing table 2 makes one rotation. When the polishing table 2 rotates several times, the film-thickness sensor 7 can scan almost the entire wafer W and measure the film thickness on almost the entire wafer W. In this embodiment, one film-thickness sensor 7 is disposed in the polishing table 2. However, a plurality of film-thickness sensors 7 may be disposed in the polishing table 2. In this case, a more detailed film thickness profile of the wafer W can be obtained, and/or the film thickness profile of the wafer W can be obtained more quickly.

The controller 40 instructs the film-thickness sensor 7 to acquire the film-thickness signals at the plurality of measurement points MP in the wafer W, creates the film-thickness profile from the plurality of film-thickness signals using the arithmetic device 120, and stores the created film-thickness profile in the memory 110. The controller 40 creates a new film-thickness profile from the plurality of newly acquired film thickness signals each time the film-thickness sensor 7 rotates with the polishing table 2 a predetermined number of times, and stores the newly created film thickness profile in the memory 110. In this manner, the controller 40 accumulates the film thickness profiles in the memory 110.

The controller 40 stores in advance a plurality of measurement zones that are set with respect to the film-thickness profile of the wafer W in order to determine the polishing endpoint of the wafer W. FIG. 4 is a schematic view showing a relationship between an example of the film-thickness profile of the wafer W and the plurality of measurement zones set for that film-thickness profile. The example shown in FIG. 4 has five measurement zones MR1, MR2, MR3, MR4, and MR5 which are set in a diameter direction from one outer circumference to the other in the film thickness profile of wafer W. The number of measurement zones is not limited to the example shown in FIG. 4, and can be set freely. The controller 40 can create the film-thickness profile as shown in FIG. 4 from the plurality of film-thickness signals sent from the film-thickness sensor 7.

In this embodiment, the controller 40 stores in advance a monitoring zone for determining the polishing endpoint of the wafer W. The monitoring zone is selected from the plurality of measurement zones. For example, the measurement zone MR2 is preselected as the monitoring zone MT, and the controller 40 detects the polishing endpoint based on the film thickness signals acquired by the film-thickness sensor 7 at the plurality of measurement points MP that exist in the monitoring zone MT(=measurement zone MR2).

FIG. 5 is a flowchart showing a polishing endpoint detecting method according to an embodiment. In this embodiment, the polishing endpoint is determined based on the film thickness of the monitoring zone MT. As shown in FIG. 5, the controller 40 instructs the polishing head 1, the polishing table 2, and the polishing-liquid supply nozzle 4 to start polishing of the wafer W (S101). Specifically, the controller 40 causes the polishing table 2, which supports the polishing pad 3, to be rotated, and the wafer W held by the polishing head 1 to be pressed against the polishing surface 3a of the polishing pad 3 to start polishing the wafer W. At this time, the polishing liquid is supplied onto the polishing surface 3a of the polishing pad 3 from the polishing-liquid supply nozzle 4.

Next, the controller 40 instructs the film-thickness sensor 7, which is mounted to the polishing table 2, to sequentially acquire signals, which correspond to the film thickness of the wafer W, at the plurality of measurement points MP as the film-thickness sensor 7 moves across the wafer W. Each time the polishing table 2 rotates a predetermined number of times, the controller 40 creates the film- thickness profile of the wafer W from these film thickness signals (S102). The predetermined number of rotations of the polishing table 2 set to create the film-thickness profile is stored in the controller 40 in advance, and may be 1 or greater than 1. When the predetermined number of rotations of the polishing table 2 is 1, the controller 40 creates the film-thickness profile of the wafer W each time the film thickness sensor 7 moves across the wafer W. The controller 40 stores the created film-thickness profile in the memory 110 (S103).

Next, the controller 40 divides the created film-thickness profile into the plurality of measurement zones MR1, MR2, MR3, MR4, and MR5 stored in advance in the memory 110, and selects the monitoring zone (MT) from the plurality of measurement zones MR1, MR2, MR3, MR4, and MR5 (S104). As described above, the monitoring zone MT is a zone that determines whether or not to terminate polishing of wafer W. The controller 40 stores an initial monitoring zone (e.g., measurement zone MR2) in advance, and immediately after polishing of wafer W has been started, the controller 40 selects the initial monitoring zone as the monitoring zone MT.

The controller 40 has monitored the film thicknesses in all measurement zones MR1, MR2, MR3, MR4, and MR5, including the monitoring zone MT, from the start to the end of polishing of the wafer W. Specifically, the controller 40 monitors the film thickness signals and/or the film thicknesses measured by the film-thickness sensor 7 at the plurality of measurement points MP that exist in each measurement zone MR1, MR2, MR3, MR4, and MR5. Accordingly, in order to detect an optimal polishing endpoint of the wafer W, the controller 40 determines whether or not the monitoring zone is selected as an optimal monitoring zone based on the film-thickness profile that is acquired each time the polishing table 2 rotates the predetermined number of times. Specifically, the controller 40 determines whether or not the monitoring-zone change requirement is satisfied based on the created film-thickness profile (S105).

The monitoring-zone change requirement is determined by condition priority in polishing of the wafer W, which is to be polished, and is stored in advance in the memory 110 of the controller 40. For example, if the priority condition is to prevent the wafer W from being insufficiently polished, it is preferable to change the monitoring zone MT to a measurement zone where the progress of polishing is slowest. In contrast, if the priority condition is to prevent the wafer W from being over-polished, it is preferable to change the monitoring zone MT to a measurement zone where the progress of polishing is the fastest.

A difference in the progress of polishing is made, for example, by comparing representative values of the film thickness measured at the plurality of measurement points MP existing in each measurement zone MR1, MR2, MR3, MR4, and MR5. The representative value of film thickness is, for example, the average value of film thickness measured at the plurality of measurement points MP existing in each measurement zone MR1, MR2, MR3, MR4, MR5. The representative value of film thickness may be the maximum value or the minimum value of film thickness measured at the plurality of measurement points MP existing in each measurement zone MR1, MR2, MR3, MR4, and MR5. Furthermore, the number of monitoring zones is freely selected, and two or more monitoring zones MT may be selected from the plurality of measurement zones. For example, the measurement zones MR2 and MR4 may be selected as the monitoring zones MT from the measurement zones MR1, MR2, MR3, MR4, and MR5.

FIG. 6 is a schematic view showing one example of the film-thickness profile that changes with polishing of the wafer W, and FIG. 7 is a schematic view showing another example of the film-thickness profile that changes with polishing of the wafer W. FIG. 6 shows an example in which amounts of remaining film in the measurement zones MR1 and MR5, which are located at the outermost peripheral area of the wafer W, increase more than amounts of remaining film in other measurement zones MR2, MR3, and MR4 as the polishing of the wafer W progresses. FIG. 7 shows an example in which an amount of residual film in the measurement zone MR3, which is located in a central area of the wafer W, increases more than amounts of residual film in other measurement zones MR1, MR2, MR4, and MR5 as polishing of the wafer W progresses. The amount of remaining film is defined as a difference between a target profile film thickness in each of the measurement zones MR1, MR2, MR3, MR4, and MR5 and the representative value in each of the measurement zones.

For example, it is assumed that the film-thickness profile changes as shown in FIG. 6, and the priority condition for polishing of the wafer W is to prevent the wafer W from being insufficiently polished. In this case, the monitoring zone MT is preferably set to the measurement zones MR1 and/or MR5 where the amount of remaining film is the largest. FIG. 6 shows an example in which the monitoring zone MT is changed according to this priority condition. Furthermore, it is assumed that the film-thickness profile changes as shown in FIG. 7, and that the priority condition for polishing of the wafer W is to prevent the wafer W from being insufficiently polished. In this case, the monitoring zone MT is preferably set to the measurement zone MR3 where the amount of remaining film is the largest. FIG. 7 shows an example in which the monitoring zone MT is changed according to this priority condition.

Furthermore, it is assumed that the film-thickness profile changes as shown in FIG. 6, and that the priority condition for polishing of the wafer W is to prevent the wafer W from being over-polished. In this case, the monitoring zone MT is preferably set to the measurement zone MR3 where the amount of remaining film is the smallest. Furthermore, it is assumed that the film-thickness profile changes as shown in FIG. 7, and that the priority condition for polishing of the wafer W is to prevent the wafer W from being over-polished. In this case, the monitoring zone MT is preferably set to the measurement zones MR1 and/or MR5 where the amount of remaining film is the smallest.

Therefore, the controller 40 stores the monitoring-zone change requirement in advance, and determines, from comparison of the accumulated film-thickness profiles, whether or not the monitoring-zone change requirement has been satisfied (S106). The monitoring-zone change requirement is set according to the priority condition for polishing of the wafer W. For example, when the priority condition for polishing of the wafer W is to prevent the wafer W from being insufficiently polished, the controller 40 compares the film-thickness profile with the target profile after the film-thickness profile is created, and changes the monitoring zone to the measurement zone where the amount of remaining film is the largest. When the priority condition for polishing of the wafer W is to prevent the wafer W from being over-polished, the controller 40 compares the created film-thickness profile with the target profile, and changes the monitoring zone to the measurement zone where the amount of remaining film is the smallest. The monitoring-zone change requirement in these cases is that the measurement zone with the smallest or largest amount of remaining film is different from the monitoring zone. When the monitoring-zone change requirement is satisfied, the controller 40 performs changing of the monitoring zone (S107).

In one embodiment, the controller 40 may calculate each difference DM1(=MR1−MR2), DM2(=MR1−MR3), DM3(=MR1−MR4), DM4(=MR1−MR5), DM5(=MR2−MR3), DM6(=MR2−MR4), DM7(=MR2−MR5), DM8(=MR3−MR4), DM9(=MR3−MR4), and DM10(=MR4−MR5) between the measurement zones MR1, MR2, MR3, MR4, and MR5, and compare these differences DM1-DM10 (absolute values) with a preset threshold value. The threshold value is stored in advance in the memory 110 of the controller 40.

When any of these differences DM1-DM10 exceeds the threshold value, the controller 40 determines that the wafer W is not uniformly polished over the surface in its entirety, and changes the monitoring zone to the measurement zone with the smallest or largest amount of remaining film. In this case, the monitoring-zone change requirement is that any of the differences DM1-DM10 exceeds the threshold value, and that the measurement zone with the smallest or the largest amount of remaining film is different from the monitoring zone.

In one embodiment, the monitoring-zone change requirement may be associated with a polishing rate, instead of the amount of remaining film. For example, it is assumed that, in the case in which the film-thickness profile changes as shown in FIG. 6, the priority condition for polishing of the wafer W is to prevent the wafer W from being insufficiently polished. In this case, the monitoring zone MT is preferably set to the measurement zone MR1 or MR5, where the progress of polishing is slowest (i.e., the polishing rate is small). Furthermore, it is assumed that, in the case in which the film-thickness profile changes as shown in FIG. 7, the priority condition for polishing of the wafer W is to prevent the wafer W from being over-polished. In this case, the monitoring zone MT is preferably set to the measurement zone MR3, where the progress of polishing is the fastest (i.e., the polishing rate is large).

In this embodiment also, the controller 40 stores the monitoring-zone change requirement in advance, and determines whether or not the monitoring-zone change requirement is satisfied by comparing the accumulated film-thickness profiles (S106). The monitoring-zone change requirement is set in accordance with the priority condition for polishing of the wafer W. For example, when the priority condition for polishing of the wafer W is to prevent the wafer W from being insufficiently polished, the controller 40 compares, after a film-thickness profile is created, this film-thickness profile with the film-thickness profile created immediately before this film-thickness profile (which is referred to as the “immediately preceding film thickness profile”), and changes the monitoring zone to the measurement zone with the lowest polishing rate. When the priority condition for polishing of the wafer W is to prevent the wafer W from being over-polished, the controller 40 compares the created film-thickness profile with the immediately preceding film-thickness profile, and changes the monitoring zone to the measurement zone with the highest polishing rate. The monitoring-zone change requirement in these cases is that the measurement zone with the lowest or highest polishing rate is different from the monitoring zone. When the monitoring-zone change requirement is satisfied, the controller 40 performs the change of the monitoring zone (S107).

In this embodiment also, the controller 40 may calculate each difference DM1, DM2, DM3, DM4, DM5, DM6, DM7, DM8, DM9, and DM10 between the measurement zones MR1, MR2, MR3, MR4, and MR5, and compare these differences DM1-DM10 (absolute values) with the preset threshold value. When any of these differences DM1-DM10 exceeds the threshold value, the controller 40 determines that the wafer W is not uniformly polished over the surface in its entirety, and changes the monitoring zone to the measurement zone with the lowest or highest polishing rate. The monitoring-zone change requirement in this case is that the difference DM1-DM10 exceeds the threshold value, and that the measurement zone with the lowest or highest polishing rate is different from the monitoring zone.

Next, the controller 40 determines whether or not the film thickness in the monitored zone MT has reached the polishing endpoint (S107). Specifically, the controller 40 determines that the polishing endpoint has been reached when the film thickness in the monitoring zone MT has reached the target film thickness. The representative value of the film thickness in the monitoring zone MT to be compared with the target film thickness is, for example, an average value of the film thickness measured at the plurality of measurement points MP included in the monitoring zone MT. The representative value of the film thickness of the monitoring zone MT compared to the target film thickness may be the maximum or minimum value of the film thickness measured at the plurality of measurement points MP included in the monitoring zone MT.

In one embodiment, the controller 40 may store in advance an allowable range that is set with respect to the target film thickness, and determine that the polishing endpoint has been reached when the film thickness in the monitored zone is within the allowable range. In this case, the controller 40 may determine that the polishing endpoint is reached when the representative value in the monitoring zone MT (e.g., any of the average, maximum, or minimum value of the film thickness measured at the plurality of measurement points MP included in the monitoring zone MT) is within the allowable range, or may determine that the polishing endpoint is reached when all the film thicknesses measured at the plurality of measurement points MP included in the monitoring zone MT are within the allowable range.

When the film thickness in the monitoring zone is determined to have reached the polishing endpoint, the controller 40 terminates polishing of the wafer W. If the film thickness in the monitoring zone has not reached the polishing endpoint, the controller 40 repeats the processes shown in S102-S107.

In a conventional substrate polishing process, the monitoring-zone was not changed during polishing of a substrate. As a result, there was a risk of insufficient polishing or over-polishing of the substrate. If the substrate is not sufficiently polished, there is a risk of short circuits due to lack of insulation between circuits. If the substrate is over-polished, problems may arise, such as an increase in resistance due to a decrease in a cross-sectional area of wiring, or the wiring itself may be completely removed and the circuits themselves may not be formed. In contrast, in this embodiment, the monitoring zone is changed based on the film-thickness profile acquired by the film thickness sensor 7 during polishing of the wafer W. This operation enables the optimal monitoring zone to be automatically selected based on the actual film-thickness profile and the priority conditions for polishing. As a result, the polishing endpoint of the wafer W can be accurately determined in accordance with the priority conditions for polishing.

FIG. 8 is a flowchart showing the polishing endpoint detecting method according to another embodiment. Configurations of this embodiment, which will not be particularly described, are the same as those of the embodiments described above, and redundant descriptions thereof will be omitted.

When the priority condition for polishing of the wafer W is an in-plane uniformity of the wafer W after polishing, the controller 40 determines that the polishing endpoint has been reached when all the film thicknesses of each measurement zone are within the allowable range that is set with respect to the target film thickness (target profile). In this case, the controller 40 often compares the representative values of film thickness in each measurement zone with the allowable range, and determines that the polishing endpoint has been reached when all of each representative value are within the allowable range. Examples of the representative value may include the average, maximum, or minimum value of the film thickness signals and/or the film thicknesses at the plurality of measurement points MP that exist in each measurement zone MR1-MR5. Therefore, the less the variation of the film thickness signals and/or film thicknesses at the plurality of measurement points MP existing in each measurement zone MR1-MR5, the better the in-plane uniformity of the wafer W after polishing. Accordingly, in this embodiment, a range of each measurement zone is changed such that the variation of the film thickness signals and/or the film thickness at the plurality of measurement points MP existing in each measurement zone MR1-MR5 is less than or equal to an allowable value.

The variation (or index value indicating the variation) of the film thickness signals and/or the film thicknesses can be obtained by any known arithmetic method. Examples of such variation (or index value indicating the variation) may include standard deviation, variance, and variation index.

In the embodiment shown in FIG. 8, as in the embodiment described with reference to FIG. 5, the controller 40 first starts polishing of the wafer W (S201), creates the film-thickness profile of the wafer W from the film thickness signals each time the polishing table 2 rotates the predetermined number of times (S202), and stores the created film-thickness profile in the memory 110 of the controller 40 (S203).

Next, the controller 40 sets the plurality of measurement zones MR1-MR5 with respect to the created film-thickness profile. For example, the memory 110 of the controller 40 stores in advance an initial measurement zones to be set with respect to the film-thickness profile that is first acquired after polishing of the wafer W is started. The controller 40 sets the initial measurement zones with respect to the first film-thickness profile acquired.

Next, in order to detect the optimal polishing endpoint of the wafer W, the controller 40 determines whether or not each of the measurement zones MR1-MR5 has become an optimal area based on the film-thickness profile acquired each time the polishing table 2 is rotated a predetermined number of times. Specifically, the controller 40 determines whether or not a measurement-zone change requirement has been satisfied based on the created film-thickness profile (S204).

The measurement-zone change requirement is determined such that a desired in-plane uniformity is obtained over the entire surface of the wafer W, and is stored in advance in the memory 110 of the controller 40. For example, the measurement-zone change requirement is whether or not the variation of the film thickness signals and/or the film thicknesses at the plurality of measurement points MP existing in each of the measurement zones MR1-MR5 is less than or equal to an allowable value. The controller 40 determines that the measurement-zone change requirement is satisfied when the variation of the film thickness signals and/or the film thicknesses exceeds the allowable value in any of the measurement zones MR1-MR5.

When the measurement-zone change requirement is satisfied, the controller 40 changes the range of each measurement zone such that the variations of the film thickness signals and/or the film thicknesses in all measurement zones MR1-MR5 are less than or equal to the allowable values (S205). In other words, the controller 40 changes a border of adjacent measurement zones. With this operation, the number of measurement points MP belonging to each measurement zone is also changed.

In one embodiment, when changing the areas of each of the measurement zones, an inflection point of the film-thickness profile between adjacent measurement zones may be obtained, and the border of said adjacent measurement zones may be shifted to this inflection point.

FIG. 9 is a schematic view showing a state in which the border between the adjacent measurement zones is changed to the inflection point of the film-thickness profile. FIG. 9 illustrates a portion of the film-thickness profile in an enlarged view. As shown in FIG. 9, the controller 40 creates the film-thickness profile that connects the film thicknesses at the plurality of measurement points MP with a smooth curve, and determines the inflection point where a slope (absolute value) of the tangent line of the curve becomes the maximum. Next, the border BL between adjacent measurement zones is moved to the inflection point, so that the areas of adjacent measurement zones are changed.

In one embodiment, when changing the areas of the measurement zones, a difference between the film thicknesses of adjacent measurement points may be obtained, and when two excess measurement points appear where these differences exceed a threshold value, the border between the adjacent measurement areas may be moved between these two excess measurement points. In this case, the measurement-zone change requirement is the appearance of the two excess measurement points.

FIG. 10 is a schematic view showing a state in which the border between adjacent measurement zones is changed between the two excess measurement points. FIG. 10 also illustrates a portion of the film-thickness profile in an enlarged view. As shown in FIG. 10, each time the film-thickness profile is created, the controller 40 calculates differences d1, d2, d3, d4, d5, . . . of the film thicknesses between adjacent measurement points MP, and compares each of these differences d1, d2, d3, d4, d5, . . . with a predetermined threshold value. The example shown in FIG. 10 assumes that d3 exceeds the threshold value.

In this case, the controller 40 determines the two adjacent measurement points MP, which are used in the calculation of the difference d3, as the two excess measurement points MPo1 and MPo2, and changes the border BL of the adjacent measurement zone between the two excess measurement points MPo1 and MPo2, thereby changing the areas of the measurement zones.

Next, the controller 40 determines whether or not the film thicknesses of all the measurement zones have reached the polishing endpoint (S206). Specifically, the controller 40 determines whether or not the film thicknesses of all the measurement zones are within the allowable range set with respect to the target film thickness. The film thickness of each measurement zone to be compared with the allowable range is, for example, the average of the film thickness signals and/or the film thicknesses at the plurality of measurement points MP existing in each measurement zone.

When the film thicknesses in all the measurement zones are determined to have reached the polishing endpoint, the controller 40 terminates polishing of the wafer W. If the film thicknesses in all the measurement zones have not reached the polishing endpoint, the controller 40 repeats the process shown in S202-S206.

In a conventional substrate polishing process, the areas of the monitoring-zones were not changed during polishing of a substrate. Therefore, as described above, there was a risk of insufficient polishing or over-polishing of the substrate. If the substrate is not sufficiently polished, there is a risk of short circuits due to lack of insulation between circuits. In contrast, in this embodiment, the areas of each monitoring-zone are changed based on the film-thickness profile acquired by the film thickness sensor 7 during polishing of the wafer W. This operation allows the optimal areas of the monitoring zones to be automatically selected based on the actual film-thickness profile and the priority conditions for polishing. As a result, the polishing endpoint of the wafer W can be accurately determined while improving in-plane uniformity that is the priority condition for polishing.

In one embodiment, the controller 40 may use a learned model constructed by performing a machine learning described below to determine or predict the monitoring zone MT to be changed, or to determine or predict the optimal ranges of the measurement zones MR1-MR5.

A machine learning is performed by a learning algorithm, which is an artificial intelligence algorithm, and the machine learning constructs a learned model that determines or predicts the appropriate monitoring zone MT from the plurality of measurement zones MR1-MR5, or determines or predicts the optimal ranges of the measurement zones MR1-MR5. Examples of the artificial intelligence algorithm include a support vector regression method, a deep learning method, a random forest method, and a decision tree method. In this embodiment, the deep learning method, which is an example of machine learning, is used.

FIG. 11 is a schematic view showing an example of machine learning. In the machine learning shown in FIG. 11, a prediction device 50 is used. This prediction device 50 is a device that is wired or wirelessly coupled to the film-thickness sensor 7 and the controller 40 to send and receive data, and outputs or predicts the appropriate monitoring zone MT, or outputs or predicts the optimal ranges of the measurement zones MR1-MR5. Although not shown, the controller 40 may be incorporated with the prediction device 50 shown in FIG. 11. The prediction device 50 is coupled to a learning device 51 that can send and receive data wired or wirelessly. The learning device 51 constructs a learned model that predicts and outputs the appropriate monitoring zone MT or the optimal ranges of the measurement zones MR1-MR5 when state variables, including at least the film-thickness profile, are inputted.

In the learning device 51, state variables are input as data to construct the learned model that predicts the appropriate monitoring zone MT or the optimal ranges of the measurement zones MR1-MR5. The state variables include at least the film-thickness profile (and the film thickness signals) acquired by the film-thickness sensor 7. In one embodiment, the state variables may further include a polishing recipe, including the priority conditions for polishing described above, the rotation rate of the polishing table 2, and the pressing force (polishing pressure) for pressing the wafer W onto the polishing pad 3 by the polishing head 1, a film type of a layer in the wafer W, and/or a film thickness of the top layer of the wafer W before polishing.

The state variables are combined with correct data, which is the film-thickness profile and the priority conditions for polishing and, if required, the appropriate monitoring zone MT pre-determined for various conditions, such as the polishing recipe, or the ranges of the optimal measurement zones MR1-MR5. A training data set composed of state variables and the correct data is input to the training device 51.

An example of the machine learning performed by the learning device 51 is described below. First, state variables, including at least a film-thickness profile, and correct data associated with the state variables are input to the learning device 51. The learning device 51 learns the appropriate monitoring zone MT or the optimal ranges of the measurement zones MR1-MR5 based on the training data set, which is the combination of the input state variables and the correct data. The machine learning performed in the learning device 51 is repeated until the constructed learned model can output the appropriate monitoring zone MT or the optimal ranges of the measurement zones MR1-MR5.

In this embodiment, the machine learning performed by the learning device 51 is a machine learning using neural networks, in particular, deep learning. Deep learning is a machine learning method based on a neural network with multiple hidden layers (also referred to as intermediate layers). In this specification, a machine learning using a neural network composed of an input layer, two or more hidden layers, and an output layer is defined as the deep learning.

FIG. 12 is a schematic view showing an example of structure of a neural network. The neural network shown in FIG. 12 has an input layer 350, a plurality of hidden layers 351, and an output layer 352. The neural network learns the appropriate monitoring zone MT or the optimal ranges of the measurement zones MR1-MR5 based on the training data set, which is composed of many combinations of input state variables and the correct data associated with the state variables. More specifically, the neural network learns a relationship between the state variables and the appropriate monitoring zone MT or the optimal ranges of the measurement zones MR1-MR5.

The learned model constructed in this manner is output from the learning device 51 to the prediction device 50. The prediction device 50 inputs the film-thickness profile, which is acquired by the film-thickness sensor 7, to the learned model, causes the appropriate monitoring zone MT or the optimal ranges of the measurement zones MR1-MR5 to be predicted, and outputs the appropriate monitoring zone MT or the optimal ranges of the measurement zones MR1-MR5 to the controller 40. The controller 40 changes the monitoring zone MT or the ranges of the measurement zones MR1-MR5 to the monitoring zone MT or the optimal ranges of the measurement zones MR1-MR5 input from the prediction device 50. More specifically, the learned model outputs the monitoring zone MT or the ranges of the measurement zones MR1-MR5 to be changed by the controller 40 based on the film-thickness profile acquired by the film-thickness sensor 7.

In one embodiment, the film-thickness signals and the film-thickness profile acquired by the film-thickness sensor 7 may be input to the learning device 51. The learning device 51 updates the learned model through machine learning based on the training data to which the newly input film-thickness profile is added. This operation enables accuracy of the appropriate monitoring zone MT or the optimal ranges of the measurement zones MR1-MR5 output from the learned model to be improved.

The controller 40, which is composed of at least one computer, runs in accordance with instructions included in a program electrically stored in the memory device 110 thereof. In other words, the controller 40 performs each of the operation steps in each embodiment described above in accordance with the instructions included in the program. The program for causing the controller 40 to perform these steps is stored in a computer-readable storage medium which is a non-transitory tangible medium, and is provided to the controller 40 via the storage medium. Alternatively, the program may be input to the controller 40 via a communication network, such as the Internet or a local area network.

The previous description of embodiments is provided to enable a person skilled in the art to make and use the present invention. Moreover, various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles and specific examples defined herein may be applied to other embodiments. Therefore, the present invention is not intended to be limited to the embodiments described herein but is to be accorded the widest scope as defined by limitation of the claims.

Claims

1. A polishing endpoint detecting method, comprising: polishing a substrate by rotating a polishing table which supports a polishing pad and pressing the substrate against a polishing surface of the polishing pad by use of a polishing head;sequentially acquiring signals, corresponding to the film thickness of the substrate, at a plurality of measurement points in the substrate when a film-thickness sensor mounted to the polishing table moves across the substrate, thereby creating a film-thickness profile of the substrate each time the polishing table is rotated a predetermined number of times;dividing the film-thickness profile into a plurality of measurement zones and selecting a monitoring zone from the plurality of measurement zones for determining a polishing endpoint of the substrate;determining whether or not the monitoring zone is changed to another measurement zone based on changes in the film-thickness profile obtained from start to end of polishing of the substrate; anddetermining a polishing endpoint of the substrate based on the signals in the monitoring zone.
2. The polishing endpoint detecting method according to claim 1, wherein selecting the monitoring zone is calculating differences in film thickness between each of the measurement zones and selecting the measurement zone with the smallest amount of remaining film as the monitoring zone when any of the differences exceeds a predetermined threshold value.
3. The polishing endpoint detecting method according to claim 1, wherein selecting the monitoring zone is calculating differences in film thickness between each of the measurement zones and selecting the measurement zone with the largest amount of remaining film as the monitoring zone when any of the differences exceeds a predetermined threshold value.
4. The polishing endpoint detecting method according to claim 1, further comprising: constructing a learned model that is constructed to output the monitoring zone to be changed when state variables, including at least the film-thickness profile, are input,wherein selecting the monitoring zone is performed based on an output when the created film-thickness profile is input to the learned model.
5. A polishing endpoint detecting method, comprising: polishing a substrate by rotating a polishing table which supports a polishing pad and pressing the substrate against a polishing surface of the polishing pad by use of a polishing head;sequentially acquiring signals, corresponding to the film thickness of the substrate, at a plurality of measurement points in the substrate when a film-thickness sensor mounted to the polishing table moves across the substrate, thereby creating a film-thickness profile of the substrate each time the polishing table is rotated a predetermined number of times;dividing the film-thickness profile into a plurality of measurement zones;determining whether or not ranges of each of the measurement zones are changed based on changes in the film-thickness profile obtained from start to end of polishing of the substrate; anddetermining a polishing endpoint of the substrate based on the signals in the plurality of the measurement zones.
6. The polishing endpoint detecting method according to claim 5, wherein changing the ranges of each of the measurement zones is obtaining an inflection point of the film-thickness profile between adjacent measurement zones, and shifting a border of the adjacent measurement zones to the inflection point.
7. The polishing endpoint detecting method according to claim 5, wherein changing the ranges of each of the measurement zones is calculating differences between measurement values of film thickness at adjacent measurement points, and shifting a border of adjacent measurement zones between two excess measurement points when the two excess measurement points appear where the difference exceeds a threshold value.
8. The polishing endpoint detecting method according to claim 5, wherein changing the ranges of each of the measurement zones is calculating variations of a plurality of measurement values of the film thickness for each of the measurement zones, and shifting a border between adjacent measurement zones such that the variations are less than or equal to an allowable value.
9. The polishing endpoint detecting method according to claim 5, further comprising constructing a learned model that is constructed so as to output the ranges of measurement zones to be changed when state variables, including at least the film-thickness profile, are inputted, wherein changing the ranges of each of the measurement zones is performed based on the output when the created film-thickness profiles are input to the learned model.
10. A program for causing a computer to execute: polishing a substrate by rotating a polishing table which supports a polishing pad and pressing the substrate against a polishing surface of the polishing pad by use of a polishing head;sequentially acquiring signals, corresponding to the film thickness of the substrate, at a plurality of measurement points in the substrate when a film-thickness sensor mounted to the polishing table moves across the substrate, thereby creating a film-thickness profile of the substrate each time the polishing table is rotated a predetermined number of times;dividing the film-thickness profile into a plurality of measurement zones and selecting a monitoring zone from the plurality of measurement zones for determining a polishing endpoint of the substrate;determining whether or not the monitoring zone is changed to another measurement zone based on changes in the film-thickness profile obtained from start to end of polishing of the substrate; anddetermining a polishing endpoint of the substrate based on the signals in the monitoring zone.
11. The program according to claim 10, wherein selecting the monitoring zone is calculating differences in film thickness between each of the measurement zones and selecting the measurement zone with the smallest amount of remaining film as the monitoring zone when any of the differences exceeds a predetermined threshold value.
12. The program according to claim 10, wherein selecting the monitoring zone is calculating differences in film thickness between each of the measurement zones and selecting the measurement zone with the largest amount of remaining film as the monitoring zone when any of the differences exceeds a predetermined threshold value.
13. The program according to claim 10, wherein selecting the monitoring zone is performed based on an output when the created film-thickness profile is input to a learned model, and the learned model is constructed so as to output the monitoring zone to be changed when state variables, including at least the film-thickness profile, are input.
14. A program for causing a computer to execute: polishing a substrate by rotating a polishing table which supports a polishing pad and pressing the substrate against a polishing surface of the polishing pad by use of a polishing head;sequentially acquiring signals, corresponding to the film thickness of the substrate, at a plurality of measurement points in the substrate when a film-thickness sensor mounted to the polishing table moves across the substrate, thereby creating a film-thickness profile of the substrate each time the polishing table is rotated a predetermined number of times;dividing the film-thickness profile into a plurality of measurement zones;determining whether or not ranges of each of the measurement zones are changed based on changes in the film-thickness profile obtained from start to end of polishing of the substrate; anddetermining a polishing endpoint of the substrate based on the signals in the plurality of the measurement zones.
15. The program according to claim 14, wherein changing the ranges of each of the measurement zones is obtaining an inflection point of the film-thickness profile between adjacent measurement zones, and shifting a border of the adjacent measurement zones to the inflection point.
16. The program according to claim 14, wherein changing the ranges of each of the measurement zones is calculating differences between measurement values of film thickness at adjacent measurement points, and shifting a border of adjacent measurement zones between two excess measurement points when the two excess measurement points appear where the difference exceeds a threshold value.
17. The program according to claim 14, wherein changing the ranges of each of the measurement zones is calculating variations of a plurality of measurement values of the film thickness for each of the measurement zones, and shifting a border between adjacent measurement zones such that the variations are less than or equal to an allowable value.
18. The program according to claim 14, wherein changing the ranges of each of the measurement zones is performed based on an output when the created film-thickness profiles are input to a learned model, and the learned model is constructed so as to output the ranges of measurement zones to be changed when state variables, including at least the film-thickness profile, are inputted.

Priority Claims (1)

Number	Date	Country	Kind
2023-051685	Mar 2023	JP	national

METHOD OF DETECTING POLISHING ENDPOINT, AND PROGRAM FOR DETECTING POLISHING ENDPOINT

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Priority Claims (1)