Substrate polishing device and film thickness calculating method

Abstract

To measure a thickness of a film to be polished with good accuracy while polishing a substrate.SOLUTION: A substrate polishing device is provided with: a polishing table provided with an eddy current sensor, which is configured to be able to rotate; a polishing head configured to be able to rotate while opposing to the polishing table, which enables a substrate to be mounted on a surface opposing to the polishing table; and a control part. The control part is configured to obtain waveform data on an output signal from the eddy current sensor during polishing of the substrate, detect a minimum point and a maximum point on the waveform data, correct the waveform data on the basis of the detected minimum point or the detected maximum point and calculate a film thickness of a surface of the substrate on the basis of the corrected waveform data.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a substrate polishing apparatus and a film thickness calculation method. [Background technology]

[0002] One type of semiconductor device manufacturing equipment is a CMP (Chemical Mechanical Polishing) apparatus. A typical CMP apparatus includes a polishing table with a polishing pad attached and a polishing head with a substrate attached. In a typical CMP apparatus, a polishing liquid is supplied to the polishing pad, and the substrate is polished by rotating at least one of the polishing table and the polishing head while the polishing pad is in contact with the substrate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-058955 Summary of the Invention [Problem to be solved by the invention]

[0004] An eddy current sensor can be used to measure the thickness of a film being polished during substrate polishing. The eddy current sensor is mounted on, for example, a polishing table. The eddy current sensor moves along a certain trajectory on the surface of the substrate as the polishing table rotates, and measures the film thickness at each point on the trajectory (see, for example, Patent Document 1). However, if there is a localized metal structure on the substrate in addition to the film (metal film) being polished, this influence makes it difficult to accurately measure the thickness of the film being polished, which is what should be measured. [Means for solving the problem]

[0005] According to one embodiment, there is provided a substrate polishing apparatus comprising: a rotatable polishing table provided with an eddy current sensor; a rotatable polishing head facing the polishing table, the polishing head being capable of mounting a substrate on a surface facing the polishing table; and a control unit, wherein the control unit is configured to acquire waveform data of an output signal from the eddy current sensor during polishing of the substrate, detect minimum or maximum points on the waveform data, correct the waveform data based on the detected minimum or maximum points, and calculate the film thickness on the surface of the substrate based on the corrected waveform data. [Brief explanation of the drawings]

[0006] [Figure 1] 1 is a front view of a substrate polishing apparatus according to an embodiment. [Figure 2] 1 is a schematic cross-sectional view showing the structure of an exemplary substrate to be polished by a substrate polishing apparatus. [Figure 3] 2 is a flowchart illustrating an algorithm of a method according to an embodiment of the present invention. [Figure 4] 10A and 10B are explanatory diagrams of a correction process for waveform data of an output signal of an eddy current sensor. [Figure 5] 4 is a flowchart illustrating an algorithm of a method according to another embodiment of the present invention. [Figure 6] FIG. 1 is a schematic diagram illustrating the concept of prominence. [Figure 7] 10A and 10B are explanatory diagrams of a correction process for waveform data of an output signal of an eddy current sensor. DETAILED DESCRIPTION OF THE INVENTION

[0007] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Therefore, the same or corresponding components are given the same reference numerals and redundant explanations are omitted.

[0008] Fig. 1 is a front view of a substrate polishing apparatus 100 according to one embodiment. The substrate polishing apparatus 100 shown in Fig. 1 is a CMP (Chemical Mechanical Polishing) apparatus. However, the substrate polishing apparatus 100 is not limited to a CMP apparatus. The substrate polishing apparatus 100 may be any apparatus that polishes a substrate by rotating a polishing table provided with an eddy current sensor.

[0009] The CMP apparatus 100 includes a polishing table 110, a polishing head 120, and a liquid supply mechanism 130. The CMP apparatus 100 further includes a control unit 140 for controlling each of the components. The control unit 140 may include, for example, a storage device 141, a processor 142, and an input / output device 143.

[0010] A polishing pad 111 is detachably attached to the upper surface of the polishing table 110. Here, the upper surface of the polishing table 110 refers to the surface of the polishing table 110 facing the polishing head 120. Therefore, the upper surface of the polishing table 110 is not limited to a surface positioned vertically upward. The polishing head 120 is provided to face the polishing table 110. A substrate 121 is detachably attached to the surface of the polishing head 120 facing the polishing table 110. The liquid supply mechanism 130 is configured to supply a polishing liquid such as slurry to the polishing pad 111. Note that the liquid supply mechanism 130 may be configured to supply a cleaning liquid, a chemical liquid, or the like in addition to the polishing liquid.

[0011] The CMP apparatus 100 can lower the polishing head 120 using a vertical movement mechanism (not shown) to bring the substrate 121 into contact with the polishing pad 111. However, the vertical movement mechanism may also be capable of moving the polishing table 110 up and down. The polishing table 110 and the polishing head 120 are rotated by a motor (not shown) or the like. The CMP apparatus 100 polishes the substrate 121 by rotating both the polishing table 110 and the polishing head 120 while the substrate 121 and the polishing pad 111 are in contact with each other.

[0012] The CMP apparatus 100 may further include an air bag 122 divided into a plurality of concentric compartments. The air bag 122 may be provided in the polishing head 120. Additionally or alternatively, the air bag 122 may be provided in the polishing table 110. The air bag 122 is a member for adjusting the polishing pressure of the substrate 121 for each region of the substrate 121. The air bag 122 is configured so that its volume changes depending on the pressure of air introduced therein. A fluid other than air, such as nitrogen gas or pure water, may be introduced into the air bag 122.

[0013] An eddy current sensor 150 is provided inside the polishing table 110. The eddy current sensor 150 is installed at a position such that the eddy current sensor 150 passes through the center of the substrate 121 when the polishing table 110 rotates during polishing. The eddy current sensor 150 is configured to induce an eddy current in the conductive layer on the surface of the substrate 121. The eddy current sensor 150 is further configured to output a signal corresponding to the thickness of the conductive layer on the surface of the substrate 121 in response to a change in impedance caused by a magnetic field generated by the eddy current. The output signal from the eddy current sensor 150 can be used to determine the film thickness of the film to be polished on the surface of the substrate 121.

[0014] Here, what affects the output signal of the eddy current sensor 150 is not limited to the film to be polished that is exposed on the top surface of the substrate 121 (a film formed over the entire top surface of the substrate 121). Fig. 2 is a cross-sectional schematic diagram showing the structure of an exemplary substrate 121 to be polished by the substrate polishing apparatus 100. As shown in Fig. 2, a dielectric film (for example, a film made of SiO2 or the like) 202 is formed over the entire top surface of this exemplary substrate 121, Furthermore, a metal film (e.g., a film made of Cu or the like) 204 is formed on the dielectric film 202 to cover it. The metal film 204 is the film to be polished and located on the outermost surface of the substrate 121. The substrate 121 may also have one or more through electrodes 206 for electrical connection between one surface and the other. Furthermore, metal wiring 208 may be embedded in the dielectric film 202 on the substrate 121. When the eddy current sensor 150 passes over or near such through electrodes 206 or metal wiring 208, eddy currents are also induced in these metal structures. The output signal of the eddy current sensor 150 is affected by this, and the signal value changes from the output signal of the eddy current sensor 150 when the eddy current sensor 150 passes through an area on the substrate 121 where the through electrodes 206 or metal wiring 208 are not present. In other words, the through electrodes 206 and metal wiring 208, which are localized metal structures formed on the substrate 121, can cause noise to be generated in the output signal of the eddy current sensor 150. The metal structure is not limited to the through electrode 206 and the metal wiring 208 embedded in the dielectric film 202 as described above, but may also include, for example, wiring and vias exposed on the top surface of the substrate 121.

[0015] 3 is a flowchart showing an algorithm of a film thickness calculation method according to an embodiment of the present invention, which can remove or reduce noise that occurs in the output signal of the eddy current sensor 150 due to local metal structures on the substrate 121. The processing of this flowchart may be performed by a processor (for example, the processor 142 of the control unit 140).

[0016] First, in step 302, an output signal of the eddy current sensor 150 for the substrate 121 is acquired. Specifically, an output signal is acquired from the eddy current sensor 150 while both the polishing head 120, to which the substrate 121 to be polished is attached, and the polishing table 110 are rotated at predetermined rotational speeds. The eddy current sensor 150 moves relative to the substrate 121 (i.e., as viewed from the substrate 121), describing an arc-shaped trajectory that corresponds to the ratio between the rotational speed of the polishing table 110 and the rotational speed of the polishing head 120. With each rotation of the polishing table 110, the eddy current sensor 150 crosses the surface of the substrate 121 along an arc-shaped trajectory with a predetermined curvature determined by the rotational speeds of the polishing table 110 and the polishing head 120. With each rotation of the polishing table 110, the eddy current sensor 150 passes through an trajectory that has the same curvature as the previous rotation but corresponds to a different arc. Therefore, signal values ​​at each point on these multiple arc-shaped trajectories are continuously obtained from the eddy current sensor 150. Hereinafter, a series of signal values ​​obtained from the eddy current sensor 150 when the eddy current sensor 150 passes through a single track on the substrate 121 will be referred to as the "profile" or "waveform data" of the output signal of the eddy current sensor 150.

[0017] Next, in step 304, a portion of the profile (waveform data) of the output signal of eddy current sensor 150 obtained in step 302 that corresponds to the outer edge of substrate 121 (for example, a strip-shaped region extending inward from the edge of substrate 121 by about several millimeters) is masked. This is because it is expected that the measurement accuracy of eddy current sensor 150 will not be very good at the outer edge of substrate 121, and therefore it is preferable to exclude the signal value of eddy current sensor 150 obtained from this portion from the subsequent calculations.

[0018] Next, in step 306, the waveform data after the processing in step 304 is normalized. Note that the processing in step 306 may be omitted.

[0019] Next, in step 308, a minimum point is searched for in the waveform data processed in step 306. Any suitable known method can be applied as the minimum point search algorithm, and a detailed description thereof will be omitted here.

[0020] Next, in step 310, correction is made to the waveform data based on the minimum points found in step 308. Specifically, multiple minimum points can be found in the waveform data in step 308, and in step 310, the multiple minimum points found are corrected. The waveform data is corrected by interpolating the points with a smooth curve or line.

[0021] FIG. 4 shows examples of waveform data before and after correction to illustrate the correction process in step 310. The horizontal axis of the graph in FIG. 4 indicates the position on the trajectory of eddy current sensor 150 (i.e., the distance from the center of substrate 121 to the center of eddy current sensor 150), and the vertical axis indicates the signal value of eddy current sensor 150. In the example of FIG. 4, waveform data 602 before correction has multiple minimum points A to N. Corrected waveform data 604 is created by connecting these multiple minimum points A to N with smooth curves or straight lines (i.e., by interpolation). Known techniques can be used to connect multiple points on a graph with smooth curves, and a detailed description thereof will be omitted here.

[0022] It is highly likely that the numerous peaks contained in the waveform data are noise from metal structures (through electrodes 206 and metal wiring 208) that exist locally on the surface or inside of the substrate 121. Therefore, by correcting the waveform data based on the minimum points of the waveform data in steps 308 and 310, it is possible to remove or reduce noise that occurs in the output signal of the eddy current sensor 150 due to local metal structures contained in the substrate 121.

[0023] Next, in step 312, in order to return the value normalized in step 306 to the original scale, the waveform data corrected in step 310 is multiplied by the reciprocal of the ratio by which the signal value of the eddy current sensor 150 was multiplied during normalization. Note that the processing of step 312 may be omitted if the above-mentioned step 306 is omitted.

[0024] Next, in step 314, a moving average in the direction along the trajectory of the eddy current sensor 150 (that is, a moving average in the horizontal direction in the graph of FIG. 4) is calculated for the waveform data processed in step 312.

[0025] Next, in step 316, the signal values ​​corresponding to the outer edge of the substrate 121 that were masked in step 304 are recombined with the processed waveform data of step 314.

[0026] Next, in step 318, a moving average is calculated for the waveform data after the processing of step 316 for a plurality of adjacent orbits of the eddy current sensor 150. The moving average in step 314 corresponds to taking a moving average in the radial direction of the substrate 121, and the moving average in step 318 corresponds to taking a moving average in the circumferential direction of the substrate 121. These moving average processes make it possible to remove fine noise that exists in the waveform data of the output signal of the eddy current sensor 150.

[0027] As a result of the above, highly accurate data on the film thickness distribution in the radial direction of the substrate can be obtained, which is not affected by the through electrodes 206 or metal wiring 208 of the substrate 121. The control unit 140 can accurately determine the polishing end point from the film thickness distribution data obtained during polishing of the substrate 121. Alternatively, the control unit 140 may increase or decrease the internal pressure of the airbag 122 based on the film thickness distribution data obtained during polishing of the substrate 121, thereby increasing the polishing pressure in regions where the film thickness is thick (i.e., regions where the polishing progress is low) and decreasing the polishing pressure in regions where the film thickness is thin (i.e., regions where the polishing progress is high). This control makes it possible to make the film thickness of the substrate 121 uniform.

[0028] 5 is a flowchart showing an algorithm of a film thickness calculation method according to another embodiment of the present invention, which is capable of removing or reducing noise that occurs in the output signal of the eddy current sensor 150 due to local metal structures on the substrate 121. The processing of this flowchart may be performed by a processor (e.g., processor 142 of control unit 140). Steps 302 to 306 and steps 312 to 318 of the algorithm according to this embodiment are the same as those in the embodiment of FIG. 3 described above, and therefore repeated explanations will be omitted.

[0029] In step 309 after step 306, a local maximum point is searched for in the waveform data processed in step 306. Any suitable known method can be applied as the local maximum point search algorithm, and a detailed description thereof will be omitted here.

[0030] Next, in step 311, the waveform data is corrected based on the local maxima found in step 309. Specifically, multiple local maxima can be found in the waveform data in step 309, and prominence is calculated for each of the multiple local maxima found in step 311. Then, for local maxima whose prominence value is greater than a predetermined threshold, the waveform data is corrected by reducing the value of the local maxima and their neighboring points on the waveform data.

[0031] Here, "prominence" is known as an index that indicates how "prominent (i.e., prominent)" a particular peak is among multiple peaks (maximum points). Figure 6 is a schematic diagram that simply explains the concept of prominence. In Figure 6, the prominence of each of peaks A, B, and C is indicated by a height P A , P B , P C For a more detailed explanation of prominence, see, for example, information sources such as https: / / jp.mathworks.com / help / signal / ug / prominence.html and Japanese Patent Application Laid-Open No. 2023-101867.

[0032] FIG. 7 shows a specific example of the correction process in step 311. The horizontal axis of the graph in FIG. 7 represents the position on the trajectory of the eddy current sensor 150 (i.e., the distance from the center of the substrate 121 to the center of the eddy current sensor 150), and the vertical axis represents the signal value of the eddy current sensor 150 (the value normalized in step 306). In the example of FIG. 7, the waveform data 902 before correction includes multiple local maxima, some of which, A to H, have prominence greater than a predetermined threshold. In the corrected waveform data 904, the signal values ​​of these local maxima (peaks) A to H and their neighboring points in the waveform data 902 before correction have been changed to predetermined values ​​that are smaller than the peak values ​​of the respective peaks. The predetermined values ​​may be, for example, values ​​obtained by multiplying the peak values ​​of the respective peaks by a predetermined attenuation rate (e.g., 30%). Note that local maxima other than A to H, whose prominence values ​​are greater than the predetermined threshold, are not subject to correction and remain intact in the corrected waveform data 904.

[0033] 3, the numerous peaks contained in the waveform data are likely to be noise from metal structures (through electrodes 206 and metal wiring 208) that are locally present on the surface or inside of the substrate 121. Therefore, by correcting the waveform data based on the local maxima of the waveform data in steps 309 and 311, it is possible to remove or reduce noise that occurs in the output signal of the eddy current sensor 150 due to local metal structures contained in the substrate 121.

[0034] Although the embodiments of the present invention have been described above based on several examples, the above-described embodiments of the invention are intended to facilitate understanding of the present invention and are not intended to limit the present invention. The present invention may be modified or improved without departing from the spirit thereof, and the present invention naturally includes equivalents thereof. Furthermore, any combination or omission of the components described in the claims and specification is possible within the scope of solving at least part of the above-described problems or achieving at least part of the effects. [Explanation of symbols]

[0035] 100 Substrate polishing equipment 110 Polishing Table 111 Polishing Pad 120 Polishing Head 121 PCB 122 Airbag 130 Liquid supply mechanism 140 Control Unit 141 Storage Devices 142 processors 143 Input / Output Devices 150 Eddy current sensor 202 Dielectric film 204 Metal Film 206 Through electrode 208 Metal wiring

Claims

1. a polishing table provided with an eddy current sensor and configured to be rotatable; a rotatable polishing head facing the polishing table, the polishing head having a surface facing the polishing table to which a substrate can be attached; A control unit; A substrate polishing apparatus comprising: The control unit acquiring waveform data of the output signal of the eddy current sensor during polishing of the substrate; Detecting a minimum or maximum point on the waveform data; correcting the waveform data based on the detected minimum or maximum points; calculating a film thickness on the surface of the substrate based on the corrected waveform data; The substrate polishing apparatus is configured as follows.

2. The control unit Detecting a plurality of minimum points on the waveform data; correcting the waveform data by interpolating the detected minimum points on the waveform data with a smooth curve or a straight line; 2. The substrate polishing apparatus according to claim 1, wherein the substrate polishing apparatus is configured as follows:

3. The control unit Detecting a plurality of maximum points on the waveform data; calculating a prominence for each of the detected local maxima; determining whether each calculated prominence is greater than a predetermined threshold; correcting the waveform data by reducing the values ​​of local maxima and their neighboring points on the waveform data having prominence determined to be greater than the predetermined threshold value; 2. The substrate polishing apparatus according to claim 1, wherein the substrate polishing apparatus is configured as follows:

4. A substrate polishing apparatus as described in any one of claims 1 to 3, wherein the waveform data is data consisting of a series of output signals obtained from the eddy current sensor when the eddy current sensor passes through one or more orbits on the polished surface of the substrate as the polishing table and the polishing head rotate.

5. 4. The substrate polishing apparatus according to claim 1, wherein the substrate has one or more metal structures locally present on the surface or inside thereof.

6. 6. The substrate polishing apparatus according to claim 5, wherein the metal structure is a through electrode or a metal wiring formed on the substrate.

7. an air bag capable of adjusting the polishing pressure on the substrate; The control unit is further configured to control an internal pressure of the airbag based on the calculated film thickness of the substrate.

4. The substrate polishing apparatus according to claim 1.

8. a polishing table provided with an eddy current sensor and configured to be rotatable; a rotatable polishing head facing the polishing table, the polishing head having a surface facing the polishing table to which a substrate can be attached; A method for calculating a film thickness in a substrate polishing apparatus comprising: acquiring waveform data of an output signal of the eddy current sensor while polishing the substrate; detecting a minimum or maximum point on the waveform data; correcting the waveform data based on the detected minimum or maximum points; calculating a film thickness on the surface of the substrate based on the corrected waveform data; A method comprising:

9. 9. The method of claim 8, wherein the step of correcting the waveform data includes the step of interpolating the detected minimum points on the waveform data with a smooth curve or a straight line.

10. The step of correcting the waveform data includes: calculating a prominence for each of the detected local maxima; determining whether each calculated prominence is greater than a predetermined threshold; a step of reducing the values ​​of the local maximum points and their neighboring points on the waveform data having prominences determined to be greater than the predetermined threshold; The method of claim 8, comprising:

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