Grinding apparatus and grinding endpoint detection method

Abstract

[Problem] The present invention enables accurate detection of the grinding endpoint even when the change in grinding friction is small. [Solution] The grinding apparatus of the present invention includes: a grinding table for holding a grinding pad; a holding part for holding a grinding object opposite to the grinding pad; and an endpoint detection part for detecting and displaying the grinding endpoint based on a signal indicating the state of the grinding pad grinding the grinding object; the endpoint detection part is configured to remove noise from the signal, and to power the noise-removed signal by an exponent greater than 1, and detect the grinding endpoint based on the power-multiplied signal.

Description

[Technical Field]

[0001] This invention relates to a grinding device and a method for detecting the grinding endpoint of the grinding device. [Previous Technology]

[0002] One type of semiconductor device manufacturing apparatus is a CMP (Chemical Mechanical Polishing) apparatus. A representative CMP apparatus includes: a polishing table on which polishing pads are mounted; and a polishing head on which a substrate is mounted as the object of polishing. In a representative CMP apparatus, polishing slurry is supplied to the polishing pads, and the substrate is polished by rotating at least one of the polishing table and the polishing head while the polishing pads are in contact with the substrate.

[0003] In the grinding process of grinding apparatuses such as CMP devices, it is important to accurately detect the grinding endpoint where the film to be removed by grinding has been removed. As a method for detecting the grinding endpoint, a conventional method involves detecting the change in grinding friction when the surface material of the object being ground is transferred to a different material through grinding (see, for example, Patent Document 1). [Prior Art Documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-098475 [Summary of the Invention]

[0005] [The problem that the invention is intended to solve]

[0006] When the surface material of the object being ground is transferred to a different material through grinding, a small change in the grinding friction force may lead to incorrect detection of the grinding endpoint due to noise. Therefore, it is required to accurately detect the grinding endpoint even when the change in grinding friction force is small. [Solution]

[0007] [Form 1] Form 1 provides a polishing apparatus comprising: a polishing table for holding a polishing pad; a holding part for holding a polishing object opposite to the polishing pad; and an endpoint detection part for detecting an endpoint indicating the end of polishing based on a signal indicating the state of the polishing pad polishing the polishing object; the endpoint detection part is configured to remove noise from the signal, multiply the noise-removed signal by an exponent greater than 1, and detect the polishing endpoint based on the exponentiated signal.

[0008] [Form 2] Form 2 provides a grinding apparatus, such as the grinding apparatus of Form 1, wherein the aforementioned endpoint detection unit is configured to perform a moving average on the aforementioned signal in order to remove noise from the aforementioned signal, and to differentiate the signal obtained by the aforementioned moving average, and then further move average the signal obtained by the aforementioned differentiation.

[0009] [Form 3] Form 3 provides a grinding apparatus, such as the grinding apparatus of Form 1 or 2, wherein the aforementioned endpoint detection unit is configured to, in the aforementioned power calculation of the noise-removed signal, power the absolute value of the aforementioned noise-removed signal by an exponent greater than 1.

[0010] [Form 4] Form 4 provides a grinding apparatus, such as any one of Forms 1 to 3, wherein a motor is provided for rotating and driving the aforementioned grinding table, and the aforementioned signal is based on the signal of the driving current of the aforementioned motor.

[0011] [Form 5] Form 5 provides a grinding apparatus, such as any one of Forms 1 to 3, wherein a motor is provided for rotating the object to be ground, and the aforementioned signal is based on the signal of the driving current of the aforementioned motor.

[0012] [Form 6] Form 6 provides a polishing apparatus, such as any one of Forms 1 to 3, wherein an acoustic or ultrasonic detector is provided, which is disposed near the aforementioned polishing table or the aforementioned object to be polished, and the aforementioned signal is a signal detected by the aforementioned acoustic or ultrasonic detector.

[0013] [Form 7] Form 7 provides a method for detecting and displaying the end point of grinding in a grinding apparatus, the grinding apparatus comprising: a grinding table for holding a grinding pad; and a holding part for holding a grinding object relative to the grinding pad; the method comprising: a step of acquiring a signal indicating the state of the grinding pad grinding the grinding object; a step of removing noise from the signal; a step of exponentiating the signal after noise removal by an exponent greater than 1; and a step of detecting the end point of grinding based on the exponentiated signal.

Implementation Method

[0015] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings described below, the same or equivalent constituent elements are marked with the same symbols, and repeated descriptions are omitted.

[0016] Figures 1 and 2 are schematic diagrams showing the overall structure of a polishing apparatus 10 according to an embodiment of the present invention. As shown, the polishing apparatus 10 includes: a polishing table 30 for holding a polishing pad 31; a top ring 50 (holding portion) for holding the object to be polished (e.g., a substrate 100 such as a semiconductor wafer shown in Figure 2) opposite to the polishing pad 31 and pressing it against the polishing surface of the polishing pad 31; a table drive motor 32 for rotating the polishing table 30; a top ring drive motor 52 for rotating the top ring 50; a power supply circuit 34 for supplying drive power 33 to the table drive motor 32; and a power supply circuit 54 for supplying drive power 53 to the top ring drive motor 52. In addition, the table drive motor 32 and the power supply circuits 34 and 54 are omitted in Figure 2.

[0017] The polishing table 30 is connected to a table drive motor 32 disposed below it via a table shaft 42. Driven by the rotation of the table drive motor 32, the polishing table 30 can rotate around the axis of the table shaft 42. A polishing pad 31 is attached to the surface of the polishing table 30. The surface 311 of the polishing pad 31 forms the polishing surface of the polishing substrate 100. An polishing slurry supply nozzle (not shown) is provided above the polishing table 30, and polishing slurry is supplied from the polishing slurry supply nozzle to the polishing pad 31 on the polishing table 30.

[0018] The top ring 50 is supported on the support arm 64 via the top ring shaft 62. The top ring shaft 62 can move the support arm 64 up and down via an up-and-down moving mechanism (not shown). By moving the top ring shaft 62 up and down, the top ring 50 can be positioned by raising and lowering the support arm 64. The top ring 50 is configured to hold a substrate 100 such as a semiconductor wafer underneath it. Specifically, as shown in FIG2, the top ring 50 includes: a retaining ring 51A that holds the outer periphery of the substrate 100 and prevents the substrate 100 from jumping out of the top ring 50; and a top ring body 51B that presses the substrate 100 against the polishing surface 311.

[0019] A top ring drive motor 52 is fixed on the support arm 64 supporting the top ring 50. Furthermore, as shown in FIG2, the top ring shaft 62 is connected to the rotating cylinder 65, and a timing pulley 66 located on the outer periphery of the rotating cylinder 65 is connected to a timing pulley 68 located on the top ring drive motor 52 via a timing belt 67. Thus, when the top ring drive motor 52 rotates, the rotating cylinder 65 and the top ring shaft 62 rotate as a unit via the timing pulley 68, the timing belt 67, and the timing pulley 66, and the top ring 50 rotates about the axis of the top ring shaft 62.

[0020] The support arm 64 is connected to the support arm drive motor 72 fixed to the support arm shaft 74. Driven by the support arm drive motor 72, the support arm 64 and the top ring 50 supported by the support arm 64 can rotate around the axis of the support arm shaft 74.

[0021] When the polishing apparatus 10 operates, firstly, the top ring 50 receives and holds the substrate 100 transported by a conveying mechanism (transfer device, not shown) at a designated receiving position. The top ring 50, having received the substrate 100 at the receiving position, moves from the receiving position to above the polishing table 30 by the rotation of the support arm 64. Next, the top ring shaft 62 and the top ring 50 descend, pressing the substrate 100 against the polishing surface 311 of the polishing pad 31. Then, the polishing table 30 and the top ring 50 rotate respectively by the table drive motor 32 and the top ring drive motor 52. Simultaneously, polishing slurry is supplied to the polishing pad 31 from a polishing slurry supply nozzle located above the polishing table 30. In this way, the substrate 100 slides into contact with the polishing surface 311 of the polishing pad 31, polishing the surface of the substrate 100.

[0022] In addition, during the polishing of the substrate 100, the support arm 64 can be periodically rotated left and right by the support arm drive motor 72, so that the top ring 50 can be polished while shaking the polishing pad 31 (that is, moving back and forth within a specified range on the polishing pad 31).

[0023] The grinding apparatus 10 of this embodiment further includes: a current detection unit 36 ​​configured to detect the drive current 33 supplied from the power supply circuit 34 to the stage drive motor 32; a current detection unit 56 configured to detect the drive current 53 supplied from the power supply circuit 54 to the top ring drive motor 52; and an end point detection unit 20 configured to detect and display the end point of grinding based on the drive currents 33, 53 or other signals indicating the grinding status. Either the current detection units 36 and 56 may be omitted.

[0024] Here, the substrate 100 (e.g., a semiconductor wafer) of the object to be polished has a multilayer structure composed of multiple different materials such as semiconductors, conductors, and insulators, and the coefficients of friction between the different material layers are different. Therefore, by polishing, the polishing friction changes when polishing the object to be polished, as the polishing friction is transferred from one layer of the multilayer structure to another different material layer. The polishing friction is presented as the driving load of each motor 32, 52 of the rotary drive polishing table 30 or top ring 50. Therefore, the currents 33, 53 flowing into each motor 32, 52 vary according to the polishing friction, that is, according to the material of the surface being polished, and can be used to detect the polishing endpoint. The detection of the polishing endpoint can be performed based on only one of the driving currents 33, 53, or both.

[0025] The endpoint detection unit 20 can be configured as a computer with a processor and memory, for example. The memory stores a program (software) containing commands that can be executed by one or more computers. The processor reads the program from the memory and executes it to perform the process of detecting the grinding endpoint. For example, the endpoint detection unit 20 can operate to obtain electrical signals or data (35, 55) corresponding to the drive current (33, 53) from the current detection unit (36, 56), process (data processing) the electrical signals or data (35, 55), identify the change in grinding friction, and detect the grinding endpoint based on the identification result.

[0026] As described above, the drive currents 33 and 53 of each motor represent the grinding state (friction force) of the object being ground, but signals other than drive currents 33 and 53 can also be used to detect the grinding endpoint. In this embodiment, the grinding apparatus 10 may have a detector 80 that detects a physical quantity reflecting the grinding state, and the endpoint detection unit 20 may also detect the grinding endpoint based on the output signal 85 of the detector 80. For example, the detector 80 may be an acoustic detector or an ultrasonic detector located near the grinding table 30 or the top ring 50 to detect the grinding sound. As described above, the grinding friction force changes as the material of the surface being ground changes during grinding, and the grinding sound also changes. Therefore, the grinding endpoint can still be detected even using the output signal from the acoustic detector or the ultrasonic detector. Other examples include the detector 80 being a force detector that directly detects the grinding friction force between the grinding table 30 and the top ring 50 as the rotational torque of the grinding table 30 or the top ring 50, or an eddy current detector as a vibration detection detector. In addition, Figure 2 depicts the detector 80 embedded in the grinding table 30, but the placement of the detector 80 is not limited to this. The detector 80 can be placed in an appropriate position depending on the type of detector 80.

[0027] Figure 3 is a flowchart showing a series of processes performed by the endpoint detection unit 20. First, the endpoint detection unit 20 acquires a signal (hereinafter referred to as the grinding signal) S1 (step 302) indicating the grinding state of the object to be ground. For example, the grinding signal S1 may be one or more of the following: i) signal 35 that can be acquired from the current detection unit 36, ii) signal 55 that can be acquired from the current detection unit 56, and iii) signal 85 that can be acquired from the detector 80. As mentioned above, the signal 35 from the current detection unit 36 ​​indicates the drive current 33 of the stage drive motor 32, and the signal 55 from the current detection unit 56 indicates the drive current 53 of the top ring drive motor 52. These signals 35 and 55 reflect the drive load of each motor 32 and 52, in other words, the frictional force of grinding the object to be ground. In addition, the signal 85 from the detector 80 is, for example, a signal indicating the grinding sound, which also reflects the grinding frictional force.

[0028] Figure 4 shows an exemplary grinding signal S1 (i.e., signal 55) obtained from the current detection unit 56. The horizontal axis of Figure 4 shows time, and the vertical axis shows signal intensity. This signal represents the drive current 53 of the top ring drive motor 52. In this example, grinding is performed while the top ring 50 is rocking against the grinding pad 31. The signal variation in the short time period in the graph originates from the rocking of the top ring 50. That is, in this example, the grinding signal S1 includes not only noise but also short-time period variations caused by the rocking of the top ring 50.

[0029] Next, the endpoint detection unit 20 removes noise from the polishing signal S1. The noise removal process may also include a plurality of processing steps. For example, the endpoint detection unit 20 may be operated to sequentially perform the step of generating signal S2 by moving average of polishing signal S1 (step 304); the step of generating signal S3 by differentiating signal S2 (step 306); and the step of further generating signal S4 by moving average of signal S3 (step 308).

[0030] Figure 5 shows an exemplary signal S2 (i.e., the signal after step 304) obtained by the endpoint detection unit 20 through moving average of the grinding signal S1 in Figure 4. In Figure 5, the periodic fluctuations of the signal caused by shaking are removed by moving average processing, and noise mixed into the signal is removed to some extent. In addition, the amplitude of the moving average period (i.e., the number of data points to be averaged) can be appropriately set considering the shaking period and assumed noise characteristics. Furthermore, in the moving average signal S2 in Figure 5, it can be seen that after the time region T1 where the signal value is relatively small, there is a time region T2 where the signal value is relatively large. As mentioned above, this is due to the change of grinding friction on the grinding object. In other words, between the former time region T1 and the latter time region T2, the grinding surface of the grinding object is transferred from one material to another. The moment of this transfer corresponds to the grinding endpoint.

[0031] Figure 6 shows an exemplary signal S4 (i.e., the signal after step 308) obtained by differentiating the signal S2 in Figure 5 by the endpoint detection unit 20 and then performing a moving average. In Figure 6, a signal with a steep peak is obtained by differentiation. As explained above, this signal peak corresponds to the grinding endpoint. Furthermore, in Figure 6, the moving average process after differentiation removes some noise from the signal, but noise remains in the foothills beyond the steep peak. The magnitude of this residual noise makes it difficult to accurately distinguish the peak portion of the signal from the noise. Therefore, there is a need to more effectively reduce noise and thus detect the grinding endpoint with higher accuracy.

[0032] In addition, the noise removal process is not limited to the steps 304 to 308. The endpoint detection unit 20 may also use other methods to remove noise from the polishing signal S1.

[0033] Returning to Figure 3, next, the endpoint detection unit 20 exponentiates the noise-removed signal (e.g., signal S4) as described above with an exponent greater than 1 (step 310). The exponent can be, for example, 2 or 3 (i.e., square or cube). Figure 7 shows an exemplary signal S5 obtained by cubed the noise-removed signal S4 of Figure 6. In Figure 7, the signal value increases further due to exponentiation (cube) at the peak and its vicinity, while the signal value decreases further due to exponentiation (cube) at the foot of the mountain, i.e., the part mainly consisting of noise. In other words, the increase in signal value due to exponentiation at the peak and its vicinity is much greater than the increase in signal value due to exponentiation at the foot of the mountain, which is mainly consisting of noise. As a result, the noise in the exponentiation-processed signal S5 is further reduced than that in signal S4, and the peak portion becomes a more prominent waveform. By using this signal S5, the grinding endpoint can be detected with high precision.

[0034] In addition, in step 310, the absolute value of the signal can also be obtained before calculating the exponentiation. That is, the endpoint detection unit 20 can also calculate the exponentiation Y according to the sign of the signal (e.g., signal S4) value X as follows: When X≧0, Y={abs (X)} When X<0, Y=-{abs (X)} N In this way, even if the exponent N uses an even or decimal value, for negative numbers X, to avoid the reversal of the sign of the exponentiation Y, or the value of the exponentiation Y becoming an imaginary number, the appropriate exponentiation signal (e.g., signal S5) can be calculated in step 310.

[0035] Next, the endpoint detection unit 20 determines whether the grinding endpoint has been reached based on the exponentially multiplied signal (e.g., signal S5) (step 312). For example, when referring to Figure 7, the endpoint detection unit 20 can determine whether the value of signal S5 exceeds a specified threshold value. In addition, depending on the friction coefficient of each layer of material constituting the object being ground, the relationship between the signal value of the first half of time T1 and the signal value of the second half of time T2 in signal S2 of Figure 5 may sometimes be opposite to the example shown in Figure 5 (that is, the signal value at time T2 is smaller than the signal value at time T1). In this case, signal S5 in Figure 7 has a convex peak at the bottom, and the endpoint detection unit 20 only needs to determine whether the value of signal S5 is lower than the specified threshold value.

[0036] When the grinding endpoint is reached in step 312, the endpoint detection unit 20 decides to end the grinding of the object being ground (step 314). Upon receiving the decision to end grinding, the grinding table 30 and the top ring 50 will stop rotating, the top ring 50 will rise from the grinding table 30, and the substrate 100 will be removed from the top ring 50 and sent to the next process (e.g., the cleaning process). Alternatively, if the grinding endpoint has not yet been reached, the endpoint detection unit 20 will return to step 302 to continue detecting the grinding endpoint and will repeat the steps after step 302 using the new time signal.

[0037] Furthermore, in the above description, the polishing signal S1 is exemplified by signal 55 from the current detection unit 56, and the waveforms of each signal in Figures 4 to 7 are displayed. However, for other signals (e.g., signal 35 from the current detection unit 36 ​​or signal 85 from the detector 80), steps 302 to 314 can be applied in the same way to detect the polishing endpoint. In addition, the polishing signal S1 in Figure 4 is performed while the top ring 50 is rocked, but the rocking of the top ring 50 may not be necessary.

[0038] As explained above, in this embodiment, by removing noise from the grinding signal and further exponentiating it with an exponent greater than 1, the non-noise portion of the signal can be made prominent from the noise portion, thereby enabling high-precision detection of the grinding endpoint. Furthermore, since the noise component of the signal is reduced through exponentiation, the moving average interval (reducing the number of data points) can be shortened in the moving average processing during noise removal. In other words, even with a shortened moving average interval, the noise in the signal can still be reduced through exponentiation. This allows for rapid detection of the grinding endpoint and prevents over-grinding of the object being ground.

[0039] The above description of embodiments of the present invention is based on some examples, but the above embodiments are for the purpose of facilitating understanding of the present invention and are not intended to limit the present invention. The present invention can be modified and improved without departing from its intent, and the present invention naturally includes its equivalents. Furthermore, within the scope of solving at least a portion of the above-mentioned problems or achieving at least a portion of the effects, the constituent elements described in the claims and specification can be arbitrarily combined or omitted. [Simplified Explanation of the Diagram]

[0014] FIG1 is a schematic diagram showing the overall structure of a polishing apparatus according to an embodiment of the present invention. FIG2 is a schematic diagram showing the overall structure of a polishing apparatus according to an embodiment of the present invention. FIG3 is a flowchart showing a series of processes performed by the endpoint detection unit according to an embodiment of the present invention. FIG4 shows an exemplary polishing signal obtained from the current detection unit. FIG5 shows an exemplary signal obtained by performing a moving average on the polishing signal of FIG4. FIG6 shows an exemplary signal obtained by performing a moving average on the differential of the signal of FIG5. FIG7 shows an exemplary signal obtained by exponentiation on the noise-removed signal of FIG6.

Claims

1. A polishing apparatus comprising: a polishing table for holding a polishing pad; a holding unit for holding a polishing object opposite to the polishing pad; and an endpoint detection unit for detecting a polishing endpoint indicating the end of polishing based on a signal indicating the state of the polishing pad polishing the polishing object; wherein the endpoint detection unit is configured to remove noise from the signal by performing a moving average on the signal, differentiating the signal obtained by the moving average, and further moving average the signal obtained by the differential, and then multiplying the noise-removed signal by an exponent greater than 1, and detecting the polishing endpoint based on the exponentiated signal.

2. The grinding apparatus of claim 1, wherein the aforementioned endpoint detection unit is configured to, in the aforementioned power calculation of the noise-removed signal, power the absolute value of the aforementioned noise-removed signal by an exponent greater than 1.

3. The grinding apparatus of claim 1 or 2, wherein a motor is provided for rotating and driving the aforementioned grinding table, and the aforementioned signal is based on the signal of the driving current of the aforementioned motor.

4. The grinding apparatus of claim 1 or 2, wherein a motor is provided for rotating the object to be ground, and the aforementioned signal is based on the signal of the drive current of the aforementioned motor.

5. The polishing apparatus of claim 1 or 2, wherein an acoustic or ultrasonic detector is provided, which is disposed near the aforementioned polishing table or the aforementioned object to be polished, and the aforementioned signal is a signal detected by the aforementioned acoustic or ultrasonic detector.

6. A method for determining the end point of a grinding apparatus, comprising detecting and displaying the end point of grinding in the grinding apparatus, the grinding apparatus comprising: a grinding table for holding a grinding pad; and a holding part for holding a grinding object relative to the grinding pad; the method comprising: acquiring a signal indicating the state of the grinding pad grinding the grinding object; removing noise from the signal by performing a moving average on the signal, differentiating the signal obtained by the moving average, and further moving average the signal obtained by the differential; multiplying the noise-removed signal by an exponent greater than 1; and detecting the end point of grinding based on the exponentiated signal.

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