POLISHING APPARATUS AND METHOD FOR DETECTING POLISHING END POINT IN POLISHING APPARATUS

Abstract

To detect a polishing end point with a high degree of precision even when a change in polishing friction force is small.SOLUTION: A polishing device includes: a polishing table for holding a polishing pad; a holding part for holding a polishing object so that it faces the polishing pad; and an end point detection part for detecting a polishing end point indicating ending of the polishing on the basis of a signal indicating a polishing state of the polishing object by the polishing pad. The end point detection part removes noise in the signal, exponentiates the signal whose noise is removed with an exponent greater than 1, and detects the polishing end point on the basis of the exponentiated signal.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a polishing apparatus and a method for detecting a polishing end point in a polishing apparatus. [Background technology]

[0002] One type of semiconductor device manufacturing equipment is a CMP (Chemical Mechanical Polishing) equipment. A typical CMP equipment includes a polishing table on which a polishing pad is attached, and a polishing head on which a substrate to be polished is attached. In a typical CMP equipment, 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.

[0003] In the polishing process in a polishing device such as a CMP device, it is important to accurately detect the polishing end point at which the film to be removed by polishing has been removed. As a method for detecting the polishing end point, a method is known in which a change in the polishing friction force when the material of the surface of the polishing object is transferred to a different material by polishing (for example, see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-098475 A Summary of the Invention [Problem to be solved by the invention]

[0005] When the change in the polishing frictional force when the surface material of the object to be polished is transferred to a different material due to polishing is small, the influence of noise may cause an erroneous detection of the polishing end point. Therefore, it is necessary to detect the polishing end point with high accuracy even if the change in the polishing frictional force is small. [Means for solving the problem]

[0006] [Form 1] According to Form 1, there is provided a polishing apparatus comprising a polishing table for holding a polishing pad, a holding section for holding an object to be polished facing the polishing pad, and an end point detection section for detecting a polishing end point indicating the end of the polishing based on a signal indicating a state of polishing of the object to be polished by the polishing pad, wherein the end point detection section is configured to remove noise from the signal, raise the noise-removed signal to a power greater than 1, and detect the polishing end point based on the powered signal.

[0007] [Form 2] According to form 2, there is provided the polishing apparatus of form 1, wherein the endpoint detection unit is configured to perform a moving average of the signal, differentiate the signal obtained by the moving average, and further perform a moving average of the signal obtained by the differentiation in order to remove noise from the signal.

[0008] [Form 3] According to Form 3, there is provided the polishing apparatus of Form 1 or 2, wherein the end point detection unit is configured to raise the absolute value of the noise-removed signal to an exponent greater than 1 in a power calculation of the noise-removed signal.

[0009] [Mode 4] According to mode 4, there is provided a polishing apparatus according to any one of modes 1 to 3, further comprising a motor for rotating the polishing table, and the signal is a signal based on a driving current of the motor.

[0010] [Feature 5] According to feature 5, in the polishing apparatus of any one of features 1 to 3, A polishing apparatus is provided that includes a motor for rotating an object to be polished, the signal being based on a drive current of the motor.

[0011] [Form 6] According to Form 6, there is provided a polishing apparatus according to any one of Forms 1 to 3, further comprising an acoustic or ultrasonic sensor arranged in the vicinity of the polishing table or the object to be polished, and the signal is a signal sensed by the acoustic or ultrasonic sensor.

[0012] [Form 7] According to Form 7, there is provided a method for detecting a polishing endpoint indicating the end of polishing in a polishing apparatus, the polishing apparatus comprising a polishing table for holding a polishing pad and a holding portion for holding an object to be polished facing the polishing pad, the method including the steps of acquiring a signal indicating a state of polishing of the object to be polished by the polishing pad, removing noise from the signal, raising the noise-removed signal to a power greater than 1, and detecting the polishing endpoint based on the exponentiated signal. [Brief description of the drawings]

[0013] [Figure 1] 1 is a schematic diagram showing an overall configuration of a polishing apparatus according to an embodiment of the present invention; [Diagram 2] 1 is a schematic diagram showing an overall configuration of a polishing apparatus according to an embodiment of the present invention; [Diagram 3] 5 is a flowchart showing a series of processes performed by an end point detection unit according to an embodiment of the present invention. [Figure 4] 4 shows an exemplary polishing signal obtained from a current sensing portion. [Diagram 5] 5 shows an exemplary signal obtained by running averaging the polishing signal of FIG. 4. [Figure 6] 6 shows an exemplary signal obtained by differentiating and then moving averaging the signal of FIG. 5. [Figure 7] 7 illustrates an exemplary signal obtained by exponentiating the denoised signal of FIG. 6. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings described below, the same or corresponding components are designated by the same reference numerals, and duplicated description will be omitted.

[0015] 1 and 2 are schematic diagrams showing the overall configuration of a polishing apparatus 10 according to an embodiment of the present invention. As shown in the drawings, the polishing apparatus 10 includes a polishing table 30 for holding a polishing pad 31, a top ring 50 (holding unit) for holding an object to be polished (e.g., a substrate 100 such as a semiconductor wafer shown in FIG. 2) so as to face the polishing pad 31 and pressing the object 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. The table drive motor 32 and the power supply circuits 34 and 54 are omitted in FIG. 2.

[0016] The polishing table 30 is connected via a table shaft 42 to a table drive motor 32 disposed below the polishing table 30. The table drive motor 32 is driven to rotate, thereby enabling the polishing table 30 to rotate about the axis of the table shaft 42. A polishing pad 31 is attached to the upper surface of the polishing table 30. A surface 311 of the polishing pad 31 constitutes a polishing surface for polishing the substrate 100. A polishing liquid supply nozzle (not shown) is provided above the polishing table 30, and a polishing liquid is supplied from the polishing liquid supply nozzle to the polishing pad 31 on the polishing table 30.

[0017] The top ring 50 is supported by an arm 64 via a top ring shaft 62. The top ring shaft 62 can move up and down relative to the arm 64 by a vertical movement mechanism (not shown). The top ring 50 can be raised and lowered and positioned relative to the arm 64 by the vertical movement of the top ring shaft 62. The top ring 50 is configured to be able to hold a substrate 100 such as a semiconductor wafer on its underside. Specifically, as shown in FIG. 2, the top ring 50 includes a retainer ring 51A that holds the outer periphery of the substrate 100 to prevent the substrate 100 from jumping out of the top ring 50, and a top ring main body 51B that presses the substrate 100 against the polishing surface 311.

[0018] A top ring drive motor 52 is fixed to an arm 64 that supports the top ring 50. As shown in Fig. 2, the top ring shaft 62 is connected to a rotating cylinder 65, and a timing pulley 66 provided on the outer periphery of the rotating cylinder 65 is connected to a timing pulley 68 provided on the top ring drive motor 52 via a timing belt 67. As a result, when the top ring drive motor 52 rotates, the rotating cylinder 65 and the top ring shaft 62 rotate together via the timing pulley 68, timing belt 67, and timing pulley 66, and the top ring 50 rotates around the axis of the top ring shaft 62.

[0019] The arm 64 is connected to an arm drive motor 72 fixed to an arm shaft 74. By driving the arm drive motor 72, the arm 64 and the top ring 50 supported by the arm 64 can rotate around the axis of the arm shaft 74.

[0020] When the polishing apparatus 10 operates, first, the top ring 50 receives and holds the substrate 100 transported by a transport mechanism (transporter) (not shown) at a predetermined receiving position. The top ring 50, which has received the substrate 100 at the receiving position, is moved from the receiving position to above the polishing table 30 by the rotation of the arm 64. Next, the top ring shaft 62 and the top ring 50 are lowered, and the substrate 100 is pressed against the polishing surface 311 of the polishing pad 31. Then, the table drive motor 32 and the top ring drive motor 52 are rotated to rotate the polishing table 30 and the top ring 50, respectively, and at the same time, a polishing liquid is supplied onto the polishing pad 31 from a polishing liquid supply nozzle provided above the polishing table 30. As a result, the substrate 100 comes into sliding contact with the polishing surface 311 of the polishing pad 31, and the surface of the substrate 100 is polished.

[0021] During polishing of the substrate 100, the arm drive motor 72 may periodically rotate the arm 64 left and right to cause the top ring 50 to oscillate relative to the polishing pad 31 (i.e., move back and forth within a predetermined range on the polishing pad 31), thereby performing polishing.

[0022] The polishing apparatus 10 of the present embodiment further includes a current detection unit 36 ​​configured to detect the drive current 33 supplied from the power supply circuit 34 to the table 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 a polishing end point indicating the end of polishing, based on the drive currents 33, 53 or another signal indicating the state of polishing. Either one of the current detection units 36, 56 may be omitted.

[0023] Here, the substrate 100 (e.g., a semiconductor wafer) that is the object to be polished has a laminated structure made up of multiple different materials, such as semiconductors, conductors, and insulators, and the friction coefficients differ between the layers of different materials. For this reason, as polishing shifts from one layer of the laminated structure to another layer of different materials, the polishing frictional force when polishing the object to be polished changes. The polishing frictional force appears as a driving load on each of the motors 32, 52 that rotate the polishing table 30 or the top ring 50. Therefore, the currents 33, 53 flowing through each of the motors 32, 52 vary according to the polishing frictional force, i.e., The end point of polishing can be detected based on either the drive current 33 or 53 or both of them.

[0024] The end point detection unit 20 may be configured as, for example, a computer having a processor and a memory. The memory may store a program (software) including one or more computer-executable instructions, and the processor may read and execute the program from the memory to perform the process of detecting the polishing end point. For example, the end point detection unit 20 may operate to obtain an electric signal or data (35, 55) corresponding to the drive current (33, 53) from the current detection unit (36, 56), calculate (data process) the electric signal or data (35, 55) to identify a change in the polishing frictional force, and detect the polishing end point based on the identification result.

[0025] As described above, the drive currents 33 and 53 of the motors indicate the state (frictional force) of polishing the object to be polished, but it is also possible to detect the end point of polishing using signals other than the drive currents 33 and 53. In such an embodiment, the polishing apparatus 10 may include a sensor 80 that detects a physical quantity reflecting the state of polishing, and the end point detection unit 20 may detect the end point of polishing based on the output signal 85 of the sensor 80. For example, the sensor 80 may be an acoustic sensor or an ultrasonic sensor installed near the polishing table 30 or the top ring 50 to detect the polishing sound. As described above, when the material of the surface to be polished changes as the polishing progresses, the polishing frictional force changes, and at this time, the polishing sound also changes. Therefore, the polishing end point can also be detected using the output signal from the acoustic sensor or the ultrasonic sensor. As another example, the sensor 80 may be a force sensor that directly detects the polishing frictional force between the polishing table 30 and the top ring 50 as the rotational torque of the polishing table 30 or the rotational torque of the top ring 50, or an eddy current sensor may be used as a vibration detection sensor. In addition, although FIG. 2 shows the sensor 80 as being embedded in the polishing table 30, the location of the sensor 80 is not limited to this, and the sensor 80 may be installed in an appropriate location depending on the type of sensor 80.

[0026] FIG. 3 is a flowchart showing a series of processes performed by the end point detection unit 20. First, the end point detection unit 20 acquires a signal (hereinafter, referred to as a polishing signal) S1 that indicates the state of polishing the object to be polished (step 302). For example, the polishing signal S1 may be one or more of i) a signal 35 that can be acquired from the current detection unit 36, ii) a signal 55 that can be acquired from the current detection unit 56, and iii) a signal 85 that can be acquired from the sensor 80. As described above, the signal 35 from the current detection unit 36 ​​is a signal that indicates the drive current 33 of the table drive motor 32, and the signal 55 from the current detection unit 56 is a signal that indicates the drive current 53 of the top ring drive motor 52. These signals 35, 55 reflect the drive load of each motor 32, 52, that is, the frictional force of polishing on the object to be polished. In addition, the signal 85 from the sensor 80 is, for example, a signal that indicates the polishing sound, which also reflects the polishing frictional force.

[0027] As an example, Fig. 4 shows an exemplary polishing signal S1 (i.e., signal 55) acquired from the current detection unit 56. The horizontal axis of Fig. 4 indicates time, and the vertical axis indicates signal strength. This signal represents the drive current 53 of the top ring drive motor 52. Note that this example is for a case where polishing is performed while the top ring 50 is oscillated relative to the polishing pad 31, and the signal fluctuations over short time periods in the graph are due to the oscillation of the top ring 50. That is, the polishing signal S1 in this example contains not only noise, but also short time period fluctuations caused by the oscillation of the top ring 50.

[0028] Next, the end point detection unit 20 performs noise removal on the grinding signal S1. The noise removal process may include a plurality of processing steps. For example, the end point detection unit 20 moves the grinding signal S1. The operation may involve sequentially executing a step of averaging to generate a signal S2 (step 304), a step of differentiating the signal S2 to generate a signal S3 (step 306), and a step of taking a moving average of the signal S3 to generate a signal S4 (step 308).

[0029] FIG. 5 shows an exemplary signal S2 (i.e., the signal after step 304) obtained by the end point detection unit 20 taking the moving average of the polishing signal S1 of FIG. 4. In FIG. 5, the moving average process removes the periodic fluctuation of the signal caused by the oscillation, and removes some of the noise mixed in the signal. The width of the period for moving average (i.e., the number of data to be averaged) may be set appropriately in consideration of the oscillation period and the expected noise characteristics. In addition, it can be seen that the moving averaged signal S2 of FIG. 5 has a time region T1 where the signal value is relatively small followed by a time region T2 where the signal value is relatively large. As mentioned above, this is due to the change in the polishing friction force against the polishing object. In other words, between the former time region T1 and the latter time region T2, the polished surface of the polishing object transitions from one material to another. The moment of this transition corresponds to the end point of polishing.

[0030] FIG. 6 shows an exemplary signal S4 (i.e., the signal after step 308) obtained by the endpoint detection unit 20 differentiating the signal S2 in FIG. 5 and then performing a moving average. In FIG. 6, a signal having a steep peak is obtained by the differentiation process. As can be understood from the above description, this signal peak corresponds to the polishing endpoint. Also, in FIG. 6, the noise of the signal is removed to some extent by the moving average process after differentiation, but noise remains in the base part other than the steep peak. Depending on the magnitude of this remaining noise, it may be difficult to accurately distinguish between the peak part of the signal and the noise. Therefore, it is required to further effectively reduce the noise and thereby detect the polishing endpoint with higher accuracy.

[0031] The noise removal process is not limited to the process shown in steps 304 to 308, and the end point detection unit 20 may remove noise from the polishing signal S1 using another method.

[0032] Returning to FIG. 3, the end point detection unit 20 then raises the signal (e.g., signal S4) from which the noise has been removed as described above to an exponent greater than 1 (step 310). The exponent of the power may be, for example, 2 or 3 (i.e., squared or cubed). FIG. 7 shows an exemplary signal S5 obtained by cubing the signal S4 from which the noise has been removed in FIG. 6. In FIG. 7, the signal value of the peak and its neighboring parts, where the signal value is large, is increased by the power (cubed), while the signal value of the base part, where the signal value is small, i.e., the part where noise is predominant, is decreased by the power (cubed) compared to the peak and its neighboring parts. In other words, the increase in the signal value due to the power at the peak and its neighboring parts is much larger than the increase in the signal value due to the power at the part where noise is predominant. As a result, the signal S5 after the power processing has further reduced noise compared to the signal S4, and the peak part has a more prominent waveform. By using such a signal S5, it is possible to detect the polishing end point with high accuracy.

[0033] Note that the absolute value of the signal may be taken prior to calculating the power in step 310. That is, the end point detection unit 20 may calculate the power Y of a signal (for example, signal S4) depending on whether the value X is positive or negative, as follows: When X ≥ 0, Y = {abs(X)} N If X<0, then Y=-{abs(X)} N In this way, even if an even or decimal value is used as the exponent N, it is possible to avoid the positive and negative sign of the power Y being inverted for a negative number X, or the value of the power Y becoming an imaginary number, and it is possible to calculate an appropriate exponentiated signal (e.g., signal S5) in step 310.

[0034] Next, the end point detection unit 20 judges whether the polishing end point has been reached based on the exponentiated signal (e.g., signal S5) (step 312). For example, referring to FIG. 7, the end point detection unit 20 may judge whether the value of the signal S5 exceeds a predetermined threshold value. Depending on the friction coefficient of the material of each layer constituting the polishing object, the magnitude relationship between the signal value at the first half of time T1 and the signal value at the second half of time T2 in the signal S2 in FIG. 5 may be opposite to that shown in FIG. 5 (i.e., the signal value at time T2 is smaller than the signal value at time T1). In such a case, the signal S5 in FIG. 7 has a downward convex peak, and the end point detection unit 20 may judge whether the value of the signal S5 falls below a predetermined threshold value.

[0035] When the polishing endpoint is reached in the determination in step 312, the endpoint detection unit 20 determines to end polishing of the object being polished (step 314). Upon receiving the determination to end polishing, the polishing table 30 and the top ring 50 stop rotating, the top ring 50 rises from the polishing table 30, and the substrate 100 is removed from the top ring 50 and transferred to the next process (e.g., a cleaning process). On the other hand, if the polishing endpoint has not yet been reached, the endpoint detection unit 20 returns to step 302 to continue detecting the polishing endpoint, and repeats the steps following step 302 using the signal of the new time.

[0036] 4 to 7 are shown by taking the signal 55 from the current detection unit 56 as an example of the polishing signal S1, but the polishing end point can also be detected by similarly applying steps 302 to 314 in the case of other signals (for example, the signal 35 from the current detection unit 36 ​​or the signal 85 from the sensor 80). Also, the polishing signal S1 in Fig. 4 is obtained when polishing is performed while the top ring 50 is oscillated, but the top ring 50 does not have to be oscillated.

[0037] As described above, according to this embodiment, the polishing signal is subjected to noise removal and further to exponentiation by an exponent greater than 1, thereby making the non-noise portion of the signal stand out from the noise portion, and thus the polishing end point can be detected with high accuracy. Furthermore, since the noise component of the signal is reduced by the exponentiation, the moving section can be shortened (the number of data items can be reduced) in the moving average process of the noise removal process. In other words, even if the moving section is shortened, the noise of the signal can be reduced by the exponentiation. This makes it possible to quickly detect the polishing end point and prevent over-polishing of the object to be polished.

[0038] Although the embodiments of the present invention have been described above based on several examples, the above-mentioned embodiments of the present invention are intended to facilitate understanding of the present invention and do not limit the present invention. The present invention may be modified or improved without departing from the spirit thereof, and the present invention naturally includes its equivalents. Furthermore, any combination or omission of each component described in the claims and specification is possible within the scope of solving at least a part of the above-mentioned problems or achieving at least a part of the effects. [Explanation of symbols]

[0039] 10 Polishing equipment 20 End point detection unit 30 Polishing Table 31 Polishing Pad 32 Table drive motor 34 Power supply circuit 36 Current detection unit 42 Table shaft 50 Top Ring 51A Retainer ring 51B Top ring body 52 Top ring drive motor 54 Power supply circuit 56 Current detection unit 62 Top ring shaft 64 Arm 65 Rotating Cylinder 66 Timing pulley 67 Timing belt 68 Timing pulley 72 Arm drive motor 74 Arm shaft 80 Sensors 100 Substrates

Claims

1. a polishing table for holding a polishing pad; a holder for holding an object to be polished so as to face the polishing pad; an end point detection unit that detects a polishing end point indicating the end of the polishing based on a signal indicating a state of polishing of the object by the polishing pad; A polishing apparatus comprising: The end point detection unit removing noise from the signal by taking a moving average of the signal, differentiating the signal obtained by the moving average, and further taking a moving average of the signal obtained by the differentiation; raising the denoised signal to an exponent greater than one; detecting the polishing end point based on the powered signal; The polishing apparatus is configured as follows.

2. 2. The polishing apparatus according to claim 1, wherein the end point detection unit is configured to raise an absolute value of the noise-removed signal to a power greater than one in a power calculation of the noise-removed signal.

3. a motor for rotating the polishing table, the signal is a signal based on a drive current of the motor; 3. The polishing apparatus according to claim 1 or 2.

4. a motor for rotating the object to be polished; the signal is a signal based on a drive current of the motor; 3. The polishing apparatus according to claim 1 or 2.

5. an acoustic or ultrasonic sensor disposed near the polishing table or the object to be polished; the signal being a signal sensed by the acoustic or ultrasonic sensor; 3. The polishing apparatus according to claim 1 or 2.

6. 1. A method for detecting a polishing endpoint indicating the end of polishing in a polishing apparatus, comprising: The polishing apparatus includes: a polishing table for holding a polishing pad; a holder for holding an object to be polished so as to face the polishing pad; Equipped with The method comprises: acquiring a signal indicative of a state of polishing of the object by the polishing pad; removing noise from the signal by taking a moving average of the signal, differentiating the signal obtained by the moving average, and further taking a moving average of the signal obtained by the differentiation; raising the denoised signal to a power greater than one; detecting the polishing endpoint based on the powered signal; A method comprising:

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