TWI894601B - Chemical mechanical polishing apparatus, method of polishing and computer program product - Google Patents

Abstract

A chemical mechanical polishing apparatus has a platen to support a polishing pad, the platen having a recess, a carrier head to hold a surface of a substrate against the polishing pad and comprising a retaining ring to retain the substrate below the carrier head, a motor to generate relative motion between the platen and the carrier head so as to polish the substrate, an in-situ acoustic monitoring system comprising an acoustic sensor arranged in the recess that receives acoustic energy from friction between the substrate and the polishing pad and from friction between the retaining ring and the polishing pad, and a controller configured to generate a value for a carrier head status parameter based on received acoustic signals from the in-situ acoustic monitoring system, and change a polishing parameter or generate an alert based on the carrier head status parameter.

Description

Chemical mechanical polishing device, polishing method and computer program product

This disclosure relates to chemical mechanical polishing, and more particularly, to determining polishing parameters based on acoustic signals received during chemical mechanical polishing.

Integrated circuits are typically formed on a substrate by sequentially depositing conductive, semiconductive, or insulating layers on a silicon wafer. One manufacturing step involves depositing a filler layer on a non-planar surface and planarizing the filler layer. For some applications, the filler layer is planarized until the top surface of the patterned layer is exposed. For example, a conductive filler layer can be deposited on a patterned insulating layer to fill trenches or holes in the insulating layer. After planarization, the remaining portion of the conductive layer between the raised patterns of the insulating layer forms vias, plugs, and traces that provide conductive paths between the thin-film circuits on the substrate. For other applications, such as oxide polishing, the filler layer is planarized until a predetermined thickness is left on non-planar surfaces. Additionally, photolithography often requires planarization of the substrate surface.

Chemical mechanical polishing (CMP) is a well-established planarization method. This planarization method typically requires the substrate to be mounted on a carrier or polishing head. The exposed surface of the substrate is typically placed on a rotating polishing pad. The carrier head applies a controlled load to the substrate, pushing it against the polishing pad. An abrasive polishing slurry is typically applied to the surface of the polishing pad.

This document discloses a chemical mechanical polishing apparatus comprising a carrier head for holding a substrate against a polishing pad. Relative motion is generated between the polishing pad and the carrier head to polish an exposed surface of the substrate. The apparatus includes an in-situ acoustic monitoring system that receives acoustic signals from the substrate and the carrier head. The acoustic monitoring system generates corresponding electronic signals, which are transmitted to a controller. The controller receives the electronic signals and, based on the signals, generates carrier head status parameters. The controller is configured to change one or more polishing parameters or generate an alarm based on the carrier head status parameters.

In one embodiment, a chemical mechanical polishing apparatus comprises: a platform for supporting a polishing pad, the platform having a recess; a carrier head for holding a surface of a substrate against the polishing pad and including a retaining ring for fixing the substrate below the carrier head; a motor for generating relative motion between the platform and the carrier head to polish the substrate; an in-situ acoustic wave monitoring system The in-situ acoustic monitoring system includes an acoustic sensor disposed in the recess, the acoustic sensor receiving acoustic energy from friction between the substrate and the polishing pad and from friction between the retaining ring and the polishing pad; and a controller configured to generate a value of a carrier head status parameter based on the acoustic signal received from the in-situ acoustic monitoring system, and change a polishing parameter or generate an alarm based on the carrier head status parameter.

In another aspect, a polishing method includes the steps of: holding a substrate against a polishing surface of a polishing pad with a carrier head; inducing relative motion between the substrate and the polishing pad such that an in-situ acoustic monitoring system passes beneath the carrier head; monitoring the carrier head with the in-situ acoustic monitoring system oriented beneath the polishing pad to generate a signal comprising a series of segments; identifying a first segment from the series of segments, the first segment corresponding to the sensor being beneath a first portion of the carrier head; identifying a second segment from the series of segments, the second segment corresponding to the sensor being beneath a second portion of the carrier head; determining a difference between the first segment and the second segment; and altering a polishing parameter or generating an alarm based on the determined difference.

The details of one or more embodiments are set forth in the accompanying drawings and the description that follows. Other features and advantages will be apparent from the description and drawings, and from the claims.

One challenge in CMP is verifying that the polishing system is operating at the desired control parameters, such as the desired rotational speed or chamber pressure. Ideally, the appropriate physical components (such as a motor or pressure regulator) are simply operated by the controller according to a recipe with the desired control parameter value. However, in reality, the actual values (such as actual rotational speed or chamber pressure) may differ from the desired values due to transient effects or system errors.

However, if the acoustic signal is correlated with a control parameter (such as chamber pressure or rotational speed), then the control parameter value determined from the acoustic signal can be used to verify or detect failure of another control parameter sensor (such as a pressure sensor or motor encoder), potentially rendering the other sensor unnecessary.

Another challenge in CMP is determining "system health." Failures during polishing (e.g., wafer slipping from the carrier head, failure to chuck or unclamp the substrate, sticking between membranes in the carrier head, unexpected lateral movement of the substrate or carrier head) can result in direct damage to the substrate being polished and require significant downtime for system maintenance. Traditionally, such failures are detected only after they occur. For example, visual inspection or a camera might detect a substrate slipping from under the carrier, or a change in the polishing rate might indicate an error.

However, if the acoustic signal is correlated with an impending error condition, it may be possible to diagnose the problem, allowing corrective action to be taken before a failure occurs.

Another CMP issue is the formation of air bubbles between the substrate and the flexible membrane during chamber pressure-boosting operations. During operation, the pressure in each pressurizable chamber is increased zone by zone according to a recipe stored in the controller. If errors occur during the pressure-boosting process, air bubbles can become trapped between the substrate and the flexible membrane. These bubbles can alter the pressure profile applied to the substrate and reduce uniformity across the wafer. There is no real-time technology to identify pressure-boosting processes that cause air bubbles to form between the membrane and the wafer.

However, if the sonic signal is correlated with an improper press-up process, it may be possible to determine if air bubbles or an improper press-up process are present, allowing corrective action to be taken before the air bubbles affect the polishing of the substrate.

Another issue in CMP is improper lubrication of the gimbal mechanism. Typically, the gimbal mechanism is lubricated, such as with grease, to reduce friction between moving parts when force is applied to the carrier head to cause gimbaling (for example, friction caused by the carrier head riding on a polishing pad with uneven thickness). If the flexible gimbal mechanism is improperly lubricated, the force required to cause gimbaling increases, potentially leading to suboptimal polishing results, direct damage to the substrate, and increased maintenance on the polishing system.

However, if the acoustic signal is monitored over a long period of time, it may be possible to determine if the gimbal mechanism is improperly greased, allowing corrective action to be taken before damage occurs to the gimbal mechanism or the substrate is damaged during polishing.

As the substrate and the carrier head's retention ring interact with the polishing layer of the polishing pad, the polishing process generates acoustic energy, at least due to the frictional contact between the two surfaces. This acoustic energy is received and processed by an acoustic sensor to produce a series of acoustic measurements, or acoustic signals.

Segmenting the acoustic signal based on which surfaces of the ring assembly or substrate are generating the acoustic information helps detect air bubbles or other erroneous polishing parameters (such as pressure or gimbal position). Detecting such errors improves system reliability and reduces system errors and polishing operation failures.

The techniques described herein can address any one or more of these problems, individually or collectively.

FIG1 illustrates an example of a polishing station of a chemimechanical polishing system 20. The polishing system 20 includes a rotatable, disk-shaped platform 24 on which a polishing pad 30 is positioned. The platform 24 can be configured to rotate about an axis 25. For example, a motor 26 can rotate a drive shaft 28 to rotate the platform 24. The polishing pad 30 can be a double-layered polishing pad having an outer polishing layer 32 and a softer backing layer 34. The polishing surface of the polishing layer 32 can include grooves 35, for example, for conveying slurry.

The polishing system 20 can include a supply port or combined supply-rinse arm 36 to dispense a polishing fluid 38, such as an abrasive slurry, onto the polishing pad 30. The polishing system 20 can also include a pad conditioning device 40 with an adjusting disk 42 to maintain the surface roughness of the polishing pad 30. The adjusting disk 42 can be positioned at the end of an arm 44 that can be swung so that the adjusting disk 42 can be swept radially across the polishing pad 30.

A carrier head 70 is used to hold the substrate 10 against the polishing pad 30. The carrier head 70 is suspended from a support structure 50 (e.g., a carousel or track) and is connected to a carrier head rotation motor 56 via a drive shaft 54, allowing the carrier head to rotate about an axis 58. Alternatively, the carrier head 70 can be swiveled laterally, such as on a slide on a carousel, by moving along a track, or by rotation of the carousel itself.

The carrier head 70 includes a housing 72 , a substrate backing assembly 74 (which includes a base 76 and a flexible membrane 78 defining a plurality of pressurizable chambers 80 ), a gimbal mechanism 82 (which may be considered part of the assembly 74 ), a load chamber 84 , a retention ring 100 , and an actuator 122 .

The housing 72 may be generally circular in shape and may be coupled to the drive shaft 54 so as to rotate therewith during polishing. A passageway (not shown) may extend through the housing 72 to provide pneumatic control of the carrier head 70. The substrate backing assembly 74 is a vertically movable assembly located below the housing 72. A universal joint 82 allows the base 76 to be universally coupled relative to the housing 72 while preventing lateral movement of the base 76 relative to the housing 72. A load chamber 84 is located between the housing 72 and the base 76 to apply a load (i.e., downward pressure or weight) to the base 76, thereby applying a load to the substrate backing assembly. The vertical position of the substrate backing assembly 74 relative to the polishing pad is also controlled by the loading chamber 84. The lower surface of the flexible film 78 provides a mounting surface for the substrate 10.

During the loading or unloading of the substrate 10 from the carrier head 70, the polishing system 20 commands the carrier head 70 to change the air pressure within the pressurizable chambers 80 according to a recipe in order to "clamp" (e.g., mount) or "declamp" (e.g., unclamp) the substrate 10 onto the carrier head 70. Generally, the flexible membrane 78 includes concentric pressurizable chambers 80, each of which is individually pressurizable. To clamp the substrate 10 onto the carrier head 70, the pressure is increased concentrically outward from the central chamber to the increasingly distant chambers. To declamp the substrate 10 from the carrier head 70, the pressure within the pressurizable chambers 80 is decreased sequentially from the outermost concentric chamber to the central chamber.

The sequential pressurization during the clamping process will expel the air trapped between the substrate 10 and the pressurizable chamber 80 until the substrate 10 is vacuum-held on the flexible membrane 78. Conversely, the de-clamping process will sequentially reduce the pressure between the pressurizable chamber 80 and the substrate 10, starting from the outermost chamber and moving inward, allowing air to intrude between the flexible membrane 78 and the substrate 10 until the substrate 10 is no longer vacuum-held on the flexible membrane 78.

The polishing system 20 includes at least one in-situ acoustic monitoring system 160. The in-situ acoustic monitoring system 160 includes one or more acoustic sensors 162 positioned beneath a side of the substrate 10 proximate to the polishing pad 30. Each acoustic sensor can be mounted at a location on the platform 24. Specifically, the in-situ acoustic monitoring system can be configured to sense acoustic energy, such as acoustic emission caused by stress in the polishing pad, substrate, or retaining ring. Generally, this acoustic energy propagates through the material in the form of compression waves (rather than bulk motion).

The acoustic sensor 162 is positioned in a recess 164 in the platform 24 and is positioned to receive acoustic energy passing through the polishing pad 30 (e.g., through the acoustic window 118 in the polishing pad 30). The acoustic sensor 162 can be connected to a power supply and/or other signal processing electronics 166 via a rotational coupling (e.g., a mercury slip ring) via a circuit system 168. The signal processing electronics 166 can, in turn, be connected to a controller 190.

In-situ acoustic monitoring system 160 can be a passive acoustic monitoring system. The passive acoustic signal monitored by acoustic sensor 162 can have a range of 50 kHz to 1 MHz, such as 200 to 400 kHz, or 200 kHz to 1 MHz. For example, to monitor the polishing of an interlayer dielectric (ILD) in shallow trench isolation (STI), a frequency range of 225 kHz to 350 kHz can be monitored. As another example, the frequency range of interest for the passive mode is 500 kHz to 900 kHz.

The portion of the backing layer 34 directly above the acoustic sensor 162 may include an acoustic window 118. The acoustic window 118 has a lower acoustic attenuation coefficient than the surrounding backing layer 34. The material of the acoustic window 118 has a sufficiently low acoustic attenuation coefficient to provide a satisfactory signal for acoustic monitoring, for example. Generally, the acoustic attenuation coefficient should be as low as possible (i.e., non-absorbing), for example, an acoustic attenuation coefficient of less than 2, to provide a satisfactory signal for acoustic monitoring.

In some embodiments, acoustic window 118 is formed from a different material than backing layer 34. This allows backing layer 34 to be composed of a wider range of materials to meet the needs of CMP operations. Acoustic window 118 can be composed of a non-porous material, such as a solid. For example, the acoustic material can be a polymer, such as polyurethane.

The sound window 118 can be wider than the sound wave sensor 162, for example as shown in FIG1 , or the widths of the two can be substantially equal (e.g., within 10%). When the sound window 118 is narrower than the sound wave sensor 162, the sensor can also be adjacent to the bottom of the backing layer 34.

The acoustic sensor 162 is a contact-type acoustic sensor 162, whose surface is connected to the backing layer 34 and/or a portion of the acoustic window 118 (e.g., directly in contact or with only an adhesive layer). For example, the acoustic sensor 162 can be an electromagnetic acoustic sensor or a piezoelectric acoustic sensor. A piezoelectric inductor can include a rigid contact plate (e.g., stainless steel or a similar material) placed in contact with the subject to be monitored, and a piezoelectric component (e.g., a piezoelectric layer sandwiched between two electrodes) on the back of the contact plate.

The acoustic sensor 162 can be secured to a portion of the backing layer 34 and/or the sound window 118 via an adhesive layer. The adhesive layer increases the contact area between the acoustic sensor 162 and the backing layer 34 and/or the sound window 118, reduces undesirable movement of the acoustic sensor 162 during the polishing operation, and reduces the presence of air pockets between the acoustic sensor 162 and the backing layer 34. However, in some embodiments, the acoustic sensor 162 directly contacts the sound window 118.

The sound window 118 extends through the backing layer 34 so that one surface (e.g., the upper surface) contacts the lower surface of the polishing layer 32. The opposite surface (e.g., the bottom surface) can be coplanar with the lower surface of the backing layer 34.

The sound window 118 can be composed of a non-porous material. Generally speaking, non-porous materials transmit sound energy with less noise and diffusion than porous materials. The compressibility of the sound window 118 material can be within a certain range of the compressibility of the surrounding matrix material 204, thereby reducing the impact of the sound window 118 on the polishing properties of the polishing layer 32. The sound window 118 can be composed of one or more of polyurethane, polyacrylate, polyethylene or another polymer with a sufficiently low acoustic impedance coefficient. The sound window 118 is shown as extending through the total thickness of the backing layer 34. The sound wave sensor 162 extends through the hole in the platform 24 to contact the bottom surface of the window 118.

In some embodiments, and as shown in FIG1 , the acoustic window 118 extends through the thickness of the cushion 30. As shown in FIG2 , the acoustic window 118 extends through both the polishing layer 32 and the backing layer 34. Here, the acoustic window 118 has a lower acoustic impedance than the surrounding polishing layer 32 and backing layer 34. The acoustic window 118 is positioned so that the top surface of the acoustic window 118 is coplanar with the polishing surface 112a, and the bottom surface of the acoustic window is coplanar with the lower surface of the backing layer 34 (e.g., lower surface 114b), which contacts the platform 24. The acoustic wave sensor 162 contacts the exposed surface of the acoustic window 118 and receives the transmitted acoustic energy.

Acoustic window 118 is formed from a different material than the polishing layer 32. This allows the backing layer 34 to be composed of a wider range of materials to meet the needs of the CMP operation. In some embodiments, the acoustic transparency of both the polishing layer 32 and the backing layer 34 is sufficiently high that an acoustic window is not required. In this case, the acoustic sensor 162 can be placed directly in contact with the lower surface of the backing layer 34.

2 , a top view of the platform 24 and supported polishing pad 30 is shown, with the substrate 10 constrained by the retention ring 100. During the polishing operation, relative motion between the pad 30 and the substrate 10 is caused by rotation of the platform 24, rotation or linear motion of the carrier head 70 pressing against the substrate 10, or a combination thereof. A sensor 162 (and window 118, if provided) is shown, which follows a path 102 relative to the reference frame of FIG. 2 as the platform 24 and supported pad 30 rotate in the direction 124. During the polishing operation, as the sensor 162 follows the path 102, the sensor 162 moves beneath various portions of the retention ring 100 and the substrate 10, for example, when the path 102 intersects a portion of the substrate 10 or a portion of the retention ring 100.

Sonic sensor 162 is in contact with window 118 and generates sonic data during the polishing operation. As it travels along path 102, sonic sensor 162 generates a series of sonic measurements. This series includes measurements taken when sensor 162 (or window 118) is not beneath or in contact with retention ring 100 or substrate 10. Data generated before sensor 162 passes beneath retention ring 100 is referred to as "leading off-wafer data," i.e., data before and including entering path portion 106. An example path portion for collecting leading off-wafer data is shown as path portion 110.

As the sensor 162 passes beneath the carrier head 70, retention ring 100, or substrate 10, it measures acoustic energy generated by contact between the carrier head 70, retention ring 100, or substrate 10 and the polishing pad 30 and window 118. Path portions 104 and 108 correspond to the sensor 162 being positioned beneath two portions of the retention ring 100, while path portion 106 corresponds to the sensor 162 being positioned beneath the substrate 10. The data generated when the sensor 162 is positioned beneath the substrate 10 (e.g., path portion 106) is referred to as "on-wafer data." Because acoustic energy is attenuated as it passes through the polishing pad 30 and window 118, the acoustic energy reaching the sensor 162 is primarily caused by friction between the polishing pad 30 (including the window 118) and the specific component directly above the sensor 162 (such as the retaining ring 100 or the substrate 10). By analyzing the portion of the signal path corresponding to a component, information about that component can be obtained.

The data generated by sensor 162 after it passes beneath the second portion of retention ring 100 (e.g., exiting path portion 108) is referred to as "trailing off-wafer data." An example path portion for collecting trailing off-wafer data is shown as path portion 112.

The controller 190 of the acoustic monitoring system 160 receives acoustic data from the acoustic sensor 162. In some embodiments, the controller displays the measured acoustic signal on a display (e.g., a computer monitor).

Referring now to Figures 2 and 3 , an exemplary acoustic signal 300 is shown. The acoustic monitoring system 160 processes the acoustic signal 300 and divides it into segments corresponding to locations where the sensor 162 is located beneath the carrier head 70 (e.g., beneath the retention ring 100 or substrate 10). The acoustic monitoring system 160 divides the acoustic signal 300 into segments based on the measured location (i.e., the position of the sensor, such as the position determined by the angular position of the platform). In some embodiments, different signal segments can be distinguished based on the average amplitude of the acoustic signal 300. The series of segments is a time-correlated sequence corresponding to acoustic data generated sequentially by the acoustic sensor 162 over a period of time.

In some embodiments, the acoustic monitoring system 160 performs signal processing on the acoustic data generated by the acoustic sensor 162 to filter (e.g., remove noise) the acoustic data before transmitting it to the controller 190. The filtering may be a low-pass filter or a running window average to smooth the measured signal from the sensor 162. In some examples, the acoustic monitoring system 160 generates an average value for the measured signal within each segment.

In the example of FIG3 , the acoustic signal 300 includes an off-wafer segment 322 corresponding to "leading off-wafer data"; segments 324 and 332 corresponding to the window 118 being below the retention ring 100, such as data collected on path portions 106 and 108; a segment 326 corresponding to the window 118 being below the carrier head 70 and not contacting the retention ring 100 or substrate 10; an on-wafer segment 328 corresponding to the window 118 being below the substrate 10, such as "on-wafer data"; and an off-wafer segment 334 corresponding to "trailing off-wafer data." During the polishing operation, friction forces push the substrate 10 against the trailing inner surface of the retention ring 100, causing the on-wafer segment 328 to be adjacent to the carrier head segment 332 in the acoustic signal 300. In some cases, segment 326 may not appear in the acoustic signal 300 received by the acoustic monitoring system 160. Typically, the gap between the base plate 10 and the retaining ring 100 on the leading side of the path 102 may be 2 mm to 3 mm, which may be smaller than the gap between the sensor 162 and, therefore, may not be practically detectable from the rest of the acoustic signal 300, e.g., indistinguishable.

The acoustic monitoring system 160 transmits the acoustic signal 300 to the controller 190. The controller 190 processes the received acoustic signal 300 to compare a characteristic value of the signal 300 with a predetermined threshold or to determine a change in a characteristic of the signal 300. Examples of signal characteristics include the average amplitude of a signal segment, the maximum or minimum amplitude within a signal segment, the intensity of a specific frequency within the signal segment's spectrum, the total power within a certain bandwidth within the signal segment's spectrum, the frequency-weighted average power, or the location (frequency) of a peak or valley within the signal segment's spectrum. In some implementations, the controller 190 determines an alternative data parameter, such as a derivative, mean, frequency-weighted average power, integral, standard deviation, or variance of the acoustic signal 300 or one or more segments of the acoustic signal 300 .

As an example, the controller 190 may determine differences between characteristic values of one or more segments of the sonic signal 300, such as a difference between an on-wafer segment 328 and an off-wafer segment 322 and/or 334, a difference between a leading carrier head segment 324 and a trailing carrier head segment 332, or a difference between an on-wafer segment 328 and an off-wafer segment 324 and/or 332. The controller 190 may also determine differences in characteristic values of the sonic signal 300 over time, such as a difference between successive rotations of the stage, a difference between two or more substrates 10, or a difference in the sonic signal 300 over an operating period of the polishing system 20 (e.g., weeks or months).

In some embodiments, the controller 190 compares a characteristic value of the sound wave signal 300 with one or more thresholds. For example, the controller 190 compares a maximum value (such as a maximum amplitude) of one or more segments of the sound wave signal 300 with a maximum threshold.

Generally speaking, the sonic monitoring system 160 determines whether a defect, incorrect or suboptimal polishing parameter, or a combination thereof, is present based on the sonic signal 300 by comparing one or more segments of the sonic signal 300 to another segment, to historical sonic signals generated using different substrates, or both. If the difference between the characteristic values of two segments of the sonic signal exceeds a threshold, then one of these issues may be indicated. If the signal power on the wafer is significantly lower than expected, or if there is a significant drop in signal power that is not associated with an equivalent decrease in the expected pressure applied to the wafer in that signal region, then a bubble may be present. If the difference between the leading edge loop signal power (324) and the trailing edge loop signal power (332) exceeds a represented acceptable range, the gimbal position may be out of line.

The controller 190 generates a carrier head status parameter value based on one or more segments of the received acoustic signal 300. Examples of carrier head status parameters include the pressure within one or more pressurizable chambers 80 or the gimbal position (e.g., height or angular deviation) of the gimbal connection mechanism 82. The controller 190 compares the carrier head status value with a threshold status value stored in the controller 190. In response to the carrier head status value exceeding the corresponding threshold value, the controller 190 may generate an alarm or modify an operating value of the polishing system 20.

In one example, the controller 190 may determine the average amplitude difference between the leading carrier head segment 324 and the trailing carrier head segment 332. This amplitude difference may indicate improper pressure in one or more chambers 80, which may result in an improper gimbal connection of the carrier head 70. The controller 190 may generate an alarm in response to this determination.

The controller 190 can determine the average amplitude difference between the leading carrier head segment 324 and the trailing carrier head segment 332 during a plurality of substrate 10 polishing operations. A determination that the amplitude difference exceeds a threshold, or that the average amplitude varies, can indicate improper lubrication of the gimbal connection mechanism 82. The controller 190 can generate an alarm in response to determining that the gimbal connection mechanism 82 should be serviced.

In another example, the controller 190 determines the variation of the segment 326 or 330 or the segment 328 on the wafer. The variation can be calculated as the standard deviation of the signal within the corresponding segment or as the difference between the maximum and minimum values within the corresponding segment. The variation can be compared with a stored variation threshold. In some examples, a high variation (i.e., exceeding the threshold) in the segment 328 on the wafer can indicate the presence of air bubbles between the substrate 10 and the polishing layer 32. Air bubbles reduce the contact area between the substrate 10 and the polishing layer 32, thereby reducing the polishing effect. Detecting air bubbles can help adjust one or more polishing parameters to remove the air bubbles, thereby improving within-wafer polishing. The controller 190 may generate an alarm, terminate the polishing process, or both in response to determining that air bubbles are present.

In some embodiments, the controller 190 generates an alert in response to receiving the acoustic signal 300 (e.g., one or more of segments 322-324 in the signal 300). Examples of alerts may include an audio or visual alert displayed on a user device. Additionally or alternatively, an alert may include a notification sent to a networked device connected to the polishing system 20.

FIG4 is a flow chart illustrating a polishing method 400 for changing polishing parameters or generating an alarm in response to detected segment differences in the acoustic signal 300.

The substrate 10 is held against the polishing layer 32 of the polishing pad 30 supported by the platform 24 (step 402), for example, by pressurization of the pressurizable chamber 80 of the carrier head 70. During the polishing operation, the substrate 10 is retained beneath the carrier head 70 by the retaining ring 100 in contact with the polishing layer 32.

Relative motion is generated between the substrate 10 and the polishing layer 32 (step 404). For example, the polishing system 20 can generate at least a portion of the relative motion by operating the motor 26 to rotate the platform 24 about the axis 25. Additionally or alternatively, the polishing system 20 can generate a portion of the relative motion by operating the carrier head rotation motor 56 to rotate the carrier head 70. In some embodiments, the polishing system 20 includes a linear actuator that is used to move the drive shaft 54 along the support structure 50, thereby generating a portion of the relative motion between the substrate 10 and the polishing layer 32. Polishing fluid 38 is added to the polishing layer 32 from the supply-rinse arm 36 to enhance the polishing of the surface of the substrate 10 that contacts the polishing layer 32.

The in-situ acoustic monitoring system 160 (step 406) monitors the carrier head 70 during the polishing operation. The acoustic monitoring system 160 includes an acoustic sensor 162 disposed within the platform 24, for example, within a recess 164 of the platform 24. The acoustic sensor 162 contacts a portion of the polishing pad 30 (e.g., a surface of the backing layer 34). In some embodiments, the acoustic sensor 162 contacts the surface of the polishing layer 32. Additionally or alternatively, the polishing layer 32 and/or the backing layer 34 include an acoustic window 118 that is contacted by the acoustic sensor 162.

As the acoustic sensor 162 passes beneath the carrier head 70 along the path 102, it receives acoustic energy corresponding to contact between the retention ring 100 or substrate 10 and the polishing layer 32. This acoustic energy is received by the acoustic monitoring system 160, which generates an acoustic signal 300 that is transmitted to the controller 190.

The controller 190 receives the acoustic signal 300 and generates a carrier head state parameter value based on the received acoustic signal 300 (step 408). The controller 190 may generate the carrier head state parameter value by dividing the received acoustic signal 300 into a series of segments and determining the difference between the segments. Alternatively or additionally, the controller 190 may generate the carrier head state parameter value by determining the difference between different acoustic signals 300 received from different substrates 10. Generating the value may include the following steps 410-414.

The acoustic signal 300 is divided into a series of segments, such as segments 322-334, by the controller 190 or the acoustic monitoring system 160. Determining the difference between the segments includes the controller 190 identifying a first segment from the series of segments 322-334 corresponding to the sensor 162 being located beneath a portion of the carrier head 70 or substrate 10 (step 410). The segments 322-334 have acoustic parameter values, such as amplitude values or variation values. The amplitude/variation value of each of the segments 322-334 is compared to a corresponding threshold value of the acoustic signal received from the carrier head 70, the retention ring 100, or the substrate 10.

The controller 190 identifies a second segment from the series of segments 322-334 corresponding to the second portion of the acoustic sensor 162 located below the carrier head 70 (step 412). The second segment corresponds to a segment different from the first segment.

The controller 190 determines a difference between the selected segments (step 414). The controller 190 compares the selected first segment and the second segment and determines a difference. In some examples, the controller 190 determines the difference by subtraction, weighted averaging, or performing a mathematical process on the segments and determining a difference between the results of the mathematical process.

Based on the determined differences, the controller 190 changes polishing parameters, generates an alarm, or both (step 416). The controller 190 determines the differences between the selected segments and determines which polishing process issue is associated with the differences. Each issue can be associated with a different difference, and the association is stored in the controller 190. For example, the polishing process issue may be air bubbles trapped between the retaining ring 100 or substrate 10 and the polishing layer 32 of the pad 30. In one example, air bubbles trapped between the substrate 10 and the carrier head 70 may cause the on-wafer segment 328 to differ from historical on-wafer segments stored in the controller 190 from a previous polishing run. As an alternative or additional example, a problem with the polishing process may be with the gimbal connection of the gimbal connection mechanism 82. The problem with the gimbal connection may cause a difference in the average and/or maximum values of the leading carrier head segment 324 and the trailing carrier head segment 332.

In some embodiments, the controller 190 determines polishing parameters corresponding to the problem. For example, if air bubbles are located between the retaining ring 100 and the polishing layer 32, the controller 190 may determine to reduce the pressure of the carrier head 70 on the polishing layer 32 to a level sufficient to force the air bubbles out of the space between the retaining ring 100 and the polishing layer 32.

In some examples, controller 190 determines a difference between the leading carrier head segment 324 and the trailing carrier head segment 332. For example, if controller 190 determines that there is a difference in the amplitude of the leading carrier head segment 324 and the trailing carrier head segment 332, controller 190 may deduce that there is an error in the gimbal position of gimbal connection mechanism 82. In one example, controller 190 increases the pressure in chamber 84 to change the height of assembly 74. In another example, controller 190 increases the gas pressure in one or more pressurizable chambers 80 to indirectly change the angular orientation of assembly 74 relative to housing 72.

In additional or alternative examples, the controller 190 generates an alert based on the determined difference, which may include a visual, audio, text, or command alert transmitted to a user device, a networked device, or a component of the polishing system 20.

5 is a block diagram of an example computer system 500. System 500 includes a processor 510, a memory 520, a storage device 530, and one or more input/output interface devices 540. Each of components 510, 520, 530, and 540 can be connected to each other, for example, using a system bus 550.

Processor 510 is capable of processing instructions for execution within system 500. As used herein, the term "execution" refers to the technique by which program code causes the processor to implement one or more processor instructions. In some embodiments, processor 510 is a single-threaded processor. In some embodiments, processor 510 is a multi-threaded processor. Processor 510 is capable of processing instructions stored in memory 520 or on storage device 530. Processor 510 can perform operations such as monitoring a polishing process using the acoustic monitoring system described herein.

Memory 520 stores information within system 500. In some embodiments, memory 520 is a computer-readable medium. In some embodiments, memory 520 is a volatile memory unit. In some embodiments, memory 520 is a non-volatile memory unit.

Storage device 530 can provide mass storage for system 500. In some embodiments, storage device 530 is a non-transitory, computer-readable medium. In various embodiments, storage device 530 can include, for example, a hard drive, an optical disk, a solid-state drive, a flash drive, a magnetic tape, or some other mass storage device. In some embodiments, storage device 530 can be cloud storage, e.g., a logical storage device comprising one or more physical storage devices distributed over and accessed using a network.

Input/output interface devices 540 provide input/output operations for system 500. In some embodiments, input/output interface devices 540 may include one or more of a network interface device (e.g., an Ethernet interface), a serial communication device (e.g., an RS-232 interface), and/or a wireless interface device (e.g., an 802.11 interface, a 3G wireless modem, a 4G wireless modem, etc.). Network interface devices allow system 500 to communicate, such as transmitting and receiving data. In some embodiments, input/output devices may include drive devices configured to receive input data and send output data to other input/output devices (e.g., a keyboard, a printer, and a display device). In some implementations, mobile computing devices, mobile communication devices, and other devices may be used.

The software may be implemented as instructions that, when executed, cause one or more processing devices to perform the processes and functions described above, such as monitoring a polishing process using the acoustic monitoring system described herein. For example, the instructions may include interpreted instructions such as script instructions, executable code, or other instructions stored in a computer-readable medium.

In some examples, system 500 is contained within a single integrated circuit package. Such systems 500 in which processor 510 and one or more other components are contained within and/or fabricated as a single integrated circuit are sometimes referred to as microcontrollers. In some embodiments, the integrated circuit package includes pins corresponding to input/output ports (e.g., pins that can be used to transmit signals to and from one or more input/output interface devices 540).

Although an example processing system is described in FIG5 , the subject matter and functional operations described above may also be implemented in other types of digital electronic circuit systems, or in computer software, firmware, or hardware (including the structures disclosed in this specification and their structural equivalents), or in a combination of one or more of the foregoing. The subject matter described in this specification (e.g., storing, maintaining, or displaying artifacts) may be implemented as one or more computer program products, i.e., one or more computer program instruction modules encoded on a tangible program carrier (e.g., a computer-readable medium) for execution by a processing system or for controlling the operation of the processing system. The computer-readable medium can be a machine-readable storage device, a machine-readable storage substrate, a memory device, or a combination of one or more of the above.

The term "system" may encompass all devices, equipment, and machinery used to process data, including, for example, a programmable processor, a computer, multiple processors, or computers. In addition to hardware, a processing system may also include the code that creates the execution environment for the associated computer program, such as the code that constitutes the processor's firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of these.

A computer program (also called a program, software, software application, script, executable logic, or code) can be written in any programming language (including compiled or interpreted languages, or declarative or procedural languages), and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file in a file system. A program may be stored as part of a file that contains other programs or data (such as one or more scripts stored in a markup language file), in a single file dedicated to the program in question, or in multiple coordinated files (such as files storing one or more modules, subroutines, or portions of code). A computer program may be deployed to execute on a single computer or on multiple computers located at one site or distributed across multiple sites and interconnected by a communications network.

Computer-readable media suitable for storing computer program instructions and data include all forms of non-volatile or volatile memory, media, and memory devices. Examples include semiconductor memory devices such as EPROM, EEPROM, and flash memory devices; magnetic disks, such as internal hard drives or removable disks or tapes; magneto-optical disks; and CD-ROMs, DVD-ROMs, and Blu-ray Discs. The processor and memory may be assisted by or incorporated into special-purpose logic circuitry. Servers are sometimes general-purpose computers, sometimes custom special-purpose electronic devices, and sometimes a combination of these.

While this specification contains many details, these details should not be construed as limitations on the scope of what may be claimed, but rather as descriptions of features specific to particular embodiments. Certain features described in this specification in the context of separate embodiments may also be combined. Conversely, various features described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable subcombination.

10: Substrate 20: Polishing System 24: Platform 25: Shaft 26: Motor 28: Drive Shaft 30: Polishing Pad 32: Polishing Layer 34: Backing Layer 35: Groove 36: Supply-Rinse Arm 38: Polishing Fluid 40: Pad Adjustment Device 42: Adjustment Plate 44: Arm 50: Support Structure 54: Drive Shaft 56: Carrier Head Rotation Motor 58: Shaft 70: Carrier Head 72: Housing 74: Assembly 76: Base 78: Flexible Membrane 80: Pressurizable Chamber 82: Universal joint mechanism 84: Loading chamber 100: Retention ring 102: Path 104: Path portion 106: Path portion 108: Path portion 110: Path portion 112: Path portion 118: Window 124: Direction 160: Acoustic monitoring system 162: Acoustic sensor 164: Recess 166: Signal processing electronics 168: Circuit system 190: Controller 300: Acoustic signal 322: Segment 324: Segment 326: Segment 328: Segment 332: Segment 334: Segment 400: Method 402: Step 404: Step 406: Step 408: Step 410: Step 412: Step 414: Step 416: Step 500: System 510: Processor 520: Memory 530: Storage Device 540: Input/Output Interface Device 550: System Bus

Figure 1 is a schematic side view of a polishing system including an in-situ acoustic monitoring system.

FIG2 is a schematic top view of a substrate being polished on a polishing pad, along with a schematic path followed by an acoustic sensor during the polishing operation and a schematic acoustic signal generated as the sensor moves along the schematic path.

FIG3 is a diagram of an example acoustic signal and segments corresponding to different portions of a ring assembly or substrate.

FIG4 is a flow chart of an example method of a polishing process.

FIG5 is a system diagram of an example computing system.

In the drawings, like reference symbols indicate like elements.

Domestic storage information (please note the storage institution, date, and number in order) None

Overseas Storage Information (Please note the storage country, institution, date, and number in order) None

10:Substrate

24: Platform

30: Polishing pad

100: Retention Ring

102: Path

104: Path section

106: Path section

108: Path section

110: Path section

112: Path section

124: Direction

162: Sonic Sensor

300: Sonic signal

Claims (18)

A chemical mechanical polishing apparatus comprises: a platform for supporting a polishing pad, the platform having a recess; a carrier head for holding a surface of a substrate against the polishing pad, wherein the carrier head comprises a retaining ring for fixing the substrate below the carrier head; a motor for generating relative motion between the platform and the carrier head so as to polish the substrate; an in-situ acoustic wave monitoring system comprising An acoustic sensor disposed in the recess receives acoustic energy from friction between the substrate and the polishing pad and from friction between the retaining ring and the polishing pad; and a controller configured to: generate a value of a carrier head status parameter based on the acoustic signal received from the in-situ acoustic monitoring system, the value indicating an error, and change a polishing parameter or generate an alarm based on the carrier head status parameter. The apparatus of claim 1, wherein the polishing parameter includes one or more of: an amount of gimbaling of the carrier head, whether a chamber in the carrier head is properly pressurized, the presence of an air bubble between the substrate and the carrier head, or whether the substrate is clamped to the carrier head. The device of claim 1, wherein the acoustic wave sensor is attached to a bottom surface of the polishing pad. The device of claim 1, wherein the polishing pad includes a sound window, and the sound wave sensor contacts a bottom surface of the sound window. The device of claim 1, wherein the controller is further configured to determine a difference between at least two different portions of the acoustic signal. The device of claim 5, wherein the controller is further configured to generate an alarm based on the difference exceeding a threshold. The apparatus of claim 6, wherein the controller is further configured to determine a difference between the acoustic signal and a historical acoustic signal from a previous substrate, wherein the historical acoustic signal is stored on the controller. The device of claim 1, wherein the controller is further configured to determine a difference in the acoustic signal from a first portion and a second portion of a surface of the retention ring. A polishing method includes the following steps: holding a substrate against a polishing surface of a polishing pad with a carrier head; inducing relative motion between the substrate and the polishing pad such that an in-situ acoustic monitoring system passes beneath the carrier head; monitoring the carrier head with the in-situ acoustic monitoring system directed beneath the polishing pad to generate a signal comprising a series of segments; and identifying a signal from the series of segments. a first segment corresponding to a sensor of the in-situ acoustic monitoring system located beneath a first portion of the carrier head; identifying a second segment from the series of segments, the second segment corresponding to the sensor located beneath a second portion of the carrier head; determining a difference between the first segment and the second segment; and altering a polishing parameter or generating an alarm based on the determined difference. The method of claim 9, wherein the first portion and the second portion of the carrier head are a first portion and a second portion of a ring assembly of the carrier head. The method of claim 9, wherein the polishing parameter is a pressure of the carrier head. The method of claim 9 further comprises the step of detecting, based on the signal, that the substrate leaves the polishing surface of the polishing pad. The method of claim 9 further comprises the step of detecting the presence of a bubble based on the signal. A computer program product comprising a non-transitory computer-readable medium having instructions for causing one or more computers to: hold a substrate against a polishing surface of a polishing pad with a carrier head; induce relative motion between the substrate and the polishing pad such that an in-situ acoustic monitoring system passes beneath the carrier head; and monitor the carrier head with the in-situ acoustic monitoring system oriented beneath the polishing pad to generate a signal. The signal includes a series of segments; identifying a first segment from the series of segments, the first segment corresponding to a sensor of the in-situ acoustic monitoring system being located beneath a first portion of the carrier head; identifying a second segment from the series of segments, the second segment corresponding to the sensor being located beneath a second portion of the carrier head; determining a difference between the first segment and the second segment; and based on the determined difference, changing a polishing parameter or generating an alarm. The computer program product of claim 14, wherein the first portion and the second portion of the carrier head are a first portion and a second portion of a retaining ring of the carrier head. The computer program product of claim 14, wherein the polishing parameter is a pressure of the carrier head. The computer program product of claim 14 further comprises the step of detecting, based on the signal, that the substrate leaves the polishing surface of the polishing pad. The computer program product of claim 14 further comprises the step of detecting the presence of a bubble based on the signal.