Polishing head with retaining ring wear sensing

Abstract

A carrier head for chemical mechanical polishing is disclosed, the carrier head comprising a housing for attachment to a drive shaft. The housing comprises an upper carrier body to be attached to a vertically stationary drive shaft and a lower carrier body vertically movable relative to the upper carrier body, the lower carrier body configured to be fixed to and suspended a retaining ring. A first flexible seal forms a loading chamber between the upper carrier body and the lower carrier body. A diaphragm assembly is arranged underneath the lower carrier body and comprises a diaphragm support and a flexible diaphragm fixed to the diaphragm support to form one or more lower pressurizable chambers. A second flexible seal forms an upper pressurizable chamber between the lower carrier body and the diaphragm support, and a sensor is fixed to the housing and configured to measure a distance between the upper carrier body and the lower carrier body.

Description

Technical Field

[0001] This disclosure relates to a carrier head for chemical mechanical polishing (CMP) and to sensing wear of a retaining ring. Background Technology

[0002] Integrated circuits are typically formed on a substrate by sequentially depositing conductive layers, semiconductor layers, or insulating layers on a semiconductor wafer. A wide variety of manufacturing processes require planarization of the layers on the substrate. For example, one manufacturing step involves depositing a filler layer on a non-planar surface and planarizing that filler layer. For some applications, the filler layer is planarized until the top surface of the patterned layer is exposed. For example, a metal layer may be deposited on a patterned insulating layer to fill trenches and holes in the insulating layer. After planarization, the remaining metal in the trenches and holes of the patterned layer forms vias, plugs, and lines to provide conductive paths between thin-film circuits on the substrate. As another example, a dielectric layer may be deposited on a patterned conductive layer and then planarized for subsequent photolithography steps.

[0003] Chemical mechanical polishing (CMP) is a recognized planarization method. This planarization method typically requires mounting a substrate on a carrier 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 to push it against the polishing pad. A polishing slurry containing abrasive particles is typically supplied to the surface of the polishing pad.

[0004] The substrate is typically held below the carrier head by a retaining ring. As the retaining ring is pressed against the polished surface, it also wears and eventually needs to be replaced. Summary of the Invention

[0005] In one aspect, a carrier head for chemical mechanical polishing includes a housing for attachment to a drive shaft. The housing includes an upper carrier body attached to a vertically stationary drive shaft and a lower carrier body movable vertically relative to the upper carrier body, the lower carrier body being configured to be fixed to and suspend a retaining ring. A first flexible seal forms a loading chamber between the upper and lower carrier bodies. A diaphragm assembly is disposed below the lower carrier body and includes a diaphragm support and a flexible diaphragm fixed to the diaphragm support to form one or more lower pressurizable chambers. A second flexible seal forms an upper pressurizable chamber between the lower carrier body and the diaphragm support, and a sensor is fixed to the housing and configured to measure the distance between the upper and lower carrier bodies.

[0006] On the other hand, a chemical mechanical polishing system includes: a platform; a motor having a vertically fixed drive shaft; a carrier head; a sensor; and a controller. The carrier head includes: a retaining ring; a housing having an upper carrier body attached to the drive shaft and a lower carrier body vertically movable relative to the upper carrier body, the lower carrier body being fixed to and suspending the retaining ring; a first flexible seal forming a loading chamber between the upper and lower carrier bodies; a diaphragm assembly disposed below the lower carrier body and having a diaphragm support and a flexible diaphragm fixed to the diaphragm support to form one or more lower pressurizable chambers; and a second flexible seal forming an upper pressurizable chamber between the lower carrier body and the diaphragm support. The sensor is fixed to the housing and configured to measure the distance between the upper carrier body and the lower carrier body, and the controller is configured to receive the measurement result from the sensor and, based on the measurement result, perform at least one of the following: i) determine whether the retaining ring should be replaced, or ii) determine the adjustment of the pressure in the loading chamber or the upper pressurizable chamber.

[0007] The advantages of the foregoing may optionally include, but are not limited to, the following: The lifespan of the retaining ring can be determined more accurately. Process control parameters can be adjusted to account for changes in the polishing rate profile due to retaining ring wear, thereby improving inter-wafer uniformity.

[0008] Details of one or more implementations are set forth in the accompanying drawings and the following description. Other aspects, features, and advantages will become apparent from the specification, the accompanying drawings, and the claims.

[0009] This invention relates to a carrier head for use in chemical mechanical polishing (CMP). Attached Figure Description

[0010] Figure 1 This is a schematic cross-sectional view of an example of a polishing device.

[0011] Figure 2 This is a schematic cross-sectional view of the carrier head.

[0012] This invention relates to a carrier head for use in chemical mechanical polishing (CMP). Detailed Implementation

[0013] Retaining rings are typically made of wear-resistant plastic. During the polishing process of many substrates (e.g., one hundred to five hundred substrates), the retaining rings wear and thin, eventually requiring replacement. However, the wear rate, and therefore the exact time when the retaining rings need to be replaced, depends on the polishing process and can vary depending on the type of retaining ring. Therefore, a technique is desired to monitor the thickness of the retaining rings.

[0014] One method for monitoring the thickness of the plastic retaining ring is to use an eddy current sensor embedded in the stage plate to sense eddy currents in the metal backing ring. Two potential problems here are that this technique is often affected by noise, and the method may not work if the plastic portion is too thick or there is no metal backing ring. Another method is to measure the vertical position of the loading cup during loading. The loading cup stops when it contacts the bottom surface of the retaining ring, and therefore the displacement will depend on the retaining ring thickness. A potential problem here is that external sensors are sensitive to environmental influences (e.g., the presence of water or slurry in the loading cup), which can interfere with the measurement results, and sensors integrated into the actuator itself may be unreliable.

[0015] One possible solution is to have the carrier head press the substrate against the polishing pad, and then use an internal sensor to measure the distance between the vertically stationary component fixed to the drive shaft and the carrier body that holds the component.

[0016] In some polishing systems, a diaphragm in the carrier head is used to apply pressure to the substrate during polishing. For example, a chamber above the diaphragm assembly can be pressurized to push the diaphragm against the substrate. However, as the retaining ring of the carrier head wears, the load on the substrate increases, leading to inhomogeneities between wafers. For instance, as the retaining ring wears, the deflection of the flexure connecting the diaphragm assembly to the carrier head increases, resulting in greater downforce on the diaphragm assembly, which in turn increases the load on the flexible diaphragm and the substrate. One possible solution is to adjust the chamber pressure applied to the diaphragm assembly to compensate for any changes in downforce from the flexure, so that the total load on the substrate remains relatively constant. Measurements of the distance between the housing and the carrier body holding the retaining ring can be used as a basis for selecting and adjusting the chamber pressure.

[0017] Figure 1 An example of a chemical mechanical polishing apparatus 100 is shown. The polishing apparatus 100 includes a rotatable disc-shaped stage 120 on which a polishing pad 110 is located. The stage is operable to rotate about an axis 125. For example, a motor 121 (e.g., a DC induction motor) can rotate a drive shaft 124 to rotate the stage 120.

[0018] The polishing pad 110 may be a two-layer polishing pad having an outer polishing layer 112 and a softer backing layer 114. In some implementations, a plurality of slurry transport grooves 116 are formed in the top surface of the polishing layer 112 of the polishing pad 110.

[0019] The polishing apparatus 100 may include a port 130 for dispensing polishing liquid 132, such as an abrasive slurry, onto the polishing pad 110. The polishing apparatus may also include a polishing pad dresser for abrading the polishing pad 110 to maintain the polishing pad 110 in a consistent abrasive state.

[0020] The polishing apparatus 100 includes at least one carrier head 140. The carrier head 140 is operable to hold the substrate 10 against the polishing pad 110 with controlled pressure, for example, during a polishing process.

[0021] The carrier head 140 may include a retaining ring 142 to hold the substrate 10 below the flexible diaphragm 144. The carrier head 140 also includes one or more independently controllable pressurizable chambers 146 defined by the diaphragm, for example, three chambers 146a-146c, which can apply independently controllable pressure to associated areas on the flexible diaphragm 144, and thereby to the substrate 10. Although for ease of illustration, Figure 1 Only three chambers 146a-146c are shown, but there may still be one or two chambers, or four or more chambers, such as five chambers.

[0022] The carrier head 140 is suspended from a support structure 150 (e.g., a carousel or track) and connected to a carrier head rotation motor 154 (e.g., a DC induction motor) by a drive shaft 152, allowing the carrier head to rotate about axis 155. Optionally, each carrier head 140 may oscillate laterally, for example, on a slider on the support structure 150, or by rotational oscillation of the carousel itself, or by sliding along the track. In typical operation, the platform rotates about its central axis 125, and each carrier head rotates about its central axis 155 and laterally translates across the top surface of the polishing pad.

[0023] A controller 190, such as a programmable computer, is connected to motors 121 and 154 to control the rotational speed of control panel 120 and carrier head 140.

[0024] See Figure 2 The carrier head 140 includes a housing 102 having an upper carrier body 104 and a lower carrier body 106, a universal joint mechanism 108 (which can be considered as part of the lower carrier body 106), a retaining ring 142 attached to the lower carrier body 106, and a diaphragm assembly 500.

[0025] The volume between the lower carrier body 106 and the upper carrier body 104 can be sealed by the upper flexible seal 164 to provide a loading chamber 111. The upper flexible seal 164 is flexible to accommodate changes in the vertical position between the upper carrier body 104 and the lower carrier body 106.

[0026] The upper carrier body 104 is fixed to the drive shaft 152 to rotate the entire carrier head 140. The upper carrier body 104 may generally be circular in shape. A passage extending through the upper carrier body 104 may be present for pneumatic control of the carrier head 140. The lower carrier body 106 is located below the upper carrier body 104 and is vertically movable relative to the upper carrier body 104. A loading chamber 111 is located between the upper carrier body 104 and the lower carrier body 106 to apply a load, i.e., downward pressure or weight, to the lower carrier body 106. The vertical position of the lower carrier body 106 relative to the polishing pad is also controlled by the loading chamber 111. In some embodiments, the vertical position of the lower carrier body 106 relative to the polishing pad is controlled by an actuator.

[0027] The universal joint mechanism 108 allows the lower carrier body 106 to move in all directions and vertically relative to the upper carrier body 104, while preventing lateral movement of the lower carrier body 106 relative to the upper carrier body 104. However, in some implementations, the universal joint is not present.

[0028] The substrate 10 is held beneath the carrier head 140 by a retaining ring 142, which holds the substrate 10 to prevent lateral movement. The retaining ring 142 also provides active edge process control; controlling the pressure on the polishing pad in a region outside the substrate but adjacent to the substrate edge can affect the polishing rate at the substrate edge. Some implementations may include an outer ring that provides positioning or reference of the carrier head relative to the surface of the polishing pad.

[0029] The volume between the lower carrier body 106 and the diaphragm assembly 500 can be sealed by a lower flexible seal 162 to form an upper pressurized chamber 134. This lower flexible seal 162 is flexible to accommodate changes in the vertical position between the lower carrier body 106 and the diaphragm assembly 500. The pressure in the upper pressurized chamber can control the downward load on the diaphragm assembly 500 and / or the vertical position of the diaphragm assembly 500 relative to the housing.

[0030] The diaphragm assembly 500 may include a diaphragm support 138 and a flexible diaphragm 144. The diaphragm support 138 may be formed of a material more rigid than the diaphragm 144, such as metal, ceramic, or hard plastic. The flexible diaphragm 144 has a circular lower portion 170 having a lower outer surface that provides a mounting surface for a substrate. The flexible diaphragm 144 also has a plurality of flaps 172 (e.g., annular flaps) extending from the inner surface of the diaphragm to define individually controllable pressurizable chambers 146. For example, the ends of the flaps 172 may be clamped to the diaphragm support 138.

[0031] In some implementations, the flexible diaphragm 144 is directly fixed to the lower carrier body 106. In this case, the lower carrier body 106 serves as a diaphragm support, and there is no upper pressurizable chamber.

[0032] Each chamber in the carrier head 140 can be fluidly coupled to an associated pressure source (e.g., pressure sources 922, 924, 926), such as a pump or pressure or vacuum line, via a passage through the upper carrier body 104 and the lower carrier body 106. One or more passages may exist for each of the loading chamber 111, the upper pressurizable chamber 134, and the lower pressurizable chamber 146. One or more passages from the lower carrier body 106 can be connected to passages in the upper carrier body 104 via flexible tubing extending inside the loading chamber 111 or outside the carrier head 140. Pressurization of each chamber can be controlled independently. Specifically, pressurization of each chamber 146 can be controlled independently. This allows for the application of different pressures to different radial regions of the substrate 10 during polishing, thereby compensating for uneven polishing rates.

[0033] The controller 190 regulates the pressure in various chambers of the carrier head 140. The controller 190 is coupled to multiple pressure sources, such as pressure sources 922, 924, and 926. Pressure sources 922, 924, and 926 may be, for example, pumps, facility gas lines, and controllable valves. Each of the pressure sources 922, 924, and 926 can be individually connected to a pressurizable chamber.

[0034] Sensor 930 measures the pressure in pressure sources 922, 924, 926, the individually pressurizable lower chamber 146, the pressurizable upper chamber 134, and the loading chamber 111. Sensor 930 transmits the measured pressure to controller 190. Controller 190 causes pressure sources 922, 924, 926 to increase and / or decrease the pressure in loading chamber 111, pressurizable lower chamber 146, and / or pressurizable upper chamber 134.

[0035] During the polishing operation performed on the carrier head 140, the retaining ring 142 wears down, and the total thickness T of the retaining ring decreases.

[0036] To monitor the thickness of the retaining ring 142, sensor 950 can measure the distance or change in distance from the upper carrier body 104 to the lower carrier body 106. Sensor 950 can be fixed to the upper carrier body 104, for example, fixed in a recess in the bottom surface of the upper carrier body 104 or attached to the bottom surface of the upper carrier body 104. Sensor 950 is positioned to measure the distance between sensor 950 and target 952. For example, target 952 can be part of the top surface of the lower carrier body 106. Alternatively, sensor 950 can be fixed to the lower carrier body 106, for example, fixed in a recess in the top surface of the lower carrier body 106 or attached to the top surface of the lower carrier body 106, and target 952 can be part of the bottom surface of the upper carrier body 104.

[0037] Sensor 950 may be a non-contact sensor that guides beam 954 to the target, such as an inductively coupled sensor, a capacitively coupled sensor, or a laser displacement sensor. Target 952 may be adapted to enhance sensor 950, for example, it may be a conductive region for an inductively coupled sensor or a reflective surface for a laser displacement sensor.

[0038] Alternatively, sensor 950 may be a contact sensor or a linear variable differential transformer (LVDT). Contact sensors are typically more sensitive and susceptible to environmental conditions, but this option is feasible because sensor 950 is located within an environmentally protected area inside carrier head 140.

[0039] During operation, chamber 111 is pressurized to push the lower carrier body 106 and retaining ring 142 downwards until the bottom surface 142a of retaining ring 142 contacts polishing pad 110. When retaining ring 142 contacts the pad, the distance between sensor 950 and target 952 is measured. Since drive shaft 152 and upper carrier body 104 are in a fixed vertical position, this ensures consistent distance measurement between upper carrier body 104 and lower carrier body 106.

[0040] Additionally, sensor 950 is connected to controller 190 and reports to controller 190 the measured distance or changes in the measured distance (e.g., a reduction in distance due to wear of retaining ring 142).

[0041] The measured distance can be subtracted from a predetermined initial thickness (e.g., the thickness of retaining ring 142 before it is attached to the carrier head for polishing) to provide the current thickness of the retaining ring. If the thickness of retaining ring 142 drops below a minimum retaining ring thickness value, controller 190 can generate an alarm indicating that retaining ring 142 needs to be replaced. Alternatively, if the measured distance exceeds the maximum variation in thickness value, controller 190 can generate an alarm indicating that retaining ring 142 needs to be replaced.

[0042] The controller 190 may also be configured to cause pressure source 922 to adjust the pressure in loading chamber 111, or pressure source 926 to adjust the pressure in upper pressurizable chamber 134, or both, to maintain the load on substrate 10 and retaining ring 142. Specifically, the controller 190 may be configured to reduce the pressure in upper pressurizable chamber 134 as the retaining ring wears and thins. For example, the controller 190 may include a lookup table that provides the pressure or pressure offset of upper pressurizable chamber 134 as a function of retaining ring thickness. The pressure offset may be subtracted from a desired pressure calculated by some other algorithm (e.g., a desired pressure calculated to control the polishing rate).

[0043] The controller and other computing device portions of the system described herein may be implemented in a digital electronic circuit system or in computer software, firmware, or hardware. For example, the controller may include a processor to execute a computer program stored in a computer program product (e.g., in a non-transitory machine-readable storage medium). Such a computer program (also referred to as a program, software, software application, or code) may be written in any form of programming language, including compiled or interpreted languages, and may be deployed in any form, including as a standalone program or as a module, component, subroutine, or other unit suitable for use in a computing environment.

[0044] In the context of a controller, “configuration” indicates that the controller has the necessary hardware, firmware, or software or combination thereof to perform the desired function during operation (as opposed to simply being programmable to perform the desired function).

[0045] While this document contains numerous specific implementation details, these should not be construed as limiting the scope of any invention or claimable protection, but rather as descriptions of features specific to particular embodiments of a particular invention. Certain features described in the context of individual embodiments in this document may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented individually or in any suitable sub-combination in multiple embodiments. Furthermore, although features may be described above as functioning in certain combinations and even initially claimed in this way, in some cases, one or more features from a claimed combination may be removed from that combination, and the claimed combination may involve sub-combinations or variations thereof.

[0046] Several embodiments of the invention have been described. However, it will be understood that various modifications can be made without departing from the spirit and scope of the invention. Therefore, other implementations are within the scope of the appended claims.

Claims

1. A carrier head for chemical mechanical polishing, comprising: A housing for attachment to a drive shaft, wherein the housing includes an upper carrier body attached to a vertically stationary drive shaft and a lower carrier body movable vertically relative to the upper carrier body, the lower carrier body being configured to be fixed to and suspend a retaining ring; A first flexible seal forms a loading chamber between the upper carrier body and the lower carrier body; A diaphragm assembly disposed below the lower carrier body, the diaphragm assembly including a diaphragm support and a flexible diaphragm fixed to the diaphragm support to form one or more lower pressurizable chambers; The second flexible seal forms an upper pressurizable chamber between the lower carrier body and the diaphragm support. as well as A sensor, fixed to the housing and configured to measure the distance between the upper carrier body and the lower carrier body.

2. The carrier head of claim 1, wherein the sensor is fixed to the upper carrier body and configured to sense the distance between the sensor and the target on the lower carrier body.

3. The carrier head as claimed in claim 2, wherein the target is the top surface of the lower carrier body.

4. The carrier head as claimed in claim 3, wherein the sensor is an optical sensor and the target is reflective.

5. The carrier head of claim 1, wherein the sensor is fixed to the lower carrier body and configured to sense the distance between the sensor and the target on the upper carrier body.

6. The carrier head as claimed in claim 5, wherein the target is the bottom surface of the upper carrier body.

7. The carrier head of claim 6, wherein the sensor is an optical sensor and the target is reflective.

8. The carrier head as claimed in claim 1, wherein the sensor is a non-contact sensor.

9. The carrier head as claimed in claim 8, wherein the sensor is an inductively coupled sensor or a capacitively coupled sensor.

10. The carrier head as claimed in claim 1, wherein the sensor is a laser displacement sensor.

11. The carrier head as claimed in claim 1, wherein the sensor is a contact sensor.

12. The carrier head of claim 11, wherein the sensor is a linear variable differential transformer (LVDT).

13. A chemical mechanical polishing system, comprising: tabletop; A motor having a vertically fixed drive shaft; The carrier head includes Keep the ring, The housing includes an upper carrier body attached to the drive shaft and a lower carrier body movable vertically relative to the upper carrier body, the lower carrier body being fixed to and suspending the retaining ring. A first flexible seal forms a loading chamber between the upper carrier body and the lower carrier body. A diaphragm assembly, disposed below the lower carrier body, includes a diaphragm support and a flexible diaphragm fixed to the diaphragm support to form one or more lower pressurizable chambers. A second flexible seal forms an upper pressurizable chamber between the lower carrier body and the diaphragm support. A sensor, fixed to the housing and configured to measure the distance between the upper carrier body and the lower carrier body; as well as A controller configured to receive measurement results from the sensor and, based on the measurement results, perform at least one of the following: i) determining whether the retaining ring should be replaced, or ii) determining an adjustment of the pressure in the loading chamber or the upper pressurizable chamber.

14. The system of claim 13, wherein the controller is configured to determine the retaining ring thickness based on the measurement results from the sensor, and to determine whether the retaining ring thickness has fallen below a threshold, and to generate an alarm if the retaining ring thickness is determined to have fallen below the threshold.

15. The system of claim 13, wherein the controller is configured to determine whether the measured distance exceeds a threshold, and if it is determined that the measured distance exceeds the threshold, generate an alarm.

16. The system of claim 13, wherein the sensor is fixed to the upper carrier body and configured to sense the distance between the sensor and a target on the lower carrier body.

17. The system of claim 13, wherein the sensor is fixed to the lower carrier body and configured to sense the distance between the sensor and the target on the upper carrier body.

18. The system of claim 13, wherein the sensor is an inductively coupled sensor, a capacitively coupled sensor, or a laser displacement sensor.

19. The system of claim 13, wherein the sensor is a linear variable differential transformer (LVDT).

20. The system of claim 13, wherein the controller is configured to determine, based on wear of the retaining ring, an adjustment of the pressure in the loading chamber or the upper pressurizable chamber to compensate for changes in load on the diaphragm assembly.

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