Polishing head with membrane position control

Abstract

To provide a carrier head improving uniformity between wafers in a chemical mechanical polishing.SOLUTION: A carrier head for chemical mechanical polishing includes a carrier body and a membrane assembly beneath the carrier body and vertically movable to the carrier body, the membrane assembly including a membrane support body and a flexible membrane fixed to the membrane support and hanging from the membrane support. A space between the carrier body and the membrane assembly above the membrane support provides a first pressurizable chamber. The flexible membrane is provided with a sensor which is supported by a membrane assembly defining a second pressurizable chamber beneath the membrane support and the carrier body, and is configured to measure a distance from the sensor to the membrane support of the membrane assembly.SELECTED DRAWING: Figure 1B

Description

[Technical field]

[0001] The present invention relates to a carrier head for use in chemical mechanical polishing (CMP). [Background technology]

[0002] Integrated circuits are generally formed on a substrate by successively depositing layers of conductive, semiconductive, or insulative materials on a semiconductor wafer. Various manufacturing processes require planarization of layers on the substrate. For example, one manufacturing process involves depositing a filler layer over 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 metal layer can be deposited on a patterned insulating layer to fill the trenches and holes in the insulating layer. After planarization, the portions of metal remaining in the trenches and holes of the patterned layer form vias, plugs, and lines to provide conductive paths between thin film circuits on the substrate. As another example, a dielectric layer can be deposited on a patterned conductive layer and then planarized to allow for subsequent photolithography steps.

[0003] Chemical mechanical polishing (CMP) is one accepted planarization method. Typically, this planarization method requires that the substrate be mounted on a carrier head. The exposed surface of the substrate is typically placed in contact with a rotating polishing pad. The carrier head provides a controllable load on the substrate to press the substrate against the polishing pad. Typically, an abrasive slurry having abrasive particles is supplied to the surface of the polishing pad. Summary of the Invention

[0004] In one aspect, a carrier head for chemical mechanical polishing includes a housing for attachment to a driver shaft, a membrane assembly underlying the housing, a space between the housing and the membrane assembly defining a pressurizable chamber, and a sensor in the housing configured to measure a distance from the sensor to the membrane assembly.

[0005] In another aspect, a chemical mechanical polishing system includes a platen supporting a polishing pad, a carrier head, and a controller. The carrier head includes a housing for attachment to a driver shaft, a membrane assembly below the housing, a space between the housing and the membrane assembly defining a pressurizable chamber, and a sensor in the housing configured to measure a distance from the sensor to the membrane assembly. The controller is configured to receive measurements from the sensor and to control a pressure source to pressurize the pressurizable chamber based on the measurements.

[0006] Advantages of the above-described configuration include, but are not limited to, the following: The sensor can detect changes in distance between the sensor and a target on the membrane assembly, for example due to wear of the retaining ring. The controller can reduce pressure in a chamber above the membrane assembly to maintain a consistent load on the substrate throughout multiple polishing operations, thus improving wafer-to-wafer uniformity.

[0007] The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other aspects, features, and advantages will become apparent from the description and drawings, and from the claims. [Brief description of the drawings]

[0008] [Figure 1A] 2 is a schematic cross-sectional view of a carrier head. [Figure 1B]1B is a schematic cross-sectional view of a portion of the carrier head of FIG. 1A. [Figure 1C] 1B is a schematic cross-sectional view of a portion of the carrier head of FIG. 1A. [Diagram 2] 13 is a schematic cross-sectional view of another embodiment of a carrier head. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] In some polishing systems, a membrane in a carrier head is used to apply pressure to the substrate during the polishing process. For example, the chamber above the membrane assembly can be pressurized to press the membrane against the substrate. However, as the retaining ring of the carrier head wears, the load on the substrate can increase, resulting in wafer-to-wafer non-uniformity. For example, as the retaining ring wears, the displacement of the flexures connecting the membrane assembly to the carrier head can increase, resulting in a larger downforce on the membrane assembly. This downforce increases the load on the substrate. A possible solution is to adjust the chamber pressure on the membrane assembly to compensate for any changes in the downforce from the flexures so that the total load on the substrate remains relatively constant.

[0010] A further problem, however, is that the actual down force exerted by the flexure on the membrane assembly is not easily measured directly. However, the distance from a sensor on the carrier head to the membrane assembly can be measured. As the measured distance decreases, the chamber pressure can be decreased, reducing the change in load on the substrate. This can reduce wafer-to-wafer non-uniformity caused by sustained ring wear. The retaining ring can then have a longer life before needing replacement.

[0011] 1A-1C, a substrate 10 may be polished by a chemical mechanical polishing (CMP) apparatus having a carrier head 100. The carrier head 100 includes a housing 102 having an upper carrier body 104 and a lower carrier body 106, a gimbal mechanism 108 (which may be considered part of the lower carrier body 106), a loading chamber 110, a retaining ring assembly (described below) connected to the housing 102 (e.g., connected to the upper carrier body 104 and / or the lower carrier body 106), an outer ring 400 connected to the housing 102 (e.g., connected to the upper carrier body 104 and / or the lower carrier body 106), and a membrane assembly 500. In some embodiments, the upper carrier body 104 and the lower carrier body 106 are replaced by a single body. In some embodiments, there is only a single ring and no retaining ring 205 or outer ring 400.

[0012] The upper carrier body 104 is fixed to a rotatable driver shaft, allowing the entire carrier head 100 to rotate. The upper carrier body 104 may be generally circular. There may be passages extending through the upper carrier body 104 for pneumatic control of the carrier head 100. The lower carrier body 106 is located below the upper carrier body 104 and is vertically movable relative to the upper carrier body 104. The loading chamber 110 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 110. In some embodiments, the vertical position of the lower carrier body 106 relative to the polishing pad is controlled by an actuator.

[0013] The gimbal mechanism 108 prevents lateral movement of the lower carrier body 106 relative to the upper carrier body 104, while allowing gimbaling and vertical movement of the lower carrier body 106 relative to the upper carrier body 104. However, in some embodiments there is no gimbal.

[0014] The substrate 10 may be retained by a retaining ring 205. The retaining ring assembly 200 may include a retaining ring 205 and a flexible membrane 300 shaped to provide an annular chamber 350 to control pressure on the retaining ring 205. The retaining ring 205 may be disposed below the flexible membrane 300 and secured thereto by, for example, a clamp 250. The load on the retaining ring 205 provides a load on the polishing pad 30. An independent load on the retaining ring 205 may allow for a constant load on the pad as the ring wears.

[0015] The retaining ring 205 may be configured to retain the substrate 10 and provide active edge process control, while the outer ring 400 may provide positioning or referencing of the carrier head relative to the surface of the polishing pad.

[0016] Each chamber of the carrier head may be fluidly connected to an associated pressure source (e.g., pressure source 922) by a passage through the upper carrier body 104 and the lower carrier body 106. The pressure source may be, for example, a pump or a pressure or vacuum line. There may be one or more passages for the annular chamber 350 of the flexible membrane 300, for the loading chamber 110, for the lower pressurizable chamber 722, and for each of the individually pressurizable inner chambers 650. One or more passages from the lower carrier body 106 may be linked to multiple passages in the upper carrier body 104 by flexible tubing that runs inside the loading chamber 110 or outside the carrier head 100. Pressurization of each chamber may be independently controlled. In particular, pressurization of each chamber 650 may be independently controlled. This allows different pressures to be applied to different radial regions of the substrate 10 during the polishing process, thereby compensating for non-uniform polishing rates.

[0017] The membrane assembly 500 can include a membrane support 716, an outer membrane 700, and an inner membrane 600. The outer membrane 700 has an inner surface 702 that can be placed in contact with the inner membrane 600 and an outer surface 704 that can provide a mounting surface for the substrate 10. A flap 734 of the outer membrane 700 can be secured to the membrane support 716 and can have a lip 714 clamped between the membrane support 716 and a clamp 736. The clamp 736 can be secured to the lower carrier body 106 by fasteners, screws, bolts, or other similar fasteners. The flap 734 can separate a lower pressurizable chamber 722 from a chamber 724. The lower pressurizable chamber 722 is configured to extend across the bottom of the inner membrane 600 and the entire side of the inner membrane 600. The inner membrane 600 is located between the lower pressurizable chamber 722 and the membrane support 716. An upper pressurizable chamber 726 is formed by the membrane assembly 500 (including the membrane support 716) and the lower carrier body 106. The upper pressurizable chamber 726 is sealed off from a chamber 728 above the flexures 900 (which may vent to the outside of the carrier head 100) by a flexure 900.

[0018] The outer membrane 700 can apply a downward pressure to most or all of the substrate 10. The pressure in the lower pressurizable chamber 722 can be controlled such that the outer surface 704 of the outer membrane 700 applies pressure to the substrate 10.

[0019] Optionally, the inner membrane 600 can define multiple individually pressurizable chambers 650 that can move vertically relative to each other. (i.e., each of the individually pressurizable chambers 650 can move vertically relative to the other individually pressurizable chambers 650 via a flexed portion 656 of the inner membrane 600 over a gap 655 located between the individually pressurizable chambers 650). The lip 652 of the inner membrane 600 is configured to be secured to the membrane support 716 with a clamp 660. The clamp 660 can be secured to the membrane support 716 by a fastener, screw, bolt, or other similar fastener. Each inner chamber 650 can individually apply downward pressure to a corresponding portion of the inner membrane 600. The corresponding portion of the inner membrane 600 can then apply downward pressure to a corresponding portion of the outer membrane 700. The corresponding portion of the outer membrane 700 can then apply downward pressure to a corresponding portion of the substrate 10.

[0020] In some embodiments, instead of having an inner membrane 600 and an outer membrane 700 , the membrane assembly 500 can have a single membrane secured to the membrane support 716 .

[0021] 1A and 1B, the lower carrier body 106 may be connected to the membrane assembly 500 using a flexible member 900. The flexible member 900 may be connected to the housing 102 (e.g., the lower carrier body 106) and the membrane assembly 500 using fasteners 902, such as adhesives, screws, bolts, clamps, or by interlocking, to name a few.

[0022] The flexible member 900 may be made from a flexible material such as rubber, e.g., silicone rubber, ethylene propylene diene terpolymer (EPDM), or a fluoroelastomer, or a plastic film, e.g., polyethylene terephthalate (PET) or polyoxymethylene. The flexible member 900 may be sufficiently stiff to resist lateral movement to keep the membrane assembly 500 centered under the housing 102. However, the flexible member 900 may be sufficiently flexible in the vertical direction to allow vertical movement of the membrane assembly 500 relative to the housing 102.

[0023] The flexure member 900 can allow the membrane assembly 500 to move vertically relative to the lower carrier body 106 by allowing the flexure member 900 to bend, e.g., undergo bending displacement. As the flexure member 900 flexes, the pressure applied by the flexure member 900 to the membrane support 716, and therefore the substrate 10, can increase or decrease.

[0024] A controller 910 may be used to regulate the pressure in the various chambers of carrier head 100. Controller 910 may be coupled to multiple pressure sources 922 (although one pressure source 922 is shown, there can be multiple pressure sources 922), pressure source 924, and pressure source 926. Pressure sources 922, 924, 926 may be, for example, pumps, facility gas lines, controllable valves, etc. Each pressure source 922 may be individually connected to pressurizable inner chamber 650, pressure source 924 may be connected to lower pressurizable chamber 722, and pressure source 926 may be connected to upper pressurizable chamber 726.

[0025] The sensors 930 can measure the pressure in the pressure sources 922, 924, 926, the individually pressurizable inner chamber 650, the lower pressurizable chamber 722, and the upper pressurizable chamber 726. The sensors 930 can communicate the measured pressures to the controller 910. The controller 910 can cause the pressure sources 922, 924, 926 to increase and / or decrease the pressure in the individually pressurizable inner chamber 650, the lower pressurizable chamber 722, and / or the upper pressurizable chamber 726.

[0026] As the carrier head 100 performs a polishing operation, the retaining ring 205 and / or the outer ring 400 may wear down. As the retaining ring 205 and / or the outer ring 400 wear down, the flexures 900 flex to apply increased downward pressure to the membrane support 716, and thereby to the substrate 10. As a result, the polishing rate of the substrate 10 increases.

[0027] 1A and 1B, to compensate for wear of retaining ring 205 and / or retaining ring 400, which would result in an increased load (i.e., applied pressure) on substrate 10, the pressure in upper pressurizable chamber 726 can be adjusted to maintain a constant total load on substrate 10.

[0028] To determine the required change in pressure, the sensor 950 can measure the distance of the change in distance from the sensor 950 to the target 954, and the controller 910 can detect the change in distance based on a signal from the sensor 950. The sensor 950 can be a radar, laser, optical, ultrasonic, or other similar proximity sensor.

[0029] The sensor 950 may be fixed to the carrier head 100, for example located within the lower carrier body 106. The sensor 950 is positioned to measure a distance between the sensor 950 and a target 954. For example, the target 954 may be part of a top surface of the membrane assembly (e.g., a top surface of the membrane support 716) below the sensor 950.

[0030] 2, in some embodiments, the sensor 950 may be fixed to the upper carrier body 104. A window 952 is located between the sensor 950 and the target 954 and passes through the lower carrier body 106. This window allows the sensor 950 to measure the distance between the sensor 950 and the target 954 without affecting the pressure in the various chambers, e.g., the loading chamber 110 or the upper pressurizable chamber 726. The chamber 110 may be depressurized to draw the lower carrier body 106 upwardly relative to the upper carrier body 104 before performing a distance measurement by the sensor 950. This can ensure that the pull apart between the lower and upper carrier bodies does not contribute to variability in the measured distance.

[0031] Returning briefly to the figure, the sensor 950 can further be connected to the controller 910 and can report the measured distance or a change in the measured distance (e.g., a decrease in distance due to wear of the retaining ring 205 and / or the retaining ring 400) to the controller 910. The controller 910 can then cause the pressure source 926 to decrease the pressure in the upper pressurizable chamber 726 to maintain the load on the substrate 10.

[0032] The controller 910 may be configured to adjust the pressure in the upper pressurizable chamber 726 based on the measured distance between the sensor 950 and the target 954. That is, when the flexure member 900 flexes to decrease the distance between the sensor 950 and the target 954, thereby increasing the pressure applied by the flexure member 900 to the substrate 10, the controller 910 may be configured to decrease the pressure in the upper pressurizable chamber 726 to compensate for the increased pressure applied by the flexure member 900.

[0033] The pressure in the upper pressurizable chamber 726 can be a function of the measured distance between the sensor 950 and the target 954. For example, as the measured distance between the sensor 950 and the target 954 decreases, the pressure in the upper pressurizable chamber 726 can decrease. The controller 910 can receive the intended pressure from the polishing recipe, represented by data stored in, for example, a non-transitory computer-readable medium, and the distance measurement from the sensor 950. The controller calculates a modified pressure for the upper pressurizable chamber 726 based on the intended pressure and the distance measurement. The amount to decrease the pressure in the upper pressurizable chamber 726 can be stored in a lookup table relating the change in pressure to the distance. The change in pressure can be a non-linear function of the distance and can depend on the design of the flexure. Additionally, the change in pressure can be stored in the lookup table as an absolute value of the pressure change or a percentage of the change relative to the intended pressure. To calculate the modified pressure, the change is applied to the intended pressure, for example, by subtraction or multiplication as necessary based on the type of change.

[0034] To determine the functional relationship between distance and pressure difference, a series of pairs of distance measurements and total downward pressure from membrane assembly 500 can be made using multiple retaining rings with different amounts of wear. Specifically, the retaining ring can be mounted on a carrier head that is placed over a pressure sensor, e.g., a pressure sensor pad, and the upper pressurizable chamber 726 is brought to a constant pressure for each set of measurements. The distance is then measured by sensor 950 and the total applied pressure from membrane assembly 500 is measured by another sensor, e.g., a pressure sensor pad. Multiple pairs of measurements can provide the increase in applied pressure as a function of distance measurement. A pressure offset for upper pressurizable chamber 726 to return the total applied pressure to a constant pressure can be calculated from this data as a function of measured distance.

[0035] The controllers and other computing device portions of the systems described herein may be implemented in digital electronic circuitry, or in computer software, firmware, or hardware. For example, a controller may include a processor and execute a computer program product, e.g., a computer program stored in a non-transitory machine-readable storage medium. Such computer programs (also referred to as programs, software, software applications, or code) may be written in any type of programming language (including compiled or interpreted languages) and may be deployed as stand-alone programs or in any form including modules, components, subroutines, or other units suitable for use in a computing environment.

[0036] In the context of a controller, "configured" indicates that the controller has the necessary hardware, firmware or software, or a combination, to perform a desired function during operation (as opposed to merely being programmable to perform a desired function).

[0037] Although this specification contains details of many specific embodiments, these descriptions should not be construed as limitations on any invention or claimed subject matter, but rather as descriptions of features specific to particular embodiments of a particular invention. Certain features described herein in the context of separate embodiments 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 in multiple embodiments separately or in any suitable subcombination. Furthermore, although multiple features have been described above as functioning in a particular combination, and even initially claimed as such, one or more features based on a claimed combination may in some cases be implemented based on that combination, and the claimed combination may be directed to a subcombination or a variation of a subcombination.

[0038] A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications can be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the appended claims.

Claims

1. A carrier head for chemical mechanical polishing, comprising: Carrier body, a membrane assembly below the carrier body and vertically movable relative to the carrier body, the membrane assembly including a membrane support and a membrane secured to and depending from the membrane support, a space between the carrier body and the membrane assembly above the membrane support providing a first pressurizable chamber, and the membrane defining a second pressurizable chamber below the membrane support; a sensor supported by the carrier body and configured to measure a distance from the sensor to the membrane support of the membrane assembly; and a controller configured to receive distance measurements from the sensor and to control a pressure source to pressurize the first pressurizable chamber based on the distance measurements.

2. The carrier head of claim 1 , wherein the controller is configured to maintain a consistent total down force on the membrane assembly even as a distance between the sensor and the membrane support changes.

3. a flexible member connecting the membrane support to the carrier body; The carrier head of claim 1 .

4. Further comprising a flexible member connecting the membrane support to the carrier body. The carrier head of claim 2 .

5. The carrier head of claim 4 , wherein the controller is configured to compensate for changes in load from the flexure member to the membrane assembly.

6. The carrier head of claim 5 , wherein the controller is configured to decrease pressure in the pressurizable chamber as the distance measurement decreases.

7. The carrier head of claim 3 , wherein the flexure seals the first pressurizable chamber.

8. The carrier head of claim 1 , wherein the carrier body is configured to be secured to a driver shaft.

9. The carrier head of claim 1 , wherein the sensor is a radar, laser, or ultrasonic sensor.

10. The carrier head of claim 1 , further comprising a target on the membrane support below the sensor.

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