Double-film carrying head for chemical mechanical polishing

Abstract

A carrier head for chemical mechanical polishing includes a base assembly connected to a membrane assembly of the base assembly. The membrane assembly includes a membrane support, an inner membrane secured to the membrane support, the inner membrane forming a plurality of individually pressurizable interior chambers between an upper surface of the membrane and the membrane support, and an outer membrane secured to the membrane support and extending below the inner membrane, the outer membrane having an inner surface and an outer surface, wherein the outer membrane defines a lower pressurizable chamber between the inner surface of the outer membrane and a lower surface of the inner membrane, where the inner surface is positioned to contact the lower surface of the inner membrane when one or more of the plurality of chambers are pressurized, and where the outer surface is configured to contact a substrate.

Description

[0001] This application is a divisional application of the invention patent application with application date of August 24, 2020, application number 202010854945.5, and invention name “Dual-membrane carrier head for chemical mechanical polishing”. Technical Field

[0002] The present invention relates to a carrier head for chemical mechanical polishing (CMP). Background Art

[0003] Integrated circuits are typically formed on a substrate by sequentially depositing conductive, semiconductive, or insulating layers on a semiconductor wafer. Various manufacturing processes require planarizing the layers on the substrate. For example, 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 metal layer may be deposited on a patterned insulating layer to fill the grooves and holes in the insulating layer. After planarization, the remaining portions of the metal in the grooves and holes of the patterned layer form vias, plugs, and wiring to provide conductive paths between thin film circuits on the substrate. As another example, a dielectric layer may be deposited over the patterned conductive layer and then planarized to enable subsequent photolithography steps.

[0004] Chemical mechanical polishing (CMP) is an acceptable planarization method. This planarization method generally requires mounting the substrate on a carrier head. The exposed surface of the substrate is generally placed against a rotating polishing pad. The carrier head provides a controllable load on the substrate to push the substrate against the polishing pad. A polishing slurry having abrasive particles is generally provided to the surface of the polishing pad. Summary of the invention

[0005] In one aspect, a carrier head for chemical mechanical polishing comprises: a base assembly; and a membrane assembly connected to the base assembly. The membrane assembly comprises: a membrane support, an inner membrane fixed to the membrane support, and an outer membrane fixed to the membrane support and extending below the inner membrane, the outer membrane having an inner surface and an outer surface. The inner membrane forms a plurality of individually pressurizable internal chambers between an upper surface of the membrane and the membrane support. The outer membrane defines a lower pressurizable chamber between the inner surface of the outer membrane and a lower surface of the inner membrane. The inner surface is positioned to contact the lower surface of the inner membrane when one or more of the plurality of chambers is pressurized, and the outer surface is configured to contact a substrate.

[0006] On the other hand, a system for chemical mechanical polishing comprises: a plurality of pressure sources, a carrier head, and a controller connected to the pressure sources. The carrier head comprises: a base assembly and a membrane assembly. The membrane assembly has: a membrane support, an inner membrane fixed to the membrane support, and an outer membrane fixed to the membrane support and extending below the inner membrane. The inner membrane forms a plurality of individually pressurizable internal chambers between an upper surface of the inner membrane and the membrane support. The outer membrane has an inner surface and an outer surface. The outer membrane defines a lower pressurizable chamber between the inner surface of the outer membrane and the lower surface of the inner membrane. The inner surface is positioned to contact the lower surface of the inner membrane when one or more of the plurality of chambers is pressurized, and the outer surface is configured to contact a substrate. The controller is configured to cause a pressure source to pressurize the internal chamber and the lower chamber so that the one or more individually pressurizable internal chambers of the inner film are pressurized to a pressure equal to or greater than the pressure of the lower chamber to supplement the pressure applied by the outer film to the substrate at a portion of the outer film corresponding to the one or more individually pressurizable internal chambers.

[0007] In another aspect, a method for chemical mechanical polishing utilizing a carrier head comprises the steps of: holding a substrate in a carrier head comprising a membrane assembly having an outer membrane and an inner membrane, the inner membrane defining a plurality of individually pressurizable internal chambers; pressurizing a lower chamber between the inner membrane and the outer membrane to a first pressure; pressurizing at least some of the plurality of individually pressurizable internal chambers to a second pressure equal to or greater than the first pressure; and generating relative motion between the substrate and a polishing pad such that pressure from the lower chamber causes polishing of the substrate at a first rate and pressure in one or more internal chambers complementarily increases polishing of the substrate in regions corresponding to the individually pressurizable internal chambers.

[0008] In another aspect, a membrane for a carrier head comprises: a plurality of chamber-defining portions, each chamber-defining portion comprising: two side walls, a bottom plate at the bottom edges of the two side walls and connecting the two side walls, and two flange portions extending inwardly from the two side walls. Adjacent chamber-defining portions of the membrane are connected by a bridge portion at the top edge between adjacent side walls of adjacent chamber-defining portions, and adjacent side walls of adjacent chamber-defining portions are separated by a gap below the bridge portion.

[0009] Implementations may include one or more of the following features.

[0010] The housing may be connected to the base assembly. The base assembly may be movable vertically relative to the housing. The base assembly may be connected to the housing by a universal joint mechanism. The base assembly may be configured to rotate about the universal joint mechanism, the universal joint mechanism having a rotation center located above the inner membrane. A flexible member may connect the base assembly and the membrane assembly. The flexible member may be sufficiently rigid to resist lateral movement, thereby keeping the membrane assembly centered below the base assembly.

[0011] Possible advantages may include, but are not limited to, one or more of the following. A dual membrane carrier head may be used to apply different pressures to different portions of a substrate, thereby obtaining a desired substrate profile during a polishing operation. For example, variations in substrate profile may be reduced. This may improve intra-wafer uniformity. The inner membrane need not be subject to wear during the polishing operation, and may not need to be replaced as frequently, if at all. Thus, the inner membrane may be more complex and have a reduced risk of failure. The inner membrane material need not have the same chemical and wear resistance as the outer membrane. Thus, the inner membrane may reduce costs.

[0012] The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1A is a schematic cross-sectional view of a carrier head.

[0014] Figure 1B yes Figure 1A Schematic cross-sectional view of a portion of a carrier head.

[0015] Figure 1C yes Figure 1A Schematic cross-sectional view of a portion of a carrier head.

[0016] Figure 2A is a schematic cross-sectional view of another embodiment of a carrier head.

[0017] Figure 2B yes Figure 1A Schematic cross-sectional view of a portion of a carrier head.

[0018] Figure 2C yes Figure 1A Schematic cross-sectional view of a portion of a carrier head.

[0019] Figure 3 is a schematic cross-sectional view of the inner membrane with an edge control zone.

[0020] Like reference numbers and designations in the various drawings indicate like elements. DETAILED DESCRIPTION

[0021] In some polishing systems, a membrane in a carrier head is used to apply a substantially uniform pressure on a substrate during polishing. However, such substantially uniform pressure cannot effectively account for non-uniformities in the polishing process, such as those caused by variations in slurry distribution or non-uniformities in the substrate prior to polishing.

[0022] One solution to the non-uniformity is to have multiple individually pressurizable chambers, each of which applies a different pressure to a local area of ​​the substrate. The manufacturing cost of a film providing multiple chambers may be high, and if such a film is in contact with the substrate, there is a risk that the film is worn and torn, so expensive parts need to be replaced. However, an outer film can be provided above an inner film providing multiple chambers. The multiple chambers of the inner film can be separated by gaps to reduce the "wall effect" or crosstalk via the walls separating adjacent chambers. Since the outer film is in contact with the substrate and the inner film is not in contact with the substrate, if the outer film is worn, it can be replaced. The inner film does not need to be worn during the polishing operation, and if there is any, it may not need to be replaced frequently, which can reduce costs. Although the outer film can be coated with chemical and wear-resistant materials, the inner film does not need to be coated, so it can be manufactured at a lower cost. In addition, the outer film is simpler, so if the outer film is indeed torn, it can be replaced at a lower cost. On the other hand, the inner film material does not need to have the same chemical and wear resistance as the outer film. The inner membrane can be fixed to the carrier head (e.g., membrane support) in a more permanent manner (e.g., by an adhesive such as epoxy). This can reduce leakage from the chamber. Also, the inner membrane can be manufactured in a mold with more complex features that facilitate attachment to the carrier base; for example, because the inner membrane is no longer a consumable item, this has less impact on cost while allowing excellent attachment, such as reducing leakage.

[0023] refer to Figure 1A-Figure 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 104 and a lower carrier 106, a universal joint mechanism 108 (which may be considered as a part of the lower carrier 106), a load chamber 110, a retaining ring assembly (discussed below) connected to the housing 102 (e.g., connected to the upper carrier 104 and / or the lower carrier 106), an outer ring 400 connected to the housing 102 (e.g., connected to the upper carrier 104 and / or the lower carrier 106), and a membrane assembly 500. In some embodiments, the upper carrier 104 and the lower carrier 106 are replaced by a single integral body. In some embodiments, there is only a single ring, lacking the retaining ring 205 or the outer ring 400.

[0024] The upper carrier 104 may be fixed to a rotatable drive shaft to rotate the entire carrier head 100. The upper carrier 104 may be generally circular in shape. There may be a passage extending through the upper carrier 104 for pneumatic control of the carrier head 100.

[0025] The lower carrier 106 is located below the upper carrier 104 and is vertically movable relative to the upper carrier 104. A load chamber 110 is located between the upper carrier 104 and the lower carrier 106 to apply a load, i.e., downward pressure or weight, to the lower carrier 106. The vertical position of the lower carrier 106 relative to the polishing pad is also controlled by the load chamber 110. In some embodiments, the vertical position of the lower carrier 106 relative to the polishing pad is controlled by an actuator.

[0026] The universal joint mechanism 108 allows the lower carrier 106 to perform universal rotation and vertical movement relative to the upper carrier 104 , while preventing the lower carrier 106 from lateral movement relative to the upper carrier 104 .

[0027] In some embodiments, the gimbal mechanism 108 has a spherical bearing 120 disposed at the lower end of the shaft 122 that extends into a recess in the outer portion 102 (see Figure 1C ). The spherical bearing 120 allows the base assembly 104 to rotate about a center of rotation (e.g., the center of the spherical bearing 120). The spherical bearing of the gimbal mechanism 108 can be lubricated to reduce friction, or coated with Teflon. A locking mechanism 128 can be used to hold the spherical bearing 120 in a gimbal housing 126 of the base assembly 104. For example, the locking mechanism 128 can be a spring-loaded lock that can lock the spherical bearing 120 and the shaft 122 in the appropriate position of the gimbal housing 126. A buffer 124 (e.g., a vibration washer) can be used to connect the gimbal housing 126 to the rest of the base assembly 104 to reduce the effects of vibration and friction caused by the spherical bearing 120 from being transmitted to the base assembly 104. However, in some embodiments, there is no gimbal.

[0028] The substrate 10 may be held below the membrane assembly 500 by a retaining ring 205. The retaining ring assembly 200 may include a retaining ring 205 and a flexible membrane 300 that is plastically formed to provide an annular chamber 350 to control the pressure on the retaining ring 205. The retaining ring 205 is located below the flexible membrane 300 and may be secured to the flexible membrane 300, for example, by a clamp 250. The load on the retaining ring 205 provides a load to the polishing pad 30. The independent load on the retaining ring 205 may allow a constant load to be maintained on the pad as the ring wears.

[0029] While the retaining ring 205 may be configured to retain the substrate 10 and provide active edge handling control, the outer ring 400 may provide positioning or referencing of the carrier head relative to the surface of the polishing pad.

[0030] Each chamber in the carrier head can be fluidly coupled to an associated pressure source (e.g., pressure source 922), such as a pump or a pressure or vacuum line, through a channel through the upper carrier 104 and the lower carrier 106. There can be one or more channels for the annular chamber 350 of the flexible membrane 300, the load chamber 110, the lower pressurizable chamber 722, the side chamber 724, and each individually pressurizable internal chamber 650. One or more channels from the lower carrier 106 can be linked to the channels in the upper carrier 104 by a flexible tube extending within the load chamber 110 or outside the carrier head 100. The pressure of each chamber can be independently controlled. In particular, the pressurization of each chamber 650 can be independently controlled. This allows different pressures to be applied to different radial regions of the substrate 10 during polishing, thereby compensating for uneven polishing rates.

[0031] The membrane assembly 500 may include a membrane support 716, an outer membrane 700, and an inner membrane 600. The membrane support 716 may be a generally disc-shaped body and may be formed of a rigid material such as stainless steel, aluminum, or hard plastic.

[0032] The outer film 700 has an inner surface 702 that can be positioned to contact the inner film 600 and an outer surface 704 that can provide a mounting surface for the substrate 10. The outer film 700 can have a peripheral portion 726 extending upward from a circular main portion that provides a mounting surface. The outer film 700 can also include two fins 734, 738 extending inward from the peripheral portion. The first fin 734 of the outer film 700 can have a lip 714 fixed to the film support 716 and can be clamped between the film support 716 and the clamp 736. The second fin 734 can similarly have a lip 714 fixed to the film support, for example, clamped between two clamps 736. The clamp 736 can be fixed to the lower carrier 106 by fasteners, screws, bolts or other similar fasteners. The first fin 734 can separate the lower pressurizable chamber 722 from the side chamber 724 located between the two fins 734, 738. The lower pressurizable chamber 722 is configured to extend across the bottom of the inner membrane 600 and the sides of the inner membrane 600. The inner membrane 600 is located between the lower pressurizable chamber 722 and the membrane support 716.

[0033] The outer film 700 may apply downward pressure on most or all of the substrate 10. The pressure in the lower pressurizable chamber 722 may be controlled to allow the outer surface 704 of the outer film 700 to apply pressure to the substrate 10.

[0034] The inner membrane 600 may define a plurality of individually pressurizable internal chambers 650 that may expand vertically relative to each other. For example, each chamber 650 may be defined by a bottom portion 654 and two sidewall portions 656 of the membrane 600. For each chamber, a flange portion 652 may extend inwardly from the two sidewall portions 656. There may be 2 to 20 individually pressurizable internal chambers 650. For each chamber 650, the flange portion 652 may be captured between a clamp 660 and a membrane support 716, thereby securing the membrane 600 to the membrane support 716. The clamp 660 may be secured to the membrane support 716 by fasteners, screws, bolts or other similar fasteners. Alternatively, the flange portion 652 may be secured to the membrane support 716 by an adhesive.

[0035] The sidewall portions 656 of adjacent chambers may be connected at their top edges by a bridge portion 658, e.g., the bridge portion 658 is coplanar with the flange portion 652. In contrast, below the bridge portion 658, adjacent sidewall portions 656 are separated by a gap 655. The separated sidewall portions 656 below are separated by a clamp 660 of the membrane 600. The sidewall portions 656 allow each individually pressurizable interior chamber 650 to expand in a vertical direction relative to adjacent pressurizable chambers 650, thereby reducing crosstalk.

[0036] Each inner chamber 650 may respectively apply downward pressure to a corresponding portion of the inner film 600, which may then apply downward pressure to a corresponding portion of the outer film 700, which may then apply downward pressure to a corresponding portion of the substrate 10. In addition, the combination of the inner film 600 and the outer film 700 that apply downward force to the substrate 10 may reduce the effect of the gap 655 between the inner chambers 650. Without the outer film, the portion of the substrate 10 corresponding to the gap (e.g., gap 655) between the inner chambers 650 may experience reduced polishing. However, the outer film 700 may reduce this effect because the outer chamber 722 may apply minimal pressure in the gap, which will thereby smooth and reduce defects caused by the gap between the inner chambers 650.

[0037] The bottom surface of the inner film 600 and / or the top surface of the outer film 700 may be textured, such as having an increased surface roughness relative to other portions of the film or being grooved, to prevent sealing between the inner film 600 and the outer film 700 .

[0038] refer to FIG. 2A to FIG. 2C , the carrier head with floating dual membrane assembly is similar to the reference Figure 1A-Figure 1C The carrier head discussed, however, base assembly 102 is movably connected to membrane assembly 500 using, for example, flexible member 900 .

[0039] The membrane assembly 500 may 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 positioned to contact the inner membrane 600 and an outer surface 704 that can provide a mounting surface for the substrate 10. The outer membrane 700 may also include two fins 734, 738 extending inwardly from a peripheral portion. The first fin 734 of the outer membrane 700 may have a lip 714 fixed to the membrane support 716 and may be clamped between the membrane support 716 and the clamp 736. The second fin 734 may similarly have a lip 714 fixed to the membrane support 716, for example, clamped between two clamps 736. The clamp 736 may be fixed to the lower carrier 106 by fasteners, screws, bolts or other similar fasteners. The first fin 734 can separate the lower pressurizable chamber 722 from the side chamber 724 located between the two fins 734, 738. The lower pressurizable chamber 722 is configured to extend across the bottom of the inner membrane 600 and the sides of the inner membrane 600. The inner membrane 600 is located between the lower pressurizable chamber 722 and the membrane support 716. The upper pressurizable chamber 726 is formed by the membrane assembly 500 (including the membrane support 716) and the lower carrier 106. The upper pressurizable chamber 722 is sealed from the chamber 728 above the flexible member 900 (which can be discharged to the outside of the carrier head 100) by the flexible member 900.

[0040] The lower carrier 106 can be connected to the membrane assembly 500 by a flexible member 900. The flexible member 900 can be an annular piece. The flexible member 900 can be connected to the housing 102 (e.g., the lower carrier 106) and the membrane assembly 500 using fasteners 902 (e.g., adhesives, screws, bolts, clamps, or by interlocking). The flexible member 900 can be composed of a flexible material such as silicone rubber or other similar elastomers, or a plastic, metal, or a composite material such as fiber-reinforced silicon. The flexible member 900 can be hard enough to resist lateral movement, thereby keeping the membrane assembly 500 centered below the housing 102. However, the flexible member 900 can be soft enough in the vertical direction to allow the membrane assembly 500 to move vertically relative to the carrier body 106.

[0041] The flexible member 900 can allow the membrane assembly 500 to move vertically relative to the lower carrier 106 by allowing the flexible member 900 to bend (e.g., bendably deflected). When the flexible member 900 bends, the pressure applied by the flexible member 900 to the membrane support 716 can be increased or decreased, and thus the pressure applied to the substrate 10 can be increased or decreased.

[0042] refer to Figure 1A and Figure 2A, the controller 910 can be used to adjust the pressure of each chamber of the carrier head 100. The controller 910 can be coupled to a pressure source 922, a pressure source 924, and a pressure source 926. The pressure sources 922, 924, 926 can be, for example, pressure chambers, hydraulic chambers, air chambers, etc. The pressure source 922 can be connected to the individually pressurizable inner chamber 650, and the pressure source 924 can be connected to the outer membrane 700, and the pressure source 926 can be connected to the upper pressurizable chamber 726 (see Figure 2A-2C ). Sensor 930 can measure pressure sources 922, 924, 926, the individually pressurizable inner chamber 650, the outer membrane 700, and the upper pressurizable chamber 726 (see Figure 2A-2C ), and the measured pressure(s) may be communicated to the controller 910. The controller 910 may cause the pressure sources 922, 924, 926 to increase and / or decrease the pressure in the individually pressurizable inner chamber 650, the outer chamber 722, the lip chamber 724, and / or the upper pressurizable chamber 726.

[0043] refer to Figure 3 In another embodiment, the carrier head has separate control of the edge control area 680. The edge control area 680 is defined by a separately pressurizable internal chamber 650a surrounded by a membrane portion 600a. The membrane portion 600a is flexibly connected to the remainder of the inner membrane 600 by a flexible member 682. An actuator (such as a bellows 684 that can increase or decrease pressure) can hingedly bend the internal chamber 650a to provide a concentrated edge load. That is, the internal chamber 650a can move semi-independently from the inner membrane 600 and the internal chamber 650. Advantageously, the internal chamber 650a can perform edge control polishing on a substrate 10 (not shown) to improve edge uniformity, for example, to reduce a check mark outline.

[0044] A controller (or "control system") may be implemented in digital electronic circuitry, tangibly embodied computer software or firmware, computer hardware, or a combination of one or more of these. Implementations of the subject matter described in this specification may be implemented as one or more computer programs, i.e., one or more modules of computer program instructions encoded on a tangible, non-transitory storage medium, to be executed by, or to control the operation of, a data processing apparatus.

[0045] This specification uses the term "configured" with respect to control systems. For a system of one or more computers to be configured to perform a particular operation or action, it means that the system has installed thereon software, firmware, hardware, or a combination thereof that, in operation, causes the system to perform those operations or actions. For one or more computer programs to be configured to perform a particular operation or action, it means that the one or more programs contain instructions that, when executed by a data processing device, cause the device to perform the operation or action.

[0046] A number of embodiments of the present invention have been described. However, it will be appreciated that various modifications may be made without departing from the spirit and scope of the present invention. For example, although Figure 1B Adjacent chambers of the inner membrane are illustrated as having sidewalls separated by gaps, but adjacent chambers may share common sidewalls. Accordingly, other embodiments are within the scope of the following claims.

Claims

1. A carrier head for chemical mechanical polishing, comprising: a base assembly; and A membrane assembly connected to the base assembly, the membrane assembly comprising: Membrane support, an inner membrane secured to the membrane support, wherein the inner membrane forms a plurality of individually pressurizable interior chambers between an upper surface of the membrane and the membrane support, wherein each of the plurality of individually pressurizable interior chambers is provided by a bottom portion and two side wall portions of the inner membrane, and wherein the side wall portions for adjacent chambers are separated by a gap, and wherein the side wall portions for adjacent chambers are connected by a bridging portion extending from a top edge of the side wall portions, and An outer membrane is fixed to the membrane support and extends below the inner membrane, the outer membrane having an inner surface and an outer surface, wherein the outer membrane defines a lower pressurizable chamber between the inner surface of the outer membrane and the lower surface of the inner membrane, so that a minimum pressure is applied in the gap by the lower pressurizable chamber, wherein the inner surface is positioned to contact the lower surface of the inner membrane when one or more of the plurality of chambers is pressurized, and wherein the outer surface is configured to contact a substrate.

2. The carrier head of claim 1, wherein for each individually pressurizable interior chamber of the inner membrane, there is included a flange portion extending inwardly from the two side wall portions.

3. The carrier head of claim 2, wherein the inner membrane is secured to the membrane support by a plurality of clamps, wherein each chamber has a clamp that clamps the flange portion to the membrane support.

4. The carrier head of claim 1, wherein the outer film comprises a central portion having a substrate receiving surface, a peripheral portion extending upwardly from an outer edge of the central portion, and a first tab extending inwardly over a portion of the film support.

5. The carrier head of claim 4, wherein the outer film includes a second tab extending inwardly over the portion of the film support, the space between the first tab and the second tab defining a lip cavity.

6. The carrier head of claim 1 comprising 2 to 20 individually pressurizable internal chambers.

7. The carrier head of claim 1 wherein the individually pressurizable interior chambers are concentric.

8. A system for chemical mechanical polishing, comprising: multiple stressors; A carrier head, the carrier head comprising: Base assembly; A membrane module, the membrane module comprising: Membrane support, an inner membrane secured to the membrane support, wherein the inner membrane forms a plurality of individually pressurizable interior chambers between an upper surface of the inner membrane and the membrane support, wherein each of the plurality of individually pressurizable interior chambers is provided by a bottom portion and two side wall portions of the inner membrane, and wherein the side wall portions for adjacent chambers are separated by a gap, and wherein the side wall portions for adjacent chambers are connected by a bridging portion extending from a top edge of the side wall portions, and an outer film secured to the film support and extending below the inner film, the outer film having an inner surface and an outer surface, wherein the outer film defines a lower pressurizable chamber between the inner surface of the outer film and the lower surface of the inner film such that a minimum pressure is applied in the gap by the lower pressurizable chamber, wherein the inner surface is positioned for contact by the lower surface of the inner film when one or more of the plurality of chambers is pressurized, and wherein the outer surface is configured to contact a substrate; and and a controller connected to one or more pressure sources, the controller being configured to cause the pressure sources to pressurize the interior chambers and the lower chamber so that one or more of the individually pressurizable interior chambers are pressurized to a pressure equal to or greater than the pressure of the lower chamber to supplement the pressure applied to the substrate by the outer film at a portion of the outer film corresponding to the one or more individually pressurizable interior chambers.

9. The system of claim 8, wherein for each individually pressurizable interior chamber of the inner membrane, there is included a flange portion extending inwardly from the two side wall portions.

10. The system of claim 9, wherein the inner membrane is secured to the membrane support by a plurality of clamps, wherein each chamber has a clamp that clamps the flange portion to the membrane support.

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