Abstract:
A flexible membrane for use with a carrier head of a substrate chemical mechanical polishing apparatus has a central portion with an outer surface providing a substrate receiving surface, a perimeter portion for connecting the central portion to a base of the carrier head, and at least one flap extending from an inner surface of the central portion. The flap includes a laterally extending first section and a vertically extending second section connecting the laterally extending first section to the central portion.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. application Ser. No. 11/054,128, now U.S. Pat. No. 7,001,257, filed on Feb. 8, 2005, which is a continuation of U.S. application Ser. No. 09/712,389, now U.S. Pat. No. 6,857,945, filed on Nov. 13, 2000, which claims priority to U.S. Application Ser. No. 60/220,641, filed on Jul. 25, 2000, each of which is incorporated by reference. 
    
    
     BACKGROUND 
     The present invention relates generally to chemical mechanical polishing of substrates, and more particularly to a carrier head for use in chemical mechanical polishing. 
     An integrated circuit is typically formed on a substrate by the sequential deposition of conductive, semiconductive or insulative layers on a silicon wafer. One fabrication step involves depositing a filler layer over a non-planar surface, and planarizing the filler layer until the non-planar surface is exposed. For example, a conductive filler layer can be deposited on a patterned insulative layer to fill the trenches or holes in the insulative layer. The filler layer is then polished until the raised pattern of the insulative layer is exposed. After planarization, the portions of the conductive layer remaining between the raised pattern of the insulative layer form vias, plugs and lines that provide conductive paths between thin film circuits on the substrate. In addition, planarization is needed to planarize the substrate surface for photolithography. 
     Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head. The exposed surface of the substrate is placed against a rotating polishing disk pad or belt pad. The polishing pad can be either a “standard” pad or a fixed-abrasive pad. A standard pad has a durable roughened surface, whereas a fixed-abrasive pad has abrasive particles held in a containment media. The carrier head provides a controllable load on the substrate to push it against the polishing pad. A polishing slurry, including at least one chemically-reactive agent, and abrasive particles if a standard pad is used, is supplied to the surface of the polishing pad. 
     SUMMARY 
     In one aspect, the invention is directed to a flexible membrane for use with a carrier head of a substrate chemical mechanical polishing apparatus. The membrane has a central portion with an outer surface providing a substrate receiving surface, a perimeter portion for connecting the central portion to a base of the carrier head, and at least one flap extending from an inner surface of the central portion. The flap includes a laterally extending first section and a vertically extending second section connecting the laterally extending first section to the central portion. 
     In another aspect, the invention is directed to a flexible membrane in which the laterally extending firts section is at least fifty percent longer than the vertically extending second section. 
     In another aspect, the invention is directed to a flexible membrane in which the vertically extending second section has a first thickness less than a second thickness of the central portion and a length about equal to the second thickness. 
     Implementations of these invention may include one or more of the following features. The flexible membrane may include a plurality of flaps, each flap including a laterally extending first section and a vertically extending second section. The flaps may be arranged annularly and concentrically. The second section may be thicker than the first section, e.g., about two to four times thicker. The central portion may be thicker than the second section, e.g., about three to six times thicker than the second section. A notch may be located in the flap at a junction between the first second and the second section. The membrane may be a unitary body. The second section may have a length comparable to a thickness of the central portion. The first section may be longer than the second section, e.g., about 1.5 to 3 times the length of the first section. 
     In another aspect, the invention is directed to a carrier head for chemical mechanical polishing of a substrate that includes a base and a flexible membrane of the invention. The flap divides a volume between the flexible membrane and the base into a plurality of chambers. 
     Implementations of the invention may include one or more of the following features. The membrane may include a plurality of flaps, and the flaps may be configured to provide three independently pressurizable chambers. The perimeter portion may be directly connected to the base. A retaining ring to surround a substrate on the substrate receiving surface. The first section of the flexible membrane may be sufficiently vertically movable so that a pressure profile applied to a substrate is substantially insensitive to retaining ring wear. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a carrier head according to the present invention. 
         FIGS. 2 and 3  illustrate an implementation of a flexible membrane for the carrier head. 
         FIG. 4  illustrates an optional implementation for an edge portion of the flexible membrane. 
         FIG. 5  is an enlarged view of a carrier head illustrating a flexible membrane with a wide connection between each flap and the base portion of the membrane. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , the carrier head  100  includes a housing  102 , a base assembly  104 , a gimbal mechanism  106  (which may be considered part of the base assembly), a loading chamber  108 , a retaining ring  110 , and a substrate backing assembly  112  which includes five pressurizable chambers. A description of a similar carrier head may be found in U.S. Pat. No. 6,183,354, the entire disclosure of which is incorporated herein by reference. 
     The housing  102  can generally circular in shape and can be connected to the drive shaft to rotate therewith during polishing. A vertical bore  120  may be formed through the housing  102 , and five additional passages  122  (only two passages are illustrated) may extend through the housing  102  for pneumatic control of the carrier head. O-rings  124  may be used to form fluid-tight seals between the passages through the housing and passages through the drive shaft. 
     The base assembly  104  is a vertically movable assembly located beneath the housing  102 . The base assembly  104  includes a generally rigid annular body  130 , an outer clamp ring  134 , and the gimbal mechanism  106 . The gimbal mechanism  106  includes a gimbal rod  136  which slides vertically the along bore  120  to provide vertical motion of the base assembly  104 , and a flexure ring  138  which bends to permit the base assembly to pivot with respect to the housing  102  so that the retaining ring  110  may remain substantially parallel with the surface of the polishing pad. 
     As illustrated in  FIG. 1 , the gimbal rod  136  and flexure ring  138  can be a monolithic body, rather than being separate pieces attached by screws or bolts. For example, the gimbal rod  136  and flexure ring  138  can be machined from one piece of raw material, such as a hard plastic or metal. A monolithic gimbal can reduce head run-out, allow easier access to the wafer sensor, simplify the carrier head rebuild procedure, and reduce or eliminate a source of cross-talk between chambers. In addition, a recess can be formed in the center of the bottom surface of the gimbal mechanism  106 . A portion of a substrate sensor mechanism, such as the movable pin as described in U.S. Pat. No. 6,663,466, can fit into the recess. Similarly, the rigid annular body  130  and the flexure ring  138  can be a monolithic body. Alternatively, the flexure ring  138  can be joined to the annular body  130 , e.g., by screws, as described in the above-mentioned U.S. Pat. No. 6,183,354. 
     The loading chamber  108  is located between the housing  102  and the base assembly  104  to apply a load, i.e., a downward pressure or weight, to the base assembly  104 . The vertical position of the base assembly  104  relative to the polishing pad is also controlled by the loading chamber  108 . An inner edge of a generally ring-shaped rolling diaphragm  126  may be clamped to the housing  102  by an inner clamp ring  128 . An outer edge of the rolling diaphragm  126  may be clamped to the base assembly  104  by the outer clamp ring  134 . 
     The retaining ring  110  may be a generally annular ring secured at the outer edge of the base assembly  104 . When fluid is pumped into the loading chamber  108  and the base assembly  104  is pushed downwardly, the retaining ring  110  is also pushed downwardly to apply a load to the polishing pad. A bottom surface  116  of the retaining ring  110  may be substantially flat, or it may have a plurality of channels to facilitate transport of slurry from outside the retaining ring to the substrate. An inner surface  118  of the retaining ring  110  engages the substrate to prevent it from escaping from beneath the carrier head. 
     The substrate backing assembly  112  includes a flexible membrane  140  with a generally flat main portion  142  and five concentric annular flaps  150 ,  152 ,  154 ,  156 , and  158  extending from the main portion  142 . The edge of the outermost flap  158  provides a perimeter portion of the membrane that is clamped between the base assembly  104  and a first clamp ring  146 . Two other flaps  150 ,  152  are clamped to the base assembly  104  by a second clamp ring  147 , and the remaining two flaps  154  and  156  are clamped to the base assembly  104  by a third clamp ring  148 . A lower surface  144  of the main portion  142  provides a mounting surface for the substrate  10 . 
     The volume between the base assembly  104  and the flexible membrane  140  that is sealed by the first flap  150  provides a first circular pressurizable chamber  160 . The volume between the base assembly  104  and the flexible  140  that is sealed between the first flap  150  and the second flap  152  provides a second pressurizable annular chamber  162  surrounding the first chamber  160 . Similarly, the volume between the second flap  152  and the third flap  154  provides a third pressurizable chamber  164 , the volume between the third flap  154  and the fourth flap  156  provides a fourth pressurizable chamber  166 , and the volume between the fourth flap  156  and the fifth flap  158  provides a fifth pressurizable chamber  168 . As illustrated, the outermost chamber  168  is the narrowest chamber. In fact, the chambers  152 ,  154 ,  156  and  158  can be configured to be successively narrower. 
     Each chamber can be fluidly coupled by passages through the base assembly  104  and housing  102  to an associated pressure source, such as a pump or pressure or vacuum line. One or more passages from the base assembly  104  can be linked to passages in the housing by flexible tubing that extends inside the loading chamber  108  or outside the carrier head. Thus, pressurization of each chamber, and the force applied by the associated segment of the main portion  142  of the flexible membrane  140  on the substrate  10 , can be independently controlled. This permits different pressures to be applied to different radial regions of the substrate during polishing, thereby compensating for non-uniform polishing rates caused by other factors or for non-uniform thickness of the incoming substrate. 
     To vacuum chuck the substrate  10 , one chamber, e.g., the outermost chamber  168 , is pressurized to force the associated segment of the flexible membrane  140  against the substrate  10  to form a seal. Then one or more of the other chambers located radially inside the pressurized chamber, e.g., the fourth chamber  166  or the second chamber  162 , are evacuated, causing the associated segments of the flexible membrane  140  to bow inwardly. The resulting low-pressure pocket between the flexible membrane  140  and the substrate  10  vacuum-chucks the substrate  10  to the carrier head  100 , while the seal formed by pressurization of the outer chamber  168  prevents ambient air from entering the low-pressure pocket. 
     Since it is possible for the vacuum-chucking procedure to fail, it is desirable to determine whether the substrate is actually attached to the carrier head. To determine whether the substrate is attached to the flexible membrane, the fluid control line to one of the chambers, e.g., the third chamber  164 , is closed so that the chamber is separated from the pressure or vacuum source. The pressure in the chamber is measured after the vacuum-chucking procedure by a pressure gauge connected to the fluid control line. If the substrate is present, it should be drawn upwardly when the chamber  162  is evacuated, thereby compressing the third chamber  164  and causing the pressure in the third chamber to rise. On the other hand, if the substrate is not present, the pressure in the third chamber  164  should remain relative stable (it may still increase, but not as much as if the substrate were present). A general purpose computer connected to the pressure gauge can be programmed to use the pressure measurements to determine whether the substrate is attached to the carrier head. The chambers that are not used for sealing, vacuum-chucking or pressure sensing can be vented to ambient pressure. 
     Referring to  FIGS. 2 and 3 , in one implementation, each of the annular flaps  150   a,    152   a,    154   a,  and  156   a,  except the outermost flap  158 , of the flexible membrane  140   a  includes a vertically extending portion  200  and a horizontally extending portion  202  (only a single flap  150   a  is shown in  FIG. 3 ). A notch  204  may be formed in the membrane at the intersection of the vertex between the vertically extending portion  200  and the horizontally extending portion  202 . The main portion  142  has a thickness T 1 , the vertically extending portion  200  has a thickness T 2  which is less than T 1 , and the horizontally extending portion  202  has a thickness T 3  which is less than T 2 . In particular, the thickness T 2  may be about ⅓ to ⅙ the thickness T 1 , and the thickness T 3  may be about ½ to ¼ the thickness T 2 . The vertically extending portion  200  may extend substantially vertically along a length L 1 , whereas the horizontally extending portion  202  may extend substantially horizontally along a length L 2  which is greater than L 1 . In particular, the length L 2  may be about 1.5 to 3 times the length L 1 . 
     In operation, when one of the chambers is pressurized or evacuated, the horizontally extending portion  202  flexes to permit the main portion  142  to move up and down. This reduces torsion or other transmission of loads to the main portion  142  of the flexible membrane through the flap that might result due to unequal pressure in adjacent chambers. Thus, unintended compressions in the main portion  142  at the junction of the flap to the main portion can be reduced. Consequently, the pressure distribution on the substrate at the region transitioning between two chambers of different pressure should be generally monotonic, thereby improving polishing uniformity. 
     Another potential advantage of the configuration of the flexible membrane is to improve wafer-to-wafer uniformity as the retaining ring wears. As the retaining ring wears, the nominal plane of the bottom of the flexible membrane will change. However, with the present invention, as the retaining ring wears, the horizontally extending portion  202  of the flexible membrane can bend to permit the bottom surface of the membrane to move vertically to the new nominal plane, without inducing a load spike where the vertical wall is joined to the main portion  142 . 
     Referring to  FIG. 4 , in another implementation, which can be combined with the other implementations, the flexible membrane  140   b  includes a main portion  142   b  and an outer portion  220  with a triangular cross-section connected to the outer edge of the main portion  142   b.  The three innermost annular flaps are connected to the main portion  142   b  of the flexible membrane  140   b,  but the two outermost annular flaps  156   b  and  158   b  are connected to the two vertices of the triangular outer portion  220 . The innermost flaps include both the horizontal portion and the vertical portion, whereas in the two outermost annular flaps  156   b  and  158   b,  the horizontal portion  224  connects directly to the triangular outer portion  220 . 
     The two outer chambers  166   b  and  168   b  can be used to control the pressure distribution on the outer perimeter of the substrate. If the pressure P 1  in the outermost chamber  168   b  is greater than the pressure P 2  in the second chamber  166   b,  the outer portion  220  of the flexible membrane  140   b  is driven downwardly, causing the lower vertex  226  of the outer portion  220  to apply a load to the outer edge of the substrate. On the other hand, if the pressure P 1  in the outermost chamber  168   b  is less than the pressure P 2  in the second chamber  166   b  (as shown in  FIG. 4 ), the outer portion  220  pivots so that the lower vertex  226  is drawn upwardly. This causes the outer edge of the main portion  142   b  to be drawn upwardly and away from the perimeter portion of the substrate, thereby reducing or eliminating the pressure applied on this perimeter portion. By varying the relative pressures in the chambers  166   b  and  168   b,  the radial width of the section of the membrane pulled away from the substrate can also be varied. Thus, both the outer diameter of the contact area between the membrane and the substrate, and the pressure applied in that contact area, can be controlled in this implementation of the carrier head. 
     Referring to  FIG. 5 , in another implementation, the flexible membrane  140   c  includes a main portion  142   c  and an outer portion  220  with a triangular cross-section connected to the outer edge of the main portion  142   c . A lower surface  144  of the main portion  142   c  provides a mounting surface for the substrate  10 . The three innermost annular flaps  150   c ,  152   c  and  154   c  are connected to the main portion  142   c  of the flexible membrane  140   c . The two outermost annular flaps  156   c  and  158   c  are connected to the two vertices of the triangular outer portion  220 . Each membrane flap  150   c ,  152   c ,  154   c ,  156   c  and  158   c  includes a thick rim  222  that is clamped between a clamp ring and the base, and a substantially horizontal portion  224  extending radially away from the rim  222 . In the case of the two outermost annular flaps  156   c  and  158   c , the horizontal portion  224  connects directly to the triangular outer portion  220 . In the case of the three innermost annular flaps  150   c ,  152   c  and  154   c , the horizontal portion  224  is connected to the main portion  142   c  by a thick wedge-shaped portion  230 , also with a triangular cross-section. The wedge-shaped portion  230  can have sloped face  232  on the same side of the flap as the rim  206 , and a generally vertical face  234  on the opposing side. In operation, when one of the chambers is pressurized or evacuated, the substantially horizontal portions  224  flex to permit the main portion  142   c  to move up or down. 
     The configurations of the various elements in the carrier head, such as the relative sizes and spacings the retaining ring, the base assembly, or the flaps in the flexible membrane are illustrative and not limiting. The carrier bead could be constructed without a loading chamber, and the base assembly and housing can be a single structure or assembly. Notches can be formed in other locations on the membrane, the different flaps may have different numbers of notches, some or all of the flaps may be formed without notches, and there can be one or more notches on the outermost flap. The flaps could be secured to the base in other clamping configurations, mechanisms other than clamps, such as adhesives could be used to secure the flexible membrane, and some of the flaps could be secure to different portions of the carrier head than the base. 
     The present invention has been described in terms of a number of embodiments. The invention, however, is not limited to the embodiments depicted and described. Rather, the scope of the invention is defined by the appended claims.