Abstract:
A flexible membrane includes a horizontal central portion, a vertical portion coupled to the central portion, a thick rim portion coupled to the vertical portion, and an extension coupled to the thick rim portion. An outer surface of the horizontal central portion provides a mounting surface configured to receive a substrate. The thick rim portion has a thickness that is greater than a portion directly adjacent to the thick rim portion. The thick rim portion is between the extension and the vertical portion and a greatest dimension of the extension is less than the thickness of the thick rim portion.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application Ser. No. 61/122,321, filed on Dec. 12, 2008, the entire contents of which is incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    This invention relates generally to chemical mechanical polishing of substrates, and more particularly to a carrier head that includes a flexible membrane for use in chemical mechanical polishing. 
         [0003]    Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, it is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, becomes increasingly nonplanar. This nonplanar surface presents problems in the photolithographic steps of the integrated circuit fabrication process. Therefore, there is a need to periodically planarize the substrate surface. 
         [0004]    One accepted method of planarization is chemical mechanical polishing (CMP). 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 moving polishing surface, such as a rotating polishing pad. The polishing pad may be either a “standard” polishing pad with a durable roughened surface or a “fixed-abrasive” polishing pad with abrasive particles held in a containment media. The carrier head provides a controllable load to 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. 
         [0005]    Some carrier heads include a flexible membrane with a mounting surface that receives the substrate. A chamber behind the flexible membrane is pressurized to cause the membrane to expand outwardly and apply the load to the substrate. After polishing, the substrate is chucked to the mounting surface, lifted off the polishing pad, and moved to another location, such as a transfer station or another polishing pad. 
       SUMMARY 
       [0006]    On one aspect, a membrane is described. The membrane is a flexible membrane including a horizontal central portion, a vertical portion coupled to the central portion, a thick rim portion coupled to the vertical portion, and an extension coupled to the thick rim portion. An outer surface of the horizontal central portion provides a mounting surface configured to receive a substrate. The thick rim portion has a thickness that is greater than a portion directly adjacent to the thick rim portion. The thick rim portion is between the extension and the vertical portion and a greatest dimension of the extension is less than the thickness of the thick rim portion. 
         [0007]    Implementations of the invention may include one or more of the following features. The membrane can have a connecting portion between the thick rim portion and the vertical portion, wherein the connecting portion is horizontal and parallel to the central portion. A cross section of the connecting portion, vertical portion and central portion can form a u-shape with the thick rim portion at one end of the u-shape. The thick rim can have a circular cross section. The extension can have a thickness that is less than 50% of the thickness of the thick rim portion. The extension can have a thickness that is less than 25% of the thickness of the thick rim portion. The extension can have a thickness that is less than 15% of the thickness of the thick rim portion. The extension can have a thickness that is less than 10% of the thickness of the thick rim portion. The flexible membrane can be formed of polychloroprene, ethylene propylene diene rubber or silicone. The horizontal central portion can be circular. The horizontal central portion can have a diameter of about 200 mm. The horizontal central portion can have a diameter of about 300 mm. The thick rim portion can have annular and the extension can have annular. The thick rim can have a cross section with a flat portion. 
         [0008]    A carrier head for retaining the substrate can include a membrane as described herein, a retaining ring surrounding the membrane and a base assembly connected to the retaining ring, wherein a cavity is between the base assembly and the membrane and the thick rim portion and extension are sealed to a component of the base assembly so that fluid cannot pass between the membrane and component. 
         [0009]    Implementations of the invention may include one or more of the following advantages. Membranes can be formed with a sealing portion that may be easy to fit into a recess of a carrier head component and seal to the walls of the recess so that fluid cannot pass between the membrane and component. Because the membrane easily fits into the recess, the membrane may be quickly and easily replaced and the non-operational time of the carrier head may be minimized. Further, because there is a higher probability of forming a membrane that does not leak, fewer membranes will be rejected as unusable, i.e., leaky or non fitting, and less time may be spent replacing rejected membranes. Less downtime for the carrier head may allow for greater manufacturing efficiency. 
         [0010]    The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0011]      FIG. 1  shows a schematic cross-sectional view of a carrier head according to the present invention. 
           [0012]      FIG. 2  shows a schematic cross-sectional view of one embodiment of a rim of a membrane. 
           [0013]      FIG. 3  shows a schematic cross-sectional view of one embodiment of a rim of a membrane. 
           [0014]      FIGS. 4-5  show a schematic cross-sectional view of a rim of a membrane in a carrier head support component. 
           [0015]      FIG. 6  shows schematic cross-sectional view of a portion of one embodiment of a membrane. 
           [0016]      FIG. 7  is a schematic backside view of a membrane. 
           [0017]      FIG. 8  is a schematic cross-sectional view of an embodiment of a membrane. 
           [0018]      FIG. 9  is a schematic cross-sectional view of a membrane held by a carrier head. 
       
    
    
       [0019]    Like reference symbols in the various drawings indicate like elements. 
       DETAILED DESCRIPTION 
       [0020]    As noted above, some carrier heads include a flexible membrane that provides a mounting surface for a substrate during and between polishing operations. The flexible membrane, or diaphragm, has a horizontal mounting surface for contacting a backside of the substrate and clamping portions that are on the ends of flaps that extend from the back of the flexible membrane. In some embodiments the clamping portion is annular. The clamping portions are used to connect the membrane to a carrier head. Some types of clamping portions have a thick rim portion or bead at the end of the clamping portion. The thick rim fits into a groove or recess in a support component of the carrier head. Because the thick rim is thicker than other parts of the flap, the flap is not easily pulled out of the recess even when the chamber behind the membrane is pressurized and the membrane flexes out away from the carrier head. 
         [0021]    The carrier head is formed of rigid pieces that are fit together. The flexible membrane fits into a component that is more rigid than the membrane. The membrane is sufficiently compliant that when an annular clamping portions is fit into a similarly sized annular recess, no fluid can pass between the membrane and the component. A space, i.e., the chamber, between carrier head and the membrane can be sealed. Sealing a cavity between the membrane and carrier head allows the cavity to be positively or negatively pressurized as required. 
         [0022]    One potential problem encountered in manufacturing is the manufacturing tolerances of different parts that are made to fit together in a final product. This may be particularly true of a membrane made of a flexible material. Flexible membranes are consumable products that are formed in greater quantity than the carrier heads. These membranes are replaced as the material wears out, e.g., becomes brittle or damaged. When the flexible membrane is formed, the thick rim at the end of the clamping portion is difficult to form with precision. If the thick rim is not within a desired tolerance, the thick rim may either not fit into the recess in which it is held by the carrier head or may not contact the edges of the recess. In either case, the thick rim may not properly seal the cavity between the carrier head and membrane. Lack of proper sealing allows for leaks and typically is an unusable membrane. 
         [0023]    By adding an extension to the thick rim, the dimension of the thick rim can be selected to be either at the target size of slightly smaller. The extension on the thick rim causes the thick rim to act as though it is a thick rim of a larger size in terms of sealing to the support component of the carrier head, while maintaining the ease of fit of a small thick rim. Because the extension has smaller dimensions than the thick rim itself, it can be referred to as a flash. Unlike most types of flash that are formed by manufacturing processes and removed, this flash is designed to be maintained on the membrane and to have uniform dimensions around the circumference of the membrane. Because the flash has an intended purpose in the final product and is designed to have specific dimensions, the flash is referred to as an engineered flash. 
         [0024]    Referring to  FIG. 1 , a substrate  10  will be polished by a chemical mechanical polishing (CMP) apparatus that has a carrier head  100 . A description of a CMP apparatus may be found in U.S. Pat. No. 5,738,574 and of a carrier head  100  may be found in U.S. Publication No. 2008/0119119, the entire disclosure of which is incorporated herein by reference. 
         [0025]    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  104 ), a loading chamber  108 , a retaining ring assembly including a retaining ring  200  and a first flexible membrane  300  shaped to provide an annular chamber  350 , a carrier ring  400 , and a substrate backing assembly  110  which includes a second flexible membrane  500  that defines a plurality of pressurizable chambers. Other features of the carrier head described for a similar carrier head may be found in U.S. Patent Application Publication No. 2006/0154580, the entire disclosure of which is incorporated herein by reference. 
         [0026]    The housing  102  can generally be circular in shape and can be connected to a drive shaft to rotate therewith during polishing. There may be passages (not illustrated) extending through the housing  102  for pneumatic control of the carrier head  100 . The base assembly  104  is a vertically movable assembly located beneath the housing  102 . The gimbal mechanism  106  permits the base assembly  104  to gimbal relative to the housing  102  while preventing lateral motion of the base assembly  104  relative to the housing  102 . 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 a polishing pad is also controlled by the loading chamber  108 . The substrate backing assembly  110  includes a flexible membrane  500  with a lower surface  512  that can provide a mounting surface for a substrate  10 . 
         [0027]    A substrate  10  can be held by a retaining ring assembly clamped to a base assembly  104 . The retaining ring assembly can be constructed from a retaining ring  200  and the flexible membrane  300 . The retaining ring  200  can be positioned beneath the flexible membrane  300  and configured to be secured to the flexible membrane  300 . 
         [0028]    The retaining ring  200  has an inner surface and a lower surface. The inner surface can be configured to circumferentially surround the edge of the substrate  10  to retain the substrate  10  during polishing. The lower surface of the retaining ring  200  can be brought into contact with a polishing pad (not shown). The retaining ring  200  has an annular upper surface that can have two annular concentric recesses. 
         [0029]    While the retaining ring  200  is configured to circumferentially surround the edge of a substrate  10  to retain the substrate, the flexible membrane  500  provides a surface  512  to mount the substrate  10 . The flexible membrane  500  has a main portion  510  that provides the substrate-mounting surface  512 . Extending from the main portion  510  is a vertically extending portion or outer annular portion  520  that can be clamped between the retaining ring  200  and the base assembly  104 . In some embodiments, the vertically extending portion is cylindrical. 
         [0030]    A thick rim portion  550  or bead is at a periphery of the membrane  500 . In some embodiments, a horizontal intermediate portion or lip bends inward toward a center of the membrane  500  and connects the thick rim  550  portion to the annular portion  520 . The thick rim  550  is configured to be secured to the base assembly  104 . 
         [0031]    Referring to  FIGS. 2 and 3 , a cross-sectional view of the thick rim portion  550  shows the thick rim portion  550  has having a diameter or thickness that is greater than an intermediate portion  553  that is between the thick rim portion  550  and the main portion  510  of the membrane  500 . An extending portion  555 , or engineered flash, extends away from the thick rim portion  550 . That is, the thick rim portion  550  is between the extending portion  555  and the main portion  510 . The extending portion  555  causes the effective thickness of the thick rim portion  550  to increase by the thickness of the extending portion  555 . 
         [0032]    In some embodiments, the thick rim portion  550  has a circular cross section ( FIG. 2 ). The diameter A equals the diameter C of the thick rim portion  550 , where the diameter A is measured perpendicular to the diameter C. The thickness B of the extending portion  555  (thickness perpendicular to the surface of the rim portion  550 ) causes the thick rim portion  550  to seal in a manner of a thick rim portion that has a diameter greater than A, such as the diameter of A+B, but will be less difficult to install than a membrane with a diameter of A+B. For example, the thick rim portion  550  may provide the sealing qualities of a thick rim portion having the dimensions shown in phantom outline  559 . The flexibility of the extending portion  555  with diameter B allows the thick rim portion  550  of diameter A plus the extending portion  555  to be forced into a groove or recess that a thick rim portion with a diameter of A+B would not, or would not easily, fit into. 
         [0033]    In other embodiments, the thick rim portion  550  has a cross section with curved portions and flat portions ( FIG. 3 ). The widest dimension D in one direction can be greater or less than the widest dimension E in a perpendicular direction to the direction at which dimension D is measured. However, the extending portion  555  behaves in substantially the same way as in the earlier described embodiment. In either a thick rim portion  550  with a circular cross section or a thick rim portion  550  with flat surfaces and curved surfaces, the thickness of the extending portion  555  (perpendicular to the surface of the rim portion  550 ) is less than a diameter, thickness or widest dimension of the thick rim portion  550 , such as less than a radius of thick rim portion  550 , such as less than less than 50%, less than 25%, less than 25%, less than 15%, less than 10%, or less than 5% of the thickness or widest dimension of the thick rim portion  550 , for example, between 5 and 10% of the radius of the diameter of the thick rim portion  550 . In some embodiments, the extending portion  555  has one or more right angles. In some embodiments, the extending portion  555  extends along a radius of the thick rim portion  550  and has sidewalls that are parallel to the radius. In other embodiments, the extending portion  555  tapers as it extends from the thick rim portion  550 . In some embodiments, the transition between the thick rim portion  550  and extending portion  555  includes an angle. 
         [0034]    The flexible membrane  500  is a generally circular sheet formed of a flexible and elastic material, for example, neoprene, polychloroprene, ethylene propylene diene rubber or silicone. The membrane  500  should be hydrophobic, durable, and chemically inert vis-à-vis the polishing process. The main portion  510  can be dimensioned to accept a 200 mm diameter substrate, e.g., the main portion  510  can be about 200 mm in diameter or slightly larger or can be dimensioned to accept a 300 mm diameter substrate, e.g., the main portion  510  can be about 300 mm in diameter or slightly larger. 
         [0035]      FIGS. 4 and 5  show a partial cross sectional view of the thick rim portion  550  and extending portion  555  in a recess  562  of a support component  565  of the carrier head assembly  104 . The thick rim portion  550  contacts the walls of the recess at contact points  578 ,  579 . The extending portion  555  is located on the thick rim portion  550  in the region of the contact points  578 . As can be seen from the two figures, the extending portion  555  can be located at either an inner contact point  578 , closer to the annular portion  520  or at an outer contact point  579  closer to the center of the membrane  500 . In some embodiments, the extending portion  555  is parallel to the plane along in which the intermediate portion  553  is oriented. In some embodiments, the extending portion  555  extends in a direction parallel to a direction that the intermediate portion  553  extends. In some embodiments, the extending portion  555  extends at a 10°, 15°, 30° or 45° angle to the plane along with the intermediate portion  553  extends. 
         [0036]    In addition to determining where to locate the extending portion  555 , a size of the extending portion  555  can be determined. In some instances, there is a range of diameters that allow the thick rim portion  550  to fit into a recess and simultaneous not allow fluid to lead between the membrane and the support component  565 . The range can be from x to y with a median target diameter z. The ends of the range, x and y, are about three standard deviations away from target diameter z. If membranes with a thick rim portion  550  were made with a target diameter of x, due to the imperfections in manufacturing, many of the membranes would leak. If membranes with a thick rim portion  550  were made with a target diameter of y, due to the imperfections in manufacturing, many of the membranes would not fit into the recess. One option is to make the thick rim portion  550  have the diameter z and make the extending portion  555  to have a thickness that is within two standard deviations of the target thickness. This thickness can be approximated by formula (2*(y−z)/3). 
         [0037]      FIG. 6  shows a partial cross-sectional view of one embodiment of a flexible membrane  500 , where only one-half of the cross section of the generally symmetric flexible membrane is shown. As shown in  FIG. 6 , the flexible membrane  500  can have a juncture between the main portion  510  and the outer annular portion  520  that has a peripheral edge hinge  530  and an annular recess  532 , located above the hinge  530  along the outer wall of the outer annular portion  520 . The peripheral edge hinge  530  can have rounded portions along its inner and outer surfaces. The peripheral edge hinge  530  and the annular recess  532  can be configured to be compliant, improving the symmetry of loading on the periphery of the substrate  10 . 
         [0038]    The outer annular portion  520  can have an annular recess  522  along its outer wall, which is configured to allow the outer annular portion  520  to flex. The outer annular portion  520  can also have an annular step  524  protruding inwardly along its inner wall. The annular step  524  can have non-horizontal (i.e., sloping) upper and lower surfaces. 
         [0039]    In some implementations, the flexible membrane  500  can have several annular flaps. The main portion  510  can have four concentric annular flaps  516 . The outer annular portion  520  can have a pair of annular flaps  526 . The annular flaps  526  connected to the outer annular portion  520  can have a horizontal portion  540  extending inwardly with a thick rim  550 . The horizontal portion  540  connects the thick rim  540  with the annular portion  520 . The upper annular flap can have a horizontal portion which is narrower (i.e., does not extend as far inwardly) than the lower annular flap. In some embodiments, the outer annular portion  520  can have an annular triangular portion, and the horizontal portions  540  of the pair of annular flaps  526  can be connected to the outer annular portion  520  through the vertices of the annular triangular portion. 
         [0040]    The innermost concentric annular flap  516  connected to the main portion  510  can include a horizontal portion extending outwardly with a thick rim, which can be configured to be secured to a base assembly  104 , and an annular angled portion  560 . The annular angled portion  560  can be joined between the main portion  510  and the horizontal portion of the annular flap  516 . The annular angled portion  560  can have a larger radius at its juncture with the main portion  510  than at its juncture with the horizontal portion. 
         [0041]    The three outermost concentric annular flaps  516  connected to the main portion  510  can include a vertical portion  570  extending from the main portion  510 , and a horizontal portion extending from the vertical portion  570  with a thick rim along the outer edge of the horizontal portion, which can be configured to be secured to a base assembly  104 . In some embodiments, the horizontal portion of a concentric annular flap  516  can have a smaller thickness than the vertical portion  570  of the concentric annular flap. In some implementations, the second and third outermost concentric annular flaps  516  can have a ratio of length of horizontal portion to length of vertical portion  570  between about 1.5 and 2.0, such as about 1.66. 
         [0042]    In some implementations, an annular flap  516 ,  526  can have one or more indentations or notches (i.e., an annular recess). A concentric annular flap  516  can have a notch  580  at the juncture between its horizontal portion and its vertical portion  570 . The notch  580  can allow the horizontal portion of the concentric annular flap  516  to flex vertically. A concentric annular flap  516  can have a notch  590  at its juncture with the main portion  510 . The notch  590  can be configured to reduce compressions in the main portion  510 . 
         [0043]    Referring to  FIG. 7 , in another embodiment, the flexible membrane  500 ′ does not include non-periphery backside flaps. A backside or plan view of the membrane shows an inner surface of the main portion  510 , the annular intermediate portion  553 , which connects the outer annular portion  520  with the annular thick rim  550 . The thick rim  550  is between the annular intermediate portion  553  and the annular extending portion  555 . As can be seen in  FIG. 8 , the outer annular portion  520 , which is cylindrical and lacks recesses, is between the circular main portion  510  and the annular intermediate portion  553 .  FIG. 9  shows a schematic cross-sectional view of the membrane  500 ′ held by a carrier head  100 ′. 
         [0044]    A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, the extending portions  555  can be at a non-parallel angle to the main portion. The features of one membrane described herein can be used with the other membrane described herein. Further, extending portions can be placed on components other than membranes, such as o-rings and the like. Accordingly, other implementations are within the scope of the following claims.