Patent Publication Number: US-2011053474-A1

Title: Polishing apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. P2009-200690, filed on Aug. 31, 2009, and the entire contents of which are incorporated herein by reference. 
     FIELD 
     The present invention relates to a polishing apparatus for polishing a work, e.g., wafer. 
     BACKGROUND 
     A single-side polishing apparatus for polishing a work, e.g., semiconductor wafer, is known. In the single-side polishing apparatus, the work held by a polishing head is pressed onto a polishing surface of a polishing plate, on which a polishing cloth is adhered, and the polishing plate is relatively moved with respect to the polishing head so as to polish the surface of the work. 
     A conventional single-side polishing apparatus is disclosed in Japanese Laid-open Patent Publication No. P2000-317819A. The single-side polishing apparatus has a polishing head for holding a wafer, the wafer is pressed onto a polishing pad (polishing cloth) adhered on a rotary polishing plate so as to polish the surface of the wafer. The polishing head comprises: a main body section facing the polishing plate and being capable of rotating; a carrier being loosely fitted in the polishing head and being capable of moving in the vertical direction; and a retainer ring enclosing the wafer and being brought into contact with the polishing pad with the wafer. The retainer ring is attached to the carrier by an O-ring, an air spraying member is provided on a lower face of the carrier, a protection sheet covers an outer face of the air spraying member, and the wafer is pressed onto the polishing pad, together with the protection sheet, by air (air layer) sprayed from the air spraying member. 
     In the polishing apparatus disclosed in Japanese Laid-open Patent Publication No. P2000-317819A, the air layer is formed between the air spraying member and the protection sheet, and the wafer is pressed onto the polishing pad (polishing cloth), together with the protection sheet, by the air layer. With this structure, even if concavities and convexities exist in a surface of the polishing cloth, the wafer is pressed, together with the protection sheet, by the air layer. Therefore, the wafer can move to follow the concavities and convexities, so that the wafer can be polished with high polishing accuracy and damaging the wafer can be prevented by the protection sheet. 
     However, in the polishing apparatus disclosed in Japanese Laid-open Patent Publication No. P2000-317819A, the O-ring is provided between the retainer ring and the carrier, so the carrier and the air spraying member fixed to the carrier hardly move in the horizontal direction. Namely, the carrier and the air spraying member can move only in the vertical direction with maintaining the horizontal state. When the wafer moves to follow the concavities and convexities of the polishing cloth, the wafer sometimes inclines with respect to the air spraying member which always maintains the horizontal state. Air is downwardly sprayed from the air spraying member. If the wafer inclines with respect to the horizontal plane, a distance between the wafer and the air spraying member is vary from place to place, so pressure applied to the wafer must be uneven and the wafer cannot be polished evenly. 
     These days, sizes of wafers are getting larger and larger. So, even if such unevenness is minute, it will highly affect the polishing accuracy. 
     SUMMARY 
     Accordingly, it is an object in one aspect of the invention to provide a polishing apparatus, which is capable of highly improving polishing accuracy. 
     To achieve the object, the polishing apparatus of the present invention, which polishes a surface of a work, comprises: 
     a polishing plate having a surface on which a polishing cloth is adhered; 
     a polishing head for pressing the work onto the polishing cloth; and 
     a driving mechanism for relatively moving the polishing head with respect to the polishing plate, 
     the polishing apparatus is characterized in, 
     that the polishing head includes:
         a main body section;   a board-shaped member having a concave part whose open end is aimed downward, the board-shaped member being suspended from the main body section and movable in the vertical direction;   a carrier being located in the concave part of the board-shaped member, being supported by the board-shaped member and being capable of inclining, in a state where a prescribed gap is formed between an outer circumferential face of the carrier and a side wall of the concave part, with respect to the horizontal plane, the carrier having a fluid feeding member which has a plurality of spraying ports from which a fluid is sprayed downward;   fluid supplying means for supplying the fluid to the carrier so as to spray the fluid downward from the fluid feeding member;   an elastic sheet being provided to the board-shaped member and covering a lower side of the fluid feeding member so as to form a first fluid chamber, the elastic sheet being capable of holding the work on a lower surface thereof;   a ring-shaped member being provided to an outer edge part of the lower surface of the elastic sheet, the ring-shaped member being capable of enclosing the work held on the lower surface of the elastic sheet;   first pressing means for pressing the board-shaped member downward so as to press the ring-shaped member onto the polishing cloth with the elastic sheet;   second pressing means for pressing the carrier downward; and   a fluid outlet for discharging the fluid from the first fluid chamber, the fluid outlet being formed in the board-shaped member, at a position higher than a lower surface of the fluid feeding member, and       

     that the work is pressed onto the polishing cloth, with the elastic sheet, by a pressing force generated by the second pressing means and applied to the carrier and inner pressure of the first fluid chamber generated by the fluid supplied to the first fluid chamber, so as to polish the work, and
         the fluid, which has been downwardly supplied into the first fluid chamber, horizontally flows outward in the first fluid chamber, collides with the side wall of the concave part and flows upward, and then the fluid is discharged outside from the fluid outlet, thereby the fluid feeding member follows movement of the elastic sheet and maintains parallel to the elastic sheet, and the fluid feeding member is centered in the first fluid chamber.       

     By employing the polishing apparatus of the present invention, the work can be uniformly polished with high polishing accuracy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described by way of examples and with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic explanation view of an embodiment of a polishing apparatus; 
         FIG. 2  is a schematic sectional view of a polishing head; 
         FIG. 3  is an explanation view showing inclination of a work; and 
         FIG. 4  is a schematic sectional view of another polishing head. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. 
       FIG. 1  is a schematic explanation view of a polishing apparatus of the present embodiment. 
     The polishing apparatus  10  comprises: a polishing plate  12  having an upper surface on which a polishing cloth  11  for polishing a work W (see  FIG. 2 ) is adhered; a polishing head  14  for holding the work W on a lower surface and pressing the work W onto the polishing cloth  11 ; and a driving mechanism for relatively moving the polishing head  14  with respect to the polishing plate  12 . 
     The driving mechanism is constituted by a first rotary driving unit (not shown) for rotating the polishing plate  12  about a rotary shaft  15  and a second rotary driving unit (not shown) for rotating the polishing head  14  about a rotary shaft  16 . Further, the polishing head  14  has a vertical driving unit (not shown) and a horizontal driving unit (not shown), holds the work W on the lower surface, and presses the work W onto the polishing cloth  11 . While pressing the work W onto the polishing cloth  11 , the driving mechanism relatively rotates the polishing plate  12  and the polishing head  14  so as to polish the lower surface of the work W. A slurry supply nozzle  18  supplies slurry to the polishing cloth  11  adhered on the polishing plate  12 . 
       FIG. 2  is a schematic sectional view of the polishing head  14 . 
     A main body section  20  has a side wall  20   a  and a concave part whose open end is aimed downward. 
     A board-shaped member  22  has a side wall  22   a  and a concave part  23  whose open end is aimed downward. The board-shaped member  22  is suspended, in the main body section  20 , by a ring-shaped rubber diaphragm  24  having enough elasticity, and capable of moving in the vertical direction. The side wall  20   a  acts as a guide for the vertical movement of the board-shaped member  22 . 
     A third fluid chamber  25  is formed, between the board-shaped member  22  and the main body section  20 , by the diaphragm  24 . Air is supplied from a compressed air source (not shown), e.g., air compressor, to the third fluid chamber  25  via a fluid path  26  formed in the rotary shaft  16  (not shown in  FIG. 2 ) of the polishing head  14 . The fluid path  26  is connected to the compressed air source by a rotary joint (not shown). The fluid path  26 , the compressed air source, etc. constitute third fluid supplying means. 
     Further, the third fluid chamber  25 , the third fluid supplying means, etc. constitute first pressing means. 
     A carrier  28  is located in the concave part  23  of the board-shaped member  22 , supported by a diaphragm  29  and capable of inclining, in a state where a prescribed gap is formed between an outer circumferential face of the carrier  28  and an inner face of the side wall  22   a  of the concave part  23 , with respect to the horizontal plane. 
     A second fluid chamber  34  is formed, between the carrier  28  and the board-shaped member  22 , by the diaphragm  29 . Air is supplied from the compressed air source (not shown) to the second fluid chamber  24  via a fluid path  35  formed in the rotary shaft  16  (not shown in  FIG. 2 ) of the polishing head  14 . The fluid path  35  is connected to the compressed air source by a rotary joint (not shown). The fluid path  35 , the compressed air source, etc. constitute second fluid supplying means. 
     Further, the third second chamber  34 , the second fluid supplying means, etc. constitute second pressing means. 
     An air reservoir  30  is formed in the carrier  28 . A fluid feeding member  31  is fixed to the carrier  28  and covers the lower side of the air reservoir  30 . A plurality of spraying ports, which are capable of spraying air downward, are formed in the fluid feeding member  31 . Air is supplied from the compressed air source (not shown) to the air reservoir  30  via a fluid path  37  formed in the rotary shaft  16  (not shown in  FIG. 2 ) of the polishing head  14 . The fluid path  37  is connected to the compressed air source by a rotary joint (not shown). The fluid path  37 , the compressed air source, etc. constitute first fluid supplying means. 
     An elastic sheet  36  covers the lower side of the fluid feeding member  31 , and an outer edge of the elastic sheet  36  is air-tightly fixed to a lower end of the side wall  22   a  of the board-shaped member  22  by suitable means (not shown). With this structure, a first fluid chamber  38  is formed under the fluid feeding member  31 . 
     The elastic sheet  36  is a two-layered sheet constituted by a sheet-shaped member  39 , which is composed of rubber and has enough elasticity, and a holding member  40 , which is provided under the sheet-shaped member  39  and has many holes for holding the work W by surface tension of water. 
     A ring-shaped member  42  composed of plastic, which encloses the work W held on a lower surface of the elastic sheet  36 , is attached to a lower edge of the elastic sheet  36 . 
     While polishing the work W, air is supplied to the third fluid chamber  25  so as to press the board-shaped member  22  downward, and the ring-shaped member  42  is pressed onto the polishing cloth  11  with the elastic sheet  36 . By downwardly pressing the polishing cloth  11  near an outer edge of the work W until reaching a level with the lower surface of the work W, excessive polishing of the outer edge of the work W can be prevented. 
     A plurality of fluid outlets  44  for discharging the fluid from the first fluid chamber  38  are formed, in the board-shaped member  22 , at positions higher than the lower surface of the fluid feeding member  31 . The fluid outlets  44  are equiangularly arranged. 
     In the present embodiment, discharge pipes  45  are respectively connected to the fluid outlets  44 , and the discharge pipes  45  are connected to a collecting pipe  46 . A relief valve  47  is provided to the collecting pipe  46 . The relief valve  47  maintains inner pressure of the first fluid chamber  38  at prescribed pressure. When the inner pressure of the first fluid chamber  38  is higher than the prescribed pressure, the relief valve  47  discharges air from the first fluid chamber  38 . 
     Note that, number of the fluid outlet  44  may be one. 
     The discharge pipes  45  are extended outside of the main body section  20  via large through-holes formed in the side wall  20   a.    
     Air discharged by the relief valve  47  may be collected and introduced to the compressed air source (not shown) to reuse. With this structure, running cost of the apparatus can be reduced and the apparatus is better for the environment. 
     Note that, the discharge pipes  45  and the relief valve  47  may be omitted. Further, the fluid may be directly discharged from the fluid outlets  44 . 
     The polishing apparatus of the present embodiment has the above described structure. Next, a polishing method in the polishing apparatus will be explained. 
     As described above, air is supplied into the third fluid chamber  25  to press the board-shaped member  22  (the press action is performed by the first pressing means) and the ring-shaped member  42  is pressed onto the polishing cloth  11  with the side wall  22   a  of the board-shaped member  22  and the elastic sheet  36  while polishing the work W, so that excessive polishing of the outer edge of the work W can be prevented. 
     Air is supplied into the second fluid chamber  34  so as to press the carrier  28  downward. Further, air is supplied into the first fluid chamber  38  so as to press the elastic sheet  36 . 
     Therefore, a pressing force for pressing the carrier  28 , which is applied by the second fluid chamber  34  (the second pressing means), and the inner pressure of the air supplied into the first fluid chamber  38  are applied to the work W via the elastic sheet  36 , so that the work W is pressed onto the polishing cloth  11  and polished thereon. 
     Note that, air supplied into the first fluid chamber  38  is always discharged outward from the fluid outlets  44 . A prescribed air layer must be always formed in the first fluid chamber  38 . Thus, the inner pressures of the first fluid chamber  38  and the second fluid chamber  34  are suitably set so as not to break the air layer in the first fluid chamber  38  by the inner pressure of the second fluid chamber  34 . By providing the relief valve  47 , the inner pressure of the first fluid chamber  38  can be easily controlled. 
     While polishing the work W, the air, which has been downwardly supplied into the first fluid chamber  38 , horizontally flows outward in the first fluid chamber  38 , collides with the inner face of the side wall  22   a  of the concave part  23  of the board-shaped member  22  and flows upward, and then the air is discharged outside from the fluid outlets  44 . The fluid outlets  44  are located at positions sufficiently-higher than a lower surface of the fluid feeding member  31 . Since the air horizontally flows outward in the first fluid chamber  38 , collides with the inner face of the side wall  22   a  of the concave part  23  of the board-shaped member  22  and flows upward, the carrier  28  (the fluid feeding member  31 ) is centered by a reactive force generated by colliding the air with the ring-shaped side wall  22   a.    
     As described above, the carrier  28  (the fluid feeding member  31 ) is floated and the carrier  28  does not directly act on the work W. Therefore, even if concavities and convexities exist on the surface of the polishing cloth  11  like gurge, the wafer can move to follow the concavities and convexities thereon. 
     In the present embodiment, the carrier  28  (the fluid feeding member  31 ) is supported by the board-shaped member  22  and capable of inclining, with respect to the horizontal plane, in a state where a prescribed gap is formed between an outer circumferential face of the carrier  28  and the inner face of the side wall  22   a  of the concave part  23 . 
     In a state where the surface of the polishing cloth  11  is horizontal, the carrier  28  (the fluid feeding member  31 ) is also horizontal. If concavities and convexities exist in the surface of the polishing cloth  11 , the work W is inclined, with respect to the horizontal carrier  28  (the fluid feeding member  31 ), as shown in  FIG. 3 . Note that, the inclination of the work W is exaggerated in  FIG. 3 . In the conventional polishing apparatus disclosed in Japanese Laid-open Patent Publication No. P2000-317819A, the horizontal state of the carrier is maintained, so a distance between the carrier (the fluid feeding member) and the work is varied, so the work cannot be uniformly pressed and cannot be evenly polished. 
     On the other hand, in the present embodiment, the carrier  28  (the fluid feeding member  31 ) is inclinable with respect to the board-shaped member  22 . As shown in  FIG. 3 , when the work W is inclined and a distance between the carrier  28  (the fluid feeding member  31 ) and the work W is varied, pressure (a reactive force) applied to the carrier  28  (the fluid feeding member  31 ) from a part X of the work W, at which the distance is short, is higher; on the other hand, pressure (a reactive force) applied to the carrier  28  (the fluid feeding member  31 ) from a part Y of the work W, at which the distance is longer, is lower. Since the work W contacts the polishing cloth  11 , one part of the carrier  28  (the fluid feeding member  31 ), which corresponds to the part X of the work W and to which the higher pressure (the reactive force) is applied, is moved away from the work W; the other part of the carrier  28  (the fluid feeding member  31 ), which corresponds to the part Y of the work W and to which the lower pressure (the reactive force) is applied, is moved close to the work W. With this action, the carrier  28  (the fluid feeding member  31 ) is inclined and made parallel to the work W. Therefore, the distance between the carrier  28  (the fluid feeding member  31 ) and the work W is made constant, so that the pressing force can be uniformly applied to the work W and the work W can be evenly polished. 
     As described above, the air pressure is applied to the carrier  28  (the fluid feeding member  31 ) so as to center the carrier  28  (the fluid feeding member  31 ). Even if the carrier  28  (the fluid feeding member  31 ) is inclined and shifted from the center of the board-shaped member  22 , the carrier  28  (the fluid feeding member  31 ) is always biased toward the center of the board-shaped member  22 . 
     In the present embodiment, the carrier  28  has the above described floating structure, and no load is applied from the work W while the polishing operation. Therefore, the diaphragm  29 , which suspends the carrier  28 , need not have high rigidity, so the carrier  28  can be easily inclinably suspended. 
       FIG. 4  is a schematic sectional view of another polishing head  14 . Note that, the structural elements shown in  FIG. 2  are assigned the same symbols and explanation will be omitted. 
     In the present embodiment, an air reservoir of the carrier  28  is divided into a plurality of reservoirs, e.g., a central air reservoir  30   a  and an outer air reservoir  30   b.  Fluid supplying means  50   a  and  50   b  respectively supply air to the air reservoirs  30   a  and  30   b . A flow volume controller  52  is provided to the fluid supplying means  50   a  so as to control flow volume of the air supplied to the air reservoir  30   a.  Another flow volume controller (not shown) may be provided to the fluid supplying means  50   b . Note that, a pressure controller or controllers may be employed instead of the flow volume controller or controllers. 
     In the present embodiment, the pressing force applied to a center zone and an outer zone of the work W can be controlled. Namely, polishing conditions can be precisely controlled. 
     Note that, the work W may be coaxially divided into three zones or more, and the pressing force can be controlled in the zones respectively. 
     In each of the above described embodiments, the fluid is air. The fluid may be a liquid. Further, the first pressing means (the third fluid chamber  25 , etc.) and the second pressing means (the second fluid chamber  34 , etc.) may be mechanical means, e.g., spring, screw mechanism. 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention has been described in detail, it should be understood that the various changes, substitutions, and alternations could be made hereto without departing from the spirit and scope of the invention.