Abstract:
A polishing head of a chemical and mechanical polishing apparatus can uniformly polishing a wafer by sticking the wafer firmly and with uniform pressure to a polishing pad. The polishing head includes a housing through which air is supplied and discharged from the head. A carrier is connected to the housing so as to be movable up and down relative to the housing. A wafer chucking device is mounted to the carrier. The wafer chucking device includes a wafer chuck body movable up and down relative to the carrier. The wafer chuck body defines a vacuum chamber therein for use in adhering a wafer to the wafer chucking device. A retainer is mounted to the periphery of the carrier, guides the wafer chuck body in its up and down movement relative to the carrier, and protects the wafer chucked by the wafer chucking device. A biasing member is used to exert a downward biasing force uniformly on the wafer chuck body. Because the wafer is held fast against the wafer chuck body, and is pressed in such a state against a polishing pad by the biasing force exerted uniformly on the wafer chuck body independently of the force used to position the retainer against the polishing pad, the wafer is forced against the polishing pad uniformly.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a chemical and mechanical polishing apparatus. More particularly, the present invention relates to the polishing head of a chemical and mechanical polishing apparatus.  
           [0003]    2. Description of the Related Art  
           [0004]    Manufacturing an integrated circuit on a semiconductor wafer often includes a chemical and mechanical polishing process used to flatten both surfaces of the wafer. The chemical and mechanical polishing process is becoming more important as semiconductor integrated circuits become more highly integrated and the diameter of wafers become larger.  
           [0005]    The chemical and mechanical polishing system used in flattening the wafer comprises a detachable device of a wafer cassette, a wafer transferring device, a polishing device, a wafer rinsing device, and a controlling device. The polishing device comprises a polishing pad, a polishing head for supporting and pressing the wafer against the polishing pad, a polishing plate to which the polishing pad is detachably mounted, a driving mechanism for rotating the polishing head relative to the polishing pad, a device for dressing the polishing pad, a mechanism for rinsing the wafer, and a slurry supplying mechanism.  
           [0006]    In the mechanical aspect of the polishing process, the polishing head and the polishing pad are rotated relative to one another at a certain speed, and material at the surface of the wafer is removed by the friction produced between the wafer and the polishing pad against which the wafer is pressed to generate a certain pressure. The rate at which material is removed from the wafer is proportional to the polishing pressure and the polishing speed. In the chemical aspect of the polishing process, a chemical reaction at the wafer surface is produced by slurry introduced between the wafer surface and the polishing pad. If the polishing pressure, the polishing speed, the amount of slurry, the friction between the surface of the wafer and the polishing pad, and the polishing temperature are uniform across the entire surface of the wafer, an extensive flattening and uniformity in the thickness of the residual film are achieved. However, in actuality, the above-mentioned factors and conditions at the surface of the wafer change over time. Accordingly, the thickness of the residual film is irregular after being polished. And, the wafer exhibits dishing and thinning phenomena. Therefore, the polishing conditions must be precisely controlled if the wafer is to be flattened satisfactorily.  
           [0007]    Various polishing apparatus and methods have been developed in an attempt to achieve a uniform polishing of a wafer. For instance, Japanese Patent Laid-open No. Hei 10-256202 discloses a polishing method and device in which dual fluid pressure chambers produce a uniform polishing. Japanese Patent Laid-open No. Hei 9-246218 discloses a polishing method and device in which an inflatable pad of polyethylene film is used to uniformly polish a wafer. A polishing device which can regulate the pressures of cells is disclosed in U.S. Pat. No. 5,605,488, and a polishing device in which a wafer is uniformly polished by using a flexible plate is disclosed in U.S. Pat. No. 5,851,136. Finally, U.S. Pat. No. 5,803,799 issued to Volodarsky discloses a polishing head for uniformly polishing a semiconductor wafer.  
           [0008]    [0008]FIG. 1 shows the polishing head of Volodarsky. The polishing head  10  includes a housing  14 , a wafer carrier  20  which is mounted to the housing  14  and has a wafer supporting surface  50 , and a wafer retainer  22  which is mounted to the housing  14  and maintains the wafer W on the wafer supporting surface  50 . Means are also provided for exerting a biasing force on the wafer carrier  20 .  
           [0009]    During the polishing process, the wafer W is stuck fast to a polishing pad P by the biasing force applied to the wafer carrier  20 . The retainer  22  retains the wafer stuck fast to the polishing pad by the wafer carrier  20 . Therefore, the wafer is retained in position and is pressed against the polishing pad by the biasing force distributed thereto via the wafer carrier  20 , so that the wafer can be uniformly polished. However, in the polishing head of Volodarsky, it is difficult to distribute the biasing force applied to the wafer carrier  20  uniformly over the wafer.  
           [0010]    Accordingly, the worked surface of the wafer is not uniformly stuck fast to the polishing pad, and the central and edge portions of the wafer are polished at different rates.  
         SUMMARY OF THE INVENTION  
         [0011]    The present invention has been made in light of the above-mentioned problem of the prior art. Accordingly, it is an object of the present invention to provide a chemical and mechanical polishing apparatus which can uniformly polishing a wafer  
           [0012]    In order to achieve the above-mentioned object of the present invention, the present invention provides a polishing head of a chemical and mechanical polishing apparatus for polishing a wafer, which holds a wafer fast against a wafer chuck body of a wafer chucking device, and in such a state exerts a downward uniform pressure on the wafer chuck body to press the wafer uniformly against a polishing pad.  
           [0013]    The polishing head includes a housing having air passageways through which air is supplied and/or discharged to and from the polishing head. A carrier is connected to the housing so as to be movable upward and downward relative thereto. The wafer chuck body is, in turn, mounted to the carrier so as to be movable upward and downward relative thereto. A retainer mounted to the periphery of the carrier guides the wafer chuck body in its upward and downward movement relative to the carrier and protects the wafer chucked to the wafer chuck body.  
           [0014]    In the present invention, the wafer chuck body and the carrier are independently movable upwardly and downwardly by air pressure. In addition, the wafer chuck body is rotated together with the retainer and the carrier, so that torsion between the carrier and the wafer chuck body is prevented. Therefore, when the wafer chucked by the wafer chuck body is stuck fast to the polishing pad, a surface of the wafer will be polished uniformly. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    The above and other objects, features and advantages of the present invention will become readily apparent by referring to the following detailed description of the preferred embodiment thereof made with reference to the accompanying drawings, of which:  
         [0016]    [0016]FIG. 1 is a cross-sectional view of a polishing head of a conventional chemical and mechanical polishing apparatus;  
         [0017]    [0017]FIG. 2 is a cross-sectional view of a polishing head of a chemical and mechanical polishing apparatus according to the present invention, and shows a carrier of the apparatus in an upper position at which a wafer is chucked to the polishing head;  
         [0018]    [0018]FIG. 3 is another cross-sectional view of the polishing head of a chemical and mechanical polishing apparatus according to the present invention, but shows a wafer being moved onto a polishing pad of the apparatus;  
         [0019]    [0019]FIG. 4 is still another cross-sectional view of the polishing head of a chemical and mechanical polishing apparatus according to the present invention, but shows the carrier moved to a downward position such that a retainer of the polishing head is placed in contact with the surface of the polishing pad; and  
         [0020]    [0020]FIG. 5 is still another cross-sectional view of the polishing head of a chemical and mechanical polishing apparatus according to the present invention, but shows a wafer in contact with the surface of the polishing pad. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]    The preferred embodiment of the present invention will be described in detail hereinafter with reference to the attached drawings.  
         [0022]    As shown in FIGS.  2  to  5 , a polishing head  100  of the chemical and mechanical polishing apparatus for polishing a wafer according to the present invention includes a housing  110  which defines an air passage system therein, a carrier  120  which is connected to the housing  110  so as to be movable up and down relative thereto, a wafer chucking device  130  which is mounted to the carrier  120 , and a retainer  140  fixed to the carrier at the periphery of the carrier  120 .  
         [0023]    The housing  110  comprises a body portion  112  which has a circular cross section, a flange portion  114  which extends radially outwardly from one end of the body portion  112 , and an extending portion  116  which extends downwardly at the center of the body portion  112 . The housing  110  is generally made of steel, such as stainless steel.  
         [0024]    The air passage system of the housing  110  comprises three passageways, i.e., a first passageway  112   a , a second passageway  112   b , and a third passageway  112   c . The first passageway  112   a  extends through the body portion  112  and the extending portion  116 . The second and third passageways  112   b  and  112   c  are disposed symmetrically with respect to the longitudinal axis of the body portion  112 .  
         [0025]    The extending portion  116  of the housing  110  is received in a central opening  122   a  formed in the carrier  120 . The extending portion includes a key (not shown) which extends radially at the outer peripheral portion thereof. The key is received in key-way (also not shown) formed in the inner peripheral surface of the carrier  120  which defines the opening  122   a . The key-way has the same width and height as the key of the extending portion  116  of the housing  110 . Accordingly, the carrier  120  will rotate together with the housing  100  when the polishing head  100  is operated. The chucking device  130  and the retainer  140  which are connected to the carrier  120  will thus rotate together with the housing  110 , as well.  
         [0026]    The first passageway  112   a  communicates with an air chamber  160  which is defined by and between the carrier  120  and the chucking device  130 . The air chamber  160  is inflated or deflated by supplying or discharging air through the first passageway  112   a . In this way, the chucking device  130  is moved relative to the carrier  120 .  
         [0027]    The second passageway  112   b  of the housing  110  is radially spaced apart from the first passageway  112   a  by a predetermined distance, and communicates with an air chamber  150  defined by and between the housing  110  and the carrier  120 . When air is supplied to the air chamber  150  via the second passageway  112   b , the carrier  120  is moved downwardly relative to the housing  110 . As a result, the retainer  140  engaged with the carrier  120  is also moved downwardly. On the other hand, when air is discharged from the air chamber  150 , a vacuum is created in the air chamber  150 . Thus, the carrier  120  is moved upwardly to its original position. In this case, the retainer  140  is moved upwardly together with the carrier  120 .  
         [0028]    The carrier  120  comprises a body portion  122 , and a flange portion  124  which extends radially from the lower end of the body portion  122 . A first through-hole, forming the opening  122   a , is formed at the center of the body portion  122  of the carrier  120 , and a second through-hole is formed at a position spaced radially outwardly from the first through-hole by a predetermined distance. A plurality of through-holes are formed about the longitudinal axis of the body portion  122  adjacent the outer periphery of the flange portion  124 .  
         [0029]    An air pipe  112   c  is fixed to the housing  110  within a through-hole to constitute the third passageway extending through the housing  10 . The air pipe  112   c  projects downwardly some distance from the lower surface of the housing  110 . A second air pipe  122   b  is fixed to carrier  120  within the second through-hole formed in the carrier  120 , and receives the projecting end of the air pipe  112   c . When the air chamber  150  formed between the housing  110  and the carrier  120  is inflated and the carrier  120  is moved downwardly, the air pipe  122   b  of the carrier  120  slides downwardly along the air pipe  112   c  of the housing  110 . And, when the air chamber  150  contracts and the carrier  120  is moved upwardly, the air pipe  122   b  of the carrier  120  slides upwardly along the air pipe  112   c  of the housing  110 .  
         [0030]    The carrier  120  also includes a connecter for connecting the carrier  120  to the housing  110 . The connecter comprises an annular inner clamp  126 , an annular outer clamp  128  which has an inner diameter larger than the outer diameter of the inner clamp  126 , and an annular resilient sheet  129 . One end of the resilient sheet  129  is fixed to the upper surface of the carrier  120  by the inner clamp  126 , and the other end of the resilient sheet  129  is fixed to the lower surface of the housing  110  by the outer clamp  128 , to thereby connect the carrier  120  to the housing  110 .  
         [0031]    More specifically, the outer peripheral edge portion of the inner clamp  126  of the connector is recessed to thereby define a step in the outer peripheral edge. The upper outer peripheral portion of the body portion  122  of the carrier also has an annular recess therein. The inner clamp  126  has a first central through-hole which forms part of the central opening  122   a  in the carrier  120 , and a plurality of second through-holes which are radially spaced from the first through-hole. The body portion  122  of the carrier  120  has tapped holes in the upper surface thereof aligned with the plurality of through-holes formed in the inner clamp  126 . The aligned through-holes receive screws by which the inner clamp  126  is fixed to the body portion  122  of the carrier  120 . When the inner clamp  126  is fixed to the upper surface of the carrier  120 , the width of the annular recess which is defined between the stepped portions of the inner clamp  126  and the body portion  122  of the carrier  120  is equal to or smaller than the thickness of the resilient sheet  129 , so that the resilient sheet  129  is securely fixed to the carrier  120 .  
         [0032]    The outer clamp  128  has a central body portion, and flange portion  128   a  which extends radially from the upper part of the body portion. The flange portion  128   a  of the outer clamp and the flange portion of the housing  110  have a plurality of corresponding through-holes. The upper end of the inner circumferential portion of the outer clamp  128  is recessed to form a step. The height of the step is smaller than the thickness of the resilient sheet  129 . Bolts extending through the through-holes formed in the flange portion  114  of the housing  110  and the flange portion  128   a  of the outer clamp  128  are threaded to nuts to fix the outer clamp  128  to the housing  110  and thereby clamp the outer end of resilient sheet  129  to the housing  110 .  
         [0033]    The annular resilient sheet  129  is basically an air bladder made of rubber or of a synthetic resin.  
         [0034]    The carrier  120  is connected to the housing  110  by the inner and outer clamps  126  and  128  and the resilient sheet  129 . After one edge of the resilient sheet  129  is located in the step formed in the upper end of the inner circumferential portion of the outer clamp  128 , the housing  110  and the outer clamp  128  are positioned such that through-holes formed in the flange portion  114  of the housing  110  are aligned with through-holes formed in the flange portion  128   a  of the outer clamp  128 . Then the bolts are passed through the through-holes formed in the flange portions  114  and  128   a  and are threaded to the nuts.  
         [0035]    Then, the inner clamp  126  and the carrier  120  are positioned such that the other end portion of the resilient sheet  129  is located in the annular recess defined by the carrier  120  and the stepped portion of the inner clamp  126 . Screws are passed through the through-holes formed in the inner clamp  126 , and into the tapped holes  126   b  which are formed in the upper surface of the carrier  120 .  
         [0036]    The retainer  140  is annular. The inner diameter of the retainer  140  is smaller than the outer diameter of the flange portion  124  of the carrier  120 , and the outer diameter of the retainer  140  is larger than that of the flange portion of the carrier  120 . The retainer  140  has an annular recess in the upper end portion thereof. The outer diameter of the recess is equal to or larger than the outer diameter of the flange portion  124  of the carrier  120 , and the depth of the recess is equal to the thickness of the flange portion  124 . Tapped holes, corresponding to the through-holes formed in the flange portion  124  of the carrier  120 , extend into the upper end of the retainer  140  at the bottom of the recess. After the flange portion  124  of the carrier  120  is seated in the recess of the retainer  140 , and the through-holes formed in the flange portion  124  of the carrier are aligned with the tapped holes formed in the retainer, screws are passed through the through-holes formed in the flange portion  124  of the carrier  120  and into the tapped holes formed in the upper surface of the retainer to connect the carrier  120  to the housing  140 .  
         [0037]    Furthermore, a plurality of elongate grooves  142  extend axially along the retainer in the inner circumferential surface of the retainer  140 . Preferably, four grooves  142  extend along the inner circumferentiasurface of the retainer  140  as spaced apart from one another by angular intervals of ninety degrees.  
         [0038]    The wafer chucking device  130  comprises an inflatable member  132 , a wafer chuck body  134  which is attached to the lower surface of the inflatable member  132 , a sheet  136  which is attached to the lower surface of the wafer chuck body  134  to prevent the rear surface of the wafer from being damaged, and a fixing means  138  which fixes the inflatable member  132  to the carrier  120 .  
         [0039]    The inflatable member  132  is annular, and is basically an air bladder made of rubber or of a synthetic resin like the annular resilient sheet  129 . The inflatable member  132  has plurality of through-holes disposed radially about the center thereof.  
         [0040]    The wafer chuck body  134  comprises an annular first member  134   a,  and a second member  134   b  which is attached to the lower surface of the first member  134 , whereby an air chamber  170  is defined between the first and second members  134   a  and  134   b.  A through-hole is formed in the central portion of the first member  134   a,  and an air flow pipe  135  is received in the through-hole. The second member  134   b  comprises a circular body portion which has an outer diameter smaller than that of the first member  134   a , and an annular wall portion which extends upwardly from the periphery of the body portion to the second member  134 . The second member  134   b  is attached to the first member  134   a  by welding or the like such that the first and second members  134   a  and  134   b  are integral. A plurality of through-holes extend through the circular body portion of the second member  134   b.    
         [0041]    The first member  134   a  of the wafer chucking member  134  comprises four protruding portions  134   a′  which protrude outwardly at the periphery thereof as spaced from one another by angular intervals of ninety degrees. The protruding protrusions  134   a′  extend into the elongate grooves  142 , respectively, formed in the inner circumferential surface of the retainer  140 , such that the chuck body  134  can be moved upwardly or downwardly relative to the carrier  140  as guided by the elongate grooves  142 .  
         [0042]    The sheet  136  is a circular film of a synthetic resin attached to the second member  134   b . The sheet  136  has a plurality of through-holes extending therethrough. The through-holes formed in the sheet  136  correspond to and are aligned with the through-holes formed in the second member  134   b  of the chuck body  134 .  
         [0043]    The fixing means  138  comprises an annular first member  138   a  and a second member  138   b . The first member  138   a  comprises a tubular body portion, and upper and lower flanges which extend radially outwardly from the lower and upper ends of the tubular body portion, respectively. A plurality of through-holes are formed about the longitudinal axis of the first member  138   a  in the upper flange of the first member  138   a . After the through-holes formed in the upper flange of the first member  138   a  are aligned with the tapped holes formed in the lower surface of the carrier  120 , screws are passed through the through-holes and into tapped holes formed in the bottom of the body portion  122  of the carrier  120 . A seal may be disposed between the lower surface of the carrier  120  and the upper surface of the upper flange of the first member  138   a  in order to seal the space  160  defined between the carrier  120  and the chuck body  134 . A plurality of through-holes are also formed about the longitudinal axis of the first member  138   a  in the lower flange of the first member  138   a.    
         [0044]    The annular second member  138   b  of the fixing member  138  has through-holes corresponding to the those formed in the lower flange of the first member  138   a . After the air pipe  135  is fitted to the second member  134   b  of the chuck body  134  within the through-hole formed at the central portion of the first member  134   a , the inflatable member  132  is bonded to the upper surface of the first member  138   a  of the chucking member  134  with the air pipe  135  passing through the through-hole formed at the center of the inflatable member  132 . Then, the outer peripheral portion of the inflatable member  132  is bent upwardly and then inwardly around the lower flange of the first member  138   a  of the fixing means  138  until the through-holes formed in the outer peripheral portion of the inflatable member  132  are aligned with the through-holes formed in the lower flange of the first member  138   a . Then, the second member  138   b  of the fixing member  138  is positioned on the outer peripheral portion of the inflating member  132  with the through-holes formed in the second member  138   a  of the fixing member  138  aligned with the through-holes formed in the lower flange of the first member  138   a  of the fixing member  138  and the through-holes formed at the outer peripheral portion of the inflatable member  132 .  
         [0045]    Before the fixing member  138  is connected to the chuck body  134 , the air flow pipe  135  mounted to the first member  134   a  of the wafer chucking member  134  and the air pipe  122   b  extending through the carrier  120  are connected by a supplying and discharging pipe  122  so that air can be supplied to and discharged from the air chamber  170  defined by the first and second members  134   a  and  134   b.    
         [0046]    Finally, fasteners are passed through the through-holes formed in the second member  138   b  of the fixing member  138 , the through-holes formed in the outer peripheral portion of the inflatable member  132  and into the holes formed in the lower flange of the first member  138   a , such that the air chamber  160  defined by the inflatable member  132 , the first member  138   a  of the fixing member  138 , and the carrier  120  is sealed.  
         [0047]    The operation of the polishing head according to the present invention will now be described with reference to the drawings.  
         [0048]    First, as shown in FIG. 2, the air is discharged from the air chamber  150  via the second passageway  112   b  of the housing  110  to create a vacuum the air chamber  150 . Once the air chamber  150  is sufficiently evacuated, the carrier  120  is held fast to the lower surface of the housing  110  by the negative pressure of the vacuum.  
         [0049]    With the carrier  120  held tightly to the lower surface of the housing  110 , the retainer  140  connected to the carrier  120  and the wafer chucking device  130  are located in an upward position. Then, air is supplied to the air chamber  160  through the first passageway  112   a  of the housing  110  to inflate the inflatable member  132 , thereby causing the chucking member  134  to move downwardly until the sheet  136  is positioned on the same plane as the bottom surface of the retainer  140 .  
         [0050]    Once the chucking member  134  is moved to this position, air is discharged from the air chamber  170 . Thus, a wafer W which is fed by a wafer feeding device (not shown) is drawn to the sheet  136  attached to the chuck body  134 .  
         [0051]    Once the wafer W adheres to the sheet  136  and covers the through-holes extending therethrough, the discharging of air from the chamber  170  creates a vacuum in the chamber  170  which causes the wafer W to adhere more strongly to the sheet  136 .  
         [0052]    Referring now to FIG. 3, air is now discharged from the air chamber  160  via the passageway  112   a  extending through the body portion  112  and extension member  116  of the housing  110 . Thus, the air chambers  150 ,  160 , and  170  are all evacuated. Therefore, the inflatable member  132  of the chucking device  130  is collapsed upward towards the fixing member  138 . Consequently, the chuck body  130  is raised and the chucked wafer W is brought above the lower surface of the retainer  140 .  
         [0053]    Then, as shown in FIG. 4, while the air chamber  160  formed between the carrier  120  and the chucking device  130  and the air chamber  170  formed between the first member  134   a  and the second member  134   b  of the chuck body  134  remain evacuated, air is supplied to the air chamber  150  formed between the housing  110  and the carrier  120 . As a result, the carrier  120  is moved downwardly. Furthermore, the retainer  140  and the chucking device  130  connected to the carrier  120  are moved downwardly together with the carrier  120 . Thus, the retainer  140  is brought into contact with the upper surface of the polishing pad. However, since the chucking device  130  is located above the lower surface of the retainer  140 , the wafer W remains off of the upper surface of the polishing pad.  
         [0054]    Then, as shown in FIG. 5, while air continues to be supplied into the air chamber  150 , and air continues to be discharged from air chamber  170 , air is supplied into the air chamber  160  formed between the carrier  120  and the inflatable member  132  of the chucking device  130  to increase the pressure in the air chamber  160 . As the pressure in the air chamber  160  is increased, the inflatable member  132  is inflated and the chucking device  130  connected to the inflatable member  132  is moved downwardly. As a result, a surface of the chucked wafer W is brought into contact with the upper surface of the polishing pad. The wafer W is stuck fast to the polishing pad by continuously increasing the pressure in the air chamber  160  formed between the carrier  120  and the chucking device  130 .  
         [0055]    Once the wafer W is stuck fast to the polishing pad, a slurry is supplied between the wafer W and the polishing pad, and the polishing head and the polishing pad are rotated relative to one another, whereby the wafer W is polished.  
         [0056]    According to the present invention, the entire surface of the wafer is forced uniformly against the polishing pad because of the pressure applied against the chuck body, by an inflated resilient member, independently of the force used to press the retainer against the polishing pad. Thus, the wafer contacts the polishing pad uniformly. Therefore, the entire surface of the wafer from the central portion to the peripheral edge thereof is uniformly polished.  
         [0057]    Although the present invention has been described in detail with respect to the preferred embodiment thereof, it is to be understood that the present invention is not limited to the preferred embodiment but that various changes and modifications can be made thereto by one skilled in the art without departing from the true spirit and scope of the present invention as defined by the appended claims.