Abstract:
According to the present invention, there is provided a polishing apparatus comprising: a rotatable turntable; a polishing cloth attached on said turntable; a slurry supply pipe which supplies a slurry onto said polishing cloth; and a polishing member which presses an object to be polished against a surface of said polishing cloth, wherein said polishing cloth once stores the supplied slurry inside said polishing cloth, and discharges the slurry when pressed by said polishing member, thereby supplying the slurry to the surface of the object.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application is based upon and claims benefit of priority under 35 USC §119 from the Japanese Patent Application No. 2003-353393, filed on Oct. 14, 2003, the entire contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to a polishing apparatus, polishing method, and semiconductor device fabrication method including a polishing process.  
         [0003]     In the recent semiconductor device fabrication field, new fabrication apparatuses have been developed as the degree of micropatterning of semiconductor elements and the density of element structures increase.  
         [0004]     Among other fabrication apparatuses, a CMP (Chemical Mechanical Polishing) apparatus is essential in, e.g., CMP processes of a DRAM or high-speed logic LSI, i.e., a metal interconnection formation process, buried element isolation region formation process, and the like.  
         [0005]     In these processes using the CMP apparatus, it is important to reduce the use amount of slurry which occupies most of the cost, in addition to improving the process performance such as the surface uniformity.  
         [0006]      FIG. 10  shows polishing cloth  100  used in the conventional polishing technique.  
         [0007]     A slurry is supplied on the polishing cloth  100  in the direction of an arrow  102 . Since the polishing cloth  100  hardly has a function of storing the slurry inside it, the slurry radially scatters on the surface of the polishing cloth  100  as indicated by arrows  103 . The polishing cloth  100  is adhered on a turntable (not shown) by a double-coated adhesive tape, and rotated in the direction of an arrow  101 .  
         [0008]      FIG. 11  is a longitudinal sectional view of the polishing cloth  100  and an object  111  to be polished in a conventional polishing apparatus.  
         [0009]     As described above, a slurry supplied onto the surface of the polishing cloth  100  scatters in the direction of the arrow  103 . The object  111  to be polished is rotated and pressed by a polishing member  112 , and polished when the slurry enters a gap between the object  111  and polishing cloth  100 .  
         [0010]     In this state, the slurry can enter the gap between the polishing cloth  100  and object  111 , so the object  111  can be polished although it is difficult to evenly supply the slurry onto the surface of the object  111 .  
         [0011]      FIG. 12  is a longitudinal cross sectional view of the polishing cloth  100  and the object  111  to be polished in another conventional polishing apparatus.  
         [0012]     In this state, the pressure, indicated by an arrow  114 , which presses a polishing member  113  into the shape of a ring is high, so almost no gap exists between the polishing cloth  100  and object  111 . This makes it difficult to allow the slurry to enter in the direction indicated by the arrow  103 , and obtain a satisfactory polishing performance.  
         [0013]     In the conventional general slurry supply method as shown in  FIG. 10 , a slurry is dropped onto the polishing cloth  100  placed on the turntable, and supplied to the whole polishing cloth by the centrifugal force obtained by the rotation of the turntable, regardless of whether the polishing apparatus shown in  FIG. 11  or  12  is used. Since most of the supplied slurry scatters on the polishing cloth as described above, less than half the supplied slurry effectively functions during polishing, and more than half the supplied slurry is wasted. If it is possible to allow a minimum necessary amount of slurry to effectively function, the use amount of slurry can be presumably reduced.  
         [0014]     In the conventional slurry supply method, however, the supply amount of slurry inevitably varies in accordance with the distance from the slurry dropping position. Therefore, to polish the entire surface of a semiconductor wafer as the object  111  to be polished, an excess slurry must be supplied to ensure a high process performance, and this increases the cost.  
         [0015]     Also, the reduction in use amount of slurry generally leads to various process performance deteriorations, e.g., not only the decrease in surface uniformity and polishing speed, but also the extension of erosion which worsens the flatness of the polishing surface and the increase in scratch.  
         [0016]      FIG. 13  shows the polishing speed and erosion as functions of the flow rate of slurry. As is apparent from this graph, when the slurry flow rate decreases, the polishing speed lowers, and the erosion increases.  
         [0017]     By contrast, in the technique disclosed in patent reference  1  presented below, a slurry is supplied from below the polishing cloth, i.e., from the surface opposite to the polishing surface. In addition, to reduce the slurry supply amount, area control is performed by dividing a turntable into four portions, and the slurry is supplied upward to a wafer when it passes by. Patent reference 1: Japanese Patent Laid-Open No. 10-94965 Unfortunately, the control mechanism is complicated, and it is difficult to evenly supply the slurry to the entire surface of a wafer.  
         [0018]     As described above, it is conventionally impossible to assure a high process performance with a simple arrangement without supplying any excess slurry, and this increases the cost.  
       SUMMARY OF THE INVENTION  
       [0019]     According to one aspect of the present invention, there is provided a polishing apparatus, comprising: 
        a rotatable turntable;     a polishing cloth attached on said turntable;     a slurry supply pipe which supplies a slurry onto said polishing cloth; and     a polishing member which presses an object to be polished against a surface of said polishing cloth,     wherein said polishing cloth once stores the supplied slurry inside said polishing cloth, and discharges the slurry when pressed by said polishing member, thereby supplying the slurry to the surface of the object.        
 
         [0025]     According to one aspect of the present invention, there is provided a polishing method, comprising: 
        attaching a polishing cloth on a turntable and rotating the polishing cloth; and     supplying a slurry onto the polishing cloth, and pressing an object to be polished against a surface of the polishing cloth by using a polishing member, thereby polishing the object,     wherein the slurry is once stored inside the polishing cloth, and discharged and supplied to a surface of the object when pressed by the polishing member.        
 
         [0029]     According to one aspect of the present invention, there is provided a semiconductor device fabrication method, comprising: 
        obtaining an object to be polished by depositing a conductive film above an insulating film formed above a semiconductor substrate, so as to fill a recess formed in the insulating film;     attaching a polishing cloth on a turntable, and rotating the polishing cloth; and     supplying a slurry onto the polishing cloth, and pressing the object to be polished against a surface of the polishing cloth by using a polishing member, thereby polishing the object and removing the conductive film except for the conductive film in the recess,     wherein when the conductive film is removed, the slurry is once stored inside the polishing cloth, and discharged and supplied to a surface of the object while pressed by the polishing member.       
 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0034]      FIG. 1  is a longitudinal cross sectional view showing the sectional structure of a polishing cloth used in a polishing apparatus according to the first embodiment of the present invention;  
         [0035]      FIG. 2  is a longitudinal cross sectional view showing the movement of a slurry when an object to be polished is polished by using the polishing cloth shown in  FIG. 1 ;  
         [0036]      FIG. 3  is a perspective view showing an outline of the overall arrangement of the polishing apparatus shown in  FIG. 1 ;  
         [0037]      FIG. 4  is a graph showing the polishing speed and erosion as functions of the flow rate of slurry when polishing is performed using the polishing apparatus shown in  FIG. 1 ;  
         [0038]      FIG. 5  is a longitudinal cross sectional view showing an element section in a certain process when a semiconductor device is fabricated by using the polishing apparatus shown in  FIG. 1 ;  
         [0039]      FIG. 6  is a longitudinal cross sectional view showing the element section in another process when the semiconductor device is fabricated by using the polishing apparatus shown in  FIG. 1 ;  
         [0040]      FIG. 7  is a longitudinal cross sectional view showing the sectional structure of a polishing cloth used in a polishing apparatus according to the second embodiment of the present invention;  
         [0041]      FIG. 8  is a longitudinal cross sectional view showing an example of the structure of a polishing member (top ring head) included in the polishing apparatus;  
         [0042]      FIG. 9  is a longitudinal cross sectional view showing another example of the structure of the polishing member (top ring head) included in the polishing apparatus;  
         [0043]      FIG. 10  is a perspective view showing the way a slurry is dropped onto polishing cloth used in a conventional polishing apparatus;  
         [0044]      FIG. 11  is a longitudinal cross sectional view showing the movement of the slurry when polishing is performed using the conventional polishing apparatus;  
         [0045]      FIG. 12  is a longitudinal cross sectional view showing the movement of the slurry when polishing is performed using another conventional polishing apparatus; and  
         [0046]      FIG. 13  is a graph showing the polishing speed and erosion as functions of the flow rate of slurry when polishing is performed using the conventional polishing apparatus. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0047]     Embodiments of the present invention will be described below with reference to the accompanying drawings.  
       (1) FIRST EMBODIMENT  
       [0048]      FIG. 1  shows the longitudinal cross sectional structure of polishing cloth  10  used in a polishing apparatus according to the first embodiment.  
         [0049]     The polishing cloth  10  has a first layer  11  and second layer  12 . The first layer  11  has a plurality of through holes  13  which extend from the upper surface to the lower surface in contact with the second layer  12 . The second layer  12  is made of a porous material having open cells. The first and second layers  11  and  12  are formed by using a polymer material such as polyurethane.  
         [0050]     When a slurry is dropped on the surface of the polishing cloth  10  in the direction of an arrow  14 , it is supplied to the second layer  12  trough the through holes  13  in the first layer  11 . In the second layer  12 , the slurry is diffused toward the circumference as indicated by arrows  15  by the centrifugal force of the rotation of a turntable, and once stored.  
         [0051]     In this state, as shown in  FIG. 2 , an object  21  to be polished is placed on the surface of the first layer  11 , and a polishing member  22  presses the object  11  in the direction of an arrow  23 , thereby discharging the slurry stored in the second layer  12 . Consequently, the slurry is discharged in the direction of arrows  16  through the through holes  13  in the first layer  11 , and supplied to the contact surface between the surface of the first layer  11  and the object  21 .  
         [0052]      FIG. 8  shows an example of the structure of the polishing member  22 .  
         [0053]     The object  21  to be polished is placed on the polishing cloth  10 , and the polishing member having a housing  201  rotates the object  21  while pressing it. The housing  201  has a guide ring  205  for holding the object  21 , an elastic sheet  204  which comes in contact with the rear surface of the object  21 , and a hollow portion  203  which improves the uniformity of polishing by applying an air pressure in the direction of an arrow  211  to the rear surface of the object  21  via the elastic sheet  204 . Also, a load necessary for polishing is applied to the inside of the housing  201  by applying an air pressure in the direction of an arrow  212 .  
         [0054]      FIG. 9  shows another example of the structure of the polishing member  22 . The polishing member  22  shown in  FIG. 9  can apply a more even pressure to the object  21  to be polished.  
         [0055]     That is, the object  21  is placed on the polishing cloth  10 , and the polishing member having a housing  221  rotates the object  21  while pressing it. The housing  221  has an airbag chamber  222 , hollow chamber  223 , and retainer ring  224 . The airbag chamber  222  is formed by a membrane  235  which is made of hard rubber and comes in contact with the rear surface of the object  21 , and a chucking plate  234 . The airbag chamber  222  applies a load necessary for polishing when an air pressure is applied in the direction of an arrow  231 . The hollow chamber  223  gives an air pressure for pressing the chucking plate  234  in the direction of an arrow  232 . The retainer ring  224  retains the object  21  to be polished, and presses the surface of the polishing cloth  10  into the shape of a ring in a position separated from the outer circumference of the object  21  when an air pressure is applied in the direction of an arrow  233  inside the housing  221 .  
         [0056]     The pressure indicated by the arrow  231  is higher than that indicated by the arrow  233 . This improves the uniformity of polishing.  
         [0057]      FIG. 3  shows an outline of the overall arrangement of a polishing apparatus usable in the embodiment of the present invention.  
         [0058]     The polishing cloth  10  is adhered by, e.g., a double-coated adhesive tape on a turntable  31  which rotates in the direction of an arrow  43 . A semiconductor wafer is set as the object  21  to be polished.  
         [0059]     A slurry  34  is dropped in a substantially central position on the polishing cloth  10  from a slurry supply pipe  33 , and diffused in the polishing cloth  10  toward the periphery by the centrifugal force. The slurry  34  is once stored as it is spread over the entire region of the polishing cloth  10 .  
         [0060]     A top ring head  22  as a polishing member rotates the semiconductor wafer as the object  21  in the direction of an arrow  42  while pressing the wafer against the polishing cloth  10 . Also, a dressing head  32  opposes the top ring head  22  on the other side of the central position of the turntable  31 , and rotates as indicated by an arrow  41  to dress the polishing cloth  10 .  
         [0061]     In the first embodiment, when pushed by the top ring head  22 , the slurry  34  once stored in the polishing cloth  10  oozes out toward the upper surface in  FIG. 3  and is supplied between the polishing cloth  10  and object  21 .  
         [0062]     Consequently, unlike in any conventional apparatus, it is possible to evenly supply the slurry to the surface in contact with the object  21  without wasting it by scattering it on the polishing cloth  10 . Also, even when the retainer ring is pressed by a high pressure by using the head shown in  FIG. 9 , the slurry can be reliably supplied to the surface in contact with the object  21 .  
         [0063]      FIG. 4  shows the polishing speed and erosion as functions of the flow rate of slurry when the polishing apparatus according to the embodiment of the present invention is used. Unlike in the conventional apparatus shown in  FIG. 13 , both the polishing speed and erosion are maintained substantially constant regardless of the slurry flow rate.  
         [0064]     Accordingly, this embodiment can reduce the cost by reducing the use amount of slurry with a simple arrangement without deteriorating the process performance.  
         [0065]     Especially in a semiconductor wafer CMP process, very many additives are contained in a slurry in order to improve the polishing performance. Since this makes the slurry expensive, the cost can be largely reduced by reducing the use amount of slurry.  
         [0066]     In order for the slurry to rapidly diffuse toward the periphery after it is dropped directly on the second layer  12  of the polishing cloth  10 , the first layer  11  may also be removed in the shape of a circle, as shown in  FIG. 1 , immediately below the slurry supply pipe, i.e., in a central region  13 a of the polishing cloth  10 .  
         [0067]     In the first layer  11  of the polishing cloth  10 , fine holes having a diameter of, e.g., 10 μm to 10 mm evenly distribute at a density of 1 to 1,000 holes/cm 2 . The first layer  11  is more desirably formed by a porous material having the linear through holes  13  as shown in  FIG. 1 .  
         [0068]     This shape can be realized by molding a porous material such as a polymer-based material into fibers or a honeycomb shape, and forming the through holes  13  substantially parallel to each other.  
         [0069]     Also, the second layer  12  can be obtained by molding, e.g., a generally used hard foamed polyurethane resin, such as a polymer-based material having open cells whose diameter is, e.g., 10 to 500 μm. However, the material is not limited to this material, and any material which can store the slurry and discharge it when pressed can be used. Examples are polystyrene-based and silicone-based polymers.  
         [0070]     A method of forming a copper damascene interconnection will be explained below as a semiconductor device fabrication method using the polishing apparatus according to the first embodiment.  
         [0071]     As shown in  FIG. 5 , an element (not shown) is formed by patterning in a surface portion of a semiconductor substrate  51 . An interlayer insulating film  52  having a film thickness of, e.g., about 3,000 Å is formed on the surface of the semiconductor substrate  51 . A recess  55  which is at least one of a trench and hole is formed in the surface of the interlayer insulating film  52 .  
         [0072]     On the entire surface including the inner surfaces of the recess  55 , a Ta/TaN layer  53  having a film thickness of, e.g., about 300 Å is formed as a liner by sputtering.  
         [0073]     In addition, a copper film  54  having a film thickness of, e.g., about 7,000 Å is deposited by sputtering and plating so as to cover the entire surface.  
         [0074]     As shown in  FIG. 6 , of the copper film  54  and Ta/TaN layer  53 , unnecessary portions except for the portions buried in the recess  55  are removed by CMP. The polishing apparatus according to the first embodiment described above is used in this CMP process.  
         [0075]     The polishing conditions can be set, for example, as follows.  
         [0076]     Two types of slurries A and B presented below are supplied onto the polishing cloth at a flow rate of 50 cc/min each. 
        Slurry A: Mixture of CMS7401+CMS7452 (manufactured by JSR (registered trademark))     Slurry B: BTS-12 (manufactured by HIROTA CHEMICAL INDUSTRY (registered trademark))        
 
         [0079]     The polishing load is 400 g/cm 2 , and the carrier/table rotational speeds are 100/100 rpm.  
         [0080]     By performing the CMP process by using the polishing apparatus according to the first embodiment, good polishing characteristics can be obtained by using a minimum necessary slurry.  
       (2) SECOND EMBODIMENT  
       [0081]     The polishing cloth  10  used in the polishing apparatus according to the first embodiment described above has a two-layered structure having the first and second layers  11  and  12 .  
         [0082]     By contrast, in a polishing apparatus according to the second embodiment, the polishing cloth has an integrated structure such as polishing cloth  10   a  shown in  FIG. 7 . The overall arrangement of the apparatus except for this polishing cloth is the same as the first embodiment, so a detailed explanation thereof will be omitted.  
         [0083]     In the polishing cloth  10   a,  a slurry dropped on the surface of the polishing cloth  10   a  enters the polishing cloth  10 a in the direction of an arrow  14 . This slurry is diffused toward the periphery as indicated by arrows  15  by the centrifugal force of the rotation of a turntable, and once stored.  
         [0084]     When the polishing cloth  10 a is pressed in the direction of an arrow  23  by a polishing member  22 , the slurry oozes out in the direction of arrows  16 , and is discharged to the surface of an object  21  to be polished.  
         [0085]     Even when the polishing apparatus of the second embodiment using the polishing cloth  10   a  as described above is used, as in the first embodiment, the slurry is once stored in the whole of the polishing cloth  10   a  by permeation, and then evenly supplied to the surface of the object  21  to be polished.  
         [0086]     In addition, according to the second embodiment, even when the head shown in  FIG. 9  is used, since the slurry is uniformly supplied to that surface of the object to be polished, which is in contact with the polishing cloth, the slurry is reliably supplied to this surface irrespective of the pressure acting on the retainer ring.  
         [0087]     A method of performing the CMP process shown in  FIG. 6  by using the polishing apparatus according to the second embodiment will be explained below.  
         [0088]     The polishing conditions can be set, for example, as follows.  
         [0089]     A slurry C presented below is supplied onto the polishing cloth at a flow rate of 300 cc/min. 
        Slurry C: CMS8301 (manufactured by JSR (registered trademark))        
 
         [0091]     The polishing load is 240 g/cm 2 , and the carrier/table rotational speeds are 50/51 rpm.  
         [0092]     In the second embodiment, as in the first embodiment described previously, a slurry is once stored in the whole of the polishing cloth, and then evenly supplied to the surface to be polished of the semiconductor substrate. Since the slurry is reliably supplied to the surface to be polished, good characteristics can be obtained.  
         [0093]     As described above, the polishing apparatuses, polishing methods, and semiconductor device fabrication methods of the first and second embodiments make it possible to reduce the cost by reducing the slurry use amount without deteriorating the process performance.  
         [0094]     Each of the above embodiments is merely an example, and hence does not limit the present invention. That is, these embodiments can be variously modified within the technical scope of the present invention.  
         [0095]     For example, in the above embodiments, a copper film is used as a conductive film to be polished in the CMP process. However, it is also possible to use a film containing at least aluminum, tungsten, titanium, niobium, tantalum, silver, vanadium, ruthenium, platinum, silicon, or an oxide, nitride, boride, or alloy of any of these materials.