Abstract:
The equipment for cleaning polishing cloth is capable of increasing pressure of washing water received by the polishing cloth, securely removing deposits from the polishing cloth and improving polishing efficiency. The equipment is used in a polishing apparatus, in which a work piece is pressed onto the polishing cloth adhered on a polishing plate and the work piece is relatively moved with respect to the polishing plate with supplying slurry to the polishing cloth so as to polish the work piece. The equipment comprises a nozzle unit having a nozzle capable of spraying high-pressure washing water toward the polishing cloth so as to clean the polishing cloth. The nozzle is a straight nozzle capable of linearly spraying the washing water and perpendicularly spraying the washing water with respect to the polishing cloth.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. P2009-79630, filed on Mar. 27, 2009, and the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The present invention relates to an equipment and a method for cleaning polishing cloth. 
       BACKGROUND 
       [0003]    Work pieces, e.g., semiconductor wafers, are polished, in a polishing apparatus, by the steps of: pressing the work pieces onto polishing cloth adhered on a polishing plate; relatively moving the polishing plate with respect to the work pieces; and supplying slurry to the polishing cloth while polishing the work pieces. 
         [0004]    By the way, in case of using the polishing cloth for a long time, various kinds of deposits, e.g., abrasion dust, slurry, reaction products, gradually deposit in the polishing cloth. The deposits will cause some problems, e.g., lowering polishing efficiency, damaging work pieces. Thus, high-pressure washing water is periodically sprayed toward the polishing cloth so as to clean the polishing cloth. 
         [0005]    One of conventional cleaning equipments is disclosed in Japanese Laid-open Patent Publication No. P7-9340A. The conventional equipment obliquely sprays high-pressure (about 50 kg/cm 2 ) washing water from a nozzle toward polishing cloth, so that deposits in the polishing cloth are floated and removed. Note that, the nozzle may be enclosed by brushing means so as to prevent the high-pressure washing water from splashing. 
         [0006]    However, in the above described conventional equipment, deposits in the polishing cloth, e.g., abrasion dust, cannot be sufficiently removed, and desired polishing efficiency cannot be obtained. 
         [0007]    Because the high-pressure washing water, which is obliquely sprayed, spreads out in a fan-like form, the deposits cannot be sufficiently removed. The inventor thinks that pressure of the washing water per unit area received by the polishing cloth is small, so this problem cannot be sufficiently solved. 
         [0008]    These days, the polishing cloth is mainly composed of foamed polyurethane. In comparison with polishing cloth composed of unwoven cloth, it is difficult to remove deposits, by spraying washing water, from the polishing cloth composed of foamed polyurethane. 
       SUMMARY 
       [0009]    Accordingly, it is an object in one aspect of the invention to provide an equipment and a method for cleaning polishing cloth, which are capable of increasing pressure of washing water received by the polishing cloth, securely removing deposits from the polishing cloth and improving polishing efficiency. 
         [0010]    To achieve the object, the equipment for cleaning polishing cloth, which is used in a polishing apparatus in which a work piece is pressed onto the polishing cloth adhered on a polishing plate and the work piece is relatively moved with respect to the polishing plate with supplying slurry to the polishing cloth so as to polish the work piece, comprises a nozzle unit having a nozzle capable of spraying high-pressure washing water toward the polishing cloth so as to clean the polishing cloth, and the nozzle is a straight nozzle capable of linearly spraying the washing water and perpendicularly spraying the same with respect to the polishing cloth. 
         [0011]    In the equipment, the nozzle unit may include a plurality of the nozzles. 
         [0012]    The equipment may further comprise a unit for moving the nozzle unit on the polishing plate. 
         [0013]    Next, the method for cleaning polishing cloth, which is used in a polishing apparatus in which a work piece is pressed onto the polishing cloth adhered on a polishing plate and the work piece is relatively moved with respect to the polishing plate with supplying slurry to the polishing cloth so as to polish the work piece, comprises the step of spraying high-pressure washing water, from a nozzle of a nozzle unit, toward the polishing cloth so as to clean the polishing cloth, the nozzle is a straight nozzle, and the straight nozzle linearly sprays the washing water and perpendicularly sprays the same with respect to the polishing cloth. 
         [0014]    In the method, pressure of the washing water which is received by the polishing cloth may be nearly equal to or greater than polishing load which is applied to the work piece while polishing the work piece. 
         [0015]    For example, the pressure of the washing water which is received by the polishing cloth is 150-350 gf/cm 2 . 
         [0016]    In the method, a main material of the polishing cloth may be foamed polyurethane. 
         [0017]    In the method, the nozzle unit may be moved on the polishing plate, with spraying the washing water from the straight nozzle, while cleaning the polishing cloth. 
         [0018]    In the present invention, by employing the straight nozzle, the pressure of the washing water received by the polishing cloth can be increased, so that deposits, e.g., abrasion dust, in the polishing cloth can be sufficiently removed. Therefore, damaging the surface of the work piece can be highly prevented, and polishing accuracy can be improved. Further, polishing efficiency can be improved, polishing time can be shortened, and a life span of the polishing cloth can be extended. 
         [0019]    The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
         [0020]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    Embodiments of the present invention will now be described by way of examples and with reference to the accompanying drawings, in which: 
           [0022]      FIG. 1  is an explanation view of a polishing apparatus; 
           [0023]      FIG. 2  is an explanation view of another example of a polishing head; 
           [0024]      FIG. 3  is an explanation view of a cleaning equipment; and 
           [0025]      FIG. 4  is an explanation view of a nozzle unit. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0026]    Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. 
         [0027]      FIG. 1  is an explanation view showing an outline of a polishing apparatus  10 . 
         [0028]    A polishing plate  12  can be rotated, in a horizontal plane, together with a rotary shaft  14 . The rotary shaft  14  is rotated by a known driving mechanism (not shown), e.g., motor. Polishing cloth  16 , whose main material is foamed polyurethane, is adhered on an upper face of the polishing plate  12 . 
         [0029]    A work piece  20 , e.g., semiconductor wafer, is held on a bottom face of each of polishing heads  18 . Each of the polishing heads  18  is rotated, together with a rotary shaft  22 , by a known driving mechanism (not shown), e.g., motor. Each of the polishing heads  18  is vertically moved by a vertical driving mechanism, e.g., cylinder unit. 
         [0030]    A slurry supply nozzle  24  supplies slurry to an upper face of the polishing cloth  16 . 
         [0031]    The work piece  20  is held on the bottom face of each of the polishing heads  18  by suitable means, e.g., surface tension of water, air suction. Each of the polishing heads  18  is moved downward so as to press the work piece  20  onto the polishing cloth  16  of the polishing plate  12 , which is rotated in the horizontal plane, with a prescribed pressing force, e.g., 150 gf/cm 2 . By rotating the polishing heads  18  together with the rotary shafts  22 , bottom faces of the work pieces  20  can be polished. The slurry is continuously supplied to the upper face of the polishing cloth  16  while polishing the work pieces  20 . 
         [0032]    Various types of polishing heads are known, so the type of the polishing heads  18  is not limited. For example, as shown in  FIG. 2 , the polishing heads  18  may be rotatably held between a center roller  26 , which is located at the center of the polishing plate  12 , and holding rollers  28 , each of which can be moved between an outer position located outside of the polishing plate  12  and an inner position located above an outer edge thereof. Each of the holding rollers  28  is held by a swing arm  32 , which can be rotated about a shaft  30 . 
         [0033]    Next,  FIG. 3  is an explanation view showing an embodiment of an equipment  34  for cleaning the polishing cloth  16 . 
         [0034]    The cleaning equipment  34  is located beside the polishing plate  12  of the polishing apparatus  10 . 
         [0035]    An elevating table  36  is vertically moved by a known mechanism, e.g., cylinder unit  38 . A movable member  40 , which can be moved to and away from the polishing plate  12 , is provided on the elevating table  36 . The movable member  40  is reciprocally moved by a suitable known mechanism (a moving unit). Constitution of the moving unit is not limited. For example, the movable member  40  may be reciprocally moved by a ball screw  42  or a cylinder unit, which is provided to the elevating table  36 . 
         [0036]    A pipe arm  46  is provided to the movable member  40 . A nozzle unit  48  is provided to a front end of the arm  46 . By reciprocally moving the movable member  40 , the nozzle unit  48  can be moved, above the polishing plate  12 , in the radial direction. 
         [0037]    As shown in  FIG. 4 , a straight nozzle  50  is attached to the nozzle unit  48 . The straight nozzle  50  is vertically fixed to a casing  54  of the nozzle unit  48  by a fixture  52 . The straight nozzle  50  is capable of linearly spraying high-pressure washing water, without spreading, toward the polishing cloth  16  and perpendicularly spraying the washing water with respect to the upper face of the polishing cloth  16 . 
         [0038]    The high-pressure washing water is supplied to the straight nozzle  50  via a flexible tube  56  and a tube  58  provided in the movable member  40  and the arm  46 . A brush member  60  is provided to a bottom face of the casing  54 . The brush member  60  encloses an outlet of the nozzle  50 , from which the high-pressure washing water is sprayed toward the polishing cloth  16 , so as to prevent splash of the high-pressure washing water. 
         [0039]    In the above described example, the moving unit moves the nozzle unit  48  linearly as described above, but the moving unit may reciprocally turn the arm  48 , to which the nozzle unit  48  is provided, about a shaft  47  as shown in  FIG. 2 . 
         [0040]    Further, the nozzle unit  48  may have a plurality of the nozzles  50  (not shown). In this case, for example, the nozzles  50  may be provided to and linearly arranged on the arm  46 . 
         [0041]    The brush member  60  may be omitted. Further, other splash-preventing means may be employed. 
         [0042]    Successively, the steps of cleaning the polishing cloth  16  will be explained. 
         [0043]    While polishing the work pieces  20 , the movable member  40  has been moved backward, and the nozzle unit  48  has been located at a standby position so as not to interrupt the process of polishing the work pieces  20 . 
         [0044]    After the work pieces  20  are completely polished, the process of cleaning the polishing cloth  16  is started. Firstly, the movable member  40  is moved above the polishing plate  12 , and the nozzle unit  48  is radially reciprocally moved, on the polishing cloth  16 , a length of a radius of the polishing plate  12  with spraying the high-pressure washing water from the straight nozzle  50  toward the polishing cloth  16 . The polishing plate  12  is rotated. With this action, the entire surface of the polishing cloth  16  can be cleaned. 
         [0045]    An experiment was performed by the cleaning equipment of the shown embodiment. The straight nozzle  50  perpendicularly sprayed the washing water with respect to the surface of the polishing cloth  16 . A spray angle of the washing water was zero degree, namely the washing water was nearly linearly sprayed toward the polishing cloth  16  without spreading. Pressure of the washing water sprayed from the straight nozzle  50  was 13 MPa, and an amount thereof was 1 l/min. An inner diameter of the outlet of the nozzle  50  was about 4 mm, and pressure of the washing water received by the polishing cloth  16  was 270 gf/cm 2 . Note that, a predetermined load, e.g., about 150 gf/cm 2 , was applied from the work pieces  20  to the polishing cloth  16  while polishing the work pieces  20 . 
         [0046]    A distance between the straight nozzle  50  and the polishing cloth  16  was about 100 mm. However, the straight nozzle  50  nearly linearly sprayed the washing water, so the pressure received by the polishing cloth  16  was not influenced by the distance therebetween. Even if the distance was varied abut ±20 mm, the pressure received by the polishing cloth  16  was nearly constant. Therefore, the distance between the straight nozzle  50  and the polishing cloth  16  need not be set severely. 
         [0047]    Further, a comparable experiment too was performed. An ordinary spray nozzle perpendicularly sprayed the washing water with respect to the surface of polishing cloth. A spray angle of the washing water was 25 degrees to clean the polishing cloth. Pressure of the washing water sprayed from the nozzle was 13 MPa, and an amount thereof was 1 l/min as well as the above described experiment. An inner diameter of the outlet of the nozzle was about 4 mm, and pressure of the washing water received by the polishing cloth was about 80 gf/cm 2 . A predetermined load, e.g., about 150 gf/cm 2 , was applied from work pieces to the polishing cloth while polishing the work pieces. 
         [0048]    A distance between the ordinary nozzle and the polishing cloth was about 100 mm as well as the above described experiment. 
         [0049]    According to the experiment performed in the cleaning equipment  34  of the embodiment, the pressure received by the polishing cloth  16  can be increased by using the straight nozzle  50 . By increasing said pressure, deposits, e.g., abrasion dust, in the polishing cloth  16 , whose main material was foamed polyurethane, could be suitably removed. In the comparable example, surfaces of the work pieces were damaged; on the other hand, in the example performed by the equipment  34  of the embodiment, deposits could be suitably removed, so that damages in the polished surfaces of the work pieces  20  could be highly reduced. In the equipment  34  of the embodiment, an occurrence rate of damage was about a half (½) of that of the comparable example. Therefore, polishing accuracy could be increased. Polishing efficiency (polishing time) could be improved about 10%. Frequency of dressing the polishing cloth  16  could be reduced from one time per three batches to one time per 10 batches. Therefore, a life span of the polishing cloth  16  could be extended. 
         [0050]    By employing the straight nozzle  50 , even if the distance between the nozzle  50  and the polishing cloth  16  was varied, the pressure received by the polishing cloth  16  was nearly constant. Therefore, fine adjustment of the distance therebetween can be omitted. 
         [0051]    Note that, by employing the straight nozzle  50 , an area of spraying the washing water is small, so it takes a long time to clean the entire surface of the polishing cloth  16 . However, in case that 20% or less of the surface of the polishing cloth  16  was not cleaned, the polished surfaces of the work pieces  20  had enough quality. 
         [0052]    If the pressure received by the polishing cloth  16  is greater, detergency is increased. However, if said pressure is too great, the polishing cloth  16  will be broken. While polishing the work pieces  20 , the pressing force applied from the work pieces  20  to the polishing cloth  16  is 150-300 gf/cm 2 . The pressure received by the polishing cloth  16  may be slightly greater than the pressing force. For example, the suitable pressure received by the polishing cloth  16  is 150-350 gf/cm 2 . 
         [0053]    In the above described embodiment, the polishing apparatus is a single-sided polishing apparatus, but the cleaning equipment of the present invention is capable of cleaning polishing cloth of a double-sided polishing apparatus. 
         [0054]    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.