Abstract:
The object of the present invention is to provide a polishing apparatus having a grinding member in a compact design that can provide high efficiency for both polishing and dressing operations, and prevents tilting of the grinding member even if the rotation axis thereof is moved away from the outer periphery of the object. A polishing apparatus for an object, comprises: an object holder for holding an object to be polished, such that a surface of the object to be polished faces upward; a dresser disk holder for holding a dresser disk for dressing, such that a dressing surface thereof faces upward; and a grinding member for polishing the object, and for being dressed by the dresser disk, by pressing and sliding the grinding member relative to the object and the dresser disk. Thereby, the surface to be polished and the dressing surface are arranged so as to be coploanar, and the grinding member having an abrasive surface facing downward, is disposed so as to straddle the surface to be polished of the object and the dressing surface of the dresser disk to perform polishing of the surface to be polished and dressing of the abrasive surface of the grinding member.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an apparatus for polishing objects such as semiconductor wafers, hard disks, glass substrates, liquid crystal display panels, and so on. 
     2. Description of the Related Art 
     A conventional chemical mechanical polishing (CMP) apparatus used in fabrication of, for example, semiconductor integrated circuit devices, is based on holding the semiconductor wafer in a rotating top ring and pressing the wafer against a polishing cloth mounted on a rotating turntable while supplying a polishing solution, including abrading particles to the polishing cloth. Hence, polishing is carried out mechanically by the abrading particles floating freely in the polishing solution, and chemically by a chemical solution at the pressing and sliding interface between the polishing cloth and the semiconductor wafer. However, such a CMP apparatus presents a problem in that, depending on the type of surface patterns and differences in the height of fine structures formed on the surface of the wafer, it was not possible to obtain a precisely polished flat and mirror surface on the wafer. 
     Therefore, in place of the CMP process, another polishing technology has been developed, based on a grinding member to produce a relative pressing and sliding motion against the wafer, in which abrading particles are bound in the grinding member and generated freely from the grinding member while water or a chemical solution is supplied at the sliding interface between the grinding member and the wafer. The polishing apparatus of the grinding member type includes variations using such as a ring-type grinding wheel attached on a supporting member or a cup-type grinding wheel having ring- shaped pellet attached on a supporting member. These grinding wheels include abrading particles bound therein. 
     FIG. 1 shows a cross sectional view of a conventional cup-type polishing apparatus using a grinding wheel. A wafer  100  is placed on the top surface of a disk-shaped wafer holder  80 . A cup-type grinding wheel  90  comprises of a grinding wheel holder  93  and a ring-shaped grinding wheel  91 , which is disposed above the wafer  100 . The grinding wheel  91  is pressed and slided against the wafer  100 . The wafer holder  80  and the wafer  100  are rotated in the direction of the arrow H while the grinding wheel  91  is rotated in the direction of the arrow J. Also, the grinding wheel  91  moves linearly in the radial direction of the wafer  100  (indicated by the arrows K). Thus, the entire surface of the wafer  100  is uniformly polished by the grinding wheel  91 . 
     In this apparatus, the wafer holder  80  is surrounded with a table surface  95  so that even if the rotational axis m of the grinding wheel  90 moves away from the outer periphery of the wafer  100 , tilting of the grinding wheel  90  is prevented by supporting the grinding wheel  91  on the table surface  95 . 
     This apparatus presents the following problems. 
     (1) In this design, it is difficult to adjust the surface levels between the wafer  100  and the table surface  95  so as to keep the same level therebetween, and basically, it is virtually impossible to attain a completely level surface. 
     (2) Polishing speed of the grinder  90  is rather slow, and the productivity is generally low. 
     (3) It is necessary to dress the grinding surface of the grinding wheel  91  after a given usage, to refurbish the polishing quality of the grinding wheel  91 , using a separate dressing tool. However, when a grinding wheel is being dressed, the wafer  100  cannot be polished. Thus, not only the productivity of polishing is lowered, but additionally, because a space must be allocated for the dressing tool, it becomes difficult to design a compact polishing apparatus using a cup-type grinding wheel. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a polishing apparatus having a grinding member of a compact design that can provide high efficiency for both polishing and dressing operations, and prevents tilting of the grinding member even if the rotation axis thereof is moved away from the outer periphery of the object being polished. 
     According to the present invention, there is provided a polishing apparatus for polishing an object using a grinding member, comprising an object holder for holding an object to be polished such that a surface to be polished is facing upward, and a dresser disk holder for holding a dresser disk for dressing the grinding member such that a dressing surface of the dresser disk is facing upward. The surface to be polished and the dressing surface are arranged so as to be coplanar. While the grinding member is polishing the object, the grinding member is being dressed by the dresser disk. 
     The grinding member has an abrasive surface which is facing downward, and the abrasive surface is disposed so as to straddle the surface of the object to be polished and the dressing surface of the dresser disk. The polishing and dressing occur as a result of the grinding member being pressed against and slid relative to the object and the dresser disk. 
     Accordingly, the polishing apparatus of the present invention provides the following advantages compared with conventional polishing apparatus having a grinding member. 
     Even when the center of rotation of the grinding member moves away from the outer periphery of the polishing object during a polishing operation, there is no danger of tilting the grinding member because the grinding member is supported also by the dresser disk. This arrangement eliminates the need for a separate table to prevent tilting, and provides an additional benefit in that dressing of the abrasive surface of the grinding member can be performed concurrently with polishing of the surface of the object. Therefore, there is no need to provide a separate dressing step to dress the abrasive surface of the grinding member, thereby increasing the polishing efficiency and providing a compact apparatus. 
     According to the present invention, a plural of object holders and a plural of dresser disk holders may be disposed for polishing a plurality of objects while the grinding member is being dressed by the plurality of dresser disks. 
     Accordingly, one grinding member can process a plurality of objects while being processed by a plurality of dresser disks, so that the polishing and dressing productivity is increased and the overall efficiency of the polishing operation is improved. 
     According to the present invention, a grinding member monitoring device may be provided to check conditions of a dressed abrasive surface of the grinding member, and a control device may be provided to control dressing conditions according to output signals from the grinding member monitoring device. 
     Accordingly, dressing conditions can be optimized by providing a grinding member monitoring device and a dressing control device. 
     According to the present invention, a weight limiting device may be provided so as to control a pressure exerted on the surface to be polished by the grinding member. 
     Accordingly, the polishing load can be decreased to a level, which is lower than the weight of the grinding member by providing a suspending device, which also facilitates vertical movements of a main pressing device to enable fine adjustment in pressure control. 
     The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings, which illustrate a preferred embodiment of the present invention by way of example. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross sectional view of the fundamental portion of a conventional cup-type polishing apparatus having a grinding wheel. 
     FIG. 2 is a perspective view of a polishing apparatus having a grinding wheel in a first embodiment of the present invention. 
     FIGS. 3A and 3B are, respectively, a plan view and a cross sectional view of the fundamental portion of the polishing apparatus shown in FIG.  2 . 
     FIGS. 4A and 4B are, respectively, a side view and a plan view of the fundamental portion of the polishing apparatus in a second embodiment of the present invention. 
     FIGS. 5A and 5B are, respectively, a plan view and a cross sectional view of the fundamental portion of the polishing apparatus in a third embodiment of the present invention. 
     FIG. 6 is a block diagram of a regeneration device. 
     FIGS. 7A and 7B are, respectively, a side view and a plan view of the polishing apparatus in a fourth embodiment. 
     FIG. 8 is a partial cross sectional view of the polishing apparatus in a fifth embodiment of the present invention. 
    
    
     In the drawings of FIG.  1  through FIG. 8, same parts or same portions are given the same reference numerals, and their repeated explanations are omitted. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 2 shows a first embodiment of the polishing apparatus. The apparatus comprises an object holder  10  for holding a polishing object  100 , such as a semiconductor wafer, which is movably fixed on a base section  40 , and a dresser disk holder  30  for holding a dresser disk  200 , which is movably fixed on the base section  40 . A cup-type grinder  50  is attached to the bottom part of a drive shaft  45  extending from an end of an L-shaped arm section  43 , which is fixed on the base section  40 . Details of the components will be presented below. 
     Object holder  10  comprises a holder body  11  and a support rod  13  extending from the bottom center of the holder body  11 , which is rotated by an internal drive (not shown). Hence, object holder  10  holds and rotates a wafer  100  to be polished by the grinder  50 . 
     Dresser holder  30  comprises a disk body  31  which holds a disk-shaped dresser  200 , and a support rod  33  extending from the bottom center of the disk body  31 , which is rotated by an internal drive (not shown). The dresser  200  has a dressing surface, which is made of a metal disk having diamond particles of #400 particle size thereon by electroplating, or diamond particles of #400 particle size fixed on a abrading sheet attached thereon. 
     The surfaces of the wafer  100  and the dresser disk  200  are disposed so as to be coplanar. 
     The top surface of the base section  40  is provided with a guide groove  41 , and the support rods  13 ,  33  for the object holder  10  and the dresser disk holder  30 , respectively, are engaged in the groove  41 . The support rods  13 ,  33  are moved in a reciprocating linear pattern in the groove  41  in the direction shown by the arrow A, by virtue of a drive mechanism (not shown) while maintaining their separation distance constant. 
     The cup-type grinding wheel  50  comprises a ring-shaped grinder  51  (or small pieces of grinding pellets arranged in a ring shape). The grinder  50  is rotated by a drive shaft  45  of a drive device (not shown) inside the arm section  43 . The grinder  50  is disposed so that the abrasive surface of the grinding wheel  51  can straddle both the wafer  100  and the dresser disk  200 , and contact both the surface to be polished of the wafer  100  and the dressing surface of the dresser disk  200 . 
     Referring to FIGS. 3A and 3B, the wafer holder  10 , dresser holder  30  and the grinder  50  are independently driven. Polishing operation is carried out by rotating the holders  10 ,  30  and the grinder  50  at the same time, while linearly reciprocating the wafer holder  10  and the dresser holder  30  relative to the grinder  50  in the direction of the arrow A, while maintaining the distance of separation between the holder  10  and the holder  30  constant. This arrangement enables the grinder  50  to polish the entire surface of the wafer  100  and, at the same time, to have the abrasive surface of the grinding wheel  51  be dressed by being in contact with the dresser disk  200 . 
     Even if the rotation center of the grinding wheel  51  moves away from the outer periphery of the surface to be polished of the wafer  100 , the grinding wheel  51  remains supported by the surface of the dresser disk  200  so that there is no danger of tilting the grinding wheel  51 . 
     FIGS. 4A and 4B show a second embodiment of the polishing apparatus having a grinding wheel, in which an arm section  62  is indicated by double-dot lines. 
     The polishing apparatus includes a pair of wafer holders  10 ,  10  and dresser holders  30 ,  30  disposed alternately in a square pattern. A grinding wheel  50  is disposed in the center of and above the square pattern. 
     Each of the wafer holders  10 ,  10  and dresser holders  30 ,  30  is driven by a respective drive motor  61  attached to a respective shaft  17 ,  37 , and a dresser pushing cylinder  66  (dresser pushing device) for pushing the dresser disk  200  is attached to the underside of the drive motor  61  for the dresser holder  30 . Also, the left pair and the right pair of the wafer holder  10  and dresser holder  30  are each driven linearly in the direction of the arrows B by the rotation of ball screws  63 ,  63 , which are disposed below the respective dresser pushing device  66  and the drive motor  61 , and which are driven by respective motors  65 ,  65 . The drive motors  65 ,  65  are variable speed motors so as to control the reciprocating motion of each pair the wafer holder  10  and the dresser holder  30  at any desired speed independently of the other pair in the direction of the arrows B. As in the first embodiment, the surfaces of the wafers to be polished and the dressing surfaces of the dresser disks  200  are disposed so as to be coplanar. 
     The grinder  50  is attached to a drive motor  71  installed on a press rod  69  of a pressing cylinder  67  (pressing mechanism), which is fixed to the center of the arm section  62  disposed above a base section  60 . 
     In this apparatus, two wafers  100 ,  100  can be polished simultaneously by placing the wafers in respective wafer holders  10 ,  10  and rotating the two pairs of wafer holder  10  and the dresser holder  30  by using the four respective drive motors  61 , while rotating the grinding wheel  50  by using the drive motor  71 . At the same time, the abrasive surface of the grinding wheel  51  is pressed against the surfaces to be polished of the wafers  100 ,  100  and the dresser disks  200 ,  200  by lowering the grinding wheel  51  via the pressing cylinder  67 , and the drive motors  65  are operated so that the wafer holders  10 ,  10  and the dresser holders  30 ,  30  are linearly moved in the direction of the arrows B. This procedure results in producing two uniformly polished wafers over their entire surfaces, as well as in performing a concurrent dressing operation on the grinding wheel  51  of the cup-type grinder  50 . 
     In the dressing operation, the pressing force of the dresser holder  30  can be adjusted by using the dresser pushing device  66  to press the dresser disk  200  against the abrasive surface of the grinding wheel  51 . The reason for providing the dresser pushing device  66  is explained in the following. If there is no pushing device for the dresser disk  200 , the surface to be polished of the wafer  100  and the dressing surface of the dresser disk  200  will be subjected to the same pressure exerted by the pressing cylinder  67 . However, this single-valued pressure is sometimes too high or too low for the dresser disk  200 . If the dressing pressure which is applied to the grinding wheel  51  is too high, service life of the grinding wheel  51  is significantly decreased. For this reason, a separate pushing device  66  is provided for the dresser holder  30  so that the load on the dresser disk  200  may be adjusted relative to the load applied on the surface to be polished of the wafer  100 . More specifically, for a dresser disk  200  having electroplated #100 diamond particles, for example, the stress on the dresser disk  200  should be less than 10 gf./cm 2  (981 Pa). This value should be changed depending on various conditions used in polishing the wafer  100 . Also, instead of using an air cylinder, a combination of motor and gears may be used for the dresser pushing device. 
     It is preferable that the dresser pushing device  66  is used, in the manner presented in this embodiment, in conjunction with two or more wafer holders  10 , each holding a wafer  100 , which are served by one grinding wheel  51  straddling the wafer holders. In such an arrangement, even if the grinding wheel moves anywhere, the design is such that the grinding wheel is always supported reliably by a plurality of wafers or polishing objects. The reason is that when the grinding wheel  51  is used in conjunction with a pair of one wafer  100  and one dresser disk  200 , if the pressure exerted by dresser disk  200  on the grinding wheel  51  is altered, there is a danger that the pressure exerted by the grinding wheel  51  on the wafer  100  may change or that the grinding wheel  51  may become tilted, causing deviation from the optimum polishing conditions. If there is no fear of such problems or the problems can be eliminated in some way it is quite acceptable to provide a dresser pushing device for the polishing apparatus in the first embodiment. 
     It is obvious that the number of wafer holders  10  and the dresser holders  30  can be changed to suit various applications. 
     FIGS. 5A and 5B show a third embodiment of a polishing apparatus having a grinding wheel. 
     The differences between the first and the third embodiments are that the condition of the abrasive surface of the grinding wheel  51  is monitored by a grinding wheel monitor  300  disposed in an appropriate location, and that the dressing parameters can be modified by a dressing control device  400 , according to the feedback signals from the grinding wheel or plate monitor  300 , as shown in FIG.  6 . 
     FIG. 6 shows a block diagram of the dressing control device  400 , which varies dressing conditions for the grinding wheel  51  by controlling the operations of the dresser-control section and the polisher-control section, according to output signals from the grinding wheel monitor  300 . For example, if it is determined that the grinding wheel  51  has not been dressed sufficiently, the pushing pressure on the dresser disk  200  may be increased or the rotational speed of the dresser disk  200  may be increased. 
     In short, a property of the dressed surface of the grinding wheel, is represented typically by a certain level of surface roughness value. It may be monitored by the grinding wheel monitor  300 , and output signals can be input into the dressing control device  400  through a feedback circuit to control the dressing parameters (for example, contact pressure between the dresser disk  200  and the grinding wheel  51 ) so that optimum dressing can be achieved at all times. 
     The grinding wheel monitor  300  may be a non-contact type transducer (optical, acoustic and the like), or contact type transducers (vibration or friction detection types or torque detection types). But it is obvious that any kind of monitor will be satisfactory if the monitor is sufficiently able to detect the dressed conditions of the abrasive surface of the grinding wheel  51 . 
     It would be evident that the third embodiment can be applied to the second embodiment or the following fourth and fifth embodiments. 
     FIGS. 7A and 7B show the polishing apparatus in a fourth embodiment, in which an arm section  62  is indicated by double-dot lines. 
     The difference between the fourth embodiment and the second embodiment shown in FIGS. 4A and 4B is that each wafer holder  10 ,  10  and dresser holder  30 ,  30  is independently movable in radial directions about the center of rotation of the grinder  50 . More specifically, respective drive motors  65  are used to rotate the ball screws  63  to drive the wafer holders  10 ,  10  and the dresser holders  30 ,  30  independently in the direction of the arrows C. 
     The reason for independent reciprocal movement for the wafer holders  10 ,  10  and the dresser holders  30 ,  30  is to enable fine adjustments of the polishing conditions for the wafer  100  and the dressing conditions for the grinding wheel  51  by the dresser disk  200 . 
     The reason for the reciprocal movement of the wafer holders  10 ,  10  and the dresser holders  30 ,  30  in radial directions about the center of rotation of the grinder  50  is to ensure that any wafer  100  or dresser disk  200  will be subjected to the grinding wheel  51  in relatively the same area at the same time (the same relative location and the same contact area). Therefore, all the wafers  100  and dresser disks  200  are respectively subjected to the same conditions of the grinding wheel  51 . 
     FIG. 8 shows a polishing apparatus in a fifth embodiment. This apparatus is different than the second embodiment apparatus shown in FIGS. 4A and 4B in that a weight limiting device is provided for the grinder  50 . More specifically, a weight  77  is attached by a rope  79  to the press rod  69  through a pulley  75  to reduce the load applied on the wafer by the grinder  50 . 
     This arrangement enables the reduction or elimination of the load exerted by the weight of the grinder  50  on the wafer  100 , thereby enabling polishing of the wafer  100  with a load that is less than the weight of the grinder  50 . Also, it is possible to reduce the load exerted by the pressing cylinder  67  that is necessary to lift the grinder  50 , so that the movement of the grinder  50  can be controlled precisely. This arrangement is also effective in reducing the load applied to the dresser disk  200 . 
     Other arrangements for limiting the weight of the grinder  50  may be applied. The weight limiting device can be attached to any location other than the press rod  69  so long as that location is on the grinder  50 . The weight limiting device can be applied to any of the foregoing embodiments but also to other types of polishing apparatus. The weight limiting device is applicable to any type of polishing apparatus in which polishing is performed by pressing an overhead grinding wheel on a polishing object while producing a relative sliding motion therebetween. 
     Although a certain preferred embodiment of the present invention has been shown and described in detail, it should be understood that various changes and modifications may be mad therein without departing from the scope of the appended claims. 
     For example, in the above examples, polishing apparatus having a cup-type grinding wheel were explained, however the present inventions is applicable not only to polishing apparatus having a grinding wheel as above mentioned, but also to polishing apparatus having a grinding member such as a disk shape and other shapes. The pressing cylinder  67  also may be replaced with other types of pushing devices, such as a motor driven pressing device. 
     Also, in some cases, the present polishing apparatus having a grinding wheel may be combined with a conventional CMP apparatus having a polishing cloth and polishing slurry so that the CMP process may be performed either before or after the polishing process performed by using a grinding member.