Abstract:
A compensating chemical mechanical wafer polishing apparatus and its related polishing method, which makes end point detection easy, minimizes slurry consumption, and requires less installation space and, in which a main polishing head of diameter smaller than the wafer and a compensating polishing head are used to polish the wafer, which is upwardly disposed in contact with the polishing heads. By means of the operation of the compensating polishing head to polish the wafer over the area where the main polishing head cannot effectively evenly polish, satisfactory polishing effect is achieved.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a chemical mechanical wafer polishing technique and, more specifically, to a compensating chemical mechanical wafer polishing apparatus and method, which achieves a satisfactory, smooth polishing effect. 
     2. Description of the Related Art 
     According to conventional chemical mechanical wafer polishing techniques, the polishing face of the wafer is disposed downwards, and the polishing pad is disposed at the bottom side of the wafer and closely attached to the wafer carrier. The area of the polishing head is greater than the wafer. During polishing, the polishing head covers the whole area of the wafer. This polishing method has numerous drawbacks as outlined hereinafter. 
     1. High difficulty in end point detection: Because the polishing surface of the wafer faces downwards, the detection of the end point detect is indirectly operated, and the weak detection signal thus obtained must be processed further for reading. If detection is made through the polishing pad or the backside of the wafer, the technical difficulty and cost become high. 
     2. High consumption of slurry: Because of cover-all architecture, much slurry is used and applied to the broad polishing area of the polishing pad, and most of the slurry are utilized having not contribution to the polishing process, in the other hand, the expensive slurry is misspent. Thus the COO(Cost of ownership) will become high with no meaning. 
     3. Wafer edge effect: Because the polishing contact pressure is not changed continuously, the edge area polishing of the wafer is ground out significantly, resulting in an edge effect. 
     4. Bulk and heavy structure: Because of cover-all architecture, the diameter of the polishing head must be greater than the diameter of the wafer. In order to obtain the uniform velocity field on the wafer with the traditional CMP polishing method, the polishing table should be mush larger then the present invention. The heavy weight of the polishing head and platen requires a big scale of driving unit to achieve the desired polishing speed. Therefore, the polishing apparatus requires much installation space and heavy weight. 
     SUMMARY OF THE INVENTION 
     The present invention has been accomplished to provide a compensating chemical mechanical wafer polishing apparatus, which eliminates the aforesaid drawbacks. It is one object of the present invention to provide a compensating chemical mechanical wafer polishing apparatus, which lowers the difficulty of end point detection, and reduces the cost. It is another object of the present invention to provide a compensating chemical mechanical wafer polishing apparatus, which consumes less amount of polishing fluid, minimizing pollution to the environment and the COO. It is still another object of the present invention to provide a compensating chemical mechanical wafer polishing apparatus, which is compact and not heavy. It is still another object of the present invention to provide a compensating chemical mechanical wafer polishing apparatus, which provides a compensating polishing function to compensate the polishing of the main polishing head. The profile of copper plating on the wafer surface is too complicated to planarize without the dynamic control of different zone pressure with the help of EPD system when traditional CMP tool is utilized, and that is a highly cost and much difficult to compare with present invention. Most of the important things is that compensating method provided a workable method to solve the problem of wafer extension at the edge which is the biggest problem of the traditional CMP apparatus. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevational view of a compensating chemical mechanical wafer polishing apparatus constructed according to the present invention. 
     FIG. 2 is an enlarged view of a part of the compensating chemical mechanical wafer polishing apparatus shown in FIG.  1 . 
     FIG. 3 is a schematic drawing showing a polishing status of the present invention. 
     FIG. 4 illustrates the arrangement of the fluid supply piping in the main polishing head according to the present invention. 
     FIG. 5 is an operational block diagram of the present invention. 
     FIG. 6A illustrates a wafer receiving status of the present invention. 
     FIG. 6B is an enlarged view of a part of FIG.  6 A. 
     FIG. 7A illustrates a polishing status of the present invention. 
     FIG. 7B is an enlarged view of a part of FIG.  7 A. 
     FIG. 8 illustrates a polishing head cleaning status of the present invention. 
     FIG. 9 illustrates the pad conditioning action of the pad conditional module of the compensating chemical mechanical wafer polishing apparatus according to the present invention. 
     FIG. 10 illustrates the main polishing head equipped with a triangular polishing pad according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. from  1  through  4 , a compensating chemical mechanical wafer polishing apparatus  10  is shown comprising a wafer carrier  11 , a polishing module  21 , a cleaning module  31 , a pad conditional module  41 , and a machine table  51 . 
     The wafer carrier  11  comprises a bearing rod  12  supported on a lifting mechanism  13  and lifted to hold a wafer. The face of the wafer carrier  11  provides a vacuum suction function to suck the wafer during polishing. 
     The polishing module  21  comprises a main polishing head  22 , and a compensating polishing head  24 . The bottom polishing pad of the main polishing had  22  can be made having a circular, annular, polygonal, or oval shape, or the shape of a three-leaf, four-leaf, five-leaf, or any of a variety of polygonal configurations. 
     The main polishing head  22  has an inflatable air chamber  30  on the inside that can be inflated to impart a downward pressure. 
     The main polishing head  22  further comprises a fluid supply piping  27 . During polishing, slurry is delivered from the fluid supply piping  27  through a perforated plate  29  and the polishing pad  23  and then directly ejected onto the polishing contact surface, preventing unnecessary waste. The compensating polishing head  24  is driven by a screw rod  25  to move back and forth relative transversely relative to the main polishing head  22 . The pressure and speed of the compensating polishing head  24  are changed subject to the position of the compensating polishing head  24  to achieve a compensation polishing operation. The polishing module  21  is mounted on a lifting holder  28  that can be moved up and down. The holder  28  is connected to a swivel arm  26 , which is controlled to move the lifting holder  28  between positions. The main polishing head  22  is a piston type polishing head. The compensating polishing head  24  can be a piston type (mechanical head), ultrasonic type, or electro-polishing type polishing head. 
     The cleaning module  31  comprises a wafer/wafer carrier cleaning water knife  32  and a pad conditional module cleaning water knife  33  disposed at two sides of the machine table  51 , and a polishing head cleaning water knife  34  disposed in the middle of the machine table  51 . When the polishing module  21  moved to a second position, the wafer/wafer carrier cleaning water knife  32  is driven to clean the processed wafer  99  and the wafer carrier  11 , at the same time the polishing head cleaning water knife  34  is driven to clean the main polishing head  22  and the compensation polishing head  24 , and at the same time the pad conditional module cleaning water knife  33  is driven to clean the diamond-dressing disk  42  of the pad conditional module  41 , enabling slurry to be completely removed from the processed wafer  99 , the main polishing head  22 , the compensation polishing head  24 , and the diamond-dressing disk  42  of the pad conditional module  41 . 
     The diamond-dressing disk  42  of the pad conditional module  41  is provided at the top of the machine table  51 . When the polishing module  21  moved to a third position, the diamond-dressing disk  42  is driven to trim the polishing pad  23 . During pad conditioning, the fluid supply piping  27  is switched to deliver deionized water instead of slurry. The supply of deionized water simultaneously removes remaining slurry from the fluid supply piping  27 . 
     Referring to FIGS. from  5  through  9 , the operation of the compensating chemical mechanical wafer polishing apparatus  10  comprises the steps of: 
     A. Wafer receiving where the bearing rod  12  of the wafer carrier  11  is lifted to the wafer receiving position, and then wafer is placed on the bearing rod  12  as shown in FIG. 6; 
     B. Wafer positioning where the bearing rod  12  of the wafer carrier  11  is lowered to the lower limit position, and the vacuum suction function of the wafer carrier  11  is started to suck the loaded wafer; 
     C: Wafer moistening where the wafer/wafer carrier cleaning water knife  32  of the cleaning module  31  is operated to moisten the wafer; 
     D. Polishing where the polishing module  21  is turned to the position above the wafer  99  at the bearing rod  12  and then lowered to the polishing elevation as shown in FIG. 7, and then the internal inflatable air chambers of the polishing heads  22  and  24  are inflated to impart a downward pressure, and then the main polishing head  22  is controlled to deliver slurry from the fluid supply piping  27  to the polishing contact surface to polish the wafer  99 , and at the same time the compensating polishing head  24  is moved with the main polishing head  22  and reciprocated by the screw rod  25  (see FIG. 3) to achieve a compensating polishing effect; 
     E. Cleaning after polishing where the polishing module  21  is moved to the cleaning position (the second position), and the water knives  32 ,  33  and  34  of the cleaning module  31  are operated to clean the wafer  99 , the diamond-dressing disk  42 , and the main and compensating polishing heads  22  and  24  respectively as shown in FIG. 8; 
     F. Wafer removal where the wafer carrier  11  is controlled to switch of vacuum suction function and to blow air, and then the bearing rod  12  is controlled to push out the wafer, and then the wafer carrier  11  is controlled to switch off air blowing valve, and then the bearing rod  12  is lowered to the lower limit position again after removal of the wafer; 
     G. Conditioning of polishing pad where the polishing module  21  is moved to the conditioning position (the third position), and then the diamond-dressing disk  42  of the pad conditional module  41  is operated to trim the bottom polishing pads  23  of the polishing heads  22  and  24 , and the main polishing head  22  is switched to supply deionized water to carry remaining polishing fluid away from the fluid supply piping  27  as shown in FIG. 9; 
     H. Cleaning after conditioning where the polishing module  21  is moved to the cleaning position (the second position), and then the water knives  32 ,  33  and  34  of the cleaning module  31  are operated to clean the wafer carrier  11 , the diamond-dressing disk  42 , and the main and compensating polishing heads  22  and  24  respectively; 
     I. Finishing where the bearing rod  12  of the wafer carrier  11  is lifted to the wafer receiving position ready to receive a next wafer, i.e. returned to the status shown in FIG.  6 . 
     As indicated above, by means of the compensating polishing head  24  to polish the wafer  99 , the invention eliminates the problem of uneven velocity field of the main polishing head  22  and, can achieve a particular compensating polishing. For example, the invention eliminates the problem of edge effect that is commonly seen in conventional wafer polishing methods. In general, the polishing technique of the present invention uses the compensating polishing head  24  to achieve compensating polishing, resulting in a satisfactory polishing effect better than conventional cover-all polishing techniques. 
     The polishing pad  23  at the bottom side of the main polishing head  22  can be made having a circular, annular, polygonal, or oval shape, or the shape of a three-leaf, four-leaf, five-leaf, or any of a variety of polygonal configurations, for example, the triangular shape as shown in FIG.  10 . The triangular polishing pad  23 ′ enhances the polishing around the center area rather than the side edge area, so as to achieve a different polishing effect. 
     The compensating polishing head  24  can be a piston type, ultrasonic type, or electro-polishing type polishing head subject to employed manufacturing process. When low stress polishing is required, it is preferable to use an ultrasonic type or electro-polishing type compensating polishing head. 
     As indicated above, the present invention achieve the following advantages: 
     1. Ease of end point detection: Because the wafer faces upwards and the polishing head does not cover the whole area of the wafer during polishing, the polishing head is not in the way of the detection of the end point detector, enabling the end point detector to directly detect the polishing surface of the wafer. Therefore, the technical difficulty and cost are relatively low. 
     2. Less consumption of slurry: Because slurry is directly supplied to the polishing contact surface, waste of slurry is eliminated. Therefore, the invention consumes less amount of slurry. 
     3. Less dimensions and weight: Because the diameter of the platen is about the radius of the wafer, and the polishing head is smaller than the wafer, the main polishing head and platen have less dimensions and weight than a cover-all polishing head and platen used in conventional designs. Due to compact design, the main polishing head can easily achieve high speed polishing, and the installation space of the machine table can be greatly reduced. 
     4. Compensating polishing: Because the compensating polishing head can polish the area where the main polishing head cannot effectively achieve, the invention achieves a better polishing effect than conventional methods. 
     5. Wide design selection range: In comparison with the conventional cover-all designs, the invention is feasible for low stress or non-stress polishing. This advantage is practical for the polishing of copper when low-k material of effective dielectric constant smaller than 2.0 is introduced to the integration with copper damascene process. 
     Although a particular embodiment of the invention has been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.