Patent Publication Number: US-6210256-B1

Title: Continuous pad feeding method for chemical-mechanical polishing

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a chemical mechanical polishing (CMP) apparatus, and particularly to a pad feeding method suitable for use in a CMP apparatus. 
     2. Description of the Prior Art 
     Semiconductor fabrication has reached the deep sub-micron stage. In the deep sub-micron stage, the feature size and the depth of focus (DOF) of photolithography equipment are reduced, and the number of multi-level metal interconnect layers is increased. Consequently, how to maintain a high degree of surface planarity for the wafer has become a major topic of investigation. 
     Before the deep sub-micron era of semiconductor production, spin-on-glass (SOG) was employed to be the principle method of planarizing a silicon wafer. However, the method obtains moderate planarity in only local areas on the wafer surface. Without a global planarization of the wafer surface, quality of development after photographic exposure is degraded and the etching end-point is difficult to determine. These disadvantages reduce the yield of the wafer, and this reduction is a reason why SOG is substituted by chemical-mechanical polishing (CMP). 
     After semiconductor fabrication reached the deep sub-micron regime, CMP apparatus becomes a necessary apparatus of globally planarizing a silicon wafer. However, the polishing pad for a chemical mechanical polisher is a consumptive element. That is, the polishing pad needs to be changed after hundreds of polishing processes are performed. 
     FIG. 1 is a schematic view showing a conventional pad feeding mechanism in a CMP apparatus. As shown in FIG. 1, the CMP apparatus has a polishing platen  102  and a wafer carrier  110 , wherein the wafer carrier  110  can hold a wafer  104  downward to the polishing platen  102 . A polishing belt  100 , serving as a plurality of polishing pads, is applied for use in the pad feeding mechanism. When a polishing pad (a portion of the polishing belt  100 ) on the polishing platen  102  needs to be changed, a terminal of the polishing belt  100  is pulled to spread out another unpolished portion of the polishing belt  100  to cover the polishing platen  102 . 
     Other portions of the polishing belt  100  are rolled for space consideration. However, when the roller-type polishing belt  100  are wholly consumed, the CMP apparatus should have a shutdown for replenishing a new polishing belt. Such replenishment is complicated and time-consuming. There is therefore a need to improve this conventional pad feeding mechanism. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a continuous pad feeding method for chemical-mechanical polishing (CMP) is disclosed. The method is suitable for use in a CMP apparatus, wherein the CMP apparatus includes a first polishing belt having two terminals. The first polishing belt serves as a plurality of polishing pads. A second polishing belt having two terminals is provided on the first polishing belt. One of the terminals of the second polishing belt is adhered to one of the terminals of the first polishing belt. 
     Preferably, the adhering step is performed as follows. A first adhesion is coated on a surface of the first polishing belt. A second adhesion is coated on a surface of the second polishing belt. The second polishing belt is put on the first polishing belt by aligning the surface of the first polishing belt with the surface of the second polishing belt. 
     The second polishing belt is put on the first polishing belt for replenishment, after the first polishing belt is almost wholly consumed. This replenishing mechanism saves the maintenance time and increases the throughput of the CMP apparatus. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by referring to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a schematic view showing a conventional pad feeding mechanism in a CMP apparatus; 
     FIG. 2 is a schematic, cross-sectional view showing a chemical-mechanical polishing (CMP) apparatus and a pad feeding mechanism according to the present invention; 
     FIG. 3A shows the terminals for adhesion of the first and the second polishing belts; 
     FIG. 3B is a schematic, cross-sectional view showing a thermal assembly for heating the thermal-fluxing glues; and 
     FIG. 4 shows the positions of the lower and the upper heating plates. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 2 is a schematic, cross-sectional view showing a chemical-mechanical polishing (CMP) apparatus and a pad feeding mechanism according to the present invention. As shown in FIG. 2, the CMP apparatus comprises a polishing platen  202  and a wafer carrier  210 , wherein the wafer carrier  210  can hold a wafer  204  downward on the polishing platen  202 . 
     A first polishing belt  200  with two terminals  212   b ,  222   b  serves as a plurality of polishing pads. After one of the terminals  222   b  is pulled, a portion of the first polishing belt  200  is spread out to cover the polishing platen  202 . Another terminal  212   b  of the first polishing belt  200  can be adhered to a second polishing belt  206  by means of back adhesion or thermal-fluxing glue or other type of adhesion. 
     Referring to FIG. 3A, the terminal  212   b  for adhesion of the first polishing belt  200  is substantially thinner than other parts of the first polishing belt  200 . A first back adhesion, thermal-fluxing glue or other type of adhesion  214   b  is coated on the terminal  212   b  for adhesion of the first polishing belt. A second back adhesion, thermal-fluxing glue or other type of adhesion  214   a  is coated on a terminal  212   a  of the second polishing belt  206 . The second adhesion  214   a  is coated on the back surface of the terminal  212   a  of the second polishing belt  206 , while the first adhesion  214   b  is coated on the front surface of the terminal  212   b  the first polishing belt  200 . By such arrangement, the second polishing belt  206  can be connected with the first polishing belt  200  by aligning the adhesion terminal  212   a  of the second polishing belt  206  with the adhesion terminal  212   b  of the first polishing belt  200 . 
     Still referring to FIG. 3A, the adhesion terminal  212   b  of the second polishing belt  200  is also substantially thinner than other parts of the second polishing belt  200 . After being connected with the first polishing belt  200 , the adhesion terminal  212   a  of the second polishing belt  206  and the adhesion terminal  212   b  of the first polishing belt  200 , in total, have a thickness which is substantially the same as that of the other parts of the first or the second polishing belts  200 ,  206 . This thickness limitation benefits serving the adhesion terminals  212   a ,  212   b  as a polishing pad. 
     If the thermal-fluxing glues serve as the adhesions  214   a ,  214   b  between the first and the second polishing belt  200 ,  206 , it is necessary to provide a thermal assembly for heating the glues. Referring to FIG.  3 B and FIG. 4, this thermal assembly can be accomplished by locating a lower heating plate  220   b  beneath the connection position  208  and locating an upper heating plate  220   a  above the connection position  208 . 
     Turning to FIG. 2, for space consideration or other purposes, the first polishing belt  200  and the second polishing belt  206  are folded up several times. It is not necessary to put the second polishing belt  206  on the first polishing belt  200  at all times. In fact, the second polishing belt  206  serves as replenishment. That is, the second polishing belt  206  is put on the first polishing belt  200  after the first polishing belt  200  is almost wholly consumed. 
     When the second polishing belt  206  is put on the first polishing belt  200 , it is not necessary to have a shutdown of the CMP apparatus. In other words, this polishing-belt replenishment is independent from the operation of the CMP apparatus. As a result, applying this replenishing mechanism saves the maintenance time and increases the throughput of the CMP apparatus. 
     Although specific embodiments have been illustrated and described, it will be obvious to those skilled in the art that various modifications may be made without departing from the spirit which is intended to be limited solely by the appended claims.