Abstract:
A grindstone having a vacuum system is applied to a pin chuck stepper. The vacuum system has a vacuum tube attached on the edge of the grindstone. When the grindstone moves on a pin chuck stage on the pin chuck stepper, the vacuum tube vacuums the pin chuck stage to free particles on the pin chuck stage.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a grindstone in a pin chuck stepper. More particularly, the present invention relates to a grindstone having a vacuum system in a pin chuck stepper. 
     2. Description of the Related Art 
     In a semiconductor process, a semiconductor wafer is fixed on a stage of a stepper in order to obtain a desired pattern on the semiconductor wafer through an exposure and development process. This is known as a photolithography process. Conventionally, the stage of the stepper is a ring-type stage, and the ring is a continuous coil. However, the semiconductor wafer cannot be horizontally placed on the ring while the particles produced during processes stick on the surface of the ring. As a result, the light cannot be precisely focused on the semiconductor wafer, and the quality of photolithography is seriously affected. Conventionally, such a situation can be prevented by using a particle-free cloth and alcohol to clean the surface of the stage. 
     The problem of the particles sticking on the surface of the ring stage can be minimized by decreasing the surface area on which the particles can stick. Thus, a pin chuck stage is introduced to a stepper. FIG. 1A is a schematic, cross-sectional view showing a pin chuck stage, and showing a problem resulting from the introduction of the pin chuck stage according to the prior art. 
     Referring to FIG. 1A. a pin chuck stage  12  is introduced to a stepper to decrease the surface area on which the particles  16  can stick, which is possible because the surface areas of the pins  14  are much smaller than that of the ring. However, it is impossible to totally prevent the particles from sticking to the tiny areas of the pins  14 . Thus, a smooth ceramic grindstone  10  is used to sweep the particles  16  from the surfaces of the pins  14  by pushing the particles  16  into gaps  15  between pins  14  as shown in FIG.  1 A. However, the particles  16  can lift and stick on the surfaces of the pins  14  again while the stage is moving or the air is flowing. Furthermore, the pin chuck stage  12  cannot be cleaned with a particle free cloth and alcohol because fibers of the cloth may entangle with the pins and damage the pin chuck stage  12 . 
     In addition, the particles  16  can be easily accumulated in the dead space  20  between the stage  12  and the pre-alignment element  18 , as shown in FIG. 1B, because of the motion of the grindstone  10 . In fact, the particle contamination mainly results in the particles sticking in the dead space  20  in a photolithography process, and it is very difficult to get rid of the particles stuck in the dead space  20 . This is a problem difficult to overcome while using a pin chuck stage in a stepper. 
     SUMMARY OF THE INVENTION 
     According to above, the invention provides a grindstone having a vacuum system in a pin chuck stepper to vacuum particles while the grindstone is sweeping the particles away. 
     The vacuum system comprises a two-layer ring tube and is attached on the edge of the grindstone. The two-layer ring tube comprises a continuous ring upper tube having a joint connected to a vacuum motor and a plurality of sausage-shaped lower tubes wherein the ring upper tube communicates with the plurality of sausage-shaped lower tubes. The sausage-shaped lower tubes are separated from each other by a space which can include a pre-alignment element, and there is a plurality of openings for inhaling particles into the stage on bottoms of the sausage-shaped lower tubes. The vacuum system is activated while the grindstone is moving on the pin chuck stage; thus particles can be inhaled by the vacuum system while the particles are pushed into gaps between pins on the pin chuck stage by the grindstone. In addition, when the grindstone is moved to a pre-alignment element, since there is a space between the sausage-shaped lower tubes, the pre-alignment element is wedged in the space between the sausage-shaped lower tubes. Then, the particles stuck in the dead space between the chuck and the pre-alignment element can be easily inhaled by the vacuum system. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings, 
     FIG. 1A is a schematic, cross-sectional view showing a pin chuck stage, and showing a problem resulting from the introduction of the pin chuck stage according to the prior art; 
     FIG. 1B is a schematic view showing the incapability of the grindstone in sweeping away the particles in the dead space between a pre-alignment element and the pin chuck stage according to the prior art; 
     FIG. 2A is a schematic, top view showing a grindstone having a vacuum system according to a preferred embodiment of the invention; 
     FIG. 2B is a schematic, bottom view showing a grindstone having a vacuum system according to a preferred embodiment of the invention; 
     FIG. 2C is a schematic, cross-sectional view showing a grindstone having a vacuum system according to a preferred embodiment of the invention; 
     FIG. 3 is a schematic, cross-sectional view showing the operation of the vacuum system attached on the edge of the grindstone according to a preferred embodiment of the invention; 
     FIG. 4A is a schematic, bottom view showing the mechanical relationship between a pre-alignment element and the pin chuck stage according to a preferred embodiment of the invention; and 
     FIG. 4B is a schematic, enlarged view showing the mechanical relationship between a pre-alignment element and the pin chuck stage according to a preferred embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention provides a grindstone having a vacuum system in a stepper to completely clean away the particles stuck on the pin chuck stage and in the dead space between the pre-alignment element and the pin chuck stage. 
     FIG. 2A is a schematic, top view showing the grindstone having the vacuum system, FIG. 2B is a schematic, bottom view showing the grindstone having the vacuum system, and FIG. 2C is a schematic, cross-sectional view showing the grindstone having the vacuum system according to a preferred embodiment of the invention. 
     Referring to FIG.  2 A through FIG. 2C, the vacuum system comprises a two-layer ring tube  100  and is attached on the edge of the grindstone  100 . The two-layer ring tube  100  comprises a continuous ring upper tube  102   a  having a joint  104  connected to a vacuum motor and a plurality of sausage-shaped lower tubes  102   b  wherein the ring upper tube  102   a  communicates with the plurality of sausage-shaped lower tubes  102   b . The diameters of the upper tube  102   a  and the lower tube  102   b  are preferably about 0.4-0.5 cm. The plurality of sausage-shaped lower tubes  102   b  are separated from each other by a space  103  in which the pre-alignment element  118  (as shown in FIG.  4 A and FIG. 4B) can wedge, and there is a plurality of openings  108  for inhaling particles  106  on the stage in the bottoms of the sausage-shaped lower tubes  102   b.    
     FIG. 3 is a schematic cross-sectional view showing the operation of the vacuum system attached to the edge of the grindstone according to a preferred embodiment of the invention. 
     Referring to FIG. 3 the vacuum system is activated while the grindstone  100  is moving on the pin chuck stage  112 . The pin chuck stage  112  has uniformly-distributed pins  114  thereon. Due to the operation of the vacuum motor  300 , particles  106  can be inhaled by the vacuum system from the openings  108  through the lower tube  102   b  and then the upper tube  102   a , and exhausted through the joint  104  while the particles are pushed into gaps  115  between pins  114  on the pin chuck stage  112  by the grindstone  100 . In order to efficiently inhale the particles  106 , the sizes of the openings  108  should be larger than the particles  106 . Preferably, the diameters of the openings  108  are about 1.5-3 μm. 
     FIG. 4A is a schematic, bottom view showing the mechanical relationship between pre-alignment elements  118  and the pin chuck stage  112 , and FIG. 4B is a schematic. enlarged view showing the mechanical relationship between the pre-alignment elements  118  and the pin chuck stage  112  according to a preferred embodiment of the invention. 
     Referring to FIG.  4 A through FIG. 4B, when the grindstone  100  is moved to one of the pre-alignment elements  118 , since the space  103  exists between the sausage-shaped lower tubes  102   b . the pre-alignment element  118  is wedged in the space  103  between the sausage-shaped lower tubes  102   b . Then, the particles  106  stuck in the dead space  120  between the pin chuck stage  112  and the pre-alignment element  118  can be easily inhaled by the vacuum system. 
     Thus, the grindstone having the vacuum system provided by the invention in a stepper can efficiently and completely clean away the particles stuck on the pin chuck stage and in the dead space between the pre-alignment element and the pin chuck stage. The invention solves the problem of particle contamination that occurs in a stepper with a pin chuck stage. 
     Other embodiments of the invention will appear to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.