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. 1A. 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.