Silicon Wafer Clamping Technology
The manufacturing of integrated circuits involves hundreds of different processing steps, and silicon wafers must be moved back and forth in those machines. To ensure the manufacturing quality of integrated circuits, the silicon wafers must remain absolutely stable during the transfer process between equipment, and they must not warp, deform, or shift when subjected to processing loads. This imposes strict requirements on silicon wafer clamping technology. Since the last century, various methods for clamping silicon wafers have been proposed due to the unique processing characteristics of silicon wafers.
Advantages of Electrostatic Chucks
Electrostatic chucks, the most popular silicon wafer clamping tool in the contemporary semiconductor industry, have the following merits over earlier silicon wafer clamping techniques:
(1) The silicon wafer won't warp or deform because the adsorption is evenly distributed across its surface;
(2) The sustained and stable adsorption force can guarantee silicon wafer processing accuracy;
(3) The electrostatic chuck causes minimal contamination and no damage to the silicon wafer;
(4) It is suitable for use in high-vacuum environments and so forth.
Ceramic Electrostatic Chuck Material
Only some businesses, including Kyocera, Applied Materials, NGK, and lam research, have developed electrostatic chuck design and manufacturing technology, while there are relatively few businesses or research institutes in China that have established design and production capabilities for electrostatic chucks.
The electrostatic chuck technology generally mastered in the globe employs alumina ceramics or aluminum nitride ceramics as the main material. Ceramic materials have favorable characteristics in terms of thermal conductivity, wear resistance, and high hardness. In comparison to metal materials, ceramic materials have inherent advantages in regard of electrical insulation.
Because of its special function, the electrostatic chuck necessitates the use of semiconductor materials rather than conductor or insulator materials (volume resistivity in the range of 103-1010Ω·cm). Therefore, the electrostatic chuck is not made of pure alumina or pure aluminum nitride; instead, other conductive substances are added in order to bring its overall resistivity up to the level that is necessary for the intended purpose.
Heat dissipation of silicon wafers is crucial in semiconductor processing. The processing uniformity and accuracy of silicon wafers will both be significantly impacted if the temperature uniformity of the silicon wafer surface cannot be guaranteed. Thus, improving the temperature uniformity of the silicon wafer surface during processing has always been an important research direction in the semiconductor industry.
In the modern silicon wafer process, the local high temperature is immediately dissipated by improving the heat dissipation on the back of the silicon wafer, which results in a uniform temperature across the surface. This method relies primarily on the electrostatic chuck to dissipate heat. Current electrostatic chucks are predominantly constructed from alumina ceramics, which have inferior thermal conductivity and mechanical properties compared to aluminum nitride ceramics. The heat dissipation of the electrostatic chuck material will have a significant effect on the temperature uniformity of the silicon wafer surface, so aluminum nitride ceramics will replace alumina ceramics as the preferred electrostatic chuck material gradually.
However, due to the much more complicated processing technology required for aluminum nitride ceramics compared to alumina ceramics, aluminum nitride ceramics are not currently used in large quantities in the relatively advanced electrostatic chuck technology. Instead, alumina, which has a relatively straightforward manufacturing process, is still used in the majority of electrostatic chucks.