Study on Shape Mchining of Silicon Surface with Solid Phase Reaction between Solid Fluorination Agent/Silicon Interface.

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Lithography is widely used in the semiconductor industry. In lithography and etching, a pattern is formed on a Si surface by the following processes : applying resist, exposure, developing and etching. N-Fluoropyridinium salt is an electrophilic fluoritation agent. The salt has high reactivity. It is expected that N-fluoropyridinium salts fluorinate Si when the salts receive electrons. In this study, we propose a new photo-etching method to form a pattern on a Si surface by fewer processes : applying N-fluoropyridinium salts and exposure. N-Fluoropyridinium salts used in this experiment were N-fluoro-3-methylpyridinium tetrafluoroborate, N-fluoro-4-methylpyridinium tetrafluoroborate and N-fluoropyridinium triflrate. The N-fluoropyridinium salts were dissolved into the solvent of asetonitril. A p-type Si (100) wafer with a resistivity of 8.5-12 Ω・cm was used. The wafer was treated to prepare an H-terminated hydrophobic surface, or to prepare an OH-terminated hydrophilic surface. The salts were applied to the prepared surface. After applying salts, the Si surface was exposed to UV or visible light from a Xe lamp through a mask. Etching depth was measured using a microscopic phase-shifting interferometer. The Si in exposed area was etched more than the Si in unexposed area. The etching of the Si could be observed by UV or visible light exposure. The Si surface was exposed to visible light with the peak wavelengths of 440, 550 and 620nm using a projector. The Si in the area of the projected pattern was etched. The etching depth increases with the light exposure time. The Si was not uniformly etched with the salts. It is necessary to apply evenly a fluoritation agent for uniform etching. These results suggest that arbitrary shape can be formed on a Si surface by the control of an exposed pattern and exposure time distribution.