Microelectronic Engineering

Comparison of vapor and liquid phase silylation processes of photoresists

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Organosilicon groups can be incorporated into photoresists, rendering them resistant to erosion by oxygen plasmas. This process, known as silylation, can be implemented using either liquid or vapor sources. A comparison of these two methods was performed using mono-,di- and trifunctional organosilicon compounds with reactive Si-N-bonds. Among the four monofunctional compounds studied, hexamethyldisilazane is about 10 times less reactive in silylation of AZ 4110 films at normal pressure (126°C) compared to tetramethyldisilazane or dimethylaminotrimethylsilane. Mixed vapors of difunctional compounds (10% of bis/dimethylamino/methylsilane) and toluene silylate resist films at 111°C at a high rate forming crosslinked materials with an increased stability in O2 plasmas (etch rate of about 50 A/min after 2 min silylation). Trifunctional compounds (tris/dimethylamino/methylsilane) do not silylate resist films due to the formation of a crosslinked diffusion barrier on the surface. Difunctional silylating agents like bis(dimethylamino)dimethylsilane effectively silylate resist films at 80-85°C in toluene soluyion (which does not contain any diffusion promotors like NMP) without any distortions or thickness loss. The chemistry of silylation is discussed. © 1991.