Comparison of vapor and liquid phase silylation processes of photoresists

Abstract

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.