DEEP TRENCHES IN SILICON USING PHOTORESIST AS A MASK

Silicon reactive ion etching using photoresist as a mask and SF6/C2ClF5-based plasma has been studied. The anisotropy is believed to be due to a film-passivation mechanism taking place on the sidewalls of the trenches, combined with a chemisorption of chlorine atoms, which inhibits the lateral etching of the silicon substrate. This effect has been observed only in the presence of the photoresist in the reactor chamber. Some experiments using silicon oxide as a masking material were carried out in order to confirm this assessment. The obtained profiles showed a significant undercut, thus proving that the passivation phenomena are related to the presence of hydrocarbons in the reactor. Finally, we achieved a trench depth of 33 mum, with a selectivity of 6 and a good anisotropy using thick photoresist as a masking material.