SURFACE ETCHING AND ROUGHENING IN INTEGRATED PROCESSING OF THERMAL OXIDE

A multichamber ultrahigh vacuum processing and analysis system has been used to study integrated thermal oxide processing, in which the final precleaning process and the thermal oxidation process are integrated by employing transfer of the wafers through ultraclean, inert ambients (purified, dry N2 and then ultrahigh vacuum). Al-gate metal oxide semiconductor capacitors show high breakdown fields (approximately 12 MV/cm) when a thin oxide passivation layer is present prior to oxidation, but low breakdown fields (< 6MV/cm) when the Si surface is initially oxygen-free. This contrasting behavior is caused by the etching of Si surfaces which occurs at elevated temperature in the presence of trace concentrations (approximately 100 ppb) of oxygen (e.g., 2Si + O2 --> 2SiO up), leading to surface roughening and then field enhancement at asperities in the structure. Oxide surface passivation prevents etching and assures the dielectric integrity of the structure.