Formation of silicon carbide in silicon substrates during CF 4/H 2 dry etching

Abstract

Silicon specimens which had been reactive ion etched in CF 4/ X%H 2 (0≤ X ≤40) and subsequently air exposed have been characterised by X-ray photoelectron emission spectroscopy. Angular rotation was used to study films deposited by the plasma process onto the Si surface. In agreement with previous studies it is found that plasma exposure of Si specimens leads to the deposition of a fluorocarbon film. An intriguing new finding was the discovery of subsurface silicon carbide. The existence of this carbide layer was found to be independent of gas composition from 0–40% H 2 for a one-minute plasma exposure. Helium ion channeling studies of the same specimens show Si near-surface disorder. A silicon-carbide formation mechanism is suggested according to which carbon is deposited below the Si surface by the bombardment of carbon containing ions, thus enabling silicon-carbon bonding.