Impact of Reactive Ion Etching Induced Carbon Contamination on Oxidation of Silicon

After NF 3 /Ar reactive ion etching (RIE) in the presence of photoresist, the thermal oxide grown on the etched silicon surface was found to be significantly thinner than the oxide of monitor wafers. X-ray photospectroscopy analysis of the surface revealed contamination by carbon, forming carbide (with C-Si bonding). It was concluded that the carbon from the photoresist mask formed C-Si bonding on the etched surface and inhibited subsequent oxidation. After CHF 3 /CF 4 /Ar RIE, drastic oxidation impairment and a high level of carbon contamination were also detected. Regardless of the origin of the carbon, C-Si bonding was identified as a cause of the oxidation impairment. Even a few atomic percent of C-Si bonding introduced on the silicon surface slows down the subsequent oxidation rate of the etched surface. On consumption of the thin C-Si containing surface region, the oxidation rate quickly returns to a normal value. Using rapid thermal oxidation (RTO), several physical characteristics of the impaired thin oxide films were investigated. Boron diffusivity and HF etching rate of the oxide indicate formation of a singular layer about 15A˙ thick near the Si/SiO 2 interface. Interface roughness is unchanged with the C-Si bonding present. The singular layer is suspected to reduce availability of the oxidant at the interface, thus suppressing the oxidation.