Low-Temperature Si Oxidation Using Inductively Coupled Oxygen-Argon Mixed Plasma

Abstract

N- and p-type Si were oxidized using an inductively coupled oxygen–argon mixed plasma at about 60°C and 300°C. The flow-rate ratio of O 2 (O 2 (O 2 + Ar)) was fixed at 80%. Capacitance–voltage ( C – V ) characteristics were improved by a combination of substrate heating at 300°C and post-thermal annealing at 500°C for 30 min in an oxygen ambient as compared with those reported previously. However, the interface-state density was about 1 ×10 12 eV -1 cm -2 , still higher than that in the device-grade thermal SiO 2 /Si interface. The conductance–voltage ( G – V ) characteristics showed rather large conductance in the accumulation region for both oxide samples grown on p- and n-Si substrates as compared with thermal oxides. The X-ray photoelectron spectroscopic (XPS) measurements revealed that a fairly uniform SiO 2 layer was formed in the upper portion of the film using this technique although the transition region was observed at the interface between oxide and Si, which was composed of the Si suboxides such as Si 2 O 3 and SiO. The thickness of this “transition” region was roughly 13–15 nm which was larger than that for the thermal oxide/Si interface. Current–voltage ( I – V ) characteristics showed that the leakage current was mainly Fowler–Nordheim (F–N) tunneling current and much smaller for the oxide on p-Si than for the oxide on n-Si. The breakdown voltage was also higher for the oxide/p-Si than for the oxide/n-Si. The reason for these findings was discussed on the basis of the F–N current mechanism.