Heat Treatment of Amorphous and Polycrystalline Silicon Thin Films with High-Pressure H₂O Vapor

Abstract

Changes in electrical and optical properties induced by heat treatment with high-pressure H 2 O vapor are discussed for low pressure chemical-vapor deposited amorphous silicon (LPCVD a-Si) and laser-crystallized polycrystalline silicon films. Heat treatment at 190°C with ∼1 ×10 6 -Pa-H 2 O vapor reduced the dark conductivity to ∼10 -11 S/cm and increased the photoconductivity to ∼10 -7 S/cm. The photoconductivity was also increased for laser-crystallized polycrystalline silicon films. Optical absorption in the photon energy range lower than 1.5 eV was reduced for the a-Si films. Heat treatment at 190–270°C resulted in a minimal change in optical band gap, which was 1.50 ±0.02 eV for the LPCVD a-Si. The increase in hydrogen concentration was less than 2 ×10 20 cm -3 after the treatment for the amorphous and polycrystalline silicon films. These results show that the heat treatment with high-pressure H 2 O vapor can reduce the defect density in the silicon films at low temperatures.