HEAT-TREATMENT OF AMORPHOUS AND POLYCRYSTALLINE SILICON THIN-FILMS WITH HIGH-PRESSURE H2O VAPOR

Changes in electrical and optical properties induced by heat treatment with high-pressure H2O vapor are discussed for low pressure chemical- vapor deposited amorphous silicon (LPCVD a-Si) and laser-crystallized polycrystalline silicon films. Heat treatment at 190 degrees C with si milar to 1 x 10(6)-Pa-H2O vapor reduced the dark conductivity to simil ar to 10(-11) S/cm and increased the photoconductivity to similar to 1 0(-7) S/cm. The photoconductivity was also increased for laser-crystal lized polycrystalline silicon films. Optical absorption in the photon energy range lower than 1.5 eV was reduced for the a-Si films. Heat tr eatment at 190-270 degrees C resulted in a minimal change in optical b and gap; which was 1.50 +/- 0.02 eV for the LPCVD a-Si. The increase i n hydrogen concentration was less than 2 x 10(20) cm(-3) after the tre atment for the amorphous and polycrystalline silicon films. These resu lts show that the heat treatment with high-pressure H2O vapor can redu ce the defect density in the silicon films at low temperatures.