Plasma-enhanced chemical vapour deposition of amorphous silicon nitride for thin film diode active matrix liquid crystal displays

The optimization of plasma-enhanced chemical-vapour-deposited amorphous SiN x H y (a-Si x H y ) layers for thin film diode (TFD) application in active matrix liquid crystal displays is discussed. The layers are deposited from SiH 4N 2 and SiH 4N 2H 2 gas mixtures and the flow dependence of the deposition rate is an important reactor characteristic. In comparison with undiluted growth the flow dependence of the deposition rate for hydrogen-diluted growth is relatively weak over a wide flow range. Also, in the case of hydrogen dilution the achieved uniformity of both the a-SiN x H y layer thickness and the a-SiN x H y optical gap is higher. The uniformity of the a-SiN x H y layer properties correlates with the uniformity of the TFD I–V characteristic, and for a-SiN x H y with an optical gap of 2.10 eV the uniformity of the I–V characteristic improves markedly with hydrogen dilution. Finally, the possibility of obtaining a selected a-SiN x H y optical gap for several compositions is discussed and a correlation between the hydrogen content of the a-SiN x H y and the TFD stability is noted.