Low-temperature silicon nitride for thin-film electronics on polyimide foil substrates

We optimized silicon nitride (SiN1) layers, deposited by 13.56 MHz plasma enhanced chemical vapor deposition (PECVD) at 150 degreesC to provide a high quality gate dielectric layer for the amorphous silicon thin film technology on polyimide foils. The layers were deposited from mixtures of silane, ammonia, and hydrogen. We varied the H-2 Bow rate from 55 to 220 seem and the rf power from 5 to 50 W. while the pressure was kept at 500 mTorr and the ratio of ammonia to silane flow at 10:1. The best film was obtained from the gas composition of SiH4:NH3:H-2 = 1:10:44 and the of power of similar to 20 W. This film grows at the rate of 1.5 Angstrom /s, has a refractive index n = 1.80, a dielectric constant epsilon = 7.46. a dielectric breakdown field >3.4 MV/cm, a Si/N ratio of similar to0.67, and a hydrogen content of similar to2 x 10(22) cm(-3), and etches in 10:1 buffered HF at a rate of 61 Angstrom /s. (C) 2001 Elsevier Science B.V. All rights reserved.