Hydrogenated Amorphous Silicon and Silicon Nitride Deposited at less than 100° C by ECR-PECVD for Thin Film Transistors

Abstract

ABSTRACTA systematic study has been made of the growth of both hydrogenated amorphous silicon (a-Si:H) and silicon nitride (a-SiN) by electron cyclotron resonance plasma enhanced chemical vapour deposition (ECR-PECVD). In the case of a-SiN, helium and nitrogen gas is injected into the system such that it passes through the resonance zone. These highly ionised gases provide sufficient energy to ionise the silane gas, which is injected further downstream. It is demonstrated that a gas phase reaction occurs between the silane and nitrogen species. It is control of the ratio of silane to nitrogen in the plasma which is critical for the production of stoichiometric a-SiN. Material has been produced at 80 °C with a Si:N ratio of 1:1.3 a breakdown strength of ∼6 MV cm−1 and resistivity of >1014 Ωcm. In the case of a-Si:H, helium and hydrogen gas is injected into the ECR zone and silane is injected downstream. It is shown that control of the gas phase reactions is critical in this process also. a-Si:H has been deposited at 80 °C with a dark conductivity of 10−11 Ω−1 cm−1 and a photosensitivity of just below 4×104. Such materials are suitable for use in thin film transistors on plastic substrates.