Materials optimization for thin film transistors fabricated at low temperature on plastic substrate

Abstract In this paper, we describe the optimization of the electronic properties and the mechanical stress in the amorphous hydrogenated silicon (a-Si:H) and amorphous silicon nitride (a-SiNx:H) layers. The goal is to obtain smaller defect density and smaller mechanical stress materials that provide low-leakage current and to prevent the peeling of the multilayer structure off the substrate. The developed fabrication process used a 90% H2 + 10% SiH4 source gas mixture for the deposition of a-Si:H and He-diluted 2.5% SiH4 + 97.5% (NH3 + N2) gas mixture for the deposition of a-SiNx:H at a substrate temperature of 120°C. The properties of the deposited film samples were measured by infrared spectroscopy, constant photocurrent method (CPM), and electron spin resonance. Optimized a-Si:H films have 11 at.% of predominantly monohydride-bonded hydrogen, CPM defect density about 4 × 1016 cm−3, and an Urbach energy of a 53 meV. In the a-SiNx:H films, He dilution results in the removal of hydrogen from SiH bonds, and in the increase of film density assisted by mechanical stress transition from tensile to compressive, while maintaining a low deep defect density.