a-Si:H TFT enhancement by plasma processing of the insulating/semiconductor interface

Thin film transistors (TFTs) made of silicon nitride and silicon carbide as dielectric were submitted to N2, H2 and O2 plasma treatment of the insulator/semiconductor interface. Silicon nitride is widely used as gate dielectric with very good bulk properties but with network matching problems at the interface with amorphous silicon. Carbon-rich silicon carbide can be an alternative as dielectric material, presenting improved SiC/a-Si interface properties, but having lower bulk performance. The purpose of such interface plasma processing is to passivate, oxidize or insert nitrogen atoms into the last deposited monolayers and observe the effect of ion bombardment in the interface. Results show an increase of the field effect mobility from 0.38 to 0.51 cm2 V−1 s−1 in the passivated (hydrogenated) a-SiNX TFTs. An improvement is also observed in a-SiCX TFTs treated with H2 plasma, but less evident. Some correlation has been found between H bonding in insulating films, extracted by FTIR measurements and the different response found for a-SiCX and a-SiNX based TFTs to H2 plasma treatment.