High-deposition-rate a-Si:H throuhg VHF-CVD of argon-diluted silane

摘要

We discuss various ways to produce hydrogenated amorphous silicon.a-Si:H, at a high deposition rate. We also present results of our recent study on the structural properties of a-Si:H films deposited at high rates using argon (Ar) dilution of silane in a 50-MHz glow discharge.The results of the depositions with Ar dilution are compared to films deposited from pure silane,Si:H_4. The deposition rate r_d is changed by varying the rf power P_rf into the discharge.We focus on the P-rf-dependence of the hydrogen (H) bonding configuration and total H- content in the film. It is observed that r_d saturates at 14 A/s for pure SiH_4 and at 22 A/s for Ar-diluted SiH_4 deposition.Upon increase of P_rf the H bonding configuration changes from mostly isolated H to mostly clustered H, and back to mostly isolated H. It is argued that Ar~* metastable atoms play an important role in the growth mechanism at intermediate P_rf, whereas at high P_rf ion bombardment through Ar~+ and SiH_x~+ (x<=3) ions becomes curcial. Two high-rate a-Si:H films are incorporated in thin-film transistors, TFTs. We presnet their characteirstics before and after illumination with calibrated light.It is shown that a-Si:H TFT s with a saturation mobility of 0.7 cm~2/Vs can be fabricated,with the complete intrinsic layer deposited at 20 A/s.