High Rate Deposition of a-SiN_xH by VHF PECVD

Abstract

Very High Frequency (VHF) has been applied to the plasma enhanced chemical vapour deposition (PECVD) of hydrogenated amorphous silicon nitride films (a-SiNx:H) to fabricate amorphous silicon (a-Si:H) thin film transistors (TFTs). Especially, the effect of the excitation frequency on the deposition rate and the film quality of a-SiNx.H deposited in a SiH4/NH3/N2 plasma has been investigated. The films were prepared by VHF (40 MHz and 60 MHz) and HF (13.56 MHz) plasma enhanced CVD.The optical bandgap, the hydrogen content, the Si-H/N-H ratio and TFT mobility for films deposited in VHF plasma did not change significantly with the increase in deposition rate up to 300 nm/min. Internal stress could be constrained to acceptable levels at very high deposition rates. In contrast, the film quality deteriorated with an increase of the deposition rate in HF plasma. There seems to be a parallel relation between the optical emission intensity and the deposition rate which depends on the excitation frequency.

VHF-PECVD for a-Si:H and a-SiN:H Film Deposition

“…thin film deposition VHF-PECVD has been applied to fabricate a-SiN x :H thin films since 1996 by Takagi et al and Meiling et al [15,16,23]. These studies were conducted to obtain a superior TFT performance with a high deposition rate under a 40 MHz excitation frequency.…”

“…Based on many theoretical studies, very high frequency (VHF, 30 300 MHz) has been used to fabricate a-Si:H thin films since 1987 [7 14]. Inspired from these applications, Meiling et al [15] and Takagi et al [16,17] applied VHF to a-SiN x :H film deposition and obtained good results.…”

High temperature line electrode assembly for continuous substrate flow VHF PECVD

“…For economical reasons and because of the increase in the device size, the rectangular substrate dimensions followed a steady growth during the last decade, starting with a diagonal length of approximately 1 m 10 years ago to 2 m in actual PECVD reactors. At the same time, an increase of the excitation frequency from the commonly used 13.56 MHz up to the low VHF range (30 -100 MHz) has demonstrated higher deposition rates of hydrogenated amorphous silicon (a-Si:H) [1,2,4] and silicon nitride (a-SiN x :H) [3] maintaining good film quality and high uniformity requirements of the film properties.…”