Characteristics of low-temperature and low-energy plasma-enhanced chemical vapor deposited SiO2

Abstract

Deposition of high quality silicon dioxides was obtained at low temperatures by a specially designed plasma chemical vapor deposition (PECVD) system. The system employed a long quartz tube as a reactor and a set of three vertically standing plates for glow discharge. The deposited oxide, which employed a large amount of helium (He) to dilute silane (SiH4) and nitrous oxide (N2O) reactants, was observed to possess excellent qualities, as compared to those of thermally grown oxides. The chemical composition used for obtaining electrical integrities of the PECVD oxides was investigated. Additionally, the effects of post-metallization annealing on the oxides were investigated in detail. Oxides deposited at a substrate temperature of 250 °C were observed to possess a low interface trap state density (Dit) of only 3×1010 cm−2 eV−1 and low total trapped charge density (Qtotal) of 5.8×1016 cm−3. Those, however, which were deposited at 350 °C, have more stable electrical characteristics under current/voltage bias-temperature stress, but their Dit and Qtotal are around 2×1011 cm−2 eV−1 and 3.4×1016 cm−3, respectively. An atom-bonding model was proposed in this present work, according to physical, chemical, and electrical analyses in accounting for phenomena of charge-trapping and also in upgrading the electrical integrity of the deposited oxides. The applicability of these low-temperature oxides toward fabricating hydrogenated amorphous-silicon thin film transistor (a-Si:H TFT’s) was investigated. Adequate electrical performances of the TFT’s with a high on/off current ratio of more than 106 and high field effect mobility (μFET) of around 0.6 cm2/V s were obtained.