The Investigation and Application of Advanced Oxynitride and Novel Stack Gate Dielectrics

• Main Authors: Yang Wen-Chih, 楊文誌
• Other Authors: Chang Kow-Ming
• Format: Others
• Language: en_US
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/46324928740209645352

博士 === 國立交通大學 === 電子工程系 === 92 === This dissertation proposes two oxynitridation methods for fabricating 1.0 nm ultrathin oxynitride films and applies these techniques to novel stack gate dielectrics. In Chapter 2, ultrathin 1.0 nm oxynitride dielectric films were grown by rapid thermal processing (RTP) in mixtures of high N2 but low O2 gas flow rate ambient at 900℃ for 15 sec. The effect of the interfacial nitrogen concentration on device characteristics, when gate oxynitride films were grown using N2/O2 mixture gas with various ratios, was investigated. The results demonstrate that the nitrogen content increases with the N2/O2 gas flow rate ratio, and that high-quality and uniform dielectric films can be formed by RTP in an optimal flow rate ratio of N2/O2 = 5/1. The 1.0 nm oxynitride film shows excellent interface properties, significantly lower leakage current, and better reliability than an SiO2 of identical thickness prepared in an O2 ambient. These excellent characteristics are explained in terms of a much stronger and much larger number of Si≡N bonds in both the bulk of the dielectric films and at the SiOxNy/Si interface region. In Chapter 3, this study further proposes the highly reliable 1.0 nm SiON gate dielectric film formed by N2O-plasma in a high-density inductively-coupled-plasma chemical-vapor-deposition (HD-ICP-CVD) system at a growth temperature as low as 300℃. This approach archives excellent interface properties (including smooth interfaces and a relatively high nitrogen concentration in the SiON film), superior charge trapping characteristics, and gate leakage current that is more than two orders of magnitude less than that of other similarly thick gate dielectrics. The impact of different HD-ICP-CVD plasma forming gases on the electrical characteristics and reliability of 1.0 nm dielectric films were also investigated extensively. Furthermore, low-temperature ultrathin oxynitride film can be as a high-quality interface layer of gate dielectric of low-temperature polycrystalline silicon (LTPS) thin-film transistors (TFTs) for improving device performance and reliability. In Chapter 5, we proposed a novel tetraethylorthosilicate (TEOS)/Oxynitride stack gate dielectric for low-temperature poly-Si thin film transistors, composed of a plasma-enhanced chemical vapor deposition (PECVD) thick TEOS oxide/ultrathin oxynitride grown by using N2O-plasma. The novel stack gate dielectric exhibits a very high electrical breakdown field of 8.5 MV/cm, which is approximately 3 MV/cm higher than traditional PECVD TEOS oxide. The novel stack oxide also has better interface quality, lower bulk-trap density, and higher long-term reliability than PECVD TEOS dielectrics. These improvements are attributed to the formation of strong Si≡N bonds of high quality ultra-thin oxynitride grown by PECVD N2O-plasma, and the reduction in the trap density at the oxynitride/poly-Si interface. In Chapter 6, high-performance poly-Si TFTs with Oxide/Nitride/Oxynitride (ONO) multilayer gate dielectrics were fabricated. The low temperature (≦ 300 ℃) ONO multilayer dielectric uses three stacked layers: the bottom-layer is very thin N2O-plasma oxynitride deposited by PECVD, the middle-layer is PECVD Si3N4, and the top-layer is TEOS oxide. The ONO gate dielectric on poly-Si films shows a very high breakdown field of 9.4 MV/cm, a longer TDDB lifetime and a lower charge trapping rate than single-layer PECVD TEOS oxide or nitride. The fabricated poly-Si TFTs with ONO gate dielectric exhibited excellent transfer characteristics, high field effect mobility of 213 cm2/Vs, and an ON/OFF current ratio of over 8 orders. Finally, this dissertation develops a novel polycrystalline silicon thin film transistors structure with the following special features: (1) a new Oxide/Nitride/Oxynitride (ONO) multilayer gate dielectric to reduce leakage current, improved breakdown characteristics, and enhanced reliability; and (2) a raised source/drain (RSD) structure to reduce series resistance. These features were used to fabricate high-performance RSD-TFTs with ONO gate dielectric. The ONO gate dielectric on poly-Si films shows a very high breakdown field of 9.4 MV/cm, a longer TDDB, larger QBD and a lower charge trapping rate than single-layer PECVD TEOS oxide or nitride. The fabricated RSD-TFTs with ONO gate dielectric exhibited excellent transfer characteristics, high field effect mobility of 320 cm2/Vs, and an ON/OFF current ratio exceeding 8 orders.