Study of SiO2 thin films in MIS devices at extremely low temperature by ICP-CVD process

• Main Authors: ShuiYi Tsai, 蔡淑儀
• Other Authors: Min-Hsiung Hon
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/42349509207766922759

碩士 === 國立成功大學 === 微機電系統工程研究所 === 94 === Scaling down the electric device dimension is an inevitable tendency with each new generation in semiconductor industry. While the dimensions of devices continue to shrink, the thickness of the insulator layer is also reduced. The shrinkage of the oxide thickness increase direct tunneling through the gate dielectric and degrades the gate oxide reliability. For minimizing the gate leakage current, many new technologies are recommended to grow a high quality thin oxide film. The future trend has also turned it into focusing on the mobility and new applications, such as the substitutions of the glass substrates by flexible plastic substrates. Low temperature fabrication of high-quality gate oxide film is one of the key issues for further development of device. In this work, we report the formation of high-quality SiO2 thin films for the gate dielectric layer by using inductively coupled plasma chemical vapor deposition (ICP-CVD) technique from silane and oxygen gas mixtures at low temperatures. The influences of deposition parameters, including SiH4/O2 ratio、deposition pressure and ICP r.f power were studied. The electrical properties including leakage current density and breakdown voltage of the silicon dioxide are determined from current-voltage (I-V) characteristics of metal- insulator- semiconductor (MIS) devices. In this study, only the (111) diffraction peak is observed in 34.3 degree, while r.f power is above 1250 Watt. Analysis of the transmission electron microscopic (TEM) diffraction patterns indicates that the SiO2 films are single crystal with high quality. Analysis of the surface of SiO2 films by atomic force microscopy reveals a smooth surface with roughness in the 2.1~6.6 nm range. From the I-V curve it can be seen that the SiO2 thin film has a good electric property as prepared at 1750 Watt. The lowest leakage current of silicon dioxide films at the gate voltage of 1 V is about 8.2×10-8 A/cm2 and the breakdown field can be obtained is 15.8 MV/cm in this study. For improving its electrical characteristics, the post-annealing was proceeding in a conventional furnace tube at high temperatures varied from 300 ℃ to 700 ℃.High temperature annealing is known to increase the film crystallize atom, which can also decrease the defects in the SiO2 thin films. After annealing at 700 ℃, it can be found that the leakage current density is about 4.6×10-9 A/cm2 at the gate voltage of 1 V and the breakdown field is about 16.2 MV/cm