The Carrier Transport and Channel Backscattering Characteristics of Nanoscale Schottky-Barrier MOSFETs

• Main Authors: Teng, An-Shun, 鄧安舜
• Other Authors: Chung, Steve S.
• Format: Others
• Language: en_US
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/27151385660472349230

碩士 === 國立交通大學 === 電子工程系所 === 98 === In advanced VLSI devices, a lot of new structures have been brought up for enhancing drain current such as strained-Si channel, high-κ dielectric, metal gate and metal source/drain. In the nanoscale channel length, the channel backscattering theory has been applied to predict the scaling-limitations of these structures successfully. Nowadays, the Schottky-barrier MOSFETs have aroused much more attention because some optimized processes become feasible. Hence, the carrier transport mechanism of Schottky-barrier MOSFETs from source to drain becomes the most popular topic in researches. In the thesis, first, we will focus on finding the effective Schottky-barrier height from the activation energy method. We can describe the effective Schottky-barrier height versus carrier transport mechanism relationship from this method. A negative effective Schottky-barrier height is found in the ON-state of the Schottky-barrier MOSFETs so that the channel backscattering theory can be used for extracting the carrier ballistic rate. In the past, the ballistic coefficient is extracted by temperature dependent method. However, the major carrier transport mechanism in the Schottky-barrier MOSFET is field emission, the temperature dependent method is failed. We practiced the effective ballistic mobility which is from mobility degradation in short channel devices. We may directly obtain the ballistic coefficient and thermal injection velocity in the linear region. Then, we derive the carrier average velocity versus thermal injection velocity relations in ON-state. By the two velocity components, the ballistic probability of the Schottky-barrier MOSFET can be extracted easily. Based on the results of this work, it was concluded that: (1) the backscattering theory is practicable from the negatively effective Schottky-barrier height, (2) the backscattering probability in the source side of Schottky-barrier is smaller than that in the conventional MOSFETs due to non-local tunneling, (3) the strained technology affects the backscattering coefficient lightly but it affects the thermal injection velocity drastically, (4) the drift-diffusion model is still workable in quasi-ballistic region. Thus, Schottky-barrier MOSFET with dopant segregation implantation and CESL(Contact-Etched Stoped Layer) can enhance the ballistic rate and thermal injection velocity that produced high speed operation in Schottky-barrier MOSFETs.