1. Department of Materials Science and Engineering, National Yang Ming Chiao Tung University, Hsinchu 300, Taiwan
2. Institute of Microelectronics, National Cheng Kung University, Tainan 701, Taiwan
3. Department of Electrophysics, Institute of Electronics, National Yang Ming Chiao Tung University, Hsinchu 300, Taiwan
4. Taiwan Semiconductor Research Institute, Hsinchu 300, Taiwan