Hot-Carrier Induced Degradation and Its Recovery in HK/MG NMOSFETs

• Main Authors: Hau-Kei Hsu, 許皓凱
• Other Authors: Win-Der Lee
• Format: Others
• Language: en_US
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/uey8z6

碩士 === 國立臺北科技大學 === 機電整合研究所 === 104 === Hot-carrier (HC) effect has always been the major reliability issue to study. In early researches, the worst degradation of HC effect is the DAHC mode at room temperature. However, recent studies reported that the worst case has been switched from DAHC to CHC mode and from low to high temperature. Most reasons are owing to BTI. However, few literatures discuss the HC degradation of nano-node nMOSFETs under bias voltages at room temperature and its recovery phenomena. As a result, the aim of this research is to study the gaps mentioned above. In this work, we use 28 nm wafer with length 0.03 μm and 0.2 μm, provided by UMC. The hafnium-based gate dielectric with a profile of HfxZryOz ( HfOx/ZrOx/HfOx ) is made with atomic layer deposition (ALD) technology. At the beginning of this research, CHC test ( Vd=Vg=1.5V ) were performed based on different channel lengths, and the result indicated that short channel device ( L=0.03 μm ) still has a problem with hot-carrier degradation. Due to this reason, by changing Vd and Vg, this research distinguishes the effect to-ward impact ionization between on-current and depletion electric field. It’s found that the effect of on-current is higher than that of depletion electric field. Similarly, we conduct more deep research on short channel devices, by changing Vg, Igs-o & Igd-o, and reversing source/drain measurement and the calculate of ΔNit & ΔNot to analyze where the degrada-tion happened. The results show that: (1) Higher Vg causes not only more impact ionization toward the degradation of drain, but also tunneling phenomenon toward the degradation of source. (2) Hot-carrier degradation mainly happened in dielectric (70~75%) and Si/SiO2 layer subsidiary (25~30%). The final topic of this research is recovery phenomena. We tried to recover the deg-radation devices by applying voltage on three conditions. The result shows that method RC (Vb=0.8 V, other terminal ground) leads to the highest recovery and its Vt recovery rate is 31.6%. It is considered that method RC is affected by impact ionization. Therefore, it may generate more electro-hole pairs. Then, injecting hole into dielectric will cause electrical recombination, and lead to recovery effect ultimately. In the future, if we want to raise the recovery rate, there are two recommended directions: (1) To produce a better recovery rate, based on method RC, we can try to apply a few negative voltages on gate terminal, so that more holes would be injected into die-lectric layer. (2) Using electron emission mechanism and holes injection mechanism alternately to lead a better recovery phenomenon.