Abstract
The ultra-thin gate dielectrics in MOSFETs remain the key element in conventional silicon-based microelectronic devices era, the SiO2 gate oxide has played a critical role in device performance and scaling. As the physical thickness of SiO2-based gate oxides approaches ~2 nm, some key dielectric parameters degrade: gate leakage current, oxide breakdown from the poly-silicon gate electrode, and channel mobility. The solution is to replace conventional SiO2 gate oxides with a material having higher permittivity (high-k). High-k insulators can be grown physically thicker for the same (or thinner) equivalent electrical oxide thickness (EOT), thus offering significant gate leakage reduction. High-k material is introduced to replace SiO2 to solve the gate leakage problem. Even though considerable performance improvement and gate leakage reduction have been achieved, new reliability challenges of high-κ devices such as the positive and negative bias temperature instability (P/NBTI) and hot carrier injection (HCI) need to be investigated. This dissertation presents an impact of reliability on a novel 28 nm CMOS logic high-k/metal-gate (HK/MG) technologies realized by stacking TiN/HfO2/SiO2. The fast transient measurement technique to reduce the post-stress transient effect due to charge trapping/detrapping in high-k dielectric is demonstrated in Chapter 2. The correlation of degradation characteristics between the P/NBTI and HCI in advanced HK/MG dielectric CMOSFET is proposed in Chapter 3. Oxygen sensitivity and the thickness effect for the optimized gate stack is discussed in Chapter 4. Chapter 5 focuses on current fluctuations in HK gate dielectric MOSFETs due to RTS amplitude distribution, the carrier lifetime estimated with RTS by using graphical extrapolation is discussed. An overview of various aging mechanisms such as NBTI, PBTI, and HCI in the 6T SRAM by AC HTOL stress is presented in Chapter 6, and a post nitridation anneal (PNA) treatment that improves the PBTI reliability is also presented in Chapter 6. Finally, conclusions are made in Chapter 7.