奈米級無摻雜型鐵電負電容材料與元件關鍵製程技術開發

As an advanced sub-7 nm technology is approached, the reduction of supply voltage (VDD) becomes a bottleneck for CMOS node scaling. To solve the scaling limitation, the research on new transistor formula to reduce VDD is required. In recent years, the semiconductor industries give priority to the research of next-generation transistors featuring ultralow leakage current and low-power operation. The ferroelectric negative capacitance field effect transistor (NCFET) is a promising candidate owing to its steep turn-on switch property under an ultralow gate overdrive. However, according to our research results published in 2017 IEDM and 2018 IRPS, the ultra-thin interfacial layer for NCFET device scaling is usually accompanied by higher interface defect density and larger leakage current. Furthermore, the poor dopant tunability limits the scalability of the ferroelectric thickness. On the other hand, the leakage through the gate stack may change the dynamic switch of the ferroelectric negative capacitance (NC) system, causing the unstable NC operation. Recently, we have successfully demonstrated the dopant-free HfO2 NCFET and published in 2018 VLSI. Based on our experimental results, it has been proved that crystallinity of dopant-free HfO2 can be effectively controlled by film thickness scaling and additional strained-gate engineering. As a result, the dopant-free HfO2 transistor shows the excellent performance of sub-35mV/dec, 35mV hysteresis and 1 pA/um off current. To meet the requirements of IoT and advanced logic devices, the remote plasma passivation was simultaneously carried out for the sake of lowering leakage current and improving device reliability. This project collaborating with Atom Semicon Co., Ltd. is mainly focused on the platform establishment of nano-scale ferroelectric thin film by Picosun ALD. To solve the issues of the poor dopant tunability of HfAlO and thermal stability of HfZrO, we focus on the research of dopant-free HfO2 negative capacitance field effect transistors. We will investigate the influence of plasma surface treatment and strained gate on the ferroelectricity of dopant-free HfO2 mainly contributed by orthorhombic phase. Besides, the interface quality of dopant-free HfO2 NCFET is also examined by material analysis and electrical reliability. Therefore, the development of dopant-free HfO2 will provide more key solutions for the fabrication of nano-scale ferroelectric devices, which is also beneficial for the promotion of Picosun ALD in semiconductor industries.