Carrier mobility in advanced channel materials using alternative gate dielectrics

The continuous downscaling in the dimension of MOSFETs yielded SiO2 gate oxide to be replaced by a high-? material Hf based gate oxide (?~20) in the 45 nm technology node. In this way, the excessive leakage current, that was the main problem in scaled devices with SiO2 gate oxide, was overcame and further scaling to 32 nm node was successfully achieved. However, for an even better performance in ultimately scaled devices (22 nm node and beyond) higher-? dielectric materials are required. Due to their thermodynamic stability, higher-? values (23-32), high band gap and band offsets relative to silicon, rareearth based ternary oxides (e. g. GdScO3, TbScO3, LaScO3, LaLuO3.) are promising dielectrics for CMOS applications. On the other hand, it is essential to use silicon on insulator (SOI) and strained silicon on insulator (sSOI) as channel materials to improve the transistor properties and lower the power consumption. In this work, as a member of rare-earth based ternary oxides, LaLuO3, LaScO3, TbScO3, and SmScO3 thin films deposited on silicon were structurally and electrically investigated. The objective of the annealing study is to find an optimized condition for an improved device performance. The films are stoichiometric and amorphous up to 800-1000 ºC, however, silicate formation is an inevitable process during film growth. While silicate formation is triggered by oxygen annealing, applying forming gas (FG) annealing after TiN metal gate helps to reduce the interfacial layer (IL) thickness via scavenging of the oxygen from the interface. Optimization of the annealing process does not affect the ? values and yields to smooth C-V curves with negligible hysteresis, low oxide and interface trap charges and low leakage current density, which of all are good sign in terms of mobility. A replacement gate process was developed for the integration of LaLuO3, LaScO3, TbScO3, and SmScO3 into MOSFETs using SOI and sSOI substrates. Long channel p-and n-type MOSFETs were successfully fabricated and promising results were achieved for devices with LaLuO3, LaScO3 and TbScO3. For these devices an interface traps level in the range of 2-4x1011 (eVcm2)-1, steep subthreshold slope down to 65 mV/dec and high Ion/Ioff ratios up to 1010 is achieved. The sSOI n-MOSFETs show strongly enhanced drain current and electron mobilities with a factor of 1.8 compared to SOI reference devices. These materials provide similar electron and hole mobilities to the reported HfO2 and HfSiON materials, while could provide an advantage of higher scalability and lower leakage current density than HfO2 due to their higher ? values.