Investigation of strain effect on the hole mobility in GOI tri-gate pFETs including quantum confinement

The strain impact on hole mobility in the GOI tri-gate pFETs is investigated by simulating the strained Ge with quantum confinement from band structure to electro-static distribution as well as the effective mobility. Lattice mismatch strain induced by HfO2 warps and reshapes the valence subbands, and reduces the hole effective masses. The maximum value of hole density is observed near the top comers of the channel. The hole density is decreased by the lattice mismatch strain. The phonon scattering rate is degraded by strain, which results in higher hole mobility.     

He离子注入对Ge中缺陷行为的影响研究

本文采用以蒙特卡罗方法为基础的SRIM软件模拟He离子注入对Ge中缺陷行为的影响,为高质量GOI(绝缘体上Ge)材料的制备提供理论指导。本文主要模拟了He离子入射角度、能量以及注入剂量对Ge材料损伤程度和溅射产额等的影响。研究表明:入射角度较小时,拖尾效应不明显,有利于避免沟道效应,同时缺陷空位数(DPA)也处于较低水平;能量增大导致离子射程增大,溅射产额减小,离表面越近的Ge中DPA变少,可以实现低DPA GOI材料的制备;离子注入剂量增大导致损伤区域增大且集中,然而更多的He离子聚集在射程附近,能够很好地降低GOI材料的剥离温度。     

Study of the surface cleaning of GOI and SGOI substrates for Ge epitaxial growth

An effective wet cleaning process, optimized for low temperature Ge epitaxial growth on thin Ge or SiGe structures with reduced surface roughening, is proposed. It is found that HF + HCl cleaning is the most effective wet cleaning method that is applicable to the low temperature thermal cleaning. It is also found that temperature of the thermal cleaning appropriate to 25-30 nm thick germanium on insulator (GOI) or silicon-germanium on insulator (SGOI) substrates is approximately 450 °C. Moreover, it is also found that the temperatures of Ge epitaxial growth even in lattice-matched systems must be reduced to around 400 °C to prevent surface roughening and those in lattice-mismatched systems also must be reduced sufficiently (300 °C for strained Ge growth on SGOI (X_eff = 0.6)) to prevent lattice relaxation as well as surface roughening. Finally, the successful formation of the compressively strained GOI structures is demonstrated by applying these wet cleaning and low temperature thermal cleaning processes and low temperature Ge epitaxy to thin SGOI substrates.