Understanding of mechanisms dominating inversion-layer mobility in strained-Si MOSFETs and establishment of guideline for the mobility enhancement

我们已经评估了应变硅MOSFET的表面粗糙度限制的迁移率和MOS接口处的表面粗糙度的量。结果发现，双轴拉伸应变增加了电子迁移率，而它稍微降低了空穴迁移率。此外，我们还提出了一种新的方法来准确地评估SiO2/Si界面粗糙度的形状和自相关函数，通过使用高分辨率透射电子显微镜（TEM）。已经发现，所提取的自相关确定的迁移率是在很好的协议与电子和空穴的实验迁移率。此外，我们还观察到应变Si MOS界面Fowler-Nordheim应力产生的界面态密度减小，这归因于应变Si MOS界面粗糙度的减小，此外，双轴拉伸应变Si p-MOSFET的增加导致MOS界面电荷引起的库仑散射限制的空穴迁移率增加，同时由于衬底杂质导致库仑散射限制的迁移率降低。这种依赖性是相反的应变硅n-MOSFET中的电子迁移率。这些应变的库仑散射迁移率的依赖性可以系统地理解的电子和空穴反转层由于拉伸应变的子带结构调制的观点。

We have evaluated surface-roughness-limited mobility of strained-Si MOSFETs and amount of surface roughness at the MOS interfaces. As a result, it has been found that bi-axial tensile strain increases the electron mobility, while it slightly decreases the hole mobility. Also, we have proposed a novel method to accurately evaluate the shape of the SiO2/Si interface roughness and the auto-correlation function by using high resolution Transmission Electron Microscope (TEM). It has been found that the mobility determined by the extracted auto-correlation is in good agreement with the experimental mobility for both electrons and holes. In addition, we have experimentally observed that the strained-Si MOS interfaces smaller densities of interface states generated by Fowler-Nordheim stress, attributed to the reduction in roughness of strained-Si MOS interfaces.Furthermore, the increase in the bi-axial tensile strain strained-Si p-MOSFETs leads to the increase in Coulomb-scattering-limited hole mobility due to MOS interface charges, while it leads to the decrease in Coulomb-scattering-limited mobility due to substrate impurities. This dependence is opposite to that of the electron mobility in strained-Si n-MOSFETs. These strain dependencies of the Coulomb scattering mobilities can be systematically understood from the viewpoint of the subband structure modulation of electron and hole inversion layers due to tensile strain.