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

我们已经评估了表面粗糙度限制应变si mosfet的迁移率和表面粗糙度在MOS界面的量。结果发现，双轴拉伸应变增加了电子迁移率，而略微降低了空穴迁移率。此外，我们还提出了一种利用高分辨率透射电子显微镜（TEM）精确评估SiO2/Si界面粗糙度形状和自相关函数的新方法。发现由提取的自相关所确定的迁移率与电子和空穴的实验迁移率都符合得很好。此外，我们还通过实验观察到，应变si - MOS界面在Fowler-Nordheim应力作用下产生的界面态密度较小，这归因于应变si - MOS界面粗糙度的降低。此外，si - p- mosfet双轴拉伸应变的增加导致MOS界面电荷导致库仑散射限制空穴迁移率的增加，而衬底杂质导致库仑散射限制迁移率的降低。这种依赖关系与应变si - n- mosfet中的电子迁移率相反。这些库仑散射迁移率的应变依赖关系可以从拉伸应变引起的电子和空穴反转层的子带结构调制的角度系统地理解。

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.