Study on physical models for understanding the properties of strained-Si MOS Transistors

沟道应变对MOSFET电学特性的影响尽管很重要，但目前还没有完全了解。因此，建立描述电学性质的物理模型是至关重要的。在这项研究中，通过对双轴拉伸应变Si MOSFET的分析，澄清了以下问题。*发现反型层电子迁移率和空穴迁移率对有效场具有普适性，η分别为1/2和1/3，与无应变Sin-MOSFET和p-MOSFET相似。*发现正偏压下n-MOSFET的栅电流随着双向拉伸应变的增加而减小，这是由于电子从反型层中隧穿而来。我们已经证明了这种隧道电流降低的定量解释是由于拉伸应变导致导带边缘降低而导致Si和SiO_2之间势垒高度的增加。*已经发现，由FN应力注入产生的界面态的密度和能量分布不随施加张应变而改变，而应力后的n-MOSFET的阈值电压漂移确实随着应变的变化而变化，这是因为应变Si nMOSFET在反转条件下的能带弯曲减少。*尽管由于衬底杂质的库仑散射限制了电子的迁移率，但随着张应变的增加，n-MOSFET中的电子迁移率增加，由于界面电荷的库仑散射限制了电子的迁移率。这些结果是由于平均电导质量的减小和与界面库仑散射中心的散射几率的增加，这两者都是由于施加张应变而增加了2倍谷电子的占有率。

The effects of the channel strain on the electrical characteristics of MOSFETs have not been fully understood yet in spite of the importance. Thus, the establishment of the physical models to describe the electrical properties is of paramount importance. In this study, following issues have been clarified by the analyses using bi-axial tensile strain Si MOSFETs.* It has been found that inversion-layer electron and hole mobility do hold the universality against the effective field with the value of η of 1/2 and 1/3, respectively, as similar with unstrained-Si n-and p-MOSFETs.* It has been found that gate current of n-MOSFETs under the positive bias, attributed to tunneling of electrons from the inversion layers, decreases with an increase in bi-axial tensile strain. We have demonstrated that this tunnel current reduction is quantitatively explained by the increase in the barrier height between Si and SiO2, caused by the lowering of the conduction band edge due to the tensile strain.* It has been found that the density and the energy distribution of interface states, generated by FN stress injection, do not change with applying tensile strain to channels, while the threshold voltage shift of n-MOSFETs after the stressing does change with strain because of the reduction in the band bending under the inversion condition in strained-Si nMOSFETs.* While electron mobility limited by Coulomb scattering due to substrate impurities in Si n-MOSFETs increases with an increase in tensile strain, the electron mobility limited by Coulomb scattering due to interface charges does decrease. These results are explained by the reduction in the averaged conductivity mass and the increase in the scattering probability with interface Coulomb scattering centers, both of which are provided by the increase in the occupancy of the 2-fold valley electrons due to applying tensile strain.