Abstract
Mobility and current drive improvements associated with the tensile strained-silicon in NMOS. The tensile strained-silicon is based on the Si/Si1-xGex or “highly-tensile” silicon nitride capping layer. This research provides a numerical simulation of finite element method to solve stress-strain behaviors of the strained-silicon. The lattice mismatch between Si and Si1-xGex is simulated in the framework of thermoelasticity. Si and Si1-xGex is assigned in different thermal-expansion coefficients such that the misfit across the interface is met. The parametric analysis is studied for the Si/Si1-xGex nano-structure of single and triple gate NMOS. It is worth noting that when the mesa length is less than 50nm, the entire surface of the top Si layer depicts compressive x-directional strain. This result indicates that an extra small Si/SiGe/Si stack mesa may be inactive for increasing the mobility of the NMOS device. The stress from the silicon nitride capping layer is uniaxially transferred to the NMOS channel through the source-drain region to create tensile strain in NMOS channel. The residual stress of the silicon nitride capping layer includes the intrinsic stress and thermal stress. This study analyzes the distribution of strain in NMOS channel by using “prestress method” proposed in this investigation to simulate the different intrinsic stress. The maximum x-directional strain of NMOS channel is 0.6% when the model is gave 1GP of the intrinsic stress of the silicon nitride capping layer under a temperature loading of -400K. The simulate result of Si/Si1-xGex is close to the experimental data of the reference. It indicates that applying the numerical simulation of finite element method to solve stress-strain behaviors of the strained-silicon is feasible. This study also gives detailed analysis about the relationship between different strained-silicon dimensions and strain distributions. The parametric studies can provide the design rule for the mechanical behavior of the nanoscale strained-silicon.