三維應力引致(001)和(110) p型場效電晶體反置層電洞遷移率變化之研究

Abstract

本篇論文的主題是要探討三種不同方式施加在元件上的應力，對於(001)/<110>和(110)/<110>之p型場效電晶體，並利用六層的k．p模擬器去計算電洞遷移率的影響。我們在這考慮了三種散射機制，分別是，光聲子散射、聲子散射以及表面粗糙散射。我們利用三種不同的物理觀點去探討三維應力所引起電洞遷移率變化的原因，第一，使用在應力模型中形變位能a□, b和d分別的影響。第二，聲子和表面粗糙度的影響。第三，則是散射時間以及傳導質量的影響。最後，結論是:(一)特別在單軸壓縮應力作用下，分別對電洞遷移率的影響時a□效應很小，b適中，d則很大。因此，我們經由實驗的校準可得到a□是2.46，b的範圍是-1.6到-2.1，而d是-3.1，上面三種參數的單位均為電子伏特；(二)在應力的作用下，聲子對電洞遷移率的改變較表面粗糙度的影響還算敏感；以及(三)當我們不考慮表面粗糙度對電洞遷移率改變的影響時，電洞遷移率改變的比例會正比於傳導質量改變之倒數和能態密度質量改變之倒數的乘積。

Hole inversion-layer mobility under three-dimensional stresses in (001)/<110> and (110)/<110> of p-MOSFETs is investigated by using a self-consistent six-band k•p solver. The three significant scattering mechanisms are included: optical phonon scattering, acoustic phonon scattering, and surface roughness scattering with the screening effect taken into account. This leads to a clearer physical insight into 3-D-stress-induced hole mobility change in terms of three parts: (1) effect of strained k•p deformation potentials a, b, and d; (2) phonon-limited and/or surface-roughness-limited mobility change; and (3) scattering-time-limited and conductivity-effective-mass-limited mobility change. Finally, the conclusions indicate that (1) for the effect of the hole mobility change, a is weak, b is moderate, and d is strong, particularly for the uniaxial compressive stress in the <110> direction. The experimentally-calibrated values are: a = 2.46eV, b = -1.6 ~ -2.1eV, and d = -3.1eV; (2) the phonon-limited mobility change is more stress-sensitive than the surface-roughness-limited one; and (3) the mobility change ratio can be related to the reversely proportional conductivity effective mass and density-of-states effective mass in the absence of the surface roughness mobility change.