現今的半導體元件中，大部分是由薄膜系統所構成，在奈米尺寸下，其應變(strain)對元件特性有顯著的影響，為了可以更清楚了解元件的特性，本實驗利用X光三光布拉格表面繞射(X-ray Three-Beam Bragg-Surface Diffraction，BSD)實驗方法進行介面應力的探討。
本實驗於國家同步輻射研究中心BL17B1光束線進行，利用對稱式布拉格繞射光和一個沿著樣品表面傳遞之表面繞射光所組成之布拉格表面繞射幾何，以能量為12keV的入射光同時激發基板與薄膜，收取空間強度分布解析介面應變。
本實驗之樣品為矽與矽鍺薄膜成長在矽基板上，以Si/Si0.8Ge0.2/Si表示，利用布拉格表面繞射之幾何，並選擇(0 0 4)/(2 0 2)、(0 0 4)/(0 2 2)、(0 0 4)/(-2 0 2)三組反射面，藉由空間強度分布圖解析得知矽鍺為三斜晶體(triclinic structure)，矽為正交晶體(orthorhombic structure)，且矽鍺為了與矽晶體匹配，將其a、b軸縮短(Δa、Δb <0)，並利用c軸釋放其應變(Δc >0)。

The semiconductor devices are composed of thin-film systems, therefore, the strain is one of the important factors to the performance of the device. We probe interfacial strains in Si/Si0.8Ge0.2/Si using three-beam Bragg-surface diffraction.
The experiment was performed on BL17B1 beamline at the National Synchrotron Radiation Research Center (NSRRC).The Bragg-surface diffraction consists of a symmetric Bragg diffraction and a surface diffraction, propagating along the interface of the sample. The incident X-rays are 12keV and excite the substrate and thin film simultaneously. The interfacial strains are analyzed according to the spatial intensity distributions.
The sample is a silicon and silicon-germanium thin films grown on the silicon substrate(Si/Si0.8Ge0.2/Si).Three reflecting surfaces,(0 0 4)/(2 0 2)、(0 0 4)/(0 2 2)、(0 0 4)/(-2 0 2), are measured in this study. We find that the silicon-germanium is a triclinic structure and the silicon is nearly a orthorhombic structure. The thin film is deformed to accommodate the lattice mismatches so that the a and b-axis are shortened and the c-axis is stretched.

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