X光三光布拉格-表面繞射(X-ray three-beam Bragg-surface diffraction, BSD)是利用複繞射產生一束沿著晶體行進的表面繞射光，藉由高解析度的CCD擷取表面繞射光的影像，探測其經過表面或者薄膜系統界面之結構變化的複繞射測量技術。根據X光動力繞射理論，表面反射的穿透深度對樣品方位角 呈現函數關係；透過數值計算的方法，定義對應實驗情況之表面繞射光穿透深度，其深度分布對矽基材為10A至373A，砷化鎵為15A至250A之間。我們利用此動力繞射效應針對晶體接近表面之不同深度處，由CCD影像測量其晶格常數，以得到三維的應變場對深度之分布。
我們利用同步輻射光源測試了兩種系統的樣品：受表面之鐵矽化合物影響之矽晶圓以及經化學蝕刻之砷化鎵、砷化銦表面。兩種鐵矽化合物β-FeSi2、FeSi以及兩種化合物之晶界對矽基板造成的應變場，可以藉由布拉格-表面繞射方法同時測量到；應變場所及之深度範圍為界面下15~70A，而測量得到之最大應變量為+0.004%(β-FeSi2)及-0.004%(FeSi)。砷化鎵與砷化銦的測量結果上，並沒有如預期詳細，粗略估計砷化鎵樣品最大的應變場座落在離表面77A處，晶格常數變化量約-0.0015%。此外在分析表面繞射光也發現額外的現象，首先是表面處理的結果破壞了原本的對稱性，即處理後的樣品具有方向性，在不同的方向上觀測到不同的繞射強度分布，在砷化鎵與砷化銦樣品上都具這樣的特性；第二則是表面繞射光對於表面的結構敏感性非常高，對於表面/界面的折射率或是粗糙度皆可以反映在繞射強度分布之形狀上。
X光布拉格-表面繞射方法可以針對樣品做精確的測量，亦可用來做初步或是定性的量測，而不需經過任何有可能造成樣品破壞或是變質的前置準備工作，對於直接觀測樣品表面具有相當的實用性。

X-ray three-beam Bragg-surface diffraction (BSD) is a technique to measure the strain field near surface or buried interface of a substrate in a thin film system, using a surface reflection of X- ray multiple diffractions. The surface diffracted beam propagates along the surface/interface and provides the information about surface/interface structure. According to the dynamical theory of X-ray diffraction, the penetration depth of a surface reflection in the 3-beam geometry is a function of the deviation of azimuthal angle ( ) from the exact position for the 3-beam case. Also from the numerical calculations the depth can be determined, for example, for a Si substrate the penetration depth is from 10 to 373A, and for GaAs is 15 to 250A. Combining with the lattice parameters measured from CCD images of the surface diffracted beam, we can obtain the distribution of 3-D strain field versus depth.
The experiments were carried out at National Synchrotron Radiation Research Center (NSRRC). Two sample systems were tested: Si-Fe interface effected in a multi-components film (β-FeSi2, FeSi) and chemical etched surface of GaAs and InAs. Using the BSD method the strain field of a Si substrate due the 3 structures, β-FeSi2, FeSi and decorated grain boundary, were measured simultaneously. Within the range of 15-70A in depth, the largest variations of lattice parameters are +0.004% for β-FeSi2 and -0.004% for FeSi. The results for GaAs and InAs are not as detail as the former. The largest strain detected of GaAs is -0.0015% at 77A below the surface. For the InAs surface the surface roughness effect detected is shown in the images by changing or distorting the pattern of surface diffracted beam. The relaxation of broken structure along certain specific directions is observed for both GaAs and InAs.
In brief, the X-ray Bragg-surface diffraction has the capabilities of extracting initial information of lattice distortion qualitatively and realizing precise measurements quantitatively. Moreover it is an non-destructive measuring technique.

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