Source of surface defects in silicon carbide epitaxial files and their elimination method

碳化硅（SIC）因其在功率器件中的应用而受到广泛关注，并表现出优于传统硅基材料的性能。高质量的大面积外延薄膜是制造kv级大功率SiC器件的必要条件。然而;在现阶段，外延薄膜的缺陷，包括表面缺陷，限制了这种器件的高产量生产。某些类型的表面缺陷形成后，会使p-n结的击穿电压降低20%至40%，从而使器件性能恶化。本研究的主要目的是利用平面透射电子显微镜（TEM）研究衬底/外膜界面表面缺陷的来源，并找到一种消除表面缺陷伴随的晶体缺陷的技术。我们成功地制备了平面视图的TEM样品，该样品在薄化区域包含衬底/外膜界面，在衬底侧进行常规离子薄化之前，通过更多的反应性等离子蚀刻去除几乎整个外膜。表面缺陷的来源是夹杂物和部分位错。能量色散x射线（EDX）光谱和微拉曼分析表明，包裹体是非常小的氧化锆（ZrO_2）颗粒。化学气相沉积（CVD）炉的绝缘体是ZrO_2颗粒最可疑的来源。ZrO_2颗粒落在SiC衬底表面并结合到外膜中可能是部分位错的来源，从而导致表面缺陷的形成。我们提出了超短激光脉冲辐照引起的相变可以用于消除SiC外延膜中的缺陷。当飞秒激光脉冲照射在SiC表面时，会形成周期性的表面微结构，称为波纹。为了研究波纹的横截面微观结构，我们进行了TEM研究，特别关注波纹下的晶体结构。在波纹的最顶端覆盖了一层约10 ~ 50纳米厚的连续非晶层。少

Silicon carbide (SIC) has been attracting much attention because of its application to power devices exhibiting superior performance to conventional Si-based ones. large-area epitaxial films of high quality are essential for the fabrication of kV-class high-power SiC devices. However ; at the present stage, imperfections in epitaxial films including surface defects impose a limitation on high-yield production of such devices. When formed, some types of surface defect deteriorate device performance by lowering the breakdown voltage of p-n junctions by 20 to 40%. The major objectives of the present study are to investigate the source of surface defects at the substrate/epifilm interface by plan-view transmission electron microscopy (TEM) and to find a technique to eliminate crystallographic defects accompanying surface defects.We were successful in preparing plan-view TEM samples which contain the substrate/epifilm interface in the thinned area by removing almost the entire epifilm with … More reactive plasma-etching prior to the conventional ion-thinning from the substrate side. The source of surface defects was composed of an inclusion and partial dislocations. Energy dispersive X-ray (EDX) spectroscopy and micro-Raman analysis unraveled that the inclusions were very small particles of zirronia (ZrO_2). The thermal insulator in the chemical vapor deposition (CVD) furnace is the most suspicious origin of ZrO_2 particles. The ZrO_2 particles which fell onto the SiC substrate surface and were ncorporated into the epifilm may have acted as the source of partial dislocations, which resulted in the formation of surface defects.We propose that phase change induced by irradiation of ultra-short laser pulses may be applied to the elimination of defects in SiC epitaxial films. When femtosecond laser pulses are irradiated on the surface of SiC, periodic surface microstructures referred to as ripples are formed. In order to study the cross-sectional microstructures of ripples, we carried out TEM studies with particular attention on the crystal structure underlying ripples. A continuous amorphous layer approximately 10 to 50 nm thick was found to cover the topmost region of ripples. Less