摘要：将块体SiC单晶中切割下的晶片经机械抛光处理后作为籽晶，用物理气相传输法(PVT)生长SiC晶体。采用离子减薄方法，分别制备了透射电镜平面样品和横截面样品。利用透射电子显微镜(TEM)观察了SiC生长晶体中与表面损伤相关的穿透位错的分布特征。所观察到的大部分穿透位错都是沿[0001]方向、柏氏矢量为a/3<11 0>的典型刃位错。刃位错呈一列列的位错墙分布，同时也有一部分呈蜂窝状结构分布，蜂窝壁总体上沿<1 00>方向排列。在位错较少的区域也可以看到一些离散的小蜂窝房孔，刃位错的密度约为107cm-2。另外，在生长的晶体中我们也观察到了螺位错，螺位错的密度大约为105cm-2，约比刃位错的密度低两个数量级。螺位错总是成对出现，且其柏氏矢量的符号相反，相隔约0.3微米。穿透位错的形成与机械抛光过程中塑性变形引起的亚表面损伤有关。64030

关键词  碳化硅单晶  物理气相传输法  机械抛光  透射电镜  位错

毕业论文 外 文 摘 要

Title  Impacts on the Dislocations in 6H-SiC Crystal by Mechanical Polishing on the Surface of Seed Crystal                    

Abstract SiC wafers cut from the bulk crystal were treated by mechanical polishing and then SiC single crystal was grown using the wafers as seed crystal and the physical vapor phase transportation method (PVT). Using ion milling method, plane TEM samples and cross-sectional TEM samples were prepared.Several characteristic features of surface-damage-related threading dislocations in SiC epitaxial layers have been investigated by transmission electron microscopy. Most of the observed threading dislocations are perfect-edge type with line direction along [0001] and Burgers vector of a/3<11 0>. The edge dislocations are arranged in form of dislocation walls or cellular structures with cell walls aligned preferentially along <1 00> directions. Some small isolated cells were also observed in the areas of lower dislocation density. The density of edge dislocations was about 107cm-2. In addition, we’ve also observed screw dislocations in the overgrowth. The density of them  was approximately 105cm-2 and is about two orders of magnitude lower than the edge dislocation density. The screw dislocations appeared in pairs with the opposite sign of Burgers vectors separated by about 0.3 μm. The formation of threading dislocations is associated with the subsurface damages caused by plastic deformation during the mechanical polishing process.

Keywords  SiC single crystal  PVT method  mechanical polishing  TEM  dislocation

1  绪论 1

1.1  SiC晶体材料简介 2

1.1.1  SiC晶体的结构 2

1.1.2  SiC晶体的特性 3

1.2  SiC晶体材料中的缺陷 4

1.3  SiC晶体材料的国内外研究现状 5

1.3.1  国外研究现状 5

1.3.2  国内研究现状及发展方向 5

1.4  SiC功率器件发展的挑战 6

1.5  SiC晶体的制备——PVT生长法 7

1.6  本课题的研究内容 9

2  实验 10

2.1  实验仪器及材料 10

2.2  实验方法 10

2.3  透射电子显微镜样品的制备