Quantitative analysis of gettering mechanism of Si device by using imagig plate and convergentbeam electron diffraction

杂质吸杂是硅器件工艺中的重要工艺之一。外在或本征吸气技术已在商业过程中得到应用。本征吸杂剂使用热处理后在硅片中形成的氧沉淀物。晶格应变或晶格缺陷被认为是杂质元素的吸纳槽。对吸气池进行定量分析，对于了解吸气机理，提高吸气效率具有重要意义。特别是，分析吸气槽附近的局部晶格应变是很有意义的。与X射线衍射仪或拉曼光谱仪相比，电子衍射法使我们能够以高空间分辨率测量局域晶格应变。在1000ﾟC氧气气氛中热处理的硅片中观察到了电子显微镜图像和会聚束电子衍射图。氧沉淀物是厚度为几纳米、边长为数百纳米的薄片。该平板平行于硅基的(100)面，边缘平行于(110)面。从平行于沉淀物平板的[012]方向的CBED图形，测量了作为与沉淀物表面距离的函数的Si基质的局部晶格应变。在压应力作用下，Si晶格在析出物的片面附近变形约4%，而在析出物边缘附近受张应力变形约3%。晶格应变随与界面距离的增加而减小，并在1微米左右消失。

Inmurity gettering is one of the important processes in Si device process. The extrinsic or intrinsic gettering technique has been used in the commercial process. The intrinsic gettering uses oxygen precipitates formed in Si wafers by heat-treatments. Lattice strains or lattice defects are considered to be gettering sinks for impurity elements. The quantitative analysis of the gettering sinks is very important to understand the gettering mechnaism and to improve gettering efficiency. In Particular it is of interest to analyze local lattice strains near the gettering sinks. Electron diffraction enables us to measure local lattice strains in high spatial resolution compared with X-ray diffraction or Ramann spectroscopy.Electron microscope images and convergent-beam electron diffraction (CBED) patterns are observed in Si wafer which is heattreated at 1000 ﾟC in oxygen atmosphere to produce oxygen precipitates. An oxygen precipitate is thin plate of several nm in thickness and several hundred nm in edge length. The plate is paralle to (100) plane of Si matrix, and the edge is parallel to (110). From the CBED patterns ovserved along [012] direction parallel to the plate of the precipitate, local lattice strains of Si matrix are measured as a function of the distance from a surface of the precipitate. Si lattices are distorted about 4% near the plate plane of the precipitate by the compressive stress, while they are distorted about 3% near the edge of the precipitate by the tensile stress. The lattice strains decrease with increase of a distance from the interface and disappear at about 1 mum.