Development of direct observation technique of single electron trap and investigation of degradation mechanism of ultra-thin gate dielectric films

利用扫描隧道显微镜(STM)和导电原子力显微镜(C-AFM)对超薄二氧化硅(SiO_2)薄膜和栅极SiO_2薄膜的退化现象进行了原子尺度和纳米尺度的观察，并用扫描隧道显微镜(STM)和扫描隧道光谱(STS)对超薄SiO_2薄膜的电荷捕获进行了原子尺度的分析。将电子从STM悬臂梁注入到Si(100)表面的超薄SiO_2薄膜中，研究了局域电子态的变化。在电子注入后，在STM图像中观察到了由于正电荷俘获而产生的亮点。这些正电荷陷阱与衬底表面固有的调光器缺陷密切相关，可以分为两种不同的类型；一种是在氧化之后出现的，另一种是在电子注入之后出现的。通过对具有不同表面缺陷密度的硅衬底的比较，提出了本征正电荷…更多的陷阱来自于Si(100)-2X1表面上的点缺陷。根据电子注入面积与光斑密度分布的关系，在硅衬底上通过电子-空穴对的产生产生电子注入感生陷阱，研究了纳米尺度的观察技术来检测工作的金属氧化物半导体(MOS)器件栅极SiO_2膜中的局部退化。在恒流应力外加SiO_2膜的电流图像中，观察到局部漏电流斑点，其中的漏电流密度是其他区域的10倍以上。这些漏电流斑点归因于SiO_2薄膜中应力诱导缺陷中的空穴。应力栅氧化硅薄膜中的漏电流点和其他背衬区域都存在空穴陷阱，但漏电流斑点的陷阱空穴密度大于背景区。陷阱空穴产生的局部电场增强了Fowler-Nordheim(F-N)隧道电流，从而出现漏电流斑点。当在同一区域重复C-AFM观察时，观察到漏点电流的增加和减少，这意味着应力引起的缺陷中的充电和放电。漏点和背景区陷阱空穴密度的增减特征不同，表明这些区域存在不同的结构缺陷。然后，当在较高电场下重复C-AFM观察时，介质击穿优先发生在漏点，这是首次通过纳米尺度的观察得到的结果。在尺寸为纳米级的下一代ULSI器件的开发中，利用扫描探针显微镜对栅电介质进行评估被认为是最基本的。较少

In this study, degradation phenomena in ultra-thin silicon oxide(SiO_2) films and gate SiO_2 films have been investigated by atomic-scale and nanometer-scale observation using scanning tunneling microscopy(STM) and conductive atomic force microscopy(C-AFM).Charge trapping in ultra-thin SiO_2 films was analyzed with atomic-scale by STM and scanning tunneling spectroscopy(STS). Injecting electrons from STM cantilever to ultra-thin SiO_2 films on Si(100) surface, change of local electronic state was studied. After the electron injection, bright spots, which are attributable to positive charge trapping, were observed in STM images. These positive charge traps are closely-linked to defects of dimmers inherent on the substrate surface and can be divided into two different types ; one exists just after the oxidation, and the other appears after the electron injection. From comparison between Si substrates with different surface defect densities, it was suggested that inherent positive charge … More traps are cluster of dimmer defects and electron-injection induced traps originate from point defects on the Si(100)-2x 1 surface. According to the relationship between electron-injected area and density distribution of bright spots, electron-injection induced traps are generated by electron-hole pair generation in Si substrate.We investigated nanometer-scale observation techniques to detect local degradations occurred in gate SiO_2 films of operated Metal-oxide-Semiconductor(MOS) devices. In current images of constant-current-stress applied gate SiO_2 films, local leakage current spots, in which leakage current density is more than 10 times larger than that in the other area, were observed. These leakage current spots are attributed to holes trapped in stress-induced defects in the SiO_2 films. Although holes are trapped in both leakage current spots and the other back ground regions in the stressed gate SiO_2 films, density of trapped holes in the leakage current spots is larger than that in the background regions. Local electric filed induced by trapped holes enhances Fowler-Nordheim(F-N) tunneling current, and then leakage current spots appear. When C-AFM observations were repeated in the same area, increase and decrease of leakage spot current were observed, which means charge and discharge in the stress-induced defects. Increasing and decreasing features of trapped hole densities are different between in leakage spots and in the background regions, which indicates different structures the defects existing in these regions. Then, when C-AFM observations were repeated at higher electric fields, dielectnc breakdown occurred preferentially at the leakage spots.These results were obtained for the first time by nanometer-scale observations. In the developments of next-generation ULSI devices, whose size us nanometer-scale, evaluations of gate dielectrics by scanning probe microscopes are thought to be fundamental. Less