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

本论文利用扫描隧道显微镜（STM）和导电原子力显微镜（C-AFM）对超薄SiO_2薄膜和栅SiO_2薄膜中的退化现象进行了原子尺度和纳米尺度的观察，并利用STM和STS对超薄SiO_2薄膜中的电荷俘获进行了原子尺度的分析。从STM悬臂梁向Si（100）表面超薄SiO_2薄膜注入电子，研究了其局域电子态的变化。在电子注入后，在STM图像中观察到归因于正电荷捕获的亮点。这些正电荷陷阱与衬底表面上固有的二聚体缺陷密切相关，并且可以分为两种不同的类型;一种是在氧化后立即存在，另一种是在电子注入后出现。通过对不同表面缺陷密度的Si衬底的比较，认为Si衬底的固有正电荷 ...更多信息 陷阱是一团较暗的缺陷，电子注入诱导陷阱起源于Si（100）2 × 1表面上的点缺陷。根据电子注入面积与亮斑密度分布的关系，在Si衬底中产生电子-空穴对，形成电子注入诱导陷阱，研究了探测MOS器件栅SiO_2膜局部退化的纳米尺度观测技术。在恒流应力作用下的栅SiO_2膜的电流图像中，观察到局部漏电流点，其漏电流密度是其它区域的10倍以上。这些漏电流点是由于SiO_2薄膜中应力诱导缺陷中的空穴引起的。虽然在应力栅SiO_2膜的漏电流点和其它背区都有空穴被俘获，但漏电流点的俘获空穴密度大于背区。陷阱空穴产生的局域电场增强了Fowler-Nordheim（F-N）隧穿电流，出现漏电流斑点。当在同一区域重复进行C-AFM观察时，观察到漏点电流的增加和减少，这意味着应力诱导缺陷中的充电和放电。在漏斑区和本底区，陷阱空穴密度的增加和减少特征是不同的，这表明漏斑区和本底区存在不同的缺陷结构。当在较高电场下重复进行C-AFM观察时，介质击穿优先发生在漏电点处，这是首次在纳米尺度下观察到的结果。在下一代超大规模集成电路（ULSI）器件（尺寸为纳米级）的开发中，利用扫描探针显微镜对栅漏进行评估被认为是至关重要的。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