2004 Fiscal Year Final Research Report Summary
Development of direct observation technique of single electron trap and investigation of degradation mechanism of ultra-thin gate dielectric films
| Project/Area Number |
13305005
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
表面界面物性
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| Research Institution | Nagoya University |
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Principal Investigator |
KONDO Hiroki Nagoya University, Graduate School of Engineering, Research assistant, 大学院・工学研究科, 助手 (50345930)
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| Co-Investigator(Kenkyū-buntansha) |
ZAIMA Shigeaki Nagoya University, Graduate School of Engineering, Professor, 大学院・工学研究科, 教授 (70158947)
SAKAI Akira Nagoya University, Graduate School of Engineering, Associate Professor, 大学院・工学研究科, 助教授 (20314031)
YASUDA Yukio Kochi University of Technology, KUT Research Institute, Professor, 総合研究所, 教授 (60126951)
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| Project Period (FY) |
2001 – 2004
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| Keywords | Scanning tunneling microscopy(STM) / Scanning tunneling spectroscopy(STS) / Conductive atomic force microscopy / Metal-oxide-Semiconductor(MOS) / Gate SiO_2 Films / Stress induced leakage current / Dielectric breakdown |
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| Research Abstract |
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
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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
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