2005 Fiscal Year Final Research Report Summary
XPS Study of electrical defects in thin HfAlOx films formed on Si substrates
| Project/Area Number |
15560025
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Thin film/Surface and interfacial physical properties
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| Research Institution | Japan Aerospace Exploration Agency |
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Principal Investigator |
HIROSE Kazuyuki Japan Aerospace Exploration Agency, associate professor, 宇宙科学研究本部・宇宙探査工学研究系, 助教授 (00280553)
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| Co-Investigator(Kenkyū-buntansha) |
HATTORI Takeo Musashi Institute of Technology, professor, 工学部, 名誉教授 (10061516)
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| Project Period (FY) |
2003 – 2005
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| Keywords | LSI / MOSFET / gate oxide / SiO_2 / dielectric constant / HfO_2 / defects / x-ray photoelectron spectroscopy |
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| Research Abstract |
Because advances in device technology cannot be made without dramatic reducing the size of metal-oxide semiconductor field-effect transistors (MOSFETs), alternative gate insulators with high electrical permittivity (high-k insulators) are being widely investigated. Unlike conventional SiO_2 gate dielectric film, high-k films exhibit significant charge trapping that causes the threshold voltage to shift over stress time. This raises an important reliability issue for high-k films. It is highly required to reveal the relations between the charge trapping phenomena in high-k film and stress.
X-ray photoelectron spectroscopy (XPS) time-dependent measurement technique we recently developed enabled us to measure the surface potential of a Si substrate covered with thin dielectric film without making electrodes and to measure the shift of the surface potential after carrier injection by x-ray. We found that the Si 2p photoelectron binding energy of a Si substrate covered with a 3 nm thick HfAlOx film increased to a saturation value during x-ray irradiation. This shift towards a higher binding energy indicates an increase in the amount of positive charges in the film, and the density of hole traps is estimated to be significantly higher than that in a SiO_2 film. Before x-ray irradiation, the interface Fermi level coincided with the valence-band maximum of the Si substrate, which indicates that the Si surface band bends upward. This means that there were negative charges already in the film before x-ray irradiation. Investigating the effects of the interlayer beneath the HfAlOx film on these trapped charges reveals that the observed hole trapping and initial electron trapping are intrinsic to the HfAlOx film.
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