Point defects in thin HfAlO x films probed by monoenergetic positron beams
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Point defects in thin HfAlOx films probed by monoenergetic positron beams Akira Uedono1, Riichiro Mitsuhashi2, Atsushi Horiuchi2, Kazuyoshi Torii2, Kikuo Yamabe1, Keisaku Yamada3, Ryouichi Suzuki4, Toshiyuki Ohdaira4, and Tomohisa Mikado4 1
Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan Semiconductor Leading Edge Technologies, Inc, 34 Miyukigaoka, Tsukuba, Ibaraki 305-8501, Japan 3 Nano Technology Research Laboratory, Waseda University, 513, Waseda-Tsurumaki, Shinjuku, Tokyo, Japan 4 National Institute of Advanced Industrial Science and Technology, Tsukuba Central-2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan 2
ABSTRACT Thin HfAlOx films grown on SiON(0.9 nm)/Si by atomic layer deposition technique were characterized by using monoenergetic positron beams. The lifetimes of positrons in the HfAlOx film after post-deposition annealing (PDA) ranged between 412-403 ps. Since these lifetimes were longer than the lifetime of positrons trapped by point defects in metal oxides, such as LaCoO3, PbTiO3, and BaTiO3, the positrons in HfAlOx films were considered to annihilate from the trapped state by open spaces which exist intrinsically in their amorphous structure. The line-shape parameter S of the Doppler broadening spectrum corresponding to the annihilation of positrons in HfAlOx films decreased by PDA, and the S value decreased with increasing an O2-content in an atmosphere during PDA (0.004-1%). The observed behavior of the S value was attributed to the shrinkage of the open spaces due to the change in the matrix structure of HfAlOx. After P+- and B+-implantation into poly-Si films grown on the HfAlOx films, the diffusion of positrons in the Si substrates toward the HfAlOx film was suppressed. This fact was attributed to positive charges introduced near the HfAlOx films. INTRODUCTION According to the international technology roadmap for semiconductors [1], the technology node for mass production will reach the 65-nm level in 2007; as a result, the need to replace SiO2 with high-dielectric (high-k) materials will be indispensable for fabrication of complementary metal-oxide-semiconductor (CMOS) devices. Among many candidates for high-k materials, binary oxides based on hafnium (HfO2) have advantages such as a moderately high dielectric constant and high thermal stability in contact with Si [2,3]. Although the electric properties of MOS structures using the binary oxides have been intensively studied, behavior of the oxides during device processing is not fully understood. This might be due to a lack of techniques to characterize thin films in the subsurface region. Positron annihilation is one established technique for investigating defects in materials [4]. Point defects in transition-metal oxides have been investigated by using positron annihilation [5-11], and the results show that positrons are a useful probe for studying vacancy-type defects in such materials. In the present study, we used monoenergetic positron beams to study defects in thin HfAlOx films deposited
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