The Element Depth Profiles in Ultrathin Silicon Oxynitride Films
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The Element Depth Profiles in Ultrathin Silicon Oxynitride Films Igor P. Asanov, Jinhak Choi, Youngsu Chung, Jaemin Choi, and Jaecheol Lee Samsung Advanced Institute of Technology, Analytical Engineering Center, P.O.Box 111, Suwon 440-600, Korea ABSTRACT Distribution of nitrogen in the thin silicon oxynitride films (less than 5 nm) obtained by plasma nitridation of SiO2 has been studied by non-destructive angular dependent XPS. For obtaining information about the element distribution in-depth the regularization technique has been applied. It is shown that the depth of nitrogen penetration increases with decreasing the SiO2 film thickness. In this case the maximum of the nitrogen distribution is enhanced and shifted to the Si-SiO2 interface. The results are compared with depth-profiling obtained by sputtering and wet chemical etching. The dependence of the binding energies on the film thickness has been studied. The influence of different factors on the chemical shift in the ultrathin films has been analyzed. INTRODUCTION For the miniaturization of ULSI devices in the deep submicron region the oxide equivalent thickness of gate dielectric has to be decreased below 5 nm [1]. In this connection, the nitrogen doped SiO2 or silicon oxynitride SiOxNy with dielectric constant higher than in SiO2 are considered as the near-term gate dielectric solution. The nitrogen incorporation provides the effective barrier to the boron atom diffusion from doped polycrystalline Si gate electrodes. It makes possible to use physically thicker films to reduce gate leakage current while maintaining the thinner oxide thickness equivalent and enhances device reliability [2]. For the various applications it is necessary to use the layers with different nitrogen distribution. One of the most efficient syntheses techniques is the plasma nitridation. At present the study of the distribution and chemical bond of nitrogen in ultrathin layers is the challenge for physical methods. By now there is the extensive literature devoted to the problem of characterization of silicon oxynitride films by XPS and AES [3-7]. For example, in the work [8] it was shown that N+ ions are the reacting species in the process of plasma nitridation. It was found several components in the N 1s spectra that related with different bonding configurations of the nitrogen atoms. In the Si 2p spectra there are two principal lines corresponding to Si0 and Si+4. The splitting between these main component increases with the thickness of film from 3.9 eV to 4.4 eV [3]. This phenomenon may be related with image charges or charging of the surface layers [9]. Also three additional peaks due to silicon atoms in the intermediary charge states are observed in the Si 2p spectra. XPS may be applied for the measurements of the element distribution in-depth by changing the take-off angle of emitted electrons or depth-profiling the surface layers by ion sputtering or chemical etching. Hence, XPS is a principal technique for the characterization and investigation of ultrathin film but
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