Elsevier

Thin Solid Films

Volume 516, Issue 11, 1 April 2008, Pages 3486-3492
Thin Solid Films

In situ observation of electron beam irradiation effects in oxidized polycrystalline Si1−xGex films

https://doi.org/10.1016/j.tsf.2007.08.081Get rights and content

Abstract

This study examined the morphological and compositional changes that occur in oxidized poly-Si1−xGex film during electron-beam irradiation in a transmission electron microscope. Before irradiation, the oxide layer was composed of a mixture of SiO2 and GeO2 phases. However, during electron-beam irradiation, there were significant changes in the microstructure and elemental distribution. For the oxidized poly-Si0.6Ge0.4 films, the agglomeration of GeO2 was observed at the surface region. On the other hand, in the case of the oxidized poly-Si0.4Ge0.6 films, the crystallization of GeO2 occurred in the oxide layer. Ge lattice fringes and twinning were also observed in the oxide layer.

Introduction

Poly-Si1−xGex has been suggested to be a favorable alternative to the currently used poly-Si gate electrode for CMOS technology. The use of poly-Si1−xGex as a gate material is expected to have a lower gate sheet resistance, higher current drive and less poly gate depletion effect compared with poly-Si gated devices. In order to use poly-Si1−xGex as a gate electrode, it is essential to understand the oxidation behavior of this material because a high quality thermal oxide on a poly-Si1−xGex layer can be used as an electrical insulator and a masking dopant barrier during implantation and diffusion. Hence, many studies have examined the oxidation behavior of SiGe alloys [1], [2], [3], [4]. Various analysis techniques e.g. X-ray photoelectron spectroscopy, auger electron spectroscopy, Rutherford backscattering spectroscopy, transmission electron microscopy etc., have been used to understand the oxidation behavior. Of these, transmission electron microscopy that is equipped with analytical attachments offers the most complete tool for characterizing SiGe alloys. However, in the contrast to the amount of research on the oxidation mechanism on the SiGe alloy, there has been no complete evaluation of this type of oxidized SiGe alloy under an irradiation environment.

This paper reports the effects of electron beam irradiation in a transmission electron microscope on oxidized poly-Si1−xGex alloys containing 40 and 60% Ge. The distribution and chemical bonding of Si, Ge, and O elements were analyzed by X-ray photoelectron spectroscopy (XPS) before irradiation. High-resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray spectrometry (EDS) and electron energy loss spectroscopy (EELS) were used to analyze the microstructure and redistribution of the elements after irradiation.

Section snippets

Experimental

Two sets of 1000 Å-thick poly-Si1−xGex films with a different Ge content (40 and 60%) were deposited by ultra-high-vacuum chemical vapor deposition (UHV-CVD) system (EUREKA 2000, Ju-sung Co. Ltd) on 8-inch wafers on which a 1000 Å thick SiO2 layer had been thermally grown. After depositing the poly-Si1−xGex films, oxidation was carried out in dry ambient at 800 °C using a conventional tube furnace.

XPS with an Al Kα source was used to determine the electronic state of Ge, Si, and O before

Irradiation effects on oxidized poly-Si0.6Ge0.4 films

In order to analyze the distribution and chemical binding state of Si, Ge, and O within the oxidized poly-Si0.6Ge0.4 films before irradiation, the XPS spectra in the energy regions around the Si 2p, Ge 2p core level were recorded. Fig. 1 shows the XPS spectra of the poly-Si0.6Ge0.4 films after dry oxidation at 800 °C for 120 min. Both Ge and Si peaks were clearly observed at the surface region. Near the surface, it was found that the chemical states of Si and Ge were Si+ 4 and Ge+ 4 instead of Si0

Conclusion

This study examined the morphological and compositional changes that occurred in oxidized poly-Si1−xGex films during the electron-beam irradiation in the TEM.

It was found that GeO2 agglomeration occurred in the oxidized poly-Si1−xGex films as a result of electron-beam irradiation. For the oxidized poly-Si0.6Ge0.4 films, the GeO2 phases agglomerated after being exposed to electron-beam irradiation. Therefore, during electron-beam irradiation, the oxide layer, which was originally a mixture of

Acknowledgements

This work was supported by “System IC 2010” project of Korea Ministry of Science and Technology and Ministry of Commerce, Industry and Energy, and Center for Nanotubes and Nanostructured Composites at Sungkyunkwan University, and in part by Brain Korea 21 program.

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