Annealing induced interdiffusion and crystallization in sputtered amorphous Si/Ge multilayers
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Annealing induced interdiffusion and crystallization in sputtered amorphous SiyGe multilayers Zs. Czig´anya) and G. Radn´oczi Research Institute for Technical Physics of the Hungarian Academy of Sciences, H-1325, Budapest, P.O. Box 76, Hungary
K. J¨arrendahl and J-E. Sundgren Department of Physics, Link¨oping University, S-581 83, Link¨oping, Sweden (Received 13 September 1995; accepted 14 April 1997)
The intermixing and crystallization of amorphous SiyGe multilayers (with individual layer thickness between 1.5 and 20 nm) and SiGe alloys produced by dc magnetron sputtering have been studied by cross-sectional transmission electron microscopy and x-ray diffraction. Measurement of the crystallization temperature as a function of the Si content showed that multilayers and alloys with equal composition crystallized at the same temperature. This implies that intermixing precedes crystallization in the multilayers. Close to the crystallization temperature, formation of Kirkendall voids was observed in the short-period SiyGe multilayers. These voids were found at positions corresponding to the original Si layers, indicating that Si diffuses faster in amorphous Ge than Ge in amorphous Si. The Ge layers in short-period SiyGe multilayers retained their amorphous state to much higher temperatures than thick amorphous Ge layers. This is shown to be due to inhibition of nucleation by the presence of the layer interfaces. A lower estimate for the Si diffusion constant in crystalline Ge is also determined.
I. INTRODUCTION
The structure and properties of amorphous multilayers are being investigated due to applications in semiconductor and photovoltaic devices1 and due to a fundamental interest in low-temperature growth mechanisms. Out of many possible material systems, SiyGe and SiySiC are among those which have received the largest attention. For films grown using vapor phase techniques a large number of process parameters will, of course, affect the resulting structure of the multilayers. The structure of amorphous Si and Ge (a–SiyGe) multilayers was studied by several different techniques such as in situ ellipsometry,2,3 x-ray diffraction,4 cross-sectional transmission electron microscopy (XTEM),5,6 and a combination of these techniques.7,8 Since sharp interfaces and dense films are desired in most applications, it is necessary to understand the relationship between process parameters and structure. For example, in the case of films grown by plasma assisted techniques (e.g., sputtering or plasma assisted chemical vapor deposition) the use of a negative bias favors growth of a dense layer with sharp interfaces.5–7 a)
Corresponding author: Tel: +36-1-1690315, Fax: +36-1-1693541, E-mail: [email protected]. J. Mater. Res., Vol. 12, No. 9, Sep 1997
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For most applications it is necessary to study the thermal stability of the films, i.e., the intermixing and crystallization properties. Several studies of thermal stability hav
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