In-situ X-ray diffraction analysis of SiGe liquid phase growth on Si using Al–Ge paste

Abstract

We performed in-situ two-dimensional X-ray diffraction measurements during a silicon-germanium (SiGe) layer formation process to analyze the liquid-phase epitaxial growth of a SiGe layer on silicon (Si) substrate by a simple method of aluminum-germanium (Al–Ge) paste screen-printing and annealing. The aluminum (Al) and germanium (Ge) from the Al–Ge paste were found to be in the liquid phase starting around 540 °C for the Al–Ge paste containing Al and Ge powders, while it starts around 430 °C for the one containing Al–Ge alloy powder. During the cooling process from the peak temperature of 900 °C down to 430 °C, a SiGe layer was epitaxially grown in the same orientation as the Si substrate. Around 430 °C, the remaining material in the liquid phase formed during the temperature increase solidified and the reaction was terminated. The XRD results suggest that most of the Al in the liquid phase exists as liquid phase from the peak temperature down to 430 °C. The Al liquid phase mediates the melting of Si and Ge, and the Si substrate functions both as a Si source, and as a seed crystal for the growth of the SiGe layer. Both samples show that the Ge concentration is sharply increased in the SiGe layer to around 13 at% at the interface and retains a uniform concentration distribution up to the Al paste matrix/SiGe interface. The change in crystallinity during the liquid phase growth indicates that the properties of the SiGe layer formed by this method can be controlled by adjusting the composition of the Al–Ge paste and the annealing temperature profile.