Impact of Buffered Layer Growth Conditions on Grown-In Vacancy Concentrations in Molecular Beam Epitaxy Silicon Germaniu
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Impact of Buffered Layer Growth Conditions on Grown-In Vacancy Concentrations in Molecular Beam Epitaxy Silicon Germanium Kareem M. Shoukri1, Yaser M. Haddara1, Andrew P. Knights2, Paul G. Coleman3, Mohammad M. Rahman4, and C.C. Tatsuyama4 Department of Electrical & Computer Engineering1 Department of Engineering Physics2 McMaster University, Hamilton, ON, Canada Department of Physics, University of Bath, Bath, BA2 7AY, United Kingdom3 Department of Electrical and Electronics Engineering, Toyama University, 3190-Gofuku, Toyama 930-8555, Japan4 ABSTRACT Silicon-Germanium (SiGe) has become increasingly attractive to semiconductor manufacturers over the last decade for use in high performance devices. In order to produce thin layers of device grade SiGe with low concentrations of point defects and well-controlled doping profiles, advanced growth and deposition techniques such as molecular beam epitaxy (MBE) are used. One of the key issues in modeling dopant diffusion during subsequent processing is the concentration of grown-in point defects. The incorporation of vacancy clusters and vacancy point defects in 200nm SiGe/Si layers grown by molecular beam epitaxy over different buffer layers has been observed using beam-based positron annihilation spectroscopy. Variables included the type of buffer layer, the growth temperature and growth rate for the buffer, and the growth temperature and growth rate for the top layer. Different growth conditions resulted in different relaxation amounts in the top layer, but in all samples the dislocation density was below 106 cm-2. Preliminary results indicate a correlation between the size, type and concentration of vacancy defects and the buffer layer growth temperature. At high buffer layer growth temperature of 500ºC the vacancy point defect concentration is below the PAS detectable limit of approximately 1015 cm-3. As the buffer layer growth is decreased to a minimum value of 300ºC, large vacancy clusters are observed in the buffered layer and vacancy point defects are observed in the SiGe film. These results are relevant to the role played by point defects grown-in at temperatures below ~350ºC in modeling dopant diffusion during processing. INTRODUCTION In the quest to manufacture faster semiconductor devices, researchers have sought to combine the properties of compound semiconductors with the processing maturity of silicon technology. For this reason silicon-germanium (SiGe) has become increasingly attractive to semiconductor manufacturers over the last decade for use in high performance devices such as heterojunction bipolar transistors and complementary metal oxide semiconductor technologies. Advances in epitaxial growth techniques, such as molecular beam epitaxy (MBE) have allowed SiGe alloy layers to be grown on Si substrates. However, high quality SiGe alloy layers are difficult to grow due to the 4.2% lattice mismatch between Si and Ge. Epitaxial SiGe layers grown above a critical
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thickness [1] leads to strain relaxation through the introduc
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