Impact of Heavy Boron Doping and Nickel Germanosilicide Contacts on Biaxial Compressive Strain in Pseudomorphic Silicon-
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0913-D02-10
Impact of Heavy Boron Doping and Nickel Germanosilicide Contacts on Biaxial Compressive Strain in Pseudomorphic Silicon-Germanium Alloys on Silicon Saurabh Chopra1, Mehmet C Ozturk1, Veena Misra1, Kris McGuire2, and Laurie McNeil2 1 Electrical and Computer Engineering, North Carolina State University, Raleigh, NC, 27695 2 Physics and Astronomy, UNC, Chapel Hill, NC, 27599
ABSTRACT In recent years, the semiconductor industry has increasingly relied on strain as a performance enhancer for both n and p-MOSFETs. For p-MOSFETs, selectively grown Si1-xGex alloys in recessed source/ drain regions are used to induce uniaxial compressive strain in the channel. In order to induce compressive strain effectively using this technology, a number of parameters including recess depth, Si1-xGex thickness (junction thickness), sidewall thickness, dopant density, dislocation density, and contact materials have to be optimized. In this work, we have studied the effects of heavy boron doping and self-aligned germanosilicide formation on local strain. Raman spectroscopy has been used to study the impact of heavy boron doping on compressive stress in Si1-xGex films. Strain energy calculations have been performed based on Vegard’s law for ternary alloys and the effect of boron on strain in Si1-x-yGexBy alloys modeled quantitatively. It will be shown that, owing to the smaller size of a boron atom, one substitutional boron atom compensates the strain due to 6.9 germanium atoms in the Si1-x-yGexBy film grown pseudomorphically on silicon. The critical thickness of Si1-x-yGexBy has been calculated for the first time based on kinetically limited critical thickness calculations for metastable Si1-xGex films. It will be shown that the critical thickness of the alloy increases as the boron content in the alloy is increased, making boron concentration an additional parameter for optimizing strain in the MOSFET. Based on these conclusions, boron concentration can be used to preserve the strain for thicker Si1-x-yGexBy films (compared to Si1-xGex films) while keeping the dislocation density low. Furthermore, we show that NiSiGe contacts can have a profound impact on the SiGe strain. Our results indicate that NiSiGe introduces additional stress in the underlying Si1-x-yGexBy, which further affects the strain induced in the channel. INTRODUCTION In applications where Si1-xGex is heavily doped with boron, smaller boron atoms can partially compensate the strain in the alloy. This effect is similar to that of carbon in Si1-x-yGexCy alloys. In this work, we have investigated the impact of boron on biaxial compressive strain in Si1-xGex alloys pseudomorphically grown on Si. The stress in the epitaxial layers was characterized by Raman spectroscopy and theoretical calculations. Using boron strain compensation, the Ge content of the alloy can be substantially increased without increasing the stored strain energy. This phenomenon can be used to increase the critical thickness for a given Ge concentration, which can have many advantages. Critical
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