UBC Theses and Dissertations
A systematic study of silicon germanium interdiffusion for next generation semiconductor devices Dong, Yuanwei
SiGe heterostructures with higher Ge fractions and larger Ge modulations, and thus higher compressive stress, are key structures for next-generation electronic and optoelectronic devices. Si-Ge interdiffusion during high temperature growth or fabrication steps changes the distribution of Ge fraction and stress, and increases atomic intermixing, which degrades device performance. It is of technological importance to study Si-Ge interdiffusion behaviours and build accurate Si-Ge interdiffusivity models. In this work, three aspects of Si-Ge interdiffusion behaviours were investigated both by experiments and by theoretical analysis. 1) Based on the correlation between self-diffusivity, intrinsic diffusivity and interdiffusivity in binary alloy systems, a unified interdiffusivity model was built over the full Ge fraction range. It provides a zero-strain, no-dopant-effect, and low-dislocation-density reference for studies of more impacting factors. This model was then validated with literature data and our experimental data using different annealing techniques. Next, with the well-established reference, the impact of biaxial compressive strain on Si-Ge interdiffusion was further investigated under two specific strain scenarios: with full coherent strain and with partial strain. 2) Complete theoretical analysis was presented to address the compressive strain’s role in Si-Ge interdiffusion. The role of compressive strain was modeled in two aspects: a) strain energy contributes to the interdiffusion driving force; b) the strain derivative q' of interdiffusivity, reflecting the strain-induced changes of both prefactor and activation energy. For the temperature range (720 °C to 880 °C) and Ge fraction range (0.36 to 0.75), a temperature dependence of the strain derivative q', q'=-0.081T+110 eV/unit strain, was reported in Si-Ge interdiffusion. 3) For the case with partial strain, the apparent interdiffusivity model developed for the case with full coherent strain in 2) was modified to reflect strain change, and it was then validated with experimental data. In summary, a set of interdiffusivity models were established based on experimental data and theoretical analysis for three strain scenarios. These models can be employed to predict the thermal stability of SiGe heterostructures, and optimize the design of SiGe structures and of thermal budgets for next-generation SiGe based devices.
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