Optical and electrical properties of Si_(1-x-y)Ge_xC_y strained layers thermally oxidized

摘要

We have investigated how the concentration of Ge and C influences the thermal oxides of Si_(1-x-y)Ge_xC_y strained epitaxial layers grown on silicon substrates. We present a reliable method to measure oxide thicknesses on these epi-layers based on spectroscopic ellipsometry. We have studied the influence of Ge and C on the dielectric function of the layer by means of variable angle spectroscopic ellipsometry. We have modeled the dependence on the dielectric function of Ge and C by means of oscillators. We have found a shift of the peak centered at 3 eV towards lower energies in Si_(1-x)Ge_x as a function of larger thermal budgets, due to the strain relief of the layer. The presence of carbon partially inhibits this shift related to the thermal budget. We have also investigated the influence of Ge and C in the capacitance response of MOS devices. The thermal processing helps to stabilize the carbon in the layer as a substitutional impurity. Ge and C modify the ideal capacitance curves in the inversion and depletion regions due to interface states generation but not in the accumulation region.