Kouji Sueoka

First principles calculations of the formation energy and deep levels associated with the neutral and charged vacancy in germanium

Density functional theory with local density approximation including on-site Coulomb interaction has been used to calculate the formation energy of the neutral and charged vacancy in germanium as a function of the Fermi level. The calculations suggest that vacancies in germanium are multiple-level acceptors with a first level at 0.02eV and a second level at 0.26eV above the valence band maximum in agreement with published experimental data. The formation energies of the neutral and charged vacancies line up well with the experimental values estimated from quenching experiments.

Thermal stress induced void formation during 450 mm defect free silicon crystal growth and implications for wafer inspection

When pulling large diameter Si crystals from a melt close to the Voronkov criterion, small changes in pulling speed and thermal gradient can lead to the formation of voids leading to detrimental pits on the polished wafer surface. The creation of voids is mainly due to the lowering of the vacancy formation energy due to increased thermal compressive stress. The small size and low density of the formed voids when pulling crystals close to the Voronkov criterion conditions are a challenge for wafer surface inspection tools and possible solutions are discussed.