Fluorine complexes in Si-SiGe-Si structures

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Description/Abstract

Fluorine-vacancy complexes have been directly observed in the Si0.94Ge0.06 layer in a Si-SiGe-Si structure, using variable-energy positron annihilation spectroscopy. These complexes are linked to the significant reduction of boron diffusion in the SiGe layer via interstitial trapping. Vacancies were introduced into the samples by ion implantation with 185 keV F+ at doses in the range 9x1014 to 1x1016 cm−2; the samples were subsequently subjected to rapid annealing in nitrogen ambient at 950 °C for 30 s. The VEPAS results, in combination with F profiles obtained by secondary ion mass spectrometry, are consistent with F4nVn complexes being associated with the SiGe layer and that they preferentially accumulate at the Si/SiGe interfaces. Their concentration is critically dependent on annealing temperature, decreasing significantly after annealing at 1000 °C.