THERMODYNAMIC BEHAVIOR OF GEO2 FORMED BY OXYGEN IMPLANTATION INTO RELAXED SI0.5GE0.5 ALLOY

The thermal stability of GeO2 formed by oxygen implantation into Si0.5 Ge0.5 alloy has been investigated and quantified. The sample used in t his experiment consisted of a 900 nm relaxed layer of Si0.5Ge0.5 alloy capped with 78 nm of silicon which was grown on a (100) Si n-type waf er. This was then implanted with a dose of 1.8 X 10(18) O+/cm(2) at 20 0 keV and specimens from the implanted region were annealed for 1 h at various temperatures. The composition and thickness of the oxide laye r, which consisted of SiO2+ GeO2 and redistribution of elemental silic on, germanium and oxygen were determined by Rutherford backscattering spectroscopy. The chemical bonding of silicon and germanium to oxygen was determined using X-ray photoelectron spectroscopy. It is found tha t the germanium was rejected from the oxide layer and segregated at th e interface between SiGe/oxide and oxide/SiGe. The driving force for t he mass transport can be attributed to the higher chemical potential o f germanium in the oxide layer, which is a consequence of the differen ce in the free energies of formation of SiO2 and GeO2.