THE STUDY OF SI0.5GE0.5 ALLOY IMPLANTED BY HIGH-DOSE OXYGEN

The effects of high dose O+ implantation into a Si0.5 Ge0.5 alloy, studied by Rutherford backscattering, infrared spectrophotometry and X-ray photoelectron spectroscopy, are reported for the first time. The alloy layers were prepared by molecular beam epitaxy (MBE) when a thick (900 nm) film of Si0.5Ge0.5 alloy followed by a 75 nm top Si layer was grown on a n-type (100) Si (rho = 5-20 OMEGA-cm) substrate. This material was, subsequently, implanted with doses of 0.6 x 10(18) O+ cm-2, 1.2 x 10(18) O+ cm-2 and 1.8 x 10(18) O+ cm-2 at an energy of 200 keV with a substrate temperature of about 500-degrees-C. Selected samples have been annealed in flowing nitrogen at temperatures of 800-degrees-C or 1000-degrees-C for 1 h. The redistribution of the implanted oxygen and the composition of the resulting structure has been investigated before and after thermal treatment. The results show that Si-O and Ge-O compound formation depends strongly on the dose of oxygen and annealing temperature. Most of the implanted oxygen reacts with Si to form SiO2. The Ge-O bonding was only observed in the buried oxide layer where the concentration of oxygen atoms was saturated. In the high dose sample and at the highest annealing temperature the SiO(x) converted to stoichiometric SiO2 with this dielectric also containing some Ge and GeO(x) (x less-than-or-equal-to 2) trapped in the silicon dioxide layer. With increasing anneal temperature decomposition of Ge-O bonding was observed and, generally, Ge atoms were found to be rejected from the oxide and segregated in the alloy layers above and below the buried oxide. The different behaviours of the Si and Ge atoms can be described in terms of the thermodynamics of the systems.