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Implantation of Si+ ions into thermal oxides grown on silicon has been used to synthesise a two phase structure consisting of Si nanocrystals in a SiO2 matrix. Various processing conditions have been used in order to modify the size and population distributions of the Si inclusions. Photoluminescence spectra have been recorded from samples annealed in nitrogen, forming gas and oxygen. Both red and blue shifts of the luminescence peaks have been observed. It is concluded that the photoluminescence is a consequence of the effects of quantum confinement but is also dependent on the presence of irradiation-induced defects or Si/SiO2 interface states.
The oxidation of Si0.5 Ge0.5 alloy has been investigated over the temperature range 800 to 1000°C . The composition of the oxide layers has been determined by 1.5 MeV Rutherford backscattering spectroscopy (RBS), infrared transmission spectroscopy (IR) and X-ray photoelectron spectroscopy (XPS). During the initial stage of oxidation, as the temperature ramps up in an oxidising ambient both Si and Ge are oxidized to form a mixed oxide in the region near the surface. Upon further oxidation, at temperatures higher than 900°C and times longer than 5 minutes, the Ge atoms are ejected by the growing oxide layer, which has the composition of Si02, and accumulate in the underlying alloy, which becomes rich in Ge.The surface oxide layer remains unchanged. The proportion of Ge02 in the near surface region, determined from IR spectra, decreases when the temperatures increases from 800°C to 1000°C. It is concluded that at 800°C Ge atoms are insufficiently mobile to be ejected from the growing oxide and both matrix species ( Si and Ge ) have equal probabilities of oxidation leading to the formation an oxide of composition Si0.5Ge0.5O2 . Supporting experiments confirm that Ge02 in the surface layer is formed during warm up of the samples oxidized at 900 and 1000°C.
RBS, SIMS, and IR measurements have been made on a SIMOX wafer, implanted with a second, low-temperature oxygen implant. These measurements indicate changes in the oxygen/silicon ratio in the buried oxide layer and differences in the annealing behaviour of the original layer and the double implant layer.
(100) silicon waferSgWere-implanted with 200keV N ions to doses of 0.95 and 1.1x1018 cm-2 at a temperature of 520°C, and then annealed at 1405°C for 30 minutes. We report here observations of the resulting microstructures. A buried ɑ-Si3N4. layer and a good quality silicon overlayer were found. Evidence of cavities in the Si3N4. layer was found in the higher dose sample. Our results suggest that the cavities are associated with the delamination which sometimes occurs during annealing.
SIMOX substrate material from two sources, both as-implanted and annealed, have been analysed by Secondary Ion Mass Spectrometry (SIMS) to determine the nitrogen concentration in the silicon overlayer. A variety of different analytical conditions were used on two different SIMS instruments to reduce the possibility of artefacts arising from the difficulties of analysing nitrogen in these materials. The nitrogen contaminant level was found to be consistently below 5 x 1017 nitrogen atoms cm-3, for all the material analysed.
The synthesis of buried layers of SiO2 and Si3N4, by ion implantation is reviewed. This process, which may be used to form device worthy silicon-on-insulator (SOI) structures, involves (i) implantation of O+ or N+ ions and (ii) high temperature processing to achieve defect annealing and chemical segregation of the implanted species.
SOI structures have been formed in (100) silicon by implanting 400 keV molecular oxygen to a dose of l.8×l018 O atoms cm−2. These samples were annealed at 1150°C for 2 hours with a SILOX cap. Oxygen depth profiles have been determined by SIMS and wafers implanted at about 500°C have been characterized by studying the regrowth kinetics, As drive in and oxidation rate in the top silicon overlay.
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