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Although silicon-on-insulator (SOI) materials made by standard energy (150–200 keV) SIMOX processes have shown great promise for meeting the needs of radiation hard microelectronics, there are still problems relating to the radiation hardness and economic viability of standard SIMOX. A low energy SIMOX (LES) process reduces cost and improves radiation hardness and increased throughput of any implanter because much smaller doses are required. In addition, the process is uniquely able to produce high quality thin SIMOX structures that are of particular interest for fully depleted device structures. In this paper, we address the formation of high quality ultrathin SIMOX structures by low energy implantation.

We have studied the formation of platinum silicide layers by ion implantation and annealing, and have determined the dependence of platinum silicide phase formation on ion implantation conditions and substrate orientation. The results indicate that in most cases, the ion implanted layer consists of PtSi phase. However, depending on the implantation and annealing conditions and substrate orientation, other phases, including Pt2Si, Pt3Si, and Pt12Si5, as well as Si and Pt microcrystals, also form.

Results are presented for the propagation loss of planar optical waveguides fabricated in SIMOX structures with Si overlayers whose thickness varies from 0.57 μm to 6.0 μm. The results demonstrate that thick Si overlayers are required to produce propagation losses below 1 dB/cm. In addition, the results of the coupling between two vertically integrated waveguides formed using two buried SiO2 layers are also reported.

We have studied Separation by IMplantation of OXygen (SIMOX) processes using very high dose rates (40–60 μA/cm2). For a dose of 4 × 1017 O+/cm2 at 160 keV, the structure formed by implantation at 50 μA/cm2 is very similar to that associated with lower dose rates. The same dose implanted at a dose rate of 60 μA/cm2, however, results in the formation of pits in the silicon surface as well as a somewhat different oxide structure. Implantation through a surface oxide layer appears to result in a structure similar to that associated with lower dose rate implantation. These and higher dose samples suggest that the threshold for pit formation is related to both dose rate and dose.

We have investigated improving the crystalline quality of epitaxial silicon grown on SIMOX by confining threading dislocations in the original Si top layer using a GeSi strained layer. Epitaxial Si/GeSi/Si structures were grown by CVD on SIMOX and Si substrates with a GeSi alloy layer about 1000 − 1500 angstroms thick with Ge concentrations of about 0−20%. A Ge concentration in the alloy layer of about 5.5% or higher appears to be necessary in order to bend any of the threading dislocations from the original SIMOX top layer. For a higher Ge concentration of about 16%, most of the threading dislocations appear to be bent and confined by the GeSi layer. In addition, the GeSi strained layers grown by CVD (at about 1000°C) appear to be high quality and no misfit dislocations were observed in the regions studied by XTEM and plane view TEM.

Substantial reduction of defect density in silicon-on-sapphire (SOS) material is required to broaden its range of applications to include CMOS and bipolar devices. In recent years, solid phase epitaxy and regrowth (SPEAR) and double solid phase epitaxy (DSPE) processes were applied to SOS to reduce the density of defects in the silicon. These methods result in improved carrier mobilities, but also in increased leakage current, even before irradiation. In a radiation environment, this material has a large increase in radiation induced back channel leakage current as compared to standard wafers. In other words, the radiation hardness quality of the SOS declines when the crystalline quality of the Si near the sapphire interface is improved.In this paper, we will demonstrate that Ge implantation, rather than Si implantation normally employed in DSPE and SPEAR processes, is an efficient and more effective way to reduce the density of defects near the surface silicon region without improving the Si/sapphire interface region. Ge implantation may be used to engineer defects in the Si/sapphire interface region to eliminate back channel leakage problems.

Because of potential “back channel” leakage problems in silicon-oninsulator (SOI) metal-oxide-semiconductor (MOS) devices, especially n-channel MOS devices which must operate in an ionizing radiation environment, it is desirable to produce Separation by IMplantation of OXygen (SIMOX) wafers which have a layer of poor quality silicon near the Si/buried SiO2 interface. At the same time, these wafers must have low defect, high quality silicon near the wafer surface for device fabrication.We have demonstrated that with Ge ion implantation and solid phase epitaxy regrowth, the surface region of the silicon top layer of the SIMOX wafer is improved and the region adjacent to the buried SiO2 is degraded. These results have been observed by RBS/channeling, XTEM, and plane view TEM.

This paper will address the formation of SIMOX structures with thick and multiple buried SiO2 layers by multiple oxygen implantation and growth of epitaxial Si by chemical vapor deposition (CVD). Our results indicate that SIMOX material can be produced with a buried layer of any thickness or with any number of distinct buried oxide layers and distinct silicon layers. Thick and double buried SiO2 layer material may be useful for high voltage isolation and electric field shielding.In addition, we have demonstrated optical waveguide action in SIMOX wafers. This suggests that in a double buried SiO2 layer system, three dimensional stacked integration of silicon waveguides is possible, including two level optical interconnects.

We have studied the effect of implantation temperature, dose step, and total dose on the buried Si02 layer formed with a multiple low dose oxygen implantation process. Furthermore, we have produced a continuous, high quality buried SiO2 layer about 1500 Å thick with a dose of only 7 × 1017 0+/cm2 at 160 keV. The thin SiO2 layer is important not only because of the possible economic advantages of reduced dose, but also because a thinner oxide layer is more radiation hard.

This work addresses the formation of Separation by IMplantation of OXygen (SIMOX) structures by multiple oxygen implantation into silicon and high temperature annealing. We observed no threading dislocation defects in the several plane view TEM and XTEM micro graphs of each of the samples implanted with a single dose of up to 8 × 1017 0+/cm2. We also demonstrated that with a multiple low-dose (3 to 4 × 1017 0+/cm2) oxygen implantation and high temperature annealing process, we are able to produce continuous and uniform buried SiO2 layers with a total dose of 1.1 × 1018 0+/cm2 (about 60% of the total dose for standard SIMOX). The density of defects is about 105/cm2. There are no silicon islands in the buried layer, no SiO2 precipitates in the silicon top layer, and the Si-SiO2 interfaces are sharp and smooth. SIMOX material with a high-quality Si top layer and a continuous buried layer has been produced with a total dose of 7 × 1017 0+/cm2 (40% of the total dose for standard SIMOX) and a two-step process. However, in this case there are a few Si islands present in the buried SiO2 layer.

We have prepared GexSi1-x/Si structures by implanting germanium into silicon surfaces and thermally annealing. Implant energies were 100 and 150 keV and the total ion doses were between 1 and 10 × 1015 ions/cm2. Ion channeling studies of these structures indicates that after annealing, the germanium atoms substitute into the silicon lattice and create a pseu-domorphic strained layer. In addition, channeling results suggest a residual band of dislocations at or beyond the ion range in the as-annealed samples.