THE FORMATION OF COMPOUND LAYERS IN SILICON BY ION-BEAM SYNTHESIS

The technique of ion beam synthesis (IBS) using high doses of energetic ions has been successfully implemented to produce a variety of compounds, the physical properties of which are dependent on the implanted species and range from insulators, e.g. SiO2, through semiconductors, e.g. SiC, to conductors, e.g. CoSi2. In this paper we study the evolution of these compounds and compare and contrast their methods of formation. To demonstrate the versatility of the technique we look at three examples of IBS layers: (1) To date most of the interest in IBS has concentrated on the production of buried oxide layers for silicon-on-insulator (SOI) device applications. Recently it has been shown that by using a series of sequential implants and high-temperature anneals the defect density in the silicon overlayer can be dramatically reduced. To study how this process occurs, we followed the redistribution of the implanted species during implantation and annealing using both 16O+ and 18O+. (2) Buried CoSi2 layers can be fabricated in (100) single-crystal silicon by implanting high doses of energetic cobalt ions at elevated temperatures. For the higher doses (≥ 4 × 1017 O+/cm2 at 350 keV), a continuous coherent layer of CoSi2 grows epitaxially during implantation. For lower doses, precipitates of both A- and B-type CoSi2 are observed. After annealing at 1000° C for 30 min, single-crystal aligned layers are produced for the higher doses, while for lower doses discrete octahedral A-type precipitates are formed. (3) The microstructures of synthesized SiC layers are more complex than analogous synthesized oxide or silicide layers. Unlike buried oxide layers, the carbon concentration at the peak of the implanted distribution does not saturate at a value equivalent to that in the stoichiometric compound, but continues to rise, reflecting the lower diffusivity of the C in the synthesized compound layer. To achieve chemical segregation of the implanted carbon, very-high-temperature (≥ 1300°C), long-time (typically 20 h) anneals are required. At the interface with the silicon substrate the synthesized layer grows with a degree of epitaxy. This is also found to occur during implantation if the temperature is ≥ 650° C. © 1990.