Buried layers of silicon oxy-nitride fabricated using ion beam synthesis

Ion beam synthesis (IBS) has been used to fabricate buried compound layers in silicon. These layers were produced by implanting combinations of O+ and N+ ions or NO+ ions at 200 keV/atom into 100 single crystal silicon maintainted at a temperature of between 5100C and 5800C. The specimens were then annealed at 12000C for two hours. It is found that the types of structure formed are highly dependent on the sequence in which the ions are implanted. When oxygen is implanted prior to nitrogen, the nitrogen segregates to the wings of the oxygen distribution where it forms an oxy-nitride. The presence of nitrogen, during the subsequent anneal is found to improve both the crystalline quality of the silicon overlayer and to reduce the impurity concentration therein. A similar improvement in the crystallinity of the silicon overlayer is also observed when oxygen and nitrogen are implanted together as NO+. Conversely if nitrogen is implanted prior to oxygen the redistribution of the impurities, during annealing, leads to a degradation in the structure, when compared to a specimen only implanted with oxygen. In this case the portion of the silicon overlayer adjacent to the buried layer, is highly defective with a high impurity concentration. Models based upon self diffusion and impurity interactions within the matrix are advanced to describe the evolution of the buried structures. (orig.)