The Role of Substrate Temperature in the Quality of Buried Oxide Layers

From the early work on high dose oxygen implantation for buried Si02 formation, it is apparent that the temperature (T) of the Si substrate during the implant has a strong influence on the quality of both the Si02 layer and the overlying Si. For substrate T's equivalent to 300 degrees C, amorphous Si is created during the implant and results in the formation of twins or polycrystalline Si is created during the subsequent high T (>1300degreesC) anneal. At higher substrate T's (>500degreesC), dynamic annealing eliminates the amorphous Si, but the implanted oxygen appears to segregate during the implant to form islands of Si02. As these islands start to coalesce during the high T anneal, they trap crystalline Si which cannot escape by diffusion. We have seen this effect clearly in substoichiometric implants, and believe it is also operative during stoichiometric implants.