Role of implant temperature in the formation of thin buried oxide layers

From the early work on high dose oxygen implantation for buried SiO//2 formation, it is apparent that the temperature of the Si substrate during the implant has a strong influence on the quality of both the SiO//2 layer and the overlying Si. This, in turn, can be related to the damage from the oxygen implant. For substrate temperatures greater than approx. 300 degree C, amorphous Si is created during the implant and leads to the formation of twins or polycrystalline Si during the subsequent-high temperature ( greater than 1300 degree C) anneal. At higher substrate temperatures ( greater than approx. 400 degree C), dynamic annealing eliminates the amorphous Si, but the implanted oxygen appears to segregate during implant leading to oxygen-rich amorphous regions imbedded in regions of crystalline material. As the amorphous regions start to coalesce and form SiO//2 during the high temperature anneal, they trap crystalline Si which cannot escape by diffusion. This process can be circumvented by using a randomizing Si implant to change the damage structure from the oxygen implant before annealing.