Method of controlling solid phase diffusion of boron dopants to form ultra-shallow doping regions

A method is provided for forming an ultra-shallow boron doping region in a semiconductor device. The method includes depositing a diffusion filter layer on a substrate, the diffusion filter containing a boron nitride layer, a boron oxynitride layer, a silicon nitride layer, or a silicon oxynitride layer, and depositing a boron dopant layer on the diffusion filter layer, the boron dopant layer containing boron oxide, boron oxynitride, or a combination thereof, with the proviso that the diffusion filter layer and the boron dopant layer do not contain the same material. The method further includes heat-treating the substrate to form the ultra-shallow boron dopant region in the substrate by controlled diffusion of boron from the boron dopant layer through the diffusion filter layer and into the substrate.