Formation of diffused layers of controllable profile of dopants - using doped glass diffusion sources and selecting of gas-ambient to influence diffusion rate of impurities through glass

摘要

A diffusion process is used to construct a semiconductor device by first depositing a silicon-oxide layer containing dopant as a diffusion source on the semiconductor surface. The diffusion process featuers a step to oxidise dopants in the oxide layer and/or a step to reduce dopants in the oxide layer by altering the diffusion ambient. Reduction is pref. a heat-treatment which uses an ambient containing H2, pref. 2-60%, especially 5-20%. The process claimed consists of a reduction step to reduce the diffusion velocity of part of the dopant contained in the glass, a first diffusion step to diffuse dopant into the substrate, an oxidation step to increase the diffusion rate of part of the dopant and then a second diffusion step. The glass-layer formed may contain several types of dopant or a single dopant. Therefore the process can also reduce and increase the diffusion rate of one of the dopants contained. Pref. combinations of dopants are As and B as well as Sb and P. In both cases it is the first dopant element which is affected by the reduction/oxidation treatments. The first diffusion step may also be combined with the reduction especially by heating up the substrates in a reducing ambient. Also claimed is the depsn. of successive glass-layers with different compsns., of which the first layer contains at least the first type of dopant (As or Sb) and the second layer contains at least the second type of dopant (B RESP..P).