Influence of dopant diffusion in sige HBTs on the transit frequency

The influence of boron oufdiJhsion fiom the base, caused by annealing, on the transit frequency is calculaled by means of process and device simulation. The outdiffiision is investigated for two transisitors with different base widths ( w ~ = 4 0 nni and wB=20 nnl) using RTA at several annealing temperatures and an annealing time of 5 seconds. Significant boron outdiflusion starts at annealing temperatures of T=115OoC and T=125OoC, depending on the inifial base width. Therefore the infuence of the outd@ion on the transit frequency up to these temperatures is negligible. For higher annealing temperatures the base widths increase dramatically and the transit frequencies drop down.