Comparison of P In Situ Spike Doped with as Implanted Poly Silicon Emitters Concerning Si/SiGe/Si HBT Application

Variants of P in situ spike doped poly-Si emitters are compared with an As implanted poly-Si emitter for use in HBTs. The main goal is the optimization of the thermal process after emitter doping. The base B diffusion is shown to be stronger influenced by the emitter dopant outdiffusion for P than for As. This effect is investigated by means of an improved B SIMS profiling, and by CV measurements at the junctions of large HBTs. The measured ac parameters of HBTs grown by MBE, RTCVD or APCVD differ in dependence on the emitter variant, first of all by the different emitter dopant outdiffusion influencing the low doped emitter (LDE) region. To quantify the outdiffusion behaviour, a n⁺p diode CV profiling of a B marker implant is used. The stronger outdiffusion of the furnace annealed P emitter compared to the RTP annealed and the As emitter, respectively, also increases the recombination controlled HBT base currents at low VBE due to a shift of the emitter-base (EB) space-charge region (SCR) deeper into the SiGe layer. A limit for reducing the annealing budget of the P in situ spike doped emitters (down to 800°C, 30s) is given both by increasing poly-Si series resistances and by contact resistances of the used Pt silicide but not by increased hole recombination. Considering all results, the P in situ doped poly-Si emitter with 2 doping spikes annealed by a short 850°C step should be a promising variant for HBT technologies.