PN-JUNCTIONS IN SILICON WITH BLOCKING CAPABILITIES BEYOND 2.5-KV PRODUCED BY RAPID THERMAL-PROCESSING

In order to reduce the long diffusion times used in the production of power-semiconductor devices, two different methods of rapid thermal pr ocessing for the doping of Si with Al have been developed (Al-diffusio n in a halogen lamp RTP-system and Al-doping via formation of A-Si eut ectic and epitaxial regrowth in a resistive graphite-heater RTP-reacto r). Dopant profiles were characterized by SIMS- and SRP-analysis. In t he case of Al-alloyed pn-junctions the quality of the recrystallized s urface, as well as the shape and flatness of the junction, were invest igated. Finally the minority-carrier lifetime of the bulk material aft er the diffusion process and the reverse blocking characteristics of t he resulting junctions were determined. It is shown that rapid thermal processing is well suited to produce pn-junctions with blocking volta ges beyond 2.5 kV. The dopant profiles of the diffused samples exhibit no indications for Al- or Al2O3-precipitates and junction depths are found to be between 1.4 and 3.2 mu m. Charge-carrier lifetimes up to 2 50 mu s after Al-predeposition have been obtained. The eutectic-doping process provides abrupt pn-junctions with very high Al-concentrations (> 10(25) m(-3)) and comparatively large junction depths (7.5 mu m) a t a maximum process temperature of 1320 K for only 10 s. Under suitabl e conditions it is possible to obtain a smooth recrystallized surface (roughness R(a) = 15 nm) and a uniform pn-junction without junction sp iking. Copyright (C) 1996 Elsevier Science Ltd.