A special two-dimensional intrinsic base doping profile is utilized to improve the output current-voltage characteristics of a vertical bipolar transistor whose intrinsic base includes a main intrinsic portion (64M). The special doping profile is achieved with a pair of more lightly doped base portions (66) that encroach substantially into the intrinsic base below the main intrinsic base portion (64M). The two deep encroaching base portions (66) extend sufficiently close to each other to set up a two-dimensional charge-sharing mechanism that typically raises the magnitude of the punch-through voltage. The transistor's current-voltage characteristics are thereby enhanced. Manufacture of the transistor entails introducing suitable dopants into a semiconductor body. In one fabrication process, a fast-diffusing dopant is employed in forming the deep encroaching base portions (66) without significantly affecting earlier-created transistor regions.
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