New technology for bipolar emitters in the deep sub-micron range

A novel technique for the formation of sub-quarter-micron emitters using epitaxial lateral overgrowth over a thin nitride pattern followed by thermal oxidation is described. Although the nitride pattern is defined by optical lithography, emitter size and tolerance are comparable to those in electron-beam lithography. Unlike the case of conventional double-poly structures, the emitter size tolerance is not affected by dry etching through the extrinsic base polysilicon; thus, only the thin nitride film has to be etched to open the emitter window. Bipolar transistors with a base width of 90 nm have been fabricated using this selective epitaxy emitter window (SEEW) technique.