Self-Aligned Bipolar Epitaxial Base n-p-n Transistors by Selective Epitaxy Emitter Window (SEEW) Technology

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A new bipolar technology is presented, which allows for very thin base formation by ultra-high vacuum/chemical vapor deposition (UHV/CVD) epitaxy and very narrow emitter width using selective epitaxial overgrowth. The key step in this selective epitaxy emitter window (SEEW) process is an in situ doped epitaxial lateral overgrowth over a thin and narrow nitride/oxide pad which forms an emitter window in the sublithographic range and provides an extrinsic base contact at the same time. Advantages over conventional double-poly self-aligned technology are 1) the very thin epitaxial base, 2) the formation of the extrinsic base after intrinsic epitaxial base deposition resulting in a guaranteed link-up, and 3) an emitter width in the deep submicrometer range by optical lithography, n-p-n bipolar transistors with 60-nm base width for 75 k intrinsic base resistance and emitter widths down to 0.2 um with 0.07-/um tolerance (a) have been fabricated using SEEW technology. Nearly ideal I-V characteristics have been achieved for these very narrow emitters. High-yield figures are demonstrated. The SEEW structure can provide very high current density at acceptable power level as it is desired to take full advantage of high-/ Si or SiGe epitaxial base technology. © 1991 IEEE