Self-aligned bipolar epitaxial base n-p-n transistors by selective epitaxy emitter window (SEEW) technology

A bipolar technology 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 is presented. 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 the very thin epitaxial base, the formation of the extrinsic base after intrinsic epitaxial base deposition resulting in a guaranteed link-up, and an emitter width in the deep submicrometer range by optical lithography. n-p-n bipolar transistors with 60-nm base width for 75 kΩ/□ intrinsic base resistance and emitter widths down to 0.2 μm with 0.07-μm tolerance (σ) 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