Heterojunction Bipolar Transistor Fabrication Using Resist Mask Edge Effects

A heterojunction bipolar transistor (HBT) formed on a semiconductor substrate having a first conductivity type, the HBT comprising:

• a collector formed by dopants of a second conductivity type that are diffused into the semiconductor substrate, wherein the collector includes:
• an elongated buried layer region having a first end portion separated from a surface of the semiconductor substrate by an intervening collector region, and a second end portion separated from the surface by an intervening collector contact region,
• a selectively implanted collector (SIC) region disposed in the collector region and extending from the surface of the semiconductor substrate to the first end portion of the buried layer region, and
• a collector sinker disposed in the collector contact region and extending from the surface of the semiconductor substrate to the second end portion of the buried layer region;
• a base structure having the first conductivity type disposed on the surface of the semiconductor substrate over the SIC region;
• and
• an emitter structure having the second conductivity type disposed on the base structure such that a lower portion of the emitter structure is positioned over the SIC region,
• wherein an average doping concentration of the SIC region is lower than an average doping concentration of the collector sinker, and
• wherein the SIC region comprises one or more primary increased-doping regions disposed at a first depth below the surface of the semiconductor substrate, and
• wherein the SIC region comprises a plurality of secondary increased-doping regions disposed at a first depth below the surface of the semiconductor substrate disposed adjacent to the surface of the semiconductor substrate, said secondary increased-doping regions having associated doping concentrations that are higher than said average doping concentration of said SIC region.

A heterojunction bipolar transistor (HBT) formed on a semiconductor substrate having a first conductivity type, the HBT comprising:

• a collector formed by dopants of a second conductivity type that are diffused into the semiconductor substrate, wherein the collector includes:
• an elongated buried layer region having a first end portion separated from a surface of the semiconductor substrate by an intervening collector region, and a second end portion separated from the surface by an intervening collector contact region,
• a selectively implanted collector (SIC) region disposed in the collector region and extending from the surface of the semiconductor substrate to the first end portion of the buried layer region, and
• a collector sinker disposed in the collector contact region and extending from the surface of the semiconductor substrate to the second end portion of the buried layer region;
• a base structure having the first conductivity type disposed on the surface of the semiconductor substrate over the SIC region;
• and
• an emitter structure having the second conductivity type disposed on the base structure such that a lower portion of the emitter structure is positioned over the SIC region,
• wherein the SIC region is formed by an SIC implant process including:
• forming an SIC implant mask including depositing a photoresist layer on the upper surface of the semiconductor substrate, and patterning said photoresist layer such that the SIC implant mask defines a plurality of mask openings that expose corresponding upper surface sections of said upper surface that are located over the collector region, and
• directing dopant particles having the first conductive type toward the SIC implant mask such that first portions said dopant particles pass directly through said plurality of mask openings and form one or more primary increased-doping regions in the collector region, and such that second portions said dopant particles are subject to mask edge effects produced by side edges of the plurality of mask openings and form a plurality of secondary increased-doping regions in the collector region between the one or more primary increased-doping regions and the corresponding surface sections of the semiconductor substrate, whereby said secondary increased-doping regions enhance said base-collector junction.