Method of manufacturing heterojunction bipolar transistor and heterojunction bipolar transistor

A method of forming a heterojunction bipolar transistor, comprising:

• depositing a first stack including an polysilicon layer and a sacrificial layer on a mono-crystalline silicon substrate surface;
• patterning the first stack to form a trench extending to the substrate, the trench having a sidewall;
• depositing a silicon layer over a resultant structure;
• depositing a silicon-germanium-carbon layer over the resultant structure;
• selectively removing the silicon-germanium-carbon layer from the sidewall of the trench;
• depositing a boron-doped silicon-germanium-carbon layer over the resultant structure;
• depositing a further silicon-germanium-carbon layer over the resultant structure;
• depositing a further boron-doped silicon layer over the resultant structure;
• forming a dielectric spacer on the sidewall of the trench;
• filling the trench with an emitter material;
• exposing polysilicon regions outside the side wall of the trench by selectively removing the sacrificial layer of the first stack;
• implanting boron impurities into the exposed polysilicon regions to define base implants;
• and
• exposing the resultant structure to a thermal budget for annealing the boron impurities.