Sige heterojunction bipolar transistor with a shallow out-diffused p+ emitter region

Abstract

A pnp SiGe heterojunction bipolar transistor (HBT) reduces the rate that p-type dopant atoms in the p+ emitter of the transistor out diffuse into a lowly-doped region of the base of the transistor by epitaxially growing the emitter to include a single-crystal germanium region and an overlying single-crystal silicon region.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to a SiGe heterojunction bipolar transistor (HBT) and, more particularly, to a SiGe HBT with a shallow out-diffused p+ emitter region.[0003]2. Description of the Related Art[0004]A bipolar transistor is a well-known structure that has an emitter, a base connected to the emitter, and a collector connected to the base. The emitter has a first conductivity type, the base has a second conductivity type, and the collector has the first conductivity type. For example, an npn bipolar transistor has an n-type emitter, a p-type base, and an n-type collector, while a pnp bipolar transistor has a p-type emitter, an n-type base, and a p-type collector.[0005]When the emitter and base are formed from different semiconductor materials, such as silicon and germanium, respectively, the interface is known as a heterojunction. The heterojunction limits the number of holes that can be injected into the emitter...

AI Technical Summary

Benefits of technology

The present invention relates to a SiGe heterojunction bipolar transistor (HBT) with a shallow out-diffused p+ emitter region. The technical effect of this invention is to improve the performance of the HBT by increasing the dopant concentration of the base and reducing the base resistance, which in turn increases the maximum frequency of the transistor. The invention includes a SiGe epitaxial structure with a very low dopant concentration, except for regions of out diffusion, and shallow trench isolation structures that touch the epitaxial structure and silicon substrate to form electrically-isolated regions. The invention also includes a p conductivity type sinker region that extends from the top surface of the silicon epitaxial structure down through the epitaxial structure and silicon substrate to touch the p+ buried region, and an n conductivity type sinker region that extends from the top surface of the silicon epitaxial structure down through the epitaxial structure and silicon substrate to touch the n+ buried region.

Problems solved by technology

Limiting the number of injected holes allows the dopant concentration of the base to be increased which, in turn, reduces the base resistance and increases the maximum frequency of the transistor.

However, an oxide layer like oxide layer 212 cannot be used with epitaxially-grown single-crystal silicon emitters to reduce the depth of the p+ out-diffused emitter region because single-crystal silicon cannot be epitaxially grown on oxide.

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