Dopant profile control in heterojunction bipolar transistor (hbt)

A method of semiconductor processing, the method comprising:

• epitaxially growing a first sub-layer of a base region on or over a collector region, the collector region being disposed on or over a semiconductor substrate;
• epitaxially growing a second sub-layer of the base region on or over the first sub-layer, epitaxially growing the second sub-layer comprising doping the second sub-layer with a first dopant;
• and
• epitaxially growing a third sub-layer of the base region on or over the second sub-layer, wherein each sub-layer of the first sub-layer, the second sub-layer, and the third sub-layer is epitaxially grown comprising a semiconductor species, a concentration of the semiconductor species in the first sub-layer being greater than a concentration of the semiconductor species in the second sub-layer, a concentration of the semiconductor species in the third sub-layer being greater than the concentration of the semiconductor species in the second sub-layer.

A method of semiconductor processing, the method comprising:

• forming a collector region on or over a semiconductor substrate, a material of the collector region being silicon;
• forming a base region on or over the collector region, forming the base region comprising:
• forming a first base sub-layer on or over the collector region, a material of the first base sub-layer being silicon germanium;
• forming a second base sub-layer on or over the first base sub-layer, a material of the second base sub-layer being silicon germanium, a concentration of germanium in the second base sub-layer being greater than a concentration of germanium in the first base sub-layer;
• forming a third base sub-layer on or over the second base sub-layer, a material of the third base sub-layer being silicon germanium, a concentration of germanium in the third base sub-layer being less than the concentration of germanium in the second base sub-layer, epitaxially growing the third base sub-layer includes doping the third base sub-layer with phosphorus;
• forming a fourth base sub-layer on or over the third base sub-layer, a material of the fourth base sub-layer being silicon germanium, a concentration of germanium in the fourth base sub-layer being greater than the concentration of germanium in the third base sub-layer;
• forming a fifth base sub-layer on or over the fourth base sub-layer, a material of the fifth base sub-layer being silicon germanium, a concentration of germanium in the fifth base sub-layer being less than the concentration of germanium in the fourth base sub-layer;
• and
• forming a cap sub-layer on or over the fifth base sub-layer, a material of the cap sub-layer being silicon;
• and
• forming an emitter region on or over the base region.