BIPOLAR JUNCTION TRANSISTOR HAVING A HIGH GERMANIUM CONCENTRATION IN A SILICON-GERMANIUM LAYER AND A METHOD FOR FORMING THE BIPOLAR JUNCTION TRANSISTOR
A method for forming a germanium-enriched region in a heterojunction bipolar transistor and a heterojunction bipolar transistor comprising a germanium-enriched region. A base having a silicon-germanium portion is formed over a collector. Thermal oxidation of the base causes a germanium-enriched region to form on a surface of the silicon-germanium portion subjected to the thermal oxidation. An emitter is formed overlying the germanium-enriched portion region. The germanium-enriched region imparts advantageous operating properties to the heterojunction bipolar transistor, including improved high-frequency/high-speed operation.
1 . A method of manufacturing a semiconductor device comprising:
forming a silicon-germanium base region, having a first upper surface, over a collector region;
reacting the base region along the upper surface to form a thermally grown oxide in the first upper surface and a germanium-enriched region below the thermally grown oxide;
annealing the semiconductor device to redistribute germanium atoms of the germanium-enriched region;
removing the thermally grown oxide to expose a second upper surface of the base region; and
forming an emitter region over the base.
2 . The method of claim 1 wherein a germanium concentration near the second surface is between about 30 percent and about 75 percent relative to the concentration of silicon near the second surface.
3 . The method of claim 1 wherein the step of reacting the base region further comprises reacting the base region within a temperature range of about 700 to about 900 degrees Celsius.