Bipolar junction transistor having a high germanium concentration in a silicon-germanium layer and a method for forming the bipolar junction transistor

Abstract

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.