Bipolar transistor with low resistance base contact and method of making the same

Abstract

Embodiments of the present invention provide a bipolar transistor with low resistance base contact and method of manufacturing the same. The bipolar transistor includes an emitter, a collector, and an intrinsic base between the emitter and the collector. The intrinsic base extends laterally to an extrinsic base. The extrinsic base further includes a first semiconductor material with a first bandgap and a second semiconductor material with a second bandgap that is smaller than the first bandgap.

1 - 20 . (canceled) 
   
   
       21 . A bipolar transistor structure, comprising:
 an emitter;   an extrinsic base having at least a layer of first semiconductor material of a first bandgap (energy gap) and a layer of second semiconductor material of a second bandgap, said second bandgap being smaller than said first bandgap;   a first set of tunable non-conductive sidewall spacers defining edges of said extrinsic base away from said emitter;   a second set of tunable non-conductive sidewall spacers formed on top of an intrinsic base and separating said emitter from said extrinsic base, said intrinsic base extending laterally to said extrinsic base;   a silicide contact formed on the layer of said second semiconductor material of said extrinsic base; and   a collector underneath said intrinsic base, wherein   said silicide is a nickel silicide or a silicide formed from a nickel alloy; said nickel alloy includes platinum (Pt),   said first semiconductor material of said extrinsic base comprises silicon (Si) and said second semiconductor material of said extrinsic base comprises silicon germanium (SiGe),   said SiGe of said second semiconductor material is further doped with boron, and has a germanium content ranging from about 5 to about 50 atomic percentage,   said boron-doped SiGe of said second semiconductor material is formed in a recess of said layer of said first semiconductor material, and   said second semiconductor material is in substantially alignment with an isolation structure underlying said extrinsic base; said isolation structure being a shallow trench isolation.   
   
   
       22 . A method of manufacturing a bipolar transistor, the method comprising:
 providing a semiconductor substrate as a collector;   forming an intrinsic base on said semiconductor substrate;   forming an extrinsic base on an outer portion of said intrinsic base, said extrinsic base having a first layer of a first semiconductor material;   forming an emitter on an inner portion of said intrinsic base, said emitter being separated from said extrinsic base by one or more sets of spacers;   forming a second layer of a second semiconductor material of said extrinsic base, said second semiconductor material having a smaller bandgap than that of said first semiconductor material; and   forming a silicide contact on top of said layer of said second semiconductor material using nickel or nickel alloy, wherein   said second layer of said second semiconductor material of said extrinsic base comprises creating a recess in said first layer of said first semiconductor material, and fill said recess with said second semiconductor material, wherein said first semiconductor material is silicon (Si) and said second semiconductor material is silicon-germanium (SiGe) having a germanium content between about 5 and 50 atomic percentage, and   said second layer of said second semiconductor material comprises applying a set of spacers to align said second semiconductor material with a shallow trench isolation structure underlying said extrinsic base.