Selective links in silicon hetero-junction bipolar transistors using carbon doping and method of forming same

1. A method of forming a transistor, comprising:

forming a P-type collector in a silicon substrate;

forming an intrinsic base on said collector, said intrinsic base including an N-type dopant species, germanium and carbon;

forming an N-type extrinsic base over a first region and a second region of said intrinsic base, said first region over said collector and said second region over a dielectric adjacent to said collector;

forming a P-type emitter on said first region of said intrinsic base; and

wherein forming said intrinsic base includes:

forming a first intrinsic silicon layer on said collector;

forming a first silicon-germanium (SiGe) layer on said first intrinsic silicon layer and doping said first SiGe layer with carbon;

forming an N-type doped SiGe layer on said first SiGe layer and doping said N-type doped SiGe layer with said N-type dopant species and carbon;

forming a second SiGe layer on said first intrinsic silicon layer and doping said second SiGe layer with carbon; and

forming a second intrinsic silicon layer on said second SiGe layer.

2. The method of claim 1 , wherein said forming of said first intrinsic silicon layer, said first SiGe layer, said N-type doped SiGe layer, said second SiGe layer and said second intrinsic silicon layer is performed by chemical vapor deposition and said method further including:

introducing said carbon and germanium during deposition of said first SiGe layer, said N-type doped SiGe layer and said second SiGe layer; and

introducing said N-type dopant species into said N-type doped SiGe layer during deposition of said N-type doped SiGe layer.

3. The method of claim 1 , wherein said forming of said first intrinsic silicon layer, said first SiGe layer, said N-type doped SiGe layer, said second SiGe layer and said second intrinsic silicon layer is performed by chemical vapor deposition and said method further including:

introducing said carbon and germanium during deposition of said first SiGe layer, said N-type doped SiGe layer and said second SiGe layer; and

introducing said N-type dopant species into said N-type doped SiGe layer by ion implantation after deposition of said first intrinsic silicon layer, said first SiGe layer, said N-type doped SiGe layer, said second SiGe layer and said second an intrinsic silicon layer.

4. The method of claim 1 , further including performing a high-temperature annealing, said high temperature annealing driving said extrinsic base into said second SiGe layer in said second region of said intrinsic base.

5. The method of claim 1 , wherein said P-type collector and said P-type emitter are each doped with boron, said N-type doped SiGe layer is doped with phosphorous and said N-type extrinsic base is doped with arsenic, antimony or both arsenic and antimony.

6. The method of claim 1 , further including:

selecting a chemical species for said N-type dopant species, said chemical species selected to have a diffusivity in silicon containing carbon that is less than a diffusivity of said chemical species in silicon without carbon.

7. A method of forming a transistor, comprising:

forming a P-type collector in a silicon substrate;

forming an intrinsic base on said collector, said intrinsic base including a first N-type dopant species, germanium and carbon;

forming an N-type extrinsic base over a first region and a second region of said intrinsic base, said first region over said collector and said second region over a dielectric adjacent to said collector, said extrinsic base including a second N-type dopant species and carbon;

forming a P-type emitter on said first region of said intrinsic base; and

wherein forming said intrinsic base includes:

forming a first intrinsic silicon layer on said collector;

forming a first silicon-germanium (SiGe) layer on said first intrinsic silicon layer and doping said first SiGe layer with carbon;

forming an N-type doped SiGe layer on said first SiGe layer and doping said N-type doped SiGe layer with said first N-type dopant species and carbon;

forming a second SiGe layer on said first intrinsic silicon layer and doping said second SiGe layer with carbon; and

forming a second intrinsic silicon layer on said second SiGe layer.

8. The method of claim 7 , wherein said forming of said first intrinsic silicon layer, said first SiGe layer, said N-type doped SiGe layer, said second SiGe layer and said second intrinsic silicon layer is performed by chemical vapor deposition and said method further including:

introducing said carbon and germanium during deposition of said first SiGe layer, said N-type doped SiGe layer and said second SiGe layer; and

introducing said first N-type dopant species into said N-type doped SiGe layer during deposition of said N-type doped SiGe layer.

9. The method of claim 7 , wherein said forming of said first intrinsic silicon layer, said first SiGe layer, said N-type doped SiGe layer, said second SiGe layer and said second intrinsic silicon layer is performed by chemical vapor deposition and said method further including:

introducing said carbon and germanium during deposition of said first SiGe layer, said N-type doped SiGe layer and said second SiGe layer; and

introducing said first N-type dopant species into said N-type doped SiGe layer by ion implantation after deposition of said first intrinsic silicon layer, said first SiGe layer, said N-type doped SiGe layer, said second SiGe layer and said second an intrinsic silicon layer.

10. The method of claim 7 , wherein said forming of said extrinsic base is performed by chemical vapor deposition said carbon is introduced in the form of carbon containing gas during said deposition.

11. The method of claim 7 , wherein said forming of said extrinsic base is performed by chemical vapor deposition and said method further including:

introducing said second N-type dopant species and carbon during deposition of said extrinsic base.

12. The method of claim 7 , wherein said forming of said extrinsic base is performed by chemical vapor deposition and said method further including:

introducing said carbon during deposition of said extrinsic base; and

introducing said second N-type dopant species by ion implantation after deposition of said extrinsic base.

13. The method of claim 7 , further including performing a high-temperature annealing, said high temperature annealing driving said extrinsic base into said second SiGe layer in said second region of said intrinsic base and into said second SiGe layer in regions of said first region of said intrinsic base not directly under said P-type emitter.

14. The method of claim 7 , wherein said P-type collector and said P-type emitter are each doped with boron, said N-type doped SiGe layer is doped with phosphorous and said N-type extrinsic base is doped with arsenic, antimony or both arsenic and antimony.

15. The method of claim 7 , further including:

selecting a first chemical species for said first N-type dopant species, said first chemical species selected to have a diffusivity in silicon containing carbon that is less than a diffusivity of said first chemical species in silicon without carbon; and

selecting a second chemical species for said second N-type dopant species ; said second chemical species selected to have a diffusivity in silicon containing carbon that is greater than a diffusivity of said second chemical species in silicon without carbon.