Silicon germanium heterojunction bipolar transistor structure and method
View Patent ↗Disclosed is an improved semiconductor structure (e.g., a silicon germanium (SiGe) hetero-junction bipolar transistor) having a narrow essentially interstitial-free SIC pedestal with minimal overlap of the extrinsic base. Also, disclosed is a method of forming the transistor which uses laser annealing, as opposed to rapid thermal annealing, of the SIC pedestal to produce both a narrow SIC pedestal and an essentially interstitial-free collector. Thus, the resulting SiGe HBT transistor can be produced with narrower base and collector space-charge regions than can be achieved with conventional technology.
1. A method of forming a semiconductor structure comprising:
providing a substrate;
selecting a first dopant and a second dopant different from said first dopant;
forming an initial semiconductor layer on said substrate, said initial semiconductor layer having a top surface;
implanting said second dopant into said initial semiconductor layer to form an implant region at a predetermined depth below said top surface;
removing defects from said top surface of said initial semiconductor layer caused by said implanting and simultaneously activating said second dopant in said implant region with minimal diffusion of said second dopant into other regions of said initial semiconductor layer by performing a laser anneal; and
forming an additional semiconductor layer on said top surface, said additional semiconductor layer being any one of in-situ doped and subsequently doped with said first dopant,
said removing said defects minimizing diffusion of said first dopant from said additional semiconductor layer into said initial semiconductor layer.
2. The method of claim 1 , said diffusion of said first dopant from said additional semiconductor layer into said initial semiconductor layer being minimized by said removing said defects such that a peak concentration of said first dopant in said additional semiconductor layer adjacent to said top surface of said initial semiconductor layer remains at least 100 times greater than a concentration of said first dopant in a diffusion region of said initial semiconductor layer between said top surface and said implant region.
3. The method of claim 1 , said forming of said additional semiconductor layer comprising epitaxially growing said additional semiconductor layer and in-situ doping said additional semiconductor layer such that a peak concentration of said first dopant in said additional semiconductor layer is greater than approximately 1×10 19 cm −3 at approximately 0.03 μm above said top surface.
4. The method of claim 1 , said removing said defects minimizing said diffusion of said first dopant from said additional semiconductor layer into said initial semiconductor layer such that a concentration of said first dopant in a diffusion region of said initial semiconductor layer between said implant region and said top surface is less than approximately 1×10 17 cm −3 .
5. The method of claim 1 , said implanting said second dopant into said initial semiconductor layer comprising implanting said second dopant such that said implant region is approximately 0.03 μm below said top surface and has an approximately uniform second dopant concentration and said laser anneal being performed to activate said second dopant in said implant region with said minimal diffusion of said second dopant into said other regions of said initial semiconductor layer such that said implant region maintains said uniform second dopant concentration.
6. The method of claim 5 , said laser anneal being performed at temperatures greater than approximately 1100° C. and using a technique that can achieve a thermal equilibrium in said initial semiconductor layer in less than approximately 10 ps to minimize diffusion of said second dopant from said implant region.
7. The method of claim 6 , said laser anneal being performed to activate said second dopant in said implant region with said minimal diffusion of said second dopant into said other regions of said initial semiconductor layer such that a concentration profile of said second dopant outside of said implant region decreases from approximately 1×10 18 cm −3 at approximately 0.02 μm below said top surface to less than approximately 1×10 17 cm −3 near said top surface.
8. The method of claim 1 , said additional semiconductor layer comprising a silicon germanium layer, said first dopant comprising boron, said initial semiconductor layer comprising a silicon layer and said second dopant comprising one of phosphorous, antimony and arsenic.
9. The method of claim 1 , said laser anneal being performed without melting said initial semiconductor layer and comprising one of a laser thermal process (LTP) and a laser spike anneal (LSA).
10. The method of claim 1 , said laser anneal being performed so as to avoid clustering of point defects and forming of extended defects and dislocation loops at said top surface.
11. A method of forming a semiconductor structure comprising:
providing a substrate;
selecting a first dopant and a second dopant different from said first dopant;
forming an initial semiconductor layer on said substrate, said initial semiconductor layer having a top surface;
implanting said second dopant into said initial semiconductor layer to form an implant region at a predetermined depth below said top surface;
removing defects from said top surface of said initial semiconductor layer caused by said implanting and simultaneously activating said second dopant in said implant region with minimal diffusion of said second dopant into other regions of said initial semiconductor layer by performing a laser anneal; and
forming an additional semiconductor layer on said top surface, said additional semiconductor layer being any one of in-situe doped and subsequently doped with first dopant,
said removing said defects minimizing diffusion of said first dopant from said additional semiconductor layer into said initial semiconductor layer such that a peak concentration of said first dopant in said additional semiconductor layer adjacent to said top surface of said initial semiconductor layer remains at least 100 times greater than a concentration of said first dopant in said initial semiconductor layer, said concentration of said first dopant in said initial semiconductor layer being less than approximately 1×10 17 cm −3 .
12. A method of forming a semiconductor structure comprising:
providing a substrate;
selecting a first dopant and a second dopant different from said first dopant;
forming a silicon layer on said substrate, said silicon layer having a top surface;
implanting said second dopant into said silicon layer to form an implant region at a predetermined depth below said top surface;
removing defects from said top surface of said silicon layer caused by said implanting and simultaneously activating said second dopant in said implant region with minimal diffusion of said second dopant into other regions of said silicon layer by performing a laser anneal; and
forming a silicon germanium layer on said top surface, said silicon germanium layer being any one of in-situ doped and subsequently doped with said first dopant, said removing said defects minimizing diffusion of said first dopant from said silicon germanium layer into said silicon layer.
13. The method of claim 12 , said diffusion of said first dopant from said silicon germanium layer into said silicon layer being minimized by said removing said defects such that a peak concentration of said first dopant in said silicon germanium layer adjacent to said top surface of said silicon layer remains at least 100 times greater than a concentration of said first dopant in a diffusion region of said silicon layer between said top surface and said implant region.
14. The method of claim 12 , said forming of said silicon germanium layer comprising epitaxially growing said silicon germanium layer and in-situ doping said silicon germanium layer such that a peak concentration of said first dopant in said silicon germanium layer is greater than approximately 1×10 19 cm −3 at approximately 0.03 μm above said top surface.
15. The method of claim 12 , said removing said defects minimizing said diffusion of said first dopant from said silicon germanium layer into said silicon layer such that a concentration of said first dopant in a diffusion region of said silicon layer between said implant region and said top surface is less than approximately 1×10 17 cm −3 .
16. The method of claim 12 , said implanting said second dopant into said silicon layer comprising implanting said second dopant such that said implant region is approximately 0.03 μm below said top surface and has an approximately uniform second dopant concentration and said laser anneal being performed to activate said second dopant in said implant region with said minimal diffusion of said second dopant into said other regions of said silicon layer such that said implant region maintains said uniform second dopant concentration.
17. The method of claim 12 , said laser anneal being performed at temperatures greater than approximately 1100° C. and using a technique that can achieve a thermal equilibrium in said silicon layer in less than approximately 10 ps to activate said second dopant in said implant region with said minimal diffusion of said second dopant into said other regions of said silicon layer such that a concentration profile of said second dopant outside of said implant region decreases from approximately 1×10 18 cm −3 at approximately 0.02 μm below said top surface to less than approximately 1×10 17 cm −3 near said top surface.
18. The method of claim 12 , said first dopant comprising boron and said second dopant comprising one of phosphorous, antimony and arsenic.
19. The method of claim 12 , said laser anneal being performed without melting said silicon layer and comprising one of a laser thermal process (LTP) and a laser spike anneal (LSA).
20. The method of claim 12 , said laser anneal being performed so as to avoid clustering of point defects and forming of extended defects and dislocation loops at said top surface.