Transistor emitter having alternating undoped and doped layers
View Patent ↗A disclosed embodiment is a method for fabricating an emitter structure, comprising a step of conformally depositing an undoped polysilicon layer in an emitter window opening and over a base. Next, a doped polysilicon layer is non-conformally deposited over the undoped layer. Thereafter, the steps of conformally depositing an undoped polysilicon layer and non-conformally depositing a doped polysilicon layer are repeated until the emitter window opening is filled. The method can further comprise a step of activating dopants. In another embodiment, an emitter structure is fabricated according to the above method.
1. A structure in a semiconductor substrate comprising:
a base;
a plurality of undoped emitter layers situated over said base layer, each of said plurality of undoped emitter layers comprising an undoped bottom and an undoped sidewall;
a plurality of doped emitter layers, each of said plurality of doped emitter layers being situated over a corresponding one of said plurality of undoped emitter layers, each of said plurality of doped emitter layers comprising a doped bottom and a doped sidewall;
said plurality of undoped emitter layers and said plurality of doped emitter layers forming an emitter.
2. The structure of claim 1 wherein each of said plurality of undoped emitter layers comprises undoped polysilicon.
3. The structure of claim 1 wherein each of said plurality of doped emitter layers comprises N type polysilicon.
4. The structure of claim 1 wherein each of said plurality of undoped emitter layers is conformal in relation to an emitter window opening.
5. The structure of claim 1 wherein each of said plurality of undoped emitter layers has a bottom thickness and a sidewall thickness, wherein said bottom thickness is approximately equal to said sidewall thickness.
6. The structure of claim 1 wherein each of said plurality of doped emitter layers is non-conformal in relation to an emitter window opening.
7. The structure of claim 1 wherein each of said plurality of doped emitter layers has a bottom thickness and a sidewall thickness, wherein said bottom thickness is greater than said sidewall thickness.
8. The structure of claim 7 wherein said bottom thickness is equal to approximately twice said sidewall thickness.