Lateral bipolar junction transistor having graded SiGe base
A lateral bipolar junction transistor is fabricated using a semiconductor-on-insulator substrate. The transistor includes a germanium gradient within a doped silicon base region, there being an increasing germanium content in the direction of the collector region of the transistor. The use of a substrate including parallel silicon fins to fabricate lateral bipolar junction transistors facilitates the inclusion of both CMOS FinFET devices and lateral bipolar junction transistors having graded silicon germanium base regions on the same chip.
1. A method comprising:
obtaining a structure comprising a plurality of parallel silicon fins adjoining an electrically insulating layer and a dummy gate extending across a plurality of the silicon fins, the fins defining a channel region having a first conductivity type beneath the dummy gate, a source region on a first side of the dummy gate, and a drain region on a second side of the dummy gate;
diffusing germanium into the channel region of the structure to form a germanium gradient within the channel region having an increasing germanium content in the direction of the drain region;
removing the drain region;
removing a portion of the electrically insulating layer beneath the drain region;
epitaxially growing a silicon region on the second side of the dummy gate and from the fins within the channel region subsequent to forming the germanium gradient;
doping the silicon region such that the silicon region has a second conductivity type opposite to the first conductivity type;
replacing the dummy gate with a gate structure operatively associated with the channel region; and
forming electrical connections to the gate structure and the silicon region.
2. The method of claim 1 , further including the steps of:
growing a germanium-containing layer on the drain region; and
thermally annealing the structure, thereby causing diffusion of germanium into the channel region.
3. The method of claim 2 , further including the step of removing the germanium-containing layer prior to epitaxially growing the silicon region.
4. The method of claim 3 , wherein the germanium-containing layer comprises silicon germanium.
5. The method of claim 3 , wherein the step of diffusing germanium into the channel region further includes causing the germanium to be diffused substantially entirely or entirely across the channel region.
6. The method of claim 1 , further including the steps of:
growing a germanium-containing region on the channel region subsequent to the step of removing the drain region; and
thermally annealing the structure, thereby causing diffusion of germanium into the channel region.
7. The method of claim 6 , further including the step of removing the germanium-containing region prior to epitaxially growing the silicon region.
8. The method of claim 7 , further including the step of forming a mask on the source region prior to the step of removing the drain region.
9. The method of claim 1 , further including the step of doping the source region simultaneously with the step of doping the silicon region.
10. The method of claim 1 , further including the step of epitaxially growing a highly doped silicon layer on the source region and the silicon region.
11. The method of claim 10 , wherein the step of diffusing germanium into the channel region includes thermally annealing a germanium-containing layer in contact with one of the channel region and the drain region.
12. The method of claim 11 , further including the steps of growing the germanium-containing layer on the drain region, removing the germanium-containing layer subsequent to thermally annealing the germanium-containing layer and, subsequent to removing the drain region, removing the portion of the electrically insulating layer beneath the drain region.
13. A method comprising:
obtaining a structure comprising a plurality of parallel silicon fins adjoining an electrically insulating layer and a dummy gate extending across a plurality of the silicon fins, the fins defining a channel region beneath the dummy gate, a source region on a first side of the dummy gate, and a drain region on a second side of the dummy gate;
diffusing germanium into the channel region of the structure to form a germanium gradient within the channel region having an increasing germanium content in the direction of the drain region;
removing the drain region;
removing a portion of the electrically insulating layer beneath the drain region;
epitaxially growing a semiconductor region on the second side of the dummy gate and from the fins within the channel region subsequent to forming the germanium gradient, removing the drain region and removing the portion of the electrically insulating layer beneath the drain region;
doping the channel region to obtain a first conductivity type within the channel region;
doping the semiconductor region such that the semiconductor region has a second conductivity type opposite to the first conductivity type;
replacing the dummy gate with a gate structure operatively associated with the channel region; and
forming electrical connections to the gate structure and the semiconductor region.
14. The method of claim 13 , wherein doping the channel region further includes implanting the channel region with dopants prior to replacing the dummy gate with the gate structure.