Methods for forming transistors
A hybrid transistor is produced to have a substrate with a first (e.g., P type) well region and a second (e.g., N type) well region with an NP or PN junction therebetween. A MOS portion of the hybrid transistor has an (e.g., N type) source region in the first well region and a gate conductor overlying and insulated from the well regions. A drain or anode (D/A) portion in the second well region collects current from the source region, and includes a bipolar transistor having an (e.g., N+) emitter region, a (e.g., P type) base region and a (e.g., N type) collector region laterally separated from the junction. Different LDMOS-like or IGBT-like properties are obtained depending on whether the current is extracted from the hybrid transistor via the bipolar transistor base or emitter or both. The bipolar transistor is desirably a vertical hetero-junction transistor.
1. A method for forming a transistor comprising:
providing a substrate having therein a first well region of a first conductivity type and a second well region of a second, opposite conductivity type, extending substantially to a first surface of the substrate, the first and second well regions forming an NP or PN junction therebetween, and wherein the first and the second well regions have therein an MOS-portion and the second well region has therein a drain or anode (D/A) portion;
forming in the MOS-portion, a gate conductor overlying and insulated from the first surface at least over the first well region and having a first lateral end adapted to substantially locate a first edge of a subsequently formed source region within the first well region and a second lateral end extending at least to the NP and PN junction;
protecting the MOS-portion while a bipolar transistor is subsequently formed in the D/A portion in the second well region;
forming the bipolar transistor in the second well region, wherein the bipolar transistor comprises an emitter region of the second conductivity type, an intrinsic base region of the first conductivity type communicating with the emitter region, and a collector region of the second conductivity type communicating with the intrinsic base region;
protecting the D/A portion and, in either order, forming the source region of the second conductivity type in the first well region and having the first edge laterally proximate the first lateral end of the gate conductor, and forming a well contact region of the first conductivity type in the first well region; and
forming multiple conductive contacts communicating respectively with the source region, the gate conductor, the intrinsic base region of the bipolar transistor and the emitter region of the bipolar transistor.
2. The method of claim 1 , further comprising forming a conductive first well region contact in the first well region and sharing a conductive contact with the source region.
3. The method of claim 1 , wherein the step of providing the substrate further comprises forming one or more shallow-trench-isolation (STI) regions extending into the substrate from the first surface.
4. The method of claim 3 , wherein the step of forming one or more shallow-trench-isolation (STI) regions further comprises, forming sub-isolation-buried-layer (SIBL) regions of the second conductivity type underlying at least some of the one or more STI regions.
5. The method of claim 1 , wherein the step of forming the bipolar transistor comprises, forming a hetero junction bipolar transistor.
6. The method of claim 5 , wherein the step of forming the hetero junction bipolar transistor comprises forming the hetero-junction bipolar transistor having a base region of a different semiconductor material than the second well region.
7. A method for forming a transistor, comprising:
providing a substrate having a first well region of a first conductivity type, a second well region of a second, opposite conductivity type and extending substantially to a first surface of the substrate, and an NP or PN junction formed between the first and second well regions;
forming a MOS portion having a source region of the second conductivity type extending to the first surface in the first well region, and having a gate conductor overlying and insulated from the first surface at least over the first well region with a first lateral end proximate the source region and a second lateral end extending at least to the NP or PN junction; and
forming a drain or anode (D/A) portion in the second well region, the D/A portion comprising a bipolar transistor having an emitter region of the second conductivity type, a base region of the first conductivity type communicating with the emitter region, and a collector region of the second conductivity type communicating with the base region, the collector region located in the second well region laterally separated from the NP or PN junction.
8. The method of claim 7 , further comprising forming a principal terminal electrically coupled to the base region and electrically isolated from the emitter region.
9. The method of claim 7 , further comprising forming a principal terminal electrically coupled to the emitter region and electrically isolated from the base region.
10. The method of claim 7 , further comprising forming a principal terminal electrically coupled to both the emitter region and the base region.
11. The method of claim 7 , further comprising forming a dielectric filled shallow trench isolation (STI) region laterally located in the second well region between the NP or PN junction and the collector region of the bipolar transistor.
12. The method of claim 11 , further comprising forming a sub-isolation-buried-layer (SIBL) region in the second well region, the SIBL region located beneath the STI region and having a dopant concentration greater than the second well region.
13. The method of claim 7 , wherein the bipolar transistor is a hetero-junction bipolar transistor.
14. The method of claim 13 , further comprising forming the base region of the bipolar transistor and the collector region from different semiconductor materials.
15. The method of claim 7 , wherein the bipolar transistor is substantially a vertical transistor with the emitter region, the base region and the collector region arranged substantially one above the other.
16. A method of forming a transistor, comprising:
providing a first well region of a first conductivity type;
providing a second well region of a second conductivity type, the second well region forming a lateral NP or PN junction with the first well region;
forming a MOS portion in at least one of the first and second well regions, the MOS portion comprising:
a source region in the first well region; and
a first well contact region in the first well region;
forming a drain or anode (D/A) portion in at least one of the first and second well regions; and
producing a substantially vertical hetero-junction bipolar transistor in the DA portion, the substantially vertical hetero-junction bipolar transistor having a base connection and an emitter connection that may be used separately or together as a principal electrode of the multifunction transistor.
17. The method of claim 16 , further comprising forming a principal electrode electrically coupled to the emitter connection.
18. The method of claim 16 , further comprising forming a principal electrode electrically coupled to the base connection.
19. The method of claim 16 , further comprising forming a common electrode electrically coupled to the source region and to the first well contact region.
20. The method of claim 16 , further comprising forming a gate conductor in the MOS portion, the gate conductor insulated at least from the first well region and extending laterally substantially from the source region to at least the NP or PN junction.