Methods of forming laterally diffused metal oxide semiconductor transistors for radio frequency power amplifiers
View Patent ↗A lateral diffused metal oxide semiconductor (LDMOS) transistor is provided. The LDMOS transistor includes a substrate having a source region, channel region, and a drain region. A first implant is formed to a first depth in the substrate. A gate electrode is formed over the channel region in the substrate between the source region and the drain region. A second implant is formed in the source region of the substrate; the second implant is laterally diffused under the gate electrode a predetermined distance. A third implant is formed to a second depth in the drain region of the substrate; the second depth is less than the first depth. A method for forming the LDMOS transistor is also provided.
1. A method for forming a lateral diffused metal oxide semiconductor (LDMOS) transistor, the method comprising:
providing a substrate having a first surface and a second surface, wherein the first surface comprises an epitaxial layer, and wherein the first surface comprises a drain region, a source region, and a channel region for the LDMOS transistor;
implanting a first dopant of a first type having a first doping concentration in the first surface of the substrate, wherein the first dopant is implanted to a first depth, and wherein the first dopant is implanted in the source region, the drain region, and the channel region;
forming a gate electrode over the channel region of the first surface of the substrate;
selectively implanting a second dopant of a second type in the source region of the first surface, the second dopant having a second doping concentration, wherein the second dopant laterally diffusing under the gate electrode a predetermined distance, and wherein the second type is different than the first type;
selectively implanting a third dopant of the first type in the drain region of the first surface, the third dopant having a third doping concentration, wherein the third dopant is implanted to a second depth, the second depth being less than the first depth;
forming a source implant in the source region; and
forming a drain implant in the drain region.
2. The method of claim 1 , further comprising forming a sinker implant in the source region, wherein the sinker implant is used to provide a connection from the source region to the second surface of the substrate.
3. The method of claim 1 , wherein the first type is an N-type dopant and the second type is a P-type dopant.
4. The method of claim 1 , wherein the gate electrode is formed from polysilicon.
5. The method of claim 1 , wherein the epitaxial layer is lightly doped relative to a doping concentration of the substrate.
6. The method of claim 1 , wherein selectively implanting the second dopant further comprises laterally diffusing the second dopant for substantially an entire length of the gate electrode.
7. The method of claim 1 , wherein forming the source implant and forming the drain implant comprise forming an N+ source implant and forming an N+ drain implant.
8. The method of claim 1 , wherein selectively implanting the third dopant further comprises implanting the third dopant with no lateral diffusion under the gate electrode.
9. The method of claim 1 , wherein the first dopant is implanted before the gate electrode is formed.
10. The method of claim 1 , wherein a net doping concentration of the drain region is greater than either of the first doping concentration or the third doping concentration.
11. A method for forming a lateral diffused metal oxide semiconductor (LDMOS) transistor, the method comprising:
providing a substrate having a first surface and a second surface, wherein the first surface comprises an epitaxial layer, and wherein the first surface comprises a drain region, a source region, and a channel region for the LDMOS transistor;
implanting a first N-type dopant having a first doping concentration in the first surface of the substrate, wherein the first N-type dopant is implanted to a first depth, and wherein the first N-type dopant is implanted in the source region, the channel region, and the drain region;
forming a gate electrode over the channel region of the first surface of the substrate;
selectively implanting a P-type dopant in the source region of the first surface, the P-type dopant having a second doping concentration, wherein the P-type dopant laterally diffusing under the gate electrode into the channel region a predetermined distance;
selectively implanting a second N-type dopant in the drain region of the first surface, the second N-type dopant having a third doping concentration, wherein the second N-type dopant is implanted to a second depth, the second depth being less than the first depth;
forming an N+ source implant in the source region; and
forming an N+ drain implant in the drain region.
12. The method of claim 11 , further comprising forming a sinker implant in the source region, wherein the sinker implant is used to provide a connection from the source region to the second surface of the substrate.
13. The method of claim 11 , wherein the gate electrode is formed from polysilicon.
14. The method of claim 11 , wherein the epitaxial layer is lightly doped relative to a doping concentration of the substrate.
15. The method of claim 11 , wherein selectively implanting the second dopant further comprises laterally diffusing the second dopant for substantially an entire length of the gate electrode.
16. The method of claim 11 , wherein selectively implanting the third dopant further comprises implanting the third dopant with minimal lateral diffusion under the gate electrode.
17. A method for forming a lateral diffused metal oxide semiconductor (LDMOS) transistor, the method comprising:
forming a first implant of a first type and a first doping density to a first depth in a substrate having a source region, a drain region, and a channel region, wherein the first implant is formed in at least the drain region and the channel region;
forming a gate electrode over the channel region;
after forming the gate electrode, forming a second implant of a second type that is different from the first type in the source region of the substrate, the second implant laterally diffused under the gate electrode into the channel region a predetermined distance, wherein the second implant overlaps a portion of the first implant within the channel region; and
forming a third implant of the first type and a second doping density that is greater than the first doping density to a second depth in the drain region of the substrate, the second depth being less than the first depth.
18. The method of claim 17 , further comprising:
forming an N+ source implant in the source region a first predetermined distance from the gate electrode; and
forming an N+ drain implant in the drain region a second predetermined distance from the gate electrode,
wherein the third implant is formed in the channel region from an edge of the gate electrode to the N+ drain implant.
19. The method of claim 17 , wherein the second implant is laterally diffused under the gate electrode for substantially an entire length of the gate electrode.
20. The method of claim 17 , wherein the first implant and the third implant each comprises an N-type dopant, and the second implant comprises a P-type dopant.