Methods of making laterally double diffused metal oxide semiconductor transistors having a reduced surface field structure
View Patent ↗An LDMOS transistor includes a substrate of semiconductor material, an insulator layer overlying the substrate, a semiconductor layer overlying the insulator layer, a RESURF region, and a gate. The semiconductor layer includes a first conductivity type well region, a second conductivity type source region in contact with the first conductivity type well region, a second conductivity type drain region. The RESURF region includes at least one first conductivity type material portion, and at least one portion of the at least one first conductivity type material portion electrically coupled to the first conductivity type well region. A semiconductor material having a second conductivity type is located below the RESURF region. The second conductivity type semiconductor material is also located over a part of the RESURF region. The gate is located over the first conductivity type well region and over the RESURF region.
1. A method of making a laterally double diffused metal oxide semiconductor (LDMOS) transistor, the method comprising:
forming a reduced surface field (RESURF) region of a first conductivity type in a second conductivity type semiconductor material, wherein the second conductivity type semiconductor material is located over an insulator layer, the insulator layer is located over a semiconductor substrate, a first portion of the second conductivity type semiconductor material remains below the RESURF region, a second portion of the second conductivity type semiconductor material remains above the RESURF region, and an opening in the RESURF region is present between the first and second portions of the second conductivity type semiconductor material, wherein the RESURF region is depleted by the first and second portions of the second conductivity type semiconductor material below and above the RESURF region;
forming a first conductivity type well region, where the first conductivity type well region partially merges with the RESURF region such that the RESURF region remains on a portion of a bottom surface and a sidewall surface of the first conductivity type well region which is electrically coupled to the RESURF region;
forming a gate over the second conductivity type semiconductor material, over the first conductivity type well region, and over the RESURF region;
forming a second conductivity type source region in the first conductivity type well region; and
forming a second conductivity type drain region over the opening in the RESURF region to allow a drain potential to spread through the opening to a full depth of the second conductivity type semiconductor material over the insulator layer to achieve a double RESURF action.
2. The method of claim 1 wherein forming the RESURF region includes implanting first conductivity type dopants into a contiguous area of the second conductivity type semiconductor material.
3. The method of claim 1 wherein forming the RESURF region includes implanting first conductivity type dopants into non contiguous areas of the second conductivity type semiconductor material.
4. The method of claim 3 , wherein after implanting, heating the second conductivity type semiconductor material, wherein the first conductivity type dopants diffuse into a contiguous area of the first conductivity type semiconductor material.
5. The method of claim 1 further comprising forming a second conductivity type well region, where the second conductivity type drain region is formed in the second conductivity type well region, and wherein a portion of the second conductivity type well region is located over the RESURF region.
6. The method of claim 1 wherein forming the RESURF region in the second conductivity type semiconductor material comprises:
implanting first conductivity type dopants into the first portion of the second conductivity type semiconductor material; and
epitaxially growing the second portion of the second conductivity type semiconductor material on the first portion of the second conductivity type semiconductor material after the implanting, wherein the second conductivity type source region and the second conductivity type drain material are formed in the epitaxially grown second portion of the second conductivity type semiconductor material.
7. The method of claim 6 wherein at least a portion of the first conductivity type well region is located in the epitaxially grown second portion of the second conductivity type semiconductor material.
8. The method of claim 1 wherein a first end of a RESURF region is located under the second conductivity type source region, wherein a second end of the RESURF region is located at the opening, and wherein the first end includes a greater concentration of first conductivity type dopants than the second end.
9. The method of claim 1 wherein a portion of the drain region is not located over the RESURF region.
10. The method of claim 1 wherein the first conductivity type is N-type and the second conductivity type is P-type.
11. The method of claim 1 , wherein the RESURF region comprises a plurality of non-contiguous portions between the drain region and the well region.
12. The method of claim 1 , further comprising:
forming deep trench isolation extending to the insulator layer.
13. The method of claim 11 , further comprising:
forming shallow trench isolation adjacent the drain region and partially underlying the gate.
14. A method of making a laterally double diffused metal oxide semiconductor (LDMOS) transistor, the method comprising:
forming an insulator layer overlying a substrate of semiconductor material;
forming a semiconductor layer overlying the insulator layer, the semiconductor layer including:
a first conductivity type well region;
a second conductivity type source region in contact with the first conductivity type well region;
a second conductivity type drain region; and
a reduced surface field (RESURF) region, the RESURF region including at least one first conductivity type material portion, at least one portion of the at least one first conductivity type material portion is electrically coupled to the first conductivity type well region and the first conductivity type well region partially merges with the RESURF region such that the RESURF region remains on a portion of a bottom surface and a sidewall surface of the first conductivity type well region, a first portion of a second conductivity type semiconductor material remains below the RESURF region, a second portion of the second conductivity type semiconductor material remains above the RESURF region, and an opening in the RESURF region is present between the first and second portions of the second conductivity type semiconductor material, wherein the RESURF region is depleted by the first and second portions of the second conductivity type semiconductor material below and above the RESURF region,
forming a gate located over the semiconductor layer, wherein the gate is located over the first conductivity type well region, and the gate is located over the RESURF region; and
forming a second conductivity type drain region over the opening in the RESURF region to allow a drain potential to spread through the opening to a full depth of the second conductivity type semiconductor material over the insulator layer to achieve a double RESURF action.
15. The method of claim 14 wherein the RESURF region is characterized as a contiguous region.
16. The method of claim 14 wherein the RESURF region is characterized as including a plurality of RESURF region portions between the drain region and the well region, which are separated laterally by the second conductivity type semiconductor material.