ESD protection device with improved bipolar gain using cutout in the body well
An integrated circuit includes an NMOS SCR in which a p-type body well of the NMOS transistor provides a base layer for a vertical NPN layer stack. The base layer is formed by implanting p-type dopants using an implant mask which has a cutout mask element over the base area, so as to block the p-type dopants from the base area. The base layer is implanted concurrently with p-type body wells under NMOS transistors in logic components in the integrated circuit. Subsequent anneals cause the p-type dopants to diffuse into the base area, forming a base with a lower doping density that adjacent regions of the body well of the NMOS transistor in the NMOS SCR. The NMOS SCR may have a symmetric transistor, a drain extended transistor, or may be a bidirectional NMOS SCR with a symmetric transistor integrated with a drain extended transistor.
1. An integrated circuit, comprising:
a substrate comprising a p-type semiconductor;
a symmetric p-channel metal oxide semiconductor (PMOS) transistor disposed in said substrate;
a p-type n-channel metal oxide semiconductor (NMOS) body well disposed in said substrate;
source and drain regions of a symmetric NMOS transistor disposed in said p-type NMOS body well; and
an NMOS silicon controlled rectifier (SCR), including:
a p-type body well disposed in said substrate, said p-type body well having a lateral cutout portion with a lower doping density than the p-type body well outside of and laterally surrounding the lateral cutout portion;
an n-type source region disposed in said p-type body well over said lateral cutout portion;
an n-type region disposed in said substrate under said lateral cutout portion, said n-type region being connected to an n-type drain region; and
a p-type body contact region, disposed in said p-type body well over said lateral cutout portion.
2. The integrated circuit of claim 1 , in which a width of said lateral cutout portion is 0.5 to 1.5 microns.
3. The integrated circuit of claim 1 , in which a p-type doping density of said lateral cutout portion is between 50 percent and 75 percent of a p-type doping density of said p-type body well outside of said lateral cutout portion.
4. The integrated circuit of claim 1 , in which an average p-type doping density of said NMOS body well is substantially equal to an average p-type doping density of said p-type body well.
5. The integrated circuit of claim 1 , in which said NMOS SCR is a bidirectional NMOS SCR, including an NMOS symmetric transistor and a drain extended NMOS transistor, wherein:
said bidirectional NMOS SCR includes a p-type symmetric transistor body well disposed in said substrate in an area for said NMOS symmetric transistor;
said p-type body well is a p-type drain extended body well in an area for said drain extended NMOS transistor and proximate to and physically separated from said p-type symmetric transistor body well; and
said n-type region disposed under said lateral cutout portion is an n-type buried layer, said n-type buried layer being electrically connected through an extended drain of said drain extended NMOS transistor to the n-type drain region.
6. An integrated circuit, comprising:
a substrate comprising a p-type semiconductor;
a symmetric PMOS transistor disposed in said substrate;
a p-type NMOS body well disposed in said substrate;
source and drain regions of an NMOS transistor disposed in said NMOS body well; and
a bidirectional NMOS SCR, including an NMOS symmetric transistor and a drain extended NMOS transistor, said bidirectional NMOS SCR including:
a p-type symmetric transistor body well disposed in said substrate in an area for said NMOS symmetric transistor;
a p-type drain extended body well disposed in said substrate in an area for said drain extended NMOS transistor and proximate to and physically separated from said p-type symmetric transistor body well, said drain extended body well having a lateral cutout portion with a lower doping density under an n-type source region disposed in said p-type drain extended body well;
an n-type buried layer disposed in said substrate under said lateral cutout portion in said p-type drain extended body well, said n-type buried layer being electrically connected to an extended drain of said drain extended NMOS transistor; and
a p-type body contact region of said drain extended NMOS transistor, disposed in said p-type drain extended body well over said lateral cutout portion.
7. The integrated circuit of claim 6 , in which a width of said lateral cutout portion is 0.5 to 1.5 microns.
8. The integrated circuit of claim 6 , in which:
an average p-type doping density of said p-type body well is substantially equal to an average p-type doping density of said p-type symmetric transistor body well; and
an average p-type doping density of said p-type body well is substantially equal to an average p-type doping density of said p-type drain extended body well, not including said lateral cutout portion.
9. The integrated circuit of claim 6 , in which said p-type symmetric transistor body well has a lateral cutout portion with a lower doping density, said lateral cutout portion in said p-type symmetric transistor body well being disposed below said p-type body contact region of said NMOS symmetric transistor and said n-type source region of said NMOS symmetric transistor.