SiGe DIAC ESD protection structure
A diode for alternating current (DIAC) electrostatic discharge (ESD) protection circuit is formed in a silicon germanium (SiGe) hetrojunction bipolar transistor (HBT) process that utilizes a very thin collector region. ESD protection for a pair of to-be-protected pads is provided by utilizing the base structures and the emitter structures of the SiGe transistors.
1. An electrostatic discharge (ESD) protection circuit comprising:
a semiconductor structure having:
a substrate of a first conductivity type;
a buried layer of a second conductivity type that touches the substrate;
a surface region of the second conductivity type that touches the buried layer and a top surface of the semiconductor structure, the surface region having a dopant concentration that is lower than a dopant concentration of the buried layer; and
an isolation region that extends down from the top surface of the semiconductor structure;
spaced-apart first and second regions of the first conductivity type that lie on the top surface of the semiconductor structure and touch the isolation region;
spaced-apart third and fourth regions of the second conductivity type that lie on and touch the first and second regions, respectively;
spaced-apart first and second contacts electrically connected to the first and third regions, respectively, and to a first pad; and
spaced-apart third and fourth contacts electrically connected to the second and fourth regions, respectively, and to a second pad.
2. The ESD protection circuit of claim 1 wherein a first area that lies below and touches the first region and a second area that lies below and touches the second region are laterally spaced apart by only the isolation region.
3. The ESD protection circuit of claim 1 wherein a face of the first region and a face of the second region touch the isolation region, directly oppose each other, and are substantially parallel.
4. The ESD protection circuit of claim 3 wherein the first region includes a region of single crystal silicon germanium and a region of polysilicon germanium, and the second region includes a region of single crystal silicon germanium and a region of polysilicon germanium.
5. The ESD protection circuit of claim 1 wherein the semiconductor structure further includes a well of the first conductivity type that extends down from the top surface of the semiconductor structure to touch the substrate.
6. The ESD protection circuit of claim 5 wherein the first region touches the surface region and the second region touches the well.
7. The ESD protection circuit of claim 6 wherein the first and second regions are silicon germanium regions.
8. The ESD protection circuit of claim 7 wherein the first region includes a region of single crystal silicon and a region of polysilicon, and the second region includes a region of single crystal silicon and a region of polysilicon.
9. An electrostatic discharge (ESD) protection circuit comprising:
a semiconductor structure having:
a substrate of a first conductivity type;
a buried layer of a second conductivity type that touches the substrate;
a surface region of the second conductivity type that touches the buried layer and a top surface of the semiconductor structure, the surface region having a dopant concentration that is lower than a dopant concentration of the buried layer;
a well of the first conductivity type that extends down from the top surface of the semiconductor structure to touch the substrate, the well being electrically connected to a first pad; and
an isolation region that extends down from the top surface of the semiconductor structure;
a first region of the first conductivity type that lies on the top surface of the semiconductor structure and touches the surface region and the isolation region, the first region being spaced apart from the well;
a second region of the second conductivity type that lies on and touches the first region; and
spaced-apart first and second contacts electrically connected to the first and second regions, respectively, and to a second pad.
10. The ESD protection circuit of claim 9 wherein the well touches the isolation region.
11. The ESD protection circuit of claim 10 wherein the semiconductor structure further includes a third region of the second conductivity type, the third region being spaced apart from the surface region, and electrically connected to the first pad.