Electrostatic discharge protection circuit device

A structure of an electrostatic discharge (ESD) protection circuit, located under a pad which is to be formed later, the structure comprising:

• a substrate having a P-well and a N-well, wherein the P-well and the N-well have an interface, wherein a pad window is selected in the substrate which crosses over the interface, wherein the pad window is located under the pad;
• a first shallow trench isolation structure, a second shallow trench isolation structure, a third shallow trench isolation structure formed in the substrate within the pad window, wherein the first shallow trench isolation structure is located over the interface, the second shallow trench isolation structure is located in the P-well and the third shallow trench isolation structure is located in the N-well, wherein the second shallow trench isolation structure encloses a first inner region that is separated from a first outer region and the third shallow trench isolation encloses a second inner region that is separated from a second outer region;
• a plurality of n-type doped regions formed in the first inner region of the P-well and in the second inner region of the N-well;
• a plurality of first p-type doped regions formed in the first outer region of the P-well and in the second outer region of the N-well;
• and
• a plurality of second p-type doped regions formed in the outer regions under the n-type doped regions, wherein one of the second p-type doped regions, which is under the second inner region, has an electrical contact with the n-type doped region in the N-well to form a first zener diode, and another of the second p-type doped regions, which is under the first inner region, has an electrical contact with the n-type doped region in the P-well to form a second zener diode.