Divided drain implant for improved CMOS ESD performance

1. A transistor structure for electrostatic discharge protection comprising:

at least two transistors formed close to each other on a substrate with their gates and sources coupled together and with the drains placed next to each other and separated as a divided drain implant structure, wherein the divided drain implant structure further comprises at least two drain implant regions separated by a lightly doped drain region and a halo implant region formed underneath; and

two pocket areas for wrapping corners of the lightly doped drain region underneath the gates of the transistors,

wherein at least one of the drain implant regions is coupled to an input/output pad of a circuit.

2. The structure of claim 1 , wherein the halo implant region has a thickness of at least 0.5 μm.

3. The structure of claim 1 , wherein all drain implant regions are coupled to the input/output pad.

4. The structure of claim 1 , wherein the divided drain implant structure has an odd number of drain implant regions separated by a lightly doped drain region and a halo implant region formed underneath.

5. The structure of claim 4 , wherein only a center implant region is coupled to the input/output pad.

6. The structure of claim 1 , wherein the transistors are NMOS devices and a parasitic npn transistor is formed by the drain implant region coupled to the input/output pad, the substrate, and the source for propagating electrostatic discharge current.

7. The structure of claim 6 , wherein the drain implant regions have N+ implants, the halo implant is of P-type, and the lightly doped drain, structure is of N-type.

8. The structure of claim 7 , wherein the transistor devices are PMOS devices, and a parasitic pnp transistor is formed by the drain implant region coupled to the input/output pad, the substrate, and the source for propagating electrostatic discharge current.

9. The structure of claim 8 , wherein the drain implant regions have P+ implants, the halo implant is of N-type, and the lightly doped drain structure is of P-type.

10. The structure of claim 1 , further comprising gate spacers formed on the sidewalls of the gates of the transistors.

11. A transistor structure for electrostatic discharge protection comprising:

at least two transistors formed close to each other on a substrate of a first type with their gates and sources coupled together and with the drains placed next to each other and separated as a divided drain implant structure;

two pocket areas for wrapping corners of the lightly doped drain region underneath the gates of the transistors;

wherein the divided drain implant structure further comprises at least two drain implant regions doped with a material of a second type that is complementary to the first type, with a lightly doped drain region of the second type and a halo implant region of the first type formed underneath for separating the drain implant regions; and

wherein at least one of the drain implant regions is coupled to an input/output pad of a circuit.

12. The structure of claim 11 , wherein the halo implant region has a thickness of at least 0.5 μm.

13. The structure of claim 11 , wherein at least the drain implant regions immediately close to the gates are coupled to the input/output pad.

14. The structure of claim 11 , wherein the divided drain implant structure has an odd number of drain implant regions separated by a lightly doped drain region and a halo implant region formed underneath.

15. The structure of claim 14 , wherein only a center implant region is coupled to the input/output pad.

16. The structure of claim 11 , wherein the transistors are NMOS transistors and the drain implant regions have N+ implants, the halo implant is of P-type, and the lightly doped drain structure is of N-type.

17. The structure of claim 11 , wherein the transistors are PMOS transistors, the drain implant regions have P+ implants, the halo implant is of N-type, and the lightly doped drain structure is of P-type.