Integrated zener diode overvoltage protection structures in power DMOS device applications

• US 5,767,550 A
• Filed: 10/16/1996
• Issued: 06/16/1998
• Est. Priority Date: 04/12/1996
• Status: Expired due to Term

• Current Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Original Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Inventors: Calafut, Daniel, Sapp, Steven, Bencuya, Izak
• Primary Examiner(s): Thomas, Tom
• Assistant Examiner(s): Hardy, David B.
• Application Number:
  US08/731,598
• Time in Patent Office: 608 Days
• Field of Search: 257/355, 257/356, 257/357, 257/340, 257/335, 257/337, 257/603, 257/409, 257/488
• US Class Current: 257/355
• CPC Class Codes: H01L 27/0251 for MOS devices
• CPC Class Codes: H01L 27/0255 using diodes as protective elements
• CPC Class Codes: H01L 29/402 Field plates
• CPC Class Codes: H01L 29/7808 the other device being a breakdown diode, e.g. Zener diode
• CPC Class Codes: H01L 29/7811 with an edge termination structure guard regions per se H01L29/0619; field plates per se H01L29/402
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: Y10S 148/126 Power FETs
• CPC Class Codes: Y10S 148/174 Zener diodes
• CPC Class Codes: Y10S 438/983 Zener diodes

Abstract

In one embodiment, modifications to the polysilicon gate, body, source, and contact masks of a DMOS process add a source-body monocrystalline gate protection diode under the gate pad by implanting an anode region beneath the gate. The anode is connected to the gate through the gate metal in the pad. In addition to the gate-source diode, there is also a connection from the drain to the gate through the anode formed by the body region beneath the gate. This embodiment includes a junction terminating field plate. The presence of the field plate creates a special protection device similar to a zener diode, but which exhibits a current/voltage characteristic similar to a thyristor. A significant feature of this embodiment is that the zener breakdown voltage is easily adjusted by a simple modification to the fabrication process. The field plate creates two opposing junctions with the spacing determined by the length of the field plate. The concentration gradients under the field plate, and hence the breakdown voltage, is controlled by suitable length of the field plate and other processing conditions. A zener breakdown programmability option is implemented so that the zener breakdown voltage is varied by suitable process selection using only one additional implant, temperature cycle, and photolithographic mask. The zener diode gate protection structure formed using the field plate has a high current per unit power; therefore, a much smaller protection structure can be implemented compared to the prior art, because much more current is conducted for a given size structure.

Claims

1. An overvoltage protection device for an input of a semiconductor device, comprising:

a substrate of a first conductivity type;

a body region of a second conductivity type within the substrate;

an input pad body region of a second conductivity type within the substrate;

a heavy body contact region of a second conductivity type within the body region having a higher doping concentration than the body region;

a source region of the first conductivity type within the body region having a higher doping concentration than the body region;

a zener cathode region of the first conductivity type within the input pad body region having a higher doping concentration than the input pad body region;

a field plate overlying the substrate and partially overlapping the body region and the input pad body region; and

a gate oxide layer between the field plate and the substrate.

2. The overvoltage protection device for an input of a semiconductor device as in claim 1, further comprising:

a gate pad metal layer overlying the substrate coupled to the zener cathode region.

3. The overvoltage protection device for an input of a semiconductor device as in claim 2, further comprising:

a source metal layer overlying the substrate coupled to the source region and the heavy body contact region.

4. The overvoltage protection device for an input of a semiconductor device as in claim 3,

wherein the field plate partially overlaps the zener cathode region.

5. The overvoltage protection device for an input of a semiconductor device as in claim 4,

wherein the field plate is made of polysilicon.

6. The overvoltage protection device for an input of a semiconductor device as in claim 5,

wherein the gate pad metal layer is coupled to the field plate.

7. The overvoltage protection device for an input of a semiconductor device as in claim 5,

wherein the source metal layer is coupled to the field plate.

8. The overvoltage protection device for an input of a semiconductor device as in claim 5,

wherein the substrate comprises an epitaxial layer overlying a heavily doped semiconductor surface of the first conductivity type.

9. The overvoltage protection device for an input of a semiconductor device as in claim 5, wherein the first conductivity type is N-type and the second conductivity type is P-type.

10. The overvoltage protection device for an input of a semiconductor device as in claim 9, wherein the body region and the input pad body region have different doping concentrations.

11. The overvoltage protection device for an input of a semiconductor device as in claim 5, wherein the gate oxide layer is approximately 400 Angstroms thick.

12. The overvoltage protection device for an input of a semiconductor device as in claim 11, wherein the field plate is approximately 5,500 Angstroms thick.