Integrated zener diode overvoltage protection structures in power DMOS device applications
First Claim
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.
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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.
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Citations
12 Claims
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1. An overvoltage protection device for an input of a semiconductor device, comprising:
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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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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Specification