CMOS device with deep current path for ESD protection

Details CMOS device with deep current path for ESD protection CMOS device with deep current path for ESD protection

1999-02-12

2001-01-02

Chaudhari, Chandra (Department: 2813)

Semiconductor device manufacturing: process

Making field effect device having pair of active regions...

Having insulated gate

C438S306000, C438S420000, C438S545000

Utility Patent

active

06169001

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of Invention
This invention pertains to semiconductor devices and in particular the protection from electrostatic discharge.
2. Description of Related Art
As the level of integration of semiconductor product has grown, device structures have shrunk leaving less volume of material to dissipate heating from current surges caused by electro-static discharge (ESD). Keeping input and output devices large enough to dissipate the energy from an ESD uses a lot of valuable semiconductor real estate. Various attempts have been made to change the path of the discharge current and provide a way to absorb the energy while allowing the transistor devices to get smaller.
In U.S. Pat. No. 5,416,351 (Ito et al.) a Zener diode is embedded into the drain of a MOS device as an ESD protection device. The ESD protection device provides a low volage trigger for avalanche breakdown to discharge the ESD current away from the drain. In U.S. Pat. No. 5,446,302 (Beigel et al.) and U.S. Pat. No. 5,637,901 (Beigel et al) a diode connected bipolar transistor device is disclosed that provides protection from ESD. The device functions as a transistor in the active region an ESD event with the current path from collector to emitter and lowering the ESD current density. In U.S. Pat. No. 5,616,943 (Nguyen et al.) ESD protection is described for a mixed voltage circuit and having multiple isolated power supplies. This is accomplished by making use of several overload protection devices. In U.S. Pat. No. 5,677,205 (Williams et al.) an ESD device is discussed which includes a pair of depletion mode MOSFET transistors are connected drain to drain in series with a path from a circuit input terminal to a circuit output terminal. A pair of diodes are connected between ground and the transistors. One diode breaks down during large voltage spikes of short duration and the other diode breaks down during relatively low voltage long duration surges.
When an electrostatic discharge happens, heating takes place in the area of the drain. This is a result of a junction breakdown at the drain which allows a large amount of current to flow. If the current is not spread out across a sufficiently large volume, the resulting heat will not be dissipated and damage to the device will result. As semiconductor devices are shrunk and integrated together in larger and larger quantities, the sensitivity to ESD becomes worse. A way is described in this invention allow small devices and at the same time permit adequate dissipation of heat from an electrostatic discharge.
SUMMARY OF THE INVENTION
In this invention a resistive block is created by implanting P+ into an area of an N+ drain to divert current flowing from the channel to the drain contact close to the surface of the semiconductor and force it deeper into the bulk of the substrate. The P+ and N+ dopants compensate each other and produce a region of low dopant level but with a high resistance to current flow that is called a “resistive block”. In creating the resistive block, a longer path for the current through a larger volume of semiconductor material is created to effect adequate dissipation of the heating caused by an ESD. The resistive block is implanted through the drain into an N-well that is located below the drain in the substrate. The resistive block runs the full width of the drain to spread out the current, and to dissipate into the semiconductor substrate by forcing the current to flow into the bulk of a semiconductor. The resulting longer current path provides a way to dissipate energy from an electrostatic discharge and at the same time allow shrinking of transistor dimensions.
To produce the resistive current block, an N-well is implanted into the P substrate under a drain region of a transistor that is to be protected from an ESD. The N-well extends the length and width of the drain area as defined by the gate structure with sidewalls and the surrounding field oxide. After the N-well is implanted, an active area within the field oxide is formed and a gate structure is formed within the active area. The N+ drain and source are ion implanted. Photoresist is then applied to the surface of the wafer, and an area within the drain is masked open to allow the resistive current block to be implanted into the drain and through to the N-well. When current from the channel flow toward the drain contact area, the resistive block detours the current down through the N+ drain, into the N-well, under the resistive block, and back up through the N+ drain to the drain contact area. This extra path length into the semiconductor bulk provides more material to dissipate the heat from and ESD.
Although a resistive current block in an N+ drain has been described, a resistive current block created by an N+ implant through a P+ drain into a P-well on an N substrate could also be used to protect a P-channel transistor from ESD damage due to excessive heating from the current discharge. The process steps are similar although the material is of opposite type.


REFERENCES:
patent: 5219770 (1993-06-01), Shirato et al.
patent: 5416351 (1995-05-01), Ito et al.
patent: 5446302 (1995-08-01), Beigel et al.
patent: 5616943 (1997-04-01), Nguyen et al.
patent: 5637901 (1997-06-01), Beigel et al.
patent: 5677205 (1997-10-01), Williams et al.
patent: 5932897 (1999-06-01), Kawaguchi et al.

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