Reduction of electric field effect in the bird's beak region of

Details Reduction of electric field effect in the bird's beak region of Reduction of electric field effect in the bird's beak region of

1989-02-24

1990-09-25

Chaudhuri, Olik

Fishing, trapping, and vermin destroying

437 47, 357 236, H01L 21425, H01L 2996

Patent

active

049593250

ABSTRACT:
The present invention constitutes an improvement of the Local Encroachment Reduction (LER) process developed by Tyler Lowrey at Micron Technology, Inc. of Boise, Idaho. LER consists of selectively etching a portion of the field oxide which has encroached into a DRAM cell's active area and then subjecting the cell to a high-energy boron implant to maintain adequate active area isolation. Although the boron implant effectively decreases the width of the depletion region between n+ active areas and p+ substrate, it has the undesirable effect of reducing the breakdown voltage at the n-p junctions in the bird's beak regions at the edges of the active regions, thus increasing the cell's susceptibility to gated-diode breakdown following creation of the cell plate. The present invention solves this problem by creating a graded junction in the bird's beak regions of the cell. The graded junction reduces the electric field intensity in the junction region, resulting in an increase in the breakdown voltage. The graded junction also minimizes the effect of gated-diode breakdown and band-band tunneling leakage.

REFERENCES:
patent: 4414058 (1983-11-01), Mueller
patent: 4637128 (1987-01-01), Mizutani
patent: 4642880 (1987-02-01), Mizutani
patent: 4830974 (1989-05-01), Chang et al.

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