Method for improving erase characteristics of buried bit line fl

Details Method for improving erase characteristics of buried bit line fl Method for improving erase characteristics of buried bit line fl

1991-01-17

1991-12-24

Hearn, Brian E.

Fishing, trapping, and vermin destroying

437 69, 437241, 437941, 148DIG114, H01L 21265, H01L 2176

Patent

active

050752456

ABSTRACT:
A process for fabricating contactless electrically programmable and electrically erasable memory cells of the flash EPROM type. The cells use elongated source and drain regions disposed beneath field oxide regions. Ammonia formed during the field oxidation process reacts with the silicon substrate to form a thin silicon nitride layer in the beak region. A thin tunnel oxide is then grown without the use of a sacrificial-oxide growth and removal method. During tunnel oxide formation lateral growth of the field oxide is inhibited by the thin nitride layer previously formed. However, the tunnel oxide thinning (due to the existence of the thin nitride layer) induced low breakdown voltage is overcome by the enhanced oxide growth in the beak due to the buried source/drain dopants. The tunnel oxide in the erase regon is therefore uniform and thin. The thin, uniform oxide in the tunnel region leads to improved erase characteristics.

REFERENCES:
patent: 4401691 (1983-08-01), Young
patent: 4780424 (1988-10-01), Holler et al.
patent: 4968641 (1990-11-01), Kalnitsky et al.
Kooi et al., "Formation if Silicon Nitride . . . Oxidized Silicon in NH.sub.3 Gas", Jnl. of Electrochemical, Soc., vol. 123, No. 7, pp. 1117-1120, 1976.
Itsumi et al., "Identification and Elimination . . . Field Oxidation", Jnl. of Electrochemical Soc., vol. 129, No. 4, pp. 800-806, Apr. 1982.
Shankoff et al., "Bird's Beak . . . Oxidation", Jnl. of Electrochemical Soc., vol. 127, No. 1, pp. 216-222, Jan. 1980.

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