Floating gate memory device having discontinuous gate oxide thic

Details Floating gate memory device having discontinuous gate oxide thic Floating gate memory device having discontinuous gate oxide thic

1994-05-16

1995-08-22

Prenty, Mark V.

Active solid-state devices (e.g., transistors, solid-state diode

Field effect device

Having insulated electrode

257325, 257335, 257401, 257406, H01L 2968

Patent

active

054442796

ABSTRACT:
A method and structure for a programmable read-only memory comprises a thin gate oxide over a source region and a thick gate oxide over the drain region. A semiconductor substrate is lightly doped and has regions of thin sacrificial oxide overlying what will become the transistor channel, source, and drain, and thick field oxide. The region that will become the transistor source is protected with photoresist, and the drain region and a portion of the channel is doped, for example, with boron. The resist and sacrificial oxide is stripped, and gate oxide is formed from the exposed silicon substrate. The more heavily doped drain and channel regions oxidize at a faster rate than the lightly doped source region, and thus the gate oxide formed is thicker. Floating and control gates are formed over the channel region, covering both the thicker and thinner gate oxide. The cell resulting from the process has increased coupling coefficient, easier programmability, and better storage of the charge on the floating gate than a conventional cell.

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