Static information storage and retrieval – Floating gate – Particular biasing
Patent
1985-05-01
1986-06-24
Fears, Terrell W.
Static information storage and retrieval
Floating gate
Particular biasing
365189, G11C 1140
Patent
active
045970602
ABSTRACT:
Using a method according to one embodiment of the present invention, an EPROM array may be fabricated providing a dense EPROM array.
First the polycrystalline silicon floating gates are formed and partially patterned on the surface of a substrate. A thin thermally grown oxide layer is then formed over the entire array. The source/drain regions are then implanted through the thin silicon dioxide layer into the substrate. Next a thick silicon dioxide layer is deposited by chemical vapor deposition on the surface of the array. The surface of the array is then coated with photoresist which, because of its nature, provides a planarized surface on the top layer of photoresist. The photoresist and the silicon dioxide layer are then etched using an etching process which provides an etching ratio of 1 to 1 between photoresist and silicon dioxide. The photoresist is completely etched away thus leaving the planarized silicon dioxide surface. The silicon dioxide layer is then further etched so that the top surfaces of the floating gates are exposed. An interlevel insulator layer is then formed on the surface of the array and the active gates are then formed on the surface of the interlevel insulator.
In another embodiment of the present invention, a step for forming refractory metal silicide regions on the bitlines of the array is included. The use of silicided bitlines in this type of array is precluded in the prior art because thick field oxide regions must be thermally grown over the silicided regions using the prior art techniques. The growth of silicon dioxide over silicided regions is very difficult if not impossible.
REFERENCES:
patent: 4532535 (1985-06-01), Gerber
Mitchell Allan T.
Paterson James L.
Fears Terrell W.
Groover III Robert
Sharp Melvin
Sorensen Douglas A.
Texas Instruments Incorporated
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