Process for producing a very high density mask ROM

Details Process for producing a very high density mask ROM Process for producing a very high density mask ROM

1994-04-08

1995-07-04

Chaudhuri, Olik

Fishing, trapping, and vermin destroying

437 45, 437 52, H01L 21265

Patent

active

054299675

ABSTRACT:
A process of fabricating a mask type ROM is described wherein second type impurity ions are implanted into a semiconductor substrate having a first opposite type background impurity to form a depletion region adjacent the surface. A plurality of parallel nitride lines are formed on the surface, and a first gate oxide formed on the spaces between the nitride lines. Subsequently, a first layer of doped polycrystalline silicon is deposited over the nitride lines, and the layer etched back to expose the top surfaces of the nitride lines. After the nitride lines are removed, a thin gate oxide layer is formed on the exposed surface of the substrate, and on the surfaces of the resultant first polycrystalline gate electrode lines. A second layer of doped polycrystalline silicon is deposited over the polycrystalline silicon lines, and it is etched back. The etch back of the first, and also the second polycrystalline silicon layers, produces an elongated central depression in each of the resultant lines. Then a layer of insulating material is deposited over the surface. A photoresist layer is deposited on the surface of the insulating layer, exposed, and developed to define the desired code implant pattern.

REFERENCES:
patent: 4959812 (1990-09-01), Momodomi et al.
patent: 5081052 (1992-06-01), Kobayashi et al.
patent: 5094971 (1992-03-01), Kanebako
patent: 5149667 (1992-09-01), Choi
patent: 5264386 (1993-11-01), Yang
patent: 5279982 (1994-01-01), Crotti

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