US 5,212,541 AGranted

Contactless, 5V, high speed EPROM/flash EPROM array utilizing cells programmed using source side injection

AssigneeNational Semiconductor Corporation

InventorAlbert M. Bergemont

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Abstract

The present invention provides a 5V only, EPROM memory cell structure that is utilizable in high speed UV-erasable or flash EPROM contactless arrays and that uses source side injection for programming. The EPROM cell structure comprises spaced-apart N-type source and drain regions that define a channel region in a P-type substrate. A first layer of insulating material overlies the channel region. A polysilicon (poly 1) floating gate is formed on the first insulating layer and overlies a first portion of the channel region that extends from the drain region to a point in the channel region intermediate the source and drain regions thereby defining a second portion of the channel region that extends from the intermediate point to the source region and over which the floating gate does not extend. The poly 1 floating gate also includes a coupling portion that extends over the field oxide that defines the active device area in which the EPROM cell is formed. A second layer of insulating material is formed over the floating gate, including the coupling portion of the floating gate. A polysilicon (poly 2) control gate overlies the floating gate but is separated therefrom by the second insulating layer. The poly 2 control gate includes an access portion that overlies the second portion of the channel region but is separated therefrom by the first layer of insulating material. A polysilicon (poly 2) coupling line overlies the coupling portion of the floating gate but is separated therefrom by the second insulating layer. This cell structure is utilized in a contactless array that relies on shared source lines, resulting in very small cell size and relatively simple decoding.

A contactless, 5V only EPROM cell array formed in a silicon substrate, the EPROM cell array comprising:

(a) an N+ source line formed in the silicon substrate;
(b) first and second N+drain lines formed in parallel with and spaced-apart from the source line on opposite sides of the source line to define respective first and second substrate channel regions therebetween;
(c) first and second field oxide strips formed in parallel with and spaced-apart from the first and second drain lines, respectively, such that the source line/drain line structure is isolated by the first and second field oxide strips to separate such structure from adjacent similar source/drain structures in the array;
(d) a layer of first insulating material formed over the channel regions;
(e) first and second array field oxide regions formed in the substrate between the first drain line and the source line and the second drain line and the source line, respectively;
(f) first and second floating gates formed on the first insulating material and overlying a first portion of the corresponding first and second channel regions, respectively, that extends from an edge of the corresponding drain region to an intermediate point of the channel region thereby defining a second portion at the channel region that extends from the intermediate point to an edge of the source line and over which the floating gate does not extend, the floating gate including a coupling portion that extends over the corresponding array field oxide region;
(g) a layer of second insulating material formed over the first and second floating gates, including the coupling portion thereof;
(h) a conductive control gate line overlying the first and second floating gates but separated therefrom by the layer of second insulating material and comprising first and second access portions overlying the second portion of the first and second channel regions, respectively, but separated therefrom by the layer of first insulating material;
and
(i) a conductive coupling line overlying the coupling portion of the first and second floating gates but separated therefrom by the layer of second insulating material.

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Abstract

Claims5