Method of fabricating EEPROM using oblique implantation
First Claim
1. A process for fabricating a semiconductor memory device comprising the steps of:
- (i) defining a device formation region comprising a plurity of memory cell transistor on a semiconductor substrate of a first conductivity type, and forming a tunnel oxide film, a floating gate, an insulating film and a control gate in this order;
wherein the plurality of memory cell transistors share a source region with a memory cell transistor disposed adjacent thereto on one side thereof and a drain region with a memory cell transistor disposed adjacent thereto on the other side thereof;
(ii) performing a first oblique ion implantation process employing an ion implantation angle of θ
with respect to a normal line to the semiconductor substrate and a second oblique ion implantation employing an ion implantation angle of -θ
°
, using the floating gate and the control gate as a mask, to form a high-concentration impurity layer of the first conductivity type in a portion adjacent to a drain formation region below the floating gate, the angle θ
being defined by the following expression;
0<
tan-1 (Ld/Hg)<
θ
<
tan-1 (Ls/Hg)<
π
/2wherein Ls is a distance between gates of the adjacent transistors sharing the source region, Ld is a distance between gates of the adjacent transistors sharing the drain region, and Hg is a total height of at least the floating gate, the insulating film and the control gate on the tunnel oxide film; and
iii) implanting ions into the semiconductor substrate from a direction generally normal to the semiconductor substrate by using the floating gate and the control gate as a mask to form source/drain regions of a second conductivity type.
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Accused Products
Abstract
A semiconductor memory device is provided which comprises: a plurality of memory cell transistors each having a tunnel oxide film formed on a semiconductor substrate of a first conductivity type, a floating gate formed on the tunnel oxide film, a control gate overlaid on the floating gate with intervention of an insulating film, source/drain regions of a second conductivity type formed in the semiconductor substrate, and a high-concentration impurity layer of the first conductivity type formed in a portion adjacent to the drain region below the floating gate by oblique ion implantation employing an implantation angle θ with respect to a normal line to the semiconductor substrate; the plurality of memory cell transistors each sharing a source region with a memory cell transistor disposed adjacent thereto on one side thereof and a drain region with a memory cell transistor disposed adjacent thereto on the other side thereof; the implantation angle θ being defined by the following expression:
0<tan-1 (Ld/Hg)<θ<tan-1 (Ls/Hg)<π/2
wherein Ls is a distance between gates of the adjacent transistors sharing the source region, Ld is a distance between gates of the adjacent transistors sharing the drain region, and Hg is a total height of the floating gate, the insulating film and the control gate on the tunnel oxide film.
65 Citations
4 Claims
-
1. A process for fabricating a semiconductor memory device comprising the steps of:
-
(i) defining a device formation region comprising a plurity of memory cell transistor on a semiconductor substrate of a first conductivity type, and forming a tunnel oxide film, a floating gate, an insulating film and a control gate in this order;
wherein the plurality of memory cell transistors share a source region with a memory cell transistor disposed adjacent thereto on one side thereof and a drain region with a memory cell transistor disposed adjacent thereto on the other side thereof;(ii) performing a first oblique ion implantation process employing an ion implantation angle of θ
with respect to a normal line to the semiconductor substrate and a second oblique ion implantation employing an ion implantation angle of -θ
°
, using the floating gate and the control gate as a mask, to form a high-concentration impurity layer of the first conductivity type in a portion adjacent to a drain formation region below the floating gate, the angle θ
being defined by the following expression;0<
tan-1 (Ld/Hg)<
θ
<
tan-1 (Ls/Hg)<
π
/2wherein Ls is a distance between gates of the adjacent transistors sharing the source region, Ld is a distance between gates of the adjacent transistors sharing the drain region, and Hg is a total height of at least the floating gate, the insulating film and the control gate on the tunnel oxide film; and iii) implanting ions into the semiconductor substrate from a direction generally normal to the semiconductor substrate by using the floating gate and the control gate as a mask to form source/drain regions of a second conductivity type. - View Dependent Claims (2, 3, 4)
-
Specification