Method for adjusting the threshold of a read-only memory to achieve low capacitance and high breakdown voltage

Claim 1

A method of manufacturing a programmed memory cell of a read-only memory array comprising the steps of: defining an active area for a field effect memory element on a semiconductor substrate having a first conductivity type, the active area having a channel region, and a source region and a drain region on opposite sides of the channel region; forming a gate insulating layer overlying at least a portion of the active area; forming a gate electrode of uniform thickness overlying the gate insulating layer and positioned over the channel region; forming a programming mask having a programming mask aperture positioned over at least a portion of the source region; implanting a doping impurity of the first conductivity type into the semiconductor substrate through the programming mask aperture to program the memory cell; implanting a doping impurity of a second conductivity type into the gate electrode and into the source and drain regions, causing the gate electrode and the source and drain regions to be doped with the second conductivity type impurity; and heating the semiconductor substrate to diffuse the doping impurity of the first conductivity type into the channel region and of the second conductivity type into the gate electrode of the source region and the drain regions.

Claim 2

A method of manufacturing a programmed memory cell of a read-only memory array comprising the steps of: defining an active area for a field effect memory element on a semiconductor substrate having a first conductivity type, the active area having a channel region, and a source region and a drain region on opposite sides of the channel region; forming a gate insulating layer overlying at least a portion of the active area; forming a gate electrode of uniform thickness overlying the gate insulating layer and positioned over the channel region; forming a programming mask having a programming mask aperture positioned over at least a portion of the source region; implanting a doping impurity of the first conductivity type into the semiconductor substrate through the programming mask aperture to program the memory cell; implanting a doping impurity of a second conductivity type into the gate electrode and into the source and drain regions, causing the gate electrode and the source and drain regions to be doped with the second conductivity type impurity; and heating the semiconductor substrate to diffuse the doping impurity of the first conductivity type into the channel region and of the second conductivity type into the gate electrode of the source region and the drain regions.

Claim 4

A method of manufacturing a programmed memory cell of a read-only memory array comprising the steps of: defining an active area for a field effect memory element on a semiconductor substrate having a first conductivity type; forming a gate insulating layer upon the active area; forming a gate electrode upon the gate insulating layer and overlaying a channel region having a source region on one side thereof and a drain region on the other side thereof; forming a programming mask having a programming aperture that overlays at least a selected portion of the source region and does not overlay any portion of the channel region into which it is desired to introduce a doping impurity having the first conductivity type into the semiconductor substrate; and programming the memory cell by implanting a first doping impurity of the first conductivity type into the semiconductor substrate at the selected portions of the source region overlaid by the programming mask aperture to program the memory cell; implanting a second doping impurity of the second conductivity type into the substrate for forming the source and drain regions; and heating the semiconductor substrate to cause the doping impurity of the first conductivity type to diffuse laterally a distance into the channel region in the active area to program the memory cell.

Claim 5

A method of manufacturing a programmed memory cell of a read-only memory array comprising the steps of: defining an active area for a field effect memory element on a semiconductor substrate having a first conductivity type; forming a gate insulating layer upon the active area; forming a gate electrode upon the gate insulating layer and overlaying a channel region having a source region on one side thereof and a drain region on the other side thereof; forming a programming mask having a programming aperture that overlays at least a selected portion of the source region and does not overlay any portion of the channel region into which it is desired to introduce a doping impurity having the first conductivity type into the semiconductor substrate; and programming the memory cell by implanting a first doping impurity of the first conductivity type into the semiconductor substrate at the selected portions of the source region overlaid by the programming mask aperture to program the memory cell; implanting a second doping impurity of the second conductivity type into the substrate for forming the source and drain regions; and heating the semiconductor substrate to cause the doping impurity of the first conductivity type to diffuse laterally a distance into the channel region in the active area to program the memory cell.

Claim 8

The method according to either of claims 4 or 5 in which the distance the impurity of the first conductivity type is diffused into the channel region is greater than 10% of the channel length but less than 80% of the channel length.

Claim 9

The method according to either of claims 4 or 5 in which the distance the impurity of the first conductivity type is diffused into the channel region is less than 50% of the channel length.