Method of late programming a read only memory

Details Method of late programming a read only memory Method of late programming a read only memory

1985-07-29

1987-03-17

Roy, Upendra

Metal working

Method of mechanical manufacture

Assembling or joining

29571, 148 15, 148187, 148DIG82, 357 236, 357 91, H01L 21265, B01J 1700, G11C 1140

Patent

active

046496297

ABSTRACT:
Transistors (10) having lateral gaps between their source and drain and the gate are interconnected in a ROM to receive program code.
In one embodiment of the invention (FIG. 3), the gaps of selected transistors (42) are subjected to a phosphorous implant (44) to create lightly doped n.sup.- regions (26,28) connecting the source (18) and drain (20) to the gate (14), and function normally. The other transistors (40) do not receive the phosphorous implant, and thus have a higher threshold voltage.
In another embodiment of the invention (FIG. 2) all of the transistors receive the phosphorous implant to create the n.sup.- regions (26,28) connecting the source and drain to the gate, and the n.sup.- regions of selected transistors (32) are counter-doped with a boron implant (34) so as to raise their threshold voltages, while the other transistors (30) are not counter-doped and function normally.
In both embodiments, programming can occur late in the processing of the ROM.

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Ohkura et al., IEEE Trans. Electron Devices, ED-26, (1979) 430.
Dill et al., Radiation Effects, 7 (1971) 45.

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