Late mask process for programming read only memories

Details Late mask process for programming read only memories Late mask process for programming read only memories

1983-07-19

1985-04-30

Roy, Upendra

Metal working

Method of mechanical manufacture

Assembling or joining

29571, 29578, 148187, 357 91, 357 236, H01L 21265, B01J 1700

Patent

active

045134944

ABSTRACT:
A late mask programming process is provided for factory programmed ROMs or logic circuitry. MOS transistors functioning as ROM cells or in logic circuitry are fabricated by a standard MOS Process. Then, a thin stop layer of silicon nitride is provided over the transistors followed by a layer of silicon dioxide. Programming is accomplished by applying a program mask and etching through the layers overlying the gate regions of selected transistors down to the silicon nitride stop layer. The silicon nitride stop layer prevents overetching and shorting of the gates. Then, ions are implanted underneath the gates of the selected MOS transistors to alter their threshold so, for example, as ROM cells they signify a different state than those cells whose transistor gates are not implanted with ions. The silicon nitride layer serves to stop the etch solution but permits the ions to pass through, penetrate the substrate and raise the thresholds of the selected transistors. The silicon dioxide layer stops the ions from being implanted into the nonselected transistors.

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patent: 4384399 (1983-05-01), Kuo
patent: 4406049 (1983-09-01), Tam et al.

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