Ldd method of coding mask rom device and ldd coded mask rom device

Abstract

A CMOS Mask ROM semiconductor device is formed in P-well NMOS region of a silicon semiconductor substrate with FOX regions on the surface thereof. A method of forming the device includes forming gate oxide over the substrate between FOX regions; forming a control gate layer over the gate oxide. Then form a gate mask over the device with and pattern a gate electrode and the gate oxide layer by etching through mask openings. Next, form an LDD mask over the device exposing the gate. Ion implant a P type dopant of a first dosage level through mask openings forming reverse type LDD implant doped P type regions. Form spacers adjacent to the electrode over the substrate. Ion implant an N type dopant of a second dosage level through the opening in the mask and aside from the spacers and the electrode into exposed portions of the substrate. The N type doped regions are thus self-aligned with the spacers and the gate and they provide a second dosage level in the substrate, the second dosage level being substantially different from the first dosage level.