National Semiconductor Corporation

Chih-Sieh Teng

Tian-I Liou

Albert M Bergemont

Min-hwa Chi

Hiekyung Chun-Min

A CMOS device that includes three-volt MOS transistor, five-volt MOS transistors, FLASH EPROM cells, poly resistors, and double-poly capacitors is formed in a single integrated CMOS process flow. The FLASH EPROM cells are formed as single-transistor memory cells that operate on low to very-low voltages.

Method for forming a mixed-signal CMOS circuit that includes

The present process comprises the use of a differential oxidation of the source/drain regions to permit elimination of the p+ implant mask normally required for formation of p-channel device in a CMOS process. A DDD procedure provides protection against hot-electron effects. A second oxide spacer is included to allow formation of salicide at the contacts to provide low sheet resistance.

Salicide compatible CMOS process with a differential oxide implant mask

The present process comprises the use of a blanket phosphorus (n-) implant coupled with a masked boron (P+) implant to permit the elimination of the conventional N+ implant and the LDD masks. The use of the blanket n- implant and the masked p+ implant allows production of an n- drain region which reduces hot-electron-induced degradation and a low concentration S/D region which is subsequently more easily counterdoped by a high concentration implant. A shallow blanket n+ implant is included prior to the P+ mask step to prevent contact resistance problems. Thereafter in the process of this invention, a salicide is formed at the sources and drains to produce a low sheet resistance in the contacts of the n-channel devices, notwithstanding the absence of the conventional thick n+ layer.

Double-diffused drain CMOS process using a counterdoping technique

An N+ poly-to-N+ silicon capacitor structure is provided by adding a single mask step to a standard CMOS process flow. The capacitor oxide between the N+ poly plate and the N+ silicon plate is grown simultaneously with gate oxide for the MOSFET devices. A high dose, deep phosphorous implant is employed to form the N+ substrate plate. This results in an excellent capacitance voltage coefficient. The resulting thin interplate oxide leads to high capacitance per unit area and, thus, small die size.

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San Jose, CA, United States of America

Chih-Sieh Teng