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Three Mask Process for IGFET Fabrication

IP.com Disclosure Number: IPCOM000075737D
Original Publication Date: 1971-Nov-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Kaplan, LH: AUTHOR [+2]

Abstract

The most critical steps in conventional insulated gate field-effect transistor (IGFET) fabrication processes with regard to final yield are the photolithographic patterning, or masking step. Normally, four such steps are required to produce the basic device. The process described produces it in only three masking steps, with correspondingly higher potential yield.

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Three Mask Process for IGFET Fabrication

The most critical steps in conventional insulated gate field-effect transistor (IGFET) fabrication processes with regard to final yield are the photolithographic patterning, or masking step. Normally, four such steps are required to produce the basic device. The process described produces it in only three masking steps, with correspondingly higher potential yield.

A blanket gate oxide layer is thermally grown and then covered with a silicon nitride layer having a thickness greater than about 200 angstroms. Holes are opened by photolithography in these layers and source/drain diffusion is performed. Another layer of silicon nitride similar in thickness to the first layer is deposited and photolithographically patterned to leave the nitride only in the gate and contact hole areas. Thermal oxidation is then performed, with the nitride layer limiting thick oxide growth only to the desired areas. The nitride is then removed (without the use of photoresist) using an etchant which does not attack the underlying oxide. A usable etchant for this purpose is molten monobasic ammonium phosphate. Phosphosilicate glass (PSG) stabilization of the gate oxide may then be accomplished, if desired, by depositing a layer of PSG thereover. Metal deposition is then performed and the metal film patterned photolithographically. All diffusion and oxidation processes used may be standard process steps and need not be changed to gain the advantage o...