Method for forming voltage-invariant capacitors for MOS type integrated circuit device utilizing oxidation and reflow techniques

Claim 1

A method for fabricating a semiconductor device having MOS transistors and voltage invariant capacitors comprising the steps of: forming on a silicon substrate, pairs of preselected diffused regions having the opposite conductivity from that of said substrate and field oxide regions adjacent said diffused regions; forming a layer of conductive material in gate areas between diffused regions of said pairs and in preselected areas on said field oxide regions; covering said substrate, including said diffused regions, said areas of conductive material and said field oxide, with a layer of phosphorous doped oxide; forming openings in said layer of phosphorous doped oxide, including contact areas, aligned with preselected diffused regions and also, preselected capacitor areas of said layer of conductive material on said field oxide; reflowing said phosphorous doped oxide by heating in an oxygen ambient to reduce sharp edges at said openings and simultaneously grow a thin oxide layer in said contact and capacitor areas; removing the thin oxide layer in said contact areas; providing a layer of metal in said contact areas and also in said capacitor areas, thereby forming the upper conductor plate of the capacitor.

Claim 2

A method for fabricating a semiconductor device having MOS transistors and voltage invariant capacitors comprising the steps of: forming on a silicon substrate, pairs of preselected diffused regions having the opposite conductivity from that of said substrate and field oxide regions adjacent said diffused regions; forming a layer of conductive material in gate areas between diffused regions of said pairs and in preselected areas on said field oxide regions; covering said substrate, including said diffused regions, said areas of conductive material and said field oxide, with a layer of phosphorous doped oxide; forming openings in said layer of phosphorous doped oxide, including contact areas, aligned with preselected diffused regions and also, preselected capacitor areas of said layer of conductive material on said field oxide; reflowing said phosphorous doped oxide by heating in an oxygen ambient to reduce sharp edges at said openings and simultaneously grow a thin oxide layer in said contact and capacitor areas; removing the thin oxide layer in said contact areas; providing a layer of metal in said contact areas and also in said capacitor areas, thereby forming the upper conductor plate of the capacitor.