Patent ID: 6165845
Filing Date: 2000-12-26
Classification: H01L

Abstract:
A method of forming a sharp poly tip in a split-gate flash memory cell comprising the steps of:providing a silicon substrate having a plurality of active and field regions defined;forming a pad oxide layer over said substrate;forming a nitride layer over said pad oxide layer;forming and patterning a first photoresist layer over said pad oxide layer to form a photoresist mask with a pattern corresponding to the floating gate of said split-gate flash memory cell;etching said nitride layer through said photoresist mask to form an opening with a tapered profile reaching said pad oxide layer underlying said nitride layer;removing said first photoresist layer;removing said pad oxide layer exposed at the bottom of said opening with a tapered profile in said nitride layer;growing gate oxide layer at the bottom of said opening with said tapered profile in said nitride layer;forming a first polysilicon layer over said substrate including said opening with a tapered profile;performing chemical-mechanical polishing (CMP) of said first polysilicon layer;oxidizing said fist polysilicon layer formed in said opening with a tapered profile, thus forming a sharp poly tip at the edge of said opening;removing said nitride layer;removing said pad oxide layer;forming an interpoly oxide layer over said substrate;forming a second polysilicon layer over said interpoly oxide; andpatterning said second polysilicon layer with a second photoresist mask having control gate pattern to form a control gate to complete the forming of said split-gate flash memory cell having said sharp poly tip.