Patent ID: 6312989
Filing Date: 2001-11-06
Classification: H01L

Abstract:
A method of forming a split-gate flash with a protruding source structure comprising the steps of:providing a semiconductor substrate having passive and active regions defined;forming a pad oxide layer over said substrate;forming a nitride layer over said pad oxide layer;forming an opening in said first nitride layer to form a source region in said substrate;performing ion implantation to form said source region in said substrate;forming a first polysilicon (Poly-1) layer in said opening to form a protruding source structure over said source region;forming a first poly-oxide layer over said Poly-1 layer;removing said nitride layer on said substrate;removing said pad oxide layer on said substrate;forming a floating gate oxide layer over said substrate, including over said protruding source structure;forming a second polysilicon (Poly-2) layer to form a floating gate over said floating gate oxide layer;removing portions of said Poly-2 layer over said substrate to isolate active regions;forming a second poly-oxide layer over said Poly-2 layer over said substrate including over said protruding source structure by oxidizing an upper part of said Poly-2 layer while leaving a lower part of said Poly-2 unoxidized to form said floating gate;removing a portion of said second poly-oxide layer, thus leaving said Poly-2 layer over said substrate partially exposed in regions other than over said protruding source structure;removing said partially exposed Poly-2 layer, and the underlying gate oxide layer;forming an inter-gate oxide layer over said substrate;forming a sharp poly-tip in said second Poly-2 layer;forming a third polysilicon (Poly-3) layer over said inter-gate oxide layer;forming a Poly-3 spacer over said inter-gate oxide layer on the vertical walls of said protruding source structure to form a spacer control gate; andperforming ion implantation to form a drain region of said flash cell having said protruding source structure.