Patent ID: 6017795
Filing Date: 2000-01-25
Classification: H01L

Abstract:
A method of forming buried source in a memory cell to increase the coupling ratio for improved program speed comprising the steps of:providing a silicon substrate having a plurality of active and field areas defined;forming a pad oxide layer over said substrate;depositing a first layer of nitride over said pad oxide layer;forming a first patterned photoresist mask over said layer of nitride, wherein said patterns correspond to source regions formed in said active areas of said silicon substrate;etching said first layer of nitride and said pad oxide through openings in said patterned photoresist mask;etching further to form a source line trench in said silicon substrate;removing said firs t photoresist mask;performing a partial selective epitaxial growth (SEG) in said trench;forming a source region in said SEG in said trench over said active regions;removing said first layer of nitride and pad oxide layer;forming a sacrificial oxide over said substrate;removing said sacrificial oxide;forming a layer of gate oxide over said substrate;depositing a first layer of polycrystalline silicon (polysilicon) over said substrate;depositing a second layer of nitride over said first layer of polycrystalline silicon;forming a second patterned photoresist mask over said second layer of nitride;etching said second layer of nitride and said gate oxide through openings in said second patterned photoresist mask;performing ion implantation through said openings in said second patterned photoresist mask;removing said second photoresist mask;performing thermal oxidation of said first layer of polysilicon to form polyoxide and define a floating gate of said memory cell;removing said second layer of nitride;etching said first layer of polysilicon using said polyoxide as a hard mask;forming interpoly oxide over said polyoxide;depositing a second layer of polysilicon over said interpoly oxide; andpatterning said second layer of polysilicon to form a control gate to complete the forming of said memory cell.