Method to fabricate a non-smiling effect structure in split-gate flash with self-aligned isolation
AssigneeTaiwan Semiconductor Manufacturing Company, Ltd.
InventorsYai-Fen Lin, Chang Song Lin, Chia-Ta Hsieh, Hung-Cheng Sung, Juang-Ke Yeh
Life of this patent
Estimating the term…
Abstract
A method is provided for forming a split-gate flash memory cell having a shallow trench isolation without the intrusion of a “smiling” gap near the edge of the trench encompassing the first polysilicon layer. This is accomplished by forming two conformal layers lining the interior walls of the trench. An exceptionally thin nitride layer overlying the first conformal oxide layer provides the necessary protection during the oxidation of the first polysilicon layer so as to prevent the “smiling” effect normally encountered in fabricating ultra large scale integrated circuits.
Claims36
A method of forming a split-gate flash memory having a non-smiling trench isolation comprising the steps of:
- providing a semiconductor substrate;
- forming a gate oxide layer over said substrate;
- forming a first polysilicon layer over said gate oxide layer;
- forming a pad oxide layer over said first polysilicon layer;
- forming a first nitride layer over said pad oxide layer;
- forming and patterning a first photoresist layer over said first nitride layer to define active regions in said substrate;
- forming a trench in said substrate by etching through patterns in said first photoresist layer;
- removing said first photoresist layer;
- forming a first conformal lining on the inside walls of said trench;
- forming a second conformal lining over said first conformal lining on the inside walls of said trench;
- depositing isolation oxide inside said trench to from shallow trench isolation (STI);
- performing chemical-mechanical polishing of said substrate;
- removing said first nitride layer;
- removing said pad oxide layer;
- forming second nitride layer over said substrate;
- forming and patterning a second photoresist layer over said second nitride layer to define floating gate;
- etching through patterns in said second photoresist layer to form openings in said second nitride layer exposing portions of said first polysilicon layer;
- removing said second photoresist layer;
- performing thermal oxidation of exposed said portions of said first polysilicon layer through said openings in said second nitride layer to form polyoxide hard mask;
- removing said second nitride layer;
- etching said first polysilicon layer using said polyoxide as a hard mask;
- forming intergate oxide layer;
- forming a second polysilicon layer over said intergate oxide layer;
- forming and patterning a third photoresist layer over said second intergate oxide layer to define control gate;
- and
- etching through said patterning in third potoresist layer to complete the forming of said split-gate flash memory.
A method of forming a split-gate flash memory having a non-smiling trench isolation comprising the steps of:
- providing a semiconductor substrate;
- forming a trench;
- forming a first conformal lining on the inside walls of said trench;
- forming a second conformal lining over said first conformal lining on the inside walls of said trench;
- forming conformal spacers;
- depositing isolation oxide inside said trench to from shallow trench isolation (STI);
- forming a floating gate;
- forming an intergate oxide;
- and
- forming a control gate to complete the forming of the split-gate flash memory cell.
A split-gate flash memory having a non-smiling trench isolation comprising:
- a floating gate;
- a trench;
- two conformal layers lining the inside walls of said trench;
- and
- a control gate.
Dependencies are inferred from the claim text.