Method of forming flash memory with separate wordline and erase gates
A method of forming a non-volatile memory cell includes forming spaced apart first and second regions in a substrate, defining a channel region there between. A floating gate is formed over a first portion of the channel region and over a portion of the first region, wherein the floating gate includes a sharp edge disposed over the first region. A tunnel oxide layer is formed around the sharp edge. An erase gate is formed over the first region, wherein the erase gate includes a notch facing the sharp edge, and wherein the notch is insulated from the sharp edge by the tunnel oxide layer. A word line gate is formed over a second portion of the channel region which is adjacent to the second region. The forming of the word line gate is performed after the forming of the tunnel oxide layer and the erase gate.
1. A method of forming a non-volatile memory cell comprising:
forming, in a substrate of a first conductivity type, spaced apart first and second regions of a second conductivity type, defining a channel region there between;
forming a floating gate disposed over and insulated from a first portion of the channel region and over a portion of the first region, wherein the floating gate includes a sharp edge disposed over the first region;
forming a tunnel oxide layer around the sharp edge;
forming an erase gate over and insulated from the first region, wherein the erase gate includes a notch facing the sharp edge, and wherein the notch is insulated from the sharp edge by the tunnel oxide layer; and
forming a word line gate disposed over and insulated from a second portion of the channel region which is adjacent to the second region, wherein the forming of the word line gate is entirely performed after the forming of the tunnel oxide layer and the forming of the erase gate.
2. The method of claim 1 , wherein the forming of the second region is performed after the forming of the word line gate.
3. The method of claim 1 , wherein the forming of the word line gate includes:
forming a high K insulation layer over the substrate; and
forming a metal block over the high K insulation layer.
4. The method of claim 1 , wherein the forming of the word line gate includes:
forming a high K insulation layer over the substrate;
forming a polysilicon block over the high K insulation layer; and
removing and replacing the polysilicon block with a metal block.
5. The method of claim 1 , wherein the forming of the word line gate includes:
forming a conductive layer having a first portion disposed over and insulated from the second portion of the channel region, and a second portion disposed over and insulated from the erase gate; and
removing the second portion of the conductive layer.
6. The method of claim 5 , wherein the forming of the word line gate further includes:
forming an insulation spacer over the first portion of the conductive layer; and
removing a portion of the first portion of the conductive layer not disposed under the insulation spacer.
7. The method of claim 1 , wherein the forming of the floating gate includes:
forming a conductive layer over and insulated from the substrate;
forming a block of insulation material on the conductive layer; and
oxidizing an upper surface of the conductive layer leaving the upper surface sloping upwardly as the upper surface reaches the block of insulation material.
8. The method of claim 7 , wherein the forming of the floating gate further includes:
forming an insulation spacer along a sidewall of the erase gate and on the conductive layer; and
performing an etch of the conductive layer adjacent the insulation spacer.
9. The method of claim 7 , further comprising:
forming a trench into the substrate; and
filling the trench with first insulation material that extends out of the trench and above a surface of the substrate, wherein the forming of the trench and the filling of the trench are performed before the forming of the conductive layer.
10. The method of claim 9 , wherein the forming of the floating gate further includes:
performing a chemical mechanical polish on the upper surface of the conductive layer and an upper surface of the first insulation material before the oxidizing such that the upper surfaces of the conductive layer and the first insulation material are planar; and
removing and replacing an upper portion of the first insulation material with second insulation material.
11. The method of claim 10 , further comprising:
etching away the second insulation material and an upper portion of the first insulation material after the oxidizing.
12. The method of claim 9 , wherein the forming of the floating gate further includes:
removing and replacing a portion of the conductive layer over the first insulation material with second insulation material before the oxidizing.
13. The method of claim 12 , further comprising:
etching away the second insulation material and an upper portion of the first insulation material after the oxidizing.
14. The method of claim 9 , wherein the forming of the floating gate further includes:
forming a block of insulation material on a portion of the conductive layer disposed over the first insulation material before the oxidizing.
15. The method of claim 14 , further comprising:
etching away the block of insulation material, a portion of the conductive layer over the first insulation material, and an upper portion of the first insulation material after the oxidizing.