Method of forming split-gate, twin-bit non-volatile memory cell
A memory device that includes a substrate of semiconductor material of a first conductivity type, first and second regions spaced apart in the substrate and having a second conductivity type different than the first conductivity type, with a continuous channel region in the substrate extending between the first and second regions. A first floating gate is disposed over and insulated from a first portion of the channel region adjacent to the first region. A second floating gate is disposed over and insulated from a second portion of the channel region adjacent to the second region. A word line gate is disposed over and insulated from a third portion of the channel region between the first and second channel region portions. A first erase gate disposed over and insulated from the first region. A second erase gate disposed is over and insulated from the second region.
1. A method of forming a pair of non-volatile memory cells comprising:
forming a first insulation layer on a semiconductor substrate;
forming a first polysilicon layer on the first insulation layer in a first polysilicon deposition process;
forming spaced apart first and second insulation blocks on the first polysilicon layer, the first insulation block having a first side facing the second insulation block and a second side facing away from the second insulation block, and the second insulation block having a first side facing the first insulation block and a second side facing away from the first insulation block;
removing a portion of the first polysilicon layer disposed between the first and second insulation blocks while maintaining portions of the first polysilicon layer disposed underneath the first and second insulation blocks and adjacent the second sides of the first and second insulation blocks;
removing the portions of the first polysilicon layer adjacent the second sides of the first and second insulation blocks while maintaining a pair of polysilicon blocks of the first polysilicon layer each disposed under one of the first and second insulation blocks;
forming a first drain region in the substrate and adjacent the second side of the first insulation block;
forming a second drain region in the substrate and adjacent the second side of the second insulation block;
forming a second polysilicon layer over the substrate and the first and second insulation blocks in a second polysilicon deposition process; and
removing portions of the second polysilicon layer while maintaining a first polysilicon block, a second polysilicon block and a third polysilicon block of the second polysilicon layer, wherein:
the first polysilicon block is disposed between the first and second insulation blocks,
the second polysilicon block is disposed over the first drain region, and
the third polysilicon block is disposed over the second drain region;
wherein the substrate includes a continuous channel region extending between the first and second drain regions.
2. The method of claim 1 , wherein one of the pair of polysilicon blocks is partially disposed over and insulated from the first drain region, and the other one of the pair of polysilicon blocks is partially disposed over and insulated from the second drain region.
3. The method of claim 1 , wherein the second polysilicon block includes a notch facing an edge of the first floating gate, and wherein the second erase gate includes a notch facing an edge of the second floating gate.
4. The method of claim 1 , further comprising:
forming a fourth polysilicon block that is disposed over and insulated from one of the pair of polysilicon blocks and under the first insulation block;
forming a fifth polysilicon block that is disposed over and insulated from the other one of the pair of polysilicon blocks and under the second insulation block.
5. The method of claim 1 , further comprising:
removing the first polysilicon block;
forming a metal block between the first and second insulation blocks; and
forming a layer of high-K insulation material between the metal block and the substrate and between the metal block and the first and second insulation blocks.
6. The method of claim 1 , wherein the first and second insulation blocks are spacers.
7. The method of claim 1 , wherein before the forming of the first and second insulation blocks, further comprising:
performing a poly slope etch to an upper surface of the first polysilicon layer, such that the upper surface included downwardly sloping portions, wherein the first and second insulation blocks are formed on the sloping portions.
8. A method of forming a pair of non-volatile memory cells comprising:
forming a first insulation layer on a semiconductor substrate;
forming a first polysilicon layer on the first insulation layer in a first polysilicon deposition process;
forming an insulation layer stack on the first polysilicon layer;
forming a second polysilicon layer on the insulation layer stack;
forming spaced apart first and second insulation blocks on the second polysilicon layer, the first insulation block having a first side facing the second insulation block and a second side facing away from the second insulation block, and the second insulation block having a first side facing the first insulation block and a second side facing away from the first insulation block;
removing portions of the second polysilicon layer, the insulation layer stack and the first polysilicon layer disposed between the first and second insulation blocks and adjacent the second sides of the first and second insulation blocks, while maintaining a pair of polysilicon blocks of the first polysilicon layer each disposed under one of the first and second insulation blocks;
forming a first drain region in the substrate and adjacent the second side of the first insulation block;
forming a second drain region in the substrate and adjacent the second side of the second insulation block;
forming a third polysilicon layer over the substrate and the first and second insulation blocks in a second polysilicon deposition process; and
removing portions of the third polysilicon layer while maintaining a first polysilicon block, a second polysilicon block and a third polysilicon block of the third polysilicon layer, wherein:
the first polysilicon block is disposed between the first and second insulation blocks,
the second polysilicon block is disposed over the first drain region, and
the third polysilicon block is disposed over the second drain region;
wherein the substrate includes a continuous channel region extending between the first and second drain regions.
9. The method of claim 8 , further comprising:
forming first insulation between the first polysilicon block and the pair of polysilicon blocks;
forming second insulation between the second polysilicon block and one of the pair of polysilicon blocks;
forming third insulation between the third polysilicon block and the other of the pair of polysilicon blocks;
wherein the first insulation is thicker than the second insulation and the third insulation.