Method of making split gate non-volatile flash memory cell
A method of forming a non-volatile memory cell on a substrate having memory cell and logic circuit regions by forming a pair of conductive floating gates in the memory cell region, forming a first source region in the substrate between the pair of floating gates, forming a polysilicon layer in both regions, forming an oxide layer over the polysilicon layer in the logic circuit region, performing a chemical-mechanical polish of the polysilicon layer in the memory cell area leaving a first block of the polysilicon layer between the floating gates that is separated from remaining portions of the polysilicon layer, and selectively etching portions of the polysilicon layer to result in: second and third blocks of the polysilicon layer disposed in outer regions of the memory cell area, and a fourth block of the polysilicon layer in the logic circuit region.
1. A method of forming a non-volatile memory cell comprising:
providing a semiconductor substrate having a memory cell region and a logic circuit region;
forming a pair of conductive floating gates disposed over and insulated from the memory cell region of the substrate;
forming a first source region in the substrate between the pair of floating gates;
forming a polysilicon layer over and insulated from the substrate in the memory cell region and the logic circuit region, wherein the polysilicon layer extends up and over, and is insulated from, the pair of conductive floating gates;
forming an oxide layer over the polysilicon layer in the memory cell and logic circuit regions;
forming a BARC layer over the oxide layer in the memory cell and logic circuit regions;
removing portions of the BARC layer disposed over the floating gates while maintaining portions of the BARC layer spaced apart from the floating gates in the memory cell region and disposed in the logic circuit region;
removing portions of the oxide layer disposed over the floating gates;
removing remaining portions of the BARC layer;
after the removing of the remaining portions of the BARC layer, performing a chemical mechanical polish on the polysilicon layer to remove portions of the polysilicon layer vertically over the floating gates such that a first block of the polysilicon layer between the floating gates and over the first source region is separated from remaining portions of the polysilicon layer;
performing a first polysilicon etch to lower an upper surface of the first block of the polysilicon layer;
removing remaining portions of the oxide layer;
selectively etching portions of the polysilicon layer to result in:
a second block of the polysilicon layer disposed over the substrate with one of the pair of floating gates disposed between the first and second blocks of the polysilicon layer,
a third block of the polysilicon layer disposed over the substrate with the other of the pair of floating gates disposed between the first and third blocks of the polysilicon layer, and
a fourth block of the polysilicon layer disposed over and insulated from the logic circuit region of the substrate;
forming a first drain region in the substrate adjacent a side of the second block of the polysilicon layer;
forming a second drain region in the substrate adjacent a side of the third block of the polysilicon layer;
forming a third drain region in the substrate adjacent a first side of the fourth block of the polysilicon layer; and
forming a second source region in the substrate adjacent a second side of the fourth block of the polysilicon layer opposite the first side of the fourth block.
2. The method of claim 1 , further comprising:
forming a pair of conductive control gates each disposed over and insulated from one of the floating gates.