Method of forming split gate memory cells
A method of forming a memory device includes forming a second insulation layer on a first conductive layer formed on a first insulation layer formed on semiconductor substrate. A trench is formed into the second insulation layer extending down and exposing a portion of the first conductive layer, which is etched or oxidized to have a concave upper surface. Two insulation spacers are formed along sidewalls of the trench, having inner surfaces facing each other and outer surfaces facing away from each other. A source region is formed in the substrate between the insulation spacers. The second insulation layer and portions of the first conductive layer are removed to form floating gates under the insulation spacers. A third insulation layer is formed on side surfaces of the floating gates. Two conductive spacers are formed along the outer surfaces. Drain regions are formed in the substrate adjacent the conductive spacers.
1. A method of forming a memory device, comprising:
forming a first insulation layer on an upper surface of a semiconductor substrate;
forming a first conductive layer on the first insulation layer;
forming a second insulation layer on the first conductive layer;
forming a trench into the second insulation layer that extends down to and exposes a portion of the first conductive layer;
etching or oxidizing the exposed portion of the first conductive layer such that the exposed portion has a concave upper surface;
forming first and second insulation spacers along sidewalls of the trench and over respective portions of the concave upper surface, wherein the first and second insulation spacers have inner surfaces that face each other and outer surfaces that face away from each other;
forming a source region in a portion of the substrate below and between the first and second insulation spacers;
removing the second insulation layer;
removing portions of the first conductive layer to form a first block of the first conductive layer under the first insulation spacer and a second block of the first conductive layer under the second insulation spacer;
forming a third insulation layer on side surfaces of the first and second blocks of the first conductive layer;
forming a first conductive spacer along the outer surface of the first insulation spacer, and a second conductive spacer along the outer surface of the second insulation spacer;
forming a first drain region in the substrate and adjacent to the first conductive spacer and a second drain region in the substrate and adjacent to the second conductive spacer.
2. The method of claim 1 , further comprising:
before the forming of the third insulation layer, removing portions of the first insulation layer such that a first portion of the first insulation layer remains under the first block of the first conductive layer and a second portion of the first insulation layer remains under the second block of the first conductive layer.
3. The method of claim 2 , wherein the forming of the third insulation layer includes forming the third insulation layer directly on portions of the substrate upper surface.
4. The method of claim 3 , wherein the first and second conductive spacers are insulated from the substrate by the third insulation layer, and are insulated from the first and second blocks of the first conductive layer by the third insulation layer.
5. The method of claim 1 , wherein the forming of the first and second conductive spacers comprises:
forming a second conductive layer over the substrate; and
performing an etch on the second conductive layer to remove portions of the second conductive layer, wherein the first and second conductive spacers are remaining spacers of the second conductive layer.
6. The method of claim 5 , wherein the forming of the second conductive layer further includes forming the second conductive layer over a logic area of the substrate, and wherein the method further comprises:
selectively removing portions of the second conductive layer to form a block of the second conductive layer over the logic area of the substrate;
forming a second source region in the substrate and adjacent to a first side of the block of the second conductive layer;
forming a third drain region in the substrate and adjacent to second side of the block of the second conductive layer opposite the first side.
7. The method of claim 6 , wherein the selectively removing portions of the second conductive layer is performed using the etch on the second conductive layer.
8. The method of claim 1 , wherein the forming of the source region comprises:
performing an implantation where particles are injected into the trench, through the first conductive layer, through the first insulation layer, and into the substrate.
9. The method of claim 1 , further comprising:
before the forming of the source region, removing a portion of the first conductive layer disposed below and between the first and second insulation spacers;
wherein the forming of the source region comprises performing an implantation where particles are injected into the trench, through the first insulation layer, and into the substrate.
10. The method of claim 1 , further comprising:
before the forming of the first and second conductive spacers, forming insulation material in the trench and between the inner surfaces of the first and second insulation spacers.
11. The method of claim 1 , wherein the etching or oxidizing the exposed portion of the first conductive layer is performed such that a portion of the first conductive layer at a center of the trench is entirely removed.