Method of manufacturing a split-gate flash memory cell with erase gate
View Patent ↗A method of forming a memory device with memory cells in a memory area, and logic devices in first and second peripheral areas. The memory cells each include a floating gate, a word line gate and an erase gate, and each logic device includes a gate. The oxide under the word line gate is formed separately from a tunnel oxide between the floating and erase gates, and is also the gate oxide in the first peripheral area. The word line gates, erase gates and gates in both peripheral areas are formed from the same polysilicon layer. The oxide between the erase gate and a source region is thicker than the tunnel oxide, which is thicker than the oxide under the word line gate.
1. A method of forming a memory device, comprising:
providing a semiconductor substrate having a memory area, a first peripheral area and a second peripheral area;
forming a first insulation layer on a surface of the substrate in the memory, first peripheral and second peripheral areas;
forming a first polysilicon layer on the first insulation layer in the memory, first peripheral and second peripheral areas;
removing the first polysilicon layer from the first peripheral and second peripheral areas, and removing portions of the first polysilicon layer from the memory area, leaving a first polysilicon block of the first polysilicon layer in the memory area, wherein the first polysilicon block has first and second opposing ends;
removing portions of the first insulation layer that are not disposed under the first polysilicon block;
forming a source region in the substrate adjacent the first end of the first polysilicon block in the memory area;
forming a second insulation layer on the surface of the substrate in the second peripheral area;
forming a third insulation layer that wraps around an upper edge at the first end of the first polysilicon block;
forming a fourth insulation layer on the surface of the substrate over the source region in the memory area;
forming a fifth insulation layer on the surface of the substrate in the memory area adjacent the second end of the first polysilicon block, and on the surface of the substrate in the first peripheral area;
forming a second polysilicon layer on the second, third, fourth and fifth insulation layers in the memory, first peripheral and second peripheral areas;
removing portions of the second polysilicon layer, leaving a second polysilicon block of the second polysilicon layer on the fourth insulation layer and over the source region, a third polysilicon block of the second polysilicon layer on the fifth insulation layer in the memory area laterally adjacent to the second end of the first polysilicon block, a fourth polysilicon block of the second polysilicon layer on the fifth insulation layer in the first peripheral area, and a fifth polysilicon block of the second polysilicon layer on the second insulation layer in the second peripheral area;
forming a drain region in the substrate adjacent the third polysilicon block in the memory area;
forming a second source region in the substrate adjacent a first side of the fourth polysilicon block;
forming a second drain region in the substrate adjacent a second side of the fourth polysilicon block opposition of the first side of the fourth polysilicon block;
forming a third source region in the substrate adjacent a first side of the fifth polysilicon block;
forming a second drain region in the substrate adjacent a second side of the fifth polysilicon block opposition of the first side of the fifth polysilicon block.
2. The method of claim 1 , further comprising:
removing a portion of an upper surface of the first polysilicon block so that the upper surface is sloped and terminates in a sharp edge at the first end of the first polysilicon block.
3. The method of claim 2 , wherein the second polysilicon block includes a notch that wraps around the sharp edge.
4. The method of claim 1 , wherein the removing of the portions of the second polysilicon layer that leaves the second, third, fourth and fifth polysilicon blocks is performed using a single polysilicon etch.
5. The method of claim 1 , wherein the removing of the first polysilicon layer from the first peripheral and second peripheral areas, and the removing of the portions of the first polysilicon layer from the memory area leaving the first polysilicon block of the first polysilicon layer in the memory area, are performed using a single polysilicon etch.
6. The method of claim 1 , further comprising:
forming spacers of insulation material on the first and second ends of the first polysilicon block; and
removing the spacer of insulation material on the first end of the first polysilicon block before the forming of the third insulation layer.
7. The method of claim 1 , wherein a thickness of the fifth insulation layer is less than a thickness of the third insulation layer.
8. The method of claim 1 , wherein a thickness of the fifth insulation layer is less than a thickness of the second insulation layer.
9. The method of claim 1 , further comprising:
forming silicide on upper surfaces of the second, third, fourth and fifth polysilicon blocks.
10. The method of claim 1 , further comprising:
forming silicide on portions of the surface of the substrate that are over the drain region, the first and second source regions and the first and second drain regions.