Semiconductor memory and semiconductor device with nitride memory elements
View Patent ↗A semiconductor memory has a gate electrode and a pair of multilayer memory elements formed on side surfaces of the gate electrode. Each multilayer memory element includes, in sequence from the gate electrode outward, a first silicon oxide layer, a charge trapping silicon nitride layer, a second silicon oxide layer, all with L-shaped cross sections, and a protective silicon nitride layer with an approximately rectangular cross section seated in the L-shape of the second silicon oxide layer. The protective silicon nitride layer protects the charge trapping silicon nitride layer from etching damage during the formation of contact holes without adding to the area occupied by the memory cell.
1. A semiconductor memory having a semiconductor substrate with a surface layer covered by an interlayer dielectric film of silicon oxide and a plurality of memory cells formed on the surface layer within the interlayer dielectric film, each memory cell including a gate electrode with a pair of side surfaces, a gate insulation film interposed between the gate electrode and the surface layer of the semiconductor substrate, a pair of highly doped diffusion regions formed in the surface layer of the semiconductor substrate on both sides of the gate electrode, and a pair of multilayer memory elements formed on the side surfaces of the gate electrode, the multilayer memory elements extending onto the highly doped diffusion regions of the semiconductor substrate, each multilayer memory element comprising:
a first silicon oxide layer formed on one of the side surfaces of the gate electrode, extending to a bottom of said one of the side surfaces and onto one of the highly doped diffusion regions;
a charge trapping nitride layer formed on the first silicon oxide layer;
a second silicon oxide layer formed on the charge storage nitride layer;
a protective silicon nitride layer formed directly on the second silicon oxide layer, so as to touch the second silicon oxide layer;
a hard mask silicon nitride layer disposed on the gate electrode; and
a silicon nitride stopper film disposed between the hard mask silicon nitride layer and the interlayer dielectric film so as to touch the hard mask silicon nitride layer, and being disposed between the multilayer memory elements and the interlayer dielectric film.
2. The semiconductor memory of claim 1 , wherein the first silicon oxide layer, the charge trapping nitride layer, and the second silicon oxide layer have L-shaped cross sections.
3. The semiconductor memory of claim 1 , wherein the first silicon oxide layer has a thickness of at most twenty nanometers.
4. The semiconductor memory of claim 3 , wherein the first silicon oxide layer has a thickness of at least three nanometers.
5. The semiconductor memory of claim 1 , wherein the charge trapping nitride layer has a thickness of at most fifteen nanometers.
6. The semiconductor memory of claim 5 , wherein the charge trapping nitride layer has a thickness of at least two nanometers.
7. The semiconductor memory of claim 1 , wherein the second silicon oxide layer has a thickness of at most twenty nanometers.
8. The semiconductor memory of claim 7 , wherein the second silicon oxide layer has a thickness of at least three nanometers.
9. The semiconductor memory of claim 1 , wherein the protective silicon nitride layer has a thickness of at most two hundred nanometers.
10. The semiconductor memory of claim 9 , wherein the protective silicon nitride layer has a thickness of at least ten nanometers.
11. The semiconductor memory of claim 1 , wherein the silicon nitride stopper film has a thickness of at most forty nanometers.
12. The semiconductor memory of claim 11 , wherein the silicon nitride stopper film has a thickness of at least ten nanometers.
13. The semiconductor memory of claim 1 , further comprising a contact plug extending through the interlayer dielectric film onto one of the highly doped diffusion regions.
14. The semiconductor memory of claim 13 , wherein the contact plug also extends partly onto the hard mask silicon nitride layer of one of the memory cells.
15. The semiconductor memory of claim 1 , each said memory cell further comprising a pair of lightly doped diffusion regions formed in the surface layer of the semiconductor substrate, extending from the highly doped diffusion regions, disposed partly beneath respective multilayer memory elements and partly beneath the gate electrode.
16. A semiconductor device including the semiconductor memory of claim 1 and a metal oxide semiconductor field effect transistor (MOSFET), the MOSFET having a gate electrode and highly doped diffusion regions formed in the surface layer of the semiconductor substrate on both sides of the gate electrode, wherein the MOSFET includes a pair of sidewalls identical in structure to the multilayer memory elements of the memory cells.