Atomic layer deposition of metal oxide materials for memory applications
Embodiments of the invention generally relate to nonvolatile memory devices, such as a ReRAM cells, and methods for manufacturing such memory devices, which includes optimized, atomic layer deposition (ALD) processes for forming metal oxide film stacks. The metal oxide film stacks contain a metal oxide coupling layer disposed on a metal oxide host layer, each layer having different grain structures/sizes. The interface disposed between the metal oxide layers facilitates oxygen vacancy movement. In many examples, the interface is a misaligned grain interface containing numerous grain boundaries extending parallel to the electrode interfaces, in contrast to the grains in the bulk film extending perpendicular to the electrode interfaces. As a result, oxygen vacancies are trapped and released during switching without significant loss of vacancies. Therefore, the metal oxide film stacks have improved switching performance and reliability during memory cell applications compared to traditional hafnium oxide based stacks of previous memory cells.
1. A method of forming a resistive random access memory cell, the method comprising:
providing a conductive layer on a substrate;
forming a host layer over the conductive layer;
annealing the host layer; and
forming a coupling layer over an exposed surface of the host layer;
wherein the conductive layer is operable as an electrode;
wherein the annealing changes a grain boundary of the exposed surface;
wherein the coupling layer and the host layer form a misaligned grain interface; and
wherein the misaligned grain interface facilitates oxygen vacancy exchange between the coupling layer and the host layer.
2. The method of claim 1 , wherein the annealing comprises plasma annealing.
3. The method of claim 2 , wherein plasma for the plasma annealing is formed using a gas comprising one of argon, oxygen, ozone, or a mixture of argon and oxygen.
4. The method of claim 1 , wherein the annealing comprises thermal annealing followed by plasma annealing.
5. The method of claim 1 , further comprising exposing the coupling layer to a temperature of between about 600° C. and 750° C. after forming the coupling layer over the exposed surface.
6. The method of claim 5 , wherein the host layer comprises a hafnium-rich oxide.
7. The method of claim 1 , further comprising forming a silicon oxide layer over the conductive layer, wherein the silicon oxide layer is formed between the conductive layer and the host layer.
8. The method of claim 7 , wherein the silicon oxide layer has a thickness of between about 2 Angstroms and 40 Angstroms.
9. The method of claim 1 , wherein the host layer comprises a crystalline metal-rich oxide.
10. The method of claim 9 , wherein the crystalline metal-rich oxide is represented by a generic chemical formula of MO X , wherein M comprises one of hafnium, zirconium, or titanium, and wherein X is within a range from about 1.65 to about 1.95.
11. The method of claim 10 , wherein X is within a range from about 1.70 to about 1.90.
12. The method of claim 10 , wherein X is within a range from about 1.75 to about 1.85.
13. The method of claim 1 , wherein the coupling layer comprises an amorphous metal-rich oxide.
14. The method of claim 13 , wherein the amorphous metal-rich oxide is represented by a generic chemical formula of MM′ Y O Z , wherein M comprises one of hafnium, zirconium, or titanium, M′ comprises one of aluminum, yttrium, or lanthanum, wherein Y is within a range from about 0.05 to about 0.50, and wherein Z is within a range from about 1.50 to about 2.50.
15. The method of claim 14 , wherein the host layer comprises a crystalline metal-rich oxide, and wherein the amorphous metal-rich oxide of the coupling layer and the crystalline metal-rich oxide of the host layer comprise a common metal.
16. The method of claim 1 , wherein Y is within a range from about 0.05 to about 0.15, and wherein Z is within a range from about 1.50 to about 2.10.
17. The method of claim 1 , wherein Y is within a range from about 0.40 to about 0.50, and wherein Z is within a range from about 2.10 to about 2.50.
18. A method of forming a resistive random access memory cell, the method comprising:
providing a conductive layer on a substrate;
forming a host layer over the conductive layer;
annealing an exposed surface of the host layer;
forming a coupling layer over the exposed surface,
wherein the conductive layer is operable as an electrode;
wherein the host layer comprises crystalline hafnium oxide;
wherein the coupling layer comprises amorphous hafnium aluminate; and
annealing an exposed surface of the coupling layer;
wherein the annealing changes a grain boundary of the exposed surface;
wherein the coupling layer and the host layer form a misaligned grain interface; and
wherein the misaligned grain interface facilitates oxygen vacancy exchange between the coupling layer and the host layer.
19. The method of claim 18 , wherein the host layer has a thickness of between about 5 Angstroms and 100 Angstroms.
20. The method of claim 18 , wherein the coupling layer has a thickness of between about 3 Angstroms and 80 Angstroms.