Low resistance monosilicide electrode for phase change memory and methods of making the same
A method is provided that includes forming a cell film stack on a substrate of a wafer, the cell film stack comprising a top silicon layer, depositing a sacrificial layer onto the top silicon layer, etching the cell film stack and the sacrificial layer to form a plurality of pillars, depositing a dielectric to fill in gaps between the plurality of pillars, planarizing the wafer to a predefined thickness for the sacrificial layer, removing the sacrificial layer, depositing nickel onto the wafer to form a nickel layer, annealing the wafer to form a di-nickel silicide layer between the nickel layer and the top silicon layer, wet etching unreacted nickel of the nickel layer to expose the di-nickel silicide layer, and annealing the wafer to form a nickel monosilicide layer from the di-nickel silicide layer and the top silicon layer, the nickel monosilicide layer forming a monosilicide electrode.
1. A method of forming a monosilicide electrode, comprising:
forming a cell film stack on a substrate of a wafer, the cell film stack comprising a top silicon layer;
depositing a sacrificial layer onto the top silicon layer;
etching the cell film stack and the sacrificial layer to form a plurality of pillars;
depositing a dielectric to fill in gaps between the plurality of pillars;
planarizing the wafer to a predefined thickness for the sacrificial layer;
removing the sacrificial layer;
depositing nickel onto the wafer to form a nickel layer;
annealing the wafer to form a di-nickel silicide layer between the nickel layer and the top silicon layer;
wet etching unreacted nickel of the nickel layer to expose the di-nickel silicide layer; and
annealing the wafer to form a nickel monosilicide layer from the di-nickel silicide layer and the top silicon layer, the nickel monosilicide layer forming the monosilicide electrode.
2. The method of claim 1 , wherein annealing the wafer to form the di-nickel silicide layer comprises thermally reacting the nickel layer and the top silicon layer such that an unreacted nickel layer remains above the di-nickel silicide layer after the annealing.
3. The method of claim 1 , wherein annealing the wafer to form the di-nickel silicide layer comprises raising a temperature of the wafer to about 260° C. for a predefined time period such that the di-nickel silicide layer forms a predefined thickness between the top silicon layer and a layer of unreacted nickel.
4. The method of claim 1 , wherein annealing the wafer to form the nickel monosilicide layer comprises raising a temperature of the wafer to above about 350° C. for a predefined time period such that the di-nickel silicide layer reacts with the top silicon layer to form the nickel monosilicide layer.
5. The method of claim 1 , wherein the top silicon layer is about 0.828 times a thickness of the nickel monosilicide layer and the nickel layer is about 0.452 times the thickness of the nickel monosilicide layer and the di-nickel silicide layer is 0.687 times the thickness of the nickel monosilicide layer and wherein the di-nickel silicide layer reacts with a portion of the silicon layer that is 0.414 times the thickness of the nickel monosilicide layer.
6. The method of claim 1 , wherein the top silicon layer is greater than 0.828 times a thickness of the nickel monosilicide layer such that annealing the wafer to form the nickel monosilicide layer by raising a temperature of the wafer to above about 350° C. for a predefined time period reacts the di-nickel silicide layer with the top silicon layer to form the nickel monosilicide layer and a residual silicon layer beneath the nickel monosilicide layer.
7. The method of claim 6 , wherein the predefined time period and a rate of temperature increase for the annealing are configured to mitigate agglomeration of the nickel monosilicide layer and are configured to form the residual silicon layer.
8. The method of claim 1 , wherein a mean grain size of grains within the nickel monosilicide layer is between about 50 nanometers and about 100 nanometers and a thickness of the nickel monosilicide layer comprises a single grain boundary and wherein the grains of the nickel monosilicide layer average about 10 to 20 nanometers.
9. The method of claim 1 , further comprising forming a titanium nitride on the nickel layer.
10. The method of claim 1 , further comprising planarizing the nickel monosilicide layer to remove a protrusion from the nickel monosilicide layer.
11. A method comprising:
forming on a substrate of a wafer a cell film stack comprising a top silicon layer;
etching the cell film stack to form a plurality of pillars;
depositing a dielectric between the plurality of pillars;
forming dielectric protrusions that extend above the plurality of pillars, the dielectric protrusions defining gaps above the top silicon layer in each of the plurality of pillars;
depositing nickel to form a nickel layer within the gaps;
annealing the wafer to form a di-nickel silicide layer between the nickel layer and the top silicon layer;
removing unreacted nickel of the nickel layer to expose the di-nickel silicide layer; and
annealing the wafer to form a nickel monosilicide electrode from the di-nickel silicide layer and the top silicon layer.
12. The method of claim 11 , wherein annealing the wafer to form the di-nickel silicide layer comprises thermally reacting the nickel layer and the top silicon layer such that an unreacted nickel layer remains above the di-nickel silicide layer after the annealing.
13. The method of claim 11 , wherein annealing the wafer to form the di-nickel silicide layer comprises raising a temperature of the wafer to about 260° C. for a predefined time period such that the di-nickel silicide layer forms a predefined thickness between the top silicon layer and an unreacted nickel layer.
14. The method of claim 11 , wherein annealing the wafer to form the nickel monosilicide layer comprises raising a temperature of the wafer to above about 350° C. for a predefined time period such that the di-nickel silicide layer reacts with the top silicon layer to form the nickel monosilicide electrode.
15. The method of claim 11 , wherein annealing the wafer to form the nickel monosilicide electrode reacts the di-nickel silicide layer with the top silicon layer to form the nickel monosilicide electrode and a residual silicon layer beneath the nickel monosilicide electrode.
16. The method of claim 11 , wherein annealing the wafer to form the nickel monosilicide electrode comprises increasing a temperature of the wafer at a rate of temperature increase to mitigate agglomeration of the nickel monosilicide electrode.
17. The method of claim 11 , wherein a thickness of the nickel monosilicide electrode comprises a single grain boundary.
18. A method comprising:
forming a plurality of pillars on a substrate of a wafer, each pillar comprising a top silicon layer;
depositing a dielectric to fill in gaps between the plurality of pillars;
planarizing the wafer to a predefined thickness;
depositing nickel onto the wafer to form a nickel layer;
annealing the wafer to form a di-nickel silicide layer between the nickel layer and the top silicon layer;
wet etching to expose the di-nickel silicide layer; and
annealing the wafer to form a nickel monosilicide layer comprising a monosilicide electrode.
19. The method of claim 18 , wherein annealing the wafer to form the di-nickel silicide layer comprises raising a temperature of the wafer to about 260° C. for a predefined time period such that the di-nickel silicide layer forms a predefined thickness between the top silicon layer and an unreacted nickel layer.
20. The method of claim 18 , wherein annealing the wafer to form the nickel monosilicide layer comprises raising a temperature of the wafer to above about 350° C. for a predefined time period such that the di-nickel silicide layer reacts with the top silicon layer to form the nickel monosilicide electrode.