Low resistance monosilicide electrode for phase change memory and methods of making the same
View Patent ↗This disclosure relates to a low-resistance monosilicide electrode and method of making the monosilicide electrode. A cell film stack is first formed on a substrate of a wafer. The top layer of this cell film stack is silicon. The cell film stack is then etched to form at least one pillar. Dielectric is deposited to fill the gaps between the pillars. The wafer is then planarized to expose the top silicon layer. The exposed top silicon layer is converted into a nickel monosilicide layer by way of a thermal solid-state reaction between nickel and the silicon layer. This nickel monosilicide layer forms the 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 having a top silicon layer;
etching the cell film stack to form a plurality of pillars;
depositing a dielectric to fill in gaps between the plurality of pillars;
planarizing the wafer to expose the top silicon layer; and
converting the exposed top silicon layer into a nickel monosilicide layer, the nickel monosilicide layer forming a monosilicide electrode.
2. The method of claim 1 , wherein converting the exposed top silicon layer into the nickel monosilicide layer comprises:
depositing nickel onto the exposed top silicon layer to form a nickel layer;
heating the exposed top silicon layer and the nickel layer to about 350 degrees Celsius such that the nickel layer reacts with the exposed top silicon layer to form the nickel monosilicide layer;
removing unreacted nickel of the nickel layer; and
planarizing the wafer.
3. The method of claim 2 , further comprising depositing titanium nitride on to the nickel layer, the titanium nitride forming a titanium nitride layer configured to prevent or mitigate oxidation of the nickel layer with oxygen and wherein the nickel layer is about 0.452 times the thickness of the nickel monosilicide layer and the exposed top silicon layer is about 0.828 times the thickness of the nickel monosilicide layer.
4. The method of claim 2 , wherein removing the unreacted nickel comprises wet etching with a mixture of sulfuric acid and hydrogen peroxide.
5. The method of claim 2 , wherein planarizing the wafer comprises applying a nickel monosilicide chemical mechanical polishing process to the wafer.
6. The method of claim 2 , wherein planarizing the wafer comprises:
depositing a dielectric film onto the nickel monosilicide layer; and
applying a dielectric chemical mechanical polishing process to the wafer.
7. The method of claim 1 , wherein the nickel monosilicide layer substantially replaces the exposed top silicon layer.
8. The method of claim 1 , wherein converting the exposed top silicon layer into the nickel monosilicide layer creates a protrusion from one or more portions of the nickel monosilicide layer, the protrusion extending above a surface of the wafer and the method further comprises planarizing the nickel monosilicide layer to remove the protrusion.