Method for fabricating copper-containing ternary and quaternary chalcogenide thin films
An apparatus for depositing a solid film onto a substrate from a reagent solution includes reservoirs of reagent solutions maintained at a sufficiently low temperature to inhibit homogeneous reactions within the reagent solutions. The chilled solutions are dispensed through showerheads, one at a time, onto a substrate. One of the showerheads includes a nebulizer so that the reagent solution is delivered as a fine mist, whereas the other showerhead delivers reagent as a flowing stream. A heater disposed beneath the substrate maintains the substrate at an elevated temperature at which the deposition of a desired solid phase from the reagent solutions may be initiated. Each reagent solution contains at least one metal and either S or Se, or both. At least one of the reagent solutions contains Cu. The apparatus and its associated method of use are particularly suited to forming films of Cu-containing compound semiconductors.
1. An apparatus for depositing a solid film onto a substrate from reagent solutions comprising:
a reservoir of a first reagent solution maintained at a first temperature at which homogeneous reactions are substantially inhibited within said first reagent solution;
a first showerhead assembly including a nebulizer configured to dispense said first reagent solution as a fine mist at said first temperature;
a reservoir of a second reagent solution maintained at a second temperature at which homogeneous reactions are substantially inhibited within said second reagent solution;
a second showerhead assembly configured to dispense said second reagent solution as a flowing stream at said second temperature;
a substrate holder configured to hold said substrate in a position to receive, in sequence, at least a portion of said fine mist of said first reagent solution and at least a portion of said flowing stream of said second reagent over a selected area of said substrate, said substrate holder further including a raised structure peripheral to said selected area whereby a controlled volume of said second reagent solution may be maintained upon said substrate and replenished at a selected rate; and,
a heater disposed beneath said substrate, said heater configured to maintain said substrate at a selected temperature, higher than at least one of said first and second temperatures, at which the deposition of a desired solid phase from said first and said second reagent solutions respectively may be initiated.
2. The apparatus of claim 1 wherein said selected temperature is at least 60° C. higher than at least one of said first and said second temperatures.
3. The apparatus of claim 1 wherein said first showerhead assembly is configured to dispense said first reagent solution as a mist having an average droplet size less than about 50 μm.
4. The apparatus of claim 1 wherein said second showerhead assembly is configured to dispense a first portion of said second reagent solution into said controlled volume defined by said raised peripheral structure and to dispense a second portion of said reagent solution outside of said controlled volume.
5. The apparatus of claim 1 further comprising a process chamber containing said showerhead assemblies, said substrate holder, and said heater.
6. The apparatus of claim 5 wherein at least a portion of said second reagent solution follows a recirculating path between said process chamber and said second reagent solution reservoir.
7. The apparatus of claim 6 wherein at least one of said first and second reagent solution reservoirs includes a device selected from the group consisting of: temperature sensors, pH meters, chemical sensors, liquid level control switches, and chillers.
8. The apparatus of claim 6 wherein said recirculating path includes a device selected from the group consisting of: pumps; valves; filters; pressure gauges; and return line reservoirs.
9. The apparatus of claim 5 wherein said process chamber may be maintained at a selected pressure.