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. A method for depositing a solid film onto a substrate from a reagent solution comprising the steps of:
providing a supply of a first reagent solution maintained at a first temperature at which homogeneous reactions are substantially inhibited within said first reagent solution;
dispensing a fine mist of said first reagent solution from a first showerhead assembly;
positioning said substrate to receive at least a portion of said fine mist of said first reagent over a selected area of said substrate;
providing a supply of a second reagent solution maintained at a second temperature at which homogeneous reactions are substantially inhibited within said second reagent solution;
dispensing a flowing stream of said second reagent solution from a second showerhead assembly;
positioning said substrate to receive at least a portion of said flowing stream of said second reagent over a selected area of said substrate;
providing a raised structure peripheral to said selected area whereby a controlled volume of said second reagent solution may be maintained upon said substrate; and,
heating said substrate and said controlled volume of said second reagent solution upon said substrate to a selected temperature, higher than at least one of said first and said second temperatures, so that deposition of a desired solid phase from said reagent solutions may be initiated.
2. The method of claim 1 wherein said solid film comprises a compound semiconductor comprising Cu, at least one other metal, and at least one nonmetal selected from the group consisting of S and Se.
3. The method of claim 2 wherein said compound semiconductor is selected from the group consisting of: CuSbS, CuSbSSe, CuInSSe, CuSnZnSe, CuInGaSSe, CuInGaS, CuAlS, CuAlSSe, CuFeS, CuFeSSe, CuLiS, CuLiSSe, CuGaS, CuGaSSe, CuSnS, CuSnSSe, CuZnS, CuZnSSe, CuAlMgS, CuAlMgSSe, CuCdS, CuCdSSe, CuCdSnS, and CuCdSnSSe.
4. The method of claim 2 wherein the composition of said solid film varies in a direction normal to a surface of said substrate.
5. The method of claim 2 wherein at least one electronic characteristic of said solid film varies in a direction normal to a surface of said substrate.
6. The method of claim 5 wherein said at least one electronic characteristic of said solid film is selected from the group consisting of: bandgap, carrier concentration, carrier mobility, and resistivity.
7. The method of claim 1 wherein said fine mist of said first reagent has an average droplet size less than about 50 μm.
8. The method of claim 1 wherein said selected temperature is at least 60° C. higher than said first and second temperatures.
9. The method of claim 1 further including the step of:
annealing said deposited film at an annealing temperature greater than said selected temperature.
10. The method of claim 9 wherein said annealing temperature is at least 200° C.
11. A method for forming a compound semiconductor film on a substrate from a reagent solution comprising the steps of:
providing a supply of a first reagent solution, containing at least one metal and at least one nonmetal selected from the group consisting of S and Se, maintained at a first temperature at which homogeneous reactions are substantially inhibited within said first reagent solution;
dispensing a fine mist of said first reagent solution from a first showerhead assembly;
positioning said substrate to receive at least a portion of said fine mist of said first reagent over a selected area of said substrate;
providing a supply of a second reagent solution, containing at least one metal and at least one nonmetal selected from the group consisting of S and Se, maintained at a second temperature at which homogeneous reactions are substantially inhibited within said second reagent solution, wherein at least one of said first and said second reagent solutions contains copper;
dispensing a flowing stream of said second reagent solution from a second showerhead assembly;
positioning said substrate to receive at least a portion of said flowing stream of said second reagent over a selected area of said substrate;
providing a raised structure peripheral to said selected area whereby a controlled volume of said second reagent solution may be maintained upon said substrate; and,
heating said substrate and said controlled volume of said second reagent solution upon said substrate to a selected temperature, higher than at least one of said first and said second temperatures, so that deposition of a desired copper-containing solid phase from said reagent solutions may be initiated.