Film growth system and method
An apparatus for depositing a solid film onto a substrate from a reagent solution includes a reservoir of reagent solution maintained at a sufficiently low temperature to inhibit homogeneous reactions within the reagent solution. The reagent solution contains multiple ligands to further control temperature stability and shelf life. The chilled solution is dispensed through a showerhead onto a substrate. The substrate is positioned in a holder that has a raised structure peripheral to the substrate to retain or impound a controlled volume (or depth) of reagent solution over the exposed surface of the substrate. The reagent solution is periodically or continuously replenished from the showerhead so that only the part of the solution directly adjacent to the substrate is heated. A heater is disposed beneath the substrate and maintains the substrate at an elevated temperature at which the deposition of a desired solid phase from the reagent solution may be initiated. The showerhead may also dispense excess chilled reagent solution to cool various components within the apparatus and minimize nucleation of solids in areas other than on the substrate. The apparatus and its associated method of use are particularly suited to forming films of II-VI semiconductors.
1. A method for depositing a solid film onto a substrate from a reagent solution comprising the steps of:
a. providing a supply of aqueous reagent solution maintained in a holding tank at a first temperature at which homogeneous reactions are substantially inhibited within said reagent solution, said reagent solution further containing at least two ligands;
b. dispensing a controlled flow of said reagent solution from a showerhead assembly, said controlled flow being periodically replenished;
c. positioning said substrate to receive at least a portion of said controlled flow of said reagent over a selected area of said substrate;
d. providing a raised structure peripheral to said selected area whereby a controlled volume of said reagent solution may be maintained upon said substrate while excess solution may be recirculated to said holding tank; and,
e. heating said substrate and said controlled volume of said reagent solution upon said substrate to a second temperature, higher than said first temperature, whereby deposition of a desired solid phase onto said substrate from said reagent solution may be initiated.
2. The method of claim 1 wherein said solid film comprises a compound of a metal and a Group VI element and said reagent solution comprises a salt of said metal and a compound containing said Group VI element, and said at least two ligands are capable of forming a stable complex with said metal.
3. The method of claim 2 wherein said metal is selected from the group consisting of: Cd; Cu; In; Al; Mn; and Zn.
4. The method of claim 2 wherein said Group VI element is selected from the group consisting of: O; S; and Se.
5. The method of claim 2 wherein said at least two ligands are selected from the group consisting of: acetic acid; triethanolamine; citric acid; potassium nitrilotriacetate; sodium citrate; ammonium hydroxide; and hydantoin.
6. The method of claim 1 wherein said second temperature is at least 60° C. higher than said first temperature.
7. The method of claim 1 wherein said controlled volume divided by said selected area of said substrate is characterized by a volume-to-surface area ratio of 0.1 to 100 mm.
8. The method of claim 7 wherein said volume-to-surface ratio is 0.1 to 10 mm.