Zinc oxide film and method for making

Abstract

A method for depositing a solid film of ZnO 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 a source of Zn, a source of O, and multiple ligands to further control solution 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 deposited film may be annealed after deposition and may be doped to enhance selected characteristics. The ZnO films made by the process have distinctive electrical and optical properties and are suitable for a variety of electronic and optical devices.

Description

CROSS REFERENCE TO RELATED APPLICATION[0001]This application claims the benefit of Provisional Application Ser. No. 60 / 940,797 filed by the present inventor on May 30, 2007, the entire disclosure of which is incorporated herein by reference.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The invention pertains to a system and method for chemically coating a variety of surfaces with zinc oxide thin films for various applications including electronics, and to zinc oxide films having novel properties.[0004]2. Description of Related Art[0005]Numerous coating processes are commonly employed in industrial applications, including electroless chemical, chemical vapor and physical vapor depositions. Physical vapor deposition is commonly used in semiconductor manufacturing applications, often employing expensive vacuum techniques in order to sustain a relatively high film growth rate. Many such processes, while performed at high temperatures (e.g., greater than 300° C.), are n...

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Benefits of technology

[0017]In accordance with another aspect of the invention, a multilayer structure comprises: a substrate material; and, a thin film of ZnO depo

Problems solved by technology

), are non-equilibrium, often resulting in non-stoichiometric proportions.

Also, due to the nature of the deposition processes, the deposited films often include relatively high defect densities.

In the case of semiconducting devices, such high defect levels can limit electrical performance characteristics.

In semiconductor device fabrication wherein p-n junctions are formed in a partial vaccuum by depositing one film over a second film or a substrate of different conductivity type, the conventional evaporative and sputtering techniques may provide unsatisfactory film qualities.

As an alternative, relatively more expensive techniques such as Chemical Vapor Deposition (CVD), Molecular Beam Epitaxy (MBE), pulsed laser deposition, and atomic layer epitaxy, are useful, especially with formation of III-V compound semiconductor materials, but satisfactory deposition processes have not been available for fabrication of thin film III-VI compound semiconductor materials.

However, the technique has provided low growth rates, e.g., 20 to 30 Å/minute, and the grown film thickness per bath cycle is limited to around 1000 Å rendering it non-suitable for volume manufacture.

With traditional chemical bath deposition techniques, efforts to increase film growth rates typically result in degradation of film quality.

This, of course, is time consuming and generally can be an expensive endeavor, wherein relatively expensive chemicals are wasted due to deposition of film materials on unwanted surfaces such as the equipment.

Particulates represent not only a waste of reagents but also a source of defects in the deposited film.

First, using a single complexing agent (generally taught to be NH4OH) prevents adequate process control: at a low concentration the solution is so unstable that unwanted homogeneous nucleation can occur, whereas at high concentration the activation energy required to form the film becomes so high that the claimed substrate temperature may not be able to overcome it to cause a film growth.

Second, the thickness of film that can be grown in a single step is very small, so to grow a film of 0.1 μm or greater, multiple cycles are needed and this will tend to introduce greater concentrations of defects.

This will also make the process cumbersome and less manufacturing friendly.

The use of NH

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