P6H-9 Discerning the Quality of ZnO Films from Their Etch Properties

Several tests have been used over the years to determine the quality of thin film zinc oxide. These tests have included coupling factor measurement, acoustic and optical loss, surface roughness, and grain size. One such test, which is especially useful when establishing the best ZnO deposition condition, is chemical etching. Chemical etching reveals considerable information about the density of the fiber grain structure, the film orientation, film strain, and can be related to coupling factor. Etching ZnO films or crystals is highly anisotropic depending upon whether the acid attacks its zinc face, its oxygen face, or laterally to its c-axis orientation. By controlling the percentage of the acid etchant in water, direct comparisons can be made of the film properties under different deposition conditions. Etch times extend as low as 100 Angstroms per second for ZnO films with dense uniform fiber grains and as high as 1000 Angstroms per second for nonuniform grain structures. This paper will present the results of etching studies on micrometer thick ZnO under a triode system of deposition which can produce very high quality films. Taking into account the etch rates and the etch pit density. Both can be used to predict the quality of the ZnO films for applications.