Reactive radio frequency sputtering of iron oxide thin films for electrical resistivity characterization

A postulate of this research was that useful semiconductors could be made in the iron oxide thin film system by controlling the ratio of Fe²⁺ to Fe³⁺ ions. For the added versatility of producing all of the oxide phases from one source (target), reactive (in an oxygen/argon atmosphere) sputtering was chosen. In addition, to avoid the problems of sputtering oxides by Electron Beam evaporation or Direct Current sputtering, the recently developed technique of Radio Frequency sputtering was employed. Thus, the iron oxide thin films were produced by reactive Radio Frequency sputtering.

The correlation between the electrical resistivity and the sputtering atmosphere (oxygen pressure) was made and plotted. Identification of the Fe²⁺ to Fe³⁺ ion ratio was impossible, but X-ray diffraction data were used to identify the iron oxide phase or phases present in each thin film. Thin films which were a mixture of oxide phases were produced and the general sputtering parameters (electrical power settings and oxygen level) required to produce these oxide mixtures have been identified. The deposition time was found to have an optimum of about ten minutes, and times in excess of this produced thin films of equivalent thickness. Differences between phase equilibria predictions and the actual phases formed during sputtering have led to the conclusion that reactive Radio Frequency sputtering of iron oxide is a non-equilibrium process.