New annealing methods of indium tin oxide films by electric current

Novel methods of indium tin oxide (ITO) annealing in vacuum by electric current flowing through the film are proposed. These methods exhibit a number of technical advantages: (i) no external heater is required, and (ii) the Joule heat is released only in the ITO films reducing the heat load to thermally sensitive substrates. Transparent and conductive films with thickness of 170 nm were deposited by reactive pulsed magnetron sputtering. In the first set of experiments Si plates covered by 500 nm SiO2 were used as substrates. Annealing was performed in direct current (DC) mode at a constant power released in the film. During annealing the film resistance, free electron density and structure evolution were monitored in situ. Similar to thermal annealing, a two-stage decrease of the resistivity was observed, however the crystallization proceeds faster at significant lower temperatures. The activation energy of crystallization for the isothermally annealed films is about 1.44 ± 0.18 eV. In the case of annealing by electric current the activation energy is reduced by nearly a factor of 2 to 0.81 ± 0.09 eV.
In a second set of experiments the ITO films deposited on fused silica substrates were annealed in vacuum by microwave radiation. In contrast to the DC mode, the annealing current was induced in the ITO film by microwaves without electrical contacts. It is shown that such treatment causes a fast film transformation from amorphous to crystalline state with a significant decrease of resistivity up to approximately one order of magnitude.