The effect of ambient atmosphere in the annealing of indium tin oxide films

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Abstract
Isochronal annealing experiments on dc‐sputtered indium tin oxide (ITO) films in inert (N2), reducing (N2/H2) and oxidizing atmospheres were cumulatively performed over the 50→500→50 °C range. Three anneal regimes have been identified. In region I, TA=50→200 °C, crystallization occurs, resulting in a sharp drop in sheet resistance (Rs) due to increasing mobility. TA?200 °C results in a minimum Rs. In region II, 200→500→200 °C, Rs is proportional to TA, increasing (decreasing) during the forward (reverse) anneal cycle. This behavior is apparently due to a temperature‐dependent active oxygen concentration and its effect on the carrier concentration. In region III, 200→50 °C, Rs is constant with TA. Optical transmission and x‐ray diffraction experiments were performed at 100 °C intervals. Successive anneals tended to increase the transmission in the visible and near‐UV regions and to decrease it in the near‐ and far‐IR region. Strong evidence of the Burstein‐Moss shift was observed and an extrapolated intrinsic band gap of 3.85 eV was determined. Free‐carrier absorption over the 2–5‐μm regions was evident after the 200 °C anneal for all ambients. From the x‐ray data, no evidence of crystallinity was observed in the as‐deposited case and for anneals up to 100 °C. For anneals in the 300–500 °C range, a grain size of the order of 600 Å with an orientation normal to the (222) plane was observed for all ambients.