Millisecond-annealing using flash lamps for improved performance of AZO layers
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Millisecond-annealing using flash lamps for improved performance of AZO layers T. Gebel1, M. Neubert2, R. Endler2, J. Weber1, M. Vinnichenko2, A. Kolitsch2, W. Skorupa2, H. Liepack1, 1 DTF Technology GmbH - Dresden Thin Film Technology, Meschwitzstr. 21, 01099 Dresden Germany 2 FZD Dresden Rossendorf, Bautzner Landstr. 400, 01328 Dresden, Germany ABSTRACT ZnO:Al films with a thickness of about 880nm were deposited by magnetron sputtering. The glass substrate was not heated neither before during nor after the deposition. Subsequently the deposited layers were treated by flash lamp annealing (FLA) at 1.3 ms. Using this method, the resistivity of the ZnO:Al films was decreased by a factor of two, down to 1.0 x 10-3 Ωcm. These results are in good agreement with results reported from rapid thermal processing or furnace annealing treatments. Despite the very short annealing time of only 1.3 ms not only the resistivity but also the transmittance in the UV and the blue range were considerably improved. INTRODUCTION The growing market of thin film applications in photovoltaics, display production and printed electronics drives the development of novel technologies for the deposition of transparent conductive oxides (TCO) [1]. The need for high throughput and cost effective production solutions motivates the research for new deposition concepts. To increase the optical transmittance and to decrease the electrical resistivity ZnO:Al (AZO) thin films are typically deposited on heated substrates. In case of magnetron sputtering (MS), the optimum deposition temperatures for AZO were found to be typically about 350°C [2]. Another approach to improve the layer quality is to perform a post deposition thermal treatment like rapid thermal processing (RTP) or furnace annealing (FA) of the samples which were not heated during deposition [4-6]. These conventional thermal processing regimes expose substrates to critical temperatures of several hundred degrees. Another disadvantage of standard annealing techniques like RTP or FA is the required processing time in the range of minutes to hours [5, 6] which is not compatible with common industrial inline-production processes. One main advantage of FLA beside the short processing time (several ms) is the possibility to confine the thermal treatment to the TCO layer. Depending on the properties of the substrate materials and the pulse duration only the surface layer with a thickness between a few tenths of nm or a few tenths of µm is heated. Accordingly, FLA is promising to treat layers on temperature sensitive substrates and due to process times in the millisecond scale it meets the requirements for the integration into efficient production lines [3].
EXPERIMENT The AZO films deposited on soda lime glass (according to ISO 8037/I, thickness 1 mm) were produced by an industry oriented inline MS system with a dynamic oscillating substrate carrier (Fig. 1). There are basically two different approaches to produce AZO using MS: The first
possibility is to sputter an Al doped Zn Target in an atmo
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