In Chemical Bath Deposition (CBD) processes, the substrates to be coated are immersed in a liquid solution of precursors. A chemical reaction forms the thin film at the interface between the substrate and the liquid. A common example is the deposition of CdS on top of copper-indium-diselenide (CIGS) absorbers in thin film photovoltaic cell manufacturing. The CIGS-coated substrate is immersed in an aqueous solution of ammoniumchloride, ammonia, cadmiumchloride and thiourea. The precursors form CdS which is deposited on the surface of the CIGS substrate.
CBD is a well-established method for depositing homogeneous layers in mass production, but thickness, quality and uniformity of the deposited layer depend on a large number of process parameters. The most decisive influences are the concentration profile of all precursors in the solution, the temperature and temperature homogeneity of the solution, the flow profile of the liquid close to the surface of the absorber, the composition, the roughness and the temperature of the surface on which the layer is deposited. A close in-line monitoring of the layer quality is therefore important for detecting process distortions as soon as they occur.
LayTec’s in-line metrology systems are used to monitor the film thickness and homogeneity of CBD layers in-line, directly after deposition. Find out more in our overview of in-line tools
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