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Video: How to Determine if a Thin Film is Dry During Spin Coating

This video demonstrates a thin film changing colour during spin coating as it dries. In this example a solution P3HT in trichlorobenzene was spin coated onto a silicon substrate with 300 nm of silicon dioxide in order to give maximum contrast. For further information, read our spin coating guide by clicking here.

Microscopy techniques will give you a more quantitative assessment of nanostructure, and surface profiling techniques can provide better thickness and roughness estimates. However all of these techniques are slow, may damage the sample or introduce additional delays or variables to a process that can be critically dependent upon timings. Furthermore they are not suitable for assessing every pixel on every substrate at every stage of a process - at least in an R&D environment.

Your eyes are the primary tool and first line of analysis for almost all device engineering, and are highly sensitive devices. With the correct lighting you can often spot a 5 nm variation in film thickness just by looking at the colour. As such, inspecting a substrate visually before and after each step is critical for understanding and improving variation and performance.

  • Does the film look uniform?
  • Is the colour (thickness) as it should be?
  • Does the surface have a glass-like, smooth-matt or rough-matt finish?
  • Are there any aggregates on the surface?
  • Are the any pin-holes or comet streaks?

In addition, with the correct lighting it is also possible to assess whether a spin coated layer is dry while the substrate is still spinning. In some cases (such as for many conjugated polymers) this is relatively easy because the film changes colour as it dries.

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