ETA Helios SCAN-tc

Coating Measurement of Solar Cells; Thickness and Color of Silicon Nitride

Silicon Nitride plays an important role in the manufacturing process of wafer-based solar cells. Measurement of its layer properties is often expensive and time-consuming.

With Helios SCAN-tc, AudioDev offers a powerful device that helps to optimize the coating process in a fraction of the time and at a much lower cost than conventional equipment.

Measurement of Silicon Nitride

Using industry-proven spectrometer technology and proprietary measurement algorithms, Helios SCAN-tc combines speed, precise measurement and easy operation – all of which are needed to optimize processes at lowest cost and shortest line downtime.

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Thickness distribution map of the Silicon Nitride AR
coating layer on a textured 156 x 156 mm pc-wafer,
measured by Helios SCAN-tc in less than 1 minute

Principle of Measurement
Phase differences between the front- and rear-side reflections of a thin layer cause interference. The frequency of this interference is proportional to the thickness of the layer. This phenomenon can be used to measure the layer thickness of very thin layers.

After recording the interference spectrum of the coated solar cell, a mathematical calculation is performed in which the layer thickness of a theoretical model of the layer stack is varied. When model and measurement match perfectly, the layer thickness is known very precisely.


Interference spectrum of Silicon Nitride coating on a
textured wafer (measurement = blue / theoretical
model = red)

Our proprietary algorithms take surface roughness of the silicon wafer into account, to enable highly accurate measurement on polished as well as rough wafers. The color of the coated wafer is calculated after measuring the reflectance spectrum at a defined angle. Standardized algorithms are applied to express the color in, for example, Lab or xyY color space.

  Download the ETA SCAN-tc product sheet