Spectroscopic Inline-Monitoring of Wet Chemical Processes

A silicon wafer undergoes several wet chemical processes during the fabrication of a solar cell. The fabrication process involves several corrosive texturing and purification baths containing aggressive chemicals such as sodium hydroxide, potassium hydroxide, hydrogen peroxide, hydrochloric acid, fluorosilicic acid, nitric acid, and hydrofluoric acid.

It is necessary to keep the respective baths stable in order to maintain the production quality of solar cells. For this purpose, continuous monitoring is required for the necessary regulation.


Common analysis techniques like ion chromatography and titration have measuring times of 6-10 minutes. A distinct advantage of UV/NIR spectroscopy over these common techniques is the ability to provide real-time inline analysis, thanks to its shorter measuring time of below one second.

The combination of an acid- proof, alkali-resistant NIR immersion probe (Picture 1), a multi-linear calibration model, and a spectrophotometer can identify the individual constituents of a chemical bath.

Figure 1. Acid-proof and alkali-resistant NIR immersion probe

Measurement Process

At first, the typical spectrum of different concentrations of the chemicals is recorded by the spectrophotometer through the probe that is submerged in the bath, followed by the creation of a calibration model from the different spectral data by means of software and multi-linear regression methods.

This computed model can then be employed during the inline measurement to determine the composition of the bath directly subsequent to the recording of the spectra.

Given that a calibration model is capable of comprising several parameters, simultaneous measurement of the concentration of all chemicals in the bath is possible without making personal contact with the adverse chemicals.

Advantages of Spectroscopic Inline-Monitoring Solution

The following are the advantages of this spectroscopic inline-monitoring solution:

  • Real-time, inline monitoring
  • Stable bath control for a constant high quality
  • Can monitor several baths simultaneously
  • Prolonged service life thanks to optimized processes
  • Improved product quality
  • Minimizing reject costs
  • Nearly maintenance-free

Fields of Application

The following are the fields of application of this spectroscopic inline-monitoring solution:

Alkaline and acidic texturing baths Hydrofluoric acid, Nitric acid, Fluorosilicic acid, Sulphuric acid
Rinsing Alkalinity/acidity
Hydrophilization Hydrogen peroxide

About Hellma Analytics Optical Immersion Probes

Hellma Analytics develops and distributes cuvettes and optical components for laboratory equipment in modern analysis technology.

Hellma Analytics specialise in:

  • Chemical and pharmaceuticals
  • biotechnology
  • food industry
  • health care
  • environment

This information has been sourced, reviewed and adapted from materials provided by Hellma Analytics.

For more information on this source, please visit Hellma Analytics.


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