Expanding Industrial Automation Capabilities with Optical Emissions Spectroscopy
Published by : Industrial Automation
Optical emission spectroscopy (OES) is a widely used analytical technique for the identification of elements in samples. It is commonplace in metal-producing industries, such as steel and copper manufacture, and in fabrication industries.
OES’s power as a technique for elemental identification has seen its widespread adoption within industrial automation. It works by detecting light emitted from atoms or molecules that have been excited to higher energy states, typically using an energetic electrical discharge source.
The excitation or discharge source promotes electrons to higher energy levels from which they subsequently relax and emit light. The emitted wavelengths of light are detected, and their specific wavelengths are characteristic of the emitting atom. An optical emission spectrometer is composed generally of three main components: the excitation source, a diffraction grating, and the detector.
The diffraction grating spatially separates the different emitted wavelengths of light, so a position and intensity sensitive detector can be used to record all the various components or spectral lines that the emitted light is composed of. What makes OES such a powerful analytical technique is that the energy spacings of the spectral lines reflect the underlying electronic structure of the emitting species.
As there may be hundreds of lines in the emission profile, these can be fit to known reference data for unambiguous assignment of the presence of an elemental species. With suitable calibration, the intensity of the light can also be used to quantify concentrations of different elemental species.
The Advantages of Using OES for Automation
The relative simplicity of optical emission spectrometers makes them ideal for integration into automated industrial processes. One common application of OES is for quality control in wafer manufacturing. Plasma deposition is commonly used to create layers of chemical species onto a substrate, and it is critical that all wafers are treated in the most similar way possible.
OES can be used to monitor the conditions in the plasma and the relative ratios of different chemical species to monitor the progression of the chemical reaction and more accurately determine the best endpoint for the processing. For this type of fabrication process, the data output of the spectrometer can be integrated as part of a feedback system with the manufacturing process.
Automation of data analysis and element identification is relatively straightforward and is suitable for use in many types of deposition processes, including atomic layer deposition for the creation of ultra-high-quality thin films. Automated OES is also a popular tool in metallurgy. OES can be used to identify a wide range of elements, including carbon and phosphorous, but works particularly well with softer metals, as they are more easily ‘sparked’ or excited during the initial excitation step.
Impurity testing as part of quality control is one common use of automated OES, but this can be extended to investigative work looking at how the presence of impurities and their relative concentrations have on the physical properties of a material.