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Electron Impact Emission Spectroscopy (EIES)
Guardian Co-Deposition Control Systems, powered by Electron Impact Emission Spectroscopy (EIES), is ideal for controlling simultaneous co-deposition of multiple materials in applications such as CIGS for photovoltaics, MBE, OLEDs and superconducting thin films.
Using EIES, the material being deposited is excited by a thermionic emitter, which results in creation of photons. The light created passes through an optical filter to a photomultiplier tube (PMT) detector, which measures the intensity of emission of the passed wavelength. The INFICON Guardian Controller then generates a signal to control the source for that material. Additional detectors, with appropriate optical filters, are used for multiple materials.
A complete Guardian system consists of at least one sensor, one detector, an optical filter, a controller/interface unit, and a PC-compatible computer (user-supplied) with Guardian software. EIES is generally used to control deposition of multiple materials, so most EIES systems include additional sensors, detectors, optical components such as beam splitters, and QCMs for calibration or controlling deposition rate for some materials. The block diagram (right) shows a typical Guardian system configuration. In this system, Guardian controls the deposition rate of four materials, using EIES for three of the materials and a QCM (Quartz Crystal Microbalance) for the fourth. (A common configuration for deposition of CIGS materials in photovoltaics applications.)
To Configure a Guardian Co-Deposition System, Consider the Following
What are the primary and secondary emission wavelengths for your deposition materials?
If different materials have peaks too close to each other, you may need to monitor a secondary wavelength, which has lower signal strength.
During the deposition process, what background gases are present in your vacuum chamber and what are the emission wavelengths for those gases?
If emissions from background gases interfere with the deposition materials, a gas compensating sensor is recommended.
EIES is most effective with the uniquely defined spectra of atomic species. Molecular species that generate unstable or broad emission spectra cannot be measured accurately. EIES is not recommended for organic materials. These, and other factors, determine the optimum EIES system configuration for each specific application.
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