Spectroscopic measurements conducted in vacuum environments range from reflection measurements during coating processes through high speed plasma monitoring during a reaction. Avantes has worked extensively with customers operating in these environments and offers a variety of instruments and accessories to meet the needs of vacuum spectroscopy.
These techniques are frequently used for sophisticated process control monitoring such as end point detection. This procedure involves monitoring a peak or wavelength range to detect a process inflecton point characterized by a spectral shift which signals the end of the process. High (~10-3 torr) and ultra-high vacuum (~10−9 torr) measurements require special consideration when selecting a spectrometer and the associated fiber optics used for sampling.
Monitoring Coating Processes in Vacuum Chambers
Layer thickness, composition, surface finish, light transmission, reflectance, polarization ability: these are some of the important parameters that need to be monitored during coating processes. They are all facilitated by spectroscopy and spectroscopic interferometry. Fiber optics provide a versatile tool to measure in remote vacuum and clean room chambers.
The illumination and detection can be organized at different fiber positions relative to the coating: to allow specular reflection, diffuse reflection, transmission, polarization, interference, fluorescence and even Raman scattering to be measured. Fiber optics can be arranged to either monitor several positions or to measure the different spatial positions or masking conditions simultaneously.
For on-line production environments, several fiber-optic sensors can be placed to monitor a production run. Ionic sources, such as plasma sources, can be monitored for spectral emission to confirm their conditional efficiency during the operating process.
A typical application for a vacuum chamber system is monitoring an on-line coating process on a web. For this type of system, a vacuum feedthrough is used to transfer light into the vacuum area and then passed into the reflectance probe. The reflected light is passed through another vacuum feedthrough to a spectrometer, usually the AvaSpec-ULS2048CL-EVO or one of our SensLine instruments when higher sensitivity is necessary. The reflectance probe can be easily disconnected using the SMA interconnects. To compensate for fluctuations in the light source, a second channel can be added for light source reference measurements.