Why should SEM, FIB chamber be cleaned with plasma cleaners?
Hydrocarbon contamination is a prevalent issue in many high vacuum analytical equipment, such as SEM, FIB, TEM, and XPS systems. Secondary electrons or high-energy photons can dissociate, cross-link hydrocarbon molecules, and create carbon deposition in the scanned regions on the surface of the sample. Plasma cleaner can remove the hydrocarbon contaminations in the chamber using process gases that contain oxygen or hydrogen.
Principle of in-situ plasm cleaning for SEM and FIB chamber
Plasma cleaner can be installed on the main imaging analysis chamber or on the load-lock chamber. Most of the users simply use ambient air to generate the plasma. During plasma cleaning, the flow control valve in the plasma source will leak 0.1-40sccm of process gas (usually ambient air) into the plasma source. Radiofrequency energy can ionize and break down the process gas to generate the plasma. Energetic electrons in the plasma can dissociate oxygen molecules to generate monatomic radical oxygen. Radical oxygen will then diffuse into the downstream chamber and react with hydrocarbon contaminations on the chamber wall or on the sample surface. The by-products are usually high vapor pressure CO2 and H2O that can be easily pumped out by the vacuum pump. During plasma cleaning, the vacuum pump should be kept running at the full speed to increase the cleaning speed and efficiency.
Plasma cleaning of SEM and FIB chamber using EM-KLEEN plasma cleaner.