EM-KLEEN and SEMI-KLEEN downstream plasma cleaner
Hydrocarbon contamination exist abundantly in ambient atmosphere. When samples are exposed to air for 1 hour, the top surface layer of the samples will be coated with a layer of hydrocarbon contamination. Hydrocarbon contamination can also be transferred into the ultra-high vacuum chamber by samples and uncleaned gases. X-ray photoelectron spectroscopy (XPS), Secondary Ion Mass Spectrometry (SIMS) and Auger Electron Spectroscopy (AES) is a surface-sensitive quantitative spectroscopic technique that measures the elemental composition at the parts per thousand to parts per billion range. If the chamber of the XPS, SIMS or AES system has been contaminated by hydrocarbon, surface analysis result won't be accurate.
SEMI-KLEEN and EM-KLEEN downstream plasma cleaners have been used on surface analysis instruments to remove the hydrocarbon contaminations inside the vacuum chamber. Process gases such as oxygen, hydrogen, clean dry air or water can be used to generate plasma inside the remote plasma cleaner. RF energy provided by the controller can ionize the process gas inside the plasma source. Radical species, such as O, O3, H and OH will be generated due to electron dissociation process in the plasma. Radical species will diffuse into the XPS, SIMS and AES chamber and react with hydrocarbon contaminant. The byproduct are usually low vapor pressure molecules that can be easily pump away.
SEMI-KLEEN downstream plasma cleaner on XPS system. Courtesy of Professor Newberg in University of Delaware.
XPS system in the University of Delaware has integrated our SEMI-KLEEN plasma cleaner to remove the hydrocarbon contaminations inside the XPS chamber. Experimental results show that 40 minute hydrogen plasma clean can totally remove the hydrocarbon signal at room temperature. Downstream plasma cleaner can also be used to remove hydrocarbon contaminations on the sample after the sample was contaminated by air exposure. XPS data from UCSD show that 2 second hydrogen plasma clean can totally remove the carbon and oxygen signal on InGaAs samples.
Blue: XPS chamber at ~110C before plasma cleaning; Red: XPS chamber at ~110C after 40 minutes of plasma cleaning using H2; Green: chamber at ~21C, only m/z = 28 (CO) remains, hydrocarbon signal gone.
Frist step: XPS analysis on clean InGaAs samples;
Second step: Hydrogen plasma cleaning using SEMI-KLEEN plasma cleaner, no added contamination from plasma cleaner;
Third step: expose the InGaAs sample in ambient air for 1 hour, hydrocarbon contamination deposits on the surface, surface is oxidized.
Fourth step: InGaAs surface after 2 second downstream hydrogen plasma cleaning using SEMI-KLEEN plasma cleaner.