Hydrogen or oxygen in-situ downstream plasma cleaner for removing carbonaceous contamination inside XPS (PES), SIMS, AES, and other high vacuum systems
EM-KLEEN and SEMI-KLEEN UHV in-situ plasma cleaner
Carbonaceous contamination in surface analysis systems (XPS, SIMS, AES)
Carbonaceous contamination (hydrocarbon and fluorocarbon) exists abundantly in the 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. Photoelectron spectroscopy, such as XPS, Secondary Ion Mass Spectrometry (SIMS), Auger Electron Spectroscopy (AES), and atom probe are 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 carbonaceous contamination, the surface analysis result won’t be accurate.
The principle of removing carbonaceous contamination on the sample surface and in the chamber for XPS, SIMS, and AES system using an in-situ plasma cleaner
SEMI-KLEEN and EM-KLEEN downstream plasma cleaners have been used on surface analysis instruments to remove the hydrocarbon contaminations in-situ inside the vacuum chamber. SEMI-KLEEN UHV in-situ plasma source is directly compatible with UHV and XHV vacuum chamber. All the sealing surfaces are either brazed metal-glass joints or metal-metal contacts. Process gases such as oxygen, hydrogen, clean dry air can be used to generate plasma inside the remote plasma source. RF energy provided by the controller can ionize the process gas inside the remote plasma source. Radical species, such as O, O3, H, and OH will be generated due to the electron dissociation process in the plasma. Radical species will then diffuse into the load-lock or the main analysis chamber on XPS, SIMS, AES, and atom probe systems and react with the carbonaceous contamination. The byproducts are usually low vapor pressure molecules that can be easily pumped away. If the downstream plasma cleaner is installed on the load-lock chamber, it can be used to remove the carbonaceous or native oxide contamination on the surface of the sample in-situ before they are analyzed inside the analysis chamber. Since the samples are cleaned in-situ, they won’t be contaminated again by exposure to the ambient air.
Hydrocarbon contamination removal data
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. Our in-situ plasma cleaners have been integrated by some XPS equipment manufacturers to clean the vacuum chamber and samples.
Downstream plasma cleaner can also be used to remove hydrocarbon contaminations on the sample after the sample was contaminated due to air exposure. XPS data from UCSD show that 2-second hydrogen plasma clean can totally remove the carbon and oxygen signal on InGaAs samples with our remote downstream plasma cleaner.
First 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 seconds downstream hydrogen plasma cleaning using SEMI-KLEEN plasma cleaner.
Rapid In-Situ Carbon and Oxygen Cleaning of In0.53Ga0.47As(001) and Si0.5Ge0.5(110) Surfaces via a H2 RF Downstream Plasma. ECS Trans. 2016 72(4): 291-302. Please download the pdf version here.