The Use of Oxygen in SEM Plasma Cleaning Equipment

Getting the most out of your SEM has in the past meant baking out your column and being vigilant about wearing gloves when handling samples. As feature sizes decrease this may not be enough. Hydrocarbon buildup in SEM vacuum chambers can lead to less than ideal resolution. The electron beam reacts with contamination and deposits carbon on the sample which can cause charging and degrade image contrast. Oxygen plasma has long been used for cleaning surfaces in a vacuum. O2 is split into oxygen ions and radicals which are effective at removing organic contaminants. Manufacturers have produced low energy plasma cleaners that pull oxygen ions and radicals out of “thin air.” While this may seem like “snake oil”, it actually does work. This approach works, is easy to use, and has very little setup, but it is very slow. If you have a “dirty” system you may spend days or weeks on an initial cleaning. We modified our Evactron® De-Contaminator to use welding grade oxygen. The investigation that we have performed indicates that there is a night and day comparison for effectiveness and speed. One or two four hour sessions with oxygen was shown to be more effective than using ambient air for weeks.