The presence of organic contaminants, be it residues, mold release agents, etc., is a common roadblock to achieving desired adhesion. Although oxygen plasma is an excellent method for removing impurities, it is essential that proper precautions are taken as it is possible to under-treat a substrate. For instance, if there is a thick layer of residue on the surface, a short exposure to plasma can create a strong bond to the upper surface of a layer that is poorly bonded to the substrate. Under stress, the residue will then break free of the substrate and the joint fails.
Once oxygen has been exposed to the RF energy field inside a vacuum chamber, it is broken down into monatomic oxygen that will then readily combine with organic hydrocarbons. The outcome is a combination of water vapor, carbon monoxide and carbon dioxide that is removed in the vacuum steam.
It is important to take into account that non-organic impurities like salts cannot be removed from a substrate by plasma cleaning. Plasma, however, can remove the binders of the salt which can then be washed away with DI water or another suitable solvent.
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