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Plasma ashing
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<h2 id="types">Types</h2> <p>Two forms of plasma ashing are typically performed on wafers. High temperature ashing, or stripping, is performed to remove as much photo resist as possible, while the "descum" process is used to remove residual photo resist in trenches. The main difference between the two processes is the temperature the wafer is exposed to while in an ashing chamber. Typical issues arise when this photoresist has undergone an implant step previously and heavy metal are embedded in the photoresist and it has experienced high temperatures causing it to be resistant to oxidizing. </p><p>Monatomic oxygen is electrically neutral and although it does recombine during the channeling, it does so at a slower rate than the positively or negatively charged free radicals, which attract one another. This means that when all of the free radicals have recombined, there is still a portion of the active species available for process. Because a large portion of the active species is lost to recombination, process times may take longer. To some extent, these longer process times can be mitigated by increasing the temperature of the reaction area. This also contribute to the observation of the spectral optical traces, these can be what is normally expected when the emission declines, the process is over; it can also mean that spectral lines increase in illuminance as the available reactants are consumed causing a rise in certain spectral lines representing the available ionic species. </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Plasma_etching/VEHxRdLI">Plasma etching</a></li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Plasma Processing: Proceedings of the Symposium on Plasma Processing. Electrochemical Society. 1987. pp. 354–. <a href="https://books.google.com/books?id=BFSuAAAAIAAJ&pg=PA354" target="_blank">https://books.google.com/books?id=BFSuAAAAIAAJ&pg=PA354</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> </ol>