Photoresist descum is the process of removing the photoresist residual in the open trenches or holes after the lithography and developing steps. The photoresist residual is usually on the nanometer scale. If the residual is not removed, it can cause a uniformity issue for the subsequent etching process. The residual can also create problems for metal deposition or the electroplating process. The photoresist descum process can be carried out with oxygen plasma in the direct mode or downstream mode. The downstream mode plasma can limit the damage caused by energetic ion sputtering.
Descum process is usually fairly short and runs at a relatively low rf power. So the change of the temperature on the wafer is not significant. Plasma systems used for descum are usually created by radiofrequency or microwave plasma at the frequency ranging from MHz to GHz.