Effect of CF4 addition on downflow ashing under atmospheric pressure

We studied the rate increase of ozone ashing under atmospheric pressure. It was verified that when an ozonizer discharge was used under atmospheric pressure, the ashing rate increased to up to one and a half times the original rate with the addtion of CF4. F element and C-F bonds, which might appear as a result of the addition of CF4, were not detected on the resist surface by Fourier transform infrared spectroscopy (FT-LR) and X-ray photoelectron spectroscopy (XPS) analyses. On the other hand, the formation of HF and an increase in CO and CO2 were observed by FT-IR analysis of the excited gas. Therefore, the increased ashing rate with the addition of CF4 is likely due to the active decomposition product which contains fluorine radicals produced in the discharge. These active species are transported under atmospheric pressure and cause H extraction from -OH groups which exist in the resist and result in improved oxidative decomposition.