Effect of ion energy on photoresist etching in an inductively coupled, traveling wave driven, large area plasma source

We report on the effect of ion energy on photoresist etching in an inductively coupled large area plasma source driven by a 13.56 MHz traveling wave with oxygen gas. To control the ion energy at the substrate surface, the electrode on which the substrate is placed is independently driven by a capacitively coupled 1 MHz power source. The etch rate increases with increasing ion energy for gas pressure ranging from 1 to 100 mTorr. Ion-induced desorption rate constants (etch yields) are shown to be proportional to the square root of the ion energy. An increase in the ion energy leads to etch-uniformity improvement over the processing area of 40 cm×50 cm, particularly at a low gas pressure of 5 mTorr. A modified photoresist etch kinetics model combined with a spatially-varying oxygen discharge model is used to explain these experimental results.