Dry etching resistance of resist base polymer and its improvement

The etching rates of resist base polymers with. several molecular weights were measured against fluorocarbon or chlorine plasma. The rate showed a minimum value at the weight-average molecular weight of approximately 10,000, and increased to a saturated value for higher molecular weights. For poly(p-hydroxystyrene) (PHS) protected with tert-butoxycarbonyl (BOC) or acetal (ACT) group, the rate became larger with increasing the protection ratio and the rate of BOC-protected PHS was lower than that of ACT-protected PHS. It was also found that the rate was significantly influenced by the prebake and increased as the temperature became higher. The etching rate of the resin with gradual cooling after the prebake was slower than that with quick cooling. These results may indicate that the dry etching resistance is independent of the density of resin film and influenced by the stability of arrangements of polymer molecules. The reduction of etching rate by the deep UV cure method have been tried. The rate decreased with the deep UV cure under N-2 gas flow, while increased in the presence of O-2 such as dry air. The films after deep UV cure under N-2 and a dry air was scarcely dissolved in any organic solvents and this implies that the polymers are crosslinking. The absorbance band of carbonyl appeared in FT-IR spectra for the case under dry air may suggest that oxygen atoms in the polymer structure influence the dry etching resistance. We have tried deep UV cue under N-2 gas flaw for KrF chemically amplified PHS based resists and obtained the same level of etching rates as novolak resin. For ArF resists, the combination of the incorporation of acryl unit into the base polymer and deep UV cure under N-2 gas flow may be an effective method for improving the dry etching resistance.