Prevention of photoresist pattern collapse by using liquid carbon dioxide

Photoresist polymers with high aspect ratios are presently cleaned with aqueous solutions. For high aspect ratios, the pattern collapses during the drying step. The origin of resist pattern collapse is the surface tension of the rinse liquid. Following a theoretical model, we present the results of a preliminary analysis on using environmentally benign liquid carbon dioxide (CO2) as a cleaning solvent. To avoid the likelihood of pattern collapse, the relative size of the actual pattern spacing (S) should be larger than the minimum allowable pattern spacing (d), which can be calculated based on the properties of the rinse liquid and the mechanical properties of the resist material. The use of CO2 as a rinse liquid should help prevent the resist pattern collapse problem.