Addition of nitrate to superheated water and its reaction mechanism with C-C cross-linked ion-implanted photoresists

Abstract

Dissolution of the high dose ion-implanted photoresist which has carbonized CC cross-linked crust layer was demonstrated by using nitrate-infused superheated water. The ion-implanted photoresist was partially dissolved in pure superheated water at 200 °C, but the crust layer was not dissolved. The dissolution of the ion-implanted photoresist was greatly improved with the addition of nitrate compounds, such as HNO3, Zn(NO3)2, Cu(NO3)2 and Fe(NO3)3, to the superheated water. In particular, the ion-implanted photoresist was completely dissolved when the nitrate-infused aqueous solution produced H+ concentrations higher than 1 × 10−5 M and NO3− concentrations higher than 0.0156 M. When H+ and NO3− ions were sufficiently present in superheated water, NO2, which is very reactive with carbon, was produced. Based on the in-situ spectroscopic analysis, it was suggested that the cleavage of the CC bond between the aromatic rings and the backbone chains in the crust structure by NO2 initiated the dissolution reaction. Additionally, 4-nitrophenol, aliphatic compounds and trans-4,4-azodiphenol were produced and then they were decomposed to the 4-aminophenol and other gases. Therefore, it was concluded that H+, NO3−, and NO2 in superheated water were the key species to dissolve the crust layer and the bulk ion-implanted photoresist.