Evaluation of photoacid generators in chemically amplified resists for x-ray lithography using an on-wafer photoacid determination technique

This paper reports an on-wafer photoacid determination technique that can be used to quickly screen materials that function as photoacid generators (PAGs). The technique includes adding a small amount of a pH-sensitive fluorophore into the resist and exposing the resist to x-rays. The acid generated during exposure reacts with the fluorophore and quenches the fluorescence. The efficiency of photoacid generation is evaluated by comparing the degree of fluorescence quenching. This technique is nondestructive, fast, and does not significantly change the resist chemical properties given the low concentration of the added fluorophore. Six compounds that can generate hydrogen halides as potential PAGs were evaluated using this on-wafer technique and the lithographic performance was evaluated for comparison. The commercial resist, Shipley SAL 605, is used as a reference for comparison. The result showed that TBBPA gave higher photoacid generation efficiency that TCBPA and PBP, but lower than that in SAL 605. The results of fluorescence measurements agree with the results obtained using normalized remaining thickness measurements. The advantages, however, of this fluorescence technique are that it is simple, fast, and requires fewer processing steps.