On-wafer spectrofluorometric evaluation of the response of photoacid generator compounds in chemically amplified photoresists

The enhanced photospeed of chemically amplified photoresists is crucial for high throughput lithography required by the semiconductor industry. The photospeed depends directly on the efficiency of the generation of photoacid during exposure, which is a function of the properties of the photoacid generator compound used in the resist. We report a novel technique for photoacid generator evaluation which is convenient, fast, and robust. This technique involves “whole wafer” imaging of resist doped with pH-sensitive fluorophores and patterned with an array of fields of varying doses. A spatially encoded map of the response of the compound under study is thus obtained in a single camera image. We measure the amount of photoacid produced as a function of dose for three photoacid generator compounds with reference to the commercial resist Shipley SAL 605. The results demonstrate a one-to-one correspondence with lithographic performance as determined by the normalized remaining thickness technique.