Dissolution Rate Monitor Tool to Measure EUV Photoresist Dissolution

The resist development step in photolithography is a complex process involving selective dissolution between exposed and unexposed photoresist. This phenomenon is commonly described by a one-to-one relation between dissolution rate and deprotection level of the photoresist. Experimentally, the dissolution rate can be obtained dynamically via a dissolution rate monitor. In EUV lithography, photoresist films are typically below 50 nm, and total dissolution of the film can be very quick. In this work, we have improved a custom built dissolution rate monitor and developed a procedure to record experimental data on dissolution rate of very thin film of EUV photoresist using multi-wavelength reflectometry. We present the results of the validation of this set-up, which ensures repeatability, good temporal resolution, and a short black-out time. The tool now available proves to be suitable for the study of EUV photoresist dissolution and can provide relevant input for lithographic software and for improving the design of photoresists. The impact of film thickness variation is presented, as well as a comparison of two chemically amplified resists with a different quencher loading.