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Dissolution properties of ultrathin photoresist films with multiwavelength interferometry

According to the ITRS, a significant decrease in lateral resolution and thickness of resists is anticipated for the forthcoming decade. In order to study in-situ the dissolution of thin resist films, a set-up based on multiwavelength interferometry was developed. Using this setup and an appropriate fitting algorithm, based on the interference function, the resist thickness vs. time is calculated. In the present work, the dissolution of PMMA in a 20-300 nm thickness range is studied. First results showed that in the case of ultra thin films of high molecular weights, dissolution proceeds smoothly after an initial surface inhibition period while thicker films present a more complex dissolution curve. In the case of low molecular weight (15K) the surface inhibition period is negligible and dissolution proceeds smoothly for the whole thickness range examined. PMMA films exposed with various DUV doses exhibit similar behavior with the unexposed films in terms of dissolution inhibition.