Modelling vacuum ultraviolet photon penetration depth and C=O bond depletion in 193 nm photoresist

Vacuum ultraviolet (VUV) photons are known to modify the bulk chemical composition of 193 nm photoresist, typically penetrating ∼100 nm and depleting carbon-oxygen bonds. Fourier transform infrared transmission measurements as a function of VUV photon fluence demonstrate that VUV-induced bond breaking occurs over a period of time. We present a model based on the idea that VUV photons initially deplete near-surface O-containing bonds, leading to deeper, subsequent penetration and more bond losses, until the remaining near-surface C-C bonds are able to absorb the incident radiation. Fitted model photoabsorption cross-sections compare well with the literature values.