Autofluorescence imaging-based nondestructive monitoring of latent patterns in photolithography

Abstract Nondestructive, post-exposure monitoring of latent photoresist patterns remains challenging because conventional metrology relies on post-development inspection, making it difficult to attribute deviations to exposure conditions. We propose an autofluorescence-imaging-based monitoring method that operates immediately after UV exposure, using excitation wavelengths spectrally separated from the exposure wavelength, and establish its performance as a measurement. To identify a suitable monitoring wavelength, latent patterns were imaged at four excitation wavelengths. Among the wavelengths tested, 561 nm provided the most stable latent-pattern signal, with only a −3.1 % change after 30 s of continuous excitation, whereas shorter-wavelength excitation caused unintended additional exposure or substantial photobleaching. The autofluorescence contrast increased nonlinearly with exposure dose and gradually approached saturation, as described by a model derived from depth-integrated photochemical conversion. Inverting the fitted response estimated the delivered dose with 6–11 % RMS error (leave-one-out), and retained sensitivity above the dose to clear, where the developed topography saturated and post-development inspection became insensitive to over-dose. In two independently conducted exposure experiments, no systematic monitoring-induced change in the developed geometry was detected, and the minimum detectable dose was 9.7 mJ/cm² at 3σ. This label-free approach enables pre-development latent-pattern imaging and quantitative dose monitoring for microscale maskless lithography and process development.