Use of interferometric lithography to characterize the spatial resolution of a photoresist film

We consider the consequences of treating a photoresist film as an element of an imaging optical system, by means of classical Fourier optics. The spatial resolution of the photoresist is described by a line spread function, or equivalently by its Fourier transform, the modulation transfer function (MTF). We then show that given a quantitative model for the development process, the MTF can be deduced from measurements of linewidth vs. dose for sinusoidal illumination patterns generated by interferometric lithography. Experimental results supporting the validity of this approach have been obtained for commercial deep-UV photoresist. This work provides a simple methodology to quantitatively describe the spatial resolution of a photoresist, which does not require highly optimized imaging optics.