A bilinear photoresist model is accurate, fast, and potentially reversible. Similar to other image-processing style (blur
kernel) models, this model represents a transformation of an aerial image into a latent image. The key difference is the
explicit recognition of the non-linearity of the process while retaining common signal processing architecture. By
applying a Volterra series expansion to the reaction-diffusion functional, a high-accuracy representation of the process is
obtained. Several methods for identifying the double-impulse response of the quadratic term of the series are discussed.
Characterization is carried out based on the bi-harmonic signal sampling method of the Bilinear Transfer Function, the
Fourier transform of the double-impulse spread function. Several photoresist systems are characterized, and strong
quadratic behavior is observed for many. The resulting estimated BTF are presented, and their differences are discussed.