High numerical aperture - Imaging implications for chemically amplified photoresists

We have extended the recent work on high numerical aperture (NA) effects in novolac photoresists to investigate the influences of s- and p-polarization at Brewster's angle on the final developable image of a chemically amplified (CA) resist. Using our interferometric lithography tool, resist films (Shipley UVII-HS) were exposed using either s- or p-polarization at both Brewster's angle (146 nm pitch), and at a small angle of incidence (400 mn pitch), where polarization effects are considered negligible. Cleaved and decorated samples were analyzed with a scanning electron microscope (SEM) which provides a measure of the spatial distribution of energy deposition in the film convolved with the image transformation that occurs during PEB. The experimental images were compared to simulated latent images using a PEB model that mimics UVII-HS behavior and a more simplified model, a blurred acid image. Our results indicate that the degraded aerial image contrast at high NA caused by the absence of an antireflection coating (ARC) leads to complex developable images. This degraded contrast can increase line-edge roughness, and affect critical dimension variation. This work reveals the need to understand the details of resist response to high NA aerial images to predict structures, and the importance of a well-designed ARC to maintain control over image formation.