PiFM Imaging of Latent EUV in t-BOC CA Resist

On EUV exposure of t-BOC resists, topographic differences arise between exposed and unexposed masked areas. Photo-induced Force Microscopy (PiFM) reveals that the topographic changes are accompanied by changes in IR activity. The peak shifts by 6 cm⁻¹ to create a very strong contrast. The strong signal at 1280 cm⁻¹ is used to identify unexposed areas while the signal at 1514 cm⁻¹ – unique to the exposed areas – identifies exposed areas.

PiFM Imaging of Latent EUV in t-BOC Chemically Amplified Resist

PiFM can be used to visualize the latent image associated with the exposed region by using the reduction in the signal associated with the vibrational mode at 1760 cm⁻¹. A commercial EUV photoresist is exposed but not developed. For the 45 nm feature size, PiFM provides a clearer image (compared to the AFM topography) due to the lack of background features. The resist was extremely under-exposed, causing only a minor change in the polymer. Due to the under-exposure, the 45 nm features are not defined in topography, but PiFM is able to detect the minor chemical changes from such small features.