Chemical Imaging of Photoresists with Coherent Anti-Stokes Raman Scattering (CARS) Microscopy

Abstract

Coherent anti-Stokes Raman scattering (CARS) microscopy is demonstrated to be a powerful imaging technique with chemical specificity for studying chemically amplified polymer photoresists. Samples of poly(tert-butyloxycarbonyloxystyrene) (PTBOCST) resist imprinted by interferometric lithography with a pattern of lines/spaces of 400 nm/400 nm and 200 nm/200 nm were used to test CARS imaging capabilities. Chemical contrast in the image is obtained by probing the carbonyl stretching vibration of the tert-butoxyl carbonyl group of PTBOCST. The experimental images demonstrate high spatial resolution (≈270 nm) and strong signal, which allows short acquisition times. Advantages and limitations of CARS in comparison with other imaging techniques with chemical specificity, such as infrared near field scanning optical microscopy (IR NSOM), are discussed.