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(tertbutyloxycarbonyloxystyrene) (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.

Ultra-Broadband Time-Resolved Coherent Anti-Stokes Raman Scattering Spectroscopy and Microscopy with Photonic Crystal Fiber Generated Supercontinuum

“…The first CARS microscopy was used to obtain the structural image of epidermal cells of onion immersed in D 2 O [21] . The water diffusion in live dictyostelium cells was researched with a broad vibrational resonance centered at 3300 cm -1 , which could not be observed with fluorescence microscopy [75] . These early experimental results have proved that the CARS microscopy is an effective complementary method of fluorescence microscopy.…”

“…By improving the temporal resolution, it is possible to image the chromosome distribution during mitosis using the symmetric stretching vibration of the DNA phosphate backbone [76] . Because of the good detectability of lipids, the structural and functional images of various living cells were obtained with CH bond of lipid [75,[77][78][79] . The sensitivity of CARS microscopy is high enough to detect lipid vesicles with sizes smaller than 300 nm in diameter [79] .…”

Coherent anti‐Stokes Raman Scattering Microscopy

“…CARS microscopy has been used in the imaging of lithographically imprinted patterns of polymer photoresist. [106] In this example, the authors converted a tert-butoxyl carbonyl group of the photoresist into a hydroxy group. With the conversion process they generated a line pattern in the sample (with a spacing of % 250 nm and consisting of converted and nonconverted areas).…”

One-laser interferometric broadband coherent anti-Stokes Raman scattering

“…Furthermore, the non-resonant scattered light interferes coherently with the resonant signal so as to distort the bandshapes (as compared to natural spontaneous Raman bandshapes). Although the signal contribution originating from the non-resonant background is often sufficient to obscure weak resonant signals, narrow-band CARS has been demonstrated to be effective in biological [4,6,7] and materials imaging [8], provided that resonant signal strength is sufficiently high with respect to the non-resonant background.…”