Pattern characterization of deep-ultraviolet photoresists by near-field infrared microscopy

Abstract

Partially hydrogenated poly(vinyl phenol) based photoresist for near UV, high aspect ratio micromachining Chemical contrast at subwavelength spatial resolution ͑/10͒ is achieved using a fiber-based, infrared near-field microscope, at 3 m wavelength. Chemically amplified polymer photoresists ͑poly͑t-butylmethacrylate͒͒, patterned by ultraviolet radiation and 250 nm thick, are imaged using infrared ͑IR͒ wavelengths situated around the OH stretch band of the polymer, a region sensitive to photochemical changes associated with latent image formation. The key technical points that enable near-field infrared absorption measurements down to 0.05% absorption sensitivity are discussed together with the major contrast mechanisms involved in image formation. The measurements are complemented by confirming studies using confocal infrared microscopy and depth profiling. The exposure dose dependence of the acid catalyzed chemistry, after the postexposure bake step, was studied on line/space patterned samples. The OH subgroup absorption maps of the patterned polymer film exhibit features that are not present in the topographical changes ͑shrinkage͒ induced by the postexposure polymer chemistry and illustrate significant potential of the IR near-field microscopy as an analytical tool for polymer chemical physics.

Coaxial tips for infrared NSOM

“…Novotny et al describe how the transmission modes decays rapidly, "faster than exponential", after a certain cutoff radius [8]. Reference [9] describes that cutoff radius as: (1) Where λ c is the cutoff wavelength, d t is the final taper diameter (two times Novotny's cutoff radius) and n f as the refractive index of the fiber. Using this equation we can see that at 2.8µm wavelength light, and the refractive index of fused quartz (1.424), the cutoff radius is ≈1.2µm.…”

“…Dragnea et al [1] performed conventional aperture-based NSOM in the IR and studied developed photoresists. They achieved a resolution of the order of /10.…”

Chemical mapping of polymer photoresists by scanning transmission x-ray microscopy

“…7,8 Chemical contrast images ͑due to selective absorption͒ have been obtained with a spatial resolution of 300 nm at 3 m ͑the OH stretching vibration͒ along with a simultaneous topographical image by using infrared near field scanning optical microscopy ͑IR NSOM͒. [9][10][11][12] Considerably higher spatial resolution is expected to be achieved by apertureless near field scanning optical microscopy when used with infrared absorption contrast. 13,14 However, this method also faces significant challenges in detecting the small signal ͑light scattered from a͒ Present address: Ecole Normale Supérieure, 75005 Paris, France.…”

Super-resolution Fourier microscopy for Mid-IR

“…CARS is a complicated nonlinear technique which requires expensive tunable sources. Scanning probe setups, in turn, suffer from inefficient coupling of IR light into the near-field taper [2], low throughput, and the necessity for substantial post-processing of collected data. Scanning probe microscopy is, furthermore, poorly suited for observing dynamic processes that span different parts of the imaged object.…”

“…To perform imaging of subcellular chemistry, as well as other nanoscale processes (e.g. photoresist reflow), submicron resolution is required.To attain chemical contrast on a submicron scale several techniques have been developed, including coherent anti-Stokes Raman spectroscopy (CARS) [1], as well as various scanning probe methods [3,2]. While successful in resolving subwavelength structures, these approaches possess several drawbacks.…”