23 June 2000 Spectroscopic characterization of acid mobility in chemically amplified resists
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Abstract
State-of-the-art microlithographic processes used to make features smaller than 0.25 microns are based upon deep-UV lithography and chemically amplified resists (CARs). In these resists, photoacid generated during exposure initiates cascading deprotection reactions during post exposure bake (PEB) to form a developable image. Reaction may not be limited to the illuminated areas since the photo-generated protons may diffuse outside this region; therefore, it is important to understand the diffusional characteristics of the photoacid. In this contribution, macroscopic free volume changes in the photoresist film were studied using multi-wavelength interferometry, and acid mobility and concentration during PEB were studied using crystal violet. This probe was added to the Shipley Apex-E 2408 DUV photoresist, and measurements were carried out in situ on quartz substrates. Crystal violet is a triphenylmethane 'propeller' molecule whose excited-state lifetime increases as the local free volume decreases, and molecular rotation is hindered. This feature can be used to characterize the free volume in the photoresist using ground- state recovery experiments. In addition, crystal violet has three protolytic forms, each with a unique absorption spectrum, and a calibration of the absorption spectrum as a function of acid concentration was used to measure the acid concentration during PEB. These studies illustrate the utility of spectroscopic techniques to characterize CARs in situ.
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Julie L. Jessop, Scott N. Goldie, Alec B. Scranton, Gary J. Blanchard, Bharath Rangarajan, Uzodinma Okoroanyanwu, Ramkumar Subramanian, Michael K. Templeton, "Spectroscopic characterization of acid mobility in chemically amplified resists", Proc. SPIE 3999, Advances in Resist Technology and Processing XVII, (23 June 2000); doi: 10.1117/12.388299; https://doi.org/10.1117/12.388299
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