Measurement of the point spread function of a soft x-ray microscope by single pixel exposure of photoresists

The monochromatic zone plate focused soft X-rays of scanning transmission X-ray microscopes (STXM) can be used to directly write patterns in common photoresists, analogous to lithography with a focused electron or ion beam. A radiation damage spreading phenomenon when patterning with high doses was recently determined to be due to the point spread function of the optical system (Leontowich et al., Applied Physics A: Materials Science and Processing 103, 1 (2011)). We have used this phenomenon to measure the point spread function of three different STXMs by making a series of single pixel exposures in a photoresist at focus over a controlled dose range. Our results suggest this measurement is sensitive to zone plate aberrations; thus, it could be valuable feedback for optimizing zone plate fabrication schemes and STXM performance.

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