Bar and Point Test Patterns Generated by Dry-Etching for Measurement of High Spatial Resolution in Micro-CT

The purpose of this work was to evaluate a novel method for manufacturing test patterns with high spatial resolution to be used for visual inspection of spatial resolution of micro-CT systems. High resolution test patterns of less than 50 mu m line widths or point diameter for inspection of the performance of a micro-CT system have not been reported before. Test patterns were created on a silicon wafer using a dry-etching method. For reference spatial resolution measurements were carried out on micro-CT systems using thin tungsten wires. The modulation transfer function (MTF) subsequently derived from a point spread function (PSF) of the wire profile was measured to determine spatial resolution at 10% of the contrast ratio. The test pattern chip was scanned under the same conditions for visual inspection of the spatial resolution. The results of the wire-based MTF calculations and visual inspection of the test patterns were found in very good agreement. In the manufacturing process some limitations were found due to over-etching and maximum etch depth for smaller patterns (5 mu m) adjacent to larger structures (150 mu m) on one chip. Nevertheless, these circumstances can be solved by using choice of pattern sizes for specific scanner setup. The novel method of creating high resolution test patterns for quick visual inspection offers a very attractive solution, but also allows for quantitative evaluation.