Characterization of advanced DUV photoresists

The first objective of this project was to characterize the lithographic performance of an advanced Acetal-based DW resist. This resist is targeted for 0.25-0.18 micron geometries. The sensitivity of film thickness and uniformity to critical process parameters such as final dry spin time in the coater, soft bake time, soft bake temperature, method of soft bake (exhaust or vacuum), exhaust and vacuum levels in the soft bake were investigated. The second objective was to compare the material and lithographic performance properties of the advanced Acetal-based DUV resist, an advanced ESCAP-based DW resist (0.18 and potentially 0.13 micron geometries), and a third generation i-line resist (0.5-0.7 micron). An advanced SVG track system that was clustered with an advanced Micrascan was used in these experiments. This lithography cluster tool represents a typical high volume production tool for device features of 0.25-micron and below. For the Acetal-based resist, the sensitivity of resist film thickness and uniformity to key process variables was determined. Bake time (-1.44 Angstrom/ second) and bake temperatures (-10.31 Angstrom/ degrees C) were found to have significant effect on mean thickness. Vacuum level (0.087 Angstrom/ in Hg), dry spin time (-0.064 Angstrom/second), bake temperature (-0.028 Angstrom/ degrees C) and bake time (-0.021 Angstrom/second) were found to have significant effect on coating uniformity. Material properties and lithographic performance comparisons showed that % E-0 swing amplitude increases and periodicity decreases as we move towards scanners with laser sources exposing resists for smaller geometries. We found that periodicity of the Acetal-based resist decreased by 31.8% as compared to the i-line resist. The percent change in the amplitude of the swing curve of the Acetal-based resist was 70%, as compared to 40% for the i-line resist. Sensitivity of thickness to spin speed decreases in the same direction. Spin speed sensitivities of the i-line and Acetal-based resists were calculated to be 2 Angstrom/rpm and 1.55 Angstrom/rpm respectively. Detailed experimentation and statistical analysis showed that advanced SVG tracks could reduce track contribution to CD (critical dimension) control to 3.4 nm.