Extreme ultraviolet imaging and resist characterization using spatial filtering techniques

This thesis provides information on extreme ultraviolet (EUV) photoresists and provides new methods to probe resist properties. Resolution and line-edge roughness are both investigated for linewidths at and below 50 nm. By using a spatial frequency doubling method, an EUV optic designed for 100-nm resolution was converted into a tool that prints dense features in the 30- to 50-nm range with low line edge roughness. Loose pitch features are shown down to 25 nm.; The primary imaging system used in these experiments incorporated coherent 13.4nm wavelength light and a 10x-Schwarzschild demagnification optic. High-resolution and high contrast test patterns were exposed into both chemically amplified and non-chemically amplified resists. Combining the 10x demagnification provided by the optic with the spatial-frequency doubling technique, a 20x reduction of the object grating pitch was obtained. For example, 0.8-mum dense lines on the object grating printed 40-nm dense lines onto the resist-coated wafer. The line and space patterns were limited to one orientation and a dense 1:1 spacing. The ability to spatial frequency double four pitches in a single exposure was also analyzed and demonstrated. When comparing multiple linewidths, this method removed wafer-processing variations from the printing experiments.; This thesis also describes work done to create specifications for a new 10x optic designed for use with these experiments. Mirror roughness simulations, mirror alignment calculations, and EUV interferometry were all done for this optic. The best full-field images were printed using this new optic.; Furthermore, this thesis presents additional spatial filtering techniques that introduce more ways to look at photoresist performance. Most notably is the method to modulate aerial image contrast. Instead of using a two-exposure process (pattern and background flood), this work integrates the contrast variation into the mask design. By changing the duty cycle of a grating, the field strengths of the diffracted orders are altered. Using spatial filtering, only the 0 and +1 orders are then used to create the field mismatch. This imbalance in the orders creates a decrease in image contrast at the wafer plane. The additional benefit of using this filtering technique is that the duty cycles on the mask do not print on the wafer. Constant linewidths are produced because all orders except for the 0 and +1 are filtered out. The resist ends up seeing only variations in contrast and not the encoded duty cycle information.; Coherence plays an essential role in these experiments. Both the spatial frequency doubling and the aerial image contrast methods utilize the coherent addition of the diffracted orders. Along with this necessary function, coherence also brings ringing effects from hard edges and amplification of defects to the imaging system. Coherence errors are investigated in both experiments and simulations.; To evaluate resist materials for EUV lithography, it is necessary to expose different test patterns with very high spatial resolution (less than 50 nm lines and spaces). To this end, all of the configurations presented here are designed to help evaluate the ultimate performance and extendibility of resist materials for future lithography techniques.