Measuring line roughness through aerial image contrast variation using coherent extreme ultraviolet spatial filtering techniques

Abstract

Line edge roughness properties for an extreme ultraviolet photoresist (Rohm and Haas/Shipley 1K) were investigated by varying the aerial image contrast of dense line and space patterns. Aerial image contrast variation was performed in single exposures by programming the modulation information on the mask. No background flood exposures were needed to reduce the contrast. The Micro Exposure Tool at Lawrence Berkeley National Laboratory was used for these experiments. Dense 50nm lines and spaces were printed with contrast levels ranging from 86.4% to 46.8%. Coherence was programmed to be 0.1 for these experiments. Results show that an increase in the aerial image contrast causes a subsequent decrease in the line edge roughness (LER). Similar effects are seen for linewidth roughness (LWR). The LER varied from 3.3nm (at 86.4% contrast) to 8.0nm (at 46.8% contrast). LWR varied from 5.3nm (at 86.4% contrast) to 12.8nm (at 46.8% contrast). All values are three sigma root-mean-square. Only a couple of dense 30nm features would print in this configuration. For these 30nm lines and spaces, the best LER was 5.6nm and LWR was 11.3nm.