Prior to scanning electron microscope (SEM) imaging, the samples were coated with a 6-nm chromium

layer (Gatan PECS, Pleasanton, CA, USA). Cleaved samples were coated at a 45° tilt with the sample cross section facing the target. The SEM buy CX-5461 imaging (Hitachi S-4800, Schaumburg, IL, USA) was conducted at 5 keV, 20 μA, and 4-mm working distance. To evaluate the pattern transfer capability of SML resist, metal lift-off was performed. By electron beam evaporation, 50 nm of chromium was deposited on nanoscale SML gratings and the resulting stack lifted-off by immersing for 1 min in an ultrasonic acetone bath. Results and discussion Figure 1 presents cross-sectional micrographs of cleaved gratings fabricated in SML using the supplier-recommended developer, MIBK/IPA (1:3). SML was found to be easy to use, and it was possible to readily fabricate gratings with an AR better than PMMA in introductory attempts with both 300- (Figure 1a,b) and >1,500-nm-thick (Figure 1c) films. In Figure 1a, a uniform 5-μm-wide

array of 200-nm-pitch gratings is patterned at an exposure line dose of 3.6 nC/cm. In comparison, similar PMMA gratings can be fabricated using approximately three times higher sensitivity. Figure 1c shows a magnified image from the center of the array measuring a thickness of 282 nm and line widths ranging from 45 to 67 nm (from top to base of gratings), resulting in ARs of 4.2 to 6.3. In Figure 1c, an array of 400-nm-pitch Ribonucleotide reductase gratings is patterned to a depth of 1,380 see more nm (no clearance) using an exposure area dose of 700 μC/cm2. From top to bottom, the line widths range from 180 to 220 nm, resulting in ARs of 6.3 to 7.7. The AR results achieved using MIBK/IPA (1:3) are not optimized and can be significantly improved; however, the much lower sensitivity compared to PMMA requires a higher sensitivity developer that maintains or even improves the AR performance. Figure 1 Cross-sectional micrographs of

SML exposed at 30 keV and developed in MIBK/IPA (1:3) for 20 s. The panels show (a) 5-μm array of 200-nm-pitch gratings in 300-nm-thick resist, (b) magnified image with thickness of 282 nm and line widths of 45 to 67 nm from top to bottom of gratings, and (c) 400-nm-pitch gratings in >1,500-nm-thick resist (no clearance) with the achieved depth of 1,380 nm and line widths of 180 to 220 nm from top to bottom of gratings. The exposure doses were (a, b) 3.6 nC/cm and (c) 700 μC/cm2, and the aspect ratios ranged from (a, b) 4.2 to 6.3 and (c) 6.3 to 7.7. The resist was cleaved and coated with a 6-nm Cr layer before imaging. The SML contrast curves for the six developers: MIBK, MIBK/IPA (1:3), IPA/water (7:3), n-amyl acetate, xylene, and xylene/methanol (3:1) are presented in Figure 2.