Highprecision automatic alignment procedure for vector scan ebeam lithography J. Vac. Sci. Technol. 15, 906 (1978); 10.1116/1.569625 High−precision skimmers for supersonic molecular beams Rev. Sci. Instrum. 46, 104 (1975);We measure the fluorescent alignment generated by ion bombardment of an Si0 2 wafer mark scanned behind a corresponding window pattern in a silicon stencil mask. We conclude that an optimized system can align to 50 nm (mean + 3!T) in less than 300 ms. Throughput is shown to be limited not by the alignment system, but by thermal loading of the mask during exposure.
A detailed study of the resolution performance of an advanced research type ‘‘Alpha Ion Projector’’ with 5× ion-optical reduction has been performed. One part of the study was done with a nickel open stencil test mask with an active field of 40 mm×40 mm with smallest line pattern openings of ≊0.7 μm width (2.0 μm periodicity). The other part was done with a silicon stencil test mask (120 mm diam, 2.5 μm thickness, 60 mm×60 mm design field) with smallest line patterns of ≊0.4 μm width (1.0 μm periodicity). The Alpha Ion Projector exposures were performed in positive (PMMA: OEBR-1000) and negative (SNR-M4, RAY-PN) resist materials with subsequent wet chemical development. The 0.15-μm resolution was obtained in the case of wafer exposures with the nickel stencil mask within the 8 mm×8 mm exposure field whereas in the case of wafer exposures with the silicon stencil mask sub-0.1-μm resolution could be achieved near the center of the exposure field at 5.2× ion-optical reduction.
A process is described for fabricating silicon masks for ion beam lithography. Masks have been fabricated with 0.02-μm features in 1.5-μm-thick silicon membranes.
We have fabricated a gate-level stencil mask for GaAs field effect transistors with 1000 gates and 1-cm2 silicon foil area. Stress relief distortion was not significant relative to the measurement error of 25 nm(1σ). The results suggest that thermal distortion is also negligible for power densities less than 10 mW/cm2 . This corresponds to a PMMA exposure time of 12 s for 120-keV H+3 ions.
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