Progress toward a raster multibeam lithography tool

Abstract

A prototype raster multibeam optics is evaluated for 45 nm mask pilot lithography. A laser beam is split into 32 beamlets, which are modulated acousto-optically then focused onto a photocathode. This generates 32 electron beams which are scanned and focused on a writing surface. Photocathode photoyield and lifetime exceed 200 nA/mW and 100 h per spot, respectively. Photoyield recovers to within 1% after 1 min fully extinguished. The size of the laser spot is 300 nm, full width half maximum (FWHM) and the size of the corresponding electron beam spots is 50 nm (FWHM) at the writing plane. In the first demonstration of multiple electron beam lithography, 200 nm line/space arrays and 100 nm isolated lines were printed with an interim four-beam datapath. Preliminary experiments and a theoretical evaluation indicate that resist outgassing does not significantly reduce photocathode performance. An improved electron-optical column has also been designed, with a 35 nm pixel pitch, and a placement accuracy of <0.8 nm over a 120 μm field of view at the cathode and the scan field of 410×10 μm at the writing plane.