Fabrication of 3 µm Bubble 80 kbit Chips

Abstract

A 3 µm bubble 80 kbit chip was designed by 1/2 scaling from the pattern for 6 µm bubble chip. To obtain a 1 µm minimum feature over a 5 mm square, projection printing was employed. By reducing the reflectance of the surface to be exposed below 33%, standing wave effects with monochromatic illumination could be minimized, and uniform 2 µm width and 1 µm gap pattern could be obtained, notwithstanding the variation in photoresist thickness and the unevenness of substrate. A standard deviation of this distribution in the pattern gap width in the fabricated 80 kbit chips was 0.067 µm when the flatness of the wafer is less than 0.5 µm/chip size. The effects of the variation in the pattern gap on the propagate margins could be ignored, if it fell in the range of 1.03 µm to 1.38 µm. Consequently, the resolution of 1±0.3 µm and uniform bias margin over 80 kbit chip area could be achieved with high yield.