Deep uv lithography

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Abstract
Using deep‐uv light ranging from 2000 to 2600 Å, submicrometer patterns in photoresist with height‐to‐width aspect ratios as high as 15 can be achieved. The well known electron‐beam positive resist, polymethyl methacrylate (PMMA), is used as the deep‐uv photoresist. Its optical absorption coefficient,dissolution rate, and sensitivity are given in the deep‐uv wavelength region. Its absorption coefficient, being a factor of two lower than that of AZ 1350J, makes it suitable for deep penetration of submicrometer‐wide beams. The negligible sensitivity at wavelengths longer than 2600 Å eliminates the need for an expensive filter. Both Xe–Hg arc lamps and deuterium spectral lamps have been used to expose the resist. Chrome or aluminum masks on quartz or sapphire substrates were found satisfactory. Chevron patterns of 1.6 μm width and 0.4 μm spacing and Y–I bars of 1.6 μm width and 0.2 μm gaps were printed in 3 μm of PMMA 2041, as well as Y–I bars of 0.5 μm width and 0.25 μm gaps in 1.78 μm of PMMA 2041. The exposure time in both cases was below 10 min.

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