The optical performance of Markie-Dyson projection optics is now well established. Designs exist for a field of view of 20mm X 40mm with diffraction-limited resolution for NA=O.7 at 248 nm and 193 nm. This translates to a practical resolution of 180 nm (kl=O.67) and hence is adequate for projected designs for the 1 G-bit memory. This optical performance has been verified in a small field prototype. The most quoted drawback to this approach is the need for 1X masks. In last year's BACUS Symposium we advanced a rational argument for the impracticability of 1X masks and then pointed out that there were assumptions behind the argument that were unjustified; in particular the required linewidth tolerance in a 1X mask might be achievable. Here we describe options for 1 X reflective optical masks that might achieve the desired linewidth control. One option is the use of aluminum as the reflecting material. A film less than 50 nm thick has nearly twice the reflectivity of the silicon used until now, and so it should be possible to develop an etching process (for such a thin film) that is adequately precise. Moreover options exist for repairing both opaque and clear defects. An interesting alternative configuration, that eliminates the need to etch the aluminum, is to use a patterned absorber on the substrate and to deposit the aluminum over the patterned absorber. The thickness of the absorber might be as thin as 6Onm with certain materials by using destructive interference to minimize the reflected intensity. A particularly intriguing extension of this idea is to exploit what is normally a drawback of standard resists in the deep ultra-violet, their strong absorption; by using a novolak resist as the absorber we might eliminate a separate etch step altogether and so achieve even tighter linewidth control.
Date of creation, presentation, or exhibit
Department, Program, or Center
Microelectronic Engineering (KGCOE)
Grenville, Andrew; Owen, Geraint; Robinson, Jeffrey; and Borkholder, David, "Masks for Markle-Dyson optics" (1993). Accessed from
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