Evaluation of the dual exposure technique

Abstract

Phase-shift masks are an important factor in the extension of optical lithography to the 50nmmode. A critical factor in their implementation is the "Dual reticle exposure technique." This technique uses two reticles: one is typically the high-resolution phase-shift reticle, and the other, a clearing or trimming reticle to remove unwanted phase edge patterns. This paper examines the result ofimplementing this technique on a very-high numerical aperture 193 nm-catadioptric-exposure system. Examples are given for the application of the "Dual Reticle Technique" including applications in which two phase-shift reticles are used to print advanced memory cells. Chromeless phase-shift masks are also shown. Issues with the implementation ofthe technique are examined. These include exposure delay effects, pattern registration, and the impact of the technique on exposure system throughput. Exposure system design developments are reported that will improve exposure system throughput with the dual reticle exposure technique. These include: Double Reticle Stages; and a new concept of exposing the two reticles simultaneously. It is noted that this dual simultaneous exposure system, when combined with a dual wafer stage system, has the potential for exposing 300mm wafers at rates up tp 150 wafers/hour in dual reticle exposure mode.