<title>Subquarter micron optical lithography with practical superresolution technique</title>

Abstract

Practical resolution, which is defined as the minimum geometry for a 1.0 micrometers depth of focus, in conventional krypton fluoride (KrF) excimer laser (248 nm) lithography is 0.30 micrometers . A new illumination technique, which uses a weak quadruple effect to enhance the depth of focus and to solve the current problems in the off-axis illumination techniques, has been developed. This new illumination technique is suitable for use with the attenuated phase shifting mask. With this combination technique, a 1.8 micrometers depth of focus using a 0.45 NA KrF excimer laser stepper can be achieved without a secondary peak in the distribution of light intensity for the various duties 0.30 micrometers space patterns. Even for hole patterns, a 2.0 micrometers common depth of focus can be achieved. These results indicate that KrF excimer laser lithography is a powerful candidate for beyond 0.25 micrometers -rule devices. It is also confirmed that i-line lithography is an expectable candidate for the second generation of 0.35 micrometers -rule devices.