Effective light source optimization with the modified beam for depth-of-focus enhancements

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Abstract
A new exposure method for the depth of focus enhancements without using the off axis filter has been developed. It makes KrF excimer laser (248 nm) lithography to a robust mass production tool beyond 2nd generation of 64 MDRAM class devices. With this new exposure method, the depth of focus for 0.35 micrometers geometries, which includes the vertical and the oblique direction images, can be enlarged more than 45%. The common depth of focus between the line images and the space images cannot be obtained with the quadrupole and the ring illumination methods for the actual sub-0.30 micrometers rule devices. Even for these devices, over 1.1 micrometers depth of focus can be achieved with this newly developed exposure method.

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