Precision improvement in optical proximity correction by optimizing second illumination source shape

We have achieved precision improvement by optimizing the second illumination source shape in our optical proximity correction system. Based on the consideration that the optical proximity effect is significantly dependent on interference conditions, we have applied a new type of modified illumination to projection optics in order to improve the correction accuracy. A new second illumination source is formed by an illumination aperture with a spindle-shaped opaque region, whose curvature is the same as that of the projection lens pupil. Through use of this aperture, pattern edges can be definitely classified according to the interference condition, and resultant improvement of the pattern size accuracy, within ±0.01 µm, which is nearly the same level as the detection limit, can be achieved.