EFFECT OF DEGREE OF COHERENCE IN OPTICAL LITHOGRAPHY USING DUMMY DIFFRACTION MASK

The effects of degree of coherence in optical lithography using the du mmy diffraction mask are investigated by simulation and experiment. In fluences on resolution and depth of focus of the repeated and isolated patterns are simulated for the several coherence factors of the illum ination. The process margins are also simulated through the exposure v s. defocus diagram. The Lithographic performances of the complex perio dic patterns are experimented. As degree of coherence (DOC) decreases, the contrast benefit is increased for Line and space(L/S) patterns si ze less than 0.5 lambda/NA where NA is the numerical aperture, and the depth of focus(DOF) benefit is increased for L/S patterns size less t han 0.65 lambda/NA. The smaller L/S patterns size is, the greater the influence of DOC is. In the isolated patterns of sub-resolution type, better lithographic performances could be obtained for the smaller coh erence factor.