T-top forming simulation using percolation theory

In KrF or ArF resist processing, a chemically amplified resist is widely used for ultralarge scale integrated device fabrication. Decomposition (positive resist) or cross linking (negative resist) is amplified by an acid catalytic reaction during post-exposure baking (FEB). T-top forming becomes a serious problem in these resists. In resist simulation, to take these characteristics into account, percolation theory is introduced. The acid and product distributions during FEB are iteratively calculated. Thus, we can conclude that the acid and product distribution in resist films are time dependent. Moreover, a resist simulator that can take into account macroscopic feature changes from microscopic molecular structural change is necessary. From resist surface observation and slow positron annihilation measurements, free volume generation is confirmed. A new resist process model, including prebake, PEB, and development for chemically amplified resists is established by the cluster model. CPU time is 1 min each for a three dimensional image and for development, which is fast enough for practical evaluation use. The defocus dependence of the resist profile agrees well with the experiment. For chemically amplified resists, decomposition or cross linking proceeds vertically rather than horizontally. Thus, a rectangular resist profile can be obtained, Simulation results based upon this model can describe T-tops or resist bridges. (C) 1997 American Vacuum Society.