| Since the introduction of electron-beam and laser-beam mask pattern generators in the 1970's, the mask making industry has faced little technical challenge in meeting mask specifications, even though IC features during this time have shrunk more than ten-fold. This is due to both the superb resolution and placement accuracy provided by mask pattern generators, and the transition in wafer exposure tools from predominantly 1X optical lithography to 5X reduction optical lithography. However, as IC minimum features continue to shrink, mask fabrication has now become critical even for 5X reduction lithography, and even more so for unity magnification lithographic approaches such as proximity x-ray and some catadioptric optical systems. Therefore, the detection and reduction of error sources in mask making is now crucial in developing the overall IC manufacturing process.; This dissertation will review five research projects with a common theme of error source detection and reduction in high-precision mask making and metrology. (1) Spatial frequency domain analysis of mask errors, in which we introduced a new way of characterizing mask errors which gives new insights into error sources. (2) Spatial frequency filtering using multiple-pass printing, in which we developed a methodology to optimize multiple-pass printing to eliminate spatially-periodic mask error sources. (3) Study of the mask error transfer process near the optical resolution limit, in which we developed an analytical model and demonstrated that the mask linewidth error may be magnified when printed on wafer. (4) Self-characterization of field distortion for mask pattern generators and optical steppers, in which we developed a new measurement technique for monitoring field distortion using inexpensive and readily available linewidth or pitch measurement systems. (5) Self-calibration of high-precision 2D lithography and metrology stages, in which we developed an algorithm that, using a rigid artifact plate, can extract the exact distortion of a 2D lithography stage, which has been a fundamental engineering problem ever since the introduction of e-beam mask pattern generators. |
