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Device design rules now approach 0.5μm geometries. Process complexities and the performance of conventional equipment necessitate a more sophisticated technique for process optimization. Statistically designed experiments (SDE) and response surface analyses have, to a limited extent, addressed this need, but have fallen short in their ability to handle several responses simultaneously. Recent articles have failed to include realistic concerns such as product throughput or materials consumption. This paper describes an efficient approach to simultaneously optimize several positive lithographic properties and industrial concerns. Process parameters such as 1) soft bake temperature, 2) focus offset, 3) exposure energy, 4) develop process, and 5) developer temperature were varied and investigated using full factorial statistical methods. The lithographic performance of a resist and developer system, whose chemistry was designed specifically for high resolution, zero bias submicron imaging, was characterized. CD uniformity, focus latitude, exposure latitude and throughput were modeled via response surface methodology, and then optimized according to the described technique. Also, a desirability function and an equipment monitoring system were considered and employed. The utility of this technique lies in the definition of conditions wherein the optimum process control and product flow are achieved simultaneously. Typically, a response surface graphically represents the effect of two variables. The described technique effectively considers many variables to establish a process window. Analysis of the full factorial design, with star and center points, was used to build individual response surfaces. The mathematical combination using linear algebraic techniques of several response surfaces is a novel approach to effectively describe the process window. The lithographic process, optimized by the described experimental techniques, exhibited wide latitude. This, coupled with equipment SQC, provided a reliable submicron lithographic process. Equipment capabilities were quantified and consistent performance reported as important factors in total process control. The resultant optimized process window was depicted by engineering data and design space centerpoints were characterized by scanning electron micrographs.
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