| Popis: |
As integrated circuit feature sizes shrink to sub-micron geometries, the need for a precisely defined and controlled photolithographic process becomes crucial. This paper outlines a method to improve an optical positive photoresist process using an innovative Response Surface Analysis (RSA) procedure. RSA has previously been employed to graphically model simple resist processes. In this procedure, exposure dose, develop time and concentration have been considered. The critical parameter (response), linewidth, is fitted to a set of linear hyperbola expressions. These expressions are then manipulated to directly calculate the conditions which replicate a desired linewidth. The associated process latitudes, response variations per process variable changes, are similarly derived. Optimal processing conditions are obtained mathematically using weighting factors derived from absolute and relative variations in the process. The accuracy and success of this procedure is demonstrated in improved linewidth control when operating at the optimal process condition. This improved control was observed in a stepper based applications laboratory. The results show the utility of this procedure as an effective tool to predict optimal processing conditions in an environment of complex variable interactions confounded by random and systematic errors. |
