Analysis of the effects of cross-field defocus on the photolithographic process window

Summary form only given. The focus-exposure process window has become an accepted standard for the characterization of stability of a photolithographic process. The process window is defined as a rectangular region in the focus-exposure plane where the process of interest is considered to perform within specifications (typically ±10% of target CD). The width of the box identifies the depth-of-focus and the box height represents the exposure latitude. Recent studies (Capsuto SPIE 1992, et al.) have shown that the defocus conditions that exist across a typical stepper exposure field can significantly impact DC performance. The proper characterization of the true process performance requires analysis of the common process window or “common corridor” which takes into account variable conditions that exist in non-laboratory environments. This study utilized a defocus map for a state of the art I-line stepper, obtained using an innovative focus monitor based on phase-shift mask technology. This defocus map was used to derive sampling plans for both real and simulated analysis based on the common corridor technique. This method resulted in a highly realistic estimate of the photolithographic process stability