PREVAIL: Dynamic correction of aberrations

The curvilinear variable axis lens concept for the PREVAIL proof-of-concept (POC) system, and its practical implementation have been described in a previous publication [H. C. Pfeiffer et al., J. Vac. Sci. Technol. B 6, 2844 (1999)]. The objective of this article is to show experimental results regarding the dynamic compensation of the deflection-dependent focus and astigmatism aberration control in the projected subfield. The POC system contains a plurality of dynamic correction elements in the imaging section between reticle and wafer. Using a pair of properly positioned stigmators, we have demonstrated nearly independent control of feature astigmatism (image quality) and subfield distortion (shape astigmatism). In this article, we will describe a technique that was used to control the subfield distortion. In addition, using three dynamic focus coils, and an inverted sensitivity matrix approach, we have also demonstrated independent control of the subfield magnification, rotation, and axial focus. (C) 2000 American Vacuum Society. [S0734-211X(00)05806-6].