Membrane mask aeroelastic and thermoelastic control

摘要

This paper describes the mechanics and control of mechanical distortions imposed on membrane masks during proximity (X-ray) lithography. Two sources of mechanical distortions are examined. The first is aeroelastic distortion caused by the coupling of aerodynamic fluid forces in the gap between the membrane and the wafer with the elastic mechanics of the membrane. Aerodynamic loadings on the membrane arise when the gap between mask and wafer is adjusted and during lateral stepping maneuvers. Results of stepping and gap closing experiments are presented. The results are correlated with numerical calculations based on Reynolds lubrication equation. Possible methods for reducing these aeroelastic distortions are examined. The second set of mechanical distortions contains those that give rise to some of the in-plane overlay errors. A thermoelastic technique for controlling in-plane errors using thermoelectric devices placed on the mask perimeter is described. Numerical and experimental results are presented.