Conformal slip-free wafer chucking using an actuated wafer table

Abstract

In semiconductor applications, such as photolithog-raphy and wafer inspection, friction forces and related slip during wafer loading and chucking at the wafer table are known to cause non-reproducible wafer deformations that result in errors between successive processing steps. To minimize these so-called overlay errors, a modified wafer table design is proposed, which can be actuated in various orthogonal low order deformation shapes that are conformal to the shape of the wafer prior to loading. According to the simulation results, the required out of plane deformation for conformal loading can be achieved and the in-plane friction forces can be reduced significantly by matching the neutral plane of the actuated wafer table and the wafer. The actuator print-through effects, however, need further attention.