Lithographic Apparatus With a Deformation Sensor

摘要

Disclosed is a lithographic apparatus comprising a member susceptible to deformation and a deformation sensor for measuring a deformation of said member. The deformation sensor comprises a first birefringence sensing element arranged to be subjected to stress in dependency of the deformation of said member and a light system configured to transmit polarized light through the first birefringence sensing element, wherein said polarized light has a first polarization state prior to being transmitted through the first birefringence sensing element. The deformation sensor further comprises a detector for detecting a second polarization state of the polarized light after being transmitted through the first birefringence sensing element and a calculation unit to determine the deformation of said member based on the first and second polarization state.