Exposure apparatus and device fabrication method

A device fabrication method comprising steps of:

• exposing a substrate using an exposure apparatus;
• and
• performing a development process for the substrate exposed,
• wherein the exposure apparatus includes:
• a projection optical system configured to project a pattern of a reticle held by a first stage onto the substrate held by a second stage;
• a measuring unit which includes an imaging optical system configured to guide light having propagated through the projection optical system to an image sensor, and is configured to measure the overall birefringence of the imaging optical system and the projection optical system;
• a calibration unit which is set on a side of an object plane of the projection optical system in order to measure a birefringence of the imaging optical system in calibrating the measuring unit, and is configured to reflect the light from the measuring unit back to the measuring unit without using the projection optical system;
• and
• a calculation unit configured to isolate, from the result of measuring the overall birefringence of the imaging optical system and the projection optical system by the measuring unit, the birefringence of the imaging optical system measured by the measuring unit by setting the calibration unit on the side of the object plane of the projection optical system, thereby calculating the birefringence of the projection optical system,
• wherein the imaging optical system includes a forward-path optical system configured to guide light from a light source to the projection optical system, and a backward-path optical system configured to guide the light having propagated through the projection optical system to the image sensor,
• the calibration unit set on the side of the object plane of the projection optical system reflects the incident light back to the measuring unit so that the measuring unit measures the birefringence of the imaging optical system, and
• the calibration unit set on the side of the object plane of the projection optical system reflects at least three different linearly polarized light components of the incident light back to the measuring unit so that the measuring unit measures a birefringence of the backward-path optical system.