Patent ID: 8018577

Claim:
In an exposure apparatus including an illumination system that directs exposure light to a reflective mask including a pattern area having a reflective surface defining a pattern, a projection-optical system that exposes the pattern on the mask onto a photosensitive substrate using the exposure light, and an illumination sensor that detects light from the illumination system that is incident on the reflective mask, a method for calibrating the illumination sensor, comprising: using the illumination sensor, located in the vicinity of the mask downstream of an optical element that directs illumination-system light directly to the mask, detecting light from the illumination system, as incident on the mask for illuminating the pattern on the mask, thereby producing first detection data; illuminating a reference reflective surface on the reflective mask with light from the illumination system, the reference reflective surface being located separately from the pattern area and comprising reflective structure configured substantially similarly to reflective structure of the reflective surface in the pattern area; at an image surface of the projection-optical system, detecting light that has passed from the reference reflective surface through the projection-optical system, thereby producing second detection data; and calibrating the illumination sensor based on the first detection data and on the second detection data.