Measurement apparatus, exposure apparatus having the same, and device manufacturing method
A measurement apparatus includes a first mask that is arranged on an object plane of a target optical system, and has a window that transmits measurement light, a second mask that has a reflection surface for reducing coherence of the measurement light, and a diffraction grating configured to split the measurement light that has been reflected on the second mask, has passed the first mask and the target optical system, wherein a distance Lg between the diffraction grating and an image plane of the target optical system satisfies Lg=m·Pg 2 /λ where Pg is a grating pitch of the diffraction grating, λ is a wavelength of the measurement light, and m is an integer except for 0.
1. A measurement apparatus comprising:
a first mask that is arranged on an object plane of a target optical system, and has plural windows that transmit measurement light;
a second mask that has a reflection surface configured to reflect transmission light that has transmitted plural windows of the first mask, the second mask being provided separate from the first mask, the second mask reflecting the transmission light on the reflection surface and reducing coherence of the reflected light in comparison with the transmission light;
a stage that drives the second mask independently of the first mask; and
a diffraction grating configured to split the measurement light that has been reflected on the second mask, has passed the first mask and the target optical system,
wherein a distance Lg between the diffraction grating and an image plane of the target optical system satisfies Lg=m·Pg 2 /λ where Pg is a grating pitch of the diffraction grating, λ is a wavelength of the measurement light, and m is an integer except for 0, and
wherein a wavefront aberration of the target optical system is calculated from measuring an interference pattern formed through interference of the measurement light split by the diffraction grating, the interference pattern being measured while the stage is driving the second mask.
2. A measurement apparatus according to claim 1 , wherein the second mask has a relief structure having a height as high as or higher than the wavelength of the measurement light, and
wherein the relief structure is formed at a period of 100 nm.
3. A measurement apparatus according to claim 1 , wherein the plural windows are two-dimensionally arranged on the first mask, and the diffraction grating is a two-dimensional grating.
4. An exposure apparatus for exposing a pattern of a reticle onto a substrate using light from a light source, said exposure apparatus comprising:
a projection optical system configured to project the pattern onto the substrate; and
a measurement apparatus according to claim 1 configured to detect a wavefront aberration of the projection optical system using the light from the light source.
5. A device fabrication method comprising the steps of:
exposing a substrate by using an exposure apparatus according to claim 4 ; and
developing the substrate that has been exposed.