Polarization interferometric architectures, preferably plane mirror types, having first and second measurement legs are provided with retardation elements, preferably, at least one set of split waveplates, comprised of two segments, tilted slightly (e.g., 2 mrad) in opposite directions with respect to each other to reduce the effects of undesirable ghost beams that otherwise would travel along the same path as the principal beams to produce significant cyclic errors. With the use of the split waveplates, double reflection ghost beams have net tilts relative to the principal measurement beam, and therefore do not contribute to interference effects. This effectively eliminates waveplate ghost reflections as a source of error. Use of the such split, tilted waveplates may be made in a variety of polarization interferometers including, but not limited to, uncompensated plane mirror, high stability plane mirror, differential plane mirror, double differential plane mirror, and dual linear/angular types.
CROSS-REFERENCE TO RELATED APPLICATION
This application is related to commonly owned co-pending U.S. patent application Ser. No. 09/384,855 filed on even date herewith.
Arranged on both sides of a thin plate are optical displacement gauges that irradiate measurement lights onto surfaces of the thin plate and receive the measurement lights reflected by the surface so as to measure displacements of the surfaces of the thin plate. Variation of thickness of the thin plate is obtained on the basis of the displacements of the surfaces of the thin plate measured by each of the optical displacement gauges. Each of the optical displacement gauges detects the displacement of a respective surface of the thin plate with high accuracy by irradiating the measurement light to the thin plate two times.
The invention relates to a polarizing beam splitter device, an interferometer module system, a lithographic apparatus, and a device manufacturing method. The polarizing beam splitter device includes an optical element and a polarizing beam splitter layer. The optical element includes a retroreflector surface having three mutually perpendicular faces of high optical quality, a radiation beam passage surface and a handling surface. By designing the optical element, in particular the handling portion, to the shape of a beam splitter element, such as a prism, the handling portion, and thus the polarizing optical beam splitter device etc. itself, may be made more compact and with fewer surfaces to be polished and/or antireflection-coated. The positioning of the parts in a beam splitter is more reliable. Devices, systems in which the polarizing beam splitter device has been incorporated, such as a polarizing beam splitter device with quarter wave plates and a reference mirror fixed thereto, may also be made more compact, accurate and reliable.
A substantially neutral filter across the white-light spectrum is obtained by minimizing the wavelength-dependent effects of filtering components and of reflective coatings on surfaces. The incoming light is captured by a first prism and directed toward the interface formed by the optical contact of a second prism with a face of the first prism, where the light is partially reflected internally and partially transmitted into the second prism. The reflected light is further reflected internally and directed toward the image surface out of the first prism. The fraction of light transmitted into the second prism is reflected back and redirected out of the system toward the incoming beam. The amount of energy directed toward the image plane is controlled by the judicious selection of the refractive indices in the two materials at the contacting interface of the first and second prisms. The second prism consists of a retro-reflector element adapted to reflect substantially all light transmitted at the interface with the first prism back along the optical path of the incoming beam.
A laser system and interferometer are disclosed comprising a laser source for generating a laser beam, and first and second adjustable elements wherein the first and second adjustable elements have limited rotational motion so rotation of the first adjustable element causes deviation of a laser beam in one plane and rotation of the second adjustable element causes deviation in a second plane, and a laser beam from the laser source is oblique to a required beam direction whereby rotation of the adjustable elements deviates the laser beam enabling alignment of the laser beam to the required beam direction. The adjustable elements may be rotatable through 90.degree.. The first and second planes may be perpendicular to the required beam direction and to each other. At least one mirror may be provided which can be angularly offset to the required beam direction.
