Abstract: Measurement cavities described herein include a cylindrical chamber having a first open end and a second open end; a first cap covering the first open end of the cylindrical chamber and a second cap covering the second open end of the cylindrical chamber, wherein the first and second caps hermetically seal the cylindrical chamber and wherein the first cap is rigidly coupled to the second cap; and a wafer holder positioned within and coupled to the cylindrical chamber. The measurement cavity has a mass m, a stiffness k, and a damping constant c configured such that the transmissibility ? x F ? of an input force at 60 Hz in the measurement cavity is reduced by a factor of at least 10 and the measurement cavity has a natural frequency of greater than 300 Hz.

Abstract: Measurement cavities described herein include a cylindrical chamber having a first open end and a second open end; a first cap covering the first open end of the cylindrical chamber and a second cap covering the second open end of the cylindrical chamber, wherein the first and second caps hermetically seal the cylindrical chamber and wherein the first cap is rigidly coupled to the second cap; and a wafer holder positioned within and coupled to the cylindrical chamber. The measurement cavity has a mass m, a stiffness k, and a damping constant c configured such that the transmissibility ? x F ? of an input force at 60 Hz in the measurement cavity is reduced by a factor of at least 10 and the measurement cavity has a natural frequency of greater than 300 Hz.

Abstract: The methods disclosed herein include recording at near-vertical first and second measurement positions respective first and second interferograms of the photomask surface and defining a difference map as the difference between the first and second interferograms. Respective first and second normal forces on the photomask are also measured at the first and second measurement positions. The change in the normal force is used define a scaling factor, which is applied to the difference map to define a scaled difference map. A compensated flatness measurement with a reduced shape contribution due to gravity is obtained by subtracting the scaled difference map from the first interferogram. An interferometer-based flatness measurement system is also disclosed.

Abstract: The methods disclosed herein include recording at near-vertical first and second measurement positions respective first and second interferograms of the photomask surface and defining a difference map as the difference between the first and second interferograms. Respective first and second normal forces on the photomask are also measured at the first and second measurement positions. The change in the normal force is used define a scaling factor, which is applied to the difference map to define a scaled difference map. A compensated flatness measurement with a reduced shape contribution due to gravity is obtained by subtracting the scaled difference map from the first interferogram. An interferometer-based flatness measurement system is also disclosed.

Abstract: A grazing-incidence interferometer includes first and second spaced-apart diffractive optical elements with a generally planar object disposed therebetween. The first diffractive optical element forms sheared first-diffracted-order light beams that reflect from opposite first and second surfaces of the object at grazing-incidence angles, while a zero-diffracted-order light beam goes unreflected. The second diffractive optical element combines the unreflected zero-diffracted-order light beam and the sheared reflected beams to form a collimated, combined beam. A 1× double-telecentric relay system relays the combined beam to a folding optical system that forms first and second interference images on a diffusing screen located at an image plane. Digital images of the first and second interference images are obtained and processed to characterize the thickness variation of the object.

Abstract: A light multiplexing system includes a color combining element and first, second, and third color channels. Each color channel includes a light source that directs light of a corresponding first, second, or third wavelength band, respectively, toward the color combining element. The color combining element includes first and second windows. The first and second windows are made of a solid transparent material and include, collectively, three coated surfaces. The surfaces may be non-contiguous. A first coated surface receives light of the first, second and third wavelength bands. The first coated surface reflects the light of the first wavelength band and transmits the light of the second and third wavelength bands. A second coated surface receives light of the second and third wavelength bands transmitted by the first coated surface. The second coated surface reflects the light of second wavelength band and transmits the light of the third wavelength band.

Abstract: A light multiplexing system includes a color combining element and two or more first, second, and third color channels. Each color channel includes a light source that directs light of a corresponding first, second, or third wavelength band, respectively, toward the color combining element. The color combining element includes first and second. The first and second windows are made of a solid transparent material and include, collectively, three coated surfaces. The surfaces may be non-contiguous. A first coated surface receives light of the first, second and third wavelength bands. The first coated surface reflects the light of the first wavelength band and transmits the light of the second and third wavelength bands. A second coated surface receives light of the second and third wavelength bands transmitted by the first coated surface. The second coated surface reflects the light of second wavelength band and transmits the light of the third wavelength band.

Abstract: A grazing-incidence interferometer includes first and second spaced-apart diffractive optical elements with a generally planar object disposed therebetween. The first diffractive optical element forms sheared first-diffracted-order light beams that reflect from opposite first and second surfaces of the object at grazing-incidence angles, while a zero-diffracted-order light beam goes unreflected. The second diffractive optical element combines the unreflected zero-diffracted-order light beam and the sheared reflected beams to form a collimated, combined beam. A 1X double-telecentric relay system relays the combined beam to a folding optical system that forms first and second interference images on a diffusing screen located at an image plane. Digital images of the first and second interference images are obtained and processed to characterize the thickness variation of the object.

Abstract: A Fizeau interferometer incorporates an off-axis paraboloidal reflector that forms virtual images of reference and test surfaces and a camera lens that converts the virtual images into real images on a camera detector surface. The camera detector surface is arranged together with the camera lens to accommodate tilting of the virtual images by the off-axis paraboloidal reflector.

Abstract: A compound common-path interferometer including first and second measurement arms for measuring a test object is arranged so that a reference optic of the first measurement arm is disconnected from a remainder of the first measurement arm and a coupling between the reference optics of the first and second measurement arms forms a monolithic measurement cavity for maintaining reference surfaces of the reference optics at a fixed spacing and orientation. Separate supports are provided for the monolithic measurement cavity and the remainder of the first measurement arm.

Abstract: A compound common-path interferometer including first and second measurement arms for measuring a test object is arranged so that a reference optic of the first measurement arm is disconnected from a remainder of the first measurement arm and a coupling between the reference optics of the first and second measurement arms forms a monolithic measurement cavity for maintaining reference surfaces of the reference optics at a fixed spacing and orientation. Separate supports are provided for the monolithic measurement cavity and the remainder of the first measurement arm.

Abstract: A Fizeau interferometer incorporates an off-axis paraboloidal reflector that forms virtual images of reference and test surfaces and a camera lens that converts the virtual images into real images on a camera detector surface. The camera detector surface is arranged together with the camera lens to accommodate tilting of the virtual images by the off-axis paraboloidal reflector.