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: Devices, systems, and methods of generating and providing a target topographic map for finishing a photomask blank are disclosed. A method includes receiving topographic data corresponding to an uncompleted photomask blank, receiving functional specifications for flatness of an acceptable photomask blank, and generating the target topographic map for first and/or second major surfaces of the blank, which provides instructions for removing material from the first and/or second major surfaces such that the first and second major surfaces achieve a flatness that passes each functional specification. The amount of material removed reflects a reduction in material necessary to pass the functional specifications.

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: Devices, systems, and methods of generating and providing a target topographic map for finishing a photomask blank are disclosed. A method includes receiving topographic data corresponding to an uncompleted photomask blank, receiving functional specifications for flatness of an acceptable photomask blank, and generating the target topographic map for first and/or second major surfaces of the blank, which provides instructions for removing material from the first and/or second major surfaces such that the first and second major surfaces achieve a flatness that passes each functional specification. The amount of material removed reflects a reduction in material necessary to pass the functional specifications.

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: An apparatus for holding a thin substrate includes a plurality of positive pressure regions including a porous material having an upper surface and a gas flowing outward from the upper surface, the gas producing a positive pressure above the upper surface in the positive pressure regions. The apparatus includes a plurality of negative pressure regions interspersed with the plurality of positive pressure regions, the negative pressure regions exerting a holding force on a bottom surface of the thin substrate. The negative pressure regions and the positive pressure regions operate to maintain the bottom surface of the thin substrate a distance from the upper surface of the porous material in the positive pressure regions. Methods of holding a thin substrate with the apparatus are 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: An apparatus for measuring the surface contour of a target area of a substrate has a light source to emit a measurement light beam. A beam splitting element defines a measurement axis and a reference axis. A substrate holder disposes the target area along the measurement axis and tilted away from normal incidence, about a tilt axis that orthogonally intersects the measurement axis, according to a predetermined tilt angle that is a function of the measurement light beam wavelength. An imaging sensor records a fringe pattern generated from the measurement light beam and a reference light beam. A computer extracts frequency profiles from the recorded fringe pattern, each profile taken in a direction that is orthogonal to the direction of the tilt axis, wherein the programmed instructions further compute changes in the contour of the target area surface according to the frequency profiles.

Abstract: An apparatus for measuring the surface contour of a target area of a substrate has a light source to emit a measurement light beam. A beam splitting element defines a measurement axis and a reference axis. A substrate holder disposes the target area along the measurement axis and tilted away from normal incidence, about a tilt axis that orthogonally intersects the measurement axis, according to a predetermined tilt angle that is a function of the measurement light beam wavelength. An imaging sensor records a fringe pattern generated from the measurement light beam and a reference light beam. A computer extracts frequency profiles from the recorded fringe pattern, each profile taken in a direction that is orthogonal to the direction of the tilt axis, wherein the programmed instructions further compute changes in the contour of the target area surface according to the frequency profiles.

Abstract: Thickness and group index variations in test strip samples of ultra-low expansion glass are made by extracting the strip samples with front and back faces oriented at an acute skew angle to the axis of the boule. The strip samples are positioned the within an interferometric measurement cavity so that a set of subcavities formed by pairings of each of two reference surfaces together with each of the front and back faces of the strip sample which each subcavity having a different optical path length spacing. The skew angle is sized to avoid diffusion effects of striae present in the boule.

Abstract: Thickness and group index variations in test strip samples of ultra-low expansion glass are made by extracting the strip samples with front and back faces oriented at an acute skew angle to the axis of the boule. The strip samples are positioned the within an interferometric measurement cavity so that a set of subcavities formed by pairings of each of two reference surfaces together with each of the front and back faces of the strip sample which each subcavity having a different optical path length spacing. The skew angle is sized to avoid diffusion effects of striae present in the boule.

Abstract: A frequency-shifting interferometer is arranged for measuring an optical profile of a test object with a continuously tunable light source. A succession of the interference images of the test object are captured together with a measure of the beam frequencies at which interference images are formed. A limited number of the captured interference images of the test object are selected so that the monitored beam frequencies approximately match a predetermined beam frequency spacing pattern. Further processing proceeds based on the selected interference images.

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 wavelength tunable system including a laser having a lasing cavity and an external cavity, the cavities having a common optical axis; a reflective grating fixed in the external cavity; a collimating lens between the lasing cavity and the reflective grating; and an adjustable reflective mirror defining one end of the external cavity and optically coupled to the fixed reflective grating, the adjustable reflective mirror pivots about the fixed reflective grating, and a method of use as defined herein.

Abstract: A frequency-shifting interferometer is arranged for measuring an optical profile of a test object with a continuously tunable light source. A succession of the interference images of the test object are captured together with a measure of the beam frequencies at which interference images are formed. A limited number of the captured interference images of the test object are selected so that the monitored beam frequencies approximately match a predetermined beam frequency spacing pattern. Further processing proceeds based on the selected interference images.

Abstract: A frequency scanning interferometer is arranged for simultaneously measuring multiple surfaces of a test object through a wide range of expected offsets. Knowledge of the expected locations of the test surfaces is compared with a sequence of ambiguity intervals based on a synthetic measurement wavelength to center the test surfaces within the ambiguity intervals.

Abstract: A wavelength tunable system including: a laser having a lasing cavity and an external cavity; a frequency-adjuster in the external cavity; and an adjustable current source to adjust the laser diode current, and a method of use as defined herein.

Abstract: A frequency scanning interferometer is arranged for simultaneously measuring multiple surfaces of a test object through a wide range of expected offsets. Knowledge of the expected locations of the test surfaces is compared with a sequence of ambiguity intervals based on a synthetic measurement wavelength to center the test surfaces within the ambiguity intervals.

Abstract: A wavelength tunable system including a laser having a lasing cavity and an external cavity, the cavities having a common optical axis; a reflective grating fixed in the external cavity; a collimating lens between the lasing cavity and the reflective grating; and an adjustable reflective mirror defining one end of the external cavity and optically coupled to the fixed reflective grating, the adjustable reflective mirror pivots about the fixed reflective grating, and a method of use as defined herein.