Optics: measuring and testing – By light interference – For dimensional measurement
Reexamination Certificate
2001-07-27
2004-08-10
Kim, Robert H. (Department: 2882)
Optics: measuring and testing
By light interference
For dimensional measurement
C356S511000
Reexamination Certificate
active
06775009
ABSTRACT:
BACKGROUND
This invention is related to optical imaging and metrology of semiconductor, data-storage, and biological materials, structures, and devices.
Practical optical data-retrieval devices employing moving media rely upon efficient and accurate detection of optical inhomogeneities representing patterns of binary bits. These bits may be encoded, for example, in optically discernable variations of topography, reflectivity, absorption or transmission.
SUMMARY OF INVENTION
The invention features systems and methods for near-field, interferometric microscopy in which a differential detection technique is used to investigate the profile of a sample, to read optical date from a sample, and/or write optical date to a sample. The systems may operate in either reflective or transmissive modes.
In general, in one aspect, the invention features an interferometric optical microscopy system for imaging an object. The system includes: (i) a measurement beam mask array having an array of aperture pairs positioned to receive radiation emitted from the object in response to a measurement beam, radiation emerging from the array of aperture pairs defining a measurement return beam; (ii) a reference beam source array positioned to receive a reference beam, the reference beam source array including an array of elements each configured to radiate a portion of the reference beam, the radiated reference beam portions defining a reference return beam; and (iii) imaging optics positioned to direct the measurement and reference return beams to the photo-detector and configured to produce overlapping conjugate images of the array of reference elements and the array of apertures pairs. The conjugate image for each aperture pair overlaps with the conjugate image of a corresponding reference element. Furthermore, the imaging optics include a pinhole array positioned in the conjugate image plane, the pinhole array having an array of pinholes each aligned with a corresponding aperture pair image. Finally, the measurement and reference beams are derived from a common source.
Embodiments of the system may include any of the following features.
Each pinhole in the pinhole array may be sized to pass only a central portion of each corresponding aperture pair image.
The system may further include a source for the measurement and reference beams. The source may be configured to direct the measurement beam to the measurement beam mask array, and each aperture in the measurement beam mask array is configured to radiate a portion of the measurement to the object to cause the object to emit the radiation. The measurement beam may contact the mask array at normal incidence. Alternatively, the source directs the measurement beam to contact the measurement mask array at an angle to a normal to the mask array, thereby introducing a phase shift between the measurement beam portions radiated to the object by the apertures in each aperture pair. Furthermore, the system may be implemented in a transmissive mode, in which case the measurement beam mask array is used only to collect radiation emitted from the object, and the system further includes a measurement beam source array positioned to receive the measurement beam. The measurement beam source array has an array of source aperture pairs positioned to radiate portions of the measurement beam to the object to cause the object to emit the radiation. The measurement beam may contact the measurement beam source array at normal incidence. Alternatively, the source directs the measurement beam to contact the measurement beam source array at an angle to a normal to the mask array, thereby introducing a phase shift between the measurement beam portions radiated to the object by the apertures in each aperture source pair.
The system may further include a multi-element photo-detector positioned to measure the radiation emerging through each pinhole. The radiation emerging through each pinhole provides an interference signal indicative of a differential property between object locations corresponding to the apertures in each aperture pair. The system may further include an electronic controller coupled to the photo-detector and configured to resolve the differential property across multiple regions of the object based on signals from the photo-detector.
In general, in another aspect, the invention features a differential microscopy system for imaging an object. The system includes a mask including an array of aperture pairs, each aperture pair having a common separation and an imaging system. During operation the mask is positioned adjacent the object to receive radiation emitted from the object. The imaging system is configured to image radiation emerging from the array of aperture pairs to produce a first conjugate image of the emerging radiation and an overlapping, second conjugate image of the emerging radiation laterally displaced relative to the first conjugate image by an amount corresponding to the aperture pair separation and a magnification of the imaging system. A superposition of the first and second conjugate images define a set of aperture pair images each corresponding to a different one of the aperture pairs. The superposition suppresses a contribution to each aperture image of a selected component of the radiation emerging from each corresponding aperture pair.
Embodiments of the system may include any of the following features.
The selected component may be an anti-symmetric component of the radiation emerging from each corresponding aperture pair.
The imaging system may be further configured to impart a selected phase shift between the first and second conjugate images, and the selected component corresponds to the selected phase shift. For example, when the selected phase shift is &pgr; (modulo 2&pgr;), the selected component is a symmetric component of the radiation emerging from each corresponding aperture pair. Additional values of the phase shift will cause the selected component to be a superposition of symmetric and anti-symmetric components of the radiation emerging from each corresponding aperture pair.
The imaging system may include an interferometer for separating and recombining the radiation emerging through the multiple sets of aperture pairs into portions that produce the first and second conjugate images. The imaging system may further include two collimating lenses defining a microscope and the interferometer may be positioned within the microscope. The interferometer may be configured to recombine the portions that produce the first and second conjugate images within the microscope and introduce a difference in propagation directions between the recombined portions. In such a case, the difference in propagation directions produces the lateral displacement between the first and second conjugate images. The interferometer may further be configured to introduce a relative phase shift between the recombined portions, and wherein the selected component is a superposition of symmetric and anti-symmetric components, the superposition being based on the relative phase shift.
Alternatively, for example, the imaging system may include a prism positioned at a pupil plane of the imaging system. The prism is positioned to contact a first portion of the imaged radiation, and not a second portion of the imaged radiation. The prism introduces a difference in propagation between the first and second portions to produce the laterally displaced first and second conjugate images. The imaging system may include two collimating lenses defining a microscope and the pupil plane may be positioned within the microscope. The prism may be further configured to introduce a relative phase shift between the first and second portions to cause the selected component to be a superposition of symmetric and anti-symmetric components.
The imaging system may further includes a pinhole array positioned in the conjugate image plane, the pinhole array having an array of pinholes each aligned with a corresponding aperture pair image. Each pinhole in the pinhole array may be sized to p
Artman Thomas R
Kim Robert H.
Zetetic Institute
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