Actinix

Other

Hoya Corporation

James J Jacob

Andrew John Merriam

Brian L Harlamoff

Timothy John Litvin

We disclose several instrument architectures for the measurement of arbitrary phase retardation on advanced lithography photomasks. These architectures combine traditional interferometric techniques with high-magnification UV microscopy. Features are interrogated using a multitude of phase probes, formed by a imaging a number of variable apertures back-illuminated by phase-coherent beams, onto the surface of the photomask with a given demagnification. The size, spacing, and orientation of the phase probes may be adjusted to suit photomask feature geometries. Means are provided to vary the relative optical phase between the phase probes. These phase probes both reflect from and transmit through the photomask; the stationary, non-localized interference fringes, formed in the regions of phase probe electric field overlap, contain information on the optical path difference between the two probes. The spatial resolution of these measurements is limited only by the resolution limit of the UV microscope, which may significantly exceed the capability of existing tools.

Architectures for high-resolution photomask phase metrology

This invention greatly improves the quality of images obtained using optical systems illuminated by coherent light. It does so by removing the undesirable psuedo-random variations in the final image due to interference speckle and inhomogeneities in the spatial intensity distribution of the light source. A bundle of light-guiding fibers is interposed between the illumination source and the imaging system. Non-uniform propagation within the fiber bundle creates a psuedo-random phase variation across the illumination beam, which gives rise to a dynamic interference speckle pattern superimposed upon the desired image acquired by the optical system. Rotating the fiber bundle around the axis of propagation, whilst simultaneously integrating the output of the photosensitive detector over a period of time, substantially removes variations due to source inhomogeneities and coherent interference.

Apparatus for beam homogenization and speckle reduction

A nonlinear optical mixer produces coherent vacuum ultraviolet radiation. A cell contains a gas mixture of xenon and a phase-matching gas. A pump laser beam selectively excites the two-photon transition in the xenon gas. A mixing laser beam is also directed towards the gas mixture. Coherent vacuum ultraviolet radiation is produced by four wave mixing of the pump and mixing laser beams. The phase-matching gas, for example mercury vapor, is used to achieve phase matching of the four wave mixing. The coherent vacuum ultraviolet radiation preferably has a wavelength of approximately 157.6 nm (the molecular fluorine line) or 121.6 nm (the Lyman-&agr; hydrogen line). In a preferred embodiment, the two laser beams are loosely-focused.

System and method for generating coherent radiation at vacuum ultraviolet wavelengths using efficient four wave mixing

An optical system for producing ultraviolet radiation includes an optical source, an optical parametric oscillator (OPO), a frequency doubler, and a mixer. The optical source produces a first beam of radiation. The OPO receives a first portion of the first beam of radiation and produces a second beam of radiation therefrom. The frequency doubler receives a second portion of the first beam of radiation and produces the second harmonic thereof. The mixer mixes the second beam of radiation and the second harmonic of the first beam of radiation to produce an ultraviolet beam of radiation. In a preferred embodiment, the optical source includes a Nd:YAG laser which is frequency doubled to produce a first beam of radiation at a wavelength of approximately 532 nm; and the ultraviolet beam of radiation has a wavelength close to one of the excimer laser lines, typically either 193 nm or 157 nm.

System and method for generating coherent radiation at ultraviolet wavelengths

Optical parametric oscillators using non-linear crystals cut for the type I interaction have an extraordinary pump beam which generates ordinary signal and idler beams. The use of an optical element to rotate the signal beam before sending this signal beam to a grating element allows for the grating element to have its dispersion plane oriented coplanar with the extraordinary crystal plane of the non-linear crystal. In this manner, for non-linear crystals which have relatively narrow acceptance angles, such as BBO crystals, the reduction in angular aperture of the parametric gain in the extraordinary plane will produce a reduction in the linewidth of the produced output. The grating translates the angular variations into variations in wavelength. If no rotator was used in the optical parameter oscillator, then in order to get the maximum efficiency out of the grating, the dispersion plane of the grating should be orthogonal to the extraordinary plane of the crystal, and therefore the narrow angular acceptance of the crystal would not result in a narrow output linewidth.

Narrow linewidth BBO optical parametric oscillator utilizing

Optical parametric oscillators using non-linear crystals cut for the type I interaction have an extraordinary pump beam which generates ordinary signal and idler beams. The use of an optical element to rotate the signal beam before sending this signal beam to a grating element allows for the grating element to have its dispersion plane oriented coplanar with the extraordinary crystal plane of the non-linear crystal. In this manner, for non-linear crystals which have relatively narrow acceptance angles, such as BBO crystals, the reduction in angular aperture of the parametric gain in the extraordinary plane will produce a reduction in the linewidth of the produced output. The grating translates the angular variations into variations in wavelength. If no rotator was used in the optical parametric oscillator, then in order to get the maximum efficiency out of the grating, the dispersion plane of the grating should be orthogonal to the extraordinary plane of the crystal, and therefore the narrow angular acceptance of the crystal would not result in a narrow output linewidth.

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Aptos, CA, United States of America

James J Jacob