Nikon Corporation

Shigeru Sakuma

Tsutomu Mizugaki

Shuuichi Takano

Masaki Shiozawa

Kazuo Kimura

Hiroki Jinbo

Norio Komine

Hiroyuki Hiraiwa

Seishi Fujiwara

Masaaki Mochida

Minako Azumi

An optical member manufacturing method of the present invention has a growth step of growing an ingot of a fluoride crystal, a plane orientation measurement step of measuring two or more crystal plane orientations of the ingot, a cutout step of cutting out an optical material from the ingot along any one of the crystal plane orientations obtained in the plane orientation measurement step, and a machining step of performing predetermined machining processing on the optical material to obtain an optical member.

Method for producing optical member

A manufacturing method for a single crystal of calcium fluoride by which it is possible to obtain a single crystal of calcium fluoride with adequately small double refraction, which can be used in optical systems for photolithography, and in particular, a single crystal of calcium fluoride with a large diameter (&oslash;200 mm or larger) having superior optical properties, which can be used for photolithography with a wavelength of 250 nm or less. A manufacturing method for a single crystal of calcium fluoride, having its optical properties improved through an annealing process in which a single crystal of calcium fluoride is contained in a sealable container, and said container is sealed and vacuumed, followed by, a process of heating with a heater arranged external to said container so that the temperature inside said container is raised to a first temperature, which is lower than the melting point of said single crystal of calcium fluoride, a process by which the temperature inside said container is maintained at said first temperature for a designated period of time, and a process by which the temperature inside said container is lowered to room temperature, wherein, the maximum temperature of the annealing process is set to be a first temperature within the range of 1020 to 1150&deg; C. Also provided is a manufacturing method for a single crystal of calcium fluoride having its optical properties improved through an annealing process such that, its maximum temperature during the thermal process is set to a first temperature which is within the range of 1020 to 1150&deg; C., and which is maintained for a designated period of time, and its cooling speed for reaching a second temperature, which is in the range of (or around) 600 to 800&deg; C., from said first temperature is set to be 1.2&deg; C./hour or less, or its cooling speed for reaching a second temperature, which is in the range of (or around) 700 to 900&deg; C., from said first temperature is set to be 1.2&deg; C./hour or less.

Manufacturing method for calcium fluoride and calcium fluoride for photolithography

A method for evaluating an optical member for photolithography composed of a fluoride crystal comprises a step of measuring a crystal plane orientation of the optical member, and a step of specifying a twin region on the basis of a result of the measurement. The twin region in an effective region of an optical element is specified as a total area of a region obtained by projection onto a plane perpendicular to an optical axis of the optical element. It is judged that the optical member is usable when the total area is not more than 10% of an effective diametric area or a partial diametric area of the optical element. The obtained optical element has satisfactory image formation characteristics because of less birefringence.

Optical member for photolithography and method for evaluating the same

The present invention provides a method for calculating the birefringence of an optical element and selecting the direction of minimum birefringence in the optical element. The birefringence of the optical element is calculated by converting known piezo-optical constants in a specified three-dimensional orthogonal coordinate system for the optical material into piezo-optical constants in an arbitrary three-dimensional orthogonal coordinate system. The amount of change in the refractive index &Dgr;n of the optical material in a first direction and the amount of change in the refractive index &Dgr;n of the optical material in a second direction which is perpendicular to the first direction are calculated using a uniaxial stress that is applied to the optical material along the first direction. The amount of birefringence as seen from a third direction perpendicular to the first direction and the second direction is determined in the arbitrary three-dimensional orthogonal coordinate system by determining the difference between the amount of change in the refractive index &Dgr;n and the amount of change in the refractive index &Dgr;n

OPTICAL ELEMENT MADE FROM FLUORIDE SINGLE CRYSTAL, METHOD FOR MANUFACTURING OPTICAL ELEMENT, METHOD FOR CALCULATING BIREFRINGENCE OF OPTICAL ELEMENT AND METHOD FOR DETERMINING DIRECTION OF MINIMUM BIREFRINGENCE OF OPTICAL ELEMENT

An optical member for photolithography made of a calcium fluoride crystal exhibits an internal transmittance of 99.5%/cm or greater with respect to light having a specific wavelength of 185 nm or shorter.

Optical member for photolithography and photolithography apparatus

A manufacturing method for a single crystal of calcium fluoride by which it is possible to obtain a single crystal of calcium fluoride with adequately small double refraction, which can be used in optical systems for photolithography, and in particular, a single crystal of calcium fluoride with a large diameter (&oslash; 200 mm or larger) having superior optical properties, which can be used for photolithography with a wavelength of 250 nm or less. A manufacturing method for a single crystal of calcium fluoride, having its optical properties improved through an annealing process in which a single crystal of calcium fluoride is contained in a sealable container, and said container is sealed and vacuumed, followed by, a process of heating with a heater arranged external to said container so that the temperature inside said container is raised to a first temperature, which is lower than the melting point of said single crystal of calcium fluoride, a process by which the temperature inside said container is maintained at said first temperature for a designated period of time, and a process by which the temperature inside said container is lowered to room temperature, wherein, the maximum temperature of the annealing process is set to be a first temperature within the range of 1020 to 1150&deg; C. Also provided is a manufacturing method for a single crystal of calcium fluoride having its optical properties improved through an annealing process such that, its maximum temperature during the thermal process is set to a first temperature which is within the range of 1020 to 1150&deg; C., and which is maintained for a designated period of time, and its cooling speed for reaching a second temperature, which is in the range of (or around) 600 to 800&deg; C., from said first temperature is set to be 1.2&deg; C./hour or less, or its cooling speed for reaching a second temperature, which is in the range of (or around) 700 to 900&deg; C., from said first temperature is set to be 1.2&deg; C./hour or less.

The present invention provides a method for calculating the birefringence of an optical element and selecting the direction of minimum birefringence in the optical element. A material for manufacturing the optical element is a fluoride single crystal with a birefringence value that is reduced compared to conventional materials. The fluoride single crystal is cut from a fluoride single crystal ingot obtained by crystal growth so that the &lcub;111&rcub; crystal planes are two parallel planes, after which the optical performance is improved by subjecting this material to a heat treatment. The birefringence of the optical element is calculated by converting known piezo-optical constants in a specified three-dimensional orthogonal coordinate system for the optical material into piezo-optical constants in an arbitrary three-dimensional orthogonal coordinate system. The amount of change in the refractive index &Dgr;n,of the optical material in a first direction along the direction of one coordinate axis of the arbitrary three-dimensional orthogonal coordinate system, and the amount of change in the refractive index &Dgr;n,of the optical material in a second direction which is perpendicular to the first direction are calculated using a uniaxial stress that is applied to the optical material along the first direction and the piezo-optical constants in the arbitrary three-dimensional coordinate system. The amount of birefringence as seen from a third direction perpendicular to the first direction and the second direction is determined in the arbitrary three-dimensional orthogonal coordinate system by determining the difference between the amount of change in the refractive index &Dgr;n,and the amount of change in the refractive index &Dgr;n

Optical element made from fluoride single crystal, method for manufacturing optical element, method for calculating birefringence of optical element and method for determining direction of minimum birefringence of optical element

An optical member is provided for use in an image-focusing optical system for guiding light having a wavelength shorter than about 300 nm. The optical member includes a calcium fluoride crystal having a sodium concentration of less than about 0.2 ppm.

Image-focusing optical system for ultraviolet laser

A projection exposure apparatus capable of projecting and exposing mask pattern images onto a substrate by means of a optical projection system, the apparatus includes an optical illumination system capable of illuminating a mask utilizing an excimer laser illuminating light source in a wavelength range of 230 nm or less, and an optical projection system including optical members that include a calcium fluoride crystal with a total alkaline earth metal impurity content of 1.times.10.sup.18 atom/cm.sup.3 or less, and which projects images of the mask pattern onto a substrate. The calcium fluoride crystal is manufactured by a method including the steps of adding a fluorinating agent to a powdered calcium fluoride forming a mixture, placing the mixture in a growing crucible inside a vacuum furnace, and evacuating the vacuum furnace. Once the vacuum furnace is evacuated, the temperature is elevated a first time inside the vacuum furnace to a temperature exceeding a melting point of the mixture and is maintained at a predetermined constant temperature inside the vacuum furnace until a polycrystalline material is formed. The polycrystalline material is then cooled and the temperature inside the vacuum furnace is elevated until the polycrystalline material is melted, wherein crystal growth of the polycrystalline material is promoted and a crystal ingot is formed.

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Chigasaki, Japan

Shigeru Sakuma