JP2005350280A - Method for producing single crystal, optical component, and aligner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for stably producing a single crystal excellent in optical characteristics in a short wavelength region, and an optical component and an aligner. <P>SOLUTION: The method for producing a single crystal comprises the steps of preparing a pretreated product by melting a crystal raw material, and preparing ingot by melting and crystallizing the pretreated product, producing a crystal by heat-treating the ingot at a temperature of the melting point or lower, and after that, inspecting fluctuation of crystal axes of the crystal and screening the crystal. Also in the screening step, a crystal having inclination of crystal axis falling within 1° range of inclination distribution is selected. Further, the inspection method of the crystal axis in the screening step is one utilizing an X-ray diffraction phenomenon. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention generally relates to a method for producing a crystalline substance, for example, a fluoride crystal suitable for various optical elements, lenses, window materials, prisms and the like used in a wide wavelength range from a vacuum ultraviolet region to a far infrared region. And the like, an optical component, and an exposure apparatus.

  Conventionally, optical articles are used in telescopes, cameras, exposure apparatuses for manufacturing semiconductor integrated circuits, and the like. In particular, high-quality optical materials are desired for semiconductor exposure apparatuses. In recent years, with the high integration of semiconductor integrated circuits, there has been an increasing demand for ultra fine pattern formation. As an apparatus for transferring a fine pattern onto a wafer, a step-and-repeat reduction projection small exposure apparatus (stepper) is frequently used. In order to achieve high integration, it is necessary to increase the resolution of the stepper projection lens. In order to increase the resolution of the projection lens, it is necessary to use exposure light having a short wavelength and to increase the numerical aperture of the projection lens, that is, to increase the aperture (particularly 300 mm or more).

  Further, the short wavelength of exposure light has progressed to g-line (wavelength 436 nm), h-line (wavelength 405 nm), i-line (wavelength 365 nm), and Kr-F excimer laser light (wavelength 248 nm). The use of F excimer laser light (wavelength 193 nm) and F2 laser light (wavelength 157 nm) is considered promising. In the wavelength region up to the i-line, it was possible to use a conventional optical lens in the optical system, but a short wavelength laser after the Kr-F excimer laser beam has low transmittance, and a conventional optical glass is used. It is impossible.

  For this reason, quartz or fluoride crystals having a high transmittance for short-wavelength light are used in the optical system of the excimer laser exposure apparatus, and fluoride crystals are used in the F2 laser exposure apparatus.

  Each lens that composes a stepper projection lens is polished with the ultimate surface accuracy, but if the glass material is polycrystalline, the polishing speed varies depending on the crystal orientation, making it difficult to ensure the lens surface accuracy. Become. Furthermore, in the case of a polycrystal, impurities are likely to be precipitated at the crystal interface, and the uniformity of the refractive index is impaired, or fluorescence is emitted by laser irradiation.

  For this reason, a large-diameter single crystal fluoride crystal is desired for a projection lens of a future semiconductor exposure apparatus.

In recent years, attention has been focused on the correlation between the optical characteristics of a fluoride crystal for semiconductor exposure apparatus in the short wavelength region, the crystal structure, and impurities contained therein. As a method for analyzing trace impurities contained in fluoride crystals, there are X-ray fluorescence analysis, inductively coupled plasma emission analysis, and inductively coupled plasma mass spectrometry. Thus, the yield is improved (for example, JP 2000-119097 A (Patent Document 1), JP 2003-165723 A (Patent Document 2)).
JP 2000-119097 A JP 2003-165723 A

  However, the correlation between crystallinity and optical characteristics is also an extremely important factor, and since they cannot be controlled, there is a problem that the quality of fluoride crystals varies greatly and the yield is low, resulting in high costs.

  The present invention has been made in view of the above-mentioned conventional problems, and the object thereof is a method for producing a single crystal and an optical component capable of stably producing a single crystal having excellent optical characteristics in a short wavelength region, It is to provide an exposure apparatus.

  In order to achieve the above object, the present invention includes a step of melting a crystal raw material to prepare a pre-processed product, a step of melting and crystallizing the pre-processed product to prepare an ingot, and the ingot at a melting point or lower. A method of manufacturing a single crystal including a step of generating a crystal by heat treatment includes a step of examining a crystal axis variation and selecting a crystal.

  Conventionally, even if heat treatment is performed, heat treatment is performed up to crystals whose optical performance is not satisfied, resulting in poor production efficiency and high production costs. According to the present invention, crystals are selected before and after heat treatment. Thus, a high-performance crystal can be efficiently and stably produced. In addition, by using these crystals, the crystals can be provided in the apparatus as prisms or etalons, and the excimer laser oscillator can narrow the wavelength of the excimer laser via the prisms or etalons, in other words, excimer. The laser can be made to have a single wavelength.

  Furthermore, according to the exposure apparatus of the present invention, if excimer laser light is irradiated onto the photosensitized resist on the substrate through the reticle pattern, even if the pattern to be formed is fine, high precision corresponding to the pattern is achieved. Latent images can be formed.

  Next, the best mode for carrying out the invention will be described in detail with reference to the drawings.

(Crystal growth)
FIG. 1 is a schematic diagram showing the crystal growth process of the present invention. In the figure, reference numeral 1 denotes a crystal raw material. The raw material 1 is melted and solidified by the pretreatment shown in 2 to remove impurities in the raw material. Using this pretreated raw material 1, crystal growth shown in 3 is performed by a crucible pulling method (Bridgeman method) or the like (for example, calcium fluoride crystal). The grown crystal is processed to an appropriate size, and the inclination distribution of the crystal axis shown in 4 is measured by Raman spectroscopy, Laue method or X-ray topography. When the X-ray topography is used, the measurement is performed by the technique as shown in FIG.

  That is, the X-ray generated from the X-ray source shown in 7 is shaped by the incident slit shown in 8, and the X-ray is incident on the crystal shown in 9 so as to satisfy the X-ray diffraction condition with respect to the crystal plane. The diffracted X-ray passes between the scattering restriction slits indicated by 10 and the diffraction intensity is detected by the detector indicated by 11. By simultaneously scanning the crystal and the detector, the diffraction intensity of the entire crystal surface can be detected. From this intensity distribution, an inclination distribution of the crystal axis can be obtained. Crystals having a crystal axis inclination distribution within 1 ° are selected and heat treatment shown in 5 is performed. After the heat treatment 5, the inclination of the crystal axis shown in 4 is again measured, and a crystal for final lens processing 6 is selected.

(Optical article)
Crystals (for example, fluoride crystals) produced by crystal growth are shaped into the required optical article shape (convex lens, concave lens, disk shape, plate shape, etc.). Further, an antireflection film may be provided on the surface of the optical article of fluoride crystal as necessary. As the antireflection film, magnesium fluoride, aluminum oxide, and tantalum oxide are desirable, and these can be formed by vapor deposition by resistance heating, electron beam vapor deposition, sputtering, or the like.

(Optical system, equipment assembly process)
By combining various optical articles such as lenses, an optical system suitable for excimer lasers, particularly ArF excimer lasers, can be constructed. An exposure apparatus for photolithography can be configured by combining an excimer laser light source, an optical system having a lens made of calcium fluoride, and a stage that can move the substrate. When this exposure apparatus is used to irradiate a photosensitized resist on a substrate through a reticle pattern with an excimer laser beam, a latent image corresponding to the pattern to be formed can be formed.

(Exposure equipment)
Hereinafter, an exposure apparatus using the optical article of the present invention will be described. Examples of the exposure apparatus include a reduction projection exposure apparatus using a lens optical system and a lens-type equal magnification projection exposure apparatus. In particular, in order to expose the entire surface of the wafer, a stepper employing a step-and-repeat method in which one small section (field) of the wafer is exposed and then the wafer is moved one step to expose the next one field is desirable. . Of course, it is also suitably used in a scanning type exposure apparatus.

  FIG. 3 shows a schematic diagram of the configuration of the exposure apparatus of the present invention. In the same figure, 21 is an illumination light source part, 22 is an exposure mechanism part, and 21 and 22 are comprised independently. That is, both are physically separated. Reference numeral 23 denotes an illumination light source, for example, a high-output large light source such as an excimer laser. Reference numeral 24 denotes a mirror, reference numeral 25 denotes a concave lens, reference numeral 26 denotes a convex lens, and reference numerals 25 and 26 serve as beam expanders, which expand the laser beam diameter to the size of an optical integrator. Reference numeral 27 denotes a mirror, and 28 denotes an optical integrator for uniformly illuminating the reticle.

  The illumination light source unit 21 includes a laser 23 to an optical integrator 28. Reference numeral 29 denotes a mirror, and reference numeral 30 denotes a condenser lens that collimates the light beam emitted from the optical integrator 28. Reference numeral 31 denotes a reticle on which a circuit pattern is drawn, reference numeral 31a denotes a reticle holder that sucks and holds the reticle, reference numeral 32 denotes a projection optical system that projects the reticle pattern, and reference numeral 33 denotes a wafer on which the pattern of the reticle 31 is printed on the projection lens 32.

  Reference numeral 34 denotes an XY stage, which holds the wafer 33 by suction and moves in the XY direction when printing is performed by step-and-repeat. Reference numeral 35 denotes a surface plate of the exposure apparatus. The exposure mechanism unit 22 includes a mirror 29 to a surface plate 35 that are part of the illumination optical system. Reference numeral 36 denotes an alignment means used for TTL alignment. Usually, the exposure apparatus is composed of an autofocus mechanism, a wafer transfer mechanism, and the like, which are also included in the exposure mechanism section 22.

  FIG. 4 shows an example of an optical article used in the exposure apparatus of the present invention, which is a lens used in the projection optical system 32 of the exposure apparatus shown in FIG. This lens assembly is constituted by combining eleven lenses L1 to L11 without adhering to each other. The optical article according to the present invention is used as a lens or a mirror shown in FIGS. 3 and 4 or as a mirror or a lens of a mirror type exposure apparatus (not shown). More preferably, an antireflection film or an increased reflection film is provided on the surface of the lens or mirror.

  The optical component made of the fluoride crystal of the present invention can be used as a prism or an etalon. FIGS. 5A and 5B are diagrams schematically showing the configuration of an excimer laser oscillator using an optical part crystal made of a fluoride crystal of the present invention. The excimer laser oscillator shown in FIG. 5A makes a resonator 83 for emitting and resonating the excimer laser, an aperture 82 for narrowing the excimer laser emitted from the resonator 83, and a single wavelength of the excimer laser. And a reflecting mirror 81 for reflecting the excimer laser.

  In addition, the excimer laser oscillator shown in FIG. 5B has a resonator 83 for emitting and resonating the excimer laser, an aperture 82 for narrowing the excimer laser emitted from the resonator 83, and a single wavelength of the excimer laser. It comprises an etalon 85 for making the laser beam and a reflecting mirror 81 for reflecting the excimer laser beam.

  The excimer laser light oscillator provided with the optical crystal made of the fluoride crystal of the present invention in the apparatus as a prism or etalon can make the wavelength of the excimer laser narrower via the prism or etalon, in other words, the excimer laser can be simply used. The wavelength can be changed. By using this exposure apparatus to irradiate the photosensitized resist on the substrate through the reticle pattern with an excimer laser beam, a latent image corresponding to the pattern to be formed can be formed.

  Next, examples of the present invention will be described. In this example, as shown in the above-described embodiment, the crystal was manufactured by the crucible pulling-down method (Bridgeman method). The manufactured ingot was processed into a disk shape and measured by the X-ray topography shown in FIG. CuKα1 was used as the X-ray source, and the incident X-ray divergence angle was set to 0.05 ° by adjusting the incident slit.

  In the measurement, the crystal plane <511> was used, and X-rays were made incident on the crystal so as to satisfy the diffraction condition. An imaging plate was used as a detector, and the entire crystal surface was measured at a scan speed of 0.5 mm / sec. A schematic diagram of the measurement results is shown in FIG. FIG. 6 expresses that there is little unevenness in diffraction intensity over the entire crystal, which means that the crystal axis variation of this crystal is within 1 °. As a result, the crystal was heat-treated. After that, as a result of performing the same measurement, since the inclination distribution of the crystal axis was within 1 °, lens processing was performed.

It is a flowchart which shows the crystal manufacturing process by this invention. 1 is a schematic view of X-ray topography. 1 is a schematic configuration diagram of an exposure apparatus according to the present invention. It is a structure schematic of the projection optical system of exposure apparatus. It is a figure which shows the structure of an excimer laser oscillator. It is an X-ray topograph.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Raw material 2 Pretreatment 3 Crystal growth 4 Crystal axis inspection 5 Heat treatment 6 Processing 7 X-ray source 8 Incidence slit 9 Crystal 10 Scattering restriction slit 11 Detector 21 Illumination light source part 22 Exposure mechanism part 23 Illumination light source 24, 27, 29 Mirror 25 Concave lens 26 Convex lens 28 Optical integrator 30 Condenser lens 31 Reticle 31a Reticle holder 32 Projection optical system 33 Wafer 34 XY stage 35 Surface plate 36 Alignment means 81 Reflective mirror 82 Aperture hole 83 Resonator 84 Prism 85 Etalon

Claims (7)

Melting a crystal raw material to produce a pre-processed product, melting and crystallizing the pre-processed product to produce an ingot, and heat-treating the ingot below the melting point to produce a crystal. A method for producing a single crystal comprising the steps of inspecting variation in crystal axes of a crystal and selecting a crystal in the method for producing a single crystal. 2. The method for producing a single crystal according to claim 1, wherein in the selection step, crystals having an inclination distribution of crystal axes of the ingot within 1 ° are selected. The method for producing a single crystal according to claim 1, wherein the crystal is a fluoride crystal. The method for producing a single crystal according to claim 1, wherein the crystal is a calcium fluoride crystal. 2. The method for producing a single crystal according to claim 1, wherein the crystal axis inspection method in the selection step is a method using a diffraction phenomenon of X-rays. An optical component using, as a constituent material, a crystal manufactured by the method for manufacturing a single crystal according to claim 1. An exposure apparatus using the optical component according to claim 6 in an optical system.

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