JP2006170811A - Multilayer film reflecting mirror, euv exposure device, and soft x-ray optical apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayer film reflecting mirror capable of preventing diffusion of noble metals into the multilayer film, and keeping oxidation prevention function for long hours, while using the noble metals as an oxidation prevention agent for the multilayer film reflecting mirror. <P>SOLUTION: The multilayer film is formed by laminating alternately an Si layer 2 and an Mo layer on a substrate 4 by a sputtering method. A cermet thin film 1 wherein Pt particles are dispersed in SiO<SB>2</SB>is formed as an oxidation prevention layer on the uppermost Si layer 2. Since Pt is confined and fixed as particles in ceramics, easy diffusion of Pt into the multilayered film can be prevented effectively. Since part of the Pt particles is exposed from the surface, adhesion of a carbon contamination can be suppressed effectively, compare with an oxidation prevention layer comprising only an oxide. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an EUV exposure apparatus, a multilayer mirror used in a soft X-ray optical instrument such as a soft X-ray microscope and a soft X-ray analyzer, an EUV exposure apparatus, and a soft X-ray optical instrument. In the present specification and claims, EUV light and soft X-ray are used interchangeably and refer to light or X-ray having a wavelength of 1 nm to 100 nm in terms of wavelength of light.

  In recent years, with the miniaturization of semiconductor integrated circuits, EUV light having a shorter wavelength (11 to 14 nm) is used in place of conventional ultraviolet rays in order to improve the resolving power of the optical system limited by the diffraction limit of light. Projection lithography techniques have been developed (see, for example, D. Tichenor, et al, SPIE 2437 (1995) 292: Non-Patent Document 1). This technique is recently called EUV (Extreme UltraViolet) lithography, and is expected as a technique capable of obtaining a resolution of 70 nm or less, which cannot be realized by conventional optical lithography using light having a wavelength of about 190 nm.

  A complex refractive index n of a substance in a wavelength region of EUV light is represented by n = 1−δ−ik (i is a complex symbol). The imaginary part k of the refractive index represents absorption of extreme ultraviolet rays. Since δ is much smaller than 1, the real part of the refractive index in this region is very close to 1. Further, k is a large value and the absorption is very large. Accordingly, a transmission / refraction type optical element such as a conventional lens cannot be used, and an optical system utilizing reflection is used.

  An outline of such an EUV exposure apparatus is shown in FIG. The EUV light 32 emitted from the EUV light source 31 enters the illumination optical system 33 and becomes a substantially parallel light beam via a concave reflecting mirror 34 that acts as a collimator mirror, and an optical integrator 35 comprising a pair of fly-eye mirrors 35a and 35b. Is incident on. As the pair of fly-eye mirrors 35a and 35b, for example, a fly-eye mirror disclosed in JP-A-11-312638 (Patent Document 1) can be used. In addition, since the more detailed structure and effect | action of a fly eye mirror are demonstrated in detail in patent document 1, and since there is no direct relationship with this invention, the description is abbreviate | omitted.

  Thus, a substantial surface light source having a predetermined shape is formed in the vicinity of the reflecting surface of the second fly's eye mirror 35b, that is, in the vicinity of the exit surface of the optical integrator 35. The light from the substantial surface light source is deflected by the plane reflecting mirror 36 and then forms an elongated arc-shaped illumination area on the mask M (the aperture plate for forming the arc-shaped illumination area is not shown). is doing). The light from the pattern of the illuminated mask M forms an image of the mask pattern on the wafer W via the projection optical system PL including a plurality of reflecting mirrors (six reflecting mirrors M1 to M6 in FIG. Form. The mask M is held on the mask stage, and the wafer W is held on the wafer stage. By moving (scanning) the mask stage and wafer stage, the entire pattern image on the mask M surface is transferred to the wafer W. The illustration of the wafer stage is omitted.

  As a reflector used in soft X-ray optical instruments such as an EUV exposure apparatus, a soft X-ray microscope, and a soft X-ray analyzer, a multilayer film is formed on a substrate, and the reflection mirror at the interface is weak. A multilayer-film reflective mirror that obtains a high reflectance by superimposing a large number of reflected lights in phase is generally used.

  In the wavelength region near 13.4 nm, when a Mo / Si multilayer film in which molybdenum (Mo) layers and silicon (Si) layers are alternately stacked is used, a reflectance of 67.5% can be obtained at normal incidence. In the wavelength region near 11.3 nm, when a Mo / Be multilayer film in which Mo layers and beryllium (Be) layers are alternately stacked is used, a reflectivity of 70.2% can be obtained at normal incidence (for example, C.I. Montcalm, “Proceedings of SPIE”, 1998, 3331, p. 42: see Non-Patent Document 2.

  These reflectors for EUV light and soft X-rays are used in a vacuum in order to prevent absorption by air.

  However, the inside of the exposure apparatus is not completely evacuated and is in an environment where organic gases such as hydrocarbons are always present. Residual gases containing hydrocarbons include those caused by oil used in the vacuum exhaust system (vacuum pump), those caused by lubricants in moving parts inside the equipment, and parts used inside the equipment (for example, electric cables) Due to the coating material).

  In the case of an EUV exposure apparatus, a wafer coated with a photoresist is introduced into a vacuum inside the apparatus. When irradiated with EUV light, hydrocarbon-containing gas is released due to evaporation of the remaining solvent, decomposition and desorption of the resin constituting the resist, and the like.

  Residual gas molecules containing hydrocarbons are physically adsorbed on the surface of the multilayer reflector. Physically adsorbed gas molecules are repeatedly desorbed and adsorbed and do not grow thick as they are.

  However, when EUV light is irradiated here, secondary electrons are generated inside the substrate of the reflector, and the secondary electrons decompose hydrocarbon molecules adsorbed on the surface to deposit carbon. Let

  As the adsorbed gas molecules are gradually decomposed and deposited, a carbon layer is formed on the surface of the multilayer mirror, and its thickness increases in proportion to the dose of EUV light (K. Boller et al., Nucl. Instr. and Meth. 208 (1983) 273: Non-patent document 3).

  When the carbon layer is formed on the surface of the multilayer film reflecting mirror, there arises a problem that the reflectance of the reflecting mirror is lowered.

  FIG. 2 shows a change in reflectance when a carbon layer is formed on the surface of the Mo / Si multilayer (uppermost layer Si). It can be seen that the reflectance does not decrease up to a thickness of 2 nm, but if the thickness is 6 nm, the reflectance decreases by 6% or more.

  In addition, when the carbon layer is thin (˜2 nm), the reflectance does not decrease because the optical constant of the carbon layer attached to the surface is close to the heavy atom layer (molybdenum layer) constituting the multilayer film. This is because it plays the same role as the heavy atom layer of the multilayer film.

  In an EUV exposure apparatus, a slight decrease in the reflectivity of the multilayer mirror greatly affects the throughput of the exposure apparatus. FIG. 3 shows a reflection using a multilayer reflector in a system using a total of 13 multilayer reflectors including six illumination systems, reflection masks, and six projection systems, assuming an actual EUV exposure apparatus. This is a result of calculating how much the rate decrease (ΔR) affects the transmittance (throughput) of the entire optical system. For example, if the reflectance per multilayer film reflector is reduced by 6%, the transmittance of the entire optical system is significantly reduced to 30% of the original value.

In order to prevent such contamination of the optical element due to the carbon layer deposition, a technique for introducing oxygen or water vapor into the use atmosphere has been developed. (See M. Malinowski et al., Proc. SPIE 4343 (2001) 347: Non-Patent Document 4)
According to this technique, oxygen radicals are generated by the decomposition of oxygen or water vapor by EUV light irradiation. Oxygen radicals react with gas molecules containing hydrocarbons physically adsorbed on the surface of the optical element and a carbon layer deposited on the surface to become carbon dioxide. Since carbon dioxide is a gas, it is evacuated by a vacuum pump to remove carbon contamination.

  However, since this method uses an oxidation reaction by oxygen radicals, not only the carbon deposited on the surface but also the surface of the multilayer film is oxidized. As a result, a decrease in reflectance due to surface oxidation cannot be ignored.

  In order to suppress the surface oxidation of the multilayer film, a method of introducing ethanol simultaneously with oxygen or water vapor has been proposed (H. Meiling et al., Abstract of 2nd International Workshop on EUV Lithography, San Francisco (2000) p. 17: See non-patent document 5). This is an attempt to balance carbon deposition with oxidation removal.

  However, although this method has been shown to be effective in principle experiments, in an actual optical system, there is a distribution of EUV light intensity in the plane of the multilayer mirror, and the deposition rate of the carbon layer is not uniform. For this reason, it is difficult to balance the deposition rate and the oxidation removal rate at all locations, which is considered impractical.

JP 11-312638 A D. Tichenor, et al, SPIE 2437 (1995) 292 C. Montcalm, “Proceedings of SPIE”, 1998, 3331, p.42 K. Boller et al., Nucl. Instr. And Meth. 208 (1983) 273 M. Malinowski et al., Proc.SPIE 4343 (2001) 347 H. Meiling et al., Abstract of 2nd International Workshop on EUV Lithography, San Francisco (2000) p. 17

  In the end, it is necessary to take measures to prevent the oxidation of the multilayer film surface on the premise that the optical element contamination due to the carbon layer deposition is removed or the adhesion prevention is performed using an oxidizing atmosphere. Precious metals such as gold (Au), platinum (Pt), rhodium (Rh), palladium (Pd), silver (Ag), osmium (Os), iridium (Ir) are stable metal materials and are not easily oxidized. Is well known. It is naturally considered that the oxidation of the multilayer film can be prevented by forming a layer made of these substances as the uppermost layer of the multilayer film.

For the purpose of preventing oxidation, a method using an oxide from the beginning is also effective. However, in the oblique incidence mirror used for the synchrotron beam line, the mirror coated with a noble metal thin film such as Pt on the surface is more susceptible to carbon contamination due to EUV light irradiation than the mirror without SiO ₂ coating. Less is known empirically. That is, the noble metal is superior to the oxide from the viewpoint of preventing contamination of the multilayer reflector.

  However, when a layer made of these noble metal materials is formed on the uppermost layer of the multilayer film, noble metal atoms diffuse and dissipate in the multilayer film over time, so that the uppermost layer material of the multilayer film is exposed. And the antioxidant effect is lost.

  Stable (low chemical reactivity) is synonymous with being difficult to bind to other substances. Precious metals generally have the property of easily diffusing through substances because of their weak bonds with other molecules.

  For example, when a Pt layer is formed as an antioxidant layer on the uppermost Si layer of a multilayer film composed of alternating layers of molybdenum (Mo) and silicon (Si), Pt atoms diffuse into the Si layer over time. As a result, the Pt layer on the surface gradually disappears and the Si layer is exposed on the surface, and the exposed Si surface is oxidized.

  The present invention has been made in view of such circumstances, and while using noble metals as an antioxidant for multilayer mirrors, it prevents diffusion of noble metals into the multilayer film and oxidizes over a long period of time. It is an object of the present invention to provide a multilayer film reflecting mirror capable of having a preventive action, an EUV exposure apparatus using the multilayer film reflecting mirror, and a soft X-ray optical apparatus.

  The first means for solving the above-mentioned problems is characterized in that an anti-oxidation layer made of a cermet thin film in which fine particles of a noble metal or an alloy mainly containing a noble metal are dispersed in ceramics is provided in the uppermost layer. A multilayer film reflector (claim 1).

  In this means, a so-called cermet in which fine particles of a noble metal or an alloy containing a noble metal as a main component are dispersed in ceramics instead of a conventional noble metal thin film or oxide thin film as an anti-oxidation layer provided on the uppermost layer of the multilayer film (Cermet: Compound of Ceramics + Metal) Thin films are used.

  In this means, since the noble metal is confined and fixed in the ceramic as fine particles, it is possible to effectively prevent the noble metal from being easily diffused into the multilayer film as in the prior art. In addition, since some of the noble metal fine particles are exposed on the surface, adhesion of carbon contamination can be effectively suppressed as compared with an antioxidant layer made of only an oxide. As the noble metal, Au, Pt, Th, Pd, Ag, Ru, Os, Ir and the like can be used, and two or more kinds of noble metals and alloys thereof may be used. Two or more types of ceramics may be used.

  A second means for solving the problem is the first means, wherein the ceramics is an oxide-based ceramics (claim 2).

As described above, ceramics confine and fix precious metals as fine particles in the ceramics. Therefore, it is possible to arbitrarily select and use those having such actions. Since it is an oxide itself, it is not oxidized any more, and the noble metal can be confined in a stable state as fine particles. As such oxide-based ceramics, silicon oxide (SiO ₂ ), zirconium oxide (ZnO), cerium oxide (CeO ₂ ), titanium oxide (TiO ₂ ), hafnium oxide (HfO ₂ ), and the like can be used. .

  A third means for solving the above-mentioned problem is an EUV exposure apparatus (Claim 3), comprising at least one multilayer film reflecting mirror of the first means or the second means.

  As described above, since the influence of contamination becomes a problem in the EUV exposure apparatus, it is effective to use the multilayer film reflecting mirror which is the first means or the second means. It is possible to prevent the reflectance of the reflecting mirror from decreasing due to contamination, and to prevent a decrease in throughput over a long period of time.

  A fourth means for solving the above-mentioned problem is a soft X-ray optical instrument (Claim 4) characterized by comprising at least one multilayer mirror of the first means or the second means. is there.

  In soft X-ray optical instruments such as a soft X-ray microscope and a soft X-ray analyzer other than the EUV exposure apparatus, if the reduction in the reflectance of the reflecting mirror due to the adhesion of contamination becomes a problem, the first means or It is effective to use a multilayer film reflecting mirror as the second means.

  According to the present invention, it is possible to prevent diffusion of noble metals into the multilayer film and to have an antioxidant action for a long time while using the noble metals as the antioxidant for the multilayer mirror. A multilayer film reflecting mirror, an EUV exposure apparatus using the multilayer film reflecting mirror, and a soft X-ray optical apparatus can be provided.

  FIG. 1 shows a cross-sectional view of a multilayer-film reflective mirror that is an embodiment of the present invention. For the sake of simplicity, the number of stacked multilayer films is drawn smaller than the actual number. In general, the multilayer mirror has a curvature, but in the figure, it is drawn as a plane mirror for the sake of simplicity.

  As the substrate 4, ULE made by Corning, which is a low thermal expansion glass, was used. Other low thermal expansion glass such as Zerodur manufactured by Schott may be used. In order to prevent the reflectance from decreasing due to the surface roughness of the substrate 4, the substrate surface was polished to a surface roughness of 0.3 nm (RMS) or less.

  A Mo / Si multilayer film was formed on the substrate 4 by sputtering. During film formation, the substrate was cooled with water and kept at room temperature. The thickness of the Si layer 2 was 4.6 nm, and the thickness of the Mo layer 3 was 2.3 nm. Therefore, the thickness (period length) of one cycle of the multilayer film is 6.9 nm. The Si layer 2 and the Mo layer 3 were alternately stacked to form a multilayer film. Starting from the Si layer 2, 46 Si layers 2 and 45 Mo layers 3 were formed.

A cermet thin film 1 in which Pt fine particles were dispersed in SiO ₂ was formed on the 46th Si layer 2 as an antioxidant layer.

The cermet thin film 1 can be formed by the same film forming apparatus as the Mo / Si multilayer film as follows. Similar to the formation of the multilayer film, SiO ₂ thin films and Pt thin films are alternately laminated. At this time, by shortening the film formation time, the film formation amount of the Pt thin film per time is extremely reduced.

For example, if the deposition time is set so that the thickness is only about 0.1 to 0.2 nm per time, such an extremely thin metal thin film cannot be a continuous thin film and grows in an island shape. . As a result, a structure in which Pt fine particles are dispersed in SiO ₂ can be formed.

The size of the Pt fine particles can be controlled by the thickness (film formation time) of the Pt layer formed at one time. (The longer the film formation time per time, the larger the fine particle diameter. When the film formation time is further increased, a continuous thin film is formed, and a Pt / SiO ₂ multilayer film is formed.)
The Mo / Si multilayer film and the cermet thin film (antioxidation layer) 1 composed of the Pt—SiO ₂ cermet thin film were continuously formed in the same film forming apparatus without breaking the vacuum.

  In this embodiment, Pt is used as the metal material to be dispersed in the cermet thin film. However, other noble metal materials such as Au, Rh, Pd, Ag, Ru, Os, and Ir, and at least of these noble metal materials are used. You may use the alloy, mixture, etc. which have one as a main component.

In this embodiment, SiO ₂ is used as the ceramic material for the cermet thin film, but other oxides such as ZnO, CeO ₂ , TiO ₂ , and HfO ₂ may be used. In addition to oxides, other ceramic materials such as nitrides and carbides can also be used.

  Thus, the produced multilayer film reflective mirror was used as a reflective mirror of the projection optical system of an EUV exposure apparatus as shown in FIG. As a comparative example, the exposure was repeated using a conventional Mo / Si multilayer reflective mirror with no coating on the surface, and the reduction in the amount of light on the wafer in both cases was compared.

Water vapor was introduced into the atmosphere of the projection optical system at a partial pressure of 1 × 10 ⁻⁶ Torr. As a result, carbon contamination deposited on the reflecting mirror surface was oxidized and removed.

  When the multilayer reflective reflector of the comparative example was used, the amount of light reaching the wafer gradually decreased as the exposure was repeated, but the multilayer reflective mirror of the embodiment of the present invention manufactured as described above was used. In such a case, the amount of light reaching the wafer did not decrease. In the comparative example, the amount of light reaching the wafer decreased because the surface of the Mo / Si multilayer film was oxidized. On the other hand, in the multilayer mirror of the example, oxidation of the multilayer film on the mirror surface was not observed.

  In this embodiment, water vapor is used as the oxidant for contamination. However, oxygen or hydrogen peroxide water vapor may be used.

It is a figure which shows sectional drawing of the multilayer film reflective mirror which is an Example of this invention. It is a figure which shows the change of a reflectance when a carbon layer is formed in the surface of Mo / Si multilayer film (uppermost layer Si). Assuming an actual EUV exposure apparatus, in a system using a total of 13 multilayer reflectors including six illumination systems, reflection masks, and six projection systems, the reflectance reduction per multilayer reflector is optical. It is a figure which shows the result of having calculated how much it has influence with respect to the transmittance | permeability (throughput) of the whole system. It is a figure which shows the outline | summary of an EUV exposure apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Cermet thin film, 2 ... Si layer, 3 ... Mo layer, 4 ... Substrate

Claims (4)

A multilayer film reflector comprising an anti-oxidation layer comprising a cermet thin film in which fine particles of a noble metal or an alloy containing a noble metal as a main component are dispersed in ceramics on the uppermost layer. 2. The multilayer reflector according to claim 1, wherein the ceramic is an oxide-based ceramic. An EUV exposure apparatus comprising at least one multilayer film reflecting mirror according to claim 1. A soft X-ray optical apparatus comprising at least one multilayer film reflecting mirror according to claim 1.

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