JP2006170813A - Multilayer reflection mirror, extreme ultraviolet (euv) exposure system and soft x-ray optic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayer reflection mirror capable of suppressing oxidation of a multilayer film formed by layering materials containing Si and Mo. <P>SOLUTION: On a glass plate 1, Mo layers 11 and Si layers 12 are deposited alternately and the surface of the topmost layer Si layer 12 is made a hydrogen termination processing Si 13. Therefore, the topmost layer Si layer becomes hard to oxidize. When an oxidizing agent is sent for oxidizing removing contamination, the reflection film is oxidized and lowering of reflectivity is suppressed. The hydrogen termination processing of the surface of the Si layer 12 is desired to be done with hydrofluoric acid treatment. <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 illuminated pattern of the mask M forms an image of the mask pattern on the wafer W via the projection optical system PL composed of a plurality of reflecting mirrors (six exemplary reflecting mirrors M1 to M6 in FIG. 3). 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.

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. The present invention has been made in view of such circumstances, and a multilayer film reflecting mirror capable of suppressing oxidation of a multilayer film formed by laminating substances containing Si and Mo, and the multilayer film reflecting mirror. It is an object of the present invention to provide an EUV exposure apparatus and a soft X-ray optical instrument using the above.

  A first means for solving the above problem is a multilayer film formed by alternately laminating a substance containing at least molybdenum and a substance containing at least silicon, or a substance containing at least molybdenum, and at least In the multilayer reflector formed by periodically laminating two or more kinds of substances including silicon, and having a multilayer film whose outermost surface is a silicon layer, the surface of the outermost silicon layer Is a multilayer film reflecting mirror characterized in that is hydrogen-terminated (Claim 1).

  In this means, the silicon layer constituting the outermost surface of the multilayer film is hydrogen-terminated. Since the hydrogen-terminated silicon is not easily oxidized, this can suppress the oxidation of the reflective film.

  A second means for solving the above-described problems is a multilayer film formed by alternately laminating at least two kinds of materials including molybdenum and at least silicon, or a material including at least molybdenum, In a multilayer film reflector having a multilayer film formed by further laminating an SiC layer on a multilayer film formed by periodically laminating two or more kinds of substances including silicon, the outermost SiC The layer is hydrogen-terminated (claim 2).

  SiC can also be subjected to a hydrogen termination treatment, which makes it difficult to oxidize. Therefore, the oxidation of the reflective film can be suppressed by forming the SiC film on the outermost surface and performing the hydrogen termination treatment.

  A third means for solving the problem is the first means or the second means, wherein the outermost silicon layer or the SiC layer is hydrogen-terminated by hydrofluoric acid treatment. This is a characteristic (claim 3).

  In this means, the hydrogen termination of the silicon layer or the SiC layer is performed by hydrofluoric acid treatment. As the hydrogen termination treatment, there is a method other than the hydrofluoric acid treatment, for example, a heat treatment in a hydrogen atmosphere. However, this method may cause the interface structure to progress and the film structure to be destroyed or deformed. Therefore, hydrogen termination treatment by hydrofluoric acid treatment is particularly preferable.

  A fourth means for solving the above-mentioned problem is the third means, characterized in that hydrofluoric acid treatment is not performed except for the multilayer film formation surface and its vicinity (claim 4). ).

  Glass is often used for the substrate of the multilayer-film reflective mirror. For this reason, if the hydrofluoric acid treatment is applied to an extra place, the substrate may be eroded and affect the dimensional accuracy. In this means, the hydrofluoric acid treatment is performed only on the multilayer film formation surface and its vicinity, so there is no such fear. Note that the “vicinity” refers to a region where the hydrofluoric acid treatment of the multilayer film formation surface is unavoidable due to work and must be performed together.

  A fifth means for solving the above-mentioned problems is an EUV exposure apparatus (Claim 5) comprising the multilayer film reflecting mirror of any one of the first to fourth means.

  As described above, since the influence of contamination becomes a problem in the EUV exposure apparatus, it is effective to use a multilayer film reflecting mirror that is one of the first to fourth means. Thereby, it is possible to prevent the reflectance of the reflecting mirror from being reduced by contamination, and to prevent a reduction in throughput over a long period of time.

  A sixth means for solving the above-mentioned problem is a soft X-ray optical instrument (Claim 6) characterized by comprising a multilayer film reflecting mirror of any one of the first to fourth means. is there.

  Even 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 is used. It is effective to use a multilayer mirror that is one of the fourth means.

  According to the present invention, a multilayer film reflecting mirror capable of suppressing oxidation of a multilayer film formed by laminating substances containing Si and Mo, an EUV exposure apparatus using the multilayer film mirror, and a soft film An X-ray optical instrument can be provided.

  Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an outline of a method for hydrogen termination in a multilayer reflector as an example of an embodiment of the present invention.

  50 pairs of Mo / Si multilayer films 2 (Mo layer: 2.8 nm, Si layer: 4.2 nm) are formed on the surface of the concave low thermal expansion glass substrate 1 polished with very high precision (glass) The surface of the substrate 1 is concave). The shape of the glass substrate 1 is close to a circular plate, and the film formation region is also a circular region. Although the uppermost layer of the multilayer film is a silicon layer having a thickness of 7 nm, since this glass substrate 1 is exposed to the air atmosphere after the film formation, an oxide layer is formed on the surface of the outermost silicon layer. Furthermore, organic stains are attached to the surface.

  This glass substrate 1 (actually a multilayer film formed on the glass substrate 1 is simply referred to as a glass substrate) is placed in a sealed container 3 as shown in FIG. The organic contamination adhering to the surface of the silicon layer is removed by irradiating ultraviolet rays from the low-pressure mercury lamp 5 while introducing nitrogen mixed with an appropriate amount of oxygen from 4. Nitrogen containing dirt is discharged from the gas discharge port 6.

  After removing the organic stains, as shown in (b), a Teflon (registered trademark) cylinder 7 is attached to the glass substrate 1 such that the end face is slightly in contact with the outer periphery of the film formation region. A 1% hydrofluoric acid solution diluted with ultrapure water having a carbon content of 50 ppb or less is introduced into the cylinder. A ring-shaped silicon rubber (not shown) is sandwiched between the contact surfaces of the cylinder 7 and the glass substrate 1 so that hydrofluoric acid does not leak out of the cylinder 7. The cylinder 7 is provided with an inlet 8 and an outlet 9 for the hydrofluoric acid solution.

  In many cases, the Mo / Si multilayer film is formed on a substrate such as quartz glass or low thermal expansion glass. Although these substrate materials are attacked by hydrofluoric acid, the multilayer reflector using EUV light is required to have a very high accuracy, so that the surface is affected, which affects positioning, substrate support, etc. That must be avoided. As described above, by preventing the hydrofluoric acid from leaking out of the cylinder 7 and limiting the region where the hydrogen termination process is performed to the multilayer film and the region in the vicinity thereof, such a problem is avoided, For example, sufficient performance can be exhibited as a multilayer mirror for an EUV exposure apparatus.

  After the hydrofluoric acid treatment, the glass substrate 1 is dried by replacing with ultrapure water and blowing dry nitrogen. The glass substrate 1 is placed on a tiltable support (not shown), and the substrate is tilted when the solution or pure water is discharged. In addition, after removing organic stain | pollution | contamination, the inside of the airtight container 3 is made into nitrogen atmosphere, and it prevents that the surface oxidizes as much as possible. Thereafter, as the projection optical system for the EUV exposure apparatus is assembled, adjusted, and installed in the apparatus, the storage environment is changed to a nitrogen atmosphere, and the working environment during adjustment, etc., is changed to a nitrogen replacement atmosphere as much as possible to oxidize the surface. Is prevented.

  Since the silicon oxide layer initially formed on the surface is removed by about 1 nm in the course of the above-described processing steps, the first uppermost silicon layer should be formed thick in view of this amount. To do.

  Moreover, as a method for hydrogen termination of the Si surface, there is a method of heating to about 1000 ° C. in a hydrogen atmosphere of about 0.1 Torr. However, when the Mo / Si multilayer film is heated to 200 ° C. or more, interfacial diffusion proceeds. Therefore, hydrofluoric acid treatment that can be treated at room temperature is suitable.

  FIG. 2 shows a cross-sectional view of a multilayer mirror as an example of 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.

  Mo layers 11 and Si layers 12 are alternately formed on the glass substrate 1, and the surface of the uppermost Si layer 12 is hydrogen-terminated Si13.

  In the above example, the thickness of the outermost silicon layer is 7 nm, but this thickness is not limited to this. The hydrogen-terminated surface has oxidation resistance, but it does not mean that oxidation does not proceed at all. When an oxide layer is formed during use, the oxide layer may be removed again by hydrofluoric acid treatment. In this case, since the outermost surface of the silicon layer is slightly removed, it is necessary to increase the thickness in anticipation of the removal amount. However, if the silicon layer is too thick, the reflectance is lowered, so that the thickness is desirably 10 nm or less.

  In this embodiment, hydrofluoric acid is used for the hydrogen termination treatment, but the chemical solution to be used is not limited to this, and an ammonium fluoride solution adjusted to about pH 8 may be used.

  In the present embodiment, the outermost surface is hydrogen-terminated in the Mo / Si multilayer film whose outermost surface is silicon. However, an SiC layer may be formed on the outermost surface and the surface may be hydrogen-terminated.

  In this way, the multilayer film reflecting mirror whose surface is hydrogen-terminated is suitable for use as the reflecting mirror for an EUV exposure apparatus shown in FIG. 3, particularly as the reflecting mirrors M1 to M6 constituting the projection optical system. .

It is a figure which shows the outline | summary of the method of the hydrogen termination | terminus process in the multilayer-film reflective mirror which is an example of embodiment of this invention. It is a figure which shows sectional drawing of the multilayer film reflective mirror which is an example of embodiment of this invention. It is a figure which shows the outline | summary of an EUV exposure apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Glass substrate, 2 ... Multilayer film, 3 ... Sealed container, 4 ... Gas inlet, 5 ... Low pressure mercury lamp, 6 ... Gas outlet, 7 ... Cylinder, 8 ... Inlet, 9 ... Exhaust, 11 ... Mo Layer, 12 ... Si layer, hydrogen-terminated Si

Claims (6)

A multilayer film formed by alternately laminating at least two types of materials including molybdenum and at least silicon, or two or more types of materials including at least molybdenum and at least silicon. A multilayer film formed by laminating a multilayer film, wherein the outermost surface of the silicon layer is hydrogen-terminated in a multilayer film reflector having a multilayer film whose outermost surface is a silicon layer. Membrane reflector. A multilayer film formed by alternately laminating at least two types of materials including molybdenum and at least silicon, or two or more types of materials including at least molybdenum and at least silicon. A multilayer reflector having a multilayer film formed by further laminating a SiC layer on a multilayer film formed by laminating the outermost layer is characterized in that the outermost SiC layer is hydrogen-terminated. Multilayer reflector. 3. The multilayer film reflector according to claim 1, wherein the outermost silicon layer or the SiC layer is hydrogen-terminated by a hydrofluoric acid treatment. 4. The multilayer film reflector according to claim 3, wherein hydrofluoric acid treatment is not performed except for the multilayer film formation surface and the vicinity thereof. An EUV exposure apparatus comprising the multilayer mirror according to any one of claims 1 to 4. A soft X-ray optical apparatus comprising the multilayer-film reflective mirror according to any one of claims 1 to 4.

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