JP2007189151A - Multilayer-film mirror and euv exposure device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayer-film mirror that allows a multilayer film to be simply peeled off, using an etchant. <P>SOLUTION: A protection layer 2 composed of a silicon oxide (SiO<SB>2</SB>) is formed on a substrate 1 by magnetron sputtering. Next, an Mo/Si multilayer film is formed in an (optical) effective region that is one size smaller than the protection layer 2. Here, although a forming region for an Mo layer 3 is formed on the entire face of the effective region, a forming region for an Si layer 4 is formed by dividing it into plural regions. Film formation is executed, in a state in which all the Mo layers 3 are jointed with each other via each gap between the divided regions. When such a multilayer film is immersed in an etchant for dissolving the Mo layers 3, since the etchant infiltrates, while successively dissolving the Mo layers 3 from the layer on the surface side, the Mo/Si multilayered film can be peeled off in a very short period of time, even if an etchant that does not dissolve the Si layers is used 4. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a multilayer film reflecting mirror and an EUV exposure apparatus using the same.

  With further progress in miniaturization of semiconductor integrated circuit elements, development of projection lithography using soft X-rays having a wavelength of about 11 to 14 nm instead of ultraviolet rays is being promoted. This technique is also recently called EUV lithography (Extreme Ultraviolet reduced projection exposure). This EUV lithography is expected as a lithography technique having a resolving power of 50 nm or less, which cannot be realized by conventional optical lithography (wavelength of about 190 nm or more).

  In this soft X-ray wavelength band, there is no transparent substance, and the refractive index of the substance is very close to 1, so that a conventional optical element utilizing refraction cannot be used. Instead, a grazing incidence mirror that uses total reflection, or a multilayer film reflector that achieves a high reflectivity by superimposing a large number of reflected light by matching the phase of weak reflected light at the interface is used. Is done.

  In such a multilayer-film reflective mirror, the material suitable for obtaining a high reflectance varies depending on the wavelength band of incident light. For example, in the wavelength band near 13.5 nm, using a Mo / Si multilayer film in which a molybdenum (Mo) layer and a silicon (Si) layer are alternately stacked on a substrate, a reflectivity of 67.5% can be obtained at normal incidence. it can. Further, in the wavelength band near 11.3 nm, when a Mo / Be multilayer film in which Mo layers and beryllium (Be) layers are alternately stacked on a substrate is used, a reflectivity of 70.2% can be obtained at normal incidence.

  In a multilayer mirror used in a projection optical system of an exposure apparatus, during exposure, the surface of the multilayer film is irradiated with EUV light, so that organic residues floating in the vicinity of the multilayer mirror (for example, exhaust system oil) Etc.) are decomposed by EUV light and adhere to the surface of the multilayer film as carbon contamination (carbon stains), or the oxidation of the multilayer film surface is contaminated and the reflectance of the multilayer film is reduced. The problem arises.

  Therefore, the multilayer mirror used in EUV lithography needs to be replaced with a new one after being used for a certain period. At this time, if the damaged multilayer film can be removed without affecting the surface of the substrate, the original substrate can be reused. A mirror can be manufactured, and there is no need to newly manufacture an expensive multilayer film reflecting mirror.

  As a method for removing the multilayer film from the substrate, a method for forming a multilayer film on a base layer that is easily dissolved with a chemical such as acid, such as Al, is known. Yes. By dissolving the underlayer with a chemical, the multilayer film formed thereon can be peeled from the substrate.

  However, when the underlayer is formed of a metal such as Al, the underlayer tends to be a microcrystalline thin film, and as a result, the surface roughness becomes rougher than the substrate surface polished very smoothly. When a multilayer film is formed thereon, there is a serious problem that the roughness of the interface increases and the reflectance decreases.

  A method of directly dissolving the multilayer film without using the base layer for peeling as described above is also conceivable. In the case of a Mo / Si multilayer film used in the vicinity of a wavelength of 13.5 nm used in EUV lithography, the Mo layer can be etched with a mixed solution of phosphoric acid, acetic acid and nitric acid. However, the etching rate is slow compared to metals such as Al. In addition, since this mixed solution does not dissolve the Si layer, it was actually difficult to peel off the Mo / Si multilayer film.

  The present invention has been made in view of such circumstances, and a multilayer film reflecting mirror capable of easily peeling a multilayer film using an etching solution, and an EUV exposure apparatus using the multilayer film reflecting mirror. The issue is to provide.

  A first means for solving the above-described problem is a multilayer-film reflective mirror formed by alternately laminating a metal-based layer and a non-metal-based layer on a substrate. The multilayer film reflecting mirror is characterized in that a film formation region of each layer containing metal as a main component is divided so that each layer containing the metal as a main component is bonded to each other.

  A second means for solving the above-mentioned problems is an EUV exposure apparatus characterized by using a multilayer film reflecting mirror as the first means.

  ADVANTAGE OF THE INVENTION According to this invention, the multilayer film reflective mirror which can peel a multilayer film easily using etching liquid, and EUV exposure apparatus using this multilayer film reflective mirror can be provided.

  Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings. 1A and 1B are diagrams showing an outline of a Mo / Si multilayer mirror according to an embodiment of the present invention, in which FIG. 1A is a plan view and FIG.

First, a protective layer 2 (thickness of several nm) made of silicon oxide (SiO ₂ ) is formed on a substrate 1 made of low thermal expansion glass by magnetron sputtering. This layer prevents the substrate from being violated when peeling off the multilayer film by etching. When a chemically stable substrate material such as quartz is used, such a protective layer 2 may be omitted. The material of the protective layer 2 may be any material that is chemically stable, such as tantalum pentoxide (Ta ₂ O ₅ ), in addition to silicon oxide. Since the protective layer made of SiO ₂ or Ta ₂ O ₅ is generally amorphous, the surface roughness does not increase unlike when a metal underlayer such as Al is formed. Therefore, even if the protective layer 2 is formed, the reflectance of the multilayer film does not decrease.

  Next, a Mo / Si multilayer film is formed by magnetron sputtering in a (optical) effective area that is slightly smaller than the protective layer 2. In this embodiment, the Mo layer has a thickness of 2.4 nm, the Si layer has a thickness of 4.5 nm, and 50 pairs of multilayer films having a period length of 6.9 nm are formed.

  At this time, the formation region of the Mo layer 3 is the entire effective region, but the formation region of the Si layer 4 is divided into a plurality. In this example, the width of the gap between the divided areas is 100 μm. In order to form the Si layer 4 in this way, only when the Si layer is formed, a mask as shown in FIG. In this mask, a wire 6 having a thickness of 100 μm is stretched on an annular plate 5, and only a shaded portion of the wire 6 is formed with a region where no Si is attached (the above gap). For this reason, it forms into a film in the state in which all the Mo layers 3 couple | bonded through this clearance gap.

  When such a multilayer film is immersed in an etching solution that dissolves the Mo layer 3, the etching solution enters while dissolving the Mo layer 3 in order from the surface side layer. Therefore, an etching solution that does not dissolve the Si layer 4 is used. However, the Mo / Si multilayer film can be peeled off in a very short time (a few minutes as an example).

  Compared to the case where Al or the like is used as the underlayer, a peeling time comparable to that when using Al or the like can be achieved. When the Al layer is used as a base, the base layer must be gradually dissolved from the peripheral portion of the multilayer film, so that the longer the effective area, the longer the time required for peeling. On the other hand, in the present embodiment, since the Mo layer 6 is sequentially dissolved from the entire surface of the multilayer film through the gap provided in the Si layer 4, the time required for peeling does not depend on the effective area, and the gap Depends on how you put it. If many gaps are provided, the time required for peeling can be shortened accordingly.

  If the gap for dividing the Si layer 4 is formed to be sufficiently smaller than the effective area of the mirror (for example, about 100 μm), the influence of the gap on the optical characteristics can be ignored. In the above description, the film formation region of the Si layer 4 is divided into a fan shape, but the division method is not limited to this.

  A peeling test of the Mo / Si multilayer film thus formed was performed. A cover was appropriately provided so that the etching solution did not come into contact with the region of the substrate 1 where the protective layer 2 was not formed, and the multilayer mirror was immersed in an etching solution composed of a mixed solution of phosphoric acid, acetic acid and nitric acid. The etching solution sequentially dissolved the Mo layer from the surface side, and the Si layer with the lower Mo layer removed was peeled off from the substrate. In this way, the entire Mo / Si multilayer film on the protective layer 2 could be peeled off.

  FIG. 3 is a diagram showing an outline of an EUV exposure apparatus which is an example of an embodiment of the present invention. The EUV light 32 emitted from the light source 31 becomes a substantially parallel light beam through a concave reflecting mirror 34 that acts as a collimator mirror, and enters an optical integrator 35 including a pair of fly-eye mirrors 35a and 35b.

  Thus, a substantial surface light source having a predetermined shape is formed in the vicinity of the reflective surface of the fly-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. Here, an aperture plate for forming an arcuate illumination region is not shown. The light reflected by the surface of the mask M is then reflected in turn by the multilayer reflectors M1, M2, M3, M4, M5, and M6 of the projection optical system 37 to form exposure light 101 on the surface of the mask M. An image of the pattern thus formed is formed on the resist 103 coated on the wafer 102.

  In this EUV apparatus, a multilayer mirror as shown in FIG. 1 is used. Therefore, when the mirror is replaced, the multilayer film can be peeled off and only the multilayer film can be renewed, so that the price of the apparatus as a whole is reduced.

It is a figure which shows the outline | summary of the Mo / Si multilayer mirror which is embodiment of this invention. It is a figure which shows the example of the mask used when forming a Si layer. It is a figure which shows the outline | summary of the EUV exposure apparatus which is an example of Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Board | substrate, 2 ... Protective layer, 3 ... Mo layer, 4 ... Si layer, 5 ... Plate body, 6 ... Wire, 31 ... Light source, 32 ... EUV light, 33 ... Illumination optical system, 34 ... Concave reflector, 35 Optical integrator 35a, 35b Fly eye mirror 36 Planar reflecting mirror 37 Projection optical system M Mask M1-M6 Multilayer reflecting mirror 101 Exposure light 102 Wafer 103 Resist

Claims (2)

  A multilayer reflector in which a metal-based layer and a non-metal-based layer are alternately stacked on a substrate, wherein the film-forming regions of the non-metal-based layers are divided Thus, the multilayer film reflecting mirror is characterized in that the layers mainly composed of the metal are bonded to each other.   An EUV exposure apparatus using the multilayer mirror according to claim 1.

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