JP2007281322A - Optical element and exposure device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical element in which the surface of an optical mirror and an electrode on a mirror holder is brought into electrical conduction. <P>SOLUTION: The optical element has the optical mirror 2, the mirror holder 12 for holding the optical mirror 2 and an electrical conduction part 14 which allows electrical conduction between the surface of the optical mirror 2 and an electrode 10 on the mirror holder 12. In this case, the electrical conduction part 14 is composed of a conductive material agitated in a solvent. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical element having an electrical conduction portion that electrically conducts between a surface of an optical mirror and an electrode on a mirror holder, and an exposure apparatus including the optical element.

In recent years, with the progress of miniaturization of semiconductor integrated circuits, in order to improve the resolving power of an optical system limited by the light diffraction limit, a wavelength shorter than this (for example, about 11 to 14 nm) is used instead of conventional ultraviolet rays. A projection exposure apparatus using extreme ultraviolet rays has been developed (see Patent Document 1).
Japanese Patent Laid-Open No. 2003-14893

  In the above-described projection exposure apparatus (EUV exposure apparatus) using extreme ultraviolet rays, since there is no substance that transmits extreme ultraviolet rays, the optical system needs to be constituted by a reflecting mirror. Since the rate is very close to 1, unlike a conventional optical element using refraction or reflection, an optical mirror or the like on which a multilayer film that enhances light by interference is formed is used.

  Here, since the usage environment of the optical mirror in the EUV exposure apparatus is generally kept in a vacuum, the surface of the optical mirror is irradiated by irradiating the optical mirror with extreme ultraviolet light (EUV light) having high energy in the vacuum. That is, electrons are emitted from the surface of the multilayer film formed on the surface of the optical mirror (see FIG. 8). When irradiation with EUV light having high energy is continuously performed, electrons are emitted until they are suppressed by self-bias, so that the surface of the multilayer film is finally charged to a positive potential. When the surface of the multilayer film is charged to a positive potential, dust in the space is attracted by the positive electric attractive force and deposited on the surface of the multilayer film. At this time, if the dust is an organic substance, the organic substance is decomposed by the EUV light and becomes a carbide to be solidified on the surface of the multilayer film, thereby deteriorating the optical performance of the optical mirror. That is, the organic matter cannot be completely removed from the environment inside the EUV exposure apparatus, and the organic matter adheres to the surface of the multilayer film by charging the surface of the multilayer film to a positive potential. Then, when the EUV light is irradiated with the organic matter attached, the organic matter is decomposed, and the carbide that absorbs the EUV light is solidified on the surface of the multilayer film, causing the optical performance of the optical mirror to deteriorate.

  In order to prevent the optical characteristics of the optical mirror from deteriorating due to the carbides adhering to the surface of the multilayer film, it is necessary to electrically connect the surface of the optical mirror to a potential control power source or ground. As an optical element in which the surface of the optical mirror is electrically connected to a potential control power source or a ground, for example, as shown in FIG. 6, a potential control power source (not shown) or a ground (not shown) and a mirror holder 30 are provided. An electrode 28 is connected to the surface of the optical mirror 20 in which the multilayer film 26 is formed on the disk-shaped substrate 22 and the electrode 28, and a conductive wire 32 is bonded to the surface of the optical mirror 20. There is an optical element fixed by using 34. Further, as shown in FIG. 7, the conductive film is formed from the surface of the optical mirror 40 on which the multilayer film 46 is formed to the flange portion 44 of the base material 42 by forming and patterning the conductive film by vacuum deposition or the like. There is an optical element in which electrical connection is ensured by wiring at 54 and sandwiching the flange portion 44 between electrodes 48 provided on the mirror holder 50.

  However, when the adhesive is applied to the surface of the optical mirror as described above, the surface shape of the optical mirror designed with high accuracy changes due to the stress accompanying volume shrinkage when the adhesive solidifies. There is a problem that the surface accuracy of the mirror is lowered and the imaging performance of the EUV exposure apparatus is lowered. Further, when forming a conductive thin film by vacuum deposition or the like, the process is complicated, which causes an increase in the manufacturing cost of the optical element. Furthermore, in order to wire the surface of the optical mirror and the electrode with a conductive thin film, the film must be formed beyond the corners 52 of the base material 42 shown in FIG. In particular, there is a problem that electrical conduction between the surface of the optical mirror and the electrode cannot be ensured.

  An object of the present invention is to provide an optical element in which the surface of an optical mirror and an electrode on a mirror holder are electrically connected, and an exposure apparatus including the optical element.

  The optical element of the present invention includes an optical mirror (2), a mirror holder (12) that holds the optical mirror (2), a surface of the optical mirror (2), and an electrode (10) on the mirror holder (12). In the optical element having the electrical conduction part (14) that electrically conducts between the electrical conduction part and the electrical conduction part (14), the electrical conduction part (14) is composed of a conductive substance stirred in a solvent. .

  The optical element of the present invention includes an optical mirror (2), a mirror holder (12) for holding the optical mirror, a surface of the optical mirror (2), and an electrode (10) on the mirror holder (12). In the optical element having the electrical conduction part (16) that electrically conducts between the electrical conduction parts (16), the electrical conduction part (16) is made of a liquid metal.

  The exposure apparatus of the present invention is characterized in that the optical element of the present invention is provided in at least a part of an optical system.

  According to the optical element of the present invention, since the electrically conductive portion is constituted by the conductive substance stirred in the solvent, the surface of the optical mirror and the mirror holder can be surely changed without changing the surface shape of the optical mirror. Electrical conduction between the upper electrode can be ensured. Therefore, since the potential of the surface of the optical mirror can be accurately controlled and carbides can be prevented from solidifying on the surface of the optical mirror, deterioration of the optical performance of the optical mirror can be appropriately suppressed.

  Further, according to the optical element of the present invention, since the electrically conducting portion is constituted by the liquid metal, the surface of the optical mirror and the electrode on the mirror holder can be surely provided without changing the shape of the surface of the optical mirror. Can be secured. Therefore, since the potential of the surface of the optical mirror can be accurately controlled and carbides can be prevented from solidifying on the surface of the optical mirror, deterioration of the optical performance of the optical mirror can be appropriately suppressed.

  Further, according to the exposure apparatus of the present invention, the optical mirror is formed between the surface of the optical mirror and the electrode on the mirror holder in at least a part of the optical system by a conductive substance or liquid metal stirred in a solvent. Since an optical element having an electrically conducting portion that is electrically conducted without changing the surface shape is provided, good exposure can be performed over a long period of time.

  An optical element according to a first embodiment of the present invention will be described with reference to the drawings. The optical element is used in, for example, an EUV exposure apparatus that uses extreme ultraviolet light (EUV light) as exposure light. FIG. 1 is a cross-sectional view of the optical element according to the first embodiment. As shown in FIG. 1, the optical element has a reflection layer having a reflection performance in the extreme ultraviolet wavelength region on the surface of a low thermal expansion glass substrate 4 (hereinafter referred to as the substrate 4) polished into a highly accurate surface shape. An optical mirror 2 on which a multilayer film 8 in which, for example, 40 pairs of Mo layers having a thickness of 2.5 nm and Si layers having a thickness of 4.5 nm are alternately stacked, is formed; And a mirror holder 12 for holding. Here, a flange 6 made of the same material as that of the base material 4 is formed on the peripheral portion of the base material 4, and the optical mirror 2 is mirrored by being held by the mirror holder 12 so as to sandwich the collar 6. It is fixed to the holder 12. The mirror holder 12 is provided with an electrode 10, and a power source (not shown) for controlling the potential of the surface of the optical mirror 2 is connected to the electrode 10.

  Further, the optical element is provided with an electrically conducting portion 14 that electrically conducts between the surface of the optical mirror 2 and the electrode 10. The electrically conductive portion 14 is made of a conductive material stirred in a solvent, for example, a silver paste obtained by stirring fine silver particles as a conductive material in a solvent such as an organic medium, It is formed by using and apply | coating (refer FIG. 2). Here, since the electrical resistance of the silver paste can be adjusted by the thickness, width, etc. to be applied, when the resistance between the surface of the optical mirror 2 and the electrode 10 is high, overcoating or application region (application) The resistance can be reduced by increasing the width. In addition, conduction between the surface of the optical mirror 2 and the electrode 10 is also performed by applying overcoating at the corners of the substrate 4, for example, at the boundary between the substrate 4 and the flange 6 shown in FIG. 2. Can be secured.

  Note that as the conductive substance, a substance made of one or more substances in the group consisting of silver, copper, aluminum, iron, gold, carbon, and molybdenum can be used. Further, after applying a conductive substance stirred in a solvent such as silver paste, the solvent may be removed by heating, for example. Even when the solvent is removed by heating or the like, there is no influence on ensuring electrical continuity between the surface of the optical mirror 2 and the electrode 10.

  According to the optical element according to the first embodiment, since the electrically conducting portion is made of the conductive material stirred in the solvent, the optical mirror can be used without changing the shape of the surface of the optical mirror. Electrical conduction between the surface of the mirror and the electrode on the mirror holder can be ensured. Moreover, even if the base material of an optical mirror has a corner | angular part, the electrical continuity between the surface of an optical mirror and the electrode on a mirror holder can be ensured. Furthermore, since the electrically conductive portion can be formed without going through a complicated process such as forming a conductive thin film, it is possible to appropriately suppress an increase in the cost of manufacturing the optical element. .

  Moreover, according to the optical element according to the first embodiment, electrical continuity between the surface of the optical mirror and the electrode on the mirror holder is ensured, and the potential of the surface of the optical mirror is reliably controlled, Since the surface of the optical mirror is prevented from being charged to a positive potential, deterioration of the optical characteristics of the optical mirror can be appropriately suppressed.

  Next, with reference to the drawings, an optical element according to a second embodiment of the present invention will be described. FIG. 3 is a cross-sectional view of an optical element according to the second embodiment. Since the optical element shown in FIG. 3 has substantially the same configuration as the optical element according to the first embodiment (see FIG. 1), only different parts will be described.

  In the optical element shown in FIG. 3, the electrode 16 is disposed on the mirror holder 12 so as to cover the outside of the effective area that does not affect the optical performance of the optical mirror 2. The electrical continuity between the surface of the optical mirror 2 and the electrode 16 is ensured by an electrical continuity 18 made of a liquid metal, for example, mercury.

  FIG. 4 is a diagram for explaining the electrical conduction portion 18 formed between the surface of the optical mirror 2 on which the multilayer film 8 is formed and the electrode 16. The electrically conductive portion 18 is configured by pouring a liquid metal such as mercury into a recess formed in the electrode 16. That is, the electrode 16 is formed with a predetermined recess, for example, a recess having a diameter of 1 mm and a depth of 1 mm, on the surface facing the optical mirror 2. Further, the electrode 16 is adjusted and disposed in the mirror holder 12 (see FIG. 3) so as to have a predetermined distance between the surface of the optical mirror 2, for example, a distance of 10 μm to 500 μm.

Here, a predetermined amount of liquid metal, for example, 1.5 mm ³ of mercury is poured into the recess formed in the electrode 16. In this case, since mercury has a strong surface tension, the electric conduction portion 18 is formed by stabilizing in a state where it rises from the depression formed in the electrode 16, that is, in a state in contact with the surface of the optical mirror 2. Therefore, the surface of the optical mirror 2 and the electrode 16 are electrically connected via mercury, and electrical conduction between the optical mirror 2 and the electrode 16 is ensured.

  According to the optical element according to the second embodiment, the electrical continuity between the surface of the optical mirror and the electrode on the mirror holder is ensured through the electrical continuity portion made of liquid metal. Therefore, the surface potential of the optical mirror can be controlled without causing a change in the surface shape of the optical mirror. In addition, since the electrically conductive portion can be formed without going through a complicated process such as forming a conductive thin film, it is possible to appropriately suppress an increase in manufacturing cost of the optical element.

  Moreover, according to the optical element according to the second embodiment, since electrical continuity is ensured between the surface of the optical mirror and the electrode on the mirror holder, the potential of the surface of the optical mirror is surely set. It is possible to control and prevent the surface of the optical mirror from being charged to a positive potential and appropriately suppress deterioration of the optical characteristics of the optical mirror.

  In addition, according to the optical element according to the first embodiment and the optical element according to the second embodiment, the Mo layer and the Si layer are alternately stacked, and the reflection performance in the extreme ultraviolet wavelength region is improved. Since the multilayer film having the reflective layer is formed, extreme ultraviolet light can be favorably reflected.

Next, an EUV exposure apparatus according to a third embodiment of the present invention will be described with reference to the drawings. FIG. 5 is a diagram showing a schematic configuration of an EUV exposure apparatus (reduction projection exposure apparatus) according to the third embodiment. In the EUV exposure apparatus shown in FIG. 5, the entire optical path is kept in a vacuum (for example, 1 × 10 ⁻³ Pa or less). The EUV exposure apparatus includes an illumination optical system IL including a light source. EUV light emitted from the illumination optical system IL (generally indicates a wavelength of 5 to 20 nm, specifically, wavelengths of 13.5 nm and 11 nm are used) is reflected by the folding mirror 301 to form a pattern. The reticle 302 is irradiated.

  The reticle 302 is a reflection type reticle, and is held by a chuck 303 a fixed to the reticle stage 303. The reticle stage 303 is configured to be movable in the scanning direction, and is configured to be capable of minute movement in the direction orthogonal to the scanning direction and in the optical axis direction. The scanning direction of the reticle stage 303 and the position in the direction orthogonal to the scanning direction are controlled with high accuracy by a laser interferometer (not shown), and the position in the optical axis direction is a reticle focus composed of a reticle focus light transmission system 304 and a reticle focus light reception system 305. It is controlled by a sensor.

  The reticle 302 is formed with a multilayer film (for example, molybdenum (Mo) / silicon (Si) or molybdenum (Mo) / beryllium (Be)) that reflects EUV light, and an absorption layer ( For example, it is patterned by nickel (Ni) or aluminum (Al). The EUV light reflected by the reticle 302 enters the optical barrel 314.

  In the optical barrel 314, a plurality (four in this embodiment) of mirrors 306, 307, 308, and 309 are installed. At least one of these mirrors 306 to 309 is configured by the optical element according to the first embodiment or the optical element according to the second embodiment. In this embodiment, although four mirrors are provided as the projection optical system, six or eight mirrors may be provided. In this case, the numerical aperture (NA) can be increased.

  The EUV light that has entered the optical barrel 314 is reflected by the mirror 306, is then sequentially reflected by the mirror 307, the mirror 308, and the mirror 309, exits from the optical barrel 314, and enters the wafer 310. Note that the reduction magnification of the projection optical system including the mirrors 306 to 309 is, for example, 1/4 or 1/5. In addition, an off-axis microscope 315 that performs alignment of the wafer 310 is installed in the vicinity of the optical barrel 314.

  The wafer 310 is held on a chuck 311 a fixed to the wafer stage 311. The wafer stage 311 is installed in a plane orthogonal to the optical axis, and is configured to be movable in a plane orthogonal to the optical axis. In addition, the wafer stage 311 is configured to be capable of minute movement in the optical axis direction. The position of the wafer stage 311 in the optical axis direction is controlled by a wafer autofocus sensor including a wafer autofocus light transmission system 312 and a wafer autofocus light reception system 313. The position of the wafer stage 311 in the plane orthogonal to the optical axis is controlled with high accuracy by a laser interferometer (not shown).

  At the time of exposure, the reticle stage 303 and the wafer stage 311 have the same speed ratio as the reduction magnification of the projection optical system, for example, (moving speed of the reticle stage 303) :( moving speed of the wafer stage 311) = 4: 1 or 5: 1 for synchronous scanning.

  According to the EUV exposure apparatus according to the third embodiment, at least one of the mirrors constituting the projection optical system is the optical element according to the first embodiment or the optical element according to the second embodiment. Therefore, it is possible to appropriately prevent deterioration of the optical performance of the mirror due to solidification of carbide on the surface of the mirror and to perform good exposure. Moreover, since the optical performance deterioration of the mirror can be appropriately prevented and the usable period of the mirror can be lengthened, the exposure apparatus can be operated efficiently and an appropriate cost reduction can be realized.

  In the third embodiment, at least one of the mirrors 306 to 309 is configured by the optical element according to the first embodiment or the optical element according to the second embodiment. The mirror and the folding mirror 301 included in the optical system IL may be configured by the optical element according to the first embodiment or the optical element according to the second embodiment.

It is sectional drawing of the optical element concerning 1st Embodiment. It is a top view of the optical mirror concerning a 1st embodiment. It is sectional drawing of the optical element concerning 2nd Embodiment. It is a figure for demonstrating the electrical conduction part concerning 2nd Embodiment. It is a figure which shows schematic structure of the EUV exposure apparatus concerning 3rd Embodiment. It is a figure for demonstrating the prior art. It is another figure for demonstrating the prior art. It is a conceptual diagram of the state from which an electron is emitted from an optical mirror.

Explanation of symbols

2 ... optical mirror, 4 ... glass substrate, 6 ... brim, 8 ... multilayer film, 10, 16 ... electrode, 12 ... mirror holder, 14, 18 ... electricity , Conductive optical part, IL, illumination optical system, 302, reticle, 303, reticle stage, 306 to 309, mirror, 310, wafer, 311, wafer stage.

Claims (8)

An optical mirror and a mirror holder for holding the optical mirror;
In the optical element having an electrical conduction portion that electrically conducts between the surface of the optical mirror and the electrode on the mirror holder,
The optical element is characterized in that the electrically conducting portion is composed of a conductive substance stirred in a solvent.   The optical element according to claim 1, wherein the solvent in the electrically conductive portion is removed. The conductive material is
3. The optical element according to claim 1, wherein the optical element is made of one or more substances selected from the group consisting of copper, aluminum, iron, gold, silver, carbon, and molybdenum. An optical mirror and a mirror holder for holding the optical mirror;
In the optical element having an electrical conduction portion that electrically conducts between the surface of the optical mirror and the electrode on the mirror holder,
The optical element is characterized in that the electrically conducting portion is made of a liquid metal.   The optical element according to claim 4, wherein the liquid metal is mercury.   The multilayer film which has the reflection layer which laminated | stacked Mo layer and Si layer alternately on the surface of the said optical mirror is formed, It is any one of Claim 1 thru | or 5 characterized by the above-mentioned. Optical elements.   The optical element according to claim 6, wherein the reflection layer has a reflection performance in an extreme ultraviolet wavelength region. An exposure apparatus comprising the optical element according to any one of claims 1 to 7 in at least a part of an optical system.

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