JP4539335B2 - Multilayer reflection mirror, EUV exposure apparatus, and contamination removal method in multilayer reflection mirror - Google Patents

Description

  The present invention relates to a multilayer film reflector used in an EUV exposure apparatus, an EUV exposure apparatus using the multilayer film reflector, and a contamination removal method in the multilayer film mirror.

  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 an 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 ultrashort ultraviolet rays. Since δ is much smaller than 1, the real part of the refractive index in this region is very close to 1. Also, since k is very large, the absorption rate is high. 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. 4 exemplarily). 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. 3 shows the 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. 4 shows the reflection per 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. It is a figure which shows the result of having calculated how much a rate fall ((DELTA) R) affects with respect to the transmittance | permeability (throughput) of the whole 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.

About two methods for preventing such contamination of the optical element due to the carbon layer deposition have been proposed. The typical ones are shown below.
(1) Radical generation by EUV light and UV light (see M. Malinowski et al., Proc. SPIE 4343 (2001) 347: Non-Patent Document 4)
Introduce oxygen or water vapor into the working atmosphere. Oxygen or water vapor is decomposed by EUV light irradiation to generate oxygen radicals. 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 gas. Since carbon dioxide is a gas, it is evacuated by a vacuum pump to remove carbon contamination.
(2) Transport of oxygen or hydrogen radicals (see S. Graham, et al., Proc. SPIE 4688 (2002) 431: Non-Patent Document 5)
Oxygen or hydrogen radicals are generated by RF discharge plasma or the like. This is transported to the mirror surface. 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 gas. Hydrogen 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 methane gas. Since carbon dioxide gas or methane gas is a gas, it is exhausted by a vacuum pump to remove carbon contamination.

JP 11-312638 A JP 2004-31491 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 S. Graham, et al., Proc.SPIE 4688 (2002) 431

  However, in the method (1), it is necessary to directly use the EUV light irradiated to the mirror as an EUV exposure apparatus for radical generation, or to provide another EUV light source or UV light source. In the former case, it is not always possible to obtain an irradiation amount of EUV light sufficient to remove carbon contamination. In the latter case, there is a problem that the apparatus becomes complicated because another light source must be provided to guide the light to the optical system. When UV light is used, there is a problem that radicals cannot be generated efficiently because the energy of photons is lower than that of EUV light. In any case, the method (1) has a problem in that a sufficient amount of radicals is not generated, so that the effect of removing carbon contamination cannot be obtained sufficiently.

  In the method (2), since it is difficult to arrange an electrode mechanism or the like for generating radicals inside the optical system, a method is adopted in which radicals are generated and transported away from the optical system. . However, since the lifetime of radicals is not so long, there is a problem that the activity of losing carbon transport is not sufficiently obtained due to loss of activity during transportation.

  The present invention has been made in view of such circumstances, and has been made in view of the above circumstances. A multilayer reflector that can efficiently remove carbon contamination attached to the surface, and the multilayer reflector. It is an object of the present invention to provide a method for efficiently removing carbon contamination adhering to the surface of a multilayer film reflecting mirror and an EUV exposure apparatus using the above.

A first means for achieving the above object is a multilayer film reflector used in an EUV exposure apparatus, comprising a mirror substrate having a ground potential and a multilayer film formed thereon, a portion peripheral edge of the multilayer film reflector is formed so as to overlap the other part has a conductive thin film which is formed continuously to the outside of the multilayer film, conductive connected to the power supply A multilayer reflector configured to apply a voltage to the multilayer film by contacting a body with the other part of the conductive thin film formed outside the multilayer film (claim) Item 1).

  In this means, a voltage is applied to the multilayer film to generate plasma near the surface of the multilayer film reflector, and ions and radicals generated in the plasma adhere to the surface of the multilayer film of the multilayer film mirror. Contamination can be removed.

  The second means for solving the above problems includes a multilayer mirror as the first means and a gas jet for blowing a gas that forms plasma when a voltage is applied to the multilayer film to the surface of the multilayer film. An EUV exposure apparatus having an apparatus (claim 2).

  In this means, a voltage is applied to the multilayer film, a gas is blown from the gas ejection device to the multilayer film, plasma is generated in the vicinity of the multilayer film, and the multilayer film reflecting mirror is generated by ions, radicals, etc. generated in the plasma. Contamination adhered to the surface of the multilayer film can be removed.

According to a third means for solving the above-mentioned problem, a voltage is applied to the multilayer film of the multilayer film reflector of the first means in the optical system, and a gas is blown to the multilayer film to reflect the multilayer film. A multilayer film reflection characterized by forming a plasma by glow discharge in the vicinity of the mirror surface and removing contamination adhered to the surface of the multilayer film of the multilayer mirror by radicals and ions generated in the plasma. A method for removing contamination in a mirror (Claim 3).

  In this means, the plasma can be controlled by the pressure of the introduced gas and the voltage applied to the multilayer film, so that radicals and ions sufficient to remove carbon contamination can be generated. Further, since plasma is formed in the very vicinity of the mirror surface to which contamination has adhered, radicals and ions generated in the plasma can be used efficiently.

  A fourth means for solving the above-mentioned problems is the third means, wherein the gas is a gas containing oxygen or hydrogen (claim 4).

  Since the main component of contamination is carbon, carbon can be removed from the surface of the multilayer film as a gaseous compound and discharged out of the system by oxidation with oxygen ions, radicals, reduction with hydrogen ions, and radicals. The gas containing oxygen or hydrogen may contain oxygen or hydrogen as a mixture, or may be a gas containing a compound such as water vapor.

  According to the present invention, a multilayer film reflecting mirror capable of efficiently removing carbon contamination adhered to the surface, an EUV exposure apparatus using the multilayer film reflecting mirror, and carbon contamination adhered to the surface of the multilayer film reflecting mirror. A method for efficiently removing a nation can be provided.

  Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a mirror of an EUV exposure apparatus projection optical system which is an embodiment 1 of the present invention. 1B is a plan view, and FIG. 1A is a cross-sectional view taken along line AA in FIG.

  A multilayer film 2 for reflection coating is formed on an aspherical mirror substrate 1 made of low thermal expansion glass. The multilayer film 2 is a multilayer film composed of alternating layers of molybdenum (Mo) and silicon (Si) designed to efficiently reflect EUV light having a wavelength of 13.5 nm. In the uppermost layer of the multilayer film 2, a layer (not shown) made of ruthenium (Ru) is formed as a capping layer for preventing the oxidation of the surface instead of the Mo layer.

  The mirror substrate 1 has three convex portions 3 for holding it. The convex portion 3 is formed integrally with the mirror substrate 1. A hardware component 5 is attached to the convex portion 3. The hardware part 5 is screwed to a holding part of a lens barrel mechanism (not shown). By adopting such a configuration, it is possible to minimize deformation of the mirror (effective reflection surface) due to holding. In addition, since the specific attachment method is described in Unexamined-Japanese-Patent No. 2004-31491 (patent document 2), the description is abbreviate | omitted. Further, the relationship between the convex portion 3 and the hardware part 5 is the same at all three locations, but only one location is shown in the figure. Such an optical system such as a mirror is installed in a vacuum chamber.

  The multilayer film 2 is formed so as to partially overlap the conductive thin film 4, and both are electrically connected. The overlapping part of the multilayer film 2 and the conductive thin film 4 may be either above or below.

  When the conductive thin film 4 is formed first (when the conductive thin film 4 is under the multilayer film 2), the surface is oxidized before the multilayer film is formed, resulting in poor electrical connection. Use a material that does not easily oxidize. Specifically, gold (Au), platinum (Pt), rhodium (Rh), ruthenium (Ru), palladium (Pd), or the like, which is a noble metal, may be used. Since the noble metal thin film is difficult to etch later, the extra portion is formed by masking the extra portion so that the thin film is formed only at the predetermined portion.

  When the multilayer film 2 is formed first (when the multilayer film 2 is below the conductive thin film 4), the material of the conductive thin film 4 may not be a noble metal. Common conductive materials such as chromium (Cr), aluminum (Al), and copper (Cu) can be used.

  The conductive thin film 4 is continuously formed up to the convex portion 3 for holding the mirror substrate 1. The edge portion 15 where the conductive thin film 4 is formed is appropriately chamfered so as not to break at the edge of the mirror substrate 1.

  The conductive thin film 4 is connected to a high frequency power source 6 of 13.56 MHz through a metal part 5. A matching box 7 is inserted between the high-frequency power source 6 and the conductive thin film 4 in order to match impedance and efficiently transmit high-frequency power. As a result, the high frequency power applied to the conductive thin film is set to 300 W in terms of effective value. The matching box 7 and the high frequency power source 6 are installed outside the vacuum chamber. The electrical connection inside and outside the vacuum chamber is made through a current introduction terminal.

  In the vicinity of the surface of the mirror substrate 1 on which the multilayer film 2 is formed, a gas injection mechanism 8 is provided for blowing gas onto the mirror surface. The gas injection mechanism 8 is a ring-shaped hollow pipe having a plurality of holes. The gas is supplied from a high-pressure gas cylinder 9 into the pipe, and the gas is injected from a hole provided in the pipe. The position and angle of the hole are appropriately determined so that the gas to be ejected is localized in the vicinity of the mirror surface. The gas injection mechanism 8 is arranged so as not to block the effective area of the mirror. A mass flow controller 14 for controlling the gas flow rate is inserted between the gas injection mechanism 8 and the high pressure gas cylinder 9. The mass flow controller 14 and the high-pressure gas cylinder 9 are installed outside the vacuum chamber. In the present embodiment, oxygen gas is used as the gas. Note that other accessory parts such as the mirror substrate 1 and the gas injection mechanism 8 as well as the high-pressure gas cylinder 9 are set to the ground potential.

When the flow rate of oxygen gas is adjusted so that the pressure in the vacuum chamber becomes 1 × 10 ⁻² Pa and a high frequency voltage is applied to the multilayer film 2, oxygen plasma due to glow discharge is generated near the mirror surface. The oxygen ions and oxygen radicals formed in (1) reach the surface of the multilayer film 2. The carbon contamination adhering to the surface of the multilayer film 2 is oxidized by oxygen radicals and oxygen ions to become a gas (carbon dioxide gas), and is removed by a vacuum exhaust device connected to a vacuum chamber.

  FIG. 2 is a diagram for explaining in more detail the method for fastening the convex portion 3 of the mirror substrate and the metal part 5 and the electrical connection from the power supply device to the multilayer film 2, and shows the BB cross section of FIG. FIG. Several methods for electrical connection from the power supply device to the multilayer film 2 are conceivable. A method of pressing the contact point on the multilayer film 2 on the mirror surface, directly soldering or screwing is also conceivable. However, since the mirror of the projection optical system of the EUV exposure apparatus is processed with a very high shape accuracy of 1 nm or less, it is easy to apply a method such as applying a force to the mirror surface or performing some processing in this way. The surface shape changes, and the imaging performance of the optical system deteriorates.

  Therefore, a slightly complicated connection method is employed in this embodiment. Among EUV exposure apparatuses, in the case of a mirror that does not require a very high shape accuracy such as a mirror for an illumination system, a simple connection method as described above may be used.

  As shown in the figure, the hardware component 5 is fixed by sandwiching the convex portion 3 from above, below, left and right. That is, it is sandwiched between the pressing members 5c and 5d from the left and right, and the upper and lower sides are sandwiched between the pressing members 5a and 5b. Each of the holding members 5c and 5d is urged so as to apply a pressing force as indicated by an arrow in the drawing from the left and right, and each of the holding members 5a and 5b is provided from above and below as indicated by an arrow in the drawing. The convex portion 3 is sandwiched and fixed by being biased. Although these mechanisms are omitted in FIG. 1, a more specific configuration is described in Japanese Patent Application Laid-Open No. 2004-31491 (Patent Document 2), and thus the description thereof is omitted.

  The conductive thin film 4 provided on the convex portion 3 is in contact with the conductive member 11 incorporated in the pressing member 5a. The conductive member 11 is electrically insulated from the pressing member 5a by an insulating member 10 formed of Teflon (registered trademark). A wiring 13 is screwed to the conductive member 11 with a screw 12.

  In this way, the conductive thin film 4 electrically connected to the multilayer film 2 and formed along the convex portion 3 is in electrical contact with the conductive member 11, and the wiring 13 is connected from the conductive member 11. By pulling out, it is possible to apply a voltage to the multilayer film 2 without processing the portion of the multilayer film 2 or applying a force.

In the above embodiment, a high frequency power supply is used as the power supply device, but a DC power supply may be used instead. In this case, the matching box 7 is not necessary. When the voltage applied to the multilayer film 2 is 500 V and the pressure of the oxygen gas to be sprayed is 5 × 10 ⁻¹ Pa, oxygen plasma can be formed.

  In the above description, oxygen gas is used as the gas, but hydrogen gas can be used instead of oxygen gas. By setting the voltage and gas pressure applied to the multilayer film 2 to the same level as that of oxygen gas, hydrogen plasma is generated, and carbon in the contamination is reduced to become gaseous methane, which is discharged out of the system.

  If water vapor is used as the gas, it reacts with carbon in the contamination to become carbon dioxide gas, which is discharged out of the system.

  In the embodiment shown in FIG. 1, the conductive thin film 4 and the multilayer film 2 are formed of different materials. In FIG. 1, the conductive thin film 4 is formed as a part of the multilayer film. However, this may be used as the conductive thin film 4. In this way, the portion corresponding to the conductive thin film 4 can be formed as a part of the multilayer film 2 and formed simultaneously with the formation of the multilayer film 2, thereby simplifying the process accordingly.

  The EUV exposure apparatus according to the embodiment of the present invention has the same basic configuration as the conventional one shown in FIG. 5, and uses a multilayer mirror as shown in FIG. The only difference is that it has a contamination removal apparatus as shown in FIG.

It is a figure which shows the mirror of the EUV exposure apparatus projection optical system which is an example of Embodiment 1 of this invention. It is a figure explaining the fastening method of the convex part 3 of a mirror substrate, and the hardware component 5, and the electrical connection from the power supply device to the multilayer film 2. FIG. 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). In a system using a total of 13 multilayer reflectors including six illumination systems, reflection masks, and six projection systems, the reflectance drop (ΔR) per multilayer reflector is the transmittance (throughput) of the entire optical system. It is a figure which shows the result of having calculated how much it influences on (). It is a figure which shows the outline | summary of an EUV exposure apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Mirror board | substrate, 2 ... Multilayer film, 3 ... Convex part, 4 ... Conductive thin film, 5 ... Metal parts, 5a-5d ... Holding member, 6 ... High frequency power supply, 7 ... Matching box, 8 ... Gas injection mechanism, 9 ... high pressure gas cylinder, 10 ... insulating member, 11 ... conductive member, 12 ... screw, 13 ... wiring

Claims (4)

A multilayer mirror used in the EUV exposure apparatus, and a multilayer film formed thereon a mirror substrate that is the ground potential, the peripheral portion and the portion of the multilayer film of the multilayer mirror Are formed so as to overlap each other, and the other part has a conductive thin film formed continuously to the outside of the multilayer film, and a conductor connected to a power source is formed on the outside of the multilayer film. A multilayer film reflector configured to apply a voltage to the multilayer film by contacting with the other part of the conductive thin film.   An EUV exposure apparatus comprising: the multilayer mirror according to claim 1; and a gas ejection device that blows a gas that forms plasma when a voltage is applied to the multilayer film onto the surface of the multilayer film.   A voltage is applied to the multilayer film of the multilayer film reflector according to claim 1 in the optical system, and a gas is blown to the multilayer film to form plasma by glow discharge in the vicinity of the surface of the multilayer film mirror. A method for removing contamination in a multilayer mirror, wherein the contamination adhered to the surface of the multilayer film of the multilayer mirror is removed by radicals and ions generated in the plasma. 4. The method for removing contamination in a multilayer mirror according to claim 3, wherein the gas is a gas containing oxygen or hydrogen.

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