JP2008305862A - Optical member, laser light source using the same, and exposure device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical member which can exhibit durability of sufficiently high level against high-fluence laser light of ≥250 mJ/cm<SP>2</SP>per pulse. <P>SOLUTION: The optical member includes a base material made of calcium fluoride and a protective film made of aluminum fluoride laminated on at least one surface of the base material, the protective film being preferably ≥30 nm thick. Such an optical member exhibits durability of sufficiently high level as a protective film of a laser amplification unit of a laser light source having an excitation light source and the laser amplification unit. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical member, a laser light source using the optical member, and an exposure apparatus using the laser light source.

In an exposure apparatus for manufacturing a semiconductor element such as an LSI, a liquid crystal display element, or a thin film magnetic head, light from a laser light source is irradiated onto a pattern on a projection original plate such as a mask or a reticle via an illumination optical system. The pattern is exposed by projecting the pattern onto a photosensitive substrate such as a wafer or a glass plate coated with a photoresist in advance via a projection optical system. In recent years, in such an exposure apparatus, a pattern transferred onto a substrate has been increasingly miniaturized. In the laser light source used in such an exposure apparatus, the wavelength is reduced from i-line (365 nm) to KrF excimer laser (248 nm), ArF excimer laser (193 nm), and further F ₂ laser (157 nm). It has been. However, in such a laser light source, there is a problem that an optical member used for a window material for a chamber of a laser amplifying unit is damaged by the laser beam and the transmittance is lowered. Therefore, in an optical member used for such a laser light source or the like, it has been studied to laminate a protective film on the substrate in order to improve durability.

For example, Japanese Patent Laying-Open No. 2006-523024 (Patent Document 1) discloses a substrate made of calcium fluoride and an optical member in which a coating material is applied to the emission surface of the optical substrate. As an example of the coating material, MgF ₂ or the like is disclosed.
JP 2006-523024 A

  However, in the conventional optical member as described in Patent Document 1, the durability of the protective film against the high fluence laser beam is not always sufficient, and high output and short pulse laser beam is repeatedly irradiated for a long period of time. In some cases, the transmittance of the optical member was lowered.

The present invention has been made in view of the above-described problems of the prior art, and can exhibit sufficiently high durability against a laser beam having a high fluence of 250 mJ / (cm ² · pulse) or more. An object is to provide an optical member, a laser light source using the optical member, and an exposure apparatus using the laser light source.

As a result of intensive studies to achieve the above object, the inventors of the present invention have laminated a protective film made of aluminum fluoride on the surface of a base material made of calcium fluoride. It has been found that sufficiently high durability can be exhibited with respect to a laser beam having a high fluence of (cm ² · pulse) or more, and the present invention has been completed.

  That is, the optical member of the present invention includes a base material made of calcium fluoride and a protective film made of aluminum fluoride laminated on at least one surface of the base material.

  The thickness of the protective film according to the present invention is preferably 30 nm or more.

  The optical member of the present invention preferably further includes a film made of magnesium fluoride or silicon oxide on the surface of the protective film.

  The laser light source of the present invention is a laser light source including an excitation source and a laser amplification unit, and the laser amplification unit includes the optical member of the present invention.

  Furthermore, an exposure apparatus according to the present invention is characterized by including the laser light source according to the present invention.

According to the present invention, an optical member capable of exhibiting sufficiently high durability against a laser beam having a high fluence of 250 mJ / (cm ² · pulse) or more, a laser light source using the optical member, and a laser thereof An exposure apparatus using a light source can be provided.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments thereof.

  First, the optical member of the present invention will be described. That is, the optical member of the present invention includes a base material made of calcium fluoride and a protective film made of aluminum fluoride laminated on at least one surface of the base material.

  The base material according to the present invention is made of calcium fluoride. The base material made of calcium fluoride is not particularly limited as long as it can be used as an optical member, and is manufactured by a known manufacturing method (for example, Bridgman method or Stock Burger method). A calcium fluoride base material can be appropriately used. Further, the shape of the base material is not particularly limited, and the design can be appropriately changed according to the intended use.

Moreover, the protective film concerning this invention is laminated | stacked on the at least one surface of the said base material, and consists of aluminum fluoride. Such a protective film made of aluminum fluoride has sufficiently high durability even for a high-fluence laser beam exceeding 250 mJ / (cm ² · pulse), so that a high-power and short-pulse laser beam is obtained. Even when it is repeatedly irradiated for a long period of time, damage to the substrate can be sufficiently prevented, and a decrease in the transmittance of the laser beam can be sufficiently prevented.

  The thickness of such a protective film is not particularly limited, but is preferably 30 nm or more. When the thickness of such a protective film is less than the lower limit, the laser durability of the protective film itself tends to decrease. Note that a thickness of about 150 nm is sufficient to exhibit a sufficient function.

  A method for producing such a protective film is not particularly limited, and a known method capable of forming a film made of aluminum fluoride can be appropriately employed. For example, a vacuum deposition method, an ion beam assisted deposition method, a gas Cluster ion beam assisted deposition method, ion plating method, ion beam sputtering method, magnetron sputtering method, bias sputtering method, ECR (Electron Cyclotron Resonance) sputtering method, radio frequency (RF) sputtering method, thermal CVD (Chemical Vapor Deposition) method, Plasma CVD method, photo-CVD method, etc. are mentioned.

  In the optical member of the present invention, it is preferable that a film made of magnesium fluoride or silicon oxide is further laminated on the surface of the protective film. By further laminating such a film made of magnesium fluoride or silicon oxide, the moisture resistance of the protective film can be further improved.

  Further, the thickness of the film made of magnesium fluoride or silicon oxide is not particularly limited as long as the film thickness is appropriately adjusted within a range not affecting the optical characteristics of the obtained optical member. It is preferred that this tends to further improve moisture resistance.

  Further, the film forming method of such a magnesium fluoride or silicon oxide film is not particularly limited, and a known method can be appropriately employed. For example, a method similar to the method for forming the protective film can be employed. Good.

The optical member of the present invention including such a base material and a protective film has high resistance to fluorine gas because the base material is made of calcium fluoride, and the laser durability of the protective film is sufficiently high. Therefore, for example, it can be suitably used as an optical member for a laser light source such as an ArF excimer laser or an F ₂ excimer laser.

  Next, the laser light source of the present invention will be described. The laser light source of the present invention is a laser light source including an excitation source and a laser amplification unit, and the laser amplification unit includes the optical member of the present invention. Hereinafter, preferred embodiments of the laser light source of the present invention will be described in detail with reference to the drawings. In the following description and drawings, the same or corresponding elements are denoted by the same reference numerals, and duplicate descriptions are omitted.

  FIG. 1 is a schematic longitudinal sectional view showing a configuration of a preferred embodiment of a laser amplification unit.

1 includes a chamber 11, a laser medium 12 enclosed in the chamber 11, two window members 13 provided on a side surface of the chamber 11, a reflecting mirror 14, and an output mirror 15. Is provided. The chamber 11, the laser medium 12, and the window member 13 constitute a laser excitation unit, and receive light from an excitation source (not shown) to generate light having a specific wavelength. In addition, the reflecting mirror 14 and the output mirror 15 are installed so as to face each other substantially in parallel with the laser excitation part interposed therebetween. Note that the space around the laser amplification unit is filled with vacuum or N ₂ gas. In FIG. 1, an arrow A indicates the optical path of the generated laser light.

  The chamber 11 constituting the laser excitation unit is not particularly limited as long as it is made of a known material capable of enclosing the laser medium 11, and a material made of a known material can be appropriately used. . The laser medium 12 is not particularly limited, and examples thereof include a medium such as ArF or KrF that generates light having a specific wavelength. Further, the window member 13 is made of the optical member of the present invention, and includes a base material 13a made of calcium fluoride and a protective film 13b made of aluminum fluoride laminated on the surface of the base material. . In addition, as an optical member of the present invention used for such a window member 13, in order to further improve moisture resistance, a film made of magnesium fluoride or silicon oxide is further provided on the surface of the protective film 13b. Also good.

  The reflecting mirror 14 is not particularly limited, and a known reflecting mirror in which a reflecting film (hereinafter referred to as a total reflecting film) that totally reflects laser light is formed on a substrate can be appropriately used. Further, the output mirror 15 is not particularly limited, and a publicly known film in which a part of the laser light is reflected and partially transmitted (hereinafter referred to as a partial transmission film) is formed on a substrate made of a material that transmits the laser light. The output mirror can be used as appropriate.

  Further, an excitation source (not shown) for supplying energy to the laser excitation unit of the laser amplification unit shown in FIG. 1 is not particularly limited, and a known excitation source (appropriately according to the intended design) For example, a flash lamp or a power source for supplying electric energy can be used as appropriate.

  In such a laser amplification section, when the laser excitation section is supplied with energy from the excitation source, laser light having a specific wavelength is generated. The laser beam generated in this manner is incident on the reflecting mirror 14 and totally reflected, and then incident on the output mirror 15 to be partially reflected and resonated. Therefore, most of the laser light reciprocates between the reflecting mirror 14 and the output mirror 15, and passes through the laser excitation unit located between the reflecting mirror 14 and the output mirror 15 many times. The light intensity (power density) is amplified every time it passes through the excitation unit. A part of the laser light whose intensity has been amplified passes through the output mirror 15 and is emitted to the outside. In the present embodiment, since the optical member of the present invention is used for the window member 13, the transmittance is sufficiently lowered due to the damage of the window member even under a condition where a high intensity laser beam passes many times. To be prevented. Therefore, the laser light source of the present invention provided with such a laser amplifying unit can irradiate laser light with high output density over a long period of time. For example, a semiconductor device, a liquid crystal display device, or a thin film magnetic head In an exposure apparatus used in a photolithography process when manufacturing a semiconductor device, an image of a pattern formed on a mask or a reticle (hereinafter referred to as a reticle) is applied to a wafer or a glass substrate (hereinafter referred to as a wafer) coated with a photoresist. It can be suitably used as a light source for exposure light during transfer exposure.

  The preferred embodiment of the laser light source of the present invention has been described above, but the laser light source of the present invention is not limited to the above embodiment. For example, the configuration of the laser amplification unit is not limited to the embodiment shown in FIG. 1, and in the present invention, the laser amplification unit may further include a magnifying optical system such as a concave lens, a convex lens, and a prism. Moreover, in the said embodiment, although the optical member of the said invention was used for the window material 13 of the laser amplification part, in the laser light source of this invention, the said optical member is provided in any site | part of a laser amplification part. For example, the optical member of the present invention may be used for the concave lens described above. Moreover, in the said embodiment, although the optical base material used for the window material 13 is what laminated | stacked the protective film 13b only on one surface of the base material 13a, it uses for such a window material 13. However, the configuration of the optical member that can be used is not limited to this, and the protective film 13b may be stacked on both surfaces of the base material 13a.

  Next, the exposure apparatus of the present invention will be described. An exposure apparatus according to the present invention includes the laser light source according to the present invention. As described above, since the exposure apparatus of the present invention includes the laser light source of the present invention, it is possible to expose and transfer a fine pattern with a laser beam having a high output density.

  In addition, such an exposure apparatus may be provided with the laser light source of the present invention as a light source for exposure light, and the configuration thereof is not particularly limited, and a configuration similar to that of a known exposure apparatus may be appropriately adopted. it can. The configuration applicable to the exposure apparatus of the present invention is not particularly limited. For example, JP-A-10-163099 and JP-A-10-214783 (corresponding US Pat. Nos. 6,341,007, 6). , 400,441, 6,549,269 and 6,590,634), JP 2000-505958 (corresponding US Pat. No. 5,969,441), US Pat. No. 6,208,407, JP Examples include configurations described in Kaihei 6-124873, JP-A-10-303114, US Pat. No. 5,825,043, and the like.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

Example 1
Using a fluorite substrate (diameter 30 mm, thickness 2-3 mm) as a base material made of calcium fluoride, forming a protective film (thickness: 70 nm) made of aluminum fluoride (AlF ₃ ) on one side of the substrate, The optical member of the present invention was obtained. In addition, the vacuum evaporation method was employ | adopted for the film-forming of the protective film, and aluminum fluoride was vapor-deposited, heating a fluorite board | substrate at 300 degreeC.

(Example 2)
After a protective film (thickness 35 nm) made of aluminum fluoride is laminated on one surface of the fluorite substrate in the same manner as in the method employed in Example 1, magnesium fluoride (MgF ₂ ) is formed on the surface of the protective film. A film (thickness: 34 nm) was further laminated to obtain the optical member of the present invention. The film made of magnesium fluoride was formed by employing the same method as the method for forming the protective film.

(Example 3)
A protective film (thickness 35 nm) made of aluminum fluoride is laminated on one surface of the fluorite substrate in the same manner as in the method employed in Example 1, and then a film made of silicon oxide (SiO ₂ ) on the surface of the protective film. (Thickness: 31 nm) was further laminated to obtain the optical member of the present invention. The film made of silicon oxide was formed by employing the same method as the method for forming the protective film.

(Comparative Example 1)
An optical member for comparison was obtained in the same manner as in Example 1 except that magnesium fluoride was deposited instead of aluminum fluoride and a film made of magnesium fluoride was laminated on the substrate as a protective film. It was.

(Comparative Example 2)
Instead of depositing aluminum fluoride, a lanthanum fluoride (LaF ₃ ) was deposited and a film made of lanthanum fluoride as a protective film was laminated on the substrate in the same manner as in Example 1 for comparison. An optical member was obtained.

[Performance evaluation of optical members obtained in Examples 1-3 and Comparative Examples 1-2]
Using the optical members obtained in Example 1 and Comparative Examples 1 and 2, laser light was irradiated from the surface side where the protective film was laminated, and the laser durability of the protective film was tested. That is, in such a test, an ArF excimer laser was used as a light source, and the laser beam was irradiated on the surface of the protective film so that the irradiation diameter of the laser beam became 1 mm. Moreover, the output density (fluence) of the laser beam was changed in the range of 100 to 350 mJ / (cm ² · pulse), and the pulse was changed in the range of 5 × 10 ^{6 to} 5 × 10 ⁷ . In addition, the site | part to which a laser beam is irradiated for every fluence to irradiate was shifted, and it was set as irradiation by 1 fluence with respect to one place of an optical member. And after irradiating a laser beam in this way, the presence or absence of destruction of the surface of a protective film was confirmed visually using the differential interference microscope (objective lens: 10 times, eyepiece: 10 times). The obtained results are shown in Table 1. In addition, the meaning of each symbol in Table 1 is as follows.
◯: There is no broken part on the surface of the protective film.
X: There is a broken part on the surface of the protective film.
―: Indicates that evaluation was not performed.

As is clear from the results shown in Table 1, it was confirmed that the optical member of the present invention (Example 1) has a sufficiently high laser durability with no breakdown even at 350 mJ / (cm ² · pulse). It was done. On the other hand, in the optical member obtained in Comparative Example 1, the maximum fluence without destruction up to 5 × 10 ⁷ pulses was 200 mJ / (cm ² · pulse), and the optical member obtained in Comparative Example 2 Therefore, it was confirmed that the maximum fluence was less than 100 mJ / (cm ² · pulse), and it was found that the laser durability was not sufficient with the protective film made of magnesium fluoride or lanthanum fluoride. .

Next, for the optical members obtained in Examples 1 to 3 and Comparative Example 1, a method similar to the above test using an ArF excimer laser as a light source was adopted, and 1 × 10 ⁸ pulses while changing the fluence. The maximum fluence at which the surface of each optical member did not break was measured. The obtained results are shown in FIG.

As is clear from the results shown in FIG. 2, in the optical members of the present invention (Examples 1 to 3), the maximum fluence is 250 mJ / (cm ² · pulse) or more in all cases, and is sufficiently advanced. It was confirmed to have laser durability.

  From these results, it was found that the optical member of the present invention can sufficiently prevent damage to the substrate even when it is repeatedly irradiated with a high-power, short-pulse laser beam for a long period of time.

As described above, according to the present invention, an optical member capable of exhibiting sufficiently high durability against a laser beam having a high fluence of 250 mJ / (cm ² · pulse) or more is used. A laser light source and an exposure apparatus using the laser light source can be provided.

  Therefore, since the optical member of the present invention is excellent in laser durability, it is particularly useful as a window material for a chamber of a laser light source. And in a laser light source provided with such an optical member of the present invention, since damage to the optical member is sufficiently prevented, it is possible to extend the life.

It is a schematic longitudinal cross-sectional view which shows the structure of suitable one Embodiment of a laser amplification part. It is a graph which shows the maximum fluence of each optical member obtained in Examples 1-3 and Comparative Example 1.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Chamber, 12 ... Laser medium, 13 ... Window material, base material 13a ... Base material, 13b ... Protective film, 14 ... Reflection mirror, 15 ... Output mirror, A ... Optical path of laser beam.

Claims (5)

  An optical member comprising: a base material made of calcium fluoride; and a protective film made of aluminum fluoride laminated on at least one surface of the base material.   The optical member according to claim 1, wherein the protective film has a thickness of 30 nm or more.   The optical member according to claim 1, further comprising a film made of magnesium fluoride or silicon oxide on a surface of the protective film.   A laser light source including an excitation source and a laser amplification unit, wherein the laser amplification unit includes the optical member according to any one of claims 1 to 3.   An exposure apparatus comprising the laser light source according to claim 4.

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