JP2005257769A - Optical thin film, optical element, exposure apparatus using same, and exposure method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical element whose reflection characteristics are uniform in the surface of a lens. <P>SOLUTION: The optical element has multilayer film configuration in which crystalline substrate and its first layer are amorphous films having optical film thickness of 0.480 to 0.520λ0 when the λ0 is defined as the center wavelength of design. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical element using an optical thin film.

  2. Description of the Related Art In optical products such as cameras, semiconductor reduced projection exposure apparatuses (hereinafter referred to as steppers) and liquid crystal projectors, optical elements having desired optical characteristics by applying optical thin films to lenses and substrates are often used. These optical elements greatly influence the performance of the product.

  Various glass materials are used for lenses and substrates of these optical elements. They are properly used according to their required characteristics and cost. Among them, it may be necessary to use a crystalline glass material.

For example, in a stepper using an ArF excimer laser or F ₂ laser light source wavelength of the ultraviolet region, therefore the output and the photon energy of the laser is large, the lens and the substrate of the element due to the decrease and heat generation quantity by causing light absorption Destruction is often a problem. Therefore, in order to reduce this light absorption, crystalline fluorite or the like is used for the glass material of the lens or substrate.

  Moreover, crystalline fluorite or the like is sometimes used as the glass material of the lens in a camera or an astronomical telescope because of the problem of chromatic aberration.

  When a crystalline glass material is used for such a lens or substrate, a crystalline optical thin film may be formed thereon from the viewpoint of optical characteristics. For example, an antireflection film as described in Patent Document 1 is an example. When the substrate and the thin film formed on the substrate are both crystalline, the growth method of the thin film may be greatly influenced by the substrate due to the relationship between the atomic plane spacing of the substrate and the atomic plane spacing of the film. For example, an epitaxial film in which the film grows in a specific direction with respect to the substrate orientation, such as an Ag film on rock salt (in the case of an Ag film on rock salt, (001) Ag // (001) NaCl) is a typical example. It is an example.

  This is no exception in crystalline optical thin films. When a crystalline optical thin film is formed on a crystalline substrate, the characteristics of the optical thin film vary greatly depending on the relationship between the atomic plane distances of the substrate and the thin film. FIG. 9 shows the difference in characteristics when the antireflection film described in Patent Document 1 is formed on the (111) fluorite substrate and the (110) fluorite substrate. This will be referred to as Conventional Example 1, and its configuration is shown below.

[Conventional example 1]
Substrate: Single crystal fluorite First layer: 0.10λ LaF ₃
Second layer: 0.30λ MgF ₂
Third layer: 0.25λ LaF ₃
Fourth layer: 0.24λ MgF ₂
Medium: Air
JP 09-329702 A

  As described above, in the conventional antireflection film and the like, the characteristics of the antireflection film may change due to the influence of the plane orientation on the film formation surface of the crystalline substrate. Furthermore, in the case of a crystalline lens, since the lens has a curvature, the crystal surface is not the same in the lens surface, and the reflection characteristics are not uniform in the lens surface. If such an optical element having a non-uniform reflection characteristic within the lens surface is used in a camera, a semiconductor reduced projection exposure apparatus, or the like, the imaging performance is degraded.

  Therefore, when a crystalline optical thin film is formed on a crystalline substrate, the first layer on the substrate is not affected by the surface orientation of the substrate in order to suppress the effect on the film due to the surface orientation of the substrate. The crystalline film is laminated by an optical film thickness of 0.480 to 0.520λ0 that does not largely lose the degree of freedom in optical design.

  By utilizing the present invention, it is possible to manufacture an optical element whose optical characteristics are not affected by the substrate or lens even if the substrate or lens is a crystalline glass material. In particular, in the case of a lens, it has a great effect on making the optical characteristics uniform within the lens surface. Further, when the antireflection film of the present invention is used, good optical characteristics can be obtained.

  Hereinafter, an antireflection film is shown as an example of the embodiment of the present invention. Needless to say, the present invention is not limited to this example.

  As shown in FIG. 1, the antireflection film as an example of the optical element according to the present invention has an amorphous low refractive index film 2 as the first layer on the crystalline substrate 1 from the substrate side, A high refractive index film 3 of a crystalline film is laminated as a layer, and a low refractive index film 4 is laminated as a third layer.

  And the film thickness of the amorphous film of the first layer is 0.480 to 0.520λ0, which is an optical film thickness that does not largely lose the degree of freedom in optical design.

The low refractive index layer used here has a refractive index lower than that of the substrate, and is MgF ₂ , AlF ₃ , NaF, LiF, CaF ₂ , SrF ₂ , BaF ₂ , Na ₃ AlF ₆ , SiO ₂ , TbF _3. Or a mixture thereof. The high refractive index layer used here has a refractive index higher than that of the substrate, and is one of NdF ₃ , LaF ₃ , GdF ₃ , DyF ₃ , PbF ₃ , SmF ₃ , YbF ₃ , and ErF ₃ . Or a mixture thereof.

The low refractive index film of the first amorphous film on the substrate is any one of AlF ₃ , SiO ₂ , ThF ₃ or a mixture thereof.

  These films are preferably formed by a method such as vacuum deposition, sputtering, ion plating, ion-assisted deposition, or ion beam sputtering.

  In addition, when the target center wavelength of the antireflection film of the present invention is 120 to 200 nm, the effect is particularly large with respect to the conventional example. Sputtering or vacuum deposition is particularly desirable when the design center wavelength of light is 165 to 200 nm, and vacuum deposition is particularly desirable when the wavelength is 120 to 165 nm.

  By applying the antireflection film as in the above embodiment to an optical element such as a lens or a prism, not only an optical element with low reflection and high transmission can be obtained, but also its optical characteristics are uniform within the substrate surface, In the film formation, it becomes possible to sufficiently ensure the reproducibility of the optical characteristics regardless of the substrate.

<Example>
Specific examples of the above embodiment will be described below.

  As shown in FIG. 1, the antireflective film of Example 1 is formed by applying a low refractive index film layer 2, a crystalline high refractive index film layer 3, and a low refractive index film 4 on a substrate 1 using a vacuum deposition method. Are sequentially stacked. The substrate glass material, film material, and film thickness are shown below.

[Example 1]
Substrate: Single crystal fluorite First layer: 0.505λ AlF ₃
Second layer: 0.248λ GdF ₃
Third layer: 0.252λ MgF ₂
Medium: Air λ is a target center wavelength, and here, λ = 157 nm. The refractive indexes of the single crystal fluorite substrate, AlF3, GdF3, and MgF2 are 1.56, 1.46, 1.80, and 1.46, respectively.

  As a comparative example of Example 1, the following antireflection film was formed using the same film forming process.

[Comparative Example 1]
Substrate: Single crystal fluorite First layer: 0.10λ MgF ₂
Second layer: 0.30λ GdF ₃
Third layer: 0.25λ MgF ₂
Medium: Air These reflection characteristics are shown in FIG. The reflectance of Example 1 is reduced, and the value is close to 0 when the incident angle is near 0 °.

  In addition, FIG. 3 shows the reflection characteristics when these examples are formed on the (111) fluorite substrate and the (110) fluorite substrate. Although the characteristics were different in Comparative Example 1, the characteristics were almost the same in Example 1. That is, in Example 1, optical characteristics independent of the surface orientation of the substrate can be obtained.

  As shown in FIG. 4, the antireflective film of Example 2 is formed by using a vacuum deposition method on a substrate 1 as shown in FIG. 4, a low refractive index film layer 5, a crystalline high refractive index film layer 6, and a low refractive index film 7. Are sequentially stacked. The substrate glass material, film material, and film thickness are shown below.

[Example 2]
Substrate: Single crystal fluorite First layer: 0.520λ AlF ₃
Second layer: 0.257λ GdF ₃
Third layer: 0.257λ MgF ₂
Medium: Air λ is a target center wavelength, and here, λ = 193 nm. The refractive indexes of the single crystal fluorite substrate, AlF ₃ , GdF ₃ , and MgF ₂ are 1.55, 1.42, 1.70, and 1.42, respectively.

  As a comparative example of Example 2, the following antireflection film was formed using the same film forming process.

[Comparative Example 2]
Substrate: Single crystal fluorite First layer: 0.550λ AlF ₃
Second layer: 0.275λ GdF ₃
Third layer: 0.275λ MgF ₂
Medium: Air These reflection characteristics are shown in FIG. In Example 2, the reflectance is lower, and the value is close to 0 when the incident angle is near 0 °. Also consider the case where these examples are developed in an actual stepper. Steppers have a very large number of lenses. For example, when the number of lenses is 100, the number of antireflection films is 200. Even if the reflectance of the antireflection film is 0.1%, the light quantity is reduced by about 20% at (0.999) ²⁰⁰ . In addition, these reflected lights become stray light and cause flare and ghost. Therefore, low reflection characteristics are good even at 0.1% in order to realize high exposure performance in the stepper. Example 2 has sufficiently low reflection characteristics even when viewed as an optical element for a stepper.

  FIG. 6 shows the reflection characteristics when these examples are formed on the (111) fluorite substrate and the (110) fluorite substrate. Although the characteristics were different in Comparative Example 2, the characteristics were almost the same in Example 2. That is, in Example 2, optical characteristics independent of the surface orientation of the substrate can be obtained.

  As shown in FIG. 4, the antireflection film of Example 3 is formed by using a vacuum deposition method on the substrate 1 to form a low refractive index layer 5, a crystalline high refractive index layer 6, and a low refractive index layer 7. Are sequentially stacked. The substrate glass material, film material, and film thickness are shown below.

[Example 3]
Substrate: Single crystal fluorite First layer: 0.480λ AlF ₃
Second layer: LaF _{3 of} 0.244λ
Third layer: 0.244λ MgF ₂
Medium: Air λ is a target center wavelength, and here, λ = 157 nm. The refractive indexes of the single crystal fluorite substrate, AlF3, GdF3, and MgF2 are 1.56, 1.46, 1.80, and 1.46, respectively.

  As a comparative example of Example 3, the following antireflection film was formed using the same film forming process.

[Comparative Example 3]
Substrate: Single crystal fluorite First layer: 0.460λ MgF ₂
Second layer: 0.234λ LaF ₃
Third layer: 0.234 MgF ₂
Medium: Air These reflection characteristics are shown in FIG. In Example 3, the reflectance is lower, and the value is close to 0 when the incident angle is near 0 °. Also consider the case where these examples are developed in an actual stepper. Steppers have a very large number of lenses. For example, when the number of lenses is 100, the number of antireflection films is 200. Even if the reflectance of the antireflection film is 0.1%, the light quantity is reduced by about 20% at (0.999) ²⁰⁰ . In addition, these reflected lights become stray light and cause flare and ghost. Therefore, in order to achieve high stepper exposure performance, low reflection characteristics are good even at 0.1%. Example 3 has sufficiently low reflection characteristics as an optical element of a stepper.

  In addition, FIG. 8 shows the reflection characteristics when these examples are formed on the (111) fluorite substrate and the (110) fluorite substrate. Although the characteristic was different in Comparative Example 3, the characteristic was almost the same in Example 3. That is, in Example 3, optical characteristics independent of the surface orientation of the substrate can be obtained.

<Example of exposure apparatus>
Next, an example in which the optical element having the optical thin film of the present invention is applied to a semiconductor exposure apparatus will be described.

  In FIG. 10, 10 is an optical axis, 20 is a light source that generates light having a wavelength of 157 nm in the vacuum ultraviolet region, 30 is an illumination optical system including an aperture stop 30A, 40 is a stage on which the reticle M is placed, and 50 is an aperture stop 50A. The projection optical system 60 includes a stage 60 on which the wafer W is placed. Light from the light source 20 is irradiated onto the reticle M via the illumination optical system 30, and an image of the device pattern on the reticle M is projected onto the wafer W by the projection optical system 50.

  In the projection exposure apparatus of the present embodiment, the optical system is formed by the lens having the optical thin film of the present invention in each of the illumination optical system 30 and the projection optical system 50. By configuring the optical system with the lens, excellent optical characteristics are realized.

<Example of Device Manufacturing Method>
Next, an embodiment of a device manufacturing method using the projection exposure apparatus shown in FIG. 10 will be described.

  FIG. 11 shows a manufacturing flow of a semiconductor device (a semiconductor chip such as an IC or LSI, a liquid crystal panel or a CCD). In step 1 (circuit design), a semiconductor device circuit is designed. In step 2 (mask production), a mask (reticle) on which the designed circuit pattern is formed is produced. On the other hand, in step 3 (wafer manufacture), a wafer is manufactured using a material such as silicon. Step 4 (wafer process) is called a pre-process, and an actual circuit is formed on the wafer by lithography using the prepared mask and wafer. The next step 5 (assembly) is called a post-process, and is a process for forming a chip using the wafer created in step 4, and the assembly process (dicing, bonding), packaging process (chip encapsulation) and the like are performed. Including. In step 6 (inspection), inspections such as an operation confirmation test and a durability test of the semiconductor device created in step 5 are performed. Through these steps, the semiconductor device is completed and shipped (step 7).

  FIG. 12 shows a detailed flow of the wafer process. In step 11 (oxidation), the wafer surface is oxidized. In step 12, an insulating film is formed on the surface of the wafer. In step 13 (electrode formation), an electrode is formed on the wafer by vapor deposition. In step 14 (ion implantation), ions are implanted into the wafer. In step 15 (resist process), a resist (sensitive material) is applied to the wafer. Step 16 (exposure) uses the projection exposure apparatus to expose a wafer with an image of the circuit pattern of the mask. In step 17 (development), the exposed wafer is developed. In step 18 (etching), portions other than the developed resist are removed. In step 19 (resist stripping), unnecessary resist after etching is removed. By repeating these steps, a circuit pattern is formed on the wafer.

  By using the manufacturing method of this embodiment, it becomes possible to manufacture a highly integrated device, which has been difficult in the past.

Antireflection film of Example 1 of the present invention Reflectance-incident angle characteristics of Example 1 and Comparative Example 1 of the present invention Reflectivity-incident angle characteristics when the substrates of Example 1 and Comparative Example 1 of the present invention are changed Antireflection film of Examples 2 and 3 of the present invention Reflectivity-incident angle characteristics of Example 2 and Comparative Example 2 of the present invention Reflectivity-incident angle characteristics when the substrates of Example 2 and Comparative Example 2 of the present invention are changed Reflectance-incident angle characteristics of Example 3 and Comparative Example 3 of the present invention Reflectivity-incident angle characteristics when the substrates of Example 3 and Comparative Example 3 of the present invention are changed Optical properties of conventional antireflection coatings The figure which shows the projection exposure apparatus which has an optical system which has the optical element of this invention Diagram showing device manufacturing flow Diagram showing wafer process

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Low refractive index layer 3 High refractive index layer 4 Low refractive index layer 5 Low refractive index layer 6 High refractive index layer 7 Low refractive index layer 20 Exposure light source 30 Illumination optical system 40 Reticle stage 50 Projection optical system 60 Wafer stage

Claims (5)

  An optical element characterized in that the crystalline substrate and the first layer thereof have a multilayer structure that is an amorphous film having an optical film thickness of 0.480 to 0.520λ0 where λ0 is a design center wavelength. The crystalline substrate according to claim 1 is any one of CaF ₂ , MgF ₂ , LiF ₂ , and LaF ₃ , and the first amorphous film on the substrate is any one of AlF ₃ , ThF ₃ , and SiO ₂ . Or an optical element characterized by being a mixture thereof.   3. The optical element according to claim 2, wherein the multilayer film on the substrate has an antireflection function for light having a wavelength of 120 to 200 nm. The multilayer film having an antireflection function according to claim 3 is AlF ₃ , YF ₃ , SiO ₂ , SiO, Al ₂ O ₃ , Y ₂ O ₃ , ScO ₃ , Pr ₆ O ₁₁ , TaO ₅ , TbF ₃ , NaF, A low refractive index film that is one of LiF, Na ₃ AlF ₆ or a mixture thereof, and one of NdF ₃ , LaF ₃ , GdF ₃ , DyF ₃ , PbF ₃ , SmF ₃ , YbF ₃ , ErF ₃ or a combination thereof An optical element comprising a high refractive index film which is a mixture. 5. The multilayer film according to claim 4, wherein λ0 is a design center wavelength, the optical film thickness of the first layer on the substrate is 0.480 to 0.520 λ0, and the optical film thickness of the second layer. Is a high refractive index film having a thickness of 0.240 to 0.260λ0, and a low refractive index film having an optical thickness of the third layer of 0.240 to 0.260λ0.

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