JP5237009B2 - Garnet-type single crystal, optical components using the same, and related equipment - Google Patents

Description

The present invention has a general structure A ₃ B ₂ C ₃ O ₁₂ (wherein the cation occupies a crystal structure having three sites of A, B, and C, A represents an element occupying the A site, and B represents An element that occupies the B site, C represents an element that occupies the C site, and O represents an oxygen atom.), An optical component using the same, and related equipment.

  In recent years, higher integration of electronic devices and higher operation speed have been demanded, and in order to meet these demands, development of pattern miniaturization technology has been remarkable. As a pattern miniaturization technique, an immersion exposure technique is known (for example, Patent Document 1).

  FIG. 4 is a diagram showing a schematic configuration of the immersion exposure apparatus described in Patent Document 1. As shown in FIG.

  The immersion exposure apparatus includes at least an illumination optical system 1 including an exposure light source ArF excimer laser, a reticle (mask) R, a projection optical system PL, a liquid supply device 5, and a liquid recovery device 6. In this immersion exposure apparatus, while the pattern image of the reticle R is transferred onto the wafer W, the space between the surface of the wafer W and the optical element 4 on the wafer W side of the projection optical system PL is filled with the liquid 7. Yes.

The optical element 4 includes a liquid having a refractive index of 1.60 to 1.66 with respect to light with a wavelength of 193 nm of an ArF excimer laser, and a base having a refractive index of 2.10 to 2.30 with respect to light with a wavelength of 193 nm. A material (lens) and an antireflection film formed on the surface of the substrate in contact with the liquid are provided. Decalin (C ₁₀ H ₁₈ ) is used for the liquid, and garnet (lutetium aluminum garnet [Lu ₃ Al ₅ O ₁₂ : LuAG], germanate, etc.) and spinel ceramic (Mg ₂ Al ₂ O ₄ etc.) are used for the base material. However, a laminated film of a metal oxide layer and a fluoride layer is used for the antireflection film. With such a configuration, reflection of light by the ArF excimer laser between the liquid and the substrate is suppressed, and a high-resolution immersion exposure apparatus is achieved.

  On the other hand, the resolution of the immersion exposure apparatus is such that the refractive index of the resist disposed on the wafer W, the refractive index of the base material (lens) of the optical element 4, and the refractive index of the liquid are small. It is known to depend on A resist having a refractive index exceeding 1.7 and a liquid having a refractive index exceeding 1.6 have been developed, and a substrate having a refractive index of 1.7 or more is required.

  Patent Document 1 describes that LuAG or the like is used as a substrate having a refractive index of 2.1 to 2.30, but the transmittance with respect to light from an exposure light source (wavelength of 193 nm in Patent Document 1) is not sufficient. Therefore, it is necessary to use an antireflection film that suppresses the reduction in reflectance. The application of such an antireflection film employs a known physical or chemical vapor deposition method, which complicates the process and leads to an increase in cost. Therefore, a base material that does not require an antireflection film is desired.

JP 2008-111304 A

  In view of the circumstances as described above, an object of the present invention is to provide a garnet single crystal having improved transmittance in the vacuum ultraviolet region, an optical component using the garnet single crystal, and related equipment.

The present invention has the following features in order to solve the above problems.
The first invention has a general structure A ₃ B ₂ C ₃ O ₁₂ (the cation-occupying site has a crystal structure having 3 sites of A, B, and C, and A represents an element occupying the A site, B represents an element occupying the B site, C represents an element occupying the C site, and O represents an oxygen atom.), And the garnet single crystal is Y ₃ Al A single crystal selected from the group consisting of ₅ O ₁₂ , Lu ₃ Al ₅ O ₁₂ and (Y _1-x Lu _x ) ₃ Al ₅ O ₁₂ (0 <x <1), which is substituted with the oxygen atom Alternatively, fluorine is contained as an element that performs either or both of filling oxygen deficiency.

  The second invention is characterized in that, in the feature of the first invention, the fluorine content is 5 mol% or less.

  According to a third invention, in the feature of the first or second invention, either the element occupying the A site, the element occupying the B site, or the element occupying the C site is substituted or a defect is filled. It contains at least one element selected from the group consisting of a monovalent element, a divalent element, and a trivalent element as an element for performing one or both of them, and an electronegativity of 1.35 or less. It is characterized by that.

  A fourth invention is characterized in that, in the feature of the third invention, the monovalent element is Li.

  A fifth invention is characterized in that, in the feature of the third invention, the divalent element is either one or both of Mg and Ca.

A sixth invention is an optical component that transmits light in the vacuum ultraviolet region, and is characterized by being formed from a garnet-type single crystal having the characteristics of the first or second invention .

A seventh invention is a semiconductor-related device having an optical component that transmits light in a vacuum ultraviolet region, wherein the optical component is an optical component having the characteristics of the sixth invention.

An eighth invention is an optical-related device having an optical component that transmits light in a vacuum ultraviolet region, wherein the optical component is an optical component having the characteristics of the sixth invention.

  The garnet-type single crystal of the present invention contains fluorine, and fluorine substitutes for oxygen atoms in the garnet-type single crystal and / or fills oxygen deficiency. By substituting fluorine atoms with oxygen atoms in the single crystal, the band gap of the single crystal increases due to the maximum electronegativity of fluorine. As a result, the absorption edge of the single crystal is shifted to the short wavelength side, and the transmittance in the vacuum ultraviolet region is improved. Further, the fluorine fills the oxygen vacancies in the single crystal, whereby the transmittance in the vicinity of the absorption edge (vacuum ultraviolet region) caused by the defects in the crystal is improved.

  In addition, since the garnet-type single crystal is known to have a high refractive index, it can be applied to optical parts such as prisms and window materials in addition to lenses of immersion exposure apparatuses. These optical components can be used for semiconductor-related equipment such as an immersion exposure apparatus and an interferometer, as well as imaging equipment including a digital camera, and optical-related equipment such as a microscope.

  Hereinafter, a garnet-type single crystal of the present invention, an optical component using the same, and related equipment will be described with reference to the drawings. The present inventors have found that the transmittance of an existing garnet-type single crystal is improved by utilizing the shift of the absorption edge in the transmission spectrum and the control of the defect density, thereby completing the present invention.

In this specification, the garnet-type single crystal is a single crystal made of a compound having a crystal structure represented by the general formula A ₃ B ₂ C ₃ O ₁₂ . Here, A is an element occupying the A site (hereinafter referred to as A element), B is an element occupying the B site (hereinafter referred to as B element), and C is an element occupying the C site (hereinafter referred to as C element). , O is an oxygen atom. That is, the garnet-type single crystal has three sites occupied by cations, the A site, the B site, and the C site, and a plurality of types of ions are allowed to dissolve at each site. For this reason, garnet-type single crystals having various compositions are formed. The material design of such a garnet-type single crystal is described, for example, in LANDOLT-BORNSTEIN Group III, 12a (Garnets and Perovskites), p. p. 22 (1.1.3: Lattice parameters of garnets), Springer-Verlag Berlin, Heidelberg, New York, 1978, and the like.

  In particular, when used as a lens (optical component) of an immersion exposure apparatus that is a semiconductor-related device, the element A can be selected from at least one selected from the group consisting of La, Gd, Y, and Lu. Can select at least one from the group consisting of Lu, Sc, Ga and Al, and the C element can be Ga and / or Al. As a matter of course, the A site and the B site may be the same element, and the B site and the C site may be the same element. When selected from these element groups, a single crystal having a high refractive index is obtained.

Among them, from the viewpoint of synthesis and practicality, Y ₃ Al ₅ O ₁₂ (hereinafter referred to as YAG) in which A element is Y, B element and C element are Al, A element is Lu, B element and C element Lu ₃ Al ₅ O ₁₂ (hereinafter referred to as LuAG), whose element is Al, and Y and Lu, and B and C elements are Al (Y _1-x Lu _x ) Al ₅ O ₁₂ (0 <x <1) (hereinafter, YLuAG) is exemplified as a preferable example.

  The present inventors aim to improve the transmittance of a garnet-type single crystal, in particular, the transmittance in the vacuum ultraviolet region (the vacuum ultraviolet region is in the range of 10 nm to 200 nm, particularly 190 nm to 200 nm). We focused on the absorption edge of the transmission spectrum of single crystal and the defects in the crystal.

  FIG. 1 is a diagram illustrating a transmission spectrum of YAG.

  YAG is a representative example of a garnet-type single crystal, and FIG. 1 shows an exemplary transmission spectrum of YAG produced by a known single crystal growth method. From the transmission spectrum shown in FIG. 1, it can be seen that the absorption edge of YAG is near the wavelength of 193 nm of the light source of the immersion exposure apparatus. Further, the transmittance of YAG at a wavelength of 193 nm is as low as about 25%, which is not practical. Further, as shown in FIG. 1 surrounded by an ellipse, the transmission spectrum shows a shoulder, which suggests that the crystal structure of the single crystal has a high defect density. The present inventor improved the transmittance by paying attention to the absorption edge and defects from such a transmission spectrum.

(1) Shift of absorption edge In the transmission spectrum shown in FIG. 1, if the absorption edge can be shifted to the short wavelength side indicated by an arrow, the transmittance in the vacuum ultraviolet region can be improved. Specifically, the absorption edge correlates with the band gap, and is simply expressed by the equation E = hc / λ (where E is the band gap, hc is the photon energy, and λ is the wavelength of the absorption edge). If the wavelength λ of the absorption edge is shortened, the band gap increases. Therefore, in order to improve the transmittance of the garnet type single crystal, it is only necessary to increase the band gap of the garnet type single crystal. To increase the band gap, the cation and the anion in the garnet type single crystal It is considered that the difference in electronegativity of suffices to increase.

  Table 1 shows Pauling's electronegativity. The values in Table 1 E. Huhey et al., “Inorganic Chemistry—Principles of Structure and Reactivity”, 4th ed. (Haper Collins, New York, 1993).

  The garnet-type single crystal of the present invention contains fluorine (F), and fluorine has the largest electronegativity as shown in Table 1. Since the ionic radius of fluorine is smaller than the ionic radius of O, it easily substitutes for O in the garnet-type single crystal, and increases the difference in electronegativity between the cation and the anion in the garnet-type single crystal. As a result, the transmittance of the garnet-type single crystal containing fluorine is improved.

  The fluorine content is preferably 5 mol% or less. Even if F is replaced by O even slightly, the band gap increases and the absorption edge shifts to the short wavelength side, so that the transmittance in the vacuum ultraviolet region is improved. If the fluorine content is more than 5 mol%, the crystal structure may not be maintained, which is not preferable.

  The garnet-type single crystal of the present invention is preferably selected from the group consisting of a monovalent element, a divalent element, and a trivalent element in addition to fluorine, and has an electronegativity of 1 It contains an element that is .35 or less. At least one element selected from the group consisting of these monovalent elements, divalent elements, and trivalent elements is replaced with a cation element (A element, B element, and C element) in the garnet-type single crystal. To do. Since the electronegativity of the selected element is 1.35 or less, the difference in electronegativity between the cation and the anion in the garnet-type single crystal can be increased. If the electronegativity is greater than 1.35, the difference in electronegativity decreases, which is not preferable. More preferably, from the viewpoints of ionic radius and electronegativity, the monovalent element is exemplified by Li and the divalent element is exemplified by Ca.

  Note that the content of the selective element is preferably 0 mol% or more and 5 mol% or less. Since the garnet-type single crystal only needs to contain at least fluorine, the garnet-type single crystal does not necessarily contain the selection element. When it is contained, if it exceeds 5 mol%, the crystal structure may not be maintained, which is not preferable.

(2) Control of defect concentration As described above with reference to FIG. 1, the shoulder in the transmission spectrum is the imperfection of the crystal structure in the single crystal, that is, defects (oxygen defects and cation defects). Due to By reducing the defect concentration, it is considered that the shoulder in the transmission spectrum disappears and the transmittance is improved.

  As described above, the garnet-type single crystal of the present invention contains fluorine (F), and fluorine has an ionic radius smaller than that of O, so that oxygen defects can be filled easily. As a result, the shoulder in the transmission spectrum disappears and the transmittance is improved. As described above, the fluorine content is preferably 5 mol% or less.

  The garnet-type single crystal of the present invention preferably contains at least one element selected from the group consisting of a monovalent element, a divalent element, and a trivalent element in addition to fluorine. . At least one element selected from the group consisting of these monovalent elements, divalent elements, and trivalent elements is a cation at a cation site (A site, B site, and C site) of a garnet-type single crystal. Defects can be filled easily. Among these, from the viewpoint of the ionic radius, preferably, the monovalent element is exemplified by Li, and the divalent element is exemplified by Mg. As the selective element, any element that can be substituted is basically applicable. However, considering the shift of the absorption edge to the short wavelength side shown in (1) above, the electric elements shown in Table 1 can be used. Elements with a negative degree of 1.35 or less are preferred. Therefore, the monovalent element selected is preferably Li, and the divalent element is preferably one or both of Mg and Ca.

The garnet-type single crystal of the present invention is produced by a known crystal growth method such as the Czochralski (CZ) method, except that the raw material melt contains a fluorine source or a fluorine source and a selected element source. Can do. The fluorine source is a group consisting of a compound of element A and fluorine constituting a garnet-type single crystal, a compound of element B and fluorine, a compound of element C and fluorine, a mixture thereof, and a gas containing fluorine. You can choose. For example, when the element A is Y, YF ₃ is adopted as the fluorine source. The gas containing fluorine, for example, gas containing fluorine some or all of Ar or _{N 2, CF 4, CH 2} F 2, CH 3 F, C 2 H 5 F, HF, etc. _{F 2} It is the gas replaced with.

  The element source includes a material composed of a single selected element, an oxide of the selected element, a compound of the A element constituting the garnet-type single crystal and the selected element, and the B element and the selected element. It can be selected from the group consisting of compounds, compounds of element C and selected elements, mixtures thereof, and fluorides thereof.

  In the garnet-type single crystal of the present invention, the absorption edge of the transmission spectrum is shifted to the short wavelength side, and oxygen vacancies are controlled, so that the transmittance in the vacuum ultraviolet region is improved. Such a garnet-type single crystal is suitable for a lens (optical component) of an immersion exposure apparatus, a lens material using high transmittance, and the like.

Although only the garnet type single crystal has been described in detail above, the above principle is based on general oxide materials (for example, (Mg, Zn) Al ₂ O ₄ , CaAl ₂ O ₄ , CaB ₂ O ₄ and LiAl _5. Cubic spinel crystal represented by O ₈ , cubic perovskite crystal, MgO, (Mg, Zn) O, LiNbO ₃ , LiTaO ₃ , Mg-doped LiNbO ₃ , Mg-doped LiTaO ₃ , Al ₂ O ₃ , TiO ₂ Etc.). It is clear that the transmittance of the general oxide material can be improved by either or both of fluorine substitution of oxygen in the oxide or filling of oxygen deficiency with fluorine.

  Next, examples will be shown to further explain the garnet-type single crystal of the present invention. Of course, the present invention is not limited to the following examples.

A garnet-type single crystal containing fluorine was produced. As the garnet-type single crystal, Y ₃ Al ₅ O ₁₂ (YAG) in which A element is Y and B element and C element are Al in the general formula A ₃ B ₂ C ₃ O ₁₂ was used. Garnet-type single crystals were grown by the Czochralski method.

4N pure Y ₂ O ₃ powder, Al ₂ O ₃ powder, and YF ₃ powder were weighed and mixed at a molar ratio of 2.9: 5: 0.2, and press molded. The pressed mixed raw material powder was filled in an Ir crucible and placed on a ceramic heat insulating material. The Ir crucible was heated to about 2000 ° C. near the melting point of the raw material mixed powder by high frequency induction heating to dissolve the raw material mixed powder. At this time, F in the melt was 0.2 mol%.

  Next, the YAG seed crystal molded in advance and fixed to the seed holder was brought into contact with the melt to adjust to the melt and to adjust the temperature. Thereafter, the garnet-type single crystal was grown by rotating at a pulling rate of 1 mm / h and a crystal rotation speed of 10 rpm.

The YAG single crystal thus obtained was observed. The observation results are shown in FIG. The obtained YAG single crystal was cut and polished, and the transmission spectrum was measured. The thickness of the measurement sample was 1 mm. The measurement results are shown in FIG. The evaluation of the YAG single crystal is as described later.
<Comparative Example 1>

In Example 1, an additive-free YAG single crystal was produced by the same procedure except that YF ₃ powder was not used. The obtained additive-free YAG single crystal was cut and polished in the same manner as in Example 1, and the transmission spectrum was measured. The measurement results are also shown in FIG.

  FIG. 2 is a photograph showing the appearance of the YAG single crystal having fluorine produced in Example 1.

  As shown in FIG. 2, even when fluorine was added, a homogeneous, colorless and transparent YAG single crystal was obtained (Example 1). The garnet-type single crystal of the present invention can be applied with an existing crystal growth method in production, which is advantageous for practical use.

  FIG. 3 is a diagram showing a transmission spectrum of a YAG single crystal measured in Example 1 and Comparative Example 1.

  As shown in FIG. 3, the transmission spectrum of Comparative Example 1 (no additive YAG) is the same as the transmission spectrum of YAG shown in FIG. Further, it can be seen from the transmission spectrum shown in FIG. 3 that the absorption edge of the transmission spectrum is shifted to the short wavelength side by containing fluorine. Specifically, the transmittance (50%) in the vacuum ultraviolet region (particularly wavelength 193 nm) of the fluorine-containing YAG single crystal of Example 1 (F-added YAG) is the transmittance of the additive-free YAG of Comparative Example 1 (25%). %). Therefore, by applying F-added YAG as a base material of an optical element of a high-resolution immersion exposure apparatus, an antireflection film can be made unnecessary and cost reduction can be achieved.

  Further improvement of the transmittance is expected by increasing the purity of the raw material from 4N to 6N.

It is the figure which illustrated the transmission spectrum of YAG. 2 is a photograph showing the appearance of a fluorine-containing YAG single crystal produced in Example 1. FIG. FIG. 3 is a diagram showing a transmission spectrum of a YAG single crystal measured in Example 1 and Comparative Example 1. 1 is a diagram illustrating a schematic configuration of an immersion exposure apparatus described in Patent Document 1. FIG.

Claims (8)

General formula A ₃ B ₂ C ₃ O ₁₂ (the site occupied by the cation has a crystal structure with three sites of A, B and C, A represents an element occupying the A site, and B represents the B site Element represents, C represents an element occupying a C site, and O represents an oxygen atom.), And the garnet single crystal is Y ₃ Al ₅ O ₁₂ , Lu _3. A single crystal selected from the group consisting of Al ₅ O ₁₂ and (Y _1-x Lu _x ) ₃ Al ₅ O ₁₂ (0 <x <1), which replaces the oxygen atom or fills an oxygen vacancy A garnet-type single crystal comprising fluorine as an element for performing either or both of the above.   The garnet-type single crystal according to claim 1, wherein the fluorine content is 5 mol% or less.   The element occupying the A site, the element occupying the B site, the element occupying the C site, or the element for performing either one or both of filling the defect, the monovalent element, the divalent element, and The garnet-type single crystal according to claim 1 or 2, wherein the garnet-type single crystal contains at least one element selected from the group consisting of trivalent elements and having an electronegativity of 1.35 or less.   The garnet-type single crystal according to claim 3, wherein the monovalent element is Li.   The garnet-type single crystal according to claim 3, wherein the divalent element is one or both of Mg and Ca. An optical component that transmits light in the vacuum ultraviolet region, optical components, characterized in that it is formed from a garnet-type single crystal according to claim 1 or 2. A semiconductor-related equipment having an optical component that transmits light in the vacuum ultraviolet region, a semiconductor related device, wherein the optical component is an optical component according to claim 6. An optical equipment having an optical component that transmits light in the vacuum ultraviolet region, optical equipment, wherein the optical component is an optical component according to claim 6.