JPH08179103A - Optical element and its production - Google Patents

Abstract

PURPOSE: To obtain an optical element having sufficient reflectivity or transmissivity and further high laser beam durability by using substance contg. a stoichiometric ratio of fluorine to metal or a substance contg. fluorine more than the stoichiometric ratio to form the film of an optical element. CONSTITUTION: The film of a compd. of fluorine and metal is formed on a substrate. The compd. having a stoichiometric composition or the compd. contg. fuorine in excess of stoichimetry are used in this case. The compd. of fluorine and metal is shown by NdFy ((y) is 3 to 3.1) or AlFz ((z) is 3 to 3.1). Namely, this antireflection film is obtained, for example, by forming the film of NdF3 12 Nd: F=1:3 to 3.1) as the high-refractive-index substance on a synthetic quartz substrate 11 with the surface polished with high precision in the optical film thickness of λ/4 (λ=193.4nm) and then forming the film of AlF3 13 (Al:F=1:3 to 3.1) as a low-refractive-index substance on the film 12 in the optical film thickness of λ/4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element used in an optical system using an excimer laser oscillating in the ultraviolet region and a lamp as a light source.

[0002]

2. Description of the Related Art At present, a reduction projection exposure apparatus is used for manufacturing highly integrated LSI. This LSI
In order to increase the degree of integration, the wavelength used for exposure has been shortened in recent years. Recently, a KrF excimer laser capable of oscillating light in a wavelength range shorter than that of a mercury lamp has been put into practical use as a light source of a reduction projection exposure apparatus. The wavelength λ of the light emitted from this KrF excimer laser is 248.4 nm. Furthermore, in the future, it is desired to use an ArF excimer laser as a light source for a reduction projection exposure apparatus. The wavelength λ of the light emitted from this ArF excimer laser is 193.4 nm.

Optical elements used in such a short wavelength region are required to have low absorption and high laser durability even if light having a short wavelength is used. This is because the case where a transmission system composed of 100 surfaces is used in a reduction projection exposure apparatus using an optical element provided with an antireflection film having a reflection loss of 0% and a film absorption of 0.3% per surface is considered. , While the transmittance of the whole system is (0.997) ¹⁰⁰ × 100 = 74.1%, the transmission system with the same structure has 0% reflection loss per surface and 0.5% film absorption. In the case of the optical element provided with the prevention film, (0.995) ¹⁰⁰ × 100 = 60.6%, resulting in a difference of 13.5% in transmittance. Further, light having a wavelength shorter than around 200 nm has a considerably high energy, and when a substance is irradiated with light having such a short wavelength, most substances absorb the light. Therefore, it is important to select a substance that absorbs a small amount of light as a material for the optical member even when it is irradiated with light having such a short wavelength. At present, a fluorine compound such as magnesium fluoride or neodymium fluoride is often used as a substance that absorbs little light even at a short wavelength, especially for antireflection films and multilayer mirrors. An example of a conventional antireflection film is shown in FIG. In FIG. 5, neodymium fluoride as the high refractive index material 31 and the low refractive index material 3 are formed on the synthetic quartz substrate 11.
Aluminum fluoride was deposited as 2. This antireflection film exhibits a transmittance as shown in FIG. Further, an example of a conventional multilayer mirror is shown in FIG. This FIG. 7 shows a BK7 substrate
1 has a multilayer film 41 formed of neodymium fluoride as a high refractive index substance and magnesium fluoride as a low refractive index substance. Then, a total of 41 layers are formed in order of neodymium fluoride, magnesium fluoride ... From the substrate 21. This multilayer mirror shows the reflectance characteristics as shown in FIG.

[0004]

However, none of the conventional optical elements formed with a film of a fluorine compound such as magnesium fluoride, neodymium fluoride, and aluminum fluoride showed sufficient transmittance and reflectance. . Further, as described later, the conventional optical element has durability against a strong laser beam at a short wavelength of 200 nm or less (hereinafter, durability against the intensity of laser light is referred to as laser durability).
There was no optical element with.

When such an optical element is mounted on a reduction projection exposure apparatus, there is a concern that the resolution may be lowered due to the low transmittance. Further, since the film forming the optical element has a large film absorption, when the formed film is irradiated with laser light, heat is generated and the film is broken due to melting or the like. Alternatively, the problem that the lens surface shape changes due to heat generation occurs. If the surface shape of the optical element is deformed, the effect appears as an aberration, and the highly integrated LSI that requires a fine circuit pattern due to the effect of the aberration.
Can no longer be manufactured.

Therefore, it is an object of the present invention to solve the above-mentioned problems with the object of obtaining an optical element having sufficient reflectance or transmittance and high laser durability.

[0007]

Therefore, according to the present invention, a film which is a compound of fluorine and a metal formed on a substrate, wherein the composition ratio of the compound is more than the stoichiometric ratio or the stoichiometric ratio. Is determined to have a film formed of a compound having an excessive composition ratio. Further, the compound of fluorine and metal is MgF _x , and x is 2 or more and 2.1 or less. In addition, the compound of fluorine and metal,
NdF _y , y is 3 or more and 3.1 or less, and AlF _z is z or more, and z is 3 or more and 3.1 or less.

Further, according to the present invention, there is provided a method of manufacturing an optical element using a vacuum vapor deposition method in which a vapor deposition material is melted and vaporized in a vacuum container to form a film of the vapor deposition material on a substrate placed in the vacuum container, The vapor deposition material is a compound of fluorine and a metal, and the method for producing an optical element uses a material in which the vapor deposition material has a composition ratio of fluorine excess to stoichiometric ratio. Also,
In the present invention, the vapor deposition material for forming an optical element using a vacuum vapor deposition method is a compound of fluorine and a metal, the composition ratio of the vapor deposition material is a composition ratio of fluorine excess than stoichiometric ratio. It is a substance with

[0009]

In order to solve the above problems, the present inventors have
The reason why the reflectance or transmittance is not improved and the reason why the laser does not have high laser durability are found. The reason is as follows. Theoretically, the material formed as an optical element is a stoichiometric material, and the transmittance of the antireflection film and the reflectance of the multilayer mirror are almost 100%. Suggests that. However, as a result of intensive studies by the inventors, it was found that the film substance actually formed as an optical element was not a stoichiometric substance. The film material actually formed had a composition ratio of Mg: F = 1: 1.90 to 1.97 when magnesium fluoride was taken as an example. Further, taking neodymium fluoride as an example, its composition ratio was Nd: F = 1: 2.90 to 2.97. Thus, the film substance of the fluorine compound that was actually formed was formed in a state of fluorine deficiency with respect to the stoichiometric ratio.

The inventors of the present invention have investigated the cause of the film formation of the fluorine compound film in the state of being deficient in fluorine. As a result, the reason is that the vacuum deposition method used as a film formation method on a substrate is used. In this case, the evaporation material is melted and evaporated, but it was found that there is a cause at this time. What is the reason,
In the case of a stoichiometric fluorine compound (for example, magnesium fluoride (hereinafter referred to as MgF ₂ )) as a vapor deposition material, Mg: F = 1: 2, and neodymium fluoride (hereinafter referred to as NdF ₃ ). ), Nd: F = 1:
3 things. ) Is used, the composition ratio of the film actually formed is such that the proportion of fluorine is small even when such a vapor deposition material is used. By the way, in this vacuum vapor deposition, the vapor deposition material is melted and evaporated by heating the vapor deposition material using an electron gun or a resistance heating boat. At this time, due to the energy given to the vapor deposition material by the electron gun or resistance heating, the fluorine is separated and the film is formed in the state where the fluorine is deficient. Therefore, a defect occurs in the structure in the film, and a film having high light absorption or low durability of light intensity is formed.

The degree of deficiency of fluorine differs depending on the difference in energy between the case of vapor deposition with an electron gun and the resistance heating boat. Such a lack of fluorine is likely to cause a very serious problem, especially for an optical element that handles short wavelength light. When used for a high-power light source such as an ArF excimer laser (oscillation wavelength λ = 193.4 nm), in addition to problems such as film absorption and deterioration of laser durability, in some cases, OH groups etc. It is also considered that they are chemically adsorbed, resulting in an increase in film absorption, a decrease in laser durability, and a decrease in mechanical film strength.

For the above reasons, the present inventors have attempted to solve such a problem by anticipating the amount of fluorine separated and using a substance having an excessive fluorine amount as the vapor deposition substance. For example, in the case of MgF ₂ , the composition ratio in the state after film formation is the stoichiometric ratio, Mg: F =
By setting the ratio to 1: 2, it is possible to prevent an increase in film absorption and a decrease in laser durability. In the case of MgF ₂ , the above composition ratio is most preferable, but Mg: F = 1: 2
Within the range of to 2.1, it is possible to effectively prevent an increase in film absorption and a decrease in laser durability. Moreover, it may be more than that.

In the present specification, the theoretical composition ratio is defined as the stoichiometric ratio such that MgF ₂ has a composition ratio of Mg: F = 1: 2. By the way, when the ratio of F to Mg exceeds 2.1, molecules (O
H groups, H ₂ O, etc.), which may lead to increased absorption of light and reduced laser durability.
_It is necessary to take measures so that ₂ O etc. will not be absorbed by the film substance. Next, taking NdF ₃ as an example, in the case of this substance,
The composition ratio of Nd: F = 1: 3, which is a stoichiometric composition ratio after film formation, is most preferable, and Nd: F = 1: 3 to 3.
Within the range of 1, it is possible to effectively prevent an increase in film absorption and a decrease in laser durability.

Further, in order to obtain the membrane substance as described above,
When the film is formed by the vacuum evaporation method, an evaporation material having a fluorine excess with respect to the stoichiometric ratio is used. As the amount of excess, in the case of vapor deposition of MgF ₂ , a vapor deposition substance in which the amount of fluorine that is considered to be deficient during vapor deposition is excessive is used. For example, if it is desired to form a film of MgF ₂ , magnesium fluoride of at least more than Mg: F = 1: 2 is used. Preferably, when the film is formed by the vacuum vapor deposition method, the amount of fluorine separated differs depending on the vapor deposition rate. However, since fluorine separates at least Mg from 1 and fluorine from 0.02 or more, Mg: F = 1:
It is preferable to use a composition having a composition ratio of 2.02 or more. Further, if NdF ₃ is taken as an example, neodymium fluoride more than Nd: F = 1: 3 is used. Preferably, as in the case of MgF2, the dissociation amount of fluorine differs depending on the vapor deposition rate, but at least neodymium and fluorine are 0.0
Nd: F = 1: 3.03 because they are separated by 3 or more.
It is preferable to use one having the above composition ratio. As described above, in the present invention, in consideration of the amount of fluorine separated during vacuum vapor deposition, a vapor deposition substance having an excess of fluorine over the stoichiometric vapor deposition substance is used, and the stoichiometric film substance or stoichiometry is used. It is possible to obtain a film substance having a composition ratio in which fluorine is in excess of that of the conventional substance. An optical element manufactured by using the film substance has low absorption of light in the film and can obtain high laser durability.

The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto.

[0016]

【Example】

(Embodiment 1) FIG. 1 is a sectional view of an antireflection film according to Embodiment 1 of the present invention. This antireflection film is an antireflection film designed and formed so as to obtain a high transmittance at the oscillation wavelength of the ArF excimer laser (λ = 193.4 nm). In FIG. 1, 11 is a synthetic quartz substrate whose surface is highly accurately polished, and 12 is NdF as a high refractive index material.
₃ (Nd: F = 1: 3 to 3.1) is formed on a synthetic quartz substrate with an optical film thickness of λ / 4, and then 13 is aluminum fluoride (hereinafter referred to as AlF ₃₎ as a low refractive index substance. (The composition ratio of this aluminum fluoride is Al: F = 1: 3 to 3.
1) is formed on the NdF ₃ film with an optical film thickness of λ / 4. Here, λ is 193.4 nm. The spectral transmittance characteristics of the optical element provided with this antireflection film are shown in FIG. In addition, as a comparative example, the structure of the antireflection film of neodymium fluoride and aluminum fluoride formed in the state of fluorine deficiency in the film mentioned in the related art is shown in FIG.
The spectral transmittance characteristics of the antireflection film are shown in FIG. FIG. 2 showing the spectral transmittance characteristics of the optical element having the antireflection film formed in Example 1 and the optical element having the antireflection film formed in the conventional fluorine-deficient state as a comparative example. It can be seen that the transmittance is remarkably increased by comparing FIG. From this, it can be easily seen that the light absorption by the film is small,
By forming the material of the film with a stoichiometrically good material, an antireflection film with less film absorption was obtained.

Further, the anti-reflection film given as a comparative example and the anti-reflection film given in the examples were compared with each other in terms of laser durability. Incidentally, the light source used for the laser durability test was light of 193.4 nm. The intensity of the light is increased, and the measurement value of the laser light intensity when damage is observed in the antireflection film is measured multiple times. The average value of the measurement results was obtained and used as the value of laser durability. Table 1 shows the results.

[0018]

[Table 1]

As can be seen from this table, the antireflection film of the comparative example had durability only up to 2.60 J / cm ² , whereas the antireflection film of Example 1 had a durability of 4.
It showed durability against light intensity of 00 J / cm ² . As described above, the antireflection film in Example 1 has sufficient durability as to laser durability. By the way, these NdF
The film of ₃ or AlF ₃ is formed by a vacuum vapor deposition method or the like which is formed by melting and evaporating by resistance heating or electron gun heating. In this film forming method, first, the degree of vacuum in the vacuum container was set to 1.0 × 10 ⁻⁵ Torr or less. After that, NdF ₃ (Nd: F = 1: 3) in which fluorine is present in excess of the stoichiometric ratio by electron gun or resistance heating
The above) was melted and evaporated to form a film of NdF ₃ on the synthetic vacuum substrate placed in the vacuum container. At this time, the vapor deposition rate was 8Å / s. Further, after the deposition of the NdF ₃ is completed, then the AlF ₃ fluorine is excessive proportion is melted evaporated from the stoichiometric ratio, was the formation of AlF _3.

By the way, the composition ratio of the vapor deposition material in Example 1 is NdF ₃ in which fluorine is in excess of at least the stoichiometric ratio. Preferably, since fluorine is separated from neodymium by 1 or more by 0.03 or more, N
It is preferable to use one having a composition ratio of d: F = 1: 3.03 or more. Also, regarding the composition ratio of the AlF ₃ vapor deposition material, AlF containing fluorine in excess of at least the stoichiometric ratio
_{Is 3} . Preferably, since fluorine is separated from aluminum by 1 by 0.03 or more, Al: F =
It is preferable to use one having a composition ratio of 1: 3.03 or more. Since the optimum composition ratio depends on the vapor deposition rate of the difference in film formation, a vapor deposition material having an optimum fluorine excess amount is used according to the vapor deposition rate when forming a film.

The vapor deposition rate is 0.5 to 1
There is no problem if it is between 5Å / s. But the deposition rate
If the speed is too fast, the degree of fluorine separation will increase.
Therefore, even if a fluorine-rich substance is used, a film lacking fluorine will result.
Is likely to be formed. By the way
In Example 1, as a material for the antireflection film, as a high refractive index substance
NdF3, AlF as low refractive index material₃Was used. Reflection
Other substances that can be used as a protective film include the substances listed below.
Can be mentioned. LaF for high refractive index materials₃, YbF
₃, SmF₃, GdF₃, DyF₃, PrF₃, EuF
₃, HoF₃Etc. For low refractive index materials,
MgF₂, CaF₂, BaF₂Etc. These substances
Also, use a vapor deposition material with excess fluorine as the vapor deposition material.
And deposit a film with a stoichiometric ratio.
Therefore, the light absorption by the film is small, and the laser durability is high.
Optical elements can be obtained. (Embodiment 2) FIG. 3 shows a second embodiment of the present invention.
It is sectional drawing of a multilayer mirror. This multilayer mirror is
Mira that can obtain high reflectance at rF excimer laser oscillation wavelength
Is The second embodiment will be described with reference to FIG.
A high-refractive-index material is formed on the substrate 31 whose surface is highly accurately polished.
NdF₃And low refractive index material MgF₂And deposited
It is configured in the multilayer film layer 32. This substrate 21 is a synthetic stone
The BK7 substrate is an English substrate, and the multilayer film 32 is NdF.₃, M
gF₂, NdF₃... MgF₂Are formed in order of
It A total of 41 layers of film are formed. About film thickness
NdF₃, MgF₂Both of these optical thicknesses are λ /
4 (λ = 193.4 nm). Also of these membranes
Regarding composition ratio, NdF₃Then Nd: F = 1: 3 ~
3.1 and also MgF₂Then Mg: F = 1: 2
2.1. Spectral reflection of multilayer mirror with the above configuration
The emissivity characteristics are shown in FIG.

As a comparative example, FIG. 7 is a cross-sectional view of a conventional multilayer mirror formed in a fluorine-deficient state.
And the spectral transmittance characteristics of the multilayer mirror are shown in FIG. The structure of the multilayer film mirror given as the comparative example is the same except the composition ratio of each film. Regarding the composition ratio, in the case of neodymium fluoride, Nd: F = 1:
2.90 to 2.97, and in the case of magnesium fluoride, Mg: F = 1: 1.90 to 1.97.

A comparison will be made between FIG. 4 showing the spectral reflectance characteristics of the multilayer mirror of Example 2 and FIG. 8 showing the spectral reflectance characteristics of the multilayer mirror formed in a fluorine-deficient state. The multilayer mirror of Example 2 has a reflectance peak of 9 in comparison with the multilayer mirror formed in the state of being deficient in fluorine.
The multilayer film mirror according to the second embodiment has a remarkably high reflectance of 95% or more, while it is only in the first half of 0%.
It can be seen that the film is less absorbed by the film.

Further, the antireflection film given as a comparative example and the multilayer mirror given in Example 2 were compared for their respective laser durability. Incidentally, the laser durability test method is the same as in Example 1. The results are shown in Table 2.

[0025]

[Table 2]

As can be seen from this table, the multilayer mirror of the comparative example had durability only up to 3.20 J / cm ² , whereas the multilayer mirror of Example 2
It showed durability against light intensity as ^{high as} 3.80 J / cm ² . As described above, the multilayer mirror in Example 2 has sufficient laser durability. Regarding the method of manufacturing this multilayer film mirror, as in the case of the first embodiment, NdF ₃ and MgF ₂ are alternately formed on the substrate 21 by resistance heating or melting / evaporating the vapor deposition sample by an electron gun. A multilayer mirror was manufactured. As for the vapor deposition material used for forming the NdF ₃ film, the composition ratio was N as in Example 1.
The one having a larger ratio of fluorine than d: F = 1: 3 was used. Further, as the vapor deposition material for forming the MgF ₂ film, one having a composition ratio higher than that of Mg: F = 1: 2 was used. With respect to the ratio, in particular, the vapor deposition sample placed in the vacuum container contains an excessive amount of fluorine in anticipation of the amount of the fluorine that separates when the vapor deposition sample melts and evaporates. In Example 2, when NdF ₃ was used as the amount of excess fluorine, Example 1 was used.
And in the case of MgF ₂ , at least M
More magnesium fluoride than g: F = 1: 2 is used.
Preferably, when the film is formed by the vacuum vapor deposition method, the amount of fluorine separated differs depending on the vapor deposition rate. However, since fluorine separates at least Mg from 1 and fluorine from 0.02 or more, Mg: F = It is preferable to use a composition ratio of 1: 2.02 or more.

By the way, in Example 2, the multilayer mirror was manufactured using NdF _{3 as} the high refractive index material and MgF ₂ as the low refractive index material, but it may be composed of other materials. Particularly, as the high refractive index material, LaF ₃ , YbF
₃ , SmF ₃ , GdF ₃ , DyF ₃ , PrF ₃ , EuF
₃ , HoF ₃ or the like can be used, and CaF ₂ , BaF ₂ or the like can be used as the low refractive index substance. Therefore, if these fluorine-excess substances are used as the vapor deposition substance, the absorption of light by the film can be reduced, and an optical element having high laser durability can be obtained.

[0028]

INDUSTRIAL APPLICABILITY As described above, according to the present invention, a film material forming an optical element is formed of a material having a stoichiometrically good composition ratio of fluorine and metal or a material having an excess of fluorine in the stoichiometric ratio. By doing so, it is possible to realize an optical element that is less absorbed by the film and has durability against high laser light intensity.

In addition, as a method for forming a film for forming an optical element by vacuum vapor deposition, by using a substance in which the composition ratio of fluorine and metal is fluorine in excess of the stoichiometric ratio as the vapor deposition material, The formed optical element is
An optical element having little absorption by the film and having durability against high laser light intensity was obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an antireflection film of Example 1.

2 is a spectral transmittance characteristic of an optical element provided with an antireflection film of Example 1. FIG.

FIG. 3 is a sectional view of a multilayer mirror according to a second embodiment.

4 is a spectral reflectance characteristic of an optical element provided with a multilayer mirror of Example 2. FIG.

FIG. 5 is a cross-sectional view of a conventional antireflection film.

FIG. 6: Spectral transmittance characteristics of an optical element provided with a conventional antireflection film.

FIG. 7 is a cross-sectional view of a conventional multilayer mirror.

FIG. 8: Spectral reflectance characteristics of an optical element provided with a conventional multilayer mirror.

[Explanation of symbols]

11 ... Synthetic quartz substrate, 12 ... Neodymium fluoride film in Example 1 13 ... Aluminum fluoride film in Example 1 21 ... BK7 substrate 22 ... Neodymium fluoride film in Example 2 Multilayer film in which films with magnesium fluoride are alternately formed 31 ... Conventional neodymium fluoride film 32 ... Conventional aluminum fluoride film 41 ... Conventional neodymium fluoride and magnesium fluoride film Multi-layer film with alternating layers

Claims (6)

[Claims] 1. A film formed on a substrate, which is a compound of fluorine and a metal, wherein the composition ratio of the compound is a stoichiometric ratio or the composition ratio of the fluorine is excessive from the stoichiometric ratio. An optical element having a film formed of a compound. 2. The optical element according to claim 1, wherein the compound is MgF _x , and x is 2 or more and 2.1 or less. 3. The optical element according to claim 1, wherein the compound is NdF _y , and y is 3 or more and 3.1 or less. 4. The optical element according to claim 1, wherein the compound is AlF _z , and z is 3 or more and 3.1 or less. 5. The evaporation material is melted and evaporated in a vacuum container,
A method of manufacturing an optical element using a vacuum vapor deposition method for forming a film of the vapor deposition material on a substrate placed in the vacuum container,
The method for producing an optical element, wherein the vapor deposition material is a compound of fluorine and a metal, and the vapor deposition material has a composition ratio of fluorine excess to stoichiometric ratio. 6. An optical element using the vacuum deposition method, which is a compound of fluorine and a metal, wherein the composition ratio of the compound has a composition ratio of fluorine excess to stoichiometric ratio. Deposition material for forming a film.