JP2000131503A - Optical member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical member which has an optical thin film formed, which has moisture resistance, which can maintain good optical characteristics in a UV region of <200 nm wavelength for a long time. SOLUTION: This optical member consists of a substrate 1 and an optical thin film for UV region comprised of a high refractive index layer and a low refractive index layer on the substrate. The difference of refractive index between the high refractive index layer and low refractive index layer is >=0.27, and either of the materials has a large solubility in water. At least the material of the outermost layer is modified to have a small solubility in water and a high density.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an ultraviolet (20)
(0 nm or less).

[0002]

2. Description of the Related Art In recent years, in order to increase the degree of integration of semiconductor devices, there is an increasing demand for a high-resolution reduction projection exposure apparatus (stepper) for semiconductor manufacturing. One method of increasing the resolution of photolithography using this stepper is to shorten the wavelength of the light source.

Recently, a stepper using a high-power laser as a light source capable of oscillating light in a shorter wavelength range than a mercury lamp has started to be put into practical use. Here, a KrF excimer laser (λ = 248) is used as an excimer laser as a light source.
nm) and an ArF excimer laser (λ = 193 nm). In the optical system of a stepper using a laser as a light source, an antireflection film and a mirror (reflection increasing film) for bending the optical path are formed in order to reduce the amount of light loss and flare and ghost due to surface reflection of optical elements such as lenses. There is a need to.

Here, when an optical thin film (anti-reflection film or mirror) is made of a film material having a large absorption for light having a wavelength of 200 nm or less or a film material having a low laser resistance,
Light loss due to absorption, substrate surface change due to absorption heat generation, and film destruction are likely to occur. Therefore, as a film material used for an optical thin film formed on an optical element such as a lens,
Those having low absorption and high laser resistance are desirable.

[0005] Film materials that can be used at a wavelength of 200 nm or less mainly include fluorine compounds such as magnesium fluoride (MgF ₂ ) and some oxides (such as aluminum oxide (Al).
₂ O ₃ ) silicon dioxide (SiO ₂ )), but from the viewpoint of designing an optical thin film, the larger the difference in refractive index between the high refractive index material and the low refractive index material, the better the optical characteristics. In particular, it has been found that the use of lanthanum fluoride (LaF ₃ ) for a high refraction material and the use of aluminum fluoride (AlF ₃ ), cryolite (Na ₃ AlF ₆ ), etc. for a low refraction material are effective.

In forming the optical thin film, as a simple method, a physical film forming method such as a vacuum evaporation method for forming a film in a vacuum atmosphere has been used.

[0007]

However, most of the optical thin films formed by the conventional vacuum evaporation method have a columnar structure and a low density. This causes the moisture and the like adhering to the surface of the multilayer film to diffuse inside.Even if a thin film material that is advantageous for the use environment is used on the outermost surface of the multilayer film, erosion inside progresses. In addition, devitrification of the thin film occurs.

In particular, when an optical thin film material having a high solubility in water as described later is used, the effect is remarkable, and dissolution and precipitation of crystals occur due to surface adsorption and internal diffusion of water. Irradiation with UV rays promotes the reaction on the surface and in the layer near the surface, and produces oxides and the like having a large crystal grain size. As an optical thin film material having high solubility in water, aluminum fluoride (Al
F ₃ ), cryolite (Na ₃ AlF ₆ ), etc., and the above aluminum fluoride has a solubility (25 g) of about 0.5 g in 100 g of water.
° C).

When such a thin film material is used, it is possible to reduce the amount of water in the environment to be used by using dry nitrogen or the like, but it is not easy to completely achieve an environment with zero moisture. Accordingly, the optical thin film material preferably has a solubility of less than about 0.01 g in 100 g of water. However, even with such a high solubility in water (solubility in water: 0.01 g or more), it must be used to satisfy the optical characteristics due to the relationship of the refractive index. There is also. An example is shown below.
FIG. 6 shows lanthanum fluoride (high refractive index layer n = 1.69) that is insoluble in water at an optical thickness of 0.25λ, and hardly soluble in water at an optical thickness of 0.25λ. Center wavelength 193.4 composed of natural magnesium fluoride (low refractive index layer n = 1.42)
FIG. 4 shows a spectral characteristic diagram of a multilayer mirror (first example) of nm.
FIG. 7 shows lanthanum fluoride (high refractive index layer n = 1.69) having an optical film thickness of 0.25λ and an optical film thickness of 0.25λ.
And water-soluble aluminum fluoride (the low refractive index layer n
= 1.39), showing a spectral characteristic diagram of a multilayer mirror (second example) having a center wavelength of 193.4 nm. From FIG.
At 193.4 nm, the reflectivity is 98%, and FIG.
As can be seen from the fact that the reflectance at 993.4 nm is 99% or more, the spectral reflectance may be higher when a material having high solubility in water is used.

However, this lanthanum fluoride (high refractive index layer)
If a mirror made of aluminum and aluminum fluoride (low refractive index layer) is continuously used in a humid environment, it is expected that the mirror will have a reflectance characteristic as shown in FIG. 8, for example. Use in an optical system leads to a decrease in exposure efficiency. Therefore, the present invention has been made in view of such a conventional problem, has moisture resistance,
It is another object of the present invention to provide an optical member on which an optical thin film capable of maintaining good optical characteristics in the ultraviolet region of 200 nm or less for a long period of time is formed.

[0011]

Means for Solving the Problems The present invention is directed to an optical member having a substrate and an optical thin film for ultraviolet region comprising a high refractive index layer and a low refractive index layer formed on the substrate. The high refractive index layer or the low refractive index layer has a refractive index difference of 0.27 or more, and any one of the materials has a property of having high solubility in water, and at least the material of the outermost layer is An optical member (Claim 1) having low solubility in water and high density is provided. Also, the present invention relates to a method for producing a high refractive index layer, which is composed of neodymium fluoride (NdF3), lanthanum fluoride (LaF
3), gadolinium fluoride (GdF3), dysprosium fluoride (DyF3), aluminum oxide (Al2O3), lead fluoride (PbF
2), one or more components selected from the group of hafnium oxide (HfO2) and mixtures or compounds thereof, wherein the material of the low refractive index layer is aluminum fluoride (AlF3), cryolite (Na3AlF6), Magnesium fluoride (MgF2), sodium fluoride (NaF), lithium fluoride (LiF), calcium fluoride (CaF), barium fluoride (BaF2), strontium fluoride (SrF3), silicon oxide (SiO2), thiolite ( N
a5Al3F14) and one or more components selected from the group consisting of a mixture or a compound thereof.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an optical member according to an embodiment of the present invention will be described with reference to the drawings. The optical member of the embodiment has a configuration including a substrate 1, a non-modified multilayer film 2 formed on the substrate 1, and a modified layer 3 formed on the non-modified multilayer film 2. The non-modified multilayer film 2 includes a high refractive index layer and a low refractive index layer, and one of the materials has high solubility in water (hereinafter, simply referred to as a deliquescent material).

The modified layer 3 is a high-refractive-index layer or a low-refractive-index layer modified at a high density, and has a low solubility in water (hereinafter simply referred to as a non-deliquescent material).
The difference in refractive index between the high refractive index layer and the low refractive index layer is preferably 0.27 or more. If there is no refractive index difference of 0.27 or more, it is meaningless to use a deliquescent material from the viewpoint of optical characteristics.

Hereinafter, a method for manufacturing an optical member according to an embodiment of the present invention will be described. FIG. 2 is a schematic view of a vacuum deposition apparatus for an ion beam assist method used in the method for manufacturing an optical member according to the embodiment of the present invention. In a vacuum chamber 21 of the vacuum evaporation apparatus shown in FIG. 2, an evaporation source (resistance heating boat) 22 for holding an evaporation material 23, a substrate holder 26 holding the substrate 1 and capable of rotating and revolving, and a gas introduction pipe 28 are provided. An ion source 29 provided and an exhaust port 27 are provided.

As the ions irradiated from the ion gun, Ar ions are mainly used, but there is no particular limitation, and Xe, F ₂ or the like is also used.
To minimize the film loss, as the irradiation energy of the ion beam, about 1μA / cm ² ~7μA / cm ² is preferred. First, a quartz glass substrate 1, after ultrasonic cleaning was set in a substrate holder 26 provided in the vacuum chamber 21, 5 × 10 ^{over 6 ~5} × 10 ^-7 torr
Then, the substrate 1 is heated to about 200 to 400 ° C.

An unmodified multilayer film 2 was formed on the substrate 1 by heating and evaporating the evaporation material 23 placed on the evaporation source 22 and scattering it toward the substrate 1. Next, the evaporation material 23 having no deliquescence placed on the evaporation source 22 is heated and evaporated to be scattered toward the substrate 1 and xenon fluoride (XeF ₂ , Xe
The substrate 1 is irradiated with an ion beam extracted from the ion source 29 into which the gas F ₄ ) has been introduced, thereby forming the modified layer 3 on the substrate 1.

Here, xenon fluoride is XeF
₂ , XeF ₄ and XeF ₆ , of which XeF ₆
Is extremely reactive, and for example, even quartz glass cannot be used because it reacts as follows. SiO ₂ + 2XeF ₆ = 2XeOF ₄ + SiF ₄ Therefore, it is preferable to use XeF ₂ and XeF ₄ alone or as a mixture.

The modified layer 3 made of a material having no deliquescence
If at least one layer is present on the outermost layer, it can prevent intrusion of moisture (play a role as a protective film), and can prevent the deliquescent material from dissolving. The modified layer 3 may be a multilayer film composed of a high-refractive-index layer and a low-refractive-index layer having no deliquescence, and in this case, can serve as a more sufficient protective film.

The total pressure during the film formation process is 1 × 10 ⁻⁶ T
The range is preferably from orr to 3 × 10 ⁻⁵ Torr. As described above, in the optical thin film system using the fluoride thin film formed by the manufacturing method of the embodiment, it is possible to eliminate an external change such as devitrification due to a use environment.

Materials for the low refractive index layer using the modified layer include magnesium fluoride (MgF2) and lithium fluoride (Li).
F), calcium fluoride (CaF), barium fluoride (BaF2),
At least one component selected from the group consisting of strontium fluoride (SrF3), silicon oxide (SiO2), and mixtures or compounds thereof. Materials for the high refractive index layer used for the modified layer include neodymium fluoride (NdF3), lanthanum fluoride (LaF
3), gadolinium fluoride (GdF3), dysprosium fluoride (DyF3), aluminum oxide (Al2O3), lead fluoride (PbF
2) one or more components selected from the group consisting of hafnium oxide (HfO2) and mixtures or compounds thereof.

As the material of the low refractive index layer used for the non-modified layer, the material is aluminum fluoride (AlF3), cryolite (Na3AlF6), thiolite (Na5Al3F14), sodium fluoride (NaF), or a mixture thereof. One or more components selected from the group of compounds. Materials for the high refractive index layer used for the unmodified layer include neodymium fluoride (NdF3), lanthanum fluoride (LaF3), gadolinium fluoride (GdF3), dysprosium fluoride (DyF3), and aluminum oxide (Al2O3).
3), one or more components selected from the group consisting of lead fluoride (PbF2), hafnium oxide (HfO2), and mixtures or compounds thereof.

As the substrate, when the optical member is an optical lens, various types of glass such as quartz glass, optical crystal materials such as fluorite, magnesium fluoride and the like, which transmit laser light, can be used. In the case of a mirror, ceramics, silicon, silicon carbide, and tungsten are used from the viewpoint of the coefficient of thermal expansion and thermal conductivity in addition to the above materials.

[0023]

Next, an embodiment of the present invention will be described with reference to FIG. FIG. 3 is a schematic cross-sectional view of the half mirror for 0 ° according to the first embodiment. This half mirror includes a quartz glass substrate 19 and lanthanum fluoride (La) having an optical film thickness of λ / 4 formed on the substrate 10 with a center wavelength of λ = 193 nm.
F ₃ , n = 1.69), a high refractive index layer 11 and an optical film thickness λ / 4 aluminum fluoride (AlF ₃ , n =
1.39) is a half-mirror composed of seven alternating layers of the low-refractive-index layer 12 made of 1.39), and the high-refractive-index layer made of lanthanum fluoride (LaF ₃ ) as the outermost layer has a high density. This is a modified layer.

Next, the procedure for manufacturing the half mirror will be described with reference to FIG. First, a quartz glass substrate 10 was prepared, subjected to ultrasonic cleaning, set in a substrate holder provided in a vacuum chamber 21, and heated to about 300 ° C. At this time, the inside of the vacuum chamber 21 is 1 × 1
It was evacuated to 0 ^{over 6} Torr.

A vapor deposition material 23 made of lanthanum fluoride (LaF ₃ ) placed on a vapor deposition source (resistance heating boat) 22 is evaporated and scattered toward the substrate 10 to form an optical film of lanthanum fluoride (λ / 4). A high refractive index layer 11 made of LaF ₃ ) was formed. Similarly, a low refractive index layer 12 made of an aluminum fluoride (AlF ₃ ) film having an optical thickness of λ / 4 was formed.

These steps are repeated three times to form up to the sixth layer counting from the substrate side, and then a seventh layer of high refractive index layer made of lanthanum fluoride (LaF ₃ ) corresponding to the outermost surface layer is formed. When forming the optical film thickness of about λ / 4, the film was formed while irradiating the substrate 10 with an ion beam having an energy of 4 μA / cm ² extracted from the ion gun 29. Example 1
FIG. 4 shows a spectral characteristic diagram at the incident angle θ = 0 ° of the half mirror manufactured as described above.

In order to compare with the half mirror manufactured in Example 1, a high refractive index layer made of lanthanum fluoride (LaF ₃ ) as the outermost surface layer was formed without using the ion beam assist method. A half mirror having the same layer configuration was formed (Comparative Example 1). The spectral characteristics of the half mirror manufactured in Comparative Example 1 at the incident angle θ = 0 ° are the same as those in FIG.

The half mirrors manufactured in Example 1 and Comparative Example 1 were subjected to the following cycle test, and changes in the appearance and transmittance of the half mirror before and after the test were examined. First, the above-mentioned half mirror is installed in a thermo-hygrostat, and the temperature and humidity in the thermo-hygrostat are (1) from room temperature to 80 ° C. over 2 hours.
After setting the atmosphere at a humidity of 60% or less, the state is maintained for 5 hours.
After setting the atmosphere at 0 ° C and humidity of 90% or more, keep the state for 5 hours. (3) Finally, set the atmosphere at -20 ° C over a period of time from the state, and keep the state for 5 hours. (4) Thereafter, the inside of the thermo-humidifier was naturally allowed to reach room temperature.

As a result, the half mirror manufactured in Example 1 had no change in appearance before and after the test, but the half mirror manufactured in Comparative Example 1 had a white cloudy appearance and devitrified after the test. Was. FIG. 5 shows the spectral transmittance characteristics of the half mirrors manufactured in Example 1 and Comparative Example 1 after the cycle test. 31 is the spectral transmittance characteristic of the half mirror manufactured in Example 1 after the cycle test, and 32 is the light transmittance characteristic of the half mirror manufactured in Comparative Example 1 after the cycle test.

4 and 5, comparing the half mirror manufactured in Example 1 with almost no change in the spectral characteristics before and after the cycle test, the half mirror manufactured in Comparative Example 1 changes greatly before and after the cycle test. It can be seen that the characteristics have deteriorated.

[0031]

As described above, the optical member according to the present invention can maintain good optical characteristics in the ultraviolet region of 200 nm or less for a long time without being restricted by the use environment.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an optical member on which an optical thin film usable in an ultraviolet region according to the present invention is formed.

FIG. 2 is a schematic view of a vacuum deposition apparatus for an ion beam assist method used in the method for manufacturing an optical member according to the present invention.

FIG. 3 is a schematic sectional view of a half mirror for 0 ° incidence according to the first embodiment.

FIG. 4 is a spectral transmittance characteristic diagram of the half mirror for 0 ° incidence according to the first embodiment.

FIG. 5 is a spectral characteristic diagram of the 0 ° incidence half mirrors of Example 1 and Comparative Example after a cycle test.

FIG. 6 illustrates a first example of a conventional example of a mirror for an ultraviolet laser in the first example.
FIG. 6 is a spectral characteristic diagram at the time of incidence.

FIG. 7 shows a second example of a conventional mirror for an ultraviolet laser in the second example.
FIG. 6 is a spectral characteristic diagram at the time of incidence.

FIG. 8 is a spectral characteristic diagram at 0 ° incidence after the ultraviolet laser mirror of the second conventional example is used in an atmosphere containing moisture.

[Explanation of symbols]

1 ... optical substrate 2 ... unmodified multilayer film 3 ... reformed layer 10 ... a quartz glass substrate 11 ... high refractive index layer (LaF ₃₎ 12 ... low-refractive index layer ( MgF ₂ ) 21—Vacuum chamber 22—Evaporation source (resistance heating vessel (nickel boat)) 23—Evaporation material 26—Substrate holder 27—Exhaust port 28—Gas introduction pipe 29 ... Ion sources

Claims (2)

[Claims] An optical member comprising: a substrate; and an optical thin film for an ultraviolet region comprising a high refractive index layer and a low refractive index layer formed on the substrate, wherein the high refractive index layer or the low refractive index layer has a low refractive index. The refractive index difference of the refractive index layer is 0.2
7 or more, and any of the materials has the property of having high solubility in water, and at least the material of the outermost layer has low solubility in water and is modified to have a high density. Optical members. 2. The material of the high refractive index layer is neodymium fluoride (NdF).
3), lanthanum fluoride (LaF3), gadolinium fluoride (GdF
3) Dysprosium fluoride (DyF3), aluminum oxide (Al2O3), lead fluoride (PbF2), hafnium oxide (HfO
2) and at least one component selected from the group consisting of a mixture or a compound thereof, wherein the material of the low refractive index layer is aluminum fluoride (AlF3), cryolite (Na3AlF6), magnesium fluoride (MgF2). , Sodium fluoride (NaF), lithium fluoride (LiF), calcium fluoride (CaF), barium fluoride (BaF2), strontium fluoride (SrF3), silicon oxide (SiO2), thiolite (Na5Al3F14) and mixtures thereof The optical member according to claim 1, wherein the optical member is one or more components selected from the group of compounds.