JP2000121801A - Optical parts and optical device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide optical parts having optical thin films which exhibit a sufficient optical characteristic to far UV light as represented by an excimer laser beam. SOLUTION: These optical parts are formed by laminating the optical thin film on a substrate 10 and the optical thin films described above contain at least one kind of the materials (AlF3, ALN, NaF, etc.), which are changed in the surface composition or shape by reaction under the use environment and are formed by coating these materials with layers consisting of materials (SiO2, Al2O3, MgF2, etc.), having the low reactivity in the external environment. The exposure device has such optical parts.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical component such as a lens, a mirror and an optical filter, and an exposure apparatus such as a stepper using the same.

[0002]

2. Description of the Related Art Optical components such as lenses, mirrors and optical filters are used in optical devices such as cameras, telescopes and microscopes. These optical components usually have an antireflection film or a reflection enhancement film on the surface. These antireflection films and reflection enhancement films are designed to have a thin film configuration so that desired optical characteristics can be obtained in a wavelength region of light to be used. For example, materials having different refractive indices are laminated, and the thickness and the number of layers of each material are determined by the interface of each material, the interface with the substrate, and the diffraction and reflection of the interface between the optical medium and the external medium and the optical component. A thin film configuration is designed by performing computer simulation.

[0003] An exposure apparatus is an optical apparatus in which such optical components are incorporated. This exposure apparatus is used in a process of manufacturing a semiconductor integrated circuit and a process of manufacturing a photomask therefor. A typical example of the exposure apparatus is a stepper.

Conventionally, g-rays (435.8 nm) and h-rays (404.7 n) have been used as illumination light sources for such an exposure apparatus.
m), an ultra-high pressure mercury lamp generating x-rays (365 nm), a xenon / mercury arc lamp, and the like have been used. Recently, however, lasers that emit far ultraviolet rays (260 nm or less) have been developed in order to produce finer integrated circuits, to improve exposure processing capability, and to achieve uniform illumination characteristics on an object to be exposed such as a wafer. Also, a laser that oscillates a light beam with a high output and a narrow spectrum width has been used. Among them, excimer lasers are one of the leading light sources because they emit high-power light with an extremely narrow spectral width.

[0005] Optical components for excimer lasers include:
JP-A-63-113501, JP-A-63-113
As described in Japanese Patent Publication No. 502-502 and the like, an optical component in which an antireflection film is vacuum-deposited is known. Also, Japanese Patent Application Laid-Open No. 7-707
No. 4, JP-A-7-72307 and the like also describe examples of forming a film by using a sputtering method.

[0006]

By designing the thin film structure as described above, an optical thin film exhibiting sufficient optical characteristics for light in the visible light wavelength region can be manufactured. However, it is difficult to produce an optical thin film exhibiting sufficient optical characteristics with respect to far ultraviolet light represented by excimer laser light.

The refractive index of an optical material is a value specific to the material. Therefore, in a film configuration using a single material, the refractive index is limited. On the other hand, there is a case where the refractive index is designed by using a mixed substance, but in this case, it is difficult to control the optical characteristics satisfactorily and uniformly over the entire surface of the thin film.

Further, in an optical device having high optical path control such as an exposure apparatus, the optical thin film is required to have very high surface controllability. Therefore, the temperature conditions for forming the optical thin film are severe, and it is difficult to apply a general film forming technique to such an optical thin film.

It is an object of the present invention to provide an optical component having an optical thin film exhibiting sufficient optical characteristics with respect to far ultraviolet light represented by excimer laser light, and an exposure apparatus using the same.

[0010]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have found that a new idea and a new approach have been proposed for the production of optical components used in the far ultraviolet wavelength region. In view of the fact that a thin film configuration should be designed, the present inventors focused on a low-refractive-index material required for a deep ultraviolet region, and completed the present invention.

That is, the present invention relates to an optical component comprising an optical thin film laminated on a substrate, wherein the optical thin film contains at least one kind of substance whose surface composition or shape changes with time in a use environment. An optical component characterized by having a layer made of a substance having low reactivity in the external environment between the optical component and the external environment.

An optical thin film used in the far ultraviolet region needs a laminated structure formed by combining materials having a large difference in refractive index. Therefore, in the present invention, for example, AlF ₃ , Al
A substance such as N or NaF whose surface composition or shape changes over time due to a reaction under the use environment (hereinafter, referred to as a “time-varying substance”) is intentionally used. An optical thin film exhibiting sufficient optical characteristics with respect to ultraviolet light. In addition, the problem of the durability of the time-varying substance can be solved by providing a layer made of a substance having low reactivity in the external environment between the time-varying substance and the external environment.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below.

The optical component of the present invention is formed by laminating an optical thin film on a substrate. Examples of the substrate include a substrate made of quartz glass or a fluorite optical material.

[0015] The optical thin film laminated on the substrate contains at least one kind of a time-varying substance. This change of the aging substance occurs, for example, by moisture absorption, deliquescence or hydrolysis. In the following description, deliquescence, which is a typical example, will be particularly described.

Table 1 below shows the refractive index and deliquescence (dissolution amount in 100 g of water) of various materials.

[0017]

[Table 1] As shown in Table 1, various materials have various refractive indexes and deliquescence. When an optical thin film is manufactured, a material to be used may be selected in consideration of the refractive index of each of such materials. Specifically, a material and a configuration of an optical thin film having desired optical characteristics are calculated by computer simulation in a wavelength region of light using an optical component. At this time, the input optical constant depends on the film quality produced by each film forming apparatus depending on the type of the material constituting the optical thin film. It is better to grasp the correlation between the amount of dependence of each material on the optical constant by the film forming apparatus and the apparatus and the film forming conditions for each material in advance. The optical constants thus obtained are input as calculation parameters, and the configuration design of the substrate of the optical component and the optical thin film is performed.

Each of the substances listed in Table 1 has sufficient transmittance for optical parts in the far ultraviolet region, which will be used in the future, and enables a combination of a low refractive index and a high refractive index. .

Among the substances listed in Table 1, there are high-refractive-index substances with low solubility in water, but low-refractive-index substances often have high water-solubility. In the present invention,
A substance having such a low refractive index and high water solubility, that is, a substance that changes with time is used. Accordingly, a laminated structure using a combination of materials having a large difference in refractive index becomes possible, and it becomes possible to obtain an optical thin film exhibiting sufficient optical characteristics with respect to far ultraviolet light.

The time-varying substance used in the present invention includes:
Among the substances listed in Table 1, for example, AlF ₃ , Na
F and the like.

However, the present invention is not limited to these. For example, in Table 1, two-component substances are extracted, but three-component substances and other substances can also be used. That is, any substance can be used without limitation as long as it has low absorption of light in the wavelength region to be used and can combine low refractive index and high refractive index.

In the above description, an example of the change with time due to deliquescence and the like has been described. However, the time-varying substance used in the present invention also includes a substance that changes with time due to hydrolysis. For example, AlN has a refractive index at a wavelength of 193 nm of about 2.58 and an extinction coefficient of about 0.02, and changes its surface shape while hydrolyzing with water in an environmental atmosphere at room temperature to release ammonia. The reaction formula is described below.

AlN + 3H ₂ O → NH ₃ + Al (OH) ₃ Further, this Al (OH) ₃ changes to Al ₂ O _{3 as} oxidation proceeds. Such a substance that changes over time due to hydrolysis can be used in the present invention as a time-changeable substance.

In addition to these, as the time-varying substance used in the present invention, for example, NaF, L
iF, KF, CsF, BaF ₂ , CdF _{2 and the} like can also be mentioned.

In the present invention, it is conceivable that the use of a time-varying substance may cause deterioration of the surface of the optical thin film during exposure to use in an environment, thereby deteriorating the optical characteristics of the entire optical component. . Therefore, at least one layer made of a substance having low reactivity in the external environment (hereinafter, referred to as a “low-reactivity substance”) is provided between the time-varying substance and the external environment. For example, when deliquescence is a problem, a low-reactivity material thin film made of a highly insoluble material may be provided on the uppermost layer of the optical thin film, thereby covering the time-varying material from the external environment.

Regarding such a problem, it is preferable to first examine the external environment in which the optical component is used. Many optical components are used in the atmosphere or in a nitrogen atmosphere at atmospheric pressure when light in the far ultraviolet region is used. As a special case,
It may be used in a reduced pressure nitrogen, argon or helium atmosphere. In each case, a small amount of organic substances and moisture are present, and these cause changes in the time-varying substance in the optical thin film. In particular, light in the deep ultraviolet region has a high energy per photon, and thus affects a wide range of substances, causing reactions such as decomposition and polymerization of the substances. In addition, the remaining water molecules may also absorb ultraviolet rays and alter the surface of the thin film in some cases.

In order to suppress such time-dependent changes and mainly deterioration of the surface layer, a material having low hygroscopicity and deliquescent is used as a low-reactive substance in order to suppress moisture absorption and deliquescence of the film material. Should just cover the top layer. When a reactive substance is present in the environment of use, a substance which does not easily react with the reactive substance may be used as a low-reactive substance, and the uppermost layer of the optical thin film may be covered. Accordingly, it is possible to suppress a change with time of the surface of the optical component and improve the durability of the optical component.

In particular, in order to recover the aging change in the optical system of the exposure apparatus such as a stepper, the manufacturing process is completely stopped, and the recovery operation is complicated. In such a case, it is very useful to provide a layer made of a low-reactivity substance in order to suppress a change with time.

As the low-reactivity material used in the present invention, among the substances listed in Table 1, for example, SiO ₂ , Al
₂ O ₃ and MgF ₂ are mentioned. In addition to these, low-reactivity substances used in the present invention include, for example, WO ₃ and Y ₂
O ₃ , Ta ₂ O ₅ , HfO _{2 and the} like are also included.

When a layer made of a low-reactivity material as described above is laminated on the uppermost layer of an optical thin film exhibiting optical characteristics optimized by computer simulation, the optical characteristics deviate from the original optical characteristics. Can be considered. Therefore, it is preferable to design in consideration of this point.
Speaking of the far ultraviolet region, for example, when covering a thin film made of a time-varying substance such as NaF or AlF ₃ ,
It is preferable to use a substance having a slightly higher refractive index than NaF or AlF ₃ but low water solubility, such as MgF ₂ or Al ₂ O ₃ .

The optical component of the present invention described above is, in particular,
This is very useful when used in an exposure apparatus. In the future, the use of an excimer laser is indispensable for an exposure apparatus, and wavelengths of 248 nm and 193 nm are candidates. As the wavelength of light used becomes shorter, substances in an environmental atmosphere that are more susceptible to reaction will be diversified, but according to the present invention described above, a good optical Parts can be provided. Also, from this point,
The optical thin film in the present invention is preferably a thin film that selectively transmits excimer laser light.

Next, a method for manufacturing the optical component of the present invention will be described.

As a method of forming an optical thin film on a substrate in order to manufacture the optical component of the present invention, various methods conventionally known as a method of forming such an optical thin film can be adopted. The method for forming the film may be selected according to the desired characteristics of the optical thin film. For example, as the film forming method, a sputtering method, a CVD method, a vacuum evaporation method, and the like can be given.

FIG. 1 is a schematic view showing a film forming apparatus capable of performing a sputtering method and a CVD method as an example of such a film forming apparatus. This apparatus is composed of a sputtering apparatus 100 and a CVD apparatus.
The apparatus 300 has a configuration in which it is connected via a load lock chamber 200, and the substrate 10 in the apparatus is provided with a substrate transport unit 400
Thus, the apparatus can be moved between the apparatuses. The sputtering apparatus 100, the load lock chamber 200, and the CVD apparatus 300 are provided with heater-equipped substrate holders 101, 201, and 301 that can move up and down, respectively. The sputtering apparatus 100 includes an Ar / O ₂ gas supply system 102,
A target 104 is provided, and the CVD apparatus 300 includes:
A CVD reaction gas supply system 302 is provided. Further, in the CVD apparatus 300 and the load lock chamber 200, respectively,
Evacuation systems 203 and 303 are provided.

As described above, the sputtering apparatus 100 and the CVD
If the apparatus 300 uses an apparatus connected via the load lock chamber 200, for example, a layer made of a time-varying substance is formed on the substrate 10 in the CVD apparatus 300, and then the load is performed without opening to the atmosphere. The substrate 10 can be transferred into the sputtering apparatus 100 through the lock chamber 200. That is, before the next film formation, it can be prevented from reacting with moisture or the like in the atmosphere.

[0036]

Embodiments of the present invention will be described below.

<Example 1> Using synthetic quartz and fluorite as substrates, each substrate was polished to flatten its surface.

Next, using the apparatus shown in FIG.
0 was carried into the plasma CVD apparatus 300, and trimethylaluminum and CF ₄ were supplied as source gases to form a thin film of about 20 nm in thickness made of AlF ₃ which was a time-varying substance. After that, the substrate 10 is transported into the sputtering apparatus 100 without being opened to the atmosphere, and a low-reactivity substance SiO ₂ film or Al ₂ film having a thickness of about 10 nm is formed on the AlF ₃ film.
An O ₃ film was formed to obtain an optical component.

Each optical component was almost transparent visually.
However, a slight coloring was observed in the case where the Al ₂ O ₃ film was formed.

<Comparative Example 1> An optical component was manufactured in the same manner as in Example 1 except that the SiO ₂ film and the Al ₂ O ₃ film were not formed. Each optical component was almost transparent visually.

<Evaluation> Each optical component produced in Example 1 and Comparative Example 1 was left for 24 hours in a humidified environment of 50% humidity and 50 ° C. As a result, the optical component of Comparative Example 1 was visually clouded and observed under a microscope. As a result, it was confirmed that fine irregularities were formed on the surface of the AlF ₃ film, and that scattered light was increased. On the other hand, in the optical component of Example 1, no change was observed by visual observation or observation under an optical microscope, and no change was observed after being left in a humidified environment although the surface roughness was measured by AFM. .

Further, the transmittance of each optical component at a wavelength around 200 nm was measured before and after the humidified environment was left. As a result, the transmittance of the optical component of Comparative Example 1 was reduced by several tens of percent. This decrease in transmittance is due to an increase in unevenness on the surface of the AlF ₃ film and an increase in scattering. On the other hand, for the optical component of Example 1, the transmittance did not decrease.

Example 2 A quartz glass substrate was used as a substrate, polished, and its surface was flattened. First, the quartz glass substrate 10 is loaded into the sputtering apparatus 100 using the apparatus shown in FIG. Was formed. Next, the substrate 10 is moved to the CVD device 300 while maintaining the vacuum atmosphere, and then the inside of the sputtering device 100 is changed to the SiO ₂ sputtering film forming condition.
And the low-reactivity material SiO
_An optical component was obtained by forming a thin film having a thickness of about 20 nm made of ₂ .

Comparative Example 2 An optical component was produced in the same manner as in Example 2 except that no SiO ₂ film was formed.

<Evaluation> Each of the optical components manufactured in Example 2 and Comparative Example 2 was left for 24 hours in a humidified environment at a humidity of 50% and a temperature of 50 ° C. in the same manner as described above. As a result, the optical component of Comparative Example 2 was visually clouded and observed under a microscope. As a result, it was confirmed that the surface irregularities of the AlN film had increased. This is considered to be due to hydrolysis of the AlN film. For confirmation, the surface was subjected to ESCA analysis, and the result was that Al ₂ O ₃ was formed. This Al ₂ O ₃ is generated as a result of hydrolysis of AlN and subsequent oxidation.

On the other hand, in the optical component of Example 2, no increase in surface scattered light and no increase in surface irregularities were observed. This optical component, was subjected to a similar ESCA analysis in the depth direction, Al and N as the next layer of the SiO ₂ layer of the outermost surface
Was confirmed, and it was found that the AlN layer was not hydrolyzed.

[0047]

According to the present invention described above, it is possible to provide an optical component having an optical thin film exhibiting sufficient optical characteristics with respect to far ultraviolet light represented by excimer laser light, and an exposure apparatus using the same. .

Further, in the present invention, by using a time-varying substance, it is possible to widen the range of use of the material constituting the optical thin film, and the time-varying substance is made of a low-reactive substance. By covering with a layer, it is possible to provide an optical component having an optical thin film that can sufficiently withstand normal use conditions.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of a film forming apparatus for manufacturing an optical component of the present invention.

[Explanation of symbols]

10 substrate 100 sputtering device 101 heater with the substrate holder 102 Ar / O ₂ gas supply system 104 target 200 load lock chamber 201 heater with the substrate holder 203 evacuation system 300 CVD apparatus 301 heater with the substrate holder 302 CVD reactive gas supply system 303 Evacuation system 400 Substrate transfer unit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 21/027 H01L 21/30 515D

Claims (5)

[Claims] 1. An optical component comprising an optical thin film laminated on a substrate, wherein the optical thin film contains at least one kind of substance whose surface composition or shape changes over time due to a reaction in a use environment. An optical component having a layer made of a substance having low reactivity in an external environment. 2. The optical component according to claim 1, wherein the substance whose surface composition or shape changes over time is a substance whose surface composition or shape changes over time due to moisture absorption, deliquescence, or hydrolysis in a use environment. 3. The optical component according to claim 1, wherein the substrate is made of quartz glass or fluorite optical material. 4. The optical component according to claim 1, wherein the optical thin film is a thin film that selectively transmits excimer laser light. 5. An exposure apparatus comprising the optical component according to claim 1. Description: