KR20050105000A - An optical properties restoration apparatus, the restoration method, and an optical system used in the apparatus - Google Patents

Abstract

It is an object of the present invention to prevent or inhibit degradation of an optical system that determines the lifetime of an optical device that delivers effects such as light transmission, diffraction, reflection, spectral generation and interference, and combinations thereof, thereby maintaining maintenance such as window replacement. It is to reduce the frequency of repair operations and to reduce the cost for such operations. The present invention provides a method for forming a near vacuum region in the presence of an active energy that excites oxidation of carbon, the near vacuum region facing a lighting surface of an optical system, OH radicals, OH ^- ions, ozone, O ₂ ^_ ion, O radicals and the step of generating negative ions or radicals of, near-vacuum area, such as unstable chemical seed containing the same oxygen atom, and a negative ion, or by reacting the deposited carbon with a radical, lighting Characterized by the steps of removing or reducing the accumulated carbon, which is deposited on the surface. In more detail, the process according to the invention provides an aqueous gas or an oxidizing gas (e.g. water vapor, oxygen, hydrogen, hydrogen peroxide, ozone, or a mixture of inert gas (including air) with said gas) while supplying active energy. Supplying a flow of an oxygen atom-containing gas such as to the near vacuum region to remove or reduce the accumulated carbon, which excites the oxidation of the supplied active energy and the accumulated carbon to form a film on the lighting surface. do.

Description

Optical property recovery device, recovery method, and optical system used in the device {AN OPTICAL PROPERTIES RESTORATION APPARATUS, THE RESTORATION METHOD, AND AN OPTICAL SYSTEM USED IN THE APPARATUS}

The present invention relates to an apparatus and method for improving reliability and lifespan of optical characteristics of an optical system by preventing, suppressing or improving the degradation of the optical characteristics of the optical system in the output light or along the optical path of the output light. The optical system is provided in a near vacuum region capable of decomposing organic components, and deposited or agglomerated on the light emitting surface, the light reflecting surface, the light emitting surface (all of which are referred to as " lighting surfaces ") of the optical system. Deterioration is caused and the surface faces the vacuum region. More particularly, the present invention relates to an optical property recovery apparatus and a method of using the same, and by using high photon energy light such as ordinary ultraviolet light or vacuum ultraviolet light, combining effects such as light transmission, refraction, reflection, spectral generation, and interference can be obtained. This optical characteristic recovery apparatus is used to improve the optical characteristics of various optical systems provided outside the light transmitting windows of various optical apparatuses.

The invention also relates to various optical devices and methods of using the same. The optical system improves the optical properties inside the light transmitting windows of various optical devices that produce combined effects such as light transmission, refraction, reflection, spectral generation, and interference, which can be applied to high optical light such as conventional ultraviolet light or vacuum ultraviolet light. Photon energy is provided in the optical path of light. More specifically, the present invention is applicable to optical systems provided with lenses, windows, etalons, prisms, reticles, reflective mirrors, and the like, and high photon energy lamps provided with such optical systems. In addition, the present invention provides optical measuring devices such as spectrometers, fluorometers, interferometers, diffractometers, as well as a variety of optical devices, including standard light sources for vacuum ultraviolet light, light sources for exciting chemical reactions, print plates and photographic applications, And various light sources for experimental applications.

[Description of Related Technology]

As an example of a conventional optical output device to which the present invention can be applied, the components and operation of a microwave excited hydrogen ultraviolet lamp will be described using FIG. 14. This device is disclosed in Non-Patent Document 1, 1967, Nobraska, Lincoln, Pied Publication, James A, R. Samson, Technique of vacuum Ultraviolet Spectroscopy, P159, Figure 5.56. The microwave oscillator 4 has a sealed tubular component provided with both ends made of the same conductive material. At conventional microwave frequencies, the lengths of the internal diaphragms and tubes and the electromagnetic distribution excited by the microwave oscillator are measured.

The microwave oscillator tuner 18 is a tubular component which is an essential component of the microwave oscillator for adjusting the microwave electromagnetic field distribution of the microwave oscillator, and its inner diameter is to seal the discharge tube 1. It is also intensively inserted into the end surface of the microwave oscillator 4 along their bore axis, and this configuration allows it to slide in the axial direction to maintain its role as an electrical guide for the microwave oscillator 4. Is done. Like the microwave oscillator 4, the material used to form the tuner 18 is copper or brass. The function for adjusting the microwave electromagnetic field distribution by the tuner 18 allows the microwave center 6 to be placed at the desired production position by adjusting the insertion depth while generating during the generation of the discharge plasma 7.

In addition, the surface of both ends of the microwave oscillator 4 is installed in such a manner that the discharge tube 1 passes. It is a general fact that the highest electric field is produced along the hole axis of the discharge tube 1, which is located along the hole axis of the microwave oscillator 4, but this is not always the case. Although the cross-sectional shape of the discharge tube 1 is circular, shapes, such as square, can also become equal.

The discharge tube 1 functions as a vacuum boundary, a flow path for the discharge gas, and a space in which the discharge plasma is generated. In the example shown in FIG. 14, the inner tube of the conductor extends along the discharge tube 1 from the microwave oscillator 4 toward the inside of the microwave oscillator in order to define the space in which the discharge plasma is generated. Thus, the discharge plasma 7 is generated in the space between the end of the microwave oscillator tuner 18 and the end of the inner tube mentioned above.

The microwave oscillator 4 is connected with a microwave supply connector 5 for transmitting microwaves. Here, the shape of the connector is coaxial, but may be a microguide type. A coaxial table or coaxial tube can be used as the delivery feed path to the coaxial connector.

The flange 17 is bonded on the end of the discharge tube 1 to the microwave oscillator tuner 18 side via an O-ring 13 to fix the lamp. There is an opening in the center of the aforementioned flange 17, which has an inner diameter corresponding to the diameter of the discharge tube 1, so that light excitation can be emitted from the discharge plasma 7 in the axial direction of the discharge tube 1. do.

The light transmitting window 8 mounted in the opening of the aforementioned flange 17 provides two functions. The first is the function as the vacuum boundary inside the discharge tube 1 with respect to the atmosphere. The second is a function of emitting extraction light from the discharge plasma 7 to the outside of the vacuum. The aforementioned microwave oscillator is described in detail in Non-Patent Document 2, "Microwave Measurement of New York, MecGraw-Hill, E.L.Ginzton, 1957".

The discharge lamp having the above-described configuration presents the following problems, but before explaining this, the concept used is defined.

The vacuum ultraviolet range is in the wavelength range of 0.2 to 200 nm. Light within this range is called ultraviolet light or vacuum ultraviolet light. Typical wavelengths of ultraviolet light are 200-380 nm (Baifukan et al., Dictionary of Physics, and National Observatory of Japan, Rita Nenpyo).

In FIG. 14, in order to distinguish the surface of the light transmitting window, the surface facing the discharge plasma 7 is called the inner surface 10, and the surface on the other side is called the outer outer surface 11.

Problem of deterioration of optical properties outside the light transmission window

In FIG. 14, when light is generated by the discharge plasma 7, in particular when ultraviolet light and vacuum ultraviolet light are generated, this light is irradiated through the inner surface 10 of the light transmitting window 8, It passes through the light transmitting window 8 and passes through an outer surface outside the light transmitting window 8.

Here, as shown in FIG. 14, normally, when ultraviolet or vacuum ultraviolet light is emitted into the atmosphere, and these lights cause significant absorption of oxygen, carbon dioxide, water vapor, and the like, a mechanism to help maintain the vacuum is provided with a flange (17). ) (I.e., outside of the light transmitting window 8). Hereinafter, the region where the vacuum is maintained is referred to as the "vacuum region".

In general, any one of various vacuum pumps can be used as a mechanism for maintaining the vacuum. Although there are a variety of oil-free drying pumps (which emit little organic gas) suitable for use, rotary turbo pumps are the most common. Thus, the vacuum region 14 contains organic gas from the vapor pressure of the oil used in the pump.

In addition, stainless steel or aluminum metal parts, or rubber parts such as O-rings are included in the vacuum area 14, and depending on the application, the vacuum area 14 may be a sample, a lens, a diffraction element, a mirror, a filter, a transmission mirror. Optical elements such as, stages, or other positioning elements. All of the materials adhered to the vacuum region 14 described above, i.e., stainless steel reservoirs, aluminum reservoirs, O-rings and other encapsulants, optical elements, work samples, positioning mechanisms, etc., should be oil free ( Most of them themselves should emit almost no organic gases).

In particular, in the semiconductor industry, the finer the processing size (circuit line width), the more the light wavelength used to manufacture an exposure pattern for a circuit has reached the vacuum ultraviolet light range. For example, the wavelength of a fluorinated excimer laser used as a light source in such applications is 193 nm (6.4 eV when converted into energy), but recently, a laser stepper device has been developed that produces a wavelength of 157 nm.

In practice, however, various factors such as lubricating oil used in mechanical drive configurations, contamination of work samples, gas release from O-rings, gas release from plastic parts, improper grease removal or cleaning of parts, or contamination by operator error. It is difficult to avoid the emission of organic gas inside the vacuum region 14 generated from. Therefore, in practical applications, the appearance of the organic gas inside the vacuum region described above should be taken into account.

The organic gas inside the vacuum region 14 has a certain probability of being adsorbed on the outer surface 11 outside the light transmitting window 8. The adsorption probability varies depending on the material constituting the light transmitting window 8 and the organic gas type, but the occurrence of self-adsorption phenomenon cannot be avoided.

When the organic gas is adsorbed on the outer surface 11, at the same time, ultraviolet light, in particular vacuum gyrobeam, generated by the plasma irradiates such organic gas so that the organic gas molecules are directly excited and in an active state. do. This produces a reaction that attracts hydrogen, which is a constituent of the organic gas, during the hydrogen removal reaction, and finally converts the adsorbed organic gas into carbon (graphite). When this state is reached, it is no longer a gas, but a solid which itself deposits and adheres on the outer surface 11 of the light transmitting window 8. Next, the carbon deposits adsorb new organic gases, and their irradiation with ultraviolet light, in particular vacuum ultraviolet light, converts them to carbon, creating a continuous buildup. As the process continues, the outer surface 11 of the light transmitting window 8 is covered with a carbon film. Since the carbon is black, as it absorbs light of various wavelengths and carbon accumulation on the outer surface 11 continues, the transmittance through the light transmission window 8 gradually decreases.

Here, in short, the organic gas is a hydrocarbon gas and the hydrogen removal reaction is expected to convert them to graphite, but in practice, the organic gas is not a hydrocarbon element, but oxygen, nitrogen, iodine, fluorine, chlorine And the like, and such organic gas may be adsorbed to the outer surface 11 of the light transmitting window 8 like hydrocarbon gas, and then through the reaction of ultraviolet light, in particular, the reaction of vacuum ultraviolet light. Through the conversion, non-gas components remain. That is, the laminate is not graphite but is an amorphous solid with carbon as its original component. For the purpose of illustrating the invention, a solid comprising primarily carbon is referred to as "carbon".

The carbon lamination phenomenon requires adsorption of organic gases and ultraviolet light, in particular vacuum ultraviolet light. As the accumulation of carbon proceeds, the intensity of the ultraviolet light, in particular the intensity of the vacuum ultraviolet light emitted from the outer surface 11 on which carbon has accumulated, is significantly reduced. The carbon stack will continue until the light intensity is exhausted. At this time, the hydrogen removal reaction cannot occur, and the accumulation of the carbon film is stopped. Thus, this process is not able to grow the carbon film indefinitely, but this phenomenon stops when the limit film thickness is reached.

In general, the above-mentioned carbon lamination phenomenon on the outer surface 11 of the light transmitting window 8 does not proceed rapidly. The problem is to reduce the transmission through the light transmission window 8 over a long period of time. In spectrographic applications, when the amount of light from the light source is reduced, this creates a drift that affects the accuracy of the measurement, and in applications involving surface treatment by ultraviolet light irradiation, due to inadequate processing caused by the reduced irradiation intensity Cause problems.

Means for solving the problem of the carbon deposition phenomenon are for the oil free vacuum region 14, but once the organics contaminate the vacuum region 14, the cleaning process becomes very difficult. Thus, as a general countermeasure against the reduced transmittance due to the carbon accumulation on the outer surface 11 of the light transmitting window 8, the light transmitting window 8 is intact by removing carbon using a cleaner or polishing. There is a way to recover or to replace the entire light transmitting window (8).

In the prior art, the decrease in the light transmittance of the light transmitting window 8, that is, the deterioration, was a factor in determining the lamp life. At the end of their life, the lamps needed to break the vacuum of the vacuum region 14 or the lamps during cleaning and replacement of the light transmitting window 8. This operation required several hours of unavailability of the lamp.

Next, a general countermeasure against deterioration of the light transmitting window due to the carbon lamination will be described.

The technique disclosed in Japanese Patent Application Laid-Open No. 2001-319618 (Patent Document 1) is described below.

In this example, the light source in question was a hydrogen lamp. When hydrogen is injected into the discharge tube, the halogen is also sealed inside as a means to increase the life of the lamp. The halogen sealed inside is in the form of an organic halogen compound. This means that the organic halogen material was introduced into the discharge region. Next, when the lamp is operated, the organic material is decomposed and a film of organic material composed of carbon is formed so as to stick to the inner wall of the discharge tube. The inner wall functions as a light transmitting window, and the adhesion of the terminals onto this wall reduces the amount of light produced. As a countermeasure, the above-mentioned Patent Document 1 allows the carbon film to be forcibly adhered to a region functioning as a light transmitting window where carbon is planned to be laminated during lamp operation, and thereafter, additional carbon during normal operation of the lamp. We propose a treatment of a pre- included lamp so that no lamination occurs. This technique is not limited by the generation of organic materials and this countermeasure considers effectively creating an environment where no new stacking occurs during lamp operation.

However, as described above with respect to the vacuum region 14, the apparatus involved (such as in spectrographic applications in which samples must be replaced, in applications in which optical elements must be adjusted, or in workpieces that need to be evacuated during surface treatment). If it is necessary to open repeatedly in order to break the atmosphere or vacuum, even if the specification in which organic impurities are introduced during the assembly or adjustment process in which such impurities are rarely added is not required, the light transmitting window 8 It is impossible to avoid deterioration.

In addition, Japanese Patent Application No. 2001-293448 (Patent Document 2) discloses, at least, (1) a process for cleaning an optical element with an organic solvent, (2) a process of irradiating the optical element with ultraviolet light upon the appearance of oxygen, and ( 3) The present invention relates to a cleaning method for removing the adsorbed organic material from the surface of the optical element by a method such as heating and cleaning the optical element. This disclosure not only has a different purpose than removing the accumulated carbon film from the surface, but also does not solve the problem of cleaning optical elements such as light transmitting windows that require vacuum to be broken.

In addition, Japanese Patent Application No. 2002-219429 (Patent Document 3) discloses a technique similar to the present invention. It is aimed at improving the accuracy and efficiency of the cleaning process and in the heated gas atmosphere containing water vapor the surface of a substrate comprising at least one of a glass substrate, a synthetic resin substrate, a ceramic substrate, a metal substrate, and a composite substrate. Wet the surface, and then irradiate the substrate with ultraviolet light in a mixed atmosphere of heated non-inert gas and water vapor to decompose the organic substance adhering to the surface of the substrate, and furthermore, reducing the active seed [H-] and oxidation. Generating an active seed [-OH] and reacting this active seed [H-] with the active seed [-OH] with a decomposition product of the organic material.

The object of the prior art is not to remove the carbon film from the surface, but in particular to irradiate the substrate surface with ultraviolet light, and to adhere the organic material to the substrate surface in accordance with a cleaning and etching process using ultraviolet light irradiation as the substrate processing means. Decompose into smaller molecules. This not only differs from the object of the present invention, but also presupposes that the substrate surface becomes a liquid in water under the reaction conditions because the conditions must be met. As a result, this method cannot be used in a general atmospheric environment, it is not possible to perform an optical element or the like which cleans the light transmitting window under vacuum conditions, and also does not solve any problems caused when breaking the vacuum.

The description so far has been limited to the phenomenon occurring at the outer surface 11 of the light transmitting window 8, but this type of carbon lamination phenomenon is not limited to the outer surface 11 of the light transmitting window 8. Usually, this is the case where the carbon lamination phenomenon occurs on the surface of the object located in the vacuum region 14 irradiated with ultraviolet light, in particular, vacuum ultraviolet light emitted from the light transmitting window 8. This phenomenon is inadequate, such as the presence of organic gas and ultraviolet light, in particular vacuum ultraviolet light appearance conditions. "Object" in the foregoing description includes mirrors for switching optical paths in spectroscopic applications, filters, lenses for concentrating light, and diffractive elements used in spectroscopic applications, ie, any of a variety of optical elements. . Hereinafter, this object is collectively referred to as an "optical element". When carbon accumulates on the optical element, this causes serious problems by reducing light transmission and light reflectivity. In practice, this causes the malfunction or deterioration of the apparatus used in the vacuum region 14.

Previously, in order to counteract the reduction in light transmission and reflection, these optical elements had to be replaced with new ones, but this approach would require high maintenance costs and shut down the device for the service time required for maintenance.

Problems due to lamp life due to deterioration of the light transmitting window 8 include various lamps using He, Ne, Ar, Kr, Xe, O ₂ , N ₂ , D ₂ (deuterium molecules), Hg, and the like; Lamps using high frequency discharge, arc discharge, glow discharge, inductive barrier discharge, or flash discharge in these discharge modes; Or similarly to the problem present in halogen lamps or carbon lamps that heat the filaments using current as the light generating means, but are not limited to the microwave-excited hydrogen ultraviolet lamps described in the previous examples.

Problem of deterioration of optical characteristics in optical system

The problem of deterioration of light transmission characteristics from short wavelength ultraviolet light is not limited to deterioration of optical properties outside the light transmission window, but also deterioration of optical properties inside the light transmission window.

Recently, in order to obtain better light transmission characteristics from short wavelength ultraviolet light, the use of SiO ₂ as a light transmission window has been developed.

Furthermore, the problem with mercury vapor lamps, where quartz glass used more than before, loses transparency, is more serious. The quartz glass of the mercury vapor lamp functions as a vacuum boundary to the outside of the lamp, and also transmits ultraviolet light generated from the light emission of mercury, but the loss of transparency degrades the light transmitting characteristics and lamp life. Is a factor of deterioration.

In Japanese Patent No. H5-325893 (Patent Document 4), for example, the loss of transparency using a light emitting tube with a metal vapor electric discharge arc tube whose surface inside of the glass bulb exhibits a surface grain size of less than micron is roughened. A countermeasure was proposed. By doing so, even after prolonged operation, it interferes with the crystallinity of the arc tube (i.e., loses its transparency), and therefore, disturbs the dockline in the light flux (luminance retention), thus for projection type displays. It is possible to maintain a high quality display with a bright screen over a long period of time.

This technique has been applied to high silicate glass or quartz glass used in arc tubes, and although conventional ultraviolet light applications could be applied in the 250 to 360 nm wavelength range, the transmittance of quartz glass is not limited to vacuum ultraviolet light of 190 nm wavelength. Decreases enough.

Further, Japanese Patent No. H3-77258 (Patent Document 6) discloses a technique for 254 nm ultraviolet light in a mercury vapor lamp at a constant pressure, wherein the inner surface of the synthetic quartz glass has an average particle diameter of 100 µm or less. It is coated with a solution of metal oxide particles of 1% to 3% having, in the example, composed of a metal oxide having an average particle diameter of 20 μm.

Further, Japanese Patent Application No. H8-212976 (Patent Document 7) includes a quartz glass tube in which an electrode is sealed at each end where a thin film coated with mercury inside and coated with Al ₂ O ₃ or the like on the inside of the tube is used. Disclosed is a technique for a discharge lamp using an arc tube, wherein the thin film is thicker on the above-described arc tube inner surface around the center of the tube than in other regions, in particular a thick film on the inner surface of the arc tube described above. The area is 1/3 to 1/2 the length of the effective light emission length, which is the distance between the electrodes on both ends of the arc tube, and the film thickness of the above-mentioned thick film ranges from 0.2 μm to 0.3 μm, while the film thickness of the other area is Is 0.1 μm to 0.15 μm.

However, in particular, the prior art associated with quartz glass used in low pressure mercury discharge lamps, by adjusting the thickness of the protective film in which mercury atoms are present as a means for dealing with the problem of the deposition of mercury on the inner wall of the arc tube. Lowering the light transmittance through the glass and dimming the discharge lamp further reduces irradiation efficiency.

In addition, the lower limit for SiO ₂ for imparting good light transmittance is about 200 nm level, and the light transmittance is significantly lowered with shorter wavelength vacuum ultraviolet light appearing at a wavelength lower than 200 nm. In addition, very short wavelength vacuum ultraviolet light on the order of 150 nm as used with high energy fluorine lasers does not only reduce the above-mentioned light transmittance, but also that the material cannot affect the application, but also does not lose transparency. Do not.

Further, in view of the fact that there is a significant decrease in the transmittance of the ultraviolet light range through the light transmitting window material through which the lamp light irradiated by the synthetic silica glass is transmitted, Japanese Patent Application H8-315771 (Patent Document 5) is improved. Disclosed is a fluorine doping technique for synthetic silica glass for the purpose of operating life.

However, only techniques for doping silica glass based deposits with fluorine compounds have a 50% transmission range in the 160-190 nm wavelength range, and using lower vacuum ultraviolet light is not applicable.

Therefore, alkali halide materials such as CaF ₂ , LiF, MgF _2, and the like have been generally used as the light transmitting window laminate when the ultraviolet light in the vacuum ultraviolet range should be transmitted.

A suitable example of the prior art is the microwave-excited hydrogen ultraviolet lamp described above, which produced vacuum ultraviolet light at a wavelength of 122 nm. Known materials that can be used in the light transmission window are CaF ₂ , LiF, MgF ₂ , and MgF ₂ is mostly used because LiF, MgF ₂ exhibits a significantly low light transmittance from their color center. However, no countermeasures against the loss of transparency of MgF ₂ have been disclosed.

That is, when manganese fluoride is used as the material for the light transmission window, such a light transmission window exhibits a poorer life than other light transmission windows, and the lamp life itself is less than half as compared to lamps using other light transmission window materials.

When using light with photon energy higher than the absorption wavelength for the material used for the light transmitting window 8, particularly when using light in the vacuum ultraviolet range, light from the discharge plasma is irradiated to the light transmitting window 8. In doing so, the light transmitting window 8 generates defects, and a so-called color center produces a color center in which the light transmittance is lowered. This phenomenon is also common to CaF ₂ , LiF, MgF ₂ and other alkali halide materials, and is caused by the slight movement of fluorine atoms from their exact location inside the lattice.

In addition, all of the above-described conventional techniques present problems associated with synthetic quartz, in particular, synthetic quartz optical systems that use conventional wavelength ultraviolet light as a light source. There is no proposal for a practical technique that is effective in preventing transmission reduction through MgF ₂ , a material used in the light transmission window for 122 nm wavelength vacuum ultraviolet light generated by microwave excited hydrogen ultraviolet lamps.

Because of this situation, the only way when the transmittance was reduced was to replace the light transmission window. In the prior art, the deterioration of the light transmitting window 8 as described above determined the factor of lamp life. In the prior art, when the life of the light transmitting window 8 of the lamp is increased, it has to be replaced by a new light transmitting window, so as to recover the light emission intensity of the lamp. Replacing the light transmitting window 8 requires breaking the lamp vacuum during times when the lamp is not available and hours of labor. In addition, during the replacement cycle, the output intensity from the light source is constantly changed. Every time the light transmission window is replaced, a calibration operation for the light intensity is required. Therefore, it is difficult to use lamps that require such long-term monitoring, such as those used for environmental measurements.

The present invention was developed to reflect the problems associated with the prior art, and employs an optical system for imparting effects such as light transmission, diffraction, reflection, spectral generation and interference, and high photons such as conventional ultraviolet light or vacuum ultraviolet light. A device and method for recovering the optical properties of various devices utilizing energy light. In particular, it is an object of the present invention to prevent or avoid deterioration of the optical system, which determines the life of the apparatus described above, by doing so, the frequency of maintenance work such as window replacement is reduced and the cost for such work is reduced.

More specifically, according to the first preferred embodiment of the present invention, the object of the present invention is to provide an external surface 11 of the light transmitting window 8 outside (for example, the light transmitting window 8 shown in FIG. 14). A device and the use thereof, which reduce or reduce the cost for such operations while reducing the frequency of maintenance work such as replacement of the optical system, by inhibiting or preventing carbon accumulation on the surface of the optical system, such as the optical system provided in FIG. To provide a method.

Another object of the present invention is to prevent or inhibit carbon accumulation on the irradiation surface and the lighting surface of the optical element in the optical path of the vacuum region, so as to extend the life of the optical device and improve the reliability of such device.

Furthermore, according to the second preferred embodiment of the present invention, after reflecting the above-mentioned problems in the prior art, light transmitting, refracting, reflecting, and spectra provided in the light path of a high photon energy light source such as plasma light and vacuum ultraviolet light. In addition, the present invention provides an optical system using a variety of devices using an effect of combining interference, and a method of using the same. The optical system is provided with the above-described lens, window, azelon, prism, reticle, provided inside a light transmitting window 8 (e.g., on the inner surface 10 of the light transmitting window 8 shown in FIG. And deterioration of an optical device such as a reflective mirror and the like, and can extend the life using various types of optical systems.

[First Preferred Embodiment]

In order to solve the above problem, the present inventors continued to study according to the following.

First, in the first preferred embodiment, a detailed analysis of the deterioration occurring outside (such as the outer surface 11) of the light transmitting window 8 facing the vacuum region 14 was performed. The apparatus used for the experiment, in which the light transmitting window 8 is adhered to the plasma exposed side of the flange 17 via an O-ring, is shown in FIG. Analysis of the surface facing the outer surface 11 of the light transmitting window 8, that is, the vacuum region 14 that is the surface emitting ultraviolet light was performed. Since no deposit was found on the inner surface 10 on the opposite side, this surface was not analyzed in detail.

Manganese fluoride (MgF ₂ ) single crystal was used as the light transmitting window 8 material, and the crystal axis (c-axis) was aligned perpendicular to the surface of the light transmitting window. The crystal size was 0.5 inch Φ × 1 mm thick. The decision was made by Ohyo Koken Kogyo Co., Ltd. It was a UV grade product manufactured by. These crystals from the same lot were prepared and the crystals used matched the quality of the crystals and the conditions of these surfaces. The crystals were analyzed after use in the ramp and the errors that caused the factor due to any variation in the lot were removed.

Experimentally, the first step is to use an optical microscope to examine the outer surface 11 of the light transmission window 8 in the center Φ8 mm range through which ultraviolet light is transmitted, in order to observe a material such as any film that may have stuck to it. It was to see. When the weakly adhered material was found to adhere to the outer surface 11, any sticky material was scraped off using plastic tongs.

Next, elemental analysis of the stuck material was performed. Elemental analysis of the outer surface 11 of the light transmitting window 8 was carried out using EPMA (analysis conditions: acceleration voltage 15 kV, irradiation current 5 × 10 ⁸ A, measuring mode: qualitative analysis, microanalysis, mapping analysis ).

As a result of the EPMA analysis, it was found that a significant amount of carbon is detected on the center Φ 8 mm through which ultraviolet light is transmitted. A donut-shaped region outside the circular center Φ8 mm outside which ultraviolet rays were transmitted was in the shadow of the flange 17, but the region where the ultraviolet light did not pass was detected, but the contamination level of carbon was detected in the donut shape. Contaminant levels in EPMA analysis mean a weak signal for carbon detection produced when analyzing the entire cleaned surface. That is, this is an undesirable sticking of the carbon that produces this signal. Thus, the carbon contamination level of the analytical device determined the measurement limits for EPMA analysis with carbon. When comparing the carbon signal level from the center Φ8 mm to the contamination signal level, it was first found to be significantly higher, confirming that the accumulation of the film shape of carbon occurred on the outer surface 11 of the light transmitting window.

As described above, with reference to the apparatus shown in FIG. 14, the mechanism for carbon lamination comprises an organic gas present in the vacuum region 14, in which the organic gas is an outer surface 11 of the light transmitting window 8. After being absorbed on), when the vacuum ultraviolet light is transmitted through the light transmitting window 8, the organic gas has accumulated on the outer surface 11 by performing a hydrogen removal reaction that converts them into carbon.

By continuously using the light transmitting window 8 in the above-described environment, carbon is accumulated over time to reduce the light transmittance. Thus, as compared with the initial state, since the light transmittance to the light transmitting window 8 is reduced, there is a clear need for some mechanism for removing carbon accumulated from the outer surface 11. Since we found that the film-like carbon lamination on the outer surface is the primary cause for deterioration of the light transmission window, the inventors have continually investigated counter measurements, leading to the completion of the invention described below.

The inventors have confirmed the approach to the problem as described below through experiments. The raw material for carbon is organic gas, but it is virtually impossible to remove them completely. In addition, in the case of not irradiating with vacuum ultraviolet light, the hydrogen removal reaction does not occur, but the device cannot perform the possibility as a light emitting device. The position of the carbon deposit coincides with the position at which the vacuum ultraviolet light is irradiated. Vacuum ultraviolet light excites the organic gas to undergo a hydrogen removal reaction, but this high photon energy rarely excites the organic gas, and many types of molecules are also excited and in an active state.

Referring to FIG. 1, the light output device of the embodiment is a 122 nm wavelength vacuum ultraviolet light output using hydrogen light emission, and the photon energy for vacuum ultraviolet light is 10.2 eV. Photon energy levels excite oxygen gas, H ₂ O gas (steam) and produce radicals with strong oxidizing power. The reason for maintaining the vacuum region 14 is that oxygen, carbon dioxide, water vapor, and other atmospheric components absorb vacuum ultraviolet light and weaken its strength. Thus, the absorbent medium, i.e., the atmospheric component, is removed by a vacuum pump or the like to create the vacuum region 14.

However, even if there were atmospheric components, since they contained O ₂ , water vapor, and the like, by appropriately reducing their concentration, radicals having oxidative power could be produced without significantly weakening vacuum ultraviolet light. When the light output device is operated under conditions in which contaminant controlled atmospheric composition coexists, and a subsequent stage vacuum region 14 is implemented, this can eliminate carbon sticking on the outer surface 11 of the light transmitting window 8. have. Further, carbon stuck to the surface of all of the optical elements located in the vacuum region 14 could be removed. The reason carbon can be removed is that carbon stuck to the outer surface 11 is generated simultaneously with carbon decomposition and radical removal, and the rate at which radicals decompose and remove carbon exceeds its formation rate. .

Since the decomposition reaction of carbon using radicals converts carbon into volatile molecules such as carbon dioxide and steam, they could be rapidly removed from the system using a vacuum pump. The radicals produced in this case are the OH radicals produced through the excitation of elemental oxygen and ozone, water vapor generated by excitation of oxygen molecules.

In addition, when the light output device operates in an atmosphere in which the concentration-controlled atmosphere composition is present and the carbon deposit is already present on the outer surface 11 of the light transmitting window 8, there is a gradual deposition and removal of carbon, so that As a result, all of the carbon is completely removed and the light transmission window 8 is preserved relative to the original light transmittance. Next, the light output device was operated without operating the subsequent vacuum region function using the optical element already having carbon accumulation, and removed carbon from the surface of this optical element which was located in the vacuum region 14.

Thus, in order not to reduce the light intensity generated by the light output device, it is possible to use the findings of the present invention to prevent deterioration of the light transmitting window of the light output device, thereby contributing to the replacement of the light transmitting window. In addition to reducing maintenance costs and maintenance time for the device, it is also possible to operate the light output device to remove the carbon already formed on the light transmitting window 8 or the optical element and maintain their original state. As a result, the maintenance cost and the maintenance cycle are reduced, so that the full performance of the vacuum region can be restored and the vacuum region 14 can be continued.

Next, a method for adjusting the concentration of the atmospheric composition in the vacuum region 14 atmosphere will be described. The gas supply may use pure oxygen gas provided from an oxygen cylinder. Alternatively, it can be supplied from the atmosphere, or it can use an air supply line already installed at the factory. It is also possible to use gas cylinders which are driven into dry air. It is also possible to use a mixture of oxygen and an inert gas such as argon, helium, which can be supplied from a gas cylinder. The gas supply pressure can be adjusted by the holes of the valve and the capacity of the gas cylinder, as described in the following configuration example, to purge the vacuum region 14 and adjust the gas partial pressure.

In addition, steam can be added to the above-described gas, or only steam can be used. Water vapor may be prepared by preparing a reservoir having water sealed therein, and then, may be added by mixing any of the above-described gases with water vapor. When using only itself, it is only necessary to inject into the vacuum region 14. The temperature of the water can be room temperature, or it can be cooled or heated. The temperature of the steam at the saturation level changes with the temperature of the water, and as in the configuration described later, the valve hole and the pump purge force can be set so that the partial pressure of the steam in the vacuum region 14 can be adjusted.

The partial pressure of the above-mentioned gas of the vacuum region 14 is determined under the following conditions. The upper limit of the partial pressure of gas should be determined based on the purpose for the absorption function for the vacuum ultraviolet light by the gas and the partial pressure which does not interfere with the operation. In certain periods, for example oxygen gas, the upper limit should be 10 mtorr units (up to 20 mtorr). If the partial pressure level is exceeded, the absorption of vacuum ultraviolet light by oxygen will reach a point of negligible, which will interfere with the functional purpose for the vacuum region 14. However, if the length of the optical path through the vacuum region 14 is very short, the influence of the oxygen concentration at the upper limit can be ignored. The exact setting of the upper limit can be determined by filling the vacuum region 14 with a specific gas partial pressure and checking whether the functional purpose is deteriorated. In particular, the amount of vacuum ultraviolet light can be measured by examining the reduction level.

The lower limit of gas partial pressure must be manually set to the above-described processing capacity for the rod. Here, "rod" denotes the outside of the light-transmitting window 8 by determining the type and concentration of organic gas present and the wavelength and intensity of the vacuum ultraviolet light 9 transmitted through the light-transmitting window 8. The rate of accumulation on the surface 11. "Processing capacity" is the rate at which carbon can be decomposed and removed by radicals generated through excitation of a gas by vacuum ultraviolet light.

In the case of the vacuum region 14 which is unknown but is produced, for example, by conventional turbomolecular pumps and dry pump exhaust systems, the vacuum region 14 in various cases is observed, with a lower limit of oxygen gas being, for example, 0.01 to 0.1 mtorr. One inventor carried out experiments. If such an oxygen gas level is present, it will represent an appropriate processing capacity for the load. Water vapor provides a level of processing capacity that is relatively higher than oxygen, with a lower limit of 0.005 to 0.01 mtorr.

In order to set the lower limit accurately, oxygen can be used to fill the vacuum area 14 actually used at a specific partial pressure, and after analyzing for sticking to the outer surface 11 of the light transmitting window 8, The optical output device can be operated. Suitable analytical methods include observation via carbon microscopy or carbon analysis via EPMA. If the analysis does not show the appearance of significant carbon deposits, the partial pressure used at this time can be found to allow proper deposition and carbon removal processing.

The following technical method proposes the present invention based on the following findings.

The invention according to claims 1 and 2 relates to a device capable of achieving the effect of the invention. The present invention provides an optical characteristic recovery apparatus for improving reliability and lifespan of optical characteristics of an optical system by preventing, suppressing, or improving deterioration of optical characteristics of an optical system disposed along an optical path of the output light or the output light. Silver is provided in the near vacuum region where organic components can decompose, and the degradation is carbon deposited or accumulated on the light emitting surface, the light reflection surface, and the light emitting surface (hereinafter collectively referred to as "lighting surface") of the optical system. And the surface is opposed to the vacuum region, and the optical characteristic recovery device is a presence of active energy that excites an oxidation reaction of carbon, and the near vacuum region is opposed to the lighting surface of the optical system. Means for forming; Means for generating anions or radicals in the near vacuum region; And means for facilitating an oxidation reaction between the anion or radicals and the carbon in the near vacuum region, wherein the optical property recovery apparatus removes accumulated carbon deposited on the lighting surface by the oxidation reaction. Or reducing, optical recovery device.

More specifically, the optical recovery device includes: means for forming the near vacuum region opposite the lighting surface of the optical system to excite oxidation of carbon; Means for generating a flow of an oxygen atom containing gas such as water gas or oxidizing gas in the near vacuum region; And means for supplying active energy to the near vacuum region to generate a carbon oxidation reaction between the oxygen atom containing gas and carbon, wherein the optical property recovery apparatus is deposited on the lighting surface by the oxidation reaction. Removes or reduces carbon.

"Near vacuum region" can be defined as high active energy excitation that excites a carbon oxidation reaction to decompose carbon by removing hydrogen from organic compounds, such as hydrocarbons. The pressure in the near vacuum region is varied by the intensity of the active energy and the oxidizing power of the oxygen atom-containing gas as described above, but may be several tens of mtorr or less.

According to claim 3, the present invention is to prevent, suppress or improve the degradation of the optical characteristics of the optical system disposed in the output light or the optical path of the output light to improve the reliability and life of the optical characteristics of the optical system The optical system is provided in a near vacuum region in which organic components can be decomposed, and the degradation is collectively referred to as the light emitting surface, the light reflecting surface, and the light emitting surface (hereinafter referred to as "lighting surface"). Generated by carbon deposited on or deposited on the surface, and the surface is opposed to the vacuum region, and the method for recovering the optical characteristic is the presence of active energy that excites the oxidation reaction of carbon. Forming the near vacuum region opposite the surface; Generating anions or radicals in the near vacuum region; And reacting anion or radicals with the deposited carbon to remove or reduce accumulated carbon deposited on the lighting surface.

More specifically, the method recovers an optical characteristic that prevents, suppresses or improves the deterioration of the optical characteristics of the optical system disposed along the optical path of the output light or the output light, thereby improving the reliability and lifetime of the optical characteristic of the optical system. As a method, the optical system is provided in a near vacuum region in which organic components can be decomposed, and the degradation is on the light emitting surface, the light reflecting surface, the light emitting surface (hereinafter collectively referred to as "lighting surface") of the optical system. Generated by carbon deposited or accumulated in the surface, and the surface is opposed to the vacuum region, and the method for recovering the optical characteristic is a step of forming the near vacuum region to excite the oxidation reaction of carbon, the high active energy Excitation is present, wherein the near vacuum region is opposite the lighting surface of the optical system; And supplying a flow of an oxygen atom-containing gas such as water gas or oxidizing gas (for example, water vapor, oxygen, hydrogen peroxide, ozone or an inert gas (including air) and a mixture thereof) to the near vacuum region, Supplying an active energy, thereby stimulating an oxidation reaction of carbon accumulated with the supplied active energy to thereby remove or reduce the accumulated carbon deposited on the lighting surface. It is done.

In addition, the above-described optical system includes diffraction, refraction, spectral generation, transmission, and diffraction control optical elements located along the optical path inside the vacuum area, as well as an optical element including light transmitting or reflecting members positioned at the boundary of the near vacuum region. And an optical component comprising an optical article to be surface treated by radiation, the optical system further comprising a positioning and holding mechanism, a container and a seal of the optical element or the optical article.

In addition, the present invention is the beam forming the optical path is a normal ultraviolet light having a wavelength of 380nm or less or a vacuum ultraviolet light having a wavelength of 200nm or less, the outputting the ultraviolet light or disposed along the optical path of the output light Optical systems include fluorine compounds such as magnesium fluoride, calcium fluoride, barium fluoride, aluminum fluoride, cryolite, thiolite or other fluorine compounds, lanthanum fluoride, cadmium fluoride, neodymium fluoride, It can be effectively applied even in the case of optical materials including metal fluoride such as yttrium fluoride or high purity oxides such as synthetic quartz glass or sapphire.

Further, a lower limit on the partial pressure of the oxygen atom-containing gas supplied to the near vacuum region is obtained when carbon from decomposition of organic components in the near vacuum region has already been grown on the surface and the opposing surface of the optical system. , Is set at a level higher than the rate of carbon accumulation. Further, an upper limit on the partial pressure of the oxygen atom-containing gas supplied to the near vacuum region may be obtained when the optical characteristic of the optical system is restored when the vacuum ultraviolet light is emitted to or emitted from the optical system. The absorption of vacuum ultraviolet light by the oxygen atom-containing gas is set below a level that cannot be neglected to perform its function inside the near vacuum region.

The upper limit value for the partial pressure of the oxygen atom-containing gas is set to a level by actually filling the near vacuum region with a partial pressure of the oxygen atom-containing gas, and then measuring the magnitude of the vacuum ultraviolet light on the optical path and examining the attenuation level thereof. do.

Further, the preferred oxygen atom containing gas is oxygen calcining, and the range between the lower limit and the upper limit for the gas partial pressure is 0.02 mtorr to 20 mtorr (preferably 0.02 mtorr to 10 mtorr), and 0.01 mtorr to 10 when the gas is water vapor. mtorr (preferably between 0.01 mtorr and 1 mtorr).

In addition, the present invention is effective when the beam formed on the optical path described above has a high photon energy group and is a beam of a predetermined wavelength of vacuum ultraviolet light wavelength.

That is, if the above-mentioned active energy is a vacuum ultraviolet light having a high photon energy, anion or radicals may be extracted from an oxygen atom-containing gas without using a separate energy source (for example, thermal energy, plasma energy, or electrical energy). Can be generated. Even with active seeds such as OH- and O- as in Patent Document 3, their pressure conditions for cleaning purposes differ from those specified in the reference.

[Preferred Second Embodiment]

In addition, in the second preferred embodiment, the degradation occurring inside the light transmitting window 8 (as in the inner surface 10) was analyzed in detail.

In order to solve the above-mentioned problems, the inventors carried out a detailed analysis of the deterioration of the light transmitting window 8 made of a fluoride material. The device used was the device shown in Fig. 14, in which a light transmitting window 8 was adhered to the plasma exposed side of the flange 17 via an O-ring. The light transmission window 8 was prepared using MgF ₂ (manganese fluoride) single crystal.

As a result, deterioration of the transmittance of the light transmission window 8 was generated by forming an oxide on the surface of the MgF ₂ crystal (tens of nm thick) after irradiation with vacuum ultraviolet rays. It was also confirmed that fluorine was reduced to tens of nm thickness in the region on the crystal surface.

In addition, by measuring the spectral transmittance to study the corresponding relationship between the color center of the light transmission window 8 and the degradation of the transmittance, the main cause of the light transmission window 8 deterioration is the absorption of the color center. It is not due to fluorine defects and oxygen present on the crystal surface.

In this respect, the following described technical means have been proposed for the invention centered on the above finding.

A first proposal for the present invention is that a protective film having a film thickness of 2 nm to 20 nm is formed at least on the light emitting side (inner side) of the optical system, thereby preventing stripping of fluorine atoms from the surface of the optical system. Characterized in that.

The difference between this invention and patent document 4 is demonstrated. Patent document 4 relates to a mercury discharge lamp having mercury sealed in an arc tube. This technique used a protective film of 0.1 μm to 0.14 μm made of alumina or the like to prevent the affinity of mercury to the inner wall of the arc tube.

On the other hand, the present invention is a vacuum ultraviolet light, in which a thin film of 2 nm to 20 nm is applied to a surface irradiated with vacuum ultraviolet light to prevent stripping off of fluorine to exchange the initial deterioration of optical properties caused by the coating. It is related to the wide range.

The reason for limiting the film thickness to 20 nm or less is because the vacuum ultraviolet light is absorbed to the point where the function as an optical element cannot be maintained when thick.

An upper limit of 2 nm or more requires uniformly covering the protective film on the crystal surface. Since the SiO ₂ , Al ₂ O ₃ , MgO, TiO ₂ or ZrO ₂ molecular diameters are suitably 1 nm, a uniform protective film for achieving the function of the present invention may be formed on the crystal surface unless the coating is more than 2 molecules thick. It cannot be provided.

If the film thickness is appropriate, even if the purpose is to protect the surface of the optical system, metal oxides such as SiO ₂ or Al ₂ O ₃ , MgO, TiO ₂ , ZrO ₂ are not inherently materials that allow vacuum ultraviolet light to pass through. The presence of this protective film allows the absorption of vacuum ultraviolet steel inside the film and reduces the amount of ultraviolet light passing through the base material, as shown in FIG. At the 20 nm thickness level, the transmittance is only 10% without film. An initial transmittance of 10% or less causes a large deterioration of the optical properties of the base material, but at the deterioration level, it cannot act as an optical system, and absorption of ultraviolet light deteriorates the quality of the protective film itself and this heat is a surface protective film from the optical system. May exfoliate or cause other damage. Therefore, a thickness of 12 nm or less, preferably 10 nm or less, will maintain the optical properties of the base material at 30 to 40%, and even in the worst case, it can maintain the optical properties of 10% or more. Therefore, due to absorption of ultraviolet light, a film thickness of 20 nm or more will not be able to impart the function of a given optical system.

In addition, since Mg oxidation occurs along with stripping of the fluorine element, at least a SiO ₂ protective film or metal oxide having a thickness of 2 nm to 20 nm, preferably 2 to 12 nm is formed on the light irradiation side of the optical system. It is desirable to prevent the stripping of fluorine atoms from the surface of the optical system.

According to the present invention, since both the oxidation of the surface of the optical system and the stripping of fluorine atoms can be suppressed, the degradation of the light transmittance of the optical system can be suppressed.

There are deposition methods in the gas phase, such as deposition, ion plating, and CVD, which can be used to form a thin film protective film, but depending on the depression or protrusion formed by the ion beam sputtering method and plasma CVD by a polishing process for an optical system. The ion beam sputtering method and the plasma CVD are particularly preferred film forming methods because a very uniform film thickness can be formed.

A second proposal of the present invention is directed to an optical system comprising a fluorine compound exposed to the plasma and having an opposing face, which is installed in an optical device having an internal region in which the plasma is present, the surface of the fluorine compound exposed to the plasma. In the phase, a protective film of 2 nm to 20 nm made of a high plasma resistance material is formed.

This proposal can suppress degradation of the light transmission ratio of the optical system by inhibiting oxidation of the surface of the optical system described above generated by stripping of fluorine atoms or other oxygen in the plasma environment.

In this case, the above-mentioned protective film may be any metal oxide such as SiO ₂ , Al ₂ O ₃ , MgO, TiO ₂ , ZrO ₂ , referred to as the above-mentioned protective film. The optical system comprises a single crystal fluorinated material having a crystal axis (c-axis) along the light emission direction and by forming the above-mentioned protective film on the optical system in which the vertical surface of the protective film is coated with SiO ₂ or metal oxide, thereby vacuum vacuum ultraviolet light. Degradation can be prevented over time from the light emission to the base material and the initial degradation of the fluorinated optical system can be compromised by the coating.

In addition, since SiO ₂ or the above-described metal oxides have higher resistance to plasma than fluorinated compounds, it is possible to prevent stripping of fluorination and oxidation of metal atoms, and as a result, they are oxides. When used as a protective film for an optical system made of a fluorinated material, it is possible to prevent further degradation of the base metal over time caused by irradiation with vacuum ultraviolet light after their initial deterioration.

The third proposal of the present invention relates to a method of using a device using the optical portion of the optical system described above, wherein a metal selected from SiO ₂ or Al ₂ O ₃ , MgO, TiO ₂ , ZrO ₂ for the optical system. Providing a protective film of 2 nm to 20 nm in oxide, wherein the film inhibits oxidation of the surface of the substrate or stripping of the component from the surface of the substrate by plasma exposure to the substrate or radiation of vacuum ultraviolet light over time. And coupling the optical system to a desired device having a plasma light source or vacuum ultraviolet light source having a higher photon energy than the absorption wavelength of the substrate of the optical system.

According to the present invention, after the initial deterioration in the characteristics by the above-described metal oxide protective film, the film is subjected to the oxidation of the surface of the substrate or the stripping of elements from the substrate caused by the radiation of vacuum ultraviolet light or exposure to plasma. The deterioration of the base material of the optical system by time can be suppressed, which means that the optical output from the base material is no longer extinguished after the operation is first started, for example, by the above-described optical output device. The reflecting mirror can extend the life of the light transmission window. In addition, this extends the interval between replacement maintenance for light transmitting windows or reflective mirrors, thereby improving the operating speed for the light output device and reducing their operating cost.

In this case, the protective film described above provides a light output suitable for compensating for the initial deterioration of the optical system as a means of increasing the life of the device and thus not causing reduced light transmission (transmittance, reduction ratio) of the overall system. It is only necessary to use a light source to provide.

That is, when the optical system is coated with the above-described protective film to prevent degradation over time by irradiation with vacuum ultraviolet light or exposure to plasma, or else elements from the base material are stripped or oxidized over time. It is only necessary to provide the light output to the device to compensate for the initial degradation caused by the protective film described above. For example, in an optical output device used as a light source for measurement, using the above-described optical system coated on one or more surfaces such as coated light transmission windows or reflective mirrors, stable light output can be obtained over a longer period of time. Maintenance applications can be used in the light output device and maintain a stable light transmittance that does not degrade to stabilize the control operation and measurement sensitivity of the device.

Detailed description of the invention

[First Preferred Embodiment]

Hereinafter, an embodiment of the first preferred embodiment of the present invention, which suppresses or removes carbon adhesion from the outer surface 11 of the light transmitting window 8, is described by way of example with reference to the drawings. In addition, preferred embodiments for inhibiting or removing carbon adhesion from the optical system located in the vacuum region 14 are described with reference to the drawings.

The present invention is not limited to the examples of these embodiments, and may be effectively applied to lamps or laser devices that generate light by electric discharge or heating.

Example 1

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure used for demonstrating the structure of the microwave excited hydrogen ultraviolet lamp used by Example 1 of 1st Embodiment which concerns on this invention.

The support member (flange 17) to which the light transmitting window 8 is attached has a disc shape, the center of which is aligned with the bore of the discharge tube 1, and includes an opening having a diameter larger than the inner diameter of the discharge tube. The window flange 17 includes an O-ring groove and forms a seal for the opening for the light transmitting window 8, and also has a hollow leaded jig 20, a bolt hole fixed thereto, and a window flange 17. And an O-ring groove connected to the discharge tube 1 to maintain the vacuum.

The internal configuration of the jig 20 employs two stage concentric circles and limits the space housing the light transmitting window 8 and the space surrounded by the discharge tube 1. On one end surrounding the discharge tube 1, the O-ring 13 was cut at an angle that is properly maintained by the pressure. In addition, a thread, not shown in the figure, is cut into the outer peripheral surface of the end thereof, and the vacuum boundary of the discharge tube 1 is formed by the hermetic cap 21 through the cylindrical opening in a seal by the O-ring 13. do. The window attachment flange 17, the jig 20 and the cap 21 are all made of metal and generally low degree of stainless steel or aluminum are used, but the material is not limited to these metals.

The operation of the microwave excited hydrogen ultraviolet lamp having the above-described configuration will be described below. First, the hydrogen discharge gas diluted with 1/100 helium from the discharge gas supply port 2 in the discharge tube 1 is supplied at 20 sccm. This discharge gas is discharged | emitted through the discharge port 3 by the vacuum pump (not shown). By adjusting the diameter of a valve (not shown) provided between the discharge gas discharge port 3 and the vacuum pump, it is also possible to adjust the discharge conductance to maintain the inside of the discharge tube 1 at about 5 Torr (665 Pa). The reason for generating the flow of the discharge gas in the direction from the light transmitting window side toward the discharge tube 1 can reduce all the pollution sources of the window 8 due to the materials generated inside the discharge tube 1 by the discharge plasma. Because there is.

Thereafter, 2.45 GHz, 50 W microwaves are supplied from the microwave supply connector to the microwave oscillator 4. This microwave can be continuous or intermittent. A regulator (not shown) disposed on a power line connected to the microwave power source and the microwave oscillator can be used to adjust the microwave power output between the power source and the load (discharge plasma) upon generation of the discharge plasma 7 in the discharge tube 1. . The hydrogen atoms excited by the discharge plasma 7 emit light at a vacuum ultraviolet light wavelength of 103 nm to 122 nm. As will be described later, since MgF ₂ is used as the material of the light transmission window 8, 103 nm light is absorbed by MgF ₂ and 122 nm wavelength vacuum ultraviolet light is used as the output lamp light (vacuum ultraviolet light 9) in the vacuum region. Is passed to (14).

When the opening of the attachment flange 17 to the light transmitting window 8 is 8 mm, the output to the vacuum region 14 is a light flux of 8 mm.

MgF ₂ (magnesium fluoride) single crystal is used in the light transmission window 8 having the crystal axis (c-axis) aligned to be orthogonal to the surface of the light transmission window. The crystal size is 0.5 inch (12.7 mm) x 1 mm thick. The decision used was Ohyo Koken Kogyo Co., Ltd. It was UV grade of the product. Plural crystals were obtained from the same lot, and the plural crystals were sorted to match the crystal quality and the surface condition in order to prove the effect of the protective film, eliminating any possible deviation in the lot.

In addition, the photodiode 12 has been positioned to receive the lamp output light 9 as a means of monitoring the amount of light output from the lamp.

While adjusting the gas to a predetermined partial pressure, oxygen gas was supplied to the vacuum region 14 using the method described later.

An oxygen gas cylinder 23 (manufactured by Nippon Sanso Corporation) was charged with pure oxygen (purity 4N) and connected to the regulator 22. After adjusting the gas pressure to 0.1kg / cm ² and adjusting the diameter of the variable leak valve 19 connected through the pipe 16c, the air flows through the air pipe 16b and then through a sealing mechanism (not shown). One gas was supplied from the tube 16a inside the vacuum region 14 to the vacuum region 14. The supply amount was approximately 1 sccm. The vacuum region 14 was discharged by a turbomolecular pump (model TP-50 manufactured by Mitsubishi Heavy Industries, Ltd., discharge rate of 50 L / min) and connected downstream to the dry pump (not shown). In this case, the oxygen gas partial pressure in the vacuum region 14 was maintained at 1 mTorr. Therefore, this condition was such that the partial pressure of the oxygen gas inside the vacuum region 14 was about 1 mTorr or more (and 10 mTorr or less).

In addition, although the experiment was performed with the valve aperture adjusted to provide 5 mTorr, 2 mTorr and 0.1 mTorr, the same effect was obtained for carbon removal as will be described later.

The variable leak valve described in the detailed description is not an item having a unique specification, it is only a device for fine diameter adjustment, and any name can be used.

Next, the photodiode 12 was used to measure the amount of change over time of the amount of light output from the microwave excited hydrogen ultraviolet lamp of the above-described configuration.

First, discharge plasma 7 was used to excite hydrogen atoms to generate vacuum ultraviolet light for 90 hours (about 4 days). Next, as a control, the test was repeated without oxygen gas supply, that is, the tub molecular pump described above was operated to maintain the same environment (0.001 mTorr), and the results were compared.

The results showed that no degradation of the transmittance of the light transmission window 8 due to carbon accumulation was observed when oxygen gas was charged during lamp operation. On the other hand, in the control, when the original light transmittance was 100%, the transmittance over the course of the test was lowered to 35% by the accumulation of carbon on the light transmission window 8.

Figure 1 shows that the carbon observed in the control experiments adhered and accumulated in the form of a film. When the lamp operates with a flow of oxygen gas, the carbon 15 shown in FIG. 1 does not adhere to the light transmitting window 8.

After the use of the oxygen gas, when the light transmission window 8 was observed under an optical microscope, no adhesion was found on the use of the oxygen gas supply, but in the control sample, the center Φ8 mm range through which the vacuum ultraviolet light was transmitted. Attached in the form of a film over. It was possible to strip the attached material scraped off with plastic tweezers along the outer surface 11 and found that the material was a film-like material that adhered to the outer surface 11 with weak adhesion.

Next, a basic analysis was performed on the adhesive material. Basic analysis was performed using EPMA (Electronic Probe X-Ray Micro Analyzer; JXA-8200 manufactured by Nippon Denshi) and measuring under analytical conditions of acceleration voltage of 15 kV and irradiation current (5E-8A); Qualitative analysis, line analysis and mapping analysis were performed on the outer surface 11 of the light transmission window 8 for the control sample. The result indicates that a significant amount of carbon has been detected in the region of 8 mm center of the outer surface 11 of the light transmission window through which ultraviolet light is transmitted. Since the ring-shaped region outside the central Φ8 mm region is in the shadow portion of the flange 17, there is an region where ultraviolet light is not transmitted. In this region, pollution level carbon was analyzed by EPMA, but there was no significant carbon adhesion. 'Pollution level' in EPMA analysis means a weak signal level for carbon, such as that obtained when analyzing a completely clean surface. The action of radiating a clean surface using an electron beam can result in the deposition of carbon and the signal level is based on the adhesion of this carbon. Thus, the contamination level of the analyzer itself determines the lower limit of measurement for EPMA analysis. The signal level from the center Φ8 mm range through which ultraviolet light is transmitted is significantly higher compared to the signal level for contamination, and this result confirms that carbon has accumulated in film form on the outer surface 11 of the light transmitting window.

7 shows the results of the line analysis of the control experiment using EPMA. The unit of the abscissa in FIG. 7 is the millimeter, which shows the analysis position with respect to the diameter of the MgF ₂ crystal, and the line analysis of the crystal was performed from edge to edge.

The vertical axis represents the intensity of the carbon signal detected in the spectral production crystal LDE2. Main analysis conditions are shown outside of the graph of FIG. 7.

From Fig. 7, it can be seen that there is a very high signal intensity from carbon in the Φ 8 mm region through which ultraviolet light is transmitted, which clearly indicates that there is a film form adhesion in the central Φ 8 mm region.

On the other hand, after the lamp was operated under the flow of oxygen, no significant carbon signal was detected from the surface of the light transmission window above the contamination level.

As described above, by operating the lamp in a state where oxygen gas was supplied, it was possible to prevent or suppress the accumulation of carbon on the light transmitting window 8.

By implementing such a countermeasure, it is possible to suppress the decrease in the transmittance of the light transmitting window, thereby reducing the cost of the maintenance operation of replacing the window as well as reducing the downtime for the lamp.

Although this embodiment irradiates a light transmission window as an example, this embodiment can be similarly applied to an apparatus using a light reflection mirror (window). Examples of such light reflecting mirrors are reflecting mirrors used in laser oscillators and lamp focusing mirrors. Further, the embodiments to be described later can be equally applied to the case of the light reflection mirrors.

Example 2

Fig. 2 is a diagram showing a microwave excited hydrogen ultraviolet lamp used to describe Example 2 of the first preferred embodiment according to the present invention. Further description of the configuration and operation of the same device as in Embodiment 1 is omitted. The specification of the light transmitting window 8 was the same as that described in Example 1. In addition, the photodiode 12 is positioned to receive the light output 9 of the lamp emission light as a means for monitoring the amount of light output from the lamp.

Water vapor is supplied to the vacuum region 14 using the following method, and adjusted to a specific gas partial pressure. A glass tube 24 (tube diameter Φ 6 mm) filled with 1 mL of water (25; distilled, ion exchanged and filtered pure water) is connected to the tube 16d via the flange 17. The configuration of the flange 17 formed an O-ring to seal the glass tube from the atmospheric state, and all the atmospheric components were discharged from the tube beforehand. Water (25) was maintained at room temperature (25 ° C.) and internal vapor pressure was 24 torr (calculated value). This steam pressure is supplied to the primary steam pressure through the tube 16d, and after adjusting the diameter of the variable leak valve 19, the steam pressure passes through the tube 16b to the atmosphere through a sealing mechanism (not shown), and the tube ( It passes through the vacuum area 14 through 16a). The feed amount was approximately 0.1 sccm. The vacuum region 14 is discharged by a turbomolecular pump (model TP-50 manufactured by Mitsubishi Heavy Industries, Ltd., discharge rate of 50 L / min; not shown in the figure) and downstream of the dry pump (not shown). Was connected. In this case, the steam partial pressure inside the vacuum region was maintained at 0.1 mTorr. Therefore, this condition was such that the partial pressure of the oxygen gas inside the vacuum region 14 was about 1 mTorr or more (and 10 mTorr or less).

In addition, experiments were performed using 1 mTorr and 0.01 mTorr, which was achieved by adjusting the valve opening, but as described below, the same effect was obtained on carbon removal.

Next, using the photodiode 12, the amount of change over time of the amount of light output from the above-mentioned microwave excited hydrogen ultraviolet lamp was measured.

First, hydrogen atoms were excited by the discharge plasma 7 to generate vacuum ultraviolet light for 90 hours (about 4 days). Next, the lamp was operated without supplying water vapor, that is, the experiment was conducted to maintain a pressure environment of 0.001 mTorr using the turbomolecular pump described above, and then the two test results were compared.

The results showed that no degradation of the transmittance of the light transmission window 8 due to carbon accumulation was observed when the lamp was operated in the water vapor supply state. On the other hand, in the control experiment, when the initial level of the light transmittance was 100%, the transmittance decreased to 35% over the measurement period due to the deposition of carbon.

The carbon 15 shown in FIG. 2 shows the film-like adhesion of the carbon observed in the control measurement, but when water vapor is supplied during lamp operation, as shown in FIG. ) Was not attached.

After the steam was used, when the outer surface 11 of the light transmission window 8 was observed using an optical microscope, no adhesion was observed for the window used while steam was supplied to the lamp, but for the control window, There was a material attached in the form of a film in the center Φ8mm region through which the vacuum ultraviolet light is transmitted. When scraping the outer surface 11 using plastic tweezers, it was found that it was possible to scrape the attachment material, indicating that a weak adhesive film-like substance was attached to the outer surface 11.

Thereafter, basic analysis was performed on the adhesive material. The results of the basic analysis by EPMA were the same as described in Example 1.

As described above, when the lamp was operated with the supply of water vapor, it was confirmed that the adhesion of carbon on the light transmission window was prevented or suppressed.

By implementing such a countermeasure, it is possible to suppress the decrease in the transmittance of the light transmitting window, thereby reducing the cost of the maintenance operation of replacing the window as well as reducing the downtime for the lamp.

Example 3

Fig. 3 is a diagram showing a microwave excited hydrogen ultraviolet lamp used to describe Example 3 of the first preferred embodiment according to the present invention. Further description of the configuration and operation of the same device as in Embodiment 1 is omitted. The specification of the light transmitting window 8 was the same as that described in Example 1. In addition, the photodiode 12 is positioned to receive the light output 9 of the lamp emission light as a means for monitoring the amount of light output from the lamp.

Atmospheric components were supplied to the vacuum region 14 using the method described below, and they were adjusted to a specific gas partial pressure.

After adjusting the aperture with the variable leak valve 19, the atmospheric component is moved through the tube 16b, passed through a sealing mechanism (not shown), and then introduced into the vacuum region 14 through the tube 16a. Atmospheric components are supplied to the vacuum region 14 by the opening of the tube. The feed amount was approximately 1 sccm. The vacuum region 14 is discharged by a turbomolecular pump (model TP-50 manufactured by Mitsubishi Heavy Industries, Ltd., discharge rate of 50 L / min; not shown in the figure) and downstream of the dry pump (not shown). Was connected. In this case, the atmospheric component inside the vacuum region was maintained at 1 mTorr. Therefore, this condition was such that the partial pressure of the atmospheric components inside the vacuum region 14 was about 1 mTorr or more (having 0.2 mTorr of oxygen alone).

In addition, although valve calibration was performed to produce a partial pressure of 0.1 mTorr (having 0.02 mTorr on oxygen alone), the effect on carbon removal was the same, as described below.

Next, using the photodiode 12, the amount of change over time of the light output during the operation of the microwave excited hydrogen ultraviolet lamp having the above-described configuration was measured.

First, hydrogen atoms were excited by the discharge plasma 7 to generate vacuum ultraviolet light for 90 hours (about 4 days). Next, as a control test, air components were not supplied during operation, and a pressure environment of 0.001 mTorr was formed using the turbomolecular pump described above, and then the two test results were compared.

When the lamp was operated with the supply of atmospheric components, no deterioration in the transmittance of the light transmission window 8 due to carbon accumulation was observed. On the other hand, in the control test, the accumulated carbon reduced the light transmittance through the light transmission window 8 from the initial value of 100% to 35% transmittance.

Although the carbon 15 shown in FIG. 3 reflects the film form adhesion of the carbon observed in the control test, when the atmospheric component is supplied during the lamp operation, the light transmission window 8 shown in FIG. There was no attachment.

After the atmospheric component is used, when the outer surface 11 of the light transmission window 8 is observed using an optical microscope, no adhesion is observed for the used window while the atmospheric component is supplied to the lamp, As for the substance, a substance adhered in the form of a film was present in the central? 8 mm region through which the vacuum ultraviolet light was transmitted. When scraping the outer surface 11 using plastic tweezers, it was found that it was possible to scrape the attachment material, indicating that a weak adhesive film-like substance was attached to the outer surface 11.

Thereafter, basic analysis was performed on the adhesive material. The results of the basic analysis by EPMA were the same as described in Example 1.

As described above, it was confirmed that the adhesion of carbon on the light transmission window was prevented or suppressed when the lamp operated with the supply of the atmospheric component.

By implementing such a countermeasure, it is possible to suppress the decrease in the transmittance of the light transmitting window, thereby reducing the cost of the maintenance operation of replacing the window as well as reducing the downtime for the lamp.

Example 4

Fig. 4 is a view showing a microwave excited hydrogen ultraviolet ray lamp used to describe the fourth embodiment of the first preferred embodiment according to the present invention, wherein the output light is used in the optical system disposed in the vacuum region 14. The method for removing the carbon to be attached will be described. Further description of the configuration and operation of the same device as in Embodiment 1 is omitted. The specification of the light transmitting window 8 was the same as that described in Example 1.

The optical element 27 of FIG. 4 is positioned to be irradiated by the lamp emitting light 9. Carbon 15 was already attached to both sides of the optical element 27 and was generated by irradiation of the optical elements 27 by the vacuum ultraviolet light 9 while the organic gas was provided in the vacuum region 14. Since the carbon 15 was attached, the light transmittance of the optical element 27 deteriorated, and a maintenance operation was required. The reason why the optical element 27 has reached this state is because the lamp was operated in a vacuum state.

Here, an interference filter for vacuum ultraviolet light is used as an embodiment of the optical element 27 used to explain carbon removal. The interference filter for vacuum ultraviolet light consists of an MgF ₂ substrate having a coating of a multilayer protective film on its surface. This configuration is a conventional configuration of an optical component such as an interference filter. This interference filter functions as a bandpass filter because it only passes light in a specific wavelength band, and when carbon 15 adheres to its surface, the transmittance for the interference filter is reduced and thus its function as an optical element deteriorates. do. Thus, at some stage of reduced transmission, it is necessary to remove carbon or replace the interference filter. In general, due to the sensitive nature of optical filters, such as interference filters with optical film coatings, it is very difficult to clean them. Cleaning can change the properties of the optical film and is easy to introduce any defects such as scratches during cleaning. Thus, in essence, no effective cleaning method is available and only the choice of replacing parts is required. However, in general, the cost of the interference filter is a problem because it is an expensive component. In Example 4, in order to prove the effect of the present invention, the lamp was operated without gas supply until the transmittance of the interference level was reduced to 50% (from the original value of 100%) so that the transmittance was strongly reduced in half, then An optical element 27 is located in the vacuum region 14.

The method of Example 1 was used to introduce oxygen gas into the vacuum region 14 under the condition that the partial pressure of the oxygen gas in the vacuum region 14 was maintained at 1 mtorr. In addition, although experiments were performed with the valve aperture adjusted to deliver 10 mTorr, 5 mTorr, 2 mTorr, 0.1 mTorr and 0.05 mTorr, the same effect was obtained for carbon removal as described below.

Next, hydrogen atoms were excited using the discharge plasma to generate vacuum ultraviolet light for 90 hours (about 4 days). When oxygen gas was supplied during the lamp operation, the adhesion of carbon 15 was removed from the surface of the optical element 27, and the transmittance of the optical element 27 was returned to its original state. When the surface of the optical element was observed under an optical microscope, no adhesion could be seen.

As described above, the carbon adhering to the optical element 27 could be removed by operating under the supply of oxygen gas.

By this method, it is possible to prevent the reduction in the light transmittance of the optical element and thus to reduce the maintenance costs associated with the optical element replacement, and the downtime of the lamp due to the maintenance.

Example 5

FIG. 5 shows a microwave excited hydrogen ultraviolet lamp used to describe Example 5 of the first preferred embodiment according to the present invention, wherein the lamp is attached to an optical system disposed in the vacuum region 14. It explains how to remove carbon. Further description of the configuration and operation of the same device as in Embodiment 1 is omitted. The specification of the light transmitting window 8 was the same as that described in Example 1.

In FIG. 5, the optical element 27 is positioned to receive the light emitted by the lamp 9.

Since the optical element is the same as that used in Example 4, its further description is omitted.

In Example 5, in order to prove the effect of the present invention, the lamp was operated without gas supply until the transmittance of the interference level was reduced to 50% (from the original value of 100%) so that the transmittance was strongly reduced in half, then An optical element 27 is located in the vacuum region 14.

The method of Example 2 was used to supply steam to the vacuum region 14 under the condition that the partial pressure of the steam in the vacuum region 14 was maintained at 1 mtorr. In addition, although experiments were conducted in which the valve aperture was adjusted to deliver 5 mTorr, 2 mTorr, 0.01 mTorr, and 0.005 mTorr of steam partial pressure, the same effect was obtained for carbon removal as will be described later.

Next, hydrogen atoms were excited using the discharge plasma to generate vacuum ultraviolet light for 90 hours (about 4 days). When water vapor was supplied during lamp operation, the adhesion of carbon 15 was removed from the surface of the optical element 27, and the transmittance of the optical element 27 was returned to its original state. When the surface of the optical element was observed under an optical microscope, no adhesion could be seen.

As described above, the carbon 15 adhering to the optical element 27 could be removed by operating under the supply of water vapor.

By this method, it is possible to prevent the reduction in the light transmittance of the optical element and thus to reduce the maintenance costs associated with the optical element replacement, and the downtime of the lamp due to the maintenance.

Example 6

Fig. 6 is a view showing a microwave excited hydrogen ultraviolet lamp used to describe Example 6 of the first preferred embodiment according to the present invention, wherein an optical element (located in the vacuum region 14 using lamp light emission) 27) A method of removing the carbon 15 adhering to it will be described. Further description of the configuration and operation of the same device as in Embodiment 1 is omitted. The specification of the light transmitting window 8 was the same as that described in Example 1.

In FIG. 6, the optical element 27 is positioned to receive the light emitted by the lamp 9. Since the optical element is the same as that used in Example 4, its further description is omitted.

In Example 6, in order to prove the effect of the present invention, the lamp was operated without gas supply until the transmission of the interference level was reduced to 50% (from the original value of 100%) so that the transmission was strongly reduced in half, then An optical element 27 is located in the vacuum region 14.

The method of Example 3 was used to supply the atmospheric component to the vacuum region 14 under the condition that the partial pressure of the atmospheric component in the vacuum region 14 was maintained at 1 mtorr.

In addition, although experiments were performed with the valve aperture adjusted to deliver atmospheric partial pressures of 2 mTorr and 0.1 mTorr, the same effect was obtained for carbon removal as will be described later.

Next, hydrogen atoms were excited using the discharge plasma to generate vacuum ultraviolet light for 90 hours (about 4 days). When the atmospheric component was supplied during the lamp operation, the adhesion of the carbon 15 was removed from the surface of the optical element 27, and the transmittance of the optical element 27 was returned to its original state. When the surface of the optical element was observed under an optical microscope, no adhesion could be seen.

As described above, by operating under the supply of atmospheric components, the carbon 15 adhering to the optical element 27 could be removed. By this method, it is possible to prevent the reduction in the light transmittance of the optical element and thus to reduce the maintenance costs associated with the optical element replacement, and the downtime of the lamp due to the maintenance.

[Preferred Second Embodiment]

Hereinafter, a second preferred embodiment of the present invention will be described, wherein the protective film is coated on the light transmitting window for the purpose of preventing or suppressing deterioration of the window. However, the present invention is not limited to this configuration, and if applicable, it can of course also be applied to lamps which emit light emitted by an electric discharge, heating or laser device.

FIG. 8 shows a diagram of a microwave excited hydrogen ultraviolet lamp and is used to describe Embodiments 1 and 3 of the present invention. The flange 17 to the light transmitting window 8 is disc shaped and includes an opening whose center is aligned with the hole line of the discharge tube 1 and which has a diameter larger than the inner diameter of the discharge tube. The window flange 17 includes an O-ring groove 13b as a means for sealing the light transmitting window 8 through the above-described opening, and a hollow lead-type jig 20 including an attachment bolt hole and an O-ring groove 13a. ) Is used to attach the discharge tube 1 and also allows the flange 17 to maintain a vacuum.

The inner surface configuration of the jig 20 is composed of a two-stage concentric hollow cylinder surrounding a space housing the light transmitting window 8 and the discharge tube 1. On the end surface of the side which surrounds the discharge tube 1, there exists the O-ring 13c provided in the surface cut diagonally corresponding to the ring diameter. In addition, a thread (not shown) is cut to the outer circumferential surface of the end thereof, so that the cylindrical opening end cap 21 can be installed, which opens the O-ring 13c properly and discharges the tube 1. Limit the vacuum boundary. The window flange 17, the jig 20 and the cap 21 are all made of metal and generally stainless steel or aluminum is used which is free of significant contamination, but the material is not limited to these metals.

The operation of the microwave excited hydrogen ultraviolet lamp having the above-described configuration will be described below. First, hydrogen gas diluted with 1/100 helium gas is supplied to the discharge tube 1 through a discharge gas supply port 2 at a flow rate of 20 sccm. The discharge gas is discharged through the discharge gas discharge port 3 by the vacuum pump (not shown), and the discharge tube 1 is adjusted by adjusting the diameter of the valve (not shown) provided between the discharge gas discharge port 3 and the vacuum pump. The emission conductance is controlled to maintain the interior at about 5 Torr (665 Pa). The reason why the discharge gas flows in the direction from the light transmitting window side 8 toward the discharge tube 1 is to discharge the plasma 7 in a direction away from the light transmitting window 8 so as to reduce the pollution source to the window 8. This is because any material generated inside the discharge tube 1 can be exhausted.

The microwave oscillator tuner 18 is cylindrical in shape and enables adjustment of the microwave electromagnetic field distribution inside the microwave oscillator, the inner diameter of which is a container of the discharge tube 1. In addition, the configuration can be inserted while being axially aligned from the end surface of the microwave oscillator 4 and is capable of sliding in the axial direction while maintaining conductivity with the microwave oscillator 4. The tuner 18 is formed of copper or brass and the same material is used for the microwave oscillator 4. The function of the tuner 18 is to adjust the microwave electromagnetic field distribution, which generates a plasma 7 based on the depth at which the generation of microwaves is concentrated at its center 6.

Thereafter, 2.45 GHz, 50 W microwaves are supplied from the microwave supply connector to the microwave oscillator 4. The supply of this microwave can be continuous or intermittent. A regulator (not shown) is arranged in the middle of a power line connecting a microwave power source and a microwave oscillator. This regulator can be adjusted to control the microwave power between the power source and the load (discharge plasma) to generate the discharge plasma 7 inside the discharge tube 1. The hydrogen atoms excited by the discharge plasma 7 generate vacuum ultraviolet light beams having a wavelength of 103 nm to 122 nm, which pass through the light transmission window 8 so that the radiation lamp light 9 is transmitted to the outside.

MgF ₂ (magnesium fluoride) single crystal is used to make the light transmission window 8, the crystal axis (c axis) of which is aligned to be orthogonal to the surface of the light transmission window.

The thin film coating of Al ₂ O ₃ (alumina) was previously provided as a protective film 10A for the surface 10 of the light transmitting window 8 before being installed at the position shown in FIG. This coating was provided using an ion beam sputtering type of membrane method.

The ion beam film forming method is described below. An Ar gas environment maintained at a pressure of 0.1 Pa is used as the film forming gas, and a 3 inch sintered Al ₂ O ₃ target (purity 4N) is shocked using a 20 kV Ar ion acceleration voltage and then transmitted through the target. Al ₂ O ₃ is sputtered onto the surface of the window 8 to form a film. Film thickness control was performed by using a quartz oscillator in advance to generate a calibration curve indicating the relationship between the number of quartz crystal oscillations and the amount of change in film thickness. This changed the corresponding oscillation time to form a film with a desired thickness.

The coating method used to form the protective film 10A is not limited to the ion beam sputtering film forming method described above. Appropriate choice of methods and apparatus can form a film of the desired composition. Still other possible methods include vapor deposition methods such as deposition methods, ion plating, CVD, and the like.

The appropriate film thickness range of the protective film 10A is determined based on the surface coverage state for the optical system and the transmission required for 122 nm vacuum ultraviolet light.

FIG. 13 shows the change in the thickness of the light transmission versus protective film when Al ₂ O ₃ is provided as the light transmission window coating as compared to the initial state without coating. As shown in Fig. 13, the degree to which the transmittance of the optical system is reduced than the transmittance in the initial state becomes a function of the thickness of the protective film. In order to lower the initial deterioration, it is desirable to use the thinnest film possible. On the other hand, in order for the protective film to be effective, all surfaces of the optical system must be covered with the protective film. Typically, the thin film is formed in an island-like configuration with respect to the optical surface in a state in which a portion of the optical surface is exposed without being a uniform film configuration in the initial stage of film formation, so that an effective protective film is not achieved.

The observation of the surface using AFM (atomic force microscope) after formation of the protective film shows that it is necessary to coat the surface with a film thickness of 2 nm or more in order to form a flat and smooth thin film.

In addition, for a sufficiently thick film thickness of 20 nm or more formed for the purpose of effectively protecting the surface of the optical system, due to the high absorption rate of vacuum ultraviolet light, together with the protective film of SiO ₂ , Al ₂ O ₃ , MgO, TiO ₂ , ZrO ₂ , It is found that the properties of the optical system in which they were used have been substantially degraded and that deterioration and heating caused by absorption by the protective film itself can cause problems with stripping or another surface of the optical system. Since such absorption of vacuum ultraviolet light impairs the expected function of the optical system, the upper limit for the film thickness is set to 20 nm or more, preferably 12 nm or more, and more preferably 10 nm or more.

 In embodiments of the present invention, the thickness of the protective film was selected to be 6 nm. At this thickness for the protective film, the transmittance for the 122 nm wavelength light was 50% of the 100% transmittance allocated for the initial situation where the protective film was not used.

In addition, the photodiode 12 was positioned to receive the lamp light emission 9 as a means for monitoring the light output of the lamp.

Next, photodiode 12 was used to measure any amount of change in light output for the microwave excited hydrogen ultraviolet lamp having the above-described configuration.

First, hydrogen atoms were excited by the discharge plasma 7 so that light was generated in the vacuum ultraviolet light wavelength range for 90 hours (about 4 days). Next, as a control experiment, the light transmission window 8 was replaced with a window without a protective film and the test was repeated to compare the results.

The following evaluation method was used. The initial transmission of the light transmission window is T ₁ (T ₀ = T _{1 in the} control experiment), and after use, that is, after 90 hours, the reduced transmission amount is T ₂ , and the amount of change in the transmission amount (ΔT [%]) Is calculated as

ΔT = (T ₁ -T ₂ ) / 90 Equation (1)

In addition, a change rate is shown as deterioration rate K [% / hr], as defined by the following formula.

K = 100ΔT / T ₀ Equation (2)

By comparing the magnitude of the deterioration rate K, it is possible to quickly quantify and evaluate the deterioration of the light transmission window 8. Of course, the lower the value of K, the lower the degree of deterioration of the light transmission window, the longer the lifetime and the less frequent the replacement.

The results show that the deterioration rate K is 0.04 K [% / hr] when the protective film Al ₂ O ₃ is used for the light transmission window 8. On the other hand, the degradation rate (K) for the control experiment was 0.46 K [% / hr], which was 11 times higher than that of the coated window. Based on this evaluation, the protective film 10A on the light transmitting window 8 brings about an appropriate improvement of about 10 times in life as compared with no coating being used.

To demonstrate the effect of the protective film 10A, before and after the use in the lamp, on the light transmitting window 8 coated with Al ₂ O ₃ as the protective film 10A, and as a control experiment, before and in the lamp, and The results of XPS surface analysis on the surface of the light transmission window without the protective film will be described later.

9 shows the analysis results for the control experiment before use. The abscissa is argon time, the magnitude of which is proportional to the sputtering depth. Sputtering time 0 minutes represents the initial phase before sputtering and corresponds to the analysis of the crystal surface. In general, the information obtained for the initial state using XPS analysis reflects the degree of natural contamination of the substance detected as an absorbent component, such as carbon, oxygen, and the like. However, these are omitted from the analysis data since they are not practical. The vertical axis represents the abundance in which various components are found by XPS.

9 shows that there is a loss of fluoride for control experiments prior to use. Traces of oxygen were found on the surface but not inside the crystal. Oxygen in the contaminants naturally absorbed on the surface is due to argon sputtering which introduces this oxygen into the crystal. Therefore, with respect to the presence or absence of oxygen in the crystal, the amount of oxygen shown in FIG. 9 should be interpreted as a very small amount to be used as a reference for correction of another analysis result.

10 shows the analysis results for the control window after being used. 10 clearly shows the fluoride loss from the surface of the control sample. In addition, the presence of significant oxygen was found to be the same depth in the crystal as the fluorinated deficient layer. Thus, in a control sample after use, the layer surface shows both fluorine deficiency and oxidation. This surface condition acts as one dimension in the reduction in transmittance for 122 nm wavelength vacuum ultraviolet light.

Next, a protective film 10A of Al ₂ O ₃ was appropriately provided on the light transmission window 8 at a thickness of 5 nm, and FIG. 5 shows the analysis result before use. Since description and analysis of a graph axis are the same as FIG. 9, further description is abbreviate | omitted. Al (aluminum), which is one of the protective film components, was newly added to the drawings. FIG. 11 shows that the fluorine and magnesium simultaneous profile extends from the surface to the inside and the simultaneous profile of oxygen and aluminum extends therein in the surface layer. Thus, despite the coating of the protective film, the reason why signals from fluorine and magnesium from the surface layer are detected in the XPS analysis is that the resolution of the XPS analysis in the depth direction is several nm. Therefore, even when attempting to measure the ideal boundary distribution, the depth of resolution cannot be widened in that form, and therefore does not appear in the profile stepwise. In addition, when sputtering is not performed for about 20 minutes, the MgF ₂ crystal of the substrate remains exposed to the thickness of the protective film of 5 nm. This is due to the difference in sputtering efficiency between Al ₂ O and MgF ₂ . Focusing on this problem, one can understand the areas where the F, Mg, O and Al profiles are simultaneously.

Finally, FIG. 12 shows the analysis results after use of the light transmitting window 8 coated with Al ₂ O ₃ of about 6 nm thickness as a protective film. The description and interpretation of the graph axes are the same as for FIG. 9, and further description is omitted. 12 shows that there is a simultaneous profile of oxygen and aluminum from the surface towards the inside. In addition, the presence of oxygen in the crystal was not confirmed. This clearly shows that the intrusion of oxygen into the interior of the crystal was prevented by the protective film.

On the other hand, there is no simultaneous profile of fluorine and magnesium from the surface and towards the center. It is clearly shown that fluorine has penetrated the protective film 10A of Al ₂ O ₃ . However, due to the presence of the protective film 10A of Al ₂ O ₃ , even when fluorine is present inside the protective film, since fluorine was not completely discharged, a deficiency of fluorine occurs as in the case of the control experiment, This is easily understood by the mechanism by which oxygen intrudes as a substituent. In fact, the formation of the fluorine deficient layer and the oxide layer as described above with reference to FIG. 10 is easily explained when considering the case where there is no protective film of FIG.

As described above, by using the protective film 10A as a coating on the light transmission window 8, it is possible to suppress the generation of a fluorine deficient layer and to prevent or suppress the presence of oxygen (oxide layer) into the crystal. In addition, as compared with the case of the control experiment, the deterioration rate (K) with which the light transmission window with the protective film coating was reduced by about 10 was achieved.

In addition, when SiO ₂ coating is used as a protective film for the light transmission window 8, the deterioration rate K is 0.06% / hr. On the other hand, the deterioration rate (K) of the control experiment is 0.46% / hr. This shows that even when SiO ₂ coating is used as the protective film, the same protection level as that of about 8 times improvement in the deterioration rate (K) can be achieved.

In addition, along with Al ₂ O ₃ , metal oxides such as MgO, TiO ₂ , and ZrO ₂ , in which lossy fading occurs under ultraviolet light radiation than fluorinated compounds, may also be used as the material for the protective film.

As described above, the optical system according to the present invention, in which a protective film is formed on the top, has an inferior optical characteristic (for example, in the case of a light transmission window, may be light transmittance) compared to that provided in a precoated state without a protective film. Have However, it is not appropriate to evaluate optical systems alone, and it is important to evaluate them as an integral part of the overall optical output device as part of a system using the optical output device. In other words, it is possible to compensate for the above-described initial inferiority of the optical system in the optical output device and to match the light output to the specifications required for the system, thereby continuing the output of the optical output device and increasing its life. In addition, it is possible to achieve the object of providing an optical output device in which the frequency of maintenance and maintenance costs for the light transmitting window are substantially reduced.

In addition, the use of the present invention for light sources used in measurement applications is particularly useful. The example performs long-term monitoring of the occurrence of environmental pollution. In general, when performing this kind of measurement, the level of signal or sensitivity at the time of measurement is proportional to the square of the light output. As described above, in the prior art, the measurement sensitivity of the light source is improved by improving the output of the light source, but it is necessary to suppress the degradation of the optical system which reduces the light output and reduces the measurement sensitivity by the resultant degradation of the optical system. have. The optical system used in the present invention extends the life of the optical output device and maintains the output characteristics stably for a long time, thereby solving the above-mentioned problems and providing an optical output device that is suitably useful for long-term environmental monitoring.

Although the above-described embodiments have been used in the example of the light transmission window, it is also applicable to an apparatus using a light reflection mirror (window). Examples of such light reflecting mirrors are focusing mirrors used in lamps and reflecting mirrors used in laser oscillators. Thus, the light reflection mirror can be used in the same embodiments.

As described above, the present invention can enable, in particular, the prevention or suppression of deterioration of the optical system by accumulation of carbon which determines the lifetime of the optical elements and the above-mentioned system and reduces the transmittance, and thus, the transmission , When used in a system using optical elements or combinations of optical effects such as refraction, reflection, spectral generation, interference, or the like, for example diffraction, refraction, spectral generation, transmission, or analytical positioning optical elements The transmissive or reflective optical elements are located within the boundary of the near vacuum region where powder can cause degradation of the optical element along the optical path of the vacuum region, or another device comprising a positioning mechanism for the container, sealing material and optical element. The surface is irradiated with an exposure mechanism (stepper) and color plating used as vacuum ultraviolet light in the semiconductor industry. Cases, reduce the frequency of the maintenance operations for replacing the optical system, thereby reducing the operating cost of the various optical apparatus using the high photon energy light such as conventional ultraviolet light or vacuum ultraviolet light.

Specifically, by preventing or suppressing a decrease in the light transmittance of the optical system caused by the accumulation of carbon on the surface thereof, it is possible to prevent and suppress deterioration of the optical system, thereby replacing the optical system and maintaining it. Reduce the frequency of operation and lower operating cost.

In addition, by preventing or suppressing the accumulation of carbon on the irradiation surface and the radiation surface of the optical system along the optical path in the vacuum region, it is possible to extend the life of the downstream device and improve the reliability of the device.

In particular, according to the present invention, it may be possible to prevent or suppress the reduction of light transmittance by carbon accumulated on the light transmitting window and other optical elements, and to extend the maintenance interval required for replacing or cleaning the light transmitting window. Can improve the operating speed of the device and reduce maintenance costs.

By preventing or suppressing the accumulation of carbon on the irradiated and radiated surfaces of the optical system and optical elements used in the vacuum region where the light output device irradiates light, it is possible to extend the life of the downstream device and improve the reliability of the device. . In addition, the method of the present invention can be applied to irradiating optical elements previously deteriorated by carbon accumulation to irradiate the degraded optical elements and to restore the optical elements to their original state.

Therefore, by the use of the present invention, a maintenance cycle for cleaning or replacing the optical elements used in the above-mentioned vacuum region can be lengthened, thereby contributing to the improvement of the operating speed of the apparatus and the reduction of the maintenance cost.

As described above, the present invention can prevent or suppress deterioration of optical systems and extend the maintenance cycles in which they must be replaced, contributing to the improvement of the operating speed of the apparatus and the reduction of maintenance costs.

In addition, by coupling the operating system according to the invention to a device utilizing light, it is possible to extend the life of such a device and to ensure stable output characteristics of the device over a long period of time.

BRIEF DESCRIPTION OF THE DRAWINGS The figure which shows the structure of the microwave excited hydrogen ultraviolet lamp used for demonstrating Example 1 of 1st Embodiment which concerns on this invention.

Fig. 2 is a diagram showing the configuration of a microwave excited hydrogen ultraviolet lamp used to describe Example 2 of the first preferred embodiment according to the present invention.

Fig. 3 is a diagram showing the configuration of a microwave excited hydrogen ultraviolet lamp used to describe Example 3 of the first preferred embodiment according to the present invention.

Fig. 4 is a diagram showing the configuration of a microwave excited hydrogen ultraviolet lamp used to describe Example 4 of the first preferred embodiment according to the present invention.

Fig. 5 is a diagram showing the configuration of a microwave excited hydrogen ultraviolet lamp used to describe Example 5 of the first preferred embodiment according to the present invention.

Fig. 6 is a diagram showing the configuration of a microwave excited hydrogen ultraviolet lamp used to describe Example 6 of the first preferred embodiment according to the present invention.

7 is an EPMA analysis of carbon adhesion to the light transmission window according to the first preferred embodiment of the present invention.

Fig. 8 is a diagram showing the configuration of a microwave excited hydrogen ultraviolet lamp used to describe a second preferred embodiment according to the present invention.

9 is a graph showing XPS depth distribution measurements for light transmission windows before use, without a protective coating.

FIG. 10 is a graph showing XPS depth distribution measurements for post-use light transmission windows without protective film coatings. FIG.

FIG. 11 is a graph showing XPS depth distribution measurements for light transmission windows before use, with a protective coating. FIG.

12 is a graph showing XPS depth distribution measurements for post-use light transmission windows with a protective coating.

Fig. 13 is a graph showing the relationship between the various thicknesses of the protective film and the light transmittance of the optical system in the initial state.

14 shows a conventional microwave excited hydrogen ultraviolet lamp according to the prior art.

* Description of the symbols for the main parts of the drawings *

1: discharge tube

2: discharge gas supply port

3: discharge gas outlet

4: microwave oscillator

5: microwave supply connector

6: microwave center

7: discharge plasma

8: light transmission window

9: vacuum ultraviolet light

10: inner surface

11: outer surface

12: photodiode

Claims (23)

An optical characteristic recovery apparatus for improving reliability and lifespan of optical characteristics of an optical system by preventing, suppressing or improving deterioration of optical characteristics of an optical system disposed along an optical path of the output light or the output light, The optical system is provided in the near vacuum region where organic components can be resolved, The deterioration is caused by carbon deposited or accumulated on the light emitting surface, the light reflecting surface, the light emitting surface (hereinafter collectively referred to as "lighting surface") of the optical system, The surface is opposite the vacuum region, The optical characteristic recovery device, Means for forming the near vacuum region opposite the lighting surface of the optical system in the presence of active energy that excites oxidation of carbon; Means for generating anions or radicals in the near vacuum region; And Means for facilitating an oxidation reaction between the anion or radicals and the carbon in the near vacuum region, And the optical property recovery device removes or reduces accumulated carbon deposited on the lighting surface by the oxidation reaction. An optical characteristic recovery apparatus for improving reliability and lifespan of optical characteristics of an optical system by preventing, suppressing or improving deterioration of optical characteristics of an optical system disposed along an optical path of the output light or the output light, The optical system is provided in the near vacuum region where organic components can be resolved, The deterioration is caused by carbon deposited or accumulated on the light emitting surface, the light reflecting surface, the light emitting surface (hereinafter collectively referred to as "lighting surface") of the optical system, The surface is opposite the vacuum region, The optical characteristic recovery device, Means for forming said near vacuum region opposite said lighting surface of said optical system to excite oxidation of carbon; Means for generating a flow of an oxygen atom containing gas such as water gas or oxidizing gas in the near vacuum region; And Means for supplying active energy to the near vacuum region to generate a carbon oxidation reaction between the oxygen atom containing gas and carbon, And the optical property recovery device removes or reduces accumulated carbon deposited on the lighting surface by the oxidation reaction. A method for recovering optical characteristics, which improves reliability and lifetime of optical characteristics of an optical system by preventing, suppressing or improving deterioration of optical characteristics of an optical system disposed along an optical path of the output light or the output light. The optical system is provided in the near vacuum region where organic components can be resolved, The deterioration is caused by carbon deposited or accumulated on the light emitting surface, the light reflecting surface, the light emitting surface (hereinafter collectively referred to as "lighting surface") of the optical system, The surface is opposite the vacuum region, The recovery method of the optical characteristics, Forming the near vacuum region opposite the lighting surface of the optical system in the presence of active energy that excites oxidation of carbon; Generating anions or radicals in the near vacuum region; And Reacting anion or radicals with the deposited carbon to remove or reduce accumulated carbon deposited on the lighting surface. A method for recovering optical characteristics, which improves reliability and lifetime of optical characteristics of an optical system by preventing, suppressing or improving deterioration of optical characteristics of an optical system disposed along an optical path of the output light or the output light. The optical system is provided in the near vacuum region where organic components can be resolved, The deterioration is caused by carbon deposited or accumulated on the light emitting surface, the light reflecting surface, the light emitting surface (hereinafter collectively referred to as "lighting surface") of the optical system, The surface is opposite the vacuum region, The recovery method of the optical characteristics, Forming the near vacuum region to excite an oxidation reaction of carbon, wherein high active energy excitation is present, the near vacuum region facing the lighting surface of the optical system; And Supplying active energy while supplying a flow of an oxygen atom-containing gas such as water gas or oxidizing gas to the near vacuum region, thereby exciting the oxidation reaction of carbon accumulated with the supplied active energy to thereby light up the lighting surface. Removing or reducing the accumulated carbon deposited on the phase. The method of claim 3, wherein The anion or radicals are unstable chemical seeds containing oxygen atoms such as OH radicals, OH ^- ions, ozone, O ₂ ^_ ions, O radicals. The method of claim 4, wherein And the oxygen atom-containing gas is water vapor, oxygen, hydrogen peroxide, ozone, or a mixture of the gas and an inert gas (including air). The method according to claim 3 or 4, The optical system includes diffraction, refraction, spectral generation, transmission and diffraction control optics, and radiated light, located along the optical path within the vacuum region, as well as optical elements comprising light transmission or reflecting members positioned at the boundary of the near vacuum region. An optical component comprising an optical article to be surface treated by And the optical system further comprises a position adjusting portion, a holding mechanism, a container and a sealing portion of the optical element or the optical product. The method according to claim 3 or 4, The beam forming the optical path is ordinary ultraviolet light having a wavelength of 380 nm or less or vacuum ultraviolet light having a wavelength of 200 nm or less, The optical system for outputting the ultraviolet light or disposed along the optical path of the output light may be a fluorine compound such as magnesium fluoride, calcium fluoride, barium fluoride, aluminum fluoride, cryolite, thiolite, or A method of restoring optical properties, which is an optical material comprising one or combinations of other fluorine compounds, lanthanum fluoride, cadmium fluoride, neodymium fluoride, yttrium fluoride, or high purity oxides such as synthetic quartz glass or sapphire . The method of claim 4, wherein The lower limit for the partial pressure of the oxygen atom-containing gas supplied to the near vacuum region is carbon when carbon from decomposition of organic components in the near vacuum region has already been grown on the surface and the opposing surface of the optical system. A method for recovering optical characteristics, which is set at a level higher than the speed of accumulation. The method of claim 4, wherein An upper limit value for the partial pressure of the oxygen atom-containing gas supplied to the near vacuum region is that the optical characteristic of the optical system is restored when the vacuum ultraviolet light is emitted to or emitted from the optical system. And the absorption of vacuum ultraviolet light by the oxygen atom-containing gas is set below a level that cannot be neglected to perform its function inside the near vacuum region. The method of claim 10, The upper limit value for the partial pressure of the oxygen atom-containing gas is determined by substantially filling the near vacuum region with a partial pressure of the oxygen atom-containing gas, and then measuring the magnitude of the vacuum ultraviolet light on the optical path to examine the attenuation level. A recovery method of optical characteristics is set. The method according to claim 3 or 4, And a beam forming the optical path is a specific wavelength beam in a vacuum ultraviolet light wavelength range. The method according to claim 3 or 4, And the beam forming the optical path is vacuum ultraviolet light having high photon energy. The method of claim 4, wherein The oxygen atom-containing gas is oxygen gas, The range between the lower limit and the upper limit for the oxygen gas partial pressure is set at a level of 0.02 mtorr to 20 mtorr. The method of claim 4, wherein The oxygen atom-containing gas is water vapor, A method for recovering optical characteristics, wherein a range between a lower limit and an upper limit for steam partial pressure is set at a level of 0.005 mtorr to 20 mtorr. An optical system comprising a fluorine compound provided to an environment exposed by vacuum ultraviolet light or plasma light having photon energy higher than the absorption wavelength of the base material of the optical system, A protective film of SiO ₂ or metal oxide having a film thickness of 2 nm to 20 nm is formed at least on the light emitting surface (inner surface) of the optical system to prevent stripping of fluorine atoms from the surface of the optical system. system. An optical system comprising a fluorine compound provided to an environment exposed by vacuum ultraviolet light or plasma light having photon energy higher than the absorption wavelength of the base material of the optical system, A protective film of SiO ₂ or metal oxide having a film thickness of 2 nm to 20 nm is formed at least on the light emitting surface (inner surface) of the optical system to prevent oxidation from the surface of the optical system. An optical system comprising a fluorine compound having a surface opposite and exposed to a plasma generated in an optical device having an internal region in which the plasma is present, 2 nm to 20 nm protective film of high plasma resistant material is formed on the surface of the fluorine compound exposed to the plasma. The method according to any one of claims 16 to 18, The optical system consists of a single crystal fluorinated material having a crystal axis (c-axis) along the light emission direction, And the vertical surface of the protective film is coated with SiO ₂ or metal oxide. The method according to any one of claims 16 to 19, The protective film of the metal oxide is selected from one of Al ₂ O ₃ , MgO, TiO ₂ or ZrO ₂ , optical system. The method according to any one of claims 16 to 20, The protective film is formed by an ion beam sputtering method or plasma CVD. Providing a protective film of a metal oxide of 2 nm to 20 nm selected from SiO ₂ , or Al ₂ O ₃ , MgO, TiO ₂ , ZrO ₂ to the optical system, wherein the protective film is formed by radiation of vacuum ultraviolet light or Inhibiting oxidation of the surface of the substrate or strip-off of components from the surface of the substrate by plasma exposure to the substrate; And Coupling the optical system to a desired device having a plasma light source or vacuum ultraviolet light source having a photon energy higher than the absorption wavelength of the base material of the optical system. The method of claim 22, The light source provides a suitable light output to compensate for internal degradation of the optical system by the protective film, And the optical system is provided on an optical path of the light source to suppress deterioration of optical characteristics after the initial deterioration of the apparatus.