JP2007173344A - Cleaning method and apparatus, exposure apparatus, and device manufacturing method - Google Patents

Abstract

An object of the present invention is to provide a cleaning method and apparatus capable of effectively removing organic contamination that cannot be removed by optical cleaning without oxidizing the surface and in a short time.
A cleaning method for cleaning an object to be cleaned, the step of maintaining a processing chamber containing the object to be cleaned in a reduced pressure or vacuum environment, a step of supplying a gas containing hydrogen to the processing chamber, And a step of converting the gas into plasma, and subjecting the object to be cleaned to surface treatment with the plasmad gas.
[Selection] Figure 2

Description

  The present invention generally relates to a cleaning method and apparatus, and more particularly, to optical elements such as lenses and mirrors used in an exposure apparatus that exposes a single crystal substrate for a semiconductor wafer, a glass substrate for a liquid crystal display (LCD), and the like. The present invention relates to a cleaning method and apparatus. The present invention is suitable for cleaning, for example, a lens used in the ultraviolet wavelength region and an optical element in which an antireflection film or an increased reflection film is applied to the lens.

  With the recent miniaturization and higher performance of electronic devices, the miniaturization of semiconductor devices used in such electronic devices has become increasingly intense. For this reason, higher resolution is required for an exposure apparatus for manufacturing such a semiconductor device.

  In order to obtain higher resolution, in recent years, it has been proposed to use an excimer laser that can emit light having a shorter wavelength than a mercury lamp as a light source. However, light absorption, scattering, and interference are more conspicuous with shorter wavelength light, and the influence of contaminants such as organic substances attached to optical elements such as lenses and mirrors as the wavelength of light from the light source becomes shorter. Is becoming increasingly difficult to ignore. The contaminant causes absorption, scattering, and / or interference of exposure light, a decrease in optical characteristics (transmission, reflection, spectral characteristics, etc.) of the optical element, and a decrease in laser durability of the optical element. As a result, the resolution and throughput are reduced, the optical element is damaged (destroyed), and the performance is reduced. For this reason, it has been proposed to use the optical element after it has been washed.

  Conventionally, cleaning of optical elements has been mainly performed by ultrasonic cleaning using a neutral or alkaline detergent, an organic solvent, or the like as a cleaning liquid, and also wet cleaning combined with acid cleaning. These cleanings remove the contamination of inorganic substances such as abrasive grains adhering to polishing optical elements such as lenses and organic substances such as wax used as a protective film by applying ultrasonic vibration to the cleaning liquid. It is.

  Recently, UV / ozone using ultraviolet light, ozone and active oxygen to remove light organic matter adhering during the drying process in wet cleaning and organic contamination adhering during storage from cleaning to film formation. Dry cleaning such as cleaning is used in combination with wet cleaning. In addition, wet cleaning of an optical element on which an antireflection film, an increased reflection film, or the like is formed may adversely affect optical characteristics. On the other hand, dry cleaning has been found to be very effective for optical elements on which an antireflection film, an enhanced reflection film or the like is formed. Some of these techniques have been conventionally proposed (for example, see Patent Documents 1 to 3).

  However, even if optical cleaning such as UV / ozone cleaning is performed on the optical element, there is organic contamination that cannot be easily removed in a short time. Such organic contamination causes a significant optical absorption loss, particularly in the wavelength region of the light source of the exposure apparatus with a shorter wavelength, and reduces the transmittance and laser durability of the optical element.

Accordingly, a method and apparatus for cleaning an optical element using a plasma gas containing active oxygen has been proposed (see, for example, Patent Document 4). Such a cleaning method and apparatus can effectively remove organic contamination that cannot be efficiently removed by optical cleaning or that requires a long time for cleaning (that is, the temperature of the optical element is increased). Can be removed in time.
Japanese Patent Laid-Open No. 2000-66003 JP-A-11-169806 Japanese Patent Laid-Open No. 11-221536 JP 2003-119054 A

Cleaning with a plasma gas containing active oxygen can perform cleaning without adverse effects on an optical glass lens made of oxide or an optical thin film made of oxide. However, for lenses made of fluoride materials represented by calcium fluoride (CaF2) used in the wavelength region of 157 nm F ₂ laser and optical thin films made of fluoride materials, surface oxidation There is concern about optical absorption loss.

  Accordingly, an object of the present invention is to provide a cleaning method and apparatus capable of effectively removing organic contamination that cannot be removed by light cleaning without oxidizing the surface and in a short time.

  In order to achieve the above object, a cleaning method according to one aspect of the present invention is a cleaning method for cleaning an object to be cleaned, the step of maintaining a processing chamber for storing the object to be cleaned in a reduced pressure or vacuum environment; And supplying a gas containing hydrogen to the processing chamber and converting the gas into plasma, and subjecting the object to be cleaned to surface treatment with the plasmad gas.

  A cleaning apparatus according to another aspect of the present invention is a cleaning apparatus for cleaning an object to be cleaned, a processing chamber for storing the object to be cleaned, an exhaust unit for maintaining the processing chamber in a reduced pressure or vacuum environment, A gas supply unit configured to supply a gas containing hydrogen to the processing chamber; and a plasma generating unit configured to convert the gas into plasma, and the object to be cleaned is surface-treated with the gas converted into plasma. And

  An optical element according to still another aspect of the present invention is characterized by being cleaned using the above-described cleaning method.

  An optical element according to still another aspect of the present invention is characterized in that the optical element is cleaned by being surface-treated with a plasma-containing gas containing hydrogen.

  An optical system as still another aspect of the present invention includes one or a plurality of the optical elements described above.

  An exposure apparatus according to still another aspect of the present invention is characterized in that the object to be processed is irradiated with light having a wavelength of 250 nm or less via the optical system described above to expose the object to be processed.

  According to still another aspect of the present invention, there is provided a device manufacturing method comprising: exposing a target object using the above-described exposure apparatus; and developing the exposed target object.

  Further objects and other features of the present invention will become apparent from the preferred embodiments described below with reference to the accompanying drawings.

  ADVANTAGE OF THE INVENTION According to this invention, the cleaning method and apparatus which can remove organic substance contamination which cannot be removed by optical washing without removing the surface effectively and in a short time can be provided.

  First, organic matter contamination to be removed by the cleaning method and apparatus of the present invention will be described. In the ultraviolet wavelength region of 250 nm or less, various organic substances that cause large optical absorption loss can be considered, but the problem as a pollutant is that the molecular weight of a plasticizer or the like is large and the vapor pressure is low, so-called low volatility. Organic matter. These sources include plastics, vinyl materials, building materials, paints, and the like, and they are often present in a general atmosphere including in a clean room.

An organic substance having a low vapor pressure, such as a plastic material, is less likely to desorb naturally when attached to the surface of the optical element than an organic substance having a high vapor pressure. In order to remove such organic substances, dry cleaning such as UV / ozone cleaning or cleaning with plasma gas containing active oxygen is required. In such dry cleaning, ozone or active oxygen is generated by UV light or plasma, organic substances attached to the optical element are burned by an oxidation reaction, and decomposed and removed into carbon dioxide (CO ₂ ) or water (H ₂ O). .

However, such removal of organic substances by oxidation also oxidizes the surface of the optical element. In particular, in an optical element made of a fluoride material used in the wavelength region of the 157 nm F ₂ laser, its surface is terminated with oxygen or an oxide is generated, thereby causing optical absorption.

Therefore, the cleaning method and apparatus of the present invention decomposes an organic substance having a low vapor pressure into a substance having a high vapor pressure (methane (CH ₄ ), ethane (C ₂ H ₆ ), etc.) that is easily desorbed from the surface of the optical element. To remove. Therefore, the cleaning method and apparatus of the present invention can remove organic substances having a low vapor pressure without causing surface oxidation.

  Furthermore, the cleaning method and apparatus of the present invention effectively prevent organic contamination on the surface without damaging the lens made of calcium fluoride sensitive to damage by energetic particles and the optical thin film made of the fluoride material. Can be removed.

  Hereinafter, a cleaning method and apparatus according to an aspect of the present invention will be described with reference to the accompanying drawings. In addition, in each figure, the same reference number is attached | subjected about the same member and the overlapping description is abbreviate | omitted. Here, FIG. 1 is a schematic sectional view showing the configuration of the cleaning apparatus 1 of the present invention.

  The cleaning apparatus 1 converts hydrogen-containing gas into plasma, and surface-treats the optical member OP as an object to be cleaned with the plasmaized gas, and cleans organic substances attached to the optical member OP. In other words, the cleaning apparatus 1 is composed of a plasma processing apparatus that generates active hydrogen, and has a high-frequency power source as a plasma generating means. The optical member OP is used in a wavelength region of 250 nm or less, and in the present embodiment, the optical member OP is an optical member in which the lens L and the holder LM that holds the lens L are integrated. However, the object to be cleaned is not limited to the optical member OP, but includes an optical element such as a lens or a mirror, a holder for holding the optical element, and an optical component in which they are integrated.

  In FIG. 1, reference numeral 10 denotes a processing chamber (or container) that can be decompressed, and stores an optical member OP as an object to be cleaned. The processing chamber 10 is maintained in a reduced pressure or vacuum environment by an exhaust pump 22 via an exhaust pipe 24. The pressure in the processing chamber 10 is controlled by a pressure adjustment valve 26 such as a conductance valve. That is, the exhaust pump 12, the exhaust pipe 24, and the pressure adjustment valve 26 constitute an exhaust unit 20 that maintains the processing chamber 10 in a reduced pressure or vacuum environment.

  Reference numeral 30 denotes a holding mechanism that holds an object to be cleaned. The holding mechanism 30 installs and fixes the optical member OP in which the lens L and the holder LM are integrated at the center of the processing chamber 10. In this embodiment, the holding mechanism 30 holds the optical member OP so that both surfaces of the optical member OP are exposed. Thereby, both surfaces of the optical member OP (that is, both surfaces of the lens L) can be cleaned simultaneously. However, the present invention is not necessarily limited to cleaning two surfaces simultaneously, such as cleaning only one surface of a mirror as an object to be cleaned, or cleaning three surfaces like a prism.

  Reference numeral 42 denotes a high frequency power source. 44a and 44b are high-frequency electrodes, and 46a and 46b are perforated plates, which are arranged on the upper and lower surfaces of the optical member OP in which the lens L and the holder LM as the objects to be cleaned are integrated. The high-frequency power source 42, the high-frequency electrodes 44 a and 44 b, and the perforated plates 46 a and 46 b constitute plasma forming means 40 for generating plasma P in the processing chamber 10.

  The perforated plates 46a and 46b disposed between the high-frequency electrodes 44a and 44b and the optical member OP (lens L and holder LM) that are the objects to be cleaned have a plurality of openings, and the high-frequency electrodes 44a and 44b It functions as a partition plate that partitions the optical member OP. The porous plates 46a and 46b are electrically grounded similarly to the processing chamber 10, and the space for generating the plasma P (that is, the interval between the high frequency electrodes 44a and 44b) can be arbitrarily controlled. Moreover, the diameter and aperture ratio of the openings of the perforated plates 46a and 46b can be arbitrarily controlled.

  In the present embodiment, the interval between the high-frequency electrodes 44a and 44b and the porous plates 46a and 46b is 30 mm, the diameter of the aperture is 5 mm, and the aperture ratio is 50%. However, the parameters of the porous plates 46a and 46b are determined in consideration of the cleaning effect of the optical member OP and the presence or absence of damage. Needless to say, if the aperture diameter or aperture ratio of the porous plates 46a and 46b is too large, the optical member OP is likely to be damaged. In the case where the optical member OP is an optical glass that is not sensitive to damage, such as synthetic quartz, the perforated plates 46a and 46b are not necessarily arranged.

  Reference numeral 52 denotes a gas supply unit, which introduces gas to be converted into plasma into the processing chamber 10 through the gas supply pipes 54a and 54b. The gas supply unit 52 and the gas supply pipes 54 a and 54 b constitute a gas supply unit 50. The gas supply unit 50 may include a filter that removes particles and organic substances from the gas supplied to the processing chamber 10 and a flow rate adjusting device that adjusts the flow rate of the supplied gas.

The gas supplied by the gas supply unit 50 is hydrogen (H ₂ ) gas or a mixed gas of hydrogen gas and inert gas. The inert gas includes, for example, at least one of argon (Ar), krypton (Kr), xenon (Xe), radon (Rn), neon (Ne), helium (He), and nitrogen (N ₂ ). Note that the reaction gas (that is, hydrogen) and the discharge gas (that is, the inert gas) may be supplied from separate supply pipes.

Reference numeral 60 denotes an N ₂ gas supply pipe. The N ₂ gas supply pipe 60 supplies N ₂ gas to the processing chamber 10 and opens the processing chamber 10 to atmospheric pressure.

  Next, referring to FIG. 1 and FIG. 2, a cleaning process of the cleaning apparatus 1, that is, a cleaning method 1000 of the optical member OP using a plasma gas containing active hydrogen will be described. FIG. 2 is a flowchart for explaining a cleaning method 1000 according to one aspect of the present invention.

  First, the optical member OP (lens L and holder LM), which is an object to be cleaned, is installed and fixed in the processing chamber 10 opened to atmospheric pressure via the holding mechanism 30 (step 1010). The lens L to be cleaned is a lens after wet cleaning, or a lens on which an antireflection film or an increased reflection film is formed. The holder LM is also subjected to wet cleaning.

  Next, the processing chamber 10 is depressurized by the exhaust unit 20 until the pressure becomes about 1 Pa or less (step 1020). Of course, the processing chamber 10 and the members accommodated in the processing chamber 10 are sufficiently cleaned so as not to be contaminated by an organic substance having a high vapor pressure by reducing the pressure. Further, the exhaust pump 22 uses a dry pump or a turbo molecular pump so that the oil and fat components do not diffuse back into the processing chamber 10.

Next, a mixed gas composed of hydrogen (H ₂ ) gas and inert (Ar, Kr, Xe, Rn, Ne, He, N _2, etc.) gas is decompressed through the gas supply pipes 54a and 54b. It is supplied to the chamber 10 (step 1030). A predetermined amount of the mixed gas is supplied to the upper and lower surfaces of the optical member OP (the lens L and the holder LM), that is, the spaces where the plasma P is generated. Note that the concentration of hydrogen gas contained in the mixed gas is adjusted by the gas supply unit 52 and is preferably 5% to 20%. The concentration of hydrogen gas contained in the mixed gas may exceed 20%, but when compared with 20% or less, there is no significant difference in the cleaning effect.

  The gas type used for the inert gas is generally Ar. However, Kr or Xe is more optimal for a lens composed of a fluoride represented by calcium fluoride or an optical element provided with a fluoride optical thin film. This is because there is a concern about damage caused by energy of charged particles such as ion energy and electron temperature existing in the space where the plasma P is generated.

  The mixed gas supplied to the processing chamber 10 is exhausted by the exhaust pump 22 and the pressure is adjusted by the pressure adjusting valve 26 connected to the exhaust pipe 24, so that the processing chamber 10 has a reduced pressure atmosphere for generating the plasma P. (Step 1040). At this time, the pressure in the processing chamber 10 is preferably about 1 Pa to 100 Pa. Within this pressure range, the plasma P can be generated stably.

  Furthermore, if the pressure in the processing chamber 10 is about 1 Pa to 100 Pa, the energy of charged particles such as ion energy and electron temperature can be kept low. For example, when the pressure in the processing chamber 10 is lower than 1 Pa, the energy of the charged particles is increased, which may damage the optical member OP (lens L). Further, under such a low pressure, the density of active hydrogen species that remove organic contamination is also relatively low, and the cleaning effect is reduced. When the pressure in the processing chamber 10 exceeds 100 Pa, the high frequency discharge becomes unstable, and the optical member OP is damaged by abnormal discharge or the like.

  Next, high-frequency power is applied at a predetermined output from the high-frequency power source 42 to the high-frequency electrodes 44a and 44b via the high-frequency power feed rod (step 1050). The frequency of the high frequency power source 42 is generally 13.56 MHz, but may be a high frequency such as 100 MHz or 200 MHz. The output of the high frequency power supply 42 is about 800 W to 1500 W or less.

  The mixed gas supplied to the processing chamber 10 is excited by the high frequency power applied to the high frequency electrodes 44a and 44b, and plasma P is generated between the high frequency electrodes 44a and 44b and the perforated plates 46a and 46b (step 1060). ).

  From the generated plasma P, active hydrogen species and low energy particles diffuse through the apertures of the perforated plates 46a and 46b, and reach the upper surface and the lower surface of the lens L and the holder LM, which are the optical members OP. Thereby, the organic matter contamination adhering to the surface of the optical member OP (lens L and holder LM), the processing hole, or the like is effectively removed in a short time.

  As described above, the cleaning method 1000 can perform surface treatment of the optical member OP with a mixed gas of plasma hydrogen gas and inert gas, and can remove organic contaminants that are difficult to remove by conventional dry cleaning in a short time. .

  Note that the energy (ion energy and electron temperature) of the charged particles reaching the optical member OP is extremely low. For example, the ion energy is about 10 eV or less and the electron temperature is about 2 eV or less. Such low ion energy and low electron temperature are extremely advantageous characteristics because they do not damage the optical member OP such as optical lens glass and optical thin film to be cleaned.

  The distance between the perforated plates 46a and 46b facing the upper and lower surfaces of the optical member OP (lens L) and the optical member OP (lens L) can be arbitrarily controlled. In this embodiment, the cleaning effect is high even if the distance between the perforated plates 46a and 46b and the optical member OP (lens L) is 50 mm or more, and the optical member OP is not damaged even if it is about 20 mm. Therefore, the cleaning apparatus 1 and the cleaning method 1000 can be applied to lenses having various shapes with different thicknesses.

  The cleaning (processing) time of the optical member OP (lens L and holder LM) is within about 10 minutes, and the temperature of the optical member OP (lens L and holder LM) hardly increases during that time.

Further, before the cleaning process (that is, generation of the plasma P), only the inert gas is supplied to the space in the processing chamber 10 where the plasma P is generated, and the inert gas is used under the same conditions as the generation conditions of the plasma P described above. It is preferable to generate the plasma. Thereby, water (H ₂ O) and oxygen (O ₂ ) molecules adsorbed on the surface of the optical member OP are removed by low energy particles from the generated inert gas plasma (ie, pretreatment step). And oxidation of the surface of the optical member OP can be prevented.

After a predetermined cleaning time (plasma excitation time), the output of the high frequency power supply 42 is stopped and the plasma P is extinguished (step 1070). Thereafter, the supply of the mixed gas is stopped, and the pressure adjustment valve 26 is closed. Furthermore, by supplying the _{N 2} gas supply line 60 the _{N 2} gas into the processing chamber 10, to open the pressure of the processing chamber 10 to atmospheric pressure (step 1080). Then, the cleaned optical member OP (lens L and holder LM) is taken out of the processing chamber 10, and the cleaning process is terminated (step 1090).

  Hereinafter, with reference to FIG. 3, a cleaning apparatus 1 </ b> A that is a modification of the cleaning apparatus 1 will be described. FIG. 3 is a schematic cross-sectional view showing the configuration of the cleaning apparatus 1A of the present invention.

  The cleaning apparatus 1A converts the hydrogen-containing gas into plasma, and surface-treats the optical member OP as an object to be cleaned with the plasmaized gas, thereby cleaning the organic matter attached to the optical member OP. In other words, the cleaning apparatus 1A is composed of a plasma processing apparatus that generates active hydrogen, and has a microwave power source that uses an antenna as plasma forming means.

  In FIG. 3, 72a and 72b are microwave generators. The microwave generators 72a and 72b include, for example, a magnetron for generating a microwave, an isolator for absorbing a reflected wave of the microwave, a tuner for impedance matching with the load side, and the like.

  74a and 74b are conductor antenna units, and 76a and 76b are microwave transparent dielectric windows. Conductive antenna units 74a and 74b house microwave transmissive dielectric windows 76a and 76b. The conductor antenna units 74a and 74b have slots for guiding microwaves, such as radial line slot antennas (RLSA) and planar multi-slot antennas (PMA). The high-density surfaces of the conductor antenna units 74a and 74b are composed of antenna copper plate members that can generate plasma P.

The microwave transparent dielectric windows 76a and 76b (conductor antenna units 74a and 74b) are disposed on the upper and lower surfaces of the optical member OP in which the lens L and the holder LM, which are objects to be cleaned, are integrated. The microwave transparent dielectric windows 76a and 76b maintain the reduced pressure or vacuum environment of the processing chamber 10 and transmit microwaves. The microwave transmissive dielectric windows 76a and 76b are made of a material such as quartz (SiO ₂ ), aluminum nitride (AlN), alumina (Al ₂ O ₃ ), for example. However, when the object to be cleaned is an optical member made of fluoride, aluminum nitride not containing oxygen as a constituent element is suitable.

  The microwave generators 72 a and 72 b, the conductor antenna units 74 a and 74 b, and the microwave transmissive dielectric windows 76 a and 76 b constitute plasma forming means 70 for generating plasma P in the processing chamber 10.

  Next, with reference to FIGS. 3 and 4, a cleaning process of the cleaning apparatus 1A, that is, a cleaning method 1000A of the optical member OP using a plasma gas containing active hydrogen will be described. FIG. 4 is a flowchart for explaining a cleaning method 1000A according to one aspect of the present invention.

  The steps from the installation and fixing of the optical member OP to the processing chamber 10 (step 1010) to the adjustment of the pressure in the processing chamber 10 (step 1040) are the same as in the cleaning method 1000, and thus the description thereof is omitted.

  After the processing chamber 10 is in a reduced pressure atmosphere for generating the plasma P, microwaves are radiated at a predetermined output from the microwave generators 72a and 72b and the conductor antenna units 74a and 74b (step 1050A). The frequencies of the microwave generators 72a and 72b are 2.45 GHz, and the outputs of the microwave generators 72a and 72b are about 800 W to 1500 W.

  The emitted microwaves excite the mixed gas supplied to the processing chamber 10 through the microwave transmissive dielectric windows 76a and 76b, and high-density plasma near the surfaces of the microwave transmissive dielectric windows 76a and 76b. P is generated (step 1060).

  From the generated plasma P, active hydrogen species that effectively decompose organic substances adhering to the optical member OP are generated at a high density, and particles having extremely low energy are diffused, so that the lens L that is the optical member OP is diffused. And the upper and lower surfaces of the holder LM. Thereby, the organic matter contamination adhering to the surface of the optical member OP (lens L and holder LM) and the processing hole is effectively removed in a short time.

The plasma P generated in the cleaning apparatus 1A has an extremely high density, and the density is 10 ¹¹ cm ^{−3 to} 10 ¹³ cm ⁻³ .
Moreover, the energy (ion energy and electron temperature) of charged particles is also extremely low, for example, ion energy is 10 eV or less, and electron temperature is 2 eV or less. As described above, having the characteristics of low energy and low electron temperature while being extremely high-density plasma does not damage the optical member OP such as the optical lens glass or the optical thin film to be cleaned. This is an advantageous property.

  The distance between the microwave transparent dielectric windows 76a and 76b and the optical member OP (lens L) can be arbitrarily controlled. In the present embodiment, the cleaning effect is high even if the distance between the microwave transparent dielectric windows 76a and 76b and the optical member OP (lens L) is 50 mm or more, and the optical member OP is damaged even if the distance is about 20 mm. I did not receive it. Therefore, the cleaning apparatus 1A and the cleaning method 1000A can be applied to lenses having various shapes having different thicknesses.

  The cleaning (processing) time of the optical member OP (lens L and holder LM) is within about 10 minutes, and the temperature of the optical member OP (lens L and holder LM) hardly increases during that time.

After a predetermined cleaning time (plasma excitation time), the microwave emission is stopped and the plasma P is extinguished (step 1070). Thereafter, the supply of the mixed gas is stopped, and the pressure adjustment valve 26 is closed. Furthermore, by supplying the _{N 2} gas supply line 60 the _{N 2} gas into the processing chamber 10, to open the pressure of the processing chamber 10 to atmospheric pressure (step 1080). Then, the cleaned optical member OP (lens L and holder LM) is taken out of the processing chamber 10, and the cleaning process is terminated (step 1090).

  Hereinafter, with reference to FIG. 5, a cleaning device 1 </ b> B that is a modification of the cleaning device 1 will be described. FIG. 5 is a schematic cross-sectional view showing the configuration of the cleaning apparatus 1B of the present invention.

  The cleaning apparatus 1B converts the hydrogen-containing gas into plasma, performs a surface treatment on the optical member OP as a cleaning object with the plasmaized gas, and cleans the organic matter attached to the optical member OP. In other words, the cleaning apparatus 1B is composed of a plasma processing apparatus that generates active hydrogen, and a direct current (DC) power source, a high frequency (RF) power source, a microwave power source, and others (to generate plasma) as plasma forming means. Has a power supply.

  In FIG. 5, 81 is a plasma generation unit. 82 a and 82 b are pipes for supplying plasma gas containing active hydrogen species to the processing chamber 10. Reference numerals 83a and 83b denote pressure regulating valves for controlling the gasified plasma containing active hydrogen species.

  84a and 84b are diffusion plates, and the active hydrogen species and charged particles supplied to the processing chamber 10 via the pipes 82a and 82b are applied to the processing chamber 10, that is, the upper surface of the optical member OP (lens L and holder LM). And for uniformly irradiating (dispersing) the lower surface. The diffusion plates 84a and 84b are a porous plate having a plurality of openings, a plate having slits, or a simple mesh plate. The diffusion plates 84a and 84b diffuse active hydrogen species and low-energy particles into the processing chamber 10, so that the cleaning process for organic contamination adhered to the optical member OP can be performed uniformly and in a short time.

  The plasma generation unit 81 is exhausted by an exhaust pump 85 through an exhaust pipe 86. The pressure of the plasma generating unit 81 is controlled to an appropriate pressure for generating plasma by a pressure adjusting valve 87 such as a conductance valve. As described above, the plasma generation unit 81, the pipes 82 a and 82 b, the pressure adjustment valves 83 a and 83 b, the diffusion plates 84 a and 84 b, the exhaust pump 85, the exhaust pipe 86, and the pressure adjustment valve 87 constitute the plasmaization means 80.

Reference numeral 52 denotes a gas supply unit that supplies a gas to be plasmatized to the plasma generation unit 81 via the gas supply pipe 54. Reference numeral 60 denotes an N ₂ gas supply pipe. The N ₂ gas supply pipe 60 supplies N ₂ gas to the processing chamber 10 and opens the processing chamber 10 to atmospheric pressure.

  Next, referring to FIG. 5 and FIG. 6, a cleaning process of the cleaning apparatus 1B, that is, a cleaning method 1000B of the optical member OP using a plasma gas containing active hydrogen will be described. FIG. 6 is a flowchart for explaining a cleaning method 1000B according to one aspect of the present invention.

  The steps from installing and fixing the optical member OP to the processing chamber 10 (step 1010) to depressurizing the processing chamber 10 (step 1020) are the same as those in the cleaning method 1000, and thus the description thereof is omitted.

Next, a mixed gas composed of hydrogen (H ₂ ) gas and inert (Ar, Kr, Xe, Rn, Ne, He, N _2, etc.) gas is supplied to the plasma generation unit 81 via the gas supply pipe 54. (Step 1030). The mixed gas supplied to the plasma generation unit 81 is exhausted by the exhaust pump 85, and the pressure is adjusted by the pressure adjusting valve 87 connected to the exhaust pipe 86 (step 1040). Thereby, the plasma generation unit 81 becomes a reduced pressure atmosphere for generating plasma, and is preferably about 1 Pa to 100 Pa, for example.

  Note that the concentration of hydrogen gas contained in the mixed gas is adjusted by the gas supply unit 52 and is preferably 5% to 20%. The concentration of hydrogen gas contained in the mixed gas may exceed 20%, but when compared with 20% or less, there is no significant difference in the cleaning effect.

  The mixed gas supplied to the plasma generation unit 81 is excited by a plasma generation power source such as a microwave or high frequency power (not shown) provided in the plasma generation unit 81 to generate plasma (step 1050B). The frequency of the microwave power source is generally 2.45 GHz and the frequency of the high frequency power source is generally 13.56 MHz. However, a high frequency such as 8.3 GHz may be used for the microwave power source and 100 MHz or 200 MHz for the high frequency power source. The output is about 1500 W or less. In the present embodiment, a high frequency power source having a frequency of 13.56 MHz is provided in the plasma generation unit 81.

  The active hydrogen species and the inert gas generated by the plasma generation unit 81 are supplied to the decompressed processing chamber 10 without being back-diffused to the plasma generation unit 81 by the pressure control valves 83a and 83b (step 1060B). Specifically, the active hydrogen species and the inert gas generated in the plasma generation unit 81 are connected to the upper surface of the optical member OP (the lens L and the holder LM) via the pipes 82a and 82b and the diffusion plates 84a and 84b. A predetermined amount is supplied to each of the lower surfaces. In other words, the upper and lower surfaces of the optical member OP are irradiated with the active hydrogen species and the inert gas.

  The mixed gas containing the active hydrogen species supplied to the processing chamber 10 is exhausted by the exhaust pump 22 and the pressure is adjusted by the pressure adjusting valve 26 connected to the exhaust pipe 24, so that the processing chamber 10 is in a reduced pressure atmosphere. (Step 1070B). At this time, the pressure in the processing chamber 10 is preferably about 1 Pa to 100 Pa. Within such a pressure range, the active hydrogen species can be efficiently supplied to the processing chamber 10. Further, the organic matter separated and desorbed from the optical member OP by the active hydrogen species is quickly exhausted without reattaching to the optical member OP.

  The distance between the diffusing plates 84a and 84b facing the upper and lower surfaces of the optical member OP (lens L) and the optical member OP (lens L) can be arbitrarily controlled. In the present embodiment, the cleaning effect is high even when the distance between the diffusion plates 84a and 84b and the optical member OP (lens L) is 50 mm or more, and the optical member OP is not damaged even when the distance is about 20 mm. Therefore, the cleaning apparatus 1B and the cleaning method 1000B can be applied to lenses having various shapes having different thicknesses.

  The cleaning (processing) time of the optical member OP (lens L and holder LM) is within about 10 minutes, and the temperature of the optical member OP (lens L and holder LM) hardly increases during that time.

Further, before the cleaning process (that is, the supply of the active hydrogen species and the inert gas), the plasma generation unit 81 generates a plasma of only the inert gas, and the low energy particles from the plasma of the inert gas are removed from the processing chamber. 10 is preferably supplied. Thereby, water (H ₂ O) and oxygen (O ₂ ) molecules adsorbed on the surface of the optical member OP can be removed (that is, a pretreatment step), and oxidation of the surface of the optical member OP can be prevented. it can.

  After a predetermined cleaning time (active hydrogen species and inert gas supply time), the output of the high-frequency power source provided in the plasma generation unit 81 is stopped, and the plasma is extinguished. In other words, the supply of the active hydrogen species and the inert gas generated by the plasma generation unit 81 to the processing chamber 10 is stopped (step 1080B). Thereafter, the supply of the mixed gas is stopped, and the pressure adjustment valve 26, the pressure adjustment valves 83a and 83b, and the pressure adjustment valve 87 are closed. Furthermore, N2 gas is supplied to the processing chamber 10 from the N2 gas supply pipe 60, and the pressure in the processing chamber 10 is released to atmospheric pressure (step 1090B). Then, the cleaned optical member OP (lens L and holder LM) is taken out of the processing chamber 10, and the cleaning process is terminated (step 1100B).

The cleaning apparatuses 1 to 1B and the cleaning methods 1000 and 1000B of the present embodiment can be applied to optical components made of a fluoride material used in an exposure apparatus that uses an F ₂ laser as a light source. In addition, optical components used in multilayer reflectors made of metals and semiconductors used in exposure apparatuses that use EUV (Extreme Ultraviolet) light as a light source are also contaminated with organic matter without causing optical absorption loss due to surface oxidation. It can be effectively removed.

  In the cleaning apparatuses 1 to 1B and the cleaning methods 1000 and 1000B, the cleaning atmosphere is reduced in pressure or vacuum. Therefore, even when the holder for holding the optical component has a complicated shape, it is possible to effectively clean organic substances having a low vapor pressure in a short time with reduced pressure or a vacuum atmosphere and active hydrogen species. it can. Further, since the removed organic matter is quickly exhausted, contamination due to reattachment can be prevented.

  An example in which cleaning of an optical member (an optical member of a semiconductor exposure apparatus) is actually attempted by the cleaning apparatus 1 and the cleaning method 1000 will be described.

FIG. 7 is a graph showing the spectral transmittance before and after the cleaning of the calcium fluoride lens substrate. FIG. 7 employs the transmittance [%] on the vertical axis and the wavelength [nm] of light applied to the washed calcium fluoride lens substrate on the horizontal axis. For cleaning, the cleaning apparatus 1 shown in FIG. 1 is used. The mixed gas is a mixed gas of 20% H ₂ / Ar, the pressure of the processing chamber 10 is 50 Pa, and the cleaning (processing) time is 10 minutes.

Referring to FIG. 7, the transmittance in the ultraviolet wavelength region of 200 nm to 140 nm shows a clear improvement in transmittance due to cleaning when comparing before and after cleaning. The effect is seen not only in the wavelength region of the 193 nm ArF excimer laser but also in the wavelength region of the 157 nm F ₂ laser. In particular, the transmittance value at 157 nm after the cleaning is almost theoretically transmitted considering the internal absorption of the substrate. It is close to the rate. Further, no damage caused by charged energy particles is observed.

FIG. 8 shows spectral transmittances immediately after forming an antireflection film for a wavelength of 157 nm made of a fluoride optical thin film on the calcium fluoride lens substrate washed in Example 1, and after washing after the film formation. It is a graph to show. FIG. 8 employs the transmittance [%] on the vertical axis and the wavelength [nm] of light applied to the washed calcium fluoride lens substrate on the horizontal axis. For cleaning, the cleaning apparatus 1 shown in FIG. 1 is used. The mixed gas is a mixed gas of 20% H ₂ / Ar, the pressure of the processing chamber 10 is 50 Pa, and the cleaning (processing) time is 10 minutes.

  Referring to FIG. 8, the transmittance in the ultraviolet wavelength region of 200 nm to 140 nm did not change when comparing immediately after film formation with that after cleaning. As a result, the cleaning apparatus 1 and the cleaning method 1000 have the optical absorption caused by surface oxidation, damage caused by energy particles, and the like on the fluoride optical thin film formed on the calcium fluoride lens substrate. It can be seen that there is no contamination inside.

FIG. 9 is a graph showing the spectral transmittance before and after cleaning of an optical member in which a calcium fluoride lens substrate formed with an antireflection film for a wavelength of 157 nm made of a fluoride optical thin film is bonded and fixed to a holder. FIG. 9 employs the transmittance [%] on the vertical axis and the wavelength [nm] of light applied to the washed calcium fluoride glass lens substrate on the horizontal axis. For cleaning, the cleaning apparatus 1 shown in FIG. 1 is used. The mixed gas is a mixed gas of 20% H ₂ / Ar, the pressure of the processing chamber 10 is 50 Pa, and the cleaning (processing) time is 10 minutes.

Referring to FIG. 9, when the transmittance in the ultraviolet wavelength region of 200 nm to 140 nm is compared before and after cleaning, a clear improvement in transmittance due to the cleaning is observed. The term “before cleaning” refers to a state in which the lens substrate on which the antireflection film is formed is left on the holding unit, and the term “after cleaning” refers to a state in which the optical member in which the lens substrate and the holding unit are integrated is cleaned. It is. In particular, in the wavelength region of the F ₂ laser of 157 nm, the transmittance in the wavelength region of 157 nm after cleaning exceeds 99%. This means that the transmittance deteriorated to 98.5% or less before washing, that is, after standing after the film formation, is restored to the transmittance immediately after the film formation. Further, as is clear from Example 2, it was found that there was no deterioration in transmittance due to damage caused by surface oxidation, energetic particles, and the like.

  Further, it was found that there is no influence on the transmittance by washing at the same time as the holding tool, and no reattachment of the removed contamination is observed even if the contaminated member is washed.

  From the results of Examples 1 to 3, it is clear that the cleaning apparatus and method of the present invention can be applied to an optical component, an optical element provided with an optical thin film, and an optical component in which the optical element and the holder are integrated. It is.

  Here, it is considered that the deterioration of transmittance before cleaning is mainly caused by organic contamination, but even when conventional dry (UV / ozone) cleaning is attempted, the deterioration of transmittance cannot be recovered in a short time. It was.

The cleaning apparatus and method of the present invention are very effective for removing organic contaminants attached to optical members used in the vicinity of the wavelength region of the 157 nm F ₂ laser as well as the wavelength region of the 193 nm ArF excimer laser. Furthermore, the cleaning apparatus and method of the present invention can remove organic contamination in a short time, which is advantageous not only for the optical characteristics of the optical member but also for improving the productivity of the exposure apparatus.

  The cleaning effect by the surface treatment using the high-density plasma according to the present embodiment is that low-energy motion that does not damage the optical member in addition to the generation of active hydrogen species that effectively decompose organic substances at a high density. The application of energy is synergistic.

  Further, even an optical member having a complicated shape can be effectively cleaned by the presence of active hydrogen species under reduced pressure. Here, the optical member having a complicated shape is a large-diameter optical member having a diameter of 500 mm or more to which a lens used in the projection optical system is fixed, an optical member having various shapes used in the illumination optical system, or the like.

  The cleaning apparatus and method of the present invention include not only a lens, a lens provided with an antireflection film or an increased reflection film as an optical component, but also an optical member in which such a lens is fixed and integrated with a holder with an adhesive or the like. It can also be applied to. Therefore, it is possible to efficiently and effectively clean the optical component before being incorporated into the exposure apparatus. The cleaning apparatus and method of the present invention can be applied particularly to cleaning of various machine parts used in an exposure apparatus for manufacturing a semiconductor device. Needless to say, the present invention can be applied to cleaning of members used in general optical apparatuses, and can also be applied to various substrates and components used for manufacturing semiconductor devices.

In addition, the cleaning apparatus and method of the present invention, in particular, as a dry cleaning technique for lenses made of fluoride materials and lenses provided with an optical thin film, as compared with conventional dry cleaning represented by UV / ozone cleaning, It is extremely effective. This is because optical characteristics and productivity can be improved without optical absorption due to damage caused by surface oxidation or plasma. Cleaning apparatus and method of the present invention, an exposure apparatus whose light source an ArF excimer laser exposure apparatus whose light source an F ₂ laser, furthermore, as a dry cleaning technique for optical components used in an exposure apparatus using EUV light as a light source Fully practical. Thereby, the performance of the exposure apparatus can be dramatically improved.

  The exposure apparatus 200 as one aspect of the present invention will be described below. It is assumed that the optical element including the lens and the mirror used in the exposure apparatus 200 is cleaned by the cleaning apparatuses 100 to 100B and the cleaning methods 1000 to 1000B described above. Here, FIG. 10 is a schematic sectional view showing the structure of the exposure apparatus 200 of the present invention.

  As shown in FIG. 10, the exposure apparatus 200 includes an illumination device 210, a reticle stage (not shown) on which the reticle 220 is mounted, a projection optical system 230, and a wafer stage 245 on which the object 240 is mounted.

  The exposure apparatus 200 is a projection exposure apparatus that exposes a circuit pattern formed on the reticle 220 to the object 240 by, for example, a step-and-repeat method or a step-and-scan method. Such an exposure apparatus is suitable for a lithography process of submicron or quarter micron or less, and in the present embodiment, a step-and-scan type exposure apparatus (also referred to as “scanner”) will be described as an example. Here, in the “step and scan method”, the wafer is continuously scanned with respect to the reticle to expose the reticle pattern onto the wafer, and after the exposure of one shot is completed, the wafer is stepped to expose the next shot. This is an exposure method for moving to an area. The “step-and-repeat method” is an exposure method in which the wafer is moved stepwise for each batch exposure of shots of the wafer and the next shot is moved to the exposure region.

  The illumination device 210 illuminates the reticle 220 on which a transfer circuit pattern is formed, and includes a light source unit 212 and an illumination optical system 214.

For example, the light source unit 212 uses a laser as a light source. Laser, ArF excimer laser having a wavelength of about 193 nm, _{F 2} laser with a wavelength of about 157 nm, may be used, EUV light having a wavelength of about 10 to 20 nm, the kind of laser is not limited, the use of a mercury lamp Good. However, as described above, the optical elements cleaned by the cleaning apparatuses 100 to 100B and the cleaning methods 1000 to 1000B are particularly suitable for ArF excimer laser, F ₂ laser, and EUV light. When EUV light is used as the light source of the light source unit 212, reflective optical elements (that is, mirrors) are used for the illumination optical system 214 and the projection optical system 230 described later.

  The illumination optical system 214 is an optical system that illuminates the reticle 220, and includes a lens, a mirror, an optical integrator, a stop, and the like. For example, a condenser lens, an optical integrator, an aperture stop, a condenser lens, a slit, and an imaging optical system are arranged in this order. The illumination optical system 214 can be used regardless of on-axis light or off-axis light. The optical integrator includes an integrator formed by stacking fly-eye lenses and two sets of cylindrical lens array (or lenticular lens) plates, but may be replaced by an optical rod. Optical elements cleaned by the cleaning apparatuses 100 to 100B and the cleaning methods 1000 to 1000B can be used as optical elements such as lenses of the illumination optical system 214.

  The reticle 220 is made of, for example, quartz, on which a circuit pattern (or image) to be transferred is formed, and is supported and driven by a reticle stage (not shown). Diffracted light emitted from the reticle 220 passes through the projection optical system 230 and is projected onto the object 240. The reticle 220 and the object to be processed 240 are in a conjugate relationship. In the case of a scanner, the pattern of the reticle 220 is transferred onto the object 240 by scanning the reticle 220 and the object 240. In the case of a step-and-repeat type exposure apparatus (also referred to as a “stepper”), exposure is performed while the reticle 220 and the object to be processed 240 are stationary.

  The projection optical system 230 uses an optical system composed only of a plurality of lens elements, an optical system having a plurality of lens elements and at least one concave mirror (catadioptric optical system), an all-mirror optical system, and the like. Can do. When correction of chromatic aberration is necessary, a plurality of lens elements made of materials having different dispersion values (Abbe values) are used, or the diffractive optical element is configured so that dispersion in the opposite direction to the lens element occurs. . Optical elements cleaned by the cleaning apparatuses 100 to 100B and the cleaning methods 1000 to 1000B can be used as optical elements such as lenses of the projection optical system 230.

  The object to be processed 240 is a wafer in this embodiment, but widely includes liquid crystal substrates and other objects to be processed. A photoresist is applied to the object to be processed 240.

  Wafer stage 245 supports object 240 to be processed. The wafer stage 245 can be applied with any configuration known in the art, and a detailed description of the structure and operation is omitted here. For example, the wafer stage 245 can move the object 240 in the XY directions using a linear motor. For example, the reticle 220 and the workpiece 240 are scanned synchronously, and the positions of the wafer stage 245 and the reticle stage (not shown) are monitored by a laser interferometer, for example, and both are driven at a constant speed ratio. The wafer stage 245 is provided on a stage surface plate supported on a floor or the like via a damper, for example. For example, the reticle stage and projection optical system 230 are provided on a lens barrel surface plate (not shown) that is supported on a base frame placed on a floor or the like via a damper or the like.

  In the exposure, the light beam emitted from the light source unit 212 illuminates the reticle 220 by the illumination optical system 214, for example, Koehler illumination. The light that passes through the reticle 220 and reflects the reticle pattern is imaged on the object 240 by the projection optical system 230. The illumination optical system 214 and the projection optical system 230 used by the exposure apparatus 200 include optical elements cleaned by the cleaning apparatuses 100 to 100B and the cleaning methods 1000 to 1000B, and are high in ultraviolet light, far ultraviolet light, and vacuum ultraviolet light. Transmits with transmittance. Thereby, the exposure apparatus 200 can provide a device (semiconductor element, LCD element, imaging element (CCD, etc.), thin film magnetic head, etc.) with high resolving power and throughput with good economic efficiency.

  Next, an embodiment of a device manufacturing method using the exposure apparatus 200 will be described with reference to FIGS. FIG. 11 is a flowchart for explaining how to fabricate devices (ie, semiconductor chips such as IC and LSI, LCDs, CCDs, etc.). Here, the manufacture of a semiconductor chip will be described as an example. In step 1 (circuit design), a device circuit is designed. In step 2 (reticle fabrication), a reticle on which the designed circuit pattern is formed is fabricated. In step 3 (wafer manufacture), a wafer is manufactured using a material such as silicon. Step 4 (wafer process) is called a pre-process, and an actual circuit is formed on the wafer by lithography using the reticle and wafer. Step 5 (assembly) is called a post-process, and is a process for forming a semiconductor chip using the wafer created in step 4. The assembly process (dicing, bonding), packaging process (chip encapsulation), and the like are performed. Including. In step 6 (inspection), inspections such as an operation confirmation test and a durability test of the semiconductor device created in step 5 are performed. Through these steps, the semiconductor device is completed and shipped (step 7).

  FIG. 12 is a detailed flowchart of the wafer process in Step 4. In step 11 (oxidation), the surface of the wafer is oxidized. In step 12 (CVD), an insulating film is formed on the surface of the wafer. In step 13 (electrode formation), an electrode is formed on the wafer by vapor deposition or the like. Step 14 (ion implantation) implants ions into the wafer. In step 15 (resist process), a photosensitive agent is applied to the wafer. Step 16 (exposure) uses the exposure apparatus 200 to expose a reticle circuit pattern onto the wafer. In step 17 (development), the exposed wafer is developed. In step 18 (etching), portions other than the developed resist image are removed. In step 19 (resist stripping), the resist that has become unnecessary after the etching is removed. By repeating these steps, multiple circuit patterns are formed on the wafer. According to this device manufacturing method, it is possible to manufacture a higher quality device than before. Thus, the device manufacturing method using the exposure apparatus 200 and the resulting device also constitute one aspect of the present invention.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the gist. For example, the cleaning apparatus and the cleaning method of the present invention can be applied not only to the optical elements used in the illumination optical system and projection optical system of the exposure apparatus, but also to all optical members and mechanical members constituting the exposure apparatus.

It is a schematic sectional drawing which shows the structure of the washing | cleaning apparatus as one side of this invention. It is a flowchart for demonstrating the washing | cleaning method as 1 side surface of this invention. It is a schematic sectional drawing which shows the structure of the washing | cleaning apparatus as one side of this invention. It is a flowchart for demonstrating the washing | cleaning method as 1 side surface of this invention. It is a schematic sectional drawing which shows the structure of the washing | cleaning apparatus as one side of this invention. It is a flowchart for demonstrating the washing | cleaning method as 1 side surface of this invention. It is a graph which shows the spectral transmission factor of the calcium fluoride lens substrate which shows the cleaning effect of the cleaning apparatus and the cleaning method shown in FIGS. It is a graph which shows the spectral transmission factor after wash | cleaning immediately after forming the antireflection film with respect to the wavelength of 157 nm which consists of a fluoride optical thin film on the calcium fluoride lens board | substrate after wash | cleaning in Example 1. FIG. . It is a graph which shows the spectral transmittance before and behind cleaning of the optical member which adhered and fixed the calcium fluoride lens substrate which formed the antireflection film which shows the cleaning effect of the cleaning device and cleaning method shown in Drawing 1 and Drawing 2 to the holder. . It is a schematic sectional drawing which shows the structure of the exposure apparatus as one side surface of this invention. It is a flowchart for demonstrating manufacture of devices (semiconductor chips, such as IC and LSI, LCD, CCD, etc.). 12 is a detailed flowchart of the wafer process in Step 4 shown in FIG. 11.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cleaning apparatus 10 Processing chamber 20 Exhaust part 22 Exhaust pump 24 Exhaust piping 26 Pressure control valve 30 Holding mechanism 40 Plasma generating means 42 High frequency power supply 44a and 44b High frequency electrode 46a and 46b Perforated plate 50 Gas supply part 52 Gas supply unit 54a and 54b Gas supply pipe 60 N ₂ gas supply pipe 1A Cleaning device 70 Plasmaizing means 72a and 72b Microwave generators 74a and 74b Conductive antenna units 76a and 76b Microwave transparent dielectric window 1B Cleaning device 80 Plasmaizing means 81 Plasma generating unit 82a And 82b Pipes 83a and 83b Pressure adjusting valves 84a and 84b Diffuser plate 85 Exhaust pump 86 Exhaust pipe 87 Pressure adjusting valve OP Optical member L Lens LM Holder 200 Exposure device 214 Illumination optical system 230 Projection optical system

Claims (12)

A cleaning method for cleaning an object to be cleaned,
Maintaining the processing chamber containing the object to be cleaned in a reduced pressure or vacuum environment;
Supplying a gas containing hydrogen to the processing chamber;
Converting the gas into plasma,
A cleaning method, characterized in that the object to be cleaned is surface-treated with the plasma gas.   The cleaning method according to claim 1, wherein the gas includes an inert gas.   The cleaning method according to claim 2, wherein the inert gas contains at least one of argon, krypton, xenon, radon, neon, helium and nitrogen.   The cleaning method according to claim 1, wherein the object to be cleaned is an optical member used in a wavelength region of 250 nm or less.   The cleaning method according to claim 1, wherein the object to be cleaned is an optical member made of a calcium fluoride material. A cleaning device for cleaning an object to be cleaned,
A processing chamber for storing the object to be cleaned;
An exhaust section for maintaining the processing chamber in a reduced pressure or vacuum environment;
A gas supply unit for supplying a gas containing hydrogen to the processing chamber;
Plasmaizing means for converting the gas into plasma,
A cleaning apparatus characterized in that the object to be cleaned is surface-treated with the plasma gas.   An optical element that is cleaned using the cleaning method according to any one of claims 1 to 6.   An optical element characterized by being cleaned by being surface-treated with a gas containing hydrogen that has been converted to plasma.   9. The optical element according to claim 7, wherein an antireflection film or an increased reflection film is formed on the optical element.   An optical system comprising one or a plurality of the optical elements according to claim 7.   An exposure apparatus that irradiates a target object with light having a wavelength of 250 nm or less via the optical system according to claim 10 to expose the target object. Exposing the object to be processed using the exposure apparatus according to claim 11;
And developing the exposed object to be processed.