JP2003119054A - Method and apparatus for cleaning optical part - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus for cleaning optical parts by which organic contaminants that can not be removed by optical cleaning and can only be removed when the optical cleaning is continued for a long time while causing an increase in the temperature of a lens or other optical parts unavoidably can uniformly be removed effectively in a short time. SOLUTION: Optical parts housed in a pressure-reducible cleaning vessel are cleaned by using gas of a plasma state obtained by a plasma generating unit. In the concrete, low-energy particles are produced from an active oxygen radical obtained by the plasma generating unit or the active oxygen radical and an inert gas between the cleaning vessel and the plasma generating unit and the produced particles are supplied to the cleaning vessel to clean optical parts.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical component cleaning method and an optical component cleaning apparatus, and more particularly to an optical component cleaning method using a plasma generator suitable for surface treatment of optical components used in a semiconductor exposure apparatus. The present invention also relates to an optical component cleaning device, for example, an optical glass lens used in the ultraviolet wavelength region, a method for cleaning an optical component in which an antireflection film or a reflection enhancing film is applied to the optical glass lens, and an optical component cleaning device.

[0002]

2. Description of the Related Art Conventionally, the mainstream of the cleaning of optical parts is ultrasonic cleaning using a cleaning liquid such as a neutral or alkaline detergent and an organic solvent, and further wet cleaning using acid cleaning in combination. These cleanings remove inorganic contaminants such as abrasive grains that adhere when polishing optical components such as lenses and organic contaminants such as wax used as a protective film by applying ultrasonic vibration to the cleaning liquid. It is a thing.

More recently, UV / UV in which ultraviolet light and ozone or active oxygen species are used in combination to remove light organic substances that cannot be removed by wet cleaning and organic substances that are contaminated during storage after cleaning after film formation Ozone cleaning device
No. 00-66003) and the like are often used for dry cleaning. In particular, wet cleaning after the formation of the antireflection film or the increased reflection film may adversely affect the optical characteristics after cleaning. From this point, dry cleaning is an extremely effective cleaning method.

[0004]

However, the above-mentioned U
Even if light cleaning is performed with a V / ozone cleaning device, etc., there is organic contamination that cannot be easily removed in a short time.
In the F2 laser wavelength region of 57 nm, there is a problem in that the optical absorption loss becomes remarkable, and the transmittance of the optical parts and the laser resistance are also lowered.

Therefore, the present invention solves the above problems and removes organic contaminants that cannot be removed by optical cleaning and the temperature of the lens and the like rises because cleaning takes a long time. It is an object of the present invention to provide an optical component cleaning method and an optical component cleaning device that can perform treatment uniformly and effectively in a short time.

[0006]

In order to achieve the above object, the present invention provides an optical component cleaning method and an optical component cleaning device configured as in the following (1) to (16). Is. (1) A method of cleaning an optical component, which cleans an optical component housed in a cleaning processing container capable of decompressing by using a gas turned into a plasma by a plasma generation device, the plasma generating device and the cleaning processing container Is separated, low-energy particles of active oxygen species or active oxygen species and an inert gas are generated by the plasma generation device, and these are supplied into the cleaning treatment container to clean the optical component. How to clean optical components. (2) The method for cleaning an optical component according to (1) above, wherein the gas to be turned into plasma is oxygen gas or a mixed gas of oxygen gas and an inert gas. (3) The inert gas is Ar, Kr, Xe, Rn, N
The method for cleaning an optical component according to (2) above, which contains at least one gas of e, He and N ₂ . (4) The plasma generation device is configured by means for exciting a gas to be turned into plasma by using microwave power or high frequency power.
The method for cleaning an optical component according to any one of (3). (5) In the plasma generation device, the pressure inside the device is controlled to suppress the energy such as ion energy and electron temperature of the charged particles of the inert gas introduced into the plasma generation device. The method for cleaning an optical component according to any one of (1) to (4) above. (6) The method for cleaning an optical component according to (5), wherein the pressure is controlled to about 10 to 100 Pa. (7) In the cleaning processing container, the optical component housed in the cleaning processing container has a pressure of 1 to
The method for cleaning an optical component according to any one of (1) to (6) above, wherein the cleaning is performed under a reduced pressure of about 100 Pa. (8) In the cleaning treatment container, an active oxygen species or low-energy particles supplied into the cleaning treatment container are uniformly dispersed by a diffusion plate facing an optical component housed in the cleaning treatment container. The method for cleaning an optical component according to any one of (1) to (7) above, wherein the component is cleaned. (9) In the above (1) to (8), the optical component is an optical glass lens used in an ultraviolet wavelength region of 250 nm or less or an optical glass lens formed with an antireflection film and a reflection enhancing film. The method for cleaning an optical component according to any one of claims. (10) The method of cleaning an optical component according to (9), wherein the optical glass lens is made of quartz or fluorite substrate. (11) A depressurizable cleaning processing container for housing and cleaning the optical component, and a plasma generator for supplying oxygen gas or a mixed gas of an oxygen gas and an inert gas into the cleaning processing container in a plasma state. An exhaust device for exhausting the inside of the container, the optical device cleaning device for cleaning the optical component housed in the cleaning processing container by the gas turned into plasma by the plasma generation device, A cleaning device for optical parts, wherein a plasma generating device and the cleaning processing container are configured separately. (12) The plasma generation device has pressure control means for controlling the pressure inside the device, and the charged particles of the inert gas introduced into the plasma generation device have the pressure control means for controlling the pressure. The optical device cleaning apparatus according to (11) above, which suppresses energy such as ion energy and electron temperature. (13) The above-mentioned (1) wherein the plasma generation device is constituted by means for exciting the gas to be turned into plasma using microwave power or high-frequency power.
1) Or the washing | cleaning apparatus of the optical component as described in said (12). (14) The cleaning processing container is provided with a diffusion plate facing the optical components housed in the cleaning processing container. Cleaning device for optical components. (15) In the above (11) to (14), the optical component is an optical glass lens used in an ultraviolet wavelength region of 250 nm or less or an optical glass lens formed with an antireflection and antireflection coating. The optical device cleaning device according to any one of the preceding claims. (16) The optical component cleaning device according to (15), wherein the optical glass lens is made of quartz or fluorite substrate.

[0007]

According to the above configuration, when cleaning the optical parts, the plasma generating device and the decompressing cleaning treatment container are separately configured, so that the active oxygen species generated by the plasma generating device and the like are separated. Can be introduced into the cleaning processing container, and the cleaning process can be performed without directly exposing the optical parts, which are the objects to be cleaned, to the plasma, which effectively prevents surface organic contamination without damaging the objects to be cleaned. Can be removed. Further, according to the above configuration, the surface of the optical component can be cleaned by the synergistic action of the active oxygen species generated by the plasma generation device or the low energy particles of the active oxygen species and the inert gas, and the UV / ozone cleaning is performed. It becomes possible to remove organic contaminants, which are difficult to remove by optical cleaning with an apparatus or the like, in a short time and without increasing the lens temperature.

It is generally pointed out that when surface treatment of an optical component is performed using plasma, charged particles having kinetic energy collide with the glass surface, resulting in damage causing optical absorption loss. Has been done. In particular, fluorspar, which is used in the ultraviolet wavelength region, has a color center due to a chemically unbonded hand (dangling bond) due to the breaking of the chemical bond on the surface. This causes a problem that the optical absorption loss in the ultraviolet region increases and the transmittance of the optical component deteriorates.

However, according to the above construction, the pressure control means for controlling the pressure in the plasma generating device is constituted, so that the ion energy and the electron temperature of the charged particles of the inert gas introduced into the plasma generating means are possessed. To
It can be suppressed to an extremely low value of 10 eV or less or 2 eV or less, respectively. In addition, the active oxygen species generated by the plasma can effectively remove the organic contamination on the surface without damaging the optical parts, particularly the fluorite lens and the fluoride optical thin film which are sensitive to the damage by the energy particles. .

Further, according to the above construction, as a dry cleaning technique for an optical component provided with an optical glass lens or an optical thin film, the optical characteristics are improved as compared with the optical cleaning represented by the conventional UV / ozone cleaning device. And, it is possible to achieve a cleaning method or apparatus that is extremely effective in improving productivity.
It can be practically used as a dry cleaning technology for optical components used not only in the 193 nm ArF excimer laser exposure apparatus at the stage of practical application but also in the 157 nm F2 laser exposure apparatus that is being developed, and the performance of the exposure apparatus can be expected to be dramatically improved.

FIG. 1 is a schematic sectional view showing an embodiment of the plasma processing apparatus used in the present invention. Reference numeral 1 denotes a depressurizable container, which can be depressurized by a pressure adjusting valve 4 while exhausting the interior of the container 1 through an exhaust pipe 3 by an exhaust pump 2 W is a lens which is an optical component, and 5 is a substrate holder for mounting and fixing the lens W in the center of the container 1. Reference numeral 6 is a plasma generation unit, 7a and 7b are pipes for introducing active oxygen species into the container 1, and 8
Reference numerals a and 8b are pressure control valves for preventing back diffusion of active oxygen species. Further, reference numerals 9a and 9b are diffusion plates for uniformly irradiating the upper surface and the lower surface of the lens W with the active oxygen species introduced into the container 1 via the diffusion plates 7a and 7b. Reference numeral 10 denotes a gas supply unit, which introduces a gas to be plasma into the plasma generation unit 6 through a gas supply pipe 11. Further, the plasma generation unit 6 is exhausted by the exhaust pump 12 through the exhaust pipe 13, and is controlled to an appropriate pressure by the pressure control valve 14 to generate plasma. Reference numeral 15 is an N ₂ gas supply pipe, and the decompression container 1 is released from the decompressed state to the atmospheric pressure by the N ₂ gas introduced therein.

Next, a method of cleaning a lens, which is an optical component, carried out by the plasma processing apparatus shown in FIG. 1 will be described with reference to FIG. The lens W, which is an optical component, is placed in the decompression container 1 opened to the atmospheric pressure, and the substrate holder 5
Install and fix by. At this time, the lens W is fixed in advance by a jig such as a dedicated worker so that it can cope with various shapes. The lens to be cleaned is the lens material glass after wet cleaning or the optical glass lens after the antireflection film or the reflection enhancing film is applied.

The decompression container 1 is decompressed by the exhaust pump 2 to a pressure of about 1 Pa or less. As a matter of course, the decompression container 1 and the parts contained in 1 are sufficiently cleaned so that the depressurization does not result in contamination by organic substances having a high vapor pressure. I'm using it.

Next, oxygen (O ₂ ) gas and inert gas (Ar, Kr, Xe, Rn, N) are introduced into the plasma generating unit 6.
A mixed gas of (e, He, N ₂ etc.) gas is introduced through the gas supply pipe 11, pressure control is performed by the exhaust pump 12 and the pressure adjusting valve 14, and the pressure is maintained at about 10 to 100 Pa.

The concentration of oxygen gas contained in the mixed gas at this time is adjusted by the gas supply unit 10, and the concentration is 5
-10% is suitable, and at most 20% is suitable amount. The oxygen concentration may exceed 20%, but when compared with 20% or less, there is no significant difference in the concentration of the active oxygen species introduced into the container 1, that is, the cleaning effect of the lens W.

The gas species used for the inert gas are:
Ar is generally used, but Kr or Xe is used for fluoride optical glass typified by fluorite glass or optical components provided with a fluoride optical thin film, which may be damaged.
Is more optimal. Further, Kr is optimal for efficiently generating active oxygen species.

The mixed gas to be turned into plasma, which is introduced into the plasma generating unit 6, is excited by microwaves or high frequency power provided in the plasma generating unit 6 to generate plasma. The frequency of microwave power source is 2.45 GHz, and the frequency of high frequency power source is 13.56
MHz is common, but 8.3 for microwaves.
With respect to GHz and high frequencies, high frequencies such as 100 MHz and 200 MHz may be used. 1500 as the output
A value of about W or less is suitable.

In this embodiment, the frequency is 13.56 MHz.
The high frequency power supply mechanism of No. 1 was provided in the plasma generation unit. Further, the pressure range of about 10 to 100 Pa is suitable for suppressing the ion energy and the electron temperature of the charged particles of the inert gas to be low, and when the pressure is lower than 1 Pa, There is a possibility that the energy possessed becomes high and the optical components are damaged. Further, under such a low pressure, the density of the active oxygen species that removes organic contaminants is relatively low and the cleaning effect is reduced. When the pressure exceeds 100 Pa, the discharge becomes unstable and the optical parts are damaged due to abnormal discharge or the like.

The active oxygen species and the inert gas generated in the plasma generation unit 6 do not back-diffuse into the plasma generation unit 6 by the pressure control valves 8a and 8b, and are piped into the depressurized container 1 through the pipes 7a, 7b and. Diffusers 9a, 9
Predetermined flow rates are introduced into the spaces on the upper and lower surfaces of the lens via b, and the upper and lower surfaces of the lens W are irradiated.

The mixed gas containing the active oxygen species introduced is exhausted by the exhaust pump 2, and pressure control is performed by the pressure adjusting valve 4 connected to the exhaust pipe 3, so that the inside of the container 1 becomes a decompressed atmosphere. . The pressure at this time is 1-10
About 0 Pa is suitable. Within this pressure range, the active oxygen species can be efficiently introduced into the container 1, and the organic substances decomposed and desorbed from the surface of the lens W by the active oxygen species are quickly exhausted without adhering to the lens W again. .

Here, the diffusion plates 9a, 9 provided on the container 1
b is for uniformly dispersing the introduced active oxygen species and charged particles in the container, and the shape of the diffusion plate may be a porous plate having a plurality of openings, a plate provided with slits, or a simple mesh plate. I don't care. The active oxygen species and low-energy particles generated in this way diffuse into the container, reach the upper and lower surfaces of the lens W that is an optical component, and perform uniform cleaning treatment of organic contaminants adhering to the lens surface. It can be done in a short time.

Furthermore, at this time, the energy (ion energy, electron temperature) of the charged particles other than the active oxygen species that reach the lens surface is extremely low, and the ion energy is 10e.
The electron temperature is about 2 eV or less. At such low ion energy and low electron temperature, the target optical parts such as the optical lens glass and the optical thin film are not damaged.

The distance between the lens W and the diffusion plates 9a and 9b facing the upper and lower surfaces of the lens W can be controlled arbitrarily, but in the present embodiment, the distance from the lens surface is 50 mm.
The cleaning effect was high even when the distance was increased, and no damage was caused even when the distance was brought close to about 20 mm. Therefore, it is possible to deal with lenses having various shapes with different thicknesses. Lens W
The processing time is within about 5 minutes, and the temperature rise of the lens W during this period is hardly observed.

After a predetermined cleaning time (plasma excitation time), the output of the high frequency power supply is stopped and the plasma is extinguished. Thereafter, the supply of the mixed gas was stopped, after closing all the pressure regulating valves, N ₂ gas was introduced from the N ₂ supply pipe 15,
The lens W washed by releasing the pressure in the container 1 to the atmospheric pressure
The cleaning process is completed by taking out.

The cleaning effect of the surface treatment using plasma according to the present embodiment depends not only on the active oxygen species that effectively decomposes organic substances, but also on the movement by low energy particles to the extent that it does not damage optical glass parts. It is considered that the application of energy acts as a synergistic effect.

In this embodiment described above, an optical glass or an optical lens substrate having an antireflection film and a reflection enhancing film formed on the optical glass is used as an optical component.
It is also applicable to a component in which such a lens substrate is fixed to a jig with an adhesive material or the like, which makes it possible to clean the lens component immediately before being incorporated in the exposure apparatus. In addition to this, the present invention can be applied to various substrates used in semiconductor manufacturing, and can also be applied to cleaning various mechanical parts used in a semiconductor manufacturing apparatus, particularly a semiconductor exposure apparatus.

[0027]

EXAMPLE An example of actually attempting to clean an optical component with the above plasma processing apparatus and cleaning method will be described. FIG. 2 shows the spectral transmittance measurement results before and after plasma cleaning of the fluorite glass substrate in this example.
Cleaning is performed by using the plasma processing apparatus shown in FIG.
O ₂ / Ar mixed gas plasma, container pressure is 20P
a, the processing time is 3 minutes.

As shown in FIG. 2, when the transmittances in the ultraviolet wavelength region of 200 nm to 140 nm are compared before cleaning and after plasma cleaning, a clear improvement in transmittance due to cleaning is observed. Not only the ArF laser wavelength region of 193 nm,
The effect is also seen in the 157 nm F2 laser wavelength region, and particularly the transmittance value at 157 nm after plasma cleaning is close to the theoretical transmittance in consideration of the internal absorption of the substrate, and damage due to charged energy particles is also observed. I can't.

Here, it is considered that the deterioration of the transmittance before cleaning is mainly caused by the contamination of organic substances.
Even if ozone cleaning was tried, the deterioration of the transmittance could not be completely recovered in a short time. From this result, it is clear that the plasma cleaning according to the present invention can be performed not only in the 193 nm ArF laser wavelength region but also in the 1
It was confirmed that it is also effective for removing organic contaminants in the vicinity of the 57 nm F2 laser wavelength, and that it can be carried out in a short time, which is advantageous not only for improving optical characteristics but also for improving productivity.

[0030]

According to the present invention, it is possible to uniformly remove organic contaminants that cannot be removed by light cleaning and the temperature of a lens or the like rises because cleaning takes a long time. It is possible to effectively realize a method of cleaning an optical component and an apparatus for cleaning an optical component that can be treated in a short time.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a plasma processing apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a spectral transmittance measurement result of a fluorite glass substrate showing a cleaning effect according to an example of the present invention.

[Explanation of symbols]

1: Decompression container 2: Exhaust pump 3: Exhaust pipe 4: Pressure adjusting valve 5: Substrate holder 6: Plasma generation unit 7a: Plasma gas supply pipe (top surface arrangement) 7b: Plasma gas supply pipe (bottom surface arrangement) 8a: Pressure Regulator valve (top arrangement) 8b: Pressure regulator valve (bottom arrangement) 9a: Diffusion plate (top arrangement) 9b: Diffusion plate (bottom arrangement) 10: Gas supply unit 11: Gas supply pipe 12: Exhaust pump 13: Exhaust pipe 14 : Pressure adjusting valve 15: N ₂ supply pipe W: Lens (optical part)

Claims (16)

[Claims] 1. A method of cleaning an optical component, which is for cleaning an optical component housed in a cleaning treatment container capable of decompressing using a gas plasma-converted by a plasma generation device, the plasma generation device and the cleaning treatment. Separate from the container,
Cleaning of optical parts, characterized in that low energy particles are generated by the plasma generation device by active oxygen species or active oxygen species and inert gas, and these are supplied into the cleaning treatment container to clean the optical parts. Method. 2. The method for cleaning an optical component according to claim 1, wherein the gas to be turned into plasma is oxygen gas or a mixed gas of oxygen gas and an inert gas. 3. The inert gas is Ar, Kr, Xe, R
The method for cleaning an optical component according to claim 2, further comprising at least one gas selected from n, Ne, He and N ₂ . 4. The plasma generating device is constituted by means for exciting a gas to be turned into plasma by using microwave power or high frequency power. How to clean optical components. 5. In the plasma generating apparatus, by controlling the pressure inside the apparatus, it is possible to suppress the energy such as the ion energy and electron temperature of the charged particles of the inert gas introduced into the plasma generating apparatus. The method for cleaning an optical component according to any one of claims 1 to 4, wherein: 6. The method of cleaning an optical component according to claim 5, wherein the pressure is controlled to about 10 to 100 Pa. 7. The cleaning processing container, wherein the optical components housed in the cleaning processing container are cleaned by reducing the pressure in the cleaning processing container to about 1 to 100 Pa. 7. The method for cleaning an optical component according to any one of 1 to 6. 8. In the cleaning treatment container, the active oxygen species or low energy particles supplied into the cleaning treatment container are uniformly dispersed by a diffusion plate facing an optical component housed in the cleaning treatment container. The method for cleaning an optical component according to claim 1, wherein the optical component is cleaned. 9. The optical component according to claim 1, wherein the optical component is an optical glass lens used in an ultraviolet wavelength region of 250 nm or less, or an optical glass lens having an antireflection and antireflection coating formed thereon. Item 1. The method for cleaning an optical component according to Item 1. 10. The method of cleaning an optical component according to claim 9, wherein the optical glass lens is made of quartz or fluorite substrate. 11. A plasma processing chamber for containing optical components and capable of decompressing, and a plasma treatment for supplying oxygen gas or a mixed gas of oxygen gas and an inert gas to the inside of the cleaning processing vessel. A cleaning device for optical parts, comprising: an apparatus and an exhaust device for exhausting the inside of the container, for cleaning the optical parts housed in the cleaning processing container by the gas turned into plasma by the plasma generation device. An apparatus for cleaning an optical component, wherein the plasma generating apparatus and the cleaning processing container are configured separately. 12. The plasma generation device has pressure control means for controlling the pressure in the device, and the charged particles of an inert gas introduced into the plasma generation device by controlling the pressure by the pressure control means. 12. The cleaning apparatus for an optical component according to claim 11, wherein the ion energy and the electron temperature of the device are suppressed. 13. The optical component according to claim 11 or 12, wherein the plasma generation device is constituted by means for exciting the gas to be turned into plasma by using microwave power or high frequency power. Cleaning equipment. 14. The cleaning processing container is provided with a diffusion plate facing the optical components housed in the cleaning processing container.
Item 10. A cleaning device for an optical component according to item. 15. The optical component according to claim 11, wherein the optical component is an optical glass lens used in an ultraviolet wavelength range of 250 nm or less or an optical glass lens provided with an antireflection and antireflection coating. 2. A cleaning device for optical parts according to item 1. 16. The cleaning apparatus for optical parts according to claim 15, wherein the optical glass lens is made of quartz or fluorite substrate.