JP2000126704A - Method and apparatus for cleaning optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the use amount of a solvent or the like by a compact constitution by introducing a mixed gas of an inert gas and ozone to a material on a surface of an optical element from a specific direction and simultaneously emitting a high energy light within a range capable of maintaining a crystal structure of the surface of the optical element. SOLUTION: A lens 3 is set in a holder 4 of a cleaning machine, and a laser beam from an excimer laser source 1 is moved in a radial direction from a center part of the lens 3, while rotating the lens 3 by a rotating state 10. The laser beam is constantly focused a surface of the lens. Movement of the laser beam in the radial direction is effected by moving a three-dimensional control stage 5 in a horizontal direction. Focusing of the laser beam on the surface of the lens is effected by a laser focus controller 2. Nitrogen gas stored in a cylinder 6 and ozone produced by an apparatus 7 are mixed by a mixing device 8 and sent to the center part of the lens 3 so as to remove contaminants on the lens 3 and sucked by a suction device 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for cleaning an optical element used for an application requiring high performance, in particular, an optical element having a very large diameter and high precision.

[0002]

_2. Description of the Related Art Conventionally, an optical element such as a lens made of a fluoride crystal material such as CaF ₂ or MgF ₂ has a good transmittance over an extremely wide wavelength band and a low dispersion. For this reason, it has been used for high-precision lenses requiring high functions, such as high-grade camera lenses and television camera lenses.

Further, the above-mentioned optical element made of a fluoride-based crystal material such as CaF ₂ or MgF ₂ has a high transmittance even for short-wavelength light such as an excimer laser. Has begun to be considered.

In the cleaning of such an optical element, conventionally, it has been general that the optical element is immersed in a cleaning liquid in a cleaning tank and cleaned by an ultrasonic cleaning method.

However, in the case where several such washing tanks are provided, and after washing with a surfactant, pure water or the like, and finally isopropyl alcohol washing is to be performed, the washing tank becomes large and the washing machine becomes large. The main body is expensive and bulky, and the amount of solvent used for drying and the like is very large.

[0006] From the viewpoint of environmental protection, it is necessary to reduce the use of a solvent or to use a cleaning method that does not use a solvent in the future.

As described above, the conventional high-precision, large-aperture lens cleaning has been performed by the so-called WET method. However, contaminants on the surface of an optical element that handles ultraviolet light having a shorter wavelength are removed. In order to remove it, cleaning by the WET method alone is not sufficient.

That is, in the wavelength region of the excimer laser, the transmittance of the optical element is reduced by a contaminant on the surface of the optical element. In particular, it has been found that an organic residue as a contaminant reduces the transmittance of the optical element. Was.

From the viewpoint of removing the organic residue, the so-called DRY cleaning method proposed in JP-A-8-509652 is considered to be effective. However, the ultraviolet / inert gas cleaning method proposed in JP-A-8-509652 cannot provide a sufficient cleaning effect as shown in a comparative example described later. This publication also describes ultraviolet / ozone cleaning. According to this description, ultraviolet / ozone cleaning is relatively effective in removing residual organic films such as photoresists,
It is not effective for polymers that are degraded by salt, dust, fingerprints, and ozone. Furthermore, it is said that there is a problem that an undesired oxide may be formed by ozone depending on a contaminant, and a separate washing step for removing the oxide is required.

[0010]

As described above,
The problems in the cleaning method by the so-called WET method, which has been generally performed in the past, are as follows: (1) The apparatus becomes large with a large-diameter lens (2) The amount of solvent used cannot be reduced (3) In the ultraviolet region For example, the characteristics of the used optical element cannot be satisfied. Further, the conventional DRY cleaning method also has problems such as insufficient cleaning effect.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and the size of a cleaning apparatus body can be controlled very compactly even with a large-diameter lens, and a solvent can be used. It is an object of the present invention to provide a cleaning method and a cleaning apparatus that can reduce or eliminate the usage amount of the optical element and the like and can satisfy the characteristics required for an optical element used at a wavelength in an ultraviolet region.

[0012]

In order to achieve the above object, a cleaning method according to the present invention comprises the steps of: mixing a mixture of ozone and a gas inert to a material on the surface of an optical element in a direction crossing the surface of the optical element; Is introduced from a direction substantially parallel or slightly angled to the optical element, and at the same time, the high-energy light within a range capable of maintaining the crystal structure of the optical element surface sufficient to remove contaminants from the optical element surface. Irradiation is performed on the optical element surface.

Further, the optical element cleaning apparatus of the present invention provides a means for supplying an inert gas and ozone to the material on the surface of the optical element, a means for mixing these gases, and a method for applying the mixed gas to the optical element. Means for introducing to the surface of the element and sufficient to remove contaminants from the surface of the optical element, but the crystal structure of the surface of the optical element can be maintained at an energy density and time within which high-energy light is irradiated at a high energy density and time. An energy light irradiating means and stage means for supporting the optical element and moving the optical element so that the irradiating light hits a predetermined portion of the optical element are provided.

The optical element is a lens made of a material having a high transmittance of ultraviolet light such as quartz, CaF ₂ or MgF ₂ , and the gas inert to the material on the surface of the optical element is nitrogen or argon. The high-energy light is excimer laser light.

In the present invention, preferably, the mixed gas is suctioned by a suction device disposed downstream of the surface of the optical element.

[0016]

In a normal lens processing step, a rough lens shape is first formed from a lens material, and then a final surface shape and surface roughness are obtained by polishing.

Therefore, the contaminants in the lens processing step differ depending on the processing step, but are basically inorganic substances such as abrasives and dust, and organic substances such as oil and fingerprints.

These contaminants are generated in each processing step of the lens and adhere by covalent bonds, electrostatic force, van der Waals force, and the like. After the final surface shape and surface roughness of the lens are obtained, an antireflection film for improving the transmittance of the lens is formed on the surface. Therefore, final cleaning after lens processing is completed is very important.

In particular, since a lens used in the ultraviolet region, for example, for an excimer laser, requires a very high transmittance, the final cleaning after lens processing affects the optical performance of the lens.

Further, it has been found that organic factors are involved in causing such transmittance deterioration in the wavelength region. Therefore, removal of organic materials on the lens surface is important in cleaning.

Against this background, in the present invention, as a method of removing contaminants from the lens surface while maintaining the crystal structure of the lens surface, the gas is applied in a direction substantially parallel or slightly at an angle across the lens surface. Wherein said gas is a mixture of one that is inert to the lens material and ozone, wherein said lens treated surface is irradiated with high energy light to remove contaminants from the treated surface; A cleaning method in which the energy by irradiation was within a range that maintained the crystal structure of the lens material was adopted.

When the cleaning is performed by such a cleaning method, a very effective result can be obtained with respect to organic contamination on the lens surface. That is, first, a mixed gas of a gas and ozone which is inert to the lens material is allowed to flow on the lens surface, and this portion is irradiated with a pulsed or continuous wave laser or a high energy lamp as an irradiation source.

In particular, when the surface of the lens is irradiated with a pulsed excimer laser, the energy instantaneously gasifies the organic matter, and the organic matter is scattered from the lens surface together with the mixed gas flow of the inert gas and ozone for cleaning. It is.

It has also been found that mixing ozone with an inert gas has better removability than the inert gas alone. It is considered that this is because the presence of ozone further promotes the effect of promoting gasification of organic substances.

As described above, according to the present invention, by providing a cleaning method of the so-called DRY method from the conventional WET method, a compact apparatus and no solvent can be used.
In addition, it is possible to provide a cleaning method and a cleaning apparatus which are capable of satisfying the transmittance characteristics in the region of ultraviolet light, and which are capable of satisfying three beats.

[0026]

Embodiments of the present invention will be described below. The description will be made with reference to the drawings for easy understanding. (Embodiment 1) FIG. 1 is a schematic structural view of a lens cleaning machine by light energy light irradiation according to an embodiment of the present invention. In the figure, 1 is an excimer laser light source, 2 is a laser beam focus control device, 3 is a lens, 4 is a lens holder, 5 is a three-dimensional control stage, 6 is an inert gas (nitrogen or argon) cylinder, and 7 is ozone generation. Device, 8 is a gas mixer, 9
Is an inhaler and 10 is a rotary stage.

First, as a pretreatment for cleaning using this lens cleaning machine, the lens 3 (outer diameter 200 m
m, radius of curvature 250 mm, convex lens, lens material CaF
₂ ) Roughness on the lens surface is removed in advance by wiping off abrasives, oils, and other dusts attached to the surface.

Next, this lens is set in the lens holder 4 of the cleaning machine according to the present invention. From the viewpoint of completely cleaning the effective portion of the lens 3, the holder 4 is structured so as to contact only the edge portion of the lens 3.

Generally, lenses have a circular outer diameter and are almost point-symmetric with respect to the center of the lens. Therefore, the lens holder 4 is configured to be rotatable around the center of the lens. In this embodiment, the lens 3 is rotated by the rotation stage 10 at a rotation speed of 10 rpm.

With the lens 3 rotated, the KrF
Excimer laser light (wavelength: 248 nm) was irradiated by an excimer laser LPX200 manufactured by Lambda Physics Co., Ltd. to 150 mj /
The laser beam (beam diameter 12 * 23 mm ² ) was moved from the center of the lens in the radial direction at a speed of 2 mm / sec while irradiating with an energy of cm ² . At this time, the focus of the laser beam was always adjusted to the lens surface. The repetition rate of the laser (laser pulse oscillation cycle) is 200 Hz
Met. The movement of the laser beam in the radial direction was performed by moving the three-dimensional control stage 5 in the horizontal direction. In addition,
The focusing of the laser beam on the lens surface may be performed by the laser light focus control device 2, but may also be performed by moving the three-dimensional control stage 5 in the vertical direction.

At the same time as the laser beam irradiation, nitrogen gas is applied at 200 ml / sec toward the center of the lens.
An inhaler 9 for inhaling the mixed gas was provided on the opposite side of the lens from a gas in which the mixed gas of ozone and ozone was mixed at 25 ml / sec. The contaminants on the lens surface are gasified by laser irradiation or fly out of the lens surface, and are sucked into the inhaler together with the mixed gas.

As a result of evaluation using a high-power microscope, a spectroscope, and the like, it was confirmed that abrasives, dust, and organic film residues could be almost completely removed.

(Example 2) As in Example 1, a lens (outer diameter 250 mm, radius of curvature 280 m) was first polished.
m, concave lenses, lens material SiO ₂ ), etc., are cleaned in advance by removing abrasives, oils, and other dusts adhering to the surfaces of the lens material, etc.

Next, this lens is set in the lens holder 4 of the cleaning machine according to the present invention. From the viewpoint of completely cleaning the effective portion of the lens, the holder 4 is structured so as to contact only the edge portion of the lens 3.

When cleaning the concave lens, as in the first embodiment, since the lens is point-symmetric with respect to the center, the processing is performed while rotating the lens around the lens center. Also in this embodiment, the lens is set to 10r.
It was rotated at a rotation speed of pm. With the lens rotated, a laser beam (beam diameter 12 * 23 mm ² ) is irradiated in the radial direction while irradiating a KrF excimer laser beam (248 nm) with an excimer laser LPX200 manufactured by Lambda Physics Co. at an energy of 200 mj / cm ² from the center of the lens. At a speed of 3 mm / sec. Also in this case, the laser beam is always focused on the lens surface. The repetition rate of the laser was 200 Hz. At the same time, a mixture of 150 ml / sec of argon gas and 40 ml / sec of ozone was sent toward the center of the lens, and an inhaler 9 for sucking the mixed gas was provided on the opposite side of the lens. The contaminants remaining on the lens surface are instantaneously gasified by the laser irradiation or jump out of the lens surface, and are sucked into the inhaler together with the mixed gas.

From the results of evaluation using a high magnification microscope, a spectroscope, and the like, it was confirmed that abrasives, dust, and organic film residues could be almost completely removed.

(Comparative Example) Cleaning was performed in the same manner as in Example 2 except that ozone was not mixed into the gas sent to the center portion of the lens. As a result, it was found that the organic film residue removal property was slightly inferior to that of Example 2 in which ozone was mixed, as a result of the evaluation.

(Embodiment of Device Production Method) Optical elements cleaned by the cleaning method of the present invention include semiconductor chips such as ICs and LSIs, liquid crystal panels, CCDs, thin film magnetic heads, and the like.
It is used for an optical system of an exposure apparatus for manufacturing a device such as a micromachine. Next, an embodiment of a device manufacturing method using an exposure apparatus having an optical system having an optical element cleaned by the cleaning method of the present invention will be described.

FIG. 2 shows a flow of manufacturing micro devices (semiconductor chips such as ICs and LSIs, liquid crystal panels, CCDs, thin film magnetic heads, micro machines, etc.). Step 1
In (Circuit Design), a device pattern is designed. Step 2 is a process for making a mask on the basis of the designed pattern. Step 3 (wafer manufacturing)
Then, a wafer is manufactured using a material such as silicon or glass. Step 4 (wafer process) is called a pre-process,
An actual circuit is formed on the wafer by lithography using the prepared mask and wafer. The next step 5 (assembly) is called a post-process, and is a process of forming a semiconductor chip using the wafer produced in step 4, and includes processes such as an assembly process (dicing and bonding) and a packaging process (chip encapsulation). including. In step 6 (inspection), inspections such as an operation confirmation test and a durability test of the semiconductor device manufactured in step 5 are performed. Through these steps, a semiconductor device is completed and shipped (step 7).

FIG. 3 shows a detailed flow of the wafer process. Step 11 (oxidation) oxidizes the wafer's surface. Step 12 (CVD) forms an insulating film on the wafer surface. Step 13 (electrode formation) forms electrodes on the wafer by vapor deposition. In step 14 (ion implantation), ions are implanted into the wafer. Step 15
In (resist processing), a photosensitive agent is applied to the wafer. Step 16 (exposure) uses the above-described exposure apparatus to print and expose the circuit pattern of the mask onto the wafer. Step 17 (development) develops the exposed wafer. In step 18 (etching), portions other than the developed resist image are removed. In step 19 (resist stripping), unnecessary resist after etching is removed. By repeating these steps, multiple circuit patterns are formed on the wafer.

By using the production method of this embodiment, it is possible to produce a highly integrated device, which was conventionally difficult to produce, at low cost.

[0042]

As described above, the optical element cleaning apparatus according to the present invention has a very compact main body as a cleaning apparatus for a large-diameter lens, and further, greatly reduces the amount of cleaning liquid such as an organic solvent. Almost no need to use. As for the cleaning performance, it has been found that a very good cleaning performance can be obtained even when the optical characteristics in the ultraviolet region are evaluated. Therefore, it can be expected that the cleaning performance will be widely used in such fields in the future.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a lens cleaning machine according to one embodiment of the present invention.

FIG. 2 is a diagram showing a flow of manufacturing a micro device.

FIG. 3 is a diagram showing a detailed flow of a wafer process in FIG. 2;

[Explanation of symbols]

1: excimer laser light source, 2: laser light focus control device,
3: lens, 4: lens holder, 5: three-dimensional control stage, 6: inert gas (nitrogen, argon) cylinder, 7:
Ozone generator, 8: gas mixer, 9: inhaler, 10:
Rotating stage.

Claims (11)

[Claims] 1. A gas mixture of ozone and a gas inert to a material on the surface of an optical element is introduced from a direction substantially parallel or slightly inclined to a direction crossing the surface of the optical element. An optical element cleaning method comprising irradiating the surface of the optical element with high-energy light that is sufficient to remove contaminants from the surface, but is high enough to maintain the crystal structure of the optical element surface. 2. The method for cleaning an optical element according to claim 1, wherein the mixed gas is sucked by a suction device disposed downstream of the surface of the optical element. 3. An optical element cleaning method according to claim 1, wherein the gas inert to the material of the optical element surface is nitrogen or argon. 4. The method for cleaning an optical element according to claim 1, wherein the material on the surface of the optical element is a material having a high transmittance of ultraviolet light. 5. The material of the optical element surface is quartz, Ca
Optics cleaning method according to claim 4, characterized in that the F ₂ or MgF _2. 6. The method for cleaning an optical element according to claim 1, wherein the high energy light is excimer laser light. 7. A means for supplying a gas and ozone that are inert to the material on the surface of the optical element, a means for mixing these gases, a means for introducing the mixed gas to the surface of the optical element, A high-energy light irradiating means for irradiating high-energy light with an energy density and time within a range sufficient to remove contaminants from the surface of the optical element but capable of maintaining the crystal structure of the surface of the optical element; An optical element cleaning apparatus, comprising: stage means for supporting the optical element and moving the optical element so that irradiation light impinges on a predetermined portion of the optical element. 8. An optical element cleaned by the method according to claim 1. 9. An optical system having an optical element cleaned by the method according to claim 1. 10. An exposure apparatus having the optical system according to claim 9. 11. A device manufacturing method for transferring a circuit pattern onto a wafer by the apparatus according to claim 10.