JP6831541B2 - Manufacturing method of optical element - Google Patents

Description

The present invention relates to a method for manufacturing an optical element, and more particularly to a method for manufacturing an optical element used for an optical system in a wavelength band from, for example, a vacuum ultraviolet region to a hard X-ray basin.

Since light in the wavelength band from the vacuum ultraviolet region to the soft X-ray region to the hard X-ray basin is absorbed by most substances, a transmission optical element cannot be used in the optical system, and reflection on the surface of the substance is used. It is necessary to use the reflected optical element. For example, the X-ray optical system generated by a large radiation facility (SPring-8, etc.) or an X-ray free electron laser (SACLA, etc.) includes various types of high-precision plane mirrors, spherical mirrors, aspherical mirrors, and the like. Reflective X-ray mirrors are used, and the X-ray mirrors are posture-controlled with high accuracy by a mirror manipulator (Patent Document 1).

Conventionally, it has been said that the accuracy of an X-ray mirror is improved by reducing the surface roughness for each frequency. For example, when condensing 10 keV light by wave optical simulation, it is necessary to manufacture a mirror so that the shape error is 2 nm or less or 1 nm RMS or less in PV. As a means for producing these, EEM (Elastic Emission Machining) processing, MSI (Microstitching interferometry), and RADSI (Relative Angle Determinable Stitching Interferometry) measurement methods can be used for production (Patent Document 2). In EEM, a processing liquid in which fine particles are dispersed is made to flow along a processing surface of an optical element material, and the fine particles are brought into contact with each other on the processing surface in a substantially unloaded state, and the fine particles and the processing surface interface at that time mutually. This is an ultra-precision processing method in which surface atoms are removed on an order close to that of atomic units by action (a kind of chemical bond) (Patent Documents 3 and 4). Although the surface of the optical element can be processed with desired accuracy by this EEM processing, there is a feature that a large number of processed fine particles (SiO _2, etc.) used in the EEM process inevitably adhere to the surface.

In the X-ray condensing mirror, some light may be scattered due to the presence of particles on the reflecting surface. However, scattering by particles is only a small part of the light and has not been regarded as particularly important until now. However, in recent years, even in a condensing mirror, particles adhering to the mirror float in a vacuum device, resulting in another optical element. Has been reported to have an adverse effect on (Non-Patent Document 1). Further, when a multilayer film is formed on the reflective surface of the optical element, the multilayer film is uneven due to the particles adhering to the surface, and the reflection characteristics are impaired.

Further, at present, the quality of X-ray beams is being improved, and the number of diffraction gratings made from ultra-high precision mirrors having a shape error of about 2 nm is increasing. If there is dust or particles on the surface of this ultra-high precision mirror, the particles serve as a mask when the diffraction grating is manufactured by using the lithography technique, and unevenness is generated in the lattice groove. There is a problem that stray light is generated due to these irregularities and affects the cutting out of light having a target wavelength (Non-Patent Document 2).

For this reason, there has been a need for a technique capable of removing particles and dust without roughening the surface by cleaning. As a cleaning technology for semiconductor substrates, it is known that surface particles, metals, and organic substances are removed by cleaning with hydrogen peroxide solution, ammonia hydrogen peroxide, and hydrofluoric acid, which is a cleaning technology generally called the RCA method. There is. However, if the optical element such as an X-ray mirror is a quartz substrate or a Si single crystal substrate and the adhered fine particles contain SiO ₂ , it is an object of the same quality, so that the adhered fine particles are completely removed by such a normal cleaning method. It was difficult to do so, and there was a problem that particles remained.

JP-A-2002-122981 Japanese Unexamined Patent Publication No. 2008-292438 JP 2000-167770 Japanese Unexamined Patent Publication No. 2006-159379

Katsuhiko Murakami, EUVL Symposium 2011, October 17 (http://www.sematech.org/meetings/archives/litho/euvl/10157EUVL/pres/Katsuhiko Murakami.pdf) Introduction to Radiated Light Beamline Optical Technology (Japanese Society for Synchrotron Radiation) p. 163

Therefore, in view of the above situation, the present invention attempts to solve the problem by using the surface of the optical element material for an optical system in the wavelength band from the vacuum ultraviolet region to the hard X-ray flow region by an excellent proven EEM process. It is an object of the present invention to provide a method for manufacturing a high-quality optical element, which is processed with high precision capable of processing, significantly reduces the amount of fine particles adhering to the surface, particularly the reflective surface, and reduces the optical influence of the fine particles.

The present invention provides a method for manufacturing an optical element having the following structure in order to solve the above-mentioned problems.

(1)
A processing liquid in which processed fine particles that are chemically reactive with the optical element material are dispersed is made to flow along the processed surface, and chemically bonded to the processed fine particles by a chemical interaction between the processed fine particles and the interface between the processed particles. An EEM processing step of creating a surface with desired accuracy by using an EEM process of removing the formed surface atoms together with the processed fine particles by decoction of the processing liquid.
In the presence of a treatment liquid containing water in which catalyst metal fine particles composed of transition metal elements are dispersed , the treatment pad and the surface of the object to be treated are relatively displaced while being in contact with each other, and the water and the surface of the catalyst metal interact with each other. The catalytic function of the catalytic metal in contact with the surface of the optical element material promotes the direct hydrolysis of the optical element material or the oxidation of the optical element material and the hydrolysis of the oxide film, and the decomposition product due to the hydrolysis is used as the optical element material. Using a catalyst-assisted etching process that does not have a processing reference surface, at least the surface of the optical element material, which is a reflective surface, is uniformly removed together with the adhered fine particles including the processed fine particles adhering to the surface. Surface treatment process and
A method of manufacturing an optical element, which is characterized by being manufactured by.

(2)
The EEM processing step is
The rotating sphere-shaped processing head that forms a high shear flow of the processing liquid along the processing surface by the rotation of the elastic rotating sphere so that the surface roughness becomes 0.13 nm RMS or less in the high frequency region (1 μm × 1 μm region). Processing process,
The rotating sphere-shaped processing head that forms a high shear flow of the processing liquid along the processing surface by the rotation of the elastic rotating sphere so that the surface roughness becomes 0.15 nm RMS or less in the medium frequency region (100 μm × 100 μm region). Processing process,
Unit machining marks by the rotary spherical machining head or unit machining marks by the nozzle-type machining head that eject the machining fluid from the nozzle to form a high shear flow of the machining fluid along the machining surface are relative to the machining surface. In the low frequency region (from 1 mm or more to the effective region of the reflective surface), the shape error is reduced to 1 nm RMS or less by numerically controlling EEM that numerically controls the residence time of the processing head and spatially determines the removal amount. The process of processing
The method for manufacturing an optical element according to (1), which comprises at least one step.

(3)
The method for manufacturing an optical element according to (1) or (2) , wherein the processing pad has a structure having a catalyst metal composed of a transition metal element at least on its surface, and the catalyst does not serve as a processing reference surface .

(4)
The cleaning method according to (3), wherein as the processing pad, a processing pad having a structure in which a non-woven fabric or a woven fabric made of a thin catalyst metal wire is provided on the surface .

(5)
The cleaning method according to (3), wherein as the processing pad, a processing pad having a structure in which a non-woven fabric or a woven fabric made of a thin catalyst metal wire is provided on the surface .

(6)
It is characterized by including a cleaning step of removing the adhered fine particles on the surface of the optical element material by the surface treatment step and then dissolving and removing the metallic fine particles adhering by the surface treatment step with an acid or an alkaline solution (1). )-(5) The method for manufacturing an optical element according to any one of 1.

(7)
The flow of the treatment liquid containing water in the surface treatment step includes a step of supplying the treatment liquid to the removal unit and flowing the treatment liquid outward from the periphery of the removal unit, and discharging the treatment liquid from the periphery of the removal unit. The method for manufacturing an optical element according to any one of (1) to (6), which includes a step.

(8)
The flow of the treatment liquid containing water in the surface treatment step includes a step of supplying the treatment liquid around the removal unit and a step of sucking the treatment liquid inward from the periphery of the removal unit and discharging the treatment liquid (1). )-(6) The method for manufacturing an optical element according to any one of 1.

(9)
The flow of the treatment liquid containing water in the surface treatment step includes any of (1) to (6), including a step of flowing the treatment liquid from the removal unit and a step of discharging the treatment liquid from the cleaning region due to overflow. The method for manufacturing an optical element according to 1.

(10)
The method for manufacturing an optical element according to any one of (1) to (6), wherein the surface treatment step is batch-treated in a treatment tank containing a treatment liquid containing water.

(11)
The method for producing an optical element according to any one of (1) to (10), wherein the optical element material is a Si single crystal or an oxide.

( 12 )
The treatment solution containing water in the surface treatment step is a mixture of pure water or ultrapure water mixed with at least one of an oxidation accelerator, a pH adjusting solution, a buffer solution, and a complex solution that helps dissolve decomposition products. , (1) to ( 11 ) The method for manufacturing an optical element according to any one of 1.

According to the method for manufacturing an optical element of the present invention, the EEM processing step capable of processing the surface of the optical element material with a desired accuracy by the EEM process having an excellent track record and the processed fine particles used in the EEM process are included. The surface treatment step includes a surface treatment step of removing the adhered fine particles from the surface of the optical element material, and the surface treatment step includes a treatment pad and an object to be treated in the presence of a treatment liquid containing water in which catalytic metal fine particles composed of transition metal elements are dispersed . The surface of the optical element material is directly hydrolyzed or the optical element material is subjected to the catalytic function of the catalytic metal in contact with the surface of the optical element material by interacting with water and the surface of the catalytic metal . Since a catalyst-assisted etching process having no processing reference plane is used, which promotes oxidation and hydrolysis of the oxide film and removes decomposition products from the hydrolysis from the optical element material, at least reflection on the surface of the optical element material is used. By uniformly removing the surface to be the surface together with the adhered fine particles including the processed fine particles adhering to the surface, the adhered fine particles can be reliably removed from the surface of the optical element material, and the number of the optical element material surfaces is large. Since only the atomic layer needs to be removed, it can be performed in a short time, and the shape accuracy and surface roughness of the surface created in the EEM processing step are not impaired. That is, in the catalyst-assisted etching process of the surface treatment step, only the portion in contact with the surface of the catalyst metal becomes the surface treatment region, so that the shape accuracy of the surface created in the EEM processing step can be maintained.

In the EEM processing step, the surface roughness is 0 in the high frequency region (1 μm × 1 μm region) by the rotating sphere type processing head that forms a high shear flow of the processing liquid along the processing surface by the rotation of the elastic rotating sphere. In the middle frequency region (100 μm × 100 μm region), a rotating sphere-shaped processing head that forms a high shear flow of the processing liquid along the processing surface by rotating the elastic rotating sphere in the process of processing to 13 nm RMS or less. In the process of processing so that the surface roughness is 0.15 nm RMS or less, the unit processing marks by the rotary spherical processing head or the processing liquid is ejected from the nozzle to generate a high shear flow of the processing liquid along the processing surface. The unit machining marks formed by the nozzle-type machining head are scanned relative to the machining surface, and the staying time of the machining head is numerically controlled to spatially determine the amount of removal. Since at least one step of processing is performed so that the shape error is 1 nm RMS or less in the effective region of the reflective surface from 1 mm or more), the surface of the optical element material is moved from the vacuum ultraviolet region to the hard X-ray flow region. It can be processed with high accuracy that can be used for optical systems in the frequency bands up to.

Further, it is more reliable by executing a cleaning step of removing the adhered fine particles on the surface of the optical element material by the surface treatment step and then dissolving and removing the metallic fine particles adhering by the surface treatment step with an acid or alkaline solution. It is possible to reduce the amount of fine particles adhering to the alkali, and it is possible to provide a high-quality X-ray optical element.

It is explanatory cross-sectional view which shows typically the change of the surface state of the optical element material by the manufacturing method of the optical element which concerns on this invention. It is a simplified explanatory drawing of the rotary ball type processing head system EEM used in the EEM processing process. It is a simplified explanatory drawing of the nozzle type processing head system EEM used in the EEM processing process. The results of observing the surfaces of the glass substrate for an X-ray optical element before processing and after processing by the rotating sphere processing head method EEM with a phase shift interference microscope and an atomic force microscope (AFM) are shown. It is a simplified explanatory drawing of the batch processing apparatus in a surface treatment process. It is a simplified explanatory drawing of the discharge water flow type processing apparatus used in a surface treatment process. It is a simplified explanatory drawing of the suction water flow type processing apparatus used in a surface treatment process. It is a simplified explanatory drawing of the rotating water flow type processing apparatus used in a surface treatment process.

Next, the present invention will be described in more detail based on the embodiments shown in the accompanying drawings. FIG. 1 schematically shows a change in the surface state of an optical element material according to the method for manufacturing an optical element according to the present invention. In the figure, reference numeral A is an optical element, 1 is an optical element material, 2 is a surface, 3 is an adhered fine particle, 4 is a processed fine particle, 5 is a contaminated fine particle, and 6 is a metallic fine particle.

According to the present invention, the optical element A causes a processing liquid in which processing particles 4 having chemical reactivity with the optical element material 1 are dispersed to flow along the processing surface, and chemicals at the interface between the processing fine particles 4 and the processing surface. An EEM processing step of creating a surface 2 with desired accuracy by using an EEM process in which surface atoms chemically bonded to the processed fine particles 4 are removed together with the processed fine particles 4 by decoction of the processing liquid by the above-mentioned interaction. (See FIGS. 1A and 1B), the treatment liquid containing water, and the surface of the catalytic metal are allowed to interact with each other, and the catalytic function causes direct hydrolysis of the optical element material 1 or oxidation of the optical element material. The processing adhering to at least the surface 2 of the optical element material surface 2, which is a reflective surface, by using a catalyst-assisted etching process for advancing the hydrolysis of the oxide film and removing the decomposition products due to the hydrolysis from the optical element material 1. It is produced by a surface treatment step (see FIG. 1C) for removing adhered fine particles 3 including fine particles 4.

Further, in the method for manufacturing an optical element of the present invention, after removing the adhered fine particles 3 on the surface 2 of the optical element material by the surface treatment step, the metal-based fine particles 6 adhered by the surface treatment step are subjected to an acid or alkaline solution. It is characterized by including a cleaning step of dissolving and removing (see FIG. 1D). Here, the adhered fine particles 3 include contaminated fine particles 4 such as dust and impurities in addition to the processed fine particles 4 used in the EEM process.

Here, the EEM processing step is
The rotating sphere-shaped processing head that forms a high shear flow of the processing liquid along the processing surface by the rotation of the elastic rotating sphere so that the surface roughness becomes 0.13 nm RMS or less in the high frequency region (1 μm × 1 μm region). Processing process,
The rotating sphere-shaped processing head that forms a high shear flow of the processing liquid along the processing surface by the rotation of the elastic rotating sphere so that the surface roughness becomes 0.15 nm RMS or less in the medium frequency region (100 μm × 100 μm region). Processing process,
Unit machining marks by the rotary spherical machining head or unit machining marks by the nozzle-type machining head that eject the machining fluid from the nozzle to form a high shear flow of the machining fluid along the machining surface are relative to the machining surface. In the low frequency region (from 1 mm or more to the effective region of the reflective surface), the shape error is reduced to 1 nm RMS or less by numerically controlling EEM that numerically controls the residence time of the processing head and spatially determines the removal amount. The process of processing
Of these, at least one step is included.

The shape and surface roughness of the optical element material and the surface of the optical element depend on the main wavelength and required accuracy of the target optical system. Then, in order to realize a certain characteristic of the optical system, it is required that the power spectral density (PSD) for each spatial frequency on the surface of the optical element is set to a specified value or less.

Examples of the optical element material include Si single crystal and oxide. Since a Si single crystal having extremely high purity and few lattice defects is provided, it is suitable as a material for a catadioptric system in the X-ray region. Further, single-component or multi-component oxides such as quartz glass and ultra-low expansion glass ceramics can also be used satisfactorily. In addition, optical element materials used in X-ray optical systems and EUV optical systems are also targeted.

FIG. 1A shows the optical element material 1 before processing. When the surface 2 of the optical element material 1 is processed into a predetermined shape and surface roughness by the EEM processing step, as shown in FIG. 1 (b), the processed fine particles 4 such as colloidal silica (SiO ₂ ) used in the EEM process and It is inevitable that other contaminated fine particles 4 adhere to the surface 2. Therefore, the adhered fine particles 3 are removed by removing only a few atomic layers from the surface 2 of the optical element material 1 by a surface treatment step using a catalyst metal. As shown in FIG. 1 (c), the catalyst metal is used. The resulting metallic fine particles 6 adhere to the surface 2. The metal-based fine particles 6 have a low number density, and can be easily dissolved and removed without changing the optical element material 1 of the base material by a cleaning step with an acid or alkaline solution. As a result, the particle-free optical element A as shown in FIG. 1D can be manufactured.

Table 1 shows the number of remaining particles adhering to the surface 2 of the optical element material 1 after each step. First, after the EEM processing step, in the case of pure water cleaning only, the number of remaining particles is 60351 in the range of 60 mm × 60 mm. After the EEM processing step, when ultrapure water was washed as a cleaning liquid using a soft cloth, the number of remaining particles was 452. Here, the cloth is a wipe using polyester ultrafine fibers. After the EEM processing step and the surface treatment step, the number of remaining particles was less than 10.

Next, the EEM processing step and the surface treatment step will be described below.

[EEM processing process]
In the EEM processing step, as described above, a processing liquid in which the optical element material 1 and the chemically reactive processed fine particles 4 are dispersed is flowed along the processed surface, and the chemical at the interface between the processed fine particles 4 and the processed surface is performed. The EEM process is used in which the surface atoms chemically bonded to the processed fine particles 4 are removed together with the processed fine particles 4 by the decoction flow of the processing liquid by the above-mentioned interaction. There are mainly a rotary ball type machining head method EEM and a nozzle type machining head method EEM depending on the method of generating the shear flow of the machining liquid.

<Rotating sphere processing head method EEM>
FIG. 2 briefly shows the rotary spherical processing head type EEM. In the rotary sphere type processing head method EEM, the elastic rotary sphere 11 and the optical element material 1 are arranged in a processing tank containing a processing liquid in which the processing fine particles 4 are uniformly dispersed in pure water or ultrapure water. By rotating the elastic rotating sphere 11 while pressing it against the surface 2 of the optical element material 1 with a constant load F, the processing liquid is entrained and flowed between the elastic rotating sphere 11 and the surface 2 to flow the processing liquid. The processing is performed while maintaining a predetermined interval by balancing the fluid dynamic pressure and the load due to the flow of the water. Reference numeral P in FIG. 2 indicates the flow of the processing liquid. As the elastic rotating sphere 11, a sphere made of polyurethane is used, and the elastic rotating sphere 11 is provided at the tip of a rotating shaft driven by a motor. Here, it is also possible to use a disk-shaped or columnar elastic rotating sphere 11.

Here, when the elastic rotating sphere 11 is rotated in a certain direction while being pressed against the surface 2 with a constant load F, the working fluid is caught between the elastic rotating sphere 11 and the surface 2 as shown in FIG. Then, a local processing liquid flow flowing in the direction along the surface 2 is generated, and the fluid dynamic pressure generated between the elastic rotating sphere 11 and the surface 2 causes the elastic rotating sphere 11 and the surface 2 to flow. A gap of about 1 μm is maintained between the two, and the machining fine particles 4 in the machining fluid pass between the surface 2 and the elastic rotating sphere 11 one after another while contacting the surface 2 with the flow of the machining fluid, and the surface thereof. The processing of the surface 2 is advanced by the chemical interaction between 2 and the processed fine particles 4.

Further, in order to continuously process the surface 2 having a large area, the unit processing marks by the rotary spherical processing head can be scanned relative to the optical element material 1. Here, the rotary sphere type processing head is a portion including the elastic rotary sphere 11. On the other hand, in order to perform local machining of the surface 2, the staying time of the rotary spherical machining head can be numerically controlled according to the machining amount obtained by subtracting the target surface profile from the surface profile before machining measured in advance. The amount of processing can be controlled for each part. The unit processing mark is a removal profile that is processed in a unit time with the position of the rotary spherical processing head stationary with respect to the surface 2 of the optical element material 1.

In the rotary ball type machining head system EEM of the present embodiment, a gap of about 1 μm is formed between the elastic rotary ball 11 and the surface 2, and it is important for non-contact machining to maintain this gap. .. Therefore, the particle size of the processed fine particles 4 that can be used here must be sufficiently smaller than the above-mentioned gap. Usually, the processed fine particles 4 made of silica (SiO ₂ ) having a particle size of about 0.1 μm are used for processing. The processed fine particles can be changed according to the optical element material to be processed.

<Nozzle type processing head method EEM>
FIG. 3 briefly shows the nozzle type processing head method EEM. In the nozzle-type machining head system EEM, the machining nozzle 21 and the optical element material 2 are immersed in the machining fluid in the machining tank, and the tip surface of the machining nozzle 21 is arranged parallel to the surface 2 of the optical element material 2. At the same time, the ejection direction is arranged perpendicular to the surface 2, and the processing liquid in which the surface atoms of the optical element material 2 and the processed fine particles 4 having chemical reactivity are uniformly dispersed is discharged to the ejection port of the processing nozzle 21. It is ejected from 22 in the liquid to generate a high shear flow of the processing liquid along the vicinity of the surface 2, and the processed fine particles 4 chemically bonded to the surface atoms are removed by the high shear flow to remove the surface atoms for processing. To proceed. Reference numeral P in FIG. 3 indicates a flow of the processing liquid.

Then, in order to continuously process the surface 2 having a large area, the unit processing marks by the nozzle-type processing head are scanned relative to the surface 2. Here, the nozzle type processing head is a portion including the processing nozzle 21. On the other hand, in order to locally process the surface 2, the residence time of the nozzle-type processing head is numerically controlled according to the processing amount obtained by subtracting the target surface profile from the surface profile before processing measured in advance. Further, the ejection port 22 of the processing nozzle 21 can have a horizontally long slit hole in addition to a circular hole. When the spout 22 is a circular hole, the unit machining mark is small, so that it is suitable for local machining, and when it is a slit hole, it is suitable for uniformly machining a wide area. The direction in which the processing liquid is ejected from the ejection port 22 of the processing nozzle 21 may be inclined with respect to the surface 2 of the optical element material 1. In that case, the profile of the unit processing mark is not symmetrical.

The processing tank is previously filled with a processing liquid in which fine particles are dispersed in pure water or ultrapure water, and the processing liquid is sprayed into the processing liquid from the processing nozzle 21 along the surface 2 of the optical element material 2. It is most efficient to create a given shear flow. In this case, the processing liquid can be circulated by a pump for use. It is also possible to put only pure water or ultrapure water in the processing tank and inject the processing liquid from the processing nozzle 21. Further, when only pure water or ultrapure water is ejected from the processing nozzle 21, a processing liquid in which processing fine particles 4 are dispersed may be supplied from another supply port according to the flow of pure water or ultrapure water. ..

Further, in the nozzle type processing head method EEM, since the gap between the tip of the processing nozzle 21 and the surface 2 of the optical element material can be relatively wide as 10 μm or more, the processed fine particles 4 having an average particle size of 10 nm to 10 μm are used. can do. However, if the particle size of the fine particles becomes too large, the surface 2 will be scratched by the contact of the processed fine particles 4, so the upper limit is practically set to about several μm, and if the particle size becomes too small, the processing adheres to the surface 2. Since it is necessary to make the shear flow for removing the fine particles 4 extremely fast, it is practically preferable to set the lower limit to about 0.1 μm. Actually, as the processed fine particles 4, the processing speed is increased by using agglomerated fine particles which are aggregates of a plurality of fine particles. As the aggregated fine particles, those in which SiO ₂ fine particles having a particle size of 1 to 100 nm are aggregated to form an aggregate having an average diameter of 0.5 to 5 μm is used. The concentration of the processed fine particles 4 (aggregated fine particles) in the processing liquid is preferably 3 to 7 vol%.

Then, if high-speed processing is performed using the aggregated fine particles and then finish processing is performed using ordinary fine particles, ultra-precision processing can be performed in a short time. It is easy to change from high-speed processing using agglomerated fine particles to finishing processing because it is only necessary to replace the processing liquid.

In FIG. 4, a glass substrate for an X-ray optical element is processed by a rotating sphere processing head method EEM, and the surfaces before and after processing are subjected to a phase shift interference microscope (Zygo, NewView) and an atomic force microscope (AFM). The results observed in are shown. The AFM image corresponds to the high frequency region in the range of 1 μm × 1 μm, and the phase shift interference microscope image corresponds to the medium frequency region in the range of 140 μm × 110 μm. In the high frequency region, the surface roughness before processing was 0.228 nmRMS (0.158 nmRa), but after processing, the surface roughness became 0.097 nmRMS (0.077 nmRa). Further, in the medium frequency region, the surface roughness before processing was 0.152 nmRMS (0.122 nmRa), but after processing, the surface roughness became 0.125 nmRMS (0.100 nmRa).

In general, the rotary spherical processing head type EEM is suitable for improving the surface roughness in the high frequency region and the medium frequency region, and the nozzle type processing head type EEM is suitable for shape correction in the low frequency region. Therefore, it is most preferable that the surface shape is first created with a predetermined accuracy by the nozzle type processing head method EEM, and then the surface roughness is uniformly improved while maintaining the shape accuracy by the rotary ball type processing head method EEM.

[Surface treatment process]
In the surface treatment step, the treatment liquid containing water interacts with the surface of the catalytic metal, and the catalytic function proceeds with the direct hydrolysis of the optical element material 1 or the oxidation of the optical element material 1 and the hydrolysis of the oxide film. Using a catalyst-assisted etching process for removing the decomposition products due to hydrolysis from the optical element material 1, the adhered fine particles 3 containing the processed fine particles 4 attached to at least the surface of the optical element material surface 2 to be a reflective surface are removed. This is the process of removing. If the optical element material 1 is an oxide, it will be directly hydrolyzed, and if it is not an oxide, oxidation and hydrolysis of the oxide film will proceed.

The catalyst-assisted etching process uses a catalyst metal that promotes both oxidation of the optical element material and hydrolysis of the oxide or oxide film, and if the optical element material is not an oxide, the optical element comes into contact with the catalyst metal. The surface of the material is oxidized, and the water molecules are dissociated to cut and adsorb the back bond between the oxygen element and other elements that make up the oxide film, and the decomposition product produced by hydrolysis is eluted into the water to form an optical element. If the material is an oxide, the water molecules dissociate and cut and adsorb the back bond between the oxygen element and other elements that make up the oxide, and elute the production of decomposition products by hydrolysis into the water. Here, by applying a mechanical force to the decomposition product, elution into water can be promoted. Further, in order to promote the oxidation of the optical element material, an oxidation accelerator may be added to a solution containing water as a main component, or a complex that assists the dissolution of decomposition products by hydrolysis, for example, ammonia may be added. .. Further, since the pH of the solution affects the processing speed, it is also preferable to adjust the pH by adding an HNO ₃ aqueous solution, a phosphate buffer solution, a KOH aqueous solution or the like to the solution.

The transition metal element is preferable as the catalyst metal, and it can be used satisfactorily as long as the d-orbital of the electron is near the Fermi level. For example, Pd, Ru, Ni, Co, Cr, Mo, etc., which have a large work function, can be used. Further, the catalyst metal may be a single metal element or an alloy composed of a plurality of metal elements.

The catalyst-assisted etching process in the surface treatment step of the present invention is basically the same as CARE (CAtalyst-Referred Etching), but in the present invention, the catalyst does not need to be a processing reference surface, and the surface of the optical element material 1 is used. The purpose can be achieved if only a few atomic layers of 2 can be uniformly removed together with the adhered fine particles 3. The processing principle of CARE is described in detail in Japanese Patent No. 5754754, Japanese Patent No. 6188152, and Japanese Patent No. 6206847.

In the surface treatment step, the catalyst metal surface and the optical element material surface 2 are relatively moved while being brought into contact with the surface 2 of the optical element material 1 at a predetermined contact pressure in the presence of a treatment liquid containing water. The step of removing the decomposition product of the surface 2 is included. In the simplest configuration, as shown in FIG. 5, the removal unit 31 and the optical element material 1 are arranged in a processing tank (not shown), and rotate and translate while being in contact with each other in a processing liquid containing water. Is to do. The method shown in FIG. 5 is a so-called batch processing apparatus. Here, the removal unit 31 has a structure in which a catalyst metal is formed on at least the surface of a processing pad 33 provided at the tip of a support portion 32 that serves as a rotation axis. Specifically, the treatment pad 33 has a structure in which the catalyst metal is embedded in a bulk of the synthetic resin or rubber and at least a part of the catalyst metal is exposed on the pad surface, or the catalyst is formed on the synthetic resin or rubber surface. It is a structure in which metal is deposited. Further, the catalyst metal fine wire may be provided on the surface of the processing pad 33, and the form thereof may be either a non-woven fabric or a woven fabric. Further, the thin catalyst metal wire may be bulk or the surface of the synthetic fiber may be plated with the catalyst metal.

Further, as the treatment liquid, it is most preferable to use a treatment liquid containing water in which catalyst metal fine particles are dispersed in a colloidal form. In this case, instead of the processing pad 33 provided with the catalyst metal on the surface, a normal processing pad used in CMP is used, and the processing pad 33 and the optical element are supported with the catalyst metal fine particles supported in the processing pad. By rubbing the material surface 2 together, the several atomic layers of the optical element material surface 2 are removed together with the adhered fine particles 3. Of course, it is also possible to use the treatment pad 33 provided with the catalyst metal on the surface and the treatment liquid in which the catalyst metal fine particles are dispersed in a colloidal form.

Here, as shown in FIGS. 6 and 7, in order to rapidly move the decomposition products and particles formed on the surface 2 of the optical element material by the action of the catalyst metal from the surface 2, the treatment liquid is forced. It is also preferable to make a flow. 6 and 7 show a flow path 34 formed at the center of the support portion 32 of the removal unit 31, and the discharge water flow type treatment device shown in FIG. 6 supports the treatment liquid containing water with the removal unit 31. A step of supplying the treatment liquid to the flow path 34 provided in the unit 32 and flowing the treatment liquid outward from the periphery of the treatment pad 33 of the removal unit 31 and a step of discharging the treatment liquid from the periphery of the removal unit 31 (not shown). The suction water flow type treatment apparatus shown in FIG. 7 includes a step (not shown) of supplying the treatment liquid containing water to the periphery of the removal unit 31 and the removal unit 31. This includes a step of sucking the treatment liquid inward from the periphery of the treatment pad 33 and discharging the treatment liquid from the flow path 34 provided in the support portion 32. Reference numerals Q in FIGS. 6 and 7 indicate the flow of the treatment liquid containing water. Here, in the configuration shown in FIG. 6, a step of discharging the treatment liquid flowing from the periphery of the treatment pad 33 of the removal unit 31 to the outside from the cleaning region by overflow may be included. This is a so-called flowing process.

The step (means) of discharging the treatment liquid from the periphery of the removal unit 31 of the discharge water flow type processing device of FIG. 6 can be configured by a suction pipe arranged around the removal unit 31 or a suction flow path provided in the removal unit 31. .. The step (means) of supplying the treatment liquid around the removal unit 31 in the suction water flow type treatment device of FIG. 7 can be configured by a discharge pipe arranged around the removal unit 31 or a discharge flow path provided in the removal unit 31. .. Of course, if the configurations shown in FIGS. 6 and 7 are arranged in the treatment tank and the treatment is performed in the treatment liquid in the treatment tank, the process of discharging the treatment liquid from the periphery of the removal unit of FIG. 6 ( Means) and the step of supplying the treatment liquid around the removal unit of FIG. 7 can be substituted by putting in and taking out the treatment liquid with respect to the treatment liquid pool in the treatment tank. That is, the step (means) of discharging the treatment liquid in the discharge water flow type treatment device corresponds to the step of mixing with the treatment liquid pool in the treatment tank, and the treatment liquid is around the removal unit 31 in the suction water flow type treatment device. The step of supplying the treatment liquid corresponds to the step of sucking the treatment liquid from the treatment liquid pool in the treatment tank.

FIG. 8 shows a rotating water flow type processing device. As the removal unit 31, a treatment liquid in which catalyst metal fine particles are colloidally dispersed in a treatment liquid containing an elastic rotating sphere 35 and water as used in EEM is used, and the surface of the optical element material is rotated by the rotation of the elastic rotating sphere 35. It is possible to create a flow Q of the treatment liquid along No. 2 and quickly move decomposition products and particles from the surface 2 from the treatment region.

[Washing process]
The cleaning step is a step of removing the adhered fine particles 3 on the surface 2 of the optical element material by the surface treatment step, and then dissolving and removing the metallic fine particles 6 adhered by the surface treatment step with an acid or an alkaline solution.

When the optical element material is a Si single crystal or an oxide, the metal-based fine particles adhering to the surface are substances completely different from the surface composition. Therefore, only the metal-based fine particles should be selectively dissolved and removed by a cleaning step. Is easy.

A Optical element 1 Optical element Material 2 Surface 3 Adhering fine particles 4 Processed fine particles 5 Contaminated fine particles 6 Metal-based fine particles 11 Elastic rotating sphere 21 Processing nozzle 22 Ejection 31 Removal unit 32 Support 33 Processing pad 34 Flow path 35 Elastic rotating sphere P processing Liquid flow Q Treatment liquid flow

Claims (12)

A processing liquid in which processed fine particles that are chemically reactive with the optical element material are dispersed is made to flow along the processed surface, and chemically bonded to the processed fine particles by a chemical interaction between the processed fine particles and the interface between the processed particles. An EEM processing step of creating a surface with desired accuracy by using an EEM process of removing the formed surface atoms together with the processed fine particles by decoction of the processing liquid.
In the presence of a treatment liquid containing water in which catalyst metal fine particles composed of transition metal elements are dispersed , the treatment pad and the surface of the object to be treated are relatively displaced while being in contact with each other, and the water and the surface of the catalyst metal interact with each other. The catalytic function of the catalytic metal in contact with the surface of the optical element material promotes the direct hydrolysis of the optical element material or the oxidation of the optical element material and the hydrolysis of the oxide film, and the decomposition product due to the hydrolysis is used as the optical element material. Using a catalyst-assisted etching process that does not have a processing reference surface, at least the surface of the optical element material, which is a reflective surface, is uniformly removed together with the adhered fine particles including the processed fine particles adhering to the surface. Surface treatment process and
A method of manufacturing an optical element, which is characterized by being manufactured by. The EEM processing step is
The rotating sphere-shaped processing head that forms a high shear flow of the processing liquid along the processing surface by the rotation of the elastic rotating sphere so that the surface roughness becomes 0.13 nm RMS or less in the high frequency region (1 μm × 1 μm region). Processing process,
The rotating sphere-shaped processing head that forms a high shear flow of the processing liquid along the processing surface by the rotation of the elastic rotating sphere so that the surface roughness becomes 0.15 nm RMS or less in the medium frequency region (100 μm × 100 μm region). Processing process,
Unit machining marks by the rotary spherical machining head or unit machining marks by the nozzle-type machining head that eject the machining fluid from the nozzle to form a high shear flow of the machining fluid along the machining surface are relative to the machining surface. In the low frequency region (from 1 mm or more to the effective region of the reflective surface), the shape error is reduced to 1 nm RMS or less by numerically controlling EEM that numerically controls the residence time of the processing head and spatially determines the removal amount. The process of processing
The method for manufacturing an optical element according to claim 1, which comprises at least one step. The method for manufacturing an optical element according to claim 1 or 2 , wherein the processing pad has a structure having a catalyst metal composed of a transition metal element at least on its surface, and the catalyst does not serve as a processing reference surface . The method for manufacturing an optical element according to claim 3 , wherein a processing pad having a structure in which the catalyst metal fine particles are supported in a CMP processing pad is used as the processing pad . The cleaning method according to claim 3 , wherein the processing pad has a structure in which a non-woven fabric or a woven fabric made of a thin catalyst metal wire is provided on the surface . The claim comprises a cleaning step of removing adhered fine particles on the surface of the optical element material by the surface treatment step, and then dissolving and removing the metallic fine particles adhering by the surface treatment step with an acid or an alkaline solution. The method for manufacturing an optical element according to any one of 1 to 5. The flow of the treatment liquid containing water in the surface treatment step includes a step of supplying the treatment liquid to the removal unit and flowing the treatment liquid to the outside from the periphery of the removal unit, and discharging the treatment liquid from the periphery of the removal unit. The method for manufacturing an optical element according to any one of claims 1 to 6, which includes a step. A claim that the flow of the treatment liquid containing water in the surface treatment step includes a step of supplying the treatment liquid around the removal unit and a step of sucking the treatment liquid inward from the periphery of the removal unit and discharging the treatment liquid. The method for manufacturing an optical element according to any one of 1 to 6. The flow of the treatment liquid containing water in the surface treatment step is a step of supplying the treatment liquid to the removal unit and flowing the treatment liquid to the outside from the periphery of the removal unit, and the treatment liquid is discharged from the cleaning region due to overflow. The method for manufacturing an optical element according to any one of claims 1 to 6, which includes the steps of The method for manufacturing an optical element according to any one of claims 1 to 6, wherein the surface treatment step is batch-treated in a treatment tank containing a treatment liquid containing water. The method for manufacturing an optical element according to any one of claims 1 to 10, wherein the optical element material is a Si single crystal or an oxide. The treatment solution containing water in the surface treatment step is a mixture of pure water or ultrapure water mixed with at least one of an oxidation accelerator, a pH adjusting solution, a buffer solution, and a complex solution that helps dissolve decomposition products. The method for manufacturing an optical element according to any one of claims 1 to 11 .