JP2009167030A - Surface flattening method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface flattening method which enables further reduction of surface roughness of an optical element and is suitable for flattening a surface of the optical element independent of its surface profile. <P>SOLUTION: The surface flattening method for flattening a convex portion 51 formed on the surface of the optical element structure 3 comprises steps of: placing the optical element structure 3 in a chamber 11 into which a chlorine gas is introduced; exposing the optical element structure 3 to a light having a wavelength longer than the absorption edge wavelength of gas molecules of the chlorine gas so as to generate a near-field light at the local area of the convex portion 51 on the surface of the optical element structure 3; dissociating the chlorine gas by the near-field light generated at the local area of the convex portion 51 to produce an active species; and etching the convex part 51 by producing a reaction product of a chemical reaction between the produced active species and the convex part. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a surface flattening method suitable for flattening the surface of an optical element and a method for producing an optical element using the same.

Conventionally, as a method for flattening optical elements such as lenses, reflecting mirrors, window plates, polarizing elements using synthetic quartz, BK7 (borosilicate crown glass), etc., for example, polishing as shown in Patent Document 1 A method has been proposed. In this polishing method, a processing apparatus having at least a fixed abrasive tool and a lens holder is used. The lens, which is an optical element, is held by the lens holder, and the held lens is used as a processing surface of the fixed abrasive tool. The lens surface is polished while the fixed abrasive tool is driven to rotate at a predetermined rotational speed by a rotary motor while being in contact with the lens, and the lens is swung in an arc shape on the processing surface of the fixed abrasive tool. . In this case, normally, a polishing liquid is appropriately introduced between the lens and the fixed abrasive tool through a nozzle or the like.
JP 2001-198784 A

  By the way, in recent years, the demand for ultra-high power lasers such as fusion lasers is increasing. Optical elements such as lenses and reflecting mirrors are also used in such ultra-high power laser devices. The optical elements used in these ultra-high power laser devices are easily destroyed by the strong electric field of the laser beam passing through the surface or inside thereof. In particular, when laser damage is caused by such ultra-high power laser light, the laser damage is further expanded from the damaged portion. For this reason, an optical element having excellent laser resistance is required in order to make an ultra-high-power laser device that is expected to increase in demand in the future practical. And it is thought that the laser tolerance of such an optical element is influenced by the surface roughness of the optical element.

  Here, the surface flattening method of the optical element currently proposed as shown in the above-mentioned Patent Document 1 is obtained by physically polishing the lens surface using a fixed abrasive tool or a polishing liquid. Therefore, it was not possible to perform polishing to irregularities smaller than the physical dimensions of the fixed abrasive tool surface and the polishing liquid. Further, in the polishing performed by introducing the polishing liquid as described above, the polishing liquid is agglomerated and solidified with the progress of the polishing process to form coarse particles, which cause scratches on the surface of the optical element. (Scratch) was formed, and fine irregularities remained on the surface of the optical element. In addition, when performing planarization using physical polishing, it is necessary to condition the optimal polishing conditions according to the material to be polished and the plate thickness, but in reality the unevenness is minimized. It was impossible to find the conditions, and it was very difficult to determine the processing conditions.

  For this reason, it is difficult to obtain an optical element having excellent laser resistance depending on the surface flattening method by physical polishing that has been proposed in the past. Therefore, it has been desired to propose a flattening method that makes it possible to perform flattening.

  In particular, with the surface flattening methods currently proposed, depending on the shape of the optical element, it is often difficult to polish the surface of the optical element itself, so that it is not limited by the surface shape of the optical element. Therefore, a technique that can flatten the surface has been desired.

  Therefore, the present invention has been devised in view of the above-mentioned problems, and the object of the present invention is to further increase the surface roughness compared with the conventionally proposed surface flattening methods of optical elements. It is an object of the present invention to provide a surface flattening method that can be reduced and is suitably used to flatten the surface of the optical element without depending on the surface shape. Another object of the present invention is to provide an optical element manufacturing method capable of manufacturing an optical element having excellent laser resistance.

  In order to solve the above-mentioned problem, the present inventor arranges the optical element in a chamber into which a chlorine-based gas is introduced, and emits light having a wavelength longer than the absorption edge wavelength of the gas molecule of the chlorine-based gas. By irradiating the convex portion with this, near field light is generated in the local region of the convex portion, and the chlorine-based gas is dissociated through a non-resonant process based on the near field light generated in the local region of the convex portion. Inventing a surface flattening method characterized in that an active species is generated, and the generated active species and the convex portion are chemically reacted to generate a reaction product to etch the convex portion. did.

  That is, the invention according to claim 1 of the present application is a surface flattening method for flattening a convex portion formed on the surface of an optical element structure, and the optical element structure is disposed in a chamber into which chlorine-based gas is introduced. By irradiating the optical element structure with light having a wavelength longer than the absorption edge wavelength of the gas molecule of the chlorine-based gas, near-field light is generated in a local region of the convex portion of the optical element structure surface. The active species are generated by dissociating the chlorine-based gas based on the near-field light generated in the local region of the convex part, and the generated active species and the convex part are chemically reacted to produce a reaction product. The above-mentioned convex part is etched by generating.

The invention according to claim 2 of the present application is characterized in that, in the invention according to claim 1, the partial pressure of gas molecules of the chlorine-based gas in the chamber is 1 × 10 ⁻⁵ Pa or more.

The invention according to claim 3 of the present application is characterized in that, in the invention according to claim 1 or 2, the energy density of the irradiated light is 1 μJ / cm ² or more.

  The invention according to claim 4 of the present application is the method of manufacturing an optical element including the step of flattening the convex portion formed on the surface of the optical element structure, and the optical element structure is placed in a chamber into which chlorine-based gas is introduced. And irradiating the optical element structure with light having a wavelength longer than the absorption edge wavelength of the gas molecule of the chlorine-based gas, so that the near-field light is applied to the local region of the convex portion on the surface of the optical element structure. Based on the near-field light generated in the local region of the convex part, the chlorine-based gas is dissociated through a non-resonant process to generate active species, and the generated active species and the convex part are A method of manufacturing an optical element, wherein the convex portion is removed by chemical reaction to generate a reaction product.

The invention according to claim 5 of the present application is characterized in that, in the invention according to claim 4, the partial pressure of gas molecules of the chlorine-based gas in the chamber is 1 × 10 ⁻⁵ Pa or more.

The invention according to claim 6 of the present application is the invention according to claim 4 or 5, characterized in that the energy density of the irradiated light is 1 μJ / cm ² or more.

  According to the invention according to claim 1 of the present application, it is possible to flatten the convex portion having a size difficult to remove by physical polishing by a simple process of introducing gas into the apparatus and irradiating light. It has become. In particular, since the reaction automatically proceeds only by introducing gas and irradiating light, there is no need to perform special control of various elements in the apparatus depending on the surface shape of the optical element structure to be flattened, The surface can be flattened. In addition, according to the first aspect of the present invention, it is possible to make the surface roughness of the optical element structure uniform over the entire irradiation range of the light, and to perform planarization for further reducing the surface roughness.

  According to the invention of claim 4 of the present application, it is possible to flatten convex portions having a size that has been difficult to remove by physical polishing, compared with an optical element obtained by physical polishing. Since the surface roughness is reduced, it is possible to obtain an optical element having superior laser resistance as compared with conventionally proposed optical elements.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.

  First, an optical element that is an object of a surface flattening method to which the present invention is applied will be described.

  The optical element that is the subject of the present invention is used as, for example, a lens, a mirror, a prism, a substrate, a beam splitter, or a polarizing element.

  The optical element in the present invention is embodied by optical element structures 3A to 3E having a shape schematically shown in FIG. As shown in FIGS. 1A and 1B, the optical element structure 3 </ b> A is an optical element called a so-called parallel plane substrate, which has a flat shape on both the front surface 31 and the back surface 32. As shown in FIGS. 1C to 1F, the optical element structures 3B and 3C are lenses having a concave curved surface 33 and a convex curved surface 34 on the front surface, and the back surface 32 is formed in a flat shape. As described above, the optical element that is the subject of the present invention includes the optical element structure 3A having a flat surface, the optical element structures 3B and C having a curved surface, and the like. However, the present invention is not limited to the illustrated shape. Moreover, the optical element structure which is the subject of the present invention is not limited to the size.

  The material of the optical element structure 3 is, for example, optical glass such as crown glass such as BK7, flint glass such as F2, synthetic quartz, calcium fluoride, lithium fluoride, barium fluoride, rock salt (NaCl). And an optical crystal such as germanium (Ge), sapphire, and zinc selenium (ZnSe).

  These optical element structures 3 are provided with convex portions 51 as schematically shown in FIG. The convex portion 51 remains on the surface of the optical element structure 3 after being subjected to physical polishing or the like, and has a size of several nm to several μm.

  Next, the surface flattening apparatus 1 used in the surface flattening method to which the present invention is applied will be described.

  The surface flattening apparatus 1 has a configuration schematically shown in FIG. The surface flattening device 1 includes a chamber 11, a stage 13 in the chamber 11, a gas supply unit 17 for supplying a gas into the chamber 11, and a light source 14 for irradiating the chamber 11 with light. I have. Further, the surface flattening device 1 includes an illumination optical system 16 that can control the shape and polarization direction of light, a reflection mirror 15 that reflects light emitted from the light source 14 to the illumination optical system 16, and a chamber 11. An opening window 18 for introducing light into the chamber 11 and an exhaust port 19 for exhausting gas in the chamber 11 are provided.

A gas mixture obtained by mixing a chlorine-based gas and an inert gas is supplied from the gas supply unit 17 into the chamber 11 at any time so as to have a predetermined pressure. This chlorine-based gas is introduced into the chamber 11 in order to flatten the optical element structure 3 having the convex portions 51. For example, Cl ₂ (chlorine), BCl ₃ (boron trichloride), CCl ₄ (Carbon tetrachloride) etc. Further, the inert gas is embodied by a gas formed by mixing any one or two or more of N2, He, Ar, Kr, Xe and the like. The reason why the chlorine-based gas is applied is that the absorption edge wavelength on the long wave side of the gas molecule of the chlorine-based gas is in a visible wide band, and light having a wavelength longer than the absorption edge wavelength is irradiated from a light source as will be described later. This is because an inexpensive visible light range lamp or white light source can be used as the light source 14.

  The stage 13 is provided with a mounting portion (not shown) for mounting the optical element structure 3 and a heating mechanism (not shown) for heating the optical element structure 3, thereby the optical element structure 3. In the case where the chlorine-based gas is etched above, the etching reaction rate can be controlled. The stage 13 may be provided with a high-precision stage mechanism (not shown) for adjusting the position of the optical element structure 3 with high accuracy.

  The light source 14 emits light having a predetermined wavelength based on control by a driving power source (not shown). As will be described in detail below, the light source 14 emits light having a wavelength longer than the absorption edge wavelength of gas molecules of the chlorine-based gas. The light source 1 is embodied by a laser diode or the like, for example.

  The illumination optical system 16 is embodied with a polarization lens, a focusing lens, and the like (not shown). As a result, the beam diameter and beam shape can be controlled in accordance with the position, size, range, and the like of the convex portion 51 on the surface of the optical element structure 3 to narrow the light irradiation range.

  Next, various conditions in the planarization method to which the present invention is applied will be described.

  First, the wavelength of light emitted from the light source 14 of the surface flattening device 1 described above will be described.

  FIG. 4 shows the relationship of potential energy with respect to the internuclear distance of gas molecules of the chlorine-based gas introduced into the chamber 11. Normally, light having a photon energy equal to or greater than the energy difference Ea between the ground level and the excited level, that is, shorter than the absorption edge wavelength of the gas molecule with respect to the gas molecule of the chlorine-based gas introduced into the chamber 11. When irradiated with light having a wavelength (hereinafter, this light is referred to as resonance light), the gas molecules are directly excited to the excitation level. Since this excited level exceeds the dissociation energy Eb, active species are generated by photodissociating gas molecules in the direction indicated by the arrows.

  In the present invention, it is not a resonance process in which a gas molecule as described above is irradiated with resonance light to directly excite the gas molecule to an excitation level and then dissociate, but from the absorption edge wavelength of the gas molecule. The substrate surface is flattened using a non-resonant process that occurs when light of a long wavelength (hereinafter, this light is referred to as non-resonant light) is applied to the gas molecules as near-field light. Do.

  When irradiated with non-resonant light that is propagating light, gas molecules are not normally excited to the excitation level, but when irradiated with non-resonant light that is near-field light, this gas molecule undergoes a non-resonant process and becomes an active species. It becomes possible to dissociate into etc. This non-resonant process is classified into process T1, process T2, and process T3 as shown in FIG. Process T1 refers to a process in which gas molecules are excited through a plurality of molecular vibration levels (multistage transition), and as a result, are excited to the excited level and then dissociated into active species. In process T2, when light having a light energy higher than the dissociation energy Eb of gas molecules (hereinafter referred to as S1 mode) is irradiated, the gas molecules are excited to the molecular vibration level of the energy level higher than the dissociation energy. As a result, it refers to the process of being directly dissociated into active species. Further, in the process T3, when light having a light energy less than Eb of gas molecules (hereinafter referred to as S2 mode) is irradiated, the gas molecules are excited through a plurality of molecular orbital levels (multistage transition), This refers to the process of being dissociated into active species after being excited to a molecular vibration level of less than Ea and greater than or equal to Eb.

  In this way, when non-resonant light, which is near-field light, is irradiated, the non-resonant process occurs when the gas molecules are irradiated to the molecular vibration level when the near-field light is irradiated to the gas molecules. This is because it can be directly excited.

  In other words, in normal photodissociation using propagating light, the electric field intensity of propagating light has a uniform distribution in a molecular size space, so that only light electrons among the nuclei and electrons that make up gas molecules Reacts, but cannot change internuclear distance. On the other hand, in the photodissociation using near-field light, the electric field intensity of the near-field light is significantly displaced in a molecular size space, resulting in an uneven distribution. For this reason, when using near-field light, not only the electrons of gas molecules but also the nuclei react, and the internuclear distance can be changed periodically, and the molecules are excited directly into the vibrational level. (Non-adiabatic chemical reaction).

  The near-field light here refers to non-propagating light that clings to the surface of the object when the surface of the object having a size of about 1 μm or less is irradiated with the propagation light. This near-field light has a very strong electric field component, but has a property that the electric field component rapidly decreases as the distance from the surface of the object increases. The thickness from the object surface at which this very strong electric field component is seen depends on the size of the object, and is of the same thickness as the size of the object. The local region in the present invention refers to a local region on the surface of an object where such a very strong electric field component is seen. For example, the minute convex portion 51 on the surface of the optical element structure 3 in FIG. The edge part at the tip.

  In the present invention, the wavelength of light emitted from the light source 14 to the optical element structure 3 is preferably 10 μm or less. This is because when the wavelength of this light exceeds 10 μm, direct excitation to the vibration level of the gas molecules hardly occurs, and the etching rate by near-field light is reduced.

In the present invention, the partial pressure of gas molecules of the chlorine-based gas introduced into the chamber 11 is preferably at least 1 × 10 ⁻⁵ Pa or more. When the partial pressure of gas molecules of the chlorine-based gas in the chamber 11 is less than 1 × 10 ⁻⁵ Pa, it is necessary for causing an etching reaction in the space near the convex portion 51 on the surface of the optical element structure 3. This is because gas molecules of the chlorine-based gas do not reach, and this makes it difficult for the etching reaction to proceed even if near-field light is generated in the convex portion 51. The partial pressure of the gas molecules of the chlorine-based gas introduced into the chamber 11 is too low, so that the etching rate becomes low, and it takes a long time to complete the flattening. Is more desirable. As a result, a sufficient amount of gas molecules of the chlorine-based gas necessary for causing the etching reaction reach in the space near the convex portion 51 on the surface of the optical element structure 3, and the planarization process can be completed in a short time. It becomes possible. The measurement of the partial pressure of gas molecules of the chlorine-based gas is performed using a partial pressure gauge such as a mass filter (not shown), but the measuring device is not particularly limited.

In the present invention, it is desirable that the energy density of light applied to the optical element structure 3 is at least 1 μJ / cm ² or more. This is because if the energy density is less than 1 μm, the etching reaction by near-field light does not proceed easily, and it becomes difficult to sufficiently planarize the surface of the optical element structure 3. Note that if the energy density of the irradiated light is too low, the etching rate becomes low, and it takes a long time to complete the planarization. Therefore, it is more desirable to set the energy density to 100 J / cm ² .

  As the pressure of gas molecules introduced into the chamber 11 and the energy density of light to be irradiated are increased, the light irradiation time can be reduced, and the work time required for flattening the optical element structure can be reduced. Is possible.

  Next, steps of a method for manufacturing an optical element including a surface flattening method to which the present invention is applied will be described.

  First, an optical element structure 3 to be subjected to surface flattening is prepared. In this case, the optical element structure 3 obtained by various molding methods such as press molding and injection compression molding is subjected to a so-called roughening step, sanding step, and polishing step, and then the surface flatness of the present invention. You may make it give a conversion method. In addition to this, the existing optical element structure 3 may be flattened instead of the newly produced optical element structure 3.

  Next, as shown in FIG. 3, the optical element structure 3 is disposed on the stage 13 in the chamber 11. In this case, a chlorine-based gas may be introduced into the chamber 11 from the gas supply unit 17 in advance, or a chlorine-based gas may be introduced after the optical element structure 3 is arranged.

  Next, as shown in FIG. 6A, light is irradiated from the light source 14 to the optical element structure 3 through the reflection mirror 15 and the like. Thereby, near-field light is generated in the local region of the convex portion 51. In this case, since the irradiated light is non-resonant light, the chlorine-based gas does not react at a flat portion on the surface of the optical element structure 3 where no near-field light is generated, and the near-field region at the tip of the convex portion 51. The reaction hardly progresses even in the concave portions between the convex portions 51 where a relatively weak near-field region is generated, and the reaction proceeds only in the local region of the convex portion 51 where the near-field light is generated. Become.

  In this case, as shown in FIG. 7, the chlorine-based gas G10 is dissociated through the non-resonance process as described above to generate the active species G11, and the active species G11 and the atoms and molecules 21a of the convex portions 51 Chemically reacts to produce a volatile reaction product G12. The reaction product G12 is discharged out of the chamber 11 by a vacuum pump (not shown) connected to the exhaust port 19.

  As the reaction proceeds, the size of the convex portion 51 is gradually refined. As a result, as shown in FIG. 6B, the surface roughness of the optical element structure 3 is reduced before the planarization. This etching reaction is performed when the convex portion 51 becomes substantially at the same level as the other atomic layers on the surface of the optical element structure 3 around it, that is, when the convex portion 51 is almost completely removed. The region where light is generated also disappears, and the planarization process ends in a self-organized manner. However, depending on the output density of the irradiated light, it may take a long time to complete the reaction. In this case, when the desired surface roughness is obtained, the surface flattening is appropriately performed. The process will be terminated.

  As described above, according to the surface flattening method to which the present invention is applied, the convex portion having a size difficult to be removed by physical polishing is introduced into the apparatus by introducing a gas into the apparatus and irradiating light. It is possible to flatten. In particular, since the reaction automatically proceeds only by introducing gas and irradiating light, there is no need to perform special control of various elements in the apparatus depending on the surface shape of the optical element structure to be flattened, The surface can be flattened. For this reason, chlorine-based gas is also applied to the concave curved surface 33 and the convex curved surface 34 having a curved surface, such as the optical element structures 3B and 3C, which have conventionally been difficult to accurately perform physical polishing. Flattening is possible without any special control by a simple process of simply irradiating the curved surface or the like with light in an atmosphere.

  The surface flattening apparatus 1 includes, for example, a gas supply unit 17 used in a photo CVD (Chemical Vapor Deposition) apparatus, a sputtering apparatus, a photo-excited etching apparatus, a reactive ion etching apparatus, an inductively coupled plasma etching apparatus, and the like. The light source 14 and the chamber 11 may be used as they are. In this case, the surface planarization method to which the present invention is applied can be realized only by changing only the wavelength of the light source of the photo-CVD apparatus. When the wavelength of the light source is changed, white light may be emitted from the light source and passed through a color filter through the aperture window 18 or the like, and monochromatic light may be emitted.

  Moreover, when the convex part 51 is too large, such as the magnitude | size is 1 mm or more, the time which reaction requires will be enormous. Therefore, in this case, physical polishing may be performed in advance, the surface of the optical element structure 3 may be polished to some extent, and the present invention may be applied as a subsequent finishing process.

  An optical element structure 3A made of synthetic quartz that has been previously physically polished with an abrasive containing cerium oxide or the like is placed on a stage 13 in the chamber 11, and the wavelength from the light source 14 to the optical element structure 3A is set. Irradiation with 532 nm light was performed so that the output density was 20 mW / cm 2. Chlorine gas was supplied from the gas supply unit 17 into the chamber 11 so that the partial pressure of the gas molecules of the chlorine gas in the chamber 11 was 100 Pa. After irradiating light for a predetermined time, the optical element structure 3A was subjected to ultrasonic cleaning at a frequency of 40 kHz and a cleaning time of 5 minutes, and then the surface shape of the optical element structure 3A was measured with an atomic force microscope. Observed over a point. The surface shape of the obtained optical element structure 3A was evaluated based on JIS B 0601, and this was defined as the surface roughness Ra.

  8 to 10 show the surface roughness for each measurement region obtained when the light irradiation time is changed to 60 min, 90 min, and 120 min, respectively. The value indicated by the square symbol indicates the surface roughness before flattening, and the value indicated by the circular symbol indicates the surface roughness after flattening.

  When the light irradiation time is 60 min, the average value of the surface roughness before flattening in each measurement region is 2.391 mm, and the average of the surface roughness after flattening in each measurement region is 2.391 mm. The value was 2.229 mm, and a reduction in surface roughness of 0.246 mm was confirmed.

  When the light irradiation time is 90 min, the average value of the surface roughness before flattening in each measurement region is 3.131 mm, and the average of the surface roughness after flattening in each measurement region The value was 2.391 mm, and a reduction in surface roughness of 0.740 mm was confirmed.

  When the light irradiation time is 120 min, the average value of the surface roughness before flattening in each measurement region is 2.719 mm, and the average of the surface roughness after flattening in each measurement region is 2.719 mm. The value was 2.374 mm, and a reduction in surface roughness of 0.345 mm was confirmed.

  In particular, in any case, variation in the surface roughness was observed depending on the measurement region before the planarization, but this variation was eliminated after the planarization. . That is, by applying the present invention, it is possible to make the surface roughness of the optical element structure 3 uniform over the entire irradiation range of the light, and to perform planarization that further reduces the surface roughness. confirmed.

Of the experimental conditions shown in FIGS. 8 to 10, the test was performed by changing only the partial pressure of the gas molecules of the chlorine gas in the chamber to 2 Pa and setting the light irradiation time to 60 minutes. ^Although the reduction of the surface roughness of about ^-1 mm was not confirmed, it is considered that the surface roughness of about 1 × 10 ^-1 mm can be reduced in principle if the light irradiation time is further increased. .

  FIG. 11 shows the surface obtained for each different energy density by changing the energy density by changing the irradiation time of light after setting the wavelength, power density, gas pressure, and type of the atmospheric gas as above. The value of the roughness reduction amount is shown. Here, the surface roughness reduction amount is the optical element structure after the surface flattening method is applied from the surface roughness value of the optical element structure before the surface flattening method to which the present invention is applied. This is the value obtained by reducing the surface roughness value of the body.

As shown in FIG. 11, as the energy density increases, the surface roughness is further reduced, and when the energy density is 100 J / cm ² or more, the surface roughness of the optical element structure is surely reduced. It is confirmed that it is reduced. Since the surface roughness tends to be further reduced as the energy density increases, for example, when light is irradiated from a light source so that the energy density is 700 J / cm ² , the surface roughness reduction amount is about 2 mm. It is considered a thing.

It is a figure for demonstrating the optical element used as the object of application of this invention, (a) is a top view of 3 A of optical element structures, (b) is the sectional view on the AA line, (c) is an optical element. A plan view of the structure 3B, (d) is a sectional view taken along the line BB, (e) is a plan view of the optical element structure 3C, and (f) is a sectional view taken along the line CC. It is a figure for demonstrating the shape of the surface of an optical element structure. It is a schematic block diagram which shows the structure of the surface planarization apparatus used in order to implement | achieve this invention. It is a figure for demonstrating resonant light and non-resonant light. It is a figure for demonstrating a non-resonance process. It is a figure for demonstrating the process of planarizing the surface of an optical element structure. It is a figure for demonstrating reaction which generate | occur | produces in the local area | region of a convex part. It is a figure shown about the surface roughness of the optical element structure planarized by the surface planarization method to which this invention is applied, and irradiation time was set to 60 minutes. It is a figure shown about the surface roughness of the optical element structure planarized by making the irradiation time into 90 minutes by the surface planarization method to which this invention is applied. It is a figure shown about the surface roughness of the optical element structure planarized by the surface planarization method to which this invention is applied, and irradiation time was 120 minutes. It is a figure which shows the relationship of the surface roughness reduction amount with respect to energy density.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Surface planarization apparatus 3 Optical element structure 11 Chamber 13 Stage 14 Light source 15 Reflection mirror 16 Illumination optical system 17 Gas supply part 18 Opening window 19 Exhaust port 51 Convex part

Claims (6)

In a surface flattening method for flattening a convex portion formed on the surface of an optical element structure,
Arranging the optical element structure in a chamber into which chlorine-based gas is introduced,
By irradiating the optical element structure with light having a wavelength longer than the absorption edge wavelength of gas molecules of the chlorine-based gas, near-field light is generated in a local region of the convex portion on the surface of the optical element structure,
Based on the near-field light generated in the local region of the convex part, dissociate the chlorine-based gas to generate active species,
A surface flattening method comprising: etching the protrusion by chemically reacting the generated active species with the protrusion to generate a reaction product. The surface flattening method according to claim 1, wherein a partial pressure of gas molecules of the chlorine-based gas in the chamber is set to 1 × 10 ⁻⁵ Pa or more. The surface flattening method according to claim 1, wherein an energy density of the irradiated light is 1 μJ / cm ² or more. In a method for producing an optical element having a step of flattening a convex portion formed on the surface of an optical element structure,
Arranging the optical element structure in a chamber into which chlorine-based gas is introduced,
By irradiating the optical element structure with light having a wavelength longer than the absorption edge wavelength of gas molecules of the chlorine-based gas, near-field light is generated in a local region of the convex portion on the surface of the optical element structure,
Based on the near-field light generated in the local region of the convex part, dissociate the chlorine-based gas to generate active species,
A method of producing an optical element, wherein the convex part is removed by chemically reacting the generated active species with the convex part to generate a reaction product. The method for producing an optical element according to claim 4, wherein a partial pressure of gas molecules of the chlorine-based gas in the chamber is 1 × 10 ⁻⁵ Pa or more. 6. The method of manufacturing an optical element according to claim 4, wherein the energy density of the irradiated light is 1 μJ / cm ² or more.

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