JP5444098B2 - Optical attenuator and optical attenuator module - Google Patents

Description

  The present invention is a light including an optical attenuator that is an element for reducing the amount of light to a desired level in an apparatus that uses light, such as a laser processing apparatus, and an operation unit that adjusts the amount of light to a desired level using the optical attenuator. The present invention relates to an attenuator module.

  As the optical attenuator, there is a variable optical attenuator that can attenuate the amount of light to a plurality of levels. The variable optical attenuators are roughly classified into three types: (1) butterfly method, (2) polarization method, and (3) film distribution method.

  The butterfly method utilizes the incident angle dependency of the transmittance of the dielectric multilayer film, and the transmittance is changed by tilting the element. This method is widely adopted because it does not cause a difference in transmittance within the beam diameter and can be downsized including the operation unit.

  The polarization method is a method in which a polarizing plate and a (λ / 2) wave plate are arranged on the optical path of laser light, and the transmittance is changed by relatively rotating the polarizing plate or the (λ / 2) wave plate. . Some use a polarizing beam splitter (PBS) instead of a polarizing plate. Although the polarization method is easy to realize, it does not function unless the light beam to be attenuated is linearly polarized light or a light beam close thereto, and does not function with circularly polarized light or random polarized light.

  The film distribution method is an element in which the transmittance is changed for each place by changing the film thickness for each place when forming a dielectric multilayer film or a metal thin film. However, the transmittance characteristics of the thin film change depending on the operating temperature, and the amount of incident light that is not transmitted is absorbed by the element, so that the temperature of the element itself rises, and the physical film thickness of the thin film increases accordingly. The transmittance changes. In high performance thin films having a large absorption coefficient, the temperature rise is more prominent. Therefore, in order to enable actual use, there is a problem in that it is necessary to continue irradiation with laser and wait until the element temperature becomes constant and the transmittance is stabilized. In addition, the use of a high-power laser may damage the thin film and make it unusable.

  Therefore, at present, the butterfly method, which has no transmittance distribution within the beam diameter, can cope with random polarization, and can cope with the downsizing of the entire apparatus, is mainly used.

  Both methods use thin films. Thin films are expensive due to their poor yield. In particular, a high-performance thin film has a higher yield because the film thickness must be strictly controlled, and the price is further increased due to the fact that the thin film material is expensive.

  In both the butterfly method and the film distribution method, those using a dielectric multilayer film, when the optical attenuator is used in a high output optical system such as a YAG laser processing apparatus, the thin film absorbs the laser beam and the thin film material is sublimated. For example, durability is an issue.

  In either method, the light beam is transmitted through the thin film. The transmittance characteristic of the thin film varies depending on the operating temperature. Further, in any case, the amount of incident light that is not transmitted is absorbed by the element, so that the physical thickness of the thin film changes and the transmittance changes as the temperature of the element itself increases. In high performance thin films having a large absorption coefficient, the temperature rise is more prominent. Therefore, in order to enable actual use, it has been necessary to continue irradiation with the laser and wait until the element temperature becomes constant and the transmittance is stabilized.

  Since the conventional method uses a thin film and has a large wavelength dependency and a narrow wavelength range, a dedicated optical element is required for each laser wavelength to be used.

  In the butterfly method, the incident angle is changed in order to change the transmittance. However, the thin film has a large dependency on the incident angle with respect to the optical characteristic, and the characteristic changes greatly with a slight difference in the incident angle. .

  An object of the present invention is to provide an optical attenuator having high durability and stable transmittance characteristics, and an optical attenuator module using the optical attenuator.

  The optical attenuator of the present invention has a fine structure composed of a concavo-convex pattern having a size such that incident light is diffracted on at least one of the front and back surfaces of a transparent glass substrate in the wavelength range of incident light. In one form, the fine structure has a constant pitch and has a plurality of regions having different filling factors (FF) indicating the ratio of the convex portion to the pitch. The ratio of the transmitted light amount of the 0th-order diffracted light to the incident light amount is different between regions having different filling factors. The ratio of the transmitted light amount of the 0th-order diffracted light to the incident light amount is changed by moving the incident position of the incident light with respect to the fine structure between regions having different filling factors.

  Incident light is not absorbed by the optical attenuator element, but is emitted from the optical attenuator element as first-order diffracted light and second-order diffracted light in addition to zero-order diffracted light.

  The pitch of the fine structure composed of the concavo-convex pattern is equal to or greater than the magnitude at which incident light diffracts. Specifically, the pitch of the fine structure is preferably in the range of 2 to 600 times the incident light wavelength. This range is determined as follows. The condition under which diffraction occurs is “pitch> incident light wavelength”. However, in a region where the pitch is equal to the incident light wavelength, the transmittance does not become zero even if the depth of the fine pattern of the fine structure is changed. FIG. 9 shows the relationship between the depth of the concavo-convex pattern having a fine structure and the transmittance of 0th-order diffracted light. The incident light wavelength of the data of FIG. 9 is 1.064 μm, and the filling factor is 0.5. For example, when the pitch is 2 μm, the transmittance of the 0th-order diffracted light is about 7% when the depth of the uneven pattern with a fine structure is 1.4 μm. In order to make the transmittance of the 0th-order diffracted light closer to 0%, the lower limit of the pitch of the fine structure needs to be at least twice the wavelength used. The upper limit of the pitch of the fine structure is not limited from the condition that diffraction occurs. However, since the diffraction angle decreases as the pitch of the fine structure increases, it becomes difficult to separate the 0th-order diffracted light (diffraction angle is 0 °) from the 1st-order diffracted light. For example, if the pitch is 100 times the incident light wavelength, the diffraction angle of the first order diffracted light is 0.57 °, if it is 500 times, it is 0.12 ° if it is 575 times, if it is 0.75, if it is 0.10 ° and 1000 times. 0.06 °. From the viewpoint of separating the 0th-order diffracted light and the 1st-order diffracted light, the upper limit of the pitch is about 600 times the incident light wavelength.

  Further, the depth of the concave portion of the fine structure is suitably 0.1% to 80% of the pitch. This range is determined as follows. According to the result of FIG. 9, for example, in the case of a fine structure with a pitch of 2 μm, the depth of the concave portion of the fine structure is set to about 0 to 1.4 μm in order to change the transmittance of the 0th-order diffracted light from the maximum value to the minimum value. It is necessary to change within the range. The depth of the concave portion of the fine structure at this time corresponds to 0% to 70% of the pitch. Similarly, Table 1 summarizes the relationship up to a pitch of 20 μm.

  As shown in FIG. 2, the transmittance of the 0th-order diffracted light takes a minimum value when the filling factor is 0.5. Therefore, from the results of Table 1, when the pitch is 1.5 μm, the depth of the concave portion of the microstructure is Must be 80% of the pitch. If the pitch is 20 μm, the depth of the concave portion of the fine structure is good at 6% of the pitch. If the pitch is further increased, the depth of the concave portion of the fine structure can be reduced. Since the pitch has an upper limit from a practical viewpoint, the depth of the concave portion of the fine structure cannot be reduced as much as possible, and the limit is about 0.1%.

  Since the fine structure is formed by dry etching, the depth of the recess is shallow in a region having a large filling factor and deep in a region having a small filling factor.

  The optical attenuator of the present invention can be used with either a glass substrate whose front and back surfaces are parallel or non-parallel. If glass substrates whose front and back surfaces are parallel to each other are used, the 0th-order diffracted light is emitted in the same direction as the incident light. On the other hand, if glass substrates whose front and back surfaces are not parallel to each other are used, the 0th-order diffracted light is emitted in a direction different from the incident light.

  The optical attenuator of the present invention includes both those in which the microstructure is formed only on one surface of the glass substrate and those formed on both the front and back surfaces.

  In the optical attenuator in which the fine structure is formed on both the front and back surfaces of the glass substrate, the fine structure of the front side surface and the fine structure of the back side surface may be the same or different. For example, the fine structure on both sides may have the same pitch, the fine structure on the front side and the fine structure on the opposite side may have the same filling factor, and the fine structure on the front side and the opposite side The filling factor of the fine structure of the surface may be different.

  In one form of the optical attenuator, the microstructure is configured so that the filling factor changes continuously or stepwise along a straight line on the surface of the glass substrate, and the filling factor of the microstructure changes in the glass substrate. When moving along a straight line in the direction, the ratio of the transmitted light amount of the 0th-order diffracted light to the incident light amount changes. Therefore, when this optical attenuator is used, the glass substrate is moved along a straight line in the direction in which the filling factor of the fine structure is changed in order to change the ratio of the transmitted light amount of the 0th-order diffracted light to the incident light amount.

  In another form of the optical attenuator, the microstructure is configured such that the filling factor changes continuously or stepwise along the circumferential direction of the circle on the surface of the glass substrate. When the center is rotated as the center of rotation, the ratio of the transmitted light amount of the 0th-order diffracted light to the incident light amount changes. Therefore, when this optical attenuator is used, the glass substrate is rotated around the center of the circle in order to change the ratio of the transmitted light amount of the 0th-order diffracted light to the incident light amount.

  In a preferred form of the optical attenuator, the optical attenuator has an antireflection film that reduces the wavelength dependency on the ratio of the transmitted light amount of the 0th-order diffracted light to the incident light amount.

  Still another form of the optical attenuator has the above-mentioned fine structure consisting of a concavo-convex pattern of a size that causes incident light to be diffracted on at least one of the front and back surfaces of a transparent glass substrate in the wavelength range of incident light. Although the same as the optical attenuator, the ratio of the transmitted light amount of the 0th-order diffracted light to the incident light amount differs depending on the incident angle of the incident light with respect to the fine structure. Therefore, when this optical attenuator is used, the ratio of the transmitted light amount of the 0th-order diffracted light to the incident light amount is changed by changing the incident angle of the incident light with respect to the fine structure.

  In a preferred form of the optical attenuator, a concavo-convex antireflection structure having a pitch equal to or less than half the wavelength of incident light is formed on the surface of the fine structure.

  In another preferable form of the optical attenuator, an antireflection film is formed on the surface of the fine structure to reduce the wavelength dependency on the ratio of the transmitted light amount of the 0th-order diffracted light to the incident light amount.

  In one form of the optical attenuator module of the present invention, when the optical attenuator has a constant fine structure pitch and has a plurality of regions having different filling factors, the optical attenuator and the incident light incident position with respect to the fine structure And a moving mechanism for displacing the glass substrate so as to move between regions having different filling factors.

  In the optical attenuator module of this embodiment, it is preferable to further dispose a condensing lens for reducing the beam diameter of incident light to the optical attenuator and a condensing lens for receiving 0th-order diffracted light transmitted through the optical attenuator. Thereby, it is possible to improve the resolution of the transmittance of the 0th-order diffracted light while suppressing the change of the filling factor within the beam diameter of the incident light.

  In another aspect of the optical attenuator module of the present invention, when the optical attenuator changes the ratio of the transmitted light amount of the 0th order diffracted light to the incident light amount by changing the incident angle of the incident light with respect to the fine structure, An optical attenuator and a moving mechanism that displaces the angle of the incident surface of the glass substrate with respect to the incident direction of the incident light so that the incident angle of the incident light with respect to the fine structure is changed.

  By combining two or more attenuators, a larger light attenuation rate than that of one attenuator may be obtained.

  When the incident light is linearly polarized light, it is preferable that a λ / 4 wavelength plate is disposed on the light incident side of the optical attenuator module of the present invention to convert it into circularly polarized light and then enter the optical attenuator.

  As a more preferable form of the optical attenuator module, a first optical branching means for branching and extracting a part of the incident light of the optical attenuator module, and a second part for branching and extracting a part of the emitted light of the optical attenuator module. Of the first and second light receiving elements for receiving and detecting the light extracted by the first and second light branching means, and the first and second light receiving elements, respectively. A moving mechanism control device that takes in the detection signal and controls the moving mechanism so that the level ratio of the detection signal corresponds to the set attenuation rate;

  The optical attenuator of the present invention diffracts light by forming a concavo-convex shape on the glass surface to reduce the transmittance, so that the glass material has stable characteristics due to temperature compared to the case of using a thin film, It has excellent durability and can be manufactured at low cost because it does not use a thin film process. Furthermore, since the glass material has less wavelength dependency, it can exhibit excellent effects such as obtaining broadband characteristics with respect to the light rays used.

(A) is a schematic sectional drawing which shows the optical attenuator of one Example, (B) is a schematic plan view. It is a graph which shows the relationship between the filling factor (FF) in the optical attenuator of one Example, and the transmittance | permeability of 0th-order diffracted light. It is a schematic plan view which shows another Example. (A) is a conceptual diagram explaining the Example which changes an incident angle, (B) is a schematic block diagram of the Example. It is a graph which shows the relationship between the incident angle and the transmittance | permeability of 0th-order diffracted light in the Example. It is process sectional drawing which shows an example of the manufacturing method of an optical attenuator. It is process sectional drawing which shows the other example of the manufacturing method of an optical attenuator. It is a block diagram which shows one Example of an optical attenuator module. It is a graph which shows the relationship between the depth of the uneven | corrugated pattern of a fine structure, and the transmittance | permeability of 0th-order diffracted light. It is a graph which shows the relationship between a polarization state and the transmittance | permeability of 0th-order diffracted light.

  An optical attenuator of one embodiment is schematically shown in FIGS. 1 (A) and 1 (B). (A) is sectional drawing along the direction where the filling factor (FF) of the uneven | corrugated shape of a fine structure is changing, (B) is a top view of the both ends.

  The glass substrate 2 is a transparent material at least in the wavelength range of incident light, and is not particularly limited. For example, quartz glass or borosilicate glass can be used. Pyrex (registered trademark) and Tempax (registered trademark) can be used as the borosilicate glass. A fine structure 4 is formed on one surface of the glass substrate 2. The fine structure 4 is composed of a repeating uneven pattern. The concavo-convex pattern is a line-and-space pattern composed of convex portions (lines) 6 and grooves (spaces) 8 extending in the direction perpendicular to the paper surface. The pitch P composed of a set of irregularities in the irregular pattern is constant. The line width of the convex portion 6 is L, and the width of the groove 8 is S. P = L + S, and L / P is a filling factor (FF). D is the depth of the groove 8.

  In this embodiment, the fine pattern of the concavo-convex pattern has a constant pitch P with respect to the horizontal direction (straight direction) shown in the figure, and the filling factor is 0.5 at the left end of the figure and approximately 1. at the right end. 0. From the left to the right in the figure, the filling factor continuously changes in the range from 0.5 to almost 1.

  Incident light enters from one surface of the optical attenuator, passes through the other surface, and becomes outgoing light. The pitch P of the concavo-convex pattern is set in the range of 2 to 600 times the wavelength of the incident light. Now, for example, laser light having a wavelength of 1064 nm is used as incident light, and the pitch P is set to 20 μm. However, the pitch P is an example, and can be set as appropriate as long as the incident light is in a range where diffraction occurs. Here, an example is shown in which laser light having a wavelength of 1064 nm is used as incident light, but the same applies to incident light having other wavelengths. For example, when laser light having a wavelength of 266 nm is used as incident light, it is appropriate to set the pitch P to 5 μm.

  When incident light enters the fine structure 4, diffraction occurs, and first-order diffracted light and second-order diffracted light are generated in addition to zero-order diffracted light transmitted in the same direction as the incident light. Since each diffracted light has a different emission direction, by guiding only the 0th-order diffracted light to be incident on the object, the transmittance of the emitted light with respect to the incident light is reduced by the generation of diffracted light other than the 0th-order diffracted light. To do.

  This embodiment utilizes the fact that the transmittance of the 0th-order diffracted light changes depending on the filling factor. In the embodiment of FIG. 1, a Tempax (registered trademark) glass substrate having a thickness of 1.0 mm is used as the glass substrate 2, the pitch P of the fine structure 4 is 20 μm, and the depth d of the groove 8 is 1.2 μm. FIG. 2 shows the measurement results of the filling factor and the transmittance of the 0th-order diffracted light in the case where circularly polarized monochromatic light having a wavelength of 1064 nm is incident as incident light in a direction perpendicular to the surface of the substrate 2. When the filling factor is 0.5, the line width L and the groove width S are equal as shown in the left end of FIG. According to this result, when the filling factor is 0.5, the diffracted light becomes first-order or higher-order diffracted light, and the transmittance of light emitted in the same direction as the incident light as zero-order diffracted light is zero. When the filling factor is smaller or larger than 0.5, the transmittance increases, and as the filling factor approaches 0 and 1, almost only the 0th-order diffracted light is present. In the embodiment of FIG. 1, the filling factor is formed so as to change within a range from 0.5 to approximately 1. Therefore, if the incident position of incident light is displaced from the left to the right in FIG. The transmittance can be varied in the range from 0 to nearly 100%.

  A specific example of filling factor change is shown. In the embodiment of FIG. 1, in the first example, the range in which the filling factor is changed is 24 mm, and the filling factor is continuously changed so that the transmittance of the 0th-order light per 2 mm changes by 10%. In the second example, the range in which the filling factor changes is 12 mm, and the filling factor is continuously changed so that the transmittance of the 0th-order light per 10 mm changes. In the third example, the range in which the filling factor is changed is 6 mm, and the filling factor is continuously changed so that the transmittance of the zero-order light is changed by 10% per 0.5 mm. The size of the light beam incident on the optical attenuator is, for example, 2 mm in diameter.

  In designing the optical attenuator of this embodiment, the filling factor is designed as follows. For example, to design the filling factor so that the transmittance of 0th-order light changes by 10% in a certain 2 mm region, the relationship in FIG. 2 is approximated by a quadratic function, and the filling factor change rate in that region is calculated. Derived by

  As the rate of change of the filling factor along a straight line is higher, the transmittance of the 0th-order diffracted light can be changed only by slightly moving the position of the incident light. The rate of change of the filling factor can be appropriately designed in consideration of the range in which incident light can be displaced according to the application.

  Since the groove width S decreases as the filling factor approaches 1, the method of forming the glass substrate by dry etching cannot be continuously manufactured to 0. Since patterns having different filling factors are formed simultaneously, the depth d of the groove varies depending on the size of the filling factor. The smaller the filling factor, the wider the groove, so that deeper grooves are formed. The larger the filling factor, the shallower the groove.

  In the embodiment of FIG. 1, since the filling factor changes along a straight line on the substrate, the substrate is moved along the linear direction so that the position of the incident light changes along the straight line. The filling factor at the position where the incident light enters the fine structure changes, and thereby the transmittance of the 0th-order diffracted light changes.

  FIG. 3 shows a second embodiment. In this embodiment, the filling factor is formed so as to change along the circumferential direction. The fine-concave pattern is formed as a repeated pattern of protrusions 9 and grooves 10 extending in the radial direction from the center of the circle.

  Also in this embodiment, the pitch P of the concavo-convex pattern having a fine structure is set uniformly along the circumferential direction, and the filling factor is formed so as to continuously change along the circumferential direction. The rate of change of the filling factor is not particularly limited, and can be set as appropriate according to the application.

  In the embodiment of FIG. 3, it is set how much the transmittance of the 0th-order diffracted light per predetermined angle is changed, the relationship of FIG. 2 is approximated by a quadratic function, and the filling factor change rate in that region is calculated. derive.

  In the embodiment of FIG. 3, by rotating the substrate around the center of the circle, the filling factor of the fine structure at the position where the incident light is incident is changed, and the transmittance of the 0th-order diffracted light is also changed. The diameter of the incident light beam is not particularly limited, but is 2 mm, for example.

  1 and 3 show a structure in which a fine structure uneven pattern is formed only on one surface of the substrate, it is also possible to form a fine structure uneven pattern on both surfaces of the substrate. In that case, the pitches of the concave and convex patterns of the fine structure of the opposing portions of the front side and the back side of the substrate may be made equal, and the filling factors may be made equal, or the filling factors may be made different. The transmittance of the 0th-order diffracted light can be variously changed according to the combination of the fine structure filling factors of the front side and the back side of the substrate. Further, the pitches of the concave and convex patterns of the fine structure of the opposing portions of the front side and the back side of the substrate are not necessarily equal.

  FIG. 4 shows a third embodiment. In the optical attenuator 12 of this embodiment, fine structures 14a and 14b are provided on both the front side and the back side of a glass substrate transparent to the wavelength of light used. Here, the microstructures 14a and 14b have the same pitch and filling factor within the surface of the substrate, and the filling factor does not differ depending on the location of the substrate surface as in the embodiments of FIGS. The embodiment of FIG. 4 does not change the transmittance of the 0th-order diffracted light due to the difference in filling factor, but changes the transmittance of the 0th-order diffracted light by varying the incident angle of the incident light with respect to the fine structure.

  As shown in FIG. 4A, the transmittance is changed by inclining the optical attenuator 12 having fine structures formed on both surfaces of the substrate with respect to the incident light incident direction. For this purpose, as shown in FIG. 4B, a mechanism for changing the tilt angle of the optical attenuator 12 with respect to incident light is provided. In FIG. 4B, reference numeral 16 denotes a laser oscillator. Laser light from the laser oscillator 16 enters the optical attenuator 12, and transmitted zero-order diffracted light is received by the light receiver 18 and detected. Here, the light receiver 18 is installed to measure the transmitted light intensity of the 0th-order diffracted light. However, in the laser processing apparatus, an object to be processed is disposed at the position of the light receiver 18.

  In the embodiment of FIG. 4, the optical attenuator formed with a fine structure uneven pattern of line-and-space, a pitch of 20 μm, and a filling factor and the depth of the recess of the fine structure uneven pattern are different in several types. FIG. 5 shows the transmittance of the 0th-order diffracted light with respect to the incident angle of the incident light. Within each optical attenuator, the filling factor of the fine structure is constant. The α rotation in the rotation direction is a rotation with the repeating direction of the unevenness of the fine structure as the rotation axis, and the β rotation is a rotation with the direction orthogonal to the rotation axis of the α rotation as the rotation direction. There is no significant difference in the transmittance of the 0th-order diffracted light between α rotation and β rotation. From the results of FIG. 5, it can be seen that the transmittance is the highest at normal incidence, and the transmittance decreases with inclination. Therefore, a desired transmittance can be obtained by setting a predetermined angle.

  As a reference example, FIG. 5 also shows the transmitted light intensity with respect to the light incident angle of a Tempax (registered trademark) substrate having no fine structure. In this case, the transmitted light is not diffracted light, but represents the ratio of the transmitted light in which incident light is divided into transmitted light and reflected light.

  FIG. 10 shows the relationship between the polarization state and the transmittance of 0th-order diffracted light. The optical attenuators have a pitch of 20 μm and a filling factor of 0.5 and 0.8. The incident light is a laser beam having a wavelength of 1064 nm and is linearly polarized light. The case where the vibration direction of the incident linearly polarized light is parallel to the direction of the groove of the fine structure composed of the concavo-convex pattern is called “TE”, and the case where the vibration direction of the incident linearly polarized light is orthogonal is called “TM”. The result of FIG. 10 shows that there is no difference between the incidence of linearly polarized TE and the incidence of TM with respect to the transmittance of the 0th-order diffracted light and does not depend on the vibration direction of the incident linearly polarized light. From this, it can be said that the incident light to the optical attenuator of the present invention may be linearly polarized light, elliptically polarized light or circularly polarized light, or may be random polarized light mixed with various polarized light.

  6 and 7 show an example of the manufacturing method.

FIG. 6 shows a first example.
(A) A glass substrate 20 is prepared, and a photoresist 22 is formed on the surface thereof as shown in (B).

  (C) The resist 22 is exposed through a mask, developed, and rinsed to form a concavo-convex resist pattern 22a.

  (D) The glass substrate 20 is patterned by dry etching using the resist pattern 22a as a mask. At this time, etching is performed somewhat deeper than the depth of the groove of the target pattern. For example, if the target depth is 2700 nm, the trench 23 formed here is patterned so as to have a depth of 3000 nm, which is 300 nm deeper than that.

  (E) After removing the resist pattern 22a, the height of the convex portions 24 of the obtained concavo-convex pattern is measured.

  (F) Next, a resist 26 is applied to the entire surface on which the concavo-convex pattern is formed. In this state, the resist 26 fills the groove 23 and also exists on the top surface of the convex portion 24.

  (G) Only the resist 26 existing on the top surface of the convex portion 24 is removed, and the resist 26 in the groove 23 is left. This resist removal step is performed by dry etching using oxygen plasma, for example.

  (H) The second dry etching is performed to etch the top surface of the convex portion 24 so that the height of the convex portion 24 becomes a desired height.

  (I) If the resist 26 remaining in the groove 23 is removed, a fine structure is completed.

  FIG. 7 shows the second manufacturing method. In this manufacturing method, a mold is first manufactured, a resin pattern is formed on the glass substrate of the product using the mold, and the glass substrate is etched using the resin pattern as a mask.

  (A) For example, a silicon substrate having a diameter of 6 inches is used as the mold material 40 in order to manufacture a mold, and an electron beam resist 42 is formed on the surface thereof.

  (B) Electron beam drawing is performed on the resist 42, and development and rinsing are performed to form a resist pattern 42a.

  (C) A die 46 having a die pattern 44 is formed on the surface of the silicon substrate by dry etching the silicon substrate 40 using the resist pattern 42a as a mask.

  Next, patterning is performed on the glass substrate using the mold 46. Since the mold 46 is repeatedly used, the patterning into the electron beam resist is performed only once when the mold is manufactured.

  (D) An ultraviolet curable resin 48 is applied to the surface of the mold 46 on which the pattern is formed, and a glass substrate 50 serving as a product substrate is pressure-bonded thereon. As a result, a fine structure pattern transferred to the resin 48 is formed on the surface of the glass substrate 50.

  (E) Ultraviolet rays are irradiated from the glass substrate 50 side to cure the resin 48 between the glass substrate 50 and the mold 46.

  (F) The metal mold 46 is removed from the glass substrate 50, the glass substrate 50 is etched by dry etching using the resin pattern 48a as a mask, and the resin pattern 48a is transferred to the glass substrate 50. At this time, the etching can be performed uniformly by performing dry etching while rotating the glass substrate 50 in the in-plane direction.

  (G) When the resin 48 a is removed, the concavo-convex pattern 52 having a fine structure is transferred to the glass substrate 50.

  (H) Thereafter, each optical attenuator element is cut out.

  The optical attenuator element is preferably formed with an antireflection structure (ARS structure) on the surface of the concavo-convex pattern having a fine structure. The antireflection structure is a concavo-convex structure that is finer than the concavo-convex pattern of the fine structure, and is a concavo-convex structure having a pitch of half or less of the wavelength of incident light. An example of the antireflection structure is an uneven structure having a pitch of 200 nm and a depth of 130 nm. By uniformly forming the concavo-convex structure on the convex and concave surfaces of the fine concavo-convex pattern, the light transmittance near 1064 nm can be maintained at 99%.

  Such an antireflection structure is formed on the surface of the glass substrate before the formation of the fine-concave uneven pattern by a photoengraving and etching method or a nanoimprint method as shown in FIG. 6 or 7 is then used to form an uneven pattern having a fine structure. However, the formation of the uneven structure having a fine structure is not obstructed by the formation of an antireflection structure in advance. .

  FIG. 8 schematically shows an embodiment of the optical attenuator module. In one embodiment, the optical attenuator 60 is provided with a moving mechanism 61. Whether the moving mechanism 61 changes the transmittance of the 0th-order diffracted light by changing the incident position of the incident light with respect to the optical attenuator 60 by linearly moving the optical attenuator 60 according to the form of the optical attenuator 60. The transmittance of the 0th-order diffracted light is changed by changing the incident position of the incident light with respect to the optical attenuator 60 by rotating the optical attenuator 60 around the rotation center, or the incident angle of the incident light with respect to the optical attenuator 60 The angle of the incident surface of the attenuator 60 with respect to the incident direction of the incident light is displaced so as to change.

An optical splitter 66 is disposed on the optical path of the laser incident light 64 as a first optical branching means for branching out a part 68 of the laser incident light 64 incident on the optical attenuator 60 from the laser light source 62 . The optical splitter 66 is provided, for example, such that a glass substrate transparent to the laser light 64 is inclined so as to reflect and extract a part of the incident light 64. Since the laser light source 62 oscillates laser light is linearly polarized light, a (λ / 4) wavelength plate is provided to change it to circularly polarized light, and the laser light 64 emitted from the laser light source 62 has circularly polarized light. .

  An optical splitter 72 is disposed on the optical path of the laser output light 70 as second optical branching means for branching out and extracting a part 74 of the output light 70 composed of the 0th-order diffracted light transmitted through the optical attenuator 60. The optical splitter 72 is also provided, for example, such that a glass substrate transparent to the laser light 64 is inclined so as to reflect and take out a part of the outgoing light 70.

  For example, a photodiode 76 is arranged as a first light receiving element to receive and detect the light 68 extracted as part of the incident light by the optical splitter 66, and the light extracted as part of the outgoing light by the optical splitter 72. For example, a photodiode 78 is disposed as a second light receiving element to receive and detect 74.

  A moving mechanism control device 80 is provided for taking in the detection signals of the photodiodes 76 and 78 and controlling the moving mechanism 61 so that the level ratio of the detection signals corresponds to the set attenuation rate. The moving mechanism control device 80 is a computer system including a computer and an interface.

  When this optical attenuator module is applied to a laser processing apparatus, the laser beam that has passed through the optical attenuator 60 is applied to an object 82 that is a workpiece.

  Since the ratio of the light extracted by the optical splitters 66 and 72 is known in advance, the attenuation rate of the laser light by the optical splitters 66 and 72 is also known in advance. Since the attenuation rate by the optical attenuator 60 can be obtained from the level ratio of the detection signals of the photodiodes 76 and 78, the intensity of the laser light applied to the object 82 can also be obtained.

  When the optical attenuator 60 changes the transmittance of the 0th-order diffracted light by changing the incident position of the incident light, the fine structure is formed so that the filling factor changes continuously or stepwise. Yes. Therefore, depending on the size of the beam diameter of the incident light applied to the optical attenuator 60, the filling factor may change within the beam diameter. In this case, the optical attenuator function of the resolution of the transmittance of the 0th-order diffracted light is reduced. Therefore, in order to reduce the beam diameter of the incident light irradiated to the optical attenuator 60 and prevent the optical attenuator function from being lowered, as shown in FIG. 8, the incident light irradiated to the optical attenuator 60 is used. It is preferable to dispose a condensing lens 90 for reducing the beam diameter of incident light on the optical axis, and dispose the condensing lens 92 at a position where the 0th-order diffracted light transmitted through the optical attenuator 60 is received. The size of the condenser lens 92 is set so that the condenser lens 92 does not receive diffracted light other than the 0th-order diffracted light, or a member that blocks diffracted light other than the 0th-order diffracted light is disposed in front of the condenser lens 92. To do.

2 Glass substrate 4 Fine structure 6 Convex part (line)
8 groove
DESCRIPTION OF SYMBOLS 9 Convex part 10 Groove | channel 12, 60 Optical attenuator 16 Laser oscillator 18 Light receiver 60 Laser light source 61 Moving mechanism 64 Laser incident light 66 Optical splitter as 1st optical branching means 68 Part of laser incident light 70 It consists of 0th order diffracted light Outgoing light 72 Optical splitter as second light branching means 74 Part of outgoing light 76 Photodiode as first light receiving element 78 Photodiode as second light receiving element 80 Moving mechanism control device 90, 92 Condensing lens

Claims (12)

An optical attenuator that attenuates incident light,
In a wavelength range of incident light, it has a fine structure consisting of repetition of a concavo-convex pattern with a size that causes incident light to be diffracted on at least one surface of the front and back surfaces of a transparent glass substrate,
The microstructure has a constant pitch,
The fine structure has a plurality of regions having different filling factors and recess depths indicating the ratio of the convex portion to the pitch, and the depth of the concave portion is shallow in a region having a large filling factor and deep in a region having a small filling factor. And
A variable attenuation factor optical attenuator characterized in that the ratio of the transmitted light amount of the 0th-order diffracted light to the incident light amount differs between regions having different filling factors and recess depths.   2. The optical attenuator according to claim 1, wherein a pitch of the fine structure is in a range of 2 to 600 times a wavelength used, and a depth of the concave portion of the fine structure is 0.1% to 80% of the pitch.   The optical attenuator according to claim 1 or 2, wherein the front and back surfaces of the glass substrate are parallel to each other, and the fine structure is formed only on one surface.   The optical attenuator according to claim 1 or 2, wherein the front and back surfaces of the glass substrate are parallel to each other, and the fine structure is formed on both the front and back surfaces of the glass substrate. The fine structure of the front surface and the fine structure of the back surface are equal in pitch,
The optical attenuator according to claim 4, wherein the fine structure of the surface on the front side and the fine structure of the surface on the back side opposite thereto have different filling factors. The microstructure is configured such that the filling factor changes continuously or stepwise along a straight line on the surface of the glass substrate,
The ratio of the transmitted light amount of the 0th-order diffracted light to the incident light amount changes when the glass substrate is moved along a straight line in the direction in which the filling factor of the microstructure is changing. Light attenuator. The microstructure is configured such that the filling factor changes continuously or stepwise along the circumferential direction of a circle on the surface of the glass substrate,
6. The optical attenuator according to claim 1, wherein when the glass substrate is rotated about the center of the circle, the ratio of the transmitted light amount of the 0th-order diffracted light to the incident light amount changes. The front and back surfaces of the glass substrate are non-parallel to each other,
The ratio of the transmitted light amount of the 0th-order diffracted light to the incident light amount changes and the emission angle of the emitted light also changes when the incident position of the incident light with respect to the fine structure is moved between regions having different filling factors. The optical attenuator as described in any one of Claims.   9. The optical attenuator according to claim 1, wherein an antireflection structure having an uneven structure having a pitch equal to or less than half the wavelength of incident light is formed on a surface of the uneven structure having a fine structure.   9. The optical attenuator according to claim 1, wherein an antireflection film is formed on the surface of the concavo-convex pattern of the fine structure to reduce the wavelength dependency with respect to the ratio of the transmitted light amount of the 0th-order diffracted light with respect to the incident light amount. . The optical attenuator according to any one of claims 1 to 10,
A moving mechanism for displacing the glass substrate so that an incident position of incident light on the fine structure moves between regions having different filling factors;
Optical attenuator module with   The optical attenuator module according to claim 11, further comprising a condenser lens for reducing a beam diameter of incident light with respect to the optical attenuator and a condenser lens for receiving 0th-order diffracted light transmitted through the optical attenuator.

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