JP2004020813A - Diffraction optical element, its manufacturing method, optical pickup system, and optical disk drive system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively solve the problem of warp of a transparent substrate due to thermal contraction of an organic material film in a manufacture process of a diffraction optical element. <P>SOLUTION: In a manufacturing method of a diffraction optical element wherein a rectangular cross section forms diffraction gratings on the organic material film adhered to and fixed on the transparent substrate due to rectangular unevenness in the form of a plurality of diffraction grating array by a process including photolithography and etching, and individually separates a plurality of the formed diffraction gratings, a prescribed curve shape is previously given to the transparent substrate 1 in order to relieve the warp of the transparent substrate produced due to the thermal contraction of the organic material film, and the transparent substrate 1 is made substantially parallel flat plates by correcting the curve shape due to the thermal contraction of the organic material film. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a diffractive optical element, a method of manufacturing the same, an optical pickup device, and an optical disk drive device.
[0002]
[Prior art]
A diffractive optical element is an “optical element that causes a desired diffraction phenomenon in light”, and is widely used as an element that performs light separation, light deflection, and the like.
[0003]
Conventionally, various types of diffractive optical elements have been known. As a new type of diffractive optical element, an organic film or a polymer film is formed on an optically transparent substrate, and the surface of these films is desirably formed by unevenness. (Japanese Patent Application Laid-Open Nos. 2000-221325, 2000-75130, and 11-174226).
[0004]
The diffractive optical element described in the above publication is a “polarization hologram element” having a birefringent film. For example, in an optical pickup device, “an optical path separation between an optical path of a light beam from the light source side and an optical path of a return light beam from the optical disk” is performed. Can be suitably used.
[0005]
To slightly supplement the description, the diffractive optical element used in the optical pickup device has a size of “about several millimeters square”, and is not manufactured separately by itself, but 100 to several hundred at a time. Manufactured.
[0006]
That is, an adhesive layer is formed on a transparent substrate having a diameter of several tens to several hundreds of mm, for example, a parallel plate-shaped transparent substrate having a diameter of 100 mm or 150 mm, and the same size as the substrate is formed on the formed adhesive layer. An organic material film of a size or one size smaller than this is placed, and is adhered and fixed to a transparent substrate by an adhesive layer. As the adhesive constituting the adhesive layer, a thermosetting adhesive or a photocurable adhesive such as an ultraviolet curable adhesive can be used.
[0007]
A plurality of (normally 100 to 200) diffraction gratings are formed on the surface of the organic material film adhered to the transparent substrate. To form a diffraction grating, a thin film made of metal or oxide is formed on an organic material film, the film is patterned by photolithography to form an etching mask corresponding to the diffraction grating group, and dry etching is performed through this mask. Can be done with
[0008]
After the formation of the diffraction grating, an overcoat layer is formed as necessary, and if necessary, a transparent counter substrate is placed on the overcoat layer to integrate the entire structure. Thereafter, cutting is performed using a dicing device to obtain individual diffractive optical elements.
[0009]
By the way, the material of the organic material film forming the diffraction grating is generally a “polymer material”, and a process involving heating in the manufacturing process of the diffractive optical element (for example, forming an adhesive layer with a thermosetting adhesive, When the organic material film is cured by heating to adhere and fix the film, or when subjected to a photoresist pre-bake or post-bake treatment in photolithography when forming an etching mask, a temperature change due to heat (the heat curing of the adhesive described above) occurs. (100-150 ° C. in some cases), causing “warping” in the transparent substrate fixed via the adhesive layer.
[0010]
When such “warpage” occurs, for example, it becomes difficult or impossible to fix the substrate at a predetermined position by “vacuum suction” when performing a diffraction grating forming step. In addition, when a diffraction grating is formed on a warped organic material film by dry etching, the warpage causes "a plurality of diffraction gratings formed at the same time to be not the same". "Variation" of optical characteristics occurs. In particular, in the case of a diffraction grating formed in a portion having a large warp, the wavefront aberration of transmitted light is degraded, and there is a case where the diffraction grating cannot be practically used.
[0011]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION It is an object of the present invention to effectively solve the above-mentioned problem of "warpage" at the time of manufacturing a diffractive optical element.
[0012]
[Means for Solving the Problems]
The method for manufacturing a diffractive optical element according to the present invention includes an organic material film bonding step, a diffraction grating forming step, and a separation step.
The “organic material film bonding step” is a step of bonding and fixing an organic material film on a transparent substrate.
[0013]
The “diffraction grating forming step” is a process including photolithography and etching, in which a plurality of diffraction gratings having a rectangular cross section are formed in a lattice array on an organic material film bonded and fixed on a transparent substrate. This is the step of doing. As described above, the number of diffraction gratings to be formed is usually 100 to several hundreds.
[0014]
The “separation step” is a step of individually separating a plurality of diffraction gratings formed in a lattice array. This separation step is usually performed using a dicing device.
[0015]
The manufacturing method according to claim 1 has the following features.
That is, in order to alleviate "warping of the transparent substrate caused by thermal contraction of the organic material film", a "predetermined curved shape" is given to the transparent substrate in advance, and the curved shape of the transparent substrate is corrected by thermal contraction of the organic material film. This makes the transparent substrate a substantially parallel plate.
[0016]
As described above, the heat shrinkage of the organic material film is caused, for example, by bonding with a thermosetting adhesive or by receiving heat in pre-baking or post-baking of a photoresist in photolithography. In the present invention, a curved shape is given to the transparent substrate side in advance, and the tensile force acting on the transparent substrate when the organic material film thermally contracts is "correcting the shape of the transparent substrate from the curved shape to a substantially parallel flat plate. It is used as "correcting power".
[0017]
The “substantially parallel flat plate” whose curved shape has been corrected can be securely held by, for example, vacuum suction, and is sufficiently focused on the photoresist layer when an etching mask is manufactured by photolithography. Say "no warp".
[0018]
In the method for manufacturing a diffractive optical element according to claim 1, the step of “giving a transparent substrate a predetermined curved shape in advance” includes machining a transparent parallel flat plate-shaped material to be a transparent substrate by machining both surfaces. (Claim 2), or a transparent parallel plate-like material to be a transparent substrate is provided by a first jig having a predetermined convex curved surface shape and a convex of the first jig. It may be performed by sandwiching and pressing with a second jig having a concave curved surface shape corresponding to the curved surface shape to give a predetermined curved shape to the transparent parallel plate shape (claim 3).
[0019]
In the method for manufacturing a diffractive optical element according to the third aspect of the present invention, the transparent parallel plate-like material to be used as the transparent substrate may be “a plurality of thin transparent plates, via a photocurable or thermosetting adhesive in a fluid state. After the deformation by the first and second jigs, the adhesive can be solidified by light or heat after the deformation by the first and second jigs (Claim 4). A thin transparent plate bonded and integrated with each other "is a transparent substrate, on which an organic material film is bonded.
[0020]
In the manufacturing method according to claim 3 or 4, an "anti-reflection film" is previously formed on a surface of the transparent parallel plate material to be a transparent substrate, which is opposite to the "surface on which the organic material film is to be bonded". It may be formed.
[0021]
In the method for manufacturing a diffractive optical element according to any one of claims 1 to 4, the “predetermined curved shape given to the transparent substrate in advance” preferably has a radius of curvature in a range of 20 m to 100 m (claim). Item 5). As the curved shape, a “convex spherical shape, a convex cylinder surface shape, or the like” is possible.
[0022]
The method for manufacturing a diffractive optical element according to any one of claims 1 to 5, wherein the transparent substrate is supported by a support jig having a convex curved surface shape that fits the curved shape of the transparent substrate. An adhesive is applied to the convex surface side, an organic material film is placed thereon, and pressing is performed from above the organic material film by a holding jig having a concave curved surface shape corresponding to the convex curved surface shape of the supporting jig, and bonding is performed. By spreading the agent uniformly between the transparent substrate and the organic material film, the organic material film can be suitably bonded to the curved transparent substrate (claim 6).
[0023]
As the adhesive, a light-curable or thermosetting adhesive is used. As described above, in a state where the adhesive is uniformly spread between the transparent substrate and the organic material film, the adhesive is irradiated with light or heated. Solidification may be performed.
[0024]
The method for manufacturing a diffractive optical element according to any one of claims 1 to 6, wherein "a plurality of diffraction gratings each having a rectangular cross section are formed on an organic material film adhered and fixed on a transparent substrate. The etching step in the diffraction grating forming step of forming a shape can be suitably performed by electron cyclotron etching (claim 7).
[0025]
The method for manufacturing a diffractive optical element according to any one of claims 1 to 7, wherein a plurality of diffraction gratings are formed on the organic material film formed in a lattice array in a manner such that “optical elements are formed in concave portions of the diffraction gratings in each diffraction grating. Transparent material can be filled to form an overcoat layer "(claim 8). In this case," a transparent counter substrate can be integrated "on the overcoat layer (claim 9). .
[0026]
The method for manufacturing a diffractive optical element according to claim 8, wherein the organic material film is an “organic birefringent film” and the overcoat layer is “an organic birefringent film having a refractive index for ordinary rays or an extraordinary ray. An isotropic optical material (a material whose optical properties do not change with direction) having substantially the same refractive index "can be used (claim 10). In this case, the obtained diffractive optical element has a different diffracting action between the ordinary ray and the extraordinary ray.
[0027]
As the “organic birefringent film” used in the method for manufacturing a diffractive optical element according to claim 10, a “polymer birefringent film having oriented molecular chains” can be used (claim 11). The polymer birefringent film used as the birefringent film can be a “polymer film in which molecular chains are oriented by stretching” (Claim 12).
[0028]
In the method for manufacturing a diffractive optical element according to any one of claims 8 to 12, an acrylic or epoxy-based material can be suitably used as a material of the “overcoat layer” (claim 13).
[0029]
A diffractive optical element according to the present invention is a diffractive optical element manufactured by the method for manufacturing a diffractive optical element according to any one of claims 1 to 13 (claim 14).
[0030]
Of the diffractive optical elements according to claim 14, the diffractive optical element manufactured by the manufacturing method according to claim 10 or 11 or 12 can be used as a "polarization hologram element" (claim 15). In this case, a "transparent counter substrate" can be integrated on the overcoat layer (claim 16), and an acrylic or epoxy-based material can be suitably used as the material of the overcoat layer (claim 17). ).
[0031]
The diffractive optical element according to claim 15 or 16 or 17 can be one in which “an antireflection film is formed on a transparent substrate to which an organic birefringent film is adhered” (claim 18).
[0032]
An optical pickup device according to the present invention is characterized in that the diffraction optical element according to any one of claims 15 to 18 is a polarization hologram element that separates an optical path of a light beam from a light source side and an optical path of a return light beam from an optical disk. (Claim 19).
[0033]
An optical disk drive device according to the present invention is directed to an optical disk drive device that performs at least one of recording, reproducing, and erasing of information on an optical disk by using an optical pickup device. It is a feature (claim 20).
[0034]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment will be described. First, an example of a manufacturing process of a diffractive optical element will be briefly described with reference to FIG.
[0035]
FIG. 1A shows a state in which an organic material film 3 is bonded on a transparent substrate 1A by an adhesive layer 2 in an “organic material film bonding step”.
[0036]
As shown in FIG. 1B, a mask film 4 is formed on the organic material film 3 using an “etching mask material” (mask film forming step). The mask film is formed of, for example, a metal such as Al or an oxide film.
[0037]
Subsequently, as shown in FIG. 1C, a resist pattern 5 corresponding to a processing mask pattern is formed on the mask film 4 by photolithography (resist pattern forming step).
[0038]
After the resist pattern 5 is thus formed, the mask film 4 is patterned by wet etching in a liquid to form a processing mask (mask forming step). At this time, the resist pattern 5 serves as a mask for wet etching, and the “exposed portion” of the mask film 4 is etched and removed. When the resist pattern 5 is removed after the etching, the mask 4M remains on the organic material film 3 as shown in FIG.
[0039]
After the mask formation step, the organic material film 3 is etched through the mask 4M to form a diffraction grating (etching step). By this etching, a diffraction grating 3A having rectangular irregularities is formed on the surface of the organic material film. The above-mentioned mask film forming step, resist pattern forming step, mask forming step and etching step are the “diffraction grating forming step”.
[0040]
As will be described later, a photoresist film is formed directly on the organic material film 3 without using the mask film 4M, patterned according to the mask pattern, and etched using the patterned resist pattern as a mask to form a diffraction grating. It can also be formed.
[0041]
FIG. 1E shows a state in which the mask 4M has been removed after the etching. On the surface of the organic material film 3 provided on the transparent substrate 1, a diffraction grating 3A having a rectangular cross section is formed. The state shown in FIG. 1E, that is, the state in which the diffraction grating 3A is formed on the organic material film 3 adhered on the transparent substrate 1A is referred to as a "diffraction element" for convenience.
[0042]
The "diffraction element" itself has a "function as a diffractive optical element (function of diffracting transmitted light)", so it can be used as it is as a diffractive optical element, but an organic material having a diffraction grating formed thereon Since the film does not always have a sufficient “physical strength”, rather than using the film as it is, as shown in FIG. It is preferable to reinforce the overcoat layer 9 by filling it with "transparent material" (Claim 8), and it is preferable to integrate the transparent counter substrate 1B on the overcoat layer 9 (Claim 9). ).
[0043]
Thus, the diffractive optical element 10 is obtained. In this case, the organic material film 3 is an “organic birefringent film”, and the overcoat layer 9 is an isotropic optical material having a “refractive index substantially equal to the refractive index of the organic birefringent film for ordinary or extraordinary light”. If the above is used, the diffractive optical element 10 is a diffractive optical element according to claim 16 and can be used as a polarization hologram element.
[0044]
If some care is taken in handling, the transparent substrate 1B can be removed from the state shown in FIG. 1 (g), and the overcoat layer 9 can be used as a "surface layer also serving as a protective film".
[0045]
Above, the description has been simplified as a single diffractive optical element, but as described above, the diffractive optical element is not manufactured separately and individually, but 100 to several hundred pieces are manufactured at a time. .
[0046]
FIG. 2 shows “a state in which a large number of diffraction gratings are formed in a lattice array” on the organic material film 3 at the stage of FIG. Reference numeral 3A indicates each of a large number of diffraction gratings formed on the organic material film 3. In the case of obtaining the diffractive optical element 10 of FIG. 1F, in the state of FIG. 2, “optically transparent material” is supplied over the entire diffraction grating of the organic material film 3 and the concave portion of each diffraction grating is provided. , Filling between the diffraction gratings to form an overcoat layer, on which a “transparent counter substrate” is further integrated, and thereafter, a portion including the individual diffraction gratings 3A is cut off by a dicing device to form a diffractive optical element. A single product (the above-mentioned “separation step”).
[0047]
FIG. 3 shows a state after the “organic material film bonding step”. In this figure, the transparent substrate denoted by reference numeral 1A and the organic material film denoted by reference numeral 3 are large in size (as shown in FIG. 2) that have not yet been separated.
[0048]
When a “parallel plate” is used as the transparent substrate 1A, the adhesive substrate 2 contracts when the adhesive 2 cures, so that the transparent substrate 1A generates “warp”. As described above, in the diffraction grating forming step, a resist pattern corresponding to the processing mask is formed on the mask film by photolithography. In this case, the photoresist is subjected to pre-baking and post-baking. The organic material film 3 is thermally contracted by the heat, and the transparent substrate 1A is further warped by the thermal contraction. FIG. 3 emphasizes such “warpage”.
[0049]
In the present invention, as described above, a curved shape is given in advance to the transparent substrate side, and the tensile stress acting on the transparent substrate when the organic material film thermally shrinks is referred to as “the shape of the transparent substrate is substantially changed from the curved shape. The transparent substrate is made into a substantially parallel flat plate by correcting the above-mentioned curved shape.
[0050]
Hereinafter, an embodiment of a characteristic portion in a method for manufacturing a diffractive optical element will be described. As a transparent parallel plate-shaped material to be a transparent substrate, a BK-7 glass plate having a diameter of φ = 100 mm and a thickness of 2 mm was used, and both sides thereof were machined to obtain a “predetermined curved shape” as shown in FIG. Is produced (claim 2).
[0051]
Specifically, one surface of the BK-7 glass plate (transparent parallel plate-like material) is roughly, medium-, and precision-polished to have a radius of curvature: R with a spherical polishing device, and then subjected to finish polishing. The roughness is Ra (center line average roughness): 5 nm or less. In this manner, a convex spherical surface having a radius of curvature: R is formed on one surface of the BK-7 glass plate.
[0052]
Next, a polishing jig (not shown) to which the finish polishing surface shape of the BK-7 glass plate has been transferred is rough-cut, medium-polished, precision-polished on the surface opposite to the above-mentioned finished-polished surface, and then subjected to final polishing. As shown in FIG. 4, the surface roughness is Ra (center line average roughness): a concave spherical surface shape of 5 nm or less, both surfaces have “the same radius of curvature: R”, and the thickness is 1.0 mm. A curved transparent substrate 1 is obtained.
[0053]
For example, if the radius of curvature: R = 30 m, the amount of curvature: W shown in FIG. 4 is 27 μm. Since the above “polishing jig” can be used repeatedly, the cost of the polishing jig can be reduced. It is also possible to use an automated mechanical polishing apparatus, which can reduce the manufacturing cost of the curved transparent substrate 1.
[0054]
Next, as shown in FIG. 5, the curved transparent substrate 1 is placed on a substrate holder 51 that can be moved in the X, Y, and Z-axis directions by the moving stage 50 so that the convex side thereof faces upward. It is fixed to the substrate holder 51 by a vacuum suction mechanism (not shown). The substrate holder 51 has a convex spherical shape having substantially the same radius of curvature: R as the transparent substrate 1, has an outer diameter of φ = 125 mm, and is one size larger than the transparent substrate 1.
[0055]
Above the substrate holder 51, an "adhesive dropping device" and a "measurement system movable in the X and Y directions for measuring the center of the adhesive and the center of the organic birefringent film" (both not shown) are provided. Have been.
[0056]
The above-mentioned measurement system detects the position using the CCD laser displacement meter 53 which reads the amount of displacement by detecting the reflected light on the surface of the adhesive 2, the transparent substrate 1, and the organic material film 3, and feeds back the position information to each moving device. (Not shown). "
[0057]
Holders 54A and 54B for holding the ends of the organic material film 3 are arranged in parallel to the substrate holder 51, and a "moment generating device (not shown) for generating a moment Mt in the holders 54A and 54B". Is provided.
[0058]
As described above, an “ultraviolet curable” adhesive 2 (manufactured by ThreeBond: trade name “TB3042”) having substantially the same refractive index as the transparent substrate 1 is provided at the center of the curved transparent substrate 1 set on the substrate holder 51. )), And the ends of the organic material film 3 cut into “110 mm × 120 mm” are held thereon by vacuum suction with the holders 54A and 54B, and are roughly positioned at the center of the transparent substrate 1. By means of the moment generator, the surface shape of the organic material film 3 deformed into a U-shape as shown in the figure is measured by the CCD laser displacement meter 53 to detect the "U-shaped center position" and measure it in advance. The amount of movement is calculated from the position information of the top of the convex shape of the adhesive 2 placed, and the U-shaped center of the organic material film 3 is aligned with the top of the convex shape of the adhesive 2 by the XY moving device.
[0059]
After the alignment of the transparent substrate 1, the adhesive 2, and the organic material film 3 is completed, the substrate holder 51 is raised in the Z direction, and stopped at the position where the adhesive 2 and the organic material film 3 contact each other at the apex. After that, the organic composite material film 3 is placed on the transparent substrate 1 while the moment Mt on the left and right sides of the organic material film 3 is gradually released.
[0060]
After the organic material film 3 has been placed on the transparent substrate 1 in this manner, as shown in FIG. 6, the diameter processed into a concave spherical shape having substantially the same radius of curvature as the curved shape of the transparent substrate 1 is R. : A pressing member 55 made of quartz glass having a diameter of 110 mm and a thickness of 20 mm is placed on the organic material film 3, and is uniformly pressed over the entire surface by a pressing means (not shown) so that the adhesive 2 spreads over the entire surface of the transparent substrate 1. The pressure is stopped, and a light intensity of 30 mW / cm is applied by an ultraviolet irradiation device (not shown) (hereinafter, referred to as “UV device”) via the pressing tool 55. ² Is irradiated from the organic material film 3 side for 200 seconds to cure the adhesive.
[0061]
After the adhesive 2 is cured, the excess portion of the organic birefringent film 3 is cut along the outer diameter of the transparent substrate 1 having a diameter of φ = 100 mm. Thereafter, the pressing tool 55 is raised, and the substrate holder 51 is vacuum-adsorbed. Is released, and the transparent substrate 1 to which the organic material film 3 is adhered is taken out.
[0062]
As described above, when the organic material film 3 is mounted on the transparent substrate 1, the conventional mounting method in which the organic material film 3 is brought into contact with the transparent substrate 1 from the center of the organic material film 3 so as to be adhered by surface contact is “at a visual level. In contrast to the occurrence of "bubble entrainment that can be confirmed", the above method was able to realize adhesion without entrainment of air bubbles.
[0063]
"Positioning of the transparent substrate 1, the adhesive 2, and the organic material film 3" means, in addition to the above-described method, recognizing the shapes of the transparent substrate 1 and the adhesive 2 by using a CCD camera and image processing, dividing the center, and positioning. It is also possible to carry out a method for performing such operations.
[0064]
In the above description, “acrylic resin-based photocurable adhesive” is used as the adhesive 2, but “epoxy resin-based photocurable adhesive” may be used. As the “transparent parallel plate-like material” to be the transparent substrate 1, in addition to the BK-7 glass substrate, a quartz glass substrate, a Pyrex (registered trademark) glass substrate, a crystalline glass (trade name: Neoceram) substrate, or the like is used. Is also good.
[0065]
As described above, by making the radius of curvature R of the concave spherical shape of the substrate holder 51 and the pressing member 55 made of quartz glass in contact with the transparent substrate 1 the same as the radius of curvature R of the transparent substrate 1, The highly accurate bonding between the transparent substrate 1 and the organic material film 3 becomes possible.
[0066]
The thickness of the organic material film 3 is preferably 0.01 mm or more from the viewpoint of easy handling. When the organic material film 3 is an “organic birefringent film in which the molecular chains are oriented by stretching to exhibit birefringence (Claim 12)”, the maximum thickness is in the range of 0.5 mm, more preferably 0. The range of 0.05 to 0.2 mm is good.
[0067]
In the example in the description, as the organic material film 3, “a film obtained by developing a birefringent property by stretching a polyester-based organic material film having a thickness of 0.1 mm” is used.
[0068]
After the organic material film 3 adhered as described above is washed in the order of "an organic solvent such as isopropyl alcohol and pure water", a ZEP-520 resist (trade name, manufactured by Zeon Chemical Co., Ltd.) is spin-coated to a thickness of 0.5 μm. To form a photoresist film, and pre-baked at a temperature of 100 ° C. for 30 minutes.
[0069]
At this time, a force of about 7.5 MPa is generated as a tensile stress in the transparent substrate 1 due to the stress caused by the thermal strain of the organic material film 3, and the shape of the transparent substrate 1 having “reverse warpage” due to the curvature Is applied, and as a result, the warpage of the transparent substrate 1 is reduced.
[0070]
As a result of measuring the warpage of the surface of the organic material film by removing the photoresist, the amount of warpage of the organic material film surface is reduced as compared with the case where the organic material film is adhered to the BK-7 glass substrate in a parallel plate state. confirmed.
[0071]
A large number of transparent substrates were prepared in which the radius of curvature R of the curved shape previously given to the transparent substrate 1 was changed to 15 m, 20 m, 30 m, 100 m, and 120 m, and the organic material film 3 (thickness: A polyester film having a birefringence developed by stretching is attached to a 0.1 mm polyester-based organic material film to form a photoresist film having a thickness of 0.5 μm in the same manner as described above. A sample baked for a minute was used as a sample.
[0072]
With respect to these samples, "whether or not vacuum suction" was performed on a stepper device and whether or not focusing was performed on the photoresist surface were examined. The results are shown below.
[0073]
"○" means "no problem", "△" requires manual correction, but "vacuum suction / focusing is possible", "x" means "vacuum suction / focusing was not possible" Case ".
[0074]
Curvature radius: R 15m 20m 30m 100m 120m
Availability of vacuum suction on stepper × ○ ○ ○ △
Acceptance of focus position × △ ○ ○ ×.
[0075]
Radius of curvature: A transparent substrate having a large R, that is, "a substrate having a small curvature" and a transparent substrate having a small radius of a curvature, that is, "a substrate having a too large curvature" had no effect.
[0076]
In consideration of the stability of the process of manufacturing the diffractive optical element and the quality of the element, it is necessary to manufacture the transparent substrate 1 while minimizing the displacement.
[0077]
On the transparent substrate 1 on which the organic material film 3 is adhered and the photoresist film is formed as described above, a pattern of “line & space: 2 μm” is repeated 300 times at a pitch of 8 mm on the organic material film 3 using a stepper device. Then, masks for 300 units of diffraction gratings (see FIG. 1C) were formed in a lattice array. The mask for one unit of the diffraction grating is formed in a rectangular shape of 1 mm × 2 mm at the center of the outer shape: 8 mm × 8 mm.
[0078]
Next, in an “etching gas atmosphere containing oxygen gas as a main component”, a line having a width of 2 μm, a depth of 3 μm, and a space having a width of 2 mm are formed with an ECR (Electron Cyclotron Resonance: Electron Cyclotron Resonance) etching apparatus manufactured by Sumitomo Metal Co., Ltd. A lattice-like array of diffraction gratings with periodic repetitions was formed. Other photolithography uses a generally known process, and a detailed description thereof will be omitted.
[0079]
Next, as shown in FIG. 7, the transparent substrate 1 having the organic material film 3 and the diffraction gratings formed in a lattice array is placed on a stainless steel plate 70 having a flattened diameter: φ = 200 mm and a thickness: 50 mm. Then, on the surface on which the diffraction grating is formed, an acrylic resin-based photocurable (optically isotropic, having a refractive index substantially equal to the refractive index for an extraordinary ray in the birefringence developed in the organic material film. ) 0.25 ml of the adhesive 71 was metered and dropped with a microsyringe, and a transparent counter substrate 5 made of BK-7 glass having an outer diameter of φ = 100 mm and a thickness of 0.5 mm, both surfaces of which were optically polished from above, was placed. Further, a pressing member 72 made of quartz glass which has been optically polished is placed thereon, and 100 gf / cm ² Is applied to spread the optically isotropic adhesive 71 over the entire surface to be bonded.
[0080]
In this state, with a UV device (not shown), the irradiation illuminance: 20 mW / cm from 150 mm above the opposing transparent substrate 5 ² For 10 minutes to cure and bond the adhesive 71. Thus, the layer of the cured adhesive 71 becomes an “overcoat layer”. Thereafter, the area where each diffraction grating was formed was cut out into 8 mm × 8 mm by a dicing apparatus and separated to obtain one unit of a diffractive optical element.
Thus, a diffractive optical element as shown in FIG. 1 (f) is obtained. This diffractive optical element is the polarization hologram element according to claim 16.
[0081]
The above-mentioned “optically isotropic adhesive” used an acrylic UV-curable adhesive from the viewpoints of easy control of characteristics such as viscosity and refractive index, and adhesiveness and transparency. The same is possible with a curable adhesive. Since these adhesives are cured by ultraviolet rays, they can be cured during pressurization, and the manufacturing process can be simplified.
[0082]
A method for obtaining an organic material film having birefringence is as follows: a polymer film such as polyethylene terephthalate is rubbed with a cloth and rubbed to form an alignment film, and a polydiacetylene monomer is vacuum-deposited on the alignment film to be aligned; After that, a method of irradiating ultraviolet light to polymerize to form an anisotropic film (J. Appl. Phys., 72, No. 3, P938-947) is known, but the process is complicated. High manufacturing cost.
[0083]
The organic material film 3 used above is an “organic polymer film in which the molecular chains are oriented (claim 11)”, which exhibits birefringence by stretching in consideration of uniformity of characteristics (claim 12). ).
[0084]
The radius of curvature: R of the transparent substrate varies depending on the coefficient of thermal expansion and the thickness of the organic material film, because the “tensile stress of the organic material film due to thermal contraction” changes. The temperature is determined experimentally in consideration of the temperature and the like, and is not limited to the above example.
[0085]
Hereinafter, another embodiment of the method of manufacturing the diffractive optical element will be described.
In this embodiment, a transparent parallel plate-like material to be a transparent substrate is sandwiched between a first jig having a predetermined convex curved surface shape and a second jig having a concave curved surface shape corresponding to the convex curved surface shape. To apply a predetermined curvature to the transparent parallel plate-like material (claim 3). In the embodiment described below, a plurality of thin transparent plates are used as the transparent parallel plate-like material to be a transparent substrate. After the photo-setting or thermo-setting adhesive laminated in a fluid state is used, the adhesive is solidified by light or heat after being deformed by the first and second jigs.
[0086]
As shown in FIG. 8, a laminated receiving jig 81 made of quartz glass having a radius of curvature R = 30 m as a radius of curvature (rough cutting, medium polishing, and precision polishing so as to form a convex spherical shape having a radius of curvature of 30 m with a spherical polishing device). Then, the surface roughness is Ra (center line average roughness): having a “convex spherical receiving surface” of 5 nm or less by finish polishing, and a pressing jig 82 made of quartz glass (for receiving the lamination receiving jig 81). Using a polishing jig on which the polished surface of the surface has been transferred, the pressed surface is roughly ground to have a concave spherical shape with a radius of curvature: R of 30 m, medium polished, precision polished, and then finished with a surface roughness Ra (center line average roughness). A) having a “concave spherical pressing surface” of 5 nm or less.
[0087]
A parallel flat plate G1 made of BK-7 glass having a diameter of φ = 100 mm and a thickness of 0.1 mm is placed on the receiving surface of the laminated receiving jig 81, and has substantially the same refractive index as that of the BK-7 glass. 0.1 ml of the ultraviolet curing adhesive S1 is dropped. A parallel plate G2 of BK-7 glass having a diameter of φ = 100 mm and a thickness of 0.1 mm is placed thereon, and 0.1 ml of the ultraviolet curing adhesive S2 is dropped thereon.
[0088]
Similarly, the parallel flat plates G3 and G4 of the same size and the same thickness as described above made of BK-7 glass are placed, and four parallel flat plates G1 to G4 are laminated via the adhesives S1 to S3.
[0089]
In this state, pressure is applied from above the stacked parallel flat plates G1 to G4 by a pressing device (not shown) using a pressing jig 82 to deform the parallel flat plates G1 to G4 and “fix the deformed state”, and UV (not shown) The apparatus irradiates ultraviolet light through a pressing jig 82 to cure the adhesives S1 to S3.
[0090]
As the adhesives S1 to S3, TB3042 (trade name of Three Bond) was used.
[0091]
In this way, as shown in FIG. 9, a “transparent substrate” including four parallel flat plates G <b> 1 to G <b> 4 which is given a curved shape by deformation and integrated by bonding is obtained.
The radius of curvature: R of both surfaces of the transparent substrate is 40 m, and the amount of curvature: W is 27 μm.
[0092]
On this transparent substrate, a group of diffraction gratings is formed in a lattice array by the same process as described above, the overcoat layer is formed and the opposing substrate is integrated, and a dicing device is used to form a 8 mm × 8 mm size. The cutout was used as a polarization hologram element.
[0093]
In the case of this method, a “transparent substrate having both surfaces having the same radius of curvature” can be realized by laminating and bonding using an inexpensive flat substrate G1 and the like, and a transparent substrate having an appropriately set “thickness” by increasing or decreasing the number of layers. Can be produced.
[0094]
Considering the easiness of making a transparent substrate by lamination, the thickness of the parallel flat plate G1 or the like to be laminated is desirably in the range of 0.03 mm to 1 mm, and considering the availability, handling, cost, and lamination cost of the thin parallel flat plate. The thickness of one parallel flat plate to be laminated is preferably 0.07 to 0.3 mm.
[0095]
FIG. 10 shows a modification of the embodiment described with reference to FIGS.
[0096]
A transparent substrate having a curved shape is formed by laminating thin parallel plates G1 to G4 of BK-7 glass via adhesives S1 to S3, and deforming by pressing to obtain a radius of curvature: R = 30 m, and a bending amount: W. = 27 [mu] m and bonded together with adhesives S1 to S3.
[0097]
In this example, when deforming by pressing with the laminated receiving surface jig and the pressing jig, the surface of the parallel flat plate G1 that is the concave ₂ The anti-reflection film H is coated.
[0098]
That is, MgF was formed on one surface of a parallel plate G1 of bK-7 glass having a diameter of φ = 100 mm and a thickness of 0.1 mm by vacuum evaporation. ₂ Is formed under a film-forming condition with no residual film stress so that λ / 4 = n · d.
[0099]
Hereinafter, as in the case of the previous embodiment, the parallel flat plates G1 to G4 are laminated, deformed by applying pressure, and cured with an adhesive to obtain a transparent substrate as shown in FIG.
[0100]
Hereinafter, the bonding of the organic material film, the formation of the diffraction grating, the formation of the overcoat layer, and the integration of the opposing substrate are performed in the same manner as described above, and the diffractive optical element is obtained through a separation process using a dicing apparatus. Since the diffractive optical element obtained in this way is coated with the antireflection film H, the light incidence efficiency is improved in use.
[0101]
On the upper side, as the organic material film is assumed to be “one in which heat shrinkage isotropically occurs”, the curved shape given to the transparent substrate in advance is such that both surfaces of the transparent substrate are “spherical surfaces having the same curvature”. However, when the heat shrinkage of the organic material film is directional and the heat shrinkage is remarkable in a specific direction, the curvature of the transparent substrate is changed to “a cylinder surface having the same curvature on both sides”. And the stress due to thermal shrinkage may act in the direction of the maximum curvature of the cylinder surface.
[0102]
FIG. 11 is a diagram showing one embodiment of the optical pickup device of the present invention. The optical pickup device focuses the light emitted from the light source 30 on the recording surface of the optical disk 40 as a light spot by the objective lens 37, and detects the return light beam reflected by the recording surface through the objective lens 37. An optical pickup device that performs at least one of recording, reproducing, and erasing of information on an optical disk 40 while guiding the optical disk 40 to a unit 39. A diffractive optical element 31 is disposed between a light source 30 and an objective lens 37.
The diffractive optical element 31 is as shown in FIG.
[0103]
In the optical pickup device shown in FIG. 11, light from a semiconductor laser, which is the light source 30, passes through the diffractive optical element 31. The diffractive optical element 31 has an organic material film of an organic birefringent film and is used as a “polarization hologram element”. Light from the light source side is transmitted through the diffractive optical element 31 as it is, and furthermore, the １ ／ wavelength plate 35 The light is transmitted and condensed as a light spot on the recording surface of the optical disk 40 by the action of the objective lens 37.
[0104]
The light reflected by the recording surface becomes a “return light beam”, passes through the objective lens 37 and the quarter-wave plate 35, becomes a linearly polarized light whose polarization plane is rotated by 90 degrees from the original direction, and enters the diffractive optical element 31. Then, the light is deflected toward the light detection unit 39 by the diffraction effect of the diffractive optical element 31. At this time, for example, astigmatism is given to the return light beam by the diffractive optical element 31, and this light beam is received by the light detection unit 39, and the focusing signal by the astigmatism method, the tracking signal by the push-pull method, and the reproduction signal are output. generate.
[0105]
That is, the optical pickup device of FIG. 11 uses the diffractive optical element according to claim 16 as a polarization hologram element 31 for separating the optical path of the light beam from the light source 30 and the optical path of the return light beam from the optical disk 40. (Claim 19).
[0106]
FIG. 12 is a diagram showing one embodiment of an optical disk drive device.
This optical disk drive device is a device that performs one or more of recording, reproducing, and erasing of information on an optical disk 40 using an optical pickup device 41. The optical disk 40 is held by a holding section 47 and is driven to rotate by a motor M as a “drive unit”.
[0107]
An optical pickup device 41 (for example, as shown in FIG. 11) is displaced and driven in the radial direction of the optical disc 40 by a displacement driving means 43 for the set optical disc 40, and performs at least one of recording, reproduction, and erasing. The control unit 45 controls various controls based on signals from the optical pickup device 41, controls the output of a reproduction signal, and controls the entire device.
[0108]
That is, the optical disk drive device shown in FIG. 12 is an optical disk drive device that performs one or more of recording, reproducing, and erasing of information on an optical disk 40 using an optical pickup device 41. It was used (claim 20).
[0109]
【The invention's effect】
As described above, according to the present invention, a novel diffractive optical element, a method for manufacturing the same, an optical pickup device, and an optical disk drive device can be realized.
In the diffractive optical element manufacturing method according to the present invention, the transparent substrate is given a predetermined curved shape in advance, and the heat shrinkage of the organic material film corrects the curved shape by using the tensile stress acting on the transparent substrate as a correcting force. The warpage of the substrate is effectively reduced, and during the diffraction grating forming step, the substrate can be securely fixed at a predetermined position by “vacuum suction”, and the “curve of the plurality of diffractive optical elements simultaneously formed due to the warp of the transparent substrate” The variation of the optical characteristics "can be effectively prevented, and the problem of the deterioration of the wavefront aberration of the transmitted light in the diffractive optical element formed in the portion having a large warp can be effectively solved.
[0110]
Therefore, the diffractive optical element according to the present invention can be manufactured at a low cost with good manufacturing yield, and the variation in optical characteristics between the elements is small.
[0111]
An optical pickup device using such a diffractive optical element as a polarization hologram element can realize a good optical pickup function, and an optical disc drive device using such an optical pickup device has good performance.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining a basic process for manufacturing a diffractive optical element.
FIG. 2 is a diagram schematically illustrating an array of diffraction gratings formed in a grid array on an organic material film adhered to a transparent substrate.
FIG. 3 is a diagram for explaining a warp of a transparent substrate due to heat shrinkage of an organic material film.
FIG. 4 is a diagram for explaining a transparent substrate having a curved shape used in the method of manufacturing a diffractive optical element according to the present invention.
FIG. 5 is a view for explaining a step of placing an organic material film on a transparent substrate via an adhesive in the embodiment of the invention.
FIG. 6 is a view for explaining a step of bonding an organic material film placed on a transparent substrate to the transparent substrate in the step of FIG. 5;
FIG. 7 is a view for explaining a step of bonding an opposing transparent substrate to an organic material film on which a diffraction grating is formed, using an adhesive to be an overcoat layer.
FIG. 8 is a view for explaining a process of deforming a transparent parallel plate-shaped material to be a transparent substrate to give a curved shape.
FIG. 9 is a view showing a transparent substrate provided with a curved shape in the step shown in FIG. 8;
FIG. 10 is a view for explaining a transparent substrate on which an antireflection film is formed.
FIG. 11 is a diagram illustrating one embodiment of an optical pickup device.
FIG. 12 is a diagram for describing one embodiment of an optical disk drive device.
[Explanation of symbols]
1A transparent substrate
2 adhesive
3 Organic material film

Claims (20)

An organic material film bonding step of bonding and fixing the organic material film on the transparent substrate,
A step of forming a plurality of diffraction gratings having rectangular irregularities in a cross-sectional shape by a step including photolithography and etching on the organic material film adhered and fixed on the transparent substrate; ,
A method of manufacturing a diffractive optical element having a separation step of individually separating a plurality of diffraction gratings formed in a lattice array,
In order to alleviate the warpage of the transparent substrate caused by the heat shrinkage of the organic material film, a predetermined curved shape is given to the transparent substrate in advance, and the curved shape is corrected by the heat shrinkage of the organic material film, whereby the transparent material is formed. A method for manufacturing a diffractive optical element, wherein the substrate is a substantially parallel flat plate. 2. The method of manufacturing a diffractive optical element according to claim 1, wherein a transparent substrate having a predetermined curved shape is produced by machining both surfaces of a transparent parallel plate material to be a transparent substrate. Device manufacturing method. The method for manufacturing a diffractive optical element according to claim 1,
A transparent parallel plate material to be a transparent substrate is sandwiched and pressed by a first jig having a predetermined convex curved surface shape and a second jig having a concave curved surface shape corresponding to the convex curved surface shape, A method for producing a diffractive optical element, wherein a transparent parallel plate material is given a predetermined curved shape. The method for manufacturing a diffractive optical element according to claim 3,
As a transparent parallel plate-shaped material to be a transparent substrate, a laminate of a plurality of thin transparent plates via a light-curable or thermosetting adhesive in a fluid state is used, and after being deformed by the first and second jigs. A method for manufacturing a diffractive optical element, wherein the adhesive is solidified by light or heat. The method for manufacturing a diffractive optical element according to any one of claims 1 to 4,
A method of manufacturing a diffractive optical element, wherein a radius of curvature of a predetermined curved shape previously applied to a transparent substrate is in a range of 20 to 100 m. The method for manufacturing a diffractive optical element according to any one of claims 1 to 5,
The transparent substrate is supported by a support jig having a convex curved surface shape that fits the curved shape of the transparent substrate, an adhesive is applied to the convex surface side of the supported transparent substrate, and an organic material film is placed thereon, and Pressing from above the organic material film by a holding jig having a concave curved surface shape corresponding to the convex curved surface shape of the supporting jig, and uniformly spreading the adhesive between the transparent substrate and the organic material film. A method for manufacturing a diffractive optical element, comprising: The method for manufacturing a diffractive optical element according to any one of claims 1 to 6,
The etching step in the diffraction grating forming step of forming a plurality of diffraction gratings having a rectangular cross section on the organic material film bonded and fixed on the transparent substrate in a grid array is performed by electron cyclotron etching. A method for manufacturing a diffractive optical element. The method for manufacturing a diffractive optical element according to any one of claims 1 to 7,
Diffraction characterized by filling an optically transparent material into the concave portions of the diffraction gratings in each diffraction grating from an organic material film in which a plurality of diffraction gratings are formed in a lattice array to form an overcoat layer. A method for manufacturing an optical element. The method for manufacturing a diffractive optical element according to claim 8,
A method for manufacturing a diffractive optical element, wherein a transparent counter substrate is integrated on an overcoat layer. The method for manufacturing a diffractive optical element according to claim 8,
The organic material film is an organic birefringent film, and the overcoat layer is an isotropic optical material having a refractive index substantially equal to the refractive index of the organic birefringent film for ordinary light or extraordinary light. A method for manufacturing a diffractive optical element, comprising: The method for manufacturing a diffractive optical element according to claim 10,
A method for producing a diffractive optical element, comprising using a polymer birefringent film in which molecular chains are oriented as the organic birefringent film. The method for manufacturing a diffractive optical element according to claim 11,
A method for producing a diffractive optical element, wherein the polymer birefringent film used as the organic birefringent film is a polymer film in which molecular chains are oriented by stretching. The method for manufacturing a diffractive optical element according to any one of claims 8 to 12,
A method for manufacturing a diffractive optical element, wherein the material of the overcoat layer is an acrylic or epoxy material. A diffractive optical element manufactured by the method for manufacturing a diffractive optical element according to claim 1. The diffractive optical element according to claim 14,
13. A diffractive optical element produced by the method for producing a diffractive optical element according to claim 10, and used as a polarization hologram element. The diffractive optical element according to claim 15,
A diffractive optical element used as a polarization hologram element, wherein a transparent counter substrate is integrated on the overcoat layer. The diffractive optical element according to claim 16,
A diffractive optical element, wherein the material of the overcoat layer is an acrylic or epoxy material. The diffractive optical element according to claim 15, 16 or 17,
A diffractive optical element comprising an antireflection film formed on a transparent substrate to which an organic birefringent film is adhered. 19. Light using the diffractive optical element according to any one of claims 15 to 18 as a polarization hologram element for separating an optical path of a light beam from a light source side and an optical path of a return light beam from an optical disk. Pickup device. In an optical disk drive device that performs one or more of recording, reproducing, and erasing of information on an optical disk using an optical pickup device,
An optical disk drive device using the device according to claim 19 as an optical pickup device.

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