JP2007234094A - Diffraction grating body, optical head device using the same, and method of manufacturing diffraction grating body - Google Patents

Abstract

An object of the present invention is to design an optimal antireflection film in a diffraction grating body corresponding to light beams of two different wavelengths, to reduce the light amount loss, and to improve the manufacturing yield of the diffraction grating body.
A first diffraction grating includes, in order from the surface of a substrate made of glass or the like, a first antireflection film comprising a first matching layer and an etching stop layer, and a diffraction grating. A convex portion 15 and a second antireflection film 18 constituted by a cover layer 16 and a second matching layer 17 are laminated. The layers of Ta ₂ O ₅ as the first matching layer 12, a for Al ₂ O ₃ etching stop layer 13, the Ta ₂ O ₅ as a diffraction grating protrusions 15, the Ta ₂ O ₅ as the cover layer 16, the As the second matching layer 17, SiO ₂ was used as a material.
[Selection] Figure 2

Description

  The present invention relates to a diffraction grating body, and an optical head device using the diffraction grating body and a method of manufacturing the diffraction grating body, particularly a diffraction grating body corresponding to light beams having two different wavelengths, and transmitting light beams having one wavelength. The present invention relates to a diffraction grating body including a diffraction grating that functions to diffract light of the other wavelength, an optical head device using the diffraction grating body, and a method of manufacturing the diffraction grating body.

Optical pickups used in optical disk devices and magneto-optical disk devices have a structure that uses a plurality of light beams having different wavelengths in order to support different types of optical disks such as CDs and DVDs. In recent years, monolithic integrated two-wavelength lasers have been put into practical use, and light sources having two different wavelengths (for example, 660 nm and 785 nm) can be formed on a single semiconductor substrate. Is planned.
Furthermore, in recent years, a semiconductor laser diode that emits a blue-violet laser (405 nm) has been developed for an optical head device capable of recording / reproducing a high-density optical disk such as a Blu-ray Disc or an HD DVD.
On the other hand, in order to reproduce the information written on the optical disk by using, for example, the light beam having the wavelength λ1 or the light beam having the wavelength λ2, the data read / write light irradiated on the pits formed on the optical disk, Tracking light to irradiate the grooves. Therefore, the optical pickup is required to make the light beam into three beams, and has a function of diffracting the incident light beam into zero-order light as a main beam and two ± first-order lights as side beams. In general, a diffraction grating is used as a means for converting the light into three beams.

7 and 8 are diagrams showing examples of the structure of a conventional diffraction grating body. A diffraction grating body 1 shown in FIG. 7 has a diffraction grating 3 formed on the entire surface of a substrate 2 made of glass or the like with a predetermined groove depth and a repetitive pitch. As shown in FIG. 7A, the diffraction grating 1 transmits the light beam having the first wavelength λ1 as it is, and the light beam having the second wavelength λ2 becomes the main beam as shown in FIG. 7B. It has a function of diffracting into zero-order light and two ± first-order lights serving as side beams.
A diffraction grating body 4 shown in FIG. 8 has a first diffraction grating 6 and a second diffraction grating 7 formed in predetermined grooves on the light incident surface and the light exit surface of a substrate 5 made of glass or the like. It is formed on the entire surface with a depth and a repeating pitch. As shown in FIG. 8 (a), the diffraction grating body 4 diffracts the light beam having the first wavelength λ1 into 0th-order light as a main beam and two ± first-order lights as side beams. As shown in b), it has a function of diffracting the light beam having the second wavelength λ2 into zero-order light as a main beam and two ± first-order lights as side beams. Therefore, the first diffraction grating 6 diffracts the light beam having the first wavelength λ1 and transmits the light beam having the second wavelength λ2 as it is, while the second diffraction grating 7 has the second wavelength λ2. While diffracting the light beam, the light beam having the first wavelength λ1 is transmitted as it is. In FIG. 8, the optical paths of the light beams having the wavelengths λ1 and λ2 are shown separately. However, this is for ease of explanation, and the light beams of the respective wavelengths actually propagate through the same optical path.

The diffraction grating body is formed by repeating a diffraction grating having a predetermined refractive index on one of the light incident surface and the light exit surface of the substrate constituting the diffraction grating body, or on both surfaces with a predetermined groove depth. By forming the entire surface with a pitch and appropriately setting the depth of the groove and the repetition pitch, the incident light beam with respect to a light beam of a desired wavelength is divided into two beams, a 0th-order light beam as a main beam and a side beam beam. Diffracted into ± first order light.
Japanese Patent No. 3457777 JP 2001-281432 A JP 2002-214420 A

The diffraction grating corresponding to the light beams of two wavelengths transmits the light beam of one wavelength, and the light beams of the other wavelength are diffracted into the zero-order light as the main beam and the two ± first-order lights as the side beams. The problem is how to reduce the light loss during diffraction.
Therefore, as a means for solving this problem, for example, there is a method disclosed in Patent Document 1. According to this, the depth of the groove of the hologram grating that diffracts only the light of the first semiconductor laser having a wavelength of 660 nm is set to about 1.7 μm where the diffraction efficiency at 660 nm is almost 0 and the diffraction efficiency is increased at 785 nm, and the wavelength is 785 nm. If the depth of the groove of the hologram grating that diffracts only the light of the second semiconductor laser is about 1.4 μm where the diffraction efficiency at 785 nm is almost 0 and the diffraction efficiency is large at 660 nm, the desired diffraction characteristics can be obtained. Explains.

However, when the grating groove depth is 1.7 μm or 1.4 μm, the diffraction grating body can theoretically reduce the light loss, but the grating groove is deep, so that a technique such as etching is used. When the lattice is formed, the shape of the lattice becomes a trapezoid, and a light amount loss occurs in the inclined portion of the trapezoid, resulting in a problem.
Further, for example, in the technique disclosed in Patent Document 2, when the incident light having the first wavelength λ1 is transmitted and the incident light having the second wavelength λ2 is diffracted, the diffraction grating is projected. It is described that the groove depth is set such that the phase difference of the transmitted light having the first wavelength λ1 is 2π between the portion and the recess. However, even in this case, the depth of the groove of the diffraction grating is about 1.3 μm, and similarly to the method disclosed in Patent Document 1 described above, the diffraction grating is deep, causing a loss of light quantity, resulting in a problem.

Therefore, as a technique for reducing the light loss caused by the deep diffraction grating, for example, there is a technique disclosed in JP-A-2002-214420. According to this, the diffraction grating body is configured by using a high refractive index material. For example, when Ta ₂ O ₅ (tantalum oxide) is used as the high refractive index material, the refractive index n of the Ta ₂ O ₅ film with respect to red light is about 2. Therefore, although the calculation formula is omitted, substituting n = 2 and the wavelength of red light λ1 = 660 nm into the predetermined calculation formula to obtain the optimum groove depth of the diffraction grating, The thickness is 660 nm. That is, the conventional diffraction grating body has a refractive index n of about 1.5, and the groove depth of the diffraction grating is required to be about 1.3 μm. That is half the value. Therefore, when a diffraction grating is formed by using a technique such as etching, the diffraction grating body can easily form a rectangular cross-sectional shape. Can be reduced. Usually, in order to reduce the cost of the diffraction grating body, inexpensive glass or resin is used for the substrate on which the diffraction grating body is formed, and an expensive high refractive index material is used only for the base material on which the diffraction grating portion is formed. To do. The diffraction grating is generally formed by depositing a high refractive index material on the surface of the substrate on which the diffraction grating body is to be formed, and forming the diffraction grating by etching.

However, when a high refractive index material is etched to form a diffraction grating, the variation in the accuracy of the depth of the groove formed by etching is very large compared to the deposition accuracy of vapor deposition. There was a problem that the manufacturing yield of the diffraction grating body was lowered due to variations in the accuracy of the depth of the grooves.
In addition, a diffraction grating body using a high refractive index material for the diffraction grating portion as described above is different from the substrate forming the diffraction grating body and the base material forming the diffraction grating. Since reflection occurs between the materials and loss of light quantity occurs, an antireflection film is required on the boundary surface. Further, since reflection occurs at the boundary surface between the diffraction grating body and air and a light amount loss occurs, an antireflection film is necessary on the surface of the diffraction grating body.
The present invention has been made in view of such conventional problems, and in a diffraction grating corresponding to light beams having two different wavelengths, an optimal antireflection film is designed to reduce light loss, An object is to improve the manufacturing yield of the diffraction grating.

In order to achieve the above object, a diffraction grating body and a manufacturing method thereof according to the present invention have the following configurations.
The diffraction grating body in the present invention includes a first diffraction grating and a second diffraction grating in which convex portions and concave portions are periodically formed on the respective surfaces of the incident surface and the exit surface of the substrate constituting the diffraction grating body. The first diffraction grating diffracts a light beam having a first wavelength (wavelength of λ1) into zero-order light as a main beam and two ± first-order lights as side beams. At the same time, the second diffraction grating transmits a light beam having a second wavelength (λ2 wavelength). The second diffraction grating has two light beams having a second wavelength which are a main beam and a zeroth-order light and a side beam. The first diffraction grating and the second diffraction grating are formed of a material having a higher refractive index than that of the substrate. And an interface between the substrate and the first diffraction grating, and the A first antireflection film is formed on each boundary surface between the plate and the second diffraction grating, and a boundary surface between the first diffraction grating and air, and between the second diffraction grating and air. A feature is that a second antireflection film is formed on each of the boundary surfaces.
According to this, in the diffraction grating body having a structure in which diffraction gratings are formed on both surfaces of the substrate constituting the diffraction grating body, reflection is performed on the boundary surface between the substrate and the diffraction grating and the boundary surface between the diffraction grating and air. Since the prevention film is formed, the diffraction grating body can reduce the light amount loss of incident light, and can exert a great effect in using the diffraction grating body.

In the diffraction grating body of the present invention, the high refractive index material forming the first diffraction grating and the second diffraction grating is Ta ₂ O ₅ or TiO ₂ .
According to this, since the diffraction grating body uses a high refractive index material as a base material constituting the diffraction grating, the groove of the diffraction grating is made shallower than a conventional diffraction grating that does not use a high refractive index material. Thus, it is possible to reduce a light amount loss due to the grooves of the diffraction grating being inclined in a trapezoidal shape.
In the diffraction grating according to the present invention, the first antireflection film forms an etching stop layer on the surface of the first matching layer after the first matching layer is formed on the surface of the substrate. It is characterized by that.
According to this, since the diffraction grating body includes the etching stop layer in the first antireflection film, a high refractive index material is vapor-deposited on the substrate of the diffraction grating body, and the diffraction grating is formed when the diffraction grating is formed by etching. The etching can be stopped at the depth of the groove. Therefore, the manufacturing yield is improved in manufacturing the diffraction grating body, and a great effect can be exhibited in reducing the cost of the diffraction grating body.

In the diffraction grating according to the present invention, the material of the first matching layer is Ta ₂ O ₅ , and the material of the etching stop layer is Al ₂ O ₃ or MgF ₂ . .
According to this, since the diffraction grating body uses Al ₂ O ₃ or MgF ₂ which is difficult to etch as the material of the etching stop layer, when the diffraction grating is formed by etching, the diffraction grating body has a predetermined groove depth. It became possible to stop etching reliably.
In the diffraction grating body according to the present invention, the second antireflection film forms a cover layer on the surfaces of the first diffraction grating and the second diffraction grating, and then on the surface of the cover layer. And a second matching layer is formed.
The diffraction grating according to the present invention is characterized in that the material of the cover layer is Ta ₂ O ₅ and the material of the second matching layer is SiO ₂ .
According to this, since the diffraction grating body includes the cover layer in the second antireflection film, the structure of the material of the convex part and the concave part of the diffraction grating is different as in this embodiment, and therefore the material that comes into contact with air. Thus, even when it is difficult to obtain an effective antireflection effect with a normal antireflection film, an effective antireflection film can be formed.

The diffraction grating body according to the present invention is a diffraction grating groove in which a light beam transmitted through the first diffraction grating and the second diffraction grating has a phase difference of 2π between the convex portion and the concave portion. It is characterized by its depth.
In the diffraction grating body of the present invention, the first wavelength is 660 nm, the second wavelength is 785 nm, the groove depth of the first diffraction grating is 6845 mm, and the width of the diffraction grating convex portion. 3.98 μm, the repetition pitch of the diffraction grating is 20.0 μm, the groove depth of the second diffraction grating is 5670 mm, the width of the projection of the diffraction grating is 5.00 μm, and the repetition pitch of the diffraction grating is 20. It is 0 μm.
According to this, the diffraction grating body is set to the depth of the groove of the diffraction grating so that the light beam transmitted through the diffraction grating body has a phase difference of 2π between the convex part and the concave part of the diffraction grating. It is possible to reduce the light loss of the light beam having a wavelength that is transmitted through the diffraction grating as it is, and to improve the diffraction efficiency of the light beam having the other wavelength.

An optical head device according to the present invention includes a light source that emits light beams having a first wavelength and a second wavelength, and an objective lens that focuses the light beams having the first wavelength and the second wavelength on an optical recording medium. An optical head device for recording / reproducing information on / from an optical recording medium, wherein the diffraction grating body described above is installed in an optical path between the light source and the objective lens. It is said.
According to this, the optical head device can easily convert the light beams of the first wavelength and the second wavelength emitted from the light source into three beams by using the diffraction grating body described above. It is very effective in configuring the head device.

  In addition, the method for manufacturing a diffraction grating body in the present invention includes a first diffraction grating in which convex portions and concave portions are periodically formed on each of an incident surface and an output surface of a substrate constituting the diffraction grating body. A method of manufacturing a diffraction grating body comprising a second diffraction grating, comprising: depositing a first matching layer on one surface of a substrate processed into a predetermined dimension; Depositing an etching stop layer on the surface of the matching layer; depositing a high refractive index material to be a diffraction grating on the surface of the deposited etching stop layer; and depositing the surface of the deposited high refractive index material A step of forming a mask pattern having a predetermined dimension, a step of etching the surface of the diffraction grating on which the mask pattern is formed up to an etching stop layer, and before etching. Depositing a cover layer on the surface of the diffraction grating body, and depositing a second matching layer on the deposited surface of the cover layer to form a first diffraction grating. Reversing the substrate constituting the diffraction grating body and depositing a first matching layer on the other surface of the substrate, and an etching stop layer on the surface of the deposited first matching layer Depositing a high refractive index material to be a diffraction grating on the surface of the deposited etching stop layer, and forming a mask pattern of a predetermined dimension on the surface of the deposited high refractive index material Etching the surface of the diffraction grating on which the mask pattern is formed up to the etching stop layer; and on the surface of the etched diffraction grating A second step of forming a second diffraction grating comprising: depositing a cover layer; and depositing a second matching layer on the surface of the deposited cover layer. Yes.

  According to this, since the diffraction grating body has an etching stop layer formed on the first antireflection film, a high refractive index material is vapor-deposited on the substrate of the diffraction grating body, and a predetermined diffraction grating is formed when the diffraction grating is formed by etching. The etching can be stopped at the depth of the groove. Accordingly, the production yield of the diffraction grating body is improved, and a great effect can be exhibited in reducing the cost of the diffraction grating body.

Hereinafter, the present invention will be described in detail based on the illustrated embodiments.
In order to reduce light loss and obtain stable diffraction grating performance, the present invention forms a diffraction grating using a high refractive index material, and forms a diffraction grating with a substrate constituting the diffraction grating body. A first antireflection film was formed between the substrate made of the material. The first antireflection film was composed of a matching layer and an etching stop layer. Therefore, the diffraction grating body can reduce reflection of light rays generated between the substrate constituting the diffraction grating body and the base material forming the diffraction grating by the matching layer. In addition, since the diffraction grating body is formed with an etching stop layer, high-refractive-index material deposited on the surface of the substrate constituting the diffraction grating body is etched to form a diffraction grating. As a result, stable diffraction grating characteristics can be obtained.

  On the other hand, on the surface of the diffraction grating body, a second antireflection film for preventing reflection generated at the boundary with air is formed, and the second antireflection film is constituted by a matching layer and a cover layer. . The diffraction grating formed on the diffraction grating body is different in the laminated structure of the material of the convex portion and the concave portion, and an effective antireflection effect cannot be obtained with a normal antireflection film. Therefore, a cover layer is formed on the surface of the diffraction grating, and a matching layer is formed thereon to form a second antireflection film. Therefore, the diffraction grating body in the present invention reduces the light loss of the diffraction grating body and improves the manufacturing yield of the diffraction grating body by forming the first antireflection film and the second antireflection film. Became possible.

  FIG. 1 is a structural diagram showing an embodiment of a diffraction grating body according to the present invention. The diffraction grating body 8 described in the present embodiment includes a first diffraction grating 10 made of a high refractive index material on each of the light incident surface and the light exit surface of the substrate 9 constituting the diffraction grating body 8. In this structure, the second diffraction grating 11 is formed on the entire surface with a predetermined groove depth and repetition pitch. As shown in FIG. 1A, the diffraction grating body 8 has a function of diffracting a light beam having a first wavelength λ1 into zero-order light as a main beam and two ± first-order lights as side beams. . Further, as shown in FIG. 1B, the diffraction grating body 8 has a function of diffracting a light beam having the second wavelength λ2 into a zero-order light serving as a main beam and two ± first-order lights serving as side beams. Have Therefore, the first diffraction grating 10 diffracts the light beam having the first wavelength λ1 and transmits the light beam having the second wavelength λ2 as it is. On the other hand, the second diffraction grating 11 diffracts the light beam having the second wavelength λ2 and transmits the light beam having the first wavelength λ1 as it is. In FIG. 1, the optical paths of the light beams having the wavelengths λ1 and λ2 are shown separately, but this is for ease of explanation, and the light beams of each wavelength actually propagate through the same optical path. In the present embodiment, a light beam having a wavelength corresponding to DVD of 660 nm is used as a light beam having a first wavelength λ1, and a light beam having wavelength 785 nm is used as a light beam having a second wavelength λ2. Each is set.

FIG. 2 is an enlarged view of a diffraction grating portion of the diffraction grating body according to the present invention. 2A shows an enlarged view of the first diffraction grating 10 in the structural diagram shown in FIG. 1, and FIG. 2B shows an enlarged view of the second diffraction grating 11 shown in FIG. .
FIG. 2A will be described. FIG. 2A is a configuration diagram of a first diffraction grating corresponding to a light beam having a wavelength of 660 nm used for a DVD. The first diffraction grating 10 includes, in order from the surface of the substrate 9 made of glass or the like, a first antireflection film 14 composed of a first matching layer 12 and an etching stop layer 13, a diffraction grating convex portion 15, The second antireflection film 18 constituted by the cover layer 16 and the second matching layer 17 is laminated. Further, each layer, the Ta ₂ O ₅ as the first matching layer 12, a for Al ₂ O ₃ etching stop layer 13, the Ta ₂ O ₅ as a diffraction grating protrusions 15, the Ta ₂ O ₅ as the cover layer 16 As the second matching layer 17, SiO ₂ was used as a material.

Next, the first antireflection film 14 will be described. The first antireflection film 14 has a function of preventing a light beam from being reflected between the substrate 9 and the diffraction grating convex portion 15 to cause a light amount loss. The present invention is characterized in that the first antireflection film 14 includes the etching stop layer 13. Although a method for manufacturing the diffraction grating will be described later, the diffraction grating is formed by depositing a high refractive index material on a substrate made of glass or the like and then etching it into a predetermined shape. The height of the diffraction grating convex portion 15 is an important factor for the diffraction grating to exhibit a predetermined function, but the etching accuracy is generally very inferior to the deposition accuracy. Therefore, in the present invention, in order to improve the etching accuracy, an etching stop layer 13 is formed on the surface of the substrate 9 so that the etching is surely stopped at a predetermined groove depth even if the etching accuracy varies. did. Therefore, the material of the etching stop layer 13 is Al ₂ O ₃ , which is a material that is difficult to be etched, compared to Ta ₂ O ₅ , which is a high refractive index material that forms the diffraction grating convex portion 15. The film thickness of each layer is calculated by a calculation method generally called a matrix method, and the example of the optimum value in the present embodiment is as follows.
First matching layer (Ta ₂ O ₅ ) = 204Å
Etching stop layer (Al ₂ O ₃ ) = 514 mm

Next, the diffraction grating convex portion 15 will be described. In the present embodiment, the diffraction grating convex portion 15 is formed of a high refractive index material, and a light beam having a wavelength transmitted through the diffraction grating is diffracted so that a phase difference between the convex portion and the concave portion of the diffraction grating is 2π. It was set to be the groove depth of the lattice. The diffraction efficiency of the diffraction grating body is determined by the height h and the width w of the diffraction grating convex portion 15, and the repetition pitch p of the diffraction grating is determined by the method of using the optical disk. The diffraction grating convex portion 15 corresponds to a DVD as an optical disk.
The phase-type diffraction efficiency can be expressed by the following equation (1) using scalar diffraction theory, where the diffraction efficiency is ηm (m-th order diffraction efficiency not including reflection).

式（１）に示すΦ（ｘ）は位相シフト関数である。位相シフト関数は回折格子の凸部高さｈとピッチｐ及び幅ｗで表すことができる。すなわち所望の回折効率とピッチｐを設定すれば式（１）より、前記高さｈ、及び幅ｗを算出することが出来る。本実施形態における回折格子体のパラメータを算出した結果は、以下のとおりであった。
ｈ＝６８４５Å、ｐ＝２０．０μｍ、ｗ＝３．９８μｍ

Φ (x) shown in Equation (1) is a phase shift function. The phase shift function can be expressed by the height h of the diffraction grating, the pitch p, and the width w. That is, if the desired diffraction efficiency and pitch p are set, the height h and width w can be calculated from the equation (1). The result of calculating the parameters of the diffraction grating body in the present embodiment was as follows.
h = 6845 mm, p = 20.0 μm, w = 3.98 μm

Next, the second antireflection film 18 will be described. Since the convex portion of the first diffraction grating 10 is made of Ta ₂ O _5, about 13% of reflection occurs at the boundary with air. Thus, the second antireflection film 18 has a function of preventing light rays from being reflected at the boundary between the first diffraction grating 10 and the air and causing loss of light quantity. In the diffraction grating body, the configuration of the material of the convex portions and the concave portions of the first diffraction grating 10 is different, and an effective antireflection effect cannot be obtained with a normal antireflection film. The convex portions of the first diffraction grating 10 are Ta ₂ O ₅ (diffraction grating convex portion 15), Al ₂ O ₃ (etching stop layer 13), Ta ₂ O ₅ (first matching layer 12) in order from the air side. ). On the other hand, the diffraction grating concave portion is composed of Al ₂ O ₃ (etching stop layer 13) and Ta ₂ O ₅ (first matching layer 12) in order from the air side. Therefore, it is difficult to obtain a desired function with a normal antireflection film having such a different multilayer structure. Therefore, the diffraction grating body is formed with the cover layer 16 once on the surface, and the second matching layer 17 is formed on the surface of the cover layer 16 to form the second antireflection film 18. The film thickness of each layer is calculated by a calculation method generally called a matrix method, and the example of the optimum value in the present embodiment is as follows.
Cover layer (Ta ₂ O ₅ ) = 853 mm
Second matching layer (SiO ₂ ) = 1251Å

Next, FIG. 2B will be described. FIG. 2B is a configuration diagram of a second diffraction grating corresponding to a light beam having a wavelength of 785 nm used for CD. The second diffraction grating 11 includes, in order from the surface of the substrate 9 made of glass or the like, a first antireflection film 21 composed of a first matching layer 19 and an etching stop layer 20, a diffraction grating convex portion 22, A second antireflection film 25 constituted by a cover layer 23 and a second matching layer 24 is laminated. Further, each layer, the Ta ₂ O ₅ as the first matching layer 19, a for Al ₂ O ₃ etch stop layer 20, the Ta ₂ O ₅ as a diffraction grating protrusions 22, the Ta ₂ O ₅ as a cover layer 23 As the second matching layer 24, SiO ₂ was used as a material.

Next, the first antireflection film 21 will be described. The first antireflection film 21 has a function of preventing a light beam from being reflected between the substrate 9 and the diffraction grating convex portion 22 and causing a loss of light quantity. In the present invention, the first antireflection film 21 is provided. The film 21 includes the etching stop layer 20. Although a method for manufacturing the diffraction grating will be described later, the diffraction grating is formed by depositing a high refractive index material on a substrate made of glass or the like and then etching it into a predetermined shape. The height of the diffraction grating convex portion 22 is an important factor for the diffraction grating to exhibit a predetermined function, but the etching accuracy is generally very inferior to the deposition accuracy. Therefore, in order to improve the etching accuracy, the diffraction grating has an etching stop layer 20 formed on the surface of the substrate 9 to ensure that the etching stops at a predetermined position even if the etching accuracy varies. Therefore, the material of the etching stop layer 20 is Al ₂ O ₃ , which is a material that is difficult to be etched, compared to Ta ₂ O ₅ , which is a high refractive index material that forms the diffraction grating convex portion 22. The film thickness of each layer is calculated by a calculation method generally called a matrix method, and the example of the optimum value in the present embodiment is as follows.
First matching layer (Ta ₂ O ₅ ) = 204Å
Etching stop layer (Al ₂ O ₃ ) = 514 mm

Next, the diffraction grating convex portion 22 will be described. In the present embodiment, the diffraction grating convex portion 22 is formed of a high refractive index material, and a light beam having a wavelength that passes through the diffraction grating is diffracted so that a phase difference between the convex portion and the concave portion of the diffraction grating is 2π. It was set to be the groove depth of the lattice. The diffraction efficiency of the diffraction grating body is determined by the height h and the width w of the diffraction grating convex portion 22, and the repetition pitch p of the diffraction grating is determined by the method of using the optical disk. The diffraction grating convex portion 22 corresponds to a CD as an optical disk.
As described above, the diffraction efficiency of the phase type diffraction grating can be expressed by the above equation (1) using the scalar diffraction theory when the diffraction efficiency is ηm (mth-order diffraction efficiency not including reflection). Therefore, a desired diffraction efficiency and pitch p are set, and the height h and the width w are calculated from the equation (1). The result of calculating the parameters of the diffraction grating body in the present embodiment was as follows.
h = 5670 mm, p = 20.0 μm, w = 5.00 μm

Next, the second antireflection film 25 will be described. Since the convex portion of the second diffraction grating 11 is made of Ta ₂ O _5, about 13% of reflection occurs at the boundary with air. Therefore, the second antireflection film 25 has a function of preventing the light beam from being reflected by the boundary surface between the second diffraction grating 11 and the air and causing a light amount loss. The configuration of the material of the convex portion and the concave portion of the second diffraction grating 11 is different, and an effective antireflection effect cannot be obtained with a normal antireflection film. The convex portions of the second diffraction grating 11 are Ta ₂ O ₅ (diffraction grating convex portion 22), Al ₂ O ₃ (etching stop layer 20), Ta ₂ O ₅ (first matching layer 19) in order from the air side. ). On the other hand, the diffraction grating recess is formed of Al ₂ O ₃ (etching stop layer 20) and Ta ₂ O ₅ (first matching layer 19) in order from the air side. Therefore, if the diffraction grating has such a different multilayer structure, it is difficult to obtain a desired function with a normal antireflection film. Therefore, the diffraction grating body is formed with the cover layer 23 once on the surface, and the second matching layer 24 is formed on the surface of the cover layer 23 to form the second antireflection film 25. The film thickness of each layer is calculated by a calculation method generally called a matrix method, and the example of the optimum value in the present embodiment is as follows.
Cover layer (Ta ₂ O ₅ ) = 853 mm
Second matching layer (SiO ₂ ) = 1251Å

  FIG. 3 is a table showing an example of numerical data of the diffraction grating body according to the present invention. FIG. 3 shows data of the first diffraction grating 10 corresponding to DVD and data of the second diffraction grating 11 corresponding to CD. Depending on the purpose of use of the optical disk, the height and width of the convex part of the diffraction grating are different. Is different. As shown in FIG. 3, both the diffraction grating corresponding to the DVD and the diffraction grating corresponding to the CD have a diffraction grating convex portion height that is about ½ that of a conventional diffraction grating body that does not use a high refractive index material. This is effective in reducing the light amount loss of the diffraction grating body.

FIG. 4 is a graph showing an example of the wavelength dependence of the amount of transmitted light of the diffraction grating body according to the present invention. FIG. 4 shows the wavelength dependence of the 0th-order transmitted light amount of the diffraction grating when a light beam having a wavelength of 660 nm corresponding to DVD is incident. FIG. 4 shows a simulation result of a conventional diffraction grating body using SiO ₂ as the base material of the diffraction grating and a diffraction grating body using Ta ₂ O ₅ which is a high refractive index material as the base material of the diffraction grating. This shows the wavelength dependency of the obtained transmitted light amount. In addition, with respect to a diffraction grating using Ta ₂ O ₅ which is a high refractive index material as a base material of the diffraction grating, the antireflection film is formed as in the case where the antireflection film is formed like the diffraction grating according to the present invention. The case of not forming was described. For conventional diffraction grating member with SiO _2, the height of the diffraction grating protrusions, becomes about 1.4 [mu] m, although light loss slope of the diffraction grating protrusions increases, Ta ₂ as the base material of the diffraction grating In the diffraction grating according to the present invention using O ₅ , the height of the convex part of the diffraction grating was about 0.68 μm, and the light loss was reduced by about 1.4%. On the other hand, as shown in FIG. 4, even when Ta ₂ O ₅ which is a high refractive index material is used as the base material of the diffraction grating, the diffraction grating body is the antireflection film described in the embodiment of the present invention. Otherwise, the effect of reducing the amount of light loss due to the use of the high refractive index material is reduced.

Although the configuration of the diffraction grating has been described above, TiO ₂ or the like can be used as the high refractive index material, and a resin or the like may be used in addition to the dielectric.
In addition, Al ₂ O ₃ is used as the etching stop layer, but MgF ₂ or the like can also be used.
Further, although SiO ₂ is used as the second matching layer, a low refractive index material such as MgF ₂ can also be used.

Next, a method for manufacturing a diffraction grating body according to the present invention will be described.
FIG. 5 is a flowchart showing a manufacturing procedure of the diffraction grating body according to the present invention. The manufacturing procedure corresponds to the first step of forming a first diffraction grating corresponding to DVD on the surface of one side of the substrate constituting the diffraction grating body and the CD on the surface of the other side. And a second step of forming a second diffraction grating.
The first process will be described. First, a substrate constituting the diffraction grating body is processed into a predetermined dimension using a crystal material such as glass or quartz, a transparent resin, or the like (step 1). Next, Ta ₂ O ₅ is deposited on the surface of one surface of the processed substrate as a first matching layer so as to have a film pressure of 204 kg (step 2). Next, on the surface of the first matching layer deposited, as an etching stop layer, the Al ₂ O ₃ is deposited to a film thickness of 514A (Step 3). Next, Ta ₂ O _{5 serving} as a diffraction grating is deposited on the surface of the deposited etching stop layer so as to have a film thickness of 6845 mm. The film pressure of the deposited film by Ta ₂ O ₅ is the height of the convex part of the diffraction grating, which is an important parameter of the diffraction grating corresponding to DVD. (Step 4).

Next, in order to perform etching when forming a diffraction grating on the surface of the deposited Ta ₂ O ₅ , a mask pattern having a predetermined dimension is formed using a photoresist or a metal film. The predetermined dimensions are a convex portion width of 3.98 μm and a repetition pitch of 20.0 μm of the diffraction grating (step 5). Next, the surface of the diffraction grating body on which the mask pattern is formed is etched up to the etching stop layer to form a diffraction grating convex portion having a predetermined height, and then the mask pattern is peeled off. The etching stop layer is made of a material that is difficult to etch, and the etching is stopped when the etching reaches the etching stop layer. (Step 6). Next, Ta ₂ O ₅ is deposited as a cover layer on the surface of the diffraction grating so as to have a thickness of 853 mm (step 7). Finally, SiO ₂ is deposited as a second matching layer on the surface of the cover layer so as to have a thickness of 1251 mm, thereby completing the deposition on one side of the diffraction grating (step 8).

Next, the second step will be described. The substrate constituting the diffraction grating is inverted, and Ta ₂ O ₅ is deposited on the other surface of the substrate as a first matching layer so as to have a film pressure of 204 Å (step 9). Next, on the surface of the first matching layer deposited, as an etching stop layer, the Al ₂ O ₃ is deposited to a film thickness of 514A (step 10). Next, Ta ₂ O _{5 serving} as a diffraction grating is vapor-deposited on the surface of the vapor-deposited etching stop layer so as to have a film pressure of 5670Å. The film pressure of the deposited film by Ta ₂ O ₅ becomes the height of the diffraction grating convex portion which is an important parameter of the diffraction grating corresponding to CD (step 11).

Next, in order to perform etching when forming a diffraction grating on the surface of the deposited Ta ₂ O ₅ , a mask pattern having a predetermined dimension is formed using a photoresist or a metal film. The predetermined dimensions are a projection width of 5.00 μm of the diffraction grating and a repetition pitch of 20.0 μm of the diffraction grating (step 12). Next, the surface of the diffraction grating body on which the mask pattern is formed is etched to the etching stop layer to form a diffraction grating convex portion having a predetermined height, and then the mask pattern is peeled off. The etching stop layer is made of a material that is difficult to etch, and the etching is stopped when the etching reaches the etching stop layer. (Step 13). Next, Ta ₂ O ₅ is deposited as a cover layer on the surface of the diffraction grating so as to have a thickness of 853 mm (step 14). Finally, SiO ₂ is deposited on the surface of the cover layer as a second matching layer to a thickness of 1251 mm to complete the diffraction grating (step 15). Note that the flowchart shown in FIG. 5 describes the manufacturing procedure for single-sided vapor deposition, but double-sided vapor deposition can be performed in the same way by simultaneously performing the single-sided vapor deposition manufacturing procedure over two steps.

  As described above, in the present embodiment, the diffraction grating body has a structure in which the diffraction grating is formed on the entire surface of the light incident surface and the output surface of the substrate made of glass or the like at a predetermined height and a repetitive pitch. The diffraction grating body has been described. Further, the present invention can be similarly applied to a diffraction grating having a structure in which the diffraction grating is formed on the entire surface of one surface of a substrate made of glass or the like with a predetermined height and pitch. is there.

The optical head device 26 shown in FIG. 6 is in a state where a light emitting element 27a that emits laser light having a wavelength λ1 of 660 nm for DVD and a light emitting element 27b that emits laser light having a wavelength λ2 of 785 nm are used for CD. Thus, the light source (light emitting unit) 27 is provided in a single casing.
In the optical head device 26, as the optical system, the diffraction grating body 8 is disposed in front of the light emission side of the light source 27, and other polarizing beam splitter (hereinafter referred to as PBS) 28, front monitor 29, and collimator lens 30. The broadband quarter-wave plate 31, the objective lens 32, the optical disc recording medium 33, and the light receiving unit 34 are arranged at predetermined positions.

  Laser light of linearly polarized light 35 emitted from one of the light emitting elements 27 a and 27 b of the light source 27 passes through the diffraction grating body 8 and becomes three-beam light and enters the PBS 28. About 90% of the incident three-beam light is reflected by the mirror surface 28a of the PBS 28 toward the optical disc recording medium 33 side, and about 10% is transmitted and detected by the front monitor 29. The intensity of the laser light emitted from the light source 27, etc. To control. The three-beam light reflected by the mirror surface 28a of the PBS 28 is adjusted to parallel light by the collimator lens 30, converted to circularly polarized laser light by the broadband quarter wavelength plate 31, and condensed by the objective lens 32. Laser light spot light is formed on the pits 33 a on the surface of the optical disk recording medium 33. The circularly polarized light 36 is reflected by the pits 33a as laser light (returned laser light) of reversely polarized circularly polarized light 37. The reflected return laser light passes through the objective lens 32, is converted into linearly polarized light 38 having a perpendicular relationship with the linearly polarized light 35 by the broadband quarter wave plate, passes through the collimator lens 30, passes through the PBS 28, and is received. Incident on the light receiving element of the unit 34.

The light receiving element of the light receiving unit 34 is formed of a pin photodiode, and the objective lens 32 is corrected in the tracking direction along the surface of the optical disk recording medium 33 according to the signal detected by this element, and is orthogonal to the disk surface. It is possible to correct in the focusing direction.
Although not shown in the drawing, the optical head device 26 is provided with a lens holder that supports the objective lens 32 in a finely movable manner, and is provided with driving means for finely driving the lens holder. The objective lens 5 can be finely driven in the tracking direction and the focusing direction by the power of the driving means.

  The technique for constructing a diffraction grating body in which the diffraction efficiency is adjusted by changing the ratio of the width and period of the convex portion of the diffraction grating in the diffraction grating body 8 corresponding to two wavelengths according to the present invention is different in two wavelengths. However, the present invention is not limited to the combination of the 660 nm wavelength and the 785 nm wavelength, and can be applied to the combination of the 405 nm wavelength and the 660 nm wavelength, or the combination of the 405 nm wavelength and the 785 nm wavelength.

1 is a structural diagram showing an embodiment of a diffraction grating body according to the present invention. It is an enlarged view of the diffraction grating part of the diffraction grating body which concerns on this invention. It is a table | surface figure which shows the example of the numerical data of the diffraction grating body which concerns on this invention. It is a graph which shows the example of the wavelength dependence of the transmitted light quantity of the diffraction grating body which concerns on this invention. It is a flowchart which shows the manufacture procedure of the diffraction grating body which concerns on this invention. It is a schematic block diagram which shows the optical head apparatus by which the diffraction grating body based on this invention is mounted. It is a figure which shows the structural example of the conventional diffraction grating body. It is a figure which shows the structural example of the conventional diffraction grating body.

Explanation of symbols

  1 .... Diffraction grating body 2 .... Substrate 3 .... Diffraction grating 4 .... Diffraction grating body 5 .... Substrate 6 ... First diffraction grating 7 .... Second diffraction grating 8. .Diffraction grating body 9 .. Substrate 10.. First diffraction grating 11.. Second diffraction grating 12.. First matching layer 13.. Etching stop layer 14. Anti-reflective coating, 15 .... Diffraction grating convex part, 16 .... Cover layer, 17 .... Second matching layer, 18 .... Second anti-reflective coating, 19 .... First matching layer, 20 .... Etching Stop layer 21... First antireflection film 22.. Diffraction grating convex part 23.. Cover layer 24.. Second matching layer 25.. Second antireflection film 26. Head device, 27 .... light source, 27a ... light emitting element, 27b ... light emitting element, 28 ... polarizing beam splitter, 28a -Mirror surface, 29-Front monitor, 30-Collimator lens, 31-Broadband quarter wave plate, 32-Objective lens, 33-Optical disk recording medium, 33a-Pit, 34-Light-receiving unit, 35 ... Linear polarization, 36 ... Circular polarization, 37 ... Circular polarization, 38 ... Linear polarization

Claims (10)

A diffraction grating body comprising a first diffraction grating and a second diffraction grating in which convex portions and concave portions are periodically formed on respective surfaces of an incident surface and an output surface of a substrate constituting the diffraction grating body. And
The first diffraction grating diffracts a light beam having a first wavelength into zero-order light serving as a main beam and two ± first-order light beams serving as side beams and transmits a light beam having a second wavelength. ,
The second diffraction grating diffracts a light beam having a second wavelength into zero-order light as a main beam and two ± first-order lights as side beams and transmits a light beam having the first wavelength. ,
The first diffraction grating and the second diffraction grating are formed of a material having a higher refractive index than the substrate, and a boundary surface between the substrate and the first diffraction grating, and the substrate A first antireflection film is formed on the boundary surface between the second diffraction grating and the boundary surface between the first diffraction grating and air, and the boundary surface between the second diffraction grating and air. The diffraction grating body is characterized in that a second antireflection film is formed. _2. The diffraction grating body according to claim 1, wherein the high refractive index material forming the first diffraction grating and the second diffraction grating is Ta ₂ O ₅ or TiO ₂ .   The first antireflection film is obtained by forming a first matching layer on the surface of the substrate and then forming an etching stop layer on the surface of the first matching layer. Item 3. The diffraction grating body according to Item 1 or 2. The material of the first matching layer is Ta ₂ O ₅ , and the material of the etching stop layer is Al ₂ O ₃ or MgF ₂ . The diffraction grating body according to one item.   The second antireflection film is formed by forming a cover layer on the surface of the first diffraction grating and the second diffraction grating, and then forming a second matching layer on the surface of the cover layer. The diffraction grating body according to any one of claims 1 to 4, wherein 6. The diffraction grating according to claim 1, wherein the material of the cover layer is Ta ₂ O ₅ , and the material of the second matching layer is SiO _2. body.   The first diffraction grating and the second diffraction grating are such that the light beam transmitted through the first diffraction grating and the second diffraction grating has a phase difference of 2π between the convex portion and the concave portion. The diffraction grating body according to any one of claims 1 to 6, wherein the diffraction grating body has a groove depth of the diffraction grating.   The first wavelength is 660 nm, the second wavelength is 785 nm, the groove depth of the first diffraction grating is 6845 mm, the width of the diffraction grating convex part is 3.98 μm, and the repetition pitch of the diffraction grating The depth of the groove of the second diffraction grating is 5670 mm, the width of the convex part of the diffraction grating is 5.00 μm, and the repetition pitch of the diffraction grating is 20.0 μm. The diffraction grating body according to any one of claims 1 to 7. A light source that emits light beams of a first wavelength and a second wavelength; and an objective lens that focuses the light beams of the first wavelength and the second wavelength on an optical recording medium; An optical head device for recording / reproducing,
An optical head device in which the diffraction grating body according to claim 1 is installed in an optical path between the light source and the objective lens. A diffraction grating body comprising a first diffraction grating and a second diffraction grating each having a convex portion and a concave portion periodically formed on the incident surface and the outgoing surface of the substrate constituting the diffraction grating body. A manufacturing method comprising:
Depositing a first matching layer on one surface of the substrate processed to a predetermined dimension; depositing an etching stop layer on the deposited surface of the first matching layer; Depositing a high refractive index material to be a diffraction grating on the surface of the etching stop layer; forming a mask pattern of a predetermined dimension on the deposited surface of the high refractive index material; and Etching the surface of the formed diffraction grating to an etching stop layer; depositing a cover layer on the etched surface of the diffraction grating; and secondly depositing a cover layer on the surface of the deposited cover layer. Depositing a matching layer; and forming a first diffraction grating comprising:
Inverting the substrate constituting the diffraction grating, depositing a first matching layer on the other surface of the substrate, and depositing an etching stop layer on the surface of the deposited first matching layer A step of depositing a high refractive index material to be a diffraction grating on the surface of the deposited etching stop layer, and a step of forming a mask pattern having a predetermined dimension on the surface of the deposited high refractive index material Etching the surface of the diffraction grating body on which the mask pattern is formed up to an etching stop layer, depositing a cover layer on the etched surface of the diffraction grating body, and the surface of the deposited cover layer And depositing a second matching layer, and comprising a second step of forming a second diffraction grating. Method of manufacturing a diffraction grating body.

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