JP3141390B2 - Method of manufacturing blazed hologram, blazed hologram, and optical head device - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for producing a blazed hologram capable of controlling the diffraction efficiency of an arbitrary order, and a light utilizing the hologram for reading and writing information on an information carrier. The present invention relates to a head device.

2. Description of the Related Art When light is incident on a hologram, generally, not only + 1st-order diffracted light but also higher-order diffracted light and conjugated diffracted light are generated. Make the shape asymmetrical. In other words, by blazing, the diffraction efficiency of the conjugated diffracted light can be made non-uniform, and the diffraction efficiency of the + 1st-order diffracted light can be increased. The sectional shape at this time is desirably a saw-tooth shape as shown in FIG. For example, as shown in FIG. 6, (a) a photoresist 2 is applied to the surface of a hologram-forming material 1, covered with a chrome mask 3, exposed, and developed, as shown in FIG. And (b) irradiating the surface of the hologram-forming material 1 with the ion beam 4 from a slanting direction to obtain a blazed hologram 81 as shown in (c). (D) is an enlargement of the main part of (c).
The slopes A and B are asymmetric.

Further, as shown in FIG. 7, the etching is repeated a plurality of times, that is, after FIG.
Exposure (d) and development (e) are performed to form a masking pattern 500, and etching is performed in this state to form a blazed hologram 82 having a saw-toothed surface as shown in (f). It is known that it can be obtained. Recently, there is a simplified optical system of an optical head using a hologram as shown in FIG. In FIG. 8, reference numeral 12 denotes a radiation light source such as a semiconductor laser. The light beam 16 (laser light) emitted from this light source passes through the hologram 83 and is incident on the condensing means 13 and is condensed on the information carrier 14. The light beam reflected on the information carrier 14 follows the original optical path and enters the hologram 83 in reverse. This hologram 83
The + 1st-order diffracted light 10 on the return path generated from the
Incident on. By calculating the output of the photodetector 15, a servo signal and an information signal can be obtained. Here, in a configuration in which the focusing unit 13 is independently movable with respect to the hologram 83 by the driving device 100, the focusing unit is
Hologram 83 when 13 moves due to track following
The light beam above also moves. For this reason, the image of the + 1st-order diffracted light on the photodetector 15 also moves, which adversely affects the servo signal. On the other hand, in FIG.
13 is provided while maintaining a constant relative position with respect to the driving device 100, even if the focusing means 13 is moved by the driving device 100 for tracking control, the light beam reflected from the information carrier 14 does not Hardly moves on the hologram 83. Therefore, the signal obtained from the photodetector 15 does not deteriorate despite the movement of the light condensing means 13.

Problems to be Solved by the Invention However, the cross-sectional shape obtained by the method shown in FIG. 6 is as shown in the enlarged view in FIG. 6 (d). That is, FIG. A is not vertical but has a slope. Further, the slope B becomes concave. As described above, in the conventional method, since only a cross-sectional shape different from the saw-tooth-shaped cross-sectional shape of FIG. 5 can be obtained, there is a problem that a sufficient intensity ratio of conjugate diffracted light cannot be obtained. Further, in the conventional example shown in FIG. 7, the intensity ratio of the conjugate diffracted light cannot be increased because of the cross-sectional shape or the step shape obtained in the blazed hologram 82. Further, in the method of FIG. 7, since etching is performed a plurality of times, several percent of the grating pitch is required for pattern matching (for example, a grating having a pitch of 10 μm).
There is a problem that extremely high precision of about 0.2 μm) is required and fabrication is difficult. Further, according to the above-described optical system configuration, as shown in FIG. 9, diffracted light is generated from the hologram 83 also in the optical path from the radiation light source 12 to the information carrier 14 (hereinafter, referred to as the outward path). The diffracted light is also reflected on the information carrier 14 and guided to the photodetector 15 by the condensing means 13. Light condensing means 13 reflected from information carrier 14
If the + 1st-order diffracted light 10 generated in the optical path (hereinafter referred to as the return path) diffracted by the hologram 83 and reaching the photodetector 15 is used for signal detection, the return path of the −1st-order diffracted light 11 generated in the forward path is used. Is also incident on the photodetector 15 at the same position as the + 1st-order diffracted light on the return path. Of the beam that has become the 0th-order diffracted light 91 on the return path in the -1st-order diffracted light 11 on the outward path and the 0th-order diffracted light 9 on the outward path, the + 1st-order diffracted light 10 on the return path is reflected at different positions on the information carrier 14, so You will have different information.
Therefore, the optical system having such a configuration that the condensing means and the hologram are integrated has a problem that the quality of the servo signal and the information signal is deteriorated by the primary light 11 on the outward path. SUMMARY OF THE INVENTION An object of the present invention is to provide a method capable of easily and accurately producing a blazed hologram having a cross-sectional shape close to an ideal sawtooth shape. In addition, the present invention, S / N
An object of the present invention is to provide an optical head device capable of detecting a signal with a good ratio.

Means for Solving the Problems In order to solve the above problems, the present invention creates a rectangular cross-sectional shape by etching, further forms a masking pattern on the surface, and irradiates an ion beam from an oblique direction to form a blazed hologram. Is prepared. The hologram is used to form an optical head. That is, in the method of the present invention, a step of selectively forming a first masking pattern on a hologram-forming material, and etching a part of the hologram-forming material using the first masking pattern as a mask; Is removed, a second masking pattern is formed again on the hologram material, and a part of the hologram material is selected by irradiating an ion beam from a direction different from a direction perpendicular to the surface of the hologram material. Etching to form a saw-toothed surface on the surface of the material. Furthermore, the present invention provides an optical head using the hologram thus formed.

Function After forming a rectangular cross-sectional shape by etching according to the present invention, and further performing ion beam etching in a diagonal direction after forming a masking pattern, pattern matching accuracy is reduced and irradiation is performed in a diagonal direction. Since the amount of etching of the ion beam is small, a cross-sectional shape closer to a saw-tooth shape can be obtained, and the difference in diffraction efficiency of conjugate diffracted light can be increased. According to the present invention, it is possible to realize an optical head capable of detecting a signal having a good S / N ratio.

Embodiment In the present invention, as shown in FIG. ₁ , after exposure of (a) by light 11 and development of (b), the surface of the hologram forming material 1 is first etched by a resist pattern 51 to form (c). After making a rectangular cross-section as shown in (d),
(E), the resist again to form a masking pattern 5 by at chrome mask 71 with light 1 _2, etching the surface of the material 1 is irradiated with the ion beam 4 in the oblique direction, as (f) A blazed hologram 8 having a saw-toothed cross-sectional shape is manufactured.

FIG. 1 (g) shows a process in which a sawtooth-shaped cross section is formed by the ion beam 4 irradiated in an oblique direction.
FIG. 1 (g) is an enlarged view as compared with (a) to (f). Here, the portion 1a of the hologram production material 1 is etched by the oblique ion beam 4. As the etching of the etched portion 5a of the masking pattern 5 progresses, the etched portion 1a of the hologram-forming material also enlarges, and a sawtooth-shaped cross-sectional shape as shown in FIG. According to the present invention, the ion beam 4 is obliquely shown in FIG.
The amount of etching by irradiating is smaller than that of the conventional example shown in FIG. 6, so that the deviation from the ideal saw tooth shape as shown in FIGS. A cross-sectional shape close to the shape can be obtained. Also, the masking pattern 5 in FIG.
It is possible to make it slightly wider as shown in the figure. That As shown in FIG. 2, the prevent making rectangular-shaped cross section for even the left by d ₁ than the left end of the projecting portion 6 of the material 1 is masking pattern 5 is formed protrudes is etched by the ion beam 4 No. Rather, in order to keep the left side of the projection 6 vertical, the masking pattern 5 may be positively widened. Also, the center line L ₁ of the convex portion 6 is
even if not protrude masking pattern to the right by d _2,
Since the hologram-forming material 1 starts to be etched after the protruding portion is etched, it does not prevent the formation of a sawtooth-shaped cross-section. Thus the first
Since the masking pattern 5 can be made slightly wider in the method shown in the figure, the alignment accuracy of the chrome mask 71 in the exposure shown in FIG. 1D can be eased.

Next, the blazed hologram 8 may be used by dividing an area into H1 to H4 as shown in FIG. 3, for example.
In this case, as shown in FIG. 3, the pitches P1, P2, P3, and P4 in one direction (X direction) are all substantially equal, and the incident direction of the ion beam 4 to be incident in FIG. When expressed, by making the direction of the oblique vector to the surface of the blazed hologram 8 coincide with the X direction, the height of the sawtooth (see FIG. 1 (f)) in any of the divided regions H1 to H4 is obtained. h) can be constant. The reason will be described below. Consider a cross section perpendicular to the surface of the blazed hologram 8 including a vector representing the incident direction of the ion beam 4 as shown in FIGS. 1 (e) and 1 (f). Since the angle of incidence of the ion beam 4 on the blazed hologram 8 is constant, when the saw tooth is viewed in such a sectional view, the angle of the slope is constant (θ in FIG. 1 (f)). Therefore, by making the pitch P constant in the direction along this cross section, that is, in the X direction shown in FIGS. 1 (f) and 3, it is possible to make h = Ptan θ also constant. As described above, making h constant means that the phase modulation amplitudes of all the divided regions (H1 to H4) are made constant, whereby the diffraction efficiency of all the regions can be made constant. . Therefore, it can be said that the diffraction efficiency of the + 1st-order diffracted light is approximately 100% in all the divided regions (H1 to H4).
Furthermore, the cross-sectional shape of the hologram manufactured by the manufacturing method of the present invention is very close to a sawtooth shape,
It is also easy to increase the diffraction efficiencies of the first and + 1st orders and lower the diffraction efficiency of the −1st order. Therefore, by using this hologram in an optical pickup device as shown in FIG. 4, it is possible to improve the light use efficiency and to reduce the stray light generated by diffraction generated from the blazed hologram 8 on the outward path. This will be described in detail below. The light beam 16 emitted from the radiation light source 12 enters the blazed hologram 8. Of the light beam 16, the light transmitted through the blazed hologram 8, that is, the 0th-order diffracted light 9 on the outward path is focused on the information carrier 14 by the focusing means 13. The 0th-order diffracted light 9 on the outward path is reflected by the information carrier 14 and follows the original optical path again to enter the blazed hologram 8. Then, the + 1st-order diffracted light 10 on the return path diffracted from the blazed hologram 8 is received by the photodetector 15 and converted into an electric signal, whereby a servo signal such as a focus servo signal or a tracking servo signal and an information signal can be obtained. At this time, the use efficiency E of light used for signal detection
Becomes E = E ₀ × E _{+ 1} ‥‥ (1). Here, E ₀ and E ₊₁ indicate the diffraction efficiencies of the 0th-order and + 1st-order diffracted light, respectively. Therefore, it is necessary to increase E ₀ and E ₁ as much as possible in order to increase the light use efficiency for the purpose of improving the S / N ratio of various signals, and it is necessary to use the blazed hologram described earlier in the present invention. It turns out that there is. Furthermore, when the light beam 15 is incident on the blazed hologram 8, the outgoing −1st-order diffracted light 11 also occurs. Of the outgoing −1st-order diffracted light reflected by the information carrier 14, the light transmitted through the blazed hologram 8 is: Photodetector 15 as stray light
Incident on. Since the stray light lowers the S / N ratio of the detection signal, it is necessary to reduce the diffraction efficiency of the -1st-order diffracted light as much as possible. It can be seen that the blazed hologram described in the present invention is also effective for this purpose.

Effect of the Invention As described above, in the present invention, a blazed hologram having a sectional shape closer to a more ideal sawtooth can be manufactured, and the difference in diffraction efficiency of conjugate diffracted light can be increased. Also, by using this blazed hologram, S / N
An optical head device capable of detecting a signal with a good ratio can be configured.

[Brief description of the drawings]

1 (a) to 1 (g) are process cross-sectional views showing a method for producing a blazed hologram of one embodiment of the present invention, in which a normal etching process of the present invention and a process of obliquely entering an ion beam are combined. FIG. 2 is an enlarged view of FIG.
FIG. 4 is an explanatory view showing a hologram pattern according to another embodiment of the present invention. FIG. 4 is a schematic explanatory view of an optical head device constituted by using the blazed hologram of the present invention. 6A to 6D are cross-sectional views of a blazed hologram having a saw-toothed cross-sectional shape, FIGS. 6A to 6D are process cross-sectional views illustrating a method of manufacturing a blazed hologram in a conventional example, and FIGS. 7A to 7F. ) Is a process diagram showing a method of manufacturing a blazed hologram in another conventional example, FIG. 8 is a schematic cross-sectional view of a conventional optical head device, and FIG. FIG. 4 is an explanatory sectional view showing an optical path of + 1st-order diffracted light of FIG. 1. Holographic material 2. Photoresist 3.
71: chrome mask, 4: ion beam, 5, 51: masking pattern, 6: convex portion, 9: 0th-order diffracted light on the outward path, 10: + 1st-order diffracted light on the return path, 11:-on the outward path 1st order diffracted light, 12 radiation source, 13 focusing means, 14 information carrier, 15 photodetector, 16 light beam.

Continued on the front page (72) Inventor Makoto Kato 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) Reference JP-A-2-214033 (JP, A) JP-A-51-117645 (JP) , A) JP-A-60-33501 (JP, A) JP-A-58-91407 (JP, A) JP-A-2-116805 (JP, A) JP-A-49-122640 (JP, A) Optical memory symposium 92 "Bladed hologram element for optical head" p. 107 to p. 108 (58) Fields surveyed (Int.Cl. ⁷ , DB name) G03H 1/04 G03H 1/18 G02B 5/32 G11B 7/135 JICST file (JOIS)

Claims (6)

(57) [Claims] A step of selectively forming a first masking pattern on the hologram-forming material, and etching a part of the hologram-forming material using the first masking pattern as a mask; Is removed, a second masking pattern is formed again on the hologram material, and a part of the hologram material is selectively etched by irradiating an ion beam from a direction different from a right angle to the hologram material surface. Forming a saw-toothed surface on the surface of the material. 2. The method for manufacturing a blazed hologram according to claim 1, wherein the masking pattern is formed such that the grating pitch in one direction on a pattern plane is substantially equal at an arbitrary portion on the pattern. A method for producing a blazed hologram. 3. The method of manufacturing a blazed hologram according to claim 1, wherein the direction of the projection vector of the incident vector of the ion beam onto the surface of the hologram forming material is substantially equal to the lattice pitch of the masking pattern. A method for producing a blazed hologram, wherein the direction is the same as the direction in which it is formed. 4. A radiation light source, a condensing means for converging a light beam emitted by the radiation light source on an information carrier, and a diffracted light beam received by the light beam reflected on the information carrier through the condensing means. An optical head device comprising: a generated hologram; and a photodetector that receives the diffracted light and converts a received light amount into an electric signal, wherein the hologram is manufactured by the method according to claim 1. An optical head device, characterized in that: 5. A blazed hologram, wherein a plurality of divided regions are formed in the plane of the blazed hologram, at least two of the divided regions have different directions in which lattice fringes extend, and a pattern of the blazed hologram is provided. A blazed hologram, wherein a pitch component of a lattice fringe in a certain one direction in a pattern plane is formed to be substantially equal in an arbitrary portion above. 6. A light source, a photodetector configured to receive a light beam and generate an output corresponding to the light amount, and an object for receiving the light beam emitted from the light source and converging the light beam on an information carrier. A lens, configured to receive the light beam reflected on the information carrier through the objective lens, split the light beam, receive the light beam, and generate an output corresponding to the light amount. An optical head device provided with a branching means for leading to a photodetector, wherein the branching means is a blazed hologram according to claim 5.