JP2586536B2 - Method of manufacturing semiconductor laser device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in the following order.

A. Industrial application fields B. Summary of the invention C. Prior art D. Problems to be solved by the invention [Fig. 4] E. Means for solving the problems F. Function G. Example [No. 1 to 3] H. Effects of the Invention (A. Industrial Application Field) The present invention relates to a method for manufacturing a semiconductor laser device, and particularly to a method for manufacturing a semiconductor laser device used as a light source in an optical head.

(B. Summary of the Invention) The present invention is directed to light reflection of a light beam emission area of a light emission end face in order to prevent laser light emitted from a semiconductor laser device from being reflected on a recording medium and a light emission end face to cause interference. In order to lower the light reflectance of the other part than the ratio, a photosensitive resist is applied to the light emitting end face, and a self-alignment method is used in which the photosensitive resist is exposed with laser light emitted from a semiconductor laser device. is there.

(C. Prior Art) An optical head using a semiconductor laser device as a light source is used for reproducing an optical disk such as a compact disk or a video disk. Optical heads generally focus and irradiate laser light emitted from a semiconductor laser device onto the surface of an optical disk, and detect laser light reflected from the optical disk surface with a photodetector to read data, detect tracking errors, and focus errors. Is what you do.

Then, a three-beam method is often used for detecting a tracking error. In the three-beam system, one laser beam emitted from a semiconductor laser device is passed through a diffraction grating to obtain three beams, and two beams (sub beams) are used for detecting a tracking error. .

By the way, in recent years, a magneto-optical disk recording technology for magnetically recording on a magneto-optical disk using light has been developed and is in the stage of practical use, but an optical head is also used for reproducing or recording on the magneto-optical disk. Can be Generally, an optical head dedicated to an optical disk is used for reproducing an optical disk, and an optical head dedicated to a magneto-optical disk is used for recording and reproducing on a magneto-optical disk. But,
It is expected that there will be a demand to be able to use one head for both magneto-optical discs and optical discs, and the optical heads for optical discs and magneto-optical discs have almost the same principle. Therefore, an attempt has been made by the present applicant company to enable recording and reproduction of a magneto-optical disk and reproduction of an optical disk with one optical head.

(D. Problems to be Solved by the Invention) [FIG. 4] However, an optical head designed to be used for both a magneto-optical disk and an optical disk has a problem in tracking error detection when used for reproducing an optical disk. There is a problem that an offset occurs. This point is specifically described as follows.

That is, when reading or recording is performed on the magneto-optical disk by an optical head dedicated to the magneto-optical disk, only about 30% of the laser light emitted from the semiconductor laser device returns to the semiconductor laser device. The interference of the laser light that travels between the semiconductor laser device and the semiconductor laser device is negligible, and the semiconductor laser of the laser light emitted from the semiconductor laser device when reproducing the optical disk with the optical head dedicated to the optical disk. Approximate return rate to device
At only 25%, interference is still of little concern.
However, when reproducing an optical disk with an optical head for both a magneto-optical disk and an optical disk, 90% of the laser light emitted from the semiconductor laser device returns to the semiconductor laser device by reflection of the optical disk because the surface of the optical disk is made of aluminum. come. As a result, the amount of laser light that is reflected by the semiconductor laser device and the optical disk and travels between them increases. This is because when a three-beam tracking method (three spots, DPP) using a diffraction grating is adopted for the optical head, the semiconductor laser device and the disk are not isolated. Then, the interference causes a large DC offset in the tracking error detection signal. FIG. 4 explains this phenomenon, and the phenomenon of this interference will be described in more detail with reference to FIG.

In the figure, a is a semiconductor laser device, a header b
Mounted on top. c is an active layer of the semiconductor laser device a, d is a light emitting end face of the semiconductor laser device a, and a point exposed on the light emitting end face d of the active layer c is a light emitting point.
e is a diffraction grating for generating three beams from one laser beam, and f is an optical disk.

When the light emitted from the light-emitting point exits the diffraction grating e, it basically makes three optical paths to reach three points on the optical disk f, but many other optical paths are generated. For example, a laser beam reaching a point on the optical disc f is reflected there and reaches a light emitting point through the diffraction grating e, and is reflected there again to an optical path reaching the point through the diffraction grating e or a point on the optical disc f. The reached laser light is reflected there, passes through the diffraction grating e, reaches a point above the light emitting point on the light emitting end face d of the semiconductor laser device a, and is reflected there and passes through the diffraction grating e to a point. The laser beam that reaches a point on the optical disc f is reflected there, passes through the diffraction grating e, reaches a point, and is an optical path that is reflected there, passes through the diffraction grating e, and reaches a point.
Thus, there are many optical paths, interference occurs at each point, and when the optical disk f is tilted from the state shown by the solid line to the state shown by the broken line or the state shown by the two-dot chain line, the respective points , And fluctuates. Then, this gives a DC offset to the tracking servo, which causes the tracking to be unstable, and in some cases, the tracking may be disabled.

This problem is related to Optical Memory Symposium '86
32 1986.12 (Co-hosted by the Japan Society of Applied Physics and the Institute of Electronics, Information and Communication Engineers)
Has also been pointed out.

There are several possible solutions to this problem. As one of them, an optical isolator consisting of a polarizing beam splitter etc. is provided between the diffraction grating and the disk, and allows the laser light from the diffraction grating to the disk to pass, but the laser light reflected by the disk and directed to the diffraction grating However, it is conceivable to prevent interference by reflection by an optical isolator, but this requires an additional optical component called an optical isolator, resulting in an increase in the number of components of the optical head and an increase in price, which is not preferable. .

Also, as described in P127-132 of the above-mentioned collection of papers, adoption of a new differential push-pull method as a tracking servo method may be one solution, but it is not completely established as a technology, There are some unknowns.

After all, the problem of interference occurs because the laser beam is reflected on the semiconductor laser device side. If the laser beam is not reflected on the semiconductor laser device side or if the amount of reflected laser light is small, the interference will occur. Since it does not occur, it is not always necessary to use an optical isolator or to adopt a new method which has not been established as a tracking servo method, instead of using the three-spot method or the like, for which technology has been established.

Therefore, what can be considered is that the header b in FIG.
This is to prevent the light returning to a point below the light emitting point from being reflected back downward at the cut portion and not returning to the diffraction grating side, as indicated by the two-dot chain line. Certainly this works for light that has returned to a point. However, it has no effect on the light that has returned to the point.

By the way, here, the light emitting end face of a general semiconductor laser device will be described. On the front side, that is, the end face on the back side of the light emitting end face on which the original laser light used for signal reading is emitted (the monitor laser light is emitted). In some cases, the rear end face is coated in order to lower the light reflectivity of (1) and increase the original laser light emission efficiency. Therefore, it is conceivable that the coating is applied to the light emitting end face, which is the front end face, to reduce the light reflectance of the light emitting end face. However, if the light emission end face is made to have a low light reflectance as a whole, oscillation in the active layer required for laser emission may not be generated, and the light emission end face is entirely coated to lower the light reflectance. It is also difficult to adopt.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a novel method of manufacturing a semiconductor laser device which does not interfere with laser light emission and does not cause interference due to reflection at a light emitting end face.

(E. Means for Solving the Problems) In order to solve the above problems, the method for manufacturing a semiconductor laser device of the present invention makes the light reflectivity different between the light beam emitting area of the light emitting end face and other portions. For this purpose, a self-alignment is performed in which a photosensitive resist is applied to a light emitting end face and the photosensitive resist is exposed with laser light emitted from a semiconductor laser device.

(F. Function) According to the method of manufacturing a semiconductor laser device of the present invention, the photosensitive resist applied to the light emitting end face is exposed to the laser beam generated by the semiconductor laser device, so that the photosensitive resist is exposed on the light beam emitting area of the photosensitive resist. Can be selectively exposed to light. Therefore, it is possible to make the light reflectivity of the light beam emission area different from that of the other parts, and to easily manufacture a semiconductor laser device in which the light reflectivity of other parts is lower than that of the light beam emission area. Can be.

(G. Embodiment) [FIGS. 1 to 3] Hereinafter, a method for manufacturing a semiconductor laser device of the present invention will be described in detail with reference to illustrated embodiments.

FIGS. 1A and 1B show an example of a semiconductor laser device to be manufactured by the manufacturing method of the present invention.
FIG. 1A is a perspective view, and FIG. 1B is a cross-sectional view.

In the drawings, reference numeral 1 denotes a semiconductor laser device, 2 denotes a light emitting end face, that is, an end face that emits an original laser beam used for signal reproduction or writing, and 3 denotes an active layer.

Reference numeral 4 denotes a light absorbing film, which is made of, for example, a photosensitive resist. The light absorbing film 4 has a portion where the active layer 3 is exposed on the light emitting end face 2,
That is, the opening 6 is formed so as not to cover the light beam emission area 5.

According to such a semiconductor laser device, the light emitting end face 2
Are exposed, that is, the light beam emission region 5
Since the other parts are covered with the light absorbing film 4, the light reflectance of the parts other than the light beam emission area 5 is significantly reduced. Therefore, the amount of light reflection at the light emitting end face 2 can be reduced, and the DC offset of tracking servo due to interference can be reduced. And
Since the light beam emitting area 5 is not covered with the light absorbing film 4, there is no possibility that laser oscillation is hindered.

 Note that the opening 6 may be provided with an anti-reflection coating.

2 (A) to 2 (C) are cross-sectional views showing an example of the method for manufacturing the semiconductor laser device shown in FIG. 1 (one embodiment of the method for manufacturing a semiconductor laser device of the present invention) in the order of steps.

First, as shown in FIG. 1A, a positive-type photoresist film 4a having a light absorbing property is applied to the surface of the light emitting end face 2 of the semiconductor laser device 1 and cured, and then shown in FIG. As described above, the semiconductor laser device 1 is caused to emit light, and the photosensitive resist 4a is exposed by the laser beam emitted from the light beam emission region 5 of the semiconductor laser device 1. Then, a portion corresponding to the light beam emission area 5 of the photosensitive resist 4a is exposed.
4b is a photosensitive portion of the photosensitive resist 4a. Thereafter, the photosensitive portion 4b of the photosensitive resist 4a is removed by etching to expose the light beam emission region 5 as shown in FIG. Incidentally, an antireflection coating may be applied to the opening 6 formed by this etching.

As described above, by causing the semiconductor laser device 1 to emit light, it is possible to reduce the light reflectance of a portion other than the light beam emission area on the light emission end face by self-alignment using laser light.

3A to 3E are cross-sectional views showing another example of the method for manufacturing the semiconductor laser device shown in FIG. 1 (another embodiment of the method for manufacturing a semiconductor laser device of the present invention) in the order of steps. is there.

First, as shown in FIG. 3A, a negative photoresist film 4c is applied to the light emitting end face 2, and then, as shown in FIG. Photoresist film by laser light emitted from emission area
4c is exposed, and then, as shown in FIG. 3C, only the photosensitive portion 4d of the photoresist film 4c is left by etching,
Next, as shown in FIG. 4D, the light absorbing film 4e is deposited, and thereafter, as shown in FIG. 4E, the photoresist film exposed portion 4d is removed. After that, the opening 6 may be provided with an anti-reflection coating.

The semiconductor laser device as shown in FIG. 1 can also be manufactured by such a method.

In addition, instead of the light absorber, a non-reflective photosensitive resist is applied, the photosensitive resist is exposed to laser light from a semiconductor laser device, and the light emitting end face is etched using the photosensitive portion of the photosensitive resist as a mask. By roughening the surface, the light reflectance of a portion other than the light beam emission region of the light emission end surface may be reduced, or the photoresist film applied to the light emission end surface may be coated with a laser light of a semiconductor laser device. In the present invention, an appropriate film is deposited on the light emitting end face, and then the deposited film is ion-implanted with the photosensitive portion of the photoresist film as a mask so that light absorption can be obtained. Various embodiments are possible.

(H. Effects of the Invention) As described above, the method of manufacturing a semiconductor laser device according to the present invention provides a semiconductor laser device in which the light reflectance of the other part is lower than the light reflectance of the light beam emission area on the light emission end face. The method according to the above, further comprising a step of applying a photosensitive resist to the light emitting end face and exposing the photosensitive resist by an optical output of the semiconductor laser device.

Therefore, the light reflectance of the light beam emission area of the light emission end face can be made different from that of the other parts by self-alignment, and the semiconductor laser device can be easily manufactured.

[Brief description of the drawings]

1 (A) and 1 (B) show an example of a semiconductor laser device to be manufactured by the manufacturing method of the present invention. FIG. 1 (A) is a perspective view, FIG. 1 (B) is a sectional view, and FIG. FIGS. 3A to 3C are cross-sectional views showing one embodiment of the method of manufacturing a semiconductor laser device of the present invention in the order of steps, and FIGS.
Is a sectional view showing another embodiment of the method of manufacturing a semiconductor laser device of the present invention in the order of steps, and FIG. 4 is an explanatory view of interference which is a problem to be solved by the present invention. DESCRIPTION OF SYMBOLS 1 ... semiconductor laser device, 2 ... light emitting end face, 4a, 4c ... photosensitive resist, 5 ... light beam emitting area.

Claims (1)

(57) [Claims] 1. A method of manufacturing a semiconductor laser device in which the light reflectivity of the other part is lower than the light reflectivity of a light beam emitting area on a light emitting end face, the method comprising: applying a photosensitive resist to the light emitting end face; Exposing the photosensitive resist by light output of a laser device. A method for manufacturing a semiconductor laser device, comprising: