JP3335917B2 - Manufacturing method of semiconductor laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing an AlGaInP-based visible light semiconductor laser used as a light source for an optical disk such as a digital versatile disk (DVD) and a magneto-optical (MO) disk.

[0002]

2. Description of the Related Art Conventionally, an AlGaInP-based visible light semiconductor laser has an oscillation wavelength of about 630 to 690 nm, which is shorter than the oscillation wavelength of AlGaAs of 780 nm. ing. Higher output is required for recording on this optical disc. At present, in AlGaInP-based visible light semiconductor lasers, a high-reflection coating film is formed on one cavity end face and a low-reflection coating film is formed on the other, thereby forming an asymmetric coat to obtain high output.

As a material of the high reflection coating film, amorphous silicon is used. The reason is,
This is because a coating film with high reflectance can be obtained by combining amorphous silicon with a material having a high refractive index and a material having a low refractive index.

A coating film of an AlGaInP-based visible light semiconductor laser is generally formed by a sputtering method. In this sputtering method, the formed amorphous silicon film is amorphous, has many dangling bonds, and has many interband levels because it is not terminated, and has an absorption coefficient for visible light. Becomes larger. Therefore, if an asymmetric coating is used, COD (optical damage) that should occur on the low reflection coating film side with high light density,
Occurs on the high reflection coating film side due to absorption of amorphous silicon.

[0005] For this reason, the COD level is limited by the high-reflection coating film, and this is a major problem for increasing the output. Further, the light absorption causes a decrease in reflectance and an increase in threshold current in the highly reflective coating film.

In order to reduce the absorption coefficient, there is a method of forming an amorphous silicon film while introducing hydrogen gas. However, in this method, the bond between silicon and hydrogen is weak, and hydrogen is released from the film. Since the refractive index changes easily, the stability of the film over time cannot be obtained.

[0007] On the other hand, Tanaka et al. Made a presentation at the 44th Lecture Meeting on Applied Physics [Preprints of the Lecture Meeting p1095 31a-NG-]
7 (1997)], use of a titanium oxide film with a small absorption coefficient instead of amorphous silicon to reduce light absorption in the high-reflection coating film, thereby limiting the COD level due to damage on the high-reflection coating film side. Prevent and COD
It has been reported that the level has been improved.

Japanese Patent Publication No. 6-42582 discloses a technique related to a dielectric multilayer coating protective film, in which high purity O ₂ is introduced by using an electron beam heating type vacuum evaporation method to form a TiO ₂ film.
A dielectric multilayer coating film formed by vapor deposition (on the low reflection coating film side) is described.

[0009]

However, the method of Tanaka et al. Has the following problems. That is,
The titanium oxide film is formed by an ECR sputtering method using a Ti target and oxygen decomposed by ECR plasma. In this method, since Ti and O are supplied independently, composition control is difficult and strict control is required, and there is a problem that it is difficult to reduce light absorption due to oxygen deficiency. Further, it is necessary to introduce oxygen activated during film formation into the chamber, and in a material system containing Al, the laser end face is oxidized.
The problem of reduced reliability occurs. On the other hand, a film having a small absorption coefficient could not be produced by the conventional sputtering method.

The above-mentioned Japanese Patent Publication No. 6-42582 discloses a technique disclosed in the present invention, that is, under a specific sputtering pressure (within a range of 0.6 to 10 Pa) by a sputtering method without introducing O _2. On the high reflection coating film side,
There is no specific description about depositing a TiO ₂ film.

The present invention has been made in view of the above, and an object of the present invention is to provide a titanium oxide film having a small absorption coefficient, which is useful for coating a high reflection film, and to provide a high reflection film with little light absorption. Equipped with a membrane coating,
Another object of the present invention is to provide a method for manufacturing a highly reliable AlGaInP-based visible light semiconductor laser.

[0012]

The above objects and objects are solved and achieved by the present invention described below. That is, the present invention provides an oscillation wavelength 630 to 6 having an active layer formed on a semiconductor substrate and a pair of cladding layers including the active layer.
In a 90 nm AlGaInP-based semiconductor laser, at least one of the cavity facets of the semiconductor laser has a structure in which a first insulator and a titanium oxide film as a second insulator are alternately laminated at least one cycle or more. And forming a titanium oxide film as the second insulator by a sputtering method using TiO2 as a plasma gas with argon containing no oxygen at a sputtering pressure of 0.6 to 10 Pa. A method of manufacturing a semiconductor laser is disclosed.

Further, the method for manufacturing a semiconductor laser according to the present invention
The method according to claim 1, wherein the first insulator is SiO ₂ or Al ₂ O _3.
s, GaAsP or GaP, and AlGaInP on the cladding layer.
Alternatively, AlGaAs is added to the active layer to form GaInP or AlGaIn.
P is included.

An AlGaInP-based semiconductor laser having an oscillation wavelength of 630 to 690 nm , comprising an active layer formed on a semiconductor substrate and a pair of cladding layers including the active layer. Wherein at least one of the cavity end faces of the semiconductor laser has a structure in which a first insulator and a titanium oxide film as a second insulator are alternately laminated at least one cycle or more, and the second insulator The titanium oxide film is characterized by being produced by a sputtering method using TiO2 as a target, with argon containing no oxygen as a plasma gas and a sputtering pressure in the range of 0.6 to 10 Pa. The first insulator is characterized by SiO2 and Al2O3. GaAs, GaAsP or GaP on the semiconductor substrate, AlGaInP or AlGaAs on the cladding layer, and Ga on the active layer.
It is characterized by containing InP or AlGaInP.

(Operation) Conventionally, a titanium oxide film produced by sputtering has a problem that the absorption coefficient is large. The reason will be described below. When a titanium oxide film is formed under conventionally used sputtering conditions, since the energy when Ar collides with the TiO ₂ target is high, the bond between Ti and O in TiO ₂ is broken and Ti-rich, that is, oxygen deficiency is caused. A titanium oxide film is formed on the semiconductor laser. The oxygen-deficient titanium oxide film has a large absorption coefficient.
Therefore, in a titanium oxide film conventionally produced by sputtering,
The absorption coefficient has increased.

In the present invention, in order to reduce the absorption coefficient,
The collision energy of Ar is reduced by the sputtering pressure to obtain a titanium oxide film having no oxygen deficiency. FIG. 3 is a diagram showing a result of examining a change in an absorption coefficient by changing a sputtering pressure. As the sputtering pressure increases, the collision energy of Ar decreases. When the pressure exceeds 0.6 Pa, the bond between Ti and O becomes difficult to be broken due to a reduction in the collision energy of Ar.
At m, the film has a low light loss with an absorption coefficient of up to several hundred cm ^-1 .

On the other hand, in order to reduce the collision energy of Ar, there is a method of reducing the sputtering power. FIG.
FIG. 4 is a diagram showing a result of examining a change in an absorption coefficient by changing a sputtering power. As a result, the absorption coefficient did not depend on the sputtering power as much as the sputtering pressure. Therefore,
To produce a titanium oxide film with low absorption, the sputtering pressure
It can be seen that it is only necessary to control the pressure to 0.6 Pa or more.

In non-hydrogenated amorphous silicon,
The absorption coefficient is 40,000 cm ^-1 at a wavelength of 650 nm. The absorption coefficient of the titanium oxide film manufactured under the above conditions is about several hundred cm ^-1 at a wavelength of 650 nm, and the absorption coefficient is greatly reduced.
Further, unlike the conventional Ti target and the titanium oxide film forming method by the ECR sputtering method using oxygen decomposed by the ECR plasma shown in FIG. 5, since oxygen is not introduced at the time of sputtering, end face oxidation does not occur. The problem of reliability deterioration does not occur.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings based on examples, but the present invention is not limited thereto.

FIG. 1 is a schematic diagram showing the structure of an AlGaInP-based visible light semiconductor laser of the present invention, and FIG. 2 is a schematic explanatory diagram showing a method (apparatus) for producing a titanium oxide film of the present invention.
FIG. 5 is a schematic explanatory view showing a conventional method for producing a titanium oxide film. Hereinafter, an embodiment of the present invention will be described with reference to these drawings. Hereinafter, the present embodiment will be described using a multipolar sputtering apparatus, but other sputtering apparatuses and sputtering methods can be used.

In the apparatus shown in FIG. 2, an AlGaInP-based visible light semiconductor laser having an oscillation wavelength of 650 nm, which is cut out from a wafer into a bar, is placed on a jig 170 such that one end face faces the target electrode. Next, after raising the substrate temperature to 200 ° C., 50 sccm of Ar is supplied as a plasma gas.
Thereafter, as a low reflection film coating 110, an Al ₂ O ₃ film is formed to a thickness of 200 nm by controlling the sputtering pressure to 0.5 Pa and the sputtering power to 1000 W. At this time, Al ₂ O ₃ 190 is used as a target.

When the low-reflection film coating is completed, the bar is inverted and the high-reflection film coating 120 is performed. The substrate temperature is set to 200 ° C. after being set on the jig 170 so that the end face faces the target electrode as in the case of the low-reflection film coating 110.
And supply 50 sccm of Ar as a plasma gas.
Then, first, the sputtering pressure was controlled to 0.5 Pa, the Al ₂ O ₃ film 130 as the first insulator was set to a sputtering power of 1000 W, and
Formed to a thickness of nm.

As a target, Al ₂ O ₃ 190 is used. Next, the sputtering pressure is controlled to 0.7 Pa, and a titanium oxide film 140 is formed on the Al ₂ O ₃ film 130 to a thickness of 70 nm. The sputtering power at this time is set to 700 W, and TiO ₂ 200 is used as a target. At this time, oxygen is not introduced. Repeat 3
After performing the sputtering twice, the sputtering pressure was controlled to 0.5 Pa and the Al ₂ O ₃
A film is formed to a thickness of 200 nm with a sputtering power of 1000 W.
Thereafter, the AlGaInP-based visible light semiconductor laser of the present invention shown in FIG.

When the AlGaInP-based visible light semiconductor laser of the present invention was evaluated, the reflectance on the high reflection film side was 90%, and the threshold current was 50 mA. On the other hand, in the case of non-hydrogenated amorphous silicon, only a reflectance of 70% was obtained due to light absorption, and the threshold current was 60 mA. Also, high reliability was obtained because oxygen was not introduced during sputtering. The AlGaInP-based visible light semiconductor laser manufactured by the method of the present embodiment was subjected to a life test at 70 ° C. and 30 mW.

[0025]

According to the present invention, the AlGaInP-based visible light of good characteristics, in which the light absorption loss on the high reflection film side is greatly reduced and the reflectance and threshold value do not decrease due to light absorption. A semiconductor laser can be manufactured. Further, there is no problem of instability over time unlike the conventional hydrogenated amorphous silicon film. Furthermore, the conventional Ti target and E
In the ECR sputtering method using oxygen decomposed by CR plasma, it is difficult to control the composition because Ti and O are supplied independently, but in the present invention, the composition control is simple because TiO ₂ originally having the same composition is used. In addition, since oxygen introduction is unnecessary,
A highly reliable laser can be easily manufactured without fear of deterioration in reliability due to oxidation of the laser end face.

According to the manufacturing method of the present invention, the light absorption loss can be greatly reduced, and the AlGaInP having good characteristics without a decrease in reflectance or a rise in threshold due to light absorption.
System visible light semiconductor laser can be manufactured. In addition, since oxygen is not introduced, a remarkable effect is exhibited such that a highly reliable laser can be easily manufactured without fear of a decrease in reliability due to oxidation of the laser end face.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing the structure of an AlGaInP-based visible light semiconductor laser of the present invention.

FIG. 2 is a schematic explanatory view showing a method for manufacturing a titanium oxide film of the present invention.

FIG. 3 is a graph showing the dependency of the absorption coefficient on the sputtering pressure when the method for producing a titanium oxide film of the present invention is used.

FIG. 4 is a graph showing the dependence of the absorption coefficient on the sputtering power when the method for producing a titanium oxide film of the present invention is used.

FIG. 5: Conventional method for producing a titanium oxide film (ECR sputtering method)
FIG.

[Explanation of symbols]

110 low reflection coating film 120 high reflection coating film 130 Al ₂ O ₃ film 140 titanium oxide film 150 sputter chamber 160 stage 170 laser bar coating jig 180 shutter 190 Al ₂ O ₃ target 200 TiO ₂ target 210 magnetic coil 220 Ti target

Claims (3)

(57) [Claims] 1. An oscillation wavelength 630 comprising an active layer formed on a semiconductor substrate and a pair of cladding layers including the active layer.
In an AlGaInP-based semiconductor laser of about 690 nm, at least one of the cavity facets of the semiconductor laser is
A structure in which a first insulator and a titanium oxide film as a second insulator are alternately laminated for at least one cycle or more, and the titanium oxide film as the second insulator is formed by sputtering using TiO2 as a target. A method for manufacturing a semiconductor laser, characterized in that the semiconductor laser is manufactured by using a plasma gas with argon containing no oxygen and a sputtering pressure in a range of 0.6 to 10 Pa. 2. The method according to claim 1, wherein said first insulator is SiO 2 or Al 2 O 3. 3. The semiconductor substrate is made of GaAs, GaAsP or GaP, and the cladding layer is made of AlGaInP or AlGaAs.
3. The method according to claim 1, wherein the active layer contains GaInP or AlGaInP, respectively.