JP2743106B2 - Semiconductor laser - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser in which laser light is emitted from an active layer of a light emitting portion through a reflecting mirror, and more particularly to a semiconductor laser in which a protective film of the reflecting mirror has a sufficient thickness. With the protection function, the degree of freedom of design can be increased and the cost of the product can be reduced.
The present invention relates to a semiconductor laser capable of preventing a thermal distortion during heating by setting a protective film having a linear expansion coefficient close to that of another portion.

[Conventional technology]

FIG. 5 is an explanatory view showing the structure of a conventional semiconductor laser.

Conventionally, in a semiconductor laser, a light emitting portion AlGaAs _a A _s
P-type on both sides of the active layer 1 AlG _{a A s} cladding layer 2 and the n-type AlGaAs _a A _s
Double hetero (DH) sandwiched by cladding layer 3
Structure is adopted. The p-type cladding layer 2 and n
The mold cladding layer 3 is provided with a p-type electrode 4 and an n-type electrode 5, respectively.

Also, in order to amplify light in the active layer 1, a crystal end face (cleavage face) in the light traveling direction is used as a reflecting mirror 6 to have a structure in which a standing wave is formed inside, thereby forming a Fabry-Perot resonator. Is composed. The reflectivity of this reflecting mirror 6 is usually
It is set to 31-32%.

However, AlGaAs _a A _s is intact oxidized over time, thus causing serious deterioration. Therefore, in order to prevent the deterioration of the reflecting mirror 6, a protective film 7 such as Al ₂ O ₃ is conventionally formed on the reflecting mirror 6. If this protective film is transparent and has a thickness of λ / 2 (where λ is the wavelength of the laser beam), there is no change in the reflectivity, so that even if this protective film is provided, there is no significant change in the characteristics as a resonator.

6 (a) to 6 (e) are explanatory views showing a conventional manufacturing process of the semiconductor laser shown in FIG.

In this manufacturing process, first, the processed wafer 11
(See FIG. 6 (a)) is sliced (see FIG. 6 (b)), and Al ₂ O _{3 is} applied to the reflecting mirror 6 of the sliced wafer 11.
Is formed by a sputtering method (see FIG. 6 (c)). The thickness of this protective film 7 is λ
/ 2. Then, the wafer 11 is sliced in a direction orthogonal to the protective film 7 (see FIG. 6D) to form a laser chip 11a (FIG. 6D).
Fig. (E). In FIG. 6E, reference numeral 12 denotes a substrate, and reference numeral 13 denotes indium.

[Problems to be solved by the invention]

Incidentally, the following properties are required for the protective film for preventing the deterioration of the reflecting mirror 6 as described above.

(1) It must be an insulating film.

(2) Be transparent and have a smooth surface.

(3) The film thickness is λ / 2 (when the reflectance is not changed).

(4) linear expansion coefficient is close to AlG _{a A s,} may not provide a thermal strain in the crystal.

(5) The film must be chemically and thermally stable.

(6) Uniform and free from defects such as pinholes.

(7) have no effect on the AlGaAs _a A _s crystals during film formation.

Of these, (2) and (3) show the reflection function,
(5) and (6) show the protection function.

However, the Al ₂ O ₃ film that has been generally used as a protective film in the past is particularly susceptible to pinholes because it is formed by the sputtering method as described above, and the chemical and thermal stability is not sufficient. Thus, the protective functions (5) and (6) were insufficient. Therefore, in order to compensate for this, the laser chip is handled by placing it in a case in which nitrogen gas is sealed. Therefore, there has been a problem that the cost is increased and the degree of freedom of design is small.

The Al ₂ O ₃ film has a coefficient of linear expansion (8 to 9 × 10 ⁻⁶ / K)
There because of the considerable difference between the linear expansion coefficient (6 × 10 ^-6 / K) of AlG _{a A s,} there is a drawback that it is also insufficient for the requirements of the above (4).

The present invention has been made to solve the problems as described above, and the protective film of the reflecting mirror has a sufficient protective function to increase the degree of design freedom and reduce the cost of the product. It is an object of the present invention to provide a semiconductor laser in which a protective film has a coefficient of linear expansion close to that of another portion and can prevent thermal distortion during heating.

[Means for solving the problem]

According to the present invention, in a semiconductor laser formed of a laminate including an active layer and a cladding layer, and the end face of the laminate is a reflection face, the end face has aluminum oxynitride (Al _x O 2).
It is characterized in that the protective film made of _y N _z) is formed.

 The active layer is, for example, AlGaAs.

(Operation)

According to the above means, since a protective film made of chemically and thermally stable aluminum oxynitride (Al _x O _y N _z ) having few pinholes is formed on the reflecting mirror of the semiconductor laser, The protective film can have a sufficient protective function. Therefore, it is not necessary to use a case in which nitrogen gas is sealed in order to supplement the protection function of the protection film as in the conventional Al ₂ O ₃ film. As a result, the degree of freedom in designing the semiconductor laser is increased, and the manufacturing cost can be reduced.

The film of aluminum the oxynitride (Al _x O _y N _z), since the coefficient of linear expansion close to the coefficient of linear expansion of the active layer (AlG _{a A s),} such as thermal distortion of the heating time of the crystals is prevented Become like

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is an explanatory view showing a semiconductor laser according to one embodiment of the present invention, FIGS. 2 (a) to (e) are explanatory views showing a manufacturing process of the semiconductor laser of FIG. 1, and FIG. 3 (a). 4 (e) are explanatory views showing another manufacturing process of the semiconductor laser shown in FIG. 1, and FIG. 4 is a view for forming a protective film of aluminum oxynitride (Al _x O _y N _z ) on a reflecting mirror of the semiconductor laser. FIG. 2 is a sectional view showing a plasma CVD apparatus.

First, a semiconductor laser according to this embodiment will be described with reference to FIG.

Reference numeral 1 is AlGaAs _a A _s active layer, 2 is p-type AlGaAs _a A _s cladding layer, 3 n-type AlGaAs _a A _s cladding layer, the p-type electrode 4, is 5 n
The mold electrode 6 is a reflecting mirror composed of a cleavage plane of the crystal, and 27 is a protective film formed to prevent the deterioration of the reflecting mirror 6. In the present embodiment, this protective film 27 is made of Al
It is characterized by being formed of aluminum oxynitride (Al _x O _y N _z ) instead of ₂ O ₃ or the like.

That is, the protective film 27 of aluminum oxynitride (Al _x O _y N _z ) has the following characteristics.

It is a good insulator. (Dielectric strength 3 × 10 ⁶ V / cm or more,
Specific resistance of 10 ¹⁴ Ω-cm or more, in the case of crystals) Chemically stable up to high temperatures. (Complete covalent bonding, in the case of crystal) High thermal conductivity and large heat dissipation effect. (3.5W / cm · K) Excellent oxidation resistance (in the case of crystals, almost no oxidation amount up to 1200 ° C) and corrosion resistance.

Coefficient of linear expansion (5 × 10 ^-6 / K) is AlG _{a A s} (6
× 10 ⁻⁶ / K).

The crystal structure is a hexagonal wurtzite type, and has a piezoelectric effect.

It is transparent.

Since it is formed by the plasma CVD method, it is uniform without pinholes and the like.

In particular, above and above, the aluminum oxynitride (Al
_x O _y N _z) protective film 27 is, as compared with the film of the conventional Al ₂ O _3, and shows that it has a more sufficient protection. Therefore, the protective film 27 of this aluminum oxynitride (Al _x O _y N _z )
By using the method described above, it is not necessary to use a case in which a nitriding gas is sealed as in the related art, so that the cost of the semiconductor laser can be reduced. In addition, since a case in which nitrogen gas is sealed is not required, and handling at a chip level becomes possible, the degree of freedom in designing a semiconductor laser can be increased.

The above description is based on this aluminum oxynitride (Al _x O _y N _z )
Protective film 27 is, as compared with the film of the conventional Al ₂ O _3, and show that close to the linear expansion coefficient of the AlG _{a A s.} Therefore, by using this protective film 27 of aluminum oxynitride (Al _x O _y N _z ), thermal distortion of the crystal during heating can be greatly suppressed.

The following table compares the characteristics of aluminum nitride (AlN) as a comparative example, Al ₂ O _{3 as} a conventional protective film, and AlGaAs as an active layer for reference. From the table below, the refractive index of AlGaAs in the active layer is 3.54. In order to match the refractive index with 3.54, it is necessary to form a protective film with a material having a refractive index close to 1.88, which is obtained from the square root of 3.54 × 1.0 (refractive index of air). On the other hand, a protective film of aluminum nitride is suitable in terms of chemical stability and linear expansion coefficient, but has a higher refractive index than that of 1.88, and has a problem in matching. On the other hand, aluminum oxynitride used as the protective film of the present invention can adjust the refractive index by changing the composition of oxygen and nitrogen, and the range is 1.
Since it can be about 6 to 1.7, it is easy to match with the active layer.

Next, a manufacturing process of the semiconductor laser shown in FIG. 1 will be described with reference to FIG.

In the manufacturing process shown in FIG. 2, first, the processed wafer 11 (see FIG. 2 (a)) is sliced (see FIG. 2 (b)), and the reflecting mirror 6 of the sliced wafer 11 is sliced.
Then, a protective film 27 of aluminum oxynitride (Al _x O _y N _z ) is formed by a plasma CVD method described later (second embodiment).
FIG. (C)). The thickness of the protective film 27 is λ / 2. The wafer 11 is further sliced in a direction perpendicular to the protective film 27 (see FIG. 2D) to form a laser chip 11a (see FIG. 2E). In FIG. 2E, reference numeral 12 denotes a substrate, and reference numeral 13 denotes indium.

Here, a method of forming a protective film of aluminum oxynitride (Al _x O _y N _z ) on the reflecting mirror 6 of the wafer 11 in FIG. 2C will be described with reference to FIG.

First, FIG. 4 shows that aluminum nitride (Al
1 shows a CVD apparatus for forming a film of N). In FIG. 4, reference numeral 31 denotes a reaction tube formed by a quartz tube or the like, and the inside thereof is a reaction chamber A. Reference numeral 32 denotes a microwave plasma generator. 32a is a microwave oscillator, and in this embodiment, is 2.45 GHz by a cyclotron.
The microwave of z is oscillated. 32b is a waveguide, 32c is a matching box, and 32d is a reflector. The wafer 11 shown in FIG. 2 (b) is set on the support member 34 in the reaction chamber A.

A gas supply nozzle 37 is provided at the upper end of the reaction chamber A. The gas supply nozzle 37 is a multiple pipe, and in this embodiment, a double pipe. A constant temperature chamber 41 is provided in the source supply unit, and a bubbler 42 is disposed inside the constant temperature chamber 41. The bubbler 42 is filled with aluminum bromide (AlBr ₃ ) as a reactive gas source. Reference numeral 43 denotes a cylinder of hydrogen gas (H ₂ ) as an introduced gas, and reference numeral 44 denotes a cylinder of nitrogen gas (N ₂ ). Reference numeral 45 is a cylinder of nitrogen gas (N ₂ ). 46 and 47 are flow controllers. The gas supplied from the bubbler 42 side is supplied into the reaction chamber A from the inner pipe of the gas supply nozzle 47 of the double pipe, and when the cylinder 45 is used, the nitrogen gas supplied from this is supplied to the gas supply nozzle 37. Is supplied to the reaction chamber A from the outer tube of the above. 21 is a mechanical booster pump, and 22 is a rotary pump. The vacuum pressure in the reaction chamber A is set by one of the two pumps.

In device embodiments, the surface position of the wafer 11 as high as l ₁ than the passage center of the microwave, the position of the lower end of the gas supply nozzle 7 and higher by l ₂ than the surface of the wafer 11, l ₁ And l ₂ are both set to 40 mm. This is because, when the position of the molding member 34 is lowered, the formed AlN is easily decomposed, and when the lower end position of the gas supply nozzle is lowered, the film is easily formed on the inner surface of the nozzle.

In this CVD apparatus, a microwave of, for example, 2.45 GHz is used to discharge the mixed gas into plasma to thereby deposit AlN at a low temperature of about 500 ° C. or less. This is due to the fact that excitation in plasma is related to the relative dielectric constant of a substance and the dielectric loss angle. That is, aluminum bromide (AlBr
₃ ) is used, and this is mixed with nitrogen gas (N ₂ ) and hydrogen gas (H ₂ ). When this gas is discharged by microwave and turned into plasma, Al and Br, N and H, Al And N, Al, Br and H, and other combinations of radicals and ions. For example, when excited by a microwave of 2.45 GHz, the relative dielectric constant and the dielectric loss angle are affected by the microwave, and the radicals and ions in the above combination are in a resonance state, separated for each element, and Al And N maintain thermodynamic equilibrium. This is reacted by the reflecting mirror 6 of the wafer 11 to form an AlN thin film as shown in FIG. 2 (c). In this case, the optimal molar ratio between AlBr ₃ and N ₂ (for example, N ₂ / AlBr
_When the molar ratio of ₃ is about 15), a polycrystalline AlN thin film having a Miller index (OOl) orientation can be obtained at a low temperature of about 430 ° C. Also, the surface roughness of the thin film becomes very smooth.

FIG. 5 shows a CVD apparatus used for forming an aluminum oxynitride film on the reflecting mirror 6. 5 that are the same as in FIG. 4 are denoted by the same reference numerals.

FIG. 4 shows a CVD apparatus, in which reference numeral 36 is a gas supply nozzle composed of a triple tube, 49 is a cylinder of laughing gas (N ₂ O) for supplying oxygen atoms, and 51 is an argon gas ( A
A cylinder for supplying r), 47a to 47d are flow controllers, and 48a to 48d are valves.

Although the gas supply nozzle 36 is a triple tube, laughing gas (N ₂ O) is supplied into the reaction chamber A from a central tube 36a. Nitrogen gas (N ₂ ) is supplied through the middle tube 36b, and aluminum bromide (AlBr ₃ ) is supplied through the outer tube 36c.
Supplied to In this way, by supplying each gas to the reaction chamber A through separate paths using a triple tube, mixing of the gases in the tube is prevented, and a compound is deposited on the inner wall of the tube by plasma. Is prevented.

Argon gas (Ar) is supplied from above the reaction chamber A (upper left in the figure) through a different path from the gas supply nozzle 36. This is because the argon gas is supplied from outside the plasma generation region in the reaction chamber A. By supplying argon gas from the outside into the plasma, separation into neutral particles, ions, electrons, and the like in the plasma is promoted. Moreover, in the case of coaxial line type microwave plasma CVD, the plasma is easily affected by the electric field,
The electric field is strong at the tube wall of the reaction chamber and weakens at the center where the substrate to be reacted is installed, resulting in a non-uniform plasma area. However, the plasma area is expanded by supplying argon gas from outside the plasma area. I will be. In addition, in the case of monoatomic molecules such as argon gas, if they are decomposed in plasma, they are not easily recombined, and even if they are recombined, they do not deprive the surrounding energy and decompose stably. To continue. Therefore, it is expected that this will be a kind of ignition source and the plasma region will be expanded. This is the same state as when the degree of vacuum is increased in conventional plasma CVD, and has disadvantages such as simply increasing the vacuum pressure, for example, inconvenience such as an increase in electron density and a decrease in film formation rate You can avoid it. By expanding the plasma region and improving the radical dissociation rate, stable synthesis can be performed and the film formation rate can be increased.

However, it is necessary to supply argon gas from outside the plasma region.If argon gas or the like is directly blown from the nozzle to the wafer 11 in the plasma, the argon film will be sputtered and the film formation rate will be reduced. Become.

Reference numeral 21a denotes an exhaust pipe for evacuating the inside of the reaction chamber A to which a mechanical booster pump or a rotary pump is connected.

In device embodiments, to increase the surface position of the wafer 11 than the passage center of the microwave by l _1, the gas supply nozzle
The lower end position of 36 is higher than the surface of wafer 11 by l ₂ , and l ₁
And l ₂ are both set to 40 mm. This is because, in the reaction chamber A, the synthesis is most easily promoted at the upper or lower part which is off the center of the plasma generation area, and when the wafer 11 is installed at the lower part of the plasma, the ejection port of the gas supply nozzle 36 is connected to the plasma area. This is because the temperature becomes medium, and a reaction occurs in the tube, and a compound is deposited on the inner surface of the tube.

In the CVD apparatus shown in FIG. 4, a microwave (for example, having a frequency of 2.45 G) is used to discharge the mixed gas and turn it into plasma.
_Hz ), whereby aluminum oxynitride can be deposited at a low temperature of about 500 ° C. or less. This is due to the fact that excitation in plasma is related to the relative dielectric constant of a substance and the dielectric loss angle. That is, aluminum bromide (AlBr ₃ ) is used as a source, mixed with nitrogen gas (N ₂ ) and laughing gas (N ₂ O), and this gas is discharged by microwaves to be turned into plasma. And Al and Br, N and H, Al and N, Al and O, Al and Br
And H or the like such as a radical bond. Further, when excited by a microwave, the relative permittivity and the dielectric loss angle are affected by the microwave, and the above-described combination of radical bonds is in a resonance state, is separated for each element, and Al, O, N Maintain thermodynamic equilibrium. This reacts with the reflecting mirror 6 of the wafer 11 to form a thin film of aluminum oxynitride (Al _x O _y N _z ).

As described above, in this CVD apparatus, aluminum bromide is used as an aluminum source, and laughing gas is used as a nitrogen source, whereby aluminum oxynitride as shown in FIG. The film is synthesized.

In this case, by changing the supply flow rate of the laughing gas, the distribution ratio between oxygen atoms and nitrogen atoms of the deposited aluminum oxynitride can be changed, and the refractive index can be set arbitrarily.

As described above, plasma CVD as shown in FIG.
Protective film 2 of aluminum oxynitride (Al _x O _y N _z )
By forming 7, a uniform protective film without pinholes can be realized as compared with the case where a protective film of Al ₂ O ₃ is formed by a conventional sputtering method.

When the protective film 27 of aluminum oxynitride (Al _x O _y N _z ) is formed by using the plasma CVD method shown in FIG. 4, the refractive index of the protective film can be freely adjusted as described above. Therefore, a semiconductor laser suitable for an optical integrated circuit can be provided.

Further, since the plasma CVD shown in FIG. 4 can be performed at a relatively low temperature, a semiconductor laser having good quality and mass productivity can be realized.

Next, FIG. 3 shows another manufacturing process of the semiconductor laser according to the present invention. In FIG. 3, parts common to FIG. 2 are denoted by the same reference numerals.

In another manufacturing process shown in FIG. 3,
The processes from (a) to (b) are the same as those in FIG. 2, but the processes after (c) are different. That is,
The processed wafer 11 was sliced (see FIG. 3 (b))
Thereafter, this is further sliced in a direction orthogonal to the reflecting mirror 6, and the laser chip 11a formed thereby is fixed to the substrate 12 via the indium 13 (see FIG. 3 (d)). Then, the laser chip 11a is put into the reaction chamber a of the CVD apparatus shown in FIG.
A film 27a of aluminum oxynitride (Al _x O _y N _z ) is formed (see FIG. 3 (e)).

In the manufacturing process shown in FIG. 3, as shown in FIG. 3 (e), aluminum oxynitride (Al _x O _y N _z )
The film 27a can be coated on the entire surface of the laser chip 11a. Therefore, the entire surface of the laser chip 11a can be protected from deterioration such as oxidation. Also, as described above, since the film of aluminum oxynitride (Al _x O _y N _z ) has a high thermal conductivity, a high heat radiation effect can be exhibited even if the entire surface of the laser chip 11a is covered in this manner.

〔effect〕

As described above, according to the present invention, a protective film made of aluminum oxynitride (Al _x O _y N _z ) having no pinholes and being chemically and thermally stable is formed on a reflecting mirror of a semiconductor laser. Therefore, the protective film can have a sufficient protective function. Therefore, it is not necessary to use a case in which nitrogen gas is sealed in order to supplement the protection function of the protection film as in the conventional Al ₂ O ₃ film. As a result, the degree of freedom in designing the semiconductor laser is increased, and the manufacturing cost can be reduced.

The film of aluminum the oxynitride (Al _x O _y N _z), since the coefficient of linear expansion close to the coefficient of linear expansion of the active layer (AlG _{a A s),} such as thermal distortion of the heating time of the crystals is prevented Become like

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a semiconductor laser according to one embodiment of the present invention, FIGS. 2 (a) to (e) are explanatory views showing a manufacturing process of the semiconductor laser of FIG. 1, and FIG. 3 (a). (E) is an explanatory view showing another manufacturing process of the semiconductor laser according to the present invention, and FIG. 4 is a plasma for forming a protective film of aluminum oxynitride (Al _x O _y N _z ) on a reflecting mirror of the semiconductor laser. FIG. 5 is a sectional view showing a CVD apparatus, FIG. 5 is an explanatory view showing a structure of a conventional semiconductor laser, and FIGS. 6 (a) to 6 (e) are explanatory views showing a conventional manufacturing process of the semiconductor laser shown in FIG. is there. 1 ... active layer, 6 ... reflecting mirror, 27 ... protective film.

Continuing from the front page (72) Inventor Yuichi Umeda Alps Electric Co., Ltd., 1-7 Yukitani Otsuka-cho, Ota-ku, Tokyo (72) Inventor Toshio Hirai 3-4-1 Takamori 91-4, Izumi-ku, Sendai City, Miyagi Prefecture ) Inventor Makoto Sasaki 3-3-1 Minami Koizumi, Wakabayashi-ku, Sendai City, Miyagi Prefecture (56) References JP-A-2-288287 (JP, A) JP-A-3-149889 (JP, A) JP-A-1 183472 (JP, A) Actually open 63-162558 (JP, U)

Claims (2)

(57) [Claims] 1. A semiconductor laser formed of a laminated body including an active layer and a clad layer, wherein an end face of the laminated body is a reflection surface, wherein the end face is formed of aluminum oxynitride (Al _x O 2).
_{( yNz} ). A semiconductor laser having a protective film formed thereon. 2. The semiconductor laser according to claim 1, wherein said active layer is made of AlGaAs.