JPH03209895A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To improve a semiconductor laser in degree of freedom of design and to decrease it in cost and to protect a protective film against heat distortion at heating by a method wherein the protective film formed of aluminum nitride(AlN) is provided to a reflective mirror. CONSTITUTION:A protective film 27 which is free from pinholes and formed of aluminum nitride(AlN) chemically and thermally stable is formed on a reflective mirror 6 of a semiconductor laser. Therefore, the protective film 27 has a function enough to serve as a protective film, so that a case charged with nitrogen gas used to supplement the protective function of the protective film 27 can be eliminated. By this setup, a semiconductor laser can be improved in degree of freedom of design and lessened in cost, and as an aluminum nitride(AlN) film is proximate to an active layer (AlNGaAs) in linear expansion coefficient, the crystal of the film can be protected against heat distortion at heating.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a semiconductor laser in which laser light is emitted from an active layer of a light emitting portion by passing through a reflecting mirror. By making it have a protective function, it is possible to increase the degree of freedom in design and reduce the cost of the product, and by making the protective film have a coefficient of linear expansion similar to that of other parts, it is possible to prevent thermal distortion during heating. The present invention relates to semiconductor lasers that can perform

[Prior Art] FIG. 6 is an explanatory diagram showing the structure of a conventional semiconductor laser.

Conventionally, in semiconductor lasers, AβG, which is the light emitting part,
A, p-type AρG on both sides of active layer 1, A.

A double hetero (DH) structure is adopted in which blood layer 2 is sandwiched with n-type A, f2G, A, and blood layer 3. The above p-type grading layer 2 and n-type grading layer 3
are provided with a p-type electrode 4 and an n-type electrode 5, respectively.

In addition, in order to amplify the light within the active layer 1, a structure is adopted in which the end face (cleavage plane) of the crystal in the direction of propagation of the light is used as a reflecting mirror 6, and a standing wave is generated internally. It consists of

The reflectance of this reflecting mirror 6 is normally set to 31 to 32%.

However, if left as is, AfiG and A will be oxidized over time, causing serious deterioration. Therefore, in order to prevent deterioration of the reflector 6, Al2203 is used for the reflector 6.
It has been conventionally practiced to form a protective film 7 such as the following. If this protective film is transparent and has a thickness of λ/2 (where n is the wavelength of the laser beam), there will be no change in reflectance, so even if this protective film is provided, there will be no major change in the characteristics of the resonator.

Further, FIGS. 7(a) to (e) are explanatory diagrams showing a conventional manufacturing process of the semiconductor laser shown in FIG. 6.

In this manufacturing process, first the processed wafer 11
(See FIG. 7(a))), and the reflecting mirror 6 of this sliced wafer 11 is
The protective film 7 of No. 08 is formed by a sputtering method (see FIG. 7(c)). The thickness of this protective film 7 is set to λ/2. Furthermore, this wafer 11
is sliced in a direction perpendicular to the protective film 7 (see FIG. 7(d)) to form a laser chip lla (see FIG. 7(e)). Note that the reference numeral 12 in FIG. 7(e) is a substrate, and the reference numeral 13 is indium.

[Problems to be Solved by the Invention] By the way, the following properties are required of 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 must be 1/2 (when the reflectance is not changed).

(4) The coefficient of linear expansion is close to that of Al2G,A, and no thermal strain is imparted to the crystal.

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

(6) Must be uniform and free from defects such as pinholes.

(7) A42G, A, and crystals should not be affected during film formation.

Among these, (2) and (3) exhibit reflex functions, and (5
) and (6) indicate protection functions.

However, the Aj2aO@ film, which has been commonly used as a protective film, is particularly prone to pinholes because it is formed by the spuckling method as described above.
Also, the chemical and thermal stability is not sufficient, and (5)
and (6) the protective function was insufficient. Therefore, in order to compensate for this, the laser chip is handled in a case filled with nitrogen gas, which increases the cost and reduces the degree of freedom in design.

In addition, the Ag2O3 film has a linear expansion coefficient (8 to 9 x 1
0-'/K) is the linear expansion coefficient (6X1
Since there is a considerable difference from 0-'/K), the above requirement (4) is also insufficient.

The present invention is intended to solve the above-mentioned problems, and provides a protective film for a reflecting mirror with a sufficient protective function, thereby increasing the degree of freedom in design and reducing 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 other parts and can prevent thermal distortion during heating.

[Means to solve the problem]

The semiconductor laser according to the present invention is a semiconductor laser in which laser light is emitted from an active layer of a light emitting portion by passing through a reflecting mirror, and the reflecting mirror includes aluminum nitride (AρN) or aluminum oxynitride (Aβ80N, ) is characterized by a protective film formed thereon.

[For production]

According to the above means, aluminum nitride (AI2N) or aluminum oxynitride (Ag, O, N), which has few pinholes and is chemically and thermally stable, can be used as a reflector for a semiconductor laser.
, ), it is possible to provide the protective film with a sufficient protective function. Therefore, unlike the conventional Aρ203 film, there is no need to use a case filled with nitrogen gas to supplement the protective function of the protective film. As a result, the degree of freedom in designing the semiconductor laser increases and manufacturing costs can also be reduced.

In addition, the linear expansion coefficient of the aluminum nitride (AlN) or aluminum oxynitride (Al2.O,N) film is close to that of the active layer (A42G, A,), so
This prevents thermal distortion of the crystal during heating.

〔Example] The present invention will be described in detail below based on the drawings.

FIG. 1 is an explanatory diagram showing a semiconductor laser according to an embodiment of the present invention, FIGS. 2(a) to (e) are explanatory diagrams showing the manufacturing process of the semiconductor laser of FIG. 1, and FIG. 3(a) ~(e) is an explanatory diagram showing another manufacturing process of the semiconductor laser of FIG. 1,
Figure 4 shows aluminum nitride (A) used as a reflector for a semiconductor laser.
5 is a cross-sectional view showing a plasma CVD apparatus for forming a protective film of aluminum oxynitride (A°C, O, N,) on a reflecting mirror of a semiconductor laser. FIG. 2 is a sectional view showing the device.

First, a semiconductor laser according to this embodiment will be explained based on FIG.

In the figure, code 1 is AΩG, A, active layer, 2 is p-type A42G,
A, blood layer, 3 is n-type AflG, A.

In the blood layer, 4 is an n-type electrode, 5 is an n-type electrode, 6 is a reflecting mirror constituted by a cleavage plane of a crystal, and 27 is a protective film formed to prevent deterioration of this reflecting mirror 6. This embodiment is characterized in that the protective film 27 is formed of aluminum nitride (Al2N) or aluminum oxynitride (An, O, N, etc.) instead of Al25Os as in the conventional case.

That is, the protective film 27 of aluminum nitride (Af2N) or aluminum oxynitride (A9., O, N,) has the following characteristics.

■It is a high quality insulator. (Dielectric strength 3 x 10'V/
cm or more, resistivity 1014 Ω-cm or more, crystal) ■ Chemically stable up to high temperatures. (Completely covalent, crystal) ■High thermal conductivity and great heat dissipation effect. (3.5W/cm
・K) ■Excellent oxidation resistance (there is almost no oxidation up to 1200°C, in the case of crystals) and corrosion resistance.

(2) The linear expansion coefficient (5X10-'/K) is close to that of Al2G, A (6X10-67 K).

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

■It is transparent.

■Since it is formed using the plasma CVD method, it is uniform and free of pinholes.

In particular, the above ■ and ■ are applicable to this aluminum nitride (A42
This shows that the protective film 27 made of aluminum oxynitride (Al203N) or aluminum oxynitride (Al2203, N) has a more sufficient protective function than the conventional Al2203 film. Therefore, by using the protective film 27 of aluminum nitride (A42N) or aluminum oxynitride (Aj2.O,N,), it becomes unnecessary to use a case filled with nitrogen gas as in the conventional case. It becomes possible to reduce the cost of lasers. Furthermore, since a case filled with nitrogen gas is no longer required and it becomes possible to handle the semiconductor laser at the chip level, the degree of freedom in designing the semiconductor laser can be increased.

In addition, the above item (■) shows that the aluminum nitride (AρN) or aluminum oxynitride (Aρ80yN) protective film 27 has a higher
, which indicates that the coefficient of linear expansion is close to that of . Therefore, this aluminum nitride (AεN) or aluminum oxynitride (A°C.

By using the protective film 27 of 0, N, ), thermal distortion of the crystal during heating can be significantly suppressed.

The table below is for comparing the characteristics of an aluminum nitride (Al2N) protective film and a conventional Aβ203 protective film.

13 Now, the manufacturing process of the semiconductor laser shown in FIG. 1 will be explained based on FIG. 2.

In the manufacturing process shown in FIG. 2, first, a processed wafer 11 (see FIG. 2(a)) is sliced (see FIG. 2(b)), and a reflector 6 of the sliced wafer 11 is coated with aluminum nitride ( A protective film 27 of aluminum oxynitride (AI2N) or aluminum oxynitride (0, N) is formed by the plasma CVD method described later (see FIG.
See C). The thickness of this protective film 27 is set to 1/2. Then, this wafer 11 is further sliced in a direction perpendicular to the protective film 27 (see FIG. 2(d)) to form laser chips lla (see FIG. 2(e)).
)reference). Note that in FIG. 2(e), reference numeral 12 indicates a substrate, and 13
is indium.

Here, in FIG. 2(C), a method of forming a protective film of aluminum nitride (AI2N) or aluminum oxynitride (Aε, OyN,) on the reflecting mirror 6 of the wafer 11 is shown in FIGS. I will explain based on this.

First, in FIG. 4, the reflecting mirror 6 is made of aluminum nitride (Aρ).
A CVD apparatus for forming a film of N) is shown. In FIG. 4, reference numeral 31 is a reaction tube formed of a quartz tube or the like, and the reaction chamber A is formed inside the reaction tube. code 32
is a microwave plasma generator. 32a is a microwave oscillator, and in this embodiment, a 2.45 GHz microwave is oscillated by a cyclotron. 32
b is a waveguide, 32c is a matching box, and 32d is a reflection plate.

The wafer 11 shown in FIG. 2(b) is placed on the support member 34 in the reaction chamber A.

A gas supply nozzle 37 is arranged at the upper end of the reaction chamber A. This gas supply nozzle 37 is a multiple pipe, and in this embodiment, it is a double pipe. In the source supply section,
A constant temperature room 41 is provided, and a bubbler 42 is arranged inside the room. This bubbler 42 is filled with aluminum bromide (Al2Br1) as a reactive gas source. Also, 43 is a cylinder of hydrogen gas (N2) which is introduced gas;
4 is a cylinder of nitrogen gas (N2). Also, the reference numeral 45 is a cylinder of nitrogen gas (N2).

46 and 47 are flow rate regulators. The gas supplied from the bubbler 42 side is supplied into the reaction chamber A from the inner pipe of the double-pipe gas supply nozzle 37, and when the cylinder 45 is used, the nitrogen gas supplied from this is supplied from the gas supply nozzle 37. 37
is supplied to reaction chamber A from the outer tube. Further, 21 is a mechanical booth pump, and 22 is a low-pressure pump. The vacuum pressure in reaction chamber A is set by either of the two pumps.

In the apparatus of the embodiment, the surface position of the wafer 11 is set much higher than the center of the microwave passage, and the lower end position of the gas supply nozzle/luer is set higher than the surface of the wafer 1 by ρ2. ．． Both l and 22 are set to 40 mm. This is because when the position of the molding member 34 is lowered, the deposited A and flN become easier to decompose.
Further, if the lower end position of the gas supply nozzle is lowered, it becomes easier to form a film on the inner surface of the nozzle.

This CVD apparatus uses microwaves of, for example, 2.45 GHz to discharge the mixed gas and turn it into plasma, thereby depositing Al2N at a low temperature of about 500° C. or lower. This is due to the fact that excitation in plasma is related to the relative permittivity of a substance and the dielectric loss angle.

That is, aluminum bromide (ARB r
s) is used, mixed with nitrogen gas (N2) and hydrogen gas (N2), and when this gas is discharged by microwaves and turned into plasma, Al2, Br, and N
Radicals and ions exist in combinations such as , H, A, +2, N, A, 9, Br, and Hl. For example, when excited by a 2.45 GHz microwave, the relative permittivity and dielectric loss angle are affected by the microwave, and the above combination of radicals and ions enters a resonant state, causing them to separate into individual elements. , A°C and N come to maintain thermodynamic equilibrium. This reacts with the reflecting mirror 6 of the wafer 11, and a thin film of AεN as shown in FIG. 2(c) is formed. In this case, AρBrs and N
Optimize the molar ratio with 2 (for example, N 2 / A +
If the molar ratio of 2 B r m is about 15), then 430
A polycrystalline AfiN thin film with a Miller index of (00° C.) orientation can be obtained at a low temperature of about 0.degree.

Furthermore, the surface roughness of the thin film becomes extremely smooth.

Further, FIG. 5 shows a CVD apparatus used to form an aluminum oxynitride film on the reflecting mirror 6. As shown in FIG. Note that parts in FIG. 5 that are common to those in FIG. 4 are given the same reference numerals.

In FIG. 5, reference numeral 36 indicates a gas supply nozzle consisting of a triple pipe;
9 is a cylinder of laughing gas (N2 o) for supplying oxygen atoms, 51 is a cylinder for supplying argon gas (Δr), 47a to 47d are flow rate regulators, 48a
~48d is a valve.

The gas supply nozzle 36 is a triple pipe,
N, o) are supplied into the reaction chamber A from the central tube 36a. Nitrogen gas (N2) is supplied from the middle pipe 36b, and aluminum bromide (A I2B r,) is supplied from the outer pipe 36.
c to the reaction chamber A. In this way, by supplying each gas to the reaction chamber A through separate routes using a triple tube, mixing of each gas in the tube is prevented, and the composite is deposited on the inner wall of the tube by plasma. is prevented.

Further, argon gas (Ar) is supplied to the gas supply nozzle 36.
It is supplied from above the reaction chamber A (upper left in the figure) via a different route. This is because argon gas is supplied from outside the plasma generation region in the reaction chamber A. By supplying argon gas into the plasma from outside, separation into neutral particles, ions, electrons, etc. 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, and the electric field is strong at the tube wall of the reaction chamber, and weaker at the center where the substrate to be reacted is installed, resulting in an insufficient plasma region. Although the plasma is uniform, the plasma region is expanded by supplying argon gas from outside the plasma region.

In the case of monoatomic molecules such as argon gas,
Once decomposed in plasma, it is difficult to recombine, and even if it recombines, it does not steal energy from the surroundings and continues to decompose stably. Therefore, it is predicted that this becomes a kind of ignition source and the plasma area is expanded. This is the same situation as increasing the degree of vacuum in conventional plasma CVD, but it also has the disadvantages of simply increasing the vacuum pressure, such as an increase in electron density and a decrease in film formation rate. You will be able to avoid this. By expanding the plasma region and improving the radical dissociation rate, stable synthesis can be achieved and the film formation rate can be increased.

However, it is necessary to supply argon gas from outside the plasma region, and if argon gas or the like is sprayed directly onto the wafer 11 in the plasma from a nozzle, the argon will create a sputtering state and reduce the film formation rate. Become.

Note that even when A and f2N are synthesized using the CVD apparatus shown in FIG. 4, the same effect can be obtained by similarly supplying Ar gas from outside the plasma generation region.

Reference numeral 21a is an exhaust pipe for creating a vacuum inside the reaction chamber A, to which a mechanical booth pump or a rotary pump is connected.

In the apparatus of the embodiment, the surface position of the wafer 11 is set higher than the center of the microwave passage by f21, the lower end position of the gas supply nozzle 36 is set higher than the wafer 11 surface by 122, and both J2+ and 122 are set at 40 mm. It is set to . This is because in reaction chamber A, synthesis is most likely to be promoted in the upper or lower part away from the center of the plasma generation area.
Moreover, if the wafer 11 is placed below the plasma, the ejection port of the gas supply nozzle 36 will be in the plasma region, a reaction will occur within the tube, and a composite will be deposited on the inner surface of the tube.

In the CVD apparatus shown in Fig. 5 above, microwaves (for example, at a frequency of 2.45
G H,1 was used, thereby making it possible to precipitate aluminum oxynitride at a low temperature of about 500° C. or lower. This is due to the fact that excitation in plasma is related to the relative permittivity of the material and the dielectric loss angle. That is, aluminum bromide (Ar2
Br, ) is used, mixed with nitrogen gas (N2) and laughing gas (N20), and when this gas is discharged by microwaves and turned into plasma, A, 9 and B
Radical bonds exist in combinations such as r, N and H, Aj2 and N, Ar2 and 0, Afl, Br and H, and so on. When further excited by microwaves, the relative permittivity and dielectric loss angle are affected by the microwaves, and the radical bonds in the above combination become resonant, splitting into each element, and A! ! , O, and N come to maintain a thermodynamic equilibrium state. Then, this reacts on the reflecting mirror 6 of the wafer 11 and aluminum oxynitride (Ar2.ON,
) is formed.

In this way, this CVD apparatus uses aluminum bromide as an aluminum source and laughing gas as a nitrogen source to produce aluminum oxynitride as shown in FIG. 2(c) using the plasma CVD method. We are trying to synthesize a film of

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

As described above, a protective film 2 of aluminum nitride (AlN) or aluminum oxynitride (Al2°0, N,) is prepared using the plasma CVD method as shown in FIGS.
By forming 7, it becomes possible to realize a uniform protective film without pinholes, compared to the case where a protective film of Al220s is formed by the conventional sputtering method.

In addition, when forming the protective film 27 of aluminum nitride (Al2N) or aluminum oxynitride (Al2.O,N,) using the plasma CVD method shown in FIGS. 4 and 5 above, as described above, Since the refractive index of the protective film can be freely adjusted, it becomes possible to provide a semiconductor laser suitable for optical integrated circuits.

Furthermore, since the plasma CVD method shown in FIGS. 4 and 5 can be performed at relatively low temperatures, it is possible to realize semiconductor lasers of good quality and mass production.

Next, FIG. 3 shows another manufacturing process for a semiconductor laser according to the present invention. Parts in FIG. 3 that are common to those in FIG. 2 are given the same reference numerals.

In the other manufacturing process shown in FIG. 3, (a)
The process from to (b) is the same as in Figure 2, but (
C) The subsequent processes are different. That is, after slicing the processed wafer 11 (see FIG. 3(b)),
Further, this is sliced in a direction perpendicular to the reflecting mirror 6, and the thus formed laser chip lla is fixed to the substrate 12 via the indium 13 (see FIG. 3(d)). Thereafter, this laser chip 11a is placed together with the substrate 12 in the reaction chamber A of the CVD apparatus shown in FIGS. 27a (see FIG. 3(e)).

In the manufacturing process shown in Fig. 3, Fig. 3 (e
), the entire surface of the laser chip lla can be coated with a film 27a of aluminum nitride (AρN) or aluminum oxynitride (,6I2°O2N,). Therefore, it becomes possible to protect the entire surface of the laser chip lla from deterioration such as oxidation. Furthermore, as mentioned above, aluminum nitride (AlN) or aluminum oxynitride (Al
2. Since the films of O, N, ) have high thermal conductivity, they can exhibit a high heat dissipation effect even if they cover the entire surface of the laser chip lla in this way.

〔effect〕

As described above, according to the present invention, the reflecting mirror of a semiconductor laser is made of aluminum nitride (AlN), aluminum oxynitride (Aβ,
Since the protective film is formed of O, N, ), it is possible to provide the protective film with a sufficient protective function. Therefore, the conventional Al2. There is no need to use a case filled with nitrogen gas to supplement the protective function of the protective film, as in the case of the O, film. As a result, the degree of freedom in designing the semiconductor laser increases and manufacturing costs can also be reduced.

In addition, the linear expansion coefficient of the aluminum nitride (Al2N) or aluminum oxynitride (Al2.O,N,) film is close to that of the active layer (ApG, A,), so
This prevents thermal distortion of the crystal during heating.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing a semiconductor laser according to an embodiment of the present invention, FIGS. 2(a) to (e) are explanatory diagrams showing the manufacturing process of the semiconductor laser in FIG. 1, and FIG. 3(a) ~(e) are explanatory diagrams showing other manufacturing processes of the semiconductor laser according to the present invention, and FIG. 4 is a plasma CVD process for forming a protective film of aluminum nitride (Al2N) on the reflecting mirror of the semiconductor laser.
A cross-sectional view of the device; FIG. 5 is a cross-sectional view of a plasma CVD device for forming a protective film of aluminum oxynitride (Al2.O,N,) on a reflector of a semiconductor laser; FIG. 6 is a cross-sectional view of a conventional semiconductor laser. Explanatory diagram showing the structure of the laser, FIG. 7(a)
-(e) are explanatory diagrams showing the conventional manufacturing process of the semiconductor laser shown in FIG. 6. DESCRIPTION OF SYMBOLS 1... Active layer, 6... Reflector, 27... Protective film. Ward 7 Ward C) So Ward

Claims (1)

[Claims] 1. In a semiconductor laser in which laser light is emitted from an active layer of a light emitting portion by passing through a reflecting mirror, a protective film made of aluminum nitride (AlN) is formed on the reflecting mirror. A semiconductor laser 2 characterized in that a laser beam is emitted from an active layer of a light emitting portion by passing through a reflecting mirror, in which a protective film made of aluminum oxynitride (Al_xO_yN_2) is formed on the reflecting mirror. A semiconductor laser characterized by