JPH02310986A - Semiconductor laser element, photomask and manufacture thereof - Google Patents

Abstract

PURPOSE:To perform a wavelength multiplex communication or a coherent communication with one semiconductor laser element sections by providing effective refractive index or/and diffraction grating pitch of resonators of respective unit semiconductor laser to be different ones from those of resonators of other unit semiconductor lasers. CONSTITUTION:Unit semiconductor laser sections A, B, C of a semiconductor laser element 1 are composed of DFB lasers, and the widths W1, W2, W3 of active layers 4 and the pitches a1, a2, a3 of diffraction gratings 21 are different (W1>W2>W3, a1>a2>a3). As a result, a laser light 20 having a wavelength of 1553nm of the emitting light is radiated from the laser section A having W1=1.5mum, a1=2405Angstrom , a laser light 20 having a wavelength of 1543nm is irradiated from the laser section B having W2=1.0mum, a2=2400Angstrom , and a laser light 20 having a wavelength of 1533nm is radiated from the laser section C having W3=0.65mum, a3=2395Angstrom .

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser device, particularly a monolithic semiconductor laser device that emits laser light of multiple wavelengths, a method for manufacturing the same, and a photomask manufacturing technique.

[Conventional technology]

Semiconductor lasers (semiconductor laser elements) are widely used as light sources for information processing devices such as digital audio discs, video discs, optical disc files, and laser beam printers, or as light sources for optical communications.

Regarding visible light semiconductor laser devices and long wavelength semiconductor laser devices, for example, see “Monthly Semiconductor World” published by Press Journal Co., Ltd.
tor World) J 19 B July 4th issue,
Published June 15, 1980, described on pages 47 to 52. This document also describes a distributed feedback type (Dis) which emits laser beams with different wavelengths from a single semiconductor laser element (chip) as one of the semiconductor laser elements for optical communication.
Tributed Feedback: DFB)
Lasers are introduced. This distributed feedback semiconductor laser with a laser array type structure can transmit signals on lights of different wavelengths through a single optical fiber, and thus becomes a light emitting source capable of wavelength division multiplexing communication.

In addition, “Electronic Materials, February 1987 issue,” published by Kogyo Kenkyukai,
P42 to P46 published on February 1, 1988, show a five-wavelength integrated semiconductor laser with a wavelength interval of 50 as a multi-wavelength integrated laser used in a wavelength division multiplexing transmission system. This document states, ``In order to set the center wavelength to 1.3 μm, the period of the internal diffraction grating is 2000 people, and in order to obtain a wavelength spacing of 50 people, the period of adjacent lasers is 9 people.'' . Furthermore, this document also describes an example of a five-wavelength multiplexing transmission system.

[Problem to be solved by the invention]

In optical communications, the need for large-capacity communications has led to a demand for semiconductor laser devices suitable for wavelength division multiplexing communications, that is, semiconductor laser devices that emit light at a plurality of mutually different wavelengths.

Conventional semiconductor laser devices of this type perform oscillation by making the period of the diffraction grating of the unit light emitting section different from the period of the diffraction grating of the other unit light emitting sections, in which the unit light emitting section becomes a distributed feedback semiconductor laser. The wavelength (emission wavelength) is changed.

However, advanced technology is required to form diffraction gratings with different periods on the same substrate. In other words, conventionally, when forming diffraction gratings with different pitches on the same substrate, interference exposure method has been considered, but with this method, it is difficult to narrow the distance between the lasers in the laser array, and it requires a lot of man-hours. will increase. Further, when forming a diffraction grating by multiple exposure, there may be problems such as difficulty in forming the diffraction grating uniformly each time.

Therefore, although this is not yet known to the public, the applicant proposed a monolithic semiconductor that emits laser light of three different wavelengths by changing the width and thickness of the resonator, that is, the effective refractive index. Proposed a laser element (patent application 1986-
No. 98115, filed April 22, 1986).

The present invention is an extension of this inventive idea.

SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor laser device that can emit laser beams with different oscillation wavelengths from individual semiconductor laser sections, and a manufacturing technique thereof.

Another object of the present invention is to provide a technique for forming diffraction gratings with different pitches on a single surface with good reproducibility.

Another object of the present invention is to provide a photomask capable of forming diffraction gratings with different pitches on a single surface and a manufacturing technique thereof.

The above and other objects and novel features of the present invention include:
It will become clear from the description of this specification and the accompanying drawings.

[Means to solve the problem]

A brief overview of typical inventions disclosed in this application is as follows.

That is, the semiconductor laser device of the present invention has a structure in which three semiconductor laser sections having a distributed feedback structure are provided in parallel on a single semiconductor substrate, and a resonator in each of these semiconductor laser sections is configured. vinegar .

The active layer, optical guide layer, and anti-meltback layer have different widths, and the pitch of the diffraction grating of each semiconductor laser section also differs from each other.

In addition, another semiconductor laser element of the present invention has a structure in which three semiconductor laser sections having a distributed feedback structure are provided in parallel on a single semiconductor substrate, and the resonance in each of these semiconductor laser sections The widths and thicknesses of the devices are different from each other, and the pitches of the diffraction gratings of each semiconductor laser section are also different from each other.

Further, in the present invention, when manufacturing a photomask used for manufacturing a zero diffraction grating in which the width of the resonator and the diffraction grating pitch are formed by photolithography to be different, a mask substrate is first prepared. next,
After densely forming V-grooves radially along one direction on the main surface of this mask substrate, a mask material in which a light-transmitting resin is bonded to a light-transmitting mask substrate is attached to the resin surface on the main surface of the mask substrate. A replica is created by superimposing them so that they are in contact with each other, and then a light-shielding substance is diagonally deposited on the resin surface of the mask material to form a light-shielding material on one inclined surface constituting the V-groove formed on the resin surface. A photomask having linear light-transmitting portions extending radially is formed by forming a vapor-deposited film.

[Effect]

According to the above means, the semiconductor laser device of the present invention is
The three semiconductor laser sections, each composed of a distributed feedback semiconductor laser, have different resonator widths and diffraction grating pitches, and therefore emit different laser beams.

Furthermore, in a semiconductor laser element having a structure in which the width and thickness of the resonator and the pitch of the diffraction grating in each semiconductor laser section are different from each other, different laser beams are emitted from each semiconductor laser section. .

The photomask used to manufacture the diffraction grating is used to form a radial array of V-grooves on the main surface of the mask substrate, to create a replica using a transparent mask material, and to form a V-groove array on the surface of the transparent mask material.
It can be manufactured with good reproducibility by inclined vapor deposition of a light-shielding substance on one inclined surface of the groove forming surface.

〔Example〕

Here, before describing embodiments, the idea of the present invention will be explained.

The oscillation wavelength (emission wavelength) λ of the distributed feedback semiconductor laser is
It is given by the following formula.

λ=2 nmtt A = (1) Here, nmtt is the effective refractive index of the portion where light propagates within the element, and 8 is the pitch of the diffraction grating.

Therefore, in order to change the oscillation wavelength of the laser, either the grating pitch 8 or the effective refractive index navy may be changed.

The above n*ff is the average refractive index of the part where light propagates, and by changing the cross-sectional shapes of the active layer, light guide layer, and anti-meltback layer, the amount of light seeping into the cladding layer changes. However, the effective refractive index n art changes. That is, the effective refractive index n, .

becomes smaller as the width of the active layer becomes narrower and as the thickness of the active layer becomes thinner. FIG. 7 shows the results of numerical calculation of the active layer width dependence of nmtt in a 1.5 μm band DFB laser. As can be seen from the same graph, the oscillation wavelength can be changed by changing the width of the active layer.

On the other hand, the effective refractive index n, 1. If the and the diffraction grating pinches are selected differently, the emission wavelength can be more easily selected.

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) In this first embodiment, three (3) unit semiconductor laser sections made up of distributed feedback semiconductor lasers are arranged in parallel, and the width of the resonator and the pitch of the diffraction grating are mutually adjusted. An example in which this is done differently will be explained.

FIG. 1 is a schematic perspective view showing an outline of a semiconductor laser device according to an embodiment of the present invention, FIG. 2 is a sectional view of the semiconductor laser device, and FIGS. 3 to 6 are similar to the steps in manufacturing the semiconductor laser device. 3 is a sectional view showing a wafer etc. which is a workpiece in each process, FIG. 3 is a sectional view showing a wafer used for manufacturing a semiconductor laser device, FIG. 4 is a sectional view of a wafer subjected to mesa etching, FIG. 5 is a perspective view showing a photomask used for mesa etching, FIG. 6 is a cross-sectional view of a wafer on which a buried layer is formed, and FIG. 7 is a perspective view of a photomask used for mesa etching.

A graph showing the correlation between active layer width and effective refractive index in a 5 μm 1FDFB laser; FIG. 8 is a perspective view showing a semiconductor laser device incorporating a semiconductor laser element according to the present invention;
FIG. 9 is a perspective view showing the state of optical coupling between the semiconductor laser element and the optical fiber.

In this embodiment, as shown in FIG. 1, a semiconductor laser element (laser diode chip) 1 has a rectangular shape, and a unit semiconductor laser section (
Three (3 unit light emitting parts) are provided in parallel with A, B, and C. Each of the unit semiconductor laser sections A, B, and C is composed of a bFB laser. In these unit semiconductor laser parts A, B, and C, the widths W, , W□, W of the active layer 4 and the pitch al of the diffraction grating 21 are
+ al + a2 are different (W
+>Wx>Ws, aH>at>as)
, As a result, the emission wavelength from the unit semiconductor laser section A of W+-1.6 am and al -2405 is 1553 nm.
emits a laser beam 20 of Ws = 1.0 pm, am
-2400 people's unit semiconductor laser section B emits laser light 20 with an emission wavelength of 1543 nm, W3 = 0.65
The unit semiconductor laser section C of μm, a = 2395 people emits laser light 20 with an emission wavelength of 1533 nm. In addition, in FIG. 1, the reference numerals of each part are omitted.

Next, the structure of the semiconductor laser device 1 will be explained.

Each of the unit semiconductor laser sections A, B, and C has the same structure except that the active layer width, that is, the portion that defines the active layer width, and the diffraction grating pitch are different as described above. therefore,
Each part will be explained simply as a unit semiconductor laser part without making distinctions between A and C.

The laser diode chip (semiconductor laser element) 1 is I
It is composed of an nGaAsP-based compound semiconductor. That is, as shown in FIG.
For example, a diffraction grating is provided on the (100) crystal plane in the direction perpendicular to the plane of the paper, and an n-type 1nGaAsP
A light guide layer 3 having a thickness of approximately 0.1 μm and having a thickness of approximately 0.1 μm.
Active layer 4 made of 1 μm InGaAsP, thickness approximately 0
．． An anti-meltback layer 5 made of p-type 1nGaAsP with a thickness of 1 pm, a cladding layer 6 made of p-type 1nP with a thickness of about 3 μm, and a cap layer 7 made of p-type nGaAsP with a thickness of about 0.3 μm are sequentially provided. . The light guide layer 3, active layer 4, anti-meltback layer 5, cladding layer 6
, a cap layer 7', the anti-melt back layer 5, the cladding layer 6 and the cap layer 7 have an inverted triangular mesa structure, and the part below the active layer 4 has a substrate 2. It has a triangular mesa structure that gradually slopes down, including the surface layer. The widths of the active layer 4 in this mesa portion are Wl, Wt, and wx in the unit semiconductor laser parts A, B, and C, as described above. Further, this inverted mesa portion has pitches al and a□ along its extending direction.

A diffraction grating is formed.

On the other hand, a multilayer buried layer 9 is formed in each region where the multilayer growth layer 8 is etched.

This multilayer buried layer 9 is formed on the substrate 2 and has a thickness of about 1 mm.
A blocking layer 10 made of p-type 1nP with a thickness of about 2.5 μm, an n-type 1nP embedding layer 11 with a thickness of about 2.5 μm formed on the blocking layer 10, and a blocking layer 11 with a thickness of about 0.5 μm formed on the embedded layer. It consists of an n-type 1nGaAsP buried cap layer 12 with a thickness of 3 pm. Further, an insulating film 13 is provided on the buried layer cap layer 12. Then, using the insulating film 13 as a mask, zinc is diffused over the surface layer of the multilayer growth layer 8 to form a p◆ type diffusion layer 14 (area marked with dots). This p÷ type diffusion layer 14 becomes an electrode contact layer. In addition, in the zero implementation, an anode electrode 15 is provided on the main surface of the laser diode chip l, and a cathode electrode 16 is provided on the back surface, that is, the lower surface of the substrate 2.
, wl.

6ttm, Wl=1.0pm, Ws-0,65am.

at =2405 people, am-2400 people B, w239
Assuming 5 people, the emission wavelength is 1553 nm as mentioned above.
The wavelengths are 1543 nm and 1533 nm.

Note that in each unit semiconductor laser section A, B, and C, when only the active layers are made different from each other without changing the diffraction grating 21, that is, the active layer width is Wl = 1.6 pm, W
z = 1.0 μm, Ws = 0°65 μm, at
-at -as If there are -2400 people, the oscillation wavelength is λ+-155, respectively, from Figure 7 and equation (1) above.
0nm, λ88-1543n, λs=1536
It oscillates at three different wavelengths of nm.

Next, a method for manufacturing the laser diode chip l having such a structure will be explained.

First, as shown in Figure 3, a compound semiconductor thin plate (
30 wafers are prepared. This wafer 30 is composed of a substrate 2 made of n-type InP and having a thickness of about 300 μm. Furthermore, the wafer 30 shown in the figure is (
100) A multilayer growth layer 8 has already been formed on the main surface, which is a crystal plane, by an epitaxial growth method. This multilayer growth layer 8 has a thickness of approximately 0.1 mm from the bottom. un's n-type 1nGa
Light guide layer 3 made of AsP, In with a thickness of about 0.1 pm
An active layer 4 made of GaAsP, an anti-meltback layer 5 made of p-type 1nP with a thickness of about 0.1 μm, a cladding layer 6 made of p-type 1nP with a thickness of about 3 μm, and a thickness of about 0.
．． Cap layer 7 made of 3 pm p-type 1 nGaAsP
It is composed of.

Next, as shown in FIG. 4, convergence L+, Lx, Ls (Ll >Lx'>
L, ), and the pitches of the diffraction gratings 21 on both sides are at + am + as (a, >a, >a,:
An insulating film 31 is provided (see FIG. 1). This insulating film 31 is provided along the <110> interosseous direction.

Further, this insulating film 31 is formed by a photomask 3 shown in FIG.
2. As shown by hatching, this photomask 32 has three light-shielding parts 34 in a light-transmitting part 33, and the widths of each light-shielding part 34 are Ll and Lx.
, Lm (Ll >L, >L, ), and both sides are diffraction gratings 21 with pitches at, a+al.

Next, the main surface of the wafer 30 is etched using an etching solution such as promethanol.

This etching is performed to a depth that reaches the surface layer of the substrate 20, and as a result, as shown in FIG.
A stripe portion 36 is provided below. The striped portion 36 has a constricted middle portion due to the etching. That is, by the etching,
As a result of the anisotropic etching, the portion above the anti-meltback layer 5 becomes an inverted mesa portion with an inverted triangular cross section having an angle θ = 60°, and remains in a stripe shape along the <110> direction of the crystal. Below active layer 4, a parabola (
It is a mesa part like that.

By the way, the width L of the insulating film 31 ((+=1°2.3)
is given by the following equation.

L! -Wi +2 dL a n (30°)・
(2) Here, Wi is the width of the active layer 4, and d is the total thickness of the anti-meltback layer 5, cladding layer 6, and cap layer 7, that is, the portion forming an effective resonator (
Hereinafter, it is the thickness of the resonator). Therefore, in this example, Wi is defined as Wr, Wz, Wx (
Since Wi>Wz>Wi) is selected,
The L+, Lx, and L3 are also selected correspondingly.

Next, as shown in FIG. 6, a multilayer buried layer 9 is formed in the depressed portion caused by the etching. This multilayer buried layer 9 includes a p-type 1nP blocking layer lO1 with a thickness of about 2 lam, which is sequentially formed on the substrate 2.
．． 5μm n-type InPt1 layer 11, thickness about 0.3p
It consists of an n-type 1nGaAsP buried cap layer 12 of m.

Moreover, after this epitaxial growth, the main surface of the wafer 30 is completely removed, i! Membrane 31 is removed. Thereafter, an insulating layer M13 made of Sin or the like is partially formed on the main surface of the wafer 30. This insulating film 13 is provided so that a region substantially corresponding to the stripe portion 36 is excluded. Next, zinc is diffused using this insulating film 13 as a mask, and P◆
A ten-shaped diffusion layer 14 is formed. This p-type diffusion layer 14 becomes an ohmic region for the electrode.

Next, although not shown, on the main surface of the wafer 30,
An anode electrode 15 having a thickness of approximately 1 μm is provided. Also,
The back surface of the wafer 30, that is, the substrate 2 is polished,
The total thickness is about 1100a. Thereafter, a cathode electrode 1 with a thickness of about 1 μm is placed on the back side of the wafer 30.
6 is formed.

Next, the wafer 30 is cut vertically and horizontally to produce a plurality of laser diode chips 1 as shown in FIG.

Such a semiconductor laser element 1 is incorporated into a semiconductor laser device 40 as shown in FIG. 8, for example. This semiconductor laser device 40 includes a box-shaped package 41,
It consists of an optical fiber cable 42 extending from one end of this package 41 and a plurality of leads 43 protruding from the periphery of the package 41. For example, four leads 43 lined up in a part of the package 41 are leads for driving the semiconductor laser element l, one of which is the cathode electrode 16, and the other three are leads for each unit semiconductor laser. These are the anode electrodes 15 of parts A, B, and C. Therefore, by applying a voltage between one lead 43, which is the cathode electrode 16, and all or part of the three leads 43, which are the anode electrode 15, wavelength division multiplex communication or coherent communication becomes possible.

Inside the insulating film 31, as shown in FIG. 9, different wavelengths λ1 . λ8. The laser beam 20 of λ is transmitted through the spherical lens 44
The light is focused and coupled to an optical fiber 45. Note that each anode electrode 15 on the main surface of the semiconductor laser element l is electrically connected to the inner end of the lead 43 via a wire 46.

According to such an embodiment, the following effects can be obtained.

(1) The semiconductor laser device of the present invention has three unit semiconductor laser sections each having a distributed feedback semiconductor laser structure. The width of the active layer and anti-meltback layer is
Since Wi, Wt, and Wi are different from each other, and the pitch of the diffraction grating of the resonator is also different from at lam lam, the effect that laser beams having different oscillation wavelengths can be emitted can be obtained.

(2) According to (1) above, since the semiconductor laser device of the present invention emits a plurality of laser beams with different oscillation wavelengths,
The effect can be obtained that it can be used as a light emission source for wavelength division multiplexing communication in optical communication.

(3) The semiconductor laser device of the present invention has a structure that emits laser beams with different oscillation wavelengths, and the change in cross section of the resonator that emits laser beams with different oscillation wavelengths and the pitch of the diffraction grating are determined by the multilayer growth layer. The etching mask for etching into stripes can be formed using the photomask shown in the same example.In addition, in forming this photomask, it is sufficient to simply change the pattern, so this new method is particularly useful. The effect is that it does not require any technology and is easy to implement.

(4) According to (3) above, the semiconductor laser device of the present invention has the effect that the diffraction grating can be manufactured by the conventionally established photolithography, so that it can be manufactured with high precision and good reproducibility, and the yield is improved. can get.

(5) Since the semiconductor laser device of the present invention can form multiple resonators with different oscillation wavelengths by changing the etching mask pattern, each resonator can be placed close to each other, and the laser array can be miniaturized. is obtained.

(6) According to the present invention, since each unit semiconductor laser section has a structure in which the resonator width and the diffraction grating pitch are changed, each desired emission wavelength can be freely selected, so wavelength multiplexing is possible. The effect of increasing the design latitude as a communication light emitting source can be obtained.

(7) According to the above (1) to (6), according to the present invention, a synergistic effect can be obtained in that a monolithic distributed feedback laser array capable of emitting light at a plurality of oscillation wavelengths can be manufactured at low cost.

(Second Embodiment) FIGS. 1O to 17 are diagrams showing other embodiments of the present invention. In each figure, FIG. 10 is a partially cutaway perspective view showing a semiconductor laser device, FIG. 11 is a perspective view of a wafer on which a diffraction grating used for manufacturing the semiconductor laser device is formed, and FIG. 12 13 is a schematic diagram showing the formation state of a mask for forming a diffraction grating, FIG. 14 is a schematic diagram showing the formation state of a photomask for forming a diffraction grating, and FIG. The figure is a schematic plan view of a photomask, FIG. 16 is a schematic cross-sectional view showing a liquid phase epitaxial growth method, and FIG. 17 is the same (cross-sectional view).

In this example, three unit semiconductor laser parts A, B, and C are monolithically formed to have a thickness of 1.5 μm as in the previous example.
An example of a laser diode chip l having a DFB laser structure that emits a band laser beam will be described.

In the laser diode chip 1 of this embodiment, a diffraction grating 21 is provided at the bottom of the optical guide layer 3, as shown in FIG. 1O. The pitch of this diffraction grating 21 is a, + am + as (at>at>as), and each of the unit semiconductor laser parts A and B.

The widths of the active layers are W+, Wt, and Wx (W+>Ws>
W, ), in addition, the thickness of the light guide layer 3, i.e. the thickness d of the resonator consisting of the light guide layer 3 and the active layer 4 and the anti-meltback layer 5.

, dx, and ds (dt > ds > ds) are also formed to be different from each other. Although FIG. 1O is partially a cross-section, the heftings are omitted to maintain a clear view.

This laser diode chip l is the same as the laser diode chip l described above, except that the diffraction grating 21 is provided at the bottom of the optical guide layer 3, and the thickness of the resonator is different for each unit semiconductor laser part A, B, and C. Since the structure is the same as that of the laser diode chip l of the first embodiment, a description of the structure will be omitted, and the thicknesses of the formation of the diffraction grating 21, the photomask used during the formation of this diffraction grating 21, and the resonator will be different from each other. I would like to explain the growth of Ebitaxia and Le, which are formed like this.

In this embodiment, the diffraction grating 21 is provided on the n-type 1nP substrate 2. In order to change the pitch of the diffraction grating 21 for each stripe section 36, the pitch of the wavefront 50 provided on the substrate 2 is set to a on one end surface side as shown in FIG.
o, gradually narrowing as it goes along the trough of the wave, and at the other end it is different from a, and the al
+a! +a, the pitch part is the unit semiconductor laser part A,
B.

The wavefront 50, which may be used as C, is formed by conventional photolithography techniques using a photomask 51 as shown in FIGS. 14 and 15. For convenience of explanation, such a wavefront 50 will be referred to as radial.

Next, a method for manufacturing the photomask 51 will be explained. The photomask 51 has a transparent portion 5 through which light passes in plan view.
2 and a hatched light-blocking part 53 that does not allow light to pass through, and a linear light-transmitting part 54 with a width of several people and a narrow line and a linear light-blocking part 55 with a narrow width of several people alternate alternately. The pattern is that they are arranged in parallel. Furthermore, the pitch of the linear transparent portions 54 matches the pitch of the wavefronts 50 shown in FIG. 11 above. That is, the pitch of the linear light-transmitting portions 54 is wide at one end, ao, gradually narrows toward the longitudinal direction of the linear light-transmitting portions 54, and is the narrowest at the other end, a7.

In manufacturing such a photomask 51, as shown in FIG. 12, a mask substrate 56 is first prepared. This mask substrate 56 consists of a transparent glass plate 57 and an aluminum layer 58 provided on one surface of this glass plate 57 to a predetermined thickness.

Therefore, the surface of the glass plate 57 is scratched with a diamond cutter 59 to remove the aluminum layer 58 in a straight line. Since the tip of the diamond cutter 59 has a V-shape, the scratching portion has a V-shaped groove 60.
becomes. For example, the number of V grooves 60 is 5000/m.
They are arranged in parallel at intervals of about m. Therefore, ■Groove 6
0 and the V-shaped peak 61 form a continuous mountain shape.

Also, during this scratching, the diamond cutter 59
are not parallel, but are operated in a direction in which the V-groove pitch gradually narrows (as→aa) or gradually widens (a,→a6), as shown in FIG.

As a result, the pitch of the chevron formed by the grooves 60 and the like becomes different from a to a at both ends.

Next, as shown in FIG. 13, the mask substrate 5
A mask material 65 is bonded to the surface having the V-groove 60 of No. 6 to create a replica. That is, the mask material 65
has a structure in which a transparent resin layer 67 is provided on a transparent quartz glass plate 66, and this resin layer 67 is attached to the mask substrate 56.
A replica is created by pressing the aluminum layer 58 onto the aluminum layer 58.

As a result, V grooves 68 and V-shaped peaks 69 are formed on the resin surface of the mask material 65.

Next, as shown in FIG. 14, the mask material 6
A light-shielding material is applied to the surface having the V-groove 68 from an oblique direction.
For example, chromium (Cr) is deposited. As a result, a light-shielding vapor deposited film 70 made of chromium is formed only on one end slope of the V-groove 68.

The area to which the light-blocking vapor deposited film 70 is attached becomes a linear light-blocking part 55, and the area to which the light-blocking vapor deposited film 70 is not attached becomes a linear light-transmitting part 54. Therefore, as shown in FIG. 14, the photoresist film 71 provided on the main surface of the wafer 30 is exposed using this photomask 51, developed, and further etched to create a wavefront as shown in FIG. A wafer 30 having 50 wafers will be obtained.

Next, an epitaxial growth method for changing the effective thickness of the resonator in each unit semiconductor laser section A, B, and C will be described. In this embodiment, the optical guide layer 3. constituting the resonator. When forming the active layer 4° anti-meltback layer 5, that is, when forming the multilayer growth layer 8 on the wafer 30 by liquid layer epitaxial growth, as shown in FIG. is obtained by tilting the angle (θ) by a predetermined angle (θ). That is, a solution holder 76 is placed on the substrate holder 75. As shown in FIG. 16, this solution holder 76 is provided with each chamber 77 along the moving direction, and based on the solution 78 accommodated in each chamber 77, the wafer 3
An epitaxial layer having a desired composition is formed on the main surface of the substrate.

In this example, since five chambers 77 are provided, the main surface of the wafer 30 is sequentially coated with light guide layers 3 . Active layer 4. Anti-meltback layer 5. A clad layer 6° and a cap layer 7 are formed.

In this way, in forming the multilayer growth layer 3, for example,
When the substrate holder 75 is tilted between 4 degrees and 6 degrees, the thickness of the resonator of each semiconductor laser section 15 becomes tt-0,345.
μm, tt = 0.350t1m, ts = 0.355
#m becomes.

According to such an embodiment, each unit semiconductor laser section A,
By changing the thickness of the active layer of B and C, tl=t,), the effective resonator thickness dt~d,) is changed, and the width of the active layer and the diffraction grating pitch are made different. Therefore, each unit semiconductor laser section A, B, and C can emit laser light 20 of a different wavelength.

According to the second embodiment, the following effects can be obtained in addition to the effects of the first embodiment. (1) According to the present invention, the width and thickness of the resonator, and even the diffraction By changing the grating pitch and the three factors, it is possible to generate laser light having a desired emission wavelength.

(2) According to the present invention, since the formation of the diffraction grating is performed using established exposure technology and etching technology using a photomask, it is possible to form the diffraction grating with good reproducibility and improve the yield. It will be done.

(3) According to the present invention, when manufacturing a photomask having a structure in which the diffraction grating pitch is changed in each part, the mask substrate is created using a diamond cutter, a replica is created, and a light-shielding material is obliquely deposited. The advantage is that it can be manufactured easily and with high precision.

(4) According to the above (1) to (3), according to the present invention, a synergistic effect is obtained in that a monolithic distributed feedback semiconductor laser device capable of emitting light at a plurality of oscillation wavelengths can be manufactured with high precision and high yield.

Although the invention made by the present inventor has been specifically explained based on Examples above, the present invention is not limited to the above Examples (although it is possible to make various changes without departing from the gist of the invention). Needless to say, for example, in the above embodiment, the widths of the optical guide layer, active layer, and anti-meltback layer that constitute the resonator were changed, but in order to change the oscillation wavelength, it is necessary to change the width of the three layers. This can also be achieved by changing the width of one of the layers.Also, depending on the crystal growth conditions, material system, and desired wavelength band, an anti-meltback layer is not necessarily necessary. Although the number of semiconductor laser sections has been explained as three, it goes without saying that the number of semiconductor laser sections is not limited to three in the present invention.
Further, in the embodiment described above, a 1nP/InGaAs semiconductor laser having a wavelength of 1.55 μm was used, but other materials may of course be used.

In the above explanation, the invention made by the present inventor was mainly applied to the manufacturing technology of a single semiconductor laser element, which is the foreground field of application, but the invention is not limited to this. It can also be applied to manufacturing technology for optical integrated circuits having laser sections.

The present invention can be applied to manufacturing techniques for semiconductor laser devices having a small number of distributed feedback semiconductor laser sections.

〔Effect of the invention〕

A brief explanation of the effects obtained by typical inventions disclosed in this application is as follows.

According to the present invention, since a monolithic semiconductor laser element can oscillate laser beams of different wavelengths, one semiconductor laser element can perform wavelength multiplexing communication or coherent communication.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view showing an outline of a semiconductor laser device according to an embodiment of the present invention, FIG. 2 is a cross-sectional view of the semiconductor laser device, and FIG. 3 is a wafer used for manufacturing the semiconductor laser device. 4 is a sectional view of a wafer on which mesa etching has also been performed. 5 is a perspective view of a photomask used for mesa etching. 6 is a sectional view of a wafer on which a buried layer has also been formed. 7 is a graph showing the correlation between the active layer width and the effective refractive index, FIG. 8 is a perspective view showing a semiconductor laser device incorporating the semiconductor laser device according to the present invention, and FIG. 9 is a graph showing the correlation between the active layer width and the effective refractive index. FIG. 10 is a perspective view showing a partially cut away state of a semiconductor laser device according to another embodiment of the present invention; FIG.
The figure is a perspective view of a wafer on which a diffraction grating is formed, FIG. 12 is a schematic diagram showing the formation of a mask for forming a diffraction grating, and FIG. 13 is a schematic diagram showing the formation of a replica for forming a diffraction grating. FIG. 14 is a schematic diagram showing the formation state of a photomask for forming a diffraction grating, FIG. 15 is a schematic plan view of the photomask, FIG. 16 is a schematic cross-sectional view showing the liquid phase epitaxial growth method, and FIG. It is also a sectional view. 1... Laser diode chip (semiconductor laser element)
, 2... Substrate, 3... Light guide layer, 4... Active layer, 5... Anti-meltback layer, 6... Clad layer, 7... Cap layer, 8... Multilayer Growth layer, 9...
Multilayer embedded layer, 10...Blocking layer, 11...
Embedded layer, 12... Embedded cap layer, 13... Insulating film, 14... p÷ type diffusion layer, 15... Anode electrode, 16... Cathode electrode, 20... Laser light, 2
DESCRIPTION OF SYMBOLS 1... Diffraction grating, 30... Wafer, 31... Insulating film, 32... Photomask, 33... Transparent part, 34...
... Light shielding part, 36... Stripe part, 40... Semiconductor laser device, 41... Package, 42... Optical fiber cable, 43... Lead, 44... Ball lens, 45...・Optical fiber, 46...Wire, 50・
...Wavefront, 51...Photomask, 52...Transparent part,
53... Light shielding part, 54... Linear transparent part, 55...
- Linear light shielding part, 56... Master substrate, 57... Glass plate, 5th... Aluminum layer, 59... Diamond cutter, 60... ■Groove, 61... V-shaped mountain ,
65... Mask material, 66... Quartz glass plate, 67
...Resin layer, 68...V groove, 69...V-shaped mountain, 7
0... Light-shielding vapor deposited film, 71... Photoresist film, 7
5... Substrate holder, 76... Solution holder, 77...
- Chamber, 78...solution.

Claims (1)

[Scope of Claims] 1. A monolithic semiconductor laser device having a plurality of unit semiconductor laser sections formed of distributed feedback semiconductor lasers, wherein the effective refractive index and/or diffraction of the resonator of each unit semiconductor laser section is A semiconductor laser device characterized in that a grating pitch is different from an effective refractive index or/and a diffraction grating pitch of a resonator of another unit semiconductor laser section. 2. The effective refractive index of the resonator of the unit semiconductor laser section is adjusted by selecting the resonator width and/or the resonator thickness. Semiconductor laser element. 3. The semiconductor according to claim 1, wherein the diffraction grating of the unit semiconductor laser section is formed by repeatedly expanding and contracting the width of the resonator along the extending direction of the resonator. laser element. 4. The diffraction grating of the unit semiconductor laser section has a wavy structure at the bottom of the resonator along the extending direction of the resonator, and each wave of this diffraction grating corresponds to each wave of the adjacent unit semiconductor laser section. 2. The semiconductor laser device according to claim 1, wherein a line that lies on an extension line of a portion and connects corresponding wave portions of adjacent unit semiconductor laser portions extends in a fan shape. 5. A step of providing a diffraction grating on the main surface of a semiconductor substrate, a step of forming a multilayer growth layer including a layer constituting a resonator by sequential epitaxial growth on the main surface of this substrate, and a step of forming the multilayer growth layer in several strips. A method for manufacturing a semiconductor laser device, comprising the steps of etching away to form a plurality of stripes made of multi-layered growth layers, and filling the spaces between the stripes with an epitaxial growth layer to form a plurality of unit semiconductor laser parts, the method comprising: The pitch of the diffraction grating is formed to be different for each unit semiconductor laser section, and the width of the resonator is formed to be different for each unit semiconductor laser section. 1. A method of manufacturing a semiconductor laser device, which comprises tilting a main surface, continuously changing the thickness of at least a layer constituting a resonator, and changing the thickness of the resonator in each stripe stepwise. 6. A photomask having a light-transmitting part through which light passes and a light-blocking part through which light does not pass, wherein the light-transmitting part has a pattern in which linear light-transmitting parts are arranged in multiple rows in parallel; A photomask characterized in that the arrangement pitch of the linear light-transmitting portions gradually changes in the longitudinal direction of the linear light-transmitting portions. 7. forming a plurality of V-grooves extending linearly on the main surface of the master substrate in a parallel state so that the arrangement pitch of the V-grooves gradually changes in the direction in which the V-grooves extend; creating a replica by overlaying a mask material in which a transparent resin is attached to a transparent mask substrate on the main surface of the master substrate and making the resin surface follow the irregularities of the main surface of the master substrate; The pitch of linear light-transmitting parts provided in parallel by the step of vapor-depositing a light-shielding substance from an oblique direction on the resin surface of the mask material and forming the light-shielding substance only on one side of the V-groove formed on the resin surface. 1. A method for manufacturing a photomask, comprising manufacturing a photomask having a structure in which the linear light-transmitting portion gradually changes in the longitudinal direction thereof.