JP2008060248A - Semiconductor laser and method for manufacturing semiconductor laser - Google Patents

Abstract

A semiconductor laser capable of improving heat dissipation by a simple process and realizing a highly reliable operation even at high light output and a method for manufacturing the same are provided.
In a semiconductor laser, light reflecting surfaces 1c and 1d are formed on both end faces in an optical waveguide direction of an optical waveguide in which an active layer is sandwiched between an n-type cladding layer and a p-type cladding layer. When the semiconductor laser 1 is viewed from the direction orthogonal to the active layer, the side surfaces at positions orthogonal to both the active layer and the light reflecting surfaces 1c and 1d, that is, the side surfaces 1a and 1b in the direction along the optical waveguide It has a zigzag shape, and the areas 1a and 1b of the side surfaces are larger than the area of a cross section passing through the optical waveguide and orthogonal to the active layer.
[Selection] Figure 1

Description

  The present invention relates to a semiconductor laser used as, for example, a light source for an optical disc system, information processing, or optical communication, and a method for manufacturing the semiconductor laser.

A semiconductor laser generally includes a configuration (optical waveguide) in which an n-type cladding layer, an active layer, and a p-type cladding layer are sequentially stacked on a substrate, and current is injected into the active layer by being sandwiched between electrodes. When the density of the injection current increases and reaches a threshold value, laser oscillation (stimulated emission) is performed from the active layer.
On the other hand, a semiconductor laser (also referred to simply as “chip”) used as a light source of a rewritable high-density optical disk device such as a CD / DVD requires a high light output operation of several tens (mW) or more. In order to support high-speed writing, higher light output is required.

In order to meet this requirement, for example, when the injection current to the active layer is increased, the light output can be increased. However, as the injection current increases, the amount of heat generated from the active layer increases, causing problems such as saturation of the light output and a decrease in the reliability of the light output operation.
As a technique for improving the heat dissipation characteristics of a semiconductor laser, for example, Patent Document 1 discloses a technique in which a heat sink is effectively reduced by reducing a thermal resistance by lengthening a resonator (lengthening a resonator). Technology 1 ”). Patent Document 2 describes a technique for improving heat dissipation by providing a heat path wire as a radiator on the chip substrate side (this technique is referred to as “conventional technique 2”).
JP 2001-148537 A JP-A-6-77584

However, although the heat dissipation characteristic can be improved by the above technique, there is a problem that it is not realistic. In other words, in the prior art 1, the chip size is increased due to the increase in the length of the resonator, and the number of chips that can be removed from the wafer is thereby reduced, resulting in an increase in cost.
On the other hand, in the prior art 2, when the chip is incorporated in the device, the device has a complicated configuration, which requires a complicated standing process, resulting in a decrease in yield and cost.

  Therefore, in order to solve the above problems, the present invention provides a semiconductor laser capable of obtaining high heat dissipation and high reliability of optical operation at high light output with a simple configuration, and high heat dissipation and optical operation at high light output. It is an object of the present invention to provide a semiconductor laser manufacturing method capable of manufacturing a semiconductor laser having high reliability at low cost.

In order to solve the above-described problems, a semiconductor laser according to the present invention reflects light on both end faces in the optical waveguide direction of an optical waveguide in which an active layer is sandwiched between a first conductive clad layer and a second conductive clad layer. In the semiconductor laser having the surface formed thereon, the area of the side surface along the optical waveguide direction is larger than the area of the cross section passing through the optical waveguide and orthogonal to the active layer.
According to this configuration, the surface area of the side surface is larger than the area of the cross section passing through the optical waveguide and orthogonal to the active layer. Thereby, the heat generated at the time of light output can be dissipated from the side surface having a large area.

Further, the side surface has a non-planar shape, or the non-planar shape is a semiconductor laser cut along an arbitrary plane parallel to the active layer when viewed from a direction orthogonal to the active layer. Sometimes, the shape of the edge corresponding to the side surface is a polygonal line shape or a curved shape.
Further, the thickness of the semiconductor laser in the direction orthogonal to the active layer of the optical waveguide is substantially constant, and the light reflecting surface of the optical waveguide has a larger area on the front surface on the light output side than on the rear surface, When the semiconductor laser is viewed from a direction perpendicular to the surface, the shape of the semiconductor laser is tapered such that the distance between the opposing side surfaces increases from the rear surface toward the front surface.

  On the other hand, a semiconductor laser manufacturing method according to the present invention includes a diffusion step of forming a laser on a wafer, a cleavage step of cleaving the wafer to form a preliminary body having a resonator, and protecting the cleavage surface of the preliminary body. A method for manufacturing a semiconductor laser, comprising: a protective film forming step for forming a film; and a separation step for separating the laser from the preliminary body on which the protective film is formed. In the separation step, the laser is etched using an etching method. It is characterized by separation.

When manufactured by this method, laser separation can be performed at low cost.
Further, the separation step is performed by a dry etching method using a jig for fixing an etching mask and a preliminary body, or the dry etching method is an ICP dry etching method. .
Furthermore, the etching mask is made of a quartz material, or the jig is made of a quartz material.

According to the semiconductor laser of the present invention, since the surface area of the side surface is enlarged, the configuration is simple and the amount of heat radiation to the outside can be increased. Thereby, the temperature rise of the semiconductor laser due to the high light output operation can be suppressed, and high heat radiation performance and highly reliable light operation can be obtained even at high light output.
Further, in the method for manufacturing a semiconductor laser according to the present invention, since the laser is separated from the preliminary body by etching, the stress generated during the separation is reduced, and damage and cracks in the active layer are suppressed. Thereby, the yield at the time of manufacturing a semiconductor laser can be improved, and as a result, an inexpensive semiconductor laser can be obtained.

  Further, when the width of the semiconductor laser (which is a dimension perpendicular to the optical waveguide direction) is shortened, secondary cleavage (which is a process of separating chips one by one) is difficult. Therefore, the width of the semiconductor laser can be shortened, which is effective for shrinking. Moreover, depending on the shape of the semiconductor laser, it can be used as a recognition pattern at the time of assembly, so that the assembly accuracy can be improved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that a ridge stripe type is used for the configuration example of the semiconductor laser described below, but this is used as an example for explaining the structural features and operations of the present invention. It is not limited to the ridge stripe type. Further, the drawings are for explaining the semiconductor laser, and the dimensional ratio such as the thickness of each layer may be different from that of the actual semiconductor laser.

1. Overall Configuration FIG. 1 is a perspective view of a semiconductor laser according to an embodiment, and FIG. 2 is a cross-sectional view of the semiconductor laser according to the embodiment.
The semiconductor laser 1 has an n-type clad layer (the “first conductivity type clad layer” of the present invention) 5, an active layer 7, a first p-type clad layer (a “second” of the present invention) on an n-type substrate 3. 9) having an etching stop layer 11, a second p-type cladding layer 13, and a block layer 15 in this order, and sandwiched between an n-side electrode 17 and a p-side electrode 19. Yes.

The n-type substrate 3 is made of, for example, GaAs, and has a length in the X direction (hereinafter referred to as “width” and indicated by “B” in the drawing) in the range of 150 to 300 (μm). The length (hereinafter referred to as “length” and indicated as “L” in the figure) is in the range of 500 to 2000 (μm), and the length in the Z direction (hereinafter referred to as “thickness”) t ”) is 100 (μm).
Each dimension here is a standard dimension, and may be outside the range of the above dimension, and the present invention is not particularly limited by the dimension.

Further, the n-type substrate 3 may be composed of not only the above GaAs but also other materials. As other materials, there are a sapphire substrate, a SiC substrate, an n-type GaN substrate, and the like, and other materials can be applied as long as a semiconductor material described later can be epitaxially grown on the substrate.
The n-type cladding layer 5 is made of, for example, (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P, the width B and the length L are the same as those of the n-type substrate 3, and the thickness thereof is about 2.0 (μm).

The active layer 7 has a multiple quantum well structure including, for example, GaInP / (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P. The width B and length L are the same as those of the n-type substrate 3 and the thickness is 0.08 (μm).
The first p-type cladding layer 9 is made of, for example, (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P, and the width B and the length L thereof are the same as those of the n-type substrate 3. The thickness is 0.08 (μm).

The etching stop layer 11 is made of, for example, Ga _0.56 In _0.44 P, and its width B and length L are the same as those of the n-type substrate 3 and its thickness is 5 to 15 (nm).
As shown in FIG. 2, the second p-type cladding layer 13 has a ridge portion 13a at a substantially central position in the width direction, and wing portions 13b and 13b on both sides thereof. The second p-type cladding layer 13 is made of, for example, (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P, and the ridge portion 13a and the wing portion 13b have a thickness of 1 to 2 (μm). is there.

  The ridge portion 13a protrudes from the etching stop layer 11 into a substantially trapezoidal shape that is tapered. The trapezoidal shape here is a so-called tapered shape in which the bottom on the etching stop layer 11 side is longer than the upper side, and the width of the top of the ridge portion 13a is in the range of about 0.8 to 3 (μm). The ridge portion 13a is not limited to a trapezoidal shape as shown in the figure, and may have another shape. Other shapes include, for example, a rectangle (vertical ridge).

In the second p-type cladding layer 13, the block layer 15 is formed except for the top portion 13c of the ridge portion 13a. This is because the range in which current can be injected into the active layer 7 is limited to the top portion 13c to increase the current density injected into the active layer 7, and light is confined in the active layer 7 to increase the light extraction efficiency.
The second p-type cladding layer 13 and the block layer 15 may be collectively referred to as a current confinement layer.

The n-side electrode 17 is an ohmic electrode formed on the surface of the n-type substrate 3 opposite to the n-cladding layer 5. Similarly, the p-side electrode 19 is opposite to the second p-type cladding layer 13 in the block layer 15. This is an ohmic electrode formed on the side.
Thereby, light is generated from the active layer 7 into which the current has been injected, and the generated light is repeatedly reflected in a state where it is confined mainly in the region sandwiched between the first p-type cladding layer 9 and the n-type cladding layer 5. Move along the Y direction. That is, an optical waveguide is formed by a structure in which the active layer 7 is sandwiched between the n-type cladding layer 5 and the first and second p-type cladding layers 9 and 13.

A protective film made of, for example, SiO ₂ , Ta ₂ O ₅ , SiON or the like is formed on both end faces in the Y direction (optical waveguide direction). Each of the protective films has a size corresponding to the end face in the length direction of the semiconductor laser. The film formed on one end face is a highly reflective film and the film formed on the other end face is low reflective. Each film has a desired reflectance (this end surface corresponds to the “light reflecting surface” of the present invention).

By providing this protective film, light is generated from the active layer 7 into which the current has been injected, the generated light moves in the optical waveguide, and laser light is efficiently oscillated from the protective film in the Y direction. The configuration (corresponding to the “resonator” of the present invention).
In the semiconductor laser 1 having the above configuration, as shown in FIG. 1, end faces in the X direction (width direction), that is, side faces 1a and 1b along the optical waveguide direction have a zigzag shape. By making the side surfaces 1a and 1b into a zigzag shape, the area can be increased as compared with the case where the side surfaces are configured as a single plane.

Thereby, the amount of heat released from the side surfaces 1a and 1b of the semiconductor laser 1 to the outside can be increased. Thereby, temperature rise due to high light output operation can be suppressed, and high heat dissipation and high reliability of light operation can be obtained even at high light output.
In particular, since the edge of the active layer 7 constituting the optical waveguide is exposed on the side surfaces 1a and 1b, the heat of the active layer 7 can be released efficiently. Furthermore, since the heat of the active layer 7 escapes from the active layer 7 to the cladding layers 5 and 9, it is effective to increase the area of the side surfaces 1a and 1b of the semiconductor laser 1.

2. Manufacturing Method Next, a manufacturing method of the semiconductor laser according to the present embodiment will be described.
The semiconductor laser 1 includes a diffusion process for forming a laser on a wafer, a cleavage process for cleaving the wafer to form a preliminary body having a resonator, and a cleavage surface (a front surface and a rear surface) of the preliminary body. )) Through a protective film forming step of forming a protective film and a chip separation step of separating the laser chip from the preliminary body having the protective film (corresponding to the “separation step” of the present invention). .

Here, since the plurality of semiconductor lasers (chips) are separated from the spare body, the spare body is the previous stage of the semiconductor laser. Here, the spare body has a rectangular shape in which the semiconductor lasers are arranged in a straight line. This is a so-called laser bar. Further, a pre-chip is the one before separation into chips (which should be a chip).
The configuration of the semiconductor laser according to the present invention is characterized by the shape of its side surface, and each layer such as a substrate and a clad layer, and further, the material constituting each layer may be the same as the conventional one. For this reason, a well-known technique can be used for the diffusion process here, for example, including a window process, a ridge formation process, an electrode process, etc., and a cleaving process and a protective film formation process also use a known technique. Therefore, the description here is omitted.

(1) Chip Separation Step FIG. 3 is a diagram for explaining a chip separation step.
The chip separation process includes a bar fixing process for fixing the laser bar 31 to the fixing jig 33, and an etching mask 37 having an opening 35 corresponding to the chip shape in the fixing jig 33 to which the laser bar 31 is fixed. 33 includes a mask setting step for setting to 33, an etching step for etching the laser bar 31, and a recovery step for recovering the chips 39 separated in the etching step.

In the present embodiment, a dry etching method, particularly a reactive ion etching method is used as the etching.
First, the laser bar 31 is in a state before the chips 39 are separated, and in this example, there are five pre-chips 41 in one laser bar 31 as shown in FIG. That is, five chips 39 are obtained from one laser bar 31. The laser bar 31 has a cleaved surface 31a at the end face in the arrow direction in FIG.

As shown in FIG. 3B, the fixing jig 33 is provided with fixing means (for example, a fixing groove 33a) for fixing the laser bar 31, and the laser bar 31 is fitted into the fixing groove 33a. I am doing so.
The fixing jig 33 of this example can fix the three laser bars 31. The fixing jig 33 is desired to be selective to a semiconductor material (laser bar) with respect to an etching gas (in this embodiment, a chlorine-based gas). For example, a quartz material is used.

When a quartz material is used for the fixing jig 33, even if quartz (SiO ₂ ) sputtered during etching adheres to the side surface of the chip 39, the quartz is an insulator, so that a laser such as a current leak is present. It does not adversely affect the characteristics.
As shown in FIG. 3C, the mask 37 used in the mask setting process has an opening 35 corresponding to the chip 39 to be chip-separated, and a portion corresponding to the opening 35 of the mask 37 in the laser bar 31. Are etched, and the chip 39 is separated from the laser bar 31.

Like the material of the fixing jig 33, the mask 37 is desired to have selectivity with a semiconductor material (laser bar) with respect to the etching gas. For example, a quartz material is used. Further, in order to prevent the etching gas from being applied to the gain region of the laser bar 31, an alignment accuracy of about ± 10 (μm) is required between the pre-chips 41.
Note that when a quartz material is used for the mask 37, even if quartz (SiO ₂ ) sputtered during etching adheres to the side surface of the chip 39, as in the case where a quartz material is used for the fixing jig 33, Since quartz is an insulator, it does not adversely affect laser characteristics such as current leakage.

In the etching process, a reactive ion etching method, for example, ICP (Inductive Coupled Plasma) etching method is used, and chlorine (for example, Cl ₄ , SiCl ₄ ) is used as an etching gas. Thereby, an etching rate of about 10 (μm / min) can be obtained, and productivity can be improved. If the thickness of the laser bar 31 is about 100 (μm), for example, chip separation can be performed in about 10 minutes.

  As in this embodiment, the shape of the edge of the side surface when the semiconductor laser 1 is viewed in plan (from the direction perpendicular to the active layer 7 of the semiconductor laser 1 (the “Z direction” in FIG. 1)). In the case of zigzag shape, chip separation by the wall opening method is impossible, but chip separation from the laser bar 31 can be easily performed by applying an etching method. The chip 39 is naturally the chip 39.

In particular, when the etching method is used for chip separation, the stress applied to the pre-chip 41 during separation can be reduced (almost no effect) compared to the case of using the cleavage method, for example, and damage to the chip 39 or micro cracks can be achieved. Can be suppressed.
Further, since the etching of the laser bar 31 is performed substantially uniformly, the yield of chip separation can be stabilized and the yield can be improved.

  The recovery step is performed using, for example, an adhesive sheet 43. In the state where the chip separation process is completed, the depth of the fixing groove 33a of the fixing jig 33 is smaller than the thickness of the chip 39, so that the upper portion of the chip 39 is overhanging from the fixing groove 33a of the fixing jig 33. . And by making the adhesive sheet 43 contact the upper surface of the chip 39, the chip 39 adheres to the adhesive sheet 43, and the chip 39 can be taken out from the fixed groove 33a. In FIG. 3D, the adhesive sheet 43 is shown as transparent so that the state of the separated chip 39 can be seen.

<Modification>
Although the present invention has been described based on the above embodiment, the content of the present invention is not limited to the specific examples shown in the above embodiment. For example, the following modifications are possible. Can be implemented.
1. Kinds of Semiconductor Lasers In the above embodiment, a ridge stripe type (structure) gain waveguide type semiconductor laser has been described. However, other types, for example, a refractive index waveguide type may be used. For example, an oxide film structure may be used instead of the ridge structure.

  In the present embodiment, the AlGaInP-based material used as a red laser has been described. However, other materials such as an AlGaAs-based material used as an infrared laser may be used. It is also possible to develop a two-wavelength monolithic structure. Furthermore, it goes without saying that stability in high temperature operation and yield improvement in chip separation can be expected when used with a GaN-based material that has poor heat dissipation and is difficult to cleave.

2. Shape of Semiconductor Laser In the embodiment, the shape of the side surfaces 1a and 1b of the semiconductor laser 1 is zigzag. However, other shapes may be used as long as the areas of the side surfaces 1a and 1b are larger than the area of the cross section passing through the optical waveguide and orthogonal to the active layer.
FIG. 4 is a view showing a modification of the planar view shape of the semiconductor laser. Note that, when the semiconductor laser is viewed in plan and the shape is different between the front surface and the rear surface of the semiconductor laser, the front and rear are shown in FIG.

  The first semiconductor laser 41 according to the modification is shaped so that its width increases as it approaches the central portion in the length direction of the side surfaces 41a and 41b (corresponding to the substantially central portion in the vertical direction in FIG. 4). As shown in FIG. 4A, the side surface shape may be a shape that protrudes on a circular arc in the lateral (semiconductor laser width) direction or a concave shape, and FIG. The shape of the side surfaces 43a and 43b may be a shape that gradually protrudes stepwise in the lateral direction as it approaches the central portion in the length direction.

  Further, the semiconductor laser may have a shape such that its width decreases as it approaches the center part of the side surface (corresponding to a substantially central part in the vertical direction in FIG. 4). For example, like the semiconductor laser 45 shown in FIG. 4C, the shape of the side surfaces 45a and 45b may be gradually recessed in a stepwise manner in the lateral direction. Of course, although not shown in figure, the shape which dents in circular arc or elliptical arc shape may be sufficient.

In the semiconductor laser 1 (and semiconductor lasers 41, 43, and 45) in the above embodiment, the light reflecting surfaces 1c and 1d have the same shape and area, but the front side light reflecting surface and the rear side light reflecting surface are the same. The shape and area of the surface may be different.
That is, the light reflecting surface may have a larger area on the front light reflecting surface which is the light output side than on the rear light reflecting surface. In this case, the side surface of the semiconductor laser in plan view is shaped so that the distance between the opposing side surfaces increases from the rear surface side toward the front surface side, and the area of the side surface passes through the optical waveguide and the active layer. It becomes larger than the area of the cross section orthogonal to.

For example, as shown in the semiconductor laser 47 in FIG. 4D, the shape in plan view may be a tapered shape in which the distance between the opposing side surfaces 47a and 47b increases linearly as the distance from the rear surface side approaches the front surface side. good.
As shown in the semiconductor laser 49 of FIG. 4E, the shape of the side surfaces 49a and 49b in a plan view is an arc or elliptical arc shape between the rear surface and the front surface having a larger area than the rear surface. The shape may be tied to

Furthermore, as in the semiconductor laser 51 shown in FIG. 4F, the shape of the plan view changes as the distance between the opposing side surfaces 51a and 51b moves from the rear surface to the front surface having a larger area than the rear surface. It may be shaped like a staircase.
In order to manufacture the semiconductor lasers 41 to 51 according to the above modification, the shape of the mask opening described in FIG. 4 may be matched with the chip shape (planar shape) separated from the laser bar.

3. Etching In the chip separation step of the embodiment, the chip separation from the laser bar is performed by the ICP dry etching method, but other dry etching methods can also be used. As another method, for example, there is a RIE (Reactive Ion Etching) method or the like.
It is also possible to use wet etching. However, since wet etching is isotropic etching, the processing accuracy may be inferior to the dry etching capable of anisotropic etching.

4). Regarding the mounting of the semiconductor laser In the above embodiment, the mounting method of the semiconductor laser or the like was not particularly described. For example, a submount method in which the semiconductor laser is mounted on the sub-substrate dedicated to the semiconductor laser may be used. A semiconductor laser may be directly mounted on the main substrate.

  The present invention can be used for a semiconductor laser having excellent heat dissipation characteristics, and the manufacturing method of the present invention can be used for manufacturing a semiconductor laser having improved heat dissipation characteristics.

1 is a perspective view of a semiconductor laser according to an embodiment. It is sectional drawing of the semiconductor laser which concerns on embodiment. It is a figure explaining a chip separation process. It is a figure which shows the modification about the planar view shape of a semiconductor laser.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor laser 1a, 1b Side surface 1c, 1d Light reflection surface 5 N-type clad layer 7 Active layer 9 1st p-type clad layer 13 2nd p-type clad layer

Claims (9)

In a semiconductor laser in which light reflecting surfaces are formed on both end surfaces in the optical waveguide direction of an optical waveguide in which an active layer is sandwiched between a first conductivity type cladding layer and a second conductivity type cladding layer,
The area of the side surface along the optical waveguide direction is larger than the area of a cross section passing through the optical waveguide and orthogonal to the active layer. The semiconductor laser according to claim 1, wherein the side surface has a non-planar shape. The non-planar shape is such that when a semiconductor laser cut along an arbitrary plane parallel to the active layer is viewed from a direction orthogonal to the active layer, the shape of the edge corresponding to the side surface is a polygonal line shape or a curved shape. The semiconductor laser according to claim 2, wherein: The thickness of the semiconductor laser in the direction orthogonal to the active layer of the optical waveguide is substantially constant,
The light reflection surface of the optical waveguide has a larger area on the front surface on the light output side than on the rear surface,
The shape when the semiconductor laser is viewed from a direction orthogonal to the active layer has a tapered shape in which the distance between the opposing side surfaces increases from the rear surface toward the front surface. The semiconductor laser according to claim 1. A diffusion process to create a laser on the wafer;
Cleaving the wafer to form a preliminary body having a resonator;
A protective film forming step of forming a protective film on the cleavage surface of the preliminary body;
A method of manufacturing a semiconductor laser, comprising: a separation step of separating the laser from the preliminary body on which the protective film is formed,
In the separation step, the laser is separated by using an etching method. A method of manufacturing a semiconductor laser. The semiconductor laser manufacturing method according to claim 5, wherein the separation step is performed by a dry etching method using a jig for fixing the etching mask and the preliminary body. The semiconductor laser manufacturing method according to claim 6, wherein the dry etching method is an ICP dry etching method. The method for manufacturing a semiconductor laser according to claim 6, wherein the etching mask is made of a quartz material. The said jig is a quartz material. The manufacturing method of the semiconductor laser of any one of Claims 6-8 characterized by the above-mentioned.

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