JP2008130869A - Method for manufacturing semiconductor laser element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a semiconductor laser element where a variation of a ridge width is reduced to make a variation of an element characteristic little. <P>SOLUTION: The method for manufacturing a semiconductor laser element includes processes of laminating at least a clad layer 3, an active layer 4, and a clad layer 5 on one surface of a semiconductor substrate 1 whose one surface 1a has a predetermined crystal orientation in order, forming a mask 8 for crystal growth which is provided with an opening 8a having a predetermined width W8a on the clad layer 5, and forming a ridge 13, which is connected with the clad layer 5 and its sectional shape is to be a reverse mesa shape to the layer-laminating direction, on the opening by crystal growth. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a semiconductor laser device, and more particularly to a method for manufacturing a semiconductor laser device having a ridge.

As one form of the semiconductor laser element, there is a semiconductor laser element having a ridge for the purpose of transverse mode control of oscillation light and current confinement.
The ridge is usually formed by an etching method, and the cross-sectional shape thereof has a trapezoidal shape in which the width on the side opposite to the substrate is narrower than the substrate side.
In particular, in a high-power type semiconductor laser device, the width of the ridge is narrowed to suppress the generation of kinks during laser oscillation, or the current blocking layer made of a semiconductor crystal is not provided to improve heat dissipation. It is known to have an air ridge structure.
An example of a semiconductor laser element having a ridge as described above is described in Patent Document 1.
Japanese Patent Laid-Open No. 11-354882

Since the width of the ridge affects element characteristics such as the occurrence of kinks when laser oscillation is performed as described above, it is desirable that the dimensional variation is small.
However, when a ridge, particularly a narrow ridge, is formed using an etching method, the variation in the width of the formed ridge becomes large due to the influence of the etching variation, so that improvement is desired.
Etching variation is caused by variations in the etching amount in the substrate (wafer) plane due to the flow of the etching solution and the non-uniformity of the reaction rate.

Etching at the time of forming the ridge is normally performed in a wafer state. However, variation in the height of the ridge is increased due to variation in etching within the wafer surface, and thus variation in element characteristics may be increased.
In order to reduce the variation in the height of the ridge, means for providing an etching stop layer between the formed ridge and the active layer is known.
However, since the etching stop layer usually absorbs part of the oscillation light oscillated in the active layer, it causes an increase in the operating current of the manufactured semiconductor laser device.

  Further, the ridge is covered with an insulating film, an opening is formed in the insulating film so that the ridge is exposed, and an electrode connected to the ridge is formed through the opening, whereby the ridge and the electrode are electrically connected. However, when the width of the ridge is narrow, the connection area between the ridge and the electrode is reduced, or the variation in the connection area is increased due to variations in the size of the opening. The element resistance value of the element increases, and the variation of the element resistance value increases.

  Accordingly, the problem to be solved by the present invention is to manufacture a semiconductor laser device that can reduce variations in the width of the ridge without providing an etching stop layer, thereby reducing variations in device characteristics of the manufactured semiconductor laser device. To provide a method.

In order to solve the above problems, each invention of the present application has the following means.
1) A method of manufacturing a semiconductor laser device, wherein at least a first conductivity type cladding layer (3) is formed on the one surface of a first conductivity type semiconductor substrate (1) having one surface (1a) having a predetermined crystal orientation. ), An active layer (4), and a second conductivity type clad layer (5), and a second crystal layer of the second conductivity type after the first crystal growth step. A mask forming step of forming a crystal growth mask (8) having a first opening (8a) having a predetermined width (W8a) on the first opening, after the mask forming step; A second crystal growth step of forming a second conductivity type ridge (13) connected to the second conductivity type clad layer and having a cross-sectional shape of a reverse mesa shape with respect to the stacking direction by crystal growth; A method for producing a semiconductor laser device (20) having
2) an insulating film forming step of forming an insulating film (15) having a second opening (15a) covering the ridge and exposing the ridge on the ridge after the second crystal growth step; After the insulating film forming step, a first electrode (17) connected to the ridge is formed on the second opening, and a second surface (1b) opposite to the stacking direction of the semiconductor substrate is formed. The method of manufacturing a semiconductor laser device according to claim 1, further comprising: an electrode forming step of forming the electrode (18).

  According to the present invention, it is possible to reduce the variation in device characteristics of the manufactured semiconductor laser device and to improve the yield.

The preferred embodiments of the present invention will be described with reference to FIGS.
FIGS. 1-5 is typical sectional drawing for demonstrating each of the 1st process-5th process in the Example of the manufacturing method of the semiconductor laser element of this invention.

<Example>
Embodiments of the method for manufacturing a semiconductor laser device according to the present invention will be described below as first to fifth steps with reference to FIGS.

(First step) [See FIG. 1]
First, using a n-type off substrate 1 made of GaAs (gallium arsenide) having a surface 1a inclined by 12 ° in the [011] axis direction from the (100) plane, the n-type off substrate 1 is used as the first crystal growth. N-type buffer layer 2 made of GaInP (gallium indium phosphide), n-type cladding layer 3 made of AlGaInP (aluminum gallium indium phosphide), strained multiple quantum well active layer 4 made of GaInP, and AlGaInP. The first p-type cladding layer 5 is sequentially formed.
Here, the n-type may be referred to as a first conductivity type, and the p-type may be referred to as a second conductivity type.
In the second and subsequent steps to be described later, the n-type may be referred to as a first conductivity type and the p-type may be referred to as a second conductivity type.

In the example, MOCVD (Metal-Organic Chemical Vapor Deposition) method was used as the first crystal growth method, and the substrate temperature during crystal growth was set to 640 ° C.
In the examples, trimethylgallium, trimethylindium, trimethylaluminum, and phosphine were used as source gases for the first crystal growth, and the pressure during crystal growth was about 9000 Pa.

(Second step) [See FIG. 2]
A SiO ₂ (silicon oxide) layer 7 is formed on the surface 5a of the first p-type cladding layer 5 by sputtering.
Next, the SiO ₂ layer 7 is etched using a photolithographic method so that the first p-type cladding layer 5 underneath is exposed, so that the etched portion has an opening having a predetermined width 8a. A mask 8 to be 8a is formed.
This mask 8 serves as a crystal growth mask for the second crystal growth described later.

(Third step) [See FIG. 3]
As the second crystal growth, on the surface 5a of the first p-type cladding layer 5 exposed in the second step, the second p-type cladding layer 10 made of AlGaInP, the p-type intermediate layer 11 made of GaInP, and GaAs The p-type cap layer 12 is sequentially formed to form a p-type ridge 13 having a reverse mesa shape in which the cross-sectional shape is wider on the side opposite to the n-type off substrate 1 than on the n-type off substrate 1 side. .

In the example, the MOCVD method was used as the second crystal growth method, and the substrate temperature during crystal growth was 640 ° C.
In the examples, trimethylgallium, trimethylindium, trimethylaluminum, and phosphine were used as source gases for the second crystal growth, and the pressure during crystal growth was about 9000 Pa.

In the second crystal growth, the second p-type cladding layer 10, the p-type intermediate layer 11, and the p-type cap layer 12 are exposed on the SiO ₂ layer 7 without crystal growth. Crystals grow only on the surface 5 a of the layer 5.
The second p-type cladding layer 10 has a cross-sectional shape that conforms to the crystal orientation of the first p-type cladding layer 5 that is the lower layer, in other words, the crystal orientation of the surface 1a of the n-type off-substrate 1. Accordingly, in the initial stage of crystal growth, crystal growth is performed so that the width on the side opposite to the n-type off substrate 1 is wider than the width on the n-type off substrate 1 side, and thereafter the first p is formed. Crystal growth is performed so as to extend in a direction orthogonal to the surface of the mold cladding layer 5.
Since the p-type intermediate layer 11 and the p-type cap layer 12 are formed on the second p-type cladding layer 10, the cross-sectional shape of the formed p-type ridge 13 is the width on the n-type off substrate 1 side. In other words, the inverted mesa shape is wider on the side opposite to the n-type off substrate 1.

(4th process) [Refer FIG. 4]
After removing the SiO ₂ layer 7, an insulating film 15 made of SiO ₂ , SiN (silicon nitride) or the like is formed on the surface 5 a of the first p-type cladding layer 5 so as to cover the p-type ridge 13 by sputtering or the like. The film is formed using a known film formation method such as a vacuum evaporation method.
Thereafter, the insulating film 15 in a predetermined range on the p-type ridge 13 is removed, thereby forming an opening 15a in which the p-type ridge 13 is exposed.

(Fifth step) [Refer to FIG. 5]
A p-side electrode 17 that is electrically connected to the p-type ridge 13 through the opening 15a is formed on the insulating film 15, and a surface opposite to the crystal growth direction of the n-type off substrate 1 (in the case of a back surface). The n-side electrode 18 is formed on 1b.
The p-side electrode 17 and the n-side electrode 18 can be formed using a well-known film formation method such as sputtering or vacuum deposition.

  Through the first to fifth steps described above, the semiconductor laser device 20 having an air ridge structure having an inverted mesa ridge having a cross-sectional shape wider than the substrate side on the side opposite to the substrate is obtained.

According to the method for manufacturing a semiconductor laser device of the present invention, the thickness of the SiO ₂ layer 7 that becomes the mask 8 (see FIG. 2) for the second crystal growth is reduced as compared with the conventional method of forming a ridge by etching. The total thickness of the second p-type cladding layer 10, the p-type intermediate layer 11, and the cap layer 12 can be made thinner.
Therefore, since this SiO ₂ layer 7 can be etched with high etching accuracy, the opening 8a of the formed mask 8 is formed with a width W8a with high dimensional accuracy.
When the p-type ridge 13 is formed in the opening 8a, the width W13 of the p-type ridge 13 and its variation, that is, the width W13 of the portion connected to the first p-type cladding layer 5 in the p-type ridge 13 and Since the variation is determined by the width W8a of the opening 8a of the SiO ₂ layer 7 and the variation, the dimensional accuracy of the width W13 of the p-type ridge 13 can be increased.
Further, in order to suppress the occurrence of kinks when the semiconductor laser element is oscillated, the width and the dimensional accuracy of the width of the p-type ridge 13, particularly the width W 13 of the portion connected to the first p-type cladding layer 5. is important.
Therefore, according to the method for manufacturing a semiconductor laser device of the present invention, the width of the ridge can be formed with high dimensional accuracy without forming an etching stop layer. Variation in kink level can be suppressed.

Further, according to the method for manufacturing a semiconductor laser device of the present invention, the ridge can be formed in an inverted mesa shape in which the cross-sectional shape is wider on the side opposite to the substrate than the width on the substrate side. A wide opening can be formed on the side ridge surface.
Accordingly, since the connection area between the ridge and the electrode is widened, the connection resistance between the ridge and the electrode can be reduced. Therefore, even when the width of the ridge is narrow, the element resistance value and element resistance of the manufactured semiconductor laser device are reduced. The variation in value can be made smaller than before.

  The embodiment of the present invention is not limited to the configuration and procedure described above, and it goes without saying that modifications may be made without departing from the scope of the present invention.

For example, in the embodiment, the n-type off-substrate 1 having the surface 1a inclined by 12 ° in the [011] axial direction from the (100) plane is used, but the present invention is not limited to this, and the p-type ridge to be formed If the cross-sectional shape of 13 is an inverted mesa shape in which the width on the side opposite to the substrate is wider than the width on the substrate side, the surface 1a of the n-type off substrate 1 can be a surface having an arbitrary crystal orientation.
For example, the surface 1a of the n-type off substrate 1 may be a surface inclined by 15 ° in addition to the above-described orientation plane.

Further, in the embodiment uses an SiO ₂ layer 7 in order to form a mask 8 made of a crystal growth mask when performing a second crystal growth is not limited to this, the SiO ₂ layer 7 Instead of this, a SiN (silicon nitride) layer may be formed and used as the mask 8.

  In the embodiment, the first conductivity type is n-type and the second conductivity type is p-type. However, the present invention is not limited to this, and the first conductivity type is p-type and the second conductivity type is n-type. Also good.

It is typical sectional drawing for demonstrating the 1st process in the Example of the manufacturing method of the semiconductor laser element of this invention. It is typical sectional drawing for demonstrating the 2nd process in the Example of the manufacturing method of the semiconductor laser element of this invention. It is typical sectional drawing for demonstrating the 3rd process in the Example of the manufacturing method of the semiconductor laser element of this invention. It is typical sectional drawing for demonstrating the 4th process in the Example of the manufacturing method of the semiconductor laser element of this invention. It is typical sectional drawing for demonstrating the 5th process in the Example of the manufacturing method of the semiconductor laser element of this invention.

Explanation of symbols

1 n-type off substrate, 1a, 5a surface, 1b surface (back surface), 2 n-type buffer layer, 3 n-type cladding layer, 4 active layer, 5 first p-type cladding layer, 7 SiO ₂ layer, 8 mask, 8a, 15a opening, 10 second p-type cladding layer, 11 p-type intermediate layer, 12 p-type cap layer, 13 p-type ridge, 15 insulating film, 17 p-side electrode, 18 n-side electrode, 20 semiconductor laser device , W8a, W13 width

Claims (2)

A method for manufacturing a semiconductor laser device, comprising:
A first conductive type cladding layer, an active layer, and a second conductive type cladding layer are sequentially stacked on the one surface of the first conductivity type semiconductor substrate having one surface having a predetermined crystal orientation. Crystal growth process of
A mask formation step of forming a crystal growth mask having a first opening having a predetermined width on the second conductivity type cladding layer after the first crystal growth step;
After the mask formation step, a second conductivity type ridge that is connected to the second conductivity type cladding layer on the first opening and has a cross-sectional shape that is a reverse mesa shape with respect to the stacking direction is obtained by crystal growth. A second crystal growth step to be formed;
A method for manufacturing a semiconductor laser device having An insulating film forming step of forming an insulating film having a second opening that covers the ridge and exposes the ridge on the ridge after the second crystal growth step;
After the insulating film forming step, the first electrode connected to the ridge is formed on the second opening, and the second electrode is formed on the surface opposite to the stacking direction of the semiconductor substrate. Forming process;
The method of manufacturing a semiconductor laser device according to claim 1, wherein:

Images