JPH0786698A - Etching method and manufacture of semiconductor laser based on the etching method - Google Patents

Abstract

PURPOSE:To manufacture a semiconductor laser which is low in a threshold current and stable in horizontal mode by holding back the expansion of the bottom of a ridge. CONSTITUTION:A n-type clad layer 106, an active layer 107, a first p-type clad layer 108, an etching stop layer 105 and a second p-type clad layer 104 makes an epitaxial growth one after another on an n-type semiconductor substrate 101. A ridge is formed with a mask 102 formed in the shape of stripes. During the formation of the ridge, the substrate is etched with a diffusion rate controllable etching solution on the way to the second p-type clad layer 104 as a first stage. As a second stage, the etching stop layer 105 is etched with a selectable etching solution. This construction makes it possible to inhibit the expansion of the bottom of the ridge, and to fix the depth of the etching and manufacture a semiconductor laser which is lower in a threshold current and stable in horizontal mode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for etching a semiconductor layer and a method for manufacturing a semiconductor laser using the same.

[0002]

2. Description of the Related Art The emission wavelength of an AlGaInP / GaAs red light emitting device is in the 6 μm band. From this, Al
The GaInP / GaAs-based red light emitting device is being actively developed as a light source for a bar code reader, a laser beam printer, an optical disk, a display and the like. Conventionally, this type of light emitting device has been used in the Institute of Electronics, Information and Communication Engineers OQE91-24
The configuration as shown in (1) was common. A first conventional example of a conventional method for manufacturing a red semiconductor laser will be described below.

A manufacturing process of a conventional red semiconductor laser will be described with reference to FIG. First, the n-type cladding layer 802 made of AlGaInP and GaI are formed on the n-type semiconductor substrate 801 made of GaAs by using the metal organic chemical vapor deposition method.
nP bulk or quantum well active layer 803, Al
First p-type cladding layer 804 made of GaInP, Ga
An etch stop layer 805 consisting of an InP single quantum well,
A second p-type cladding layer 806 made of AlGaInP is sequentially epitaxially grown. Although a resistance reduction layer made of GaInP and a cap layer made of GaAs are often added, the description thereof is omitted here.

Next, after depositing a silicon oxide film on the second p-type cladding layer 806, the mask 807 is formed by patterning the silicon oxide film into stripes (FIG. 8A). Next, the ridge 808 is formed by etching the second p-type cladding layer 806 with a sulfuric acid-based etching solution (FIG. 8B). At this time, the etching stop layer 805 takes advantage of the fact that the etching rate with respect to the sulfuric acid-based etching solution is about one-tenth that of the second p-type cladding layer 806.
Then, the n-type buried layer 80 is formed using the mask 807.
9 is selectively grown (FIG. 8C). After removing the mask 807, a p-type buried layer 810 is grown. Finally, the first electrode 811 made of Au-Ge / Ni, Cr
A second electrode 812 made of / Au / Pt / Au is formed (FIG. 8D).

In the structure obtained as a result of the above steps, the lower portion of the active layer 803 where the ridge 808 is not formed is lower than the lower portion of the active layer 803 where the ridge 808 is formed. Since it becomes low, the transverse mode is confined.

Next, a second conventional example will be described. A
When the wavelength is further shortened by using the 1GaInP / GaAs system, the ordering peculiar to this system becomes a problem. When ordering occurs, the energy gap becomes small and it becomes difficult to shorten the wavelength. However, the surface is (10
Only a few degrees from the (100) plane, not the 0) plane [011]
When a substrate inclined in the direction is used, ordering can be prevented. The upper surface (main surface) of a normal (100) substrate, that is, the (100) surface is a surface including a straight line parallel to the [011] direction. Since the [0-1-1] direction is opposite to the [011] direction, [0-1-
A straight line parallel to the [1] direction is also included in the (100) plane. In the present specification, “a substrate tilted from the (100) plane in the [011] direction” means that the normal line of the upper surface of the substrate is not oriented in the [100] direction and the normal line is from the [100] direction. [01
It means a substrate which is rotated by a predetermined angle in the [1] direction or the [0-1-1] direction. In addition, the above normal and [10
The angle formed with the [0] direction is called an "off angle",
A substrate whose off-angle is not 0 degree is referred to as an “inclined substrate”.

When such a substrate is used, the emission wavelength can be shortened and a higher carrier concentration can be realized. As a result, a red semiconductor laser with a wavelength of 640 nm can be manufactured. Each manufacturing process of the second conventional example is the same as each manufacturing process of the first conventional example except that the substrate used is different.

[0008]

Problems to be Solved by the Invention FIGS. 9 (a) and 9 (b)
FIG. 4 is a detailed view of a ridge portion of a red semiconductor laser manufactured by a conventional method. 9A shows a case where a normal n-type (100) substrate 901 is used, and FIG. 9B shows an n-type tilted substrate 90.
The case where 9 is used is shown. 9 (a) and 9 (b)
Respectively on the n-type semiconductor substrate 901 or 909,
An n-type clad layer 903 made of AlGaInP, an active layer 904, a first p-type clad layer 905 made of AlGaInP, an etching stop layer 906 made of a GaInP single quantum well, and a second p-type clad layer 907 made of AlGaInP are formed. After that, the second p-type cladding layer 907 is etched using the mask 908 or 906.

As shown in FIG. 9A, a ridge 90 is formed.
If a sulfuric acid-based etching solution is used when forming
02 bottom widens, resulting in an increase in threshold current,
Transverse mode becomes unstable. In particular, when a tilted substrate is used, as shown in FIG. 9B, the side surface on the right side of the bottom of the ridge 910 in the figure becomes gentle, so that the ridge 910 is not inclined.
The bottom of the figure spreads out to the right in the figure. As a result, ridge 9
Asymmetry occurs in 10 and transverse mode instability is further increased. In addition, when the normal line of the substrate surface is rotating in the [0-1-1] direction, the bottom of the ridge 910 is [0-1-
1] direction, but when the normal to the substrate surface is rotating in the [011] direction, it spreads in the [011] direction.

Another problem of the prior art is that the etching stop layer 906 is thin and thus the etching stop time is short, and it is difficult to judge the end of etching. The etching stop layer 906 is made of GaInP having a composition sufficiently different from that of the second p-clad layer 907 in order to secure selectivity. In this case, the quantum well layer is required to be thinner than the active layer so as not to absorb light emission. Therefore, the actual etching stop time becomes very short even if the material selection ratio is sufficient. Also,
Since the change in interference color when the etching stopper layer is exposed is very small, it is difficult to judge the end of etching.

The present invention has been made to solve the above problems, and an object thereof is to provide an etching method and a semiconductor laser manufacturing method in which the spread of the ridge bottom is reduced.

Another object of the present invention is to provide an etching method and a semiconductor laser manufacturing method in which the symmetry of the bottom of the ridge is maintained when an inclined substrate is used.

Still another object of the present invention is to provide an etching method and a semiconductor laser manufacturing method in which the etching stop time is sufficiently long and the judgment of the etching stop is easy.

[0014]

According to the etching method of the present invention, a multilayer structure including a first semiconductor layer and a second semiconductor layer in contact with the upper surface of the first semiconductor layer is epitaxially grown on a semiconductor substrate. A step of forming a mask on the multilayer structure, a first etching step of selectively etching a part of the second semiconductor layer using a diffusion-controlled first etching solution, A second etching solution that preferentially etches the second semiconductor layer over the first semiconductor layer is used to etch the second semiconductor layer up to the upper surface of the first semiconductor layer. 2 etching steps are included, whereby the above object is achieved.

The surface of the semiconductor substrate is (100)
A tilted substrate tilted from the plane may be used.

A method of manufacturing a semiconductor laser according to the present invention is a first method.
A step of epitaxially growing a conductivity type clad layer, an active layer, a first second conductivity type clad layer, an etching stop layer, and a second second conductivity type clad layer in this order on a semiconductor substrate; A step of forming a mask on the second conductivity type clad layer, and a first etching step of selectively etching a part of the second second conductivity type clad layer using a diffusion-controlled first etching solution And using the second etching solution that preferentially etches the second second-conductivity-type cladding layer over the etching stopper layer,
A second etching step of etching the conductive clad layer to reach the upper surface of the etching stop layer is included, whereby the above object is achieved.

The semiconductor substrate has a surface of (100)
A tilted substrate tilted in the [011] direction from the plane may be used.

In one embodiment, the stripe-shaped first mask along the direction perpendicular to the [011] direction is used as the second mask.
On the second conductive type clad layer, and [01]
A second side covering the side of the [1] direction or one side of the [0-1-1] direction
Forming a mask on the second second-conductivity-type cladding layer, and the first etching step uses the first and second masks to remove the second mask. In the second etching step, the second mask is removed and then the second mask is used to selectively etch a part of the second conductivity type cladding layer. This is a step of etching the conductive clad layer to the surface of the etching stopper layer.

In one embodiment, in at least one of the first etching step and the second etching step, the first etching step is performed in a direction parallel to the surface of the semiconductor substrate.
The step of forming a flow of the etching liquid or the second etching liquid is included.

In one embodiment, in at least one of the first etching step and the second etching step, the semiconductor substrate is irradiated with light from an oblique direction to form a shadowed portion by the mask. Including steps.

In one embodiment, a step of growing a multiple quantum well layer as the etching stop layer and a step of determining an etching end point based on a change in interference color of the etching stop layer are included.

[0022]

In the etching method according to the present invention, a part of the second semiconductor layer which is in contact with the upper surface of the first semiconductor layer is selectively etched by using the diffusion-controlled first etching solution. Since the first etchant is diffusion-controlled, a relatively deeply etched recess is formed in the etched portion of the second semiconductor layer. The depression is formed in a region adjacent to the non-etched portion of the second semiconductor layer. A relatively large amount of the etchant of the first etching liquid is supplied to the region adjacent to the non-etched portion of the second semiconductor layer. This is because the etchant of the first etching liquid is not consumed in the non-etched portion of the second semiconductor layer. When the surface reaction rate-controlling etching solution is used, the above-mentioned depression is not formed.

After forming a recess in a region adjacent to the unetched portion of the second semiconductor layer, a second etching is performed on the second semiconductor layer. This second etching is performed using a second etching solution that preferentially etches the second semiconductor layer over the first semiconductor layer. The preferential etching of the second semiconductor layer over the first semiconductor layer means that the etching selection ratio of the second semiconductor layer to the first semiconductor layer is large. As a result of the second etching, a portion in which the spread of the bottom portion is suppressed is formed from the second semiconductor layer and is left on the first semiconductor layer.

A method of manufacturing a semiconductor laser according to the present invention is
After epitaxially growing the first conductivity type clad layer, the active layer, the first second conductivity type clad layer, the etching stopper layer, and the second second conductivity type clad layer in this order on the semiconductor substrate, the second conductivity type clad layer is formed. A mask is formed on the second conductivity type clad layer. Then, the above etching method is performed. As a result, a second second-conductivity-type cladding layer whose shape is defined by a mask is obtained on the etching stopper layer. Due to the same action as that described above, the lateral spread of the bottom of the second second-conductivity-type cladding layer is suppressed. The second second-conductivity-type cladding layer patterned by the etching and the unetched first second-conductivity-type cladding layer constitute a second-conductivity-type cladding layer having a ridge portion. Since the bottom of the ridge does not spread laterally, the problems of the prior art resulting from the lateral spread of the bottom of the ridge are solved. Since the bottom of the ridge does not spread laterally, the ridge symmetry is hardly broken even when an inclined substrate is used.

By forming a stripe-shaped first mask along the direction perpendicular to the [011] direction on the second second-conductivity-type cladding layer, a ridge along the direction perpendicular to the [011] direction is formed. A second conductivity type cladding layer having the same is obtained. First
Forming a second mask covering one of the two long sides located on the [011] direction side of the mask on the second second-conductivity-type cladding layer, and then using the first and second masks. By selectively etching a part of the second second-conductivity-type cladding layer, a recess can be selectively formed on the [0-1-1] direction side as viewed from the second mask. In this way, the etching amount of the side wall where the ridge has a gentler slope can be made larger than the etching amount of the other side, and the asymmetry of the ridge can be suppressed.

When a flow of the etching solution is created across the ridge, the etching solution is retained by the vortex generated by the ridge itself on the ridge side wall portion downstream of the flow, and fresh etching solution is always supplied upstream. This improves the symmetry of the ridge when the inclined substrate is used.

The etching rate can be reduced by irradiating light with a specific wavelength depending on the material and the etching solution. Thus, reducing the etching amount of only a specific portion on the substrate improves the symmetry of the ridge when the inclined substrate is used.

If a multiple quantum well structure is introduced into the etching stop layer, it is possible to easily judge the etching stop based on the change of the interference color due to the change of the composition and the refractive index in the vicinity of the surface due to the etching. According to the multiple quantum well structure, the total film thickness of the etching stopper layer can be increased.

[0029]

1 (a) and 1 (b) are sectional views showing a manufacturing process for forming a ridge of a red semiconductor laser according to the present invention. First, n on the n-type GaAs semiconductor substrate 101.
-Type (Al0.6Ga0.4) 0.5In0.5P (1 μm) n-type cladding layer 106, multiple quantum of Ga0.5In0.5P (100 angstrom) / (Al0.6Ga0.4) In0.5P (40 angstrom) Active layer 107 consisting of wells, p-type (Al0.6G
a0.4) In0.5P (0.25 μm) first p-type cladding layer 108, p-type Ga0.5In0.5P (60 Å)
Etching stop layer 105 made of p-type (Al0.6Ga
0.4) A second p-type cladding layer 104 made of In0.5P (0.9 μm) is sequentially epitaxially grown.

Then, a stripe-shaped mask 102 is formed. This is made of, for example, a silicon oxide film, but a silicon nitride film may be used. Then, etching is performed to form a ridge 903 using the mask 102. At this time, as a first step, the second p-type cladding layer 104 is etched halfway by using the first diffusion-controlling etching liquid whose diffusion phenomenon controls the reaction when the etching reaction occurs. As the first etching liquid, a liquid in which acetic acid, hydrochloric acid, and hydrogen peroxide were mixed at a ratio of 36: 3: 1 was used. Alternatively, as the first etching liquid, a liquid obtained by mixing bromine (Br) and methanol (CH ₃ OH) at a ratio of 1: 100 may be used. Here, the thickness of the second p-type cladding layer 4 was 0.9 μm, and etching was performed by about 0.5 μm. Next, as a second step, AlGaInP and G
Etching is carried out using a second etching solution composed of sulfuric acid having selectivity for aInP. This etching ends when it reaches the etching stop layer 105.

FIG. 2 shows the relationship between the shape of the ridge obtained by the above method and the etching amount of the first etching liquid. In FIG. 2, the vertical axis represents the degree of inclination of the side wall of the ridge 201, and h represents the height of the ridge 201 as shown in the inset. Also, c is ridge 2
01 represents the spread width at the bottom. It should be noted that this ridge shape is etched to the etching stop layer in FIG.
The state of (b) is shown. The horizontal axis represents the etching amount of the first step using the first etching solution, and for example, in the case of a GaAs semiconductor substrate (off angle 0 °),
When the etching amount in the step is 0 μm, that is, when all etching is performed using the second etching solution, c / h is
It becomes 1.0. On the other hand, the etching amount of the first step is 0.5
When it is set to μm, c / h is about 0.7. This indicates that just the (111) plane appears on the surface of the side wall. On the other hand, when a semiconductor tilted substrate whose surface is tilted in the [011] direction from the (100) plane (off angle 10 °) is used, the degree of tilt of the side surface of the ridge 902 in the [0-1-1] direction is shown in the figure. As shown, c / h takes a large value of 2.0 when the first-stage etching is not performed. On the other hand, when the first-stage etching is performed by 0.5 μm, c /
The h was 1.0, and the symmetry was considerably improved. These effects are obtained because the depression at the bottom of the ridge 201 is suppressed from expanding due to the use of the diffusion-controlling etchant. The characteristics improved as a result will be described below.

FIG. 3 is a current vs. light output characteristic diagram of the red semiconductor lasers of the conventional example and the example when the GaAs semiconductor tilted substrate is used. Thus, the threshold current was reduced. Traditionally, the kink that was caused by the instability of the transverse mode,
The transverse mode was stable and was not detected until instantaneous optical damage (COD) occurred. Needless to say, the conductivity type may be reversed in polarity.

Other characteristics of the example of the present invention and the conventional example were evaluated. The characteristics evaluated are the temperature dependence of the far field pattern (FFP), the substrate off angle dependence of the photoluminescence (PL) intensity, and the device life of the semiconductor laser.

The evaluation results will be described below with reference to the drawings. FIG. 10A shows a conventional FFP, and FIG.
0 (b) indicates the FFP of this embodiment. In the figure, the solid line shows the light intensity distribution along the direction perpendicular to the active layer, and the broken line shows the light intensity distribution along the direction parallel to the active layer. The FFP measurement was performed in the range of 20 to 50 ° C. In the figure, the FFP of the conventional example is shown by a relatively thick curve. This means that the thicker curve indicates that the FFP changes depending on the measured temperature.

FIG. 11 shows the full width at half maximum of FFP FWHM (Fu
ll Width at Half Maximum). As can be seen from the figure, the FFP of the semiconductor laser produced by using the etching method according to the present invention has a smaller temperature dependence than the conventional example. The reason that the conventional example has an FFP that greatly changes depending on the temperature is that as the temperature rises, the current spreads laterally in the asymmetric stripe ridge and the current flows. According to the etching method of the present invention, since the shape of the stripe-shaped ridge portion is adjusted, the problem due to the spread of the current in the ridge hardly occurs.

FIG. 12 shows the photoluminescence (PL) of a semiconductor laser whose active layer has a quantum well structure.
It shows how the intensity changes depending on the substrate off-angle. In FIG. 6, symbols “○”, “△”,
"□" and "▽" indicate that the thickness of the well layer included in the active layer is 1 nm, 2.5 nm, 5 nm, and 10 n, respectively.
The data in the case of m is shown. As can be seen from FIG. 12, the larger the substrate off angle, the stronger the PL intensity. This means that the band cap of the active layer increases as the substrate off angle increases. In order to realize a short wavelength semiconductor laser, the substrate off angle is preferably 8 degrees or more. According to the conventional etching method,
If a substrate having an off angle of 8 degrees or more is used, a striped ridge with high symmetry cannot be obtained, and it is difficult to shorten the oscillation wavelength.

FIG. 13 is a graph showing the life of the device.
FIG. 13 shows how the drive current (mW) required to obtain a light output of 3 mW changed according to the operating time (operating temperature 50 ° C.). As can be seen from the figure, the drive current was stable over the entire operating time range tested.

In the above embodiment, it can be mentioned that the side wall where the ridge skirt does not spread is also etched too much. As a result, there is a limit to the improvement of symmetry when using a tilted substrate. Some new methods were investigated to further improve the symmetry. One is to change the amount of etching on both sides of the ridge using two masks. Etching is performed in advance on the side wall with a gentle slope so that more etching is performed than on the side wall with a steep slope.

4A to 4D are sectional views of the manufacturing process. On the n-type GaAs semiconductor substrate 401, the n-type clad layer 405, the active layer 406, and the first p-type clad layer 40.
7, etching stop layer 408, second p-type cladding layer 4
After epitaxially growing 09, a first mask 402 made of a stripe-shaped silicon oxide film along the [0-11] direction is formed.

Then, [011] of the first mask 402.
A second mask 403 made of a resist that covers the side on the direction side (left side in the drawing) is formed (FIG. 4A). Here, the first-stage etching is performed to etch only the ridge sidewall on the [0-1-1] direction side (right side in the figure) (FIG. 4B). Depending on the inclination direction, only the side wall of the ridge on the [011] direction side is etched by the first-stage etching. After that, the second mask 403 is removed (FIG. 4C), and finally the second-stage etching is performed (FIG. 4D). As described above, the symmetry is improved by pre-etching only the side wall of the ridge, which is essentially asymmetric due to the inclination of the substrate, on the side with a gentle inclination (right side in the figure). You can

As a second method for further improving the symmetry, a method using the flow of the etching solution was examined.
In the case of a diffusion-controlled etching solution, the amount of unreacted etching species supplied to the portion to be etched greatly affects the etching rate. The symmetry can be improved by forming a flow in the etching solution and reducing the etching rate of the side wall portion having a steep slope. FIG. 5A is a schematic view of the method for carrying out the method, and FIG. 5B is a sectional view at the time of etching. This is an etching method that controls the etching shape by creating a flow parallel to the substrate surface during etching. The beaker 501 is filled with the etching solution and the stirrer 502 creates a flow 503 of the etching solution. A substrate 504 on which a stripe-shaped mask is formed is fixed to a substrate support 505 as shown in the figure, and set along the side surface of the beaker 501. At this time, the stripe direction is set to be perpendicular to the flow 503 of the etching solution.
As shown in FIG. 5B, the flow 507 of the etching solution on the surface of the substrate 506 forms streamlines as shown with respect to the mask 508 and the ridge 509 formed by etching. As a result, immediately after the ridge 509, the vortex 10
Occurs. In this portion, the supply of unreacted new etching solution is reduced and the etching rate is reduced. If this phenomenon is utilized and setting is made so that the vortex 511 is generated on the side surface where the inclination becomes steep, the etching rate at that portion is reduced and the symmetry can be improved.

As a third method for improving symmetry,
There is a method that utilizes the decrease in etching rate due to irradiation with light. FIG. 6 is a sectional view showing the method. When we etch AlGaInP crystals with sulfuric acid,
It has been confirmed that when the light having a wavelength of about 600 nm is irradiated, the etching rate of the irradiated portion is reduced to about 1/2. By utilizing this phenomenon, etching for controlling the shape can be performed. Striped mask 601
Is formed on the substrate 602, and the substrate 60 is exposed to the etching solution.
Dip 2 Then, as shown in FIG. 55, the substrate 602 is irradiated with light 603 from an oblique direction. With such a structure, one ridge 6 is formed as the etching progresses.
A portion 605 which is a shadow for the light 603 only on the side surface of 04.
Is formed. The shadowed portion 605 has a higher etching rate than other substrate surfaces. As a result, ridge 6
It is possible to control the shape of 04. For example, when an inclined substrate as shown in the first embodiment of the present invention is used,
If the side surface having a gentle inclination is arranged so as to form a shadow, the etching of that portion is performed faster than other portions, and the symmetry of the ridge is improved.

By the above method, the symmetry of the ridge formed on the tilted substrate could be improved. However, since the above three methods all change the etching rate on both sides of the ridge, the time to reach the etching stop layer is different. As a result, if the etching stop time in the etching stop layer is short, there is a possibility that the lower layer is etched through the etching stop layer. In order to solve this point, the introduction of multiple quantum well layers was examined.

FIG. 7 shows the structure of the etching stop layer according to the second embodiment of the present invention. FIG. 7A shows a conventional etching stop layer and the layer structure above and below it,
GaInP single quantum well layer 70 as an etching stop layer
1 is sandwiched between AlGaInP cladding layers 702 and 703. Here, GaInP is used to perform selective etching by utilizing the difference in etching rate due to the difference in composition. However, since this material absorbs light emitted from the active layer when it is a bulk, it must be made into a quantum well and the energy gap must be increased by the quantum effect to suppress the absorption. as a result,
The film thickness becomes several tens of angstroms and the etching stop time becomes short. Further, it is difficult to judge that the etching reaches the etching stop layer because the change of the interference color on the surface is poor.

In the embodiment of the present invention, as shown in FIG. 7B, the etching stop layer is a GaInP multiple quantum well layer 7.
04. The GaInP multiple quantum well layer 704 is made of AlG.
It is composed of four aInP barrier layers (40 Å) and five GaInP well layers (60 Å). As a result, the etching stop time can be extended without absorbing the light emitted from the active layer. As mentioned earlier, this is very effective for etching tilted substrates.
In addition, since the structure is a multiple quantum well layer structure, the interference color changes every time etching reaches a layer having a different refractive index, and a sharper change occurs than in the case of a single quantum well layer. As a result, it becomes easy to determine the end of etching.

[0046]

According to the etching method of the present invention, the first etching using the diffusion-controlled etching solution and the second etching using the etching solution capable of selective etching are combined to spread the bottom of the ridge. Can be suppressed. The effect is large when the semiconductor inclined substrate is used, and the symmetry of the cross section of the bottom of the ridge is maintained. If the stripe ridge of the semiconductor laser is formed by using this etching method, the reduction of the threshold current and the stabilization of the transverse mode can be achieved.

Further, by using a two-step etching process using two masks, a ridge having better symmetry can be formed on the inclined substrate. If the etching liquid flows perpendicularly to the mask formed in a stripe shape, a vortex is formed downstream of the ridge and the shape of the ridge can be controlled. By irradiating the substrate with light from an oblique direction, the etching rate can be controlled and the shape of the ridge can be controlled. By introducing the multiple quantum well layer in the etching stop layer, the etching stop time can be lengthened. Furthermore, it is possible to easily determine the end of etching by changing the interference color.

[Brief description of drawings]

FIG. 1 is a sectional view showing a manufacturing process in an embodiment of the present invention.

FIG. 2 is a characteristic diagram of etching depth and shape in an example of the present invention.

FIG. 3 is a current versus light output characteristic diagram of the light emitting device in the embodiment of the present invention.

FIG. 4 is a cross-sectional view showing a manufacturing process using two masks in an example of the present invention.

FIG. 5A is a schematic view of an etching apparatus using a flow in an embodiment of the present invention, and FIG. 5B is a cross-sectional view illustrating etching for forming a ridge.

FIG. 6 is a cross-sectional view showing a manufacturing method using light in an example of the present invention.

FIG. 7 is a structural diagram of an etching stop layer according to an embodiment of the present invention.

FIG. 8 is a sectional view showing a conventional manufacturing process.

FIG. 9 is a sectional view showing the shape of a conventional light emitting device.

10A is a light intensity distribution diagram along a direction perpendicular to an active layer in a conventional FFP, and FIG. 10B is a light intensity distribution along a direction perpendicular to an active layer in the FFP of the present embodiment. Figure

FIG. 11 is a full width at half maximum FWHM (Full Width at) of FFP.
Figure showing temperature dependence of Half Maximum)

FIG. 12 is a diagram showing how the photoluminescence (PL) intensity changes depending on the substrate off angle in a semiconductor laser whose active layer has a quantum well structure.

FIG. 13 is a diagram showing how the drive current (mW) required to obtain an optical output of 3 mW changed according to the operation time.

[Explanation of symbols]

 101 n-type semiconductor substrate 101 102 mask 102 103 ridge 103 104 second p-type cladding layer 105 etching stop layer 201 ridge 401 n-type semiconductor substrate 402 first mask 403 second mask 404 ridge 501 beaker 502 stirrer 503 etching solution Flow 504 Substrate 505 Substrate support 506 Substrate 507 Flow of etching liquid 508 Mask 509 Ridge 510 Vortex 601 Mask 602 Substrate 603 Light 604 Ridge 605 Shadow part 701 GaInP single quantum well layer 702 AlGaInP clad layer In703 Pd layer In703 GaInP multiple quantum well layer 801 n-type semiconductor substrate 802 n-type clad layer 803 active layer 804 first p-type clad layer 805 etching stop layer 80 The second p-type cladding layer 807 mask 808 ridge 809 n-type buried layer 810 p-type buried layer 811 first electrode 812 second electrode 901 n-type semiconductor substrate 909 n-type semiconductor inclined substrate 910 asymmetric ridges

Claims (8)

[Claims] 1. A step of epitaxially growing a multilayer structure including a first semiconductor layer and a second semiconductor layer in contact with an upper surface of the first semiconductor layer on a semiconductor substrate, and forming a mask on the multilayer structure. A first etching step of selectively etching a part of the second semiconductor layer using a diffusion-controlled first etching solution, and a second etching step of the second semiconductor layer rather than the first semiconductor layer. A second etching step of etching the second semiconductor layer to reach the upper surface of the first semiconductor layer by using a second etching liquid that preferentially etches the semiconductor layer. 2. The semiconductor substrate has a surface of (100)
The etching method according to claim 1, wherein an inclined substrate inclined from the surface is used. 3. A step of epitaxially growing a first conductivity type clad layer, an active layer, a first second conductivity type clad layer, an etching stop layer, and a second second conductivity type clad layer in this order on a semiconductor substrate. And a step of forming a mask on the second second-conductivity-type cladding layer, and selectively using a diffusion-controlled first etching solution to selectively remove a part of the second second-conductivity-type cladding layer. And a second etching solution that preferentially etches the second second-conductivity-type cladding layer over the etching-stopping layer, and the second second-conductivity-type cladding layer. And a second etching step of etching to reach the upper surface of the etching stop layer. 4. The semiconductor substrate has a surface of (100).
The method of manufacturing a semiconductor laser according to claim 3, wherein a tilted substrate tilted in the [011] direction from the plane is used. 5. A step of forming a stripe-shaped first mask along a direction perpendicular to the [011] direction on the second second-conductivity-type cladding layer, and two steps of the first mask. A second mask that covers one of the long sides in the [011] direction or in the [0-1-1] direction is
And a step of forming it on the second second-conductivity-type cladding layer, wherein the first etching step uses the first and second masks to form the second second-conductivity-type cladding layer. A step of selectively etching a part of the layer, wherein in the second etching step, after removing the second mask, the second mask of the second conductivity type is formed using the first mask. The method of manufacturing a semiconductor laser according to claim 4, which is a step of etching the substrate to the surface of the etching stop layer. 6. A step of forming a flow of the first etching solution or the second etching solution in a direction parallel to a surface of the semiconductor substrate in at least one of the first etching step and the second etching step. The etching method according to claim 1. 7. A step of irradiating the semiconductor substrate with light from an oblique direction to form a shadowed portion by the mask in at least one of the first etching step and the second etching step. The etching method according to claim 1. 8. The method according to claim 1, further comprising: a step of growing a multi-quantum well layer as the etching stop layer; and a step of determining an etching end point based on a change in interference color of the etching stop layer. Manufacturing method of semiconductor laser.