JPH0277184A - Manufacture of semiconductor laser - Google Patents

Abstract

PURPOSE:To obviate thermal transformation of a quantum well of a mesa stripe and leakage of current at an unrequired P-N junction during diffusion of Si by reusing a mask which has been used for formation of the mesa stripe as a mask for lift-off of an Si film. CONSTITUTION:After a mesa stripe 9 is formed by etching, Si is diffused into the regions other than the mesa stripe 9 so that an Si layer 10 is formed on an active layer 4 and a quantum well is made disordered. Since the depth to which Si is to be diffused is decreased by the etching, there is no need of performing high-temperature heat treatment for a long period of time. Further, since Si as an N-type dopant is used for the LD structure on the N-type substrate 1, the area of an unrequired P-N junction can be minimized. Si is vapor deposited with a photoresist mask 8, and then the stripe mask is dissolved to remove the Si deposited thereon. Accordingly, the diffused Si can be patterned in a self-aligned manner only on the bottom of the mesa stripe. ln this manner, a semiconductor laser can be manufactured with high yield.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a semiconductor laser used in the fields of optical information processing and optical communication.

(Prior Art) Semiconductor lasers are widely used in optical information processing, optical communications, etc. due to their small size and low power consumption.

Furthermore, in order to use this in a large number of integrated optical ICs, lower power consumption and higher yield than the current situation are required. Quantum well lasers have been actively researched in recent years to meet these demands.

An example of this type of report is a semiconductor laser described in Ablide Physics Letters, Vol. 47, page 1239. In this semiconductor laser, the quantum wells included in the active layer are disordered by Si diffusion to form a substantially buried structure. However, in this structure, the diffusion depth was as deep as 111 m or more in order to diffuse Si into the surface, and the Si diffusion conditions required a long period of 8.5 hours at a high temperature of 850°C. In such high-temperature and long-term heat treatment, S
It is expected that thermal alteration will occur even in the quantum well in the region where i-diffusion does not occur, resulting in deterioration of laser characteristics. Therefore, as a method often used to reduce the diffusion depth, there is, for example, a semiconductor laser described in Electronics Letters, Vol. 22, page 1117. In this semiconductor laser, mesa etching is performed to reduce the necessary diffusion depth of Zn diffusion. However, the Zn diffusion used in this semiconductor laser had the disadvantage that leakage current was large because unnecessary Pn junctions were formed over a large area on both sides of the Pn junction in the active layer of the mesa stripe. . To solve this problem, an n-type impurity such as Si may be diffused in a semiconductor laser with an n-type substrate. Therefore, it is sufficient to diffuse Si after performing mesa etching. However, when Si is diffused, it is not preferable to diffuse it over the entire surface as in the Electronics Letters document, as this will eliminate the current path. Therefore, it becomes necessary to diffuse only the bottom of the mesa stripe. Therefore, by performing mesa stripe patterning and Si diffusion patterning twice.
Although problem 1 can be solved, there is a problem in that the yield is low because it is necessary to align mesa stripes with a thickness of about 1 to 3 pm.

Therefore, the purpose of the present invention is to eliminate the thermal deformation of quantum wells in mesa stripes during Si diffusion as described above, and to eliminate unnecessary Pn
It is an object of the present invention to provide a method for manufacturing a semiconductor laser which has no junction leakage current and can be manufactured at a high yield.

(Means for Solving the Problems) In order to solve the above points, the semiconductor laser manufacturing method of the present invention includes a step of forming a first conductivity type cladding layer above a first conductivity type semiconductor substrate. , forming an active layer including a quantum well above the first conductivity type cladding layer;
a step of forming a second conductivity type cladding layer above the active layer; a step of forming a stripe mask for selective etching above the second conductivity type cladding layer; A step of forming a mesa stripe by etching a part of the conductivity type cladding layer, a step of vapor depositing a first conductivity type impurity after this etching step, and a step of dissolving only the stripe mask after this vapor deposition step. The method includes a step of removing the impurity on the stripe mask, and a step of spreading the impurity only to the bottom of the mesa stripe by heat treatment after this, and disordering the quantum wells included in the active layer in this region. It is characterized by

(Function) In the semiconductor laser of the present invention, mesa stripes are formed by etching, and then Si is diffused into regions other than the mesa stripes to disorder the quantum wells in the active layer.

In this manufacturing method, the depth to which Si must be diffused becomes shallow due to etching, so that the long-term high-temperature heat treatment as described above is not necessary. Furthermore, since n-type Dohant 81 is used for the LD structure on the n-type substrate, the area of unnecessary Pn junctions can be reduced.

Furthermore, regarding the step of performing the Si diffusion described above only at the bottom of the mesa stripe, in the manufacturing method of the present invention, Si is evaporated with the photoresist mask used to form the mesa stripe left in place, and then the stripe mask is dissolved. A method is used to remove Si. This method is usually called lift-off, but in the present invention, the photoresist mask used when forming mesa stripes is used as is for lift-off of Si, and patterning of Si diffusion is performed only at the bottom of mesa stripes using a self-line. I can do it. In this way, a semiconductor laser could be manufactured with high yield according to the present invention.

Furthermore, in order to enhance the effects of the present invention, it is effective to carry out the heat treatment step for Si diffusion without a protective film. In this case, compared to the case where a protective film is attached, there is no effect of stress due to differences in thermal expansion coefficients between the protective film and the semiconductor during heat treatment, so thermal alteration of the active layer, which becomes the light emitting layer, can be reduced. . Therefore, a crystal with high luminous efficiency and good characteristics of low threshold current were obtained.

(Example) Next, an example of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a method of manufacturing a semiconductor laser according to a first embodiment of the present invention. First, as shown in FIG. 1(a), an n-type cladding layer 2 (n-A
lxcGal-xcAs, 0.45≦0.85. thickness 0.8 to 3 pm), n-type guide layer 3 (n-AlxgGa
l-xgAs, Xg<XC, thickness 500~3000
(typically 1000 layers), active layer 4 (GaAs quantum well, thickness 50-200 layers), P-type guide layer 5 (P-Al
xgGal-xgAs, thickness 500-3000 (typically 1000), P-type cladding layer 6 (P-Alxc
A P-type cap layer 7 (P-GaAs, thickness 1000-5000 pm) is grown by crystal growth. Next, as shown in FIG. 1(b), a mask 8 made of photoresist is formed by photolithography, and mesa stripes 9 are formed using this as a mask. The width of the mesa stripe 9 is 1 to 10 μm, typically 2 to 3 pm, and the distance from the bottom of the mesa stripe 9 to the active layer 4 is approximately 1,000 to 5,000 people. As the etching method, in addition to conventional chemical etching using a mixture of phosphoric acid and hydrogen peroxide, selective etching using HF' or the like can be used.

For HF-based liquids, if the A1 composition of the P-type guide layer 5 is set to 0.35 or less, etching will be higher with A1 composition (>0.4).
) It is convenient to use this method because it is possible to etch only the P-type cladding layer 6 and automatically stop the etching when it reaches the P-type guide layer 5.

In this case, it is necessary to remove the P-type cap layer 7 by separate etching before using the HF-based etching solution. Further, dry etching such as reactive ion beam etching (RIBE) may be used as the etching method. In this case, since the etching depth can be precisely controlled, etching can be stopped at a targeted location, and since there is little side etching, it is easy to form a narrow stripe width (~111 m). Also, 5i02 was used as a mask instead of photoresist.
An insulating film such as the above may also be used. In this case, there is less side etching during mesa etching due to good adhesion.
It also has the advantage of good heat resistance against temperature increases during the next step of Si vapor deposition. Next, a particularly Si film 10 (thickness ~5000 layers) shown in FIG. 1(C) is formed. A vacuum evaporation method is preferable as a method for forming this, because as shown in the figure, the Si film 10 is formed with discontinuities. When using a method such as sputter evaporation that involves a large amount of wrapping around the side surface, the S on the side surface does not form as shown in the figure.
When the P-type electrode 14 was formed on the mesa stripe 9 to expand sales of Si in this area where the active layer 4 was deposited,
This is not preferable since the Pn junction made of the above may be short-circuited. Next, as shown in FIG. 1(d), the Si film 10 on the mesa stripe 9 is removed by lift-off. If the mask is a positive resist, lift-off can be easily performed using an organic material such as acetone. If the mask is made of an insulating film such as 5i02, it can be lifted off using buffered HF. Next, Si diffusion was performed. Si diffusion was performed at 850° CIHr in a hydrogen atmosphere. It was effective to cover the surface of the laser wafer with a dummy GaAs substrate in order to prevent As from being desorbed from the GaAs surface during Si diffusion. Also, instead of this, arsine (AsH3)
There is a method of mixing gas with hydrogen gas and flowing it, or putting As powder and a laser wafer together in a vacuum ampoule.
A method of heat treatment in an As atmosphere may also be used. In this process, heat treatment is performed without a protective film such as a SiN film, so there is no thermal stress caused by the difference in thermal expansion coefficient between the protective film and GaAs, and thermal metamorphosis of the active layer 4 of the mesa stripe 9 can be suppressed as much as possible. . Therefore, the light emitting efficiency of the active layer 40 in the mesa stripe 9 serving as the light emitting region was high, and an even lower Ith could be achieved than in the case of heat treatment with a protective film. In addition, the required diffusion depth by mesa etching is 2000~
Because the population was short (3,000 people), the diffusion time required only 850° CIHr, which was shorter than the 8.5 hours reported in previous literature. However, this condition needs to be changed depending on the depth of mesa etching and the A1 composition profile in the thickness direction. The diffusion depth is 2000~4 under this condition.
There were about 000 people. At this time, since the Si film 10 was present only at the bottom of the mesa stripe 9, the Si diffusion region 11 was formed only there, and the quantum wells of the active layer 4 in this region became disordered. Next, as shown in FIG. 1(e), the insulating film 13
form. Next, the insulating film 13 above the mesa stripe 9
Remove only. This is patterned using conventional photolithography techniques. Next, P-type electrode 14 and n
The mold electrode work 5 is formed and completed.

As explained above, in the manufacturing method of the present invention, the mask 8 used to form the mesa stripe 9 is used again as a mask for lift-off of the Si film 10, so that Si
Since the diffusion region 11 can be formed in a self-aligned manner only at the bottom of the mesa stripe 9, a semiconductor laser with a small leakage current and a low threshold current can be manufactured with a high yield.

Next, a second embodiment will be described using FIG. 2. This embodiment is completely the same as the first embodiment up to the step of vapor deposition of the Si film 10 shown in (a) to (C), so the explanation will be omitted.

In the diffusion of Si in (d), a protective film 12 such as a SiN film is used.
After formation, the process was carried out at 850° CIHr in a hydrogen atmosphere. In this case, there is a drawback that thermal stress is generated between the protective film 12 and the crystal, but it also has the advantage that desorption of As can be easily prevented. Next, after removing the 81 film 10 and the protective film 12 by dry etching or the like, an insulating film 13 is formed. Since the subsequent electrode steps are the same as those in the first embodiment, their explanation will be omitted. In the second embodiment described above, Si diffusion was carried out in a hydrogen atmosphere, but the diffusion is not limited to this, and may be carried out in other atmospheres such as a vacuum or a nitrogen atmosphere. -C may also be used.

In the embodiments described above, the active layer has a single-layer structure of a single quantum well, but the active layer is not limited to this, and may have a multi-layer structure such as a multi-quantum well structure. In addition, in this example, A1 is used as the material system.
Although the gaAs/GaAs system was used, it is not limited to this, and InG
It goes without saying that other materials such as aAsP/InP and InAlGaAs/InP are also applicable. Further, in the embodiments described above, Si was used as the element to be diffused, but impurities such as Zn, Mg, and Ga can also be used. However, when using P-type impurities such as Zn and Mg, it is necessary to form a laser structure on a P-type substrate. Also G
It has been recently discovered by the present inventors that a behaves as an n-type impurity when introduced into AlGaAs, so it is thought that it can be applied to a laser structure on an n-type semiconductor substrate.

Further, in the embodiments described above, the impurity Si was left without being removed in the first embodiment, but was removed by etching in the second embodiment. This problem is not so essential, and in either case, according to the manufacturing method of the present invention, a good semiconductor laser can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a process diagram showing a method for manufacturing a semiconductor laser according to a first embodiment of the present invention. FIG. 2 is a process diagram showing a method for manufacturing a semiconductor laser according to a second embodiment of the present invention. In the figure, 1... n-type GaAs substrate, 2... n-type cladding layer, 3... n-type guide layer, 4... active layer, 5...
・P-type guide layer, 6...P-type cladding layer, 7...P
Mold cap layer, 8... Mask, 9... Mesa stripe, 10... Si film, 11... Si diffusion region, 12
... protective film, 13 ... insulating film, 14 ... P-type electrode, 15 ... n-type electrode.

Claims (1)

[Claims] forming a first conductivity type cladding layer above the first conductivity type semiconductor substrate; forming an active layer including a quantum well above the first conductivity type cladding layer; and forming a first conductivity type cladding layer above the first conductivity type cladding layer; a step of forming a second conductivity type cladding layer; a step of forming a stripe mask for selective etching above the second conductivity type cladding layer; and a step of forming a part of the second conductivity type cladding layer using the stripe mask. a step of forming a mesa stripe by etching; a step of vapor depositing a material containing a first conductivity type impurity after this etching step; and a step of forming a mesa stripe on the stripe mask by dissolving only the stripe mask after this vapor deposition step. The method is characterized by comprising a step of removing the impurity, and then a step of diffusing the impurity only to the bottom of the mesa stripe by heat treatment to disorder the quantum wells included in the active layer in this region. A method of manufacturing a semiconductor laser.