JPH04100291A - Manufacture of optical semiconductor device - Google Patents

Abstract

PURPOSE:To obtain a manufacturing method excellent in yield wherein the number of times of growth is reduced and the controllability of wavelength is improved, by making a first epitaxial layer thicker than a second epitaxial layer, and making the height of the second epitaxial layer effectively equal to a part of the first epitaxial layer. CONSTITUTION:In the case of selective growth using selection mask, the growth speed changes remarkably. The growth speed in a first belt type region 1c can be controlled by changing the width and the covering area of a selection mask 3. By using the difference of the growth speed, the thickness ratio of a first quamtum well structure 6a to a second quantum well structure 6b can be changed. Thereby the ratio of the quantum level energy gap of the first quantum well structure 6a to the quantum level energy gap of the second quantum well structure 6b can be easily controlled. Further, since the surface height of the first region 1a is made lower than that of the second region 1b to begin with, the heights of the first quantum well structure 6a and the second quantum well structure 6b can be controlled to be equal, by epitaxially growing the first belt type region 1c and the second region 1b at the same time.

Description

[Detailed Description of the Invention] [Summary] A manufacturing method that is easy to manufacture, has a high yield, and improves wavelength controllability, relating to a method of manufacturing an optical semiconductor device, particularly a method of manufacturing a semiconductor laser with a monolithic external modulator. forming a first mask covering a predetermined region of a semiconductor substrate and etching the semiconductor substrate to form a first region whose surface is lower than the predetermined region; is a second region, and after forming a second mask on the first region to expose a strip-shaped first region connected to the second region, the strip-shaped first region and the first strip-shaped region are connected to the second region. a step of simultaneously performing epitaxial growth on two regions, forming a first epitaxial layer on the strip-shaped first region and a second epitaxial layer on the second region; The thickness is greater than the thickness of the second epitaxial layer, and the height of the second epitaxial layer is formed by a method of manufacturing an optical semiconductor device that is substantially equal to the height of a portion of the first epitaxial layer. do.

Further, the first epitaxial layer includes a first quantum well structure, the second epitaxial layer includes a second quantum well structure, and the first quantum well structure is used as a core of a light emitting part of the laser, A method for manufacturing an optical semiconductor device is constructed in which the second quantum well structure is used as a core of an optical modulation section.

[Industrial application field]

The present invention relates to a method of manufacturing an optical semiconductor device, and more particularly to a method of manufacturing a monolithic semiconductor laser with an external modulator.

Laser devices with less wavelength chirping are required as future optical communication devices for ultra-high-speed transmission. Distributed feedback lasers with external modulators have been proposed as devices that meet these demands.

[Conventional technology]

FIG. 5 is a cross-sectional view for explaining a conventional distributed feedback laser with an external modulator, and la and lb are semiconductor substrates.

6a is a multiple quantum well structure in the laser region, 6b is a multiple quantum well structure in the modulator region + 7a, 7b is a waveguide layer, 1
0 is a cladding layer, 8 is a diffraction grating, and 11 is a contact layer.

15 represents a protective film, 16 represents a P electrode, 17 represents an N electrode, and 19 represents an etching stop layer.

The multiple quantum well structure 6a in the laser region and the multiple quantum well structure 6b in the modulator region are formed as follows.

First, the multi-quantum well structure 6a in the laser region is stacked with M
Grows on the entire surface by OVPE method or MBE method. Its configuration is as follows, for example.

InGaAsP (wavelength 1-3 μm) 80 people 5 layers I
4 layers of nGaAs 80 people Next, this laminated layer formed in the modulator region is removed by etching, the laser region is masked, and a multiple quantum well structure 6b is grown in the modulator region by MOVPE or MBE. Its structure is as follows, for example.

InGaAsP (wavelength 1.3 um) 80 people 5 layers I
r1l;aAs 60 people The distance of the repetition period of the multiple quantum well structure 6b in the four-layer modulator region is shorter than that of the multiple quantum well structure 6a in the laser region.

FIG. 4 is a diagram showing energy levels of a multiple quantum well structure, in which (a) shows a laser region and (b) shows a modulator region.

The energy gap E□ between the quantum levels of the multiple quantum well structure 6b in the modulator region is equal to the energy gap E□ of the multiple quantum well structure 6b in the laser region.
It is larger than the energy gap EgI of a.

When a voltage is applied to the modulator region, the energy gap of the multiple quantum well structure 6b in the modulator region is adjusted to be equal to that of the multiple quantum well structure 6a in the laser region.

However, since the multiple quantum well structure 6a in the laser region and the multiple quantum well structure 6b in the modulator region are formed independently, in order to match the wavelength and improve optical coupling,
There is a problem that strict control is required during the manufacturing process, resulting in a drop in yield. Further, since the number of growths is multiple, there is a problem that the yield is further reduced and the throughput is low.

[Problem to be solved by the invention]

An object of the present invention is to provide a high-yield manufacturing method that reduces the number of times of growth and improves wavelength controllability by simultaneously epitaxially growing a quantum well structure 6a in a laser region and a quantum well structure 6b in a modulator region. shall be.

[Means to solve the problem]

1(a) to (c) are diagrams for explaining the present invention in detail, in which 1 is a semiconductor substrate, la is a first region, lb is a second region, 2 is a first mask, 3 is the second mask,
4a, 5a, 6a, 7a are the first epitaxial layers, 6a is the first quantum well structure, 4b, 5b, 6
b, 7b represents the second epitaxial layer, and 6b represents the second quantum well structure.

The above-mentioned problem is solved by the first
After forming a mask 2, etching the semiconductor substrate 1 to form a first region 1a whose surface is lower than the predetermined region ib; After forming a second mask 3 in the region 1a to expose the strip-shaped first region 1c connected to the second region 1b,
Epitaxial growth is performed simultaneously on the strip-shaped first region 1c and the second region 1b, and a first epitaxial layer 4a+ 5a+ 6a+ 7a+ is formed on the strip-shaped first region 1c.
A second epitaxial layer 4b, 5 is formed in the second region 1b.
b, 6b, and 7b, and the first epitaxial layer 4a+ 5a+ 6a.

The thickness of 7a is the same as that of the second epitaxial layer 4b, 5b,
6b.

7b, the second epitaxial layer 4b
, 5b, 6b, and 7b are solved by a method for manufacturing an optical semiconductor device in which the heights of the first epitaxial layers 4a, 5a, 6a, and 7b are formed substantially equal to the height of a portion of the first epitaxial layers 4a, 5a, 6a, and 7a.

Further, the first region 1 is placed in the first region 1a of the semiconductor substrate 1.
A mask 3 was formed to expose the region a in a band shape, and the first region 1a and the second region 1b continuous thereto were etched using the mask 3 as a mask, so that the bottom surface was etched in the first region 1a. A groove 1d lower than the surface of the second region 1b is formed, and then epitaxial growth is performed simultaneously on the groove 1d and the second region 1b, and first epitaxial layers 4a, 5a, 6a are formed in the groove 1d.

7a, a second epitaxial layer 4b in the second region 1b;
.

5b, 6b, 7b, the thickness of the first epitaxial layer 4a, 5a, 6a, 7a is the same as that of the second epitaxial layer 4b, 5b, 6b,
Thicker than the thickness of 7b (.

The second epitaxial layer 4b, 5b, 6b, 7
The height of b is the first epitaxial layer 4a, 5a+
The problem is solved by a method of manufacturing an optical semiconductor device in which the height of the parts 6a and 7a is substantially equal.

Further, the first epitaxial layers 4a, 5a, 6
a.

7a is a double heterostructure including a first quantum well structure 6a, and the second epitaxial layers 4b, 5b, 6b.
.

7b is a double heterostructure and includes a second quantum well structure 6b, the thickness of the first quantum well structure 6a is greater than the thickness of the second quantum well structure 6b, and the second quantum well structure 6
The height of b is equal to the height of a part of the first quantum well structure 6a, the first quantum well structure 6a is used as the core of the light emitting part of the laser, and the second quantum well structure 6b is used as the light modulation part. The problem is solved by a method for manufacturing an optical semiconductor device that has the core of

[Effect] According to selective growth using a selective mask, the growth rate changes significantly. Also, if a 9-select mask is used, the etch rate will also vary greatly.

The growth rate in the strip-shaped first region 1c can be controlled by changing its width and the area covered by the selection mask 3. Therefore, by taking advantage of this difference in growth speed, the first
The ratio of the thicknesses of the first quantum well structure 6a and the second quantum well structure 6b can be changed.

This makes it easy to control the ratio of the energy gap between the quantum levels of the first quantum well structure 6a and the energy gap between the quantum levels of the second quantum well structure 6b.

Moreover, since the height of the surface of the first region 1a is initially formed to be lower than the surface of the second region 1b, by epitaxially growing the strip-shaped first region 1c and the second region 1b at the same time, The heights of the first quantum well structure 6a and the second quantum well structure 6b can be adjusted to be the same. In this way, the first quantum well structure 6a and the second
The optical coupling property of the quantum well structure 6b is improved.

A two-selection mask 3 can also be used to first form a step between the first region 1a and the second region 1b.

When etching is performed using a mask that exposes the strip-shaped first region 1c, the etching rate of the strip-shaped first region 1c becomes higher due to the influence of the mask than that of the second region 1b, which is not affected by the mask. A step is formed between the region 1a and the second region 1b.

Furthermore, since the first quantum well structure 6a and the second quantum well structure 6b can be obtained by one-time growth, the process is simple and the yield is high (throughput is improved).

The first quantum well structure 6a is used as the core of the light emitting part of the laser,
If the second quantum well structure 6b is used as the saw core of the optical modulation section,
A good semiconductor laser with an external modulator can be obtained.

〔Example〕

Figure 2 (a) to (m) are Below is a diagram for.

I will explain.

Explaining the process of the example Please refer to these figures. See Figure 2(a) As the semiconductor substrate 1, an n·-InP substrate is used.

A first mask 2 is formed in the second region 1b. The first mask 2 is formed by sputtering 5iOz, and is made of n-InP.
Adhesion to the substrate 1 is low. The second region ib is the region forming the modulator.

Using the first mask 2 as a mask, the n''-1nP substrate 1 is
Etch with methanol. The etching goes around to the bottom of the mask, forming a smooth step and forming a first region 1a whose two surfaces are lower than the surface of the second region 1b. The step difference is approximately 0.1 μm. The first region 1a is a region where a laser is formed.

See Figure 2(b) A second mask 3 is formed in the first region 1a.

The second mask 3 is made by depositing SiO□ by thermal CVD method.
Etching is performed as a selective growth mask.

The width of the exposed strip-shaped first region 1c is 30 μm,
The width of the second mask 3 on both sides thereof is 100 μm.

Referring to FIG. 2(c), epitaxial growth is simultaneously and continuously performed on the band-shaped first region 1c and the second region 1b at a growth temperature of 590° C. using the MOCVD method. FIG. 2(c) shows an AA cross-sectional view after growth.

0.1 μm (4a) 4b Buffer layer n”-InP (5a
) 5b Waveguide layer Si-doped n-1nGaAsP (
Emission wavelength 1.3 μm) 200 people (6a) 6b Multiple quantum well structure (emission wavelength 1.3 μm) Undoped InGaAsP 60 people 6-layer undoped InGaAs 60 people 5 layers (7a) 7b Waveguide layer Zn-doped p-1nGaAsP (emission wavelength 1.3μ
m) 0.14 μm 6a is the first multiple quantum well structure,
6b is the second multiple quantum well structure, 4a to 7a
4b to 7b are the growth to the band-shaped first region 1c, and 4b to 7b are the second region 1c.
furthermore, the thickness shown above is on the second region lb. Band-shaped first region 1c
The thickness at the top.

This is approximately 1.3 times the value shown above.

The centers of the first multiple quantum well structure 6a and the second multiple quantum well structure 6b are approximately at the same height.

Referring to FIG. 2(d), the second mask 3 is peeled off and the waveguide layer 7a is coated with a pitch of 2400.
A human first-order diffraction grating 8 is formed.

See Figure 2(e) A third mask 9 is formed in the second region 1b.

The third mask 9 is made by depositing 5 iOz by thermal CVD method.
Etching is performed as a selective growth mask.

The width of the exposed band-shaped second region is 30 μm, and the width of the second mask 3 on both sides thereof is 100 μm. FIG. 2(e) is a perspective view of this state.

Referring to FIG. 2(f), a Zn-doped p-InP cladding layer 10 with a thickness of 1.0 μm is grown on the entire surface, and then a cap of Zn-doped p”-1nGaAsP (emission wavelength 1.3 μm) with a thickness of 0.2 μm is grown. A layer 11 is grown, provided that this thickness is different from that of the first region l.
The thickness on the second region lb is approximately 1.3 times this value.

See FIG. 2(g). This figure is a top view. A fourth mask 12 of 5 iOz having a window of width 300 μm between the first region (laser region) and the second region (modulator region) is formed on the upper surface.

Referring to FIG. 2(h), the cap layer 11 is removed by selective etching using the fourth mask 12 as a mask.

See FIG. 2(i). This figure is a top view. 2 width 3 on the top surface spanning the first region (laser region) and the second region (modulator region), on the first epitaxial layer and on the first epitaxial layer.
Fifth mask 1 of striped SiO□ with a width of 0 μm
form 3.

FIG. 2 (see D) This figure is a sectional view taken along the line B-B. Using the fifth mask 13 as a mask, mesa etching is performed up to the n'''-1nP substrate 1.

Referring to FIG. 2(k), high-resistance Fe-doped InP 14 is embedded and grown in the mesa-etched area by MOVPE.

FIG. 2(1) A protective film 15 of Sin is placed on the reference buried layer 14, and contact holes are formed in the laser region and modulator region.

A p-electrode 16 of Ti/Pt/Au is formed. Further, on the back surface, a pole 17 is formed to n of AuGe/8U.

Refer to FIG. 2 (w+). This figure is a sectional view taken along line A-A. An end face is formed by cleavage, and a non-reflection coating film 18 is formed on the end face.

In this way, a monolithic external modulator-equipped distributed feedback laser was fabricated.

FIGS. 3(a) and 3(b) are diagrams for explaining the steps of another embodiment.

In this example, the second mask 3 described above is used to form a step between the first region 1a and the second region 1b.

Referring to FIG. 3(a), a mask 3 is formed on a semiconductor substrate 1. Mask 3 is thermal CV
SiO□ is deposited by method D and etched as a 9-selective growth mask. The width of the exposed band-shaped first region 1c is 30 μm, and the width of the second mask 3 on both sides thereof is 1
00 μm.

Using the reference mask 3 in FIG. 3(b) as a mask, the band-shaped first region 1c and second region 1b are etched.

The band-shaped first region 1c is etched at a higher etching rate than the second region 1b, and is etched deeper than the etched surface of the second region 1b, forming a groove 1d.

The subsequent steps are shown in FIGS. 2(c) to (a) of the above-mentioned embodiment.
The process is similar to +).

In this embodiment, a mask that forms a step between the first region 1a and the second region 1b, and a mask that forms a step between the first region 1a and the second region 1b are used.
This has the advantage of reducing man-hours because masks can be shared for epitaxial growth.

Note that, of course, a GaAs substrate can be used as the substrate. According to the inventor's experimental results, GaAs
When growing the same <GaAs on the substrate, the width of the 5iOz selective growth mask is 500 μm, and the interval between the masks is 10 μm.
m, and the supply ratio of TEG and AsH is 1:40. If the growth temperature is 690″C.

The growth rate in a stripe region with a width of 10 μm is approximately 10 times the growth rate in a region completely unaffected by the three-selective growth mask.

〔Effect of the invention〕

As explained above, according to the two aspects of the present invention, a monolithic external modulator-equipped distributed feedback laser can be manufactured with high yield. First, a step is formed on the semiconductor substrate, and the laser emitting section and the light modulating section formed on both sides of the two steps are simultaneously epitaxially grown, thereby improving the optical coupling between the laser emitting section and the optical modulating section.

The present invention will greatly contribute to the future development of optical communication devices for ultra-high-speed transmission.

[Brief explanation of drawings]

FIGS. 1(a) to 1(c) are diagrams for explaining the present invention in detail. FIGS. 2(a) to 2(m) are diagrams for explaining the steps of the example. FIGS. 3(a) and 3(b) are diagrams for explaining the steps of another embodiment. FIG. 4 is a diagram showing energy levels of a multiple quantum well structure. FIG. 5 is a cross-sectional view for explaining a conventional distributed feedback laser with an external modulator. In fig. 1 is a semiconductor substrate, and n''-InPla is a first region, which is a laser region. 1b is a second region, which is a modulator region. 1c is a strip-shaped first region. 1d is a groove. 2 is a groove. The first mask is SiO□. The second mask is StO□. 4a+4b is a buffer layer of n-1nP. 5a and 5b are waveguide layers of n-1nGaAsP.
. 6a is a first quantum well structure, which is a first multiple quantum well structure, and is an undoped MQW. 6b is a second quantum well structure, which is a second multiple quantum well structure and is an undoped MQW. 7a and 7b are waveguide layers made of p-InGaAsP. 8 is a diffraction grating. 9 is the third mask, SfO□. 10 is a cladding layer made of p-InP. Is 11 the key? The whelk layer is p”-InGaAs
P+12 is the fourth mask and is 5ift. 13 is a fifth mask made of SiO□. 14 is a buried layer made of Fe-doped InP. 15 is a protective film of 5 iOz. 16 is a p-electrode made of Ti/Pt/Au. 17 is an n-electrode made of AuGe/Au. 18 is a non-reflective coating film. Figure 1 for explaining the principle of the present invention Figure 2.5iOz Diagram 2 (°C 1) Diagram for explaining the process text of the major decision 1 Figure 2 (3) of the same figure 2 (2) (j) (k) The process palace of #j Prisoner of O Figure 2 (Part 4) (d) Iya's implementation of the process of execution

Claims (1)

[Scope of Claims] [1] After forming a first mask (2) that covers a predetermined region (1b) of a semiconductor substrate (1), the semiconductor substrate (1) is etched so that the surface of the semiconductor substrate (1) covers the predetermined region (1b). (1b) Lower first
forming a region (1a) in which the predetermined region (1b) is a second region (1b), forming a second mask (3) in the first region (1a), and forming a second region (1b) in the first region (1a); A strip-shaped first region (1c) connected to the second region (1b)
After exposing the strip-shaped first region (1c) and the second region (1b), epitaxial growth is simultaneously performed on the strip-shaped first region (1c), and a first epitaxial layer (4) is grown on the strip-shaped first region (1c).
a, 5a, 6a, 7a), a second region (1b)
forming an epitaxial layer (4b, 5b, 6b, 7b) of the first epitaxial layer (4a, 5a, 6a, 7a).
The thickness of the second epitaxial layer (4b, 5b, 6b
, 7b), and the height of the second epitaxial layer (4b, 5b, 6b, 7b) is substantially equal to the height of a portion of the first epitaxial layer (4a, 5a, 6a, 7a). 1. A method for manufacturing an optical semiconductor device, characterized in that the device is formed to have the same shape as the semiconductor device. [2] The first region (1a) of the semiconductor substrate (1)
Form a mask (3) that exposes the region (1a) in a strip shape, and use the mask (3) as a mask to expose the first region (1a).
and a second region (1b) that is continuous thereto, and a second region (1b) whose bottom surface is etched in the first region (1a).
A groove (1d) lower than the surface of the region (1b) is formed, and then epitaxial growth is simultaneously performed on the groove (1d) and the second region (1b), and a first epitaxial layer is formed in the groove (1d). (4a, 5a, 6a, 7a), and a second epitaxial layer (4b, 5b, 6) in the second region (1b).
b, 7b), the first epitaxial layer (4a, 5a, 6a, 7a)
The thickness of the second epitaxial layer (4b, 5b, 6b
, 7b), and the height of the second epitaxial layer (4b, 5b, 6b, 7b) is substantially equal to the height of a portion of the first epitaxial layer (4a, 5a, 6a, 7a). 1. A method for manufacturing an optical semiconductor device, characterized in that the device is formed to have the same shape as the semiconductor device. [3] The first epitaxial layer (4a, 5a, 6a
, 7a) is a double heterostructure with a first quantum well structure (6
a), said second epitaxial layer (4b, 5b
, 6b, 7b) is a double heterostructure and includes a second quantum well structure (6b), the thickness of the first quantum well structure (6a) being greater than the thickness of the second quantum well structure (6b). ,
The height of the second quantum well structure (6b) is equal to the height of a part of the first quantum well structure (6a), and the first quantum well structure (6a) is used as the core of the light emitting part of the laser. 3. The method of manufacturing an optical semiconductor device according to claim 1, wherein the second quantum well structure (6b) is used as a core of an optical modulation section.