JP2003060284A - Fabrication method of optical integrated device - Google Patents

Abstract

(57) [Problem] To provide a method of manufacturing an optical integrated device in which a growth step is small and a step is not increased when engaging with a DFB-LD by a butt joint method. SOLUTION: This method is a method for manufacturing an optical integrated device in which a passive element is coupled to a distributed feedback semiconductor laser element and integrated. In this method, a stacked structure including the active layer 16 is formed on a substrate, and then a diffraction grating layer 20 is grown, and the diffraction grating layer on a laser element formation region is etched to form a diffraction grating 22. Forming a mask 28 that embeds the diffraction grating and covers the laser element formation area 24 and exposes the passive element formation area 26; Exposing the substrate in the element forming region; and forming a laminated structure forming the passive element on the substrate in the passive element forming region by a butt-coupling method with respect to the laminated structure and the diffraction grating of the distributed feedback semiconductor laser element. Having.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an optical integrated device in which a passive element is coupled to a distributed feedback semiconductor laser element by a butt-coupling method and integrated, and more specifically, an optical integrated device with high product yield and throughput is provided. It relates to a method by which integrated devices can be produced.

[0002]

2. Description of the Related Art A distributed feedback semiconductor laser device (hereinafter referred to as D
An optical integrated device in which an EA modulator is coupled to and integrated with a FB-LD) is an external modulation type optical device in which an external modulator such as an LN (LiNbO ₃ ) modulator is combined with a DBF-LD driven under a constant current. Since the module configuration is significantly smaller than that of the device, it is attracting attention as a key device that can achieve the downsizing and cost reduction required for a DWDM device. In particular, the above-mentioned DFB-LD
The optical integrated device that combines the EA modulator and the EA modulator is important as a communication light source in the metropolitan system,
It has become a key device in the optical communication field.

By the way, the EA modulator using the quantum well structure has a quantum confined Stark effect (Qunatum Confined S).
By applying a reverse bias voltage using the tark effect), the absorption edge of the exciton (exciton) is moved to the long wavelength side (low energy side) to absorb and quench the emitted light of the DFB-LD. It is an optical element capable of The extinction ratio changes depending on the quantum well structure of the EA modulator such as the thickness of the well layer and the number of well layers. Therefore, in order to maximize the characteristics of the optical integrated device, the DFB-LD and EA
It is important that the quantum well structure of the modulator is formed with the optimum number of well layers and thickness.

Therefore, as a method for optimally configuring each of the quantum well structures of the DFB-LD and the EA modulator, D
After the laminated structure forming the FB-LD is formed on the substrate, the laminated structure of the DFB-LD on the EA modulator forming region is removed, and then the laminated structure forming the EA modulator is formed on the EA modulator forming region. A butt joint (butt joint) method of selectively growing and joining the two has been developed.

Here, referring to FIG. 7, a method described in Japanese Patent Laid-Open No. 62-194691 will be described as a conventional method for manufacturing an optical integrated device in which a DFB-LD and an EA modulator are integrated. . FIGS. 7A to 7C are cross-sectional views for explaining the steps when the optical integrated device is manufactured by the conventional first method. As shown in FIG. 7A, the diffraction grating 64 is formed on the substrate 62 in the laser region A and the modulation region B, and then the optical waveguide layer 66 (corresponding to the clad layer), the active layer 68, and the active layer 68 are formed. The protective layer 70 is sequentially epitaxially grown. Next, as shown in FIG. 7B, a SiN _x film is formed on the entire surface of the protective layer 70 and patterned to form a mask 72 covering the laser region A, and the laminated structure of the modulation region B and the diffraction grating 64. Are exposed to expose the substrate 62. Subsequently, as shown in FIG. 7C, an optical waveguide layer 74 including an active layer and an InP layer 76 are epitaxially grown on the substrate 62 in the modulation region B.

That is, the optical integrated device 80 when an optical integrated device in which the DFB-LD and the EA modulator are integrated is formed by applying the first conventional method described in the above publication,
As shown in FIG. 8, the diffraction grating 84 formed on the DFB-LD formation region of the substrate 82, the buffer layer 86 grown under the low temperature and low growth rate condition and having the diffraction grating 84 embedded therein, the active layer 88, and A protective layer 90 for the active layer 88 is provided.
Further, in the optical integrated device 80, the laminated structure constituting the EA modulator, that is, the lower clad layer 92, the active layer 94, and the upper clad layer 96 is regrown on the EA modulator forming region, and the DFB-LD is formed. The laminated structure and the butt joint are formed. Further, the optical integrated device 80 has the upper clad layer 98 and the DFB- which are regrown on the entire surface of the substrate.
The LD and EA modulator contact layers 100A and 100B are provided. Here, the substrate 82 is the same as the substrate 62 of the above-mentioned publication.
The diffraction grating 84 and the buffer layer 86 of the FB-LD correspond to the diffraction grating 64 and the optical waveguide layer 66 of the above publication, respectively, and the lower cladding layer 92 of the EA modulator is the cladding layer of the optical waveguide layer 74 of the above publication. It corresponds to the part.

According to the first conventional method, when regrowth of the laminated structure of the EA modulator is performed while the step difference between the substrate surface and the active layer generated in the DFB-LD formation region is low,
Since the laminated structure of the A modulator is regrown and butt-jointed to the laminated structure of the DFB-LD, abnormal growth does not occur in the epitaxial regrowth layer of the EA modulator, and a relatively flat layer structure can be obtained. I am trying.

By the way, the wavelength difference Δλ _sg between the gain peak wavelength (s) of the active layer of the DFB-LD section and the oscillation wavelength (g) determined by the pitch (cycle) of the diffraction grating has constant characteristics such as temperature characteristics and threshold values. For this reason, it is preferable that the optical integrated devices are aligned so as to be uniform. Therefore, in the first conventional method of forming the diffraction grating before the active layer, the wavelength difference Δλ _sg is made uniform between the optical integrated devices because the pitch of the diffraction grating is uniquely determined. In order to make them uniform, it is necessary to strictly control the gain peak wavelength of the active layer. However, it is actually extremely difficult to strictly control the gain peak wavelength because it is necessary to strictly control the composition of the active layer and the film thickness of the quantum well structure. As a result, the wavelength difference Δλ _sg may be largely deviated within the wafer surface or between lots. Further, since the number of times of regrowth is large, there has been a problem that characteristics are deteriorated and yield is reduced due to mixing of particles.

Therefore, it has been proposed that the active layer is formed first, and then the diffraction grating having a period matched to the gain peak wavelength thereof is formed so that the wavelength difference Δλ _sg is made uniform between the optical integrated devices. There is.

Here, a method of forming an active layer and then a diffraction grating will be described as a second conventional method with reference to FIG. In the second conventional method, first, the lower clad layer 104, the active layer 106, the upper clad layer 108, and the diffraction grating layer are formed on the entire surface of the substrate 102, and the diffraction grating layer is etched to form the diffraction grating 110. To do. Then, a GOG (Grating Over Growth) layer 11 is formed on the diffraction grating 110.
2 has a relatively large film thickness, for example, I having a film thickness of 100 nm
The nP layer or the like is grown at a low temperature and a low growth rate, and the diffraction grating 11
0 is embedded and the diffraction grating 110 is flattened. Then, a 400 nm-thick InP layer or the like is continuously grown at a normal growth rate to form a part of the upper clad layer 120 (this structure corresponds to the laminated structure on the left side in FIG. 9). Next, the laminated structure in the EA modulator forming region is selectively removed to expose the substrate surface, and subsequently, the laminated structure constituting the EA modulator, that is, the lower clad layer 114, the active layer 116, and the upper clad layer 118 is formed. Re-grow to form butt joint, then upper clad layer 120
Are regrown to form contact layers 122A, B of the DFB-LD and EA modulator.

[0011]

By the way, in the above-mentioned second conventional method, the GOG layer is grown on the diffraction grating. However, in the process of growing the GOG layer on the diffraction grating, the number of epitaxial growth steps of the compound semiconductor layer is increased, and the process becomes complicated. Also, GOG
By providing the layer, the step difference in forming the laminated structure of the EA modulator becomes large, and abnormal growth as shown in FIG. 10 easily occurs. When selectively growing the laminated structure of the EA modulator, as shown in FIG.
When it is about 00 nm, the regrowth surface is 20
Only about ~ 30 nm rises, but Fig. 10 (b)
As shown in, for example, when the step difference is about 900 to 1000 nm, the regrowth surface is 200 to 300 n from the step upper surface.
It rises above m.

Therefore, according to the present invention, the number of growth steps is small, and when the DFB-LD is engaged by the butt joint method,
Provided is a method for manufacturing an optical integrated device in which a step is prevented from becoming large.

[0013]

In order to achieve the above object, an optical integrated device manufacturing method according to the present invention is a method for manufacturing an optical integrated device in which a passive element is coupled to a distributed feedback semiconductor laser element and integrated. In, a step of forming a laminated structure including an active layer on a substrate and then growing a diffraction grating layer, and etching the diffraction grating layer at least on the distributed feedback semiconductor laser element forming region to form a diffraction grating Steps, a step of burying the diffraction grating on the distributed feedback semiconductor laser element forming area and forming a mask covering the distributed feedback semiconductor laser element forming area, and etching and removing the laminated structure on the passive element forming area. A step of exposing the substrate in the passive element formation region and a laminated structure for forming the passive element on the substrate in the passive element formation region It is characterized by a step of forming a bond scheme butt against the layer structure.

According to the method of the present invention, after forming the diffraction grating,
Immediately without growing the GOG layer, a passive element, for example, a laminated structure forming an EA modulator layer is grown by a butt coupling method (butt joint method) after the diffraction grating is formed, and then the GOG layer is grown. As a result, the number of regrowth interfaces is reduced, and the step when regrowth of the laminated structure of the passive element is lower than in the conventional method. Abnormal growth is suppressed, yield is improved, and throughput can be improved without deteriorating device characteristics. Further, since the diffraction grating is covered with the mask when forming the laminated structure of the passive element, it is not deformed due to the thermal history during the formation of the laminated structure.

Preferably, in the step of forming the laminated structure forming the passive element, the laminated structure forming the passive element is formed up to the compound semiconductor layer positionally corresponding to the diffraction grating of the distributed feedback semiconductor laser element. Then, the mask is removed, and the cladding layer / diffraction grating filling layer (GO
G layer) is grown. The mask is formed of a dielectric film such as SiN _x or SiO _x film. Examples of passive elements include optical waveguides, optical modulators, and optical amplifiers. The manufacturing method according to the present invention is not limited to the laser structure and the passive device structure of the distributed feedback semiconductor laser device, and the composition and film thickness of the compound semiconductor layer constituting them.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described specifically and in detail with reference to the accompanying drawings. The film forming method, the composition and film thickness of the compound semiconductor layer, the ridge width, the process conditions and the like shown in the following embodiments are merely examples for facilitating the understanding of the present invention. It is not limited to this example. Embodiment 1 This embodiment is a distributed feedback semiconductor laser device (hereinafter,
This is an example of an embodiment in which the method for producing an optical integrated device according to the present invention is applied to the production of an optical integrated device in which a DFB-LD) and an EA modulator are combined and integrated by a butt joint method. 1 (a) to 1 (c), 2 (d) to (f), and FIGS. 3 (g) and 3 (h) respectively show an EA modulator coupled to a DFB-LD according to the method of the present embodiment. FIG. 6 is a cross-sectional view taken along a laser stripe for each step when manufacturing an integrated optical integrated device. Also, FIG.
(A) to (c), FIG. 5 (d) to (f), and FIG.
(G) and (h) are respectively FIG. 1 (a) to (c),
Line I in FIGS. 2 (d) to 2 (f) and FIGS. 3 (g) and 3 (h).
It is a sectional view of -I. However, FIG. 4C corresponds to FIG.
II is a cross-sectional view taken along line II-II of FIG.

First, as shown in FIGS. 1A and 4A, the n-type InP clad layer 14 and the InGaAs are sequentially formed on the n-type InP substrate 12 by MOCVD or the like.
An active layer 16 having a P-based multi-quantum well structure, a p-type InP clad layer 18, and a diffraction grating formation layer 20 made of a compound semiconductor having a bandgap wavelength of 1.5 μm, which is a diffraction grating, are epitaxially grown. Then, for example, EB
A diffraction grating pattern is formed by a drawing method, and irregularities of the diffraction grating 22 are formed by a dry etching method. here,
The diffraction grating 22 may be selectively formed on the DFB-LD formation region 24.

Next, as shown in FIGS. 1B and 4A, a dielectric film such as SiN is formed on the entire surface of the substrate and patterned to cover the DFB-LD formation region 24, and E
A mask 28 exposing the A modulator formation region 26 is formed. Then, the diffraction grating formation layer 20, the p-type InP clad layer 18, the active layer 16, and the n-type InP clad layer 14 in the EA modulator formation region 26 are removed by a dry etching method or the like, as shown in FIG. And the n-type InP substrate 12
The substrate surface of is exposed.

Next, as shown in FIGS. 1C and 4C, EA is formed on the exposed substrate surface of the n-type InP substrate 12.
As a laminated structure of the modulator, an n-type InP clad layer 30, an active layer 32 of an InGaAsP-based multiple quantum well structure, and a p-type InP clad layer 34 are sequentially epitaxially grown by MOCVD or the like. Since the diffraction grating 22 is covered with the SiN mask 28 when the laminated structure of the EA modulator is formed, it is not deformed due to thermal history.

After removing the mask 28, the GOG layer / p-type InP clad layer 36 is regrown on the entire surface of the substrate. Subsequently, a dielectric film is formed on the entire surface and patterned, and
As shown in FIGS. 5D and 5D, a striped mask 38 having a width of, for example, about 2 μm is formed. Then DF
The laminated structure of the B-LD formation region 24 and the EA modulator formation region 26 is etched to the upper portion of the n-type InP substrate 12 by a dry etching method or the like, and then, as shown in FIGS.
As shown in (e), the mesa 40 is formed. Next, FIG.
As shown in (f) and FIG. 5 (f), a semi-insulating Fe-doped InP layer 42 and an n-type InP layer 44 are sequentially grown to fill both sides of the mesa 40 to form a lateral current confinement structure. Form. The provision of the semi-insulating Fe-doped InP layer 42 serves as an electron trap layer, and at the same time,
The purpose is to reduce the parasitic capacitance.

Next, the striped mask 34 is removed, and as shown in FIGS. 3 (g) and 6 (g), p-type In is formed.
P clad layer 46, p-type InGaAsP contact layer 4
8 is deposited. Subsequently, as shown in FIG. 3H, the contact layer 48 is etched to remove DFB-LD 50 and E.
In order to electrically separate the A modulator 52 and reduce the capacity, as shown in FIG. 6H, the laminated structure is removed along the laser stripe structure. Then p-type InGaAsP
After forming the p-side electrodes 54 and 56 of the DFB-LD 50 and the EA modulator 52 on the contact layer 48 and further polishing the back surface of the n-type InP substrate 12 to adjust the substrate thickness to a predetermined thickness, the back surface is formed. A common n-side electrode 58 is formed. Thereby, the optical integrated device 60 in which the DFB-LD 50 and the EA modulator 52 are coupled and integrated by the butt joint method can be manufactured.

The device characteristics of the manufactured optical integrated device 60 are equal to or better than those of the optical integrated device manufactured by the conventional method. For example, when the applied voltage to the EA modulator is -2V,
An extinction ratio of 10 dB or more could be obtained. As a result of aging test, reliability is MTTF = 1 at room temperature.
It could be confirmed that × 10 ⁶ hours or more was secured. Furthermore, since the number of re-growths was small, the number of re-growth interfaces could be reduced.
It was possible to confirm the superiority of the method of the present invention.

In the method of this embodiment, an InGaAsP-based EA having a lattice constant close to or close to the InP substrate is used.
An optical integrated device in which a DFB and an EA modulator are integrated is taken as an example, but an optical integrated device in which an InGaAlAs-based EA-DFB having a lattice constant or a lattice constant close to an InP substrate and a passive element are integrated is manufactured. It goes without saying that it can also be applied to. Furthermore, the present invention is not limited to the InP substrate, and can be applied to the fabrication of an optical integrated device in which a DFB-LD having a laminated structure having a lattice constant or a lattice constant close to that of a GaAs substrate and a passive element are integrated. Further, instead of the EA modulator, for example, an MMI (Multi Mode) that is a waveguide is used.
Interference) The present invention can also be applied to the production of an optical integrated device in which a coupler or the like is integrated in a DFB-LD.

[0024]

According to the method of the present invention, a passive element such as an EA modulator layer is formed by a butt-coupling method (butt joint method) without growing a GOG layer as in the conventional method after forming a diffraction grating. The structure is grown and then the GOG layer is grown. This allows
Since the number of regrowth interfaces is reduced and the step difference in regrowth of the laminated structure of the passive element is lower than that of the conventional method, mixing of particles and the like and abnormal growth of the regrowth layer are reduced as compared with the conventional method. It is suppressed, the yield is improved, and the throughput can be improved without deteriorating the device characteristics. In addition, since the diffraction grating is covered with the mask when the laminated structure of the passive element is formed, the diffraction grating is not deformed by the thermal history during the formation of the laminated structure. Therefore, the diffraction grating has a uniform size between the optical integrated devices, and the characteristics of the optical integrated devices do not vary.

[Brief description of drawings]

1A to 1C are views each showing a laser stripe along each step in manufacturing an optical integrated device in which an EA modulator is coupled to a DFB-LD and integrated according to the method of the embodiment. FIG.

2 (d) to 2 (f) are respectively shown in FIG.
FIG. 3C is a cross-sectional view following a laser stripe in each step when manufacturing the optical integrated device according to the method of the embodiment example, subsequent to (c).

3 (g) and 3 (h) are respectively FIG. 2 (f).
6B is a cross-sectional view of a laser stripe in each step of manufacturing an optical integrated device according to the method of the embodiment, following FIG.

4 (a) and 4 (b) are respectively FIG.
It is sectional drawing of line I-I of (a) to (b). Figure 4
FIG. 1C is a sectional view taken along the line II-II in FIG.

5 (d) to 5 (f) are respectively shown in FIG.
It is sectional drawing of line II of (d) to (f).

6 (g) and 6 (h) are respectively FIG. 3 (g).
And (h) is a sectional view taken along line I-I.

FIG. 7A to FIG. 7C are cross-sectional views each illustrating a process when an optical integrated device is manufactured by the first conventional method.

FIG. 8 is a cross-sectional view showing a configuration of an optical integrated device manufactured by a conventional first method.

FIG. 9 is a cross-sectional view showing a configuration of an optical integrated device manufactured by a second conventional method.

10 (a) and 10 (b) are diagrams for explaining abnormal growth of a regrown layer, respectively.

[Explanation of symbols]

12 n-type InP substrate 14 n-type InP clad layer 16 InGaAsP active layer with multiple quantum well structure 18 p-type InP clad layer 20 Diffraction grating forming layer 22 diffraction grating 24 DFB-LD formation region 26 EA modulator formation area 28 masks 30 n-type InP clad layer 32 InGaAsP-based multiple quantum well structure active layer 34 p-type InP clad layer 36 GOG layer and p-type InP clad layer 38 Striped mask 40 Mesa 42 Semi-insulating Fe-doped InP layer 44 n-type InP layer 46 p-type InP clad layer 48 p-type InGaAsP contact layer 50 DFB-LD 52 EA modulator 54, 56 p-side electrode 58 n-side electrode 62 Substrate having laser region A and modulation region B 64 diffraction grating 66 Optical Waveguide Layer 68 Active layer 70 InP protective layer 72 Mask 74 Optical Waveguide Layer 76 InP layer 82 substrate 84 diffraction grating 86 buffer layer 88 Active layer 90 Protective layer 92 Lower clad layer 94 Active layer 96 Upper clad layer 98 Upper clad layer 100A, B contact layer 102 substrate 104 Lower clad layer 106 Active layer 108 upper clad layer 110 diffraction grating 112 GOG (Grating Over Growth) layer 114 Lower clad layer 116 Active layer 118 Upper clad layer 120 Upper clad layer 122A, B contact layer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takeji Yamaguchi             2-6-1, Marunouchi, Chiyoda-ku, Tokyo             Kawa Electric Industry Co., Ltd. F-term (reference) 2H079 AA02 AA13 BA01 CA05 DA16                       DA22 EA03 HA04 KA18                 5F073 AA22 AA64 AA74 AB12 AB21                       CA17 CB02 DA05 DA24

Claims (4)

[Claims] 1. A method of manufacturing an optical integrated device in which a passive element is integrated with a distributed feedback semiconductor laser element to form an integrated optical device, wherein a laminated structure including an active layer is formed on a substrate, and then a diffraction grating layer is grown. A step of etching at least the diffraction grating layer on the distributed feedback semiconductor laser element forming region to form a diffraction grating; and a step of filling the diffraction grating on the distributed feedback semiconductor laser element forming area with a distributed feedback semiconductor laser. A step of forming a mask covering the element formation region, a step of etching and removing the laminated structure on the passive element formation region to expose the substrate of the passive element formation region, and a step of forming the passive element on the substrate of the passive element formation region. And a step of forming the laminated structure to be formed on the laminated structure of the distributed feedback semiconductor laser device by a butt coupling method. A method for manufacturing a device. 2. In the step of forming a laminated structure forming a passive element, a laminated structure forming a passive element is formed up to a compound semiconductor layer positionally corresponding to a diffraction grating of a distributed feedback semiconductor laser element. The mask is removed, and a cladding layer / diffraction grating filling layer is grown on the entire surface of the substrate.
A method for manufacturing the optical integrated device according to. 3. The method for manufacturing an optical integrated device according to claim 1, wherein the mask is formed of a dielectric film. 4. The optical integrated device according to claim 1, wherein any one of an optical waveguide, an optical modulator, and an optical amplifier is formed on the passive element forming region. device.