JP6043698B2 - Manufacturing method of optical semiconductor device - Google Patents

Description

  The present invention relates to an optical semiconductor device manufacturing method, and more specifically to an integrated optical semiconductor device manufacturing method in which a plurality of semiconductor elements are integrated on a single substrate.

  High functionality and high performance of optical semiconductor elements used in optical communication modules and optical communication systems are desired. 2. Description of the Related Art Conventionally, there is a semiconductor integration technique that monolithically integrates a plurality of semiconductor elements on the same substrate as a method for realizing higher functionality and higher performance of an optical semiconductor element. Distributed feedback lasers (hereinafter referred to as DFB lasers) that integrate electro-absorption modulators (hereinafter referred to as EA modulators) are typical devices (integrated devices) using this semiconductor integration technology. External modulator integrated DFB (integrated optical semiconductor device) in which this EA modulator (optical semiconductor element) and DFB laser (optical semiconductor element) are integrated on the same substrate Is small and capable of high-speed modulation exceeding 10 gigabits / second, and since chirping (fluctuation of the oscillation wavelength during modulation) is small, it has the advantage of less waveform degradation when used for long-distance optical fiber transmission. . Conventionally, this external modulator integrated DFB laser is a multi-layer composed of InGaAs and InGaAsP materials sandwiched between InP clad layers doped n-type and p-type on an InP substrate by metal organic vapor phase epitaxy (MOVPE). Crystal growth of strained quantum well structure. After processing this into a DFB laser, in order to integrate the optical modulator, unnecessary portions are removed by etching, crystal growth of the optical modulator portion is performed again, and so-called butt joint coupling is performed.

As another integration technique for integrating another DFB laser and a modulator, there is selective region growth in which a raw material is not grown on a part of a substrate before crystal growth so as to be masked with SiO ₂ or the like. With this mask, the film thickness and composition of the quantum well layer can be changed due to changes in vapor phase diffusion during MOVPE growth, migration of raw materials from the mask portion, and the like. Development of a technique for performing the laser portion and the modulator portion by one growth by changing the size of the mask has been performed.

Tomonobu Tsuchiya et al., “In situ Deep Etching for an InGaAlAs buried Heterostructure by Using HCI Gas in a Metalorganic Vapor Phase Epitaxy Racor,” Japanese Journal of Applied Physics, 2004, Vol. 43, No. 10A, pp. L 1247- L 1249

  However, in the butt joint connection, when the laser and the modulator portion are formed, the quantum well of the modulator grows in the vicinity of the laser side wall, resulting in excess loss. In recent years, an InGaAlAs-based DFB laser has been developed with the aim of improving temperature characteristics. However, this material causes oxidation of the Al-containing material at the regrowth interface, resulting in deterioration of characteristics and reliability. It is.

In the selective region growth method using a mask, there is a problem that it is difficult to independently grow the strain and film thickness of the multiple quantum wells constituting the laser part and the modulator part as designed. Furthermore, since both are formed in a single growth, the number of stacked quantum wells cannot be controlled independently, and the laser and modulator structures cannot be optimized. It is difficult to achieve both low voltage operation. Further, in the material containing Al, there is a problem that deposits are easily generated on the SiO ₂ of the mask, and the effect of selective region growth is diminished.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide a semiconductor integrated type optical semiconductor device manufacturing method capable of realizing an optical module that transmits a smaller and faster optical signal. Is to provide.

  In order to achieve such an object, an optical semiconductor device manufacturing method according to one aspect of the present invention is a manufacturing method of an optical semiconductor device in which a plurality of semiconductors are integrated on one semiconductor substrate. Growing a quantum well structure on a ridge having two regions in contact with each other formed on the semiconductor substrate by vapor phase epitaxy under a predetermined pressure; and under a pressure different from the predetermined pressure And gas etching the quantum well structure.

  In one embodiment, the quantum well structure can be grown by metal organic vapor phase epitaxy, and the quantum well structure can be etched by reactive gas edging. In one embodiment, a distributed feedback laser having the multiple quantum well structure is integrated in an active layer in one of the two regions of the optical semiconductor device, and another one of the two regions of the optical semiconductor device. For example, an optical modulator composed of the multiple quantum well structure having an absorption edge shorter than the oscillation wavelength of the distributed feedback laser is integrated. The material of the multiple quantum well structure is any one of InGaAsP, InGaAlAs, InGaAsN, and InGaAs, and a material in which the oscillation wavelength of the distributed feedback laser is 1.1 μm or more and 1.6 μm or less is selected. The quantum well layer has a thickness to achieve the oscillation wavelength of the distributed feedback laser and a strain between crystal lattices.

  As described above, according to the present invention, it is possible to provide a method of manufacturing an integrated optical semiconductor device that can realize an optical module that transmits a small and high-speed optical signal.

It is a figure which shows an InGaAlAs quantum well structure. It is a figure for demonstrating one Embodiment of this invention, (a) is a figure which shows the upper surface of the board | substrate with which the pattern was formed, (b) is sectional drawing of the quantum well structure laminated | stacked on the board | substrate, (c) ) Is a cross-sectional view of a quantum well structure edged after being stacked on a substrate.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, the principle of the present invention will be described.

  In the metal organic vapor phase epitaxy (MOVPE method), when there is an uneven pattern on the substrate, diffusion in the gas phase occurs, so the growth rate on the ridge increases and the growth rate of the groove portion decreases. In addition, since the vapor phase diffusion constant varies depending on the mass of Ga, In, Al, and intermediate products, which are Group III materials, the composition of the grown semiconductor also varies. The effect becomes more prominent as the pattern width is narrower. Therefore, in the present invention, a structure in which the film thickness and composition of the laser part and the modulator part are controlled can be formed by a single crystal growth process by designing the pattern width so as to utilize these characteristics of the MOVPE method. .

For example, according to the present invention, since the laser and the modulator are integrated in a single crystal growth, the connection part between the laser part and the modulator is not exposed to the air. Therefore, it is possible to suppress the oxidation of the surface, and to manufacture a highly reliable part with reduced occurrence of defects. Further, according to the present invention, since the composition of the multiple quantum well layer is continuously formed from the laser portion to the modulator portion, it is possible to suppress generation of extra reflected return light and connection loss. In addition, since problems such as deposits on the mask, which has been a problem in selective area growth using a SiO ₂ mask, do not occur in principle, it can be applied to any material.

  As a means of optimally controlling the number of stacked quantum wells in the laser part and modulator part with a single crystal growth, a gas containing halogen such as chlorine after the growth of multiple quantum wells in the laser and modulator formed on the pattern Alternatively, an organic metal raw material is introduced into the reaction tube. As a result, the III-V semiconductor is decomposed into an organic metal containing halogen and etched. Therefore, the multiple quantum well layer is etched from above, and the number of removed multiple quantum wells can be controlled by the concentration of the etching gas, the temperature of the reaction furnace, and the gas flow time. However, the reaction of the etching gas is also affected by the vapor phase diffusion in the vicinity of the pattern substrate. Therefore, the etching rate also increases in the region where the growth rate is increased during crystal growth. Therefore, if the pressure in the reactor is the same as the crystal growth, the number of multiple quantum wells can sometimes be changed between the laser unit and the modulator unit. Can not. Therefore, in the present invention, the pressure in the reactor is increased from the pressure at the time of crystal growth, the vapor phase diffusion of the etching gas is increased, and the difference in the etching rate due to the concavo-convex pattern is increased, so that the quantum well of the laser part is increased. The number of stacked layers and the number of stacked quantum wells in the modulator section are made different. This makes it possible to manufacture an integrated optical semiconductor device that achieves both low threshold operation of the laser and low voltage operation of the modulator.

  In an embodiment of an integrated optical semiconductor device manufacturing method in which a semiconductor laser and an EA modulator are integrated, MOVPE growth is performed on a substrate on which a concavo-convex pattern is formed in order to integrate the semiconductor laser and the EA modulator. Then, multiple quantum wells having different compositions and film thicknesses are formed by vapor phase diffusion. Furthermore, by introducing a gas containing halogen at an increased pressure in the reactor, etching with increased gas phase diffusion due to the uneven pattern can be performed, and the number of quantum wells in the laser can be controlled to be less than that of the EA modulator. it can.

[Example]
Although the actual reaction process in the reactor is complex, the simplified chemical reaction formulas for the InGaAlAs MOVPE growth reaction process and etching process are as follows.
(During growth)
x (CH ₃ ) ₃ In + y (C ₂ H ₅ ) ₃ Ga + z (CH ₃ ) ₃ Al + AsH3 → In _x Ga _y Al _z As + (3x + 6y + 3z) CH ₄
(During etching)
In _x Ga _y Al _z As + 3 (x + y + z) HCl → xInCl ₃ + yGaCl ₃ + zAlCl ₃ + AsH ₃ + H ₂

Since the surface reaction of these chemical reactions is fast, the rate is mainly determined by the amount of raw material supplied near the substrate surface. This supply rate changes in-plane growth rate due to the diffusion of the raw material if there is an uneven pattern or mask in a thin layer near the surface called a boundary layer. The simulation was performed by modeling the gas phase diffusion in the boundary layer with irregularities on the substrate surface. Here, the diffusion constant: D is proportional to the average velocity of molecules in the gas phase: v _t multiplied by the mean free path, and the mean free path is proportional to the reciprocal of pressure: P. Therefore, for example, the higher the pressure in the reaction tube, the smaller the mean free path and the smaller the diffusion constant. By changing the pressure in the reaction tube when the quantum well structure is grown and when etching is performed with a gas containing halogen, the change in speed due to the uneven pattern of the substrate is controlled. The value of D / k (diffusion constant / adsorption coefficient) was obtained by fitting experiment and simulation, and the integration of quantum well laser and EA modulator was estimated from the growth pressure dependence.

  FIG. 1 shows a stacked structure diagram of quantum wells used in this experiment. The quantum well is composed of an InGaAlAs barrier layer (barrier layer) 1 and an InGaAlAs quantum well layer (QW layer) 2.

  FIG. 2A shows a structural diagram of a substrate on which a ridge-like pattern is formed. The ridge pattern is the same material as the substrate. FIG. 2A is a view as seen from above the substrate surface. The ridge width is changed from the middle, and the width is changed to 50 μm and 500 μm. The height of the ridge was 15 μm. By changing the width, the raw material concentration around the ridge changes due to diffusion, and the growth rate can be controlled. According to the calculation results, the growth rate ratio for the laser (LD) part and electroabsorption optical modulator (EA) part formed in the 50 μm wide and 500 μm wide areas, respectively, is 1.1, and hydrogen chloride gas etching. The etching rate ratio was 1.8. Table 1 shows the results of estimation of the LD well and EA quantum wells, the thickness of the barrier layer, and the number of periods. Since it is well known that the oscillation wavelength in the quantum well laser and the absorption wavelength in the EA modulator are determined by the thickness and composition of the quantum well layer, description of these combinations is omitted here. As an optical semiconductor device suitable for communication, the material of the quantum well structure is any one of InGaAsP, InGaAlAs, InGaAsN, and InGaAs, and a material having a laser part wavelength of 1.1 to 1.6 μm can be selected.

  In this way, by changing the ridge width of the LD part and modulator part, reducing the growth pressure during quantum well growth to 24 Torr, and increasing the pressure during etching to 200 Torr, the LD part and EA part Fabrication of a structure with an optimal number of quantum well periods was possible by batch growth.

  Using this technique, the ridge (FIG. 2A) is patterned on the InP substrate in advance, and after the optical confinement layer and the quantum well active layer (1, 2) are grown (FIG. 2B), the pressure is changed. Etching is performed (region indicated by 4 in FIG. 2C), and the pressure is returned again to grow a light confinement layer (not shown). A diffraction grating is dug in the LD portion, and an InP cladding layer and a contact layer (not shown) are grown. The optical confinement layer may be grown as necessary, and may be omitted. After that, as a processing process, the ridge mesa for guiding light is etched, both sides are filled with a dielectric film, the back side is polished, electrodes are formed, both ends are cleaved, and the LD side is coated with high reflectivity By applying an anti-reflection coating on the EA side, an EA modulator integrated DFB laser can be realized. By using such an active layer collective growth technique, it is possible to achieve both lower threshold of LD and lower voltage drive of EA.

  In this example, HCl is used as an etching gas, but methyl chloride (CH 3 Cl) or carbon tetrabromide (CBr 4) may be used.

  As described above, according to the present invention, there is an excellent effect that an EA-DFB integrated quantum well semiconductor laser having an oscillation wavelength in the communication wavelength band and having high performance can be obtained.

1 InGaAlAs barrier layer 2 InGaAlAs quantum well layer 3 InP substrate 4 Hydrogen chloride etched in the reaction tube with increased pressure

Claims (4)

A manufacturing how an optical semiconductor device in which a plurality of semiconductor elements are integrated on a single semiconductor substrate,
Growing a multiple quantum well structure on a ridge having two regions with different pattern widths in contact with each other formed on the semiconductor substrate by a vapor phase growth method under a predetermined pressure;
Under higher pressure than the predetermined pressure, the saw including a etching the multiple quantum well structure, the pattern width is narrow regions of said two areas of said optical semiconductor device is the active layer A distributed feedback laser having a multiple quantum well structure is integrated, and an area having a wide pattern width in the two regions of the optical semiconductor device has an absorption edge having a wavelength shorter than the oscillation wavelength of the distributed feedback laser. The optical modulator having the multiple quantum well structure is integrated, and the etching allows the number of well layers of the multiple quantum well structure of the distributed feedback laser to be the number of well layers of the multiple quantum well structure of the optical modulator. The manufacturing method characterized by making it less than the number of layers . The manufacturing method according to claim 1, wherein the vapor deposition method is an organic metal vapor deposition method.   The manufacturing method according to claim 1, wherein the etching is performed by reactive gas etching. The material of the multiple quantum well structure is any one of InGaAsP, InGaAlAs, InGaAsN, and InGaAs, and a material having an oscillation wavelength of the distributed feedback laser of 1.1 μm to 1.6 μm is selected, and the multiple quantum well the process according to any one of claims 1 to 3 structure is characterized in that it has a distortion between the thickness and the crystal lattice to achieve the oscillation wavelength before Symbol distributed feedback laser.

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