JP6703440B2 - Semiconductor optical modulator and method of making the same - Google Patents

Description

The present invention relates to a semiconductor optical modulator and a manufacturing method thereof, and more particularly to a structure of an optical input/output waveguide portion of a semiconductor optical modulator and a manufacturing method thereof.

With the increase in capacity of optical communication systems in recent years, high-order multilevel modulation/demodulation transmission technology using coherent signal processing technology has been actively developed. In the transmission method using the high-order multilevel modulation/demodulation transmission technology, a combination of a DC diode and an external optical modulator is used in the transmitter. Here, as a typical external optical modulator used in the optical communication system, there is an LN optical modulator made of LiNbO ₃ . The LN optical modulator controls the phase of light by applying an electric field in the optical waveguide and changing the refractive index in the optical waveguide by the electro-optic effect. Such an optical modulator can function as a high-performance switch by combining a large number of optical waveguides such as an optical phase modulator and a Mach-Zehnder type optical modulator. However, the LN optical modulator has an optical waveguide length of cm order, which is very large as compared with peripheral components, and as a result, there is a problem that the size reduction of the transmitter is limited. As a structure for solving this problem, an InP optical modulator using the same operation principle as the LN optical modulator has been proposed (Non-Patent Document 1).

K. Tsuzuki, T. Ishibashi, T. Ito, S. Oku, Y. Shibata, R. Iga, Y. Kondo and Y. Tohmori “40 Gbit=s nin InP Mach-Zehnder modulator with ap voltage of 2.2 V” Electronics Letters, vol. 39, no. 20, pp. 1464-1466, 2003.

FIG. 1 is a diagram showing a semiconductor optical modulator according to an embodiment of the present invention, FIG. 1(a) is a top view of the semiconductor optical modulator, and FIG. 1(b) is (a) A-A. It is sectional drawing in'. In the optical modulator 100, a semiconductor high-mesa optical waveguide structure 103 is formed on a ground contact layer 112 formed on a semi-insulating InP substrate 111. The signal electrode 102 is formed on the upper surface of the phase modulation portion of the semiconductor high-mesa optical waveguide structure 103, and the ground electrodes 101 are formed on both sides of the phase modulation portion of the semiconductor high-mesa optical waveguide structure 103. An organic film 105 is formed between the ground electrode 101 and the signal electrode 102 on the upper surface of the ground contact layer 112, and an insulating film is formed on a portion other than the ground electrode 101, the signal electrode 102, and the organic film 105 on the upper surface of the ground contact layer 112. It is covered with 104.

Referring to FIG. 1B, in the phase modulator of the semiconductor optical modulator 100, the ground contact layer 112 is formed on the semi-insulating InP substrate 111. A 1-semiconductor high-mesa optical waveguide structure 103 including a first cladding layer 113, a core layer 114, and a second cladding layer 115 is provided on the ground contact layer 112. The semiconductor high-mesa optical waveguide structure 103 is protected by an insulating film 104 and an organic film 105. The ground electrode 101 is formed on the portion of the ground contact layer 112 where the organic film 105 is not formed, and the signal electrode 102 is formed on the second cladding layer 115.

As shown in FIG. 1, the semiconductor optical modulator 100 realizes a high speed operation by using a traveling wave electrode structure for propagating an optical signal and an electric signal in the same direction as the signal electrode 102 (Non-Patent Document 1). 1). The signal electrode 102 can realize a high band of 40 Gbit/s or more by making it sufficiently thick (Non-Patent Document 1).

Here, in the semiconductor optical modulator 100, in order to connect the semiconductor high-mesa optical waveguide structure 103 to the optical fiber, it is necessary to form the end face of the input/output optical waveguide into a shape that allows easy connection to the optical fiber. In general, the InP substrate 111 is polished to a thickness of 300 μm or less, and a vertical input/output optical waveguide end face is formed by cleavage. 2 and 3 are cross-sectional views of the BB′ and CC′ portions in the semiconductor optical modulator 100 of FIG. The portions BB′ and CC′ in FIG. 2 are the end faces of the input/output optical waveguide of the semiconductor optical modulator 100. Referring to FIG. 2, the semiconductor optical modulator 100 includes a semi-insulating InP substrate 111, a ground contact layer 112 on the semi-insulating InP substrate 111, a first cladding layer 113 on the ground contact layer 112, and a first cladding layer 113. The groove portion 201 reaching the ground contact layer 112 is formed beside the semiconductor high-mesa optical waveguide structure 103 including the core layer 114 on the first cladding layer 113 and the second cladding layer 115 on the core layer 114. The whole is covered with the insulating film 104.

Here, the optical waveguide structure of the BB′ and CC′ portions of the semiconductor optical modulator 100 of FIG. 1 is basically the same structure, and the width of the optical waveguide is about 2 μm to 5 μm. However, when the end surface of the optical waveguide structure is formed by cleavage, a large impact is applied to the end of the optical waveguide structure, and as shown in FIG. 3, a part of the end surface of the optical waveguide is chipped (301), resulting in a large decrease in yield. There is.

As a method for solving this problem, a method of removing the insulating film 104 and then cleaving is conceivable. However, when the insulating film 104 is removed by dry etching, the semiconductor surface may be damaged and light loss may be increased. There is. Although it is possible to remove the insulating film 104 by wet etching with hydrofluoric acid or the like, it is difficult to control and the insulating film in an unintended region may be etched.

In order to solve such a problem, a first aspect of the present invention is a semiconductor optical modulator, which comprises a semi-insulating InP substrate and a ground contact layer formed on the semi-insulating InP substrate. A semiconductor high-mesa optical waveguide structure formed on the ground contact layer, comprising: a first clad layer formed on the ground contact layer; a core layer formed on the first clad layer; A semiconductor high-mesa optical waveguide structure including a second cladding layer formed on a core layer, an insulating film covering the semiconductor high-mesa optical waveguide structure, and one of the insulating films on the side of the semiconductor high-mesa optical waveguide structure. An organic film having a height lower than that of the first cladding layer of the semiconductor high-mesa optical waveguide structure, the organic film being formed in a light input/output portion of the semiconductor high-mesa optical waveguide structure. It is characterized by

A second aspect of the present invention is a method for manufacturing a semiconductor optical modulator, which comprises sequentially growing a ground contact layer, a first cladding layer, a core layer, and a second cladding layer on a semi-insulating InP substrate. A step of forming a semiconductor high-mesa optical waveguide structure by etching, a step of growing an insulating film so as to cover the second cladding layer and the semiconductor high-mesa optical waveguide structure, and an organic film formed on the insulating film. And a step of removing the organic film to a position lower than the height of the first cladding layer of the semiconductor high-mesa optical waveguide structure while leaving a part of the insulating film beside the semiconductor high-mesa optical waveguide structure. , wherein the organic film is formed on the light input and output portion of said semiconductor mesa waveguide structure and said Rukoto.

The physical strength of the input/output optical waveguide structure of the semiconductor optical modulator having an InP substrate is increased, the damage of the input/output optical waveguide structure due to the impact at the time of cleavage is suppressed, and the production yield of the semiconductor optical modulator is improved. ..

It is a figure which shows the structure of a semiconductor optical modulator. (A) is a top view which shows the structure of a semiconductor optical modulator, (b) is sectional drawing of the AA' part of (a). FIG. 2 is a cross-sectional view of BB′ and CC′ portions in FIG. 1. FIG. 2 is a cross-sectional view of BB′ and CC′ portions in FIG. 1. It is a figure which shows the structure of a semiconductor optical modulator. (A) is a top view which shows the structure of a semiconductor optical modulator, (b) is sectional drawing of DD' part of (a). FIG. 5 is a cross-sectional view of EE′ and FF′ portions in FIG. 4 . FIG. 5 is a cross-sectional view of EE′ and FF′ portions in FIG. 4 . FIG. 5 is a cross-sectional view of EE′ and FF′ portions in FIG. 4 .

Here, embodiments of the present invention will be described with reference to the drawings.

FIG. 4 is a diagram showing a semiconductor optical modulator according to an embodiment of the present invention, FIG. 4(a) is a top view of the semiconductor optical modulator, and FIG. 4(b) is (a) DD. It is sectional drawing in'. Referring to FIG. 4B, in the phase modulator of the semiconductor optical modulator 400, the ground contact layer 412 is formed on the semi-insulating InP substrate 411. A semiconductor high-mesa optical waveguide structure 403 including a first cladding layer 413, a core layer 414, and a second cladding layer 415 is provided on the ground contact layer 412. The semiconductor high-mesa optical waveguide structure 403 is protected by an insulating film 404 and an organic film 405. A ground electrode 401 is formed on a portion of the grant contact layer 412 where the organic film 405 is not formed, and a signal electrode 402 is formed on the second cladding layer 415. Referring to FIG. 4A, an organic film 405 is formed between the ground electrode 401 and the signal electrode 402 on the upper surface of the ground contact layer 412, and the ground electrode 401, the signal electrode 402 and the organic electrode 405 on the upper surface of the ground contact layer 412 are formed. The portion other than the film 405 is covered with the insulating film 404.

FIG. 5 is a cross-sectional view of EE′ and FF′ portions of FIG. Portions EE′ and FF′ in FIG. 4 are portions of the input/output optical waveguide end face of the semiconductor optical modulator 400. Referring to FIG. 5, the semiconductor optical modulator 400 includes a semi-insulating InP substrate 411, a ground contact layer 412 on the semi-insulating InP substrate 411, a first cladding layer 413 on the ground contact layer 412, and a first clad layer 413. The core layer 414 on the first clad layer 413, the second clad layer 415 on the core layer 414, and the insulating film 404 on the second clad layer 415 are provided. A groove 501 reaching the ground contact layer 412 is formed beside the semiconductor high-mesa optical waveguide structure 403, and an organic film 405 is formed on the bottom surface of the groove 501.

6 and 7 are cross-sectional views of EE′ and FF′ portions showing the manufacturing process of the semiconductor optical modulator 400 of FIG. Referring to FIG. 6, a semiconductor optical modulator 400 includes a semi-insulating InP substrate 411, a ground contact layer 412, a first clad layer 413, a core layer 414, and a second clad layer 415, which are sequentially formed in a metal organic vapor phase. It grows by the growth method or the molecular beam epitaxy method. Next, after a SiO ₂ mask for forming the groove 501 is formed on the second cladding layer 415, a semiconductor including the first cladding layer 413, the core layer 414, and the second cladding layer 415 is formed by dry etching. A high-mesa optical waveguide structure 403 is formed, and the SiO ₂ mask is removed by wet etching. At this time, the width of the semiconductor high-mesa optical waveguide structure 403 is 2 μm to 5 μm.

Referring to FIG. 7, insulating film 404 is deposited on semiconductor optical modulator 400 having semiconductor high-mesa optical waveguide structure 403 formed thereon, organic film 405 is applied by spin coating, and organic film 405 is cured by annealing. After that, the organic film is removed by etching, leaving a part of the organic film 405. At this time, the phase modulation portion is etched until the ground contact layer appears, and the end face portion of the input/output optical waveguide is covered with the organic film until the height of the organic film 405 becomes lower than that of the first cladding layer 413. Etch 405.

In this etching process, in the end face portion of the input/output optical waveguide, since the width of the groove 501 is small, the etching solution does not penetrate into the organic film, the organic film becomes thick, and the organic film is left unintentionally. It is formed. Since the insulating film 404 has a sufficiently high selection ratio (etching rate ratio) with respect to the organic film 405, the organic film 405 is dry-etched to a height lower than that of the first cladding layer 413. However, the insulating film 404 does not disappear.

Since the input/output optical waveguide end face structure of this embodiment holds the input/output optical waveguide by the organic film 405, the impact of the cleavage applied to the end of the input/output optical waveguide is mitigated, and the damage of the input/output optical waveguide is suppressed. .. The height (thickness) when leaving the organic film 405 is required to some extent in order to maintain the strength, but it is necessary to prevent it from becoming too high. This is because if the thickness is too high (thickness), the physical strength of the organic film 405 increases and the organic film 405 itself cannot be cleaved. For example, in the present embodiment, when the thickness of the first cladding layer is 2 μm and the thickness of the organic film is 0.01 or more and less than 2 μm, the physical strength of the input/output optical waveguide structure is increased, It is possible to suppress damage to the optical waveguide structure during cleavage and improve the yield of the InP optical modulator. On the other hand, when the height of the organic film 405 is 2 μm or more, the organic film 405 itself cannot be cleaved.

The first cladding layer 413 and the second cladding layer 415 may be either InP or InGaAsP. The core layer 414 may be either InGaAsP/InP or InAlGaAs/InAlAs. Further, the insulating film 404 may be made of SiO ₂ or SiON. Furthermore, the organic film 405 may be either BCB or polyimide. Further, in the present embodiment, an example of one Mach-Zehnder type optical modulator is given, but the effect of the present invention can be obtained even in an optical modulator in which a plurality of Mach-Zehnder type optical modulators are integrated.

100, 400 semiconductor optical modulator 101, 401 ground electrode 102, 402 signal electrode 103, 403 semiconductor high-mesa optical waveguide structure 104, 404 insulating film,
105, 405 Organic film 111, 411 InP substrate,
112, 412 ground contact layer,
113, 413 first cladding layer,
114, 414 core layers,
115, 415 second cladding layer,
201, 501 Groove portion 301 chipped

Claims (2)

A semi-insulating InP substrate,
A ground contact layer formed on the semi-insulating InP substrate;
A semiconductor high-mesa optical waveguide structure formed on the ground contact layer,
A first cladding layer formed on the ground contact layer,
A core layer formed on the first cladding layer,
A second cladding layer formed on the core layer,
A semiconductor high-mesa optical waveguide structure comprising
An insulating film covering the semiconductor high-mesa optical waveguide structure,
An organic film that is partially covered on the insulating film beside the semiconductor high-mesa optical waveguide structure and has a height lower than that of the first cladding layer of the semiconductor high-mesa optical waveguide structure,
Equipped with
The organic layer is a semiconductor optical modulator according to claim Rukoto formed on the light input and output portion of said semiconductor mesa waveguide structure. A step of sequentially growing a ground contact layer, a first cladding layer, a core layer, and a second cladding layer on the semi-insulating InP substrate,
Forming a semiconductor high-mesa optical waveguide structure by etching,
Growing an insulating film to cover the second cladding layer and the semiconductor high-mesa optical waveguide structure;
Forming an organic film on the insulating film,
Removing the organic film to a position lower than the height of the first cladding layer of the semiconductor high-mesa optical waveguide structure while leaving a part of the insulating film on the side of the semiconductor high-mesa optical waveguide structure.
Equipped with
The organic layer is how to create a semiconductor optical modulator according to claim Rukoto formed on the light input and output portion of said semiconductor mesa waveguide structure.

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