JP2003101044A - Connection structure of optical waveguide and semiconductor light-receiving element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To set a semiconductor light-receiving element which is arranged on a substrate in such a manner that a light-receiving surface is almost in parallel to the light-propagating direction of an optical waveguide, for receiving the propagating light effectively. SOLUTION: The light propagates on the optical waveguide 16 which is provided with clad parts 13, 15 formed on the substrate 11 and a core part 14 in the clad parts 13, 15. This connection structure located between the optical waveguide 16 and the semiconductor light-receiving element 12 is used for detecting the propagating light by using the semiconductor light-receiving element 12 which is arranged in the vicinity of the core part 14 on the substrate 11. In the structure, the semiconductor light- receiving element 12 is installed on an installation part whose surface is formed almost flat in shape by burying an electrode wiring 18 for installing the element 12 in an upper surface of the substrate 11, so that the element 12 is not largely bent. As a result, the increase of a dark current which is caused by stresses corresponding to the bending, generation of cracks in the element 12, and generation of peeling, wrinkles and cracks on a wiring of element 12 can be restrained, and the propagating light can be received effectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide having a high reliability for receiving and detecting light propagated by an optical waveguide formed on a substrate by a semiconductor light receiving element arranged on the same substrate. And a semiconductor light receiving element.

[0002]

2. Description of the Related Art In an optical circuit board, an optoelectronic circuit board, or the like, in order to optically connect the propagating light propagated by an optical waveguide formed on the board to a semiconductor light receiving element arranged on the same board, to receive the light. Various types of optical waveguides and semiconductor light receiving elements are used in the connection structure.

FIG. 3 is a sectional view showing an example of a conventional connection structure between an optical waveguide and a semiconductor light receiving element. In the connection structure shown in FIG. 3, a semiconductor light receiving element is formed on the electrode wiring 38 formed on the substrate 31.
32 is fixed and arranged, and the lower clad 33 /
Optical waveguide 36 composed of core portion 34 and upper cladding portion 35
Are formed. The core portion 34 is surrounded by the lower clad portion 33 and the upper clad portion 35 and is disposed in the clad portion.

In this connection structure, the propagating light propagating through the core portion 34 has its electromagnetic field field 37 spreading outside the core portion 34 as shown in FIG. The light receiving surface of the semiconductor light receiving element 32 arranged in the vicinity of 34 can be optically coupled to receive light.

[0005]

However, in the conventional connection structure as shown in FIG. 3, when the semiconductor light receiving element 32 is mounted on the electrode wiring 38, the electrode of the semiconductor light receiving element 32 is provided in the peripheral portion thereof. Since there is a gap between the vicinity of the center of the semiconductor light receiving element 32 and the upper surface of the substrate 31, the central portion of the semiconductor light receiving element 32 may curve toward the substrate 31 side as shown in FIG. This is particularly noticeable when the thickness of the semiconductor light receiving element 32 is as thin as several μm. When the semiconductor light receiving element 32 is curved in this way, the dark current of the semiconductor light receiving element 32 increases due to the stress generated at the curved portion, or in extreme cases, the semiconductor light receiving element 32 is cracked or the semiconductor light receiving element 32 is cracked. Due to peeling, wrinkles, and cracks in the metal wiring formed on the semiconductor light receiving element 32, the semiconductor light receiving element 32 may be destroyed, or the characteristics as the light receiving element may deteriorate and the expected characteristics may not be obtained. The problem arises.

On the other hand, in Japanese Patent Laid-Open No. 2000-215371, it has been proposed to fill the gap between the center of the semiconductor light receiving element 32 and the substrate 31 with an optical adhesive. However, in this case, the semiconductor light receiving element 32 is curved due to contraction when the optical adhesive material is cured, and stress is applied, which causes a problem. Further, it is not easy to fill the gap generated at the step of the electrode having a thickness of about several μm with a resin such as an optical adhesive.

The present invention has been made in view of the above-mentioned problems in the prior art, and an object thereof is to arrange propagating light propagating in an optical waveguide formed on a substrate in the vicinity of the optical waveguide on the substrate. It is an object of the present invention to provide a connection structure between an optical waveguide and a semiconductor light receiving element, which has a high reliability and can be received and detected by the semiconductor light receiving element.

[0008]

A connection structure of an optical waveguide and a semiconductor light receiving element according to the present invention provides a propagating light propagating through an optical waveguide having a clad portion formed on a substrate and a core portion in the clad portion. A connection structure of an optical waveguide and a semiconductor light receiving element for detecting with a semiconductor light receiving element arranged with a light receiving surface in the vicinity of the core portion on the substrate substantially parallel to the core portion, The device is characterized in that it is installed in an installation part having a substantially flat surface by burying electrode wiring for installing a semiconductor light receiving device on the upper surface of the substrate.

Further, in the connection structure of the optical waveguide and the semiconductor light receiving element of the present invention, the propagation light propagating in the optical waveguide having the clad portion formed on the substrate and the core portion in the clad portion is propagated on the substrate. In the connection structure of an optical waveguide and a semiconductor light receiving element for detecting with a semiconductor light receiving element arranged with the light receiving surface in the vicinity of the core portion substantially parallel to the core portion, the semiconductor light receiving element has an upper surface. An electrode on the upper surface of the electrode and its vicinity by a wiring conductor that electrically connects the electrode and an electrode wiring for mounting the semiconductor light receiving element formed on the upper surface of the substrate around the semiconductor light receiving element. It is characterized by being covered.

According to the connection structure of the optical waveguide and the semiconductor light receiving element of the present invention, the semiconductor light receiving element is installed in such a manner that the surface of the semiconductor light receiving element is formed substantially flat by burying the electrode wiring for mounting the semiconductor light receiving element on the upper surface of the substrate. Since the semiconductor light receiving element is installed in the installation section, the semiconductor light receiving element can be installed in the installation section without causing a large curve or distortion.

Further, according to the connection structure of the optical waveguide and the semiconductor light receiving element of the present invention, the semiconductor light receiving element has an electrode on the upper surface, and this electrode of the semiconductor light receiving element and the upper surface in the vicinity thereof have the electrode and the semiconductor. Since the semiconductor light receiving element is covered by the wiring conductor that electrically connects to the electrode wiring for installing the semiconductor light receiving element formed on the upper surface of the substrate around the light receiving element, Since it is installed in a flat state without riding, the semiconductor light receiving element can be installed without causing bending or distortion.

Therefore, according to the present invention, it is possible to suppress an increase in dark current and a decrease in sensitivity due to the stress caused by the bending and distortion of the semiconductor light receiving element, and to prevent the semiconductor light receiving element from being cracked or the semiconductor light receiving element. Since it is possible to prevent peeling, wrinkles, and cracks from occurring in the metal wiring formed on the element, it is possible to provide a highly reliable connection structure between the optical waveguide and the semiconductor light receiving element.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a connection structure between an optical waveguide and a semiconductor light receiving element of the present invention will be described in detail with reference to the drawings.

1 and 2 are cross-sectional views showing an example of an embodiment of a connection structure between an optical waveguide and a semiconductor light receiving element of the present invention.

In the example shown in FIG. 1, the semiconductor light receiving element 12 is arranged in an installation portion whose surface is formed to be substantially flat by embedding the electrode wiring 18 for installing the semiconductor light receiving element on the substrate 11 on the upper surface of the substrate 11. It is fixed and installed, and an optical waveguide 16 composed of a lower clad portion 13, a core portion 14, and an upper clad portion 15 is formed on it. Further, an electrode wiring 18 for voltage application and photocurrent detection is formed on the lower surface of the semiconductor light receiving element 12.

In the example shown in FIG. 2, the semiconductor light receiving element 22 is fixedly arranged on the substrate 11, the electrodes formed on the upper surface of the semiconductor light receiving element 22 and the substrate 11 around the semiconductor light receiving element 22.
A wiring conductor 28 is formed so as to cover the electrode on the upper surface of the semiconductor light receiving element 22 and the upper surface in the vicinity thereof while electrically connecting to the electrode wiring for installation of the semiconductor light receiving element (shown by the filled portion) formed on the upper surface of the And on top of that,
An optical waveguide 16 including a lower clad portion 13, a core portion 14, and an upper clad portion 15 is formed.

In the connection structure of the optical waveguide and the semiconductor light receiving element of the present invention, a semiconductor light receiving element 12 in which a photoelectric circuit including an electric circuit and the optical waveguide is formed on the substrate 11 and which is embedded in the optical waveguide.・ Various substrates that function as a support substrate for 22 and are used as substrates for handling optical signals, such as optical integrated circuit substrates and optoelectronic mixed substrates, such as silicon substrates, alumina substrates, glass ceramic substrates, and multilayer ceramic substrates. Thin film multilayer ceramic substrates, plastic electrical wiring substrates, etc. can be used.

A substrate is provided with an electrode wiring 18 for installing a semiconductor light receiving element.
As a method of forming an installation portion having a substantially flat surface by burying it on the upper surface of 11, the electrode wire 18 is formed in advance with a groove in which the electrode wire 18 is embedded by a pressing method or an etching method, and then a screen is formed. The material of the electrode wiring 18 may be embedded in the groove by using a printing method, a thin film metal wiring fine processing technique, or the like. When the electrode wiring 18 is embedded and formed on the upper surface of the substrate 11 made of a resin material, the substrate 11
After the electrode wiring 18 is formed on the upper surface of the substrate, the electrode wiring 18 may be embedded in the resin of the substrate 11 by pressure pressing. After that, the surface of the installation portion may be further flattened by polishing, an etch back method, or the like. As the degree of flattening of the surface of the installation portion, the step due to the electrode wiring 18 may be about 1 μm or less.

As a material for the electrode wiring 18 and the wiring conductor 28, a single body using a well-known wiring conductor material such as Au, Ti, Pd, Pt, Al, Cu, W and Cr, or a single layer or a multi-layer made of an alloy thereof is used. Use your body. Also, AuSn
-A solder material such as AuGe may be used as the uppermost layer.

Optical waveguide 16 used in the connection structure of the present invention
Various optical materials capable of forming an optical waveguide can be used as the forming material of (1), and among them, it is preferable to use a siloxane-based polymer. If the optical waveguide is made of a siloxane-based polymer, the lower and upper clad portions 13 and 15 are made of a siloxane-based polymer, and the core portion 14 is made of an optical waveguide 16 made of a siloxane-based polymer containing a metal such as titanium (Ti). Thereby, the optical waveguide 16 having a desired refractive index difference between the cladding portions 13 and 15 and the core portion 14 can be easily manufactured by controlling the titanium content, and the light receiving with the semiconductor light receiving elements 12 and 22 can be performed. It becomes easy to design a structure with good efficiency. Further, since the optical waveguide 16 can be formed at a low temperature of about 100 ° C. to 300 ° C., even when the optical waveguide 16 is formed on the semiconductor light receiving elements 12 and 22 by embedding them, the semiconductor light receiving element 12・ No thermal damage to 22. In addition, the film surface is excellent in flatness / smoothness irrespective of the surface state of the base, and when the optical waveguide 16 is formed so as to embed the semiconductor light receiving elements 12/22, a surface that causes scattering loss. It is preferable because the unevenness can be alleviated.

As such a siloxane-based polymer,
Any resin can be used as long as it has a siloxane bond in the polymer skeleton, and examples thereof include polyphenylsilsesquioxane, polymethylphenylsilsesquioxane, and polydiphenylsilsesquioxane.

Further, the core portion 14 and the clad portions 13 and 15
The metal contained in is not limited to titanium, but germanium (Ge), aluminum (Al),
Erbium (Er) or the like can also be used. In order to form the core portion 14 containing these metals, a siloxane-based polymer layer to which the metal alkoxide is added may be formed and processed into a desired shape and size.

The siloxane polymer used for the cladding portions 13 and 15 may contain the same metal as described above.
In that case, a difference in refractive index may be provided depending on the difference in content with the core portion 14.

In addition, in order to control the refractive index, the refractive index may be controlled by changing the composition of, for example, a siloxane polymer, in addition to adding a metal. Alternatively, a photopolymerization type siloxane polymer may be used to utilize the change in the refractive index caused by the difference in the light irradiation amount.

In addition to the above, the material of the optical waveguide 16 is transparent so that light can be propagated with low loss, and is made of a core member and a clad member which can obtain a desired refractive index difference. Various materials can be used as long as they are combined. Other than siloxane-based polymers, for example, fluorinated polyimide / polymethylmethacrylate (PMMA) /
A resin optical material such as polycarbonate (PC) that can be applied in a solution state is preferably used. Alternatively, an inorganic material such as silica produced by a vapor phase growth method may be used.

As a method of manufacturing the optical waveguide 16, first, a substrate
The lower clad portion 13 is formed on the upper portion 11. Next, after a core layer to be the core portion 14 is formed, photolithography and RI are performed.
The core portion 14 is formed in a predetermined shape by using a well-known thin film microfabrication technique such as E (Reactive Ion Etching). After that, the upper clad portion 15 is formed by coating. According to this thin film microfabrication technique, when forming the core portion 14, the core portions 14 having different widths can be easily manufactured. In addition, when a photo-curable siloxane-based polymer is used, when the unirradiated area is soluble in a specific solution and the cured area becomes insoluble, the core pattern can be easily formed by a method similar to the photolithography method. Can be formed. By using such a planar microfabrication technique, core patterns of the present invention having partially different core widths can be easily formed.

The semiconductor light receiving elements 12 and 22 arranged and installed on the substrate 11 are, for example, Si.Ge.InP.GaAs.
A semiconductor light receiving element manufactured using a semiconductor material such as InAs / InGaAsP, which is a pn photodiode
pin photodiode, phototransistor, MSM
A semiconductor light receiving element such as a (Metal-Semiconductor-Metal) photodiode or avalanche photodiode is used.

[0028]

EXAMPLES Next, concrete examples of the connection structure between the optical waveguide and the semiconductor light receiving element of the present invention will be described.

Example 1 As shown in FIG. 1, the refractive index is 1.447.
Electrode wiring 18 made of Au was formed by a lift-off method in a groove having a depth of 1.5 μm formed on the upper surface of the quartz substrate 11 by photolithography and dry etching.
After that, the upper surface of the substrate 11 was flattened by lapping so that the maximum height Rmax of the surface roughness was about 0.1 μm or less in the mounting region of the installation portion of the semiconductor light receiving element 12.

Next, the semiconductor light receiving element 12 has a thickness of 1 μm.
Prepare an MSM photodiode with a light-receiving surface of 100 μm square and a ladder-type electrode wiring made of Ti / Pt / Au formed on InGaAs, and make the MSM electrode face down to make electrical connection with the electrode wiring 18. It was placed in the installation section and fixed. After that, heat treatment was performed so that good electrode connection was obtained.

Next, a step index type optical waveguide 16 was formed in which the clad portions 13 and 15 were made of a siloxane polymer and the core portion 14 was made of a titanium-containing siloxane polymer. The thickness of each part of the optical waveguide 16 is 2 μm for the lower clad part 13, 7 μm for the core part 14 and 8 μm for the upper clad part 15.
And The width of the core portion 14 was 7 μm. The clad portions 13 and 15 have a refractive index of 1.448, and the core portion 14 has a refractive index of 1.4533.
And

Further, in order to detect an electric signal from the semiconductor light receiving element 12, a part of the electrode wiring 18 was exposed by a dry etching technique and electrically connected to an external electric circuit.

With respect to the connection structure between the optical waveguide of the present invention and the semiconductor light receiving element having the structure shown in FIG. 1 manufactured in this manner, the wavelength of 1.3 μm from the optical input port 17 to the optical waveguide.
The light intensity was measured by propagating m light and detecting the propagating light leaking from the core portion 14 in the semiconductor light receiving element 12.
It has been confirmed that the optical waveguide 16 and the semiconductor light receiving element 12 have an optical coupling efficiency of about 7%, and the propagating light can be detected with sufficient intensity.

Further, neither destruction of the semiconductor optical device 12 nor remarkable deterioration of characteristics was observed before and after the formation of the optical waveguide 16.

Example 2 As shown in FIG. 2, the refractive index is 1.447.
On the upper surface of the quartz substrate 11 as the semiconductor light receiving element 22 having a thickness of 1
MSM with a light receiving surface of 100 μm square in which a ladder type electrode wiring made of Ti / Pt / Au is formed on μm InGaAs
Type photodiode was installed with the MSM electrode facing up. At this time, the semiconductor light receiving element 22 and the quartz substrate 11 were brought into close contact with each other by the Van der Swirl force.

Next, after forming a photoresist pattern, Ti / Pt having a total thickness of 2 μm is formed by an electron beam evaporation method.
/ Au layer is formed, an unnecessary portion is removed by a lift-off method, and an MSM electrode on the upper surface of the semiconductor light receiving element 22 and an electrode for mounting the semiconductor light receiving element provided on the upper surface of the substrate 11 around the semiconductor light receiving element 22. Wiring conductor 28 that electrically connects to the wiring
Was formed. The wiring conductor 28 electrically connects the MSM electrode of the semiconductor light receiving element 22 and the electrode wiring of the substrate 11, and covers the MSM electrode of the semiconductor light receiving element 22 and the peripheral portion of the upper surface in the vicinity of the MSM electrode. The adhesion strength between the substrate 11 and the substrate 11 is increased.

Next, a step index type optical waveguide 16 was formed in which the clad portions 13 and 15 were made of a siloxane polymer and the core portion 14 was made of a titanium-containing siloxane polymer. The thickness of each part of the optical waveguide 16 is 2 μm for the lower clad part 13, 7 μm for the core part 14 and 8 μm for the upper clad part 15.
And The width of the core portion 14 was 7 μm. The clad portions 13 and 15 have a refractive index of 1.448, and the core portion 14 has a refractive index of 1.4533.
And

Further, in order to detect an electric signal from the semiconductor light receiving element 12, a part of the wiring conductor 28 was exposed using a dry etching technique and connected to an external electric circuit.

Regarding the connection structure between the optical waveguide of the present invention and the semiconductor light receiving element thus manufactured, an optical input port
When light having a wavelength of 1.3 μm is propagated from 17 to the optical waveguide and the propagating light leaked from the core portion 14 is detected by the semiconductor light receiving element 22 to measure the light intensity, the optical waveguide 16 and the semiconductor light receiving element 22 are Has an optical coupling efficiency of about 5%, and it was confirmed that the propagating light can be detected with sufficient intensity.

Further, neither destruction of the semiconductor optical device 22 nor remarkable deterioration of characteristics was observed before and after the formation of the optical waveguide 16.

[Example 3] For comparison with the examples of the present invention, trial evaluation of comparative examples according to the conventional example was performed.

As shown in FIG. 3, an electrode wiring 38 made of Au having a thickness of 1.5 μm was formed on the upper surface of the quartz substrate 11 having a refractive index of 1.447. Next, as a semiconductor light receiving element 12, an MSM photodiode having a light receiving surface of 100 μm square, in which a ladder type electrode wiring made of Ti / Pt / Au was formed on InGaAs having a thickness of 1 μm, was used, with the MSM electrode facing downward.
It was placed and fixed so that it could be electrically connected to 38. After that, heat treatment was performed so that good electrode connection was obtained.

Next, a step index type optical waveguide 36 was formed in which the clad portions 33 and 35 were made of a siloxane polymer and the core portion 34 was made of a titanium-containing siloxane polymer. The thickness of each part of the optical waveguide 36 is 2 μm for the lower clad 33, 7 μm for the core 34 and 8 μm for the upper clad 35.
And The width of the core portion 34 was 7 μm. The clad portions 33 and 35 have a refractive index of 1.448, and the core portion 34 has a refractive index of 1.4533.
And

Further, in order to detect an electric signal from the semiconductor light receiving element 32, a part of the electrode wiring 38 was exposed by a dry etching technique and connected to an external electric circuit.

An attempt was made to evaluate the connection structure between the optical waveguide and the semiconductor light receiving element according to the conventional example manufactured in this way, and the semiconductor light receiving element 32 was formed before and after the formation of the optical waveguide 36.
As a result, the dark current of the photodiode has increased about 50 times. Further, in some cases, the characteristics of the photodiode were not obtained during the evaluation. As a result of observing a cross section of this with an SEM (scanning electron microscope), as a result of the semiconductor light receiving element 32 being curved, peeling was observed in the metal wiring formed on the semiconductor light receiving element 32.

[0046]

As described above, according to the connection structure of the optical waveguide and the semiconductor light receiving element of the present invention, the surface of the semiconductor light receiving element is improved by burying the electrode wiring for mounting the semiconductor light receiving element on the upper surface of the substrate. Since the semiconductor light receiving element is installed in the installation portion formed to be substantially flat, the semiconductor light receiving element can be installed without causing a large curve or distortion in the installation portion.

Further, according to the connection structure of the optical waveguide and the semiconductor light receiving element of the present invention, the semiconductor light receiving element has the electrode on the upper surface, and the electrode of the semiconductor light receiving element and the upper surface in the vicinity thereof have the electrode and the semiconductor. Since the semiconductor light receiving element is covered by the wiring conductor that electrically connects to the electrode wiring for installing the semiconductor light receiving element formed on the upper surface of the substrate around the light receiving element, Since it is installed in a flat state without riding, the semiconductor light receiving element can be installed without causing bending or distortion.

Therefore, according to the present invention, it is possible to suppress an increase in dark current and a decrease in sensitivity due to the stress caused by the bending and distortion of the semiconductor light receiving element, and to prevent the semiconductor light receiving element from being cracked or receiving light. Since it is possible to prevent peeling, wrinkles, and cracks from occurring in the metal wiring formed in the element, it is possible to provide a highly reliable connection structure between the optical waveguide and the semiconductor light receiving element.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of an embodiment of a connection structure between an optical waveguide and a semiconductor light receiving element of the present invention.

FIG. 2 is a sectional view showing an example of an embodiment of a connection structure between an optical waveguide and a semiconductor light receiving element of the present invention.

FIG. 3 is a sectional view showing an example of a conventional connection structure between an optical waveguide and a semiconductor light receiving element.

[Explanation of symbols]

11, 31 ... Substrate 12, 22, 32 ... Semiconductor light receiving element 13、33 ・ ・ ・ ・ ・ Lower clad 14、34 ・ ・ ・ ・ ・ Core part 15、35 ・ ・ ・ ・ ・ Upper clad 16, 36 ・ ・ ・ ・ ・ Optical waveguide 18, 38 ... Electrode wiring 28 ........ Wiring conductor

Claims (2)

[Claims] 1. A light receiving surface for propagating through a light waveguide having a clad portion formed on a substrate and a core portion in the clad portion and having a light-receiving surface near the core portion on the substrate A connection structure of an optical waveguide and a semiconductor light receiving element for detection by semiconductor light receiving elements arranged in parallel, wherein the semiconductor light receiving element has electrode wiring for mounting the semiconductor light receiving element embedded in the upper surface of the substrate. Accordingly, the connection structure between the optical waveguide and the semiconductor light receiving element is characterized in that the optical waveguide and the semiconductor light receiving element are installed in an installation part having a substantially flat surface. 2. A light receiving surface for propagating light propagating through an optical waveguide having a clad portion formed on a substrate and a core portion in the clad portion is provided in the vicinity of the core portion on the substrate, and a light receiving surface is substantially formed on the core portion. A connection structure of an optical waveguide and a semiconductor light receiving element for detection by semiconductor light receiving elements arranged in parallel, wherein the semiconductor light receiving element has an electrode on an upper surface, and the electrode and the periphery of the semiconductor light receiving element. The optical waveguide and the semiconductor light receiving element characterized in that the electrode and the upper surface in the vicinity thereof are covered with a wiring conductor for electrically connecting the electrode wiring for mounting the semiconductor light receiving element formed on the upper surface of the substrate. Connection structure with.