JP2592752B2 - Semiconductor optical waveguide device and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to various semiconductor optical waveguide devices for performing light intensity modulation, optical switching, and the like using an optical waveguide, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, optical waveguide elements, such as an optical (intensity) modulator, an optical switch, an optical polarization plane control element, and a light propagation mode control element, are formed of a single crystal semiconductor having an electro-optical effect such as GaAs or InP. A single-mode-propagating optical waveguide is formed, its shape is devised, electrodes are provided in an appropriate shape, and light passing through the optical waveguide is controlled by an electro-optic effect.

[0003] Specifically, a periodic table I such as GaAs or InP is used.
In the case of using a compound semiconductor composed of Group II and Group V, another mixed crystal having a different refractive index, for example, in the case of GaAs, AlGa having a lower refractive index than GaAs on a GaAs substrate.
An As layer is formed by epitaxial growth, and a GaAs layer is further formed thereon by epitaxial growth.
An optical waveguide is formed in the As layer.

However, such a method has some limitations. First, it is difficult to practically obtain a film thickness of 5 μm or more due to the problem of the growth rate and the strain in the crystal generated during the growth. Usually, the optical fiber used for optical communication is a single mode type,
The core diameter (portion where light is confined) is about 10 μm. Therefore, when optical coupling is performed with an optical waveguide having a thickness of 5 μm or less, coupling loss due to mismatch of diameters becomes extremely large.

[0005] In addition, since epitaxial growth is difficult if the lattice constants do not substantially match, an expensive compound semiconductor substrate must be used for the substrate, the types of films that can be formed thereon are restricted, and mass productivity is low. There were problems such as bad things.

[0006]

As described above, in a semiconductor optical waveguide device composed of a compound semiconductor epitaxially grown multilayer film, an expensive compound semiconductor substrate must be used as the substrate, which has a large coupling loss between the optical waveguide and the optical fiber. There is a problem that there are restrictions on the semiconductors that can be used, and mass productivity is poor due to epitaxial growth.

The present invention solves the above-described problems, and provides a structure having a uniform refractive index of the optical waveguide portion and a thickness corresponding to the diameter of the optical fiber core, thereby greatly reducing the coupling loss with the optical fiber. It is intended to reduce to.

[0008]

In order to solve the above-mentioned problems, the present invention provides a single crystal semiconductor substrate having an electro-optical effect, which is bonded to a glass substrate using low melting point glass or silicon or a silicon compound. It has an optical waveguide formed by a refractive index difference from a glass substrate, and controls light passing through the optical waveguide by an electro-optic effect.

[0009]

According to the present invention, it is possible to obtain a semiconductor optical waveguide element which has a small coupling loss with an optical fiber, can use an inexpensive glass substrate, has few restrictions on the semiconductors that can be used, and has excellent mass productivity.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction of a semiconductor optical waveguide device according to each embodiment of the present invention, particularly when applied to an optical modulator, and a method of manufacturing the same will be described with reference to the drawings.

(Embodiment 1) FIGS. 1 and 2 show a first embodiment of the configuration of this embodiment. FIG. 1 shows an overall perspective view,
This shows a case where the present invention is applied to an optical modulator. In FIG. 1, reference numeral 1 denotes a glass substrate, 2 denotes a single crystal semiconductor substrate having an electro-optical effect bonded to the glass substrate 1, and more specifically, GaAs. The substrate 3 is an input / output optical waveguide formed on the GaAs substrate 2, 4 is one of the first branched optical waveguides branched from the input portion into two, 5 is the other second branched optical waveguide, Reference numerals 6 and 7 denote electrodes formed on both sides of the second branch optical waveguide 5, and reference numeral 8 denotes a bonded low melting point glass layer.

FIG. 2 shows A of the central portion of the optical modulator shown in FIG.
FIG. 2 is a cross-sectional view of FIG. 2A, and as shown in FIG. 2, the cross section of the first and second branch optical waveguides 4 and 5 has a trapezoidal head portion, and has a so-called ridge-type optical waveguide structure. . The cross-sectional shape of the input / output optical waveguide 3 is also the same. Reference numeral 9 denotes a guided light propagation unit.

The configuration of the optical modulator itself is what is called a Mach-Zehnder type, in which light incident from the input portion of the input / output optical waveguide 3 is branched into two, and one of the branched second optical waveguides 5 is formed. (The first branch optical waveguide 4 may be used)
An electric field is applied to the electrodes by the electrodes 6 and 7, and by the electro-optic effect,
By changing the refractive index of the optical waveguide portion to change the propagation speed of the guided light,
By making the phase of the light different at the recombination part,
In this configuration, the intensity of light at the output section of the input / output optical waveguide section 3 is modulated.

If two layers having a difference in the refractive index of a certain degree or more are laminated, light can be confined to the one having a larger refractive index, and an optical waveguide can be formed. Since the refractive index of GaAs is about 3.6 and the refractive index of glass is usually in the range of 1.4 to 1.6, the light of GaAs
It is easily confined in the substrate 2. GaAs substrate 2
When the ridge structure is provided, the portion under the ridge has a larger effective refractive index than the other portions, so that the light is confined under the ridge, and the lower portion of the ridge acts as an optical waveguide.

In this case, the optical waveguide has a trapezoidal or rectangular head and a uniform refractive index inside, so that the center of the guided light is near the center of the optical waveguide and has a shape close to a circle. . The cross section of the input / output optical waveguide section 3 also has the same shape, and therefore, the coupling efficiency with the optical fiber section structure having a diameter of 10 μm is extremely good.

A typical value of each dimension is that the thickness of the glass substrate 1 is 1
mm, the thickness of the GaAs substrate 2 was 7 μm, the height of the ridge was 3 μm, the width of the optical waveguide was 10 μm, the length of the branch optical waveguide was 1 cm, and the total length of the optical waveguide was 3 cm. Electrodes 6 and 7 used aluminum.

With the above-described configuration, the coupling loss with the optical fiber is reduced to 1.0 dB or less on one side by bonding and fixing using an adhesive whose refractive index is matched. When a conventional epitaxially grown layered optical waveguide is used, a similar coupling and fixing method results in a typical coupling loss of about 1.
It was greatly improved from 5 to 3 dB. The performance as an optical modulator was almost the same as that of a conventional GaAs optical waveguide. The measurement was performed at a wavelength of 0.8 μm.

(Embodiment 2) FIG. 3 shows a second embodiment of the configuration of the optical waveguide device of this embodiment. FIG. 3 is a perspective view of the whole, which shows a case where the present invention is applied to an optical modulator. In FIG. 3, reference numeral 10 denotes a silicon layer for bonding the glass substrate 1 and the GaAs substrate 2. In addition, the same components as those in the first embodiment shown in FIG. 1 are denoted by the same reference numerals.

Here, the refractive index of the silicon 10 is different from that of GaAs.
If it is made sufficiently thinner than the substrate 2, the glass substrate 1
Due to the difference in refractive index between the GaAs substrate 2 and the GaAs substrate 2, light can be effectively confined toward the GaAs substrate 2 having a large refractive index, and an optical waveguide can be formed.

By using polycrystalline silicon or amorphous silicon as silicon, almost the same effect was obtained in each case. Thus, the light incident on the GaAs substrate 2 was confined in the thin plate. Further, by providing the ridge structure, the portion under the ridge has a larger effective refractive index than the other portions, so that light is confined under the ridge, and thus the ridge lower portion acts as an optical waveguide. The shape of the waveguide in this case was almost the same as that of the first embodiment, and therefore, the coupling efficiency of the optical fiber with the circular optical waveguide structure was extremely good.

As a typical value of each dimension, the film thickness of silicon 10 is
When the size was 0.5 μm and other dimensions were the same as in Example 1, almost the same characteristics as in Example 1 were obtained. For example, the coupling loss with the optical fiber was 1.0 dB or less on one side, as in the case of Example 1, and could be greatly improved.

(Embodiment 3) FIG. 4 shows a third embodiment of the configuration of the optical waveguide device of the present embodiment. FIG. 4 shows a perspective view of the whole, which shows a case where the present invention is applied to an optical modulator. In FIG. 4, reference numeral 11 denotes a glass substrate 1 and a GaAs substrate 2.
Is a layer of a silicon compound for bonding the layers. In addition, FIG.
The same reference numerals are given to the same components as those in the first embodiment shown in FIG.

Here, the refractive index of the silicon compound 11 is Ga
Although it is different from As, if the thickness is about 100 nm to 1 μm and is sufficiently thinner than the GaAs substrate 2, the difference in the refractive index between the glass substrate 1 and the GaAs substrate 2 also results in the GaAs substrate 2 having a larger refractive index. The light can be effectively confined in the substrate, and an optical waveguide can be formed.

By using silicon oxide or silicon nitride as the silicon compound, almost the same effect was obtained in each case. Thus, the light incident on the GaAs substrate 2 was confined in the thin plate. Further, by providing the ridge structure, the portion under the ridge has a larger effective refractive index than the other portions, so that light is confined under the ridge, and thus the ridge lower portion acts as an optical waveguide. The shape of the waveguide in this case was almost the same as that of the first embodiment, and therefore, the coupling efficiency of the optical fiber with the circular optical waveguide structure was extremely good.

As a representative value of each dimension, when the thickness of the silicon compound 11 is 0.5 μm and other dimensions are the same as those in the first embodiment, almost the same characteristics as in the first embodiment are obtained. For example, the coupling loss with the optical fiber is 1.
It was below 0dB, which was a great improvement.

(Embodiment 4) A first example of a method of manufacturing an optical waveguide device according to this embodiment will be described.

First, the surfaces of the mirror-polished glass substrate and the GaAs substrate were extremely cleaned by etching. Specifically, the glass substrate was a hydrofluoric acid-based etchant, and the GaAs substrate was a sulfuric acid-hydrogen peroxide etchant, and the respective surfaces were extremely clean and flat by etching.

Next, a low-melting-point glass thin film was formed on one surface of each with a thickness of 0.3 μm by sputtering.

Next, the low melting point glass thin films are brought into contact with each other,
The glass substrate and the GaAs substrate were overlapped and heated to a temperature near the melting point of the low-melting glass. As a result, the low-melting glass was softened or melted, and a strong bond was obtained. Although the thickness of the bonding layer slightly varies depending on the heat treatment temperature, generally, the higher the temperature, the smaller the thickness formed by sputtering.

Next, the GaAs substrate was thinned by mechanical polishing and etching.

After reducing the thickness to 10 μm, an etching mask is formed on the pattern of the optical waveguide structure shown in Embodiment 1 by photolithography, and etching is performed.
The portion other than the optical waveguide was etched away by 3 μm.

A photoresist was used as a mask, and a sulfuric acid-hydrogen peroxide hydrofluoric acid type etching solution was used as an etching solution.

Thereafter, the resist mask was removed, and an aluminum electrode was formed by ordinary photolithography and etching techniques. Thus, the structure of the optical waveguide device shown in Example 1 (FIG. 1) was obtained. The coupling characteristics of this element with the optical fiber were the same as those in Example 1.

(Embodiment 5) A second example of a method for manufacturing an optical waveguide device of the present embodiment will be described.

In the same manner as in Example 4, the surfaces of the mirror-polished glass substrate and the GaAs substrate were made extremely clean and flat by etching.

Next, an amorphous silicon thin film was formed with a thickness of 0.25 μm on each side by sputtering.

Next, the surface of the amorphous silicon film is cleaned and hydrophilized with a hydrofluoric acid-based etchant, and the amorphous silicon thin films are brought into contact with each other immediately after being immersed in pure water. ° C
At a temperature of As a result, a strong bond was obtained via the amorphous silicon film. The higher the heat treatment temperature, the higher the strength of the joint.

Thereafter, aluminum electrodes were formed in the same manner as in Example 4 to obtain the structure of the optical waveguide device shown in Example 2 (FIG. 3). The coupling characteristics of this element to an optical fiber were the same as in Example 2.

(Embodiment 6) A third example of a method for manufacturing an optical waveguide device of this embodiment will be described.

In the same manner as in Example 4, a mirror-polished, clean and flattened glass substrate and a GaAs substrate
A polycrystalline silicon thin film having a thickness of 0.25 μm was formed on each surface by chemical vapor deposition (CVD).

Next, in the same manner as in Example 5, the surface of the polycrystalline silicon film is cleaned with a hydrofluoric acid-based etching solution and the surface is hydrophilized. Then, heat treatment was performed at a temperature of 100 to 700 ° C. As a result, a strong bond was obtained via the polycrystalline silicon film. The higher the heat treatment temperature, the higher the strength of the joint.

Thereafter, aluminum electrodes were formed in the same manner as in Example 4 to obtain the structure of the optical waveguide device shown in Example 2 (FIG. 3). The coupling characteristics of this element to an optical fiber were the same as in Example 2.

(Embodiment 7) A fourth example of a method for manufacturing an optical waveguide device of this embodiment will be described.

In the same manner as in Example 4, a mirror-polished, clean and flattened glass substrate and a GaAs substrate
A silicon oxide thin film was formed on each surface with a thickness of 0.25 μm by chemical vapor deposition (CVD).

Next, in the same manner as in Example 5, the surface of the silicon oxide film was cleaned with a hydrofluoric acid-based etchant, and the surface of the silicon oxide film was hydrophilized. The heat treatment was performed at a temperature of 100 to 700 ° C. As a result, a strong bond was obtained via the silicon oxide film. The higher the heat treatment temperature, the higher the strength of the joint.

Thereafter, aluminum electrodes were formed in the same manner as in Example 4 to obtain the structure of the optical waveguide device shown in Example 3 (FIG. 4). The coupling characteristics of this device to an optical fiber were the same as those in Example 3.

(Embodiment 8) A fifth example of the method of manufacturing the optical waveguide device of the present embodiment will be described.

In the same manner as in Example 4, a mirror-polished, clean and flattened glass substrate and a GaAs substrate
A silicon nitride thin film was formed on each surface with a thickness of 0.25 μm by chemical vapor deposition (CVD).

Next, in the same manner as in Example 5, the surface of the silicon nitride film was cleaned and hydrophilized with a hydrofluoric acid-based etchant, and the silicon nitride thin films were contacted immediately after immersion in pure water. The heat treatment was performed at a temperature of 100 to 700 ° C. As a result, a strong bond was obtained via the silicon nitride film. The higher the heat treatment temperature, the higher the strength of the joint.

Thereafter, aluminum electrodes were formed in the same manner as in Example 4 to obtain the structure of the optical waveguide device shown in Example 3 (FIG. 4). The coupling characteristics of this device to an optical fiber were the same as those in Example 3.

(Embodiment 9) FIG. 5 shows a fourth embodiment of the configuration of the optical waveguide device of the present embodiment. FIG. 5 is a perspective view of the whole, which shows a case where the present invention is applied to an optical modulator. In FIG. 5, reference numeral 2 'denotes an InP substrate. In addition, the same components as those in the embodiment shown in FIG. 1 are denoted by the same reference numerals.
With this configuration, an optical waveguide device similar to that of the first embodiment can be obtained based on the same principle as that of the first embodiment.

The shape of the waveguide in this case is almost the same as that of the first embodiment, and therefore, the coupling efficiency of the optical fiber with the circular optical waveguide structure is extremely good.

When the same values as those of the first embodiment were taken as representative values of the respective dimensions, almost the same characteristics as those of the first embodiment were obtained. With the above configuration, the coupling loss with the optical fiber is 1.0 dB on one side, as in the first embodiment.
The result was as follows, which was greatly improved. The measurement was performed at a wavelength of 1.3 μm.

(Embodiment 10) A sixth example of a method for manufacturing an optical waveguide device according to this embodiment will be described.

In the same manner as in Example 4, the surfaces of the mirror-polished, clean and flattened glass substrate and the InP substrate were
By cleaning with an etching solution, forming a low-melting glass film by sputtering, and performing heat treatment on the surfaces thereof, a strong bond was obtained.

Thereafter, aluminum electrodes were formed in the same manner as in Example 4 to obtain the structure of the optical waveguide device shown in Example 9 (FIG. 5). The coupling characteristics of this element to an optical fiber were the same as in Example 9.

Similarly, in the case of InP, the fifth embodiment
By the same manufacturing method as described in Examples 1 to 8, an optical waveguide element joined by silicon or a silicon compound could be obtained. The various characteristics were almost the same as those in Example 9.

The heat treatment effect of the bonding strengthening in Examples 5 to 8 and the like, for example, the bonding strength increased several times even when the temperature was maintained at 100 ° C. for about 1 hour, and a strength of several tens kg / cm ² was obtained. In general, the higher the temperature and the longer the time, the higher the bonding strength. However, when the temperature was raised to 700 ° C. or more, arsenic or phosphorus escaped from the surface of the GaAs or InP substrate became severe, so that the characteristics of the surface were greatly deteriorated and the performance as an optical waveguide device was deteriorated. Therefore, the heat treatment temperature was preferably 700 ° C. or less.

In the case of the manufacturing method using silicon or a silicon compound for the bonding as shown in Examples 5 to 8, etc., the thermal expansion coefficient of the glass substrate is adjusted to the thermal expansion coefficient of the compound semiconductor to be bonded. Can be performed at a higher temperature, and there is no separation even if the processing for thinning is performed by strong polishing, or the effect of operating the optical waveguide element stably at higher temperatures is obtained. And
I liked it.

The bonding using silicon or a silicon compound is as follows.
By hydrophilic treatment of the surface of each silicon or silicon compounds, hydroxyl group in water is surface adsorption to the surface, believed to have joined in the binding force of the ion. When heat treatment is performed in this state, it is considered that hydroxyl group hydrogen gradually escapes from the bonding interface, and the remaining oxygen becomes a nucleus, thereby strengthening the bonding.

Therefore, in the embodiment, the example of GaAs and InP has been described as an example of the single crystal semiconductor.
Even if other III-V compound semiconductors such as AlGaAs, InGaAs, InGaAsP, etc. are used, they are joined by using silicon or a silicon compound to form an optical waveguide element in the same manner, and the same effect as that of the present embodiment can be obtained. it is obvious. It is also clear in principle that the method using the low melting point glass described in Examples 1 and 3 can simultaneously form an optical waveguide element using another single crystal semiconductor.

Since the optical communication is generally performed in a single mode, the thickness of the substrate on which the optical waveguide is formed is desirably the thickness of the substrate propagating in a single mode.

In this embodiment, an example of the configuration of the optical modulator has been described. However, since the feature of this embodiment lies in the configuration of the optical waveguide itself, basically, various optical waveguide devices using the optical waveguide are used. The present invention can be widely and generally applied, and is not limited to an optical modulator, but can be applied to various optical waveguide elements such as an optical switch, an optical polarization plane control, and a propagation mode control.

In this embodiment, a specific example of dimensions is shown, but the present invention is not limited to this example.

In this embodiment, an example in which two substrates are joined is shown, but three or more substrates can be joined.
For example, it is also possible to bond three substrates and to form an optical waveguide element on the uppermost and lowermost substrates, and the present invention is not limited to the bonding of two substrates.

The epitaxially grown film is extremely sensitive to the surface treatment of the substrate to be grown and various manufacturing conditions during the growth, so that it is difficult to always obtain the same film quality and to increase the yield, but it is difficult to increase the yield. In this case, since a compound semiconductor substrate having excellent characteristics can be selected and used from the beginning, a compound semiconductor optical waveguide having stable characteristics can always be obtained, and this method is clearly superior in mass productivity. Although an expensive single crystal semiconductor substrate must be used for epitaxial growth, glass can be used in the method of this embodiment. The price of glass is
The method according to the present embodiment is about two orders of magnitude cheaper than a single crystal compound semiconductor and is overwhelmingly advantageous in terms of cost.

[0067]

The present invention has the above-described structure and manufacturing method, and has the following effects.

As the optical waveguide, a structure having a uniform refractive index of the waveguide portion and a thickness corresponding to the diameter of the optical fiber core was easily obtained, so that the coupling loss with the optical fiber could be greatly reduced.

In addition, since a junction is used instead of epitaxial growth as a manufacturing method, inexpensive (two orders of magnitude cheaper than a compound semiconductor substrate) glass can be used for the substrate, and there are few restrictions on the compound semiconductor that can be used, and excellent mass productivity is achieved. Things.

[Brief description of the drawings]

FIG. 1 is an overall perspective view showing a configuration of an optical waveguide device according to a first embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is an overall perspective view showing a configuration of an optical waveguide device according to a second embodiment of the present invention.

FIG. 4 is an overall perspective view showing a configuration of an optical waveguide device according to a third embodiment of the present invention.

FIG. 5 is an overall perspective view showing a configuration of an optical waveguide device according to a fourth embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Glass base, 2 ... Single crystal semiconductor substrate (GaAs substrate), 2 '... InP substrate, 3 ... Input / output optical waveguide part, 4
... first branch optical waveguide, 5 ... second branch optical waveguide,
6, 7: electrode, 8: low melting point glass layer, 9: guided light propagation part, 10: silicon, 11: silicon compound.

Continuation of the front page (56) References JP-A-49-98258 (JP, A) JP-A-57-89712 (JP, A) JP-A-52-78454 (JP, A) JP-A-63-49732 (JP, A) JP-A-4-123018 (JP, A) JP-A-58-223106 (JP, A) JP-A-60-51700 (JP, A) JP-A-4-116816 (JP, A) APPL. PHYS. LETT. VOL. 56 NO. 24 p. 2419-P. 2421 (June 1990)

Claims (5)

(57) [Claims] 1. A glass substrate having a periphery having an electro-optic effect.
Single crystallization comprising a combination of groups III and V
The compound semiconductor is the glass substrate or the single crystal compound
Silicon film or silicon formed on a predetermined portion of a semiconductor substrate
The silicon film or the silicon compound through a compound film
Direct bonding and lamination due to hydroxyl or oxygen on the film surface
The single crystal compound semiconductor substrate,
Optical waveguide confined by the difference in refractive index from a lath substrate
A semiconductor optical waveguide device comprising: 2. A single crystal semiconductor having an electro-optic effect.
And GaAs or InP is used.
The semiconductor optical waveguide device according to claim 1. 3. The method according to claim 1 , wherein the silicon compound is silicon oxide or nitrided.
2. The semiconductor light according to claim 1, wherein silicon is used.
Waveguide element. 4. A glass substrate and a periphery having an electro-optic effect.
Single crystallization comprising a combination of groups III and V
At least one substrate surface of the compound semiconductor substrate
Forming a silicon compound film and bonding the substrates
A process of hydrophilizing the surface of the planned site
Joining process by overlapping and joining by heat treatment
And conducting light to the single crystal compound semiconductor substrate.
Forming a wave path.
A method for manufacturing an optical waveguide device. 5. The method according to claim 1 , wherein the silicon compound is silicon oxide or nitrided.
The semiconductor light according to claim 4, wherein silicon is used.
A method for manufacturing a waveguide element.