JP3024555B2 - 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 an optical waveguide device for modulating an optical wave transmitted through an optical waveguide, switching an optical path, and the like. The present invention relates to an optical waveguide dehice and a method for manufacturing the same.

[0002]

2. Description of the Related Art Optical path switching and light modulation are indispensable for practical use of an optical communication system. Optical waveguide devices used for this purpose are promising. As a substrate on which a dielectric optical waveguide used for an optical switch or an optical modulator is formed, a lithium niobate system or a lithium tantalate system is used. An optical waveguide is formed by patterning metal Ti or the like on these substrates and thermally diffusing them, changing the refractive index with the substrates. Switching and modulation of the optical path are performed by applying an electric field to the optical waveguide, utilizing the electro-optic effect of the substrate (a phenomenon in which the refractive index changes with the electric field) and the interference of guided light. The electrode formed for this purpose is formed on the optical waveguide via an optical buffer layer of Al ₂ O ₃ , SiO ₂ or the like in order to suppress the propagation loss of the guided light.
Depending on the substrate orientation, there is a case where the buffer layer is not interposed, but in many cases, the buffer layer is interposed from the viewpoint of modulation efficiency.

For example, FIG. 14 shows a configuration example of an optical modulator using a Z-cutLiNbO ₃ substrate. (A) is a plan view, and (b) is a cross-sectional view. The incident light L1 is propagated through the optical waveguide 12 formed on the lithium niobate niobate substrate (LiNbO ₃ ) 11, and the Mach-Zehnder type modulation unit 16
Split the wave into two. In order to provide a phase difference between the two optical waveguides 12 in the Mach-Zehnder type modulator 16, an electric field is applied to each waveguide by a control electrode 14 formed on the optical waveguide 12 via a buffer layer 13. After that, they are multiplexed again, and the light intensity of the emitted light L2 is modulated. In this structure, when the temperature of the device changes, the charge generated by the pyroelectric effect of the substrate 11 and the charge unevenly distributed under the control electrode 14 cause, for example, an optical modulation path due to a newly created internal electric field. Bias point shifts with temperature. In addition, an anti-electric field generated by polarization of impurities in the buffer layer 13 during electric field control causes the operating point of the optical modulator to shift with the electric field application time.
Causes a drift phenomenon.

In order to suppress such a bias-free operating point shift, for example, in the technique described in Japanese Patent Application Laid-Open No. Hei 5-88125, as shown in FIG. It has been proposed that an antistatic film 15 is formed by applying a solvent in which is dispersed, and the above-mentioned operating point shift is suppressed by the antistatic film 15.

On the other hand, functions required for this type of optical waveguide device include DC drift suppression and drive voltage reduction in addition to the above-described suppression of the device-free operating point shift.
For this reason, Japanese Patent Application No. 6-309707 proposes a technique of forming an antistatic film 15A into a plurality of parallel slits between control electrodes 14, as shown in FIG.

[0006]

The structure shown in FIG.
When the antistatic film is formed in the optical waveguide device described above , the buffer layer 13 is usually provided on the substrate 11 and
A method of forming the electrode 14 for use, forming an antistatic film on the entire surface thereof, and selectively etching the antistatic film by photolithography is adopted. When an antistatic film is to be formed between the control electrodes 14, the flatness of the surface is lost due to the difference in surface height between the control electrodes 14 and the buffer layer 13 . Irregularities occur on the surface of the photoresist film. For this reason, the photomask pattern cannot be brought into close contact with the photoresist due to the unevenness, and it becomes difficult to transfer the photomask pattern to the photoresist with high accuracy. As a result, the dimensional accuracy of the formed antistatic film is reduced, and it becomes difficult to obtain the initial characteristics of the optical waveguide device, and the production yield of the antistatic film, in other words, the productivity of the optical waveguide device is deteriorated. The problem arises.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical waveguide device and a method for manufacturing the same, which improve the characteristics by improving the dimensional accuracy of the antistatic film and improve the productivity.

[0008]

The optical waveguide device of the present invention, in order to solve the problem] has a terrace structure at a position adjacent to the buffer layer on the optical waveguide formed in the substrate, on the terrace structure, the light guide A control electrode formed in close proximity to the waveguide;
Between them, a plurality of antistatic films formed in a slit shape are formed , and the terrace structure is formed to have a thickness approximately equal to that of the buffer layer and a width larger than the width of the antistatic film. It is characterized by the following. Here, the terrace structure is
It is made of the same or another insulating material as the buffer layer. Further, the terrace structure has a configuration in which the terrace structure is in close contact with the buffer layer at a position adjacent to the buffer layer or is divided into a plurality. Further, the terrace structure is preferably formed at a position symmetrical with respect to the optical waveguide.

Further, the manufacturing method of the present invention includes a step of forming an optical waveguide on the substrate, a step of forming a buffer layer on the optical waveguide on the substrate, and a step of forming a film of a required material on the entire surface in the same manner as the buffer layer. A step of forming a terrace structure at a position close to the optical waveguide by selectively etching by a photolithography step, a step of forming an antistatic film on the entire surface, and a photolithography step. The antistatic film has a width dimension at least on the terrace structure smaller than the terrace structure , and the control electrode
The method includes a step of forming a pattern so as to leave a plurality of slits, and a step of forming a control electrode on the optical waveguide on the buffer layer.

[0010]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view of the first embodiment of the present invention. LiNbO ₃ substrate 1 having electro-optic effect
Is diffused at a temperature of 900 to 1100 ° C. on the surface of the substrate to produce an optical waveguide 2 having a large refractive index in a region having a depth of 3 to 10 μm in the substrate. Such an S waveguide on the optical waveguide 2
The iO ₂ buffer layer 3 is formed to a thickness of 500 to 2000 nm. Further, a terrace structure 6 is formed between the optical waveguides 2 using a part of the SiO ₂ buffer layer 3. Then, Si is placed on the substrate 1 or the terrace structure 6.
Is formed in a required pattern, and a control electrode 4 is formed on the buffer layer 3 on the optical waveguide, thereby producing a light intensity modulator.

FIG. 2 is a diagram showing a method of manufacturing the light intensity modulator of FIG. 1 in the order of steps. First, as shown in FIG. 2A, an optical waveguide 2 is formed on a Z-cut LiNbO ₃ substrate 1. This is because the Z-cutLiNbO ₃ substrate 1
An optical waveguide 2 is formed by forming a Ti film (not shown) into a required pattern by photolithography and then selectively diffusing Ti into the substrate 1 by a thermal diffusion method.
Then, as shown in FIG. ₂ (b), SiO 2 on the entire surface
After the film is formed, a desired pattern is formed by photolithography technology, a buffer layer 3 is selectively formed on the optical waveguide 2, and a terrace structure 6 is formed on the substrate 1 between the buffer layers 3. . Further, as shown in FIG. 2C, a Si film was formed as an antistatic film on the entire surface, and although not shown, a photoresist film was formed thereon, and a photomask was adhered to the photoresist film. Exposure on the
Development is performed to form a photoresist mask, and the antistatic film 5 is formed in a required pattern using the photoresist mask. Then, after removing the photoresist mask as shown in FIG. 2D, a control electrode 4 is formed on the buffer layer 3.

Since the terrace structure 6 having the same thickness as the buffer structure 3 is formed between the buffer layers 3, the surface height of the antistatic film 5 formed on the terrace structure 6 can be reduced. The position is the same as the position of the antistatic film on the layer 3, and flattening between the two is realized. Therefore, the photomask is in close contact with the photoresist above the buffer layer 3 and above the terrace structure 6, and the dimensional accuracy of the photoresist mask formed by the photomask is high. The pattern size of the antistatic film formed by the mask is also formed with high precision. As a result, the characteristics in the device-free operating point shift, the DC drift, the drive voltage, and the like are improved, and at the same time, it is possible to form the antistatic film with high accuracy, and to improve the manufacturing yield.

FIG. 3 shows the Si according to the embodiment of FIG.
The result of comparing the production yield at the time of forming the antistatic film with the production yield of the conventional device is shown. Thus, FIG.
In the embodiment, the production yield about three times that of the conventional product could be secured. The characteristics of this optical modulator include an operating voltage of 2.8 V, an insertion loss of 4.0 dB, an extinction ratio of 30 dB, and an optical modulation band of 5 Gb /.
s.

FIG. 4 is a view showing a second embodiment of the present invention. Here, the terrace structure 6A is formed of a material having an insulating property different from that of SiO ₂ constituting the buffer layer 3. In this case, after the buffer layer 3 is formed, an insulating film is formed again, and the insulating film is formed by a photolithography process so as to remain only between the buffer layers 3, thereby forming the terrace structure 6A. Subsequent configuration is the same as that of the process of FIG. 2, and the antistatic film 5 is formed on the substrate including the terrace structure 6A. In the second embodiment, since the terrace structure 6A can be formed in a process independent of the buffer layer 3, a high-precision manufacture of the terrace structure is possible by controlling the thickness and the etching process.

FIG. 5 is a view showing a third embodiment of the present invention. Here, the terrace structure 6B is formed of a material having a different conductivity from each of the buffer layer 3 and the antistatic film 5. The manufacturing method is the same as in the second embodiment.
Also in this case, the flattening of the photoresist can be achieved by the terrace structure 6B, and a highly accurate antistatic film is formed. In general, many conductive materials have better adhesiveness to a photoresist than an insulator such as SiO ₂ , and are suitable for fine processing in a photolithography process.

FIG. 6 is a view showing a first reference example . The terrace structure 6C is formed of the same material as the conductive antistatic film 5. After forming the optical waveguide 2 on the substrate 1 and forming the buffer layer 3, a conductive antistatic film is formed, and a terrace structure 6C is formed by a photolithography process. An antistatic film is formed thereon again, and a pattern is formed by a photolithography process to form an antistatic film 5. Also in this case, the flattening of the photoresist can be achieved by the terrace structure 6C, and the precision of the antistatic film 5 can be improved. Also,
When the antistatic film 5 is etched, the terrace structure 6C is also etched at the same time, so that it is not necessary to strictly control the etching end point, and a very fine structure can be realized.

FIG. 7 is a view showing a fourth embodiment of the present invention. In this embodiment, a terrace structure 6D is formed adjacent to the buffer layer 3 and in close contact therewith. When the terrace structure is formed of the same material as the buffer layer 3 as in the first embodiment, by adopting such a structure, the buffer layer 3 and the terrace structure 6D are formed as an integrated pattern by photolithography. Because it can be formed by the process,
The flatness is enhanced, and the thickness of the antistatic film 5 formed thereon is also made uniform, which promotes high precision.

FIG. 8 is a view showing a second reference example of the present invention, and a terrace structure 6E is formed adjacent to and close to the buffer layer 3 similarly to the fourth embodiment. However, a conductive material is used here as the material of the terrace structure 6E.
In this case, since the terrace structure 6E and the buffer layer 3 are adjacent to each other, even when the terrace structure 6E is formed in a step different from that of the buffer layer 3, the flatness of the antistatic film 5 on the terrace structure 6E is improved. Fine processing can be ensured by the close contact with the photoresist obtained because the terrace structure 6E is a conductive material.

FIG. 9 is a view showing a third reference example of the present invention, and a terrace structure 6F is formed adjacent to the buffer layer 3 similarly to the sixth embodiment. Here, the terrace structure 6
The material of F is the same as the antistatic film 5. By adopting such a structure, the advantages described in the sixth embodiment and the fourth embodiment can be obtained as they are, and by etching the antistatic film 5, a plurality of very fine structures (charged (A multi-slit structure of the protective film).

FIG. 10 is a diagram showing a fourth reference example, in which a plurality of terraces are arranged in close proximity as a terrace structure 6G. Even in such a configuration, the terrace structure 6G
The antistatic film 5 formed thereon can be formed with high precision. In this embodiment, since the area of the terrace structure 6G can be reduced, the concentration of stress in the terrace structure 6G can be reduced, and the influence of the stress on the substrate 1 can be prevented. That is, the electro-optic effect occurs due to the stress, and the refractive index of the optical waveguide 2 changes depending on the temperature, thereby lowering the operation stability of the device. In particular, the stress generated near the optical waveguide 2 is a problem because it directly affects the device. In this regard, in this embodiment, the distortion due to the substrate stress is reduced, and the temperature stability of the optical waveguide device is improved. The material of the terrace structure 6G may be the same as the material of the buffer layer or the antistatic film, or may be a different material.
Further, a combination thereof may be used.

FIG. 11 is a view showing a fifth reference example of the present invention. In this case, a plurality of optical waveguides 2 have a line-symmetric terrace structure 6H for each optical waveguide. Thereby, the temperature stability of the eighth embodiment can be further improved. That is, even if a temperature change occurs in this device and a stress is generated in a region of one optical waveguide 2 and the refractive index of the region changes, a similar refractive index change also occurs in the adjacent optical waveguide 2. It has become. Accordingly, although the refractive index of each waveguide changes, if the change is the same, the shift of the operating point with respect to the temperature change is suppressed, and the temperature stability can be further improved as compared with the eighth embodiment. Here, the material of the terrace structure formed for dispersing the stress is not particularly limited, and a material that can be most easily processed can be employed.

The present invention is not limited to the above-described devices and processes, provided that the same structure can be obtained irrespective of the above embodiments. Needless to say, materials other than those described above can be used for the terrace structure and the antistatic film.

[0023]

As described above, according to the present invention, in a device for controlling light using an optical waveguide, a terrace structure having a thickness similar to that of a buffer layer is provided in proximity to the optical waveguide, and this terrace structure is provided. Since an antistatic film having a small width is formed on the upper surface, the antistatic film enables suppression and reduction of an operating point shift, a DC drift, a driving voltage, and the like in an optical waveguide device, thereby improving device characteristics. In addition, the terrace structure enables the antistatic film to be flattened, enabling the antistatic film to be formed with high accuracy, thereby improving the production yield, and improving the temperature stability to stabilize the operation of the device. There is an effect that the property can be improved.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a structure of a first embodiment of the present invention.

FIG. 2 is a view showing a manufacturing method of the first embodiment in the order of steps.

FIG. 3 is a diagram showing a comparison between the first embodiment and a conventional manufacturing yield.

FIG. 4 is a perspective view showing a structure of a second embodiment of the present invention.

FIG. 5 is a perspective view showing a structure of a third embodiment of the present invention.

FIG. 6 is a perspective view showing a structure of a first reference example of the present invention.

FIG. 7 is a perspective view showing a structure of a fourth embodiment of the present invention.

FIG. 8 is a perspective view showing a structure of a second reference example of the present invention.

FIG. 9 is a perspective view showing a structure of a third reference example of the present invention.

FIG. 10 is a perspective view showing a structure of a fourth reference example of the present invention.

FIG. 11 is a perspective view showing the structure of a fifth reference example of the present invention.

FIG. 12 is a perspective view of an example of a conventional optical waveguide device.

FIG. 13 is a perspective view of another example of the conventional optical waveguide device.

FIG. 14 is a plan view and a cross-sectional view of an optical waveguide device to which the present invention can be applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Optical waveguide 3 Buffer layer 4 Control electrode 5 Antistatic film 6, 6A-6H Terrace structure

Claims (6)

(57) [Claims] An optical waveguide formed on a substrate and transmitting a light wave; a buffer layer formed on the optical waveguide; a control electrode formed on the buffer layer on the optical waveguide;
Formed in close proximity to the optical waveguide and of the control electrode;
In between, the optical waveguide device comprising a plurality of antistatic films formed in the shape of a slit , has a terrace structure at a position adjacent to the buffer layer on the substrate, the antistatic film on the terrace structure An optical waveguide device, wherein the terrace structure is formed with a thickness substantially equal to a thickness of the buffer layer and a width larger than a width of the antistatic film. 2. The optical waveguide device according to claim 1, wherein the terrace structure is made of the same or different insulating material as the buffer layer. 3. An optical waveguide device according to claim 1 or 2, wherein the terrace structure is formed in a state of close contact with the to the buffer layer at a position adjacent to the buffer layer. Wherein said terrace structure, the optical waveguide device according to any one of claims 1 to 3 are divided into a plurality. Wherein said terrace structure, the optical waveguide device according to any one of claims 1 to 4 are formed at positions symmetrical across the waveguide. 6. A step of forming an optical waveguide on a substrate, a step of forming a buffer layer on the optical waveguide on the substrate, and forming a film of a required material on the entire surface to a thickness similar to that of the buffer layer. Forming a terrace structure at a position close to the optical waveguide by selectively etching by a photolithography process, and forming an antistatic film on the entire surface;
The width of the antistatic film is smaller than that of the terrace structure at least on the terrace structure by a photolithography process , and a plurality of slits are formed between the control electrodes.
And forming a control electrode on the optical waveguide on the buffer layer. 2. A method for manufacturing an optical waveguide device, comprising: