JPH1026745A - Optical waveguide device and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical waveguide device which is improved in characteristics by enhancing dimensional accuracy of a static-proof film and, simultaneously, is achieved in the improvement of the productivity, and its manufacturing method. SOLUTION: The optical waveguides 2 are formed on a LiNbO3 substrate 1, and a SiO2 film is formed thereon, and thereafter, is formed into a required pattern to form buffer layers 3. Simultaneously, a terrace structure 6 is formed between the buffer layers 3. Further, static-proof films 5 are formed on the entire surface, photoresist masks are formed thereon, and the static-proof films are formed into the required pattern by utilizing these photoresist makes. furthermore, a control electrode 4 is formed on the buffer layer 3. The terrace structure 6 makes it possible to platter the surface of the static-proof films 5, thereby the pattern formation by the photoresist masks is executed with a high accuracy.

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 the 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]

When such an antistatic film is formed, the antistatic film is usually formed on the entire surface of the substrate 11 and then selectively etched by photolithography. The method of forming is adopted,
When an antistatic film is to be formed between the control electrodes 14 formed in the previous process,
The flatness of the surface is lost due to the difference between the surface height of the substrate 11 and the surface height of the substrate 11, and the surface of the photoresist film in the photolithography process becomes uneven. 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]

An optical waveguide device according to the present invention has a terrace structure at a position adjacent to a buffer layer on an optical waveguide formed on a substrate, and an antistatic film is formed on the terrace structure. Is formed. Here, the terrace structure is made of any one of the same material as the buffer layer or another material such as an insulating material, a conductive material, or an antistatic film. 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 comprises the steps of forming an optical waveguide on a substrate, forming a buffer layer on the optical waveguide on the substrate, forming a film of a required material on the entire surface,
A step of selectively etching by a photolithography step to form a terrace structure at a position close to the optical waveguide; a step of forming an antistatic film over the entire surface; and a step of forming the antistatic film by at least the terrace by a photolithography step. The method includes a step of forming a pattern so as to remain on the structure, 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 fourth embodiment of the present invention. 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. In addition, 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 fifth 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 sixth embodiment of the present invention. As in the fifth embodiment, a terrace structure 6E is formed adjacent to and close to the buffer layer 3. 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 seventh embodiment of the present invention, in which a terrace structure 6F is formed adjacent to the buffer layer 3 similarly to the sixth embodiment. Here, the material of the terrace structure 6F is the same as that of 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 Multi-slit structure of prevention film)
Can be formed.

FIG. 10 is a view showing an eighth embodiment of the present invention, in which a plurality of terraces are arranged in close proximity as a terrace structure 6G. Even in such a configuration, the antistatic film 5 formed on the terrace structure 6G can be formed with high accuracy. 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. Especially 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 buffer layer or the antistatic film, a different material, or a combination thereof.

FIG. 11 is a diagram showing a ninth embodiment of the present invention. Here, a plurality of optical waveguides 2a and 2b have a line-symmetric terrace structure 6H for each optical waveguide. The symmetric structure makes it possible to further enhance the temperature stability of the eighth embodiment. That is, even if a temperature change occurs in this device and a stress is generated in the region of the optical waveguide 2a and the refractive index of the region changes, a similar refractive index change also occurs in the adjacent optical waveguide 2b. Has become. Therefore, although the refractive index of each waveguide changes,
If the change is the same, the operating point shift 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 stress dispersion is not particularly limited,
The one that makes the process the easiest can be adopted.

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 is provided near the optical waveguide, and an antistatic film is formed on the terrace structure. Therefore, this antistatic film makes it possible to suppress or reduce the operating point shift, DC drift, drive voltage, etc. in the optical waveguide device, improve device characteristics, and flatten the antistatic film by the terrace structure. As a result, it is possible to improve the manufacturing yield by enabling the antistatic film to be formed with high accuracy, and to improve the operation stability of the device by increasing the temperature stability.

[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 fourth embodiment of the present invention.

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

FIG. 8 is a perspective view showing a structure of a sixth embodiment of the present invention.

FIG. 9 is a perspective view showing a structure of a seventh embodiment of the present invention.

FIG. 10 is a perspective view showing the structure of an eighth embodiment of the present invention.

FIG. 11 is a perspective view showing a structure of a ninth embodiment 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 (8)

[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;
An optical waveguide device comprising: an antistatic film formed in proximity to the optical waveguide, wherein the optical waveguide device has a terrace structure at a position adjacent to the buffer layer on the substrate, and the antistatic film is formed on the terrace structure. An optical waveguide device, comprising: 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. The optical waveguide device according to claim 1, wherein the terrace structure is made of a conductive material. 4. The optical waveguide device according to claim 1, wherein the terrace structure is made of the same material as the antistatic film. 5. The optical waveguide device according to claim 1, wherein the terrace structure is formed at a position adjacent to the buffer layer so as to be in close contact with the buffer layer. 6. The optical waveguide device according to claim 1, wherein the terrace structure is configured to be divided into a plurality. 7. The optical waveguide device according to claim 1, wherein the terrace structure is formed at a position symmetrical with respect to the optical waveguide. 8. A step of forming an optical waveguide on the substrate, a step of forming a buffer layer on the optical waveguide on the substrate, a step of forming a film of a required material on the entire surface, and selectively etching the film by a photolithography step. Forming a terrace structure at a position close to the optical waveguide, forming an antistatic film on the entire surface, and forming a pattern so that the antistatic film is left at least on the terrace structure by a photolithography process. And a step of forming a control electrode on the optical waveguide on the buffer layer.