JPH04268531A - Signal electrode for optical waveguide device and its formation - Google Patents

Abstract

PURPOSE:To improve the adhesiveness to a substrate and the heat radiation, and to improve the performance and reliability of an optical waveguide device by providing a specific signal electrode for the optical waveguide device. CONSTITUTION:Signal electrodes 3, e.g. a progressive wave signal electrode and a ground electrode are formed on the optical waveguide 2, including branching optical waveguides 2a and 2b formed on the substrate 1 with electrooptic effect through a buffer layer 5. The signal electrode 3 and ground electrode 4 are constituted of thin metallic base electrodes 3a and 4a and thick metallic plating layer electrodes 3b and 4b. A projection metallic pattern 30 is formed on one side of the metallic base layer electrode 3a of the thin signal electrode 3, e.g. at the outside part. Thus, the projection metallic pattern 30 is formed and then this part is acted for prevention against underetching at the time of, for example, metallic base layer etching and serves as a heat radiation fin when a signal current flows to the narrow-width signal electrode 3 to reduce the heat strain, so that the signal electrode 3 is prevented from being peeled off.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal electrode for an optical waveguide device and a method for forming the same. Specifically, when configuring optical waveguide devices such as high frequency band optical modulators and optical switches using substrates with electro-optic effects, the adhesion of signal electrodes used therein, such as traveling wave signal electrodes, to the substrate is important. The present invention relates to an electrode structure and a method for forming the same, which improve the performance and reliability of an optical waveguide device by improving heat dissipation.

0002

[Background Art] In recent years, advances in optical fibers and laser light sources
As development progresses, various systems and devices that apply optical technology, including optical communication, have come into practical use and are widely used. There has become a need for technology to control optical signals at high speed using optical waveguide devices, such as high-speed optical modulation technology.

For example, in high-speed optical communication systems with transmission speeds up to about 1.6 Gbps, a method of directly modulating a laser diode (LD) has been used, but as the modulation frequency becomes higher, the time of the modulated light wavelength increases. small fluctuations,
The so-called chirping phenomenon and the dispersion characteristics of optical fibers impose limitations on high-speed and long-distance communications.

On the other hand, as a high-speed optical modulation method, an external modulation method in which semiconductor laser light is externally modulated is well known. In particular, a Mach-Zehnder type external modulator is considered to be promising, in which a branched optical waveguide is provided on a substrate having an electro-optic effect and driven using a signal electrode, for example, a traveling wave signal electrode.

FIG. 4 is a diagram showing an example of the basic configuration of an optical modulator.
The figure (a) is a plan view, and the figure (b) is a YY sectional view. In the figure, numeral 1 indicates a substrate having an electro-optic effect processed into a flat surface, for example, a LiNbO3 or LiTaO3 substrate. 2 is an optical waveguide with branched optical waveguides 2a and 2 in the middle.
b is formed. This optical waveguide is usually made by selectively diffusing a metal such as Ti on the surface of a substrate only to the optical waveguide portion, so that the refractive index of that portion is slightly larger than that of the surrounding portions. 3 is a signal electrode, for example, a traveling wave signal electrode, and 4 is a ground electrode. Reference numeral 5 denotes a buffer layer for reducing absorption of light into the metal electrode layer on the optical waveguide, and a thin film such as SiO2 is usually used.

The signal electrode 3 and the ground electrode 4 are formed on the optical waveguide via a buffer layer 5 by vapor deposition or plating of a metal such as Au. Now, for example, DC light emitted from a semiconductor laser (not shown) enters from the optical waveguide 2 on the left side and is split into two by the branching optical waveguides 2a and 2b. When a signal voltage is applied from 6, a phase difference occurs between the branched lights due to the electro-optic effect in the branched optical waveguides 2a and 2b provided on the substrate. The two lights are combined again, and a modulated optical signal output is taken out from the single optical waveguide 2 on the right side, and is converted into an electrical signal by a photodetector (not shown). The branch optical waveguide 2
If a signal voltage is applied so that the phase difference between the two lights at a and 2b becomes π or 0, the optical signal output can be obtained as an ON-OFF pulse signal, for example. Note that RT is a terminating resistor.

[0007] Normally, electrodes for such optical waveguide devices use gold (Au), which has low electrical resistance, as the electrode material in order to pass high-speed microwaves, and are made to be as thick as possible. I have to. Therefore, plating technology is generally applied to its formation. An example is shown below.

FIG. 5 is a diagram showing an example of a conventional electrode forming method, showing the main steps in order. The figure (A) is a top view (electrode and waveguide arrangement on the substrate), and the figure (B) is a YY cross-sectional view of the figure (A).

Step (1): For example, optical waveguides 2 (2a, 2
b) is formed by, for example, a Ti diffusion method, and then a buffer layer 4 of, for example, SiO2 with a thickness of 500 nm is formed.
Sputter forming the film. Gold (Au) having a thickness of 150 nm, for example, is deposited thereon as a metal underlayer 34 .

Step (2): A thickness of 10 μm is applied to the portion of the processed substrate other than the area where the signal electrode 3 and the ground electrode 4 are to be formed.
A resist pattern 7 of about m length is formed as shown in the figure. Step (3): For example, on the metal base layer 34 on which the resist pattern 7 of the treated substrate is not formed,
Metal plated layer electrodes 3b and 4b made of a gold plated layer are formed to a thickness matching the upper surface of the resist pattern 7 as shown in the figure. For example, such gold plating is carried out using a cyan gold plating solution at a temperature of 65°C at a rate of 3mA/3mA.
It is formed by electroplating for about 30 minutes at a current density of cm2.

Step (4): The resist pattern 7 on the treated substrate is removed using an appropriate stripping solution. Step (5): The above-mentioned treated substrate is etched for about 30 seconds in a mixed aqueous solution of iodine and potassium iodide to remove the Au of the metal base layer 34 in areas other than the formation areas of the signal electrode 3 and ground electrode 4. An optical waveguide device, for example, a Mach-Zehnder type optical modulator, is formed by dissolving and removing.

0012

[Problems to be Solved by the Invention] However, the electrodes of optical waveguide devices formed by the above-mentioned conventional electrode forming method, especially,
Since the signal electrode 3 has a narrow electrode width of usually 10 μm or less, when etching the metal base layer 34 in the final step of electrode formation, the metal base layer 34 is etched as shown in FIG. Underetch 34' in layer 34
This causes the adhesion with the substrate 1 to deteriorate. Moreover,
Due to distortion caused by the difference in thermal expansion between the substrate and the electrodes in addition to the effect of heat generation due to the signal current, a serious problem arises in that peeling of the signal electrode 3 is further accelerated and the reliability of the optical waveguide device is impaired. A solution is needed.

[0013]

[Means for Solving the Problems] The above problems are solved in a signal electrode for an optical waveguide device arranged so as to control light propagating in an optical waveguide 2 formed on a substrate 1 having an electro-optic effect. This problem can be solved by using a signal electrode for an optical waveguide device in which protruding metal patterns 30 are formed in places on at least one side of the signal electrode 3. Specifically, a portion that will become the protruding metal pattern 30 is formed on a thin metal base layer electrode 3a, and the protruding metal pattern 3
This problem can be effectively solved by using a signal electrode for an optical waveguide device in which a thick metal plating layer electrode 3b is formed on the metal base layer electrode 3a except for the portion where the value becomes 0.

[0014]

[Operation] According to the present invention, the narrow signal electrode 3 is patterned at the stage of the metal base layer 34 so that it does not come into contact with the etching solution when unnecessary parts are etched in a later process. In addition to preventing etching, since the protruding metal pattern 30 is formed in places on at least one side of the narrow signal electrode 3, the area of the metal base layer 34 is increased, the adhesion strength is increased, and the signal current is Since it functions as a heat dissipation fin against the heat generated by the signal electrode 3 due to the flow, thermal distortion is also reduced and separation of the signal electrode 3 from the substrate 1 is prevented.

[0015]

[Embodiment] Fig. 1 shows an embodiment of the present invention, in which (A) is a plan view, (B) is a sectional view taken along line X-X, and (C) is a cross-sectional view taken along line X-X.
is a Y1-Y1 cross-sectional view, and (D) is a Y2-Y2 cross-sectional view. In the figure, 30 is a protruding metal pattern.

[0016] The same parts as those explained in the above drawings are given the same reference numerals, and the explanation of the same parts will be omitted. For example, a buffer layer 5 is formed on an optical waveguide 2 including branched optical waveguides 2a and 2b formed on a substrate 1 in which the surface of a LiNbO3 Z plate is mirror-polished.
As shown, a signal electrode 3, for example, a traveling wave signal electrode and a ground electrode 4 are formed via the electrode. Both the signal electrode 3 and the ground electrode 4 are composed of thin metal base layer electrodes 3a, 4a and thick metal plating layer electrodes 3b, 4b.

In this example, a protruding metal pattern 30 is formed on one side of the metal base layer electrode 3a of the thin signal electrode 3, for example, on the outer side as shown. The size and arrangement of the protruding metal pattern 30 are, for example, 10 mm thick.
They may be formed to have a thickness of 0 to 200 nm, a width of 10 to 20 μm, a protrusion length of 20 to 30 μm, and an interval of about 100 μm.

Since such a protruding metal pattern 30 is formed, that portion is not subjected to processing during the manufacturing process.
For example, it works to prevent under-etching when etching a metal base layer, and also acts as a heat dissipation fin when a signal current flows through the narrow signal electrode 3 and generates heat, reducing thermal distortion. is prevented from peeling off from the substrate 1, and reliability is greatly improved compared to conventional device configurations. If the protruding metal pattern 30 has a size like the above example, an optical waveguide device, for example,
This does not affect the characteristics of the optical modulator in any way.

In the above embodiment, the protruding metal pattern 30 was formed only on one side of the metal base layer electrode 3a of the signal electrode 3, that is, on the outside, but it would be more effective if it was formed on both sides, that is, on the inside and outside. Needless to say, it will increase. Furthermore, not only the metal base layer electrode 3a but also the thick metal plating layer electrode 3b thereon may be formed continuously. Furthermore, it goes without saying that it may also be formed on the inner end surface of the ground electrode 4 if necessary.

FIGS. 2 and 3 are diagrams (Part 1) and (Part 2) showing an embodiment of the electrode forming method of the present invention, in which the main steps are illustrated in order. In addition, the same figure (a)
is a top view (electrode and waveguide arrangement on the substrate), and figure (b) is a YY cross-sectional view at the position shown in figure (a).

Step (1): For the substrate 1, for example, a Z plate of LiNbO3 having a size of 40 mm x 2 mm and a thickness of 1 mm is mirror-polished. Ti was vacuum-deposited on this substrate to a thickness of about 100 nm, and treated by a normal photoetching method so that Ti remained in the portion corresponding to the optical waveguide 2 including the branched optical waveguides 2a and 2b.
The optical waveguide 2 is formed by heating at 500 C for 10 hours to thermally diffuse Ti into LiNbO3. The length of the branched optical waveguide portion was adjusted to 25 mm, the width of the optical waveguide was adjusted to 7 μm, and the interval between the branched optical waveguides 2a and 2b was approximately 1
The thickness is 5 μm, and the angle of the branch portion is approximately 2°. Next, a SiO2 film is formed as a buffer layer to a thickness of 500 nm by vacuum evaporation. Further, a metal base layer 34, for example, of gold (Au) with a thickness of 150 nm is formed thereon.
) deposit the film.

Step (2): Metal base layer 3 of the above-mentioned treated substrate
4, a region that will become the signal electrode 3 and the ground electrode 4, the outer periphery of the substrate, and a protruding metal pattern 30 that connects them;
As shown in the figure, an etch hole 31 is formed by photo-etching, leaving the bridge portion 30', which is the portion where it becomes.

If such a bridge portion 30' does not exist, the signal electrode 3 is thin, so that patterning causes non-negligible electrical resistance, resulting in non-uniformity in the thickness of the plating film. However, the provision of the bridge portion 30' helps to supply the current necessary for plating to the narrow signal electrode 3 from the outside, and provides a metal plating layer electrode 3b with a uniform thickness.

Step (3): Apply a thickness of 10 mm on the above-mentioned treated substrate.
After spin-coating a resist with a thickness of about .mu.m, for example, a resist pattern 7 with a thickness of about 10 .mu.m is formed in areas other than the regions that will become the signal electrodes 3 and ground electrodes 4, as shown in the figure.

Step (4): On the metal base layer 34 on which the resist pattern 7 of the treated substrate is not formed,
For example, a metal plating layer electrode 3b consisting of a gold plating layer
, 4b are formed to a thickness matching the upper surface of the resist pattern 7 as shown in the figure. Such gold plating is formed, for example, by electroplating at a current density of 3 mA/cm2 for about 30 minutes using a cyan gold plating solution with a liquid temperature of 65°C.

Step (5): By removing the resist pattern 7 of the above-mentioned treated substrate with a suitable stripping solution, a metal bottom with bridge portions 31' and etched holes 31 formed on the outside and inside of the signal electrode 3 is formed as shown in the figure. Stratum 34, i.e. gold (A
The deposited film u) is exposed.

Step (6): On the metal plated layer electrodes 3b, 4b made of the gold plated layer on the above-mentioned processed substrate, for example, a layer slightly wider than the electrode pattern width of the metal plated layer electrodes 3b, 4b, that is, a side plate is formed. As shown in the figure, a resist pattern 8 having a thickness of, for example, about 1 μm is formed in such a width that the end portions are covered with the resist.

Step (7): The exposed portion of the metal base layer 34 consisting of the gold plating layer of the above-mentioned treated substrate is etched for about 30 seconds in a mixed aqueous solution of iodine and potassium iodide, for example. After dissolving and removing the Au, if the resist pattern 8 is removed with an appropriate stripping solution, an optical waveguide device in which a protruding metal pattern 30 is formed on at least one side of the signal electrode 3 of the present invention, such as a Mach-Zehnder type optical device, can be obtained. A modulator is created.

The optical waveguide type device manufactured in this way does not cause peeling of the signal electrode 3, and furthermore,
Good heat dissipation results in stable operating characteristics and improved reliability. In the above embodiments, the case of a Mach-Zehnder type optical modulator was shown as an example, but it goes without saying that the present invention can be applied to various other optical waveguide devices.

Furthermore, the above-mentioned embodiments are merely examples, and it goes without saying that other materials and detailed processes may be selected and used as appropriate, as long as they do not go against the spirit of the present invention.

[0031]

As explained above, according to the present invention, since the protruding metal pattern 30 is formed in some places on at least one side of the narrow signal electrode 3, the metal base layer 34 is etched in that part. In addition to suppressing underetching, it is possible to obtain a plating film with a uniform thickness.
Since the signal electrode 3 functions as a heat dissipation fin for the heat generation of the signal electrode 3 caused by the signal current, thermal distortion is also reduced.
The performance of the optical waveguide device is improved.
This greatly contributes to improving quality and reliability.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram (part 1) showing an example of the electrode forming method of the present invention.

FIG. 3 is a diagram (part 2) showing an example of the electrode forming method of the present invention.

FIG. 4 is a diagram showing an example of the basic configuration of an optical modulator.

FIG. 5 is a diagram showing an example of a conventional electrode forming method.

[Explanation of symbols]

1 is the board, 2 is an optical waveguide, 2a and 2b are branched optical waveguides, 3 is a signal electrode, 4 is a ground electrode, 3a and 4a are metal base layer electrodes; 3b and 4b are metal plated layer electrodes, 5 is a buffer layer, 7 and 8 are resist patterns, 30 is a protruding metal pattern; 30' is the bridge part 31 is an etch hole, 34 is a metal base layer;

Claims (2)

[Claims] 1. A signal electrode for an optical waveguide device arranged so as to control light propagating in an optical waveguide (2) formed on a substrate (1) having an electro-optic effect, comprising:
A signal electrode for an optical waveguide device, characterized in that a protruding metal pattern (30) is formed in places on at least one side of the signal electrode (3). 2. A thin metal base layer electrode (3a) is formed in a portion that will become the protruding metal pattern (30), and the metal base layer electrode (3a) excluding the portion that will become the protrusion metal pattern (30). 2. The method of forming a signal electrode for an optical waveguide device according to claim 1, further comprising forming a thick metal plating layer electrode (3b) thereon.