JPH0643412A - Production of optical control device - Google Patents

Abstract

PURPOSE:To provide the process for production of the novel and revolutionary optical control device which can be improved in pattern accuracy and can be drastically decreased in DC drift by buffer layers with simple stages. CONSTITUTION:This process for production of the optical control device by forming control electrode layers 5 via the buffer layers 4 on optical waveguides 2 provided in the surface layer part or on the surface of a substrate 1 having an electrooptical effect consists in laminating a resist layer 3 on the substrate 1 exclusive of at least a part of the regions made to remain on the optical waveguides 2 and successively laminating the buffer layers 4 and the control electrode layers 5 on at least a part of the regions on the optical waveguides 2, then removing the resist layer 3. The buffer layers 4 are formed by executing sputtering in a gaseous atmosphere contg. gaseous oxygen.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an optical control device such as a waveguide type optical modulator or optical switch used for optical communication, optical sensors, optical information processing and the like.

[0002]

2. Description of the Related Art Nowadays, with the practical application of a next-generation large-capacity optical communication system, there is a strong demand for speeding up of an optical control device which is one of the constituent elements of the system. Therefore, a waveguide type optical control device using a substrate having an electro-optic effect characterized by high speed has been studied, and for example, a lithium niobate (LiNbO3; hereinafter abbreviated as LN) single crystal substrate is used. Since a channel optical waveguide formed by diffusing titanium (Ti) can obtain a very low loss of about 0.1 to 0.2 dB / cm, various optical control devices in which a control electrode is added to such a structure are provided. Is being actively researched.

Usually, in an optical control device using such an electro-optic effect, a TM is provided between the optical waveguide and the control electrode.
A low-refractive-index dielectric film called a buffer layer, for example, an oxide film such as silica (SiO2) or alumina (Al2 O3) is used for the purpose of reducing attenuation of mode light due to leakage to the metal film. However, when a DC voltage is applied to the control electrode on this buffer layer, the charged ions move in the buffer layer, and the ions are absorbed by the electrode, canceling the externally applied electric field, and the intensity of the output light. DC due to so-called buffer layer
A phenomenon called drift occurred, which was a practical problem.

Therefore, a method of cutting the buffer layer between two electrodes is effective as a means for solving the above-mentioned problem. For example, as shown in FIG. 2, a surface layer portion of the crystal substrate 11 having an electro-optical effect is formed. The optical waveguide 12 is formed (see FIG.
(A)), after that, the patterning of the buffer layer 13 is performed (FIG. 2B), and further, the patterning of the control electrode layer 14 is performed using a manufacturing technique similar to this (FIG. 2B).
(C); Method 1) is known (for example, JP-A-56-1).
(See Japanese Patent No. 65122).

Further, as shown in FIG. 3, for example, an optical waveguide 22 is formed on the surface layer portion of a crystal substrate 21 having an electro-optical effect (FIG. 3A), and then a buffer layer 23 is formed by using a thin film forming technique. And the control electrode layer 24 are sequentially formed (see FIG.
(B)), and further, the resist layer 25 is patterned into a control electrode shape by using a photolithography technique (FIG. 3C), and then the buffer layer 23 and the control electrode layer 24 are each formed with a suitable etching solution. A method (FIG. 3 (d); Method 2) for patterning is known.

[0006]

However, the method 1 described above requires an additional photolithography step for forming the buffer layer in addition to the formation of the optical waveguide and the control electrode. However, there are problems that the process is complicated and the number of processes is increased, for example, it is necessary to keep the substrate surface clean.

Further, in the technique of the above-mentioned method 2, although high temperature annealing can be performed after forming the buffer layer, it is difficult to select an etching solution when the control electrode layer is a noble metal, or the buffer layer is difficult to select. It is necessary to select an etching solution suitable for both the control electrode layer and the control electrode layer, which complicates the process and deteriorates the pattern accuracy due to side etching.

[0008]

[Object] Therefore, the present invention solves the above-mentioned problems, improves the pattern accuracy in a simple process, and significantly reduces the DC drift due to oxygen deficiency in the buffer layer. It is an object to provide a method for manufacturing a control device.

[0009]

In order to achieve the above object, a method of manufacturing a light control device according to the present invention comprises a buffer layer on an optical waveguide provided on a surface layer portion or surface of a substrate having an electro-optical effect. A control electrode layer is formed through the resist layer, a resist layer is laminated on the substrate leaving at least a partial region on the optical waveguide, and then a buffer layer and a control electrode are formed on at least a partial region on the optical waveguide. It is characterized in that layers are sequentially laminated, and then the resist layer is removed.

Particularly, the buffer layer is preferably formed by sputtering in a gas atmosphere containing oxygen gas.

[0011]

According to the method of manufacturing the light control device of the present invention,
Since the pattern formation of the buffer layer is performed at the same time as the formation of the control electrodes, the manufacturing process can be greatly simplified as compared with the conventional manufacturing method, and the pattern accuracy becomes good.

In addition, by performing sputtering for forming the buffer layer in a gas atmosphere containing oxygen, a high temperature annealing for a long time as in the prior art (see, for example, Japanese Patent Laid-Open No. 59-181318) is performed. Since oxygen vacancies in the buffer layer made of oxide can be compensated for, the buffer layer and the control electrode layer can be continuously manufactured, and DC drift due to oxygen vacancies in the buffer layer can be significantly reduced.

[0013]

Embodiments of the present invention will be described in detail with reference to the drawings. First, both sides are optically polished to a thickness of 0.5-1.0
Prepare a dielectric substrate (hereinafter simply referred to as substrate) 1 of LN single crystal (Z-cut; cut face is (001) face) of optical grade of about mm and ultrasonically clean it with pure water, acetone, etc. Do enough. After that, for example, a general photoresist used in a normal semiconductor device manufacturing process is applied on the surface of the substrate 1 by a spin coating method to a thickness of about 0.5 to 1.5 μm, and then exposed under appropriate conditions. By developing, the width of the contact surface between the resist layer and the substrate is 0.1 to several μ compared to the pattern width of the resist surface layer.
A resist pattern having an inversely tapered cross section, which is widened by about m, is obtained. This can be easily formed by using a conventional so-called photolithography technique, and forms a pattern shape for forming an optical waveguide described later.

Next, a titanium (Ti) thin film is formed in a thickness of about 20 to 200 nm on the region of the resist pattern by a well-known vacuum vapor deposition method or RF sputtering method, and then the substrate 1 is formed. By immersing the resist layer in acetone to melt it, an optical waveguide-shaped Ti film having a stripe width of several μm and the above thickness is obtained. After that, it is heated for about 10 hours in an electric furnace at about 1000 ° C. in which a humidified or dry argon (Ar) or oxygen (O 2) gas atmosphere or a mixed atmosphere gas thereof is flowed at a flow rate of several liters per minute, and Ti is heated for about 10 hours. Was thermally diffused to the surface layer of the substrate 1 to form the optical waveguide 2 having a desired shape (see FIG. 1A). Incidentally, such a technique for forming an optical waveguide can be applied to various optical waveguides other than the above-mentioned embedded optical waveguide,
For example, this technique can be applied to a ridge type optical waveguide. That is, the optical waveguide 2 may be provided on the surface of the substrate 1. First, a titanium film is formed on the entire surface of the substrate 1 by using the above-described thin film forming technique, and the titanium film is formed on the surface layer of the substrate by the method described above. After diffusion, a titanium film having an optical waveguide shape may be formed by using the above-mentioned photolithography technique and thin film forming technique, and the titanium diffusion region other than the titanium film loading region may be removed by dry etching or the like. it can.

Next, as shown in FIG. 1B, a resist layer 3 finely processed into a control electrode pattern is formed to a thickness of about 1 to 2 μm by the photolithography technique described above. At this time, it is important that the cross-sectional shape of the resist layer 3 is an inverse taper shape, because good lift-off described below can be performed without leaving minute fragments such as burrs at the pattern edge portion. It should be noted that the resist layer 3 is left in the substrate 1 at least in a region including a part of the optical waveguide 2.
It may be stacked on top.

Next, as shown in FIG. 1C, a low refractive index oxide dielectric such as silica (SiO2) or alumina (Al2 O3) having a film thickness of about 0.2 to 2 .mu.m is formed by RF sputtering or the like. One layer or a plurality of layers of the buffer layer 4 consisting of was formed on the surfaces of the resist layer 2 and the substrate 1. Here, the buffer layer 4 is also formed on the resist layer 3, but the buffer layer 4 may be laminated on at least a part of the optical waveguide 2 except the region where the resist layer 3 is laminated.

Here, a mixed gas of argon and oxygen is used as a sputtering gas, and the flow rate ratio is 10 / 0.5 to 10.
/ 2 is suitable. Further, the film formation was carried out at a pressure of 2 to 5 mTorr and a RF power of 100 to 300 W during sputtering film formation (the optimum value varies depending on the apparatus and film forming conditions). It should be noted that these mixed gases are not limited to argon and oxygen, and may be any gas containing at least oxygen gas.

Then, platinum (Pt), gold (Au), silver (Ag), chromium (C) are produced by the same manufacturing method as for the buffer layer 4.
r), aluminum (Al), tantalum (Ta), nickel (Ni), titanium (Ti), etc. One or a plurality of control electrode layers 5 made of other metal are laminated on the buffer layer 4.

Here, the buffer layer 4 and the control electrode layer 5 can be continuously formed by, for example, a multi-source vacuum deposition method or an RF sputtering method using a multi-target, and the formation of the buffer layer as in the prior art. The photolithography process performed later is not necessary, and it is not necessary to keep the substrate in a clean state while maintaining the vacuum state at this time, and the process can be greatly simplified.

Next, the resist layer 3 is dissolved with acetone or the like to form a desired pattern of the oxide buffer layer 4 and the control electrode layer 5. At this time, a solvent such as acetone is used for the substrate 1.
Does not cause damage as in the case of using a strong acid etching solution such as hydrofluoric acid, and does not damage the resist layer 3 and the substrate 1 depending on the material when forming a pattern with the etching solution. It is possible to solve the problem that it becomes difficult to select, and the problem of deterioration of pattern accuracy due to side etching,
Furthermore, there is no complexity of using a plurality of etching solutions when a structure in which a plurality of layers of thin films are stacked is used, and pattern formation can be easily realized with any material and with a structure in which a plurality of layers are stacked. It

Results of comparison of DC drift (generally short-time DC drift) due to the buffer layer between the light control device manufactured according to the above-described embodiment and the light control device in which the buffer layer is formed by sputtering with argon alone. , A significant improvement in relaxation characteristics was observed. That is, FIG. 4 (a)
In contrast to the applied voltage waveform shown in FIG. 4, a DC drift on the order of several minutes was conventionally recognized as shown in FIG. 4B, whereas according to this embodiment, as shown in FIG. Almost no DC drift on the order of a few minutes was observed. In the figure, V indicates a half-wave voltage, and τ is a relaxation time.

Further, as a result of measuring the refractive index and the resistivity of the oxide film sputtered with this mixed gas of argon and oxygen, the refractive index was smaller and the resistivity was higher than that of the argon alone. . This indicates that the oxygen deficiency of the buffer layer was compensated and the buffer layer was densified, and a correlation with improvement in device characteristics was observed.

[0023]

As described above, according to the method of manufacturing the light control device of the present invention, the patterning of the buffer layer is performed simultaneously with the formation of the control electrode, so that the manufacturing process is greatly simplified as compared with the conventional manufacturing method. It is possible to provide an excellent manufacturing method that can realize the pattern accuracy and can make the pattern accuracy extremely good.

Further, since the buffer layer is formed by sputtering in a gas atmosphere containing oxygen, oxygen vacancies in the buffer layer can be compensated for without performing high temperature annealing for a long time as in the conventional case. The buffer layer and the control electrode layer can be continuously manufactured, and DC drift due to the buffer layer can be significantly reduced without performing high-temperature annealing on the buffer layer.

Further, according to the present invention, since the resist layer can be easily removed with an organic solvent such as acetone, it is easy to form the buffer layer or the control electrode in a multi-layer structure made of various materials. is there.

[Brief description of drawings]

1A to 1D are diagrams showing respective steps of an example according to the present invention.

2A to 2C are diagrams showing respective steps of a conventional example.

FIG. 3A to FIG. 3D are diagrams showing respective steps of another conventional example.

FIG. 4 is a diagram showing DC drift characteristics of a buffer layer of an optical control device manufactured by a manufacturing method of the present invention and a conventional method.

[Explanation of symbols]

1 ... Substrate 2 ... Optical waveguide 3 ... Resist layer 4 ... Buffer layer 5 ... Control electrode layer

Claims (2)

[Claims] 1. A method of manufacturing a light control device, comprising a control electrode layer formed on a surface layer portion or a surface of a substrate having an electro-optical effect on a surface portion or a surface of the substrate through a buffer layer. Laminating a resist layer on the substrate leaving at least a partial region, then sequentially laminating a buffer layer and a control electrode layer on at least a partial region on the optical waveguide, and then removing the resist layer. A method for manufacturing a light control device, comprising: 2. The method for manufacturing a light control device according to claim 1, wherein the buffer layer is formed by sputtering in a gas atmosphere containing oxygen gas.