JPH04159515A - Production of optical waveguide type control element - Google Patents

Abstract

PURPOSE:To relieve the damages, stresses, etc., to a substrate (waveguide) formed at the time of electrode pattern formation and to prevent the deterioration of device characteristics by patterning a thin film for electrodes covering optical waveguides by dry etching, then completing the electrode patterning by wet etching. CONSTITUTION:Two pieces of the Ti-diffused waveguides 12, 13 are formed on a lithium niobate crystal substrate 11, the X-axis of which is perpendicular to the substrate plane. Control electrodes are installed via a buffer layer 14 consisting of an SiO2 film on the optical waveguides. Mask patterns are then formed by a photoresist and are dry etched by an ion beam sputtering device after the formation of the mask patterns to form the Au electrodes 17, 18. Finally, the Ti is patterned by chemical etching (wet etching) to form the Ti electrodes 19, 20 and the resist is removed. The damages, stresses, etc., generated on the substrate (waveguide) at the time of the electrode pattern formation are relieved in this way. The production tolerance of the device is increased and the yield is improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical switch that modulates light waves, switches optical paths, etc. in optical communications, etc., and particularly relates to an optical switch that modulates light waves, switches optical paths, etc. This invention relates to waveform optical switches.

[Conventional technology]

Optical communication systems are being put into practical use, and more advanced systems with large capacity and multiple functions are being developed. New functions such as switching functions of optical transmission networks, high-speed connections between terminals in optical data buses, and switching are required, and the need for optical switching networks that make these functions possible is increasing. Optical switches currently in use mechanically move prisms, mirrors, fibers, etc., and have drawbacks such as slow speed, insufficient reliability, and large size that makes them unsuitable for matrix formation. There is. A waveguide type optical switch that uses an optical waveguide installed on a substrate is currently being developed as a means to solve this problem, and has features such as high speed, integration of multiple elements, and high reliability. In particular, those using ferroelectric materials such as LiNbO3 crystals have features such as low light absorption, low loss, and high efficiency due to large electro-optic effects.

FIG. 2 shows a perspective view of a directional coupling type optical switch, which is an example of a conventional waveguide type optical switch. A leading waveguide 12, 13 is formed by diffusing a metal such as Ti into a LiNbO3 crystal substrate 11 that is cut out and shaped perpendicularly to the optical axis. These optical waveguides i12 and 13 are installed close to each other with an interval of about several μm to constitute an optical directional coupler 24, and a buffer layer (not shown in the figure) is placed on the optical waveguides 12 and 13. Control electrodes 25,26 are installed. Although there are several methods for forming the control electrodes 25 and 26, the most common method is anisotropic etching (dry etching) in which a mask pattern is faithfully transferred. The basic operating principle of this switch is that first, a light wave 27 incident from the end face of one of the optical waveguides, for example, the optical waveguide 12, propagates through the optical waveguide 12, and at the optical directional coupler 24, the optical wave 27 enters the adjacent optical waveguide 13. The energy is transferred to the optical directional coupler 2.
If the length of 4 is made to match the complete bond length Lc, the length is 10
0% of the energy is transferred to the optical waveguide 13 and becomes the output light 28. On the other hand, when a voltage is applied between the control electrodes 25 and 26, the refractive index of the optical waveguide 12 and 13 changes due to the electro-optic effect, and the refractive index of both becomes asymmetric, resulting in a difference in the phase between the light waves propagating through them. A mismatch occurs and the coupling state changes, and under an appropriate applied voltage, energy is transferred to the original optical waveguide 12 and becomes emitted light 29.

In addition to the directional coupling type mentioned above, waveguide optical switches include total reflection type, balanced bridge type, Y-branch type, etc., but these types are relatively effective at reducing switch voltage and crosstalk, which are important for optical switches. It is known that the directional coupling type is the one that can be easily lowered and has the simplest configuration.

[Problem to be solved by the invention]

As described above, in the directional coupling type optical switch, it is necessary to form an electrode pattern on the waveguide in order to control switching of the optical path. However, in conventional methods using anisotropic etching (dry etching), even a small amount of overetching causes damage, which deteriorates device characteristics and reduces yield. Therefore,
In order to increase device manufacturing tolerance and improve yield, it is necessary to alleviate damage to the substrate (waveguide) that occurs during electrode pattern formation.

[Means to solve the problem]

The present invention comprises a process of selectively forming an optical waveguide on the surface of a substrate, a process of forming a thin film for an electrode so as to directly or indirectly cover the optical waveguide, and a process after patterning the thin film for an electrode by tri-etching. This method of manufacturing an optical waveguide type control element is characterized by comprising the step of completing electrode patterning by wet etching.

[Effect]

An electrode pattern consisting of one or multiple thin films is formed on a crystal substrate in which an optical waveguide is formed by thermal diffusion or the like in a crystal having optical anisotropy such as lithium niobate or lithium tantalate. In the case of multilayers, an electrode material with a slower etching rate than other thin films is used for the lowest layer film, that is, the electrode thin film closest to the substrate surface, and the upper layer is anisotropically etched (dry etching). ) Damage caused by etching and stress due to pattern effects are stopped (absorbed) at this bottom layer, and finally only this bottom layer is wet-etched. In the case of one layer, patterning is performed by dry etching, leaving about several hundred thin films. Thereafter, the remaining portion is etched by wet etching to form a pattern. This prevents the substrate (waveguide) from being damaged by anisotropic etching (dry etching), and also alleviates stress caused by electrode patterning.

Although wet etching is inferior to dry etching in terms of pattern processing accuracy and reproducibility, it has the advantage of not damaging the crystal substrate. Furthermore, by making the film thinner, the undercut caused by side etching can be kept small as long as the etching rate for dry etching is taken into consideration. Therefore, by alleviating damage, stress, etc. to the substrate (waveguide) that occurs during electrode pattern formation, it is possible to increase device manufacturing tolerance and improve yield.

〔Example〕

FIG. 1 is an explanatory diagram of the manufacturing process of an optical waveguide type control element according to an embodiment of the present invention. In the optical waveguide type control element of this embodiment, two Ti diffusion waveguides 12 and 13 are formed on a lithium niobate crystal substrate 11 whose Z axis is perpendicular to the substrate surface.

These optical waveguides constitute an optical directional coupler by being placed close to each other at intervals of about several μm, and a control electrode is placed on the optical waveguides via a buffer layer 14 made of a SiO2 film. The method for forming the control electrode is to first form a buffer layer 1.
A Ti thin film 15 and then an Au thin film 16 are formed by sputtering so as to cover 4 (FIG. 1(a)). At this time, the thickness of Au is approximately ten to several times as thick as that of Ti. Next, after forming a mask pattern using photoresist, dry etching is performed using an ion beam etching device to form an Au electrode. 17.
18 (FIG. 1(b)). When a small amount of oxygen is mixed in the etching gas, the etching rate of Ti becomes extremely slow, and as a result, only Au can be selectively etched. Therefore, the Ti is finally buttered by chemical etching (wet etching).
Electrodes 19 and 20 are formed and the resist is removed (see Figure 1 (
C)). Since the Ti film thickness is very thin compared to the total film thickness of the control electrode, undercuts due to side etching can also be minimized. Therefore, by alleviating damage, stress, etc. to the substrate (waveguide) that occurs during electrode pattern formation, deterioration of device characteristics can be prevented, manufacturing tolerance can be increased, and yield can be improved.

FIG. 3 is a cross-sectional view of an optical waveguide type control element that does not require a buffer layer. Two Ti diffusion waveguides 12 are placed on a lithium niobate crystal substrate 31 whose X axis is perpendicular to the substrate surface.
．． 13 is formed, and light switching is performed by applying an electric field parallel to the substrate surface using a control electrode 35 installed on the substrate surface. In a guided waveguide type control element that does not require such a buffer layer,
This is particularly effective since there is no buffer layer. The manufacturing method is the same as that shown in FIG. 1 (however, the buffer layer forming step is omitted).

In addition, in the example, the thin film for the electrode had a two-layer structure, but 1
It may be formed in layers. In this case, the patterning can be completed by removing the thin film to a thickness of several hundred using a dry etching process.

[Effects of the Invention] As explained above, the present invention includes a step of selectively forming an optical waveguide on the surface of a substrate, a step of forming an electrode thin film so as to directly or indirectly cover the guide waveguide, and a step of forming an electrode thin film so as to cover the guide waveguide directly or indirectly. A method for manufacturing an optical waveguide type control element, which is characterized by the step of patterning a thin film by dry etching and then completing electrode patterning by wet etching, allows the substrate (
This has the effect of alleviating damage and stress to waveguides, preventing deterioration of device characteristics, increasing manufacturing tolerance, and improving yield.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the manufacturing process of an optical waveguide type control element according to an embodiment of the present invention, FIG. 2 is a perspective view of a conventional example, and FIG. 3 is a cross-sectional view when a buffer layer is not required. . 11.31...Lithium niobate crystal substrate, 12゜1
3...Ti diffused waveguide, 14...buffer layer (Si
O2 membrane), 1! 5-Ti film, 16-Au film, 17
゜18-A, u electrode, 19.2O-Tiii pole, 24-
... Directional coupler, 25, 26.35 ... Control electrode,
27...Incoming light, 28.29...Outgoing light.

Claims (1)

[Claims] 1. A step of selectively forming an optical waveguide on the surface of a substrate, a step of forming an electrode thin film so as to directly or indirectly cover the optical waveguide, and a step of forming an electrode thin film by forming a plurality of electrode thin films. 1. A method for manufacturing an optical waveguide type control element, comprising the steps of patterning by dry etching to leave about 100 Å, and then completing electrode patterning by wet etching. 2. A step of selectively forming an optical waveguide on the surface of the substrate, a step of forming at least two or more types of electrode thin films having different etching rates so as to directly or indirectly cover the optical waveguide, and the electrode thin film. After patterning by dry etching leaving at least the bottom layer,
A method for manufacturing an optical waveguide control element, comprising the step of completing electrode patterning by wet etching.