JPS5977413A - Formation of optical waveguide - Google Patents

Abstract

PURPOSE:To facilitate the connection with an external circuit by etching away a part of a stripe electrode for voltage application after an optical waveguide is formed on a substrate, and then forming a bonding pad for the connection with the external circuit by a lift-off method. CONSTITUTION:A high-resistance Ga-As layer 23 is grown on a Ga-As substrate 24, etc., by a liquid phase epitaxial method. A metallic film of Al, etc., is vapor- deposited on the phase 23 and then two metallic stripes 21 and 22 are formed by photolithography. The phase 23 is etched by using those stripes 21 and 22 as protection films to form ridge type optical waveguides 31 and 32. Then, metallic parts at one-side end 33 and 34 of the stripes 21 and 24 are removed by photolithography. Then, electrodes 28 and 29 for bonding pads are formed by the lift- off method. Thus, the connection between a reverse-surface electrode 25 and electrodes 28 and 29 is made easily and securely and two close optical waveguides 31 and 32 are driven independently and easily.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to the formation of a three-dimensional optical waveguide called a ridge type among optical thin film waveguides used in optical integrated circuits, etc.
In particular, the present invention relates to a method of forming an optical waveguide suitable for an optical modulator using an electro-optic effect.

[Prior art]

There are several types of optical waveguides, one of which is a ridge-type waveguide having the configuration shown in FIG. 1, which is often used in modulators, switches, etc. that utilize electro-optic effects.

Figure 1 is a diagram showing the configuration of a conventional optical waveguide of this type.
4 is a gallium arsenide substrate, 23 is a high-resistance gallium arsenide epitaxially grown film, and 11 and 12 are striped patterns formed by partial etching of the epitaxial film. Since the refractive index effectively increases in the lower part of the stripe batten, the incident light can efficiently propagate without being diffused in the lateral direction.

Note that the following explanation will proceed by taking as an example a case where gallium arsenide is used.

Electrodes are formed on the front surface of such waveguide stripes and the back surface of the substrate, and a voltage is applied to both.The change in refractive index due to the electro-optic effect of the waveguide layer enables various active functions such as optical modulation and optical switches. It is possible to perform certain actions. For this purpose, an external circuit for electrode application and 2
1. It is necessary to connect electrodes such as 22 and 25. However, the width of the waveguide portion 11 or 12 is generally on the order of several microns, and the surface is uneven.
It is difficult to conduct wiring between the electrodes in such a small portion and the outside.

Due to the above-mentioned difficulties, conventionally a needle was placed on the striped electrode to connect it to the outside. However, this method requires complicated connection procedures and lacks stability, making it difficult to use in practical devices.

There is also a method of forming electrodes for connection to external circuits by mask vapor deposition. However, the dimensional accuracy or alignment accuracy of the battens formed by mask vapor deposition is 10 μm.
It is very difficult to do the following. Therefore, when a plurality of components such as an optical integrated circuit are formed on the same substrate, the above method cannot be used because of the accuracy of the four parts.

[Purpose of the invention]

The purpose of the present invention is to overcome the above-mentioned difficulties by removing a part of the striped electrode for voltage application by etching after forming a waveguide, and then forming a bonding band for wire bonding with an external circuit. The purpose is to make connection with an external circuit much easier by forming it by lift-off.

[Summary of the invention]

In order to achieve the above object, the method for forming an optical waveguide of the present invention involves depositing a metal film in a three-dimensional optical waveguide formed on an electro-optic crystal such as a dielectric or semiconductor, or an amorphous substrate such as glass. After that, a stripe pattern is formed using photoresist, and the substrate is etched using the metal stripe as a protective film. After that, a part of the metal stripe is removed by etching, and then the % electrode for voltage application/reduction is lifted off. It has a process of forming by.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. 2B. This figure shows an optical switch consisting of two thin film waveguides formed on a gallium arsenide substrate, and was manufactured as follows. A high-resistance gallium arsenide layer 23 is formed on a gallium arsenide substrate 24 with a thickness of approximately 400 μm by a liquid layer epitaxial method.
A metal film of gold or aluminum was deposited thereon to a thickness of 0.2 μm. Two stripes 21 and 22 having a width of 4 μm and an interval of 8 μm were formed on this metal film by a normal photolithography process. Next, using this metal film as a protective film, the gallium arsenide film was etched by 1 μm to form ridge-type waveguides 31 and 32. Thereafter, the metal portions 33 and 34 were removed by etching using a conventional photolithography technique, and then electrodes 28 and 29 for bonding pads were formed by a lift-off method.

The waveguides 31 and 32 formed by the above method have a diameter of about 1
A bonding band having a size of 00×100 μm 2 and an external circuit can be easily connected with a metal wire. Moreover, since the electrode for the bonding band is formed after removing a portion of the end of the electrode by etching, insulation between the waveguides is very easy. It becomes easy to drive the waveguides independently.

Although the case of two waveguides has been described in this embodiment, the present method can also be applied as is to an optical circuit having a more complicated structure.

Furthermore, although this embodiment has been described using a GaAs substrate as an example, the present invention is not limited to the above materials.

〔Effect of the invention〕

According to the present invention, it is possible to easily connect the uneven optical waveguide formed on the substrate to other parts.

[Brief explanation of drawings]

FIG. 1 is an external view of a conventional ridge-type optical waveguide, and FIG. 2 is a plan view and a front view of an optical waveguide according to an embodiment of the present invention (bonding bands 28 and 29 are not shown). 10... External circuit connection terminal, 21.22... Stripe electrode, 23... High resistance gallium arsenide epitaxial layer, 24... Gallium arsenide substrate, 25... Back electrode, 28.29...・Pounding pad, 31°3
2... Optical waveguide. Agent Patent Attorney Toshiyuki Usuda

Claims (1)

[Claims] In the three-dimensional optical waveguide formed on the substrate, after depositing a metal film, the entire stripe pattern is formed using photoresist, the substrate is etched using the metal stripe as a protective film, and the subsequent forming process is carried out. A method for forming an optical waveguide, comprising: