JPS60189726A - Formation of electrode of ridge type light guide - Google Patents

Abstract

PURPOSE:To easily form an electrode on a flank of a ridge type light guide or between light guides by forming a metallic film on a ridge type light guide on a substrate and then providing a passivation film thereupon and flattening the light guide, and removing only the metallic film from the light guide. CONSTITUTION:The ridge type light guide 3 is formed on the substrate 1, and the metallic layer 2 is deposited according to the shape of the light guide. Then, the passivation film 4 is formed on the metallic layer 2 to flatten the ridge shape. This passivation film is thicker on outside of the light guide than on the light guide 3, and the metal 2 on the light guide is therefore exposed earlier than the metal outside the light guide when the whole substrate is etched. When the etching speed of metal is equal to or faster than that of the passivation film 4, further etching removes the metal 2 on the light guide 3, the metal on the flank of the ridge part is protected by the passivation film 4, and a flank electrode is formed.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a method for forming an optical instantaneous circuit used in the fields of optical communication and optical measurement, and in particular to a method for forming an optical switch and an optical modulator using the electro-optic effect. The purpose of this research is to provide optical devices that can be driven at low voltages.

[Background of the invention]

In recent years, the practical application of optical communication and optical measurement has progressed rapidly, and research and development on high-performance optical elements is actively being carried out. Optical switches and optical modulators, which are the components of optical integrated circuits, are used in a wide range of fields as they become smaller and more reliable, and their manufacturing processes are also basic and have a wide range of applications in forming other optical devices. It is something like that. Many types of optical switches and optical modulators have been proposed, such as reflection type and directional coupler type, and three-dimensional optical waveguide configurations include buried type, diffused type, loaded type, ridge type, etc. is cited as a representative example.

For example, as shown in FIG. 1, a Y plate of LiNb0. In the directional coupler-type guiding waveguide using the optical waveguide, the electrode is formed on the surface of the substrate, and the lateral component of the electric field applied to the optical waveguide mainly contributes to the electro-optic effect. In a diffusion-type optical switch, it is difficult to efficiently overlap the light propagation region and the applied electric field and drive the switch at a low voltage, and it is also difficult to form electrodes between the waveguides.

On the other hand, the ridge type optical waveguide as shown in Fig. 2
Optical waveguides can be easily formed by ion etching, etc., and they have the advantage of high light energy confinement efficiency and resistance to bending. Furthermore, by forming electrodes on the side surfaces of the ridge-shaped optical waveguide, an external electric field is efficiently applied to the light propagation region, and its lateral component is large, so a large electro-optic effect can be expected at low voltage.

[Purpose of the invention]

An object of the present invention is to provide a method for easily forming electrodes on the sides of a ridge-shaped optical waveguide or between optical waveguides in order to form an optical element that can be driven at a low voltage as described above.

[Summary of the invention]

If the waveguide width of the ridge-shaped optical waveguide is sufficiently wide, it is possible to place a photoresist on the optical waveguide after forming the ridge and form side electrodes by lift-off. but,
When the waveguide width is several μm.

It is extremely difficult to form a photoresist pattern overlapping the ridge. According to the present invention, side electrodes can be easily formed regardless of the width of the optical waveguide.

Hereinafter, an outline of the manufacturing process according to the present invention will be explained with reference to FIG. First, a lid-shaped optical waveguide 3 is formed on a substrate 1 (FIG. 3a), and a metal layer 2 is formed thereon to be deposited according to the shape of the optical waveguide (FIG. 3b). At this time, metal layer 2
is formed with the same thickness both on the waveguide 3 and outside the waveguide. Next, a passivation film 4 is formed on the metal layer to flatten the ridge shape (FIG. 3C). The passivation film 4 protects the optical element and protects it from the external atmosphere.
It generally refers to a film that stabilizes the surface of a device, but here, a planarizable film that is formed for the above purpose and has a small effect on optical characteristics is simply referred to as a passivation film. This passivation film 4 is thicker outside the waveguide than on the waveguide 3. Therefore, if the entire substrate is etched, the metal 2 on the waveguide appears on the surface earlier than the metal outside the waveguide.

If the etching speed of the metal is similar to or faster than that of the passivation film, the metal 2 on the waveguide 3 will be removed by further etching, the metal 2 on the side surface of the ridge will be protected by the passivation film 4, and the side electrode will be removed. formed (Fig. 3d). Alternatively, when the metal film on the waveguide appears on the surface, by selectively chemically etching only the metal film on the waveguide and L, the metal layer is separated on the waveguide and electrodes are formed on the side of the waveguide. be done. Connection with external electrodes can be easily made by etching the passivation film entirely or partially.

[Embodiments of the invention]

The manufacturing method according to the present invention is applied to a LiNbO3 directional coupler type optical switch, and the cross section and overall structure are as shown in FIG.

Example I First, 1,jNbo of Y plate with 2 μm Ti diffusion layer
A pattern of a directional coupling dish-shaped leading waveguide was drawn on the substrate of No. 3 using photoresist, and a ridge-shaped optical waveguide was formed by ion etching using this photoresist as a mask. The height of the ridge is 1 μm, and the height is 3 to 7 μm. Next, an AQ layer was formed on the entire surface of the substrate by vacuum deposition. AQ
, the layer follows the shape of the ridge and has a thickness of 3000 on both the top and outside of the waveguide.
It was a person. Since the LiNbO3 ridge-shaped optical waveguide has a trapezoidal cross section and the side surfaces of the waveguide have an inclination of 60 to 70', the AQ layer is also deposited on the side surfaces of the waveguide. PIQ is uniformly applied onto this AQ layer using a spinner. The thickness of the PIQ was 0.2 μm on the waveguide and 0.7 μm outside the waveguide, and the thickness was flattened. The entire substrate thus formed is etched by 1' on-milling. The etching conditions are the initial vacuum level of 10
-' t, orr or less, Ar partial pressure 8 X l O''-'
t, orr, acceleration voltage 600■, ion current density 0
, 4 mA/can2. ,.

Here, the etching speed of NAQ and PIQ is 14 each.
0 people/mjn and 135 people/min, which are about the same level, so even if the A fi on the waveguide is completely etched and bent, the Afi on the outside of the waveguide (including the sides) remains and the waveguide The A1 layer was separated between the two layers, and electrodes were formed on the sides of the ridge-shaped waveguide.

Example ■ In Example I, when the AM on the waveguide was exposed to the outside, etching by ion milling was stopped and the entire substrate was immersed in phosphoric acid to remove only the AQ exposed on the waveguide. Side electrodes were formed by selective etching.

〔Effect of the invention〕

As shown in Example L below, according to the present invention, electrodes can be easily formed on the side surfaces of the ridge type optical waveguide.
Optical devices that are efficiently driven at low voltage can be manufactured.

[Brief explanation of drawings]

Figure 1 shows LjNb03 using the conventionally proposed Y plate.
A sectional view of a directional coupler type optical waveguide, FIG. 2 is a cross-sectional view of a ridge-type optical waveguide having side electrodes corresponding to FIG. 1, and FIG. It is a process of formation. FIG. 4 shows an example of the present invention in which Li
FIG. 3 is a diagram showing the structure of a NbO3 directional coupler type optical switch. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Electrode, 3... Optical waveguide, 4...
...Passivation film. Figure 1 Figure 2 Figure 3 (C) ((L)

Claims (1)

[Claims] After forming a metal film to be deposited according to the shape of the optical waveguide on the ridge-shaped optical waveguide formed on the substrate, a passivation film is further provided on top of it to flatten the shape of the optical waveguide, and then chemical A ridge-shaped optical waveguide and a method for forming its electrodes, characterized in that the ridge-shaped optical waveguide is manufactured by removing only the metal film on the optical waveguide by etching, either physically or mechanically.