JPH04289804A - Manufacture of optical waveguide device - Google Patents

Abstract

PURPOSE:To make damages and defects due to discharge during manufacturing process less likely to occur and shorten heating and cooling time of a substrate when the temperature of the substrate changes by supplying ionized gas around the substrate. CONSTITUTION:An inert gas is used as the ionized gas to be supplied into a vacuum deposition chamber 4 from an ionized gas supplying unit 8. Prior to the vacuum deposition, the deposition chamber 4 is evacuated. When a substrate 2 is heated, ionized gas is supplied in the vicinity of the substrate 2. The supply of the ionized gas is stopped when the temperature of the substrate 2 becomes constant. A film is deposited on the surface of the substrate 2 by evaporating a deposition material 12 by means of an electron gun 14. Ionized gas is supplied later around the substrate 2 when the substrate 2 is cooled down to the room temperature. This prevents electric discharge which otherwise occurs on the surface of the substrate 2 when it is heated and cooled.

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 waveguide device.

[0002] As a form of optical devices such as optical modulators,
There is an optical waveguide device that is configured to form an optical waveguide on a waveguide substrate and control a light beam while confining it within the optical waveguide. Optical waveguide devices have the advantage of being easy to miniaturize due to their structure and can be mass-produced using planar technology, etc., as well as being able to effectively apply electric and magnetic fields and reducing power consumption. have. In this type of optical waveguide device, when the waveguide substrate is made of a ferroelectric crystal, charges are induced by the pyroelectric effect when the waveguide substrate is heated or cooled in a thermal diffusion process, etc., and if the amount of the charges is large. There is a need for a method for manufacturing an optical waveguide device that can prevent such damage from occurring due to discharge occurring in the waveguide substrate.

0003

[Prior Art] Conventionally, as a manufacturing method for an optical waveguide device having an optical modulation function, for example, an optical waveguide is formed by thermally diffusing Ti onto a substrate made of LiNbO3, and electrodes are loaded onto the optical waveguide. method is known. In this case, Z-cut LiNbO is used, which makes it easy to obtain an optical waveguide with a shape that allows low-loss coupling with an optical fiber.
3 is often used.

0004

[Problems to be Solved by the Invention] However, in the method for manufacturing an optical waveguide device as described above, in order to form an optical waveguide and electrodes on a waveguide substrate, a vapor deposition process, a photolithography process, a thermal diffusion process, etc. are used. It becomes necessary to heat the substrate in the process. In general, ferroelectric crystals have an electro-optical effect and also a pyroelectric effect in which polarized charges appear on the surface when heated. When a temperature change is applied to a Z-cut substrate, charges with different polarities are generated on the front and back surfaces of the substrate. If the amount of charge accumulates and increases rapidly, sparks may be generated, damaging the substrate or the film formed on the substrate, or creating defects that become light scatterers inside the substrate crystal. If such damage or defects occur, it becomes impossible to obtain the desired characteristics of the optical waveguide device, which is a problem.

This phenomenon will be schematically explained with reference to FIG. The substrate 2 made of ferroelectric crystal has (A
), and the charges on its front and back surfaces are balanced with the charges in the atmosphere. If this substrate 2 is heated rapidly, as shown in (B), the charge on the front and back surfaces of the substrate 2 will increase significantly due to the pyroelectric effect, and the supply of charge from the atmosphere will not be in time, causing discharge. Become.

Conventionally, in order to prevent such discharge, the temperature change per unit time during heating and cooling of the substrate is reduced to reduce the charge generated by the pyroelectric effect and the charge supplied from the atmosphere. A method has been proposed to prevent imbalance. However, this method has the problem that it takes a long time to heat and cool the substrate, resulting in poor productivity.

The present invention was created in view of the above circumstances, and provides a method for manufacturing an optical waveguide device having a substrate made of ferroelectric crystal, which is less likely to cause damage or defects due to discharge, and which is less likely to cause damage or defects due to the heating and heating of the substrate. The purpose is to provide a method that does not require a long time for cooling.

[0008]

[Means for Solving the Problems] The method of the present invention provides a method for manufacturing an optical waveguide device including a step of applying a temperature change to a substrate made of a ferroelectric crystal. It is designed to supply ionized gas to the surrounding area.

[0009]

[Effect] If ionized gas is supplied around the substrate when the temperature of the substrate changes, even if the temperature of the substrate changes rapidly, charges will be generated on the front and back surfaces of the substrate due to the pyroelectric effect. It is possible to balance the charge supplied to the atmosphere by the ionized gas, making it difficult for discharge to occur. As described above, according to the present invention, it is possible to prevent damage and defects caused by discharge without requiring a long time to heat and cool the substrate.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram for explaining a first embodiment of the present invention in which the method of the present invention is applied to a film deposition process in an optical waveguide device. In the figure, 4 is a vapor deposition chamber, 6 is a table provided above the vapor deposition chamber 4 for placing the material to be vaporized, and 2 is an optical waveguide made of ferroelectric crystal such as LiNbO3 placed on the table 6. 8 is an ionized gas supply device 10 that supplies ionized gas to the vicinity of the substrate 2 in the deposition chamber 4;
is a vacuum pump for evacuating the inside of the deposition chamber 4; 12 is a deposition material provided below the table 6 in the deposition chamber 4; and 14 is an electron beam applied to the deposition material 12 to evaporate the deposition material. An electron gun 16 indicates a heating means for heating the substrate 2 to an appropriate temperature.

[0012] The heating temperature of the substrate 2 varies depending on the type of vapor deposition material, etc., but in the vapor deposition process of the diffusion source metal of the waveguide type optical modulator and the electrode formation process, a heating temperature of, for example, 100 to several hundred degrees Celsius is adopted. be done. When depositing a metal material such as an electrode on a substrate, if the inside of the deposition chamber 4 is in an oxidizing atmosphere, the deposited metal will oxidize and it will not be possible to form a good diffusion source or electrode base. As the ionized gas supplied from the ionized gas supply device 8 into the deposition chamber 4, ionized inert gas such as N2 or Ar is employed. Ionization of the gas can be performed by a conventional method using electric discharge or microwaves.

First, prior to vapor deposition, the inside of the vapor deposition chamber 4 is evacuated and the substrate 2 is heated to a predetermined temperature. When heating the substrate, the ionized gas described above is supplied from the ionized gas supply device 8 to the vicinity of the substrate 2, since there is a possibility that discharge may occur between the front and back surfaces of the substrate due to the pyroelectric effect. Thereby, even if the substrate 2 is heated rapidly, there is no risk of damage or defects caused by discharge.

Once the substrate 2 has been heated and its temperature has become constant, the supply of ionized gas into the deposition chamber 4 is stopped, and the deposition material 12 is evaporated by the electron gun 14 to be deposited on the surface of the substrate 2. Perform the required film deposition.

When the film deposition on the surface of the substrate 2 is completed, the heating means 16 is stopped and the substrate 2 is cooled to room temperature. At this time, in the same way as when heating the substrate 2,
Ionized gas is supplied around the substrate 2. This results in
Discharge during cooling of the substrate can be prevented.

Depending on the amount of ionized gas supplied, the substrate 2
When heating is completed, the charge generated by the pyroelectric effect and the charge in the atmosphere around the substrate may not be sufficiently balanced. In this case, it is preferable to continue supplying the ionized gas for a while even after the substrate 2 reaches a certain temperature.

FIG. 2 is a diagram for explaining a second embodiment of the present invention in which the method of the present invention is applied to a thermal diffusion process of a waveguide substrate. In the figure, 18 is a horizontal heating furnace, 20 is a table for mounting a substrate provided in the heating furnace 18, 2 is a substrate made of ferroelectric crystal such as LiNbO3 placed on the table 20, and 22 24 is a heating means for heating the inside of the heating furnace 18 so that the substrate 2 reaches the diffusion temperature, and 24 is a heating means for heating the inside of the heating furnace 18 at a predetermined mixing ratio so that the inside of the heating furnace 18 becomes an appropriate oxidizing atmosphere at the heating temperature. 26 is an ionized gas supply device that supplies ionized gas around the substrate 2 in the heating furnace 18; 28 is an ionized gas supply device that supplies an atmosphere adjustment gas consisting of oxygen and water; each represents.

The reason why gas for atmosphere adjustment is supplied into the heating furnace 18 is because the substrate 2 is heated to a high temperature during the diffusion process, and if an appropriate oxidizing atmosphere is not maintained, LiNbO
This is because there is a risk that Li2O will diffuse into the atmosphere from the substrate 2 made of 3.3 and the surface layer of the entire surface of the substrate will have a high refractive index. The heating temperature for thermally diffusing Ti into LiNbO3 is, for example, about 1050°C.

As described above, in this embodiment, since the mixed gas of oxygen and water is used to adjust the atmosphere inside the heating furnace 18, the ionized gas supplied from the ionized gas supply device 8 to the inside of the heating furnace 18 is an ionized gas. Oxygen is suitable.

In the manufacturing process of optical waveguide devices, the thermal diffusion process is one of the processes in which the heating temperature of the substrate is the highest. Therefore, applying the present invention to this process will prevent the heating of the substrate etc. caused by the pyroelectric effect. Extremely effective in preventing damage and consequences from occurring.

By the way, in the manufacturing process of a waveguide type optical device, a photoresist is applied to the surface of a substrate made of ferroelectric crystal, and prebaking or exposure is performed to improve the adhesion of the photoresist before exposure. Post-baking may be performed to improve the adhesion of the subsequent photoresist. During pre-baking or post-baking, it is necessary to heat the substrate to about 100° C., so the present invention can be applied to such cases as well. In this case, an ionized gas that does not alter the quality of the resist, such as an ionized inert gas, is selected.

[0022]

[Effects of the Invention] As explained above, according to the present invention,
In a method for manufacturing an optical waveguide device equipped with a substrate made of ferroelectric crystal, it is possible to prevent damage or defects to the substrate etc. due to electric discharge without requiring a long time for heating and cooling the substrate. This has the effect of making it possible to

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining a case where the method of the present invention is applied to a film deposition process as a first embodiment of the present invention.

FIG. 2 is a diagram for explaining a case where the method of the present invention is applied to a thermal diffusion process of a substrate as a second embodiment of the present invention.

FIG. 3 is an explanatory diagram of problems in the prior art.

[Explanation of symbols]

2 Board 8,26 Ionized gas supply device

Claims (3)

[Claims] 1. A method for manufacturing an optical waveguide device including the step of applying a temperature change to a substrate (2) made of a ferroelectric crystal, wherein at least when the temperature of the substrate (2) changes, the temperature of the substrate (2) changes. A method for manufacturing an optical waveguide device characterized by supplying ionized gas to the surrounding area. 2. The step of applying a temperature change to the substrate (2) is a heating and cooling step in a film deposition step for the substrate (2), and the gas is an inert gas. 1. A method for manufacturing an optical waveguide device according to 1. 3. The method according to claim 1, wherein the step of applying a temperature change to the substrate (2) is a heating and cooling step in a thermal diffusion step for the substrate (2), and the gas is oxygen. A method of manufacturing the optical waveguide device described above.