JPH0727941A - Production of waveguide - Google Patents

Abstract

PURPOSE:To provide a process for production to obtain a waveguide which is good in light confinement by increasing the refractive index of only the part to be formed as the waveguide. CONSTITUTION:After a Ti film 2 is formed on the surface of an LiNbO3 substrate 1, the Ti film 2 is etched or diced with a patterned photoresist 3a as a mask and the LiNbO3 surface is etched or diced with the formed Ti pattern 2a as a mask to build in a ridge structure. Further, the Ti pattern 2a left as a mask is thermally diffused to produce the Ti-diffused LiNbO3 waveguide having the waveguide part 1a of the ridge structure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical component in the field of communication information processing, and more particularly to a ridge type high speed optical modulator having a ridge-structured waveguide having a high refractive index on the surface of a substrate made of a dielectric optical material. The present invention relates to an applicable waveguide manufacturing method.

[0002]

2. Description of the Related Art Conventionally, guided light control by electro-optic effect has been applied to an optical modulator using a ferroelectric crystal typified by LiNbO ₃ .

[0003] For example, in the fall of 1991, Proceedings of the Japan Society of Applied Physics (10a-ZN-1) and the like have a ridge structure in which LiNbO ₃ is used as a substrate and Ti formed on the substrate surface (by thermal diffusion) is added. Optical modulator (Ti
A diffused LiNbO ₃ waveguide) is shown.

In particular, the Ti diffusion L shown in this prior art
The manufacturing method of the iNbO ₃ waveguide is as follows. First, the surface of the LiNbO ₃ substrate is dry-etched to form a ridge structure portion to be a waveguide portion, and then a Ti film to be diffused only on the upper surface of the ridge structure portion is selectively formed. It was manufactured by diffusing Ti (increasing the refractive index) in the waveguide portion of the ridge structure by thermally diffusing it at a predetermined temperature for a predetermined time (for example, at 1050 ° C. for about 5 hours).

[0005]

SUMMARY OF THE INVENTION Conventional waveguides, especially T
The manufacturing method of the i-diffused LiNbO ₃ waveguide is as described above.
Ti which is partially diffused on the upper surface of the ridge structure formed in advance as a waveguide on the LiNbO ₃ surface so as to cause a refractive index change different from that of other substrate regions.
Since the film was formed selectively, if the Ti film was not actually formed with sufficient accuracy, or due to uncertain factors such as the vibration of the substrate, the Ti film was not formed even on unnecessary parts. It may be filmed, so that only T
There was a problem that it was difficult to diffuse i.

The present invention has been made in order to solve the above problems, and makes it possible to diffuse Ti only in the ridge structure portion, and Ti diffusion LiN having good light confinement.
It is an object of the present invention to provide a manufacturing method for obtaining a bO ₃ waveguide.

[0007]

In the method of manufacturing a waveguide according to the present invention, in the first step, after forming a transition metal film on the surface of a substrate made of a dielectric optical material, a patterned photoresist is used. This transition metal film is etched or diced into a waveguide shape as a mask, and in the second step, the surface of the dielectric optical material is etched or diced using the patterned transition metal film as a mask to form a ridge on the surface. A ridge-structured waveguide is manufactured by forming a structure portion (a portion serving as a high-refractive-index waveguide portion) and further thermally diffusing the transition metal film left as a mask in the third step. I am trying.

LiNbO is used as the dielectric optical material.
_Although there are electro-optic crystals such as ₃ , LiTaO _3, etc., they show a large electro-optic effect, have a relatively large figure of merit and electromechanical coupling coefficient as an acousto-optic material, and can easily form a low-loss thin-film waveguide. By being able to do it, LiNbO ₃
Single crystals have been widely used as substrate materials for waveguide functional devices (eg optical modulators).

Further, as transition metals to be diffused in the dielectric optical material which finally becomes the substrate, Ti, V, Ni and C are used.
There are u etc., but from the already reported experimental examples,
The waveguide with Ti diffused shows the best propagation characteristics,
Further, no remarkable decrease in crystallinity or reduction in electro-optical effect due to Ti diffusion has been reported.

In view of the above, the inventors of the present invention are able to diffuse Ti only in the ridge structure portion, and as a waveguide having good optical confinement, the production technique for obtaining a Ti-diffused LiNbO ₃ waveguide is particularly aimed. Specifically, LiNbO ₃ is used as the dielectric optical material, and a metal Ti film or a TiO ₂ film is used as the transition metal film.

[0011]

According to the method of manufacturing a waveguide of the present invention, a transition metal film is formed on the surface of a dielectric optical material to be a substrate, the transition metal film is preformed, and the ridge structure portion ( Since it is configured to be used as a mask for forming a high refractive index waveguide portion), no alignment is necessary.

Further, since the patterned transition metal film is used as a mask for forming the ridge structure on the surface of the dielectric optical material, when the desired ridge structure is formed, the transition metal for diffusion is already formed. Is in the same state as that selectively deposited on the upper surface of the ridge structure.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. In the figure, the same parts are designated by the same reference numerals and the description thereof will be omitted.

FIGS. 1 to 3 are process diagrams for explaining the method of manufacturing a waveguide according to the present invention, which will be described below in three steps.

First, the first step will be described with reference to FIG. In this first step, as shown in FIG.
A Ti film 2 (or a TiO ₂ film) is deposited on the entire surface of the NbO ₃ substrate 1 by sputtering or electron beam evaporation to about 70
nm (By the way, the melting point of the metal Ti film is extremely high).

Then, as shown in FIG.
After a photoresist 3 is spin-coated on the film 2 by 1 to 2 μm, a waveguide mask pattern 4 is formed on the photoresist 3.
Is transferred by photolithography to pattern the photoresist 3 into a photoresist pattern 3a having a predetermined shape (waveguide shape) (FIG. 1C).

Then, this photoresist pattern 3a
The Ti film 2 deposited on the entire surface of the LiNbO ₃ substrate 1 with the mask as a mask is dry-etched (reactive ion etching: Reactive Ion) by a CF ₄ gas which is a reactive gas.
Etching, which will be referred to as RIE hereinafter), thereby forming a Ti film 2
Is patterned into a waveguide shape (hereinafter referred to as Ti pattern 2a) (FIG. 1D).

Next, the second step will be explained with reference to FIG.
Reveal In this second step, as shown in FIG.
Patterning into a waveguide shape in the above-mentioned first step
Photoresist pattern 3a and Ti pattern 2
LiNbO using a as a mask ₃The surface of the substrate 1 is
C which is₂F₆To CCl_FourTo the mixed gas with gas added
More dry etching (RIE), LiNbO₃substrate
A ridge structure portion 1a to be a waveguide portion 1b is formed on one surface.
It

Next, the third step will be described with reference to FIG. In the third step, as shown in FIG. 3A, first, the resist pattern 3 used as the mask in the second step is used.
a was removed by an O ₂ asher, followed by LiNbO ₃
As shown in FIG. 3B, the Ti pattern 2a (sample) existing on the upper surface of the ridge structure 1a formed on the surface of the substrate 1 is thermally diffused at 1050 ° C. for 5 hours. 1b is formed.

In this embodiment, for convenience of explanation, the ridge structure portion 1a and the waveguide portion 1b are distinguished from each other, but the difference between them is whether or not Ti, which is a transition metal, is diffused therein. Only. In addition, the Ti film 2 and LiN
The surface of the bO ₃ substrate 1 was patterned by dry etching, but the method is not particularly limited to this method, and the same effect can be obtained by patterning by dicing.

In the second step, the Ti pattern 2 is used.
Since a serves as a mask for etching the surface of the LiNbO ₃ substrate 1, naturally, it is accurately positioned on the upper surface of the ridge structure (see FIG. 3A) without alignment.

Ti-diffused LiN obtained through the above steps
An SEM photograph of the cross section of the bO ₃ waveguide is shown in FIG. Further, the inventors have confirmed that in the Ti-diffused LiNbO ₃ waveguide shown in FIG. 4, Ti is diffused only in the waveguide section 1b and the optical confinement is good.

That is, FIG. 5 shows a near-field image of the Ti-diffused LiNbO ₃ waveguide manufactured by the method of manufacturing a waveguide according to the present invention (FIG. 5A) and its light intensity distribution (FIG. 5B). (A schematic diagram of what is confirmed by a photograph), showing an enlarged near-field image when light having a wavelength of 820 nm is guided. From this figure, it can be confirmed that optical confinement is satisfactorily performed in the waveguide portion 1b in which Ti is diffused. The line AA ′ in FIG. 5A is a line showing the surface of the substrate 1.

[0024]

As described above, according to the present invention, the ridge structure is formed on the surface of the dielectric optical material using the previously formed transition metal film such as Ti as a mask, and the transition metal used as the mask is ridged. Since the sample is used as it is as a sample to be thermally diffused in the structure portion, there is an effect that the conventional alignment for selectively depositing a transition metal on the upper surface of the ridge structure portion is not required at all.

Further, since the patterned transition metal film is used as a mask for forming the ridge structure on the surface of the dielectric optical material, when the ridge structure is formed, the transition metal for diffusion is already formed. The same state as when the film is formed on the upper surface of the ridge structure portion can be realized, and therefore, Ti can be surely diffused only to the ridge structure portion on the surface of the dielectric optical material.

[Brief description of drawings]

FIG. 1 is a first view of a method of manufacturing a waveguide according to the present invention.
FIG. 6 is a process chart for explaining the process of FIG.

FIG. 2 is a second view of the method for manufacturing a waveguide according to the present invention.
FIG. 6 is a process chart for explaining the process of FIG.

FIG. 3 is a third view of the method for manufacturing a waveguide according to the present invention.
FIG. 6 is a process chart for explaining the process of FIG.

FIG. 4 is a Ti-diffused LiNbO ₃ waveguide manufactured by the method of manufacturing a waveguide according to the present invention, which is LiNbO.
₃ is an SEM photograph showing a fine pattern formed on a waveguide substrate.

FIG. 5 is a diagram showing a near-field image and its light intensity distribution of a Ti-diffused LiNbO ₃ waveguide manufactured by the method for manufacturing a waveguide according to the present invention.

[Description of Reference Signs] 1 ... LiNbO ₃ substrate, 1a ... Ridge structure part, 1b ... Waveguide part, 2a, Ti film (Ti pattern), 3a, 3a ...
Photoresist, 4 ... Waveguide mask pattern.

Claims (3)

[Claims] 1. A first step of forming a transition metal film on a surface of a substrate made of a dielectric optical material, and etching or dicing the transition metal film into a waveguide shape by using a patterned photoresist as a mask. A second step of forming a ridge structure portion serving as a waveguide portion on the surface of the dielectric optical material by etching or dicing the surface of the dielectric optical material using the patterned transition metal film as a mask; Forming a ridge-structured waveguide portion having a high refractive index on the surface of the dielectric optical material by thermally diffusing the transition metal film left as a mask on the upper surface of the ridge structure portion which becomes the waveguide portion. A method of manufacturing a waveguide, including the step of 3. 2. The method of manufacturing a waveguide according to claim 1, wherein the dielectric optical material is LiNbO ₃ . 3. The transition metal film is a Ti film or a Ti film.
_{3. The} method of manufacturing a waveguide according to claim 1, wherein the waveguide is an O ₂ film.