JP2000352636A - Production of optical waveguide element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately align the positioning pattern in the substrate side and the positioning pattern in the mask side by forming the positioning pattern in the substrate side by a dry etching method. SOLUTION: After a lithium niobate substrate 1 is cleaned, a photoresist is applied on the substrate 1. Then a mask for the optical waveguide pattern is used to form the optical waveguide pattern in the resist on the substrate 1 while cruciform positioning patterns 2B in the substrate side are formed at four positions. Then the optical waveguide pattern except the positioning patterns 2B in the substrate side is covered with a mask 6 to prevent dry etching of the optical waveguide pattern and to only dry etch the positioning patterns 2B in the substrate side by, for example, an ion milling device. As for the mask 6, for example, a metal material such as aluminum, stainless steel and titanium is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing an optical waveguide device used for an optical modulator or the like.

[0002]

2. Description of the Related Art An optical waveguide element used for an optical modulator or the like is formed, for example, by forming an optical waveguide pattern of a Ti (titanium) thin film on a LiNbO ₃ (lithium niobate) substrate and then performing a thermal diffusion process to perform light diffusion. A waveguide is formed, and a pair of electrode thin films are formed near the optical waveguide so as to sandwich the optical waveguide. The substrate material is displaced by the piezoelectric effect due to an electric field applied between the electrodes, and is refracted. A rate change is caused, thereby modulating the light passing through the optical waveguide. Such an optical waveguide formed by the Ti diffusion method is completed after a photolithography step, a film formation step, and a thermal diffusion step, and after a processing step and an assembly step.

With reference to FIGS. 13 and 14, a process of manufacturing an optical waveguide by the Ti diffusion method will be briefly described. First, a resist pattern of an optical waveguide made of a photoresist 2 is formed on the upper surface of the substrate 1 (FIG. 13A), and a Ti film is formed thereon (FIG. 13B). Thereafter, the resist 2 is lifted off to remove the unnecessary Ti film on the substrate 1 (FIG. 13C).
Is heated at a predetermined temperature for several hours to diffuse Ti into the substrate 1 to form the optical waveguide 4 (FIG. 14A). Electrode thin film 5
Are arranged in the vicinity of the optical waveguide 4 and are formed as a pair with the optical waveguide 4 interposed therebetween (FIG. 14B).

Generally, the pattern width of an optical waveguide is usually several μm.
m (depending on the wavelength used, multi-mode or single mode, etc.), and the gap between the electrodes varies depending on the specification, but is about 10 μm. Also, the modulation index mp
Is expressed by the following equation: mp = ζ · k · l · n · r · Vm / g. Here, ζ is the modulation efficiency, k is the wave number of the laser beam, l is the electrode length, n is the refractive index, r is the electro-optic constant, Vm is the modulation voltage, and g is the gap between the electrodes. The modulation index is an important index when the optical waveguide is used as a device. If the modulation efficiency ζ changes for some reason, the modulation index mp changes according to the above equation.

[0005] The alignment between the optical waveguide pattern and the electrode pattern is performed by positioning an alignment pattern (substrate-side alignment pattern) composed of a Ti diffusion path formed on the substrate at the same time as the formation of the optical waveguide pattern, and an electrode pattern mask. Alignment with the alignment pattern (mask-side alignment pattern)
That is, it is performed by overlapping and aligning.

[0006]

However, the conventional substrate-side alignment pattern is a Ti pattern formed by thermal diffusion similarly to the optical waveguide. Therefore, as shown in FIG. 1 to about 30
The shape is raised and the corners are rounded. Therefore, when observed with an optical microscope, the edge (the boundary between the pattern portion and the other portion) appears blurred as shown in FIG. As a result, it is very difficult to accurately align the substrate-side alignment pattern and the mask-side alignment pattern.

Therefore, as shown in FIG. 17A, it is difficult to accurately arrange a pattern of the optical waveguide 4 of about 6 μm to about 7 μm between the electrodes 5 of about 10 μm, for example, and as shown in FIG. Occurs,
Problems such as a propagation loss of the waveguide light propagating through the optical waveguide 4 due to the electrode 5 and a variation in modulation index due to a change in modulation efficiency occur, which adversely affects device performance.

The present invention has been made in view of the above problems, and has as its object to provide a method of manufacturing an optical waveguide device capable of accurately aligning a substrate-side alignment pattern and a mask-side alignment pattern.

[0009]

In order to solve the above-mentioned problems, the present invention provides a method of forming a substrate-side alignment pattern formed on a substrate by a dry etching method capable of obtaining etching anisotropy. The edge of the alignment pattern is clearly shown, thereby making it possible to accurately and easily perform the alignment (overlay) with the mask-side alignment pattern.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

In this embodiment, an X-cut lithium niobate substrate is used, and a Y-branch type optical waveguide modulator as shown in FIG. 11 is formed by a Ti thermal diffusion method as shown in FIG. A description will be given in accordance with a manufacturing process.

First, after cleaning the lithium niobate substrate, a photoresist is coated on the substrate. Thereafter, as shown in FIG. 2, an optical waveguide pattern 2A made of a resist is formed on the substrate 1 using the optical waveguide pattern mask,
Four cross-shaped substrate-side alignment patterns 2B are formed (step S1). Next, the optical waveguide pattern 2
In order to prevent A from being dry etched, as shown in FIG.
And only the substrate-side alignment pattern 2B is dry-etched by, for example, an ion milling device (step S2). FIG. 8 shows the substrate-side alignment pattern 21B after performing dry etching for several minutes. The mask 6 is made of a metal material such as aluminum, stainless steel, and titanium.

FIGS. 4 and 5 show an embodiment in which a plurality of substrates 1 are simultaneously processed. Etching jig 7 for four substrates 1
Arranged on the upper rubber sheet 8, a mask 9 having an opening 9 a in a portion corresponding to the alignment pattern 2 B on each substrate 1 is fixed to the etching jig 7 via a plurality of screws 10 while also serving as a substrate presser. I do. Then, the etching jig 7 is disposed inside the ion milling device 11 shown in FIG. 6, and the substrate-side alignment pattern 2B is dry-etched by the ion beam 13 irradiated from the ion source 12. An example of the etching conditions at this time will be described below. Ion current 600 mA Ion acceleration voltage 700 V Beam incident angle with respect to the normal direction of the substrate surface 0 degree Etching time 3 minutes 30 seconds Introduced gas Argon (Ar) 2 × 10 ^-4 Torr

Next, a Ti film having a thickness of several tens nm is formed by an electron beam evaporation method or the like (step S3). At this time, the substrate-side alignment pattern 21B formed in step S2 is covered with the masks 14 as shown in FIG. 9, so that a Ti film is not formed on the alignment pattern 21B.

Subsequently, while the substrate 1 on which the Ti film is formed is immersed in acetone, the substrate is subjected to ultrasonic cleaning and lift-off is performed to remove unnecessary Ti adhering to portions other than the optical waveguide pattern 2A.
The film and the resist 2 are peeled and removed (Step S
4). Next, the substrate 1 is heated at about 1000 ° C. for several hours to diffuse Ti into the substrate 1 (Step S5). T
The portion where i is diffused is ~ x from the refractive index of lithium niobate
Since the ^{height is} about 10 ⁻² , this portion becomes the optical waveguide 4 that confine the light.

Next, the electrode thin film 5 (see FIG. 14) is patterned (step S6). The patterning of the electrode thin film 5 is performed in the same manner as the patterning of the optical waveguide.
Using the electrode pattern mask 15 as shown in FIG.
An electrode pattern is formed. In the case of the X-cut lithium niobate substrate, since the electrode pattern and the waveguide pattern are arranged as shown in FIG. 17A, their alignment is important.

That is, the conventional thermal diffusion pattern (FIG. 16)
Since the pattern edge is not sharp in the substrate-side alignment pattern, the edge of the alignment pattern is blurred when observed with a microscope. Therefore, it is very difficult to accurately align the substrate-side alignment pattern and the mask-side alignment pattern 15A similarly formed in a cross shape.

On the other hand, according to the present embodiment, FIG.
As shown in FIG. 7, the edge of the alignment pattern 21B formed by the dry etching method is formed in a direction perpendicular to the surface of the substrate 1 as shown in FIG. 16 makes it possible to observe the image more sharply than the conventional alignment pattern shown in FIG.
The alignment with 5A becomes accurate and easy, and the alignment accuracy is improved. In addition, since the alignment accuracy is improved, variations in the modulation efficiency of the elements are reduced.

Also, since the alignment accuracy is improved, the optical waveguide 4 and the electrode thin film 5 due to misalignment can be improved.
The waveguide light does not suffer from propagation loss due to interference with the electrodes. As a result, in the case of the Y-branch type waveguide device as in the present embodiment, a defect due to insufficient output light quantity on the electrode 5 side and an imbalance failure between the output light quantity on the electrode 5 side and the output light quantity on the non-electrode side are reduced. it can.

By aligning the cross-shaped intersections of the alignment patterns 21B and 15A at four positions on the substrate, the alignment between the substrate-side alignment pattern 21B and the mask-side alignment pattern 15A is completed.
The electrode thin film 5 is formed on the substrate 1 through the opening 15a of the electrode pattern mask 15 by an electron beam evaporation method or the like (Step S7). In the present embodiment, an Au film with a Ti film as a base is used as the electrode thin film 5. Then, Ti
The unnecessary electrode film other than the electrode pattern is peeled off in the same manner as the lift-off (Step S8).

Subsequently, a protective film such as silicon dioxide is formed by vapor deposition or the like to protect the electrode thin film 5 and the like (step S).
9), patterning of the window for extracting the electrode is performed in the same manner as the patterning of the optical waveguide (step S10).
Then, a protective film window is formed by chemical etching (step S11). Then, the substrate 1 in a wafer state
Is cut off, and the end face is polished to a mirror surface in order to couple the light to the optical waveguide 4, thereby producing the optical waveguide element 16 as shown in FIG. 11 (Step S12). Optical waveguide device 1
Finally, the electrode film 6 is bonded and fixed to the base, housed in a housing (holder) (not shown), and the electrode thin film 5 and the external electrode are wire-bonded through the window of the protective film (S13).

Although the embodiment of the present invention has been described above, the present invention is, of course, not limited to this, and various modifications can be made based on the technical idea of the present invention.

For example, in the above embodiment, the optical waveguide device 16 is described by taking as an example a light modulation device based on the electro-optic effect using LiNbO ₃ as a substrate. However, the present invention is not limited to this. For example, the substrate may be LiTaO ₃ or the like. The present invention is also applicable to a light polarizing element using an acousto-optic effect using another piezoelectric material or using LiNbO ₃ as a substrate.

In the above embodiment, the substrate-side alignment pattern 21B and the mask-side alignment pattern 15A are both formed in the same shape.
As shown in the figure, the mask-side alignment pattern 15A may be formed in a cross shape formed at substantially the same interval as the line width of the substrate-side alignment pattern 21B. The substrate 1 and the electrode pattern mask 15 may be aligned by housing the substrate-side alignment pattern 21B. Note that these alignment patterns do not necessarily have to be formed in a cross shape, but may be formed in other shapes.

Further, in the above embodiment, the ion milling apparatus is used to form the substrate-side alignment pattern 21B. However, instead of this, the RIE (Reacti
Other dry etching methods, such as a (veIon Etching) method, can also be used.

[0026]

As described above, according to the manufacturing method of the optical waveguide device of the present invention, since the substrate-side alignment pattern is formed by the dry etching method, the edge of the alignment pattern is clearly defined by the etching anisotropy. Observation is possible, and this makes alignment with the mask side alignment pattern accurate and easy, and
The alignment accuracy is also improved. In addition, since the alignment accuracy is improved, variations in the modulation efficiency of the elements are reduced.

According to claims 2 and 3,
The effect of the formation of the substrate-side alignment pattern on the optical waveguide and the influence of the formation of the optical waveguide on the substrate-side alignment pattern can be avoided. Contributes to accurate alignment work with alignment patterns.

[Brief description of the drawings]

FIG. 1 is a flowchart of a method for manufacturing an optical waveguide device according to an embodiment of the present invention.

FIG. 2 is a plan view showing a relationship between an optical waveguide pattern formed on a substrate and an alignment pattern.

FIG. 3 is a plan view illustrating an aspect when dry etching a positioning pattern on a substrate.

FIG. 4 is a plan view illustrating a relationship between a substrate and a mask when a plurality of substrates are simultaneously processed.

FIG. 5 is an exploded perspective view of FIG.

FIG. 6 is a schematic configuration diagram of a dry etching apparatus containing a substrate.

FIG. 7 is a diagram illustrating a cross-sectional shape of an alignment pattern according to the present embodiment.

FIG. 8 is a photograph of an alignment pattern on a substrate in the present embodiment.

FIG. 9 is a plan view illustrating an embodiment when a metal film is formed on the optical waveguide pattern.

FIG. 10 is a plan view illustrating an aspect when patterning an electrode pattern.

FIG. 11 is a plan view of the manufactured optical waveguide element.

FIG. 12 is a diagram illustrating another mode of the alignment pattern formed on the substrate and the electrode pattern mask.

FIG. 13 is a schematic view showing a manufacturing process of the optical waveguide device, wherein A shows a resist pattern of the optical waveguide, B shows a film forming process, and C shows an optical waveguide pattern after lift-off.

14A and 14B are schematic diagrams illustrating a process of manufacturing an optical waveguide element, wherein A illustrates a process of thermally diffusing a formed metal film into a substrate, and B illustrates a process of forming an electrode film.

FIG. 15 is a diagram showing a cross-sectional shape of a conventional alignment pattern on a substrate by thermal diffusion.

FIG. 16 is a photograph of an alignment pattern on a substrate in the related art.

FIG. 17 is a schematic diagram showing a positional relationship between an optical waveguide and electrodes on a substrate, wherein A shows a state where the electrodes are arranged at regular positions with respect to the optical waveguide, and B shows a state where the electrodes are arranged at regular positions. Indicates a state in which they are not arranged.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Photoresist, 2A ... Optical waveguide pattern, 21B ... Substrate side alignment pattern, 4 ... Optical waveguide, 5 ... Electrode thin film, 6, 9, 14 ... Mask, 15 ... Electrode pattern mask, 15A ... Mask Side alignment pattern.

Claims (4)

[Claims] 1. A method of manufacturing an optical waveguide device having a pair of electrode thin films which is arranged near a light waveguide after a pattern of the optical waveguide is formed on a substrate and sandwiches the optical waveguide device. The alignment of the pattern of the optical waveguide and the pattern of the electrode thin film is performed by comparing a substrate-side alignment pattern formed on the substrate and a mask-side alignment pattern formed on the pattern mask of the electrode thin film. A method for manufacturing an optical waveguide element, wherein the method is performed by overlapping, wherein the substrate-side alignment pattern is formed by a dry etching method. 2. The method according to claim 1, wherein the pattern of the optical waveguide is masked when the substrate-side alignment pattern is formed by a dry etching method. 3. The optical waveguide is formed by thermally diffusing a metal film formed along the pattern of the optical waveguide element. When forming the metal film, the substrate-side alignment pattern is masked. The method of manufacturing an optical waveguide device according to claim 1, wherein: 4. The method of manufacturing an optical waveguide device according to claim 1, wherein both the substrate-side alignment pattern and the mask-side alignment pattern have a cross shape.