JP3554178B2 - Manufacturing method of optical waveguide device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing an optical waveguide device, and more particularly, to a method for manufacturing an optical waveguide device in which an optical waveguide is formed on a substrate by thermal diffusion of metal.
[0002]
[Prior art]
In general, an optical waveguide has a function of confining radiation in a certain region and guiding and propagating the energy flow parallel to the axis of the path. Therefore, at present, the size of an optical component is reduced by changing a light waveguide represented by an optical fiber cable to an optical waveguide.
[0003]
As the optical waveguide, for example, a GaAs-based or InP-based semiconductor waveguide, an oxide film formed on Si, a dielectric (glass) waveguide using a glass substrate, or a ferroelectric formed of LiNbO ₃ or LiTaO ₃ crystal There is a body crystal waveguide.
[0004]
In particular, as an optical element, such as an optical waveguide type modulator, capable of carrying information on a light beam transmitted through an optical waveguide through an electrode, a Ti diffusion in which Ti is diffused into a LiNbO ₃ crystal substrate having excellent electro-optical characteristics. A type LiNbO ₃ waveguide is used.
[0005]
The Ti-diffused LiNbO ₃ waveguide is formed by depositing Ti on a LiNbO ₃ crystal substrate to form a Ti film having a thickness of several hundreds of mm, and thermally diffusing at a temperature of about 1000 ° C. for 4 to 10 hours to locally refract. The optical waveguide is manufactured by increasing the ratio. At this time, the amount of Ti to be thermally diffused is adjusted by the thickness of the Ti film formed by vapor deposition.
[0006]
However, when the Ti film is manufactured by a film forming apparatus such as a vacuum evaporation apparatus, the characteristics of the waveguide after thermal diffusion may vary even though the thickness of the Ti film is adjusted to be the same.
[0007]
[Problems to be solved by the invention]
The present invention has been made in view of such problems, and in a method of manufacturing an optical waveguide element in which an optical waveguide is formed by metal thermal diffusion of a metal film on a substrate, variations in waveguide loss are small, and It is an object of the present invention to provide an improved method for manufacturing an optical waveguide device having a low level of loss.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, a method for manufacturing an optical waveguide device according to the present invention is a method for manufacturing an optical waveguide device, wherein the optical waveguide is formed by thermal diffusion of metal of a metal film deposited on a substrate. The quality of the metal film is determined by measuring the degree of oxidation of the metal film deposited thereon, and the non-defective product is transferred to a thermal diffusion process.
[0009]
The present inventors have conducted various studies on the causes of variations in the waveguide characteristics when the thickness of the metal film is adjusted to the same value. As a result, the present inventors have found that contamination due to contamination of a chamber of a film forming apparatus such as a vacuum evaporation apparatus and a degree of vacuum. It has been found that variations in the degree of oxidation of the metal film occur due to variations in the water vapor partial pressure, etc., which cause variations in the waveguide characteristics.
[0010]
Therefore, the degree of oxidation of the metal film is measured, and substantially only the non-defective metal film having the degree of oxidation within a predetermined range is processed in the heat diffusion step, so that the variation in the loss of the waveguide is small, and Thus, a good optical waveguide element having a low loss level can be obtained. Here, the predetermined degree of oxidation can be appropriately set according to the individual required quality level of the optical waveguide and the like.
[0011]
At this time, the sheet resistance is used as an evaluation index of the degree of oxidation of the metal film, and the sheet resistance of the metal film within the range of 20 to 45 Ω / □ is regarded as a non-defective product and is transferred to the heat diffusion step, whereby the metal film is The degree of oxidation can be easily and appropriately grasped, and the effects of the present invention described above can be suitably exerted.
[0012]
In the method of manufacturing an optical waveguide device according to the present invention, the effect of the present invention described above is more suitably exhibited by forming an optical waveguide by thermal diffusion using a LiNbO ₃ substrate as a substrate and using Ti as a metal. be able to.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a method for manufacturing an optical waveguide device according to the present invention will be described with reference to FIGS.
[0014]
The optical waveguide device 10 manufactured by the manufacturing method according to the present embodiment shown in FIG. 1 has an optical waveguide 14 of a predetermined shape formed on a LiNbO ₃ substrate 12, and a polarizer 16 on the optical waveguide 14, and A phase modulator 18 is provided.
[0015]
The size of the LiNbO ₃ substrate 12 of the manufactured optical waveguide element 10 is such that the width (Z direction in FIG. 1) is about 3 mm, the length in the optical waveguide 14 direction (Y direction in FIG. 1) is about 30 mm, and the polarization is The size of the element 16 is approximately 1 mm at a portion corresponding to the length direction of the optical waveguide 14 (Y direction in FIG. 1), and approximately 2 mm at a portion corresponding to the width direction of the optical waveguide 14 (Z direction in FIG. 1). It is.
[0016]
As shown in FIG. 2, in the optical waveguide device 10, an optical waveguide 14 is formed on a LiNbO ₃ substrate 12 by thermal diffusion of Ti, and an Al ₂ O ₃ film 20 and an Al film 22 are formed on the optical waveguide 14. A polarizer 16 to be formed is provided.
[0017]
In this case, the thickness of the LiNbO ₃ substrate 12 is about 1 mm, and the width and the depth of the optical waveguide 14 are both several μm. The thickness of each film of the polarizer 16 laminated on the optical waveguide 14 is 500 ° for the Al ₂ O ₃ film 20 and 3000 ° for the Al film 22.
[0018]
A method for manufacturing the optical waveguide device 10 according to the present embodiment will be described below.
[0019]
As shown in FIG. 3, first, a LiNbO ₃ substrate 12 is prepared and washed (FIG. 3A). Next, a photoresist is applied on the LiNbO ₃ substrate 12 to form a photoresist film 13 (FIG. 3B). Thereafter, the photoresist film 13 is exposed and developed to provide an opening 15 for forming the optical waveguide 14 (FIG. 3C). Thereafter, a Ti film 17 having a thickness of 400 ° is formed on the entire surface of the photoresist film 13 including the opening 15 (FIG. 3D). The Ti film is formed by vapor deposition at a normal temperature of 2.0 × 10 ⁻⁴ Pa using a vapor deposition apparatus. Next, the photoresist film 13 on the LiNbO ₃ substrate 12 is lifted off to remove the Ti film 17 formed on the photoresist film 13 together with the photoresist film 13 (FIG. 3E). Next, the sheet resistance Rs of the Ti film 17 is measured by a method described later, and when the sheet resistance Rs is in the range of 20 to 45 Ω / □, it is determined that the Ti film 17 is good, and then LiNbO ₃ The substrate 12 is placed in a thermal diffusion furnace, and Ti is thermally diffused at a temperature of about 1000 ° C. for 4 to 10 hours to perform a heat treatment. By this heat treatment, the Ti film 17 is oxidized and diffused into the LiNbO ₃ substrate 12 to form the optical waveguide 14 by Ti diffusion (FIG. 3F). Further, the optical waveguide device 10 shown in FIG. 1 is completed by providing the polarizer 16 and the phase modulator 18 by a conventional method. If the sheet resistance Rs of the Ti film 17 formed by vapor deposition is out of the range of 20 to 45 Ω / □, the Ti film 17 is determined to be defective, and is removed from the subsequent manufacturing steps.
[0020]
Here, the measurement of the sheet resistance Rs of the Ti film 17 is performed by a method using a four probe method as shown in the conceptual diagram of FIG.
[0021]
That is, current i (A) is applied by pressing four probes 28 provided at equal intervals S (cm) on Ti film 17 formed on LiNbO ₃ substrate 12, and voltage e (V) is measured. Thus, the sheet resistance Rs is obtained using the following equation.
[0022]
First, the resistivity ρ (Ω / cm) of the Ti film 17 is
ρ = (e · π · t · F) / (i · ln2)
It is represented by Here, π is the pi, t is the thickness (unit: cm) of the Ti film 17, and F is based on the assumption that the Ti film 17 is extended infinitely in comparison with the interval S between the probes 28. This equation is a correction coefficient when the condition is not satisfied (when the distance between the end of the Ti film 17 and the probe 28 is 10 times or less of the distance S between the probes 28). In the present embodiment, the thickness of the Ti film 17 is 400 °, and the spacing S between the probes 28 of the four probe device used is 0.1 cm, so that the correction coefficient F is set to 1. At this time, the sheet resistance Rs is
Rs = ρ / t
And from the above formula,
Rs = ρ / t = (π / ln2) · (e / i)
The sheet resistance Rs (Ω / □) is obtained by measuring the current i and the voltage e.
[0023]
When measuring the sheet resistance Rs in the manufacturing process, a method of putting a dummy wafer for measuring the sheet resistance Rs into each deposition batch, a method of providing an area for measuring the sheet resistance Rs on a product wafer, or the like is used.
[0024]
FIG. 5 shows the relationship between the sheet resistance Rs and the loss of the waveguide. Here, as conditions for manufacturing the optical waveguide of the optical waveguide element 10 for measuring the sheet resistance Rs, the thickness of the Ti film 17 is set at two levels of 400 ° and 450 °, and the oxygen partial pressure during the deposition of the Ti film 17 is variously changed. The Ti films 17 having various degrees of oxidation were obtained, and the sheet resistance Rs and the loss of the waveguide were measured for each.
[0025]
As is clear from FIG. 5, by setting the sheet resistance Rs within the range of 20 to 45, the value of the loss of the waveguide is reduced, and the variation thereof is set within the narrow range of 4.1 to 4.5. On the other hand, when the sheet resistance Rs is less than 20 or more than 45, the loss of the waveguide increases in any case, and a large variation occurs up to 7.5, which is preferable. I understand that there is no. Here, within the range of a suitable (non-defective) Ti film 17, the relationship between the sheet resistance Rs and the loss of the waveguide tends to be substantially the same, despite the fact that the thickness of the Ti film 17 is different from 400 ° and 450 °. From the above, it can be seen that the method of measuring the sheet resistance Rs is more effective than the usual method of strictly adjusting the thickness of the Ti film 17 as a means for managing the waveguide characteristics. In addition, in the method of using the ordinary resistance R as an index of the degree of oxidation instead of the sheet resistance Rs, it is necessary to form a pattern for measuring the resistance R on a wafer, and the dimensional accuracy of the pattern is directly changed. The sheet resistance Rs measurement method is more useful than this method because it affects the accuracy of the resistance R measurement.
[0026]
As a method for measuring the sheet resistance Rs, a method utilizing an eddy current generated in the Ti film 17 by an external magnetic field or the like can be used.
[0027]
FIG. 6 shows the sheet resistance Rs of the Ti film 17 of the optical waveguide device 10 according to the present embodiment and the concentration of oxygen contained in the Ti film 17 measured by SIMS (secondary ion mass spectrometry) (oxygen atoms on an arbitrary scale). (Peak intensity). There is a high degree of correlation between the sheet resistance Rs and the oxygen concentration, and it has been verified that the sheet resistance Rs is useful as an index of the oxygen concentration (oxidation degree). Further, as shown in FIGS. 5 and 6, it was also found that there was a correlation between the loss of the waveguide and the degree of oxidation of the Ti film 17.
[0028]
【The invention's effect】
As described above, according to the method for manufacturing an optical waveguide device according to the present invention, the method for manufacturing an optical waveguide device in which an optical waveguide is formed by thermal diffusion of metal of a metal film deposited on a substrate includes: The quality of the metal film is determined by measuring the degree of oxidation of the metal film deposited on the substrate, and the non-defective product is transferred to a thermal diffusion process.
[0029]
Therefore, the degree of oxidation of the metal film is measured, and substantially only the non-defective metal film having the degree of oxidation within the predetermined range is processed in the heat diffusion step, so that the optical waveguide element with less variation in the waveguide characteristics. Can be achieved.
[0030]
At this time, sheet resistance is used as an evaluation index of the degree of oxidation of the metal film, and a metal film having a sheet resistance in the range of 20 to 45 Ω / □ is regarded as a non-defective product and transferred to the heat diffusion step. In addition, the degree of oxidation of the metal film can be suitably and easily measured.
[0031]
Further, in the method of forming an optical waveguide by diffusion of Ti on a LiNbO ₃ substrate, the effect of the present invention can be more suitably exerted.
[Brief description of the drawings]
FIG. 1 is a plan view of an optical waveguide device manufactured by a manufacturing method according to an embodiment.
FIG. 2 is a sectional view taken along line II-II of the optical waveguide device of FIG.
FIG. 3 is a view for explaining a step of manufacturing the optical waveguide device of FIG. 1;
FIG. 3A shows a step of cleaning the LiNbO ₃ substrate,
FIG. 3B shows a step of forming a photoresist film on a LiNbO ₃ substrate,
FIG. 3C shows a step of exposing and developing the photoresist film to form an opening;
FIG. 3D shows a step of forming a Ti film on the photoresist film,
FIG. 3E shows a step of measuring the sheet resistance of the Ti film by lifting off the photoresist film, leaving only the Ti film for the optical waveguide,
FIG. 3F is a diagram showing a step of forming an optical waveguide on a LiNbO ₃ substrate by thermal diffusion.
FIG. 4 is a conceptual diagram for explaining a measurement principle when a four-probe method is used as a sheet resistance measuring method.
FIG. 5 is a diagram showing the relationship between the sheet resistance of the Ti film of the optical waveguide element according to the present embodiment and the loss of the waveguide.
FIG. 6 is a diagram showing the relationship between the sheet resistance of the Ti film and the concentration of oxygen contained in the Ti film of the optical waveguide device according to the present embodiment.
[Explanation of symbols]
10 ... optical waveguide device 12 ... LiNbO ₃ substrate 14 ... optical waveguide 16 ... polarizer 17 ... Ti film (metal film) 18 ... phase modulator 20 ... _Al 2 _{O 3} film 22 ... Al film 28 ... probe

Claims (3)

In a method for manufacturing an optical waveguide device, wherein an optical waveguide is formed by thermal diffusion of metal of a metal film deposited on a substrate, the degree of oxidation of the metal film deposited on the substrate is measured to determine the quality of the metal film. And transferring the non-defective product to a heat diffusion process. 2. The manufacturing method according to claim 1, wherein sheet resistance is used as an evaluation index of the degree of oxidation of the metal film, and a sheet having a sheet resistance in the range of 20 to 45 Ω / □ is transferred to the heat diffusion step as a non-defective product. A method for manufacturing an optical waveguide device, comprising: _{3. The} method according to claim 1, wherein an optical waveguide is formed on the LiNbO3 substrate by diffusion of Ti.

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