JPH062105A - Optical waveguide film and production of optical waveguide - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to form a core film for an optical waveguide having a high refractive index on a substrate having a low refractive index layer with a small warp, and to obtain the film thickness and the refractive index. The present invention provides a novel optical waveguide film and a method for manufacturing an optical waveguide, which is easy to control, and has a film with good transmittance that does not contain impurities. According to the present invention, a substrate is placed in an upper portion of a vacuum chamber and heated, and Si ₃ is placed in a lower portion of the substrate.
After arranging an evaporation source accommodating a N ₄ tablet, while introducing O ₂ gas into the vacuum chamber, the tablet is irradiated with an electron beam to evaporate the electron beam so that Si _x O _y N 4 is deposited on the substrate. _The feature is that an optical waveguide film of _z is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an optical waveguide core film having a high refractive index by an electron beam evaporation method.

[0002]

2. Description of the Related Art Conventionally, a method as shown in FIG. 6 has been known as a method for manufacturing a glass waveguide. In this method, a buffer layer and a core layer are sequentially deposited on a substrate by a flame deposition method, etc., and after sintering these layers, the above glass layer is patterned, and finally a cladding layer having a refractive index lower than that of the core layer is formed above. It is formed on the entire surface of the patterned glass layer. The material of this core layer is P ₂ O ₅ , GeO ₂ , TiO ₂ .
SiO ₂ is used comprising one selected additive from among ₂ of the refractive index control additives.

[0003]

DISCLOSURE OF THE INVENTION By the way, as a result of examining the above-mentioned conventional manufacturing method, the present inventor found that the following drawbacks were formed, and after forming a glass porous film, the temperature was 1300 ° C. or higher. Since it is a method of transparent vitrification by sintering at high temperature, the shrinkage rate of the glass porous film at the time of sintering varies depending on the addition amount of the refractive index control additive, and the thickness of the transparent vitrified film changes. However, it is not possible to control the glass film online.

In order to manufacture a glass waveguide having a large refractive index difference between the core and the clad, a core glass film having a high refractive index containing a refractive index control additive is formed on the buffer layer, and the entire substrate is Warpage occurs due to the difference in the coefficient of thermal expansion, and the amount of warpage becomes a large value far exceeding 10 μm, so it is difficult to pattern an optical circuit with high dimensional accuracy. In this respect, there is a limit to increase the difference in refractive index.

It has also been found that there is a limit to the difference in refractive index between the core and the clad. That is, even if a porous film for core having a high refractive index is deposited, the additive for controlling the refractive index is volatilized in the sintering process, and it is difficult to realize a core layer having a high refractive index, and the maximum refractive index is 1.47. Never exceeded. Therefore, the relative refractive index difference is limited to about 1%.

When the core layer containing a large amount of the refractive index controlling additive is patterned by a dry etching process, the etching side surface becomes rough due to the difference in etching rate between the SiO ₂ forming the core layer and the additive, and Increases the scattering loss.

[0007] Since the sintering process is performed twice, it takes a long time for manufacturing, and there is also a cost for utilities such as electricity, gas and water, so that it is difficult to reduce the cost.

At the time of sintering, the refractive index control additive diffuses in the glass film, has a refractive index distribution in the glass film thickness direction, and it is difficult to obtain a uniform refractive index in the glass film thickness direction.

Therefore, the present invention has been devised in order to effectively solve the above-mentioned problems, and its main purpose is to provide a substrate having a core film for an optical waveguide having a high refractive index and a low refractive index layer. Provided is a novel optical waveguide film and a method for manufacturing an optical waveguide, which can form a film with a small warp on the upper surface, can easily control the film thickness and the refractive index, and can form a film with good transmittance without fear of containing impurities. To do.

[0010]

According to a first aspect of the present invention, a substrate is placed in an upper portion of a vacuum chamber to heat the same, and Si ₃ N ₄ is placed in a lower portion of the substrate.
After arranging the evaporation source accommodating the tablet of the above, while introducing O ₂ gas into the vacuum chamber, the tablet is irradiated with an electron beam to evaporate the electron beam and the Si _x O _y N _z on the substrate. The second invention forms an optical waveguide film, and the second invention provides an evaporation source containing a Si ₃ N ₄ tablet and an evaporation source containing a tablet of a refractive index controlling oxide in a lower portion of the substrate. After arranging, while introducing O ₂ gas into the vacuum chamber, the tablets were irradiated with an electron beam to evaporate each of them and S containing at least one refractive index controlling oxide on the substrate.
The optical waveguide film of i _x O _y N _z is formed. Also,
In a third aspect of the present invention, the evaporation source disposed in the vacuum chamber contains a mixture of SiO ₂ and Si ₃ N ₄ powder in a desired weight ratio and solidifies into a tablet by hot pressing. While introducing O ₂ gas into the inside, the tablet is irradiated with an electron beam to evaporate the electron beam to form an optical waveguide film of Si _x O _y N _z on the substrate. The invention provides a substrate having a refractive index lower than that of the optical waveguide film formed by the above manufacturing method, or a low refractive index having a lower refractive index than that of the optical waveguide film obtained by the above method. It uses a substrate on which a layer is preformed.
The fifth invention is that the optical waveguide film obtained by any one of the above-mentioned manufacturing methods is processed into a substantially rectangular pattern by photolithography and dry etching, and then a refractive index lower than that is formed on the surface of the substantially rectangular pattern. To cover the cladding film with a high index.

[0011]

Since the present invention is the manufacturing method as described above,
According to the first invention, the refractive index (value at wavelength 0.63 μm)
It is possible to form a high-refractive-index film having a value of 1.465 to a value close to 2.0, and even if this film is formed on a SiO ₂ substrate, no large warpage occurs. Further, in the present invention, since the film is formed by the electron beam evaporation method as described above, the film can be formed while monitoring the film thickness, and the film thickness can be formed with good controllability. Furthermore, the refractive index can be easily controlled by adjusting the degree of vacuum during film formation, that is, the amount of O ₂ partial pressure. Further, since the film is formed in vacuum, it is possible to form a film with a small transmittance of impurities and a high transmittance.

Further, according to the second invention, a film having a refractive index higher than that of the film of the first invention can be formed, and the addition of the refractive index controlling oxide causes refraction. Besides adjusting the rate, it also serves to match the coefficient of thermal expansion between the film and the substrate.

Next, according to the third invention, Si _x O _y N
_z of x, y, z can be easily obtained optical waveguide film was set to a desired value, moreover, the melting point of SiO ₂ and Si ₃ N ₄ is 1500 ° C. and 1900 ° C., has a value relatively close Therefore, it is convenient for evaporating with an electron beam.

According to the fourth invention, the substrate is made of glass (quartz system, multi-component system), semiconductor (Si, GaAs,
InP, etc., ferroelectrics (LiNbO ₃ , LiTaO ₃₎
Etc.), magnetic materials, sapphire, etc. can be used, so that optical devices (amplification, oscillation, modulation, multiplexing, demultiplexing, distribution, etc.) having various functions can be manufactured. Moreover, it also helps reduce costs.

Finally, according to the fifth aspect of the invention, since the optical waveguide film obtained by the above method is used, low loss, ultra small size,
An optical waveguide type circuit with low cost and high dimensional accuracy can be easily manufactured.

[0016]

An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows an embodiment of an electron beam vapor deposition apparatus 1 used in the method for producing an optical waveguide film of the present invention. As shown in the figure, an umbrella-shaped substrate holder 6 is arranged in an upper part of the vacuum chamber 2 which is evacuated to a high vacuum by a vacuum exhaust system 10, and a plurality of substrates made of SiO ₂ are provided on the lower surface of the substrate holder 6. 7 are held, and these substrates 7 are heaters 8 located above the substrate holder 6.
It is designed to be heated to a desired temperature. Further, a vessel-shaped evaporation source 3 is arranged below the substrate 7, and a tablet 4 obtained by solidifying Si ₃ N ₄ powder is accommodated in the evaporation source 3. An electron gun 5 is provided near the evaporation source 3 so that the tablet 4 housed in the evaporation source 3 is irradiated with an electron beam to evaporate the electron beam. An oxygen gas introduction system 9 is connected to the bottom of the vacuum chamber 2 so that oxygen gas can be introduced into the vacuum chamber 2.

Next, the manufacturing method of the present invention will be described.

As shown in FIG. 1, first, the plurality of substrates 7 held on the substrate holder 6 by the heater 8
While heating in the range of 0 to 400 ° C, the vacuum exhaust system 10
The inside of the vacuum chamber 2 is evacuated to a high vacuum by. Next, when the tablet 4 housed in the evaporation source 3 is irradiated with an electron beam from the electron gun 5, as shown in the figure, fine particles of Si ₃ N ₄ constituting the tablet 4 are evaporated, so that the substrate 7 is deposited on the substrate 7. Be applied. Where chamber 3
By introducing oxygen gas from the oxygen gas introduction system 9 into the inside, a vaporized Si _x O _y N _z film is formed and formed on the substrate 7. The values of x, y, and z of Si _x O _y N _z can be adjusted by the substrate temperature, oxygen gas, flow rate, vacuum degree, and gun current of the electron gun. In addition, in the method of FIG. 1, as a method of accurately controlling the film on the substrate by controlling the values of x, y and z of Si _x O _y N _z , in addition to the above method, SiO ₂ and Si on the tablet 7 are used. _{A method in which 3} N ₄ powder is mixed in a desired weight ratio and hardened by hot pressing is preferably used. The reason is SiO ₂ and Si ₃ N
_This is because the melting points of ₄ are close to each other and vaporize in a similar state. By the way, the refractive index of the Si _x O _y N _z film (value at a refractive index of 0.63 μm) can be changed from 1.465 to nearly 2.0 depending on the values of x, y, and z.

As described above, according to the present invention, it is possible to form a high refractive index film having a refractive index (value at a wavelength of 0.63 μm) of 1.465 to a value close to 2.0. S
Even if it is formed on the iO ₂ substrate, a large warp does not occur. Furthermore, the refractive index can be easily controlled by adjusting the degree of vacuum during film formation, that is, the amount of O ₂ partial pressure.
Further, since the film is formed in vacuum, it is possible to form a film with a small transmittance of impurities and a high transmittance. If ozone is introduced instead of oxygen, Si _x O
x of _y N _z, y, control of the value of z becomes easier, also it is possible to suppress the occurrence of stress in the substrate 7 during deposition.

Next, FIG. 2 shows a second embodiment of the present invention. In this embodiment, the lower part of the vacuum chamber 3 is
Two evaporation sources 3 and 3a are provided through a partition plate 16, and tablets 4 and 4a having different components are housed in the evaporation sources 3 and 3a. These tablets 4 and 4a are supplied with electrons from electron guns 5 and 5a, respectively. By irradiating a beam, these tablets 4 and 4a are vaporized separately. Then, Si ₃ N ₄ is used for one tablet 4 as in the above embodiment, and S is used for the other tablet 4a.
GeO ₂ to iO ₂ or SiO _2, TiO _2, Ta ₂
An oxide containing at least one refractive index controlling oxide such as O ₅ or Nb ₂ O ₃ is used. The addition of the oxide for controlling the refractive index acts as a matching agent for the coefficient of thermal expansion between the film and the substrate, in addition to adjusting the refractive index. That is, tablet 4
By adjusting the gun current of the electron gun 5a to a, the addition amount of the oxide for controlling the refractive index can be arbitrarily controlled. In FIG. 2, the partition plate 16
Is for preventing evaporants from one evaporation source from mixing into the other evaporation source.

As described above, according to this embodiment, it is possible to form a film having a refractive index higher than that of the film of the first embodiment, and moreover, to form the refractive index controlling oxide. In addition to adjusting the refractive index, the addition also serves to match the coefficient of thermal expansion between the film and the substrate. Next, FIG. 3 shows a third embodiment. In this embodiment, another evaporation source 3 is provided in the lower part of the vacuum chamber 2 shown in the second embodiment.
b, and further, a film thickness monitor light source 11, a photodetector 12, and a film thickness monitor glass 13 are provided above and below the vacuum chamber 2. Then, the Si ₃ N ₄ tablet 4 is placed in the first evaporation source 3, and SiO ₂ or SiO ₂ is GeO ₂ in the _second evaporation source 3 a.
A tablet 4a made of a refractive index controlling oxide such as TiO ₂ , Ta ₂ O ₅ or Nb ₂ O ₃ is put, and a tablet 4b made of the above refractive index controlling oxide is put in the remaining one evaporation source 4b. By irradiating the respective tablets 3, 3a, 3b with electron beams from the electron guns 5, 5a, 5b provided in the vicinity of the respective evaporation sources 4, 4a, 4b, at least the refractive index controlling additive is The seeded optical waveguide film may be formed on the substrate 7. In addition, adjustment of the above-mentioned additives is performed by each electron gun 5, 5a,
It can be controlled by arbitrarily changing the current value of 5b. Further, since a mechanism for monitoring the film thickness during the film formation on the substrate 7 is attached to this apparatus,
During film formation, the film thickness can be controlled online by detecting light from the film thickness monitor light source 11 through the film thickness monitor glass 13 from the lower part to the upper part by the photodetector 12.

As described above, according to this embodiment, Si _x O
_y N _z of x, y, z can be easily obtained optical waveguide film was set to a desired value, moreover, the melting point of SiO ₂ and Si ₃ N ₄ is 1500 ° C. and 1900 ° C., relatively close values Therefore, it is convenient for evaporating with an electron beam. In addition, since the film is formed by the electron beam evaporation method as described above also in this embodiment, the film can be formed while monitoring the film thickness, and the film thickness can be formed with good controllability. Further, as the substrate, glass (quartz type, multi-component type), semiconductor (Si, GaAs, InP, etc.), ferroelectric (Li)
NbO ₃ , LiTaO _{3 and the} like), magnetic materials, sapphire and the like can be used, so that optical devices having various functions (amplification, oscillation, modulation, multiplexing, demultiplexing, demultiplexing,
Distribution, etc.) can be manufactured, and at the same time, it is also useful for cost reduction.

Next, FIG. 4 shows an embodiment of a method for producing an optical waveguide from the optical waveguide film obtained by the above invention. This manufacturing method is roughly divided into six processes. First, as shown in (a) of FIG.
Forming a buffer layer 14 having a refractive index n _b on the substrate 15;
After forming the core film (refractive index nw) 16 thereon by the method of the invention shown in FIGS. 1 to 3, the core film 16 is formed.
A metal film 17 for a metal mask is formed on top. Here, the thicker the buffer layer 14 is, the smaller the propagation loss can be made. Therefore, the thickness is preferably in the range of several μm to several tens of μm. The film thickness of the core film 16 is several μ in the case of single mode propagation.
The range from m to several tens of μm is preferable. Next, as shown in (b) and (c) of FIG. 4, a photoresist film is applied on the metal film 17, exposed to ultraviolet light through a mask, and the photoresist film 18 is used as a mask to etch the metal film. To do. The etching of this metal film is NF
Dry etching is performed using ₃ gases. Then, as shown in FIG. 4D, the photoresist pattern 18 on the upper surface is removed, and then dry etching is performed using the metal mask 17 to pattern the core film 16 into a substantially rectangular shape. In this case, the etching is performed on the buffer layer 14
Also to a depth such that it is slightly etched. This etching is performed using CHF ₃ gas. The core film 16 is Si
_In the case of _x O _y N _z , an integral structure in which N is bonded to Si,
For example Therefore, dry etching can be performed almost uniformly, and a pattern with substantially no side surface roughness of the core 16 can be obtained. By the way, Ge, P, Al, Ti are used for the conventional core.
Refractive index controlling additives such as 5 to 10% by weight
Since it is included, the side surface of the core is roughened due to the difference in etching rate between SiO ₂ and the above-mentioned additive. And
As shown in FIG. 4E, the metal pattern 17 is removed by etching, and finally, as shown in FIG. 4F, the cladding film 1 having a value lower than the refractive index nw of the core 16.
By coating 9 (refractive index nc <nw), an optical waveguide can be obtained. Here, the clad film 19 is formed by plasma CVD, thermal CVD, flame deposition,
A manufacturing method such as a coating method can be used.

Next, FIG. 5 is a sectional view of an optical waveguide which can be realized by the method for manufacturing an optical waveguide of the present invention. The optical waveguide 15a shown in (a) of the drawing has a structure in which, for example, quartz glass (quartz, Vycor glass, etc.) is used for the substrate 15, and the buffer layer 20 is also used as the substrate 15. An optical waveguide 15b shown in FIG. 4B has an optical waveguide structure realized by the manufacturing method of FIG. 4, and the substrate 15 is made of glass (quartz-based glass, multi-component glass),
Semiconductors (Si, InP, GaAs, etc.), ferroelectrics (L
iNbO ₃ , LiTaO _3, etc.), a magnetic material or the like can be used, and the degree of freedom in designing the optical waveguide can be expanded. Further, the optical waveguide 15c shown in (c) of the figure has a so-called ridge type optical waveguide structure in which the thickness of the cladding 21 is thin.

As described above, according to the present invention, since the optical waveguide film obtained by the above method is used, low loss, ultra small size,
An optical waveguide type circuit with low cost and high dimensional accuracy can be easily manufactured.

[0027]

In summary, according to the present invention, a core film for an optical waveguide having a high refractive index can be formed on a substrate having a low refractive index layer with a small warp, and the film thickness and the refractive index can be controlled. It is possible to easily form a film having a high transmittance without the possibility of containing impurities. As a result, there is an excellent effect that an optical waveguide type circuit with low loss, ultra small size, low cost and high dimensional accuracy can be realized.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of the present invention.

FIG. 2 is a schematic view showing a second embodiment of the present invention.

FIG. 3 is a schematic diagram showing a third embodiment of the present invention.

FIG. 4 shows an example of a method for producing an optical waveguide from the optical waveguide film obtained by the present invention.

FIG. 5 is a cross-sectional view of various optical waveguides that can be realized by the optical waveguide manufacturing method of the present invention.

FIG. 6 is a process drawing showing an example of a conventional method for manufacturing a glass waveguide.

[Explanation of symbols]

 2 chamber 3 evaporation source 4 tablet 7, 15 substrate 14 buffer layer 16 core 19 clad layer

Claims (5)

[Claims] 1. A substrate is placed in an upper part of a vacuum chamber and heated, and Si ₃ N ₄ is placed in a lower part of the substrate.
After arranging the evaporation source accommodating the tablet of the above, while introducing O ₂ gas into the vacuum chamber, the tablet is irradiated with an electron beam to evaporate the electron beam and the Si _x O _y N _z on the substrate. A method of manufacturing an optical waveguide film, which comprises forming an optical waveguide film. 2. A substrate is placed in the upper part of the vacuum chamber and heated, and Si ₃ N ₄ is placed in the lower part of the substrate.
After arranging the evaporation source accommodating the tablet and the evaporation source accommodating the tablet of the oxide for controlling the refractive index, these tablets are irradiated with an electron beam while introducing O ₂ gas into the vacuum chamber. A method of manufacturing an optical waveguide film, comprising: evaporating each of them to form an optical waveguide film of Si _x O _y N _z containing at least one refractive index controlling oxide on the substrate. 3. A substrate is placed in the upper part of the vacuum chamber to heat it, and an evaporation source is placed in the lower part of the substrate. Then, SiO ₂ and Si ₃ N ₄ powder is desired in the evaporation source. The mixture was mixed at a weight ratio and solidified into a tablet by hot pressing, and while the O ₂ gas was introduced into the vacuum chamber, the tablet was irradiated with an electron beam to evaporate the electron beam and to deposit it on the substrate. To Si _x O _y N _z
A method for manufacturing an optical waveguide film, comprising forming the optical waveguide film according to claim 1. 4. A substrate having a refractive index lower than that of a film formed by the method for producing an optical waveguide film according to claim 1, or an optical waveguide film obtained by the above method. The method for producing an optical waveguide film according to claim 1, wherein a substrate having a low refractive index layer having a refractive index lower than that of the refractive index is previously formed on the surface of the low refractive index layer. 5. The optical waveguide film obtained by the manufacturing method according to any one of claims 1 to 4 is processed into a substantially rectangular pattern by photolithography and dry etching, and then, on the surface of the substantially rectangular pattern, A method for manufacturing an optical waveguide, which comprises forming a cladding film having a refractive index lower than this by coating.