JPH05181031A - Optical waveguide and its production - Google Patents

Abstract

PURPOSE:To inexpensively produce the optical waveguide which has a large refractive index difference between a core and a clad and is small in warpage and low in loss. CONSTITUTION:This optical waveguide has the projecting core 2 consisting of SiONH formed by a plasma CVD method on an SiO2 substrate 1. The refractive index nw of this core 2 is selectable from a 1.46 to 1.57 range and is, therefore, not required to be further incorporated therein with additives for controlling the refractive index. SiO2, is used for the clad 3 covering the core 2 and further, the SiO2, contg. at least one kind of the additives for controlling the refractive index, such as B, P and F, is used to increase the specific refractive index difference and to adjust the coefft. of thermal expansion is used. The specific refractive index difference between the core 2 and the clad 3 can be changed within a range from 0.17 to 7.0% if the SiO2. is used for the clad 3. The film of the SiONH has the value approximate to the coeffts. of thermal expansion of the SiO2. substrate 1 and the clad 3 and, therefore, the warpage decreases.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ridge type optical waveguide and a method for manufacturing the same, and more particularly to a core of the optical waveguide made of SiON.
Concerning what is composed of H.

[0002]

2. Description of the Related Art With the progress of optical fiber communication, optical devices are required to be mass-produced, highly reliable, unadjusted coupling, automatic assembly, and low loss. In order to solve these problems, a waveguide type optical device has been attracting attention.

Among the optical waveguides, the silica glass optical waveguide is particularly promising as a future optical waveguide because it has a low loss and a connection loss with an optical fiber is very small. Conventionally,
A flame deposition method shown in FIG. 12 is known as a method for manufacturing a quartz glass optical waveguide. This is (A) a porous film 24 for buffer made of quartz glass on a silicon substrate 21.
a and an additive for controlling the refractive index (Ti or G) on the film.
porous film 22 for core made of quartz glass containing e)
a is formed, and (B) a transparent optical waveguide film having the buffer layer 24 and the core layer 22b is formed by heating and making them transparent. (C) and (D) The convex core layer 2 is formed by patterning by a dry etching process using the mask 25.
A three-dimensional optical waveguide having 2 is formed. (E) A clad porous film 23a made of silica glass is formed on the three-dimensional optical waveguide, and (F) the clad layer 23 is formed by heating and transparentizing the film (Miyashita:
Optical waveguide technology, 1. Recent optical waveguide technology, O plus
E, No. 78, pp. 59-67).

[0004]

However, the above-mentioned FIG.
The method of manufacturing the silica glass optical waveguide of No. 2 has the following problems.

(1) When a core glass film having a high refractive index containing a refractive index control additive is formed on a buffer layer in order to manufacture a glass waveguide having a large refractive index difference between the core and the clad, The entire substrate is warped due to the difference in the coefficient of thermal expansion, and the amount of the warpage becomes a large value far exceeding 10 μm. Therefore, 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.

(2) In addition to the reason (1) above, it has 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 of FIG. 12B, and a core layer having a high refractive index can be realized. It was difficult, and never exceeded 1.47. Therefore, the relative refractive index difference Δ is limited to about 1% at most.

(3) When the core layer containing a large amount of the refractive index controlling additive is patterned by a dry etching process as shown in FIG. 12D, S constituting the core layer is formed.
The etching side surface becomes rough due to the difference in the etching rate between iO ₂ and the above-mentioned additive, which increases scattering loss.

(4) The sintering process is performed twice (FIG. 12B).
And (F)), which requires manufacturing time and utility costs (that is, electricity, gas, water, etc.), which makes it difficult to reduce costs.

The object of the present invention is to solve the above-mentioned drawbacks of the prior art by finding an optimum core material, and to reduce warpage even if the refractive index difference between the core and the clad is increased.
Another object of the present invention is to provide an optical waveguide which is extremely low in etching roughness on the side surface of the core, low in loss, ultra-compact and low in cost.
Another object of the present invention is to provide a method for manufacturing a low cost optical waveguide.

[0010]

The optical waveguide of the present invention According to an aspect of the refractive index n _w convex core periphery a refractive index n _c (n _c of the <
In the optical waveguide covered with (n _w ) clad, SiONH is used as the material of the core. The material of the core is composed of SiONH, at least the coefficient of thermal expansion,
Refractive index controlling additives that significantly change physical properties such as softening temperature are not included.

Further, the above-mentioned optical waveguide manufacturing method has a low refractive index.
Substrate or low refractive index n_b(N_b<N_w) Buff
SiH on the substrate_Four(Or Si (OC
₂H _Five)_Four) And N₂O and N if necessary₂Using
The number of SiONH films is increased by the vapor phase chemical vapor deposition method (CVD method).
Step of forming from 10 μm to 10 μm and a film of SiONH
Convex by photolithography and dry etching
Pattern processing and the processed pattern surface
It comprises a step of coating a clad film on the top.
It In this case, the change in the refractive index during the manufacturing process is small.
After forming the SiONH film,
Is processed into a convex pattern and then in an inert gas atmosphere
Process of heat treatment at a temperature lower than the softening temperature of SiONH
Is desirable to add.

[0012]

The SiONH for the core has little difference in the coefficient of thermal expansion from the substrate, so that the warpage is small and it is easy to pattern an optical circuit with high dimensional accuracy. That is,
It is possible to realize a waveguide type optical circuit having extremely little polarization dependence. In addition, the SiONH core porous film deposited on the substrate is a refractive index control additive (for example, SiO ₂
Has a high refractive index even if it does not contain B, P, Ge, Ti, Al, Ta, Zn, etc.), so that the volatilization of additives in the sintering process becomes a problem. In addition, a core layer having a high refractive index can be realized, and the relative refractive index difference between the core and the clad can be made much larger than in the conventional case. In addition, since the additive is not included, even if patterning is performed by a dry etching process, unevenness on the etching side surface due to the difference in etching rate due to SiO ₂ and the additive is eliminated, and scattering loss due to it is eliminated. There will be no increase. Further, since the relative refractive index difference can be made more than twice as large as the conventional one, various waveguide type optical circuits (for example, Mach-Zehnder type optical filters) can be miniaturized in an area of one digit or less. As a result, the optical circuit loss can be significantly reduced, and a large amount of optical circuits can be produced from a single wafer substrate, which can be expected to significantly reduce the cost.

Since the core layer made of the SiONH film is formed by CVD, the sintering process is not necessary. Especially, when the cladding is also formed by plasma CVD or low pressure CVD, a transparent glass film for cladding is directly formed. Is not required at all, so that the manufacturing time is shortened, the utility cost is not required, and the cost can be easily reduced. Further, it is possible to suppress the change in the refractive index during the manufacturing process to be small.

The SiONH for the core used in the present invention
A suitable film can be obtained by forming the film by a plasma CVD method. That is, 100 to 100 substrates in a plasma atmosphere
It is heated in the range of 350 ° C., and, for example, SiH ₄ , N ₂ O and N ₂ gases are fed into this plasma atmosphere to form a film. It is important that the obtained film contains a small amount of N and H in SiO ₂ , and the refractive index can be controlled by adjusting the N content. That is, the higher the N content, the higher the refractive index. The formed film is SiO _X N _Y H _Z (x, y> 0, real number of z ≧ 0), and x decreases as y and z increase. As the refractive index is smaller, x approaches 2 and y decreases. vice versa,
The higher the refractive index, the more y increases, and x becomes smaller than 2. H
Is contained because it is formed by the low temperature plasma CVD method,
The higher the refractive index is, the lower the refractive index is, and the lower the refractive index is, the higher the refractive index is. However, the content thereof is in the range of 0.001 to several weight%. Further, the content of H increases as the film is formed in a low temperature plasma atmosphere, and decreases as the temperature increases. Therefore, the refractive index can be controlled by adjusting the N and H contents. Therefore, the high refractive index difference of the present invention,
The range of refractive index of the core suitable for realizing a low polarization dependent, low loss, and ultra-small optical waveguide is in the range of 1.46 to 1.57.

[0015]

1 is a sectional view of a ridge type optical waveguide according to an embodiment of the present invention. The substrate 1 is made of SiO ₂ glass. Plasma C is formed on the convex core 2 having a substantially rectangular cross section.
A SiONH glass film formed by the VD method is used. The refractive index n _w of this core 2 is, as described later,
It can be selected from the range of 1.46 to 1.57. The cladding 3 is made of SiO ₂ , or SiO ₂ is made of B, P, F,
A material containing at least one additive for controlling the refractive index such as Here, for example, when SiO ₂ is used for the clad 3, the relative refractive index difference between the core 2 and the clad 3 (or the substrate 1) can be changed within the range of 0.17% to 7.0%. If a SiO ₂ film with B or F added to the clad is used, the relative refractive index difference can be further increased. Further, these additives can also be used for adjusting the coefficient of thermal expansion. In the conventional method, the relative refractive index difference was limited to about 1% at most, but in the configuration of this embodiment, it can be made about 7 times larger than the conventional one. Moreover, since this SiONH film has a value close to the coefficient of thermal expansion of the SiO ₂ substrate 1 and the clad 3 (about 5 × 10 ⁻⁶ / ° C.),
There is almost no warp of the substrate during film formation, and an optical circuit with high dimensional accuracy can be patterned.

As an example, a SiONH film having a refractive index of 1.472 was formed on an SiO ₂ substrate to a thickness of 8 μm, and the amount of warpage of the substrate was measured. As a result, the warpage of the substrate is 3μ
It was found to be m or less, and the amount of substrate warpage due to film formation was extremely small. From this, SiO ₂ and SiON
It was experimentally confirmed that there is almost no difference in the coefficient of thermal expansion from H. The substrate on which the SiONH film was formed was heated in an N ₂ gas atmosphere at 1000 ° C., which is lower than the softening temperature of SiONH (<1600 ° C.), and heated for 3 hours. However, the temperature raising time was 2 hours and the temperature lowering time was 4 hours. When the amount of warpage of the substrate was measured in the same manner, the amount of warpage was 4 μm.
It was found that the residual stress in SiONH was extremely small. This is extremely advantageous in realizing optical components with little polarization dependency for coherent optical communication, such as Mach-Zehnder type optical filters, ring resonators, and narrow-band optical multiplexers / demultiplexers. Incidentally, the SiO of this embodiment
FIG. 2 shows the comparison result of the warp amount of the substrate between the core film using NH and the conventional SiO ₂ —TiO ₂ based core film. The heat treatment step is carried out if necessary, but in this step, heating in an atmosphere of an inert gas (N ₂ , Ar, etc.) is essential for reducing the change in refractive index. That is, when heat treatment is performed in an oxidizing atmosphere, SiON
This is because N and H in H react with O ₂ to cause a decrease in refractive index. It is highly preferable to perform the heat treatment in a reducing atmosphere containing an inert gas and H ₂ .

Since the core 2 of this embodiment does not contain P, Ge, Al, Ti, B and the like as the refractive index controlling additives as in the prior art, the core 2 is formed during the optical waveguide manufacturing process. Does not lower the refractive index. Also, when processing the core into a convex structure by a dry etching process,
It is possible to perform etching at a substantially constant speed, and it is possible to realize a core side surface with less side surface roughness.

FIG. 3 is a sectional view of an optical waveguide according to another embodiment of the present invention. A Si substrate is used as the substrate 1a, a buffer layer 4 having a refractive index n _b (n _b <n _w ) is provided on the substrate 1a, and the core 2 surrounded by the clad 3 is convexly formed on the buffer layer 4. It is the formed structure. The material of the buffer layer 4 may be the same as the material of the clad 3, and its refractive index n _b is about the same as the refractive index n _c of the clad 3, or n _b <n _c or n _b > n _c. May be

FIG. 4 shows an embodiment of the method for manufacturing an optical waveguide of the present invention. First, on the SiO ₂ substrate 1, as will be described later,
SiONH which becomes the core layer 2a by the plasma CVD method
Deposit the film. The thickness of this SiONH is several μm to several tens of μm when a single mode optical waveguide is realized,
When realizing a multimode optical waveguide, it is 10 μm or more
To 100 μm (FIG. 2 (A)). Next, the convex core pattern 2 is processed by dry etching using a reactive ion etching device (FIG. 2B). After that, a film of the clad 3 is deposited by a method such as a plasma CVD method or a CVD method (FIG. 7C). The cladding 3 may have a film thickness of 5 μm or more. When the clad 3 is formed by the plasma CVD method, the low pressure CVD method, or the like, a transparent glass film can be formed, so that the subsequent high temperature heat treatment step may be omitted. When the SiO ₂ film is formed by the flame deposition method, the atmospheric pressure CVD method, or the like, or the clad film 3 containing at least one refractive index control additive such as B, F, or P in SiO ₂ is formed, the film is porous. Since it is qualitative, it requires a high temperature heat treatment step after that. In that case, pre-SiO ₂ film for the refractive index change suppression by a method such as low-temperature plasma CVD method SiONH core pattern on the surface of the convex or SiO _2,
And at least one additive for controlling the refractive index such as B, F and P.
After forming a refractive index change suppressing layer having a low refractive index n _p (n _p <n _w ) containing seeds, or after performing a heat treatment in an inert gas atmosphere in advance to suppress the change of the refractive index. It is important to form a clad film. Because S
We have discovered a phenomenon that when the iONH film is heat-treated at a high temperature in an atmosphere containing O ₂ gas, N and H in the SiONH film diffuse or react with O ₂ , resulting in a significant decrease in the refractive index. Is. In addition, inert gas and H ₂
It is very preferable to perform the heat treatment in a reducing atmosphere containing, for example.

Table 1 shows the results of measuring the in-plane distribution of the film thickness and the refractive index of the core layer 2a in the case where the core layer 2a of FIG. 4A is formed, and the measurement positions are the points shown in FIG. is there. The characteristics before heat treatment are those after film formation, and the characteristics after heat treatment are
After film formation, 1000 ° C., N ₂ atmosphere (N gas flow rate: 10 l
/ Min) and shows the characteristics after heat treatment for 3 hours. As described above, since the refractive index control additive is not contained in the core layer 2a, the refractive index characteristics before and after the heat treatment change only to the extent of the difference due to the change in the density. That is, unlike the conventional method, the heat treatment does not significantly reduce the refractive index due to the volatilization of the refractive index control additive. Further, the warp of the substrate was 4 μm or less, which was a value that caused almost no problem.

[0021]

[Table 1]

FIG. 6 shows the above-described plasma CV on the substrate 1.
3 is a schematic view of an apparatus for forming a SiONH film by the D method. In the plasma CVD device 5, a shower electrode 6 and a lower electrode 7 which are two parallel plate electrodes are provided on the upper and lower portions, and a high frequency voltage is applied from a high frequency power source 12 between these electrodes. The inside of the device 5 is evacuated to a vacuum by the exhaust device 14. The substrate 1 is placed on the lower electrode 7, and is heated to several hundreds of degrees Celsius by applying a voltage 11 to the heater 10 below the electrode 7. The upper shower electrode 6 uniformly ejects the gas (SiH ₄ and N ₂ O, or N ₂ may be introduced if necessary) sent from the direction of arrow 91 between the parallel plate electrodes. Therefore, it has a shower structure in which the inside is hollow and a large number of holes are formed in the electrode facing surface. The shower head electrode 6 is insulated from the plasma CVD device 5 by an insulator 13. With such a device configuration, the SiONH film is formed in a reduced pressure state. Note that, in FIG. 6, the upper electrode and the lower electrode may be attached opposite to each other, and gas may be blown upward from below to form a film.

Specific examples of film forming conditions for realizing the above-described high refractive index will be described below. Figure 7 shows N ₂ O / S
It shows the relationship between the iH ₄ ratio and the refractive index (value at a wavelength of 0.63 μm). As you can see from the figure, 1.46
A value of ˜1.68 could be achieved. However, when the refractive index exceeds 1.57, S is not SiONH but S
Since the physical properties are close to i _x N _y , it is not preferable for the optical waveguide of the present invention.

FIG. 8 shows the results of measuring the refractive index of SiONH formed by changing the substrate temperature of the lower electrode 7 in FIG. It is shown that the refractive index can be adjusted also by the substrate temperature.

As a concrete example of FIG. 1, a thickness of 1 mm,
A SiONH film having a refractive index shown in Table 1 of about 8 μm was deposited on a quartz glass substrate 1 having a diameter of 3 inches, and then a WSi film was formed to about 1 μm by a sputtering method. A linear pattern having a width of 10 μm was patterned thereon by a photolithography process. Then, by dry etching process, the WSi film is patterned using NF ₃ gas with the photoresist film as a mask, and then CH
The SiONH film was dry-etched using F ₃ gas. After that, a SiO ₂ film is formed on the surface by plasma CVD.
It was formed to a thickness of μm. Then, SiO is formed by the flame deposition method.
A film of _2- B ₂ O ₃ -P ₂ O ₅ was formed to a thickness of about 40 μm. Then, after heat treatment at 1300 ° C., dicing the end surface of the substrate,
Polished to make an optical waveguide, wavelength from 1.3 μm to 1.6
As a result of measuring the loss wavelength characteristic with 0 μm band light, a loss of 0.03 dB / cm was realized at the lowest value.

FIG. 9 is a photograph of the result of patterning the core film on the SiO ₂ substrate by the dry etching process by a scanning electron microscope. The core pattern of SiONH of this embodiment and the SiO of the conventional example are taken. ₂
It is shown by comparing the core pattern of -TiO _2. As can be seen from FIG. 9A, the side surface of the conventional SiO ₂ —TiO ₂ core pattern is greatly roughened by etching.
On the other hand, the side surface of the SiONH core pattern of this embodiment shown in FIG. 7B shows almost no etching roughness. That is, it has been shown that the core having the structure of this example can be etched very uniformly, and it is considered that this has realized a significant reduction in loss.

FIG. 10 shows a Mach-Zehnder type optical filter constructed by using the SiONH core of this embodiment and a conventional Si.
It is a comparison of the sizes of the optical filters configured by using an O ₂ —TiO ₂ core. As you can see from the figure,
The area can be reduced to two digits or less, and thereby drastic cost reduction can be expected. Table 2 shows the result of calculating how low the loss of the optical filter is, and shows that the loss can be significantly reduced by using the configuration of the present embodiment.

[0028]

[Table 2]

The content of H in the core can be reduced by high temperature heat treatment. The size can also be reduced by processing in an atmosphere containing chlorine gas. For example, as shown in FIG. 11, after forming the SiONH film for the core on the substrate by the plasma CVD method,
When N ₂ and Cl ₂ are introduced into the electric furnace 15 as shown by an arrow 171 and heat treatment is performed in a N ₂ and Cl ₂ gas atmosphere, H contained in the film can be reduced and a SiON film can be formed. .. If the film can be changed to such a film in which H is not mixed, the effect of absorption loss due to the OH group is almost eliminated, so that the loss can be further reduced.

[0030]

As described above, according to the present invention, the following effects are exhibited.

(1) According to the optical waveguide described in claim 1, since the core is made of SiO _X N _Y H _Z having a high refractive index and a thermal expansion coefficient close to that of the clad or the substrate, a high relative refractive index is obtained. A difference, low polarization dependence, low loss, and ultra-miniaturized waveguide can be realized.

(2) According to the optical waveguide of the second aspect, since SiONH having a high refractive index and a thermal expansion coefficient close to that of the clad or the substrate is used for the core, a high relative refractive index difference can be provided. Moreover, since the warp of the substrate due to the difference in the thermal expansion coefficient hardly occurs, it is possible to perform patterning with high dimensional accuracy. Further, unlike the conventional case, it is not necessary to add a refractive index control additive for changing physical properties such as a thermal expansion coefficient and a softening temperature in the core, so the core during the dry etching process caused by the additive is not required. The etching roughness on the side surface can be extremely reduced.

(3) According to the optical waveguide of the third aspect, since the refractive index of the core is set within a predetermined range, it is possible to obtain a higher relative refractive index difference than before, and the core serves as an optical waveguide. It is possible to avoid unfavorable physical properties.

(4) According to the optical waveguide of claim 4, since a higher relative refractive index difference can be obtained by using SiO ₂ for the clad and the coefficient of thermal expansion is almost the same, the substrate It is possible to realize an optical circuit that does not warp and has small polarization dependence. Further, the relative refractive index difference can be further increased by adding a predetermined refractive index controlling additive to SiO ₂ in the clad.

(5) The optical waveguide described in claim 5 can be applied to any optical waveguide regardless of the presence or absence of a buffer layer.

(6) According to the optical waveguide of the sixth aspect and the method of manufacturing the optical waveguide of the eighth aspect, since the core is formed by plasma CVD, the sintering process at the time of forming the core becomes unnecessary, It can be manufactured at low cost. Further, by forming the film at a low temperature, the N content can be easily controlled, and thereby the refractive index of the core can be changed within an extremely wide range. Further, the stress generated in the formed film is extremely small, and as a result, the substrate hardly warps.

(7) According to the optical waveguide of the seventh aspect, an optical waveguide having almost no warp can be realized, an optical circuit with high dimensional accuracy can be obtained, and polarization for coherent optical communication. It is possible to easily realize an optical component having little dependence.

(8) According to the optical waveguide manufacturing method of the ninth aspect, the change in the refractive index of the core can be reduced by the heat treatment, and since the substrate hardly warps, the polarization dependence is extremely small. The waveguide type optical circuit can be realized at an extremely low cost. Further, since it is possible to drastically reduce the size, it is possible to expect a significant cost reduction.

(8) According to the optical waveguide manufacturing method of the tenth aspect, it is possible to realize an optical waveguide with extremely small absorption loss due to OH groups.

(9) According to the optical waveguide manufacturing method of the eleventh aspect, it is possible to suppress a decrease in the refractive index of the core during the manufacturing process.

[Brief description of drawings]

FIG. 1 is a sectional view of an optical waveguide according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing the warpage of the substrate with respect to the relative refractive index difference according to the present embodiment in comparison with the conventional example.

FIG. 3 is a sectional view of an optical waveguide according to another embodiment of the present invention.

FIG. 4 is a schematic process diagram of a method of manufacturing an optical waveguide according to an embodiment of the present invention.

FIG. 5 is a plan view of the substrate showing measurement positions on the substrate for examining the characteristics of the core formed by the method of the embodiment of the present invention.

FIG. 6 is a schematic diagram of a plasma CVD apparatus according to an embodiment of the present invention.

FIG. 7 is an N ₂ O film formed by a method according to an embodiment of the present invention.
/ Refractive index characteristic diagram of the core layer relative to SiH ₄ ratio.

FIG. 8 is a refractive index characteristic diagram of the core layer with respect to the temperature of the substrate formed by the method of the example of the present invention.

FIG. 9 is an explanatory diagram comparing core patterns of a conventional example and this example.

FIG. 10 is an explanatory diagram comparing a Mach-Zehnder type optical filter according to a conventional example with the conventional example.

FIG. 11 shows H contained in the SiONH film according to the present embodiment.
Schematic view of a heat treatment apparatus for reducing heat.

FIG. 12 is a schematic process diagram of a conventional method for manufacturing an optical waveguide.

[Explanation of symbols]

1 SiO ₂ 2 core (SiONH) 2 core pattern (SiONH) 2a core layer (SiONH) 3 clad 4 buffer layer 5 plasma CVD device 6 shower electrode 7 lower electrode 8 plasma 91 SiH ₄ , N ₂ O 92 gas 10 heater 11 voltage 12 High frequency power supply 13 Insulator 14 Exhaust device

Claims (11)

[Claims] 1. An optical waveguide comprising a convex core having a refractive index of n _w and an outer periphery of a clad having a refractive index of n _c (n _c <n _w ) covered with SiO _x N _Y H _Z. (X, y>
An optical waveguide characterized by using 0, z ≧ 0). 2. A waveguide outer peripheral refractive index of the convex core of refractive index n _w is covered with cladding _{n c (n c <n w} ), for using SiONH the material of the core Characteristic optical waveguide. 3. The optical waveguide according to claim 2, wherein the refractive index n _{w has} a value in the range of 1.46 to 1.57. 4. The optical waveguide according to claim 2 or 3, wherein the material of the clad is SiO ₂ or SiO ₂ and at least one additive for controlling the refractive index such as B, P, F, Ge and Ti. An optical waveguide characterized by being exposed. 5. The optical waveguide according to any one of claims 2 to 4, wherein the core has a refractive index n _b (n _b (n) formed on a substrate having a refractive index of n _s (n _s <n _w ). _b <
An optical waveguide formed on a buffer layer of (n _w ). 6. The optical waveguide according to claim 2, wherein the SiONH core is formed by a plasma CVD method. 7. The optical waveguide according to claim 5, wherein SiO ₂ is used for the substrate. 8. SiH ₄ or Si (OC ₂ H ₅ ) ₄ and N ₂ O are required on a substrate having a refractive index of n _s or on a buffer layer having a refractive index of n _b formed on the substrate. According to N
₂ by chemical vapor deposition with a refractive index of n _w (n _s <
a step of forming a SiONH film of n _w , n _b <n _w ),
Optical process including a step of processing a SiONH film into a convex pattern by photolithography and dry etching, and a step of coating the processed convex pattern surface with a clad film having a refractive index n _c (n _c <n _w ). Waveguide manufacturing method. 9. The method of manufacturing an optical waveguide according to claim 8, wherein after the formation of the SiONH film or after processing into a convex pattern, the above S is formed in an inert gas atmosphere.
A method of manufacturing an optical waveguide, characterized in that a step of performing heat treatment at a temperature lower than the softening temperature of iONH is added. 10. The method of manufacturing an optical waveguide according to claim 9, wherein in the heat treatment step, a gas containing chlorine is mixed with an inert gas atmosphere to remove H in the SiONH film to form a SiON film. A method for manufacturing an optical waveguide characterized by the above. 11. The method of manufacturing an optical waveguide according to claim 8, wherein after the SiONH film is processed into a convex pattern,
A method of manufacturing an optical waveguide, characterized in that a step of forming a refractive index change suppressing layer by a plasma CVD method is introduced.