JP3031066B2 - Method for manufacturing oxide film and method for manufacturing optical waveguide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an oxide film and a method for manufacturing the same.
The present invention relates to a method for manufacturing an optical waveguide .

[0002]

2. Description of the Related Art With the development of optical communication, optical devices have been required to have mass productivity, high reliability, no adjustment at the time of connection, ease of automatic assembly, low loss, and the like. Therefore, waveguide type optical devices have come to attract attention in order to meet these requirements.

[0003] Among the optical waveguides, in particular, a silica glass optical waveguide is considered to be promising because the waveguide itself has a low loss and a connection loss with an optical fiber is very small.

FIG. 5 shows a conventional flame deposition method for manufacturing this type of silica-based glass optical waveguide (Miyashita: Optical waveguide technology, 1. Recent optical waveguide technology, O plus E, N).
o. 78 pp. FIG. 59 is an explanatory diagram of FIG.

As shown in FIG. 1, a buffer porous film 2 made of quartz glass is first formed on a Si substrate 1 and a refractive index control additive (T) is formed on the buffer porous film 2.
i, Ge, etc.) to form a core porous film 3 made of quartz glass (a).

The substrate 1 on which the porous films 2 and 3 are formed is
The buffer layer 2 is made transparent by heating (sintering).
a and a planar optical waveguide film having a core layer 3a is formed (b).

A mask 4 is formed on the core layer 3a by photolithography (c).

A pattern of a core layer 3b having a substantially rectangular cross section is formed on the buffer layer 2a by a dry etching process (d).

On the buffer layer 2a and the core layer 3b, a clad porous film 5 made of quartz glass is formed (e).

The clad porous film 5 is heated to be transparent to form a clad layer 5b (f).

[0011]

However, the above-described method of manufacturing a silica glass optical waveguide has the following problems.

(1) In order to produce a glass waveguide having a large difference (refractive index difference) between the refractive index of the core layer and the refractive index of the cladding layer, a glass having a high refractive index containing an additive for controlling the refractive index. When the film is formed on the buffer layer, the entire substrate warps due to the difference in thermal expansion coefficient, and the amount of the warp is 10 μm.
, It is difficult to pattern a high-precision optical circuit, and there is a limit in increasing the refractive index difference.

(2) There is a limit to the relative refractive index difference between the core layer and the cladding layer. That is, even if a porous film for a core having a high refractive index is deposited, the additive for controlling the refractive index volatilizes in the sintering process of FIG. 5B, so that 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 is limited to at most about 1%.

(3) When the core layer containing a large amount of the additive for controlling the refractive index is patterned by a dry etching process as shown in FIG.
Due to the difference between the etching rate of O _{2 and} the etching rate of the additive, the surface of the etching layer becomes rough in an uneven shape, and the scattering loss increases.

(4) In order to form a core layer having a high refractive index, an additive for controlling the refractive index such as Ti, Ge, Al, or P must be added in an amount of 10 mol% or more. However, the coefficient of thermal expansion changes greatly with this. Therefore, when the core layer is formed, the substrate is warped, which leads to the problem described in (1).

(5) When the additive for controlling the refractive index is increased,
Absorption and scattering losses increase, making it difficult to realize a low-loss optical waveguide.

Accordingly, an object of the present invention is to solve the above-mentioned problems and to reduce the occurrence of substrate warpage during the production of an oxide film.
In addition to forming an oxide film with high refractive index and high transparency,
An object of the present invention is to provide a method for manufacturing a low-loss, high-precision, low-cost optical waveguide.

[0018]

According to the present invention, a porous film of SiO ₂ is formed on a substrate, and the porous film is heated in an NH ₃ atmosphere containing He to form a transparent film. It is formed on an oxide film.

Further, the present invention is a core layer formed on the substrate, in the manufacturing method of the optical waveguide forming a cladding layer having a refractive index lower than the refractive index of the core layer to the core layer and the substrate, SiO ₂ glass A porous film of SiO _{2 serving as} a core layer is formed on a substrate having a layer having a refractive index substantially equal to the refractive index of the substrate, and the porous film is heated in an NH ₃ atmosphere containing He to form a transparent oxide film. Then, an oxide film is formed on a core layer having a substantially rectangular cross section by photolithography and dry etching, and the core layer is formed so as to be covered with a cladding layer having a refractive index lower than that of the core layer.

[0020]

According to the above construction, a porous film of SiO ₂ is formed on a substrate, and this porous film is heated in an NH ₃ atmosphere containing He to form a transparent oxide film. Since N is contained in the oxide film in the process of changing from the film to the transparent oxide film, the refractive index can be increased, and warpage is less likely to occur. By forming this transparent oxide film on the core layer by photolithography and dry etching, an optical waveguide with high precision, low loss and low cost can be formed.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is an explanatory view showing a method of manufacturing an oxide film according to the present invention.

As shown in FIG. 1A, first, a porous film 11 for a core made of SiO ₂ is formed on a substrate 10.
The material of the substrate 10 is glass (quartz glass, multi-component glass, etc.), semiconductor (Si, GaAs, InP, Si with oxide film, etc.), magnetic material, ferroelectric material (LiNbO ₃ , LiT
aO ₃ etc.) is used.

The porous film 11 is made of SiO ₂ or SiO
₂ , Ge, P, Ti, Al, Nb, Zn, Zr, Na,
Those containing at least one kind of additive for controlling the refractive index such as K and B are used. The porous film 11 is formed by a flame deposition method, a flame hydrolysis method, a thermal CVD method, a sol-gel method, or the like, and the film thickness is selected from a range of several μm to one hundred and several tens μm. .

Next, as shown in FIG.
The substrate 10 on which the substrate 1 is formed is placed in a glass tube 13 of an electric furnace 12.
Then, He gas and NH ₃ gas are introduced into the glass tube 13, and the temperature of the electric furnace 12 is increased and heated to form a transparent oxide film. In addition, there are the following two methods as the heating method, and either method may be used.

In the first heating method, the porous film 11 is heated at a temporary sintering temperature (about 500 to 1200 ° C.) before it becomes transparent, and then kept at the sintering temperature (about 1300 to 1450 ° C.) to be transparent. It is a method to become. The second heating method is a method in which the sintering temperature is maintained and the material is made transparent at one time.

The introduction of He gas is performed by introducing N gas into the porous film 11.
There is an effect of facilitating the mixing of water, an effect of facilitating degassing in the porous film 11, and an effect of facilitating the transparency of the porous film 11. If the above-described heating is performed in a pressurized atmosphere, N can be more effectively added to the porous film 11.

FIG. 1C is a cross-sectional view of the substrate 10 on which the transparent core oxide film 11a has been formed as described above.

Here, a specific example of the above-described method for manufacturing an oxide film will be described.

[0030] Using the Si substrate (3 inch diameter, thickness 0.45 mm) to the substrate 10, SiO ₂ on the Si substrate -
The P ₂ O ₅ -B ₂ O ₃ based porous film 11 was formed to a thickness of about 20μm by flame hydrolysis deposition. This porous membrane 11
Was formed on the transparent oxide film 11a by sintering. Although the refractive index of the oxide film 11a is about 1.458 (a value at a wavelength of 0.63 μm), as shown in FIG. 1B, the oxide film 11a is sintered by changing the NH ₃ gas flow rate in an NH ₃ gas atmosphere. (Temperature about 1350 ° C, time about 3 hours)
An oxide film 11a having a refractive index in the range of 1.90 could be obtained. Moreover, the warpage of the substrate 10 on which the oxide film 11a was formed was only 35 μm or less.

FIG. 2 is an explanatory view showing a method of manufacturing a waveguide using an oxide film manufactured by the method shown in FIG.

The substrate 10 on which the oxide film 11a shown in FIG. 1A is formed is the substrate 10 formed by the above-described steps from FIG. 1A to FIG. 1C.

On the oxide film 11a formed on the substrate 10, a mask metal film (for example, a WSi film) 15 is formed by a sputtering method. The thickness of the metal film 15 is preferably in the range of several thousand angstroms to 1 μm (FIG. 2B).

After applying a photoresist on the metal film 15, a mask pattern 16 of the photoresist film is formed by a photolithography process such as ultraviolet exposure, baking, development, and fixing (FIG. 2C).

The metal film 15 is dry-etched using the mask pattern 16 to form a metal pattern 15a. This dry etching is performed in a plasma atmosphere using, for example, NF ₃ gas (FIG. 2D).

Further, the oxide film 11a is
Dry etching is performed using 5a as a mask to form oxide film 1.
1b is formed. For this etching, for example, CHF ₃
Gas is used (FIG. 2 (e)).

The metal film 15 on the oxide film 11b is peeled off by dry etching (FIG. 2F).

Finally, as shown in FIG.
A so-called embedded optical waveguide in which the cladding film 17 made of a material lower than the refractive index 1b is formed and the oxide film 11b is embedded can be obtained.

Next, the operation of the embodiment will be described.

A porous film 11 of SiO ₂ is formed on a substrate 10 and heated in an NH ₃ atmosphere to form the porous film 11 on a transparent oxide film 11a.
Since the oxide film 11a contains N in the process of changing into the oxide film 11a, the refractive index can be increased, and the substrate 10 is less likely to warp. By forming the oxide film 11a on the core layer by photolithography and dry etching, an optical waveguide with high precision, low loss and low cost can be formed.

FIG. 3 is an explanatory view showing another embodiment of the method of manufacturing an oxide film according to the present invention, and FIG. 4 shows a method of manufacturing a waveguide using the oxide film manufactured by the method shown in FIG. FIG.

FIG. 3 is different from the embodiment shown in FIG. 1 in that the first clad film 2 having a low refractive index value is previously formed on the substrate 10.
0 is formed and used as a buffer layer, and a porous film 11 for N containing N is formed thereon.
By forming the first cladding film 20 on the substrate 10, any of glass, semiconductor, magnetic material and ferroelectric material can be used as the material of the substrate 10. The refractive index of the first cladding film 20 is lower than the refractive index of the oxide film.

4 is different from the embodiment shown in FIG. 2 in that a first clad film 20 is previously formed on a substrate 10 as a substrate with an oxide film for a core shown in FIG. The point is that an oxide film 11a is formed thereon. The subsequent steps of FIG. 4B to FIG. 4G include the same steps as FIG.

As described above, according to the present embodiment, the substrate 1
Since the porous film 11 of SiO ₂ is formed on the substrate 0 and heated in an NH ₃ atmosphere to form the porous film 11 on the transparent oxide film 11a, the substrate 10 is hardly warped at the time of manufacturing. An oxide film having a high refractive index and high transparency can be formed.

Further, SiO ₂ which is a core layer on the substrate 10 having a layer of substantially equal refractive index to the refractive index of the SiO ₂ glass
Is formed in a transparent oxide film 11a by heating the porous film 11 in an NH ₃ atmosphere, and the oxide film 11a is formed into a core layer having a substantially rectangular cross section by photolithography and dry etching. Is formed so as to cover this core layer with a cladding layer having a refractive index lower than the refractive index of the core layer, so that a low-loss, high-precision, low-cost optical waveguide can be manufactured.

[0046] That is, (1) a high refractive index in the range of the refractive index on the substrate from 1.46 to 1.90, and good transparency, Si _x without further little warped on substrate 10 O _y N _z transparent oxide film 1
1a can be formed, and the value of the refractive index of the oxide film 11a can be controlled by the concentration of the NH ₃ gas, the temperature for heat transparency, and the heating time.

(2) Since the additive for controlling the refractive index can be used as an additive for adjusting the thermal expansion coefficient between the substrate and the oxide film, substrates of various materials can be used.

(3) By adding He gas during the heat-transparency, N can be easily mixed into the porous film, and the transparency of the porous film can be promoted. By further adding Cl gas, the OH groups contained in the porous film can be removed, and the content of OH groups in the oxide film containing transparent N is minimized. Can be.

(4) An optical waveguide having a relative refractive index difference of about 0.5-10% can be realized. Also, since the substrate hardly warps, an optical circuit with little polarization dependence can be realized, and a pattern with a high dimensional accuracy can be patterned during photolithography, thus achieving an optical circuit according to a desired design value. can do.

Also, by realizing a high relative refractive index difference, an ultra-small optical circuit having a size of 1/3 to 1/50 or less can be achieved as compared with a conventional waveguide type optical circuit. Further, with the miniaturization, it is possible to achieve low loss and low cost. Further, it is possible to obtain an optical circuit having less so-called scattering loss with less core side roughness during dry etching.

(5) The refractive index of the core can be selected over a wide range, and by adding an additive for controlling the refractive index to the core, the optical waveguide function can be realized even when various substrates having different coefficients of thermal expansion and refractive indexes are used. And the thermal expansion coefficient can be balanced.

[0052]

In summary, according to the present invention, the following excellent effects are exhibited.

(1) A high refractive index and good transparency on a substrate, and a Si _x
O _y N _z can form a transparent oxide film, moreover the concentration of the refractive index values NH ₃ gas in the oxide film, the heating clearing temperature can be controlled by heating time.

(2) Glass, semiconductor, magnetic material,
Various materials such as a ferroelectric can be used.

(3) When He gas is added during heating and transparency, N can be easily mixed into the porous film, and the transparency of the porous film can be promoted.
By further adding Cl gas, the OH groups contained in the porous film can be removed, and the content of OH groups in the oxide film containing transparent N is minimized. Can be.

(4) It is possible to realize an optical waveguide having a relative refractive index difference of about 0.5 to several tens%, and has little polarization dependency.
A core pattern of a high dimension system can be formed.

Also, by realizing a high relative refractive index difference, an ultra-small optical circuit of 1/3 to 1/50 or less can be achieved as compared with a conventional waveguide type optical circuit. Further, with the miniaturization, it is possible to achieve low loss and low cost. Further, it is possible to obtain an optical circuit having less so-called scattering loss with less core side roughness during dry etching.

(5) The refractive index of the core can be selected over a wide range, and by adding an additive for controlling the refractive index to the core, the optical waveguide function can be realized even when various substrates having different coefficients of thermal expansion and refractive indexes are used. And the thermal expansion coefficient can be balanced.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing one embodiment of a method of manufacturing an oxide film according to the present invention.

FIG. 2 is an explanatory view showing a method of manufacturing a waveguide using an oxide film manufactured by the method shown in FIG.

FIG. 3 is an explanatory view showing another embodiment of the method of manufacturing an oxide film according to the present invention.

FIG. 4 is an explanatory view showing a method for manufacturing a waveguide using an oxide film manufactured by the method shown in FIG. 3;

FIG. 5 is an explanatory diagram for explaining a conventional flame deposition method for manufacturing a silica glass optical waveguide.

[Explanation of symbols]

 Reference Signs List 10 base plate 11 porous film 11a, 11b oxide film 12 electric furnace 13 glass tube

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ identification code FI G02B 6/13 G02B 6/12 N // H01L 27/15 M (58) Fields surveyed (Int. Cl. ⁷ , DB name) C03B 8/00 C03B 19/12 C03B 19/14

Claims (3)

(57) [Claims] 1. A process for producing an oxide film, comprising forming a porous film of SiO ₂ on a substrate and heating the porous film in an NH ₃ atmosphere containing He to form a transparent oxide film. Method. 2. The NH ₃ atmosphere further contains Cl _2.
The method for manufacturing an oxide film according to claim 1, wherein
Law. 3. A core layer is formed on a substrate, and the core layer and the core layer are formed.
A substrate having a refractive index lower than that of the core layer on the substrate;
In the method for manufacturing an optical waveguide having a pad layer formed thereon, the method for producing
_{(2) On} a substrate having a layer with a refractive index substantially equal to that of glass
A porous SiO ₂ film serving as a core layer is formed on the
Heating the film in an NH ₃ atmosphere containing He, a transparent oxide film
The oxide film is formed by photolithography and dry etching.
The core layer having a substantially rectangular cross section is formed by etching.
Layer having a refractive index lower than that of the core layer.
Optical waveguide formed so as to be covered with a pad layer
Manufacturing method.