JP3208744B2 - Manufacturing method of 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 optical waveguide having a wide application in the field of optical communication components.

[0002]

2. Description of the Related Art On an Si substrate on which an optical waveguide element is formed,
An optical waveguide having a Si bench capable of mounting a semiconductor optical element such as a semiconductor light source and a semiconductor photodetector has been developed. FIG. 4 is a process chart showing a method for manufacturing such an optical waveguide.

First, a procedure for forming an optical waveguide element on a Si substrate 1 (FIG. 4A) will be described. To form the optical waveguide element, initially to form a glass film having the composition SiO ₂ on the entire surface of the Si substrate 1 by an electron beam evaporation method as a buffer layer 2 (Figure 4 (b)). Next, the buffer layer 2
A core glass film 3 having a composition of SiO ₂ —TiO ₂ is formed thereon by an electron beam evaporation method (FIG. 4C). Next, the core glass film 3 is processed by photolithography and reactive ion etching to form the core 4 (FIG. 4D). Further, on the buffer layer 2 including the core 4, a SiO ₂ —B ₂ O ₃ —P ₂ O ₅ based porous glass layer 5 is formed by a flame deposition method.
It is deposited to a thickness of 00 to 400 μm (FIG. 4E). This was transferred into an electric furnace and subjected to a heat treatment in a He gas atmosphere to make the porous glass layer 5 transparent and vitrified to form SiO ₂ —B ₂ O ₃ —
Forming a cladding layer 6 made of P ₂ O ₅ glass;
Thus, the optical waveguide element 7 is formed (FIG. 4F).
The temperature of the heat treatment is 1330 ° C. Here, the dopant materials of B ₂ O ₃ and P ₂ O ₅ are added for the purpose of lowering the transparent glass temperature, and the refractive index of the cladding layer needs to be equal to that of the buffer layer 2 in terms of optical characteristics. is there.

[0004] Next, on the Si substrate 1 on which the optical waveguide element 7 is formed, a Si bench 10 for mounting a semiconductor optical element such as a semiconductor light source or a semiconductor photodetector is formed. In order to form the Si bench 10, it is necessary to expose the Si surface other than the optical waveguide element 7 on the Si substrate 1. For this, first, a metal film 8 is formed on the surface of the cladding layer 6 by a sputtering method.
(G)). Furthermore, the Si substrate 1 is formed by photolithography.
A pattern 9 for exposing the surface of is formed.
(H)). An excess quartz-based glass layer is scraped off based on the pattern 9 using reactive ion etching to form a Si bench 10.

[0005]

However, in the above-described method for manufacturing an optical waveguide, when SiO ₂ glass is formed as a buffer layer on a Si substrate to a thickness of 15 μm or more which does not impair the optical characteristics, the Si There is a problem that the Si substrate is warped due to a difference in linear expansion coefficient of the SiO ₂ glass. The magnitude of this warpage depends on the thickness of the buffer layer, and the thicker the film thickness, the larger the amount of warpage. Also,
Since a core glass film having a thickness of 6 to 8 μm is further formed on the buffer layer, the warpage of the Si substrate is further increased.

Thereafter, a core is formed by using photolithography and reactive ion etching.
Due to the warpage of the substrate, it is difficult to form a highly accurate pattern for forming a core by photolithography.

After the formation of the cladding layer, the amount of warpage reaches up to 150 μm, and patterning by photolithography for forming a Si bench becomes extremely difficult. Further, since this warp is also taken over by the optical transmission module in which an optical element is mounted on the optical waveguide and an optical fiber is connected, a highly accurate optical transmission module cannot be obtained.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art, and to minimize the warpage of the Si substrate after the formation of the buffer layer and the core glass film, and to minimize the warpage of the Si substrate after the formation of the cladding layer. An object of the present invention is to provide a waveguide, a method of manufacturing the same, and an optical transmission module.

[0009]

SUMMARY OF THE INVENTION Fabrication of the optical waveguide of the present invention
The method comprises the steps of: providing a buffer layer having a thickness t ₀ on a surface of a Si substrate ;
And a core glass having a film thickness t ₁ on the buffer layer.
Forming a buffer film and a core glass film.
To correct the warpage of the Si substrate caused by
The thickness t ₂ of the same composition as the buffer layer
The first quartz glass film is coated on the back surface of the Si substrate with an electronic beam.
Then, the core glass film is applied.
To form a core, on the buffer layer containing the core
After forming the porous glass layer, the porous glass layer is made transparent.
Vitrification to form a cladding layer having a thickness t ₃ ,
The reaction of the Si substrate caused by forming the cladding layer
On the first quartz glass film to correct
The same composition as the buffer layer or the cladding layer.
Beam evaporation of a second quartz glass film with a thickness t ₄
After forming by the method, the residual formed on the surface of the Si substrate
The Si substrate is removed by removing an excess quartz glass layer.
The surface is exposed to form a Si bench .

[0010]

In the above-described method of manufacturing an optical waveguide, the thickness of the first quartz glass film formed on the back surface of the Si substrate is set to effectively correct the warpage of the Si substrate caused by the formation of the buffer layer and the core glass film. t ₂ is t ₀ + t ₁ ≧ t ₂
It is preferable that This is because if t ₀ + t ₁ <t ₂ , overcorrection occurs and reverse warpage occurs. It is preferable that the thickness t ₄ of the second quartz glass film further formed on the surface of the first quartz glass film is t ₃ ≧ t ₄ . Similarly, if t ₃ < ₄ , the correction becomes excessive and reverse warpage occurs.

[0012]

[0013]

When the buffer layer and the core glass film are formed on the Si substrate, the Si substrate is warped. After forming the buffer layer and the core glass film, a quartz glass film having the same composition as the buffer layer is formed on the back surface of the Si substrate. When formed, the warpage of the Si substrate is reduced.

When a clad layer is further formed, Si
Although the substrate warps, even after forming the cladding layer,
When a quartz glass film having the same composition as the buffer layer and the cladding layer is formed on the back surface of the Si substrate, the warpage of the Si substrate is reduced.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 2 is a cross-sectional view of the optical waveguide according to the present embodiment. The optical waveguide has an optical waveguide element 28 on a Si substrate 20.
And a Si bench 31.

More specifically, the optical waveguide is a Si substrate 2
The optical waveguide element 2 includes a buffer layer 21, a core 24 provided on the buffer layer 21, and a clad layer 26 provided on the buffer layer 24 including the core 24 on the surface of the optical waveguide element 2.
8 is provided. Further, an Si bench 31 for mounting an optical element is provided on a part of the exposed surface of the Si substrate 20. The Si bench 31 removes excess quartz glass layers (21, 24, 26) formed on the surface of the Si
It is formed by exposing the substrate surface.

On the other hand, on the back surface of the Si substrate 20, a first Si substrate warpage correcting quartz glass film 23 for correcting the warpage of the Si substrate 20 generated in the process of providing the buffer layer 21 and the core 24, Further, a second substrate-warp correcting quartz glass film 27 for correcting the warpage of the Si substrate 20 generated in the process of providing the clad layer 26 is provided.

As described above, the optical waveguide according to the present embodiment has the S
A quartz glass film for correcting the warpage of the substrate
Since it is provided over the layers, a highly accurate optical waveguide without warpage can be obtained.

Next, a method of manufacturing the above-described optical waveguide will be described with reference to FIG.

First, an optical waveguide device is formed on a Si substrate 20. In order to form this optical waveguide element, first, a SiO ₂ glass film is formed on a surface of a Si substrate 20 (FIG. 1A) having an outer diameter of 3 inches and a thickness of 1 mm by electron beam evaporation.
A buffer layer 21 was formed by depositing a thickness of μm (FIG. 1B).
The refractive index n ₀ of the buffer layer 21 was measured with a prism coupler manufactured by Metrion (PC-2010), and as a result, n ₀ = 1.4576. Here, the warpage of the Si substrate 20 on which the buffer layer 21 was formed was 50 μm.

Next, a core glass film 22 having a refractive index of n ₁ is formed to a thickness of 8 μm on the buffer layer 21 by an electron beam evaporation method (FIG. 1C). The refractive index n ₁ was determined by a prism coupler to be n ₁ = 1.4620. Here, the warpage of the Si substrate 20 on which the core glass film 22 was formed was 80 μm.

As described above, the buffer layer 2 is formed on the Si substrate 20.
After the first and core glass films 22 are formed, in order to correct the warpage, a SiO ₂ glass film is deposited on the back surface of the Si substrate 20 by an electron beam evaporation method to a thickness of 30 μm, and the first Si substrate warp correcting quartz system is used. A glass film 23 (FIG. 1)
(D)). Here, by forming the first Si substrate warp correcting quartz glass film 23 on the back surface of the Si substrate 20,
The warpage of the substrate 20 was reduced to 〜5 μm.

Next, a 1 μm-thick WSi film (not shown) was formed on the surface of the core glass film 22 by magnetron sputtering. Further, a resist (not shown)
After coating, the core pattern was transferred by a mask aligner, and the core glass film 22 was etched by reactive ion etching (RIE) to form a core 24 (FIG. 1E).

The Si substrate 20 on which the core 24 is formed is placed on a heated turntable, and the flame is deposited using a flame deposition method.
First, an SiO ₂ —B ₂ O ₃ —P ₂ O ₅ based porous glass layer 25 is formed to a thickness of 300 μm (FIG. 1F). Thereafter, the substrate 20 is placed in the quartz glass furnace tube in the electric furnace,
The porous glass layer 25 was made transparent and vitrified by maintaining it at a temperature of 1330 ° C. for 1 hour in an e gas atmosphere to form a cladding layer 26 having a thickness of 25 μm (FIG. 1 (g)). The cladding layer 26 has a refractive index n ₂ of 1.4576,
It was confirmed that it was the same as the buffer layer 21. In this embodiment, the width and height of the core 24 are both 8 μm,
4. The relative refractive index difference between the buffer layer 21 and the cladding layer 26 is 0.3%. Here, the amount of warpage of the Si substrate 20 on which the cladding layer 26 was formed increased to 50 μm again.

Next, in order to correct this warp, a SiO ₂ glass film is further deposited on the quartz glass film 23 for correcting the warp formed on the back surface of the Si substrate 20 by 25 μm by electron beam evaporation. Thus, a second quartz glass film 27 for straightening the Si substrate was formed (FIG. 1H). Here, the amount of warpage of the Si substrate 20 was reduced to 裏面 5 μm by forming the second Si substrate warp correcting quartz glass film 27 on the back surface of the Si substrate 20.

Next, an Si bench for mounting a semiconductor optical device such as a semiconductor light source and a semiconductor photodetector is formed on the Si substrate 20. To form this Si bench,
It is necessary to expose the Si surface other than the optical waveguide element section 28 formed on the Si substrate 20.

For this, first, a metal film 29 is formed on the surface of the cladding layer 26 by a sputtering method.
(I)). Further, a Si bench pattern 30 for exposing the Si surface is formed by photolithography (FIG. 1 (j)). Excess quartz glass layers (21, 2) are formed by reactive ion etching based on the pattern 30.
6) to form a Si bench 31 (FIG. 1)
(K)).

Thus, an optical waveguide provided with the quartz glass waveguide element 28 and the Si bench 31 is formed on the Si substrate 20. In the manufacturing process, after forming a buffer layer and a core glass film, a quartz glass film for correcting substrate warpage is formed on the back surface of the Si substrate to correct the warpage of the buffer layer and the substrate caused by the formation of the core glass film. Therefore, it is easy to form a high-precision pattern for forming the core. Also, after the formation of the clad layer, a quartz glass film for correcting the substrate warpage is formed on the back surface of the Si substrate to correct the warpage of the substrate caused by the formation of the clad layer. Becomes easier. As a result, a highly accurate optical waveguide can be formed.

The optical waveguide thus formed is finally mounted with an optical element and connected to an optical fiber to form an optical transmission module. In this optical transmission module, as shown in FIG. 3, a semiconductor light source 32 such as an LD (laser diode) and a semiconductor photodetector 33 such as a PD (photodetector) are mounted on a Si bench 31.
The optical axis is coupled to the end of the core 24 facing the first. on the other hand,
An optical fiber 34 is connected to an end of the optical waveguide by a connector 35 and is optically coupled to an end of the core 24. Even in this case, since the optical waveguide is a high-precision optical waveguide without warpage, optical axis coupling can be performed with high accuracy, and a highly accurate optical transmission module can be configured.

[0030]

According to the waveguide manufacturing method of the present invention, S
After forming the buffer layer and core glass film on the i-substrate ,
The quartz glass film composed of the same composition as the
Formed on the back of the plate to correct the warpage of the Si substrate
Is extremely low, and the patterning of the core in the next process is extremely
It can be performed with high accuracy. Also, clad layer formation
Later, a quartz glass film is also applied to the backside of the Si substrate.
Extremely high warpage for forming and correcting the warpage of Si substrate
And the next step of Si bench patterning is extremely
Ru can be done with Umate high accuracy.

[0031]

[0032]

[Brief description of the drawings]

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

FIG. 2 is a cross-sectional view of an optical waveguide according to an embodiment of the present invention.

FIG. 3 is a perspective view of an optical transmission module according to an embodiment of the present invention.

FIG. 4 is a process chart of a conventional optical waveguide manufacturing method.

[Explanation of symbols]

 Reference Signs List 20 Si substrate 21 Buffer layer 22 Core glass film 23 First Si substrate warpage correcting quartz glass film 24 Core 25 Porous glass layer 26 Clad layer 27 Second Si substrate warping correcting quartz glass film 28 Optical waveguide element 29 Metal film 30 Si bench pattern 31 Si bench

──────────────────────────────────────────────────続 き Continuing on the front page (72) Keiichi Higuchi 5-1-1, Hidaka-cho, Hitachi City, Ibaraki Prefecture Inside the Opto-System Research Laboratories, Hitachi Cable Ltd. (72) Naoto Uezuka, Hitachi City, Ibaraki Prefecture 5-1-1, Hidakacho Opto-System Research Laboratories, Hitachi Cable, Ltd. (72) Tatsuo Teraoka Inventor 5-1-1, Hidaka-cho, Hitachi City, Ibaraki Pref. (56) References JP-A-63-184708 (JP, A) JP-A-6-53464 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 6/12-6 /14

Claims (3)

(57) [Claims] A battery having a film thickness of t ₀ on a surface of a Si substrate.
A buffer layer having a thickness t ₁ on the buffer layer.
Forming a glass layer, the buffer layer and the core glass;
Straightening of Si substrate warpage caused by film formation
A film having the same composition as the buffer layer
A first quartz glass film having a thickness of t ₂ is formed on the back surface of the Si substrate.
Formed by electron beam evaporation, and then the core glass
Forming a core by processing a film, and the buffer including the core
After forming a porous glass layer on the porous glass layer, the porous glass
Form a cladding layer having a thickness t ₃ layers with transparent glass
Formed by forming the cladding layer
On the first quartz glass film to correct the warpage of the substrate
And the same composition as the buffer layer or the cladding layer.
A second quartz glass film having a thickness t ₄ composed of
After being formed by the vapor deposition method, the shape is formed on the surface of the Si substrate.
By removing the surplus quartz-based glass layer formed
Exposing the Si substrate surface to form a Si bench
A method for manufacturing an optical waveguide. 2. The method of manufacturing an optical waveguide according to claim 1, wherein
A first quartz-based gas formed on the back surface of the Si substrate.
The film thickness t ₂ is t ₀ + t ₁ ≧ t ₂ der Ruhikarishirube waveguide manufacturing method of Las film. 3. An optical waveguide according to claim 1, wherein
In the fabrication method, the first quartz glass film surface is further shaped.
The thickness t ₄ of the second quartz glass film to be formed is t ₃ ≧ t ₄ A method for manufacturing an optical waveguide.