JPH0815540A - Optical waveguide and its production - Google Patents

Abstract

PURPOSE:To decrease stresses and to make polarization characteristics small by separating a waveguide part consisting of a core part disconnected by a groove and a clad part covering this part from a substrate. CONSTITUTION:The groove 60 for stress relieving is formed on the clad layer 40 on both sides of the core part 30 along the core part 30. Band shape parts 46 of the clad layer 40 cross this groove 60. The part covering the core part 30 of the clad layer 40 is called as the clad part 45 and the rectangular parallelepiped-shaped structure consisting of the core part 30 and the clad part 45 is called as the waveguide part 50. This waveguide part 50 is disconnected from the clad layer 40 on the circumference exclusive of a band shaped part 46. Further, a recessed part 70 is formed at a silicon wafer 10 under the waveguide part 50, by which the waveguide part 50 is separated from the substrate. The waveguide part 50 has a so-called air bridge structure in which the waveguide part 50 is separated from the silicon wafer 10 and the circumferential clad layer 40.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide mainly used in the field of optical communication and a manufacturing method thereof.

[0002]

2. Description of the Related Art An optical waveguide is manufactured by forming a core part and a clad layer covering the core part on a substrate using a thin film technique, and is used in the field of optical communication as an optical component having an optical branching and optical coupling function. Used frequently.

As a conventional optical waveguide, a lower clad layer made of quartz glass is laminated on a silicon wafer, a quartz glass layer having a high refractive index is laminated thereon, and then patterned by reactive ion etching to form a core portion. It is known that an upper clad layer made of quartz glass is laminated on top of this.

For the core portion and the clad layer, glass particles are sprayed onto a silicon wafer by using a flame deposition method to deposit a glass particle layer, which is then sintered, and thereafter,
It is slowly cooled and formed into a transparent glass.

[0005]

However, since the silicon wafer and the glass waveguide layer formed on the silicon wafer have different thermal expansion coefficients, stress is not generated inside the waveguide layer during gradual cooling after sintering. appear. In particular, since the core part is embedded in the clad layer that is in contact with the entire surface of the substrate, the core part has a structure that receives film stress from the entire upper clad layer and the lower clad layer. Therefore, the conventional optical waveguide has a problem that a large anisotropy occurs in the optical characteristics and the polarization characteristics (PDL) are large.

The present invention has been made to solve the above problems, and provides an optical waveguide in which the stress generated inside the core portion is reduced and the polarization characteristic is small, and a method for producing the optical waveguide. With the goal.

[0007]

In order to solve the above-mentioned problems, the optical waveguide of the present invention has a core portion which is an optical waveguide portion, and the core portion is embedded, and has a lower refractive index than the core portion. A waveguide layer including a clad layer is an optical waveguide formed on a substrate, and grooves are formed along the core part in the clad layers on both sides of the core part. It is characterized in that the waveguide portion including the core portion and the cladding portion covering the core portion is separated from the substrate.

Here, it is preferable that the clad portion of the waveguide portion is in contact with the substrate at a part thereof. Further, it is preferable that the reinforcing material is filled between the waveguide portion and the substrate and in the groove formed in the clad layer. Further, the core portion and the clad portion may be made of glass containing quartz, and the substrate may be made of silicon.

Further, the method for producing an optical waveguide of the present invention is a waveguide layer comprising a core portion which is an optical waveguide portion and a clad layer in which the core portion is embedded and which has a refractive index lower than that of the core portion. A first step of preparing an optical waveguide formed on a substrate, a second step of forming grooves along the core portion in the clad layers on both sides of the core portion by the first etching, and a second step And a third step of separating the substrate and the clad layer by leaving an area for supporting the core part by performing the second etching by injecting an etching solution into the groove of the clad layer formed in Step 1. .

Here, after the third step, it is preferable to further include a step of flowing a reinforcing material into the groove formed in the clad layer to solidify it. Further, the first step is a step of preparing an optical waveguide in which a waveguide layer made of glass containing quartz is formed on a silicon substrate, and the first etching may be reactive ion etching.

[0011]

According to the optical waveguide of the present invention, the film stress applied from the substrate to the side surface of the core portion via the cladding layer is released by the groove formed in the cladding layer, and the waveguide portion is separated from the substrate. As a result, the film stress applied to the upper and lower surfaces of the core part from the substrate via the clad part of the waveguide part is also released. As a result, the internal stress of the core is significantly reduced.

Further, in the method of manufacturing the optical waveguide of the present invention,
Grooves are formed in the clad layers on both sides of the core portion by the first etching to release the film stress applied to the side surface of the core portion,
Then, an etching solution is flown into this groove to carry out a second etching, thereby separating the substrate and the clad layer leaving a portion supporting the core portion, and the film stress applied to the upper and lower surfaces of the core portion. To release. As a result, the optical waveguide of the present invention in which the internal stress of the core is significantly reduced can be obtained.

[0013]

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

FIG. 1 is an overall perspective view showing the structure of the optical waveguide 100 of this embodiment. As shown in FIG. 1, the optical waveguide of the present embodiment is formed by forming a waveguide layer 20 having a layer thickness of about 70 μm on a silicon wafer 10 having a thickness of 1 mm. The waveguide layer 20 is composed of a 1 × 8 branch type core portion 30 made of quartz glass, and a clad layer 40 made of quartz glass in which the core portion 30 is embedded and which has a lower refractive index than the core portion 30. .

Grooves 60 for releasing stress are formed in the clad layer 40 on both sides of the core portion 30 along the core portion 30, and the strip-shaped portions 46 of the clad layer 40 cross the groove 60. A portion of the cladding layer 40 that covers the core portion 30 is referred to as a cladding portion 45, and a rectangular parallelepiped structure including the core portion 30 and the cladding portion 45 is referred to as a waveguide portion 50. Are separated from the surrounding cladding layer 40 except for.

Further, a recess 70 is formed in the silicon wafer 10 below the waveguide section 50, whereby the waveguide section 50 is separated from the substrate 10. As described above, the optical waveguide of this embodiment has a so-called air bridge structure in which the waveguide portion 50 is separated from the silicon wafer 10 and the surrounding cladding layer 40.

FIG. 2 is a partial cross-sectional perspective view showing this air bridge structure. The hatched area 15 is
It is the surface of the silicon wafer 10. As shown here, the air bridge structure is a structure in which the waveguide portion 50 separated from the wafer 10 and the surrounding cladding layer 40 is supported on the wafer 10 by the support portion 80 located below the strip portion 46. Is.

In this embodiment, the supporting portions 80 are arranged at seven places in total, and between the end on the single core side and the Y branch portion,
And provided between the Y branch portions. The supporting portion 80 is a part of the wafer 10 and is built in the wafer 10 by a method described later. Since the support part 80 may affect the optical branching if it is arranged near the branch part, the support part 80 is arranged in the middle of the branch parts apart from the branch part as in the present embodiment. Is preferred.

FIG. 3 shows an optical waveguide 100 of FIG.
It is a figure which shows the cross-section structure along the -A 'line, and has shown the air bridge structure of a present Example. As shown in FIG. 3, the cladding layer 40 is composed of a lower cladding layer 41 formed on the silicon wafer 10 and an upper cladding layer 42 formed thereon. The core portion 30 has a cross section of 8 × 8 μm. The thickness of the waveguide portion 50 is about 70 μm, which is the same as that of the cladding layer 40, and the width thereof is 50 μm.

4 and 5 are sectional views showing a structure for supporting the waveguide section 50. FIG. 4 shows a sectional structure of the optical waveguide 100 taken along the line BB 'in FIG. 1, and FIG. FIG. 7 is a side sectional view of the waveguide section 50, the band-shaped section 46, and the support section 80. As shown in FIG. 5, the waveguide portion 50 is supported on the silicon wafer 10 by the support portion 80 existing under the strip portion 46, and the waveguide portion 50 and the wafer 10 are provided on both sides of the support portion 80. A hollow portion 85 formed by interposing air therein is formed.

The method of manufacturing the optical waveguide of this embodiment will be described below. 6 to 8, FIG. 10 and FIG. 11 are views showing the manufacturing process of this embodiment. In this embodiment, the thickness is 1 mm
After preparing an optical waveguide having a waveguide layer formed on the silicon wafer, the optical waveguide is manufactured by etching the optical waveguide.

First, an optical waveguide 200, which is a basis for manufacturing the optical waveguide 100 of this embodiment, is prepared. This is produced as follows.

First, as shown in FIG. 6, a lower cladding layer having a thickness of 30 μm and a core portion 30 having a cross section of 8 × 8 μm are formed on a silicon wafer having a thickness of 1 mm. In particular,
First, the first clad layer to be the lower clad layer by the flame deposition method
Deposit a layer of fine glass particles. This is an oxyhydrogen flame burner, which is used as a raw material for the glass particles during oxyhydrogen flame.
A gas such as l ₄ is sent together with O ₂ which is a carrier gas, and is blown onto the silicon wafer 10. Next, by the same method, a second glass fine particle layer to be the core portion 30 is deposited on the first glass fine particle layer.

When forming the first glass fine particle layer, gases of BBr ₃ and POCl ₄ which are dopant raw materials are sent into the oxyhydrogen flame together with SiCl ₄ . When forming the second glass fine particle layer, BBr ₃ and PO are used.
In addition to Cl ₄ , in order to increase the refractive index of the core portion 30, GeC
Inject gas of l ₄ .

Next, the silicon wafer 10 on which the first and second glass fine particle layers are laminated is heated and melted in a sintering furnace, and then gradually cooled to make each layer a transparent glass. As a result, the lower cladding layer 41 and the core glass layer to be the core portion 30 are formed on the silicon wafer 10.

Then, the core glass layer is patterned by reactive ion etching to form a 1 × 8 branched core portion 30 (FIG. 6). The pitch of the cores at the 8-core end is 250 μm.

Next, as shown in FIG. 7, an upper clad layer 42 that covers the core portion 30 is formed. Specifically, a third glass fine particle layer to be the upper clad layer 42 is laminated on the lower clad layer 41 and the core portion 30 by the flame deposition method. This is B that is a dopant material for oxyhydrogen flame.
Br ₃ gas and POCl ₄ gas are sent together with SiCl ₄ and blown onto the upper surfaces of the core portion 30 and the lower cladding layer 41 using an oxyhydrogen flame burner. After that, this glass fine particle layer is heated in a sintering furnace and then gradually cooled to be a transparent vitrification, which becomes an upper clad layer 42. The upper clad layer 42 is combined with the lower clad layer 41 to form a clad layer 40 in which the core portion 30 is embedded.

From the upper surface of the core portion 30 to the upper clad layer 42
The thickness to the upper surface of is 30 μm. As a result, the waveguide layer 20 having a layer thickness of about 70 μm is formed on the silicon wafer 10.
And an optical waveguide 100 having an air bridge structure
The optical waveguide 200 which is the basis of the above is completed (FIG. 7).

Then, the optical waveguide 200 is etched to form the optical waveguide 100.

As shown in FIG. 8, thick film resist patterns 91 and 92 are formed on the upper surface of the upper clad layer 42 by a normal resist process. A resist pattern (waveguide portion pattern) 92 for forming the waveguide portion 50 is formed above the core portion 30. Openings 93 for forming the stress releasing grooves 60 are formed on the left and right sides of the waveguide pattern 92. The width of each of the openings 93 and the waveguide pattern 92 is about 50 μm (FIG. 8).

FIG. 9 is a diagram showing the planar shape of this resist pattern. The hatched areas in FIG. 9 indicate resist patterns 91 and 92.
Thus, the opening 93 is formed along the waveguide pattern 92. Considering the hatched region as the upper surface of the waveguide layer 20 and the white region as the stress releasing groove 60, the resist pattern of FIG. 9 has a planar shape of the optical waveguide of this embodiment. Equal (Figure 9).

Next, as shown in FIG. 10, the waveguide layer 20 below the opening 93 is selectively removed by reactive ion etching (RIE) using the resist patterns 91 and 92 as mask layers to remove the silicon wafer 10 from the silicon wafer 10. Expose the surface. The etching gas is C ₂ F ₆ , and the flow rate is 50 scc
m, and the atmospheric pressure is 5 Pa. Since this RIE is anisotropic etching, the removal of the waveguide layer 20 requires removal of the wafer 10.
Progresses almost perpendicular to the surface of. Thereby, the core portion 30
Grooves for stress release along the core portion 30 are formed in the cladding layers 40 on both sides of the core portion 30 and the waveguide portion 50 including the core portion 30 and the cladding portion 45 surrounding the core portion 30 is formed (FIG. 1).
0). The stress releasing groove 60 may be formed by etching as in the present embodiment, or may be formed by grinding the waveguide layer 20 by dicing.

Then, as shown in FIG. 11, the silicon wafer 10 is dipped in a KOH solution which is an etching solution to perform wet etching of silicon. KOH flows into the groove 60 formed by RIE, isotropically etches from the exposed surface of the wafer 10, and the wafer 10 under the waveguide portion 50 is removed. Wafer 10
The waveguide portion 50 is separated from the wafer 10 by the concave portion 70 formed in.

A portion other than the groove 60 is a resist pattern 91.
Since it is masked by and 92, the etching does not proceed. Since KOH has a sufficiently higher etching rate for Si than SiO ₂ , the waveguide layer 20 exposed on the side surface of the groove 60 is hardly removed. After etching is completed, the resist patterns 91 and 92 are removed (FIG. 11).

Thus, the optical waveguide 100 of this embodiment shown in FIGS. 1 and 3 is completed. Even if the resist patterns 91 and 92 are left, the optical waveguide can be sufficiently used in optical communication. However, since stress may be applied from the resist patterns 91 and 92, it is more preferable to remove it as in this embodiment.

The optical waveguide 1 of this embodiment produced in this way
00 is separated from the clad layer 40 excluding the band-shaped portion 46 by the stress releasing groove 60, so that the thermal expansion coefficient of silicon of the wafer (substrate) 10 and quartz glass of the waveguide layer 20 is 00. Wafer 10 due to the difference in
Through the upper clad layer 42 and the lower clad layer 41 on the side of the waveguide section 50, the film stress applied to the side surface of the core section is released. In addition, the waveguide section 50 includes the support section 80.
Since it is separated from the wafer 10 except for, the film stress applied to the upper and lower surfaces of the core portion 30 from the wafer 10 via the clad portion 45 of the waveguide portion 50 is also released. Therefore, as shown by the arrow in the waveguide section 50 of FIG. 12, the compressive stress applied to the core section 30 is significantly reduced, and the internal stress of the core section 30 is also significantly reduced. As a result, the influence of the internal stress of the core portion 30 on the guided light is also reduced, so that the optical waveguide 100 of this embodiment has a small polarization characteristic (PDL).

Example 2 FIG. 13 is a view showing the cross-sectional structure of the optical waveguide 110 of this example. The optical waveguide 110 is the same as the optical waveguide 100 of the first embodiment, except that the concave portion 70 and the groove 60 of the silicon wafer 10 are filled with the ultraviolet curable resin (reinforcing material) 95, and thereby the strength of the optical waveguide is increased. This optical waveguide 110 is the same as in the first embodiment.
After manufacturing 00, a gel-like ultraviolet curable resin 95 is flown in from the stress releasing groove 60 and irradiated with ultraviolet rays to be solidified. Since the waveguide portion 50 is once separated from the silicon wafer 10 and the cladding layer 40, the internal stress of the core portion 30 is released.
Even if the ultraviolet curable resin 95 is interposed between the both, the state in which the internal stress of the core portion 30 is sufficiently reduced is maintained.
Therefore, the optical waveguide 110 of this embodiment also has a small polarization characteristic. It should be noted that the concave portion 70 and the groove 60 are not limited to being filled with the ultraviolet curable resin 95, and other reinforcing materials such as infrared curable resin and solder can be used.

The present invention is not limited to the above embodiment, but various modifications can be made. For example, the effect of the present invention is obtained by separating the waveguide part from the substrate and the clad layer, so that any other structure may be used as long as this condition is satisfied. Therefore, the resist pattern used for forming the stress releasing groove 60 is not limited to that shown in FIG. 9, and various planar shapes are conceivable.

Although FIG. 14 shows an example of the resist pattern, the width of the opening 93 may not be uniform along the waveguide portion pattern 92 like this pattern. In the optical waveguide manufactured using the resist pattern of FIG. 14, most of the waveguide layer 20 was removed by forming the groove 60, so that the reinforcing material is introduced into the groove 60 as in the second embodiment. From the viewpoint of strength, it is preferable to solidify.

Further, an optical waveguide in which the waveguide layer 20 is formed on the silicon wafer 10 on which the oxide film (SiO ₂ ) is formed is prepared, and the optical waveguide of the present invention is manufactured by etching the optical waveguide. Of course, it is possible. In this case, the waveguide layer 20 and the oxide film are removed by RIE or the like to form the stress releasing groove 60, and the etching liquid is introduced into the exposed surface of the wafer 10 to expose the wafer 10 as in the first embodiment. If wet etching of 10 is performed, the wafer 10 as the substrate and the waveguide 50
It is possible to obtain the optical waveguide of the present invention in which and are separated.

Further, in the embodiment, the concave portion 70 is formed by etching the wafer 10 and the waveguide portion 50 is separated from the wafer 10. However, the lower portion of the clad portion 45 forming the waveguide portion 50 is selectively formed. It is also possible to separate by etching and removing.

In the embodiment, the silicon wafer 10 is isotropically etched to form the recess 70 and the waveguide portion 50 and the wafer 10 are separated, but the plane orientation of the wafer surface is selected. The waveguide portion 50 can be separated from the wafer even by anisotropic etching. For example, a silicon wafer 1 having a (100) surface
1, the groove 71 having a V-shaped cross section as shown in FIG.
Is formed on the wafer 11 to obtain an optical waveguide in which the waveguide section 50 is separated from the wafer 11.

[0043]

As described in detail above, in the optical waveguide of the present invention, the film stress applied to the side surface of the core portion is released by the groove formed in the cladding layer, and the waveguide portion is separated from the substrate. By doing so, the film stress applied to the upper and lower surfaces of the core portion is also released. As a result, the internal stress of the core portion is significantly reduced, so that an optical waveguide having small polarization characteristics can be realized.

Further, according to the method of manufacturing an optical waveguide of the present invention, a groove is formed in the cladding layer by the first etching to release the film stress applied to the side surface of the core portion, and the etching liquid is further added to the groove. And the second etching is performed to separate the substrate and the clad layer, leaving the portion supporting the core portion, and release the film stress applied to the upper and lower surfaces of the core portion. As a result, the internal stress of the core portion is significantly reduced, and the optical waveguide of the present invention having a small polarization characteristic can be obtained.

[Brief description of drawings]

FIG. 1 is an overall perspective view showing the structure of an optical waveguide 100 according to a first embodiment.

FIG. 2 is a partial cross-sectional perspective view showing an air bridge structure.

3 is a diagram showing a cross-sectional structure of the optical waveguide 100 taken along the line AA ′ in FIG.

4 is a diagram showing a cross-sectional structure of the optical waveguide 100 taken along the line BB ′ of FIG.

FIG. 5 is a side sectional view showing a waveguide section 50, a strip section 46, and a support section 80.

FIG. 6 is a first diagram showing a manufacturing process of the first embodiment.

FIG. 7 is a second diagram illustrating the manufacturing process of the first embodiment.

FIG. 8 is a third diagram illustrating the manufacturing process of the first embodiment.

FIG. 9 is a diagram showing a planar shape of a resist pattern.

FIG. 10 is a fourth diagram illustrating the manufacturing process of the first embodiment.

FIG. 11 is a fifth diagram illustrating the manufacturing process of the first embodiment.

FIG. 12 is a diagram showing internal stress of the core portion 30.

13 is a diagram showing a cross-sectional structure of an optical waveguide 110 of Example 2. FIG.

FIG. 14 is a plan view showing an example of a resist pattern.

FIG. 15 is a diagram showing a cross-sectional structure of an optical waveguide produced by anisotropically etching a silicon wafer 11.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Silicon wafer, 20 ... Waveguide layer, 30 ... Core part, 40 ... Clad layer, 45 ... Clad part, 46 ... Band part, 50 ... Waveguide part, 60 ... Stress release groove | channel, 70 ... Recessed part, 80 … Supporting part.

Claims (6)

[Claims] 1. An optical waveguide in which a waveguide layer composed of a core portion which is an optical waveguide portion and a core layer which is embedded and has a refractive index lower than that of the core portion is formed on a substrate, A groove is formed in the clad layer on both sides of the core part along the core part, and a waveguide part including the core part separated by the groove and the clad part covering the core part is separated from the substrate. An optical waveguide characterized in that 2. The optical waveguide according to claim 1, wherein the clad portion of the waveguide portion is in contact with the substrate at a part thereof. 3. The optical waveguide according to claim 1, wherein a reinforcing material is filled between the waveguide portion and the substrate and in the groove formed in the clad layer. 4. An optical waveguide in which a waveguide layer composed of a core portion which is an optical waveguide portion and a core layer which is embedded and has a refractive index lower than that of the core portion is formed on a substrate. A first step of preparing, a second step of forming grooves along the core portion in the cladding layers on both sides of the core portion by first etching, and the clad formed in the second step A third step of separating the substrate and the clad layer by leaving an area supporting the core portion by flowing an etching liquid into the groove of the layer and performing the second etching. Manufacturing method. 5. The method of manufacturing an optical waveguide according to claim 4, further comprising a step of injecting a reinforcing material into a groove formed in the cladding layer to solidify the reinforcing material, following the third step. . 6. The first step is a step of preparing an optical waveguide in which a waveguide layer made of glass containing quartz is formed on a silicon substrate, and the first etching is reactive ion etching. 5. The method of manufacturing an optical waveguide according to claim 4, wherein