JPH0777622A - Production of substrate type optical waveguide - Google Patents

Abstract

PURPOSE:To provide the process for production of the substrate type optical waveguide which has the high accuracy of pattern transfer at the time of production and lessens scattering loss of light. CONSTITUTION:A substrate 8 is subjected to etching, by which a projecting line part 10 is formed on its flat surface 8a and a clad material is laminated on the flat surface 8a and on the upper surface 10b of the projecting line part. A clad material layer 11b is formed on the flat surface 8a and a lower clad layer 11a is formed on the upper surface 10b of the projecting line part. A core material is then laminated on the clad material layer 11b and the lower clad layer 11a and a core material layer 12b is formed on the clad material layer 11b. An optical waveguide 12a is formed on the lower clad layer 11a and a clad material is laminated on the upper and side faces of the lower clad layer 11a and the optical waveguide layer 12a to form an upper clad layer 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a substrate type optical waveguide which is used for optical communication, an optical information processing system and the like and can reduce the scattering loss of light.

[0002]

2. Description of the Related Art In recent years, in the fields of optical communication systems, optical information processing systems, etc., demands for higher speed and smaller size of the systems are increasing, and optical devices, optical components, etc. constituting these systems are being used. On the other hand, demands for higher speed, smaller size, and higher reliability are increasing. A substrate type optical waveguide is one of these optical devices.

The substrate type optical waveguide is one in which an optical waveguide layer (core layer) is formed on a silicon (Si) substrate, and this optical waveguide layer is embedded with a clad layer. The optical waveguide layer is made of silica (SiO2) glass having a high refractive index, and the cladding layer is made of silica glass having a lower refractive index than that of the optical waveguide layer. It has become so. In addition, this substrate-type optical waveguide has excellent compatibility with a silica-based optical fiber that is widely used in optical communication systems, and has low loss.
It also has various features such as high reliability and small size.

The substrate type optical waveguide is manufactured, for example, by the method shown in FIG. First, as shown in FIG. 2A, a glass film for core (core material) 2 is formed on a substrate 1. Next, the sample obtained in (a) is heat-treated at a high temperature to form a dense film. Then, as shown in FIG. 2B, WSix
The film 3 is formed. This WSix film 3 is used because it cannot be used as a mask only by the photoresist when the thick glass film for core 2 is etched in the next step. Next, a photoresist 4 is applied on the WSix film 3 and is patterned by photolithography as shown in FIG. 2 (c). After that, as shown in FIG. 2D, the WSix film 3 is patterned by dry etching using the photoresist film 4 as a mask. Next, as shown in FIG. 2E, the core glass film 2 is patterned by dry etching using the photoresist film 4 and the WSix film 3 as a mask. Then, as shown in FIG. 2F, the photoresist film 4 and the WSi
x The film 3 is removed and the core glass film 2 is used as an optical waveguide layer,
Finally, as shown in FIG. 2 (g), the cladding layer 5 is formed above the cladding layer 5 to complete the manufacture of the substrate type optical waveguide 6.

[0005]

However, in the substrate type optical waveguide according to the conventional manufacturing method, there is no problem when the thickness of the optical waveguide layer is relatively small, but when the thickness is large, There was such a problem. That is, in the step of FIG. 2E for patterning the glass film for core 2 by dry etching, the etching selectivity between the glass film for core 2 and the photoresist film 4 or the WSix film 3 cannot be made large, so that the etching gas As a result, the photoresist film 4 and the WSix film 3 are gradually etched, and the photoresist film 4 and the WSix film 3 which should be the mask are removed by the time the etching of the thick core glass film 2 is completed. The surface of the glass film for core 2 underlying the WSix film 3 is also etched, and in extreme cases, the film thickness of the glass film for core 2 is reduced, or the surface of the glass film for core 2 is roughened to complete the process. There has been a problem that the scattering loss of the optical waveguide increases.

Therefore, in order to solve the above problem, W
A method of increasing the thickness of the Six film 3 has been considered, but when this method is used, the substrate 1 warps due to thermal stress due to the difference in expansion coefficient during film formation, and the resolution deteriorates during patterning by photolithography. As a result, there arises a problem that the pattern transfer accuracy is lowered. Further, as another method, a method of increasing the film thickness of the photoresist film 4 has been considered, but also in this case, there arises a problem that the pattern transfer accuracy is lowered during patterning by photolithography.

The present invention has been made in order to solve the above problems, and an object of the present invention is to provide a method of manufacturing a substrate type optical waveguide having a high pattern transfer accuracy and a small light scattering loss.

[0008]

In order to achieve the above-mentioned object, a method of manufacturing a substrate type optical waveguide according to the present invention comprises a step of etching a top surface of a substrate to form a ridge having a substantially rectangular cross section on a flat surface. A clad material is formed on the flat surface and the upper surface of the ridge, a clad material layer is formed on the flat surface, and a lower clad layer is formed on the upper surface of the ridge. A core material is laminated on the clad material layer and the lower clad layer to form a core material layer on the clad material layer, and an optical waveguide layer is formed on the lower clad layer; The upper cladding layer is formed by laminating a clad material above and on the side of the optical waveguide layer.

[0009]

According to the method of manufacturing the substrate type optical waveguide of the present invention, after the substrate is etched to form the ridges, the clad material, core material and clad material are not subjected to patterning processing such as etching. Since the optical waveguide layer whose periphery is covered with the upper clad layer and the lower clad layer is formed only by sequentially stacking the materials, the optical waveguide layer having a smooth surface is formed.

[0010]

EXAMPLE Next, an example of a method of manufacturing a substrate type optical waveguide according to the present invention will be described with reference to FIG. FIG. 1 is a diagram showing a manufacturing process of the substrate type optical waveguide 7 in this embodiment. First, after coating the photoresist 9 on the silicon substrate 8, the photoresist 9 is patterned by photolithography as shown in FIG. The pattern width of the photoresist 9 is 8 μm.

Next, using this photoresist film 9 as a mask, dry etching with an etching amount of 43 μm is carried out using a gas such as CF 4 / O 2 or C 2 F 6. Then, after the etching is completed, as shown in FIG.
A ridge 1 having a rectangular cross section with a width of 8 μm and a height of 43 μm.
0 is formed. In this dry etching, side etching is as small as possible, that is, highly anisotropic, for example, reactive ion etching (RIE).
Etching is performed under appropriate conditions by using a method such as the above, and the side wall surface 10a of the protrusion 10 is as flat as possible.
It is made to stand upright with respect to a.

Next, after removing the photoresist 9,
The clad layer, the core layer, and the clad layer are formed in this order on the substrate. First, as the clad material, quartz glass to which phosphorus (P), boron (B) or the like has been added in order to control the softening temperature and the refractive index is used, and this is deposited on the substrate 8 by the flame deposition method (hereinafter referred to as the FHD method). To form a film. When performing this FHD method, compared with the FHD method in the normal film formation,
A low-refractive-index quartz glass layer having a thickness of 35 μm is formed by setting the substrate temperature to be low while allowing the fine-particle quartz soot, which is the base of the quartz glass, to be deposited on the substrate 8 from a high position. When the film is formed under such conditions,
As shown in (c), no film is formed on the side wall surface 10a of the ridge 10, and the clad layer (low-refractive-index quartz glass layer) 11a is formed only on the ridge upper surface 10b and the flat surface 8a. 11
b is formed.

Next, as the core material, silica glass added with germanium (Ge), titanium (Ti) or the like in order to have a higher refractive index than that of the clad material is used, and this is FHD
By the method, a film is continuously formed on the sample shown in FIG. Also in this case, as in the above step, as shown in FIG. 1D, the film is not formed on the side wall surface 10a of the ridge portion 10 but only on the ridge portion upper surface portion 10b and the flat surface portion 8a. Under such conditions, the core layers (quartz glass layers with high refractive index) 12a and 12b having a thickness of 8 μm are formed.

Next, as the clad material, quartz glass having the same composition as the clad material is used, and this is continuously deposited on the sample shown in FIG. 1 (d) by the FHD method.
In this step, unlike the above two film forming steps,
As shown in (e), the conditions for producing quartz soot or various conditions such as the substrate temperature are readjusted so that the deposition reaction of quartz soot also occurs on the side wall surface 10a of the protrusion 10.
A clad layer (a low-refractive-index quartz glass layer) 13 having a thickness of 85 μm is formed so as to cover the ridge 10 and the clad layer 11a and the core layer 12a above the ridge. Finally, the entire substrate is kept at a high temperature, and the laminated quartz glass layers are sintered to make each quartz glass layer transparent, and the production of the substrate type optical waveguide 7 is completed.

In the substrate type optical waveguide 7 shown in FIG. 1 (e) manufactured through the above steps, the clad layer 11a above the ridge 10 is a lower clad layer having a thickness of 35 μm.
The core layer 12a above the protrusion 10 is a square optical waveguide layer having a cross section of 8 × 8 μm.
a, the cladding layer 1 above and on the side of the optical waveguide layer 12a
3 is an upper clad layer having a thickness of 85 μm, and an optical waveguide 12a whose periphery is covered with the upper and lower clad layers 11a and 13 is formed. On the other hand, since the clad material layer 11b having a thickness of 35 μm and the core material layer 12b having a thickness of 8 μm are formed on the flat surface 8a of the substrate 8 as well, the core material layer 12b having a high refractive index is provided on the portion other than the optical waveguide 12a. However, the core material layer 12b has a smaller film thickness than the upper, lower clad layers 11a and 13 or the clad material layer 11b, and does not affect the propagation characteristics as an optical waveguide.

In this embodiment, after the substrate 8 is first etched to form the ridges 10, the clad layer, the core layer, and the clad layer are sequentially and continuously formed to form the substrate mold. The optical waveguide 7 can be manufactured. That is, after forming the core layer or the clad layer, it is not necessary to perform etching processing on these layers to perform patterning. Therefore, unlike the conventional manufacturing method in which the core layer is formed and then patterned, the defect that the core layer is not etched and the surface of the core layer is roughened at the time of etching does not occur, and the optical waveguide layer 1
A smooth interface between 2a and the upper and lower clad layers 11a and 13 is formed, so that a substrate type optical waveguide with less light scattering loss can be manufactured.

Since patterning is performed directly on the surface of the substrate 8, for example, a glass film for core,
Like the conventional manufacturing method in which patterning is performed after forming a WSix film or the like, the stress caused by the difference in the coefficient of thermal expansion of each film causes the substrate to warp, so that there is no problem that accurate patterning cannot occur The transfer accuracy can be improved.

Further, since the mask for patterning only needs one photoresist layer, the clad layer and the core layer can be continuously formed in the film forming step, and the manufacturing process can be simplified in various steps. The manufacturing cost of the mold optical waveguide can be reduced.

Although a silicon substrate is used as the substrate 8 in this embodiment, a substrate such as a quartz substrate or a sapphire substrate may be used instead. Also, the substrate 8
Although dry etching was used as a method for etching the film, wet etching using mixed nitric acid such as hydrofluoric acid-nitric acid can also be applied. However, even in that case, as described above, it is preferable to set various conditions so that the etching is as highly anisotropic as possible. Further, the specific amount such as the etching amount of the substrate 8 or the film thickness of the core layer and the clad layer in this embodiment is not limited to this, and various settings can be made.

[0020]

As described above in detail, in the method of manufacturing a substrate type optical waveguide according to the present invention, after the substrate is etched to form the ridges, the clad layer, the core layer and the clad layer are formed. Since the substrate type optical waveguide can be manufactured without patterning by sequentially forming the film, the core layer is also etched during the etching after the core layer is formed. It is possible to manufacture a substrate-type optical waveguide with less scattering loss of light without causing problems. Further, since the upper surface of the substrate is patterned, the pattern transfer accuracy can be improved without causing the substrate to warp due to the influence of the stress of various films.

[Brief description of drawings]

FIG. 1 is a diagram showing each manufacturing step in one embodiment of a method for manufacturing a substrate type optical waveguide according to the present invention.

FIG. 2 shows a conventional method for manufacturing a substrate-type optical waveguide,
It is a figure which shows each manufacturing process.

[Explanation of symbols]

7 ... Substrate type optical waveguide, 8 ... Substrate, 10 ...
... upper surface of protrusion, 11a ... lower clad layer, 11b ... clad material layer, 12a ... optical waveguide layer, 12b ... core material layer, 1
3 ... Upper clad layer

Front page continued (72) Kensuke Shima Shima 1440 Rokuzaki, Sakura City, Chiba Prefecture Fujikura Sakura Plant, Ltd. (72) Inventor Takuya Iku, 1440 Rokuzaki, Sakura City, Chiba Prefecture Fujikura Sakura Plant, Ltd.

Claims (1)

[Claims] 1. An etching process is applied to an upper surface of a substrate to form a ridge having a substantially square cross section on a flat surface, and a clad material is laminated on the flat surface and the ridge. A clad material layer is formed on a flat surface, a lower clad layer is formed on the upper surface of the ridge, and a core material is laminated on the clad material layer and the lower clad layer, and the clad material layer is formed on the clad material layer. Forming a core material layer, forming an optical waveguide layer on the lower clad layer, and laminating a clad material above and below the lower clad layer and the optical waveguide layer to form an upper clad layer. And a method for manufacturing a substrate type optical waveguide.