JPH05188227A - Waveguide - Google Patents

Abstract

(57) [Abstract] [Purpose] To improve the moisture resistance of the waveguide. [Structure] A cladding layer 120b and a waveguide pattern 180 are formed on a Si substrate 110 (FIGS. 1A and 1B).
Then, a SiN (silicon nitride) film 220 having high moisture resistance is formed by plasma CVD to 3000 angstroms (FIG. 1C). Next, the cladding layer 120b of SiO ₂ having a refractive index lower than that of the core layer 150 is deposited by FHD or CVD and sintered to embed the waveguide pattern 180 (FIG. 1 (d)). After that, the SiN film 230 may be formed again by plasma CVD (FIG. 1E).
Thereby, a waveguide having the waveguide pattern 180 as a core is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide which is one of optical components in the field of communication information processing.

[0002]

2. Description of the Related Art As a method for producing a waveguide, there is "Optical No. 1".
Volume 8 No. 12 (1989.12) p.681 ”is generally used. A brief description of this method is as follows. A lower clad layer and a core waveguide layer are laminated on the substrate. Next, the core waveguide layer is etched so as to leave a predetermined pattern to process the waveguide pattern. Then, the upper clad layer is laminated to form a waveguide.

[0003]

It is considered that a waveguide is integrated with other optical components to form an optical IC. And combining this optical IC with an optical fiber,
Optical signal processing in optical communication is performed. Therefore, the light I
C will be installed together with the optical fiber in various fields such as outdoors, underwater and undersea. At this time, in an environment with a large amount of water, there is a high possibility that the OH groups of water molecules will penetrate into the inside of the optical IC and enter the core where the optical signal of the waveguide propagates. If the waveguide inside the optical IC deteriorates due to this,
The light for communication is absorbed by the OH group of the water molecule, and the attenuation of the optical signal increases. In addition, the mechanical strength will also decrease. As described above, in the above-mentioned waveguide, no countermeasure is taken in an environment with a large amount of water, which causes a serious problem in reliability. The waveguide is important as a basic technique of the optical IC, but it has a problem in moisture resistance as described above.

In view of the above problems, it is an object of the present invention to provide a waveguide having higher moisture resistance.

[0005]

In order to solve the above-mentioned problems, the waveguide of the present invention comprises a core, a clad having a refractive index smaller than that of the core, and a moisture-proof film (for example, SiN, etc.).

Further, a moisture resistant film may be further provided on the outside of the clad.

Alternatively, a silicon substrate is provided with a core and a lower clad layer and an upper clad layer having a smaller refractive index than that of the core with the core interposed therebetween, and a moisture resistant film is provided between the upper clad layer and the core. It may be characterized.

[0008]

In the waveguide of the present invention, the moisture resistant film is provided between the core and the clad (or the upper clad layer). Therefore, even in an environment with a large amount of water, the moisture resistant film prevents the water (OH group) from penetrating into the core. That is, the core through which the optical signal propagates is protected by the moisture resistant film,
Moisture resistance is improved.

When a moisture resistant film is further provided outside the clad, the clad is protected by this moisture resistant film, and the moisture resistance is further improved.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the outline of the steps of an embodiment of the method for producing a waveguide of the present invention. The process will be described with reference to this figure.

First, a clad layer 120a of SiO ₂ is deposited on a silicon substrate (Si substrate) 110 by a flame deposition method (FHD) or CVD and sintered, and then a clad layer 120a is provided with a predetermined impurity concentration by FHD. A core layer 150 of SiO ₂ having a higher refractive index than that of about 10 μm is formed (FIG. 1A). Next, a waveguide pattern 180 is formed by dry etching according to a predetermined pattern so as to leave that portion (FIG. 1B). And SiN (silicon nitride) with high moisture resistance is formed by plasma CVD.
The film 220 is formed to 3000 angstroms (see FIG. 1).
(C)). Here, since SiN has a relatively high refractive index, it is necessary to thin the SiN film 220 so that the waveguide pattern 180 functions as a core after fabrication. Also,
In order to have good moisture resistance, it is necessary to make the thickness sufficient to cover the waveguide pattern 180 without causing pinholes. The SiN film 220 is formed to a thickness that satisfies both of these.

Next, the core layer 1 is formed by FHD or CVD.
SiO ₂ clad layer 120 having a refractive index lower than 50
b is deposited and sintered to embed the waveguide pattern 180 (FIG. 1D). After that, S is again formed by plasma CVD.
The iN film 230 may be formed (FIG. 1E). Thereby, a waveguide having the waveguide pattern 180 as a core is formed.

The waveguide thus formed has a SiN film 220 which is a moisture resistant film provided between the core and the clad (FIGS. 1D and 1E). Therefore, the OH group of water that has permeated the clad is blocked by the SiN film 220 and prevented from permeating the core. Since the core is protected by the SiN film 220 as described above, deterioration of the core due to OH groups of water molecules is prevented, moisture resistance is improved, and life is extended and reliability is high. .. In addition, SiN is formed on the clad layer 120b.
In the waveguide having the film 230 (FIG. 1E), the clad is also protected by the moisture resistant film, and the OH group of water is less likely to enter the clad. Therefore, deterioration of mechanical strength due to OH group of water is prevented, moisture resistance is further improved, and long life and high reliability are obtained.

The present invention is not limited to the above-described embodiment, but can be variously modified.

For example, since the moisture resistant film can be formed by the process established in the current semiconductor process, the SiN film is used, but other materials may be used as long as they can form a clad. Further, there is a Si substrate below the core, which prevents the penetration of OH groups, but in order to further improve the moisture resistance, a moisture resistant film (SiN) is provided between FIGS. 1 (a) and 1 (b). The waveguide pattern 180 may be formed after it is provided so that the lower side of the core is also protected by the moisture resistant film. Further, the combination of the core and the clad may be another combination as long as there is a difference in refractive index so that it can operate as a waveguide.
Although silicon is used for the substrate, it is not limited to this.

[0016]

As described above, according to the waveguide of the present invention, the core through which an optical signal propagates is protected by the moisture resistant film, and the moisture resistance is improved. Therefore, deterioration of the core is suppressed even in an environment with a lot of water. It is possible to obtain a long life and high reliability.

When a moisture resistant film is further provided on the outside of the clad, the clad is also protected by this moisture resistant film to prevent deterioration of mechanical strength and improve the moisture resistance, so that the clad has a long life and high reliability. Can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic view of the process of the present invention.

[Explanation of symbols]

110 ... Si substrate, 120a, 120b ... Clad layer,
180 ... Waveguide pattern, 220, 230 ... SiN film.

Claims (3)

[Claims] 1. A waveguide comprising a core, a clad having a refractive index smaller than that of the core, and a moisture resistant film between the core and the clad. 2. The waveguide according to claim 1, further comprising a moisture resistant film outside the clad. 3. A silicon substrate having a core and a lower clad layer and an upper clad layer having a smaller refractive index than that of the core with the core sandwiched between the core and the moisture resistant layer between the upper clad layer and the core. A waveguide comprising a film.