JPH0313907A - Production of substrate type optical waveguide - Google Patents

Abstract

PURPOSE:To lower the propagation loss of the optical waveguide by thermally oxidizing an Si substrate to form an SiO2 layer and forming a metal to increase the refractive index of the SiO2 layer on the SiO2 layer to a prescribed shape and then thermally diffusing this metal in an oxidation atmosphere. CONSTITUTION:The Si substrate 11 is thermally oxidized for 35 hours at 1,100 deg.C by using a hydrogen combustion method or the like to form the SiO2 layer 17 having 4mum film thickness. Ti is deposited at 200Angstrom thickness by sputtering, etc., as the metal 6 to increase the refractive index of the SiO2 layer 17 on the SiO2 layer 17. This metal 6 is patterned to a stripe shape by photolithography and the SiO2 layer 18 is deposited by sputtering therein. These layers are subjected again to the thermal oxidation and thermal diffusion for 72 hours at 1,100 deg.C by using the hydrogen combustion method, etc., to simultaneously form an SiO2 clad layer 19 and the optical waveguide 20. The generation of roughening by etching on the side faces of the optical waveguide is obviated in this way and, therefore, the propagation loss is lowered.

Description

[Detailed Description of the Invention] U Industrial Field of Application This invention relates to the fields of optical communications and optical information processing, and is a method for manufacturing a substrate-type optical waveguide suitable for use in optical multiplexers/demultiplexers, optical multiplexers/branchers, etc. Regarding.

"Conventional technology J Conventionally, substrate-type optical waveguides include ■Glass optical waveguide formed by ion exchange.

■L forming optical waveguide by Ti diffusion or proton exchange
iNbO5 optical waveguide.

■CVD (Chemistry) on fused silica or Si substrate
c-al Vapor Deposition) method.

■ 5iOtTi formed by sputtering on a Si substrate
O! optical waveguide.

and so on.

In the above-mentioned glass optical waveguide (2), as shown in Fig. 2, ions 2 such as Na'' are diffused into a glass substrate 1 made of fused silica (SiOt) by electric field ion exchange, etc., and the ions originally contained in the glass substrate 1 are 3 to ion 2 (Na
), the refractive index is controlled by replacing the optical waveguide 4 with
form.

Next, in the L iN bo 3 optical waveguide by Ti diffusion (2), after patterning a metal 6 such as Ti (titanium) on the L i N bo substrate 5 in a stripe shape (the third
The metal 6 is thermally diffused to form an optical waveguide 7 with a high refractive index (see FIG. 3(c)). Moreover, LiNb0. In the optical waveguide, L
A drive-shaped negative pattern is created on the iNbos substrate 5 using a metal film resist 8 (see FIG. 4(a)). Then, this LiNbO3 substrate 5 is immersed in a benzoic acid (C, H, Cool) solution 9, and Li0
and H6 in the LiNbO5 substrate 5.
An optical waveguide 10 having a high refractive index of xL l +-xN bo 3 is formed (see FIG. 4(b)).

Next, SiO
In the 2-Tilt optical waveguide, the fused silica or Si substrate 1
A SiOx lower cladding layer 12, a SiOt-Tio optical waveguide layer 13, and a SiOx upper cladding layer 14 are sequentially formed on 1 by CVD or sputtering (see FIGS. 5(a) and 5(b)). Resist on this! 5 to create a striped positive pattern (see FIG. 5(c)). Then, RYE (reactive ion etching) was performed to make the optical waveguide layer 13 three-dimensional.
After etching both ends to form the optical waveguide 13a (see FIG. 5(d)), the resist 15 is removed (
(See Figure 5(e)).

"Problems to be Solved by the Invention" By the way, the above-mentioned glass optical waveguide (■) and L (■)
Since the iN bOs optical waveguide does not use St as a substrate, it is difficult to provide a guide groove on the substrate for connecting optical fibers, and it is also difficult to integrate electronic devices such as photodetectors on the same substrate. The problem arises that it is difficult. Furthermore, in the case of the Ti-diffused optical waveguide described in (2), the length-to-width ratio of the resulting optical waveguide increases;
A problem arises in that splice loss increases when optical fibers with a lateral ratio of 1:I are spliced.

In addition, for the Sin and -Tilt optical waveguides created on the Si substrates shown in (1) and (2) by CVD and sputtering, the SiOx cladding layer and the SiOx Ti1t optical waveguide layer are etched over several microns in order to make them three-dimensional. There is a need. As a result of this etching, the side surfaces of the optical waveguide are roughened, resulting in increased optical loss, and when RIE is used as the etching, there arises the problem that etching takes a long time and is poor in mass productivity.

This invention was made in view of the above-mentioned problems, and is a substrate type that can reduce connection loss with optical fibers, is excellent in mass production, and can create a low-loss optical waveguide. A method for manufacturing an optical waveguide can be provided.

"Means for Solving the Problem" In order to solve such problems, in the invention according to claim 1, a SiO2 layer is formed by thermally oxidizing a Si substrate, and the 5iO9 layer is formed on the SiOx layer. A metal that increases the refractive index of the layer is formed into a predetermined shape, and SiOx
The invention according to claim 2, characterized in that after depositing the layer, SiO, a cladding layer, and a high refractive index optical waveguide are simultaneously formed by thermally diffusing the metal in an oxidizing atmosphere. The invention is characterized in that a metal oxide is used as the metal.

"Operation" First, a SiOx layer is formed by thermally oxidizing the Si substrate 11, and a metal or metal oxide that increases the refractive index of the SiO2 layer is formed in a predetermined shape on the SiOx layer. Deposit a Si0g layer on top. and,
By thermally diffusing the metal or metal oxide in an oxidizing atmosphere, SiO! A cladding layer and a high refractive index optical waveguide are formed simultaneously.

"Embodiments" Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a process diagram showing a method for manufacturing a substrate type optical waveguide according to an embodiment of the present invention. First, as shown in FIG. 1(a), the S, i substrate 11 is heated using a hydrogen combustion method.
By thermal oxidation at 100℃ for 35 hours, the film thickness was reduced to 4μm.
Form a layer 17 of Sin. Next, by sputtering or the like on the Sign layer 17, Ti is deposited to a thickness of 200 as a metal 6 that makes the SiOx layer 17 have a high refractive index (see FIG. 1(b)). Then, this metal 6 is patterned into stripes having a width of 6 μm by photolithography, and a 5iOy layer 18 having a thickness of 2 μm is deposited thereon by sputtering (see FIG. 1(C)). This was thermally oxidized and thermally diffused again at 1100°C for 7 hours using a hydrogen combustion method, etc., to form SiO, a cladding layer 19, and a high refractive index optical waveguide 20 at the same time (Fig. 1(d)
)reference).

The optical waveguide 20 obtained by such a manufacturing method had a width of about 8 μm and a thickness of about 4 μm. Furthermore, the metal (Ti) 2 atoms that make the 5iOz cladding layer 19 have a high refractive index are
As a result of Auger electron spectroscopy, it was found that there was a Gaussian distribution in the depth direction of the optical waveguide 20, and that it was also present on the substrate surface. Further, the propagation loss of this optical waveguide 20 was 0.3 dB/cm.

Note that the metal 6 forming the above-mentioned high refractive index optical waveguide 20
Examples include transition metals other than Ti such as Ni and Cu, or Tiot, Geot, and Bto3. A
Metal oxides such as lto, 3 and the like may be used.

"Effects of the Invention" As explained above, according to the present invention, the 5iOt cladding layer is a high-quality 5ins film formed by thermal oxidation, so it is possible to reduce the propagation loss of the optical waveguide. Since the 5iOz cladding layer and the optical waveguide are formed using this method, it is excellent in mass production, and since the side surfaces of the optical waveguide are not roughened due to etching, propagation loss can be reduced. Furthermore, the refractive index of the optical waveguide according to the present invention is lower than that of the L iN bos optical waveguide and is close to the refractive index of the optical fiber, so that connection loss with the optical fiber can be reduced, and the thermal diffusion process In this case, since the metal serving as the diffusion source is diffused into the upper and lower 5iOz layers, the aspect ratio of the optical waveguide becomes smaller, so that an advantage is obtained that connection loss with the optical fiber can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a process diagram showing a method for manufacturing a substrate type optical waveguide according to an embodiment of the present invention, and FIGS. 2 and 3 show methods for manufacturing a glass optical waveguide and an L r N bo 3 optical waveguide, respectively. The process diagram, Figure 4, is L by the proton exchange method.
A process diagram showing the method for manufacturing an iNbO3 optical waveguide, FIG.
FIG. 2 is a process diagram showing a method for manufacturing an optical waveguide. Fig. 1 6...Metal, 11...Si substrate, l
7, 18...Sin, layer, 19...5
ins cladding layer, 20... optical waveguide.

Claims (2)

[Claims] (1) A SiO_2 layer is formed by thermally oxidizing the Si substrate, a metal that increases the refractive index of the SiO_2 layer is formed in a predetermined shape on the SiO_2 layer, and a SiO_2 layer is formed on the SiO_2 layer.
A method for manufacturing a substrate type optical waveguide, characterized in that after depositing an O_2 layer, a SiO_2 cladding layer and a high refractive index optical waveguide are simultaneously formed by thermally diffusing the metal in an oxidizing atmosphere. (2) The method for manufacturing a substrate-type optical waveguide according to claim 1, wherein a metal oxide is used as the metal.