JPH01196006A - Quartz optical waveguide film - Google Patents

Abstract

PURPOSE:To obtain a low-loss optical waveguide film which has no blur by forming a quartz glass film on a sapphire substrate across a silicon film. CONSTITUTION:The silicon film 32 which has good adhesive strength to quartz glass is formed on the sapphire substrate 31 having high temperature resistance and the quartz glass optical waveguide film is formed on this silicon film 32. This sapphire substrate 31 has either an R nor a C surface. When the sapphire substrate 31 has the R surface, a crystal silicon film with a surface azimuth (100) as the silicon film 32 is matched well. The silicon layer is not limited to the crystal silicon film and a polycrystal or amorphous silicon film is also usable. Consequently, the problems of a blur and the deformation of the substrate are solved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a silica-based optical waveguide film that is a starting material for a silica-based optical waveguide that is a component of a waveguide type optical component.

[Conventional technology]

Conventionally, silica-based optical waveguides have been formed on quartz glass substrates or silicon substrates. FIG. 6 is a cross-sectional view illustrating the manufacturing process of this silica-based optical waveguide. In FIG. 6, 1 is a silicon substrate or quartz glass substrate, 2a
is a glass fine particle layer for buffer, 2b is a buffer layer, 3a is
3b is a core layer, 3c is a core path, and 4 is a grid layer glass. The steps are as follows: (a) A buffer glass fine particle layer 2a and a core glass fine particle layer 3a are sequentially formed on the substrate 1 by a flame hydrolysis reaction of a glass forming raw material gas containing 5iCQ4 (silicon tetrachloride) as a main component. (b) These glass fine particle layers are heated and made transparent together with the substrate in an electric furnace to form a buffer layer 2b.
, a quartz-based optical waveguide film consisting of a core layer 3b, and then (c)
Unnecessary portions of the core layer 3b are removed by reactive ion etching to form a rich core path 3c, and then (d
) A cladding layer glass 4 having a refractive index difference equivalent to that of the buffer layer is deposited to cover the core path 3c.

Through the above process, it is possible to obtain a silica-based optical waveguide with a relatively low loss on the order of 0.1 dB/cM, but there is a problem that a slight "cloudiness" remains in the silica-based optical waveguide film after it is heated and made transparent. However, in order to obtain a completely transparent quartz-based optical waveguide film, it was necessary to set the final temperature reached at the time of heating and transparency to a sufficiently high temperature. However, at a temperature of 1400° C. or higher, a problem occurred in that the substrate deformed. Therefore, it has been proposed to use a sapphire substrate that can withstand high temperatures in place of the silicon substrate or the quartz glass substrate (see Japanese Patent Application No. 62-83039).

[Problem to be solved by the invention]

According to the proposed technique, the heating transparency temperature can be set to 1400° C. or higher, and a completely transparent silica-based glass film without "fogging" can be obtained without deforming the substrate.

However, with such a quartz-based optical waveguide film on a sapphire substrate, there is a problem that the optical waveguide film often "peels off" from the sapphire substrate when processing the optical waveguide film to fabricate a waveguide type optical component. occurred.

This is thought to be because the silica-based glass optical waveguide film receives strong stress from the sapphire substrate due to the difference in thermal expansion coefficient, and the adhesion between the optical waveguide film and the substrate is lost to this stress. .

The purpose of the present invention is to solve the above-mentioned problems of the prior art, and to provide a high-quality product that is free from clouding, deformation of the substrate, warping, and peeling of the optical waveguide film from the substrate. The object of the present invention is to provide a silica glass-based optical waveguide film with good reproducibility.

[Means to solve the problem]

The above purpose is to create a structure in which a silicon (Si) crystal thin film or amorphous thin film is interposed between a sapphire (AQzoi) substrate and a silica glass (SiO2) based optical waveguide film formed on this substrate. This is achieved by:

That is, the essence of the present invention is to adopt a configuration of a sapphire substrate, a silicon film, and a silica glass optical waveguide film, and the conventional technology in which a silica glass optical waveguide film is directly formed on a sapphire substrate is as follows. They have different basic configurations.

[Effect]

By forming a silicon film with good adhesion to quartz glass on a sapphire substrate that can withstand high temperatures, and forming a quartz glass optical waveguide film on this silicon film, we are able to overcome the conventional method using a silicon substrate. The problems of "fogging" and deformation of the substrate "warping" in the technology and the problem of r-peeling in the proposed prior art using a sapphire substrate are solved.

FIG. 1 is a sectional view showing the basic structure of the silica-based optical waveguide film of the present invention, and FIG. 2 is a sectional view of the silica-based optical waveguide film proposed in the aforementioned Japanese Patent Application No. 83039/1983. In Figures 1 and 2, ii, 21 is a sapphire substrate, 12.22
is a buffer layer, 13.23 is a core layer, and 14 is a silicon layer. It is easy to fabricate a leading waveguide from the glass film shown in FIG. 1 by using steps similar to those shown in FIG. 61 (c) and (d). T in the first @ indicates the thickness of the silicon layer 14. Although the film thickness T is typically between 0.1 and 1, the present invention is effective even outside this range.

〔Example〕

(1) An embodiment of the present invention will be explained with reference to FIGS. 3 and 4. FIG. 3 is a cross-sectional view of an embodiment of the silica-based optical waveguide film (for single mode) according to the present invention, where 31 is a sapphire substrate;
32 is a silicon film, 33 is a quartz-based glass buffer layer, 3
14 is a quartz-based glass core layer, and symbol T is the thickness of the silicon film 32. The diameter of the sapphire substrate 31 is 7
5mm, thickness is 0.5mm, 10 sides even on rR surface.
But that's fine. The thickness of the buffer layer 33 is 20/71I+, and the thickness of the core layer 34 is 8#ll. When the sapphire substrate 31 is "R-plane", the silicon film 32 has a plane orientation (100).
crystalline silicon films are well matched.

The thickness T of the silicon film 32 is 0.6I! It is m. The silicon layer is not limited to a crystalline silicon film, and polycrystalline or amorphous silicon films can also be used.

The core layer 34 contains Ti02 as a dopant for controlling the refractive index.
(Titanium dioxide) is added (Gem, (germanium oxide) can also be used as a dopant), and the relative refractive index difference Δ between the core and cladding is adjusted to Δ=0.25%.The buffer layer 33 and The core layer 34 was formed by transparently vitrifying the deposited glass fine particle film at a temperature of 1500° C. by the method described below.Sapphire substrate 3
In the case of a crystalline silicon film, the silicon film 32 is formed on the silicon film 1 by CVD (Chemical Vapor Depo
(Chemical vapor deposition) method [Reference: Journal of Crystal Growth (J, of
Crystal Growth), 59 (1982)
, 485-498), and in the case of a polycrystalline or amorphous silicon film, a sputtering method was used.

FIG. 4 is a schematic diagram of a glass particle deposition apparatus for producing the silica-based optical waveguide film shown in FIG. 3. Fourth
In the figure, 41 is a turntable, 42 is a sapphire substrate having a crystalline silicon film (part 31.32 in FIG. 3), 43 is a table driving device, 44 is a glass particle synthesis torch, 45 is a torch driving device, 46 is a raw material gas supply device, 47 is an exhaust pipe, 48 is an exhaust gas treatment device, 49
is the central processing unit. The operating procedure of the device is as follows. 5iC from the raw material gas supply device 46 to the synthesis torch 44
j1. Synthesize glass fine particles containing Sin as a main component by a flame hydrolysis reaction of the frit gas in an acid/hydrogen flame at the tip of a torch by supplying a frit gas containing as a main component, oxygen, and hydrogen gas, This material is deposited on a silicon film-coated sapphire substrate 42 placed on a turntable 41. During this deposition period, a dopant for controlling the refractive index (TiO2 or GeCΩ4) in the glass forming raw material gas is added.
By changing the concentration of , the buffer layer and the core layer can be formed separately.

Hereinafter, specific manufacturing conditions will be described. First, a buffer layer was deposited under the following conditions by arranging a plurality of sapphire substrates with silicon films each having a diameter of 75 mm on a turntable having an effective diameter of 1 m.

Table rotation speed 10 rpm Torch movement speed 30 (21/min Raw material gas supply rate SiCQ, 100 cc/min BCQ, 5
cc/min PCQ, 5cc/min deposition time 50 minutes, and for another 20 minutes, TiCQ4 was added to the source gas as a dopant for controlling the refractive index at a rate of lcc/min (5 cc/min in case of GeCΩ4). A core layer was deposited.

The thus deposited glass particle film was put into an electric furnace together with the substrate, the furnace temperature was raised to 1500°C at a rate of 500°C/hour, and the film was held at 1500°C for 1 hour to obtain transparent vitrification. Thereafter, the silica-based optical waveguide film shown in FIG. 3 was obtained by cooling in a furnace to around room temperature.

The silica glass-based optical waveguide film fabricated on the sapphire substrate with a silicon film interposed in the above manner is extremely transparent with no "cloudiness", and no "peeling" of the glass film is observed at all. A high quality silica glass optical waveguide film with good reproducibility was obtained.

In this example, the reason why an extremely transparent glass film was obtained was that there was no deformation of the substrate even when the maximum temperature reached at the time of transparent vitrification was 1500°C (at least 1400°C or higher). The problem of peeling was solved because of the good adhesion between the quartz glass film and the silicon film, and between the silicon film and the sapphire substrate. In fact, the (100) plane of silicon crystal and the (01) plane of sapphire
12) The lattice constants of the planes are well matched, and bonds (adhesion) at the atomic level are formed. On the other hand, since the quartz glass film and the silicon film are also based on the same Si element, they have good adhesion.

(2) In implementing the present invention, a point to be noted is the change in the thickness of the silicon film. That is, when the deposited glass fine particle film is made transparent at high temperature, the composition of the oxygen gas and glass fine particles in the transparent vitrification atmosphere? A certain Sin,,B,
03. Due to the diffusion of oxygen atoms from P, O, TiO2, etc., a part of the silicon film is oxidized to become Sin. Figure 5 shows the oxidation time and the oxidation to Sio. These are the experimental results obtained by determining the relationship between the film thickness and the film thickness using temperature as a parameter. This is a case where a (100) plane of crystalline silicon is used as the silicon film. From Figure 5, when the initial film thickness is 0.1μ, it is 1500°C.

The crystalline silicon film disappears after one hour of transparent vitrification. However, after transparent vitrification in this way,
Even when the silicon film disappeared, no "peeling" was observed, indicating that the use of the silicon film was effective in improving adhesion. This is considered to be because the bond between the silicon film and the sapphire film at the atomic level also effectively acts as a SiO□ converter.

(3) By implementing the present invention, further improvement in dimensional accuracy in optical waveguide formation has been realized. That is, in the photolithography process (ultraviolet exposure) during the formation of the optical waveguide shown in FIG. As a result, the core passage 3c shown in FIG. 6 could be manufactured with high dimensional accuracy. This was an improvement resulting from implementation of the present invention over initial expectations.

〔Effect of the invention〕

According to the present invention, since a silica-based glass film is fabricated on a sapphire substrate with a silicon film interposed therebetween, the final temperature reached at the time of transparent vitrification can be 1400°C or higher, resulting in an extremely low temperature without "fogging". It has the advantage of being able to produce a lossy quartz-based optical waveguide film, solving the problem of peeling, and stably producing a high-quality optical waveguide film. Furthermore, in the photolithography process for forming the optical waveguide, reflected light from the bottom surface of the sapphire substrate can be blocked by the silicon film, which has the advantage of improving the dimensional accuracy of the optical circuit. Furthermore, according to the present invention, there is an advantage that it is easy to realize a low loss in a leading waveguide having a particularly large relative refractive index difference between the core and the cladding, and therefore, there is also an advantage that the dimensions of the entire optical circuit can be reduced. . In addition, the silica-based optical waveguide film of the present invention does not "peel off" from the substrate despite strong stress from the sapphire substrate, so it can be used as a waveguide for polarization control that utilizes stress birefringence induced in the optical waveguide by stress. There is an advantage that the optical waveguide film of the present invention can also be utilized in the configuration of optical components.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view showing the basic structure of the silica-based optical waveguide film of the present invention, Fig. 2 is a cross-sectional view of a silica-based optical waveguide film proposed in the prior art shown for comparison, and Fig. 3 is a cross-sectional view of the invention. FIG. 4 is a schematic diagram of the glass deposition apparatus for the embodiment. FIG. 5 is an actual measurement diagram of the relationship between oxidation time and oxide film thickness. FIG. 2 is a diagram illustrating a manufacturing process of a conventional quartz-based optical waveguide. Explanation of symbols 11, 21... Sapphire substrate 12, 22... Buffer layer 13, 23... Core layer 14... Silicon layer 31... Sapphire substrate 32... Silicon film 33... Quartz Based glass buffer layer 34...Quartz based glass core layer 42...Sapphire substrate 44 having a crystalline silicon film
... Glass particle synthesis torch 45 ... Torch drive device 46 ... Raw material gas supply device 48 ... Exhaust gas treatment device 49 ... Central control device, patent applicant Nippon Telegraph and Telephone Corporation agent patent attorney
Junnosuke Nakamura Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5 Image quality 4ji Ryogokaku (-1Nυ Fig. 6 〉Base body (also quartz sword, fake upper head 2b 2b - 1 + 3b --- core 1 b 3C-11 lower Y each 4・-crat'/h"ys, 2b, j

Claims (1)

[Claims] 1. In a silica-based optical waveguide film that is a constituent material of a silica-based optical waveguide, silicon (Si) is placed between a sapphire (Al_2O_3) substrate and a quartz glass (SiO_2)-based optical waveguide film formed on the sapphire substrate. A quartz-based optical waveguide film characterized by having a crystal thin film or an amorphous thin film interposed therebetween.