JPS592008A - Production of embedding type quartz optical waveguide - Google Patents

Abstract

PURPOSE:To form a waveguide without forming any gap in the stage of providing a quartz layer having the refractive index larger than the refractive index of a quartz substrate as a waveguide on the substrate and forming a quartz clad layer for embedding the waveguide by applying RF electric power on the electrode on the substrate side and performing sputtering. CONSTITUTION:A quartz layer 4 contg. a doping material having the refractive index larger than the refractive index of a quartz substrate 3 is deposited on said substrate, and a Ti layer 6 and a photoresist layer 7 are provided thereon. The resist layer is allowed to remain in the waveguide pattern, and with the resist as a mask, the layer 6 is etched, then with the Ti as a mask, the layer 4 is etched to form core glass 4, whereafter quartz glass 8 is sputtered on the core glass. In the stage of sputtering, the substrate 3 is mounted to an electrode 9 by using an RF sputtering device and a quartz target 11 is placed on an electrode 11, then the sputtering is accomplished by applying RF electric power on the electrode 9. The embedding type waveguide having a small transmission loss without forming any gap between the glass 8 and the core in the stage of depositing said glass is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a buried quartz optical waveguide for an optical integrated circuit, which has low loss, excellent temperature stability, and long-term reliability.

With the development of optical fiber transmission technology, it is desired that functions such as optical branching, optical filtering, and optical demultiplexing, which were conventionally performed in space, be realized using optical waveguide circuits. In particular, optical waveguides using silica glass as a medium are expected to have low loss, are suitable for coupling with optical fibers, and are expected to be mechanically and chemically stable waveguides, so several manufacturing methods have been proposed. ing. 1st
The figure shows the method for manufacturing a quartz optical waveguide using the chemical vapor deposition method (
Literature: Mori et al. Technical Report OQE 80-135, Institute of Electronics and Communication Engineers
.

1980). Sunawachi, Mass 70-Controller MF
810j4.oxygen whose flow rate was controlled by OI. G
e014. The vapors of PCl, , and BBr are introduced into the high-temperature furnace 2, where S10, which becomes the main component of the waveguide, is introduced into the high-temperature furnace 2.
．． and Gem as an impurity, , P, O,, B, 0.
After fine particles are generated and deposited on a quartz substrate 3, they are turned into transparent glass by heat treatment to form the core 4 of the waveguide. Waveguides fabricated by this method lack uniformity, resulting in large scattering losses, and are unsuitable for applications such as directional couplers that require uniform propagation constants.

Since it involves heat treatment at about 1,500°C, it has drawbacks such as being prone to cracking. As another method, the inventor previously proposed a method for manufacturing a quartz optical waveguide using sputtering (Japanese Patent Application No. 199490/1983).

This method is superior to the above chemical vapor deposition method in terms of uniformity and no heat treatment, but since there is no process to melt the quartz glass through heat treatment, it is necessary to fabricate and embed the waveguide on any uneven surface. I can't. For example, when quartz is sputtered onto a 10 μm square groove provided on a quartz substrate or a grating with a pitch of approximately 171 m, a hollow portion is created without being filled.

FIG. 2 shows a cross-sectional view obtained through experiments and microscopic observation by the inventor. (a) shows a 10 μm square groove, and (b) shows a state in which quartz is sputtered onto the groove shown in (a). (0)+1 This is the case of a grating with a pitch of approximately 1 μm. 3 is a quartz substrate, 4 is a sputtered quartz film, and 5 is a hollow portion. As can be seen from this result, the above method cannot embed a substrate with unevenness, and this is a fatal drawback as a method for manufacturing a buried ring wave path.

In order to eliminate these drawbacks, the present invention provides an optically bound waveguide manufacturing method in which the core is formed by completely filling the grooves and protrusions of the substrate by applying RF power to the substrate side during sputtering. The purpose is to propose.

In order to achieve the above object, the present invention deposits a quartz layer having a higher refractive index than the substrate on a quartz substrate by sputtering using quartz or quartz doped with a dopant as a target, and deposits a quartz layer with a higher refractive index than that of the substrate, and guides the quartz layer. In the process of embedding the core by depositing a quartz layer to become the cladding by sputtering again using quartz as a target, on the etched material leaving the desired shape to become the core of the wave channel, during the second sputtering, The gist of the invention is a method 1 for manufacturing a buried quartz optical waveguide characterized by applying RF power to a substrate-side electrode.

Furthermore, the present invention etches a round groove in the desired shape to be the core of a waveguide on a quartz substrate, and performs sputtering using quartz or quartz doped with a dopant as a target. When depositing a quartz layer with a high refractive index, fill the groove with the target material while applying RP power to the electrode on the substrate side, and deposit the target material until the surface becomes flat. The gist of the invention is a method for manufacturing a buried quartz guided waveguide, which is characterized by etching until the surface is exposed, and then depositing a quartz layer to be used as a cladding by sputtering again using quartz as a target.

Next, embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments are merely illustrative, and it goes without saying that various changes and improvements may be made without departing from the spirit of the invention.

FIG. 3 is an example showing a procedure for manufacturing an optical waveguide according to the present invention. In the figure, 3 is a substrate of quartz glass, 4 is a core glass deposited by sputtering, 6 is a T1 vapor deposited film used as a mask for dry etching the quartz, 7 is a photoresist, and 8 is a clad glass deposited by sputtering. It is. (a) shows a state in which core glass 4 is deposited on substrate 3, T1 film 6 is deposited, and photoresist is applied using a spinner. (b) is the state in which the resist has been removed leaving the waveguide pattern), (c)
) to etch T1 using the Lujist as a mask,
In (a), the core glass 4 is etched using T1 as a mask. In (e), silica glass 8, which will become a cladding, is deposited by sputtering on the core glass 4 remaining in the shape of a protrusion. In normal sputtering, voids are created as shown in FIG. In this example, the generation of voids is prevented by applying RF power to the substrate-side electrode, and it is possible to deposit the cladding while completely embedding the core as shown in FIG. 3(e). The mechanism of the process of preventing the generation of voids by applying RF power to the substrate side can be interpreted as follows. First, in normal sputtering, there is no directionality in the adhesion of deposited quartz fine particles, so where there is a step on the substrate, the quartz particles are deposited in an overhang shape so as to cover the top surface of the step. The situation is shown in FIG. 4(a). The area below the overhang becomes a shadow, so the quartz particles cannot reach it, creating a void. If the deposition continues as it is, as shown in (b), the layers will be deposited with the voids 5 remaining. On the other hand, when RF power is also applied to the substrate side, deposition and etching proceed simultaneously. While deposition is internal, etching progresses faster on inclined surfaces (Reference: S.

Matsuo, JJAP, vow, 15. No,
7. p, 1253. (1976)).

Therefore, the deposition in the lateral direction is suppressed, and on the contrary, as shown in (c), the walls are piled up while being scraped, resulting in a trapezoidal shape. Therefore, sputtered quartz particles are prevented from reaching the grooves. Since there is nothing left, the groove is completely filled as shown in (, i). Note that each step of = (a) to (d) was obtained by cross-sectional observation of experimental results by the present inventor. Experimentally, it was possible to fill the trench by applying RF power of 1/7 to 1/1 of the RF power per unit area applied to the target to the substrate.

Specifically, the power on the target side was set to "Vcm2*" and the power on the board side was set to 3.

FIG. 5 shows the RF sputtering apparatus used in this example.

3 is a quartz substrate, 9 is an electrode on the substrate side, 10 is an RF power source on the substrate side, 11 is a quartz target containing quartz or Dogue material,
12 is a target side electrode, 13 is a target side RF power source, 14 is a shutter, 15 is a Pelger, and 14.1
5 is grounded.

FIG. 6 shows another embodiment of the invention. The difference from the previous embodiment is that, in contrast to the core part left in a protruding shape as shown in (a) in Figure 3, in this embodiment the core part is buried in a groove. ing. That is, (a) the T1 film 6 is placed on the substrate 3;
7 photoresist 7 is applied on the evaporated film, (b) the resist in the 4-wave path pattern portion is removed, and (c) the pattern is transferred to the 71 film.

(a) Using the Tt film as a mask, a core groove is formed in the quartz substrate by etching, and then the photoresist 7 is removed. (e) Fill the groove with quartz glass 4 to serve as the core by sputtering. At this time, similar to the previous embodiment, RF power similar to the target side RF power is applied to the substrate side. When the core glass is deposited sufficiently, the top surface becomes flat as shown in (e). Next, as shown in (f), the core glass 4 is etched down to the surface of the original substrate 3. A clad glass 8 is deposited thereon by sputtering, and the core glass is embedded in the groove of the substrate 3 as shown in FIG. 3(g).

FIG. 7 shows an example of applying the present invention to grating embedding. Reference numeral 16 indicates a grating provided on the upper surface of the core glass. (a> Deposit thin core glass 4 on quartz substrate 3 by sputtering.

(b) forming a grating on the core glass;

Interferometry and dry etching of quartz can be used to form the grating. (C) Similar to the previous example, quartz to be a cladding is deposited by sputtering while applying RF power to the substrate side. Experimentally 1
When sputtering silica glass on a grating with a pitch of μm and a depth of 0.5 μm, the RF power on the target side is “8”ffi” and the RF power on the substrate side is “16”/Cm!
And so. As a result, complete embedding as shown in FIG. 6(c) was confirmed by electron microscope observation of the cross section.

The target used in the present invention is one to which cine particles are added by chemical vapor deposition (Reference: Japanese Patent Application No. 56-19
9490), a sintered body of quartz and impurities can also be used, and a difference in refractive index between the core and the cladding can also be created by using pure quartz itself. This is because the refractive index of quartz deposited by sputtering can be slightly higher than that of the target. For example, Ar pressure lXl0-'Torr, target side RF power 170
When using W, a relative refractive index difference of 0.29% was obtained. This is sufficiently large as the relative refractive index difference required for the waveguide.

As described above, according to the present invention, the core and cladding of a waveguide having a complex structure are deposited using only quartz sputtering, so that all steps are unified to a low-temperature dry process. Therefore, it is suitable for mass production without exposing it.
No damage or deformation due to heat treatment. Furthermore, since the film formed by sputtering is uniform and has little scattering, it has the advantage that it is possible to manufacture a waveguide circuit element with low loss and high precision.

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[Brief explanation of drawings]

Figure 1 shows an apparatus for producing a quartz optical waveguide using a conventional chemical vapor deposition method, Figures 2 (a) to (c) are cross-sectional views of the waveguide showing voids created by ordinary quartz sputtering, and Figures 3 (a1 to
(θ) is a diagram explaining the manufacturing process according to the present invention, the fourth
Figures (a) to (d) are explanatory diagrams showing other examples of voids formed by sputtering, and Figures 7 (a) to (0) illustrate the process when the present invention is applied to the silk production of waveguides with gratings. show. l...mass flow controller, 2...high temperature furnace, 3...
...Quartz substrate, 4...Quartz glass serving as the core, 5...
・Gap, 6... T1 vapor deposition film, 7... Photoresist, 8... Quartz glass serving as cladding, 9... Substrate side electrode, 10... RF power source, 11... Target, 1
2...Target side electrode, 13...RF power supply, 14
...Shutter, 15...Pelger, 16...Grating Patent Applicant Figure 2 Figure 3 Figure 6 = 43- Figure 7 (a)

Claims (2)

[Claims] (1) A quartz layer with a high refractive index is deposited on a quartz substrate by adding a dopant to quartz and sputtering using a special target, and this quartz layer should be used as the core of the waveguide. In the process of embedding the core by depositing a quartz layer to be used as a shiflad again by sputtering using quartz as a target on the etched surface while leaving the desired shape, during the second sputtering, R
A method for manufacturing a buried quartz optical waveguide, the method comprising applying F power to a substrate-side electrode. (2) A groove with the desired shape to be the core of the waveguide is formed on the quartz substrate by etching, and the substrate is formed on the quartz substrate by sputtering using quartz or quartz with dopant 'fr: added as a target. When depositing a quartz layer with a high refractive index, the grooves are filled with the target material while applying RF power to the substrate-side electrode, and the target material is deposited until the surface becomes flat, and then the first surface of the quartz substrate is deposited. 1. A method for manufacturing a embedded quartz optical waveguide, which comprises etching the quartz optical waveguide until it appears, and then depositing a quartz layer to be used as a shiflad by sputtering again using quartz as a target.