JP2000121859A - Production of buried optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate buried proximity core parts, to diminish residual strains by a high-temperature heat treatment, to eliminate the need for a special process know-how and to enhance the production yield. SOLUTION: A glass film which constitutes a lower clad film 12 is deposited by an ionization vapor deposition method or a plasma CVD method on a substrate 10 consisting of silicon or synthesize quartz, etc., (a). Amorphous silicon, etc., which constitute a mask 14 are deposited by a CVD method on this lower clad film 12 and a resist mask 16 is patterned thereon (b). The mask 14 is formed by RIE by using this resist mask 16 (c) and grooves 13 for forming the core parts are etched by using this mask 14 (d). A core layer 16 is deposited on the lower clad film 12 (e). The surface of the substrate is planarized by a chemical and mechanical polishing method in such a manner that the core material 16 remains only in the grooves 13 (f). An upper clad film 18 is deposited thereon (g).

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 buried optical waveguide used in an optical communication transmission system or an optical measuring system, and more particularly to a method of manufacturing a buried optical waveguide in which a method of forming a core portion is improved. About.

[0002]

2. Description of the Related Art As a conventional method of fabricating a buried optical waveguide, a manufacturing process as shown in FIG.
twave Technology Vol.6 NO.6, June 1988, `` Sili
ca -Based Single -Mode Waveguides on Silicon
and their Application to Guided -Wave Optical
Interferometers ”) have been adopted. FIG. 2 is a process cross-sectional view showing a process for manufacturing a conventional silica-based optical waveguide.
This optical waveguide is formed using a photolithography process using a flame hydrolysis deposition method and reactive ion etching. Hereinafter, a conventional optical waveguide manufacturing process will be described. First, as shown in FIG.
Glass particles obtained by flame hydrolysis of a gaseous material whose main component is silicon tetrachloride in an oxyhydrogen flame are sprayed and deposited on the top of the glass. At this time, by changing the dopant concentration of the glass fine particles to form the lower cladding layer 21 and the core layer 23 having different refractive indices, 2
It has a layer structure. Next, in FIG. 2B, the glass fine particle film (the lower clad layer 21 and the core layer 23) of FIG. The lower clad film 22 and the core film 24 are two-layer glass films. Next, in FIG. 2C, an amorphous silicon 26 serving as a mask is formed on the core film 24 by chemical vapor deposition (CVD).
osition) and LSI (Large Scale)
Integration: A resist mask 28 is formed by a photolithography technique which is a fine processing technique of a large scale integrated circuit.

Next, in FIG. 2D, an amorphous silicon 26 is anisotropically etched by reactive ion etching (RIE) using a CBrF ₃ gas or the like using a resist mask 28 to form a core portion. And a mask 26 are formed. Next, in FIG. 2E, reactive ion etching (RI) using C ₂ F ₆ gas or the like is performed using the above-described amorphous silicon mask 26.
Unnecessary portions of the core film are removed by anisotropic etching according to E), and a desired core portion 24 can be formed by leaving a ridge-shaped core film. Next, in FIG. 2F, a glass fine particle film 28 is deposited again by flame hydrolysis deposition so as to cover the ridge-shaped core portion 24. Here, P ₂ O ₅ , B ₂ O _3, or the like is generally added to lower the softening point temperature and facilitate the embedding of the core portion. Lastly, the glass fine particle film 28 is subjected to a high-temperature heat treatment in an electric furnace so that the core portion 24 is heated.
The optical waveguide is completed by forming a transparent upper clad glass film 29 covering the substrate. As described above, the conventional embedded optical waveguide is manufactured through the above-described steps. An advantage of this manufacturing method is that a thick cladding layer (upper and lower thicknesses of 50 μm) for protecting the core portion 22 can be deposited, and the adjacent cladding layers are arranged at intervals of several μm.
There is a point that the gap between the core portions of the optical waveguide can be filled with the clad material.

[0004]

However, in such a conventional method of manufacturing a buried optical waveguide,
A high-temperature heat treatment step is required twice after depositing the lower cladding layer 21 and the core layer 23 (FIG. 2B) and after depositing the glass fine particle film 28 (FIG. 2G). Therefore, there is a problem that the residual stress increases due to the difference in the thermal expansion coefficient due to the difference in the material of the added impurity, and the characteristics of the optical waveguide are deteriorated. Further, since special process know-how for handling glass particles is required, there is a problem that the production yield is reduced. Therefore, as a film formation method that does not require a vitrification step by the above-described high-temperature heat treatment, there are an ionization vapor deposition method, a plasma CVD method, and the like.
There has been a problem that the cladding material cannot be reliably filled between two adjacent optical waveguide core portions at intervals of several μm. The present invention has been made in view of the above circumstances, and when forming a core portion of an optical waveguide, reduces residual stress due to a high-temperature heat treatment step, facilitates embedding of a nearby core portion, and has special process know-how. It is an object of the present invention to provide a method of manufacturing a buried optical waveguide which does not require a high manufacturing yield and has a high production yield.

[0005]

To achieve the above object, according to the present invention, a step of depositing a lower cladding layer on a substrate and a step of forming an optical waveguide pattern in the lower cladding layer are provided. Forming an etching process, depositing a core layer on the lower cladding layer, flattening the surface leaving only the core material embedded in the groove, the core material is embedded in the groove, Depositing an upper cladding layer on the lower cladding layer having a planarized surface. According to this, a lower clad layer is deposited on a substrate, a groove for forming a pattern of an optical waveguide is etched in the lower clad layer, and then a core layer is deposited on the entire surface, and only the core material embedded in the groove is formed. , And the upper cladding layer is deposited thereon. For this reason, even when the core portions of the two optical waveguides are close to each other, the cladding material or the like can be easily filled.

According to a second aspect of the present invention, in the method of manufacturing a buried optical waveguide according to the first aspect, the step of depositing the lower clad layer and the step of depositing the upper clad layer are performed by heat treatment. A film forming method that does not require a vitrification step is used. According to this, Claim 1
In the method of manufacturing the embedded optical waveguide described in (1), a film forming method that does not require a vitrification step by heat treatment is used, so that the residual stress due to the high-temperature heat treatment step is reduced, and the adjacent core portion can be easily buried. Since no process know-how is required, the production yield can be increased. According to a third aspect of the present invention, in the method of manufacturing a buried optical waveguide according to the second aspect, at least one of an ionization vapor deposition method and a plasma CVD method is used as a film forming method that does not require a vitrification step by the heat treatment. It is what you do. According to this, since the film is formed by using the ionization vapor deposition method, the plasma CVD method, or the like, a film formation method which does not require a vitrification step by heat treatment can be realized.

[0007]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a process cross-sectional view showing a manufacturing process of a buried optical waveguide according to the present embodiment. Here, a case where a quartz-based optical waveguide is manufactured will be particularly described. A feature of the present embodiment is that even when a film forming method that does not require a vitrification step by a heat treatment is used, embedding between adjacent core portions can be easily performed. First, the manufacturing method according to the present embodiment will be described with reference to FIG.
As shown in (a), a glass film serving as a lower cladding film 12 is formed on a substrate 10 made of silicon, synthetic quartz, or the like by an ionization vapor deposition method, which is a film formation method that does not require a vitrification step by heat treatment, or plasma. It is deposited by a CVD method or the like. Next, as shown in FIG. 1B, a mask 14 is formed on the deposited lower clad film 12.
After depositing amorphous silicon or the like by CVD or the like, a resist mask 15 is patterned thereon using a photolithography technique which is an LSI fine processing technique. Next, in order to form a groove for forming a core portion, CB is used as an etchant for the resist mask 15.
using rF ₃ gas or the like, reactive ion etching (RI
By E), a mask 14 made of amorphous silicon is formed (FIG. 1C).

Next, C ₂ F _{6 is used} as an etchant for the mask 14 made of amorphous silicon.
Using a gas or the like, an unnecessary portion is removed by reactive ion etching (RIE) to form a groove 13 for forming a core portion (FIG. 1D). Next, as shown in FIG. 1E, a core layer 16 is deposited on the lower clad film 12 to bury the core material in the groove 13. Since the core layer 16 to be deposited is required to adjust the refractive index as a core portion, TiO ₂ , GeO _2, etc. are several W
An SiO ₂ film to which t% is added is used. Then, FIG.
As shown in (f), the surface of the substrate is planarized by a chemical polishing method such as wet etching or a mechanical polishing method using an abrasive, etc., so that the core material 16 remains only in the groove 13. To do. And finally, Figure 1
As shown in (g), the core material 16 is embedded,
By forming an upper clad film 18 on the lower clad film 12 having a flattened surface, a buried optical waveguide is completed. Of course, as the method of forming the upper cladding film 18, an ionization vapor deposition method or a plasma CVD method that does not require a vitrification step by heat treatment is used.

As described above, according to the above embodiment, when forming the core portion 16, the groove 13 is formed in the lower clad film 12, and the core material is buried in the groove 13 to flatten the surface. Thereafter, since the upper clad film 18 is deposited, the clad material can be reliably filled between the core portions even when a plurality of core portions are close to each other on the order of several μm. In particular, when the above manufacturing method is used, even when a film is formed by using an ionization vapor deposition method or a plasma CVD method that does not require a vitrification step by a high-temperature heat treatment, it is easy to embed between adjacent core portions. In addition, the residual stress due to the difference in thermal expansion coefficient can be minimized, and special process know-how is not required, so that a buried optical waveguide having a high production yield can be manufactured. In the above embodiment, various optical waveguides such as a quartz optical waveguide, a plastic optical waveguide, an optical semiconductor optical waveguide, and an optical waveguide using an optical crystal (lithium niobate, lithium tantalate, etc.) are used as the optical waveguide material. Can be applied.

[0010]

As described above, according to the first aspect of the present invention, even when the core portions of the two optical waveguides are close to each other, the cladding material or the like can be easily provided therebetween. Can be filled. According to the second aspect of the present invention, the residual stress due to the high-temperature heat treatment step is reduced, the adjacent core portion can be easily buried, and no special process know-how is required, so that the production yield can be increased. it can. According to the invention described in claim 3,
A film formation method that does not require a vitrification step by heat treatment can be realized.

[Brief description of the drawings]

FIGS. 1A to 1G are process cross-sectional views showing a manufacturing process of a buried optical waveguide according to the present embodiment.

FIGS. 2A to 2G are process cross-sectional views showing a process for manufacturing a conventional silica-based optical waveguide.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Substrate 12 Lower clad film (lower clad layer) 13 Groove 14 Mask 16 Core part (core layer, core material) 18 Upper clad film (upper clad layer)

Claims (3)

[Claims] A step of depositing a lower clad layer on the substrate; a step of forming a groove for forming an optical waveguide pattern in the lower clad layer by etching; and a step of depositing a core layer on the lower clad layer. Planarizing the surface while leaving only the core material embedded in the groove; and depositing an upper clad layer on the lower clad layer having the core material embedded in the groove and having a planarized surface. A method for manufacturing a buried optical waveguide, comprising: 2. The method according to claim 1, wherein the step of depositing the lower cladding layer and the step of depositing the upper cladding layer use a film forming method that does not require a vitrification step by heat treatment. A method for manufacturing a buried optical waveguide. 3. A film forming method which does not require a vitrification step by the heat treatment, is an ionization vapor deposition method or a plasma CVD method.
3. The method according to claim 2, wherein the method is performed using at least one of the methods.