WO2010098295A1

WO2010098295A1 - Optical waveguide, optical waveguide circuit, and method for manufacturing optical waveguide circuit

Info

Publication number: WO2010098295A1
Application number: PCT/JP2010/052668
Authority: WO
Inventors: 真也渡邊; 森生高橋
Original assignee: 日本電気株式会社
Priority date: 2009-02-25
Filing date: 2010-02-23
Publication date: 2010-09-02
Also published as: JP2012112984A

Abstract

Disclosed is an optical waveguide (1) which is configured to comprise a core (11) through which light is waveguided, a cladding layer (12) that covers the core, and a low moisture permeability member (13) that covers an exposed portion of the cladding layer and has a moisture permeability lower than that of silicon oxide.

Description

Optical waveguide, optical waveguide circuit, and method of manufacturing optical waveguide circuit

The present invention relates to an optical waveguide, an optical waveguide circuit, and a method of manufacturing the optical waveguide circuit.

Among various optical devices that realize optical communication, devices utilizing Planner Light-wave Circuits (PLCs) can utilize the process of manufacturing semiconductor circuits, so the devices can be downsized and highly functional, It has the feature of being excellent in integration.

Usually, an optical waveguide manufactured by PLC manufacturing technology is realized as follows. First, a lower cladding layer is formed on a silicon (Si) substrate, and then a core film through which light is guided is formed.

Here, using a photomask designed to realize various functions, a core is formed in a desired layout by photolithography and dry etching.

Then, after passing through the reflow layer film-forming for embedding a core depending on the case, the upper clad layer is formed into a film. The reflow layer optically functions as a clad in the same manner as the upper and lower clad layers.

In the optical waveguide circuit manufactured in this manner, for example, AWG (Arrayed Waveguides Grating) for multiplexing and dividing a plurality of wavelengths, VOA (Variable Optical Attenuator) for attenuating incident light by a desired amount, and incident light Various functions can be provided depending on the layout of the core, such as an optical switch for outputting to a desired port.

The characteristics representing the optical characteristics of the optical waveguide itself are represented by insertion loss (or propagation loss) and PDL (Polarization Dependent Loss). Usually, the smaller the two, the better.

Here, PDL is a phenomenon in which the insertion loss of the optical waveguide varies depending on the polarization state of light, and is expressed as the amount of divergence between the insertion loss in TE (Transverce Electric) mode and the insertion loss in TM (Transverce Electromagnetic) mode. .

Such deviation is largely due to birefringence possessed by the optical waveguide. Birefringence means that the optical waveguide has a different refractive index depending on the direction. The dominant cause of the occurrence of birefringence is the internal stress of the optical waveguide (in other words, the stress acting to balance with the stress received from the outside).

As described above, the optical waveguide is manufactured by laminating a silicon oxide film to be a clad or a core on a substrate. At this time, the process usually requires heat treatment at a very high temperature of around 1000 ° C.

For this reason, when the substrate is silicon or the like, the wafer is warped due to the difference in thermal expansion coefficient between the deposited silicon oxide film and the substrate, and the produced optical waveguide receives large stress from the wafer. This stress generates PDL.

Therefore, techniques have been used to reduce stress or balance so as not to have directionality by various means.

As one means among them, a structure is proposed in which the optical waveguide is separated from the silicon substrate. It is a technique of partially floating the optical waveguide from the silicon substrate in the form of a bridge and relieving stress from the substrate to reduce the PDL. Such a structure is called a bridge structure.

Hereinafter, in describing this bridge structure, an effect other than PDL reduction can be obtained by this structure. The effect will be described using a “thermo-optical phase shifter” as an example.

In the optical waveguide circuit, a method of adding a function using the TO (Thermo-Optic) effect is often used. This is a technology in which a glass material constituting an optical waveguide circuit actively utilizes a physical phenomenon in which the refractive index changes due to heat.

For example, a Mach-Zehnder interferometer composed of a directional coupler based on an optical waveguide circuit has a structure in which input light is branched into two, propagated the same length, and then recombined.

A metal heater is provided on one of the waveguide paths branched here, and the phase of the light to be guided can be changed by heat generated by supplying power to the heater. In this way, when the branched waveguides are coupled, the interference state changes according to the phase difference of the light guided through the two waveguides, and the intensity of the output light can be changed.

For example, if the phase difference is set to a half wavelength of light, both branched light beams cancel each other at the time of coupling, so the output becomes almost zero. Also, if the phase difference is zero or an integral multiple of the wavelength, the input light intensity can be substantially taken out. Here, the part that changes the phase is called a thermo-optic phase shifter.

It is possible to make a Mach-Zehnder interferometer function as an optical switch by utilizing these phenomena. In addition, since the phase difference can be arbitrarily given, it becomes possible to use as an optical attenuator by utilizing continuous phase change.

In order to operate the optical device realized in this manner, since power is supplied to the heater for control, it is desirable that the power consumption necessary for the operation be small.

In general, the power required to shift the light having a wavelength of 1550 nm used in optical communication by a half wavelength is about 400 mW when no modification is made to the optical waveguide.

However, if they require, for example, 40 channels of control, approximately 16 W of power is required. Since this power is very large, power consumption is generally reduced by applying various devices to the optical waveguide circuit.

An optical waveguide having the following structure is typical as a general technology for reducing power consumption of a thermo-optic phase shifter realized by a planar lightwave circuit.

A groove is formed at a position away from the optical waveguide of the portion functioning as a phase shifter by a predetermined distance. The groove is filled with air or evacuated, but the heat conductivity of the gas is sufficiently smaller than the silicon oxide film forming the cladding, so the heat generated from the heater is diffused to the cladding You can prevent.

Therefore, the power consumption can be significantly reduced. Such a structure is called a ridge structure. Further, the optical waveguide portion formed by being sandwiched by the grooves is simply referred to as a ridge.

Usually, a thermo-optic phase shifter having such a ridge structure is realized by the following manufacturing method.

After the optical waveguide is formed as described above, a metal film to be a heater is formed on the upper cladding layer by a sputtering apparatus or a vapor deposition apparatus.

Next, a heater is formed in a desired layout by photolithography using a photomask and a milling apparatus.

Next, as in the step of forming the core, a groove is formed at a desired position by a dry etching apparatus. At this time, the heater needs to be sufficiently protected by a resist so that the heater is not damaged by dry etching.

In the ridge structure, the following method is generally used to further increase the thermal efficiency.

(1) Thicken the lower cladding layer of the optical waveguide. As a result, the thermal resistance between the core and the silicon substrate is increased, and the flow of heat to the silicon substrate is suppressed.

(2) Narrow the width of the ridge. In the case of the ridge structure, the thermal diffusion is dominated by the outflow from the ridge to the silicon substrate. Therefore, as the width of the ridge is narrowed, the junction area between the ridge and the silicon substrate is reduced, and thermal diffusion is suppressed.

However, each of these methods has limitations for the following reasons.

(1) As the lower cladding layer becomes thicker, the stress applied to the film becomes stronger, and the wafer is more likely to be cracked. Also, due to the strong stress, the birefringence increases and the PDL of the optical waveguide increases. Further, the thicker the film, the longer the manufacturing process time.

(2) If the ridge width is made too thin, the guided light will feel rough on the ridge sidewalls, and the loss due to scattering will increase.

Even if such measures are implemented as much as possible, the power consumption effect that can usually be realized with the ridge structure is about half as much suppression as in the normal case, and the value of 8 W for 40 channels Is not small enough.

Therefore, in addition to the ridge structure, a technique proposed as a method of further reducing power consumption is the adoption of the bridge structure described at the beginning. As described above, the bridge structure is a structure in which the optical waveguide is separated from the silicon substrate and floated like a bridge.

In the case of a thermal phase shifter which already has a ridge structure, it is realized by separating the ridge from the silicon substrate. The bridge structure suppresses the thermal diffusion to the silicon substrate in the same manner as the ridge structure suppresses the thermal diffusion to the cladding, so that a further significant power consumption reduction effect can be obtained.

Further, as described above, the bridge structure has the feature of reducing PDL by releasing the stress from the substrate generated from the difference in linear expansion coefficient between the optical waveguide film and the substrate.

For this reason, adoption of the bridge structure in the thermo-optic phase shifter brings about two great effects of low power consumption and low PDL.

Hereinafter, such a structure is called a bridge structure again. Also, the waveguide portion floating in a bridge shape is referred to as a bridge.

The bridge structure can be realized by a technique called sacrificial layer etching which is well known as MEMS (Micro Electro Mechanical Systems) technology. An example of the technology is disclosed in Japanese Patent Laid-Open No. 2004-37524 (hereinafter referred to as Patent Document 1).

As disclosed in Patent Document 1, this technique is a method in which a sacrificial layer is deposited in advance on a substrate, and finally only this layer is isotropically etched.

This method is realized by etching with hydrogen fluoride water by using a silicon substrate and using PSG (Phospho Silicate Glass: phosphorus glass) or the like as a sacrificial layer.

When phosphorus is doped into the silicon oxide film, it has an early etching rate to hydrogen fluoride water, so that it is possible to selectively etch only PSG.

Although this method has the advantage of not requiring a special device, it is essential to form a sacrificial seed film between the lower cladding layer and the silicon substrate.

The problem with this method is not only the increase in the number of film formation steps. The silicon oxide film stacked on the sacrificial layer must be adjusted in refractive index and softening temperature to function as a waveguide while maintaining high etching selectivity to the sacrificial layer.

This means that the design process of the entire manufacturing process is largely lost. In addition, since hydrogen fluoride also etches silicon oxide films other than the sacrificial layer film more or less, design and technology for manufacturing without damage as an optical waveguide are required.

Therefore, there is a method of etching a silicon substrate as an alternative means. In this case, since the sacrificial layer is unnecessary, the bridge structure can be realized without any influence on the conventional established optical waveguide manufacturing process.

Such a method is described, for example, in “Bridge-Suspended Silica-Waveguide Thermo-Optic Phase Shifter and Its Application to Mach-Zehnder Type Optical Switch (A. Sugita et al., Trans. IEICE, Vol. E 73 (1990)) pp. 105-109) "(hereinafter referred to as non-patent documents).

Although disclosed in the non-patent document, etching of a silicon substrate is generally realized by forming a ridge structure and then exposing the silicon to a gas or solution for etching.

Although non-patent documents only mention etching a silicon substrate by dry etching, isotropic etching of the silicon substrate can be realized by using a gas such as xenon fluoride.

Further, as another example of the related art, the invention of a silicon thin wire optical waveguide having an air bridge structure is disclosed in Japanese Patent Application Publication No. 2001-521180 (hereinafter referred to as Patent Document 2).

Furthermore, a thermo-optical phase shifter for forming an insulating film as a protective layer on a cladding layer on which a heater is formed is disclosed in JP-A 2004-279993 (hereinafter referred to as Patent Document 3), paragraphs 0053 and 0054. And FIG. 3 (b).

However, the following problems are encountered in any of the ridge structure and the bridge structure in addition to the method of etching the silicon substrate as described above.

Usually, in the fabrication of the optical waveguide, it is necessary to embed the core so that voids do not occur, so a film having a relatively low softening point is used for the buried layer and the upper cladding layer.

These are typified by PSG and BPSG (Borophospho Silicate Glass) in which phosphorus, boron and the like are doped into NSG (Non-dope Silicate Glass) not doped with anything.

However, such membranes have the disadvantage that they are very sensitive to moisture. That is, since phosphorus and boron have a characteristic of easily reacting with moisture, they will be deposited on the surface when exposed to an environment containing moisture.

In particular, in an optical waveguide having a ridge structure or a bridge structure, the distance from the core to the external environment is very short, and the deterioration of PSG and BPSG constituting the cladding around the core due to moisture brings about a change in refractive index and stress. The characteristics of the waveguide are easily changed.

On the other hand, although the invention which forms an insulating film into a film as a protective layer on the cladding layer in which the heater was formed is disclosed by the above-mentioned patent document 3, this is only forming the insulating layer on the heater upper surface. The configuration is completely different from the invention of covering the exposed part of the cladding layer as in the present invention.

Therefore, the problems to be solved by the present invention are not disclosed in any of the above-mentioned Patent Documents 1 to 3 and non-patent documents.

One of the objects of the present invention is to provide an optical waveguide, an optical waveguide circuit, and a method of manufacturing an optical waveguide circuit capable of preventing the deterioration of the cladding around the core due to moisture.

The optical waveguide according to one aspect of the present invention has low moisture permeability, which is a member having a lower moisture permeability than silicon oxide, which covers the core through which light is guided, the cladding layer covering the core, and the exposed portion of the cladding layer. And a member.

An optical waveguide circuit according to one aspect of the present invention is configured to include the above-described optical waveguide and a silicon substrate supporting the optical waveguide.

Furthermore, in the method of manufacturing an optical waveguide circuit according to one aspect of the present invention, a first cladding layer and a core layer are sequentially formed on a silicon substrate, and a core is formed on the core layer by photolithography and etching. Forming a second cladding layer covering the core, forming grooves in the first and second cladding layers at a predetermined distance from each of both side surfaces of the core by photolithography technology and etching technology; In the exposed portions of the first and second cladding layers, the first low moisture-permeable member, which is a member having lower moisture permeability than silicon oxide, is formed.

FIG. 1 is a cross-sectional view of the optical waveguide of the first embodiment of the present invention. FIG. 2 is a cross-sectional view of an optical waveguide circuit according to a second embodiment of the present invention. FIG. 3 is a flow chart showing the processing procedure of the method of manufacturing the optical waveguide circuit of the third embodiment of the present invention. FIG. 4A is a cross-sectional view of an optical waveguide circuit according to a fourth embodiment of the present invention. FIG. 4B is a cross-sectional view of the optical waveguide circuit according to the fifth embodiment of the present invention. FIG. 4C is a cross-sectional view of the optical waveguide circuit according to the sixth embodiment of the present invention. FIG. 4D is a cross-sectional view of the optical waveguide circuit according to the seventh embodiment of the present invention. FIG. 4E is a cross-sectional view of the optical waveguide circuit according to the eighth embodiment of the present invention. FIG. 5A is a schematic cross sectional view showing a processing procedure of a method of manufacturing the thermo-optic phase shifter of the ninth embodiment of the present invention. FIG. 5B is a schematic cross sectional view showing a processing procedure of a method of manufacturing the thermo-optic phase shifter of the ninth embodiment of the present invention. FIG. 5C is a schematic cross sectional view showing a processing procedure of a method of manufacturing the thermo-optic phase shifter of the ninth embodiment of the present invention. FIG. 5D is a schematic cross sectional view showing a processing procedure of a method of manufacturing the thermo-optic phase shifter of the ninth embodiment of the present invention. FIG. 5E is a schematic cross sectional view showing a processing procedure of a method of manufacturing the thermo-optic phase shifter of the ninth embodiment of the present invention. FIG. 5F is a schematic cross sectional view showing a processing procedure of a method of manufacturing the thermo-optic phase shifter of the ninth embodiment of the present invention. FIG. 5G is a schematic cross sectional view showing a processing procedure of a method of manufacturing the thermo-optic phase shifter of the ninth embodiment of the present invention. FIG. 5H is a schematic cross sectional view showing a processing procedure of a method of manufacturing the thermo-optic phase shifter of the ninth embodiment of the present invention. FIG. 5I is a schematic cross sectional view showing a processing procedure of a method of manufacturing the thermo-optic phase shifter of the ninth embodiment of the present invention. FIG. 5J is a schematic cross sectional view showing a processing procedure of a method of manufacturing the thermo-optic phase shifter of the ninth embodiment of the present invention. FIG. 5K is a schematic cross sectional view showing a processing procedure of a method of manufacturing the thermo-optic phase shifter of the ninth embodiment of the present invention. FIG. 5L is a schematic cross sectional view showing a processing procedure of a method of manufacturing the thermo-optic phase shifter of the ninth embodiment of the present invention. FIG. 6 is a flow chart showing the processing procedure of the method of manufacturing the thermo-optic phase shifter of the ninth embodiment. FIG. 7A is a schematic cross sectional view showing a processing procedure of a method of manufacturing a bridge structure according to an eleventh embodiment of the present invention. FIG. 7B is a schematic cross sectional view showing a processing procedure of the manufacturing method of the bridge structure of the eleventh example of the present invention. FIG. 7C is a schematic cross sectional view showing a processing procedure of the manufacturing method of the bridge structure of the eleventh example of the present invention. FIG. 7D is a schematic cross sectional view showing a processing procedure of a method of manufacturing a bridge structure of the eleventh embodiment of the present invention. FIG. 7E is a schematic cross sectional view showing a processing procedure of a method of manufacturing a bridge structure according to an eleventh embodiment of the present invention. FIG. 7F is a schematic cross sectional view showing a processing procedure of a method of manufacturing a bridge structure according to an eleventh embodiment of the present invention. FIG. 7G is a schematic cross sectional view showing a processing procedure of a method of manufacturing a bridge structure of an eleventh example of the present invention. FIG. 7H is a schematic cross sectional view showing a processing procedure of a method of manufacturing a bridge structure according to an eleventh embodiment of the present invention. FIG. 7I is a schematic cross sectional view showing a processing procedure of a method of manufacturing a bridge structure according to an eleventh embodiment of the present invention. FIG. 7J is a schematic cross sectional view showing a processing procedure of a method of manufacturing a bridge structure according to an eleventh embodiment of the present invention. FIG. 7K is a schematic cross sectional view showing a processing procedure of a method of manufacturing a bridge structure of the eleventh embodiment of the present invention. FIG. 7L is a schematic cross sectional view showing a processing procedure of a method of manufacturing a bridge structure according to an eleventh embodiment of the present invention. FIG. 8 is a flow chart showing the processing procedure of the manufacturing method of the bridge structure in the eleventh embodiment. FIG. 9A is a schematic cross sectional view showing a processing procedure of a method of manufacturing a bridge structure according to a twelfth embodiment of the present invention. FIG. 9B is a schematic cross sectional view showing a processing procedure of the manufacturing method of the bridge structure of the twelfth example of the present invention. FIG. 9C is a schematic cross sectional view showing a processing procedure of a method of manufacturing a bridge structure according to a twelfth embodiment of the present invention. FIG. 9D is a schematic cross sectional view showing a processing procedure of the manufacturing method of the bridge structure of the twelfth embodiment of the present invention. FIG. 9E is a schematic cross sectional view showing a processing procedure of a method of manufacturing a bridge structure according to a twelfth embodiment of the present invention. FIG. 9F is a schematic cross sectional view showing a processing procedure of a method of manufacturing a bridge structure according to a twelfth embodiment of the present invention. FIG. 9G is a schematic cross sectional view showing a processing procedure of the manufacturing method of the bridge structure of the twelfth example of the present invention. FIG. 9H is a schematic cross sectional view showing a processing procedure of a method of manufacturing a bridge structure according to a twelfth embodiment of the present invention. FIG. 9I is a schematic cross sectional view showing a processing procedure of a method of manufacturing a bridge structure according to a twelfth embodiment of the present invention. FIG. 9J is a schematic cross sectional view showing a processing procedure of a method of manufacturing a bridge structure according to a twelfth embodiment of the present invention. FIG. 9K is a schematic cross sectional view showing a processing procedure of a method of manufacturing a bridge structure according to a twelfth embodiment of the present invention. FIG. 9L is a schematic cross sectional view showing a processing procedure of a method of manufacturing a bridge structure according to a twelfth embodiment of the present invention. FIG. 10 is a flow chart showing the processing procedure of the manufacturing method of the bridge structure in the twelfth embodiment. FIG. 11A is a plan view for explaining an example of a support of the bridge structure of the present invention. 11B is a cross-sectional view of a portion of line segment BB in FIG. 11A. FIG. 11C is a cross-sectional view of the portion of line segment AA in FIG. 11A. FIG. 12 is a perspective view showing a process of forming a pillar by isotropic etching on a silicon substrate. FIG. 13 is a perspective view showing a process of forming a pillar by isotropic etching on a silicon substrate. FIG. 14 is a cross-sectional view showing an example of the heat insulating groove provided in the optical waveguide of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the attached drawings.

The first embodiment relates to an example of an optical waveguide. FIG. 1 is a cross-sectional view of the optical waveguide of the first embodiment of the present invention. Referring to FIG. 1, the optical waveguide 1 is configured to include a core 11 through which light is guided, a cladding layer 12 covering the core 11, and a low moisture permeability member 13 covering an exposed portion of the cladding layer 12. The low moisture-permeable member 13 is a member having lower moisture permeability than silicon oxide.

According to the first embodiment, since the exposed part of the cladding layer 12 is covered with the low moisture-permeable member 13, it is possible to prevent the deterioration of the cladding layer 12 around the core 11 due to moisture.

The second embodiment relates to an example of an optical waveguide circuit. FIG. 2 is a cross-sectional view of an optical waveguide circuit according to a second embodiment of the present invention. The same components as in FIG. 1 will be assigned the same reference numerals and descriptions thereof will be omitted.

Referring to FIG. 2, the optical waveguide circuit 2 is configured to include the silicon substrate 14 and the optical waveguide 1. The optical waveguide 1 is configured to include a core 11 through which light is guided, a cladding layer 12 covering the core 11, and a low moisture-permeable member 13 covering an exposed portion of the cladding layer 12.

In the present embodiment, a structure in which the optical waveguide 1 is separated from the silicon substrate 14 and floated like a bridge (hereinafter referred to as “bridge structure”) is employed.

In addition, the structure which mounts the optical waveguide 1 on the silicon substrate 14 is also possible.

According to the second embodiment, since the exposed part of the cladding layer 12 is covered with the low moisture-permeable member 13, it is possible to prevent the deterioration of the cladding layer 12 around the core 11 due to moisture. Therefore, the optical waveguide circuit 2 capable of preventing the deterioration of the cladding layer 12 due to moisture is obtained.

The third embodiment relates to an example of a method of manufacturing an optical waveguide circuit. FIG. 3 is a flow chart showing the processing procedure of the method of manufacturing the optical waveguide circuit of the third embodiment of the present invention.

Referring to FIG. 3, in the method of manufacturing an optical waveguide circuit, a first process S1 for forming a lower cladding layer and a core layer on a silicon substrate, and a second process S2 for forming a core by photolithography and dry etching. A third process S3 of covering the core with the upper cladding layer, and a fourth process S4 of forming an optical waveguide by removing the cladding layer at a predetermined distance from both sides of the core by photolithography and dry etching And a fifth process S5 of forming a low moisture-permeable member on the exposed portion of the cladding layer of the optical waveguide.

According to the third embodiment, since the exposed portions of the upper and lower cladding layers are covered with the low moisture permeability member, it is possible to prevent the deterioration of the cladding layer around the core due to moisture. Therefore, a method of manufacturing the optical waveguide circuit 2 capable of preventing the deterioration of the cladding layer due to moisture is obtained.

Next, the configuration of the optical waveguide circuit of the fourth to eighth embodiments will be described. FIGS. 4A to 4E are cross-sectional views showing the optical waveguides of the fourth to eighth embodiments of the present invention, respectively.

The fourth embodiment relates to another example of the optical waveguide circuit.

FIG. 4A is a cross-sectional view of an optical waveguide circuit according to a fourth embodiment of the present invention. The same components as those shown in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted.

Referring to FIG. 4A, the optical waveguide circuit 3 is an example of a structure having a thermo-optic phase shifter.

The optical waveguide circuit 3 is configured to include a silicon substrate 14 and an optical waveguide 4. The optical waveguide 4 includes a lower cladding layer 15, a core 11 provided on the lower cladding layer 15, a buried layer 16 covering the core 11, an upper cladding layer 17 provided on the buried layer 16, and an upper cladding. Low-moisture-permeable member covering exposed portions of a heat generating member (hereinafter referred to as a "heater") 18 provided on the layer 17, the core 11, the lower cladding layer 15, the upper cladding layer 17, the embedded layer 16 and the heater 18 And 13 are included.

In this embodiment, a bridge structure in which the optical waveguide 4 is separated from the silicon substrate 14 and floated like a bridge is employed. Moreover, the ridge structure which provided the heat insulation groove (not shown) in the site | part which only predetermined distance separated from each of the both sides | surfaces of the optical waveguide 4 is also employ | adopted. Furthermore, as an example of the low moisture-permeable member 13, the low moisture-permeable member 13 is formed of a silicon nitride film.

The heat insulation groove (not shown) is filled with air or evacuated, but since the thermal conductivity of the gas is sufficiently smaller than the film forming the cladding, the heat generated from the heater 18 It is possible to prevent diffusion into the cladding.

In this embodiment, since the entire bridge structure including the heater 18 is covered with the silicon nitride film, the lower cladding layer 15 and the upper cladding layer 17 around the core 11 are completely covered with the silicon nitride film.

Silicon nitride films are known to have lower moisture permeability than silicon oxides because the crystal structure is very dense. This property is the same for silicon oxynitride (SiON), and a silicon oxynitride film can be used instead of the silicon nitride film in this embodiment.

According to the fourth embodiment, with such a structure, the entrance and exit of moisture is interrupted between the core 11 functioning as the optical waveguide 4, the lower cladding layer 15, the upper cladding layer 17, and the outside. As a result, it is possible to prevent a change in refractive index and stress due to film deterioration.

The fifth embodiment relates to another example of the optical waveguide circuit. FIG. 4B is a cross-sectional view of the optical waveguide circuit according to the fifth embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the structure similar to the structure shown in FIG. 1, and the description is abbreviate | omitted.

Referring to FIG. 4B, the optical waveguide circuit 5 is an example of a structure having a thermo-optic phase shifter.

The optical waveguide circuit 5 is configured to include a silicon substrate 14 and an optical waveguide 6. The fifth embodiment has a structure in which a part of silicon nitride film (SiN) is embedded in the upper cladding layer 17. The other configuration is the same as that of the fourth embodiment.

According to the fifth embodiment, the same effect as the fourth embodiment can be obtained.

The sixth embodiment relates to another example of the optical waveguide circuit. FIG. 4C is a cross-sectional view of the optical waveguide circuit according to the sixth embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the structure similar to the structure shown in FIG. 1, and the description is abbreviate | omitted.

Referring to FIG. 4C, the optical waveguide circuit 7 is an example of a structure having a thermo-optic phase shifter.

The optical waveguide circuit 7 is configured to include a silicon substrate 14 and an optical waveguide 8. The sixth embodiment has a structure in which a part of silicon nitride film (SiN) is embedded in the lower cladding layer 15. The other configuration is the same as that of the fourth embodiment.

According to the sixth embodiment, the same effect as that of the fourth embodiment can be obtained.

The seventh embodiment relates to another example of the optical waveguide circuit. FIG. 4D is a cross-sectional view of the optical waveguide circuit according to the seventh embodiment of the present invention. The same components as those shown in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted.

Referring to FIG. 4D, the optical waveguide circuit 9 is an example of a structure having a thermo-optic phase shifter.

The optical waveguide circuit 9 is configured to include a silicon substrate 14 and an optical waveguide 10. The seventh embodiment is not a complete bridge structure, but is an example in the case of having an intermediate structure of a ridge structure and a bridge structure. The other configuration is the same as that of the fourth embodiment.

According to the seventh embodiment, the same effect as that of the fourth embodiment can be obtained.

The eighth embodiment relates to another example of the optical waveguide circuit. FIG. 4E is a cross-sectional view of the optical waveguide circuit according to the eighth embodiment of the present invention. The same components as those shown in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted.

Referring to FIG. 4E, the optical waveguide circuit 21 is an example of a structure having a thermo-optic phase shifter.

The optical waveguide circuit 21 is configured to include a silicon substrate 14 and an optical waveguide 22. As shown in the eighth embodiment, when there is no need for a bridge structure and there is no problem even with a simple ridge structure, as shown in the figure, the effect of solving the problem can be achieved simply by forming a silicon nitride film (SiN) after forming the heat insulation groove Is obtained.

According to the eighth embodiment, the same effect as that of the fourth embodiment can be obtained.

The ninth embodiment relates to an example of a method of manufacturing a thermo-optic phase shifter according to the present invention. 5A to 5L are schematic sectional views showing the processing procedure of the method of manufacturing the thermo-optic phase shifter according to the ninth embodiment of the present invention. FIG. 6 is a flow chart showing the processing procedure of the method of manufacturing the thermo-optic phase shifter of the ninth embodiment. However, the apparatus used in the following description, the film type used, etc. are an example, and this invention is not limited to these.

First, SiN 52 is deposited on the silicon substrate 14 by CVD or the like (S11 in FIG. 5A and FIG. 6).

Next, NSG to be the material of the lower cladding layer 15 and SiON to be the material of the core layer 54 are deposited by the same apparatus (FIG. 5B and S12 in FIG. 6).

The core 11 is formed by photolithography and dry etching techniques, and heat treatment is performed as needed (FIG. 5C and S13 in FIG. 6).

Thereafter, a film having a low softening point such as BPSG or PSG to be the embedded layer 16 for embedding the core 11 or the upper cladding layer 17 is formed, and heat treatment is performed as required (S14 in FIG. 5D and FIG. 6).

Next, a metal film such as Pt or Ti to be a heater is formed on the upper cladding layer 17 by a sputtering apparatus or a vapor deposition apparatus, and the heater 18 is formed right above the core by photolithography and etching (FIG. 5E and FIG. 6 S15).

Next, an SiN 59 covering the heater 18 is formed on the upper cladding layer 17, and a chromium film 60 serving as a stopper layer is formed later from above (FIG. 5F and S16 in FIG. 6).

Next, a resist 61 having a predetermined pattern is formed on the chromium film 60 by photolithography. Subsequently, dry etching is performed on the resist 61 to remove the cladding layer at a predetermined distance from both sides of the core, thereby forming a heat insulation groove (FIG. 5G and S17 in FIG. 6).

After removing the resist 61, SiN 62 is formed on the exposed surface of the silicon substrate 14 (corresponding to the bottom of the heat insulation groove) and the chromium film 60 (S18 in FIG. 5H and FIG. 6) and dry etching is performed again (FIG. 5I and S19 of FIG. 6). Since RIE (Reactive Ion Etching) used for dry etching is anisotropic, the SiN 62 deposited on the side wall of the adiabatic groove is hardly removed, and only the SiN 62 on the chromium film 60 and the SiN 62 at the bottom of the adiabatic groove are removed. Since the etching rate for the chromium film 60 of RIE is slower compared to SiN 62, the chromium film 60 serves as a stopper layer to complete the etching.

Thereafter, the chromium film 60 is removed by an etchant (FIG. 5J and S20 in FIG. 6).

Finally, silicon is etched isotropically with xenon fluoride gas or the like (FIGS. 5K and S21 in FIG. 6), and all the silicon just under the waveguide is etched except a pillar portion (not shown) which becomes a bridge. (FIG. 5L and S22 in FIG. 6), the bridge structure is completed.

Here, without depositing the underlying SiN 52, if the SiN film is formed after the formation of the heat insulating groove in the step described in FIG. 5G, the structure of FIG. 4E is obtained. Further, if the SiN 59 formed in the step described in FIG. 5F is formed so as to be sandwiched between the upper cladding layers, the structure shown in FIG. 4B is obtained. If the SiN 52 formed in the process described in FIG. 5A is formed so as to be sandwiched between the lower cladding layers, the structure shown in FIG. 4C can be obtained.

According to the ninth embodiment, since the exposed part of the cladding layer is covered with the low moisture-permeable member (SiN film in this embodiment), it is possible to prevent the deterioration of the cladding layer around the core due to moisture.

The tenth embodiment relates to the distance from the heat insulating groove side wall to the core of the thermo-optic phase shifter according to the present invention. The above-mentioned FIG. 4E is used for the description of the tenth embodiment.

The distance from the heat insulation groove side wall 13a shown in FIG. 4E to the core 11 is d. The light propagating with the core 11 generally propagates while leaking to a certain extent to the lower cladding 15 and the upper cladding layer 17.

SiN has a refractive index of around 2 and higher than the refractive index of a general core 11. When depositing a SiN film on the side wall 13a, d needs to be large enough so that propagating light is not coupled to the SiN film . On the other hand, if d is too large, the heat from the heater 18 easily escapes to the silicon substrate 14 side, and the power consumption as a phase shifter is increased.

For this reason, d needs to select an optimal value. In general, when the relative refractive index difference Δ of the waveguide is 0.7%, d is optimally about 15 μm, and when the relative refractive index difference Δ of the waveguide is about 6%, d is preferably about 3 μm. It is. These can be determined by simulation using BPM (business process management).

According to the tenth embodiment, it is possible to obtain the optimum distance from the heat insulation groove side wall to the core.

The eleventh embodiment relates to a method of manufacturing a bridge structure using sacrificial layer etching according to the present invention. 7A to 7L are schematic sectional views showing the processing procedure of the method for manufacturing a bridge structure in the eleventh embodiment of the present invention. FIG. 8 is a flow chart showing the processing procedure of the manufacturing method of the bridge structure in the eleventh embodiment.

First, the sacrificial layer 63 is formed on the silicon substrate 14 by CVD or the like (S31 in FIGS. 7A and 8). The sacrificial layer 63 is preferably a PSG film or the like having a high etching rate by BHF (buffered hydrofluoric acid). Further, SiN 52 is formed on the sacrificial layer 63.

Next, NSG to be a material of the lower cladding layer 15 and SiON to be a material of the core 54 are formed (FIG. 7B and S32 in FIG. 8).

The core 11 is formed by photolithography and dry etching techniques, and heat treatment is performed as needed (FIGS. 7C and S33 in FIG. 8).

Thereafter, a film having a low softening point such as BPSG or PSG to be the buried layer 16 or the upper cladding layer 17 is formed, and heat treatment is performed as needed (FIG. 7D and S34 in FIG. 8).

Next, a metal film such as Pt or Ti to be a heater is formed on the upper cladding layer 17 by a sputtering apparatus or a vapor deposition apparatus, and the heater 18 is formed right above the core by photolithography and etching (FIG. 7E and FIG. S35 of 8).

Next, SiN 59 covering the heater 18 is formed on the upper cladding layer 17, and a chromium film 60 serving as a stopper layer is formed thereafter from above (FIG. 7F and S 36 in FIG. 8).

Next, a resist 61 having a predetermined pattern is formed on the chromium film 60 by photolithography. Subsequently, dry etching is performed from above the resist 61 to remove the cladding layer at a predetermined distance from both sides of the core, thereby forming a heat insulating groove (FIG. 7G and S37 in FIG. 8).

Next, the structure shown in FIG. 7G is immersed in BHF or the like to selectively etch the sacrificial layer 63 (FIG. 7H and S38 in FIG. 8), and a bridge structure is formed (FIG. 7I and S39 in FIG. 8).

Thereafter, the resist is removed and SiN 62 is deposited (FIG. 7J and S40 in FIG. 8).

By dry etching, the SiN 62 on the bottom of the heat insulation groove (the upper surface of the silicon substrate 14) and the chromium film 60 is removed (FIG. 7K and S41 in FIG. 8).

Finally, the chromium film 60 is removed to complete the bridge structure (FIG. 7L and S42 of FIG. 8).

According to the eleventh embodiment, a bridge structure using sacrificial layer etching is obtained.

The twelfth embodiment relates to a method of passivating the optical waveguide with SiN after bridging the optical waveguide in one example of the present invention. 9A to 9L are schematic sectional views showing the processing procedure of the method for manufacturing a bridge structure of the twelfth embodiment of the present invention. FIG. 10 is a flow chart showing the processing procedure of the manufacturing method of the bridge structure in the twelfth embodiment.

First, SiN 52 is deposited on the silicon substrate 14 by CVD or the like (S51 in FIGS. 9A and 10).

Next, NSG to be the material of the lower cladding layer 15 and SiON to be the material of the core layer 54 are deposited by the same apparatus (FIG. 9B and S52 in FIG. 10).

The core 11 is formed by photolithography and dry etching techniques, and heat treatment is performed as needed (FIGS. 9C and S53 in FIG. 10).

Thereafter, a film having a low softening point such as BPSG or PSG to be the buried layer 16 or the upper cladding layer 17 is formed, and heat treatment is performed as needed (FIG. 9D and S54 in FIG. 10).

Next, a metal film such as Pt or Ti to be a heater is formed on the upper cladding layer 17 by a sputtering apparatus or a vapor deposition apparatus, and the heater 18 is formed right above the core by photolithography and etching (FIG. 9E and FIG. 10 S55).

Next, SiN 59 covering the heater 18 is formed on the upper cladding layer 17, and a chromium film 60 serving as a stopper layer is formed thereafter (FIG. 9F and S56 in FIG. 10).

Next, a resist 61 having a predetermined pattern is formed on the chromium film 60 by photolithography. Subsequently, dry etching is performed from above the resist 61 to remove the cladding layer at a predetermined distance from both sides of the core, thereby forming a heat insulating groove (FIG. 9G and S57 in FIG. 10).

Next, the top surface of the silicon substrate 14 is isotropically etched with xenon fluoride gas or the like (FIGS. 9H and S58 in FIG. 10) to form a bridge structure (FIG. 9I and FIG. 10 S59).

The resist 61 is removed, and SiN 62 is deposited thereon (FIGS. 9J and S60 in FIG. 10).

Next, the SiN 62 on the bottom of the heat insulation groove (upper surface of the silicon substrate 14) and the chromium film 60 is removed by dry etching (FIG. 9K and S61 in FIG. 10).

Finally, the chromium film 60 is removed to complete the bridge structure (FIG. 9L and S62 in FIG. 10).

According to the twelfth embodiment, a bridge structure in which the cladding layer is passivated with SiN after being bridged is obtained.

The thirteenth embodiment relates to the configuration of a support of a bridge structure. 11A to 11C are configuration diagrams showing an example of a support of the bridge structure of the present invention. FIG. 11A is a plan view of the phase shifter portion. 11B is a cross-sectional view of a portion of line segment BB in FIG. 11A. FIG. 11C is a cross-sectional view of the portion of line segment AA in FIG. 11A.

In the optical waveguide portion shown in FIGS. 11A and 11B, the lower cladding layer 15, the buried layer 16 and the upper cladding layer 17 are formed in order. The core 11 is provided in the buried layer 16, and the heater 31 is provided on the upper cladding layer 17. SiN is provided in the top layer and the bottom layer of the optical waveguide portion.

For example, the heat insulating groove 32 is formed in the shape as shown in FIG. 11A with respect to the buried layer 16, the lower cladding layer 15, and the upper cladding layer 17, and then the upper surface of the silicon substrate 33 is etched. As a result, as shown in FIG. 11C, the portion of the line segment AA shown in FIG. 14 is completely side edged from the upper surface of the silicon substrate 33 which is the base portion of the optical waveguide portion to a predetermined depth. The part is a bridge structure. On the other hand, as shown in FIG. 11B, in the portion of the line segment B-B shown in FIG.

12 and 13 are perspective views showing the process of forming the pillars 34 by isotropic etching on a silicon substrate. FIG. 12 shows a state before isotropic etching is performed on a silicon substrate, and FIG. 13 shows a state after performing isotropic etching on a silicon substrate.

For example, the external perspective view of the structure shown in FIG. 5J corresponds to FIG. 12, and the cross-sectional structure shown in FIG. 5K corresponds to the cross section of the portion of line segment B-B in FIG. The cross sectional structure corresponds to the cross section of the portion of the line segment AA in FIG. In FIG. 12 and FIG. 13, for the sake of convenience, the SiN film formed around the optical waveguide portion is partially omitted.

According to the thirteenth embodiment, the bridge structure and the support of the thermo-optic phase shifter according to the present invention are obtained.

The fourteenth embodiment relates to the configuration of the heat insulating groove. FIG. 14 is a cross-sectional view showing an example of the heat insulating groove provided in the optical waveguide of the present invention. FIG. 14 is a cross-sectional view in which the cross-sectional structure shown in FIG. 5G is expanded and displayed in the lateral direction (the left and right directions parallel to the sheet centering on the drawing).

As shown in FIG. 14, in the phase shifter portion 41, grooves are formed on both sides of the waveguide core 42 at a predetermined distance in the lateral direction from the waveguide core 42. As described above, a groove which is provided in the laminated film including the cladding 45 and the cladding 46 so as to separate the phase shifter portion 41 and which reaches the surface of the silicon substrate is referred to as a heat insulating groove 43.

According to the fourteenth embodiment, since the heat insulating groove 43 is provided so that the heat from the heater 44 does not escape via the clad 45 and the clad 46, power consumption can be reduced.

SiN films are known to have lower moisture permeability than silicon oxides because the crystal structure is very compact. By covering the phase shifter portion 41 shown in FIG. 14 with the SiN film, the entrance and exit of water is interrupted between the core and the cladding functioning as the optical waveguide and the outside, and as a result, the refractive index and stress change due to film deterioration Can be prevented.

As one example of the effect of the present invention, it is possible to prevent the deterioration of the core due to the moisture of the cladding around the core.

The bridge structure according to the present invention is applicable not only to the optical waveguide circuit but also to other fields such as fabrication of a cantilever in the field of MEMS (Micro Electro Mechanical Systems) etc., instead of the bridge structure by sacrificial layer etching. .

Although the present invention has been described above with reference to the embodiments and the examples, the present invention is not limited to the above embodiments and the examples. The configurations and details of the present invention can be modified in various ways that can be understood by those skilled in the art within the scope of the present invention.

This application incorporates all the contents of Japanese Patent Application No. 2009-041601 filed on February 25, 2009, and claims priority based on this Japanese application.

1, 4, 6, 8, 10, 22

Optical waveguide

2, 3, 5, 7, 9, 21 Optical waveguide circuit 11 Core 12 Clad layer 13 Low

moisture permeability member

14, 33 Silicon substrate 15 Lower clad layer 16 Buried layer 17

Upper cladding layer

18, 31, 44

Heater

32, 43 Heat insulation groove 34 Support 41 Phase shifter portion 42

Waveguide core

45, 46 Cladding

Claims

A core through which light is guided,
A cladding layer covering the core;
A low moisture-permeable member, which is a member that has a lower moisture permeability than silicon oxide and covers the exposed portion of the cladding layer;
An optical waveguide.
In the optical waveguide according to claim 1,
An optical waveguide, wherein a heat generating member is provided on the cladding layer.
In the optical waveguide according to claim 2,
An optical waveguide is further provided at a position separated by a predetermined distance from each of both side surfaces of the core, and further includes a groove for preventing heat from the heat generating member from diffusing through the cladding layer.
In the optical waveguide according to any one of claims 1 to 3,
The optical waveguide, wherein the low moisture-permeable member is made of a compound containing silicon and nitrogen.
An optical waveguide according to any one of claims 1 to 4;
A silicon substrate supporting the optical waveguide;
An optical waveguide circuit.
In the optical waveguide circuit according to claim 5,
The optical waveguide circuit, wherein the optical waveguide is a bridge structure in which a space is formed in a part between the optical waveguide and the silicon substrate.
Forming a first cladding layer and a core layer sequentially on the silicon substrate,
Forming a core on the core layer by photolithography technology and etching technology;
Forming a second cladding layer covering the core;
Forming a groove in the first and second cladding layers at a predetermined distance from each of both side surfaces of the core by photolithography and etching techniques;
A method of manufacturing an optical waveguide circuit, wherein a first low moisture-permeable member, which is a member having lower moisture permeability than silicon oxide, is formed in exposed portions of the first and second cladding layers.
In the method of manufacturing an optical waveguide circuit according to claim 7,
A method of manufacturing an optical waveguide circuit, wherein a heat generating member is formed on the second cladding layer after forming the second cladding layer covering the core.
In the method of manufacturing an optical waveguide circuit according to claim 7 or 8,
When the first clad layer and the core layer are sequentially formed on the silicon substrate, a second low moisture-permeable member which is a member of the same quality as the first low moisture-permeable member is the silicon substrate and the Formed between two cladding layers,
The upper surface of a portion of the upper surface of the silicon substrate in contact with the second low moisture-permeable member after forming the first low moisture-permeable member on the exposed portion of the first and second cladding layers A method of manufacturing an optical waveguide circuit, wherein a space is formed between the second low moisture-permeable member and the silicon substrate by removing silicon to a predetermined depth.