JP2666751B2 - Manufacturing method of optical waveguide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical waveguide, and more particularly, to a method for manufacturing an optical waveguide in which a core on a stripe formed on a substrate is buried by cladding.

[0002]

2. Description of the Related Art FIG. 3 is a sectional view of a waveguide showing an example of a conventional optical waveguide device. After forming a lower clad layer 8 formed on the substrate 1 and a core layer 3 made of a material having a higher refractive index than the lower clad 8, the striped core 3b is formed by etching. When an optical waveguide is formed by embedding with the upper cladding layer 9, the embedding of the upper cladding layer 9 is incomplete in a structure in which the cores are arranged close to each other, and the air layer 10 is generated between the cores. ing. The air layer 10 thus generated needs to be removed because characteristics such as propagation loss, filter characteristics, and polarization dependence of the optical waveguide deteriorate.

[0003] For this purpose, for example, Japanese Patent Laid-Open Publication No.
As disclosed in reference numeral 509, the embedding characteristics are improved by controlling the shape before embedding. FIG. 4 shows a method for improving the embedding characteristics using this method.
A lower clad layer 8 formed on the substrate 1 and a core layer made of a material having a higher refractive index than the lower clad layer 8 are formed, and a striped core 3b formed by etching is formed.
A spreading layer 11 is formed on the substrate 3 and the substrate 1 is heated to a temperature not lower than the reflow temperature of the material forming the core 3b, thereby removing the reentrant corners of the core 3b and improving the embedding of the upper cladding layer 9.

Conventionally, when the upper cladding layer 9 is formed, a structure in which the cores are arranged close to each other and the upper cladding layer 9 are buried by melting and manufacturing the fine quartz powder. ing. On the other hand, there is known a technique in which an etching hole is filled with a quartz-based film by reflowing at a low temperature of 800 ° C. or less using glass mixed with boron and phosphorus.

[0005]

In the above-mentioned method for removing the reentrant corners of the core by reflowing the core,
Since the shape of the core changes, a rectangular optical waveguide cannot be obtained, resulting in a problem that the polarization dependence of the waveguide characteristics is caused.

In the above method of melting the fine quartz powder to form an upper clad layer, generally, a high temperature of 1000 ° C. or more is required to melt the fine quartz powder. There is a problem that the stress remains and the birefringence of the optical waveguide characteristics increases, and that it is difficult to form a waveguide on a substrate on which metal wiring and the like are formed. Since the boron contained in the glass mixed with boron and phosphorus and the impurities such as germanium and titanium contained in the core diffuse into each other in the film, a variation occurs in the cross-sectional refractive index distribution of the optical waveguide. As a result, there has been a problem that the polarization dependence of the optical waveguide characteristics such as propagation loss is increased.

SUMMARY OF THE INVENTION It is an object of the present invention to bury a region close to the core without changing the shape of the core and without using a process that raises the temperature to a temperature higher than 850 degrees. It is to enable the manufacture of a small optical waveguide.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a method of manufacturing an optical waveguide in which a stripe-shaped core formed on a substrate is embedded with a clad, and wherein a first lower clad layer and the first lower clad layer are formed on the substrate. After forming a core layer made of a material having a lower reflow temperature than the layer and etching the core layer to form a striped core, the core is made of a material having a reflow temperature higher than the reflow temperature of the material forming the core. Forming a first upper clad layer, which is a layer covering the second upper clad layer, and then forming a second upper clad layer having a lower reflow temperature than the material of the first upper clad layer on the first upper clad layer; After maintaining the substrate at a temperature higher than the reflow temperature of the second cladding layer, a third upper cladding layer is formed on the second upper cladding layer. Note that a second lower clad layer may be formed between the first lower clad layer and the core layer. For the second lower cladding layer, a material having a lower reflow temperature than the material of the core layer and the first lower cladding layer is used.

[0009]

In order to form a first upper clad layer having a higher reflow temperature than the material of the core so as to cover the core, and then to form a second clad layer made of a material having a lower reflow temperature than the material of the core, The diffusion of the impurities contained in the core and the second cladding layer can be suppressed. For this reason, it becomes easy to control the refractive index distribution of the cross section of the core and the second cladding layer, and it is possible to manufacture a device in which the polarization dependence of the characteristics of the optical waveguide is small.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a process chart relating to a first embodiment according to the present invention. FIG. 1A shows a step of forming a first lower cladding layer 2 and a core layer 3a having a higher refractive index than the first lower cladding layer 2 on the substrate 1 in the optical waveguide. A silicon substrate is used as the substrate 1, and glass (hereinafter referred to as PSG) containing phosphorus as an impurity is used as the first lower cladding layer 2.
Glass having a thickness of 0 μm and glass containing germanium and phosphorus as impurities (hereinafter referred to as GPSG) was formed as the core layer 3 a with a thickness of 6 μm. The material of the first lower cladding layer 2 needs to have a reflow temperature sufficiently higher than that of the material of the core layer 3a in order to reduce the diffusion of impurities.

FIG. 1B shows a step of processing the core layer 3a into a striped core 3b by a reactive ion beam etching apparatus after patterning the optical waveguide by photolithography. The width of the stripe was 6 μm. The etching apparatus is not limited to the reactive ion beam etching apparatus, and any method can be used as long as it is a method capable of forming a core in a stripe shape by reactive ion etching or the like.

FIG. 1C shows a step of forming the first upper cladding layer 4. The material of the first upper cladding layer 4 preferably has a refractive index close to that of the first lower cladding layer 2. 0.15 μm PSG as the first upper cladding layer
Formed. It is necessary that the reflow temperature of the material of the first upper cladding layer is higher than the reflow temperature of the material forming the core 3b.

FIG. 1D shows a step of forming the second upper clad layer 5. A glass (hereinafter, referred to as BPSG) containing boron and phosphorus as impurities was formed as the second upper cladding at 1.6 μm. The material of the second upper cladding layer 5 needs to have a lower reflow temperature than that of the first upper cladding layer 4. The material of the second upper cladding layer 5 preferably has a refractive index close to that of the first lower cladding layer 2.

FIG. 1E shows a step of making the second upper cladding layer 5 forward tapered by reflow. The reflow was performed at 800 ° C. for 3 hours in an oxygen atmosphere containing water vapor. When performing in an atmosphere that does not contain water vapor, the reflow temperature is 8
About 50 degrees is desirable. The atmosphere is not limited to the oxygen atmosphere as long as the atmosphere causes reflow.

FIG. 1F shows a step of forming a third upper cladding layer 6. 10 μm of PSG as the third cladding layer
m was formed. Since the cross-sectional shape of the optical waveguide has a forward tapered shape due to the pre-reflow step, the embedding is easy. The material of the third upper cladding layer 6 preferably has a refractive index close to that of the first lower cladding layer 2. Note that P
For the formation of SG, GPSG and BPSG, tetraethoxysilane (TEOS), phosphine tetramethoxide (T
MOP), germanium tetramethoxide (TMG),
An atmospheric pressure chemical vapor deposition method using a tetraethoxyboron (TEB) source was used.

The inventor uses the material having a reflow temperature higher than the reflow temperature of the material of the core 3b and the second upper cladding layer 5 for the first upper cladding layer 4 so that the core 3b and the second upper cladding layer 5 include the material. It has been found that the diffusion of impurities can be suppressed and the change in the refractive index can be suppressed. Therefore, the optical waveguide formed by the process of FIG. 1 has a good embedding in a region where the core 3b is close, has a square core shape, has a small birefringence because of using a low-temperature process, and Since the refractive index distribution of the cross section is easily controlled, an optical waveguide having small polarization dependence of the waveguide characteristics can be obtained. Further, since a low-temperature process is used, a waveguide can be formed on a substrate on which a metal film or the like is formed.

FIG. 2 is a flow chart showing a second embodiment according to the present invention. The difference from the first embodiment is that the first lower cladding layer 2 and the third upper cladding layer 6 are made of the same material as the second upper cladding layer, and the core layer 3a and the third This means that the second lower clad layer 7 made of a material having a lower reflow temperature than the material of the first lower clad layer 2 is formed.

In both the first and second embodiments, the second upper clad layer 5
, The formation of the third upper cladding layer 6 can be omitted. As a material of the substrate 1, silicon is generally used.
a first lower clad layer 2, a second lower clad layer 7, a core layer 3a, a first
As a material used for the upper cladding layer 4, the second upper cladding layer 5, and the third upper cladding layer 6, it is common to use a quartz glass containing phosphorus, boron, germanium, titanium, or the like as an impurity. Further, silicon nitride or SiON can also be used. The formation method is not limited to the CVD method, the EB evaporation method, the sputtering method, and the flame deposition method, and is not limited. For the second upper clad layer 7 and the first lower clad layer 4, it is necessary to use a material higher than the reflow temperature of the material used for the reflow layer 5 and the core 3b, and it is desirable that the refractive index is closer to that of the clad layer. When the refractive index is different from that of the cladding layer, it is necessary to reduce the thickness so as not to affect the optical electric field in the cross section. Second
It is desirable that the thickness of the upper cladding layer 5 be sufficiently smaller than the wavelength of light to be propagated through the waveguide.

[0019]

By using the method for manufacturing an optical waveguide according to the present invention, a device having a good embedding of the upper cladding layer in a region where the core of the waveguide is close and having a small birefringence can be manufactured by using a low-temperature process. Can be manufactured. Also,
Since it is a low-temperature process, a waveguide can be formed on a substrate on which a metal film or the like is formed.

[Brief description of the drawings]

FIGS. 1A to 1F are process diagrams of a method for manufacturing an optical waveguide according to a first embodiment of the present invention.

FIGS. 2A to 2F are process diagrams of a method for manufacturing an optical waveguide according to a second embodiment of the present invention.

FIG. 3 is a cross-sectional view showing an example of a conventional optical device.

FIG. 4 is a cross-sectional view of an optical waveguide manufactured using a method disclosed in Japanese Patent Application Laid-Open No. 1-267509.

[Explanation of symbols]

 Reference Signs List 1 substrate 2 first lower clad layer 3a core layer 3b core 4 first upper clad layer 5 second upper clad layer 6 third upper clad layer 7 second lower clad layer 8 lower clad layer 9 upper clad layer 10 air layer 11 Layer

Claims (2)

(57) [Claims] 1. A method of manufacturing an optical waveguide in which a stripe-shaped core formed on a substrate is embedded by cladding, wherein a first lower cladding layer and a material having a lower reflow temperature than the first lower cladding layer are formed on the substrate. A core layer formed by forming a striped core by etching the core layer, and then covering the core with a material having a reflow temperature higher than the reflow temperature of the material forming the core. Forming an upper cladding layer, forming a second upper cladding layer having a lower reflow temperature than the material of the first upper cladding layer on the first upper cladding layer, and further forming the substrate on the second upper cladding layer; A method for manufacturing an optical waveguide, comprising forming a third upper clad layer on the second upper clad layer after maintaining the temperature higher than the reflow temperature of the layer . 2. A method of manufacturing an optical waveguide in which a stripe-shaped core formed on a substrate is embedded by cladding, wherein a reflow of materials of a first lower cladding layer, the first lower cladding layer and the core layer is performed on the substrate. After forming the second lower cladding layer having a reflow temperature higher than the temperature and the core layer, a striped core is formed by etching, and the first upper layer is formed of a material having a reflow temperature higher than the reflow temperature of the material forming the core. Forming a cladding layer , and then forming a second upper cladding layer having a lower reflow temperature than the material of the first upper cladding layer on the first upper cladding layer; Forming a third upper clad layer on the second upper clad layer after maintaining the temperature higher than the reflow temperature of the optical waveguide. Method.