JP2002189140A - Optical waveguide device and method of manufacturing the same - Google Patents

Abstract

(57) Abstract: Provided is an optical waveguide device capable of suppressing occurrence of warpage in an optical waveguide device and obtaining good optical characteristics even when heat treatment is performed in a manufacturing process, and a method of manufacturing the same. . A substrate (1) constituting an optical waveguide device (1).
2, the density of each of the core layer 16 and the cladding layer 18 is set to about 5% by mass of hydrogen fluoride and about 35% by mass.
And the etching rate at a temperature of 20 ° C. using buffered hydrofluoric acid containing ammonium fluoride.
A numerical condition of 0 ° / min or less is given. This allows
The difference in the amount of contraction and expansion due to heating in each layer is reduced, and the occurrence of warpage in the optical waveguide device 1 during heat treatment is suppressed,
An optical waveguide and an optical circuit having good optical characteristics are realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide device having an optical waveguide formed on a substrate by a predetermined waveguide pattern, and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, with the development and expansion of optical communication technology, in addition to light emitting devices and light receiving devices, and optical waveguides such as optical fibers, various types of optical multiplexer / demultiplexers, optical switches, optical modulators and the like have been developed. The development and use of optical circuit devices having various functions have been promoted.

[0003] As such an optical circuit device, an optical waveguide device having a planar waveguide type optical circuit using a planar optical waveguide formed on a substrate by a predetermined waveguide pattern (optical circuit pattern) is used. The planar waveguide type optical waveguide device has advantages such as integration of an optical circuit, downsizing of the optical waveguide device, and cost reduction, because the degree of freedom of the configuration of the waveguide pattern is large. . When a planar waveguide type optical circuit is used, an electronic circuit can be integrated with the optical circuit on the same substrate.

In a planar waveguide type optical circuit, an optical waveguide formed on a substrate is composed of a core layer and a cladding layer. That is, a cladding layer having a lower refractive index than the core layer is deposited on the core layer formed on the substrate by a predetermined waveguide pattern so as to cover the substrate and the core layer. At this time, the core layer functions as an optical waveguide due to the refractive index distribution in the laminated structure.

[0005]

SUMMARY OF THE INVENTION In an optical waveguide device using a planar waveguide type optical circuit having the above-described structure, in the manufacturing process, an optical waveguide is formed by depositing a core layer and a cladding layer on a substrate. Later, heat treatment may be performed for the purpose of adjusting the optical characteristics of the optical waveguide.

When the heat treatment is performed on the optical waveguide device in this manner, even if the heat treatment is performed at a temperature lower than the softening point temperature of the substrate or the like (for example, about 1500 ° C. for a quartz substrate). , A substrate in an optical waveguide device, a core layer,
Each layer (each part) of the cladding layer contracts or expands by heating. At this time, in each of the substrate, the core layer, and the cladding layer, shrinkage caused by heating,
If the expansion conditions are different from each other, the shrinkage /
The difference in the amount of expansion causes the optical waveguide device to warp (see Japanese Patent Application Laid-Open No. 2000-193836).

For example, if the amount of contraction of the substrate is smaller than the amount of contraction of the core layer and the cladding layer, or if the amount of expansion of the substrate is larger than the amount of expansion of the core layer and the cladding layer, in the optical waveguide device, the core layer In addition, warpage occurs in which the surface on the cladding layer side is concave. At this time, a tensile stress is applied to the core layer and the cladding layer in a direction parallel to the substrate.

In the optical waveguide device, if the amount of contraction of the substrate is larger than the amount of contraction of the core layer and the cladding layer, or if the amount of expansion of the substrate is smaller than the amount of expansion of the core layer and the cladding layer, In addition, warpage occurs in which the surface on the side of the cladding layer becomes convex. At this time, in the core layer and the cladding layer,
A compressive stress is applied in a direction parallel to the substrate.

As described above, when warpage occurs in the optical waveguide device due to the difference in the amount of contraction / expansion in each layer, the pitch of the waveguide pattern in the planar waveguide optical circuit formed on the substrate (the pitch of the optical waveguide). (Array interval) deviates from the designed value. At this time, there arises a problem that the optical characteristics of the optical waveguide and the optical circuit are deteriorated, and that the characteristics vary from product to product.

Further, when an excessive stress is applied to the core layer and the cladding layer, the refractive index in the direction in which the stress is applied changes due to the photoelastic effect, and the anisotropy of the refractive index in the core layer serving as the optical waveguide. Causes sexuality. This anisotropy of the refractive index causes unnecessary polarization dependence in the optical characteristics of the optical waveguide and the optical circuit.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and even when heat treatment is performed in a manufacturing process, the occurrence of warpage in an optical waveguide device is suppressed, and good optical characteristics are obtained. And a method for manufacturing the same.

[0012]

In order to achieve the above object, an optical waveguide device according to the present invention comprises (1) a substrate and (2) an optical waveguide formed on a substrate by a predetermined waveguide pattern. And (3) a cladding layer formed on the substrate so as to cover the substrate and the core layer, and having a lower refractive index than the core layer.
(4) Hydrogen fluoride of approximately 5% by mass ratio and approximately 35 by mass ratio
% Of each layer was evaluated by the etching rate at a temperature of 20 ° C. using buffered hydrofluoric acid containing 5% ammonium fluoride, and the etching rates of the substrate, the core layer, and the cladding layer were each 5000 ° C./min.
It is characterized by the following.

In the above optical waveguide device, the fineness of each layer (substrate, core layer, and clad layer) constituting the optical waveguide device is evaluated by an etching rate, and the etching rate (density) of each layer is determined. On the other hand, numerical conditions of 5000 ° / min or less are given. At this time, as described later, the difference in the amount of shrinkage / expansion in each layer is reduced, so that the occurrence of warpage in the optical waveguide device is suppressed even when heat treatment is performed in the manufacturing process. Thereby, an optical waveguide and an optical circuit having good optical characteristics are realized.

With respect to the numerical condition given to the etching rate, by setting the condition according to the configuration of the optical circuit included in the waveguide pattern, a favorable condition is obtained for the optical circuit in each optical waveguide device. Optical characteristics can be realized.

That is, when the waveguide pattern of the core layer has a directional coupler, the etching rates of the substrate, the core layer, and the cladding layer are each 2.
It is preferably at most 000 ° / min. As an optical circuit having a directional coupler, for example, there is a Mach-Zehnder type optical circuit (MZI).

Further, when the waveguide pattern of the core layer has an array waveguide composed of a plurality of channel waveguides, the etching rates of the substrate, the core layer, and the cladding layer are each 1000 ° / min. The following is preferred. As an optical circuit having an arrayed waveguide section, for example, there is a waveguide diffraction grating type optical circuit (AWG).

Further, the method for manufacturing an optical waveguide device according to the present invention comprises the steps of (1) using buffered hydrofluoric acid containing approximately 5% by mass of hydrogen fluoride and approximately 35% by mass of ammonium fluoride by mass. When the density of each layer was evaluated by the etching rate at a temperature of 20 ° C., the etching rate was 5%.
While preparing a substrate of not more than 000Å / min,
Oxygen gas, organosilicon compound gas, and organometallic gas are introduced into the vacuum vessel on which the substrate is placed, and the oxygen gas, organosilicon compound gas, and organometallic gas are reacted in an inductively coupled high-frequency plasma state in the vacuum vessel. As a result, when the etching rate is 5000 ° / min or less,
An optical waveguide film forming step of forming an optical waveguide film made of silicon oxide doped with a metal element contained in an organic metal gas on a substrate; and (2) an optical waveguide film formed on the substrate with a predetermined conductivity. Patterning with a waveguide pattern, a core layer forming step of forming a core layer constituting the optical waveguide,
(3) An oxygen gas and an organic silicon compound gas are introduced into a vacuum vessel in which a substrate having a core layer is placed, and the oxygen gas and the organic silicon compound gas are reacted in an inductively coupled high-frequency plasma state in the vacuum vessel. A cladding layer forming step of forming a cladding layer made of silicon oxide and having a lower refractive index than the core layer on the substrate so as to cover the substrate and the core layer at an etching rate of 5000 ° / min or less, (4) A heat treatment step of performing a heat treatment at a predetermined heating temperature on the substrate and the core layer and the clad layer formed on the substrate.

In the above-described method of manufacturing an optical waveguide device, an inductively coupled type in which a core layer and a clad layer are formed on a substrate by introducing source gases into a vacuum vessel and reacting them in an inductively coupled high-frequency plasma state. Plasma CV
It is based on the D method. According to this manufacturing method, it is possible to suppress the occurrence of warpage in the optical waveguide device after the heat treatment step, by forming each layer so as to satisfy the above numerical conditions of the etching rate (density).

In the heat treatment step, the heating temperature is set at 6.
The heat treatment is preferably performed at a temperature in the range of 00 ° C to 1200 ° C. By setting the heating temperature within this temperature range, the heating temperature can be set lower than the softening point temperature of the substrate and at which a sufficient effect of adjusting the optical characteristics can be obtained.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of an optical waveguide device and a method of manufacturing the same according to the present invention will be described below in detail with reference to the drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description. Also, the dimensional ratios in the drawings do not always match those described.

First, the basic configuration of a planar optical waveguide forming an optical circuit in the present optical waveguide device and the principle of the optical waveguide device according to the present invention will be described.

FIG. 1 is a sectional view showing the configuration of a planar optical waveguide in an embodiment of the optical waveguide device according to the present invention. In FIG. 1, one of the planar optical waveguides formed on the substrate by a predetermined waveguide pattern (optical circuit pattern) and constituting an optical circuit in the optical waveguide device.
The cross-sectional structure of this optical waveguide is shown by a vertical cross section orthogonal to the direction in which the optical waveguide extends.

This optical waveguide device 1 is an optical circuit device provided with a planar waveguide type optical circuit composed of an optical waveguide formed on a predetermined substrate such as a quartz substrate, and includes a substrate 12, a core layer 16, (Overcladding layer) 18.

The core layer 16 has a substantially rectangular cross section.
It is formed on the substrate 12 by a predetermined waveguide pattern. The core layer 16 forms a planar optical waveguide through which light is guided in the optical waveguide device 1. In addition, the cladding layer 1
8 is formed on the substrate 12 so as to cover the substrate 12 and the core layer 16. This cladding layer 18 has a lower refractive index than the core layer 16, and
Function as an optical waveguide capable of guiding light.

In the optical waveguide device 1 provided with the planar waveguide type optical circuit composed of the planar optical waveguide having the above-described configuration, the core layer 16 and the clad layer 18 are deposited on the substrate 12 in the manufacturing process as described later. After that, heat treatment may be performed on each layer (including the substrate 12).
The inventor of the present application has studied the warpage generated in the optical waveguide device 1 during this heat treatment. As a result, the amount of warpage generated greatly depends on the density of each layer (each part) of the optical waveguide device 1. I got the knowledge.

That is, when the heat treatment is performed, each layer of the optical waveguide device 1 contracts or expands due to heating, but the amount of contraction / expansion changes depending on the density of each layer. At this time, the amount of warpage generated in the optical waveguide device 1 changes similarly due to the difference in the amount of contraction and expansion.

In the optical waveguide device according to the present invention, each layer (substrate 12, core layer 16, and cladding layer 18)
By applying certain conditions to the density of each layer, the difference in the amount of shrinkage and expansion caused by heating in each layer is reduced. Thereby, even when heat treatment is performed in the manufacturing process, occurrence of warpage in the optical waveguide device is suppressed.

When warpage occurs in the optical waveguide device, a shift occurs in the pitch of the waveguide pattern in the planar waveguide type optical circuit formed on the substrate. Further, when stress is applied to the core layer 16 and the cladding layer 18 due to the warpage, the photoelastic effect causes anisotropy of the refractive index in the optical waveguide, which causes unnecessary polarization dependence in the optical characteristics. On the other hand, by suppressing the occurrence of warpage as described above, an optical waveguide and an optical circuit having good optical characteristics can be realized.

Further, the inventor of the present application has found that an etching rate at the time of etching each layer can be used as an index for quantitatively evaluating the fineness of each layer of the optical waveguide device. If the layer to be etched is dense (fine grain), the etching rate of that layer will be small (slow). On the other hand, if the layer is not dense (coarse grain), the etching rate of the layer becomes large (fast).

Therefore, it is possible to quantitatively evaluate the fineness of each layer by the etching rate of each layer. In the optical waveguide device according to the present invention, the substrate 1
2. By giving a predetermined numerical condition to each of the etching rates of the core layer 16 and the cladding layer 18, the amount of warpage generated in the optical waveguide device 1 is reduced.

Here, in the evaluation of the denseness of each layer by the etching rate, an etching solution for evaluation is as follows.
Buffered hydrofluoric acid (BHF) used as a general etching solution was used. More specifically, approximately 5% by mass of hydrogen fluoride and approximately 35% by mass
Hydrofluoric acid containing ammonium fluoride (other about 60% of water is water) as an etching solution for evaluation,
The etching rate was derived at a temperature of 20 ° C. (room temperature).

For the derivation of the etching rate, for example, a method of performing etching at a temperature of 20 ° C. using the above-mentioned buffered hydrofluoric acid for a preset etching time and measuring the amount of etching can be used. Hereinafter, when simply referred to as "buffered hydrofluoric acid", it means buffered hydrofluoric acid having the above-described composition. In addition, the term "etching rate" refers to an etching rate at a temperature of 20 ° C. using buffered hydrofluoric acid having the above composition.

With respect to the correlation between the etching rate used for quantitative evaluation of the density of each layer and the amount of warpage generated in the optical waveguide device during the heat treatment, the cladding layers 18 having different etching rates (density) were formed. Each of the optical waveguide devices 1 was prepared and confirmed.

As the substrate 12, a quartz substrate having a thickness of 1 mm and an etching rate of 700 ° / min was prepared. Then, a core layer 16 is formed on the substrate 12 by a predetermined waveguide pattern, and a 30 μm thick cladding layer (overcladding layer) 18 made of pure quartz (SiO ₂ ) is further etched thereon by a predetermined etching. Rate (Dense)
It formed so that it might become. After that, 800
The substrate 1 is subjected to a heat treatment (annealing treatment) at 6 ° C. for 6 hours.
2, the amount of warpage generated in the optical waveguide device 1 including the core layer 16 and the cladding layer 18 was evaluated.

FIG. 2 shows the etching rate (horizontal axis, Å / min) of the clad layer 18 of the optical waveguide device 1 formed under the above-described configuration and conditions at a temperature of 20 ° C. using buffered hydrofluoric acid. The stress acting on the cladding layer 18 due to the warpage of the optical waveguide device 1 after the heat treatment (vertical axis,
7 is a graph showing a correlation with the pressure (MPa). Here, the stress shown on the vertical axis in FIG. 2 is a numerical value obtained by calculating the stress applied to the cladding layer 18 based on the amount of warpage of the substrate 12. This stress generated in the cladding layer 18 was a tensile stress in a direction parallel to the substrate. The stress in the direction perpendicular to the substrate is almost zero.

In the data shown in the graph of FIG. 2, the etching rates are 1000 / min and 2000 / min, respectively.
/ Min, and 5000 ° / min clad layer 1
8, three types of optical waveguide devices 1 were prepared. Then, the amount of warpage of the substrate 12 was evaluated for each optical waveguide device, and the stress was approximately 0.5 MPa, 2.5 MPa,
And a tensile stress (warpage) of 14.0 MPa.

Further, in the graph of FIG.
The optical waveguide device 1 (substrate 12)
An example of the amount of warpage itself is 1 mm thick.
When a pure quartz layer having a thickness of 20 μm is deposited on the quartz substrate 12 and heat-treated, the amount of warpage is 1 at an etching rate of the pure quartz layer of 800 ° / min for a substrate length of 80 mm.
μm, warpage 3 μm at 2000 ° / min, 5000 °
/ Min, the warpage amount was 15 μm, and at 6000 ° / min, the warpage amount was 30 μm.

These results are obtained because the clad layer 18 becomes denser (the etching rate becomes smaller).
This shows that the amount of warpage in the optical waveguide device and the generation of stress applied to the cladding layer are suppressed. This applies not only to the cladding layer 18 but also to the core layer 16.

It is considered that the above-mentioned correlation between the density (etching rate) of each layer and the amount of warpage is due to the fact that in a layer having a low density, the layer shrinks during heat treatment and changes to a more dense state. By utilizing this fact, by giving a predetermined numerical condition to the etching rate of each layer of the optical waveguide device, the amount of contraction and expansion in each layer is reduced, and the warpage generated in the optical waveguide device at the time of heat treatment. Can be suppressed.

Numerical conditions for the etching rate of each layer are based on the above-mentioned data and other data, and based on the results of examination based on the above data and other data, the substrate 12, the core layer 16, and the cladding layer 18 at a temperature of 20 ° C. using buffered hydrofluoric acid. It is preferable that the etching rates are each 5000 ° / min or less.

At this time, as described above, the difference in the amount of contraction and expansion between the layers is reduced, and the occurrence of warpage in the optical waveguide device during the heat treatment is suppressed. Accordingly, in an optical waveguide device including an optical circuit having a relatively simple configuration such as a linear optical waveguide, an optical waveguide and an optical circuit having sufficiently good optical characteristics are realized. Further, even in an optical waveguide device including an optical circuit having a complicated configuration, the optical characteristics are similarly improved.

When the waveguide pattern of the core layer 16 includes an optical circuit having a directional coupler, the buffered hydrofluoric acid of the substrate 12, the core layer 16, and the cladding layer 18 is removed. It is preferable that the etching rates used are respectively 2000 ° / min or less.

FIG. 3A shows, as an example of such an optical circuit, a planar optical waveguide having a waveguide pattern constituting a Mach Zender Interferometer (MZI) including two directional couplers 2a. 4 shows the optical waveguide device 2 formed. In the optical waveguide device having such an optical circuit, the etching rate is set to 2000Å / m as described above.
By setting in or less, good optical characteristics as an optical circuit can be obtained.

Further, the waveguide pattern of the core layer 16 is
In the case of including an optical circuit having an arrayed waveguide composed of a plurality of channel waveguides, the etching rates of the substrate 12, the core layer 16, and the cladding layer 18 using buffered hydrofluoric acid are each 1000 ° C. / Min
The following is preferred.

FIG. 3B shows, as an example of such an optical circuit, an arrayed waveguide section 3a comprising a plurality of channel waveguides.
Waveguide grating type optical circuit (AWG, Arrayed Wave
2 shows an optical waveguide device 3 in which a planar optical waveguide is formed by a waveguide pattern forming a guide grating. In an optical circuit such as an AWG, its optical characteristics are particularly sensitive to a shift in the pitch of the waveguide pattern and an anisotropy in the refractive index caused by the warpage of the optical waveguide device 1. Therefore, in the optical waveguide device including such an optical circuit, by setting the etching rate to 1000 ° / min or less as described above, it is possible to obtain good optical characteristics as an optical circuit.

Generally, the etching rates of the substrate 12, the core layer 16, and the cladding layer 18 are each 5000 °.
/ Min within the range of 2000 ° / min depending on the configuration of the planar waveguide type optical circuit in each optical waveguide device 1.
It is preferable to set a suitable numerical value of the etching rate for each such as not more than / min or not more than 1000 ° / min.

For example, in the above example, in the case of an optical circuit including an arrayed waveguide, the etching rate is 1000 ° / m.
Although the condition is set to in or less, the condition of 1000 ° / min or less may be set depending on the configuration of an optical circuit not including the arrayed waveguide. In addition, even for a general optical waveguide device including an optical circuit having a relatively simple configuration, 2000 ° / min or less, or 1000 ° / mi.
It goes without saying that the optical characteristics are further improved by giving the condition of n or less.

Further, of the substrate 12, the core layer 16, and the cladding layer 18 constituting the optical waveguide device 1, the substrate 1
With respect to 2, for example, the etching rate of a quartz substrate is about 600 to 700 ° / min, and normally satisfies the numerical condition of 1000 ° / min or less for the etching rate. In this case, the above-described conditions of the respective etching rates may be applied to the core layer 16 and the clad layer 18 formed on the substrate 12.

Next, an example of a method for manufacturing an optical waveguide device according to the present invention will be described. In the manufacturing method described below, a substrate 1 is introduced by introducing an oxygen gas, an organosilicon compound gas, and an organometallic gas into a vacuum vessel and reacting them in an inductively-coupled high-frequency plasma state.
2 is formed by an inductively coupled plasma CVD method (ICP-CVD method) in which a core layer 16 and a cladding layer 18 are formed (see Japanese Patent Application Laid-Open No. 10-221557).

FIG. 4 is a schematic diagram showing a manufacturing apparatus used in the above-described method of manufacturing an optical waveguide device by the ICP-CVD method. The manufacturing apparatus of the optical waveguide device shown in FIG. 4 includes a vacuum vessel 30 for generating inductively coupled high-frequency plasma therein. The vacuum vessel 30 includes a gas inlet 32, a gas outlet 34, and a high-frequency inlet window 36.
have.

The gas inlet 32 is an opening for introducing an oxygen gas, an organic silicon compound gas, and an organic metal gas into the vacuum vessel 30. In this gas inlet 32,
A gas introduction system (not shown) including a gas supply device for supplying each gas and a gas flow control device for adjusting the gas introduction amount is connected.

The gas exhaust port 34 is an opening for exhausting the gas in the vacuum vessel 30. The gas exhaust port 34 is connected to a gas exhaust system (not shown) including a vacuum pump and an exhaust amount adjusting valve for adjusting the exhaust conductance.

The high-frequency introduction window 36 is connected to the vacuum vessel 30.
This is for allowing the high-frequency electromagnetic field generated by the coil 50 provided outside to pass into the vacuum vessel 30.

An electrode plate 40 on which the substrate 12 is mounted is provided below the inner space of the vacuum vessel 30. A high-frequency power supply 44 for adjusting the refractive index is connected to the electrode plate 40 via a matching circuit 42. High frequency power supply 4 for refractive index adjustment
The electrode plate 4 outputs high-frequency power having a frequency of several hundred kHz to several MHz and an output power of several tens W to several hundred W.
Apply to 0. Thereby, the refractive index of each optical waveguide layer formed on the substrate 12 is adjusted by the power value applied to the electrode plate 40. In addition, a coolant circulation pipe 46 for circulating a coolant such as cooling water or cooling oil is provided inside or around the electrode plate 40 when the temperature of the electrode plate 40 rises due to the applied high-frequency power.

The coil 50 provided above the vacuum vessel 30 and close to the high frequency introduction window 36 is
This is for generating inductively coupled high-frequency plasma in the internal space 0. The coil 50 is connected to a high-frequency power source 54 for plasma generation via a matching circuit 52. The plasma-generating high-frequency power supply 54 outputs high-frequency power having a frequency of several tens of MHz and an output power of several hundred W to several thousand W, and applies the high-frequency power to the coil 50.

A method for manufacturing an optical waveguide device using the manufacturing apparatus shown in FIG. 4 will be described. FIG. 5 (a) to (d)
FIG. 4 is a process chart schematically showing one embodiment of a method for manufacturing an optical waveguide device according to the present invention. The method for manufacturing the optical waveguide device according to the present embodiment includes four steps: an optical waveguide film forming step, a core layer forming step, a cladding layer (overcladding layer) forming step, and a heat treatment step.

In the following, the method of manufacturing the optical waveguide device will be described assuming that the numerical conditions for the etching rate of each layer are set to 5000 ° / min or less. As described above, it is preferable that the numerical conditions be appropriately changed according to the configuration of the optical circuit in each optical waveguide device.

First, an optical waveguide film forming step is performed, and the substrate 1
An optical waveguide film 14 is formed on 2 (see FIG. 5A). First, a substrate 12 such as a quartz substrate having an etching rate of 5000 ° / min or less is prepared, and the substrate 12 is placed on the electrode plate 40 in the vacuum chamber 30 in the manufacturing apparatus shown in FIG. Then, the vacuum vessel 30 is sealed, and the coolant is circulated through the coolant circulation pipe 46.
The electrode plate 40 is cooled to maintain the temperature at 200 ° C. or less, and the inside of the vacuum vessel 30 is evacuated to 10 ^-5 Pa or less by a vacuum pump connected to the gas exhaust port 34.

Next, an oxygen gas 100 cm ³ / min (= scc) is supplied by a gas introduction system connected to the gas introduction port 32.
m: Standard cc / min, the same applies hereinafter), silicon alkoxide 10 cm ³ /
min and germanium alkoxide 5 cm ³ / min as an organic metal gas are introduced into the vacuum vessel 30. Further, the pressure inside the vacuum vessel 30 is set to 10 Pa by a displacement adjusting valve provided at the gas exhaust port 34.

Here, as the organic silicon compound gas,
TEOS (Tetraethoxy Silane) and TMOS (Tetramet
Silicon alkoxides such as hoxy silane) are preferred. In addition, germanium (Ge) is used as the organic metal gas.
And titanium (Ti), phosphorus (P), boron (B), aluminum (Al), erbium (Er), arsenic (A)
s), gallium (Ga), sulfur (S), tin (S
Alkoxides such as n) and zinc (Zn) are also suitable. The types of these gases and the introduction ratio of the organosilicon compound gas and the organometallic gas are determined by the refractive index values set for the optical waveguide film 14 formed on the substrate 12 and serving as the core layer 16. It is adjusted appropriately according to.

Subsequently, the output power 50 W to 50 W at a frequency of 400 kHz, for example, is supplied by the high frequency power supply 44 for adjusting the refractive index.
A high-frequency power of 0 W is applied to the electrode plate 40, and a high-frequency power source 54 for plasma generation
A high frequency power of 3.55 MHz and an output power of 1000 W is applied to the coil 50, and this state is maintained for a predetermined time.

When high frequency power is applied to the coil 50,
A high-frequency electromagnetic field is generated by the electromagnetic induction, and the high-frequency electromagnetic field is transmitted through the high-frequency introduction window 36, and a high-frequency electromagnetic field is also generated in the internal space of the vacuum vessel 30. And, the oxygen gas supplied into the vacuum vessel 30 by the high-frequency electromagnetic field,
The organosilicon compound gas and the organometallic gas are heated to a high temperature and ionized to be in a plasma state.

The plasma generated in the vacuum chamber 30 as described above is called inductively coupled high frequency plasma. In the method of manufacturing the optical waveguide device according to the present embodiment, the optical waveguide film is deposited on the substrate 12 using the inductively coupled high-frequency plasma. That is, the oxygen gas, the organosilicon compound gas, and the organometallic gas in the plasma state react in the vacuum vessel 30. Then, as shown in FIG. 5A, an optical waveguide film 14 made of silicon oxide doped with a metal element (Ge in the case of germanium alkoxide) contained in the organometallic gas is deposited on the substrate 12. . Here, the specific film forming conditions of the optical waveguide film 14 are such that the etching rate of the obtained optical waveguide film 14 is 5000 ° / m.
In is set to be less than or equal to in.

Optical waveguide film 1 having predetermined refractive index and thickness
When the substrate 4 is formed on the substrate 12, the output of the high-frequency power source 44 for adjusting the refractive index and the high-frequency power source 54 for generating plasma are stopped, and the gas inlet 32 and the gas outlet 34 are closed. Further, the coolant circulation pipe 46
Is stopped, and the substrate 12 on which the optical waveguide film 14 is formed is taken out of the vacuum container 30. Thus, the optical waveguide film forming step is completed.

Subsequently, a core layer forming step is performed, and the optical waveguide film 14 is patterned by a predetermined waveguide pattern to form a core layer 16 (see FIGS. 5B and 5C). A resist is applied to the entire surface of the substrate 12 on which the optical waveguide film 14 is formed, and photolithography is performed by using a mask 20 having a predetermined pattern corresponding to a waveguide pattern of an optical circuit in the optical waveguide device 1 to be manufactured. The waveguide pattern is exposed and transferred (FIG. 5B). Then, by performing dry etching using the obtained resist pattern as a mask, unnecessary portions of the optical waveguide film 14 are removed, and the core layer 16 constituting the optical waveguide is formed (FIG. 5C). Thus, the core layer forming step is completed.

Subsequently, a cladding layer forming step is performed, and the cladding layer 1 covering the substrate 12 and the core layer 16 is formed on the substrate 12.
8 (see FIG. 5D). This cladding layer forming step is performed by the same step as the above-described optical waveguide film forming step. However, depending on the composition of the core layer 16 and the cladding layer 18, the film forming conditions such as the gas supplied into the vacuum vessel 30 are different.

First, in the manufacturing apparatus shown in FIG. 4, the substrate 12 on which the core layer 16 is formed is placed on the electrode plate 40 in the vacuum vessel 30. Then, the vacuum vessel 30 is sealed, and the coolant is circulated through the coolant circulation pipe 46.
The electrode plate 40 is cooled to maintain the temperature at 200 ° C. or less, and the inside of the vacuum vessel 30 is evacuated to 10 ^-5 Pa or less by a vacuum pump connected to the gas exhaust port 34.

Next, an oxygen gas 100 cm ³ / min and a silicon alkoxide 10c as an organic silicon compound gas are supplied by a gas introduction system connected to the gas introduction port 32.
Each gas of m ³ / min is introduced into the vacuum vessel 30.
Further, the pressure inside the vacuum vessel 30 is set to 10 Pa by a displacement adjusting valve provided at the gas exhaust port 34.

Subsequently, the output power 50 W to 60 W at a frequency of 400 kHz, for example, is supplied by the high frequency power supply 44 for adjusting the refractive index.
A high-frequency power of 0 W is applied to the electrode plate 40, and a high-frequency power source 54 for plasma generation
A high frequency power of 3.55 MHz and an output power of 1000 W is applied to the coil 50, and this state is maintained for a predetermined time.

When high-frequency electric power is applied to the coil 50 to generate a high-frequency electromagnetic field in the vacuum vessel 30, the vacuum vessel 30
The oxygen gas and the organic silicon compound gas supplied into the inside are heated to a high temperature and ionized, and the state becomes an inductively coupled high frequency plasma state. Then, the oxygen gas and the organosilicon compound gas in the plasma state react in the vacuum vessel 30, and as shown in FIG. 5D, a clad made of silicon oxide and having a lower refractive index than the core layer 16. Layer 18
Is deposited on the substrate 12 so as to cover the substrate 12 and the core layer 16. Here, the specific film forming conditions for the clad layer 18 are such that the etching rate of the obtained clad layer 18 is 5.
It is set so as to be 000 ° / min or less.

When the clad layer 18 having a predetermined refractive index and a predetermined thickness is formed on the substrate 12 and the core layer 16, the output of the high-frequency power supply 44 for adjusting the refractive index and the high-frequency power supply 54 for generating plasma are stopped, and the gas is stopped. Inlet 3
2 and the gas exhaust port 34 are closed. Further, the circulation of the coolant by the coolant circulation pipe 46 is also stopped, and the substrate 1 on which the core layer 16 and the clad layer 18 are formed on the surface is also provided.
2 is taken out of the vacuum container 30. Thus, the cladding layer forming step is completed.

After the formation of the core layer 16 and the clad layer 18 is completed, a heat treatment step is subsequently performed to perform a heat treatment on the substrate 12 and the core layer 16 and the clad layer 18 formed on the substrate 12. . This heat treatment is performed for the purpose of adjusting or optimizing the optical characteristics of the planar optical waveguide constituting the optical circuit in the optical waveguide device 1, and the like.
The heating is performed at a predetermined heating temperature lower than the softening point temperature of the substrate 12 such as a quartz substrate.

As a suitable heating temperature lower than the softening point temperature of the substrate 12 and attaining a sufficient effect of adjusting the optical characteristics, a heating temperature in a temperature range of 600 ° C. to 1200 ° C. is preferable. Alternatively, 700 to 100
Preferably, the heating temperature is within a temperature range of 0 ° C. The heat treatment is performed on the optical waveguide device 1 for a predetermined time at the set heating temperature, and when the heat treatment process is completed, all the processes of manufacturing the optical waveguide device 1 are completed.

According to the manufacturing method using this ICP-CVD method, each layer is formed so as to satisfy the above numerical conditions of the etching rate (density), and the occurrence of warpage in the optical waveguide device after the heat treatment step is performed. Can be sufficiently suppressed. That is, it is possible to form a sufficiently dense core layer and a low cladding layer on the substrate before the heat treatment step. In the heat treatment step, heat treatment at a high temperature for vitrifying each layer is unnecessary, and heat treatment at a heating temperature lower than the softening point temperature of the substrate can be performed as described above.

The etching rate of each layer is usually reduced by doping a metal element or the like. On the other hand, in a layer of pure SiO ₂ , the etching rate tends to increase. In contrast, in the above-described embodiment, the cladding layer 18 made of pure SiO ₂ is formed.
According to the CP-CVD method, even such a layer of pure SiO ₂ can be formed as a sufficiently dense layer.

A specific example of the optical waveguide device and the method for manufacturing the same according to the above embodiment will be described. In the following examples, 110 U of buffered hydrofluoric acid manufactured by Daikin Industries, Ltd. was used as an etching solution for evaluating the etching rate, and the temperature was set to approximately 20 ° C.
Each of the etching rates was evaluated under (room temperature). The specific composition of the buffered hydrofluoric acid used was a test value, where hydrogen fluoride was 4.81% by mass ratio and ammonium fluoride was 35.6% by mass ratio.

First, the etching rate is 700 ° / mi
A quartz substrate of n is prepared as the substrate 12, and the above-described ICP
An optical waveguide film 14 made of SiO ₂ doped with GeO ₂ was deposited on the substrate 12 to a thickness of 6 μm by a CVD method. The etching rate of the formed optical waveguide film 14 with buffered hydrofluoric acid is 700 to 1700 ° / min.
Met. Subsequently, the optical waveguide film 1 is formed using ordinary fine processing techniques such as photolithography and dry etching.
4 is patterned, and an AWG waveguide pattern in which the interval (pitch) between input / output ports is 250 μm (FIG. 3B)
The core layer 16 was formed.

Next, pure Si is deposited by ICP-CVD.
A cladding layer 18 made of O _{2 is}
And a thickness of 20 μm to cover the core layer 16.
The etching rate of the formed cladding layer 18 with buffered hydrofluoric acid was 1000 to 2000 ° / min. Then, the optical waveguide device 1 in which the core layer 16 and the clad layer 18 were formed on the substrate 12 was subjected to a heat treatment (annealing treatment) at 800 ° C. for 6 hours in an oxygen atmosphere.

After the heat treatment, the substrate 12 of the optical waveguide device 1
Inspection of the warpage of the core layer 1
6 was warped in the shrinking direction, but the amount of warpage was as small as 1 μm or less in a range of 10 cm on the substrate 12. The distance between the input and output ports in the optical circuit of the AWG is -0.1 with respect to the designed distance of 250 μm.
It was within the range of μm.

Further, regarding the stress in the optical waveguide caused by the warpage of the optical waveguide device 1, the polarization dependent loss (PDL) which is affected by the anisotropy of the refractive index caused by the stress among the optical characteristics of the AWG. Was examined, the obtained PD
L was 0.2 dB or less, which was a sufficiently small PDL value as compared with the conventional case.

The optical waveguide device and the method of manufacturing the same according to the present invention are not limited to the above embodiments and examples, and various modifications are possible. For example, the method of manufacturing the optical waveguide device is not limited to the method described above, and another manufacturing method may be used as long as a sufficiently dense layer can be formed. Also,
The lower limit of the etching rate of each layer is set to 500 ° / m from the conditions such as the etching rate of the substrate used.
It is preferable to be in or more.

Further, with respect to the configuration of the optical waveguide device, the above embodiment has described the optical waveguide device having a structure in which the core layer and the over cladding layer are laminated on the substrate. On the other hand, even in the case of the structure in which the under cladding layer, the core layer, and the over cladding layer are laminated on the substrate, the same conditions as those of the over cladding layer are applied to the under cladding layer, and the above-described optical waveguide is formed. It is possible to apply the configuration of the device and the manufacturing method. Further, the substrate is not limited to the quartz substrate, and another substrate such as a silicon substrate may be used.

[0083]

The optical waveguide device and the method of manufacturing the same according to the present invention have the following effects as described in detail above. That is, the density of each layer (substrate, core layer, and cladding layer) constituting the optical waveguide device is evaluated by an etching rate at a temperature of 20 ° C. using buffered hydrofluoric acid, and the etching rate of each layer ( According to the optical waveguide device and the method of manufacturing the optical waveguide device, each of which has a numerical condition of 5000 ° / min or less with respect to (density), the difference in the amount of contraction / expansion between the layers during the heat treatment is reduced. Therefore, even if heat treatment is performed in the manufacturing process,
The occurrence of warpage in the optical waveguide device is suppressed, and an optical waveguide and an optical circuit having good optical characteristics are realized.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a planar optical waveguide in an embodiment of an optical waveguide device.

FIG. 2 is a graph showing a correlation between an etching rate of a clad layer using buffered hydrofluoric acid and a stress applied to the clad layer after heat treatment.

FIG. 3 is a plan view showing a configuration of an optical waveguide device including (a) a Mach-Zehnder type optical circuit and (b) a waveguide diffraction grating type optical circuit.

FIG. 4 is a configuration diagram showing a manufacturing apparatus used in a method of manufacturing an optical waveguide device by an ICP-CVD method.

FIG. 5 is a process chart schematically showing one embodiment of a method for manufacturing an optical waveguide device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical waveguide device, 12 ... Substrate, 14 ... Optical waveguide film, 16
... Core layer, 18 ... Clad layer, 20 ... Mask, 30 ... Vacuum container, 32 ... Gas inlet, 34 ... Gas exhaust, 36 ...
High frequency introduction window, 40: electrode plate, 42: matching circuit, 44:
High frequency power supply for adjusting refractive index, 46 ... coolant circulation pipe, 5
0: coil, 52: matching circuit, 54: high frequency power supply for plasma generation.

Continued on the front page (72) Inventor Kenji Koyama 1-chome, Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa F-term (reference) in Yokohama Works, Sumitomo Electric Industries, Ltd. 2H047 KA04 KB04 PA24 TA00 TA21

Claims (5)

[Claims] 1. A substrate, formed on the substrate by a predetermined waveguide pattern,
A core layer forming an optical waveguide; and a clad layer formed on the substrate so as to cover the substrate and the core layer, and having a lower refractive index than the core layer, and having a mass ratio of about 5%. When the densities of the respective layers were evaluated by an etching rate at a temperature of 20 ° C. using buffered hydrofluoric acid containing hydrogen fluoride of about 35% by mass and ammonium fluoride, the substrate and the core layer , And the etching rate of the cladding layer is 5000
光 / min or less. 2. The waveguide pattern of the core layer includes a directional coupler, and the etching rates of the substrate, the core layer, and the cladding layer are each 2000 Å / min or less. 2. The optical waveguide device according to claim 1, wherein 3. The waveguide pattern of the core layer includes an arrayed waveguide composed of a plurality of channel waveguides, and the etching rate of the substrate, the core layer, and the cladding layer is set to be equal to or smaller than that of the core layer. , Each 1000Å
2. The optical waveguide device according to claim 1, wherein the ratio is not more than / min. 4. The density of each layer is adjusted by an etching rate at a temperature of 20 ° C. using buffered hydrofluoric acid containing approximately 5% by mass of hydrogen fluoride and approximately 35% by mass of ammonium fluoride by mass. At the time of evaluation, a substrate having the etching rate of 5000 ° / min or less was prepared, and an oxygen gas, an organosilicon compound gas, and an organometallic gas were introduced into a vacuum vessel in which the substrate was placed. By reacting the oxygen gas, the organosilicon compound gas, and the organometallic gas in an inductively coupled high-frequency plasma state in the inside, the metal element contained in the organometallic gas is doped at an etching rate of 5000 ° / min or less. Forming an optical waveguide film made of silicon oxide on the substrate, and forming the optical waveguide film on the substrate. Patterning the formed optical waveguide film with a predetermined waveguide pattern to form a core layer forming an optical waveguide; and forming the core layer on the substrate in which the substrate is placed. By introducing an oxygen gas and an organic silicon compound gas into the vacuum vessel and causing the oxygen gas and the organic silicon compound gas to react in an inductively coupled high-frequency plasma state in the vacuum vessel, whereby the etching rate becomes 500.
A cladding layer forming step of forming a cladding layer made of silicon oxide and having a lower refractive index than the core layer at 0 ° / min or less on the substrate so as to cover the substrate and the core layer; And performing a heat treatment at a predetermined heating temperature on the core layer and the clad layer formed on the substrate. 5. The method of manufacturing an optical waveguide device according to claim 4, wherein in the heat treatment step, the heat treatment is performed with the heating temperature being in a temperature range of not less than 600 ° C. and not more than 1200 ° C.