JP2002189139A - Method for manufacturing optical waveguide deice - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical waveguide device in which a polarization dependent loss is reduced by controlling the generation of strain in a core area. SOLUTION: In a method for manufacturing the optical waveguide device, an under clad layer 2 and a core layer 3 are deposited on a quarts substrate 1 and further a cap layer 4 whose refractive index is equal to that of the under clad layer 2 is deposited on the core layer 3 successively under the same value of high frequency power by the use of a plasma CVD(chemical vapor deposition) device. After the core area is formed, an over clad layer 5 is deposited on the quartz substrate 1 in which the core area is formed. When the over clad layer 5 is deposited, an output value of high frequency power is gradually raised from the output value of high frequency in the deposition of the under clad layer 2 or the like. Thus, since the core area is encircled by a silicon oxide film having about the same density, strain is not exerted on the core area. Then, the generation of strain in the core area is controlled and the polarization dependent loss is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for fabricating an optical waveguide device by depositing an optical waveguide layer including a cladding region and a core region on a substrate using a plasma vapor deposition apparatus.

[0002]

2. Description of the Related Art Conventionally, optical waveguide devices have been used for plasma chemical vapor deposition (PC).
It is manufactured by a manufacturing method using the VD) method. In this manufacturing method, TEOS (Tetraethoxysilane) gas, oxygen (O ₂ ) gas, and the like are used as source gases, and first, a lower cladding layer and a core layer made of silicon oxide are sequentially formed on a substrate. Next, after the core layer is patterned by photolithography, a core region is formed by etching. Thereafter, the above-mentioned raw material is used again, and an upper clad layer is formed on the lower clad layer having the core region.

[0003]

As a result of the research by the present inventors, when an optical waveguide device is manufactured by the above-described manufacturing method using the PCVD method, the polarization-dependent loss is sufficiently reduced. Turned out not to be. And
Further studies on the cause of the polarization dependent loss revealed that there was a difference in the quality of the silicon oxide film deposited by the PCVD method around the core region. That is, when the upper cladding layer is deposited by the PCVD method, the deposition rate at the upper corner of the core region tends to increase, and thus an overhang called overhang is formed. When an overhang is formed, supply of a source gas (such as ions generated by plasma) to the side wall of the core region is hindered, so that the density of silicon oxide on the side wall decreases. Was. For this reason, silicon oxides having different densities are formed between the upper portion and the side wall portion of the core region, and the stress resulting from the difference in density is applied to the core region. As a result, distortion occurs in the core region, and this distortion causes polarization-dependent loss.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an optical waveguide device in which polarization-dependent loss is reduced by suppressing the occurrence of distortion in a core region. Aim.

[0005]

Therefore, a method of manufacturing an optical waveguide device according to the present invention comprises forming an optical waveguide layer including a cladding region and a core region on a substrate by using a plasma vapor deposition apparatus, and forming an optical waveguide device. A method for manufacturing a waveguide device, comprising: (1) using a plasma vapor deposition apparatus, at a predetermined high-frequency power value, a lower cladding layer, a core layer, and a cap layer having a refractive index equal to that of the lower cladding layer. Are sequentially formed on the substrate, and (2) a predetermined part of the cap layer and the core layer is removed to form a core region having a cap layer on the upper portion and through which light is confined and propagated. (3) When forming an upper cladding layer on a substrate having a core region having a cap layer thereon by using a plasma vapor deposition apparatus, the high-frequency power value is set to a value equal to the above-mentioned predetermined high-frequency power value. Gradually increase from To.

That is, in the above-described manufacturing method, PCVD
After the lower cladding layer and the core layer are sequentially deposited on the substrate using the apparatus, a cap layer having the same refractive index as the lower cladding layer is deposited on the core layer. Here, the high-frequency power supplied when depositing the cap layer is the same as when depositing the lower clad layer and the core layer. Therefore, the core layer and the cap layer have substantially the same film quality, and no stress is generated between the two layers.

After that, when a predetermined portion of the cap layer and the core layer is removed, the core layer having a cap layer on the upper portion which remains without being removed becomes a core region through which light propagates.

Next, an upper cladding layer is deposited by a PCVD apparatus on the cladding layer having a core region having a cap layer thereon. At this time, immediately after the start of the deposition, the high-frequency power is supplied at a power value equal to the high-frequency power supplied when the lower cladding layer, the core layer, and the cap layer are deposited. Gradually increase.

Immediately after the start of the formation of the upper cladding layer, the overhang is small, and as the formation of the upper cladding layer progresses, the overhang increases rapidly. Therefore, source gas (such as ions generated by plasma)
Although it is relatively easy to reach the side wall of the core region immediately after the start of the formation of the upper cladding layer, it is difficult to reach the side wall when an overhang is formed.

According to the above-described manufacturing method, at the start of the formation of the upper clad layer, the high-frequency power supplied to the electrode provided in the chamber of the PCVD apparatus is made equal to that at the time of depositing the lower clad layer and the core layer. High frequency power is gradually increased during deposition. As the high-frequency power increases, a voltage for drawing ions and the like generated by the plasma to the side wall portion, that is, a so-called pull-in voltage can be increased. Therefore, the source gas (such as ions generated by plasma)
Even after the overhang is formed, the high pull-in voltage can be drawn to reach the side wall of the core region. Therefore, a silicon oxide film with high density can be formed on the side wall of the core region. Therefore, the density of the upper cladding layer formed on the side wall of the core region can be made substantially the same as the density of the core region. Therefore, the stress generated between the core region and the upper cladding layer formed on the side wall of the core region can be sufficiently reduced. As a result, no distortion occurs in the core region, and the occurrence of polarization-dependent loss is sufficiently suppressed.

Further, the density of the upper clad layer deposited on the cap layer becomes higher than the density of the cap layer due to an increase in high-frequency power, so that a stress due to the density difference may occur. However, this stress is generated at a position distant from the core region due to the presence of the cap layer, and can be sufficiently absorbed by the cap layer, so that the stress does not reach the core region. Therefore, no distortion occurs in the core region, and no polarization-dependent loss occurs.

In the above description, the configuration in which the lower cladding layer, the core layer, and the cap layer are deposited on the substrate has been described. However, if a quartz glass substrate is used as the substrate, the deposition of the lower cladding layer becomes unnecessary. Then, the core layer and the cap layer may be deposited on the quartz glass substrate. Even in this case, no distortion occurs in the core region, and the occurrence of polarization-dependent loss can be sufficiently suppressed.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a method for manufacturing an optical waveguide device according to the present invention will be described below with reference to the drawings. In the following description, the same elements will be denoted by the same reference symbols, without redundant description. In the drawings, the dimensional ratios, including the ratio of the thickness of each layer grown on the quartz substrate, do not always match those described.

FIGS. 1A to 1C are schematic views showing steps of manufacturing an optical waveguide device by the manufacturing method of the present embodiment, and a cross section of the optical waveguide device after completion of each step. This manufacturing method is roughly divided into three steps of an optical waveguide layer deposition step, a core region formation step, and an over cladding layer deposition step, and these steps are sequentially performed. (1) Optical waveguide layer deposition process

First, using a PCVD apparatus, a quartz substrate 1
An under cladding layer 2, a core layer 3, and a cap layer 4 are sequentially deposited thereon.

Here, TEOS gas and O ₂ gas are preferable as raw materials used for depositing each of the above layers 2 to 4. When depositing the core layer 3, a refractive index increasing agent such as Ge is added so that the core layer 3 has a higher refractive index than the other layers. As a raw material for Ge, tetramethylgermanium (T
etra Methyl Germanium (TMGe) is preferred because it is easy to handle.

First, the quartz substrate 1 is placed on a susceptor in a chamber of a PCVD apparatus, and the quartz substrate 1 is heated to a predetermined temperature. Then, argon (Ar) gas or hydrogen
A TEOS gas and an O ₂ gas are supplied to a chamber together with a diluent gas such as a (H ₂ ) gas, and the pressure in the chamber is adjusted to a predetermined pressure value by a pressure regulator. Then, a predetermined high-frequency power is supplied to an electrode provided in the chamber to generate plasma in the chamber, and the deposition of the under cladding layer 2 is started.

The thickness of the under cladding layer 2 is a predetermined thickness.
At which point, TEOS gas and O _TwoGas supply
The supply of TMGe is started while continuing, and the deposition of the core layer 3 is started.
start. Thereby, the supply of TMGe allows the core layer 3
Is added to the core layer 3 so that the refractive index of the core layer 3 is undercracked.
Higher than the refractive indexes of the doped layer 2 and the cap layer 4, and later
The formed core region can be suitably provided.

Subsequently, when the thickness of the core layer 3 reaches a predetermined thickness, only the supply of TMGe is stopped, and the deposition of the cap layer 4 is started. Since the supply of TMGe is not performed, the refractive index of the cap layer 4 deposited here is the same as the refractive index of the under cladding layer 2. When the cap layer 4 reaches a predetermined thickness, TEOS gas and O
The supply of the _two gases is stopped to terminate the deposition of the cap layer 4. Then, after cooling the quartz substrate 1, each layer 2-4
The quartz substrate 1 on which is formed is taken out of the chamber. Thus, as shown in FIG. 1A, a quartz substrate 1 on which the under cladding layer 2, the core layer 3, and the cap layer 4 are formed is obtained. (2) Core region forming step

Next, the step of forming the core region will be described. First, a resist is applied on the cap layer 4 to form a resist film. Next, the core region pattern is exposed and transferred to the resist film by photolithography using a mask having a predetermined pattern, and the resist film other than the transfer pattern is removed with an organic solvent or the like. Subsequently, the quartz substrate 1 is subjected to reactive ion etching (Reactive Io etching).
n Etching: RIE) The substrate is placed on a susceptor in the apparatus, and etching is performed to remove the cap layer 4 and the core layer 3 where no resist film is formed (FIG. 1B). As a result, a core region through which light is guided is formed. (3) Over cladding layer forming process

The core area pattern is formed by the core area forming step.
The quartz substrate 1 on which the pattern is formed is again
Place it on the susceptor in the chamber. The quartz substrate 1 is heated to a predetermined temperature.
Temperature, and after the temperature is stabilized, argon (Ar)
Gas or hydrogen (H_Two) Supply gas and TEOS gas
And O_TwoGas and gas into the chamber,
Is adjusted to a predetermined pressure value. After that, (1) Deposition of optical waveguide layer
In the process, the under cladding layer 2, the core layer 3, and the key
Equal to the high frequency power supplied when the cap layer 4 was deposited.
Supply high frequency power to the electrodes provided in the chamber
Then, plasma is generated in the chamber. This allows
The deposition of the overcladding layer 5 is started.
Immediately after the start, increase the high-frequency power at a predetermined rate.
Go. After that, when the film thickness reaches a predetermined value,
Power supply, TEOS gas and O _TwoTurn off gas supply
Then, the deposition of the over cladding layer 5 is completed. this
Thereby, the quartz substrate 1 on which the optical waveguide is formed is obtained.
After that, the quartz substrate 1 is taken out of the chamber,
Processing such as singing is appropriately performed to obtain the optical waveguide device 10.
(FIG. 1 (c)).

Next, the operation of the method for manufacturing an optical waveguide device according to the present embodiment will be described with reference to FIG. FIG. 2 is a schematic diagram showing a shape of the over cladding layer 5 when the same layer 5 is formed by the manufacturing method of the embodiment.

As shown in FIG. 2, silicon ions and oxygen ions generated by the plasma are transferred to the cap layer 4.
Is easily adsorbed to the corner C at the upper part of the substrate, so that the deposition rate at the corner C is higher than that of the other parts. Therefore, an overhang O is formed in this portion. When such overhangs O are formed, active species such as ions are transferred to the core layer 3.
It is difficult to reach the side wall portion. Therefore, the density of the silicon oxide film S on the side wall is likely to decrease. However, according to the manufacturing method of the present embodiment, as the overhang O is formed and it becomes difficult for active species such as ions to reach the side wall, the high-frequency power supplied to the chamber of the PCVD apparatus increases. . Therefore, ions and the like are
Will be more effectively drawn to the side walls of the
A decrease in the density of the silicon oxide film A formed on the side wall can be prevented. At this time, the density of the silicon oxide film S can be made uniform and uniform with the core layer 3 by appropriately adjusting the rate of increase in the high-frequency power. By doing so, no stress is generated between the silicon oxide film S and the core layer 3, and no distortion occurs in the core region. As a result, the occurrence of polarization dependent loss is suppressed.

Since the over-cladding layer 5 is deposited while increasing the high-frequency power, the density of the over-cladding layer 5 deposited on the cap layer 4 also becomes gradually higher than the density of the cap layer 4. . Therefore, the cap layer 4
And the over cladding layer 5 generates stress. However, this stress does not reach the core layer 3 because it can be absorbed by the cap layer 4. Therefore, no distortion occurs in the core region, and there is no possibility that polarization-dependent loss occurs.

In the above, if a quartz glass substrate is used as the substrate, the deposition of the lower clad becomes unnecessary, and only the core layer and the cap layer need be deposited on the quartz glass substrate first.

The method for manufacturing the above-described optical waveguide device will be described more specifically with reference to examples. In the present embodiment, an arrayed waveguide type diffraction grating (Arrayed Waveguide
Grading: AWG) Make a device. This AWG device has 16 input waveguides, 120 arrayed waveguides, and 16 output waveguides sequentially coupled via a slab-type waveguide section.

First, the susceptor in the chamber of the PCVD device
The quartz substrate 1 was placed on the table. This quartz substrate 1 has a diameter
The thickness is 100 mm and the thickness is 1.0 mm. The susceptor
It is heated by a heater provided inside,
Thus, the temperature of the quartz substrate 1 is maintained at 400 ° C. Continued
And TEOS gas and O together with Ar gas in the chamber.
_TwoGas was supplied to the chamber. At this time, vacuum pump
The chamber is evacuated by the pump, and the pressure in the chamber is set to 1.
It was adjusted to 0 Pa. Then, it was provided in the PCVD apparatus.
High-frequency power of 1000 W output power (frequency
(13.56 MHz) to supply plasma in the chamber
And the deposition of the under cladding layer 2 was started.

The thickness of the under cladding layer 2 is set to 5 μm.
And the deposition of the core layer 3 was started. Specifically, the supply of TMGe was started at the time when the time for depositing the 5 μm-thick undercladding layer 2 calculated from the deposition rate determined in the preliminary experiment had elapsed. Thus, the deposition of the under cladding layer 2 is completed, and the deposition of the core layer 3 is started. During the deposition of the core layer, the supply amounts of the TEOS gas and the O ₂ gas and the high-frequency power supplied to the chamber are the same as the supply amounts and the power during the deposition of the under cladding layer 2.

The supply amount of TMGe at the time of depositing the core layer 3 is 0.5.
It was 95 sccm. The concentration of Ge added by the TMGe supply becomes 23 wt%, and the refractive index of the core layer 3 is increased by 0.75% as compared with the refractive index of the under cladding layer 2 by this addition. The thickness of the core layer 3 was 6 μm. That is, after the elapse of a desired time obtained from the deposition rate, the supply of TMGe was stopped to terminate the deposition of the core layer 3 and subsequently, the deposition of the cap layer 4 was performed. When depositing the cap layer 4, the deposition conditions such as the supply amount of the raw material gas and the high-frequency power are the same as the conditions when depositing the under cladding layer 2. The thickness of the cap layer 4 is 5 μm, and after a lapse of the deposition time obtained from the deposition rate,
The supply of the high-frequency power was stopped, and the supply of the TEOS gas and the O ₂ gas was stopped, and the deposition of the cap layer 4 was completed.

From the chamber of the above PCVD apparatus, each layer 2 to 2
After taking out the quartz substrate 1 with the 4 formed thereon, a resist was applied on the cap layer 4 to form a resist film. Next, a predetermined pattern was patterned by photolithography.

Subsequently, the quartz substrate 1 on which the core region pattern-shaped resist film is formed is placed on a susceptor in a reaction chamber of the RIE apparatus, and then a C ₂ F ₆ gas as an etching gas and an H ₂ gas With 50 sccm and 5 sccm respectively
And set the pressure in the reaction chamber of the RIE etching apparatus to 1.0.
It was adjusted to Pa. Then, high-frequency power (3
(00W, 13.56 MHz), and the cap layer 4 and the core layer 3 where the resist film was not formed were etched to form a core region having a predetermined pattern.

After completion of the etching, the quartz substrate 1 on which the core region pattern was formed was taken out of the reaction chamber of the RIE apparatus, and the resist film remaining on the quartz substrate 1 was removed by ashing. Next, the substrate 1 was placed on a susceptor in a chamber of a PCVD apparatus. The quartz substrate 1 was heated to a temperature of 400
After the temperature was stabilized up to ° C. and the temperature was stabilized, the Ar gas was supplied and the TEOS gas and the O ₂ gas were supplied to the chamber, and the pressure in the chamber was adjusted to 0.7 Pa. After that, high-frequency power of 1000 (W) output power was supplied to the electrodes provided in the chamber, plasma was generated in the chamber, and deposition of the over cladding layer 5 was started. Immediately after the deposition, the output value of the high-frequency power was gradually increased so as to reach 1200 (W) by the end of the deposition of the overcladding layer 5 having a thickness of 15 μm.

At the time of depositing the over cladding layer 5, TM
Since Ge is not supplied, the refractive index of this layer 5 is substantially the same as that of the under cladding layer 2 and the cap layer 4. When the film thickness became 15 μm, the supply of the high-frequency power was stopped, the supply of the TEOS gas and the supply of the O ₂ gas were stopped, and the deposition of the over cladding layer 5 was completed. As described above, the quartz substrate 1 having the core region and the cladding region was obtained. Thereafter, the quartz substrate 1 was taken out of the PCVD apparatus and diced to obtain an AWG device.

Next, the transmission light spectrum of this AWG device was measured. FIG. 3 is a graph showing a transmitted light spectrum of the AWG device of the example. From the results in the figure, TE (Transverse-electric) polarization and TM (Transver-
For both se-magnetic) polarizations, the loss is minimum at a wavelength of about 1549 (nm), and the difference in wavelength (PDλ) at which the loss of both polarizations is minimum is only 0.005 nm. Was.

For comparison, an AWG device having the same configuration as that of the example was manufactured by a conventional manufacturing method, and the same measurement was performed. The conventional manufacturing method is that the under cladding layer 2 and the core layer 3 are deposited on the quartz substrate 1 with high frequency power of 1000 (W), and then photolithography and RI
E forms a core region pattern, and deposits the over cladding layer 5 while keeping the high-frequency power constant at 1000 (W). That is, in the conventional manufacturing method, (a) the cap layer 4 is not formed, and (b) the output power value of the high-frequency output is kept constant at 1000 (W) when the over clad layer 5 is deposited. Is different from the manufacturing method of the embodiment.

FIG. 4 shows a transmitted light spectrum of a conventional AWG device. From the figure, it was found that the difference between the center wavelengths of the TE polarization and the TM polarization was 0.021 nm. Thus, the difference between the center wavelengths in the conventional AWG device is 0.005 in the AWG device according to the above embodiment.
The value is larger than the result of nm. From these results, the effect of the manufacturing method of the example is understood.

While the embodiments and examples of the method for manufacturing an optical waveguide device according to the present invention have been described above, the present invention is not limited to these and can be variously modified. For example, in the above embodiment, when depositing the over cladding layer 5, the output power value of the high-frequency power is changed from 1000 (W) to 12 (W).
Although it was increased to 00 (W), it may be appropriately adjusted within the range of the power value at the time of depositing the under cladding layer 2, the core layer 3, and the cap layer 4 or more.

In the above embodiment, 1000 (W) is applied between the start and the end of the deposition of the over cladding layer 5.
Was 1200 to (W) so as to increase the output value of the high-frequency power from increasing the output value of the high frequency power during a period t _f of example to between the core region 3, 3 are filled with silicon oxide Then, it may be constant. Further, the output value is increased during the period t _f , and thereafter, for example,
It may be gradually reduced to 1000 (W), which is the same as when the under cladding layer 2, the core layer 3, and the cap layer 4 are deposited. Needless to say, the density of the silicon oxide forming the core region and the over cladding layer should be substantially the same, and accordingly the rate of increase in the output value of the high-frequency power should be appropriately adjusted so that the stress applied to the core region can be suppressed.

If a quartz glass substrate is used as the substrate,
The step of depositing the lower cladding layer is not required, thereby simplifying the step and reducing the manufacturing cost.

The plasma CVD apparatus used in the method for manufacturing an optical waveguide of the present invention may be a parallel plate type plasma CVD apparatus or an inductively coupled plasma CVD apparatus.

Further, the etching apparatus used is RIE.
However, the present invention is not limited to this, and a plasma etching apparatus to which a method such as ECR or ICP is applied may be used.

Further, Ge is added to the core layer 3 so that
However, instead of this, a refractive index lowering agent is added to the under cladding layer 2, the cap layer 4, and the over cladding layer 5 so that the refractive index of the core layer 3 is relatively increased. Is also good. As a refractive index lowering agent, boron
(B) and fluorine (F) can be suitably used. These materials include TMB (Trimethylboron) and TOF
S (Triethoxyfluorosilane) and the like.

Further, TMGe was used as a raw material for Ge, but other organic metal gas containing Ge, for example, TMOGe
(Tetramethoxygermanium) may be used. Although TEOS was used as a raw material of silicon, for example, TMOS (TetramethoxySilane) may be used instead.

[0044]

As described above, according to the method of manufacturing an optical waveguide device according to the present invention, the lower clad layer, the core layer, A cap layer having a refractive index equal to that of the lower cladding layer is sequentially formed. Then, after the core region is formed, the upper cladding layer is formed on the core region having the cap layer and the lower cladding layer with high-frequency power higher than that at the time of forming the lower cladding layer and the like. Therefore, the core region is surrounded by silicon oxide having substantially the same density, and no stress is applied to the core region. Therefore, occurrence of distortion in the core region is suppressed,
Polarization dependent loss is reduced.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a step of manufacturing an optical waveguide device by the manufacturing method of the present embodiment, and a cross section of the optical waveguide device after completion of each step.

FIG. 2 is a schematic view showing the shape of an over cladding layer when the over cladding layer is formed by the manufacturing method of the embodiment.

FIG. 3 is a graph showing a transmitted light spectrum of the AWG device of the example.

FIG. 4 is an AWG manufactured by a conventional manufacturing method.
4 is a graph showing a transmitted light spectrum of the device.

[Explanation of symbols]

1: quartz substrate, 2: under cladding layer, 3: core layer,
4: cap layer, 5: over cladding layer, S: silicon oxide film, C: corner, O: overhang.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shigeru Semura 1-chome, Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa F-term in Sumitomo Electric Industries, Ltd. Yokohama Works 2H047 KA04 PA05 QA07 TA22

Claims (2)

[Claims] An optical waveguide layer including a cladding region and a core region is formed on a substrate using a plasma vapor deposition apparatus,
A method for manufacturing an optical waveguide device, comprising: using the plasma vapor deposition apparatus, at a predetermined high-frequency power value, a lower cladding layer, a core layer, and a cap layer having a refractive index equal to that of the lower cladding layer. After sequentially forming on the substrate, by removing a predetermined part of the cap layer and the core layer, the core having the cap layer on the upper part, light is confined and propagated Forming a region, and forming the upper cladding layer using the plasma vapor deposition apparatus on the substrate having the core region having the cap layer on the upper portion, the high-frequency power value is changed to the predetermined high-frequency power. A method for manufacturing an optical waveguide device, wherein the value is gradually increased from a value equal to the value. 2. A manufacturing method for manufacturing an optical waveguide device by forming an optical waveguide layer including a core region and an upper cladding region on a quartz glass substrate using a plasma vapor deposition apparatus. Using a deposition apparatus, at a predetermined high-frequency power value, after sequentially forming a core layer and a cap layer having a refractive index equal to the quartz glass substrate on the quartz glass substrate, the cap layer and the core layer By removing a predetermined part, the core region having the cap layer on the upper portion and forming the core region through which light is confined and propagated, the core region having the cap layer on the upper portion is provided. When forming an upper cladding layer on the quartz glass substrate using the plasma vapor deposition apparatus, the high-frequency power value is gradually increased from a value equal to the predetermined high-frequency power value, A method for manufacturing an optical waveguide device, comprising: