JP3279495B2 - Optical waveguide film forming method - 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 forming an optical waveguide film of an optical waveguide used for optical information processing and optical communication.

[0002]

2. Description of the Related Art Conventionally, various methods have been known for forming an optical waveguide film to be a core layer of an optical waveguide on a substrate, such as a flame deposition method (FHD method) and a parallel plate type. Plasma CVD method, inductively coupled plasma CVD
The law is known.

In the flame deposition method, SiCl ₄ is hydrolyzed at a high temperature to deposit fine particles of SiO ₂ on a substrate, and then the deposited layer is sintered at a high temperature of 1000 ° C. or more to be vitrified. It is assumed that.

[0004] A parallel plate type plasma CVD method (for example, Japanese Patent Application Laid-Open Nos. 8-133785 and 8-2622)
No. 60), a substrate is placed between an upper electrode plate and a lower electrode plate arranged in parallel in a vacuum vessel, and plasma is generated between the upper electrode plate and the lower electrode plate; The reaction gas is activated in the plasma to deposit an optical waveguide film on the substrate.

In the inductively coupled plasma CVD method (see, for example, JP-A-8-262250), a substrate is placed in a vacuum vessel, high-frequency power is applied to a coil to generate plasma, and dichlorosilane is generated in the plasma. (SiH ₂
Cl ₂ ) is activated to deposit an optical waveguide film on the substrate.

[0006]

However, each of the above-mentioned conventional methods has the following problems. That is,
The flame deposition method requires two steps, a deposition step and a vitrification step, to form an optical waveguide film. In addition, since deposition conditions and sintering conditions are different for each type of dopant, fine control of control parameters is required. However, there is a problem that workability is poor because of the necessity. In addition, since a high heat treatment at 1000 ° C. or higher is required, it is difficult to integrate the transistor and other electric elements on the same substrate.

[0007] The parallel plate type plasma CVD method does not have the problems of the above-described flame deposition method. However, since the plasma generated by the parallel electrode plates has a low density, the deposition rate of the optical waveguide film on the substrate is low, and thus there is a problem that it takes a long time to form the optical waveguide film.

The conventional inductively coupled plasma CVD method does not have the problems of the above-described flame deposition method, and the deposition rate of the optical waveguide film on the substrate is relatively high. However, since dichlorosilane is used as a reaction gas, the embedding property (step coverage) is poor. That is,
As shown in the cross-sectional view of FIG. 6, an optical waveguide film formed on a substrate 1 is patterned by a conventional inductively coupled plasma CVD method to form a core layer 2, and an over cladding layer 3 is further formed thereon. Is deposited, the over cladding layer 3 is not formed on the side surface of the core layer 2. Therefore, there is a problem that a fine waveguide pattern cannot be embedded or the waveguide pattern is broken. In addition, since dichlorosilane is used, there is a problem in that the inside of the metal chamber and piping is deteriorated, and there is a risk of impairing the safety of an operator, resulting in poor workability.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and is capable of forming an optical waveguide film with excellent workability and a high film forming speed, and which does not require high heat treatment. It is an object to provide a film forming method.

[0010]

According to a method for forming an optical waveguide film according to the present invention, an oxygen gas, an organic silicon compound gas and an organometallic gas are introduced into a vacuum vessel on which a substrate is placed, and the oxygen gas is introduced into the vacuum vessel. Reacting the organosilicon compound gas and the organometallic gas in an inductively-coupled high-frequency plasma state to form a silicon oxide doped with a metal element contained in the organometallic gas on the substrate as an optical waveguide film. .

According to this optical waveguide film forming method, the oxygen gas, the organic silicon compound gas and the organic metal gas introduced into the vacuum vessel react as inductively coupled high-frequency plasma, and as a result, remain on the substrate. Then, a silicon oxide doped with a metal element contained in the organic metal gas is formed as an optical waveguide film.

The organometallic gas includes Ge, Ti, P,
It is an alkoxide containing at least one element of B, Al, Er, As, Ga, S, Sn and Zn. The refractive index of the optical waveguide film doped with any of these elements is set according to the type of the element.

Further, the present invention is characterized in that the refractive index of the optical waveguide film is set by adjusting the introduction ratio of the organosilicon compound gas and the organometallic gas into the vacuum vessel. Further, the present invention is characterized in that a substrate is placed on an electrode plate in a vacuum vessel, and high-frequency power applied to the electrode plate is adjusted to set the refractive index of the optical waveguide film.

[0014]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

First, prior to the description of the optical waveguide film forming method according to the present embodiment, an example of a manufacturing apparatus suitable for performing the optical waveguide film forming method according to the present embodiment will be described. FIG. 1 is a diagram illustrating the configuration of the manufacturing apparatus.

A vacuum vessel 30 for generating inductively coupled high-frequency plasma therein has a gas inlet 32, a gas exhaust port 34, and a high-frequency inlet window 36. The gas inlet 32 is an inlet for introducing an oxygen gas, an organic silicon compound gas, and an organic metal gas, and is connected to a gas supply device (not shown) for supplying these gases. A gas flow controller (not shown) for adjusting the volume is provided. Gas exhaust port 3
Reference numeral 4 denotes a port for exhausting the gas in the vacuum vessel 34, to which a vacuum pump (not shown) is connected, and an exhaust amount adjusting valve (not shown) for adjusting the exhaust conductance is provided. ing. The high-frequency introduction window 36 is
This is for transmitting a high-frequency electromagnetic field generated by the coil 50 provided outside the vacuum vessel 30 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. The electrode plate 40 is connected to a high-frequency power supply 44 for adjusting the refractive index via a matching circuit 42 and a cooling water circulation pipe 46.
Is connected. The high-frequency power supply 44 for adjusting the refractive index 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 and applies the same to the electrode plate 40. The purpose of this is to adjust the refractive index of the optical waveguide film formed on the clad 12 depending on the power value applied to the optical waveguide. The matching circuit 42 performs impedance matching between the refractive index adjusting high frequency power supply 44 and the electrode plate 40 to efficiently apply the high frequency power output from the refractive index adjusting high frequency power supply 44 to the electrode plate 40. Things. Since the temperature of the electrode plate 40 rises due to the applied high-frequency power, the cooling water circulation pipe 46 suppresses the temperature rise by circulating the cooling water inside or around the electrode plate 40.

The coil 50 provided above the vacuum vessel 30 and close to the high frequency introducing window 36 is
For generating inductively-coupled high-frequency plasma in the internal space, and a high-frequency power supply for plasma generation 54 is connected via a matching circuit 52. The plasma generating high-frequency power supply 54 has a frequency of several tens of MHz and an output power of several hundred W
It outputs high-frequency power of several thousand W and applies it to the coil 50. The matching circuit 52 performs impedance matching between the plasma-generating high-frequency power supply 54 and the coil 50 to efficiently apply the high-frequency power output from the plasma-generating high-frequency power supply 54 to the coil 50. is there.

Next, a method of forming an optical waveguide film according to the present embodiment and a method of manufacturing an optical waveguide from the formation of the optical waveguide film to the completion of the optical waveguide will be described. The manufacturing process of the optical waveguide is roughly divided into three processes, and includes an optical waveguide film forming process, a core layer forming process and an over cladding layer forming process according to the present embodiment. FIG. 2 is an explanatory diagram of a manufacturing process of the optical waveguide. When the optical waveguide film forming step according to the present embodiment is completed, the optical waveguide film 14 is formed on the substrate 12.
Are formed (FIG. 2A). In the core layer forming step, the resist applied to the surface is exposed through the mask 20 (FIG. 2B), and the core layer 16 is formed by etching the optical waveguide film 14 (FIG. 2C). ). Then, in the over cladding layer forming step, the over cladding layer 18 is formed on the substrate 12 and the core layer 16 (FIG. 2D). Hereinafter, the manufacturing process of the optical waveguide will be described in detail.

First, an optical waveguide film forming step is performed, and the substrate 1
The optical waveguide film 14 is formed on 2. FIG. 3 is a flowchart of the optical waveguide film forming process according to the present embodiment. This optical waveguide film forming step includes the following steps.

In step S11, the substrate (for example, a quartz substrate) 12 is placed on the electrode plate 40 in the vacuum vessel 30, and then the vacuum vessel 30 is closed. The plate 40 is cooled to maintain the temperature at 200 ° C. or lower, and the inside of the vacuum vessel 30 is evacuated to 10 ^-5 Pa or lower by a vacuum pump connected to the gas exhaust port 34.

In the following step S12, the gas inlet 32
100 sccm of oxygen gas, 10 sccm of silicon alkoxide as an organic silicon compound gas, and 5 sccm of germanium alkoxide as an organic metal gas by a gas supply device and a gas flow control device connected to
Is introduced into the vacuum vessel 30 and the gas exhaust port 3
The vacuum vessel 30 is controlled by the displacement control valve provided in the vacuum vessel 30.
The internal pressure is 10 Pa.

Here, as the organic silicon compound gas,
TEOS (Tetraethoxy Silane) and TMOS (Tetramet
Silicon alkoxides such as hoxy silane) are preferred. As the organic metal gas, in addition to germanium (Ge), titanium (Ti), phosphorus (P), boron (B), aluminum (Al), erbium (Er), arsenic (A)
s), gallium (Ga), sulfur (S), tin (Sn)
And alkoxides such as zinc (Zn) are also suitable. Further, the introduction ratio of the organosilicon compound gas and the organometallic gas is appropriately adjusted according to the desired value of the refractive index of the optical waveguide film formed on the substrate 12.

In the following step S13, a high-frequency power of, for example, 400 kHz and an output power of 50 W to 500 W is applied to the electrode plate 40 by the high-frequency power supply 44 for adjusting the refractive index, and the high-frequency power supply 54 for generating plasma, for example, has a frequency of 13 kHz. Output power 1000 at .56 MHz
The high frequency power of 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, so that a high-frequency electromagnetic field is also generated in the internal space of the vacuum vessel 30. Then, the gas (oxygen gas, organosilicon compound gas, and organometallic gas) in the vacuum vessel 30 is heated to a high temperature by the high-frequency electromagnetic field and ionized to be in a plasma state. The plasma generated in this way is called inductively coupled high frequency plasma. Then, these gases turned into plasma react, and as a result, silicon oxide doped with a metal element contained in the organometallic gas is formed on the substrate 12 as the optical waveguide film 14 (FIG. 2A )).

When the electron density of the plasma in the vacuum chamber 30 was measured by a probe, it was confirmed that high-density plasma having an electron density of 10 ¹³ or more was obtained. This is because, in the present invention, the high-frequency power is applied to the coil 50 to generate the inductively coupled high-frequency plasma, so that the effect of induction heating is added. It is thought that it was done. In addition, a frequency of 4
The high frequency power having a power value of 300 W at 00 kHz is
And the above-mentioned plasma state was continued for about 15 minutes to form the optical waveguide film 14 on the substrate 12. The thickness of the obtained optical waveguide film 14 was 8 μm, and the refractive index of the optical waveguide film 14 was Was 1.4615. Further, the power value of the high-frequency power output from the high-frequency power supply
When the optical waveguide film 14 was formed at each value from W to 500 W, it was confirmed that the refractive index of the optical waveguide film 14 had a linear relationship with the power value.

When the optical waveguide film 14 having the desired refractive index and thickness is formed on the substrate 12 as described above, the high-frequency power supply 44 for adjusting the refractive index and the high-frequency power supply 5
4, the output of each gas is stopped, the gas inlet 32 and the gas outlet 34 are closed, and the cooling water circulation pipe 4
The circulation of the cooling water by 6 is also stopped, and the substrate 12 (FIG. 2A) on which the optical waveguide film 14 is formed is taken out of the vacuum vessel 30. Thus, the optical waveguide film forming step is completed.

As described above, the method for forming an optical waveguide film according to the present invention requires only one step and uses a gas which can be easily handled, and thus is excellent in workability. In addition, since the high-temperature sintering step, which was required in the flame deposition method, is not required in the present method, the substrate 12 does not reach a high temperature. Therefore, electric elements such as transistors are integrated on the substrate 12. It is possible to Also, the substrate 12 is placed on the electrode plate 40 in which the cooling water is circulated by the cooling water circulation pipe 46, which also prevents the substrate 12 from becoming hot. Further, since the gas is reacted as inductively coupled high-frequency plasma to form the optical waveguide film 14, the film forming speed of the optical waveguide film 14 is high. Further, the refractive index of the optical waveguide film 14 depends on the type of the metal element contained in the organometallic gas, the introduction ratio between the organosilicon compound gas and the organometallic gas, and the power value of the high-frequency power applied to the electrode plate 40. By adjusting any of the above, the initial value is set, so that the refractive index of the optical waveguide film 14 can be easily controlled.

Subsequently, a core layer forming step is performed to pattern the optical waveguide film 14 into a core layer 16 having a predetermined shape. That is, a resist is applied to the entire surface of the substrate 12 on which the optical waveguide film 14 is formed, and the waveguide pattern is exposed and transferred by photolithography using a mask 20 having a predetermined pattern (FIG. 2B). Then, by performing dry etching using the resist pattern obtained by the photolithography as a mask, unnecessary portions of the optical waveguide film 14 are removed, and the core layer 16 is formed.
(C)). About 90 minutes of C
When F ₄ RIE was performed, the height of the core layer 16 was 8.5.
μm.

Finally, an over cladding layer forming step is performed to form an over cladding layer 18 on the substrate 12 and the core layer 16. FIG. 4 is a flowchart of the over cladding layer forming step. This over cladding layer forming step includes the following steps.

In step S21, the substrate 12 on which the core layer 16 is formed is placed on the electrode plate 40 in the vacuum vessel 30.
And the vacuum vessel 30 is sealed, and the cooling water circulation pipe 4
The cooling water is circulated by 6 to cool the electrode plate 40 so as to maintain it 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.

In the following step S22, the gas inlet 32
100 sccm of oxygen gas and 10 sccm of organic silicon compound gas are introduced into the vacuum vessel 30 by a gas supply device and a gas flow control device connected to the vacuum vessel 30, and the vacuum vessel 30 is provided by a displacement control valve provided at a gas exhaust port 34. The internal pressure is 10 Pa.

In the subsequent step S23, a high-frequency power of, for example, 400 kHz and an output power of 50 W to 600 W is applied to the electrode plate 40 by the high-frequency power source 44 for adjusting the refractive index, and the high-frequency power source 54 for generating plasma, for example, has a frequency of 13 kHz. Output power 1000 at .56 MHz
The high frequency power of 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. 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. (Oxygen gas and organic silicon compound gas) are heated to a high temperature to be in a plasma state. Then, these gases react, and as a result, an over cladding layer 18 made of silicon oxide is formed on the substrate 12 (FIG. 2D). When the overcladding layer 18 was formed on the substrate 12 by maintaining such a plasma state for about 60 minutes, the thickness of the obtained overcladding layer 18 was 30 μm.

When the overcladding layer 18 having the desired thickness is thus formed on the substrate 12, the outputs of the refractive index adjusting high-frequency power supply 44 and the plasma generating high-frequency power supply 54 are stopped, and the gas inlet 32 and the gas exhaust port 34 are closed, and the circulation of the cooling water by the cooling water circulation pipe 46 is also stopped, so that the substrate 12 having the core layer 16 and the over cladding layer 18 formed on the surface (FIG.
(D) is taken out of the vacuum container 30. Above,
The over cladding layer forming step ends.

When the cross section of the optical waveguide manufactured as described above was observed with an electron microscope, good embedding characteristics were obtained as shown in the cross-sectional view of FIG. According to the above-described overcladding layer forming step, after the organosilicon compound gas adheres to the upper surface of the substrate 12 and the upper surface and side surfaces of the core layer 18, the organosilicon compound reacts with oxygen to react with the silicon oxide. Is generated, so that this silicon oxide is also formed on the side surface of the core layer 16 as the over cladding layer 18.

[0037]

As described above in detail, according to the present invention, oxygen gas, organosilicon compound gas and organometallic gas introduced into the vacuum vessel react as inductively coupled high-frequency plasma. On the substrate, a silicon oxide doped with a metal element contained in an organic metal gas is formed as an optical waveguide film.

Therefore, the optical waveguide film forming step according to the present invention is completed in one step, and a gas which is easy to handle is used, so that the workability is excellent. In addition, since the high-temperature sintering step, which was required in the flame deposition method, is not required in the present method, the substrate does not reach a high temperature, and electric elements such as transistors can be integrated on the substrate. It is. Further, since the gas is reacted as inductively coupled high-frequency plasma to form the optical waveguide film, the film formation speed of the optical waveguide film is high. Further, the refractive index of the optical waveguide film depends on the type of the metal element contained in the organometallic gas, the introduction ratio of the organosilicon compound gas to the organometallic gas, and the power value of the high-frequency power applied to the electrode plate. Is adjusted to an initial value, so that the refractive index of the optical waveguide film can be easily controlled.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a configuration of a manufacturing apparatus suitable for performing an optical waveguide film forming method according to an embodiment.

FIG. 2 is an explanatory diagram of a manufacturing process of an optical waveguide.

FIG. 3 is a flowchart of an optical waveguide film forming process according to the embodiment.

FIG. 4 is a flowchart of an over cladding layer forming step.

FIG. 5 is a cross-sectional view of an optical waveguide manufactured by the optical waveguide film forming method according to the embodiment.

FIG. 6 is a cross-sectional view of an optical waveguide manufactured by a conventional inductively coupled plasma CVD.

[Explanation of symbols]

12: substrate, 14: optical waveguide film, 16: core layer, 18: over cladding layer, 20: mask, 30: vacuum vessel, 32
... gas inlet, 34 ... gas exhaust port, 36 ... high frequency introduction window, 40 ... electrode plate, 42 ... matching circuit, 44 ... high frequency power supply for refractive index adjustment, 46 ... cooling water circulation pipe, 50 ... coil, 52 ... matching circuit , 54 ... High frequency power supply for plasma generation.

Continuation of front page (56) References JP-A-8-262250 (JP, A) JP-A-8-262260 (JP, A) JP-A-8-260156 (JP, A) JP-A-6-59147 (JP, A) JP-A-8-166520 (JP, A) JP-A-8-262251 (JP, A) JP-A-7-41951 (JP, A) JP-A-7-41953 (JP, A) V. Bazilenko et. Al. , Electronics Letters, June 20, 1996, Vol. 32 No. 13, pp. 1198-1199 M.P. Svalgaard et. a l. , Electronics Letters, August 18, 1994, Vol. 30 No. 17, pp. 1401-1403 Takeshi Shimoda et. al. , 1996, IEICE General Conference, March 11, 1996, Electronics 1, p. 230 (58) Fields surveyed (Int. Cl. ⁷ , DB name) G02B 6/12-6 / 14 G02F 1/00-1/035 G02F 1/29-3/02 C03C 15/00-23/00 C03B 1/00-5/44 C03B 8/00-8/04 C03B 19/12-20/00 C23C 16/00-16/50

Claims (4)

(57) [Claims] 1. An oxygen gas in a vacuum vessel in which a substrate is placed.
Introduce organosilicon compound gas and organometallic gas,
The oxygen gas, the organosilicon compound gas and the organometallic gas are reacted in an inductively coupled high-frequency plasma state in the vacuum vessel, and a silicon oxide doped with a metal element contained in the organometallic gas is used as an optical waveguide film. Forming an optical waveguide film on the substrate. 2. The method according to claim 1, wherein the organometallic gas is Ge, Ti, P,
An alkoxide containing at least one element of B, Al, Er, As, Ga, S, Sn and Zn;
The method for forming an optical waveguide film according to claim 1, wherein: 3. The refractive index of the optical waveguide film is set by adjusting an introduction ratio of the organosilicon compound gas and the organometallic gas into the vacuum vessel. Optical waveguide film forming method. 4. The method according to claim 1, wherein the substrate is placed on an electrode plate in the vacuum vessel, and a high-frequency power applied to the electrode plate is adjusted to set a refractive index of the optical waveguide film. The method for forming an optical waveguide film according to claim 1.