JP2984130B2 - Glass film for optical waveguide by plasma CVD method and method for manufacturing optical waveguide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a glass film for an optical waveguide containing a rare earth element by a plasma CVD method.

[0002]

2. Description of the Related Art In recent years, research and development for realizing a laser or an optical amplifier by adding a rare earth element into a core of a glass waveguide has attracted attention.

FIG. 3 shows a conventional example of a method of adding a rare earth element into a core of a glass waveguide. In other words, the core porous glass film on the substrate obtained by the step of forming a glass optical waveguide film having a cladding layer around the core portion and the core portion on which light propagates on the substrate is converted into a rare-earth element by transition. Immersion in a solution containing one or more elements selected from metal elements, adding the elements to the core at a predetermined concentration, drying and sintering, photolithography, dry etching process on the core surface This is a method of obtaining a rare-earth element-doped glass waveguide for a laser or an optical amplifier by depositing a cladding layer (Japanese Unexamined Patent Publication No. Hei 2-2508).
No. 3).

[0004]

However, the above-described conventional method for manufacturing a rare-earth-element-doped glass waveguide has the following disadvantages.

(1) It has been difficult to uniformly add a rare earth element to the core. That is, since the above-described method is a method of impregnating the liquid into the glass porous film, the glass porous film has a concentration distribution in the thickness direction,
The concentration gradient of the rare earth element in the core portion has caused a decrease in the excitation efficiency.

(2) It has been difficult to add a large amount of rare earth elements into the core.

(3) After depositing a porous glass film, it is difficult to control the film thickness and the refractive index because it is a method of sintering this to form a transparent glass.

(4) It is easy for impurities to enter through the liquid,
It was difficult to reduce the loss.

(5) Since the sintering step is required twice, the number of steps is large, and it has been difficult to reduce the manufacturing cost.

Therefore, the present invention has been devised in order to effectively solve the above problems, and a main object of the present invention is to uniformly add a rare earth element to a glass film using a plasma CVD method and to improve the uniformity of the rare earth element. An object of the present invention is to provide a glass film for an optical waveguide and a method for manufacturing an optical waveguide by a plasma CVD method, in which the amount of addition can be easily controlled and the manufacturing process is simplified.

[0011]

Means for Solving the Problems To achieve the above object, a first invention is to dispose a substrate having a low refractive index layer on one of a pair of electrodes opposed to each other in a reaction vessel, A high-frequency power is applied between the electrodes to generate plasma, and a mixed vapor of a refractive index controlling dopant and an organic oxysilane and a vapor containing a rare earth element are guided by separate transport systems, respectively, and the plasma atmosphere is introduced. each direct <br/> blown in to form a transparent glass layer containing a high refractive index controlling dopant rare earth elements having a refractive index higher than that in the heated low refractive index layer surface of the substrate to 1000 ° C. or less Things. Further, the second invention is such that the electrodes are disposed so as to be opposed in either the up-down direction or the left-right direction, and the third invention is that at least one of the mixed steam and the steam containing a rare earth element is used. Is such that one of the electrodes is sprayed into the plasma atmosphere like a shower. Further, the fourth invention the metal film is formed on the surface of the glass film formed in the first invention, formation Then co photoresist pattern on the metal film surface
The metal pattern is formed by patterning the metal film using the photoresist pattern as a mask, the glass film is patterned using the metal pattern as a mask, and the photoresist and the metal film are separated to form a glass pattern. The glass pattern surface is coated with a low refractive glass film having a refractive index lower than the refractive index of the glass.

As the organic oxysilane used in the present invention, for example, Si (OCH ₃ ) ₄ and Si (OC ₂ H ₅ ) ₄
Etc. can be used. Dopan for refractive index control
The capital of the liquid for example _{PO (OC 2 H 5) 3} , B (O
C ₂ H ₅ ) ₄ , Ge (OC ₂ H ₅ ) ₄ , Sb (OC ₂ H)
₅ ) A liquid containing at least one kind of ₄ , Al (OC ₂ H ₅ ) ₄ or the like is used. Further, as the vapor containing the rare earth element, a rare earth compound which is solid at room temperature, for example, R (DP
M) ₃ , R (HFA) ₃ , R (FOD) _3, or other rare earth elements or the like are heated and vaporized. Note that R is E
Rare earth elements such as r, Nd, Sm, Eu, Yb, Pr and La, and DPM is 2,2,6,6-tetramethy
l-3,5-heptanedione, HFA is 1,
1,1,5,5,5-Hexafluoro-2,4-
pentanedione, FOD is 1,1,1,2,2
2,3,3-Heptafluoro-7,7-dim
ethyl-4,6-octanedione,
Each chemical formula is as shown below.

[0013]

[0014]

According to the present invention, as described above, the two kinds of vapors are transported by separate transport systems, and as a result, the scattering loss on the surface of the low refractive index layer of the substrate is extremely low, and the transparent core glass is provided. A film can be formed. Also, directly into the plasma atmosphere, a vapor containing a rare earth element, including the refractive index control dopant preparative since the mixed vapor of the organic oxysilane, a rare earth element and a refractive index control beam dopa <br/> down bets required Ru can be mixed in uniformly in the glass film without vaporizing the. Further, since the vapor containing the rare-earth element is mixed at a temperature of a few hundred degrees Celsius in a plasma atmosphere of 1000 ° C. or less, the temperature gradient in the plasma atmosphere can be prevented from drastically lowering. Can reduce the non-uniformity of the rare earth element content. Further, the amount of the rare earth element added to the glass film can be easily controlled by adjusting the heating temperature of the compound containing the rare earth element and the flow rate of the carrier gas G for carrying the vapor. Moreover, since the obtained glass film is a transparent glass film, thereafter, without heat treatment, a metal film is formed thereon, a resist film is patterned by photolithography, a metal film is patterned by dry etching, and a glass film is patterned. Thereby, the optical waveguide can be easily realized, and the manufacturing method thereof is also simplified.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 shows an embodiment of a plasma CVD apparatus used in the manufacturing method of the present invention.

As shown, an upper electrode 3 is provided in a closed housing 2 which is a reaction vessel of the plasma CVD apparatus 1.
And lower electrode 4 on which three substrates 6a, 6b, 6c are mounted
Are provided so as to face each other.
A plasma 5 is generated by applying a high frequency (frequency: 13.56 MHz) power between the four.

The upper electrode 3 is connected to a gas supply pipe 8 which is one of vapor transport systems having a valve 8a. The gas supply pipe 8 has two gas supply tanks 7 connected thereto.
a, 7b are connected to these gas supply tanks 7a, 7b.
b, mixed with each other and passed therethrough, and indicated by arrow Y
_As shown in FIG. ₂ , supply is made to the upper electrode 3 side. Furthermore, this upper electrode 3, and a plurality of gas ejection holes 3b are disc-shaped formed gas shower unit 3a provided, to indicate the steam supplied from the gas supply pipe 8 to the arrow Y ₁ The plasma 5 generated between the electrodes 3 and 4
It is designed to spray evenly inside.

[0019] This is the gas supply tank 7a liquid 14a of the organic oxysilane is stored, stored liquid 14b of the refractive index control dopant metropolitan in one of the gas supply tank 7b, these liquids 14a, 14b are respectively gas supply tank 7a, a thermostat 13a which is provided so as to surround the 7b, is maintained at a predetermined temperature at 13b.

The gas supply tanks 7a and 7b are provided with gas ejection pipes 15a and 15b, respectively. As shown by arrows 9a and 9b in the drawing, an oxidizing gas and an inert gas containing the oxidizing gas are provided. Alternatively gas supply tank 7a any inert gas, the liquid in 7b 14a, 14
blown into the b, and organic oxysilane and refractive index control beam dopant bets are stored is vaporized by bubbling with these gases, and to feed to the gas supply pipe 8.

The gas supply pipe 8 is provided with a heating means such as a heater (not shown) and is heated to a temperature equal to or slightly higher than the temperature of the thermostatic bath 13. When the steam is conveyed, the steam is cooled and liquefied to prevent accumulation in the steam. The heating temperature of the gas pipe 8 is usually several tens of degrees Celsius.

On the other hand, a heater (not shown) is attached below the lower electrode 4 so that the substrates 6a, 6b and 6c can be heated to 1000 ° C. or less. Also,
The center of the bottom of the housing 2 is formed with an exhaust port 9, further liquid nitrogen trap 1 to the exhaust port 9
0, a rotary pump 11 and an exhaust device 12 are connected in order to evacuate the inside of the sealed housing 2.

A storage container 18 for storing a compound 16 containing a rare earth element, which is usually solid at normal temperature, is connected to the side of the closed housing 2. This storage container 18
Is provided with a heater 17 and an introduction pipe 19 for introducing the carrier gas G into the container 18, and heats the stored compound 16 containing a rare earth element to more than one hundred and several tens of degrees Celsius,
This is vaporized, and the vapor is converted into carrier gas G.
At the same time, the plasma is introduced into the plasma 5 generated between the electrodes 3 and 4 via an introduction tube 18a which is another transport system.

Next, a method for forming a glass film for an optical waveguide of the present invention using the plasma CVD apparatus 1 will be described.

First, the inside of the closed housing 2 is evacuated by driving the liquid nitrogen trap device 10, the rotary pump 11 and the exhaust device 12, and then the substrates 6a, 6b, 6c placed on the lower electrode 4 in this state. Is heated to 1000 ° C. or lower by a heater (not shown), and high-frequency power is applied between these upper and lower electrodes 3 and 4 to generate plasma 5.

Next, the valve 8a of the gas supply pipe 8 is opened to open the liquid 14 stored in the gas supply tanks 7a and 7b.
The mixed vapor of a and 14b is uniformly jetted from the electrode 3 side into the plasma 5 in the closed housing 2 in a shower shape, and at the same time, the vapor containing the rare earth element is directly introduced into the plasma 5 atmosphere from the introduction pipe 18a. Then, the liquids 14a and 14b and the vapor containing the rare earth element are deposited on the low refractive index layers of the substrates 6a to 6c mounted on the electrode 4, and the refractive index controlling dopant having a high refractive index and the rare earth element are vaporized. the will form a SiO ₂ glass film containing. In this example, Si (OC ₂ H ₅ ) ₄ was used as the organic oxysilane of the liquid 14a, Ge (OC ₂ H ₅ ) ₄ was used as the refractive index controlling dopant of the liquid 14b, and Compound 1 was used.
Substrate 6a, using Er (DPM) ₃ as 6 respectively ,
About 10 g of SiO ₂ film containing Ge and Er on 6b and 6c.
and μm formed, the SiO ₂ films by changing many manufacturing conditions, the film is a transparent film, its thickness and the inner surface of the substrate index homogeneity was good and ± 0.2% and ± 0.01% .

Usually, the compound 16 is vaporized by heating at a temperature of one hundred and several tens of degrees C. or more. The vaporized vapor is transported into the closed housing 2 by a carrier gas G such as an oxidizing or inert gas in the transport system maintained at the above temperature, and is directly blown into the plasma 5 atmosphere. Plasma 5 as the introduction to this hundred ℃ above kept vapor in the plasma 5 including the rare earth elements shown in the arrow Y ₁
It has the effect of compensating for the disturbance of the plasma flow due to the low-temperature steam blown into the inside. On the other hand, the vapor of organic oxysilane (usually liquid at normal temperature) containing the refractive index controlling dopant supplied from the gas supply pipe 8 oxidizes the oxidizing gas or the oxidizing gas in the gas supply pipe 8 kept at several tens of degrees Celsius. And transported directly into the plasma 5 atmosphere. Here, the reason that the two kinds of vapors are transported by separate transport systems and directly led into the atmosphere of the plasma 5 is that, when the same transport system is used, the transport system is difficult due to the vaporization temperature of one compound 16. However, at such a high temperature, the organic oxysilane containing the other dopant is liable to cause a decomposition reaction, so that SiO ₂ -based fine particles are generated in the middle of the transport system. This is because the fine particles are sent into the atmosphere of the plasma 5 and mixed into the glass film deposited on the substrate. That is, as a result of the experiment, it was found that the glass fine particles mixed in the glass film had a size of several μm to 10 μm, which caused scattering loss when an optical waveguide was formed. Thus, as described in the present invention, the two types of vapors are directly transported into the plasma 5 atmosphere by separate transport systems, and as a result, a transparent core glass film having extremely low scattering loss was successfully formed. In addition, since a vapor containing a rare earth element at a temperature of a few hundred degrees Celsius and an organic oxysilane vapor containing a dopant for controlling a refractive index at a temperature of several tens degrees Celsius are mixed in a low-temperature plasma atmosphere of 1000 ° C. or less, the rare earth element and the refractive index The control dopant could be uniformly mixed into the glass film without unnecessary vaporization. Further, since the vapor containing the rare earth element is mixed in the plasma atmosphere at a temperature of not less than 1000 ° C. while maintaining the temperature at a hundred and several tens of degrees Celsius, it is possible to suppress an extreme decrease in the temperature gradient in the plasma atmosphere. Can reduce the non-uniformity of the rare earth element content. Further, the amount of the rare earth element added to the glass film can be easily controlled by adjusting the heating temperature of the compound containing the rare earth element and the flow rate of the carrier gas G for carrying the vapor. Moreover, since the obtained glass film is a transparent glass film, the metal film is formed thereon, the resist film is patterned by photolithography, the metal film is patterned by dry etching, and the glass film is patterned without heat treatment. By doing so, an optical waveguide can be realized.

As described above, the organic oxysilanes include, in addition to Si (OC ₂ H ₅ ) _{4 of} this embodiment,
For example, Si (OCH ₃ ) ₄ or the like can be used. As the liquid for the dopant for controlling the refractive index, Ge (OCH ₃ ) of this embodiment is used.
In addition to C ₂ H ₅ ), for example, PO (OC ₂ H ₅ ) ₃ , B
(OC ₂ H ₅ ) ₄ , Sb (OC ₂ H ₅ ) ₄ , Al (OC
_A liquid containing at least one kind of ₂ H ₅ ) ₄ or the like can be used.

Next, a method of forming an optical waveguide using this glass film will be described.

First, a metal film for a metal mask, for example, W, Ti, Cr, WSi or the like is formed on the glass film surface to a thickness of 0.5 to 1 μm by sputtering. After performing photolithography for forming a photoresist pattern on the metal film, a dry etching process is performed. In this case, first, metal etching is performed using the photoresist pattern as a mask, and then the glass film is etched using the photoresist and metal pattern as a mask to obtain a substantially rectangular pattern. Finally, the photoresist and the metal film are removed.
Thereafter, a clad glass film is coated on the pattern surface. The refractive index of the clad glass film is lower than that of the upper lath film.

Next, FIG. 2 shows another embodiment of a method and an apparatus for manufacturing a glass film for an optical waveguide by the plasma CVD method of the present invention. This embodiment is different from the method and the apparatus of FIG. A point is a point at which a vapor containing a rare earth element is blown into the plasma 5. That is, in the present embodiment, the steam cover 3c is provided so as to surround the outer periphery of the upper electrode 3 provided with the disk-shaped gas shower section 3a, and the steam cover 3c is provided from the vessel 18 for generating steam containing a rare earth element. Introductory pipe 18
a, and a vapor containing a rare-earth element is blown into the plasma 5 from the outer periphery of the upper electrode 3 provided with the disk-shaped gas shower portion 3a. This method makes it possible to spray the vapor into the plasma 5 more uniformly. As a result, it is possible to uniformly doped with a rare earth element further SiO ₂ in the glass film containing a refractive index controlling dopant and.

[0032] The above embodiment has a pair of electrodes 3 and 4 is configured to be positioned at the top and bottom, the present invention is not limited thereto, one fixed to the substrate, for example If there is a means, the electrodes 3 and 4 may be arranged facing each other so as to be located on the left and right. Further, the position of the exhaust port 12 may be provided on the side surface or the upper portion instead of the bottom portion in the reaction vessel 2. That is, in FIG. 1 and FIG.
It may be on any of the directions. Also, the number of substrates is not limited to the above embodiment, but can be changed as needed.

[0033]

In summary, according to the present invention, the rare earth element can be uniformly added to the glass film.
The addition amount can be easily controlled, and a transparent glass film can be formed. In addition, since the manufacturing method is simple, there is an excellent effect that the manufacturing cost can be easily reduced.

[Brief description of the drawings]

FIG. 1 is a schematic view showing one embodiment of a plasma CVD apparatus used in the present invention.

FIG. 2 is a schematic view showing another embodiment of the plasma CVD apparatus used in the present invention.

FIG. 3 is a schematic view showing a method for manufacturing a conventional rare earth element glass waveguide.

[Explanation of symbols]

2 reaction containers 3 and 4 substrate 5 plasma 6a, 6b, 6c substrate 8a, 18a transport system 14a organic oxysilane 14b for refractive index control dopant preparative 16 rare-earth compound

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuyuki Imoto 3550 Kida Yomachi, Tsuchiura-shi, Ibaraki Hitachi Advanced Research Center Co., Ltd. (56) References JP-A-3-220506 (JP, A) JP Hei 3-122281 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G02B ^6/ 12-6/14

Claims (4)

(57) [Claims] 1. A substrate having a low refractive index layer is disposed on one of a pair of electrodes opposed to each other in a reaction vessel, and a high-frequency power is applied between the electrodes to generate plasma, and a refractive index is generated. The mixed vapor of the control dopant and the organic oxysilane, and the vapor containing the rare earth element are respectively guided by different transport systems and directly blown into the plasma atmosphere, respectively, and the low refraction of the substrate heated to 1000 ° C. or less is performed. A method for producing a glass film for an optical waveguide by a plasma CVD method, comprising forming a transparent glass film containing a refractive index controlling dopant having a higher refractive index and a rare earth element on the surface of a refractive index layer. 2. The method for producing a glass film for an optical waveguide by a plasma CVD method according to claim 1, wherein the electrodes are arranged so as to face either the vertical direction or the horizontal direction. 3. The plasma according to claim 1, wherein at least one of the mixed vapor and the vapor containing the rare earth element is blown from one of the electrodes into a plasma atmosphere like a shower. A method for producing a glass film for an optical waveguide by a CVD method. 4. A substrate having a low-refractive-index layer is disposed on one of a pair of electrodes opposed to each other in a reaction vessel, and a high-frequency power is applied between the electrodes to generate a plasma, The mixed vapor of the control dopant and the organic oxysilane, and the vapor containing the rare earth element are respectively guided in separate transport systems, and are directly blown into the plasma atmosphere, respectively, and heated to 1000 ° C. or less. After forming a transparent glass film containing a higher refractive index controlling dopant and a rare earth element on the surface of the low refractive index layer of the substrate, a metal film is formed on the surface of the glass film, and the metal film is formed. A photoresist pattern is formed on the surface, and the metal film is patterned using the photoresist pattern as a mask to form a metal pattern. The metal pattern is used as a mask. Patterning the glass film, peeling the photoresist and the metal film to form a glass pattern, and coating the glass pattern surface with a low refractive glass film having a refractive index lower than that of the glass. A method for manufacturing an optical waveguide, comprising: