JP3157693B2 - Method for producing silica glass-based deposit - 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 silica glass-based deposit useful as a base material for an optical fiber or a glass for an LSI photomask substrate.

[0002]

2. Description of the Related Art In a facility for producing silica glass as a base material for optical fibers, in addition to gaseous materials such as hydrogen and oxygen, SiO ₂
SiCl ₄ , which is a raw material for glass, and GeCl _{4, which} is a doping raw material for forming a refractive index distribution in glass, are provided as liquid raw materials for production. In the vapor phase axial (VAD) method, each liquid raw material is vaporized together and supplied to an oxyhydrogen flame burner to be used for forming a glass fine particle deposit. Conventionally, in these methods, SiCl ₄ and GeCl ₄ are filled in each raw material container, and a carrier gas having a controlled flow rate such as Ar gas is used.
The desired raw material is vapor-phase diffused in the carrier gas by bubbling the gas into the glass raw material in each raw material container, and each raw material vapor is generated as a mixed gas with the carrier gas and supplied to the burner. FIG. 2 conceptually illustrates this.

In FIG. 1, reference numeral 1 denotes a carrier gas flow controller, reference numeral 2 denotes a glass raw material container (hereinafter referred to as a container), and reference numeral 3 denotes a glass raw material (hereinafter referred to as a raw material). Since P is the two-component system of the raw material vapor, P is the total gas phase pressure in the container 2, φ is the saturation degree, t is the container temperature, and p (t) is the saturated vapor pressure of the raw material at the temperature t. The partial pressure of the raw material vapor in the vessel 2 is represented by φp (t). Further, since the partial pressure of the carrier gas in the vessel 2 is represented by P-φp (t), the following equation holds when q is the carrier gas flow rate and Q is the accompanying raw material vapor flow rate. Q: q = raw material partial pressure φp (t): carrier gas partial pressure P−φp (t) (1) That is, the accompanying raw material vapor flow rate Q is calculated by the following equation. Q = q × φp (t) / {P-φp (t)} (2)

In order to keep the raw material vapor flow rate Q constant,
(2) In the equation, the values of q, φ, p (t) and P may be kept constant. The carrier gas flow rate q is precisely controlled to a constant value by a mass flow controller. As a technique for keeping the degree of saturation φ constant, for example, it is disclosed in Japanese Patent Publication No. 61-1378, but according to this method, a container filled with the same liquid material is divided into a front and a rear stage, and a carrier for bubbling is divided. The saturation degree φ can be maintained at almost 100% with good reproducibility by connecting in series by a gas conduit and maintaining the temperature at a high temperature by the temperature of the vessel at the preceding stage.

[0005]

In the equation (2), the flow rate q of the carrier gas is controlled by the mass flow meter (MFC), so that the responsiveness is high in addition to the high accuracy. On the other hand, the raw material concentration φp (t) / (P−φp (t)) is determined from a plurality of factors, and the response is extremely slow. Therefore, in the carrier gas method, the raw material vapor flow rate Q is It is considered that the ideal control method is to keep the raw material vapor concentration at a constant value by equalizing and stabilizing various conditions in the phase and to control the raw material vapor concentration by the carrier gas flow rate.

However, in the VAD method, the flow resistance of the raw material vapor flow path in the vessel to the flame burner is small, and the gas phase pressure in the vessel is all 0.01 kg / cm ² or less. Even if the carrier gas flow rate q, the saturation degree φ, and the temperature t of the container are kept constant as in the conventional supply method, the gas pressure P in the container becomes atmospheric pressure π → π ± △ π. When it changes, the gas pressure in the vessel P → P ± △ π
, And the accompanying raw material vapor flow rate Q changes by ΔQ represented by the equation (3). ΔQ = q × φp (t) [1 / {P ± △ π-φp (t)} -1 / {P-φp (t)}… (3)

Conventionally, when the atmospheric pressure π fluctuates as described above, the concentration term φp (t) / ｛P-φ in the equation (2) due to this fluctuation.
Carrier gas flow term q so as to cancel the fluctuation of p (t)｝
The method of responding by changing
It is disclosed in Japanese Patent Publication No. 4-33738. In this method, .DELTA..pi. Detected by the atmospheric pressure sensor 5 in FIG.
(t) [1 / {P ± △ π-φp (t)} -1 / {P-φp (t)}] is immediately calculated, and the new set value of the carrier gas flow rate which is increased or decreased accordingly is set to the carrier. The signal is transmitted to the gas flow controller 1. As described above, the set value of the carrier gas flow rate q is reduced or increased in accordance with the rise or fall of the raw material concentration in the container gas phase, thereby maintaining the accompanying raw material vapor flow rate Q at a constant value. However, in this method, the carrier gas flow rate is changed, and as a result, the bulk density of the surface of the deposited base material due to the temperature fluctuation of the oxyhydrogen flame of the burner is different from before and after the change, and this is the case during the transparent vitrification. As a result, a delicate refractive index variation site is created in the site, and there is a problem that the optical characteristics of the preform are poor and the optical glass is striae.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and a liquid material such as a liquid silicon compound is filled in each material container, and a carrier gas is bubbled into each of the material containers to vaporize them separately. A mixed gas with a carrier gas is obtained, this mixed gas is supplied to a burner, and the burner performs flame hydrolysis in an oxyhydrogen flame to generate fine particles, and these fine particles adhere to a rotating seed rod. A method for manufacturing a silica glass-based deposit by depositing, comprising: a calculating means for estimating a concentration fluctuation from a detected fluctuation value of atmospheric pressure; and a control means for correcting a carrier gas flow rate from the concentration fluctuation estimated value. When controlling the steam supply flow rate of the raw material to be constant, the carrier gas is added to the gas mixture immediately before the gas mixture is supplied to the burner. The scan of the same component of the gas is intended to be subject matter of the method for producing a silica glass-based deposit to the addition of flow rate corresponding to changes in atmospheric pressure maintaining the flow rate of the carrier gas components in the mixed gas to be constant.

Hereinafter, the present invention will be described specifically. FIG. 1 is an explanatory view of the present invention, in which 1 is a first carrier gas flow controller, 2 is a liquid material container (container), 3 is a material, 5 is an atmospheric pressure sensor, 6 is a correction calculator, and 7 is a The first and second carrier gas flow controllers comprise two carrier gas flow controllers and are connected to an atmospheric pressure sensor 5 and a correction calculator 6.
The raw material SiCl ₄ is injected into the container 2 by the raw material supply pipe 11,
The first carrier gas is supplied from a carrier gas introduction pipe 8, and a mixed gas of the raw material vapor and the carrier gas is sent from a raw material vapor supply pipe 9 to a burner (not shown), and an O ₂ gas (not shown) separately supplied is provided. And H ₂ gas (not shown), flame-hydrolyzed by an oxyhydrogen flame to produce oxide fine particles, which are deposited and deposited on a rotating seed rod (not shown) to form a silica glass-based deposit. In this process, a gas having the same composition as the first carrier gas is used as the second carrier gas in this step, in order to compensate for the first carrier gas flow rate changed according to the fluctuation of the atmospheric pressure, the second carrier gas flow controller 7 is used. Immediately before the burner, it is mixed with the mixed gas of the source gas and the first carrier gas. The first and second carrier gas flow controllers 1 and 2 each have a correction arithmetic unit 6 connected to an atmospheric pressure sensor 5 to control the flow rate q of the first and second carrier gases according to the fluctuation of the atmospheric pressure. _1, q ₂ is controlled, and the feed material vapor amount Q and the carrier gas total flow amount q
= Q ₁ + q ₂ is made constant.

However, there is a problem that the amount of the raw material vapor Q to be supplied is reduced when the carrier gas is reduced. As a result, the present inventors have repeatedly studied and found that the concentration of the raw material vapor in the gas phase of the container is reduced. By setting high and constant, the first
Also carrier gas flow rate q ₁ is set lower than the conventional flow rate q can be done without reducing the raw material steam amount Q, the flow rate of the difference q ₂ (= q-q ₁₎ as the second carrier gas The flow rate was controlled by a mass flow controller from another line, and the mixed gas with the first carrier gas was introduced and mixed at a position immediately before being supplied to the burner. This (2) the concentration term in formula φp (t) / {P- φp (t)} first by changing the carrier gas flow to claim q ₁ so as to cancel the variation of keeping the raw material vapor flow rate Q constant, At the same time, the second carrier gas flow rate q ₂ is changed by the same amount so that the total carrier gas flow rate q ₁ + q ₂ (= q) is always kept constant. The method of setting the raw material vapor concentration in the gas phase in the container high may be performed by, for example, increasing the heating temperature of the container. This first carrier gas flow rate q
_{If the} ratio (volume ratio, hereinafter the same) of _{1 to} the raw material vapor supply flow rate Q is less than 0.25, it is necessary to maintain the temperature of the raw material container at 50 ° C. or more, and it is difficult to stabilize the gas phase saturation of the container. Further, the ratio of the first carrier gas flow rate q ₁ of the second carrier gas flow rate q _2, it is controlled on preferably 0.20 or more. Carrier gas total flow q ₁ + q ₂ (=
The ratio of q) to the raw material vapor supply flow rate Q is preferably 0.30 or more. The larger the ratio, the lower the temperature in the raw material container and the higher the accuracy of the raw material vapor flow control, but the lower the flame temperature. The problem is that
It is preferably 0.30 to 2, more preferably 0.50 to 1.5
It is. Examples of the silica glass-based deposit of the present invention include a porous glass preform for an optical fiber preform and an optical silica glass used for a photomask substrate for LSI.

[0011]

According to the present invention, a liquid material such as a liquid silicon compound is charged into a material container, and a carrier gas is bubbled into the material containers to separately vaporize each of them to obtain a mixed gas with the carrier gas. Supply, and in the same burner, the respective particles are generated by flame hydrolysis in an oxyhydrogen flame, and the fine particles are adhered and deposited on a rotating seed rod. When controlling the vapor supply flow rate of the liquid raw material to be constant by providing arithmetic means for estimating the concentration fluctuation from the detected fluctuation value of the atmospheric pressure and control means for correcting the carrier gas flow rate from the concentration fluctuation estimation value, the mixing is performed. Immediately before the gas is supplied to the burner, a gas having the same composition as the carrier gas flows through the mixed gas in accordance with the fluctuation of the atmospheric pressure. To maintain the gas flow rate of the carrier gas component in the mixed gas at a constant level. As a result, the flow rate of the supplied raw material vapor and the flow rate of the carrier gas are always kept constant, so that an optical fiber preform that is homogeneous in the axial direction with good reproducibility and an optically transparent and uniform synthetic quartz glass without striae can be obtained. it can.

[0012]

EXAMPLES Examples and comparative examples of the present invention will be described below. Example 1 Core material SiCl ₄ was obtained by using a material vapor supply device shown in FIG.
At a temperature of 40 ° C in the liquid SiCl ₄ container, the volume ratio between the SiCl ₄ vapor flow rate and the Ar gas total flow rate was set to 1.21, and the SiCl ₄ vapor flow rate was
121SCCM (Standard volume flow per minute (CC), the same applies hereinafter), Ar
Total gas flow rate 100SCCM, Ar gas flow rate q ₁ of the first carrier gas 68SCCM, Ar gas flow rate q ₂ of the second carrier gas was set to 32 sccm. During this time, the atmospheric pressure was measured with a barometer
Although it fluctuated in the range of 1.033 to 1.053 kg / cm ² , the control flow rate q ₁ of the mass flow controller flow rate of the Ar gas of the first carrier gas blown into the raw material container was corrected and controlled at 68 to 70 SCCM, and the second carrier was controlled. The control flow q ₂ of the mass flow controller flow of Ar gas is 32
The correction was controlled at ~ 30 SCCM. As a result, the flow rate of SiCl ₄ vapor supplied to the core burner was kept constant at 121 SCCM, and the total flow rate q ₁ + q ₂ of Ar gas as a carrier gas was kept constant at 100 SCCM.

On the other hand, GeC as a liquid raw material for the core dough punt
l ₄ using the raw material supply apparatus of FIG. 2 of the prior art from this effect becomes small since the flow rate is small in the Ar gas of the carrier gas for, and fed to the core burner as follows.
The Ar gas of 50 SCCM was bubbled into the liquid in the raw material container of liquid GeCl ₄ kept at a temperature of 30 ° C., and GeCl ₄ vapor was entrained to send the gas to the core burner. When the gas phase pressure in the container is 0.01 KG (1.043 kg / cm ² ), the temperature in the container
At 30 ° C., the volume ratio of GeCl ₄ vapor to Ar gas in the gas phase is 0.18. During this time, the control flow rate of the Ar gas mass flow controller flow rate was controlled by the atmospheric pressure sensor and the flow rate correction controller in the range of 50 to 52 SCCM, but the GeCl ₄ vapor supplied to the burner was constantly kept at 50 SCCM. Was.

The liquid raw material for cladding SiCl ₄ is prepared by using a raw material vapor supply device shown in FIG.
l SiCl ₄ vapor flow rate and the Ar gas total flow volume ratio in the raw material container temperature 40 ° C. for ₄ is set to 1.21, 605S and SiCl ₄ vapor flow
CCM, the total flow rate of Ar gas q ₁ + q ₂ was set at 500 SCCM, the Ar gas flow rate q ₁ of the first carrier gas was set at 399 SCCM, and the Ar gas flow rate q ₂ of the second carrier gas was set at 161 SCCM. During the reaction, the atmospheric pressure fluctuated in the range of 1.033 to 1.053 kg / cm ^{2 with} a barometer, but the control flow rate q of the Ar gas of the first carrier gas blown into the container by the mass flow controller q
₁ was controlled to be corrected at 340 to 350 SCCM, and the control flow q ₂ of the mass flow controller flow rate of Ar gas as the second carrier gas was controlled to be corrected to 160 to 150 SCCM. As a result, the flow rate of the SiCl ₄ vapor supplied to the clad burner was 605 SCCM, and the total Ar flow rate q _{1 of the} carrier gas was ₁
+ Q ₂ was always kept constant at 500 SCCM.

In this way, the raw material vapor for the core and the raw material vapor for the clad are respectively sent to the core and clad burners to produce a porous glass base material by the VAD method.
Dehydrate at 1,200 ° C, sinter at 1,500 ° C, diameter 30mm, length 50
0mm single-mode preform (△ n = 0.3%)
Were produced and their refractive index displacement in the longitudinal direction was examined using a refractive index distribution analyzer. The results shown in Table 1 were obtained.

[0016]

[Table 1] From the results in Table 1, it was found that the variation in the lot of Δn was small.

Comparative Example 1 Core material SiCl ₄ was prepared by bubbling 100 SCCM of Ar gas as a carrier gas into a liquid in a container of liquid material SiCl ₄ maintained at a temperature of 35 ° C. using a material vapor supply apparatus shown in FIG. The gas is supplied to the core burner at a flow rate of 82 SCCM, accompanied by SiCl ₄ vapor. Gas phase pressure of 0.01 KG (1.
At 043 kg / cm ² ), the volume ratio of the flow rate of the SiCl ₄ vapor to the flow rate of the Ar gas in the gas phase was set to 0.82 at a temperature of 35 ° C. in the container. During this time, the control flow rate of the Ar gas mass flow controller fluctuated in the range of 100 to 103 SCCM by the atmospheric pressure sensor and the flow rate correction controller, but the SiCl ₄ vapor flow rate supplied to the core burner was kept constant at 82 SCCM. Was. Example 1 for GeCl _{4 as} a liquid material for dough punts
During this period, the control amount of the mass flow controller flow rate of Ar gas was changed to 50 to 52 SCCM, and the vapor flow rate of GeCl ₄ supplied to the core burner was kept constant at 50 SCCM.

The cladding raw material SiCl ₄ was prepared by using a raw material vapor supply device shown in FIG. 2 different from the core raw material, and using carrier gas Ar in the liquid in the container of the liquid raw material SiCl ₄ maintained at a temperature of 35 ° C. SiC by bubbling 500 SCCM of gas
l ₄ Steam is supplied to the cladding burner. When the gas pressure in the vessel is 0.01 KG (1.043 kg / cm ² ) and the temperature in the vessel is 35 ° C., the flow rate of SiCl ₄ vapor in the gas phase is 410 SCC.
M was set, and the volume ratio to the Ar gas flow rate was set to 0.82. During this time, the control flow rate of the mass flow controller flow rate of the carrier gas Ar gas changed within the range of 500 to 515 SCCM by the atmospheric pressure sensor and the flow rate correction controller, but the SiCl ₄ gas flow rate supplied to the cladding burner was always 410 SCCM. Kept constant.

In this way, the raw material vapor for the core and the raw material vapor for the clad are respectively sent to the core and clad burners to produce a porous glass base material by the VAD method, which is dehydrated at 1,200 ° C. in the same manner as in Example 1. After sintering at 1,500 ° C., five single-mode preforms (Δn = 0.3%) having a diameter of 30 mm and a length of 500 mm were manufactured, and the refractive index displacement in the longitudinal direction was examined using a refractive index distribution analyzer. However, the results shown in Table 2 were obtained.

[0020]

[Table 2] From the results in Table 2, it was found that the variation of Δn was large.

Example 2 Using a raw material vapor supply apparatus shown in FIG. 1, a liquid raw material SiCl ₄ was used as a raw material,
The volume ratio of the SiCl ₄ vapor flow rate to the carrier gas O ₂ gas total flow rate is set to 1.0, the SiCl ₄ vapor flow rate is set to 20 SLM (standard volume flow rate per minute (L), the same applies hereinafter), and the carrier gas O ₂ gas total The flow rate is 20 SLM and the first carrier gas O ₂
The gas flow rate q ₁ 14SLM, was set O ₂ gas flow rate q ₂ of the second carrier gas to 6.0SLM. During this time, the atmospheric pressure was 1.033
The control flow rate q ₁ of the mass flow controller flow rate of the O ₂ gas of the first carrier gas blown into the container is corrected and controlled at 14.0 to 14.5 SLM, and the second carrier gas is varied in the range of 1.053 kg / cm ^2. Control flow q ₂ of mass flow controller flow of gas O ₂ gas is 6.0 ~
Correction was controlled by 5.5SLM. As a result, the flow rate of the SiCl ₄ vapor supplied to the burner was kept constant at 20 SLM, and the total flow rate q ₁ + q ₂ of the O ₂ gas as the carrier gas was kept constant at 20 SLM.

In this manner, SiCl ₄ vapor is supplied to the burner, and silica glass fine particles are generated by flame hydrolysis.
Five transparent glass bodies having a length of 100 mm and a length of 1,000 mm were produced.
Next, striae was examined along the longitudinal direction of the glass body with a strain tester SVP-10P [manufactured by Toshiba Corporation] in which a polarizing plate and a light source were combined, and the results shown in Table 3 were obtained.

[0023]

[Table 3] From the results in Table 3, it was found that strong stria was not observed in each lot, and that there was little weak stria.

COMPARATIVE EXAMPLE 2 A carrier gas O ₂ gas flow rate of 20 SLM is bubbled into a liquid inside a container of liquid raw material SiCl ₄ maintained at a temperature of 35 ° C., and a vapor flow rate of 14 SLM of SiCl ₄ is entrained and sent to a burner. At a gas phase pressure of 0.10 KG (1.133 kg / cm ² ) in the vessel, at a vessel temperature of 35 ° C., the volume ratio of the SiCl ₄ vapor flow rate to the carrier gas O ₂ gas flow rate in the gas phase is 0.71.
Set to. During this time, the control flow rate of the O ₂ gas mass flow controller flow rate changed in the range of 20.0 to 20.6 SLM by the atmospheric sensor and the flow rate correction controller, but the flow rate of SiCl ₄ vapor supplied to the burner was kept constant at 14 SLM. .

In this manner, SiCl ₄ vapor is supplied to the burner in the same manner as in Example 2, and silica glass fine particles are generated by flame hydrolysis. Five 1,000 mm transparent glass bodies were manufactured. Next, over the longitudinal direction of the glass body,
Striae was examined using a strain tester SVP-10P (manufactured by Toshiba Corporation) in which a polarizing plate and a light source were combined. The results shown in Table 4 were obtained.

[0026]

[Table 4] From the results in Table 4, strong stria was observed in each lot, and many weak stria were also observed.

[0027]

According to the present invention, the glass raw material vapor and the carrier gas are supplied to the burner at a constant flow rate without being affected by the fluctuation of the atmospheric pressure. It is possible to obtain a silica glass-based deposit useful as a homogeneous silica glass having a stria-free optical property.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a raw material vapor supply device according to the present invention.

FIG. 2 is a longitudinal sectional view of a raw material vapor supply device in a conventional method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... 1st carrier gas flow controller 2 ... Liquid raw material container (container) 3 ... Liquid raw material 5 ... Atmospheric pressure sensor 6 ... Correction arithmetic unit 7 ... 2nd carrier gas flow controller 8 ... Carrier gas injection pipe 9 ... Raw material Vapor sending pipe 11 ... Liquid raw material liquid supply pipe 12 ... Bubble

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-129033 (JP, A) JP-A-57-47738 (JP, A) JP-A-61-254242 (JP, A) JP-A-63-164 288922 (JP, A) Hikaru 1-170439 (JP, U) (58) Fields studied (Int. Cl. ⁷ , DB name) C03B 8/04 C03B 37/018

Claims (3)

(57) [Claims] 1. A raw material container is filled with a liquid raw material such as a liquid silicon compound, and a carrier gas is bubbled into the raw material container to separately vaporize each of them, thereby obtaining a mixed gas with the carrier gas, and supplying the mixed gas to the burner. Then, in the same burner, each particle is generated by flame hydrolysis in an oxyhydrogen flame, and these particles are attached and deposited on a rotating seed rod. When controlling the vapor supply flow rate of the liquid raw material to be constant by providing arithmetic means for estimating the concentration fluctuation from the fluctuation value of the atmospheric pressure and control means for correcting the carrier gas flow rate from the concentration fluctuation estimation value, the mixed gas is Immediately before being supplied to the burner, a gas having the same composition as that of the carrier gas is added to the mixed gas at a flow rate corresponding to the change in atmospheric pressure. And maintaining the flow rate of the carrier gas component in the mixed gas at a constant level. 2. The method for producing a silica glass-based deposit according to claim 1, wherein the fine particles are a silica glass-based deposit deposited as a porous material on the seed rod. 3. The method for producing a silica glass-based deposit according to claim 1, wherein the fine particles are a silica glass-based deposit which is heated and vitrified while being deposited on the seed rod.