JP3192571B2 - Method for producing silica-based glass - 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 useful as a preform for a silica glass optical fiber or an LSI photomask substrate.

[0002]

2. Description of the Related Art In a facility for producing silica glass as an optical fiber core member , in addition to gaseous materials such as hydrogen and oxygen, Si
SiCl ₄ , which is a raw material of O ₂ glass, and GeCl _{4, which} is a doping raw material for forming a refractive index distribution in the glass, are supplied as liquid raw materials for production. In the vapor phase alignment (VAD) method, each liquid raw material is vaporized together and supplied to an oxyhydrogen flame burner to form 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 of which flow rate is controlled, for example, Ar gas, is bubbled into the liquid glass raw material in each raw material container to thereby obtain each desired raw material. It vaporized and diffused in the carrier gas, and each raw material vapor was generated as a mixed gas with the carrier gas and supplied to the burner. This is shown conceptually in FIG.

In FIG. 2, reference numeral 11 denotes a carrier gas flow controller, 12 denotes a raw material container (container, the same applies hereinafter), 13 denotes a liquid raw material ,
14 is a pressure gauge, 15 is an atmospheric pressure sensor, 16 is a correction calculator , 18 is
Carrier gas injection pipe, 19 is raw material steam supply pipe, 20 is
In the liquid material supply pipe , since the gas phase in the container is a two-component system of carrier gas and material vapor diffused in the carrier gas, P is the total pressure in the container 12, φ is the saturation degree, and t is the container. If the temperature and p (t) are the saturated vapor pressure of the raw material at the temperature t, the partial pressure of the raw material vapor in the container 12 is φ
Since p (t) is represented and the partial pressure of the carrier gas in the container 12 is represented by P-φp (t), the following equation is established when q is the carrier gas flow rate and Q is the accompanying raw material vapor flow rate. Q: q = raw material vapor 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 (2). 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 accurately controlled by a mass flow controller (MFC). As a method for keeping the saturation φ constant, there is a method disclosed in Japanese Patent Publication No. 61-1378. According to this, a container filled with the same liquid material is divided into front and rear stages, connected in series by a bubbling carrier gas conduit, and maintained at a high temperature by the temperature of the container at the front stage, so that the saturation degree φ is almost 100%. A bubbler two-stage system in which the ratio is held at% is disclosed.

In the equation (2), as described above, since the carrier gas flow rate q is controlled by the MFC, the responsiveness is fast in addition to the high accuracy, but φp (t) / {P−φp (t )} Term is determined from a plurality of factors and the response is extremely slow, so in the carrier gas method, the raw material vapor flow rate Q is
The ideal control method is to keep the raw material vapor concentration at a constant value by equalizing and stabilizing various conditions in the gas phase in the vessel 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 path is small, and the gas phase pressure in the vessel is 0.01 kg / cm ² gauge or less. Since the pressure fluctuates, even if the carrier gas flow rate q, the saturation degree φ, and the temperature t in the container are kept constant as in the conventional supply method, the atmospheric pressure becomes π →
When it changes to π ± △ π, the gas pressure in the container also changes from P → P ± △ π, and the raw material vapor flow rate Q becomes △ Q expressed by the equation (3).
Only change. ΔQ = q × φp (t) [1 / {P ± △ π-φp (t)} -1 / {P-φp (t)}] (3)

Conventionally, when such a large pressure π varied, the concentration term .phi.p (t) / {P in formula (2) according to this variation
This was achieved by changing the carrier gas flow term q so as to cancel the fluctuation of −φp (t)｝ (Japanese Patent Publication No. 4-33).
No. 738). According to this, △ π detected by the atmospheric pressure sensor 15 in FIG. 2 is transmitted to the correction arithmetic unit 16, and the arithmetic unit 16 performs the concentration fluctuation φp (t) [1 / {P ± △}.
π−φp (t)} −1 / {P−φp (t)}] is calculated immediately,
The new set value of the carrier gas flow rate increased / decreased according to this is transmitted to the carrier gas flow rate controller 11. 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 gas phase concentration, so that the raw material vapor flow rate is maintained at a constant value.

[0008]

However, when the carrier gas flow rate q is reset and the correction width is large, a sudden change in the carrier gas flow rate is caused, and the carrier gas flow rate greatly fluctuates. Causes the temperature fluctuation of the oxyhydrogen flame, the bulk density of the surface of the deposited base material changes before and after the change, and becomes inhomogeneous. This contributes to poor characteristics. In addition, a large change in the carrier gas flow rate due to the automatic resetting of the carrier gas flow rate may cause a change in the saturation of the raw material vapor in the gas phase in the container. However, it is difficult to predict the saturation fluctuation width due to the atmospheric pressure fluctuation, and if the saturation fluctuates, the correction of the raw material steam supply flow rate may not be performed accurately. Therefore, a method of maintaining a saturation of 100% by a two-stage bubbler method is considered to be effective, but this method has a problem that the apparatus becomes complicated.

[0009]

The inventors of the present invention have made various studies to solve the above-mentioned problems. As a result, the higher the pressure P of the gas phase in the vessel, the higher the change in the atmospheric pressure variation rate △ π / π. effects on raw steam flow fluctuation rate △ Q / Q Noting that decreases, which has completed the present invention examined this pressure P, the first invention, the silicon compound is vaporized and A dope compound vaporized as necessary is flame-hydrolyzed in an oxyhydrogen flame to generate silica fine particles and fine particles of a dope material, and these fine particles adhere and deposit on a rotating seed rod. the method of manufacturing a glass, the liquid material in the liquid material and doped compounds of silicon compounds was filled in each of the source container, pipe blowing a carrier gas to the carrier gas in these liquid materials Ri blown bubbling vaporizing, in the liquid raw material supply method for supplying a mixed gas of the carrier gas and the raw material vapor to a burner, the gas phase pressure gauge pressure 1 kg / cm ² or more 2 kg / cm of less than ² in the respective source container you to
SUMMARY OF THE INVENTION A gist of the present invention is a method for producing a silica-based glass by maintaining a predetermined pressure at a predetermined pressure .

The gas pressure in the raw material container is 1 kg / c gauge pressure.
If it is less than m ² , the effect is not enough and the gauge pressure is 2 kg / c
Since m ² or more to become the line pressure is practically problematic too high, this value needs to be a gauge pressure 1 kg / cm ² or more 2 kg / cm of less than ^2, preferably gauge pressure 1.0 ~1.6kg / cm ² is better. Hereinafter, the present invention will be described specifically. FIG. 1 is an explanatory view of the present invention, in which 1 is a carrier gas flow controller,
2 is a liquid material container (container), 3 is a liquid material, 4 is a pressure gauge, 5 is an atmospheric pressure sensor, 6 is a correction calculator, 7 is a throttle valve, 8 is a carrier gas blowing pipe, 9 is a raw material vapor supply pipe, Reference numeral 10 denotes a liquid material supply pipe. Above construction present invention in the conventional method differs, in the present invention by installing the throttle valve 7 in the raw material gas stream path of the container-flame burner path, each
Gas pressure in each raw material container is gauge pressure 1kg / cm ² or more 2kg
/ cm ² is maintained at a predetermined pressure .

A second aspect of the present invention is a method for maintaining the degree of saturation of the raw material vapor in the gas phase in the vessel at a constant value of 99% or more, which comprises a vaporized silicon compound and, if necessary, The diffusion coefficient of the raw material vapor component of the doping compound vaporized in the carrier gas component is D, and the radius of the carrier gas injection port of the carrier gas injection pipe is r.
_O , and the carrier gas jet depth in the liquid
When _{a, D · Le / (r O} 2 √ (r O · g)); it is an gist method for manufacturing the silica glass the value is 2.0 or more (g gravitational acceleration). This will be described for Figure 1, the liquid material of the silicon compound or doped compound filled in a container 2, a carrier gas through the inlet tube 8 into this liquid material is blown, feedstock vapor with carrier gas burner than the supply pipe 9 In the present invention, in order to maintain the saturation of the raw material vapor at a constant value of 99% or more, the structure of the blowing pipe 8 for the carrier gas is set. , D ・ Le / (r _O ² √ (r _O ・ g)) should be 2.0 or more.
is there. Here If the value of ^{_{D · Le / (r O 2}} √ (r O · g)) is less than 2.0, the saturation of the feedstock vapor of the container in the gas phase there is a problem that less than 99%, the the value is required and this <br/> to 2.0 or more, preferably from 2.0 to 4.0.

Examples of the silica-based glass obtained by the method of the present invention include a preform for an optical fiber and a silica glass for an LSI photomask substrate. Doped compound of the present invention is a compound to be doped in order to adjust the refractive index of the optical fiber preform, which compounds such as well such as Ge and Ti or fluorine is known ones can be exemplified.

[0013]

The first invention of the present invention is explained by the following equation (4) introduced from the equations (2) and (3). ΔQ / Q = -P / ｛P-φp (t)｝ × (π / P) × (△ π / π) (4) That is, the raw material vapor flow rate Q and the carrier gas which are the reaction conditions in the oxyhydrogen flame Since the flow rate q is controlled to be constant to the specified value, the value of the concentration term φp (t) / {P−φp (t)} shown on the right side of equation (2) becomes Q / q and is constant. Become.
Therefore decided vessel vapor concentration in this manner, and it is necessary to hold it at a constant value. In the equation (4), the setting condition φp (t) / {P−φp (t)} is under a constant value, so that P
/ {P-φp (t)} Under the condition that the value is constant (> 1), the larger the gas pressure P in the vessel, the smaller the π / P value with respect to the atmospheric pressure fluctuation rate △ π / π. Therefore, it is explained that ΔQ / Q becomes small. However, the upper limit of the line pressure of the supplied carrier gas is generally about 2 kg / cm ² gauge pressure.
It is less than kg / cm ² .

On the other hand , the gas pressure P in the vessel is 1 kg / c gauge pressure.
When held in m ² or more pressure, and becomes like automatic opening and closing valves required by two-stage bubbler method for preventing the liquid material flowing back from the gas blowing pipe, a two-stage bubbler system complexity of the apparatus is unavoidable Become. The second invention of the present invention is a method of maintaining a constant saturation of 99% or more by only one vaporizer without using a two-stage bubbler method. While the bubbles generated by blowing the carrier gas into the raw material liquid in the container rise in the liquid phase, the raw material vapor component diffuses and penetrates into the bubbles, and the mixed gas of the raw material vapor and the carrier gas that has reached the gas phase The ratio of the raw material vapor in the carrier gas is increased by diffusion from the gas-liquid interface before passing through the gas phase and escaping outside the container.

The saturation in the bubble phase, in the container carrier gas blow pipe jets radius r _O by determined cell diameter Dp and during liquid blow tube carrier gas ports depth depends Le contact time θ etc. As a result of investigating these factors, the diffusion coefficient D, bubble diameter Dp, and contact time θ (bubble rising time) of the raw material vapor component in the carrier gas component are determined by the equation (5). if the degree of saturation of the raw material vapor in the gas phase was concluded that it is possible to maintain a constant value of 99.5%. D · θ / (Dp / 2) ² > 0.85 (5) In addition, the contact time θ is obtained by calculating the carrier gas injection port depth Le in the liquid of the carrier gas injection pipe from the flotation separation formula in the liquid. Equation (6) is given by dividing by the bubble rising speed u, and the bubble rising speed u is expressed by the formula (7) from the literature. θ = Le / u (6) u = √ (3.03 Dp · g) (7) where 500 <Re≡Dp · u · ρ / μ <100,000 g; gravitational acceleration Dp; bubble diameter μ; liquid viscosity ρ; Liquid density (Literature; Handbook of Chemical Engineering, Chapter 14.4, pp. 101) Then, Equation (8) is obtained from Equations (5) and (6). D · θ / (Dp / 2) ² = D · (Le / u) / (Dp / 2) ² > 0.85 (8) Further, Expression (9) is obtained from Expressions (7) and (8). D · Le / (Dp ² √ (Dp · g))> 0.37 (9) Assuming that the bubble diameter Dp is proportional to the carrier gas outlet radius r ₀ of the carrier gas injection pipe, carrier gas of various design specifications is used. As a result of designing and studying the blowing pipe, Equation (10) was derived from Equation (9). D · Le / (r _O ² √ (r _O · g))> 2.0… (10)

[0016]

The present invention will be described below with reference to examples and comparative examples. Example 1 For liquid SiCl ₄ and liquid GeCl _{4 as} core materials, Ar gas was used as a carrier gas at a flow rate of 300 SCCM (standard volume flow rate per minute (CC), respectively) using the liquid material supply device shown in FIG. 1 separately. Same) and blow at 30SCCM, flow rate 250S
CCM SiCl ₄ vapor and 3.0SCCM GeCl ₄ vapor were converted to H ₂ gas.
20SLM (standard volume flow rate per minute (L), same hereafter), O ₂ gas 20SLM and sent to core burner for flame hydrolysis
Fine particles of SiO ₂ and GeO ₂ were generated and deposited on a rotating seed rod. At the same time, liquid SiCl ₄
The Ar gas was blown in at a flow rate of 500 SCCM as a carrier gas using the liquid material supply device shown in FIG.
Flow rate of 410SCCM SiCl ₄ vapor to H ₂ gas 20SLM, O ₂ gas
The resultant was sent to a cladding burner together with 20SLM and subjected to flame hydrolysis to produce SiO ₂ fine particles, which were deposited on the seed rod to prepare a porous glass base material. At this time, SiCl ₄ for core and
GeCl ₄ and by adjusting the respective throttle valve 7 for clad SiCl ₄ to maintain the pressure within each of the source container to 1.01 kg / cm ² gauge, also core SiCl ₄ and GeCl ₄ and clad Si
The saturation of the raw material vapor in each raw material container of Cl ₄ was kept at 100%. The fluctuation range of the atmospheric pressure during this period is 1.033 to 1.053k
Although the absolute value was g / cm ^{2, the} flow rate of each raw material vapor was kept constant by adjusting the flow rate of the carrier gas by the carrier gas flow rate controller 1. The porous glass base material thus obtained is dehydrated at 1,200 ° C., sintered at 1,500 ° C. to produce five single-mode optical fiber preforms each having a diameter of 30 mm and a length of 500 mm. When the change in the refractive index difference Δn in the longitudinal direction was examined, the results shown in Table 1 were obtained.

Comparative Example 1 The procedure of Example 1 was repeated except that the throttle valve 7 was not used. The results are shown in Table 1. At this time, the pressure in each container was 0.01 kg / cm ² gauge, and the fluctuation range of the atmospheric pressure during this period was 1.033 to 1.053 kg / cm ² absolute value.

[0018]

[Table 1] From the results shown in Table 1, it can be seen that Example 1 has a smaller variation δΔn of Δn than Comparative Example 1.

Example 2 Example 2 was carried out in the same manner as in Example 1 except that the flow rate control of the carrier gas by the atmospheric pressure sensor was not performed. The fluctuation range of the atmospheric pressure during this period is 1.033 to 1.053 kg
/ cm ^{2 was the} absolute value. Table 2 shows the results.

[0020]

[Table 2] From the results in Table 2, it can be seen that the influence of atmospheric pressure fluctuation is small because the variation Δn of Δn is small.

Example 3 In Example 1, SiCl _{4 was} used as a raw material for the core and for the clad.
The carrier gas injection pipe of the above was used to adjust the carrier gas outlet outer diameter r ₀ = 0.002 m and the carrier gas outlet depth Le = 0.25 m.
D = 5.3 × 10 ⁻⁶ m ^{2 /} sec., G = 9.8 m ² /
sec as., this value where the value calculated in the ^{_{D · Le / (r O 2}} √ (r O · g)) is 2.4, the degree of saturation of SiCl ₄ vapor in the gas phase of the container at this time is 100 %Met. For comparison, the carrier gas injection pipe was r ₀ = 0.003 m and Le = 0.2 m.
^{_{D · Le / (r O 2}} √ (r O · g)) of the value 0.7, and the degree of saturation of SiCl ₄ vapor in the gas phase of the container at this time was 90%.

[0022]

According to the present invention, the effect of the gas pressure fluctuation in the vessel due to the atmospheric pressure fluctuation is reduced, and the saturation of the raw material vapor of the silicon compound and the doping compound in the gas phase is reduced by 99%.
By maintaining the above-mentioned constant high value and supplying it to the burner, a silica-based glass having uniform optical characteristics could be produced.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a liquid material supply device for explaining the present invention.

FIG. 2 is a longitudinal sectional view showing a conventional liquid raw material supply device.

[Explanation of symbols]

 1, 11 ... Carrier gas flow controller 2,12 ... Liquid raw material container (container) 3,13 ... Liquid raw material 4,14 ... Pressure gauge 5,15 ... Atmospheric pressure sensor 6,16 ... Correction calculator 7 ... Throttle valve 8 , 18… Carrier gas injection pipe 9,19… Raw material supply pipe 10,20… Liquid raw material supply pipe

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-288922 (JP, A) JP-A-61-205629 (JP, A) JP-A-61-71832 (JP, A) JP-A-59-1987 92933 (JP, A) JP-A-61-295249 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C03B 8/04 C03B 37/018

Claims (2)

(57) [Claims] The present invention relates to a seed rod for rotating silica particles and a dope material by flame hydrolysis of a vaporized silicon compound and, if necessary, a doping compound in an oxyhydrogen flame. In a method for producing a silica-based glass, which is deposited and deposited on a liquid material, a liquid material of a silicon compound and a liquid material of a doping compound are filled in respective material containers, and a carrier gas is injected into these liquid materials by a carrier gas blowing pipe. In the liquid raw material supply method in which the mixed gas of the carrier gas and the raw material vapor is supplied to the burner by vaporizing by blowing and bubbling, the gas pressure in each raw material container is set to a gauge pressure of 1 kg / cm ² or more and less than 2 kg / cm ^2. method for producing a silica-based glass, characterized in that to hold the definitive predetermined pressure to. 2. The diffusion coefficient of the vaporized silicon compound and, if necessary, the vaporized doping compound in the carrier gas component of the raw material vapor component is D, the radius of the carrier gas outlet of the carrier gas injection pipe is r _O , When the depth of the carrier gas outlet in the liquid is Le,
D ・ Le / (r _O ² √ (r _O・ g)) (g is the gravitational acceleration) value is 2.0
The method for producing a silica-based glass according to claim 1, which is as described above.