JP3186446B2 - Method for producing silica 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 silica glass, and more particularly to a method for producing silica glass used for an optical communication optical fiber preform or an LSI photomask substrate.

[0002]

2. Description of the Related Art Silica glass is generally produced by using silicon tetrachloride (SiCl ₄ ) as a glass raw material gas and germanium tetrachloride (GeCl ₄ ) as a dopant, and subjecting this to flame hydrolysis in an oxyhydrogen flame. Silica fine particles and dopant fine particles are deposited on a rotating seed rod to form a porous silica base material, which is baked and transparently vitrified. Hereinafter, this will be described based on the silica glass manufacturing apparatus shown in FIG.

FIG. 2 (a) shows that SiCl ₄ is used as a glass raw material gas.
FIG. 1 is a longitudinal sectional view of a porous silica preform manufacturing apparatus using a silicon compound such as SiCl ₄ , which is a metal or glass container 21 containing a silicon compound such as SiCl _4.
O ₂ gas or N ₂ gas whose flow rate is controlled by a gas flow controller 22 such as a mass flow controller (MFC);
Inert gas such as Ar gas is forcibly ventilated to vaporize SiCl ₄ by bubbling, and this is constantly supplied to the core forming burner 23 and the clad forming burner 24. is air also GeCl ₄ gas vaporized in the inert gas of GeCl ₄ were forced aeration in the same manner as described above as a dopant accommodated in the container 21 of the same type as the container 25 for the SiCl _4.

[0004] O ₂ gas and H ₂ gas are sent to the core forming burner 23 and the cladding forming burner 24.
Since an oxyhydrogen flame is created here, the SiCl ₄ and GeCl ₄ sent to these burners are converted into silica fine particles and GeO ₂ fine particles 26 by flame hydrolysis in this oxyhydrogen flame, which rotates. 2 (b)
Grows as a porous silica matrix 28 shown in
This method is known as the VAD method.

As described above, in the VAD method, a liquid material such as SiCl ₄ or GeCl ₄ uses O ₂ gas or an inert gas.
It is supplied by a so-called carrier gas method, and the vaporization rate in this method is the carrier gas rate,
Although it depends on the temperature and the degree of saturation, etc., it is practically temperature,
It is controlled by a carrier gas flow rate with a high degree of responsiveness and a constant saturation. However, since the degree of saturation is determined by the gas-liquid contact time when ventilating into the container, there is a problem that the degree of saturation is not always maintained at a constant value within the operating range of the carrier gas flow rate. A two-stage bubbler method in which one bubbler is used as a supersaturation tank and the second bubbler is used as a condensation tank (see Japanese Patent Application Laid-Open No. Hei 4-341340). Structure consisting of gas supply equipment (actually fair
Without a valve for controlling the flow rate and an MFC downstream of the vaporizer, a flow meter is installed for each raw material flow path, and the monitored value is fed back to the vaporization temperature controller. A method for controlling the liquid temperature (see Japanese Patent Application Laid-Open No. 5-22256) is disclosed.

[0006]

However, when a liquid material is vaporized by a carrier gas, the vaporization rate by bubbling is controlled by the temperature and the saturation, and is controlled by the flow rate of the carrier gas. Is provided with a vaporizer . Even when no carrier gas is used, the main purpose is to avoid the harmful effects of using the carrier gas, and a vaporizer is provided for each steam line. Therefore, in this VAD system, a vaporization vessel is installed for each vapor line of the burner. However, in the production of a porous silica preform for an optical fiber preform, it is necessary to further diversify the refractive index distribution. It is necessary to carry out by the VAD method which requires SiCl ₄ and the dope material at the same time. Therefore, this requires the arrangement of a large number of vaporizers in the VAD method manufacturing equipment, which complicates the equipment management and increases the cost of the equipment. Disadvantage.

[0007] In this case, a vaporizer is installed for each vapor line. When the liquid supply corresponding to the vaporization flow rate becomes lower than the required flow rate, the supply becomes intermittent and the start and stop of each line is started. In addition, large load fluctuations during the transition to the steady state make it difficult to complete continuous replenishment and induce fluctuations in the vaporizer liquid temperature, which can cause fluctuations in the steam flow rate. It is necessary to install a heat exchanger in the liquid line or make the vaporizer volume large enough to keep the liquid temperature fluctuation in the vaporizer within the allowable range over the fluctuation range of the replenishment liquid flow rate. However, there is a disadvantage that it becomes complicated and costs increase.

For this reason, there is a method in which the volume of the vaporizer is made sufficiently large so that the liquid is not replenished during the production of one unit of the base material. The problem of big change arises,
When this liquid raw material contains high-boiling components in addition to SiCl ₄ as a main component with a low boiling point , it gradually becomes high in high-boiling components, and the concentration of high-boiling components in vaporized vapor also increases. The disadvantage is that this liquid component also has to be renewed in its entirety.

[0009]

SUMMARY OF THE INVENTION The present invention is directed to a method for producing silica glass which overcomes the disadvantages, disadvantages and problems of the present invention, comprising the steps of: removing a vaporized silicon compound and / or a vaporized doping compound from an acid; Flame hydrolysis is performed in a hydrogen flame to generate silica fine particles and / or dope material fine particles, and these fine particles are deposited on a rotating seed rod or a transparent silica glass seed rod heated to a glass melting temperature or higher. In the method for producing a porous glass base material or a transparent silica glass body by heating, one or more oxyhydrogen flame burners for generating silica fine particles and / or dope material fine particles are prepared, and the burner is used to vaporize a silicon compound and / or a flow path for venting of the dope compounds equipped single or plural, and the liquid silicon compound and / Other comprises one by one group the container liquid dope compound is stored at all times for each type, which the heating medium is controlled with high temperature from the holding temperature of each liquid material, or a heat conduction phenomenon due to the temperature difference between the heating element Use each compound volume
Gas phase pressure is within the back pressure of all compound vapor vent channels
In at least than the maximum pressure value 0.35 kg / cm ² higher pressure value
The latent heat of vaporization is applied so as to be held in the tank, and each of the vaporized compounds is discharged from each container via a temperature sensor and a piping element of a flow control valve to a single or a plurality of burners for each of a plurality of burners. It is supplied to the ventilation channel.

That is, the present inventors have conducted various studies to develop a method of manufacturing silica glass for an optical fiber for optical communication and an LSI photomask substrate.
In the method for producing silica glass by the method D, one or a plurality of oxyhydrogen flame burners that generate silica fine particles and / or dope material fine particles are prepared, and the burner contains a vaporized silicon compound and / or a doping compound. One or more ventilation channels are provided, and a liquid silicon compound and / or a liquid doping compound are stored in containers for each type, and heated storage mediums are stored in these storage containers. Alternatively, by using a heating element, the gas phase pressure of each
At least 0.35 of the maximum pressure value in the air flow back pressure
giving latent heat of vaporization so as to maintain the pressure value kg / cm ² have high vaporize these compounds, be supplied each compound the vaporized single or plurality of air flow passages of the burner, the silicon compound Constant flow of the doping compound
Since it is supplied to the burner in an amount and a ratio, a silica base material having a calculated refractive index distribution is obtained, which is of high purity, and the replacement of each consumed compound is easily performed. The inventors have found that the advantage that the production of this silica glass can be carried out continuously is given, and completed the present invention. This will be described in more detail below.

[0011]

The method for producing silica glass according to the present invention comprises the steps of:
In the method for producing a silica glass in the method D, one or more oxyhydrogen flame burners provided with a single or a plurality of gas passages for a vaporized silicon compound and / or doping compound are prepared, and a liquid silicon compound and / Or prepare a container for storing a liquid dope compound for each type, put a heat medium or a heating element controlled at a high temperature in this container, and maintain the gas phase pressure in the container at a predetermined value,
The vaporized compounds are supplied to a ventilation passage of a burner to generate silica fine particles and / or dopant fine particles by flame hydrolysis of these compounds in an oxyhydrogen flame, from which silica carrier rods are manufactured. However, according to this, a silica base material having the calculated refractive index distribution can be obtained, and the replacement of each consumed compound can be easily performed, so that silica glass can be continuously obtained.

The production of silica glass according to the present invention is carried out, for example, with the apparatus shown in FIG. FIG. 1 is a longitudinal sectional view showing a porous silica preform manufacturing apparatus according to the present invention. As shown in FIG. 1 (a), this is an evaporation vessel 1 containing SiCl ₄ as a silicon compound. Heat transfer tube PIC2
The superheated steam is introduced through the above, and this SiCl ₄ is vaporized by indirect heating by the latent heat of condensation of the steam, and the SiCl ₄ gas is passed through the gas ventilation flow path 3, the flow controllers 4 and 5, the core forming burner 6, the cladding Air is supplied to the forming burner 7.

The core forming burner 6 is contained in an evaporation vessel 8, is vaporized by superheated steam from the TIC 19, and reacts as a mixed gas having a constant partial pressure ratio with the second component introduced by the PIC 9. GeCl ₄ as a dopant to be sent to the air is also sent through the flow controller 10 . this
The SiCl ₄ vapor and GeCl ₄ vapor are converted into silica fine particles and GeO ₂ fine particles 11 by flame hydrolysis in an oxyhydrogen flame in a core forming burner 6 and a cladding forming burner 7, and are deposited on a rotating target 12. As shown in FIG. 1 (b), it grows as a silica glass fine particle deposit 13, and at this time, the SiCl ₄ solution and GeCl ₄
The liquid is continuously supplied with SiCl ₄ liquid and GeCl ₄ liquid from pumps 14 and 15, and the waste liquid is continuously discarded by pumps 16 and 17.

In this case, the SiCl ₄ and GeCl ₄ generated here
Vapors are sent to the burner through the gas vent channel 3 and the flow controllers 4, 5, and 10. These piping and control valves are heated to at least 10 ° C higher than the compound vapor. be left to prevent recondensation of compound vapor Te good, vapor pressure of the compound container conductivity as at least 0.35 kg / cm ² higher pressure value than the maximum pressure value in the back during pressurization of the vent passage It is preferable to supply heat.

In the present invention, the heat medium or heating element heated to a high temperature as described above is contained in the containers 1 and 8 storing liquid compounds such as SiCl ₄ and GeCl _4. The liquid compound is vaporized by applying this latent heat of vaporization due to the temperature difference from the liquid temperature.The volume of this container exceeds 0.5 g / mincm ² in vapor mass velocity per unit area of gas-liquid interface. Then, the convection in the liquid phase becomes intense, and the gas phase pressure may fluctuate in a cycle of several minutes. Therefore, it is preferable that the pressure does not exceed 0.5 g / min · cm ² . In the case where the gas phase in the container is a two-component system in which a gas of a liquid compound is used as a first component and an inert gas such as O ₂ or Ar or N ₂ gas is used as a second component,
This means that the area A (cm ² ) of the gas phase interface in the container is A ≧ 44.8√ with respect to the flow rate Q (cm ³ / min) at the maximum load of the second component gas.
The second component gas may be supplied continuously or indefinitely so that the gaseous phase pressure is maintained at a constant value as a structure that becomes Q. According to this, the saturation of the compound gas in the second component gas is achieved. The degree is kept at 99% or more.

In the present invention, the liquid compound is continuously replenished from the pumps 14 and 15 as described above, and the power transporting equipment using this pump may be a pressure transporting equipment using N ₂ pressurization. Is the pump 16, as described above,
The waste liquid may be discharged according to step 17, but the amount of the waste liquid may be about 1.0 to 10% of the consumption flow rate. According to this, the substance having a higher boiling point than the liquid compound is concentrated or nonvolatile in the liquid in the container. This has the advantage that generation of residual concentrated particles of sexual impurities is prevented. The replenishment of the container is controlled using the total flow rate of the evaporative consumption and the discharge as a set value.

[0017]

Next, examples of the present invention and comparative examples will be described. Examples 1 and 2 and Comparative Example 1 (1) Three apparatuses for manufacturing silica glass particle deposits are juxtaposed, and an SiCl ₄ vaporization facility is shared with an inner diameter of 200 mmφ and a capacity of 10
And l share evaporator one, to a hot water 80 ° C. as a heat source
The evaporator gas phase pressure was adjusted to 0.5 kg / cm ² , 69
℃, and 6 oxyhydrogen flame burners
l ₄ Steam is operated at a differential pressure of 0.4
Flow rate to one line of SiCl ₄ vapor while controlling flow rate at kg / cm ²
When 20 g / min and 120 g / min were supplied by 6 units, the evaporation mass velocity at the gas-liquid interface in the vessel in this case was 0.38 g / cm ² min.

Next, silica fine particles generated by flame hydrolysis in the oxyhydrogen flame are deposited on a rotating heat-resistant carrier to form a porous silica matrix, which is melt-vitrified to form silica glass. Examination of the physical properties revealed that no heterogeneous sites such as striae were detected, and the number of bubbles was 1 / kg or less.

(2) In the above method for producing a porous silica base material, except that the flow rate of SiCl ₄ vapor in one line is 25 g / min and the amount of evaporation of one common evaporator is 150 g / min.
When the porous silica preform was manufactured under exactly the same conditions as those described above, the evaporation mass velocity at the gas-liquid interface in the container at this time was 0.48 g / cm ² , and the silica glass manufactured therefrom was not affected by striae or the like. No homogeneous part was detected and only one bubble /
kg or less.

(3) For comparison, in the above-described method for producing a porous silica preform, the flow rate of one line of SiCl ₄ vapor was 30 g / min, and the evaporation amount of one common evaporator was 180 g / min. others are were produced silica soot preform under the same conditions as above, the evaporation mass velocity at the gas-liquid interface in the vessel at this time was ² minutes 0.57 g / cm, flow rate variation of the steam in this case When the silica glass, which was generated at a high frequency and was obtained by converting this porous silica base material into a transparent glass, was examined, a large number of striae were detected, and 10 bubbles /
kg was included. (The results are summarized in Table 1.)

[0021]

[Table 1]

Examples 3 and 4, Comparative Example 2 (1) In the production of a porous silica preform, two porous silica preform manufacturing apparatuses each having one large burner and one small burner consuming SiCl ₄ vapor were used. Table 2 shows the raw material steams used for the large and small burners in these apparatuses, and their back pressure, MFC operating pressure and steam flow rate are also shown in Table 2. In addition, the SiCl ₄ vaporization equipment is a common evaporator, which uses hot water of 80 ° C as a heat source and adjusts the heating amount to raise the evaporator gas phase pressure to 0.5 kg / cm ² and 69 ° C.
From the common evaporator to two porous silica preform manufacturing equipment, two burners SiCl ₄ vapor consumption line and SiCl ₄
Supplying SiCl ₄ vapor and GeCl ₄ vapor to the mixed gas consumption line of vapor and GeCl ₄ vapor, performs flow detection control operation differential pressure 0.40~0.49kg / cm ² at MFC commercial high-temperature steam, the steam line Was heated to 75 to 85 ° C. by a heating device.

In addition, the evaporator 1 which shares the GeCl ₄ vaporization equipment is also used.
The evaporator gas phase pressure may be maintained at 0.5 kg / cm ² and 43 ° C. by adjusting the heating amount using hot water of 50 ° C. as a heat source. The ratio is Ar: GeCl ₄ = 4.6: 1 in volume ratio. In addition,
Both SiCl ₄ vapor and GeCl ₄ vapor have an inner diameter of 25 cmφ and a capacity of 5
Since the liter shared evaporator was used, the evaporation mass velocity at the gas-liquid interface in the vessel was 0.022 g / cm ² min, 0.0004 g, respectively.
5 g / cm ^2'll minutes, the area A of the gas-liquid interface is 490 cm ^2, the second component gas flow Q value calculated because it is 106cm ³ / min becomes larger than 44.8√Q value 461Cm ^2, At this time, the liquid raw material, gas phase pressure, vaporization flow rate, and gas flow rate of the second component were as shown in Table 3.

The thus supplied SiCl ₄ vapor, G
Silica fine particles and GeO ₂ fine particles generated by flame hydrolysis in an oxyhydrogen flame using eCl ₄ vapor are deposited on a heat-resistant carrier to form a porous silica matrix, which is then melt-vitrified to form silica glass. However, when this was examined, no heterogeneous site such as striae was detected, and the number of bubbles was 1 / kg or less.

(2) However, for comparison, in the above-described apparatus, G was maintained at a gas phase pressure of 0.5 kg / cm ² and 35 ° C.
In the evaporator of eCl ₄ , Ar as the second component gas
Maximum load of the gas, 150 cm ³ / min flow rate and the other creates a porous silica preform in exactly the same conditions as described above, was prepared silica glass which was molten vitrified, this compound GeO ₂ content level but rather less than the specified value, the gas-liquid interface area 490c
m ² was smaller than the calculated 44.8√Q value of 550 cm ² .

[0026]

[Table 2]

[Table 3]

[0027]

According to the present invention , pulsating flow, trouble caused by blockage of the blowing pipe, and adverse effects caused by bubbling can be avoided.
Liquid compound containers are consolidated into one group for each type of compound
Since equipment cost and management cost becomes cheaper, the cost does not rise even if size of the evaporation vessel, a continuous reduction of replenishing the liquid compound supply amount of the evaporation vessel is large, a continuous constant flow waste
Realized, stable gas phase pressure of raw material compounds in vaporization vessel
Source gas from a single vaporization vessel to multiple burners.
Air can be sent at a fixed flow rate.

[Brief description of the drawings]

FIGS. 1 (a) and 1 (b) are longitudinal sectional views of an apparatus for producing a porous silica base material according to the present invention.

FIGS. 2 (a) and 2 (b) are longitudinal sectional views of an apparatus for producing a porous silica base material according to a conventional method.

[Explanation of symbols]

1,8,21,25 ... Evaporation vessel 2,9 ... PIC 3 ... Gas ventilation passage 4,5,10,22 ... Flow controller 6,23 ... Core forming burner 7,24 ... Clad forming burner 11, 26: Silica fine particles, GeO ₂ fine particles 12, 27 ... Seed rod (target) 13, 28 ... Porous silica base material 14, 15, 16, 17 ... Pump 19 ... TIC

Continuation of the front page (72) Inventor Hideo Hirasawa 2-13-1, Isobe, Annaka-shi, Gunma Shin-Etsu Chemical Co., Ltd. Precision Functional Materials Laboratory (56) References JP-A-63-303825 (JP, A) JP-A-3-54130 (JP, A) JP-A-61-205635 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C03B 8/04 C03B 37/018 B01J 7/02

Claims (8)

(57) [Claims] 1. A vaporized silicon compound and / or a vaporized doping compound are flame-hydrolyzed in an oxyhydrogen flame to generate silica fine particles and / or dope material fine particles. In a method for producing a porous glass base material or a transparent silica glass body by attaching it to a seed rod or a transparent silica glass seed rod heated to a melting temperature of glass or higher, fine silica particles and / or doped material fine particles are generated. One or a plurality of oxyhydrogen flame burners are provided, the burners are provided with one or a plurality of flow paths through which a vaporized silicon compound and / or doping compound are passed , and a liquid silicon compound and / or a liquid dope are provided. One container in which the compound for use is always stored for each type. Using the heat transfer phenomenon caused by the temperature difference between the heating medium controlled by the temperature or the heating element , each compound volume
Gas phase pressure is within the back pressure of all compound vapor vent channels
In at least than the maximum pressure value 0.35 kg / cm ² higher pressure value
The latent heat of vaporization is applied so as to be held in the tank, and each of the vaporized compounds is discharged from each container via a temperature sensor and a piping element of a flow control valve to a single or a plurality of burners for each of a plurality of burners. A method for producing silica glass, which is supplied to a ventilation channel. 2. The silica glass according to claim 1, wherein the piping section and the control valve body which are in contact with the compound vapor are heated to at least 10 ° C. higher than the gas phase temperature of the vessel to prevent recondensation of the compound vapor. Production method. 3. Each liquid material container contains a liquid according to the amount of consumption.
To supply the material, it is necessary to use a pump-powered transportation facility.
The method for producing silica glass according to claim 1, further comprising a pressure transportation facility using N ₂ pressurization . 4. The method of claim 1 , wherein the latent heat of vaporization of the liquid compound is applied to the inside of the container.
The evaporation mass velocity per unit area of the gas-liquid interface is 0.5 g / cm ² min.
The method for producing silica glass according to claim 1 , wherein the temperature is not exceeded. 5. The method according to claim 1 , wherein the latent heat of vaporization of the liquid compound is applied.
Container vapor phase, a liquid compound as the first component, O ₂ Gasuma
Other Ar, 2 and inert gas and the second component such as N ₂ formation
The method for producing silica glass according to claim 1, wherein the silica glass is composed of divided systems . 6. An area A (cm ² ) of a gas-liquid interface in a container ,
For the flow rate Q (cm ³ / min) at the maximum load of the second component gas
The structure is such that A ≧ 44.8√Q.
The amount of heating from the heating medium or heating element is controlled so that
Control so that the gas pressure is maintained at a constant value.
The component gas is supplied continuously or at irregular times.
The method for producing silica glass described in 1 above. 7. In a compound vapor supply facility, a pump
Liquid from the container to the waste storage tank by powered transport
The method for producing silica glass according to claim 1 , wherein a waste liquid facility for transferring a substance is provided . 8. The liquid compound container according to the consumption flow rate thereof.
1. By discharging liquid compounds at a flow rate of 0 to 10%,
Concentration of substance with higher boiling point than liquid compound in liquid in container
In addition to preventing shrinkage, replenishment of the container
2. The method according to claim 1, wherein a total flow rate of the discharge is controlled as a set value.
The method for producing silica glass described in 1 above.