JP2000247649A - Manufacturing method of synthetic quartz - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce products which are free of air bubbles and microscopic defects at a low cost by specifying the purity and metal impurity concentration of the glass raw material to be oxidized or flame-hydrolyzed. SOLUTION: The synthetic quartz is produced by subjecting the glass raw material having the purity of >=99.99% and the metal impurity concentration of <500 ppm to an oxidation reaction or flame hydrolysis reaction. Since the purity of the raw material is sufficiently highly, the entrained supply of impurities, such as SiCl4 derivative, of a high boiling point in the splashes of bubbling does not occur and the high-strength synthetic quartz containing extremely less impurities is obtain when bubbling is executed with a carrier gas, for example, Ar. Since there is no residue of the impurities in a bubbling vessel, the operation may be continuously continued without the closure of an ejection port of the carrier gas. The synthetic quartz to be produced is free from density changes, growth stripes, etc., in either of the longitudinal direction and radial direction and the fluctuation in characteristics with lapse of time is suppressed.

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 synthetic quartz used for various optical materials, optical fibers, jigs for semiconductor production equipment, and the like, and more particularly, to a method for depositing glass fine particles produced by using a VAD method or the like. The present invention relates to a synthetic quartz which is obtained by sintering a so-called soot deposit in a heating furnace, turning it into a transparent glass, and suitably used as a base material for an optical fiber.

[0002]

2. Description of the Related Art As a method for producing synthetic quartz, for example, M
A CVD method, a VAD method, an OVD method, and the like can be given. VAD
According to the method, a combustible gas (H ₂ , CH ₄ , C ₂
H _{6 and the} like, and a glass raw material is charged together with a carrier gas into a flame in which a gas composed of an auxiliary gas (such as O ₂ ) is burned, and glass fine particles generated by a flame hydrolysis reaction or an oxidation reaction are rotated. The soot deposit is formed by adhering and depositing the starting target material while moving it relative to the burner. Next, the soot deposit is sintered in a heating furnace and is made vitrified to obtain a base material for an optical fiber.

In the MCVD method, a raw material gas is supplied together with a carrier gas into a quartz tube serving as a clad, glass fine particles are deposited inside the quartz tube, and the glass material is formed into a transparent glass to be used as a base material for an optical fiber. The optical fiber preform manufactured in this manner is heated, and if necessary, reduced in diameter to a predetermined diameter to form a preform, which is drawn to obtain an optical fiber. At this time, as a method of supplying the raw material gas into the oxidation or flame hydrolysis reaction system, a method of bubbling with a carrier gas, a method of mixing a raw material gas obtained by directly vaporizing a glass raw material with another gas as necessary, A method of leading a reaction system through a controller is known.

As a glass raw material, SiCl ₄ or the like is usually used. For example, SiCl ₄ includes SiCl _4-n (OH) _n and SiCl _{4- n On / 2,} which are derivatives thereof.
Is contained as an impurity. These derivatives have a high boiling point, are concentrated in the raw material vaporizer, are transported together with the gasified SiCl ₄ in the form of droplets, adhere to the pipes and flow rate regulators, remain, and close the on-off valves and flow rate regulators. Cause a decrease in controllability.

[0005] When the purity of the raw material is low, when bubbling is performed with a carrier gas, impurities are entrained in the bubbling droplets and reach the reaction system. As a result, bubbles and microscopic bonding defects occur in the synthetic quartz, and the strength of the manufactured synthetic quartz decreases. Furthermore, such synthetic quartz has large fluctuations in the density and refractive index in the longitudinal direction and the radial direction, causing fluctuations in characteristics. In addition, some of the impurities remain in the bubbling tank, block the carrier gas outlet, and cause the production to be stopped.

When the glass material is directly vaporized, Si
The derivative of Cl ₄ is also vaporized and carried into the reaction system to form bubbles in the synthetic quartz or cause microscopic defects. Further, since a part of the derivative remains in the raw material vaporizer, the heat transfer coefficient between the glass raw material and the vaporizer changes, and a stable vaporized state cannot be maintained. Further, these derivatives also adhere to the inside of the raw material flow regulator, which hinders flow control, and makes the supply of the raw material to the reaction system unstable. As a result, the manufactured synthetic quartz has large fluctuations in characteristics such as a change in density in a longitudinal direction and a radial direction, and a fluctuation in refractive index is emphasized.

[0007]

As described above, synthetic quartz is produced by bubbling or directly vaporizing a glass raw material and subjecting it to oxidation or flame hydrolysis. Conventionally,
Despite the fact that the glass raw materials used have a high content of impurities such as derivatives of the raw material compounds, no measures have been taken against the impurities. For this reason, the produced synthetic quartz has caused deterioration of the physical and optical characteristics particularly due to impurities.

[0008] In addition, glass impurities contain metal impurities. Most of the metal impurities are not sent into the reaction system because of their high boiling points, but some are sent into the reaction system, which adversely affects the properties of the synthetic quartz produced. Desirably, there is no such metal impurity, but that is not possible. For this reason, the drain valve is periodically opened to drain liquid, and metal impurities are taken out of the system.

When the glass raw material contains a large amount of metal impurities,
Even metal impurities are carried into the reaction system by bubbling or direct vaporization by a carrier gas. As a result, synthetic quartz containing a large amount of metal in the joint is produced.
Synthetic quartz containing even a small amount of metal is, for example, around 750 nm to 1,400 nm for vanadium, and 70% for cobalt.
Absorption occurs in a wavelength range around 0 nm to 800 nm. As a result, for example, the transmission loss of an optical fiber obtained by processing the synthetic quartz is increased. As described above, it is better that the glass raw material does not contain any impurities, but it is extremely costly to realize this.

An object of the present invention is to specify the purity of a glass raw material and the amount of metal impurities which are acceptable as a glass raw material in view of the cost of refining the glass raw material and the quality characteristics of the synthetic quartz, thereby making it possible to produce the synthetic quartz at a low cost. It is to provide a manufacturing method.

[0011]

That is, according to the method for producing synthetic quartz of the present invention, when producing synthetic quartz using an oxidation reaction or a flame hydrolysis reaction, the purity of a glass raw material to be oxidized or flame-hydrolyzed is reduced to 99%. .99% or more. As a result, the purity of the raw material was 99.
When the bubbling is performed with a carrier gas such as Ar, an impurity such as a derivative of SiCl ₄ having a higher boiling point is not supplied accompanying the bubbling droplets. Synthetic quartz manufactured from a small amount of glass raw material has no bubbles or microscopic bonding defects, and high-strength synthetic quartz is manufactured. Further, since there is no residual impurity in the bubbling tank, the operation can be continuously performed without blocking the ejection opening of the carrier gas.

[0012] Even when the glass raw material is directly vaporized, impurities do not reach the reaction system, so that high-strength synthetic quartz can be obtained. Also, since no impurities remain in the raw material vaporizer,
The heat transfer coefficient between the glass raw material and the vaporizer does not change, and a stable vaporized state can be maintained for a sufficiently long time, so that the raw material supply to the reaction system can be stabilized. As a result, the synthetic quartz produced is
There is no change in density or growth stripes in any of the longitudinal direction and the radial direction, and fluctuation of characteristics over time is suppressed.

The metal impurity concentration in the glass raw material is 500
It is preferably less than ppm, preferably less than 50 ppb. When using glass materials controlled in this way,
No metal impurities are carried into the reaction system due to bubbling by the carrier gas or direct vaporization of the source gas. In addition, during the production of synthetic quartz, it is important to periodically measure the metal impurity concentration in the raw material vaporizer used when supplying the glass raw material into the reaction system and manage it within a predetermined range. The concentration is less than 500 ppm, preferably 50 pp
It is desirable to keep it below b. As a result, the produced synthetic quartz does not contain a metal, so that it has a very high purity, and there is no optical absorption in a specific wavelength range of the metal.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments according to the present invention will be described in more detail with specific examples.

(Embodiment 1) Oxygen was applied to the burner by using the VAD method.
_In a flame formed by supplying ₂ gas = 10 SLM and H ₂ gas = 7 SLM, SiCl ₄ having a purity of 99.99% was used.
= 10 g / min, accompanied by bubbling of Ar = 0.5 SLM, to generate glass fine particles, grow in the longitudinal direction while depositing the glass fine particles at the tip of the rotating starting material, and grow in the longitudinal direction. A soot deposit having a length of 500 mm was prepared. No bubbles were observed in the synthetic quartz rod obtained by converting this soot deposit into a vitrified transparent glass in a heating furnace. Further, the diameter of this synthetic quartz rod was reduced as an optical fiber preform to obtain a preform. When this is heated and drawn, breakage of the optical fiber is 1% at a proof level of 1%.
Once per 00 km. In addition, the production of synthetic quartz was performed for a total of 100 lots for 50 hours per lot, and there was no blockage at the Ar gas outlet as a carrier gas.

(Embodiment 2) Using a VAD method, the burner is
_In a flame formed by supplying ₂ gas = 10 SLM and H ₂ gas = 7 SLM, SiCl ₄ having a purity of 99.99% was used.
Is directly vaporized by a vaporizer, and supplied while adjusting the flow rate by a mass flow controller (hereinafter, referred to as MFC) so as to be 10 g / min to produce glass fine particles.
Glass particles are grown in the longitudinal direction while being deposited on the tip of the rotating starting material, and have an outer diameter of 120 mm and a length of 700 mm.
mm soot deposits were made. No bubbles were observed in the synthetic quartz rod obtained by converting this soot deposit into a vitrified transparent glass in a heating furnace. Further, when the preform obtained by processing the synthetic quartz rod was heated and drawn, the breakage of the optical fiber was 0.9% per 100 km at a proof level of 1%.
It was times. Also, the production of synthetic quartz is limited to 5 per lot.
In 100 hours, a total of 100 lots were manufactured, but no growth stripes due to fluctuations in the raw material supply amount were observed. Furthermore, MF
No control abnormality of C occurred, and stable supply of raw materials was performed.

(Embodiment 3) Oxygen is added to the burner by using the VAD method.
_In a flame formed by supplying ₂ gas = 10 SLM and H ₂ gas = 7 SLM, SiCl ₄ having a purity of 99.99% and a metal impurity concentration of 400 ppm is directly vaporized by a vaporizer so as to be 10 g / min. The glass fine particles are generated by supplying the MFC at a controlled flow rate, and are grown in the longitudinal direction while depositing the glass fine particles on the tip of the rotating starting material. A soot deposit having an outer diameter of 120 mm and a length of 700 mm is formed. Produced. No bubbles were observed in the synthetic quartz rod obtained by converting this soot deposit into a vitrified transparent glass in a heating furnace. Furthermore, the optical fiber obtained by heating and drawing the preform obtained by processing this synthetic quartz rod has no optical absorption in the intrinsic wavelength region of metal, and could be used as an optical fiber for long-distance communication. .

(Comparative Example 1) Using the same apparatus as in Example 1, O ₂ gas = 10 SLM and H ₂ gas = 7 S
In a flame formed by supplying LM, Si having a purity of 98%
Cl ₄ = 10 g / min was supplied by bubbling with Ar = 0.5 SLM to generate glass fine particles,
Glass particles are grown in the longitudinal direction while being deposited on the tip of the rotating starting material, and have an outer diameter of 100 mm and a length of 500 mm.
mm soot deposits were made. In the synthetic quartz rod obtained by converting this soot deposit into a transparent vitrified glass in a heating furnace, three bubbles are present.
Two were confirmed. Further, when the preform obtained by processing the synthetic quartz rod is heated and drawn, the breakage of the optical fiber is 1% per 100 km at a proof level of 1%.
Five times. In addition, the production of synthetic quartz was performed for a total of 20 lots for 50 hours per lot, but the injection port of Ar as a carrier gas was blocked by impurities, and the production was stopped to replace the injection port (injection tube). I had to do it.

(Comparative Example 2) Using the same apparatus as in Example 2, the burner was supplied with O ₂ gas = 10 SLM and H ₂ gas = 7 S
In a flame formed by supplying LM, Si having a purity of 98%
Cl ₄ is directly vaporized and supplied by a vaporizer, and the generated fine glass particles are grown in the longitudinal direction while depositing the fine glass particles on the tip of the rotating starting material.
A soot deposit having a length of 0 mm and a length of 700 mm was prepared. When this soot deposit was vitrified in a heating furnace, 40 bubbles were confirmed in the synthetic quartz rod. Further, when the preform obtained by processing the synthetic quartz rod is heated and drawn, the breakage of the optical fiber is reduced to a proof level of 1%.
18 times per 100 km. In addition, when synthetic quartz was manufactured for a total of 18 lots for 50 hours per lot, a change in the heat transfer state of the vaporizer caused SiCl.
The supply amount of No. ₄ fluctuated, and adhesion of impurities in the MFC was confirmed. In the manufactured synthetic quartz, striped patterns due to fluctuation of the refractive index were observed at intervals of about 2 mm in the longitudinal direction.

(Comparative Example 3) Using the same apparatus as in Example 3, O ₂ gas = 10 SLM and H ₂ gas = 7S
10 g / min of SiCl ₄ having a purity of 98% and a metal impurity concentration of 550 ppm are directly vaporized and supplied by a vaporizer into a flame formed by supplying the LM, thereby producing glass fine particles and rotating starting material. The glass particles were grown in the longitudinal direction while depositing glass microparticles on the tip of the soot to produce a soot deposit having an outer diameter of 120 mm and a length of 700 mm. Thirty bubbles were confirmed in the synthetic quartz rod in which the soot deposit was vitrified in a heating furnace. Further, an optical fiber obtained by heating and drawing a preform obtained by processing the synthetic quartz rod has an optical absorption in a specific wavelength range of a metal of 1,3.
It existed at around 00 nm and could not be used as a practical optical fiber.

[0021]

The method for producing synthetic quartz of the present invention has the above-mentioned structure, and can produce synthetic quartz without bubbles and microscopic bonding defects. Further, by controlling the purity and the impurity concentration of the glass raw material to be equal to or lower than the set values, the injection port (injection pipe) of the carrier gas is not blocked, and the stable operation of the raw material vaporizer and the flow rate regulator can be performed. Further, since the metal impurity concentration in the glass raw material is less than 500 ppm,
Substantially no metals are mixed in the reaction system. As a result, synthetic quartz having high strength and no optical absorption loss inherent to metal can be stably and efficiently manufactured. Further, by periodically measuring and managing the impurity concentration in the vaporizer, the production is not stopped, and the production can be performed stably at low cost.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroyuki Koide 2-3-1-1, Isobe, Annaka-shi, Gunma Prefecture Shin-Etsu Kagaku Kogyo Co., Ltd. Precision Functional Materials Laboratory (72) Inventor Hiroshi Tsumura Annaka-shi, Gunma 2-13-1, Isobe Shin-Etsu Chemical Industry Co., Ltd. Precision Functional Materials Research Laboratory (72) Inventor Hideo Hirasawa 2-13-1, Isobe, Annaka-shi, Gunma Prefecture Shin-Etsu Chemical Co., Ltd. Precision Functional Materials Research Laboratory F-term (Reference) 4G014 AH15 4G021 EA01 EA03 EB01 EB13 EB26 4G062 AA06 BB02 CC07 MM04

Claims (3)

[Claims] 1. A method for producing synthetic quartz, wherein the purity of a glass raw material to be oxidized or flame-hydrolyzed is 99.99% or more when producing synthetic quartz using an oxidation reaction or a flame hydrolysis reaction. . 2. The method according to claim 1, wherein the concentration of metal impurities in the glass raw material is 500.
The method for producing synthetic quartz according to claim 1, wherein the amount is less than ppm. 3. The synthetic quartz according to claim 2, wherein, when the glass raw material is supplied into the reaction system, the concentration of metal impurities in the raw material vaporizer for vaporizing the glass raw material is periodically measured and controlled to less than 500 ppm. Production method.