JP3520541B2 - Quartz glass burner, quartz glass produced using the same, method for producing quartz glass using quartz glass burner - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quartz glass burner having a multi-tube structure, a method for producing quartz glass using the quartz glass burner, and quartz glass produced using the quartz glass burner. Quartz glass manufactured using these burners and manufacturing methods is used as a material for semiconductor mask substrates, optical lenses, and the like.

[0002]

2. Description of the Related Art Conventionally, an exposure apparatus called a stepper has been used in an optical lithography technique for exposing and transferring a fine pattern of an integrated circuit on a wafer such as silicon. The light source of this stepper is g-line (436 nm) to i-line (365 nm) with the recent high integration of LSI.
nm), and further KrF (248 nm) and ArF (19 nm)
(3 nm) Shorter wavelengths are being promoted to excimer lasers.

Generally, the optical glass used as an illumination system or a projection lens of a stepper has a low light transmittance in a wavelength region shorter than the i-line, and therefore synthetic quartz glass or CaF ₂ (fluorite) is used instead of the conventional optical glass. It has been proposed to use a fluoride single crystal such as stone. Quartz glass used as an optical element for this ultraviolet lithography is required to have high transmittance in the ultraviolet region and high homogeneity of the refractive index distribution.

Synthesis for ensuring high transmittance in the ultraviolet region
The method is a high-purity synthesis method, that is, the source gas (Si
In order to send out compound gas etc. and Si compound gas etc.
(Rear gas is used at the same time) and possible for heating and reaction
Combustible gas and supporting gas (H ₂Gas, O₂Gas etc.)
The quartz glass powder in the flame.
The flame hydrolysis method is generally used.

However, it is unavoidable that the silica glass produced by this synthetic method has a refractive index distribution,
Various proposals have been made as manufacturing methods and devices. As a quartz glass burner, in Japanese Patent Publication No. 2-5694, in the method and apparatus for producing a synthetic quartz ingot, conscious of high transmittance,
A quartz glass burner for reducing residual bubbles is disclosed (shown in FIG. 3). Further, in the quartz glass burner of JP-A-64-28239, there is disclosed a design of a quartz glass burner as a jig for appropriately performing heat treatment or thermal processing on an object to be processed.

On the other hand, quartz glass used as an optical element for ultraviolet lithography has a large diameter corresponding to the shape of a projection lens in recent years. In order to synthesize large-diameter quartz glass, it is necessary to supply a large amount of combustible gas, a combustion-supporting gas, and a raw material gas, and at the same time, to efficiently react a large amount of the raw material gas. As a means to obtain this large firepower,
It is conceivable to increase the area of the combustible gas ejection port of the burner to supply a large amount of combustible gas.

However, it is difficult to form a flame with a uniform temperature distribution in the radial direction in a multi-tube burner for the purpose of large thermal power. Moreover, if the gas flow velocity is extremely increased, the ejection port becomes a resistance and the supply gas becomes It becomes difficult to flow or the gas flows unevenly, and a good flame cannot be formed. As a result, the large-diameter quartz glass used as an optical element for ultraviolet lithography and the required high homogeneity of the refractive index distribution could not be obtained.

[0008]

In the quartz glass burner of Japanese Patent Laid-Open No. 64-28239, an expansion part is provided in front of the gas ejection thin tube in order to eliminate the gas deviation even when the burner ejection port has a large diameter. It has been devised by providing such as. As a result, a flame with a large diameter can be secured, but the burner's ability was insufficient for synthesizing quartz glass.

On the other hand, in the burner as shown in FIG.
Large-diameter quartz glass could not be obtained. The purpose of the present invention is to
Quartz glass that can be used as a material for semiconductor mask substrates, optical lenses, etc., especially large-diameter quartz glass with a highly uniform refractive index distribution synthesized by the ideal temperature distribution of the synthesis surface, its manufacturing method, and its synthesis The present invention provides a burner made of quartz glass having a multi-tube structure for use.

[0010]

Means for Solving the Problems The present inventors have proposed, as a burner corresponding to an increase in diameter, a burner which is a reaction gas portion (a raw material circular tube for ejecting a raw material gas such as a Si compound),
Plural combustion ring-shaped tubes that eject flammable gas and supporting gas to react with raw material gas to obtain quartz glass powder)
And combustion gas part (outermost combustion ring-shaped tube and combustion thin tube for obtaining sufficient temperature in the furnace to obtain quartz glass powder), and to further increase the temperature in the reaction gas part. It has been found that the reaction gas portion has a quintuple pipe structure.

Therefore, in the present invention, as a first means, a quartz glass burner has a hexagonal tube structure composed of a circular tube for raw material and a ring tube for combustion, and the combustion thin tube is used for the outermost combustion. Inside the ring-shaped tube, they were arranged at equal intervals on the circumference of a circle concentric with the hexagonal tube. As a result, large combustion power can be obtained in the combustion gas portion (the outermost ring-shaped tube for combustion and the thin tube for combustion), so that the temperature inside the furnace is raised and the raw material gas is made to react efficiently and the deposition rate of the quartz glass powder is increased. Can be increased. Therefore, quartz glass can be produced efficiently, which is economical. In addition, since multiple combustion thin tubes are placed at equal intervals on the circumference of a concentric circle with the hexagonal tube, an ideal temperature distribution (a temperature distribution in a spherical shape with a central symmetry with a single extreme value) You can get a stable flame.

As a result, the use of the above-mentioned quartz glass burner made it possible to synthesize quartz glass without striae and having a centrally symmetric refractive index distribution with a single extreme value in the cross section including the incident optical axis. When quartz glass is used in a semiconductor manufacturing apparatus, the ideal refractive index distribution has no difference in refractive index, but in reality it is impossible to manufacture quartz glass having no refractive index distribution. That is, regardless of the refractive index distribution, a certain degree of refractive index difference occurs. But,
Depending on the shape of the refractive index distribution, it is possible to reduce the refractive index difference by correcting the lens shape and the optical axis when assembling the optical system. This correctable refractive index profile is considered to be an important physical property because it has only one central value and a single extreme value with respect to the optical axis of the incident light when quartz glass is used as the optical element. To be

In the above quartz glass burner according to the present invention, when the vitrification reaction is promoted, the temperature of the synthetic surface is raised to assist the capture, and the temperature distribution of the synthetic surface has one extreme value. At the same time, in order to achieve central symmetry, the combustion ring tube and the combustion thin tube have a tapered structure, and the focal length of the combustion ring tube is shorter than the focal length of the combustion thin tube, so that the reaction gas portion is a synthetic surface. Alternatively, it is preferable to design the burner so as to focus on the front side of the synthetic surface.

Further, in designing the burner, in addition to the fact that the diameter of the burner itself becomes large according to the shape of the silica glass to be synthesized, the amount of supply gas used at the time of synthesis is assumed and the burner is supplied. It is important to consider that the gas flow velocity is neither too fast nor too slow. Therefore, in the present invention, as a second means, in a method for producing quartz glass using a quartz glass burner having a multiple tube structure of a raw material circular tube and a combustion ring tube, a combustible gas and a support gas are used. The flow velocity of the flammable gas was set in the range of 5 to 50 m / s, and as a third means, the ratio of the flow velocity of the gas ejected adjacent to the combustion ring tube was set in the range of 1 to 0.4.

Assuming that the synthetic quartz glass has a diameter of 200 mm or more, the amount of gas supplied is estimated, and the quality of the synthetic quartz glass is also examined. As a result, when the gas flow velocity exceeds 50 m / s, the mixing of gases remains incomplete. The gas reaches the synthetic surface and lowers the temperature of the synthetic surface. On the contrary, when the supply gas flow rate is lower than 5 m / s, the combustible gas and the combustion supporting gas are burned in the vicinity of the burner and the burner itself is deteriorated. Then, the quartz glass forming the burner is peeled off on the synthetic surface to cause bubbles and spot-like heterogeneity. Further, even if it does not come off from the burner, it volatilizes and floats in the furnace, causing impurities to be mixed in the glass, and deformation of the burner causes turbulence in the flame. As a result, stable synthesis cannot be performed, so it is necessary to sufficiently consider the supply gas flow rate.

Further, even if the gas flow velocity is suppressed within the above range, when the relative difference between adjacent gases becomes large, the mixing of the gases is also suppressed and the combustion reaction and the vitrification reaction are affected. For this reason, when the relative difference of the gas flow rates was shaken in a matrix, when the ratio of the flow rates (the ratio when the faster of the adjacent gas flow rates is 1) exceeds the range of 1 to 0.4, the reaction rate I found out that it got worse. Therefore, when designing a multi-tube burner as in the present invention, it is necessary to consider the gas flow rate and also the difference between adjacent gas flow rates. The second and third means of the present invention are not limited to the burner having the hexagonal tube structure described in the first means, but are means common to other multi-tube burners.

Next, it is conceivable that the factors other than the gas flow rate and that the gases in the reaction gas portion are too far apart from each other will result in insufficient mixing of the gases. Then, not only the synthesis temperature becomes heterogeneous, but also the synthesis temperature itself does not rise and the reaction becomes inactive. Therefore, in order to increase the reaction rate with respect to the input raw material, as a fourth means of the present invention, as a fourth means of the present invention, the distance between the gas ejected adjacently from the combustion ring-shaped tube of the quartz glass burner (that is, the thickness of the quartz glass tube, the clearance) ) Is 2 mm
I did the following.

Further, if the ejection of the flammable gas and the combustion-supporting gas in the reaction gas portion causes a variation in clearance, the gas flow becomes uneven, and the temperature distribution on the synthesis surface becomes eccentric. As the fifth means of the present invention,
This variation was suppressed to 0.2 mm or less. The fourth and fifth means of the present invention are not limited to the burner having the hexagonal tube structure described in the first means, and are common to other multi-tube burners.

[0019]

The quartz glass burner of the present invention for synthesizing the above-mentioned quartz glass having a large diameter and a refractive index distribution required as an optical element for ultraviolet lithography will be described in detail below. The factors that control the refractive index distribution of quartz glass can be broadly divided into impurities and the structure of glass. Of these, the source gas for impurities,
It is largely due to the purity of flammable gases, combustion-supporting gases, furnace materials, etc., and the amount and ratio of gases during synthesis. On the other hand, the fact that the structure of glass is determined during synthesis is largely due to the temperature distribution on the synthesis surface.

Therefore, in the quadruple tube structure as shown in FIG. 3, the raw material gas and the combustion-supporting gas are supplied (reaction gas portion) using a double-tube quartz glass burner to synthesize quartz glass. The homogeneity of temperature distribution and refractive index of synthetic quartz glass was measured. The results are shown in Fig. 4. As can be seen from the figure, the temperature distribution on the synthetic surface and the homogeneity of the refractive index of the synthetic quartz glass correspond, and the refractive index is high in the low temperature part during synthesis, and conversely the low refractive index in the high temperature part. It was

That is, the present inventors confirmed that the refractive index distribution of the silica glass to be synthesized corresponds to the temperature distribution of the synthesized surface by measuring the temperature distribution. Based on this fact, it was considered to synthesize quartz glass useful as a material for optical elements by controlling the temperature in the furnace and the synthesis surface temperature. Then, the inventors of the present invention focused on a burner which is also a means for controlling the temperature in the furnace and the synthesis surface, and an epoch-making quartz glass burner capable of controlling the refractive index distribution of the synthesized quartz glass. I came to propose.

In the burner design, conventionally, a burner at a trial production stage is actually used for synthesis, and the design is adopted if the physical properties and the like of the object to be synthesized have desired values. Therefore, the burner has a large individual difference and is not reproducible, which has been a problem in terms of stable supply of the compound and cost. The present invention has solved this problem by finding a correspondence between the structure of the burner and the synthetic quartz glass.

Now, as the glass diameter increases, the size of the furnace becomes larger, and the flow rate of the raw material gas required for its synthesis also increases. As a result, with the conventional burner as shown in FIG. 3, it was not possible to obtain a large thermal power and ability to raise the temperature in the furnace to a temperature sufficient to synthesize quartz glass. Further, as described above, when the temperature in the furnace is lowered and the amount of heat applied to the glass is insufficient, when observed from the direction perpendicular to the growth direction of the glass, inhomogeneity in the refractive index called striae occurs. Therefore, the temperature of the synthetic surface for obtaining the homogeneity of quartz glass that can be used as a material for optical elements for ultraviolet lithography was examined. Focusing on the temperatures of the combustible gas, the combustion-supporting gas, and the raw material gas, the raw material gas at the time of synthesis has a smaller reaction heat than other gases, and thus the temperature becomes the lowest in the furnace. This raw material gas is hydrolyzed in the flame and is deposited on the synthesis surface, but the temperature of the portion where the raw material gas is sprayed and the fine particles are deposited is naturally the lowest.

Therefore, the temperature at the center of the synthetic surface becomes lower and lower due to the increase in the flow rate of the raw material gas accompanying the increase in the diameter of the glass. When the conventional burner is used for the synthesis, the extreme value as shown in FIG. The temperature distribution has three or more, and correspondingly, the quartz glass has a refractive index distribution as shown in FIG. 4 (b). In this way, with a multi-tube burner for the purpose of mere large thermal power or a burner that simply increases the gas flow rate with a conventional burner design, the combustible gas, the combustion-supporting gas, and the raw material gas are not sufficiently mixed, and The temperature of the composite surface does not rise sufficiently,
As a result, the vitrification reaction with respect to the input raw material gas became insufficient, and the phenomenon that the capture rate deteriorated occurred.

Therefore, by using the burner of the present invention, it becomes possible to create an ideal temperature distribution on the composite surface (a temperature distribution having one extreme value and having a central symmetry and a very gentle temperature distribution). It has become possible to simultaneously control the refractive index distribution and increase the aperture. A cross section of the quartz glass burner of the present invention is shown in FIGS. In order to raise the temperature in the furnace, the combustion gas portion, that is, the flammable and combustion-supporting gas of the outermost combustion ring-shaped tube and combustion thin tube is used, and the reaction gas portion for the reaction to vitrify the raw material gas, That is, the quintuple pipe is used.

In a large-diameter furnace, it was impossible to supply the amount of gas required to raise the temperature in the furnace to a sufficiently high temperature by the conventional burner due to the pressure loss in the burner. However, if the combustion gas portion is provided as described above and the structure is as shown in FIGS. 1 and 2, mixing of the combustible gas and the combustion-supporting gas is promoted and the temperature in the furnace can be kept high. . In addition, by calculating the quartz glass tube to be used from the gas flow rate and using the one that matches the flow rate, the pressure loss in the burner can be reduced, and a large amount of gas flow rate can be passed at one time.

In order to eliminate striae generated in the direction perpendicular to the growth direction of quartz glass, it is necessary to keep the temperature of the composite surface sufficiently high. It became possible to suppress the generation of reason. The temperature distribution of the synthetic surface, which is an important factor that determines the refractive index distribution, can be controlled by controlling the reaction gas portion.

[0028]

Example 1 A quartz glass burner having a quintuple tube structure for the reaction gas portion shown in the conceptual diagram of the present invention and FIGS. 1 and 2 was constructed and manufactured by a thin quartz glass tube. This quartz glass burner was used in a furnace having an internal volume of 126 l to synthesize quartz glass. Table 1 shows the dimensions of each part of the quartz glass burner used, the supply gas flow rate during synthesis, and the gas flow rate at that time.

[0029]

[Table 1]

As a result of synthesizing under the above conditions, a quartz glass having a high transmittance and a high homogeneity of φ200 mm which can be used as an optical element for ultraviolet lithography was obtained. Furthermore, the temperature distribution of the composite surface measured by the infrared camera had one extreme value, and was a central symmetry and a very gentle spherical shape.
Then, when the homogeneity of the refractive index of the silica glass synthesized by this burner was measured by an interferometer, the refractive index corresponding to the temperature distribution of the synthetic surface (a spherical distribution with one extreme and central symmetry and very gentle) It was distributed (see FIG. 5).

[0031]

Example 2 Using the synthesis furnace described in Example 1, quartz glass having the same diameter was synthesized. Using a quartz glass burner manufactured under the conditions as shown in Table 2, the gas flow rate of the quintuple tube during the synthesis was made smaller than 5 m / s to perform the synthesis.

[0032]

[Table 2]

When this burner was used for synthesizing, countless bubbles and spots (heterogeneous) were observed due to deterioration of the burner.
I was able to. Therefore, the refractive index homogeneity could not be measured.

[0034]

Example 3 Using the synthesis furnace described in Example 1, silica glass having the same diameter was synthesized. Table 3 shows the dimensions of each part of the burner used, the amount of gas used during synthesis, and the gas flow rate at that time.

[0035]

[Table 3]

Thus, when the refractive index homogeneity of the silica glass synthesized under the condition that the flow velocity difference between adjacent gases is large and the flow velocity ratio is smaller than 0.4 is measured by an interferometer,
As shown in FIG. 6, the distribution has many extreme values and is not corrected.

[0037]

Example 4 Using the synthesis furnace described in Example 1, silica glass having the same diameter was synthesized. Table 4 shows the dimensions of each part of the burner used, the amount of gas used during synthesis, and the gas flow rate at that time.

[0038]

[Table 4]

As described above, when the refractive index homogeneity of the synthesized quartz glass was measured by an interferometer in the state where the clearance of the adjacent gas was large and the flow velocity was small, as shown in FIG. The PV value of the homogeneity (difference between the maximum value and the minimum value of the refractive index) was as large as 5.0 × 10 ^−6, and the homogeneity was poor.

[0040]

As described above, according to the present invention, it is possible to obtain a quartz glass burner capable of controlling the temperature distribution on the composite surface. This makes it possible to control the refractive index distribution of the obtained quartz glass and increase the diameter. Further, if the quartz glass burner of the present invention is used, quartz glass having no striae and having a centrally symmetric refractive index distribution with a single extreme value in the cross section including the incident optical axis can be obtained. If this quartz glass is used in a device such as ultraviolet lithography, an optical system having an ideal refractive index difference (generally, the smaller the better) can be obtained by assembling the optical system.

Further, since a quartz glass having no striae is obtained, there is no cost for the secondary treatment for erasing striae, and it is possible to prevent a decrease in ultraviolet transmittance due to contamination. Furthermore, the efficiency of the vitrification reaction per unit raw material can be improved, and as a result, the amount of deposits in the furnace that cause fluctuations in exhaust gas, bubbles, and spots can be reduced, and stable synthesis can be performed.

Further, by combining the first to fifth means of the present invention to more accurately define the relationship of the burner configuration and the gas flow velocity when using the burner, the burden of burner production is reduced. Therefore, the performance of the obtained quartz glass can be predicted to some extent.

[Brief description of drawings]

FIG. 1 is a sectional view of a burner representative of the present invention.

FIG. 2 is a diagram of a taper structure taken along the line AA in FIG.

FIG. 3 is a cross-sectional view of a conventional multi-tube burner.

FIG. 4 is a correspondence diagram of (a) temperature distribution of a synthesis surface and (b) corresponding refractive index homogeneity during synthesis of quartz glass.

FIG. 5 is a view showing a refractive index distribution of the quartz glass obtained in Example 1.

FIG. 6 is a diagram showing a refractive index distribution of the quartz glass obtained in Example 3.

FIG. 7 is a diagram showing a refractive index distribution of the quartz glass obtained in Example 4.

[Explanation of symbols]

1 Circular tube for raw material 2 Combustion ring tube 3 Combustion thin tubes

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroyuki Hiraiwa Inventor Hiroyuki Hiraiwa 3 2-3 Marunouchi, Chiyoda-ku, Tokyo Nikon Corporation (56) References JP-A-5-9035 (JP, A) JP-A-64- 28239 (JP, A) JP-A-7-138028 (JP, A) JP-B 2-5694 (JP, B2) (58) Fields investigated (Int.Cl. ⁷ , DB name) C03B 8/04 C03B 20 / 00 F23D 14/58

Claims (5)

(57) [Claims] 1. A circular tube for raw material, which is arranged in the center and ejects the raw material gas, and a plurality of ring-shaped tubes for combustion, which are arranged concentrically around it and ejects flammable gas and supporting gas. A quartz glass manufacturing method using a quartz glass burner having a plurality of combustion thin tubes arranged inside the outermost combustion ring-shaped tube for ejecting combustion-supporting gas, wherein the burner is a circular material The pipe and the combustion ring-shaped tube have a hexagonal tube structure, and the combustion thin tubes arranged inside the outermost combustion ring-shaped tube are equidistant on the circumference of a circle concentric with the hexagonal tube structure. Is a burner that is arranged, in which the raw material gas is blown into the flame obtained by burning the combustible gas and the combustion-supporting gas in the manufacturing method, and quartz glass powder is deposited by flame hydrolysis or thermal decomposition. ,
A method for producing quartz glass, characterized in that the flow rates of the combustible gas and the combustion supporting gas are in the range of 5 to 50 m / s. 2. A circular tube for raw material, which is arranged in the center and ejects the raw material gas, and a plurality of ring-shaped tubes for combustion, which are arranged concentrically around this and eject the combustible gas and the combustion supporting gas. A quartz glass manufacturing method using a quartz glass burner having a plurality of combustion thin tubes arranged inside the outermost combustion ring-shaped tube for ejecting combustion-supporting gas, wherein the burner is a circular material The pipe and the combustion ring-shaped tube have a hexagonal tube structure, and the combustion thin tubes arranged inside the outermost combustion ring-shaped tube are equidistant on the circumference of a circle concentric with the hexagonal tube structure. Is a burner that is arranged, in which the raw material gas is blown into the flame obtained by burning the combustible gas and the combustion-supporting gas in the manufacturing method, and quartz glass powder is deposited by flame hydrolysis or thermal decomposition. ,
The ratio of the velocity of gas ejected adjacent to the combustion ring tube is 1
The method for producing quartz glass is characterized in that it is 0.4. 3. A circular tube for raw material, which is arranged in the center and ejects the raw material gas, and a plurality of ring-shaped tubes for combustion, which are arranged concentrically around the central tube and eject the combustible gas and the combustion supporting gas. In a burner made of quartz glass having a plurality of combustion thin tubes arranged inside the outermost combustion ring-shaped tube and ejecting a combustion-supporting gas, the burner comprises a raw material circular tube and a combustion ring-shaped tube. The combustion thin tubes arranged inside the outermost combustion ring-shaped tube are burners arranged at equal intervals on the circumference of a circle concentric with the above-mentioned hexatube structure. The distance between the gas ejected from the ring-shaped pipe for use next to each other is 2
A quartz glass burner characterized by being less than or equal to mm. 4. A circular tube for raw material, which is arranged in the center and ejects the raw material gas, and a plurality of ring-shaped tubes for combustion, which are arranged concentrically around this and eject the combustible gas and the combustion supporting gas. In a burner made of quartz glass having a plurality of combustion thin tubes arranged inside the outermost combustion ring-shaped tube and ejecting a combustion-supporting gas, the burner comprises a raw material circular tube and a combustion ring-shaped tube. The combustion thin tubes arranged inside the outermost combustion ring-shaped tube are burners arranged at equal intervals on the circumference of a circle concentric with the above-mentioned hexatube structure. A burner made of quartz glass, characterized in that the variation of the distance between the gas ejected from the ring-shaped pipe for adjacent use is 0.2 mm or less. 5. The quartz glass burner according to claim 3 or 4, wherein the combustion ring-shaped tube and the combustion thin tube have a tapered structure, and the focal length of the combustion ring-shaped tube is the combustion thin tube. A quartz glass burner characterized by being shorter than the focal length of.