JP2009298670A - Synthetic quartz glass and production method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a production method for producing a synthetic quartz glass in which the distribution of birefringence value in the optical axis is controlled, and the distribution of birefringence value in a direction vertical to the optical axis is reduced. <P>SOLUTION: The production method for producing a synthetic quartz glass comprises: a heating step where a synthetic quartz glass block is heated to the temperature range of 500 to 1,300°C at ≥300°C/hr; and a cooling step where the synthetic quartz glass block held at the above temperature range is cooled at ≥50°C/hr. In at least the heating step in the heating step and the cooling step, temperature control is performed in such a manner that the temperature change of the synthetic quartz glass block in a direction becoming an optical axis when used as an optical material is made smaller than the temperature change of the synthetic quartz glass block in a direction vertical to the above direction. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to synthetic quartz glass and a method for producing synthetic quartz glass.

  2. Description of the Related Art Conventionally, an exposure apparatus called a projection exposure apparatus is used in an optical lithography technique that exposes and transfers a fine pattern of an integrated circuit onto a wafer such as silicon. The light source of this exposure apparatus has been shortened from i-line (365 nm) to KrF (248 nm) and ArF (193 nm) excimer lasers with the recent high integration of LSI.

  In general, the optical glass used in an illumination optical system of an exposure apparatus that uses a light source having a wavelength longer than i-line or a projection optical system has a significantly reduced light transmittance with respect to light having a wavelength shorter than i-line. Especially for light in the wavelength region of 250 nm or less, most optical glass does not transmit light. For this reason, quartz glass or fluoride crystals such as fluorite are used in an exposure apparatus that uses an excimer laser as a light source. Quartz glass and fluorite are also widely used materials for ultraviolet and vacuum ultraviolet optics.

When synthetic quartz glass is used in an optical system of an optical lithography apparatus, it is necessary to expose so that an integrated circuit pattern having a large area has a high resolution. Therefore, an optical member of synthetic quartz glass must be of very high quality. Required. For example, the refractive index distribution of the member is required to be 10 ⁻⁶ or less in a very large aperture having a diameter of 250 mm or more. Also, reducing the amount of birefringence, that is, reducing the internal distortion of the optical member is as important as improving the homogeneity of the refractive index distribution. Furthermore, since the total optical path length of the illumination optical system and projection optical system of the exposure apparatus using an excimer laser exceeds 1 m, the internal transmittance of the glass material used to avoid the loss of the light amount is 99.75%. A high transmittance of / cm is required.

  Such a large-diameter quartz glass having reduced birefringence, high homogeneity of refractive index distribution, high transmittance, and ultraviolet resistance has been conventionally produced by a vapor phase synthesis method called a direct method. In an exposure apparatus using an excimer laser, in order to maintain a high transmittance, it is necessary to adjust the hydrogen molecule concentration, which is known as one of the UV resistance improving factors, to an appropriate value. Hydrogen molecules are taken into quartz glass during vapor phase synthesis.

  Synthetic quartz glass is obtained as an ingot by the vapor phase synthesis method, and various stresses derived from the thermal history during production remain in the ingot of the synthetic quartz glass. Therefore, the homogeneity of the refractive index and the birefringence value inside the glass cannot be said to be good, and it is not suitable as an optical element of an exposure apparatus. Further, since the synthetic quartz glass ingot is rapidly cooled by the air after the synthesis is completed, the structure determination temperature is high and the ultraviolet resistance is poor. Therefore, annealing is performed after manufacturing in order to adjust the structure determination temperature to an appropriate value to improve ultraviolet resistance and to release residual stress and improve homogeneity such as refractive index and birefringence value. It is common.

  Patent Document 1 includes a first step of obtaining a synthetic quartz glass ingot, an annealing treatment of the synthetic quartz glass ingot, and a second step of cooling at a predetermined temperature drop rate to a predetermined temperature range after the annealing treatment, The synthetic quartz glass block obtained in the second step is heated to a predetermined temperature range, held for a predetermined time, and further cooled to a predetermined temperature range at a predetermined temperature decrease rate. A manufacturing method is disclosed.

  Further, in Patent Document 2, the heating rate of heating in the step corresponding to the third step described in Patent Document 1 and the cooling rate of cooling are studied.

It is also known to suppress the distribution of birefringence values as a whole exposure apparatus by combining a plurality of optical members so that the distribution of birefringence values in the optical axis direction of each optical member cancel each other. (Patent Documents 1 and 2).
International Publication No. 01/12566 Japanese Patent Laid-Open No. 2005-022921

  In an exposure method using short-wavelength light such as KrF (248 nm) or ArF (193 nm) excimer laser, it is conceivable to use a high NA lens in order to further improve the resolution. In a high NA lens, the angle formed between the optical axis and the optical path is large, and not only the distribution of the birefringence value in the optical axis direction of the optical member but also the birefringence value in the lateral direction, that is, the direction perpendicular to the optical axis direction. It is also necessary to consider the distribution of.

  However, annealed synthetic quartz glass members used as optical members can sufficiently improve refractive index homogeneity and UV resistance, but homogenize birefringence values and control the distribution of birefringence values. It is not easy to improve the birefringence value performance such as. Further, when an exposure apparatus is configured by arranging a large number of optical members such as lenses formed from such synthetic quartz glass, the birefringence of each optical member is integrated, and a large birefringence is formed in the entire exposure apparatus. End up.

  The conventional method for producing synthetic silica glass has a problem that the birefringence value in two directions, ie, the optical axis direction and the direction perpendicular to the optical axis, cannot be sufficiently controlled when a synthetic quartz glass block is used as an optical material. there were.

  Accordingly, an object of the present invention is to provide a manufacturing method capable of manufacturing a synthetic quartz glass in which the distribution of birefringence values in the optical axis direction is controlled and the distribution of birefringence values in the direction perpendicular to the optical axis is reduced. And a synthetic quartz glass obtained by the manufacturing method thereof.

  The present invention provides a heating step of heating a synthetic quartz glass block to a temperature range of 500 ° C. or more and 1300 ° C. or less at a rate of 300 ° C./hour or more, and a synthetic quartz glass block held within the temperature range of 50 ° C./hour. A method of producing synthetic quartz glass comprising: a cooling step for cooling as described above, wherein at least one of the heating step and the cooling step in the direction of the optical axis when used as an optical material in the heating step. Provided is a method for producing synthetic quartz glass, in which temperature control is performed to make the temperature change of the quartz glass block smaller than the temperature change of the synthetic quartz glass block in the direction perpendicular to the direction.

  The present invention also provides a synthetic quartz glass that can be obtained by the method for producing a synthetic quartz glass.

  According to the method for producing synthetic quartz glass of the present invention, the production of synthetic quartz glass in which the distribution of birefringence values in the optical axis direction is controlled and the distribution of birefringence values in the direction perpendicular to the optical axis is reduced. Is possible.

  The method for producing synthetic quartz glass of the present invention includes a heating step and a cooling step, and the temperature control described above is performed at least in the heating step among these steps. Hereinafter, preferred embodiments of the production method of the present invention will be described step by step.

  The heating step is a step of raising the temperature of the synthetic quartz glass block to 300 ° C./hour or more to a temperature range of 500 ° C. or more and 1300 ° C. or less.

  Here, the synthetic quartz glass block refers to a synthetic quartz glass ingot itself obtained by a production method such as a direct method described below, or a synthetic quartz glass cut out from the ingot.

  The direct method, which is a method for producing a synthetic quartz glass ingot, can be carried out as follows, for example. That is, a raw material gas obtained by diluting a high purity silicon tetrachloride gas or an organic silicon compound with a carrier gas is ejected from the center of a quartz glass burner, and oxygen gas and hydrogen gas are mixed and burned. Then, the silica glass fine particles are generated by hydrolysis reaction with water generated by the combustion of oxygen gas and hydrogen gas around the burner, or by causing the raw material gas to undergo a combustion reaction with the flame to generate the quartz glass fine particles. The quartz glass ingot is obtained by depositing on a target made of an opaque quartz glass plate below the burner and performing operations such as rotation, swinging, and pulling down, and simultaneously melting and vitrifying with the combustion heat of oxygen gas and hydrogen gas. .

  At this time, if the ingot is rotated and heated so that the temperature distribution becomes uniform in the circumferential direction of the ingot, the birefringence distribution of the ingot can be formed in a rotationally symmetrical manner, and the synthetic quartz formed from the ingot The distribution of birefringence values of the glass block can also be rotationally symmetric.

  The synthetic quartz glass ingot produced in this way is used as it is as a synthetic quartz glass block, or cut into a predetermined shape and used as a synthetic quartz glass block. That is, the synthetic quartz glass block may be a synthetic quartz glass ingot itself or a lump of a size from which a plurality of target optical members can be taken out, but it has the shape of the target optical member or is polished. It is preferable to have a shape in which a target optical member can be obtained by performing finishing processing such as.

  In addition, the manufacturing method of a synthetic quartz glass ingot is not necessarily restricted to a direct method, VAD methods (Vapor Phase Axial Deposition method), such as a soot method, OVD method, and an indirect method, can also be employ | adopted.

  The “direction to be the optical axis when used as an optical material” is determined for the synthetic quartz glass block thus obtained. Here, “the direction to be the optical axis when used as an optical material” (hereinafter sometimes simply referred to as “optical axis direction”) refers to the synthetic quartz glass obtained by the production method of the present invention. This is the light transmission direction when used as an optical material such as a lens, and can be arbitrarily determined from the shape of the synthetic quartz glass block, manufacturing conditions, and the like.

  The “direction to be the optical axis when used as an optical material” is preferably the direction of the rotation axis at the time of production of the synthetic quartz glass ingot from which the synthetic quartz glass block is collected. That is, it is preferable that the center of the synthetic quartz glass ingot and the center of the synthetic quartz glass block coincide. Here, “collected” includes two cases: a case where a synthetic quartz glass ingot is cut out and collected, and a case where the synthetic quartz glass ingot is used as it is.

  In particular, the synthetic quartz glass block preferably has a cylindrical shape, and the optical axis direction is preferably perpendicular to the surface in contact with the center of one end surface of the cylindrical shape. Here, the center of the end face means the center of rotation (intersection of the rotation axis and the end face) when the synthetic quartz glass ingot is rotated, and the center of gravity of the end face otherwise. The end face may be flat or curved, but is preferably flat in view of ease of carrying out the heating step. Moreover, it is preferable that both end surfaces are parallel.

  After determining the optical axis direction in this way, the temperature change of the synthetic quartz glass block in the optical axis direction (hereinafter referred to as “optical axis direction temperature change”) is the temperature of the synthetic quartz glass block in the direction perpendicular to the direction. Temperature control is performed so as to be smaller than the change (hereinafter referred to as “vertical direction temperature change”). This temperature control is performed during the heating step, but is preferably performed over the entire period of the heating step.

  When the temperature change in the optical axis direction is made smaller than the temperature change in the vertical direction, the heat flux flowing from both end faces of the synthetic silica glass block along the optical axis direction to the center of the synthetic silica glass block is in a direction other than the optical axis (light (The direction perpendicular to the axis is included) is smaller than the heat flux flowing in the center. Thereby, the distribution of birefringence values in the optical axis direction can be controlled, and the distribution of birefringence values in the direction perpendicular to the optical axis can be reduced.

  As a method for making the temperature change in the optical axis direction smaller than the temperature change in the vertical direction, a method of performing temperature control by covering both end faces of the synthetic quartz glass block in the optical axis direction with a heat insulating material is effective. That is, in the heating step, it is preferable to raise the temperature at 300 ° C./hour or more up to a temperature range of 500 ° C. or more and 1300 ° C. or less with both end faces of the synthetic quartz glass block covered with a heat insulating material. Such a temperature increase can be carried out by holding the synthetic quartz glass block in a heating furnace and setting the temperature to be increased to 300 ° C./hour or more up to a temperature range of 500 ° C. to 1300 ° C.

  Any heat insulating material may be used as long as the temperature change in the optical axis direction can be made smaller than the temperature change in the vertical direction, and the material and shape thereof are arbitrary. For example, refractory bricks, glass wool, alumina, and the like can be used.

The synthetic quartz glass finally obtained is preferably subjected to the above temperature control so that the strain amount (nm / cm) meets the following conditions (1) and (2).
(1) When the distribution of strain (nm / cm) in the optical axis direction is measured from the center to the periphery of the synthetic quartz glass cross section perpendicular to the optical axis (length from the center to the periphery: L), The strain amount from the center to 0.8 L is within ± 3 nm / cm (preferably within ± 2 nm / cm, and further within ± 1 nm / cm), and the strain amount is between 0.8 L and L The absolute value of (nm / cm) is set to exceed 3 (preferably 5, or 10).
(2) When the distribution of strain (nm / cm) in the direction perpendicular to the optical axis is measured, the strain is within ± 3 nm / cm (preferably within ± 2 nm / cm, and further within ± 1 nm / cm). To be.

  Here, the amount of strain (nm / cm) will be briefly described. The amount of birefringence (birefringence value) is expressed by Δn = Re / t (Δn is the amount of birefringence, Re is the retardation, and t is the thickness of the sample). When the retardation Re is expressed in terms of the product of thickness, the unit of retardation Re is nm, and the unit of t is cm, the unit of birefringence Δn can be expressed by (nm / cm). In a solid such as glass, the amount of birefringence is proportional to the stress, and the stress is proportional to the magnitude of strain. Therefore, the amount of birefringence (birefringence value) is also called the amount of strain. Therefore, controlling the amount of strain is synonymous with controlling the amount of birefringence (birefringence value).

  In the present invention, with respect to the birefringence value in the optical axis direction, when the fast axis direction and the radial direction of the optical member (perpendicular to the optical axis of the synthetic quartz glass) are parallel, plus (+), vertical If it is, a minus (-) is attached. In addition, the birefringence value in the lateral direction (perpendicular to the optical axis of the synthetic quartz glass) is plus (+) when the fast axis direction and the optical axis direction of the optical member are parallel, and minus (+) when perpendicular. -) Is attached.

  When the measured value of the birefringence value is small, the fast axis is not necessarily completely parallel or perpendicular to the optical axis direction of the optical member, and may have an inclination. In such a case, the birefringence value is plus (+) when the angle of the fast axis with respect to the direction perpendicular to the optical axis direction is smaller than 45 degrees, and minus (-) when larger than 45 degrees. You can handle it.

  Examples of the method for measuring the birefringence value include a phase modulation method and a rotation analyzer method. In the phase modulation method, the optical system includes a light source, a polarizer, a phase modulation element, a sample, and an analyzer. A He—Ne laser or a laser diode is used as the light source, and a photoelastic converter is used as the phase modulation element.

  The light from the light source becomes linearly polarized light by the polarizer and enters the phase modulation element. The light beam from the phase modulation element projected onto the sample is modulated light whose polarization state changes continuously from linearly polarized light to circularly polarized light and linearly polarized light by the element. When measuring, rotate the sample around the incident light beam at the measurement point on the sample, find the peak of the detector, and measure the amplitude at that time. Find the magnitude of the phase difference. Note that when a Zeeman laser is used as the light source, measurement can be performed without rotating the sample. Further, a phase shift method or an optical heterodyne interference method may be used. In the rotation analyzer method, the sample configuration between the light source and the photodetector is sandwiched between the polarizer and the rotation analyzer, and while rotating the analyzer placed behind the sample, The signal from the detector is measured, and the phase difference is obtained from the maximum value and the minimum value of the signal from the detector.

  In the present invention, when “distribution of birefringence value (amount of strain) in the optical axis direction” is referred to, “the direction in which the laser for birefringence value measurement is irradiated is set to the optical axis direction” with respect to synthetic quartz glass In addition, how the birefringence value (strain amount) measured (in the thickness direction of the synthetic quartz glass) is in the cross section perpendicular to the optical axis (in the radial direction of the circular cross section when the synthetic quartz glass is cylindrical) It means that it is distributed.

  On the other hand, the phrase “distribution of birefringence value (amount of strain) in the direction perpendicular to the optical axis” refers to the synthetic quartz glass “the direction in which the laser for measuring the birefringence value is irradiated is perpendicular to the optical axis.” The birefringence value (strain amount) of the measured (side surface direction of the synthetic quartz glass) in the section along the optical axis (vertical or horizontal direction of the rectangular section when the synthetic quartz glass is cylindrical) It means that it is distributed.

  As described above, by covering the both end surfaces with the heat insulating material, it becomes easy to reduce the temperature difference between the surface and the central portion in the optical axis direction, and the distortion is reduced in the region extending from the surface to the central portion. This improves the uniformity of the birefringence distribution in the direction perpendicular to the optical axis of the synthetic quartz glass block.

  On the other hand, surfaces other than both end surfaces of the synthetic quartz glass block (hereinafter sometimes referred to as “side surfaces”) are not thermally insulated, so that when viewed from a cross section perpendicular to the optical axis, The temperature difference at the periphery (near the side surface) increases. For this reason, distortion increases in a region extending from the surface of the side surface to the central portion.

  Under such temperature control, the distribution of birefringence values in the optical axis direction of the synthetic quartz glass block is substantially constant from the center to the outer periphery through the main heating step and the cooling step described later, and the outer periphery. A distribution that increases extremely at the periphery is possible.

  The heating rate in the heating step is 300 ° C./hour or more as described above. When the rate of temperature increase is smaller than 300 ° C./hour, heat is easily transferred from the side surface to the center of the synthetic quartz glass block at the time of temperature increase, and the temperature difference between the surface and the center of the synthetic quartz glass block is reduced. For this reason, it is difficult to form the distribution of the birefringence value (distortion amount) as described above. The heating rate is preferably 500 ° C./hour or more, and more preferably 1000 ° C./hour or more.

  The synthetic quartz glass block is heated to a temperature range of 500 ° C. or higher and 1300 ° C. or lower. When the lower limit of the temperature range is less than 500 ° C., the birefringence value hardly changes, and when it is higher than 1300 ° C., the birefringence value distribution is deteriorated or the concentration of hydrogen molecules in the synthetic quartz glass block is reduced. It is easy to reduce the physical properties as an optical glass member. The heating of the synthetic quartz glass block is preferably performed to a temperature range of 900 to 1200 ° C, and more preferably to a temperature range of 1000 to 1100 ° C.

  In the heating step, the synthetic quartz glass block may be rapidly heated to the heating temperature in the above temperature range at the above temperature increase rate, and then held at the heating temperature in this temperature range. This makes it easy to form a gentle gradient of the birefringence value (distortion amount) distribution. Such a temperature holding operation needs to be completed at least before the central portion of the synthetic quartz glass block reaches the heating temperature.

  Subsequent to the heating step, a cooling step of cooling the synthetic quartz glass block maintained within the temperature range at 50 ° C./hour or more is performed.

  In the cooling step, it is preferable to cool to a temperature of less than 500 ° C. at a temperature lowering rate of 50 ° C./hour or more. When cooling at a rate slower than 50 ° C./hour, the amount of heat transferred from the side surface of the synthetic quartz glass block to the central portion increases, so the temperature of the side surface and the temperature of the central portion formed by the rapid temperature rise in the heating process As a result, the distribution of birefringence values in the direction of the optical axis becomes uniform over the entire surface perpendicular to the optical axis, and control as in the above condition (1) becomes impossible, which is not preferable.

  The cooling rate in the cooling step is preferably 200 ° C./hour or more, and more preferably 500 ° C./hour or more.

  Also in the cooling step, it is preferable to implement temperature control that makes the temperature change in the optical axis direction smaller than the temperature change in the vertical direction. As the method, there is a method of covering both end faces of the synthetic quartz glass block in the optical axis direction with a heat insulating material, covering both end faces of the synthetic quartz glass block with a heat insulating material, and performing a heating step. Cooling may be performed at a temperature of ° C / hour or more.

  By performing the heating step and the cooling step described above, a synthetic quartz glass in which the distribution of birefringence values in the optical axis direction is controlled and the distribution of birefringence values in the direction perpendicular to the optical axis is reduced is obtained. Can do.

  Prior to the heating step, the synthetic quartz glass block used in the heating step or the synthetic quartz glass ingot from which the glass block is collected is heated to a heating temperature of 900 ° C. or higher and held at the heating temperature. An annealing step of cooling at a temperature of 10 ° C./hour or less to a temperature of 0 ° C. or less can also be performed.

  900-1200 degreeC is preferable and the heating temperature in an annealing process has more preferable 1000-1100 degreeC. The cooling rate is preferably 10 ° C./hour or less, and more preferably 5 ° C./hour or less.

  In the present invention, the optical member may be formed by performing processing such as grinding, polishing, and centering on the synthetic quartz glass after completion of the cooling step. The optical member made of synthetic quartz glass thus produced has the above-described birefringence value distribution, and therefore can be suitably used for applications such as an optical lens of a semiconductor exposure apparatus and an optical lens of a liquid crystal exposure apparatus. .

  Hereinafter, an embodiment in which the manufacturing method of the present invention is carried out using a heat treatment furnace will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view showing a heat treatment furnace in which a synthetic quartz glass block is accommodated. A heat treatment furnace 1 shown in FIG. 1 is configured to be capable of accommodating a cylindrical synthetic quartz glass block 2, and a furnace 13 that can uniformly heat the furnace 12 and a furnace that forms the bottom surface of the furnace 12. A floor plate 14 is provided inside the furnace wall 10. Two refractory bricks 15 as base materials are installed in parallel on the top of the hearth plate 14 with a space 11 therebetween, and the outer diameter of the synthetic quartz glass block 2 is formed on the top of the two refractory bricks 15. A synthetic quartz block 2 sandwiched between heat insulating materials 3 having a substantially corresponding outer peripheral shape is installed. The heat insulating material 3 can be a heat-resistant brick.

  The y-axis direction in FIG. 1 is the direction that should be the optical axis (the optical axis direction when the synthetic quartz glass block 2 is used as an optical member after being subjected to a heat treatment step and a cooling step). The x-axis direction is a direction perpendicular to the y-axis direction.

  The synthetic quartz glass block 2 installed in the heat treatment furnace 1 may be subjected to annealing treatment. The interior of the heat treatment furnace 1 is uniformly heated by the in-furnace heater 13, whereby the synthetic quartz glass block 2 is heated to a temperature in the range of 500 ° C. to 1300 ° C. at a temperature increase rate of 300 ° C./hour or more. (Heating process). If necessary, after holding at a temperature of 500 ° C. or higher and 1300 ° C. or lower for a certain time, the furnace heater 13 is controlled to cool the synthetic quartz glass block 2 at 50 ° C./hour or higher (cooling step).

  In the heating step and the cooling step, since both end surfaces in the y-axis direction of the synthetic quartz glass block 2 are covered with the heat insulating material 3, the heat flux flowing to the central portion of the synthetic quartz glass block 2 along the y-axis is It becomes smaller than the heat flux flowing in the central part of the synthetic quartz glass block 2 along the x-axis direction. As a result, the distribution of birefringence values in the optical axis direction (the birefringence values obtained by irradiating the laser in the y-axis direction on the surface along the x-axis) is controlled, and the birefringence values in the direction perpendicular to the optical axis are controlled. It is possible to obtain a synthetic quartz glass in which the distribution of refraction values (the distribution of birefringence values obtained by irradiating a laser in the x-axis direction on the surface along the y-axis) is reduced.

  EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example and a comparative example, this invention is not limited to a following example at all.

The synthetic quartz glass blocks of Example 1 and Comparative Example 1 were produced as follows.
[Example 1]
(Annealing treatment)
A synthetic quartz glass block having a diameter of 250 mm and a thickness of 65 mm was annealed in a furnace in which the following conditions were set. First, the temperature was raised to 1100 ° C. at 140 ° C./hour, held at 1100 ° C. for 10 hours, then cooled to 500 ° C. at 10 ° C./hour and allowed to cool. The atmosphere was air.

(Heat treatment process)
The synthetic quartz glass block after the annealing treatment was subjected to heat treatment in a heating furnace as shown in FIG. As shown in FIG. 1, the synthetic quartz glass block after the annealing treatment was in a state in which the upper and lower surfaces, that is, both end surfaces in the y-axis direction were sandwiched between heat-resistant bricks. The heat-resistant brick was used as a heat insulating material, and the area of the surface in contact with the synthetic quartz glass block was 200 mm × 200 mm and the thickness was 70 mm. As the heat treatment, first, a heating step of raising the temperature to 1200 ° C. at a heating rate of 1200 ° C./hour and holding for 20 minutes was performed, and then a cooling step of lowering the temperature at 800 ° C./hour was performed.

  The strain distribution of the synthetic quartz glass after the heat treatment thus obtained is shown in FIGS. In addition, the heterodyne interferometry was used for the measurement of the distortion amount of the obtained sample. The measurement ranges of the strain amount in the optical axis direction and the strain amount in the direction perpendicular to the optical axis direction were both from the center of the synthetic quartz glass block to 5 mm from the outer periphery. The wavelength used for the measurement was 632.8 nm, which is the oscillation wavelength of the helium neon laser.

  FIG. 2 is a diagram showing a strain distribution in the optical axis direction of the synthetic quartz glass block of Example 1. The amount of strain changed from about 0 mm to about 1 nm / cm from the center of the glass block toward the outer side in the radial direction to about 100 mm, and was +18.6 nm / cm at 120 mm. That is, the distribution width of the strain amount in the optical axis direction was 18.6 nm / cm. FIG. 3 is a diagram showing the distribution of strain in the direction perpendicular to the optical axis. The strain amount was +1 nm / cm at the maximum, -0.5 nm / cm at the minimum, and the distribution width was 1.5 nm / cm. When the distribution width of the strain amount in the direction perpendicular to the optical axis was divided by the distribution width of the strain amount in the optical axis direction, it was 0.08.

[Comparative Example 1]
A synthetic quartz glass block after heat treatment was obtained in the same manner as in Example 1 except that a synthetic quartz glass block having a diameter of 250 mm and a thickness of 60 mm was used and the upper and lower surfaces were not sandwiched between heat-resistant bricks. The distribution of strain of the synthetic quartz glass block after the heat treatment is shown in FIGS.

  FIG. 4 is a diagram showing the distribution of strain in the optical axis direction of the synthetic quartz glass block of Comparative Example 1. The amount of distortion changes from about 0 to +1 nm / cm from the center of the glass block to the outer side in the radial direction to about 60 mm, about +5 nm / cm at 100 mm, and +17.9 nm at 120 mm. / Cm. That is, the distribution width of the strain amount in the optical axis direction was 17.9 nm / cm. FIG. 5 is a diagram showing the distribution of strain in the direction perpendicular to the optical axis of the synthetic quartz glass block of Comparative Example 1. The maximum was +1 nm / cm, the minimum was -2 nm / cm, and the distribution width was 3 nm / cm. When the distribution width of the strain amount in the direction perpendicular to the optical axis was divided by the distribution width of the strain amount in the optical axis direction, it was 0.17.

  From Example 1 and Comparative Example 1, in Example 1, the quartz glass block is provided with a heat insulating material (heat-resistant brick) on both end surfaces in the direction to be the optical axis, so as compared with Comparative Example 1, It was possible to reduce the strain distribution in the direction perpendicular to the optical axis direction while maintaining the same strain distribution in the optical axis direction. Further, the amount of strain in the optical axis direction of Example 1 increased rapidly in the vicinity of the outer periphery, and the distribution was appropriately controlled.

It is sectional drawing which shows the heat processing furnace which accommodated the synthetic quartz glass block inside. It is a figure which shows distribution of the distortion amount of the optical axis direction of the synthetic quartz glass block of Example 1. FIG. It is a figure which shows distribution of the distortion amount of the orthogonal | vertical direction with the optical axis of the synthetic quartz glass block of Example 1. FIG. It is a figure which shows distribution of the distortion amount of the optical axis direction of the synthetic quartz glass block of the comparative example 1. It is a figure which shows the distribution of the amount of distortions of the orthogonal | vertical direction with the optical axis of the synthetic quartz glass block of the comparative example 1. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Heat treatment furnace, 2 ... Synthetic quartz glass block, 3 ... Heat insulating material, 10 ... Furnace wall, 11 ... Space, 12 ... In-furnace, 13 ... In-furnace heater, 14 ... Hearth board, 15 ... Fire brick.

Claims (6)

A heating step of heating the synthetic quartz glass block to a temperature range of 500 ° C. or more and 1300 ° C. or less at 300 ° C./hour or more, and cooling the synthetic quartz glass block held in the temperature range at 50 ° C./hour or more. A method for producing synthetic quartz glass comprising a cooling step,
In at least the heating step of the heating step and the cooling step,
Implementing temperature control in which the temperature change of the synthetic quartz glass block in the direction to be the optical axis when used as an optical material is smaller than the temperature change of the synthetic quartz glass block in the direction perpendicular to the direction, A method for producing synthetic quartz glass.   The method for producing synthetic quartz glass according to claim 1, wherein the temperature control is performed by covering both end faces of the synthetic quartz glass block with a heat insulating material in a direction to be an optical axis when used as an optical material. .   The method for producing synthetic quartz glass according to claim 1 or 2, wherein the optical axis is a rotation axis at the time of production of a synthetic quartz glass ingot from which the synthetic quartz glass block is collected.   The synthetic quartz glass block has a cylindrical shape, and the optical axis is an axis perpendicular to a surface in contact with the center of one end surface of the cylindrical shape. A method for producing synthetic quartz glass. Before the heating step,
The synthetic quartz glass block used in the heating step or the synthetic quartz glass ingot from which the glass block is collected is heated to a heating temperature of 900 ° C. or higher, held at the heating temperature, and then 10 ° C. to a temperature of 500 ° C. or lower. The manufacturing method of the synthetic quartz glass as described in any one of Claims 1-4 which implements the annealing process cooled at / hour or less.   A synthetic quartz glass obtainable by the method for producing a synthetic quartz glass according to any one of claims 1 to 5.

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