JP4288413B2 - Quartz glass molding method and molding apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a molding method and a molding apparatus for forming a uniform quartz glass into a predetermined shape by applying pressure while accommodating and heating the quartz glass in a mold.
[0002]
[Prior art]
A projection exposure apparatus (or photolithography apparatus) is mainly used for transferring an integrated circuit pattern such as an IC or LSI. The projection optical system used in this apparatus is required to have a higher exposure power over a wide exposure area and the entire exposure area as the integrated circuit is highly integrated. In order to improve the resolving power of the projection optical system, the exposure wavelength is shortened or the numerical aperture (NA) of the projection optical system is increased.
[0003]
As for the exposure wavelength, the wavelength is being shortened from g-line (436 nm) to i-line (365 nm), KrF (248 nm), and ArF (193 nm) excimer laser. In order to further increase the integration, a method of using an F ₂ (157 nm) excimer laser, an X-ray, and an electron beam as a light source is currently being studied. Among them, a reduction projection exposure apparatus using an F ₂ excimer laser that can be manufactured by making use of the design concept so far has been attracting attention.
[0004]
In general, optical glass used as a lens member of an illumination optical system or a projection optical system of a reduction projection exposure apparatus using a light source having a wavelength longer than that of i-line has a light transmittance drastically decreased in a wavelength region shorter than that of i-line. In particular, most optical glasses do not transmit light in the wavelength region of 250 nm or less. Therefore, only quartz glass and calcium fluoride crystals can be used as the material of the lens constituting the optical system of the reduction projection exposure apparatus using an excimer laser as a light source. These two materials are indispensable materials for correcting chromatic aberration in the excimer laser imaging optical system.
[0005]
Another important element for printing a circuit on a wafer with a reduction projection exposure apparatus is a reticle. As a material used for this reticle, not only excimer laser durability but also thermal expansion due to heat generation of the substrate becomes a big problem. Therefore, a method called a direct method (flame hydrolysis, which has good durability and low thermal expansion coefficient). The quartz glass synthesized by the method for producing transparent quartz glass by the above method is used.
[0006]
In the direct method, a combustion supporting gas (oxygen-containing gas, for example, oxygen gas) and a combustible gas (hydrogen-containing gas, for example, hydrogen gas or natural gas) are mixed and burned in a quartz glass burner, and the center of the burner is mixed. A high-purity silicon compound (for example, silicon tetrachloride gas) is diluted as a raw material gas with a carrier gas (usually oxygen gas) and ejected, and the raw material gas is reacted (hydrolyzed) by combustion of the surrounding oxygen gas and hydrogen gas. Reaction) to generate quartz glass fine particles, and the quartz glass fine particles are deposited on a target made of an opaque quartz glass plate which is disposed below the burner and performs rotation, swinging and lowering movement, and at the same time, the oxygen gas In addition, quartz glass ingots are obtained by melting and vitrification by the combustion heat of hydrogen gas.
[0007]
According to this method, since it is easy to obtain a quartz glass ingot having a relatively large diameter, an optical member having a desired shape and size can be manufactured by cutting out a block from the ingot.
[0008]
In recent years, in order to obtain an optical member having a large area, such as a large lens or reticle, or a large liquid crystal display, a quartz glass lump such as a pre-formed ingot is formed into a flat shape by heating and pressing. Therefore, a molding method for expanding the area is used.
[0009]
In this molding method, a quartz glass lump is accommodated in a mold and heated, and then molded by pressing with a pressure plate. Thereafter, the quartz glass lump is gradually cooled in the mold, or further annealed, and subjected to one opposing surface. A molded body having a predetermined shape with an enlarged area can be obtained.
[0010]
In order to perform such heat-pressure molding, for example, in a graphite mold, heat-pressure molding is performed at a temperature of 1700 ° C. or higher in a helium gas atmosphere with an absolute pressure of 0.1 Torr to atmospheric pressure. Then, a method of rapidly cooling to 1100 to 1300 ° C. is known. Also, a method of pressure molding at 1600 ° C. to 1700 ° C. using a graphite mold having a structure that relieves stress caused by a difference in thermal expansion coefficient between quartz glass and a mold mold (see Patent Document 1 below). ) And a molding apparatus in which the graphite mold has a vertical structure with two or more divisions (see Patent Documents 2 and 3 below). Furthermore, a method of forming a coating layer made of quartz powder on the inner surface of a graphite mold and performing pressure molding at 1550 ° C. to 1700 ° C. (see Patent Document 4 below) is also known.
[0011]
[Patent Document 1]
Japanese Patent Publication No. 4-54626.
[0012]
[Patent Document 2]
JP-A-56-129621.
[0013]
[Patent Document 3]
JP-A-57-67031.
[0014]
[Patent Document 4]
Japanese Patent Application Laid-Open No. 2002-22020.
[0015]
[Problems to be solved by the invention]
However, in the conventional heat and pressure molding, the quartz glass is heated to a moldable temperature by holding the mold containing the quartz glass lump for a predetermined time in a chamber heated to a predetermined temperature by a uniformly heatable heater. It was. Therefore, when a cylindrical or prismatic quartz glass lump is formed by pressing in the longitudinal direction, since almost the entire quartz glass lump is uniformly heated to a moldable temperature and softened, There was a case where the quartz glass block was deformed and bent at the middle part or the lower part, so-called buckling.
[0016]
However, when buckling occurs and molding is performed from the middle or lower part of the quartz glass lump, the buckled part becomes a boundary surface and a large number of bubbles are generated, and the residual strain of the resulting quartz glass increases. It became clear that optical inhomogeneity tends to occur.
[0017]
In particular, when forming optical members such as large lenses, mirrors, and reticles that are required for batch exposure of large areas in recent years, a larger quartz glass lump is used in the chamber of a large molding apparatus. It had to be heated for a longer time, more likely to buckle and optically non-homogeneous.
[0018]
Therefore, the present invention provides a molding method and a molding apparatus capable of molding a homogeneous quartz glass with little residual strain by suppressing a molding abnormality such as buckling when the quartz glass lump is heated and pressed. For the purpose.
[0019]
[Means for Solving the Problems]
The invention according to claim 1 which solves the above-mentioned problem is to pressurize the quartz glass mass between the opposing portion by accommodating the quartz glass mass in a mold and heating it, and moving the pressure part. In the method of forming into a predetermined shape, the pressure distribution is performed by the pressure unit while the temperature distribution of the quartz glass block is controlled so that the pressure unit side is higher in temperature than the facing unit side.
[0020]
The invention according to claim 2 is characterized in that, in addition to the configuration of claim 1, the width of the temperature distribution of the quartz glass block is 5 ° C. or more and 50 ° C. or less.
[0021]
Furthermore, the invention according to claim 3 is a mold having a hollow portion capable of accommodating a quartz glass lump, a pressurizing portion movably disposed in the hollow portion, and the quartz glass accommodated in the hollow portion. Heating means for heating the lump, and pressing the quartz glass lump by pressing the quartz glass lump to the bottom side while heating the quartz glass lump with the heating means to form a predetermined shape. The apparatus is characterized in that the heating means heats the pressure portion side of the quartz glass block so as to have a higher temperature than the bottom side of the mold.
[0022]
According to a fourth aspect of the present invention, in addition to the configuration of the third aspect, the heating means is disposed on the side surface side of the mold, and the amount of heat generated is independent between the pressurizing portion side and the bottom portion side. And is configured to be adjustable.
[0023]
Furthermore, the invention according to claim 5 is the bottom heater for heating the bottom surface portion of the quartz glass block, the heating means being arranged on the bottom surface side of the mold in addition to the configuration according to claim 3 or 4. It is characterized by having.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
[Embodiment 1]
Embodiment 1 of the present invention will be described below.
[0025]
FIG. 1 shows a molding apparatus according to this embodiment.
[0026]
This molding apparatus 10 has an ingot or a part of synthetic quartz glass produced using a silicon compound such as silicon tetrachloride, silane, or organic silicon as a raw material, or a refractive index of Ge, Ti, B, F, Al, or the like. From quartz glass ingots such as synthetic quartz glass ingots and parts thereof to which the components to be changed are added, for example, large liquid crystal masks, reticles for photomasks such as semiconductor masks, and large optical imaging systems It is an apparatus for molding a plate-like body having a wide surface such as a lens material or other large glass blocks.
[0027]
In this molding apparatus 10, a heat insulating material 12 provided over the entire surface of a metal vacuum chamber 11 and a plurality of carbon heaters 13 a and 13 b as heating means provided in a vertical wall of the heat insulating material 12 are provided. Furthermore, a mold 15 having a hollow portion 21 is accommodated in a substantially central portion inside the vacuum chamber 11. Here, the carbon heaters 13 a and 13 b are configured so that the amount of heat generated can be adjusted independently, and are arranged side by side up and down around the entire side of the mold 15.
[0028]
The mold 15 includes a bottom portion 18 having a bottom plate 16 and a receiving plate 17, and a side wall portion 20 formed in a cylindrical shape on the top of the bottom portion 18, and a hollow portion 21 is formed by the cylindrical side wall portion 20 and the bottom portion 18. Is formed.
[0029]
The hollow portion 21 is provided with a top plate 23 as a pressurizing portion having a shape corresponding to the shape of the hollow portion 21, and a pressing surface 23 b (upper surface) of the top plate 23 is disposed outside the vacuum chamber 11. By pressing with a cylinder rod 26 of a hydraulic cylinder as a forming means, it can move to the bottom 18 side of the mold 15 as an opposing surface.
[0030]
The hydraulic cylinder provided with the cylinder rod 26 is configured to move by being pressurized by adjusting the hydraulic pressure supplied from the outside, but the detailed illustration is omitted.
[0031]
The mold 15 and the top plate 23 have heat resistance and strength against the temperature and pressure at the time of forming the massive quartz glass 25, and hardly contaminate impurities even if they contact the massive quartz glass 25 at the time of molding. It is made of a material, here all made of graphite.
[0032]
Next, the case where the massive quartz glass 25 is shape | molded by the method of this embodiment using the shaping | molding apparatus 10 of the above structures is demonstrated. First, the mold 15 is formed by combining the bottom plate 16, the receiving plate 17, and the side wall portion 20 in the vacuum chamber 11. Then, a massive quartz glass 25 is disposed in the hollow portion 21 of the mold 15. In this embodiment, a synthetic quartz glass ingot is used as the massive quartz glass 25, and in order to shorten the lead time, the preheat is previously performed at a temperature of less than 300 ° C. before being accommodated in the hollow portion 21 of the mold 15. It is preferable to use the above.
[0033]
Then, the top plate 23 is disposed on the top of the massive quartz glass 25 accommodated in the hollow portion 21, and the pressing portion 26 a of the cylinder rod 26 of the hydraulic cylinder is brought into contact with the pressing surface 23 b of the top plate 23. To do. Then, the inside of the vacuum chamber 11 is replaced with an inert gas, and the pressure inside the vacuum chamber 11 is set to, for example, 1 × 10 ⁴ Pa to 1 × 10 ⁵ Pa.
[0034]
Next, the massive quartz glass 25 accommodated in the mold 15 and the hollow portion 21 thereof is heated by the carbon heaters 13a and 13b. At the time of this heating, first, the carbon heaters 13a and 13b are caused to generate heat, and the inside of the vacuum chamber 11 is heated at a temperature rising rate of 500 to 1000 ° C./hr. Then, the amount of heat generated by the carbon heater 13a on the upper side of the mold 15, that is, on the top plate 23 side is increased, so that the temperature on the top plate 23 side (that is, the upper portion) of the massive quartz glass 25 is increased. , The heat generation amount of the carbon heaters 13a and 13b is controlled so as to be higher than the lower part.
[0035]
In this state, the temperature is sufficiently heated to the inside of the massive quartz glass 25, for example, for 15 to 45 minutes, so that the width of the temperature distribution of the massive quartz glass 25, that is, the top on the top plate 23 side. The temperature difference between 25 a and the bottom surface portion 25 b on the bottom 18 side of the mold 15 can be set to 5 ° C. or more and 50 ° C. or less. Here, if the temperature distribution of the massive quartz glass 25 is less than 5 ° C., the sufficient buckling suppression effect is reduced. On the other hand, if it is higher than 50 ° C., the sufficient buckling suppression effect is obtained, but the quartz glass is obtained. Since the temperature gradient in the pressure direction of 25 is too large, the pressure deformation of the quartz glass 25 occurs in a narrow range. As a result, the time required for the pressure deformation becomes long, and various problems occur. For example, the contamination due to impurities increases, and the cycle time required for one molding increases, resulting in a decrease in production efficiency and a decrease in refractive index homogeneity.
[0036]
Further, in this molding, it is preferable to raise the temperature of the entire bulk quartz glass 25 to a molding temperature not lower than the crystallization temperature and not higher than the softening point, specifically 1570 ° C. to 1670 ° C. At the time of pressing the vicinity of the top portion 25a of the massive quartz glass 25 in the stage, it is sufficient that at least the top portion 25a side reaches the molding temperature.
[0037]
Then, by controlling and adjusting the hydraulic pressure to the hydraulic cylinder in a state where the massive quartz glass 25 is heated in this way, the cylinder rod 26 is moved downward, and the top portion 23 of the top plate 23 is moved by the pressing portion 26a of the cylinder rod 26. The pressing surface 23b is pressed. As a result, the top plate 23 moves in the pressing direction on the bottom 18 side of the mold 15, and the massive quartz glass 25 is pressed between the bottom plate 18 of the pressing surface 23 a of the top plate 23.
[0038]
Then, since the top 25a side of the quartz glass 25 has a higher temperature than the bottom surface 25b side, the top 25a side is more easily deformed than the bottom surface 25b side, and when pressed by the pressing surface 23a of the top plate 23, the top 25a side Will be sequentially transformed.
[0039]
At this time, when the descending speed of the top plate 23 is set to 5 to 15 cm / min, for example, the top plate 23 can be more easily deformed from the top 25a side.
[0040]
Further, it is preferable that the pressure applied from the top plate 23 at the time of molding is such that the pressure of the top plate 23 is reduced at the initial stage of the molding and becomes the maximum applied pressure at the final stage, for example, at the initial stage. the pressure in terms of per unit area of the pressing surface 23a of the 0.3~1.5Kg / cm ^2, at the final stage of molding can be 1.0~5.0Kg / cm ^2. By setting it as such a range, it can be made to change easily from the top part 25a side.
[0041]
Then, when the quartz glass 25 is formed into a plate-shaped body having a predetermined shape, the pressurization by the top plate 23 is finished. Thereafter, the quartz glass 25 molded into a plate shape is cooled while being placed in the mold 15, and the molding is completed by removing the molded body from the vacuum chamber 11.
[0042]
When the massive quartz glass 25 is molded as described above, the massive quartz glass 25 accommodated in the hollow portion 21 of the mold 15 is heated at a temperature higher than the top portion 25a on the top plate 13 side than the bottom portion 18 side of the mold 15. Since the carbon heaters 13a and 13b are heated so that the top plate 23 side of the massive quartz glass 25 is easily formed from the bottom 18 side, when the massive quartz glass 25 is pressurized by the top plate 23 during molding, the top plate 23 It can shape | mold sequentially from the side. Therefore, the bulky quartz glass 25 in the hollow portion 21 is unlikely to buckle during molding, and the residual strain of the obtained plate-like quartz glass 25 can be suppressed, so that a homogeneous plate-like body is obtained.
[0043]
Here, since the carbon heaters 13a and 13b whose heat generation amount can be adjusted independently are arranged side by side in the pressurizing direction of the side surface of the mold 15, the massive quartz glass accommodated in the hollow portion 21 of the mold 15 is arranged. 25 is easily heated so as to form a temperature distribution in the pressurizing direction.
[0044]
In the first embodiment, the example of forming at a temperature not lower than the crystallization temperature and not higher than the softening point temperature has been described. However, the forming temperature may be higher than the crystallization temperature of the quartz glass 25, for example, a part of the softening point. It is also possible to mold at a higher temperature.
[0045]
In the above, an example in which two carbon heaters 13a and 13b having different calorific values are used as the heating means has been described. However, three or more heaters may be arranged. In addition, heating is performed by arranging one heater on the side surface of the mold 15 and partially varying the amount of heat generation, or using a heater with a uniform amount of heat generation and shielding the bottom surface portion 25b with a shielding plate or the like. It is also possible to vary the amount.
[0046]
[Embodiment 2]
In the molding apparatus according to the second embodiment, as shown in FIG. 2, the carbon heater 13 disposed on the side surface on the top plate 23 side of the mold 15 and the ring 18 at the bottom 18 of the mold 15 are disposed in the vertical wall of the heat insulating material 12. A bottom heater 27 is provided which is embedded in the shape and heats the bottom surface portion 25 b of the massive quartz glass 25. The other configuration is the same as that of the first embodiment.
[0047]
Even in such a molding apparatus 10, the top 25a side of the massive quartz glass 15 is heated to a higher temperature than the bottom surface 25b side by adjusting the amount of heat generated by the carbon heater 13 and the bottom heater 27. It is possible to suppress buckling of the massive quartz glass 25 in the middle of molding.
[0048]
In addition, when the bottom heater 27 for heating the bottom surface portion 25b of the quartz glass 25 is provided as described above, the inside of the massive quartz glass 25 can be easily heated, and the massive quartz glass 25 having a large cross section perpendicular to the pressing direction can be obtained. However, it can be easily heated up to the inside and molding can be facilitated.
[0049]
In the second embodiment, the carbon heater 13 disposed on the side surface of the mold 15 is one that can generate a uniform amount of heat over the entire surface. However, as shown in FIG. It is also possible to arrange a carbon heater.
[0050]
【Example】
Examples will be described below.
[0051]
Example 1
Using a molding apparatus as shown in FIG. 1, from a massive quartz glass 25 made of a synthetic quartz glass ingot having a diameter of 50 cm and a height of 70 cm, a plate-like quartz having a square shape of 100 cm on a side and a thickness of 13.7 cm Glass 25 was molded.
[0052]
In this molding, the pressure in the vacuum chamber 11 is reduced to 0.67 Pa with a vacuum pump, and then pure nitrogen gas is filled to a pressure of 10 kPa, and then the block-like quartz is heated at a rate of 400 ° C./hr. The temperature of the mold 15 corresponding to the top portion 25a of the glass 25 is 1640 ° C., the temperature of the mold 15 corresponding to the bottom surface portion 25b is 1620 ° C., and the distribution width is controlled to be 20 ° C. And then held for 40 minutes.
[0053]
At this time, the temperature of the mold 15 was measured with a two-color thermometer.
[0054]
Thereafter, the top plate 23 was pressed by the cylinder rod 26 at an initial load of 5 ton and a press speed of 1 mm / sec to form an ingot. When the press load reached 25 tonnes, the pressurization was terminated and cooled.
[0055]
When the obtained plate-like body was observed for strain by an orthogonal crossed Nicols method, no strain due to buckling during molding was observed.
[0056]
Example 2
Using a molding apparatus as shown in FIG. 2, the temperature of the mold 15 corresponding to the top portion 25a is 1650 ° C., the temperature of the mold 15 corresponding to the bottom portion 25b is 1600 ° C., and the distribution width is 50 ° C. A plate-like quartz glass 25 was formed in the same manner as in Example 1 except that the temperature was raised.
[0057]
When the obtained plate-like body was observed for strain by an orthogonal crossed Nicols method, no strain due to buckling during molding was observed.
[0058]
Example 3
A plate is formed in the same manner as in Example 1 except that the temperature of the mold 15 corresponding to the top portion 25a is 1650 ° C., the temperature of the mold 15 corresponding to the bottom portion 25b is 1550 ° C., and the width of the distribution is 100 ° C. A shaped quartz glass 25 was formed.
[0059]
When the distortion of the obtained plate-like body was observed by the orthogonal crossed Nicols method, the distortion caused by buckling during the molding could not be confirmed, but some impurities were mixed in before the molding. It was. Further, deterioration of the refractive index homogeneity was observed.
[0060]
Comparative Example 1
Except that one carbon heater having a size corresponding to the carbon heaters 13a and 13b is mounted, the same molding apparatus as in FIG. 1 is used, and the temperature is raised by uniformly heating the carbon heater. In the same procedure as in No. 1, a plate-like quartz glass was molded. In this molding, the temperature of the mold 15 corresponding to the top portion 25a was 1670 ° C., the temperature of the mold 15 corresponding to the bottom surface portion 25b was 1667 ° C., and the distribution width was 3 ° C.
[0061]
When the obtained plate-like body was observed for strain by an orthogonal crossed Nicols method, streak-like strain due to buckling during molding was confirmed. In addition, a large number of bubbles were generated in the vicinity of the streak-like strain generation site. This part is presumed to be a buckled part.
[0062]
Comparative Example 2
A plate-like quartz glass was molded in the same manner as in Example 1 except that the temperature of the mold 15 corresponding to the top portion 25a and the bottom portion 25b was both set to 1630 ° C.
[0063]
When the obtained plate-like body was observed for strain by an orthogonal crossed Nicols method, streak-like strain due to buckling during molding was confirmed. In addition, a large number of bubbles connected in a planar shape were generated in the vicinity of the streak-like strain generation site, as in Comparative Example 1 above.
[0064]
【The invention's effect】
As described above in detail, according to the first aspect of the present invention, the temperature distribution of the quartz glass block is adjusted and pressurized so that the pressurizing part side is higher in temperature than the opposed part side. The pressure part side is easily formed from the facing part side, and can be formed in order from the pressure part side during pressurization. Therefore, buckling of the quartz glass lump hardly occurs during the molding, and it is easy to mold the quartz glass homogeneously while suppressing residual strain.
[0065]
Furthermore, according to the second aspect of the invention, since the width of the temperature distribution of the quartz glass block is 5 ° C. or more and 50 ° C. or less, it is possible to more reliably suppress the occurrence of buckling during the molding.
[0066]
According to the invention described in claim 3, the heating means for heating the quartz glass lump accommodated in the hollow portion of the mold heats the pressure portion side of the quartz glass lump so as to be higher than the bottom side. Therefore, when the quartz glass lump is pressurized by moving the pressure part to the bottom side of the mold during molding, it is possible to mold sequentially from the pressure part side. For this reason, the quartz glass lump is less likely to buckle in the hollow portion of the mold during molding, and it is easy to form a molded body uniformly by suppressing the residual strain of the quartz glass molded into a predetermined shape.
[0067]
Furthermore, according to the invention described in claim 4, since the heating means is arranged on the side surface side of the mold and is configured such that the heat generation amount can be adjusted independently on the pressurizing portion side and the bottom portion side. It is easy to adjust the temperature of the quartz glass block accommodated in the hollow portion.
[0068]
Further, according to the invention of claim 5, since it has a bottom heater that is arranged on the bottom surface side of the mold and heats the bottom surface portion of the quartz glass lump, it is easy to heat to the inside of the quartz glass lump, Even in the case of a quartz glass lump having a large cross section perpendicular to the pressing direction, it can be heated to the inside and can be molded more easily.
[Brief description of the drawings]
FIG. 1 is a schematic longitudinal sectional view showing a part of a molding apparatus according to Embodiment 1 of the present invention.
FIG. 2 is a schematic longitudinal sectional view showing a part of a molding apparatus according to Embodiment 2 of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Molding apparatus 11 Vacuum chamber 13, 13a, 13b Carbon heater 15 Mold 18 Bottom part 20 Side wall part 21 Hollow part 23 Top plate (pressure plate)
25 Quartz glass block 26 Cylinder rod (forming means)
27 Bottom heater

Claims (5)

In a method of forming a predetermined shape by pressurizing the quartz glass lump with a facing part by moving the pressure part by accommodating and heating the quartz glass lump in a mold,
A method for molding quartz glass, wherein the pressure distribution is performed by the pressure unit in a state in which the temperature distribution of the quartz glass block is controlled such that the pressure unit side is higher in temperature than the facing unit side. The method for molding quartz glass according to claim 1, wherein a width of a temperature distribution of the quartz glass block is 5 ° C. or more and 50 ° C. or less. A mold having a hollow part capable of accommodating a quartz glass lump, a pressurizing part arranged movably in the hollow part, and a heating means for heating the quartz glass lump accommodated in the hollow part, An apparatus for pressurizing and forming the quartz glass block into a predetermined shape by moving the pressure unit to the bottom side of the mold while heating the quartz glass block with the heating means,
The quartz glass molding apparatus, wherein the heating means heats the pressure portion side of the quartz glass block so as to be higher in temperature than the bottom side. 4. The quartz according to claim 3, wherein the heating unit is disposed on a side surface side of the mold, and is configured to be capable of independently adjusting a heat generation amount on the pressing portion side and the bottom portion side. Glass molding equipment. 5. The quartz glass molding apparatus according to claim 3, wherein the heating unit includes a bottom heater that is disposed on a bottom surface side of the mold and heats a bottom surface portion of the quartz glass lump.

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