JP5287574B2 - Heat treatment method for synthetic quartz glass - Google Patents

Description

  The present invention is suitable for excimer laser irradiation, particularly ArF excimer laser irradiation, and also for quartz glass substrates such as synthetic quartz mask substrates for photomasks used for ArF immersion technology, etc. With regard to a heat treatment method for synthetic quartz glass to obtain a synthetic quartz glass that is excellent in properties and has little change in light transmittance upon use, in particular, for applications that require a lower birefringence, and more recently The present invention relates to a heat treatment method for synthetic quartz glass which is a material for use in a quartz wafer substrate having a low birefringence, for an optical component for producing a high-quality display on a large TV or the like.

  In recent years, with the progress of miniaturization of exposure patterns accompanying the high integration of VLSI, exposure light sources are also required to have shorter wavelengths in lithography apparatuses (stepper apparatuses) that draw circuit patterns on semiconductor wafers. As a result, the KrF excimer laser (wavelength 248 nm) has become the mainstream from the conventional i-line (wavelength 365 nm) as the light source of the exposure apparatus, and in recent years, the practical application of ArF excimer laser (wavelength 193 nm) has begun. The introduction of immersion technology to make it easier.

  In addition to optical components such as lenses, windows, prisms, etc. used in exposure devices, the synthetic quartz mask substrate for photomasks, which is the original version of IC circuits, as the wavelength of light sources becomes shorter and the NA of lenses increases. As for the so-called reticle, a highly accurate one has been demanded. In particular, for ArF excimer lasers, high UV transmission, high uniformity of transmission, stability and uniformity of transmission with respect to excimer laser irradiation, etc., as in the case of optical components such as projection lenses, by switching to polarized illumination of the light source In addition, there are many extremely important issues such as low birefringence and uniformity of birefringence.

  On the other hand, in the display field such as televisions, as typified by liquid crystal televisions, plasma televisions, rear professional televisions, etc., especially with the progress of thinner and larger screens, the development of high-definition and high-quality displays will be eagerly pursued. It is being advanced. For example, there is also a demand for a synthetic quartz glass wafer substrate having a low birefringence for an optical component for making a liquid crystal display have a higher contrast.

In general, a method for producing a synthetic silica glass ingot which is a raw material for a synthetic silica glass substrate includes a direct method in which silica fine particles obtained by flame hydrolysis of a silica raw material are melted and deposited and a silica raw material is used. There are two production methods called the soot method in which silica fine particles obtained by flame hydrolysis are deposited and grown and then transparent vitrified.
Normally, in order to avoid contamination with metal impurities that cause UV absorption, for example, in the direct method, a silane compound such as high-purity silicon tetrachloride or silicone compound vapor is directly introduced into an oxyhydrogen flame, and this is introduced into the flame. It is hydrolyzed to produce silica fine particles, which are deposited on a heat-resistant substrate such as quartz glass that directly rotates and melted into glass to produce transparent synthetic quartz glass.

  The transparent synthetic quartz glass produced in this way exhibits good light transmission up to a short wavelength region of about 190 nm, and in addition to ultraviolet laser light, specifically i-line, KrF (248 nm), XeCl (308 nm ), XeBr (282 nm), XeF (351 nm, 353 nm), excimer laser light such as ArF (193 nm), and the fourth harmonic (250 nm) of YAG, etc., have been used as transmission materials.

  For example, in the case of ArF excimer laser, the transmittance for ultraviolet light is most important for the light having a wavelength of 193.4 nm, but in the case of synthetic quartz glass, the transmittance for light in this wavelength region is the impurity. Decreases depending on the content. Typical of these impurities are alkali metals such as Na and metal elements such as Cu and Fe. In the case of synthetic quartz glass, the concentration of these metal impurities contained in the obtained synthetic quartz glass can be measured with a sensitive detector by using raw materials such as silanes and silicones with extremely high purity. Although it is possible to reduce to a level that cannot be detected even when measured (<1 ppb), Na and Cu have a relatively large diffusion coefficient with respect to synthetic quartz glass, so that they diffuse from the outside by heat treatment, These processes are often contaminated, and special care is needed to prevent such contamination from occurring.

  In addition to the impurities described above, it is known that inherent defects present in the synthetic quartz glass also affect the transmittance. This defect means that oxygen is excessive or insufficient with respect to the Si—O—Si structure constituting the synthetic quartz glass, for example, oxygen deficiency defect (Si—Si: having absorption at 245 nm), oxygen excess defect ( (Si-O-O-Si: absorption at 177 nm) is famous, but in the case of synthetic quartz glass for ultraviolet applications, such defects are excluded from the beginning at least at a level that can be measured by spectrophotometry. Therefore, it is said that more subtle defects, such as extremely stretched or compressed Si—O—Si bonds, or a state where the Si—O—Si bond angle is out of the stable region, will be a problem. Yes.

  It is said that such a finer defect causes minute absorption in the ultraviolet region with a wavelength of 200 nm or less. These are considered to be caused by the production method of the synthetic quartz glass, for example, the central portion in the plane perpendicular to the growth direction of the synthetic quartz glass ingot produced by the direct method as described above. A subtle difference in transmittance between the outer peripheral portion and the outer peripheral portion exists, for example, at about 0.5% at an ArF excimer laser wavelength of 193.4 nm. This is considered to be due to the temperature distribution of the growth and melting surface of silica, and the surface temperature of the outer peripheral part is lower than that of the central part. .

  Japanese Patent Application Laid-Open No. 7-61823 (Patent Document 1) discloses a method for reducing the growth rate of synthetic quartz by a direct method to 2 mm / hr or less as means for removing these unstable structures. Although this method seems to be an effective means, since the growth rate is very slow, the productivity is poor and there is an economical problem.

  As an effective method for improving the ultraviolet transmittance of an ingot, Japanese Patent No. 2762188 (Patent Document 2) discloses that absorption of light having a wavelength of 200 nm or less caused by contamination of a synthetic quartz glass molded body in a heat treatment step has a wavelength of 150 It is also disclosed that it disappears by irradiating with ultraviolet light having a wavelength in the range of ˜300 nm, preferably 180 to 255 nm.

  Next, an important characteristic as with the ultraviolet transmittance is the stability of the synthetic quartz glass to the excimer laser irradiation. In particular, the ArF excimer laser is said to be easily damaged five times as much as the KrF excimer laser, and is an extremely important factor.

  As a phenomenon that occurs when a synthetic quartz glass is irradiated with an ArF excimer laser, the bond of Si—O—Si is cleaved by the very strong energy of the laser beam, and a paramagnetic defect called E ′ center (e-prime center) occurs. There is a phenomenon in which absorption occurs at 215 nm. This leads to a decrease in the transmittance of synthetic quartz glass for 193.4 nm. Also, structurally, it is said to be dependent on the amount of OH groups in the glass, which is called laser compaction or rarefaction, in which the network structure of synthetic quartz glass rearranges and the glass density increases and the refractive index increases. It is also well known that it causes a decrease in the refractive index and a refractive index decrease phenomenon.

  In order to improve the stability of such synthetic quartz glass to laser irradiation, the intrinsic defects of the synthetic quartz glass are reduced as described above, and at the same time, the concentration of hydrogen molecules in the synthetic quartz glass is set to a certain level or more. Is known to be extremely effective.

  In addition, since hydrogen molecule in synthetic quartz glass inhibits damage to synthetic quartz glass due to excimer laser irradiation, it has been eagerly studied since it was disclosed in JP-A-1-212247 (Patent Document 3). This is a well-known fact.

As disclosed in Japanese Patent Application Laid-Open No. 7-43891 (Patent Document 4), this hydrogen molecule is particularly subjected to an accelerated irradiation test using ArF excimer laser with high energy (100 mJ / cm ² · pulse). In addition, if there are many hydrogen molecules, the absorption at a wavelength of 193.4 nm at the initial stage of irradiation increases, but if the irradiation is continued for a long time thereafter, the absorption is relaxed. Conversely, when there are few hydrogen molecules, the absorption at 193.4 nm in the initial stage of irradiation is small, but the absorption increases with long-term irradiation. Therefore, it is necessary to appropriately adjust the concentration of hydrogen molecules contained in the synthetic quartz glass.

  In particular, synthetic silica glass ingots by direct method aiming at productivity and improving yield are produced under excessive conditions compared to the oxygen stoichiometric amount in the oxyhydrogen balance, depending on the manufacturing conditions. The produced synthetic quartz glass ingot contains a large amount of hydrogen molecules, and initial irradiation absorption upon irradiation with the ArF excimer laser tends to increase.

There are two methods for containing an appropriate amount of hydrogen molecules in synthetic quartz glass. One is a method in which hydrogen molecules are contained in the growth ingot by appropriately adjusting the ratio of hydrogen or propane and oxygen as combustion gases during the growth of the synthetic quartz glass ingot. With this method, the hydrogen molecule concentration in the synthetic quartz glass ingot can be adjusted in the range of about 0 to 2 × 10 ¹⁹ molecules / cm ³ .
Another method is a method of thermally diffusing hydrogen molecules by heat-treating a synthetic quartz glass body in a hydrogen atmosphere. This method has the advantage that the hydrogen molecule concentration can be precisely controlled.

As described above, various proposals have been made for the initial transmittance and excimer laser resistance of the synthetic quartz glass member, and a method for obtaining a high-quality one can be appropriately implemented.

  Particularly recently, for example, in the actual use of ArF excimer laser, in addition to the suppression and uniformity of the initial absorption of laser irradiation, the presence of residual birefringence in the synthetic quartz glass substrate for optical components and photomasks, and laser irradiation Changes in the birefringence inside are becoming important.

  The birefringence in the synthetic quartz glass is generally a synthetic quartz glass produced from the above-described synthetic quartz glass manufacturing method, usually in an ingot state. At the time of cooling during the hot forming process, the strain is mainly detected as a strain due to residual thermal stress.

As a method for removing the strain caused by the residual thermal stress and reducing the birefringence, for example, in the manufacturing process of the optical member, a heat treatment (annealing) with slow cooling is performed to remove the strain in the quartz glass. It is common practice to do this in consideration of the thermal properties of quartz glass. In general, the definition of Littleton is widely used for this thermal characteristic, and the temperature at which the strain disappears in 15 minutes is the annealing point (1 × 10 ¹² Pa · s), and the viscous flow of the glass cannot occur. It is defined as a strain point (4 × 10 ¹³ Pa · s) at which the strain in the glass cannot be removed below this temperature.

  However, when aiming for a lower birefringence value, a temperature distribution is generated between the central portion and the outer peripheral portion of the workpiece when the temperature is lowered in the heat treatment, and the temperature distribution remains as a difference in the density of the workpiece. It was not possible to improve the refractive index distribution and birefringence to a level that could be expected sufficiently.

For these heat treatments, various methods have been proposed for quartz glass. In particular, as a heat treatment method for a projection lens material of an exposure machine using the above-described excimer laser light source, for example, Japanese Patent Laid-Open No. 2002-167227 (Patent Document 5) discloses a heat treatment container and a flat cylindrical composite as a heat treatment method. A method of improving the refractive index distribution and birefringence has been proposed in which the quartz glass body is accommodated and the heat dissipation rate at the center of the object to be processed is set higher than the surrounding heat dissipation rate with the gap filled with SiO ₂ powder. .

However, with these methods, the birefringence value can be reduced to 1 nm / cm or less at a part of the object to be processed, the central part, but the distribution of the outer peripheral part is still higher than the central part, resulting in material loss. . In addition, it is necessary to use a high-purity SiO ₂ powder when filling the object to be processed into the SiO ₂ powder, which is not satisfactory in terms of cost and work efficiency.

JP 7-61823 A Japanese Patent No. 2762188 Japanese Patent Laid-Open No. 1-212247 JP 7-43891 A JP 2002-167227 A

  The present invention has been made in view of the above circumstances, and a quartz glass substrate such as a reticle used for excimer laser irradiation, particularly ArF excimer laser irradiation, ArF immersion technology, and a synthetic quartz mask substrate for photomasks. A synthetic quartz glass substrate that is suitable for use, has excellent light transmittance, uniform transmittance, and has little change in light transmittance during use, and is particularly suitable for applications that require a lower birefringence, Recently, an object of the present invention is to provide a heat treatment method for synthetic quartz glass, which is a material for low birefringence quartz wafer substrates, etc., for optical components for producing high-quality displays on large televisions and the like.

  As a result of intensive studies to achieve the above-mentioned object, the present inventors have hot-molded a synthetic quartz glass ingot into a desired shape in the temperature range of 1700 to 1900 ° C. above the softening point, and obtained the synthetic quartz glass block For example, the block is cut into a block having a thickness of about 50 mmt or less, the obtained block is heat-treated (annealed), and the block is further irradiated with ultraviolet light for a certain period of time. When manufacturing a synthetic quartz glass substrate, the block cut after hot molding of the synthetic quartz glass ingot is a polygonal column or cylinder, and the height thereof is shorter than the diagonal line of the bottom surface of this polygonal column, or Shorter than the outer diameter of the bottom of the cylinder, provide a gap between these blocks, stack multiple blocks without contacting each other, and heat-treat in an atmosphere furnace And a synthetic quartz glass having a high birefringence of 2 nm / cm or less, particularly 1 nm / cm or less, and a high acquisition rate of a substrate having a birefringence of 2 nm / cm or less, particularly 1 nm / cm or less from the cut block. A good photomask that can obtain a substrate and can be used for an excimer laser, particularly for an ArF excimer laser exposure machine, to increase the contrast on a Si wafer, by using a synthetic quartz glass substrate having a low birefringence. High contrast can be obtained when it is used as a synthetic quartz glass substrate for optical components, and these low birefringence substrates are made into wafers and used as low birefringence wafer substrates for optical components aiming at high definition of liquid crystal displays. As a result, the inventors have made the present invention.

Accordingly, the present invention provides the following heat treatment method for synthetic quartz glass.
Claim 1:
A synthetic quartz glass ingot was hot-molded in the range of 1700 to 1900 ° C., and the molded synthetic quartz glass was cut into blocks having a thickness of 50 mm or less. a heat treatment method of the synthetic quartz glass to be implemented as the heat treatment step in the manufacture of transparent synthetic quartz glass substrate in the substrate, by stacking a plurality of synthetic silica glass block, hit the heat-treating them in an atmosphere furnace The synthetic quartz glass block is a polygonal column or a cylinder, and the height thereof is shorter than the diagonal line of the bottom surface of the polygonal column or the outer diameter of the bottom surface of the column, and the main surface of the glass block between blocks is provided a gap between the blocks by lay glass jig gap set at the four corners and the bottom of the block and its Stacked without contacting the installation surface, was heated to 1000 to 1300 ° C., thereafter the temperature was kept constant time, it cooled in the following cooling rate -20 ° C. / hr to 800 to 1000 ° C., further 100 A method for heat treatment of synthetic quartz glass, characterized by cooling to 300 ° C. at a temperature lowering rate of −40 ° C./hr or less .
Claim 2 :
The heat treatment method of the synthetic quartz glass of claim 1 Symbol mounting width of the gap between the synthetic quartz glass block is characterized in that it is a 10 to 100 mm.
Claim 3 :
The method for heat-treating synthetic quartz glass according to claim 1 or 2 , wherein a gap is provided between the lowest synthetic quartz glass block and the furnace bottom.
Claim 4 :
The height of the synthetic quartz glass block is less than or equal to half the diagonal of the bottom surface in the case of a polygonal column, and is less than or equal to half the outer diameter of the bottom surface in the case of a cylinder. Item 4. The method for heat-treating synthetic quartz glass according to any one of Items 1 to 3 .
Claim 5 :
The method for heat treatment of synthetic quartz glass according to any one of claims 1 to 4 , wherein the maximum value of the birefringence of the entire main surface in the synthetic quartz glass block is 2 nm / cm or less.
Claim 6 :
Synthetic quartz glass substrate, heat treatment method according to any one of claims 1 to 5 is prepared synthetic quartz substrate of ArF excimer laser irradiation for photo masks.

  According to the present invention, for example, an excimer laser, particularly an ArF excimer laser, and a synthetic quartz mask substrate material for a photomask used for an ArF immersion technique or the like, that is, a so-called reticle material can be used. Synthetic quartz glass which is a raw material for excimer laser synthetic quartz glass substrates and optical component substrates for high-definition displays, which has a low refractive index and uniform transmittance distribution, and is less deteriorated. Can provide.

It is the schematic which shows an example of the manufacturing apparatus of synthetic quartz glass. It is explanatory drawing which shows the setting method of a synthetic quartz glass block. It is a top view which shows the synthetic quartz glass block set to the furnace body (furnace body bottom part).

  First, the raw material synthetic quartz glass ingot will be described in terms of the method for producing the synthetic quartz glass ingot in the present invention. The silica raw material compound is vapor-phase hydrolyzed or oxidatively decomposed with an oxyhydrogen flame to produce silica fine particles on the target. And a method of producing a synthetic quartz glass ingot by melting it into a molten glass (so-called direct method).

  In this case, an organosilicon compound is used as the silica raw material compound, preferably a silane compound represented by the following general formula (1) or (2), or a siloxane compound represented by the following general formula (3) or (4). Used.

R _n SiX _4-n (1)
(In the formula, R represents a hydrogen atom or an aliphatic monovalent hydrocarbon group, X represents a halogen atom or an alkoxy group, and n represents an integer of 0 to 4.)
(R ¹ ) _k Si (OR ² ) _4-k (2)
(Wherein R ¹ and R ² represent the same or different aliphatic monovalent hydrocarbon groups, and k is an integer of 0 to 3).

(In the formula, R ³ represents a hydrogen atom or an aliphatic monovalent hydrocarbon group, m is an integer of 1 or more, particularly 1 or 2, and p is an integer of 3 to 5.)

Here, the aliphatic monovalent hydrocarbon group of R, R ¹ , R ² and R ³ has 1 to 4 carbon atoms such as methyl group, ethyl group, propyl group, n-butyl group, tert-butyl group and the like. C3-C6 cycloalkyl groups, such as an alkyl group and a cyclohexyl group, C2-C4 alkenyl groups, such as a vinyl group and an allyl group, etc. are mentioned. Examples of the hydrolyzable group for X include a halogen group such as a chlorine group and an alkoxy group such as —OCH ₃ and —OCH ₂ CH ₃ .

Specific examples of the silane compound represented by the general formula (1) or (2) include SiCl ₄ , CH ₃ SiCl ₃ , Si (OCH ₃ ) ₄ , Si (OCH ₂ CH ₃ ) ₄ , and CH ₃ Si (OCH). ₃ ) _{3 and the} like, and examples of the siloxane compound represented by the general formula (3) or (4) include hexamethyldisiloxane, hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, and the like. It is done.

  Then, each of raw material silane or siloxane compound, hydrogen, carbon monoxide, flammable gas such as methane, propane, and flammable gas such as oxygen is supplied to a quartz burner forming an oxyhydrogen flame.

  In addition, as for the burner which supplies flammable gas, such as a silane compound and hydrogen, and combustion-supporting gas, such as oxygen, a multi-pipe, especially a triple tube or a quintuple burner can be used for the center part like usual. Moreover, the apparatus which manufactures a synthetic quartz glass ingot can use any of a vertical type or a horizontal type.

To produce a synthetic quartz glass substrate having a low birefringence of the present invention from the obtained synthetic quartz glass ingot,
(I) Hot forming into a desired shape within a temperature range of 1700-1900 ° C,
(Ii) cutting a hot-cast synthetic quartz glass block with a thickness of 50 mmt or less,
(Iii) annealing the cut synthetic quartz glass block having a thickness of 50 mmt or less by the heat treatment method of the present invention;
(Iv) A transparent synthetic quartz glass substrate is manufactured through the steps of slicing the annealed synthetic quartz glass block to form a substrate and then polishing.

  More specifically, after removing the fine silica powder (soot) adhering to the surface of the synthetic quartz glass ingot produced as described above with a cylindrical grinder, etc., the dirt adhering to the surface is etched in hydrofluoric acid. Rinse thoroughly with pure water or ultrapure water and dry in a clean booth. Next, hot molding is performed to obtain a desired shape. This is a vacuum melting furnace. Using a high-purity carbon material or the like as a mold material, a synthetic quartz glass ingot is charged into the mold material so that a high-purity carbon sheet material is interposed between the mold material and the synthetic quartz glass ingot. Hold under an inert gas such as argon at a slightly lower pressure than atmospheric pressure for 30 to 120 minutes at a temperature in the range of 1700 to 1900 ° C., and further expand the cylindrical ingot to obtain a cylindrical shape with a diameter of 200 to 320 mmφ, for example. A synthetic quartz glass block, or a synthetic quartz glass block having a polygonal column shape such as a rectangular column having a bottom surface of 130 mm × 130 mm to 200 mm × 200 mm square with a prismatic shape.

  Next, it is preferable that the synthetic quartz glass block produced by this hot molding is in the height direction, in the case of a polygonal column, not more than half of the diagonal of the bottom surface, and in the case of a cylinder, the outer diameter of the bottom surface It is preferable to set it to 1/2 or less. For example, it slices in order in the range of the thickness of 10-50 mmt, Preferably the range of the thickness of 30-40 mmt is cut out as a block. If it is thinner than 10 mmt, there is a possibility that diffusion of impurities and the like may diffuse up to the inner central portion in the annealing process performed in the next step. On the other hand, if it is thicker than 50 mmt, it may be difficult to reduce the birefringence to 2 nm / cm or less, particularly 1 nm / cm or less during the annealing process in the next step.

In order to remove the strain caused by the residual thermal stress in the block sliced and cut from the synthetic quartz glass block, a so-called annealing treatment is performed. This annealing process uses a normal high-temperature atmosphere furnace. In the present invention, the method of setting the synthetic quartz glass block in the annealing furnace is as follows.
(1) A plurality of synthetic quartz glass blocks having a thickness of 50 mmt or less are stacked and set. At this time, the number may be increased by stacking two or more, preferably 3 to 5, according to the size of the furnace to be used.
(2) When stacking the synthetic quartz glass blocks, the same synthetic quartz glass member between the synthetic quartz glass blocks, for example, a square block having a width of 10 mm or less and a thickness of 10 to 100 mm or a cylindrical block of about 10 mmφ is described above. A total of about four pieces are installed, one at each of the four corners of the main surface of the glass block, and gaps are provided between the blocks. The height of the gap is preferably 10 to 100 mm, particularly preferably about 30 to 60 mm. At this time, an air gap may be provided by placing a similar corner or cylindrical block between the lowermost block and the hearth. In addition, a space | gap means that nothing other than gas exists between blocks.
(3) A plurality of stacked synthetic quartz glass blocks are placed in a furnace. Depending on the size of the furnace, for example, about 6 pieces may be set in 3 rows so that 2 pieces are arranged side by side. In this way, it is preferable to place about 12 to 30 pieces in the furnace.

  If the height of the gap between the synthetic quartz blocks is lower than 10 mm, or if the blocks overlap each other, a heat insulating effect occurs between the blocks in the cooling process during the annealing process in the next step, and the inside of the blocks A gap occurs between the cooling process and the temperature program for controlling the annealing furnace temperature, and the cooling rate of the block internal temperature is delayed from the temperature control program, resulting in a rapid cooling state as a result. The present inventors have found that there is a risk that it becomes difficult to reduce strain due to residual thermal stress. On the other hand, if it is higher than 100 mm, the number of blocks to be stacked is limited from the height in the furnace, which may not be efficient.

  After setting the synthetic quartz glass block in this manner, it is kept for 5 hours or more, particularly 5 to 10 hours in an annealing temperature of 1000 to 1300 ° C. in the atmosphere or in an inert gas atmosphere such as nitrogen, and then several hours or more. The temperature is slowly cooled to a temperature range of 800 to 1000 ° C. near the strain point temperature at a temperature lowering rate of −20 ° C./hr or less, particularly −1 to −15 ° C./hr. Thereby, the birefringence in the synthetic quartz glass block can be suppressed to 5 nm / cm or less. Furthermore, when lowering the birefringence lower, in addition to the adjustment of the maximum temperature and the cooling rate to near the strain point, the temperature is below −40 ° C./hr, particularly − By slowly slow cooling at 1 to −20 ° C./hr, it can be suppressed to 2 nm / cm or less, further 1 nm / cm or less, for example. The birefringence measurement method is as described later.

  At this time, it is preferable to lower the rate of temperature decrease, and the rate of temperature decrease from the annealing temperature of 1000 to 1300 ° C. to the vicinity of the strain point temperature of 800 to 1000 ° C. is preferably −5 ° C./hr or less, more preferably −2 ° C./hr or less. Then, the rate of temperature reduction from 100 to 300 ° C. is preferably −10 ° C./hr or less, particularly preferably −5 ° C./hr or less.

  As described above, the temperature lowering rate is adjusted so that a temperature gap between the temperature inside the block and the annealing furnace does not occur. In this case, by combining with the synthetic quartz glass block setting method, the entire birefringence value of the entire block main surface can be made 2 nm / cm or less, particularly 1 nm / cm or less.

  When the synthetic quartz glass block produced in this way is used for an ArF excimer laser photomask substrate, for example, in order to further improve the initial transmittance of ArF at a wavelength of 193 nm, for example, ultraviolet irradiation is performed. May be. The ultraviolet irradiation is preferably performed for 0.1 to 50 hours, particularly 5 to 40 hours, using a low-pressure mercury lamp, a metal halide lamp, a mercury xenon lamp, an excimer lamp, or the like.

Further, if the synthetic quartz glass block is manufactured by the direct method, the hydrogen molecule concentration in the block after the annealing treatment is about 5 × 10 ^{15 to} 5 × 10 ¹⁷ molecules / cm ^3. The initial concentration and long-term resistance at the time of ArF excimer laser irradiation are adjusted to an appropriate concentration. In the case of the direct method, the hydrogen molecule concentration is adjusted by adjusting the supply balance for each of the silica raw material compound, the combustible gas such as hydrogen, and the flammable gas such as oxygen when producing the synthetic quartz glass ingot. Is done. The method for measuring the hydrogen molecule concentration is as described later.

Furthermore, in the case of so-called soot methods such as the VAD method, OVD method, and MCVD method, the above-described hydrogen molecules are not contained in the synthetic quartz glass member formed into a transparent glass from the porous body. After the heat treatment as described above, 5 × hydrogen molecules in the synthetic quartz glass substrate are heat-treated for several hours at a temperature of 400 ° C. or lower under a pressure of atmospheric pressure or higher in a hydrogen atmosphere in an atmosphere furnace in a slice substrate. When about 10 ^{15 to} 5 × 10 ¹⁷ molecules / cm ³ are contained, ArF excimer laser resistance can be obtained.

  The annealed synthetic quartz glass block grinds each surface with a surface grinder and simultaneously finishes each surface in parallel. Next, this is subjected to slicing processing, chamfering processing of each side, lapping processing, pre-polishing processing, final polishing processing, and conventional polishing processing steps. For example, for a synthetic quartz glass substrate for excimer laser, a 6 inch square A so-called normal size 6025 substrate having a thickness of 6.35 mmt can be manufactured. Moreover, a wafer substrate can also be produced by enlarging and molding into a cylindrical shape when hot-molding from a synthetic quartz glass ingot. For example, it is possible to produce an 8-inch φ thickness of about 1 mmt, and it can be used as a low birefringence substrate for optical components for high definition and high contrast.

EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example.
In the following examples, the internal transmittance, the hydrogen molecule concentration, and the birefringence are measured as follows.
Internal transmittance:
It was measured by an ultraviolet spectrophotometry (specifically, a transmittance measuring device (Cary 400) manufactured by VARIAN).
Hydrogen molecule concentration:
It was measured by laser Raman spectrophotometry (specifically, the method shown in Zhurnal Priklandnoi Specktroskopii Vol. 46 No. 6 pp. 987 to 991, 1987). The instrument used was NRS-2100 manufactured by JASCO Corporation, which was measured by the photon counting method. The measurement of hydrogen molecule concentration by argon laser Raman spectrophotometry may vary depending on the sensitivity curve of the detector, so the value was calibrated using a standard sample.
Birefringence:
The value at room temperature (25 to 28 ° C.) was measured using a birefringence measurement apparatus (specifically, a birefringence measurement apparatus (ABR-10A) manufactured by UNIOTPT).

[Example 1]
As a raw material, 3000 g / hr of methyltrichlorosilane is supplied to a quartz burner forming a flame from oxygen 12 Nm ³ / hr and hydrogen 30 Nm ³ / hr, and oxidized or burned to produce silica fine particles, which are rotated. A synthetic quartz glass ingot was obtained by depositing on a quartz target and melting into glass at the same time.

In this case, as shown in FIG. 1, a quartz glass target 2 is mounted on a rotating abutment 1, while an argon gas 5 is introduced into methyltrichlorosilane 4 placed in a raw material evaporator 3. 5 is accompanied by vapor of methyltrichlorosilane 4 and mixed with oxygen gas 6 to supply to the central nozzle of the quartz burner 7, and the burner 7 further includes the above mixed gas as a center. Sequentially, oxygen gas 8, hydrogen gas 9, hydrogen gas 10, and oxygen gas 11 are supplied from the inside to the outside, and the raw material methyltrichlorosilane and oxyhydrogen flame 12 are ejected from the burner 7 toward the target 2 to obtain silica fine particles 13 Were deposited on the target 2 and simultaneously melted into a transparent glass to obtain a synthetic quartz glass ingot 14.
The synthetic quartz glass ingot controls the raw material methyltrichlorosilane at a constant flow rate per hour, and adjusts the burner settings to maintain a constant shape of the silica melt growth surface and oxyhydrogen gas introduced from each nozzle of the burner The flow balance was adjusted. As a result, a 140 mmφ × 350 mm synthetic quartz glass ingot was cut out.

Next, in order to remove unmelted silica (soot) adhering to the surface of the synthetic quartz glass ingot, after grinding the surface with a cylindrical grinder, the surface is washed with 5% in a 50% by mass hydrofluoric acid solution. After soaking for a period of time, it was washed away in a pure water tank and dried in a clean booth.
This surface-treated synthetic quartz glass ingot is placed in a high-purity carbon mold in which a high-purity carbon sheet is set inside in a vacuum melting furnace and heated at a temperature of 1780 ° C. for 40 minutes in an argon gas atmosphere. 160 mm × 160 mm × 210 mmL of synthetic quartz glass block. The hydrogen molecule concentration of this synthetic quartz glass block was 4 × 10 ¹⁸ molecules / cm ³ .
After removing the burrs from the synthetic quartz glass block, it was sliced to a thickness of about 40 mm to obtain 4 blocks. In this way, 24 blocks having the same shape and size were produced.

  Next, these 24 blocks were set in an atmospheric pressure furnace. First, as a jig for setting a gap between blocks, several synthetic quartz glass having a surface of about 10 mm × 30 mm × 60 mm ground and etched with HF liquid were prepared. Subsequently, a synthetic quartz glass plate having a thickness of about 10 mmt is laid on the atmospheric pressure hearth, and, as shown in FIG. 2 (a), the gap length between the synthetic quartz glass blocks shown in Table 1 and The gap setting jig 21 is set at the four corners of the main surface of the synthetic quartz glass block 22, the synthetic quartz glass block is placed thereon, and the gap setting jig is placed in the same manner as described above. ), Synthetic quartz glass blocks were stacked in four stages. Six of these stacked blocks 23 were set in a furnace equipped with a heater 24 shown in FIG.

After setting, the temperature was raised to 1150 ° C. in an atmospheric pressure atmosphere for about 5 hours, and then held for 5 hours. After slow cooling to 900 ° C. at a rate of temperature decrease of −2 ° C./hr, the temperature was further cooled to 200 ° C. at a rate of temperature decrease of −5 ° C./hr, and the electric furnace was turned off.
After cooling to room temperature, the electric furnace door was opened and each block was taken out. Six blocks of these blocks were subjected to squareness and surface treatment with a surface grinder to finish 6 inches square.

  The in-plane distribution of these blocks was measured by measuring the birefringence of the main surface of the block and the 6-inch square surface at intervals of 5 mm by the method described above. As a result, it was found that the maximum value of the birefringence of all 24 blocks charged in the atmospheric pressure furnace was 1 nm / cm or less.

Furthermore, these synthetic quartz glass blocks are irradiated with a low-pressure mercury lamp for 24 hours and then subjected to normal slicing, chamfering, lapping, and polishing, and then a synthetic that is a typical representative size of 6.35 mm in thickness of 6 inches square. A quartz glass substrate was obtained.
As a result of measuring the birefringence of the polished transparent synthetic quartz glass substrate over the entire surface, it was found that the maximum value was 1 nm / cm or less in all the numbers as in the case of the measurement result in the block.

[Examples 2 to 4]
The synthetic quartz glass block was heat-treated under the conditions shown in Table 1 in the same manner as in Example 1, and the birefringence was measured.

[Comparative Example 1]
The same treatment as in Example 1 was performed except that the thickness of the synthetic quartz glass block was set to 100 mm and not stacked.

[Comparative Example 2]
The same processing as in Example 2 was performed except that the gap between the synthetic quartz glass blocks was eliminated and the blocks were directly overlapped.

The results of Examples 1 to 4 and Comparative Examples 1 and 2 are shown in Table 1.
Further, a 10 mm × 6.35 mm × 90 mm sample was cut out from the synthetic quartz glass substrate produced in Example 1, and four surfaces (10 mm × 90 mm two surfaces, 6.35 mm × 90 mm two surfaces) were polished, As a result of measuring absorbance at a wavelength of 215 nm by hydrogen molecule concentration and ArF excimer laser irradiation, the transmittance change was 0.5% or less in terms of a converted value at a wavelength of 193 nm. Further, after cutting a 30 mm square sample from this substrate, the transmittance at a wavelength of 193.4 nm and the transmittance distribution in the substrate plane with respect to the 30 mm square surface were measured, and as a result, the internal transmittance was 99.60% to 99%. The transmittance distribution in the substrate plane (ΔT%, wavelength 193.4 nm) was 0.2% or less.

DESCRIPTION OF SYMBOLS 1 Abutment 2 Quartz glass target 3 Raw material evaporator 4 Methyltrichlorosilane 5 Argon gas 6 Oxygen gas 7 Burner 8 Oxygen gas 9 Hydrogen gas 10 Hydrogen gas 11 Oxygen gas 12 Oxyhydrogen flame 13 Silica fine particles 14 Synthetic quartz glass ingot 21 Gap Glass jig for setting 22 Synthetic quartz glass block 23 Four-stage stacking of synthetic quartz glass block 24 Furnace heater

Claims (6)

A synthetic quartz glass ingot was hot-molded in the range of 1700 to 1900 ° C., and the molded synthetic quartz glass was cut into blocks having a thickness of 50 mm or less. Then, the obtained block was heat-treated, and this block was further sliced. a heat treatment method of the synthetic quartz glass to be implemented as the heat treatment step in the manufacture of transparent synthetic quartz glass substrate in the substrate, by stacking a plurality of synthetic silica glass block, hit the heat-treating them in an atmosphere furnace The synthetic quartz glass block is a polygonal column or a cylinder, and the height thereof is shorter than the diagonal line of the bottom surface of the polygonal column or the outer diameter of the bottom surface of the column, and the main surface of the glass block between blocks is provided a gap between the blocks by lay glass jig gap set at the four corners and the bottom of the block and its Stacked without contacting the installation surface, was heated to 1000 to 1300 ° C., thereafter the temperature was kept constant time, it cooled in the following cooling rate -20 ° C. / hr to 800 to 1000 ° C., further 100 A method for heat treatment of synthetic quartz glass, characterized by cooling to 300 ° C. at a temperature lowering rate of −40 ° C./hr or less . The heat treatment method of the synthetic quartz glass of claim 1 Symbol mounting width of the gap between the synthetic quartz glass block is characterized in that it is a 10 to 100 mm. The method for heat-treating synthetic quartz glass according to claim 1 or 2 , wherein a gap is provided between the lowest synthetic quartz glass block and the furnace bottom. The height of the synthetic quartz glass block is less than or equal to half the diagonal of the bottom surface in the case of a polygonal column, and is less than or equal to half the outer diameter of the bottom surface in the case of a cylinder. Item 4. The method for heat-treating synthetic quartz glass according to any one of Items 1 to 3 . The method for heat treatment of synthetic quartz glass according to any one of claims 1 to 4 , wherein the maximum value of the birefringence of the entire main surface in the synthetic quartz glass block is 2 nm / cm or less. Synthetic quartz glass substrate, heat treatment method according to any one of claims 1 to 5 is prepared synthetic quartz substrate of ArF excimer laser irradiation for photo masks.