Sintering and groove sinking integrated system and method for preparing photomask quartz substrate

Abstract

The sintering and groove sinking integrated system comprises a sintering furnace, a groove sinking furnace, a weighing mechanism, a driving mechanism and a groove sinking mold, the weighing mechanism is connected with the driving mechanism, the driving mechanism is connected with a quartz rod, the bottom end of the sintering furnace is connected with the top end of the groove sinking furnace, and inner cavities of the sintering furnace and the groove sinking furnace are communicated; and the groove sinking die is arranged in the groove sinking furnace. The sintering furnace and the groove sinking furnace are integrally arranged, and the quartz rod is directly subjected to groove sinking shaping after being sintered, so that the production time is effectively shortened, and the production cost is reduced; a driving mechanism is used for hanging and driving a quartz rod to descend, the quartz rod enters a groove sinking furnace after being densified in a sintering area, and the quartz rod is gradually melted and spread in a groove sinking mold from the bottom, so that the problems of stripes, bubbles, poor uniformity and large stress in a product caused by folding and toppling due to the fact that the length-diameter ratio of the quartz rod is too large are solved; production of large-size, low-defect, high-performance and high-purity products is achieved, and the method can be applied to development of IC photomask substrates.

Description

Technical Field

[0001] The invention relates to the technical field of quartz substrate preparation, and in particular to a sintering tank sink integrated system and method for preparing a photomask quartz substrate. Background Art

[0002] Quartz glass is an amorphous material composed of a single component of silicon dioxide. It is a special industrial technical glass with low expansion coefficient, high temperature resistance, thermal shock resistance, good chemical stability and electrical insulation, and can transmit ultraviolet and infrared rays. It is widely used in the production of semiconductors, electric light sources, semiconductor communication devices, lasers, optical instruments and other industrial fields. As for semiconductor photomask substrates, substrates made of quartz glass have the best chemical stability, high hardness, low expansion coefficient and strong light transmittance. It is suitable for the production of products with higher precision requirements and is widely used in IC photomasks.

[0003] Synthetic quartz has excellent optical properties such as high purity, high transmittance, good uniformity, low stress, no streaks, no particle structure, no bubbles, no inclusions, no fluorescence, and resistance to laser damage. It also has excellent thermal, electrical, mechanical and chemical properties. It is the key material selected for 193nm band lithography system. The requirements for lithography-grade quartz materials are extremely high. Its optical uniformity alone needs to be within 1.0×10 -6 In the past few years, the requirements for the uniformity and transmittance of quartz materials have become increasingly higher, which means that the requirements for the preparation of quartz blanks are also becoming more and more stringent.

[0004] There are many quartz glass production processes, one of which is the VAD (vacuum arc degassing) method for synthesizing quartz. VAD is an indirect synthesis method. The process characteristics of this synthesis method are: high deposition efficiency, fast rate, low hydroxyl content, and this method is a vapor deposition method with a simple process route. The raw materials are SiCl4, hydrogen and oxygen, which are widely available and low in cost.

[0005] The quartz products produced by the VAD method have extremely low impurity content and have the significant advantages of high resistance to laser damage, high optical uniformity and low absorption coefficient. However, due to its size, its application scenarios are limited. In order to meet various application requirements, the quartz rod materials deposited by the VAD method usually need to be modified by groove sinking to reach specific application sizes. Groove sinking is to soften the quartz glass at high temperature to achieve the purpose of secondary molding. However, the quartz rods produced by the VAD method, due to their large aspect ratio, are prone to tipping and folding during the glass softening stage during groove sinking, resulting in bubbles, streaks, high stress, poor uniformity and other problems in the product. In severe cases, it will cause damage to the graphite mold, resulting in material waste and increased costs.

[0006] Optical uniformity is an important indicator for measuring the optical quality of quartz glass. It indicates the degree of uniformity of the refractive index inside an isotropic medium. When light passes through an inhomogeneous medium, the wavefront will be distorted. The magnitude of the distortion depends on the product of the refractive index difference and the thickness. This will reduce the resolution and imaging quality, which will cause the optical system to fail to achieve the expected function or even fail to work properly. Stress birefringence is another important indicator for measuring optical quartz glass. Its main effects are: (1) the processing process can easily cause the material to collapse and break, (2) during the precision processing, stress is continuously released, which can easily cause problems with the processing of the surface shape, and (3) when the polarized light system is used, it will cause the quality of the optical system to decline. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a sintering and slot sinking integrated system and method for preparing a photomask quartz substrate. A sintering-slot sinking integrated system is developed, in which a VAD deposited quartz rod is driven by a driving mechanism to gradually descend, and after sintering and densification in a sintering furnace, it gradually descends to a slot sinking furnace. The quartz rod is gradually subjected to high temperature from bottom to top to form molten quartz and spread out in a slot sinking mold. The quartz substrate after slot sinking has excellent performance, and the VAD deposited quartz rod is avoided from being easily folded and tipped over during slot sinking due to the large aspect ratio, thereby causing the product to easily have stripes, bubbles, poor uniformity and high stress.

[0008] In order to solve the above technical problems, the present invention provides, on one hand, a sintering slot sink integrated system for preparing a photomask quartz substrate, comprising a sintering furnace, a slot sink furnace, a weighing mechanism, a driving mechanism and a slot sink mold;

[0009] The weighing mechanism is connected to the driving mechanism, the driving mechanism is connected to the quartz rod, and the weighing mechanism, the driving mechanism and the quartz rod are vertically arranged in sequence from top to bottom and are located directly above the sintering furnace;

[0010] The bottom end of the sintering furnace is connected to the top end of the trough sink furnace, and the internal cavities of the two are connected;

[0011] The groove sinking mold is arranged in the groove sinking furnace, and the groove sinking mold is located directly below the quartz rod.

[0012] The present invention combines the sintering process after the VAD process with the slot sinking process, and integrates the sintering furnace and the slot sinking furnace. The quartz rod deposited by the VAD is driven downward by a driving mechanism, and after sintering and densification in the sintering zone of the sintering furnace, it continues to descend to the slot sinking furnace. The bottom to the top of the quartz rod gradually enter the high-temperature slot sinking area of ​​the slot sinking furnace in sequence, and after high temperature, molten quartz is formed and falls and spreads in the slot sinking mold. During the process, the quartz rod is suspended by the driving mechanism, and gradually melts and softens from the bottom and falls into the slot sinking mold, and the weight change of the quartz rod is detected by the weighing mechanism, and the rate of quartz rod descent is regulated by the driving mechanism, thereby controlling the weight reduction rate of the quartz rod. The overall melting and softening of the quartz rod is avoided, and the folding and dumping problems caused by the large aspect ratio are avoided, thereby causing the quartz substrate to have stripes, bubbles, poor uniformity and stress difference.

[0013] Furthermore, the sintering furnace comprises a furnace core tube, and the outer circumference of the furnace core tube is sheathed with a first thermal insulation layer, a first heater and a second thermal insulation layer from top to bottom.

[0014] Furthermore, the groove sinking furnace includes a furnace body, a second heater is arranged on the outer periphery of the upper part of the furnace body, and the groove sinking mold is located in the area surrounded by the second heater.

[0015] Furthermore, the furnace core tube is made of high-purity JGS3 quartz material, and the first heater and the second heater are graphite heaters.

[0016] Furthermore, it also includes a supporting platform located in the trough sinking furnace, which is arranged below the trough sinking mold and is used to support the trough sinking mold; a liftable furnace door is arranged at the bottom of the trough sinking furnace, and the supporting platform is arranged above the furnace door, and the trough sinking mold enters and exits the trough sinking furnace through the liftable furnace door.

[0017] Furthermore, it also includes a PLC module, which is connected to the weighing mechanism and the driving mechanism. When the tank sinks, the weighing mechanism detects the change in product weight and controls the driving mechanism to adjust the descending speed of the quartz rod.

[0018] Furthermore, graphite paper is placed in the groove sinking mold, the thickness of the graphite paper is 0.5-1.0 mm, and the ash content is less than 20 ppm.

[0019] Another aspect of the present invention provides a method for preparing a photomask quartz substrate, using the system described in the first aspect, comprising the following steps:

[0020] S1, hanging the VAD deposited quartz rod to the lower end of the driving mechanism, and the driving mechanism drives the bottom end of the quartz rod to descend to the sintering area of ​​the sintering furnace;

[0021] S2, the heater of the sintering furnace is started, and when the temperature of the sintering zone is raised to 1400-1450°C, the driving mechanism drives the quartz rod to rotate and descend, and the quartz rod is sintered and densified in the sintering zone. When the bottom end of the quartz rod descends to the connection between the sintering furnace and the trough sink furnace, the driving mechanism is stopped, and the heater of the sintering furnace controls the temperature of the sintering zone to drop to 750-900°C;

[0022] S3, the heater of the tank sinking furnace is started, and when the temperature of the tank sinking area rises to 1750-1805°C, the driving mechanism drives the quartz rod to gradually descend into the tank sinking furnace, and the quartz rod gradually forms molten quartz from bottom to top through high temperature and is spread out in the tank sinking mold for tank sinking. During the tank sinking process, the weighing mechanism monitors the weight change of the quartz rod in real time;

[0023] S4, when the weighing mechanism detects that the weight of the quartz rod is reduced to 0, the driving mechanism stops, and after standing for 1-4 hours, the driving mechanism starts to rise and reset;

[0024] S5, the tank sinking furnace is cooled to 1050-1150°C for constant temperature annealing for 24-72h, and then cooled to room temperature, and a photomask quartz substrate is obtained after fine processing.

[0025] Furthermore, in S1, the descending speed of the quartz rod is 10-400 mm / min.

[0026] Furthermore, in S2, the descending speed of the quartz rod is 0.5-10 mm / min, and the rotating speed is 0.1-10 r / min.

[0027] Furthermore, in S2, the heating time of the sintering furnace is 2-4 hours.

[0028] Furthermore, in S3, the heating time of the trough sinking furnace is 8-10 hours.

[0029] Furthermore, in S3, the weighing mechanism detects the weight change of the quartz rod, and adjusts the descending speed of the quartz rod through the PLC linkage control driving mechanism, so that the weight reduction rate of the quartz rod is 0.5-5kg / min.

[0030] Furthermore, in S4, when the weight of the quartz rod is reduced to 0, the head of the quartz rod is just located at the connection between the sintering furnace and the trough sinking furnace. Under the high temperature of the trough sinking furnace, affected by gravity, the head of the quartz rod is separated from the effective section.

[0031] Furthermore, in S5, the cooling rate of the trough sinking furnace to 1050-1150°C is 50-200°C / h; the cooling to room temperature is specifically: cooling to 600-700°C at a rate of 3-10°C / h, and then naturally cooling to room temperature.

[0032] Furthermore, in S2, the weighing mechanism detects the weight of the quartz rod to detect whether the quartz rod is broken during the sintering and densification process.

[0033] Beneficial effects of the present invention:

[0034] The present invention integrates the sintering furnace and the groove sinking furnace, and the VAD-deposited quartz rods are directly subjected to groove sinking shaping after sintering, which effectively shortens the production time and reduces the production cost.

[0035] The present invention adopts a driving mechanism to suspend and drive the quartz rod to gradually descend, and after being densified in the sintering zone, it gradually enters the trough sink furnace, and gradually melts and softens from the bottom and spreads out in the trough sink mold, thereby avoiding the problems of folding and tipping due to the large aspect ratio of the quartz rod, which further causes stripes, bubbles, poor uniformity and high stress in the product.

[0036] The present invention solves the problem of limited application of VAD quartz rods due to their size by means of groove sinking modification, realizes the production of large-size, low-defect, high-performance, and high-purity products, and can be applied to the development of IC photomask substrates. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic structural diagram of a sintering tank-sink integrated system for preparing a photomask quartz substrate of the present invention;

[0038] Figure 2 In the figure, a, b, and c are schematic diagrams of the structure of the sintering, groove sinking, and groove sinking end states of the sintering groove sinking integrated system for preparing a photomask quartz substrate of the present invention, respectively;

[0039] Explanation of the numbers in the figure: 1. weighing mechanism, 2. driving mechanism, 3. trough sinking mold, 4. quartz rod, 5. furnace core tube, 6. first insulation layer, 7. first heater, 8. second insulation layer, 9. furnace body, 10. second heater, 11. supporting platform, 12. furnace door. DETAILED DESCRIPTION

[0040] The present invention is further described below in conjunction with specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0041] Example 1

[0042] This embodiment relates to a sintering tank sink integrated system for preparing a photomask quartz substrate, such as Figure 1As shown, it includes a sintering furnace, a slot sink furnace, a weighing mechanism 1, a driving mechanism 2 and a slot sink mold 3; the weighing mechanism 1 is connected to the driving mechanism 2, the driving mechanism 2 is connected to the quartz rod 4, the weighing mechanism 1, the driving mechanism 2 and the quartz rod 4 are arranged vertically in sequence from top to bottom and are located directly above the sintering furnace; the bottom end of the sintering furnace is connected to the top end of the slot sink furnace, and the internal cavities of the two are connected; the slot sink mold 3 is arranged in the slot sink furnace, and the slot sink mold 3 is located directly below the quartz rod 4. In this embodiment, the sintering slot sink integrated system for preparing the photomask quartz substrate combines the sintering process after the VAD process with the slot sink process, and the sintering furnace and the slot sink furnace are integrated. The quartz rod 4 deposited by VAD directly undergoes the slot sink process after sintering, thereby improving production efficiency and saving costs.

[0043] In this embodiment, the system suspends the VAD deposited quartz rod 4 through the driving mechanism 2, and drives the quartz rod 4 to move downward. After sintering and densification in the sintering zone of the sintering furnace, it continues to descend to the slot sink furnace. The bottom to the top of the quartz rod 4 gradually enter the high-temperature slot sink area of ​​the slot sink furnace, and after high temperature, the molten quartz falls and spreads in the slot sink mold 3. During the process, the quartz rod 4 is suspended by the driving mechanism 2, and gradually melts and softens from the bottom and falls into the slot sink mold 3, and the weight change of the quartz rod 4 is detected by the weighing mechanism 1, and the rate of quartz rod 4 descent is regulated by the driving mechanism 2, thereby controlling the weight reduction rate of the quartz rod 4. The overall melting and softening of the quartz rod 4 is avoided, and the folding and dumping caused by the large aspect ratio lead to problems such as stripes, bubbles, poor uniformity and stress difference on the quartz substrate.

[0044] Specifically, the sintering furnace includes a furnace core tube 5, the outer circumference of which is sleeved with a first insulation layer 6, a first heater 7 and a second insulation layer 8 from top to bottom, the first heater 7 is arranged between the first insulation layer 6 and the second insulation layer 8, and the insulation area of ​​the first heater 7 forms a high-temperature sintering area. The trough sink furnace includes a furnace body 9, the outer circumference of the upper part of the furnace body 9 is provided with a second heater 10, the trough sink mold 3 is located in the area surrounded by the second heater 10, the second heater is arranged on the upper part of the furnace body 9, and a high-temperature trough sink area is formed in the area surrounded by the second heater 10. The material of the furnace core tube 5 is high-purity JGS3 quartz material, and the first heater 7 and the second heater 10 are graphite heaters.

[0045] Specifically, it also includes a support platform 11 located in the trough sink furnace, the support platform 11 is arranged below the trough sink mold 3, and is used to support the trough sink mold 3; a liftable furnace door 12 is arranged at the bottom of the trough sink furnace, and the support platform 11 is arranged above the furnace door 12, and the trough sink mold 3 enters and exits the trough sink furnace through the liftable furnace door 12, and graphite paper is placed in the trough sink mold 3, the thickness of the graphite paper is 0.5-1.0mm, and the ash content is less than 20ppm. Specifically, the components of the driving mechanism to realize the lifting and rotating functions are conventional means, which will not be described here, and can realize the lifting and rotating of the quartz rod, and can be composed of a lifting motor, a rotating motor and a connecting rod.

[0046] Preferably, a PLC module (not shown in the figure) is also included, and the PLC module is connected to the weighing mechanism 1 and the driving mechanism 2. When the tank sinks, the weighing mechanism 1 detects the change in product weight and controls the driving mechanism 2 to adjust the descending speed of the quartz rod 4 in a linked manner.

[0047] Example 2

[0048] This embodiment relates to a method for preparing a photomask quartz substrate, using the system described in Embodiment 1, and comprising the following steps:

[0049] S1. VAD deposited quartz rod 4 (diameter 320 mm, density 0.5 g / cm 3 , effective weight 50kg) is hung to the lower end of the driving mechanism 2, and the driving mechanism 2 drives the bottom end of the quartz rod 4 to descend to the sintering zone of the sintering furnace. The descending speed of the quartz rod 4 is 100mm / min, and the weighing system records the weight of the quartz rod 4 in real time;

[0050] S2, the first heater 7 of the sintering furnace is started, the sintering zone is heated to 1430°C for 2h, and the driving mechanism 2 drives the quartz rod 4 to rotate and descend, wherein the descending speed of the quartz rod 4 is 1mm / min, and the rotating speed is 3r / min. The quartz rod 4 is sintered and densified in the sintering zone, as shown in FIG. Figure 2 As shown in a, when the bottom end of the quartz rod 4 drops to the connection between the sintering furnace and the tank sink furnace, the driving mechanism 2 stops, and the first heater 7 of the sintering furnace controls the sintering zone to cool down to 800°C;

[0051] S3, the second heater 10 of the tank sinking furnace is started, the tank sinking area is heated to 1800°C for 8 hours, the driving mechanism 2 drives the quartz rod 4 to gradually descend into the tank sinking furnace, and the quartz rod 4 is gradually formed into molten quartz from bottom to top through high temperature and spread out in the tank sinking mold 3. Figure 2 As shown in b, during the sinking process, the weighing mechanism 1 monitors the weight change of the quartz rod 4 in real time, and adjusts the descending speed of the quartz rod 4 through the PLC linkage control driving mechanism 2, so that the weight reduction rate of the quartz rod 4 is 0.5kg / min;

[0052] S4, when the weighing mechanism 1 detects that the weight of the quartz rod 4 is reduced to 0, the driving mechanism 2 stops and stands for 2 hours. At this time, the head of the quartz rod 4 is just located at the connection between the sintering furnace and the tank sinking furnace. Under the high temperature of the tank sinking furnace, under the influence of gravity, the head of the quartz rod 4 is separated from the effective section, and then the driving mechanism 2 starts to rise and reset. Figure 2 As shown in c;

[0053] S5, the tank sink furnace is cooled to 1130℃ at a rate of 50℃ / h for constant temperature annealing for 48h, then cooled to 650℃ at a rate of 5℃ / h, and the second heater is turned off and the temperature is naturally cooled to room temperature, and the quartz ingot is taken out through the lifting furnace door 12 at the bottom of the tank sink furnace. After fine processing, the size is φ355mm×205mm, the transmittance at 193nm is 99.6% / cm, and the optical non-uniformity is 2×10 - 6 ppm, photomask quartz substrate with stress birefringence 2nm / cm.

[0054] Example 3

[0055] This embodiment relates to a method for preparing a photomask quartz substrate, using the system described in Embodiment 1, and comprising the following steps:

[0056] S1. VAD deposited quartz rod 4 (diameter 320 mm, density 0.5 g / cm 3 , effective weight 45kg) is hung to the lower end of the driving mechanism 2, and the driving mechanism 2 drives the bottom end of the quartz rod 4 to descend to the sintering zone of the sintering furnace. The descending speed of the quartz rod 4 is 200mm / min, and the weighing system records the weight of the quartz rod 4 in real time;

[0057] S2, the first heater 7 of the sintering furnace is started, the sintering zone is heated to 1435°C for 2h, and the driving mechanism 2 drives the quartz rod 4 to rotate and descend, wherein the descending speed of the quartz rod 4 is 1.5mm / min, and the rotating speed is 3r / min. The quartz rod 4 is sintered and densified in the sintering zone, such as Figure 2 As shown in a, when the bottom end of the quartz rod 4 drops to the connection between the sintering furnace and the tank sink furnace, the driving mechanism 2 stops, and the first heater 7 of the sintering furnace controls the sintering zone to cool down to 850°C;

[0058] S3, the second heater 10 of the tank sinking furnace is started, the tank sinking area is heated to 1780℃ for 8h, the driving mechanism 2 drives the quartz rod 4 to gradually descend into the tank sinking furnace, and the quartz rod 4 is gradually formed into molten quartz from bottom to top through high temperature and spread out in the tank sinking mold 3 for tank sinking, as shown in FIG. Figure 2As shown in b, during the sinking process, the weighing mechanism 1 monitors the weight change of the quartz rod 4 in real time, and adjusts the descending speed of the quartz rod 4 through the PLC linkage control driving mechanism 2, so that the weight reduction rate of the quartz rod 4 is 0.6 kg / min;

[0059] S4, when the weighing mechanism 1 detects that the weight of the quartz rod 4 is reduced to 0, the driving mechanism 2 stops and stands for 2 hours. At this time, the head of the quartz rod 4 is just located at the connection between the sintering furnace and the tank sinking furnace. Under the high temperature of the tank sinking furnace, under the influence of gravity, the head of the quartz rod 4 is separated from the effective section, and then the driving mechanism 2 starts to rise and reset. Figure 2 As shown in c;

[0060] S5, the tank sink furnace is cooled to 1100℃ at a rate of 80℃ / h for constant temperature annealing for 36h, then cooled to 680℃ at a rate of 7℃ / h, and the second heater is turned off and the temperature is naturally cooled to room temperature, and the quartz ingot is taken out through the lifting furnace door 12 at the bottom of the tank sink furnace. After fine processing, the size is φ345mm×210mm, the transmittance at 193nm is 99.5% / cm, and the optical non-uniformity is 3×10 - 6 ppm, photomask quartz substrate with stress birefringence of 2.3nm / cm.

[0061] In summary, the present invention integrates the sintering furnace and the slot sink furnace, and the VAD deposited quartz rod is directly slot-shaped after sintering, which effectively shortens the production time and reduces the production cost. The present invention uses a driving mechanism to hang and drive the quartz rod to gradually descend, and gradually enter the slot sink furnace after densification in the sintering zone, and gradually melt and soften from the bottom and spread out in the slot sink mold, avoiding the folding and tipping caused by the large aspect ratio of the quartz rod, and then causing the problem of stripes, bubbles, poor uniformity and high stress in the product. The present invention solves the problem of limited application of VAD quartz rods due to size by modifying the slot sink, and realizes the production of large-size, low-defect, high-performance and high-purity products, which can be applied to the development of IC photomask substrates.

[0062] The above-described embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or changes made by those skilled in the art based on the present invention are within the protection scope of the present invention. The protection scope of the present invention shall be subject to the claims.

Claims

1. A sintering tank sink integrated system for preparing a photomask quartz substrate, characterized in that: It includes a sintering furnace, a tank sinking furnace, a weighing mechanism, a driving mechanism and a tank sinking mold; The weighing mechanism is connected to the driving mechanism, the driving mechanism is connected to the quartz rod, and the weighing mechanism, the driving mechanism and the quartz rod are vertically arranged in sequence from top to bottom and are located directly above the sintering furnace; The bottom end of the sintering furnace is connected to the top end of the trough sink furnace, and the internal cavities of the two are connected; The groove sinking mold is arranged in the groove sinking furnace, and the groove sinking mold is located directly below the quartz rod.

2. The sintering tank sink integrated system for preparing a photomask quartz substrate according to claim 1, characterized in that: The sintering furnace comprises a furnace core tube, and a first heat-insulating layer, a first heater and a second heat-insulating layer are sleeved on the outer circumference of the furnace core tube from top to bottom.

3. The sintering tank sink integrated system for preparing a photomask quartz substrate according to claim 1, characterized in that: The groove sinking furnace comprises a furnace body, a second heater is arranged on the outer periphery of the upper part of the furnace body, and the groove sinking mold is located in the area surrounded by the second heater.

4. The sintering tank sink integrated system for preparing a photomask quartz substrate according to claim 1, characterized in that: It also includes a support platform located in the trough sinking furnace, the support platform is arranged below the trough sinking mold, a liftable furnace door is arranged at the bottom of the trough sinking furnace, and the support platform is arranged above the furnace door.

5. The sintering tank sink integrated system for preparing a photomask quartz substrate according to claim 1, characterized in that: Graphite paper is placed in the groove sinking mold, the thickness of the graphite paper is 0.5-1.0 mm, and the ash content is less than 20 ppm.

6. A method for preparing a photomask quartz substrate, using the system according to any one of claims 1 to 5, characterized in that: The steps include: S1, hanging the VAD deposited quartz rod to the lower end of the driving mechanism, and the driving mechanism drives the bottom end of the quartz rod to descend to the sintering area of ​​the sintering furnace; S2, the heater of the sintering furnace is started, and when the temperature of the sintering zone is raised to 1400-1450°C, the driving mechanism drives the quartz rod to rotate and descend, and the quartz rod is sintered and densified in the sintering zone. When the bottom end of the quartz rod descends to the connection between the sintering furnace and the trough sink furnace, the driving mechanism is stopped, and the heater of the sintering furnace controls the temperature of the sintering zone to drop to 750-900°C; S3, the heater of the tank sinking furnace is started, and when the temperature of the tank sinking area rises to 1750-1805°C, the driving mechanism drives the quartz rod to gradually descend into the tank sinking furnace, and the quartz rod gradually forms molten quartz from bottom to top through high temperature and is spread out in the tank sinking mold for tank sinking. During the tank sinking process, the weighing mechanism monitors the weight change of the quartz rod in real time; S4, when the weighing mechanism detects that the weight of the quartz rod is reduced to 0, the driving mechanism stops, and after standing for 1-4 hours, the driving mechanism starts to rise and reset; S5, the tank sinking furnace is cooled to 1050-1150°C for constant temperature annealing for 24-72h, and then cooled to room temperature, and a photomask quartz substrate is obtained after fine processing.

7. The method for preparing a photomask quartz substrate according to claim 6, wherein: In S2, the descending speed of the quartz rod is 0.5-10 mm / min, and the rotating speed is 0.1-10 r / min.

8. The method for preparing a photomask quartz substrate according to claim 6, wherein: In S3, the weighing mechanism detects the weight change of the quartz rod, and adjusts the descending speed of the quartz rod through the PLC linkage control driving mechanism, so that the weight reduction rate of the quartz rod is 0.5-5kg / min.

9. The method for preparing a photomask quartz substrate according to claim 6, wherein: In S5, the cooling to room temperature specifically includes: cooling to 600-700°C at a rate of 3-10°C / h, and then naturally cooling to room temperature.

10. The method for preparing a photomask quartz substrate according to claim 6, wherein: In S2, the weighing mechanism detects the weight of the quartz rod to detect whether the quartz rod is broken during the sintering and densification process.

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