Methods for preventing thermal damage during single crystal furnace shutdown

Abstract

The present invention provides a method for preventing thermal field damage when a single crystal furnace is stopped. The method includes the following steps: 1. When there is residual molten silicon liquid in the quartz crucible, a crystal is pulled, and the first length of the crystal enters a water-cooled heat shield; 2. After the crystal is pulled to the second length, the crystal pulling is stopped, and one end of the crystal is in contact with the surface of the molten silicon liquid; 3. After the crystal is stationary, the heating power of the auxiliary heater at the bottom of the single crystal furnace is reduced to zero; 4. The main heaters around the single crystal furnace reduce the power in three stages until the heating power of the main heater is reduced to zero; 5. After cooling for a certain period of time, the single crystal furnace is disassembled. According to the method of the embodiment of the present invention, a single crystal of a certain length can be pulled to increase the heat transfer volume, accelerate the condensation rate of the molten silicon liquid in the middle of the quartz crucible, reduce stress concentration, and the heater on the single crystal furnace stops heating in a step-by-step manner, slowing down the condensation rate of silicon around the quartz crucible, and leaving a stress release area, thereby maximally ensuring the integrity of the thermal field.

Description

Technical Field

[0001] The present invention mainly relates to the technical field of crystal material processing equipment, and in particular to a method for preventing thermal field damage of a single crystal furnace when it is shut down. Background Art

[0002] During an unconventional shutdown, the liquid silicon will expand in volume during the solidification and cooling process, and the crystallization order of the liquid silicon is that the crystallization surface is formed first on the liquid surface, and the crystallization surface will extend downward as the temperature decreases. However, the liquid silicon near the middle and bottom forms an insulation layer due to the upper crystallization, resulting in a large temperature gradient between the liquid silicon in the middle and bottom and the upper crystallization surface. This change will form stress that is difficult to release from the top under the inverse curve of temperature and time.

[0003] The volume change of liquid silicon will seek weak points around the quartz crucible, but this volume change is often constrained by the quartz crucible and the crucible band supporting the quartz crucible and cannot proceed freely, thus generating internal stress. The stress reaches its maximum as it gradually contacts the outside world at room temperature, making the container and the supporting container unable to withstand it and causing damage. Summary of the Invention

[0004] In view of this, the present invention provides a method for preventing thermal field damage when a single crystal furnace is shut down, which is used to guide the internal heat source stress of the thermal field of the single crystal furnace to avoid the formation of a large temperature between the liquid silicon at the bottom of the quartz crucible and the crystallization surface of the upper liquid silicon when the molten silicon liquid condenses, thereby generating stress and damaging the integrity of the thermal field.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] According to the method for preventing thermal field damage during shutdown of a single crystal furnace according to the first embodiment of the present invention, the single crystal furnace comprises: a quartz crucible for containing molten silicon liquid, a water-cooled heat shield arranged above the quartz crucible, a secondary heater arranged at the bottom of the single crystal furnace, and a main heater arranged around the quartz crucible and below the water-cooled heat shield.

[0007] The method comprises:

[0008] Step 1, when there is residual molten silicon liquid in the hot field quartz crucible, pulling the crystal, and the first length of the crystal enters the water-cooled heat shield;

[0009] Step 2: After the crystal is pulled to a second length, the pulling of the crystal is stopped, so that the crystal is stationary and one end of the crystal is in contact with the surface of the molten silicon liquid, and the first length is smaller than the second length;

[0010] Step 3, after the crystal is stationary, the heating power of the secondary heater at the bottom of the single crystal furnace is reduced to zero;

[0011] Step 4: The power of the main heaters around the single crystal furnace is reduced in three stages until the heating power of the main heaters drops to zero;

[0012] Step 5: Dismantle the single crystal furnace after cooling for a certain period of time.

[0013] Preferably, the heating power of the sub-heater is 15 kW when pulling the crystal.

[0014] Preferably, the main heater has a heating power of 45-60 kW when pulling the crystal.

[0015] Preferably, when the residual molten silicon liquid in the quartz crucible is 250-450 kg, the second length of the crystal is between 300-500 mm.

[0016] Preferably, the first length is between 200-400 mm.

[0017] Preferably, the three stages in step 4 are step-by-step power reductions, wherein in the first stage, the power of the main heater is reduced by 10 kW in 30 minutes.

[0018] Preferably, in step 4, in a second stage after the first stage, the power of the main heater continues to decrease by 15 kW at 60 minutes.

[0019] Preferably, in step 4, in the third stage after the second stage, the power of the main heater drops to zero after 90 minutes and the heating is stopped.

[0020] Preferably, circulating cooling water is provided in the water-cooled heat shield to quickly cool the crystal.

[0021] Preferably, the pulled crystal is a dislocation single crystal or a polycrystal.

[0022] The above technical solution of the present invention has at least one of the following beneficial effects:

[0023] According to the method for preventing thermal field damage by stopping a single crystal furnace in an embodiment of the present invention, a single crystal of a certain length can be pulled to increase the heat transfer volume, accelerate the condensation rate of the molten silicon liquid in the middle of the quartz crucible, allow the single crystal to enter the water-cooled heat screen, increase the heat transfer source, stop the auxiliary heating at the bottom of the single crystal furnace, accelerate the lower crystallization rate, reduce stress concentration, and stop the heating of the heater on the single crystal furnace in a step-by-step manner, slow down the condensation rate of silicon around the quartz crucible, and leave a stress release area, thereby maximizing the integrity of the thermal field. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic diagram of a method for preventing thermal field damage during shutdown of a single crystal furnace according to an embodiment of the present invention;

[0025] Figure 2 This is a cross-sectional view of the thermal field of an embodiment of the present invention and a positional relationship diagram of the single crystal, the water-cooled heat shield, and the molten silicon liquid.

[0026] Reference numerals:

[0027] Quartz crucible 10;

[0028] Molten silicon liquid 20;

[0029] Main heater 30;

[0030] Auxiliary heater 40;

[0031] Crystal 50;

[0032] Water-cooled heat shield 60. DETAILED DESCRIPTION

[0033] The following first describes in detail the method for preventing thermal field damage when shutting down a single crystal furnace according to an embodiment of the first aspect of the present invention with reference to the accompanying drawings.

[0034] In order to facilitate understanding of the method for preventing thermal field damage during shutdown of a single crystal furnace in the present application, the structure of the single crystal furnace is first described. Figure 2 As shown, the single crystal furnace includes: a quartz crucible 10 for containing molten silicon liquid 20, a water-cooled heat shield 60 arranged above the quartz crucible 10, a sub-heater 40 arranged at the bottom of the single crystal furnace, and a main heater 30 arranged around the quartz crucible 10 and below the water-cooled heat shield 60.

[0035] The following combination Figure 1 and Figure 2 , the method for preventing thermal field damage of a single crystal furnace when shutting down according to an embodiment of the present invention is described in detail, such as Figure 1 As shown, the method includes:

[0036] In step S100 , when there is residual molten silicon liquid in the hot field quartz crucible 10 , a crystal 50 is pulled, and a first length of the crystal 50 enters the water-cooled heat shield 60 .

[0037] In step S200 , after the crystal 50 is pulled to the second length, the pulling of the crystal 50 is stopped, so that the crystal 50 is stationary and one end of the crystal 50 contacts the surface of the molten silicon liquid, and the first length is smaller than the second length.

[0038] Step S300: After the crystal 50 comes to rest, the heating power of the sub-heater 40 at the bottom of the single crystal furnace drops to zero.

[0039] In step S400 , the power of the main heaters 30 around the single crystal furnace is reduced in three stages until the heating power of the main heaters 30 drops to zero.

[0040] Step S500: dismantle the single crystal furnace after cooling for a certain period of time.

[0041] It should be noted that the method for preventing thermal field damage during shutdown of a single crystal furnace of the present invention is more applicable when the quartz crucible 10 is intact without leakage or slightly siliconized. The single crystal with normal regular crystal arrangement 50 cannot be pulled due to mechanical or software reasons of the single crystal furnace, or the crucible wall of the quartz crucible 10 is deformed or bubbles are formed, which affects the single crystal pulling. At this time, an unconventional shutdown is required. Since the temperature in the furnace is still very high when the shutdown is required, in order to avoid thermal field damage, the method for preventing thermal field damage during shutdown of a single crystal furnace of the embodiment of the present invention needs to be used for unconventional shutdown.

[0042] For example, when there is 250-450 kg of molten silicon liquid 20 remaining in the quartz crucible 10, a section of crystal 50 is first pulled from the liquid level position of the molten silicon liquid 20 through the steps of seeding, shoulder release, shoulder rotation, and equal diameter. The crystal 50 can be a single crystal or a polycrystalline material. The single crystal or polycrystalline material is a single crystal or polycrystalline material of the same volume that does not form a regular crystal arrangement and does not belong to a single crystal product produced normally.

[0043] In step S100, a first length of the pulled crystal 50 enters the water-cooled heat shield 60, wherein the water-cooled heat shield 60 can quickly cool the crystal 50. The heat in the quartz crucible 10 is conducted from the high-temperature molten silicon liquid 20 to the low-temperature crystal 50 in the water-cooled heat shield 60, increasing the heat source. Therefore, the heat source stress inside the quartz crucible 10 can be conducted out to avoid damage to the thermal field.

[0044] In step S200, the second length of the pulled single crystal or polycrystalline material is the total length of the pulled crystal 50, wherein the second length can be determined according to the residual amount of the molten silicon liquid. When the residual amount of the molten silicon liquid is more, the total length of the pulled crystal or polycrystalline material is longer. For example, when there is 250-450 kg of molten silicon liquid 20 remaining in the quartz crucible 10, a single crystal or polycrystalline material with a length of 300-500 mm can be pulled upward. Generally, the single crystal or polycrystalline material with a total length of 300-500 mm enters the water-cooled heat shield 60 with a length of about 200-400 mm. When the pulled crystal 50 reaches the second length, the pulling of the crystal 50 is stopped, and the crystal 50 of the second length remains stationary, with one end in contact with the surface of the molten silicon liquid and the other end entering the water-cooled heat shield 60. Thus, by pulling a single crystal or polycrystalline material of a certain length, the heat transfer volume of the molten silicon liquid 20 can be effectively increased, and the condensation speed of the middle molten silicon liquid 20 can be accelerated. At the same time, the crystal 50 is allowed to enter the water-cooled heat shield 60 to increase the heat transfer source, thereby maximizing the integrity of the thermal field.

[0045] In step S300, after the crystal 50 is pulled, the power of the sub-heater 40 at the bottom of the single crystal furnace is reduced to zero. According to one embodiment of the present application, the sub-heater 40 at the bottom of the single crystal furnace has a heating power of 15 kW when pulling the crystal 50. That is, when the crystal 50 is pulled to the second length, the heating power of the sub-heater 40 at the bottom of the single crystal furnace is reduced from 15 kW to zero. Therefore, stopping the heating at the bottom of the single crystal furnace first can accelerate the crystallization speed of the lower portion of the quartz crucible 10 and reduce the stress concentration within the quartz crucible 10.

[0046] According to one embodiment of the present application, in step S400, when the main heater 30 is pulling the crystal 50, the heating power can be 45-60 kW, and the power is reduced in three stages, which are the first stage, the second stage, and the third stage. For example, when the heating power of the main heater 30 is 45 kW when pulling the crystal 50, in the first stage, the power of the main heater 30 is reduced by 10 kW after 30 minutes, and the heating power is 35 kW at this time. In the second stage, the power of the main heater 30 is further reduced by 15 kW after 60 minutes, and the power is 20 kW. In the third stage, the power of the main heater 30 is further reduced by 20 kW after 90 minutes, that is, it is reduced to zero, and heating is stopped. By stopping the heating of the main heater 30 in a step-by-step manner, the condensation rate of silicon around the quartz crucible 10 is slowed down, a stress release area is vacated, the stress release to the surrounding areas is weakened, and the thermal field loss during unconventional shutdown is reduced or achieved.

[0047] The power coordination of the main heater 30 and the auxiliary heater 40 is to reduce the temperature gradient between the upper and lower parts of the quartz crucible 10, slow down the heat release rate of the molten silicon liquid 20 during crystallization, reduce the concentrated generation of short-term stress, and promote the gradual release of stress from the crystallization part of the upper part of the quartz crucible 10.

[0048] In step S500, after cooling for a certain period of time, according to one embodiment of the present application, the cooling time is about 7-8 hours. When the temperature in the single crystal furnace drops below 300°C, the single crystal furnace can be dismantled to obtain the thermal field components in the furnace that are not damaged by stress and clean them. The cleaned thermal field components can enter the next furnace for crystal processing.

[0049] According to one embodiment of the present application, circulating cooling water is provided in the water-cooled heat shield 60 to quickly cool down the crystal 50. Thus, the crystal 50 of the first length enters the water-cooled heat shield, which can take away the heat of the crystal 50 to the greatest extent during the circulation process. It is a heat transfer body with a good heat dissipation effect, which doubles the heat transfer capacity and thus fully releases the internal stress.

[0050] According to one embodiment of the present application, the pulled crystal 50 is a dislocated single crystal 40 or a polycrystal. The reason for the unconventional furnace shutdown is that the crystal 50 cannot be pulled normally. Generally, the quartz crucible 10 is not damaged. The single crystal cannot be pulled due to mechanical or software reasons of the single crystal furnace, or the wall of the quartz crucible 10 is deformed or bubbles are formed, affecting the single crystal pulling. The pulled crystal 50 does not form a single crystal of the same volume with regular crystal 50 arrangement, and is a dislocated single crystal 40 or a polycrystal.

[0051] According to the method for preventing thermal field damage by stopping a single crystal furnace in an embodiment of the present invention, a single crystal of a certain length can be pulled to increase the heat transfer volume, accelerate the condensation rate of the molten silicon liquid in the middle of the quartz crucible, allow the single crystal to enter the water-cooled heat screen, increase the heat transfer source, stop the auxiliary heating at the bottom of the single crystal furnace, accelerate the lower crystallization rate, reduce stress concentration, and stop the main heater on the single crystal furnace in a step-by-step manner to slow down the condensation rate of silicon around the quartz crucible, leaving a stress release area, thereby maximizing the integrity of the thermal field.

[0052] Other structures and operations of the novel seed crystal processing equipment according to the embodiment of the present invention are understandable and easy to implement for those skilled in the art, and therefore will not be described in detail.

[0053] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preventing thermal field damage during unconventional shutdown of a single crystal furnace, characterized in that: The single crystal furnace comprises: a quartz crucible for containing molten silicon liquid, a water-cooled heat shield arranged above the quartz crucible, a secondary heater arranged at the bottom of the single crystal furnace, and a main heater arranged around the quartz crucible and below the water-cooled heat shield. The method comprises: Step 1, when there is residual molten silicon liquid in the quartz crucible, pulling the crystal, and the first length of the crystal enters the water-cooled heat shield; Step 2: After the crystal is pulled to a second length, the pulling of the crystal is stopped, so that the crystal is stationary and one end of the crystal is in contact with the surface of the molten silicon liquid, and the first length is smaller than the second length; Step 3, after the crystal is stationary, the heating power of the secondary heater at the bottom of the single crystal furnace is reduced to zero; Step 4: The power of the main heaters around the single crystal furnace is reduced in three stages until the heating power of the main heaters drops to zero; Step 5: Dismantle the single crystal furnace after cooling for a certain period of time.

2. The method according to claim 1, characterized in that When the crystal is pulled, the heating power of the sub-heater is 15 kW.

3. The method according to claim 1, characterized in that When the crystal is pulled, the heating power of the main heater is 45-60 kW.

4. The method according to claim 1, wherein When the residual molten silicon liquid in the quartz crucible is 250-450 kg, the second length of the crystal is between 300-500 mm.

5. The method according to claim 4, characterized in that The first length is between 200-400 mm.

6. The method according to claim 1, characterized in that The three stages in step 4 are step-by-step power reductions, wherein in the first stage, the power of the main heater is reduced by 10 kW in 30 minutes.

7. The method according to claim 6, characterized in that In step 4, in the second stage after the first stage, the power of the main heater continues to decrease by 15 kW at 60 minutes.

8. The method according to claim 7, characterized in that In the step 4, in the third stage after the second stage, the power of the main heater drops to zero at 90 minutes and the heating is stopped.

9. The method according to claim 7, characterized in that Circulating cooling water is provided in the water-cooled heat shield to quickly cool the crystal.

10. The method according to claim 1, characterized in that The crystal is pulled into a dislocation single crystal or polycrystal.

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