Nitrogen protection system for crystal pulling and accurate flow control method thereof

Abstract

The invention provides a nitrogen protection system for crystal pulling and an accurate flow control method thereof. The system comprises a nitrogen storage device, a first control valve, a second control valve, a third control valve and a control module, the control module is electrically connected with the first control valve, the second control valve and the third control valve. One end of the first control valve is connected with the nitrogen storage device, and the other end of the first control valve is connected with a first gas inlet formed in one side of the upper end of an auxiliary furnace chamber of the crystal pulling furnace; one end of the second control valve is connected with the nitrogen storage device, and the other end is connected with a second gas inlet formed in the furnace bottom of the main furnace chamber of the crystal pulling furnace; one end of the third control valve is connected with the nitrogen storage device, and the other end is connected with a third gas inlet formed in the upper end of one side of the main furnace chamber of the crystal pulling furnace. According to the nitrogen protection system for crystal pulling and the accurate flow control method of the nitrogen protection system, accurate control over protection gas for crystal pulling is achieved, and the quality of finished crystal pulling products is indirectly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of crystal pulling, and in particular to a nitrogen protection system for crystal pulling and a method for accurately controlling the flow rate thereof. Background Art

[0002] Crystal pulling is one of the links in chip manufacturing. The crystal pulling process is as follows: high-purity polysilicon is placed in a sealed crucible, and after the air is evacuated with argon gas, the polysilicon is heated to 1420 degrees to melt and form liquid silicon. Then, a long single crystal silicon seed is brought into contact with the liquid surface, and while rotating, it is slowly pulled upward to form a cylindrical silicon rod. In actual production, a crystal pulling furnace is used to complete the process. The control of the protective gas in the crystal pulling furnace is directly related to the quality of the finished product of the crystal pulling, so the control of the protective gas in the crystal pulling furnace is extremely important. Summary of the invention

[0003] One of the purposes of the present invention is to provide a nitrogen protection system for crystal pulling and a method for accurately controlling its flow rate, thereby achieving accurate control of the protective gas for crystal pulling and indirectly improving the quality of the finished crystal pulled product.

[0004] A nitrogen protection system for crystal pulling provided by an embodiment of the present invention includes: a nitrogen storage device, a first control valve, a second control valve, a third control valve and a control module;

[0005] Among them, the control module is electrically connected to the first control valve, the second control valve and the third control valve respectively; one end of the first control valve is connected to the nitrogen storage device, and the other end is connected to the first air inlet arranged on one side of the upper end of the auxiliary furnace chamber of the crystal pulling furnace; one end of the second control valve is connected to the nitrogen storage device, and the other end is connected to the second air inlet arranged at the bottom of the main furnace chamber of the crystal pulling furnace; one end of the third control valve is connected to the nitrogen storage device, and the other end is connected to the third air inlet arranged on the upper end of one side of the main furnace chamber of the crystal pulling furnace.

[0006] Preferably, at least one air distribution plate is provided at the upper end of the furnace-attached chamber; a through hole is provided in the middle of the air distribution plate.

[0007] Preferably, a plurality of first air outlets are provided at the bottom of the main furnace chamber.

[0008] Preferably, a plurality of second air outlets are provided on the furnace top of the auxiliary furnace chamber.

[0009] Preferably, the third gas inlet is connected to an annular gas outlet pipeline arranged above the crucible through a pipeline; the annular gas outlet pipeline is fixed to the upper end of the main furnace chamber through at least one telescopic mechanism.

[0010] Preferably, a plurality of air outlet holes are evenly distributed on the outer circumference of the annular air outlet pipe.

[0011] Preferably, the annular air outlet pipeline is provided with two left and right air passages.

[0012] Preferably, a plurality of air outlet holes are evenly distributed on the circumference of the inner and outer sides of the annular air outlet pipe.

[0013] The present invention also provides a flow rate precision control method, which is applied to any of the above-mentioned nitrogen protection systems for crystal pulling, comprising:

[0014] Before feeding the raw materials into the crucible of the crystal pulling furnace, the telescopic mechanism is controlled to extend the annular gas outlet pipeline into the bottom of the crucible;

[0015] Put in raw materials, control the third control valve and the second control valve to open, and fill nitrogen into the crystal pulling furnace;

[0016] Control the first air outlet to close and perform sampling and detection on the air outflow from the second air outlet;

[0017] When the detection data meets the preset conditions, the third control valve and the second control valve are controlled to close, the filling of nitrogen into the crystal pulling furnace is stopped, and the telescopic mechanism is controlled to move the annular gas outlet pipeline out of the crucible.

[0018] Preferably, the flow rate precision control method further includes:

[0019] During the crystal pulling process, the first control valve is controlled to open so that the first gas inlet injects nitrogen into the furnace at a preset initial rate;

[0020] Controlling the second air outlet to close and sampling and testing the air out of the first air outlet;

[0021] The air intake rate of the first air intake port is controlled according to the detection data.

[0022] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description and the accompanying drawings.

[0023] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0025] Figure 1 This is a schematic diagram of a nitrogen protection system for crystal pulling in an embodiment of the present invention;

[0026] Figure 2A schematic diagram of a crystal pulling furnace in an embodiment of the present invention;

[0027] Figure 3 A schematic diagram of a flow rate precision control method according to an embodiment of the present invention;

[0028] Figure 4 It is a schematic diagram of another method for precise flow control according to an embodiment of the present invention. DETAILED DESCRIPTION

[0029] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0030] The embodiment of the present invention provides a nitrogen protection system for crystal pulling, such as Figure 1 to Figure 2 As shown, it includes: a nitrogen storage device 1, a first control valve 2, a second control valve 3, a third control valve 4 and a control module 5;

[0031] In the process of pulling single crystal silicon, nitrogen is often used as a protective gas to isolate the silicon melt from harmful gases such as oxygen and water vapor in the air and prevent silicon from being oxidized at high temperatures. Oxidation will lead to the introduction of impurities in silicon, affecting the purity and quality of single crystal silicon. Atmosphere control: In the Czochralski (CZ) crystal pulling method, nitrogen is used to control the atmosphere during the crystal pulling process to ensure that the silicon melt is cooled in an oxygen-free or low-oxygen environment. This helps to improve the crystallization quality and crystal structure of single crystal silicon. Cooling assistance: The thermal conductivity of nitrogen is lower than that of argon, so in some crystal pulling processes, nitrogen can be used as a cooling medium to help quickly cool the molten silicon and promote the growth of single crystals. Pollution prevention: Nitrogen can also be used to flush and purify crystal pulling equipment, remove air and other gases in the equipment, so as to prevent contamination of single crystal silicon during the crystal pulling process. Safety effect: Nitrogen is an inert gas and is not easy to burn, so the use of nitrogen in the crystal pulling process can reduce the risk of fire and explosion;

[0032] Among them, the control module 5 is electrically connected to the first control valve 2, the second control valve 3 and the third control valve 4 respectively; one end of the first control valve 2 is connected to the nitrogen storage device 1, and the other end is connected to the first air inlet 13 arranged on one side of the upper end of the auxiliary furnace chamber 12 of the crystal pulling furnace; one end of the second control valve 3 is connected to the nitrogen storage device 1, and the other end is connected to the second air inlet 15 arranged at the bottom of the main furnace chamber 11 of the crystal pulling furnace; one end of the third control valve 4 is connected to the nitrogen storage device 1, and the other end is connected to the third air inlet 17 arranged on the upper end of one side of the main furnace chamber 11 of the crystal pulling furnace.

[0033] Among them, at least one air distribution plate 21 is arranged at the upper end of the auxiliary furnace chamber 12; a through hole is arranged in the middle of the air distribution plate 21. A plurality of first air outlets 14 are arranged at the bottom of the main furnace chamber 11. A plurality of second air outlets 16 are arranged at the furnace top of the auxiliary furnace chamber 12. The third air inlet 17 is connected to the annular air outlet pipeline 19 arranged above the crucible through a pipeline; the annular air outlet pipeline 19 is fixed to the upper end of the main furnace chamber 11 through at least one telescopic mechanism 18. A plurality of air outlet holes are evenly distributed on the outer circumference of the annular air outlet pipe.

[0034] For precise control of flow rate, we must first clarify the work of the crystal pulling furnace, which can be summarized as including: putting in raw materials, heating the raw materials to melt, and crystal pulling (pulling the finished product out of the molten liquid by rotating the pulling head).

[0035] In the process of putting in raw materials, the flow control method includes: before putting raw materials into the crucible of the crystal pulling furnace, controlling the telescopic mechanism 18 to move the annular gas outlet pipe 19 into the bottom of the crucible; putting in raw materials, controlling the third control valve 4 and the second control valve 3 to open, and filling nitrogen into the crystal pulling furnace; controlling the first gas outlet 14 to close and sampling and detecting the gas outlet from the second gas outlet 16; when the detection data meets the preset conditions, controlling the third control valve 4 and the second control valve 3 to close, stopping the filling of nitrogen into the crystal pulling furnace, and controlling the telescopic mechanism 18 to move the annular gas outlet pipe 19 out of the crucible; the process of heating the raw materials to melt does not involve the control of the protective gas; in the process of crystal pulling, the flow precision control method includes: controlling the first control valve 2 to open, so that the first gas inlet 13 injects nitrogen into the furnace at a preset initial rate; controlling the second gas outlet 16 to close and sampling and detecting the gas outlet from the first gas outlet 14; controlling the gas intake rate of the first gas inlet 13 according to the detection data.

[0036] After the raw materials are put in, nitrogen is introduced into the raw materials through the annular gas outlet pipe 19 to blow out the trace gases attached to the surface of the raw materials, and nitrogen is introduced through the second air inlet 15 to fill the furnace with protective gas, thereby achieving comprehensive filling of the furnace body with protective gas; before filling the furnace body with protective gas, a vacuum operation is first performed; due to the shape and accumulation of the raw materials, there are positions where the gas from the annular gas outlet pipe 19 cannot be purged, and therefore, the telescopic mechanism 18 can be synchronously controlled to slightly extend and retract (any value from ±1mm to ±1cm), thereby achieving a slight vibration of the annular gas outlet pipe 19 in the raw material, thereby improving the discharge effect of the attached trace gases. Due to the difference between the space inside the crucible and the space inside the furnace, it is necessary to control the air intake amount and air intake time of the annular air outlet pipe 19 and the second air inlet 15 differently. The specific control method is as follows: first, the space inside the furnace body is divided into three parts by the plane where the bottom of the crucible is located and the plane where the upper end face is located, and the volume of the lower space, the volume of the middle space, and the capacity of the crucible are determined; then the end face of the crucible is extended upward to divide the upper space into two parts, and the upper space is horizontally layered from top to bottom with equal distance; in this way, the filling of the protective gas can be divided into four steps, namely: the first step is to fill the lower space through the second air inlet 15, the second step is to fill the middle space through the second air inlet 15 and the space inside the crucible through the annular air outlet pipe 19, the third step is to fill the upper space through the second air inlet 15 and the annular air outlet pipe 19, and the fourth step is to fill the space of the auxiliary furnace chamber 12. In summary, according to the pre-configured first air inlet The rate-controlled second air inlet 15 takes in air first. When the air intake reaches nitrogen equal to the volume of the lower space, the second step is entered. According to the difference between the volume of the crucible and the volume of the raw material in the crucible, and the ratio of the volume of the middle space, the first air intake rate is multiplied by the first air intake rate to obtain the second air intake rate of the third control valve 4 corresponding to the annular air outlet pipeline 19. After the nitrogen equal to the volume of the middle space is filled in again through the second air inlet 15, the third step is entered. In the third step, the product of the ratio of the volume of the extended area of ​​the crucible of each layer to the remaining space in the furnace of the same layer and the first air intake rate is used as the third air intake rate of the third control valve 4 corresponding to the annular air outlet pipeline 19. Whenever the air intake of the second air inlet 15 is the same as the volume of the remaining space in the furnace of the current layer, the third air intake rate is adjusted until the upper space is filled. Then the fourth step is entered to maintain the third air intake rate and the first air intake rate until the auxiliary furnace chamber 12 is also filled. For determining the difference between the capacity of the crucible and the volume of the raw material in the crucible in the second step, the mass of the raw material can be determined first, and the volume of the raw material can be calculated based on the known density of the raw material, and then the final difference can be determined.

[0037] During the crystal pulling process, nitrogen is purged from top to bottom through the first air inlet 13 to remove impurities in the crystal pulling process; the amount of impurities is determined by sampling and detecting the gas at the first air outlet 14, and then the rate of the purging airflow is controlled to ensure that the impurities are removed as much as possible. Specifically, the sampling and detection can be performed by a dust particle counter; according to the monitoring results of the dust particle counter and the current rate, the pre-configured rate control table is queried to obtain the target rate; and the rate is adjusted according to the target rate; the monitoring results, the current rate and the target rate in the rate control table are correspondingly associated. In addition, the air distribution plate 21 is set to evenly distribute the airflow and control the direction of the airflow.

[0038] In order to guide the purge gas flow, the telescopic mechanism 18 can be controlled to place the annular gas outlet pipe 19 at a preset height (any value between 1 cm and 2 cm) above the upper surface of the liquid, and exhaust gas to the periphery to guide the direction of the nitrogen gas flow entering from the first gas inlet 13. The rate of nitrogen introduction into the annular gas outlet pipe 19 is any value between 1 / 10 and 1 / 2 of the rate of nitrogen introduction into the first gas inlet 13.

[0039] In addition, the annular gas outlet pipeline 19 can also be used to flush the crucible at the end of crystal pulling or before the start of crystal pulling to remove the attached trace gas and impurities.

[0040] In one embodiment, a nitrogen protection system for crystal pulling includes: a nitrogen storage device 1, a first control valve 2, a second control valve 3, a third control valve 4 and a control module 5;

[0041] Among them, the control module 5 is electrically connected to the first control valve 2, the second control valve 3 and the third control valve 4 respectively; one end of the first control valve 2 is connected to the nitrogen storage device 1, and the other end is connected to the first air inlet 13 arranged on one side of the upper end of the auxiliary furnace chamber 12 of the crystal pulling furnace; one end of the second control valve 3 is connected to the nitrogen storage device 1, and the other end is connected to the second air inlet 15 arranged at the bottom of the main furnace chamber 11 of the crystal pulling furnace; one end of the third control valve 4 is connected to the nitrogen storage device 1, and the other end is connected to the third air inlet 17 arranged on the upper end of one side of the main furnace chamber 11 of the crystal pulling furnace.

[0042] Among them, at least one air distribution plate 21 is arranged at the upper end of the auxiliary furnace chamber 12; a through hole is arranged in the middle of the air distribution plate 21. A plurality of first air outlets 14 are arranged at the bottom of the main furnace chamber 11. A plurality of second air outlets 16 are arranged on the furnace top of the auxiliary furnace chamber 12. The third air inlet 17 is connected to an annular air outlet pipeline 19 arranged above the crucible through a pipeline; the annular air outlet pipeline 19 is fixed to the upper end of the main furnace chamber 11 through at least one telescopic mechanism 18. The annular air outlet pipeline 19 is provided with two left and right air ducts. A plurality of air outlet holes are evenly distributed on the circumference on the inner and outer sides of the annular air outlet pipeline 19. The left and right air ducts are respectively connected to the air outlet holes arranged on the outer periphery and the inner periphery.

[0043] like Figure 3 As shown, the method for accurately controlling the flow rate of the nitrogen protection system for crystal pulling includes:

[0044] Step 1: Before feeding the raw materials into the crucible of the crystal pulling furnace, control the telescopic mechanism to extend the annular gas outlet pipeline into the bottom of the crucible;

[0045] Step 2: Add raw materials, control the third control valve and the second control valve to open, and fill nitrogen into the crystal pulling furnace;

[0046] Step 3, controlling the first air outlet to close and sampling and testing the air out of the second air outlet;

[0047] Step 4: When the detection data meets the preset conditions, the third control valve and the second control valve are controlled to close, the filling of nitrogen into the crystal pulling furnace is stopped, and the telescopic mechanism is controlled to move the annular gas outlet pipeline out of the crucible.

[0048] The gas outflow from the second gas outlet is detected by an oxygen content detector or a nitrogen content detector, and when the oxygen content is less than or equal to a preset first threshold value or the nitrogen content is greater than or equal to a preset second threshold value, it is determined that the detection data meets the preset conditions;

[0049] In addition, if Figure 4 As shown, the flow precision control method also includes:

[0050] Step S1, during the crystal pulling process, controlling the first control valve to open so that the first air inlet injects nitrogen into the furnace at a preset initial rate;

[0051] Step S2, controlling the second air outlet to close and sampling and testing the air out of the first air outlet;

[0052] Step S3: controlling the air intake rate of the first air inlet according to the detection data.

[0053] In order to guide the purge gas flow, the telescopic mechanism can be controlled to place the annular gas outlet pipeline at a preset height (any value between 1 cm and 2 cm) above the upper surface of the liquid, and the gas is discharged to the periphery to guide the direction of the nitrogen gas flow entering the first gas inlet. The rate of nitrogen introduced into the annular gas outlet pipeline is any value between 1 / 10 and 1 / 2 of the rate of nitrogen introduced into the first gas inlet, and the crystal pulling product is blown and cooled through the inner peripheral gas outlet; the rate of the inner periphery is any value between 1 / 10 and 1 / 2 of the outer peripheral rate. At this time, multiple third control valves need to be configured, and the third control valves are divided into two groups, which are respectively connected to the airways on both sides to achieve separate control.

[0054] In addition, when the inside of the crucible is purged after the raw materials are placed, the ratio of the air intake volume of the air channel located in the outer circle to the air intake volume of the air channel located in the inner circle is controlled to be any value between 1:2 and 1:10.

[0055] In one embodiment, the connecting pipeline between the third control valve 17 and the annular gas outlet pipeline 19 is connected to the side wall inside the furnace through an elastic body 20, so as to avoid interference with the crystal pulling action when the telescopic mechanism 18 is extended or retracted.

[0056] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A nitrogen protection system for crystal pulling, It is characterized in that include: A nitrogen storage device, a first control valve, a second control valve, a third control valve and a control module; Among them, the control module is electrically connected to the first control valve, the second control valve and the third control valve respectively; one end of the first control valve is connected to the nitrogen storage device, and the other end is connected to the first air inlet arranged on one side of the upper end of the auxiliary furnace chamber of the crystal pulling furnace; one end of the second control valve is connected to the nitrogen storage device, and the other end is connected to the second air inlet arranged at the bottom of the main furnace chamber of the crystal pulling furnace; one end of the third control valve is connected to the nitrogen storage device, and the other end is connected to the third air inlet arranged on the upper end of one side of the main furnace chamber of the crystal pulling furnace.

2. The nitrogen protection system for crystal pulling according to claim 1, It is characterized in that At least one air distribution plate is arranged at the upper end of the furnace-attached chamber; a through hole is arranged in the middle of the air distribution plate.

3. The nitrogen protection system for crystal pulling according to claim 1, It is characterized in that A plurality of first air outlets are arranged at the bottom of the main furnace chamber.

4. The nitrogen protection system for crystal pulling according to claim 1, It is characterized in that A plurality of second air outlets are arranged on the furnace top of the auxiliary furnace chamber.

5. The nitrogen protection system for crystal pulling according to claim 1, It is characterized in that The third gas inlet is connected to an annular gas outlet pipeline arranged above the crucible through a pipeline; the annular gas outlet pipeline is fixed to the upper end of the main furnace chamber through at least one telescopic mechanism.

6. The nitrogen protection system for crystal pulling according to claim 5, It is characterized in that A plurality of air outlet holes are evenly distributed on the outer circumference of the annular air outlet pipe.

7. The nitrogen protection system for crystal pulling according to claim 5, It is characterized in that The annular air outlet pipeline is provided with two left and right air passages.

8. The nitrogen protection system for crystal pulling according to claim 6, It is characterized in that A plurality of air outlet holes are evenly distributed on the circumference of the inner and outer sides of the annular air outlet pipe.

9. A method for precise flow control, applied to the nitrogen protection system for crystal pulling as claimed in any one of claims 1 to 8, It is characterized in that include: Before feeding the raw materials into the crucible of the crystal pulling furnace, the telescopic mechanism is controlled to extend the annular gas outlet pipeline into the bottom of the crucible; Put in raw materials, control the third control valve and the second control valve to open, and fill nitrogen into the crystal pulling furnace; Control the first air outlet to close and perform sampling and detection on the air outflow from the second air outlet; When the detection data meets the preset conditions, the third control valve and the second control valve are controlled to close, the filling of nitrogen into the crystal pulling furnace is stopped, and the telescopic mechanism is controlled to move the annular gas outlet pipeline out of the crucible.

10. The flow rate precision control method according to claim 9, It is characterized in that Also includes: During the crystal pulling process, the first control valve is controlled to open so that the first gas inlet injects nitrogen into the furnace at a preset initial rate; Controlling the second air outlet to close and sampling and testing the air out of the first air outlet; The air intake rate of the first air intake port is controlled according to the detection data.

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