Crystal pulling method for reducing microdefects in large-size crystal bar

Abstract

A crystal pulling method for reducing microdefects in a large-size crystal bar relates to the field of crystal bar pulling and comprises the steps of feeding, melting, necking growth, shouldering growth, equal-diameter growth and tail growth. Wherein after charging is completed, high-purity nitrogen with the purity being 99% or above is firstly charged, the pressure of the nitrogen is 0.08-0.6 MPa, and then the high-purity nitrogen is heated to 1500 DEG C or above to melt the monocrystalline silicon raw material; in the equal-diameter growth process, the furnace pressure of the single crystal furnace is adjusted to be 16 kPa to 38 kPa, and the nitrogen flow is adjusted to be 59 slpm to 101 slpm. By optimizing process parameters, particularly replacing argon with high-purity nitrogen, and accurately controlling conditions such as furnace pressure, nitrogen flow, magnetic field intensity and the like, microdefects in the crystal are remarkably reduced, and the mechanical strength and the yield of the crystal are improved.

Description

Technical Field

[0001] The present invention relates to the field of crystal bar pulling, and specifically to a crystal pulling method for reducing microdefects in large-size crystal bars. Background Art

[0002] During the pulling process of large-size crystal bars, the generated native microdefects (such as COP, FPD, LSTD, LPD, etc.) are the main factors affecting the quality of silicon wafers. Semiconductor silicon wafers are usually used to manufacture microelectronic components. In the rapidly developing silicon technology, the requirements for the quality of semiconductor wafers are getting higher and higher. Regardless of the manifestation forms of these microdefects, they are essentially octahedral cavity defects composed of vacancies. The inner walls of the cavities are silicon dioxide precipitates several nanometers thick, with sizes around 100 to 200 nanometers. These microdefects have an important impact on the performance and yield of very large scale integrated circuits.

[0003] Microdefects will also seriously affect the performance uniformity of end products. These microdefects will cause a significant reduction in the local carrier mobility or an increase in leakage current. Under a high-power magnifying glass, these tiny defect points can be seen. They are like fine cracks, damaging the crystal structure, and the internal electric field distribution of the crystal will also become uneven accordingly, resulting in the phenomenon of electric field concentration or electric field shielding effect in local areas, thereby further exacerbating the performance non-uniformity, making the performance of the entire device unstable and affecting the reliability and stability of the final product.

[0004] In the prior art, argon is mostly used as a protective gas during the crystal pulling process. However, argon has limited inhibitory effect on microdefects and high cost. Therefore, there is an urgent need for a crystal pulling method that can effectively reduce microdefects and improve the crystal quality. Summary of the Invention

[0005] The present invention provides a crystal pulling method for reducing microdefects in large-size crystal bars. By optimizing process parameters, especially by using high-purity nitrogen to replace argon and combining with precise control of conditions such as furnace pressure, nitrogen flow rate, and magnetic field strength, the microdefects in the crystal are significantly reduced, and the mechanical strength and wafer yield of the crystal are improved.

[0006] To achieve the above object, the specific solution adopted by the present invention is: a crystal pulling method for reducing microdefects in large-size crystal bars, including feeding, melting, necking growth, shoulder growth, isodiametric growth, and tail growth; among them, after the feeding is completed, high-purity nitrogen with a purity of more than 99% is first filled, the nitrogen pressure is 0.08 - 0.6 MPa, and then it is heated to above 1500 °C to melt the single-crystal silicon raw material; during the isodiametric growth process, the furnace pressure of the single-crystal furnace is adjusted to 16 kPa - 38 kPa, and the nitrogen flow rate is adjusted to 59 slpm - 101 slpm.

[0007] As a further optimization of the above technical solution: The crystal pulling method specifically includes the following steps.

[0008] S1. Feeding: Put the single-crystal silicon raw material into the crucible in the single-crystal furnace.

[0009] S2. Melting: After closing the single-crystal furnace and evacuating, fill it with high-purity nitrogen. The purity of the nitrogen is above 99%, the nitrogen pressure is 0.08 - 0.6 MPa, and heat it to above 1500 °C to melt the single-crystal silicon raw material into a silicon melt.

[0010] S3. Necking growth: After the temperature of the silicon melt stabilizes, slowly immerse the seed crystal into the silicon melt, and quickly lift the seed crystal upward so that the diameter of the grown seed crystal is reduced to 4 - 6 mm to form a thin neck.

[0011] S4. Shoulder growth: After growing the thin neck, reduce the pulling speed so that the diameter of the crystal increases to the required size to form a shoulder.

[0012] S5. Equal-diameter growth: After growing the thin neck and the shoulder, control the pulling speed and temperature to achieve equal-diameter growth.

[0013] S6. Tail growth: After completing the equal-diameter growth, first reduce the diameter of the crystal bar until a pointed tip is formed and separated from the liquid surface. The grown crystal bar is lifted to the upper furnace chamber for cooling and then taken out, thus completing one growth cycle.

[0014] As a further optimization of the above technical solution: In step S6, after the equal-diameter growth ends, reduce the diameter of the crystal bar at a speed of 0.2 mm per minute until a pointed tip is formed and separated from the liquid surface.

[0015] As a further optimization of the above technical solution: During the melting process, the nitrogen flow rate is 120 - 150 L / min.

[0016] As a further optimization of the above technical solution: During the equal-diameter growth process, adjust the magnetic field center position according to the central position of the silicon liquid height so that the magnetic field center position is flush with the central position of the silicon liquid height.

[0017] As a further optimization of the above technical solution: The method for controlling the magnetic field center position to be flush with the central position of the silicon liquid height is specifically as follows: Determine the silicon liquid height according to the pulling speed of the equal-diameter growth to obtain the central position of the silicon liquid height, and then adjust the magnetic field according to the central position of the silicon liquid height so that the magnetic field center position is flush with the central position of the silicon liquid height.

[0018] As a further optimization of the above technical solution: During the equal-diameter growth process, the intensity of the magnetic field is 2000 Gs - 2200 Gs.

[0019] As a further optimization of the above technical solution: during the isodiametric growth process, the crucible rotation speed is maintained at 0.6 rpm to 7.5 rpm, and the crystallization rotation speed is 12 rpm to 18 rpm.

[0020] As a further optimization of the above technical solution: during the isodiametric growth process, the liquid outlet distance is adjusted to 25 mm to 36 mm.

[0021] As a further optimization of the above technical solution: during the isodiametric growth process, the continuous adjustment of the pulling speed and temperature is controlled to keep the diameter of the crystal bar within plus or minus 2 mm.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention significantly reduces the micro-defects of single-crystalline silicon and improves the survival rate of crystals by finely adjusting the furnace pressure, liquid outlet distance, gas flow rate, crucible rotation speed, and crystallization rotation speed during the isodiametric process. During this process, the precise control of the furnace pressure ensures the stable flow of the silicon melt, and the optimization of the liquid outlet distance effectively prevents the melt from splashing and uneven cooling, further reducing the generation of micro-defects. The adjustment of the gas flow rate replaces the traditional argon gas flow with a nitrogen gas flow, greatly suppressing the micro-defects in silicon, enhancing the mechanical strength of the silicon material, significantly increasing the wafer yield, and having a low breakage rate, thus significantly reducing the production cost of single-crystalline silicon. In addition, the use of nitrogen gas flow also enhances the internal gettering ability of the silicon wafer, improves the mechanical strength of the silicon wafer, suppresses the void-type defects, and further greatly suppresses the micro-defects in silicon. Specific Embodiments

[0024] The following further elaborates on the technical solution of the present invention in combination with specific embodiments. For parts not detailedly recorded and disclosed in the following embodiments of the present invention, such as the specific structures of the crucible and the single-crystal furnace, etc., they should all be understood as the prior art known or should be known to those skilled in the art.

[0025] The crystal pulling method of the present invention includes steps such as feeding, melting, necking growth, shoulder growth, isodiametric growth, and tail growth, as follows:

[0026] S1. Feeding: Put the single-crystalline silicon raw material into the quartz crucible in the single-crystal furnace.

[0027] S2. Melting: After closing the single-crystal furnace and evacuating, fill it with high-purity nitrogen with a purity of more than 99%. The nitrogen pressure is controlled at 0.08 - 0.6 MPa, and then heated to above 1500 °C to melt the single-crystalline silicon raw material into a silicon melt. During the melting process, the nitrogen gas flow rate is maintained at 120 - 150 L / min.

[0028] S3, Necking growth: After the temperature of the silicon melt stabilizes, slowly immerse the seed crystal into the silicon melt, and then quickly lift the seed crystal upward so that the diameter of the grown seed crystal is reduced to 4 - 6 mm to form a thin neck.

[0029] S4, Shoulder growth: After the necking growth is completed, reduce the pulling speed so that the crystal diameter gradually increases to the required size to form a shoulder.

[0030] S5, Equal-diameter growth: After the neck and shoulder growth are completed, enter the equal-diameter growth stage. In this stage, continuously adjust the pulling speed and temperature so that the diameter of the crystal bar is maintained between plus or minus 2 mm; adjust the furnace pressure of the single crystal furnace to 16 kPa - 38 kPa, and the nitrogen flow rate to 59 slpm - 101 slpm; adjust the magnetic field center position according to the center position of the silicon liquid height so that the magnetic field center position is flush with the center position of the silicon liquid height, and the magnetic field intensity is maintained at 2000 Gs - 2200 Gs; keep the crucible rotation speed at 0.6 rpm - 7.5 rpm, and the crystallization rotation speed at 12 rpm - 18 rpm; adjust the liquid orifice distance to 25 mm - 36 mm.

[0031] S6, Tail growth: After the equal-diameter growth ends, gradually reduce the diameter of the crystal bar until a sharp point is formed and separated from the liquid surface. The grown crystal bar is lifted to the upper furnace chamber and cooled for a period of time before being taken out to complete one growth cycle.

[0032] Example 1

[0033] S1, Charging: Accurately weigh an appropriate amount of single-crystal silicon raw material and carefully place it into the quartz crucible in the single crystal furnace, ensuring that the raw material is evenly placed to avoid accumulation or deviation.

[0034] S2, Melting: Close the single crystal furnace and start the vacuum pump to evacuate the furnace to a certain vacuum degree. Subsequently, fill it with high-purity nitrogen with a purity of 99.9%, so that the nitrogen pressure reaches 0.3 MPa, turn on the heating device, and slowly raise the temperature to 1550 °C. During the entire melting process, keep the nitrogen flow rate at 130 L / min until the single-crystal silicon raw material is completely melted into a silicon melt.

[0035] S3, Necking growth: When the temperature of the silicon melt stabilizes at 1550 °C, slowly immerse the seed crystal into the silicon melt at a speed of 0.1 mm per second. After the seed crystal is fully in contact with the silicon melt, quickly lift the seed crystal upward at a speed of 1 mm per second until the diameter of the grown seed crystal is reduced to 5 mm to form a thin neck.

[0036] S4, Shoulder growth: After the necking growth is completed, reduce the pulling speed to 0.5 mm per minute. As time goes by, the crystal diameter gradually increases. During the growth process, closely monitor the change in the crystal diameter. When the diameter reaches the required size, stop adjusting the pulling speed and the shoulder growth is completed.

[0037] S5. Equal-diameter growth: Enter the equal-diameter growth stage, continuously adjust the pulling speed and temperature to keep the diameter of the ingot stable within the range of the target size ±2 mm. Adjust the pressure in the single crystal furnace to 25 kPa, and the nitrogen flow rate is 80 slpm; calculate the height of the silicon melt according to the pulling speed, determine the center position of the silicon melt height, adjust the magnetic field to make the center position of the magnetic field coincide with the center position of the silicon melt height, and keep the magnetic field intensity at 2100 Gs; set the crucible rotation speed to 4 rpm and the crystallization rotation speed to 15 rpm; adjust the liquid orifice distance to 30 mm. During the entire equal-diameter growth process, continuously monitor various parameters to ensure their stability.

[0038] S6. Tail growth: After the equal-diameter growth ends, gradually reduce the pulling speed, and reduce the diameter of the ingot at a speed of 0.2 mm per minute until a cusp is formed and separated from the liquid surface. Lift the grown ingot to the upper furnace chamber, cool it in the furnace chamber for 2 hours, and then take it out to complete one growth cycle.

[0039] Example 2

[0040] S1. Feeding: Accurately weigh an appropriate amount of single crystal silicon raw material and carefully place it into the quartz crucible in the single crystal furnace, ensuring that the raw material is evenly placed to avoid accumulation or deviation.

[0041] S2. Melting: Close the single crystal furnace, start the vacuum pump to evacuate the furnace to a certain vacuum degree. Then, fill it with high-purity nitrogen with a purity of 99.2%, make the nitrogen pressure reach 0.6 MPa, turn on the heating device, and slowly raise the temperature to 1580 °C. During the entire melting process, keep the nitrogen flow rate at 150 L / min until the single crystal silicon raw material is completely melted into a silicon melt.

[0042] S3. Necking growth: When the temperature of the silicon melt stabilizes at 1580 °C, slowly immerse the seed crystal into the silicon melt. After the seed crystal is fully in contact with the silicon melt, lift the seed crystal upward until the diameter of the grown seed crystal is reduced to 5 mm to form a thin neck.

[0043] S4. Shoulder growth: After the necking growth is completed, reduce the pulling speed. As time goes by, the crystal diameter gradually increases. During the growth process, closely monitor the change in the crystal diameter. When the diameter reaches the required size, stop adjusting the pulling speed, and the shoulder growth is completed.

[0044] S5. Equal-diameter growth: Enter the equal-diameter growth stage, continuously adjust the pulling speed and temperature to keep the diameter of the ingot stable within the range of the target size ±2 mm. Adjust the pressure in the single crystal furnace to 16 kPa, and the nitrogen flow rate is 101 slpm; calculate the height of the silicon melt according to the pulling speed, determine the central position of the silicon melt height, adjust the magnetic field so that the central position of the magnetic field is flush with the central position of the silicon melt height, and keep the magnetic field strength at 2000 Gs; set the crucible rotation speed to 7.5 rpm and the crystallization rotation speed to 12 rpm; adjust the liquid orifice distance to 36 mm. During the entire equal-diameter growth process, continuously monitor various parameters to ensure their stability.

[0045] S6. Tail growth: After the equal-diameter growth ends, gradually reduce the pulling speed, and reduce the diameter of the ingot at a speed of 0.2 mm per minute until a cusp is formed and separated from the liquid surface. Lift the grown ingot to the upper furnace chamber, cool it in the furnace chamber for 2 hours, and then take it out to complete one growth cycle.

[0046] Example 3

[0047] S1. Loading: Accurately weigh an appropriate amount of single-crystal silicon raw material and carefully place it into the quartz crucible in the single crystal furnace, ensuring that the raw material is evenly placed to avoid accumulation or deviation.

[0048] S2. Melting: Close the single crystal furnace, start the vacuum pump to evacuate the furnace to a certain vacuum degree. Then fill it with high-purity nitrogen with a purity of 99.2%, make the nitrogen pressure reach 0.08 MPa, turn on the heating device, and slowly raise the temperature to 1500 °C. During the entire melting process, keep the nitrogen flow rate at 120 L / min until the single-crystal silicon raw material is completely melted into a silicon melt.

[0049] S3. Necking growth: When the temperature of the silicon melt is stable at 1500 °C, slowly immerse the seed crystal into the silicon melt. After the seed crystal is in full contact with the silicon melt, lift the seed crystal upward until the diameter of the grown seed crystal is reduced to 4 mm to form a thin neck.

[0050] S4. Shoulder growth: After the necking growth is completed, reduce the pulling speed. As time goes by, the diameter of the crystal gradually increases. During the growth process, closely monitor the change in the crystal diameter. When the diameter reaches the required size, stop adjusting the pulling speed, and the shoulder growth is completed.

[0051] S5. Equal-diameter growth: Enter the equal-diameter growth stage, continuously adjust the pulling speed and temperature to keep the diameter of the ingot stable within the range of the target size ±2 mm. Adjust the furnace pressure of the single crystal furnace to 38 kPa, and the nitrogen flow rate is 59 slpm; calculate the height of the silicon melt according to the pulling speed, determine the center position of the silicon melt height, adjust the magnetic field to make the center position of the magnetic field coincide with the center position of the silicon melt height, and keep the magnetic field intensity at 2200 Gs; set the crucible rotation speed to 7.0 rpm and the crystallization rotation speed to 18 rpm; adjust the liquid orifice distance to 25 mm. During the entire equal-diameter growth process, continuously monitor various parameters to ensure their stability.

[0052] S6. Tail growth: After the equal-diameter growth is completed, gradually reduce the pulling speed to reduce the diameter of the ingot at a speed of 0.2 mm per minute until a cusp is formed and separated from the liquid surface. Lift the grown ingot to the upper furnace chamber, cool it in the furnace chamber for 2 hours, and then take it out to complete one growth cycle.

[0053] By detecting the ingots prepared in this embodiment, the results show that the number of micro-defects is significantly reduced, and the mechanical strength and wafer yield of the crystal are significantly improved.

[0054] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for reducing micro defects in a large-size crystal rod, comprising feeding, melting, necking growth, shoulder growth, equal diameter growth and tail growth, characterized in that: After the feeding is completed, high-purity nitrogen with a purity of more than 99% is first filled in, the nitrogen pressure is 0.08~0.6MPa, and then heated to above 1500℃ to melt the single crystal silicon raw material; during the equal-diameter growth process, the single crystal furnace pressure is adjusted to 16kPa~38kPa, and the nitrogen flow rate is adjusted to 59slpm~101slpm.

2. A crystal pulling method for reducing micro defects in large-sized crystal ingots according to claim 1, characterized in that: The crystal pulling method specifically comprises the following steps: S1. Adding materials: placing the single crystal silicon raw material into the crucible in the single crystal furnace; S2, melting: close the single crystal furnace, evacuate and fill with high-purity nitrogen, the purity of nitrogen is more than 99%, the nitrogen pressure is 0.08-0.6MPa, heat to more than 1500℃ to melt the single crystal silicon raw material into silicon melt; S3, necking growth: when the temperature of the silicon melt is stable, the seed crystal is slowly immersed in the silicon melt, and the seed crystal is quickly lifted upward to reduce the diameter of the grown seed crystal to 4-6 mm to form a thin neck; S4, shoulder growth: After the neck is grown, the pulling speed is reduced so that the diameter of the crystal increases to the required size to form a shoulder; S5, equal diameter growth: After the thin neck and shoulder are grown, the pulling speed and temperature are controlled to achieve equal diameter growth; S6. Tail growth: After the completion of equal diameter growth, the diameter of the crystal rod is first reduced until a sharp point is formed and separated from the liquid surface. The grown crystal rod is lifted to the upper furnace chamber for cooling and then taken out, completing a growth cycle.

3. A crystal pulling method for reducing micro defects in a large-sized crystal ingot according to claim 2, characterized in that: In step S6, after the equal diameter growth is completed, the diameter of the crystal rod is reduced at a speed of 0.2 mm per minute until a sharp point is formed and separated from the liquid surface.

4. A crystal pulling method for reducing micro defects in a large-sized crystal ingot according to claim 1, characterized in that: During the melting process, the nitrogen flow rate is 120-150 L / min.

5. The crystal pulling method for reducing micro defects in large-sized crystal ingots according to claim 1, characterized in that: During the equal-diameter growth process, the center position of the magnetic field is adjusted according to the center position of the silicon liquid height, so that the center position of the magnetic field is flush with the center position of the silicon liquid height.

6. A crystal pulling method for reducing micro defects in a large-sized crystal ingot according to claim 5, characterized in that: The method for controlling the center position of the magnetic field to be aligned with the center position of the silicon liquid height is specifically as follows: determine the silicon liquid height according to the pulling speed of equal-diameter growth to obtain the center position of the silicon liquid height, and then adjust the magnetic field according to the center position of the silicon liquid height to make the center position of the magnetic field aligned with the center position of the silicon liquid height.

7. A crystal pulling method for reducing micro defects in a large-sized crystal ingot according to claim 6, characterized in that: During the equal-diameter growth process, the intensity of the magnetic field is 2000Gs to 2200Gs.

8. The crystal pulling method for reducing micro defects in large-sized crystal ingots according to claim 1, characterized in that: During the equal diameter growth process, the crucible rotation speed is maintained at 0.6 rpm to 7.5 rpm, and the crystallization rotation speed is maintained at 12 rpm to 18 rpm.

9. A crystal pulling method for reducing micro defects in a large-sized crystal ingot according to claim 1, characterized in that: During the equal diameter growth process, the liquid mouth distance is adjusted to 25mm~36mm.

10. The crystal pulling method for reducing micro defects in a large-sized crystal ingot according to claim 1, characterized in that: During the equal-diameter growth process, the pulling speed and temperature are continuously adjusted to keep the diameter of the crystal rod between plus or minus 2 mm.