Methods to reduce the size of lightly boron-doped Czochralski single-crystal silicon BMD

Abstract

This invention provides a method for reducing BMD (bulk diameter variation) in large-size lightly boron-doped Czochralski single-crystal silicon, belonging to the technical field of lightly doped crystal pulling methods. In different shoulder-forming stages, different shoulder slopes, ingot pulling speeds, crucible rotation speeds, and power adjustment ranges are preset. Specifically: the shoulder slope is the ratio of shoulder height to shoulder diameter, with a slope of 0-1.11; the ingot pulling speed is 54 mm / h to 59 mm / h; the crucible rotation speed is 4 rpm to 5.5 rpm; the ingot rotation speed is 5-8 rpm; the furnace pressure is 8 kPa to 10 kPa; and the power adjustment range... With a power of -2.3kW to -0.5kW, a spire-shaped shoulder with a conical upper part and a frustum-shaped lower part is drawn. This structure has a larger physical volume and mass than the conventional arc-shaped or gently sloping shoulder, which is equivalent to actively constructing an "oxygen impurity enrichment zone" at the crystal head. During the shoulder formation process, the supersaturated oxygen impurities in the melt preferentially accumulate in this thick shoulder region due to the segregation effect and are effectively "locked" in it, thereby significantly reducing the total amount of residual oxygen that can enter the crystal interior during the constant diameter stage, and thus reducing the BMD content during the constant diameter stage.

Description

Technical Field

[0001] This invention relates to the field of lightly doped crystal pulling methods, specifically to a method for reducing BMD in large-size lightly boron-doped Czochralski single-crystal silicon. Background Technology

[0002] As integrated circuit (IC) manufacturing processes continue to evolve towards 7 nm, 5 nm, and even more advanced processes, unprecedented quality requirements are being placed on silicon single-crystal substrates, which serve as device carriers. Micro-defects within the substrate, especially bulk micro-defects (BMDs), have become one of the key bottlenecks restricting device performance and yield.

[0003] In the Czochralski process for growing semiconductor-grade silicon single crystals, crystal growth typically involves the following stages: seed crystal contact and pulling, necking, shouldering, body growth, and tail growth. The shouldering stage is a crucial transition from the necked, narrow-diameter seed crystal to the target diameter body growth stage. Its quality directly determines the crystal integrity, defect distribution, and stability of the subsequent body growth segment.

[0004] Currently, the industry commonly uses a "forked" shoulder formation process in the shoulder formation stage of 12-inch semiconductor-grade silicon single crystals. The "forked" shoulder refers to a crystal shoulder profile that exhibits a distinct forked or multi-faceted shape during the shoulder formation process. This allows for rapid increase in the shoulder diameter to quickly enter the constant-diameter growth stage. This process shortens the shoulder formation time and improves production efficiency to a certain extent, and is therefore widely used in industrial production.

[0005] However, with the continuous miniaturization of integrated circuit manufacturing processes and the shrinking feature sizes of devices, the requirements for defect density in silicon single-crystal substrates are becoming increasingly stringent, highlighting the inherent limitations of traditional "forked" shoulder-type bonding processes. In the "forked" shoulder structure, there are significant abrupt curvature changes at the edge of the crystal shoulder, leading to localized thermal stress concentration in the shoulder region. According to thermoelastic analysis, stress singularities are generated at the curvature discontinuity, and this stress field is sufficient to induce dislocation slip bands in the silicon crystal. These dislocation slip bands not only constitute structural defects in the crystal head region but also become the core sites for the preferential nucleation of bulk microdefects (BMDs)—especially void-type defects—during subsequent cooling. The presence of BMD defects severely degrades the gate oxide integrity (GOI) of the device and significantly increases the leakage current, posing a fatal threat to the reliability of advanced process devices. Summary of the Invention

[0006] In view of this, the present invention provides a method for reducing BMD in large-size lightly boron-doped Czochralski single-crystal silicon.

[0007] The technical solution adopted by this invention to solve its technical problem is:

[0008] A method for reducing the oxygen content in large-size lightly boron-doped Czochralski single-crystal silicon BMD includes the following steps: At different shoulder-growing stages, different shoulder-growing slopes, ingot pulling speeds, crucible rotation speeds, and power adjustment ranges are preset to reduce the oxygen content during the constant-diameter process. The shoulder-growing slope is the ratio of shoulder height to shoulder diameter; the shoulder-growing slope is 0-1.11; the ingot pulling speed is 54 mm / h to 59 mm / h; the crucible rotation speed is 4 rpm to 5.5 rpm; the ingot rotation speed is 5-8 rpm; the furnace pressure is 8 kPa to 10 kPa; and the power adjustment range is -2.3 kW to -0.5 kW.

[0009] Preferably, for pulling 8-inch crystal ingots, the different shoulder-forming stages include a first shoulder-forming stage and a second shoulder-forming stage, wherein the first shoulder-forming stage and the second shoulder-forming stage are a continuous shoulder-forming process;

[0010] For pulling 12-inch crystal ingots, the different shoulder-forming stages include a first shoulder-forming stage, a second shoulder-forming stage, and a third shoulder-forming stage, and the first shoulder-forming stage, the second shoulder-forming stage, and the third shoulder-forming stage are a continuous shoulder-forming process;

[0011] Wherein: the first stage of shoulder expansion refers to a shoulder expansion height from 0 to below 80mm, the second stage of shoulder expansion refers to a shoulder expansion height from above 80mm to below 200mm, and the third stage of shoulder expansion refers to a shoulder expansion height from above 200mm to below 260mm.

[0012] Preferably, in the first stage of shoulder formation, the shoulder slope first increases and then decreases, the crystal rod pulling speed first remains stable and then gradually decreases, the power adjustment range first decreases and then increases, the crucible rotation speed remains stable, and the furnace pressure remains stable.

[0013] Preferably, in the second stage of shoulder formation, the shoulder slope gradually decreases, the crystal rod pulling speed gradually decreases, the power adjustment range first increases and then decreases, the crucible rotation speed first remains stable and then gradually increases, and the furnace pressure first remains stable and then increases.

[0014] Preferably, in the third stage of shoulder formation, the shoulder slope first decreases and then increases, the crystal rod pulling speed first remains stable and then increases and remains stable, the power adjustment range gradually decreases, the crucible rotation speed remains stable, and the furnace pressure remains stable.

[0015] Preferably, the shoulder slope of the first stage of shoulder formation is 0-1.11, the crystal rod pulling speed is 58mm / h~59mm / h, the power adjustment range is -2.3kW~-1.8kW, the crucible rotation speed is 4rpm, and the furnace pressure is 8kPa.

[0016] Preferably, for pulling 12-inch crystal ingots, the shoulder slope of the second stage of shoulder formation is 0.77-1.07, the crystal ingot pulling speed is 54mm / h~58mm / h, the power adjustment range is -2.3kW~-1.5kW, the crucible rotation speed is 4rpm-5.2rpm, and the furnace pressure is 8kPa-9.5kPa.

[0017] Preferably, for pulling 8-inch crystal ingots, the shoulder slope of the second stage of shoulder formation is 0.77-1.07, the crystal ingot pulling speed is 54mm / h~58mm / h, the power adjustment range is -2.3kW~-1.5kW, the crucible rotation speed is 4rpm-5rpm, and the furnace pressure is 8kPa-9kPa.

[0018] Preferably, the shoulder slope of the third stage of shoulder formation is 0.71-0.81, the crystal rod pulling speed is 54mm / h~55mm / h, the power adjustment range is -1.5kW~-0.5kW, the crucible rotation speed is 5.2rpm-5.5rpm, and the furnace pressure is 9.5kPa-10kPa.

[0019] Preferably, the crystal rod rotates at a speed of 5 rpm to 8 rpm.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] This invention provides a method for reducing the oxygen content in large-size, lightly boron-doped Czochralski single-crystal silicon BMDs. Different shoulder-growing slopes, ingot pulling speeds, crucible rotation speeds, and power adjustment ranges are preset at different shoulder-growing stages to reduce the oxygen content during the constant-diameter process. Specifically: the shoulder-growing slope is the ratio of shoulder height to shoulder diameter; the shoulder-growing slope is 0-1.11; the ingot pulling speed is 54 mm / h to 59 mm / h; the crucible rotation speed is 4 rpm to 5.5 rpm; the ingot rotation speed is 5-8 rpm; the furnace pressure is 8 kPa to 10 kPa; and the power adjustment range is -2.3 kW to -0.5 kW. This method produces a pyramidal shoulder structure with a conical upper part and a frustum-shaped lower part. This structure has a larger physical volume and mass than conventional arc-shaped or gently sloping shoulder structures, effectively creating an "oxygen impurity enrichment region" at the crystal head. During the shoulder formation process, supersaturated oxygen impurities in the melt preferentially accumulate in the thick shoulder region due to segregation effect and are effectively "locked in," thereby significantly reducing the total amount of residual oxygen that can enter the crystal interior during the constant diameter stage. Therefore, the oxygen concentration in the melt is already at a lower level at the start of constant diameter growth, and its bulk microdefect (BMD) is significantly reduced. At the same time, the spire-shaped shoulder acts as a "buffer zone" in subsequent constant diameter growth, effectively suppressing oxygen re-incorporation caused by melt convection fluctuations. Thus, actively enriching oxygen during the shoulder formation stage allows the oxygen content of the constant diameter section of the crystal rod to be stably reduced to below the target threshold, resulting in a significant decrease in bulk microdefect (BMD) density. Oxygen precipitation nucleation inside the constant diameter crystal rod is effectively suppressed, ultimately yielding a high-purity, low-defect, large-size, lightly boron-doped Czochralski single-crystal silicon product. Attached Figure Description

[0022] Figure 1 These are images of the shoulder shape in Examples 1 and 2.

[0023] Figure 2 This is a picture of a shoulder shape at scale 1.

[0024] Figure 3 This is a graph showing the oxygen content results for Example 1 and Comparative Example 1.

[0025] Figure 4 This is a diagram showing the BMD test data method for Example 1 and Comparative Example 1.

[0026] Figure 5 The images show the BMD results for Example 1 and Comparative Example 1.

[0027] Figure 6 Box plots showing the survival rates of Example 1, Comparative Example 1, and Comparative Example 2.

[0028] in: Figure 3 Example 1 is the oxygen value of the example, Comparative Example 1 is the oxygen value of the prior art comparative example, and the average oxygen value of the comparative example is the average value of mass-produced using the process of Comparative Example 1. Figure 5Example 1 is the BMD value of the example, Comparative Example 1 is the BMD value of the prior art comparative example, and the average BMD of the comparative examples is the average value of mass production using the process of Comparative Example 1. Figure 6 Comparative Example 1 shows the survival rate of the prior art, Comparative Example 2 shows the survival rate of the embodiment, and Embodiment 1 shows the survival rate of the optimized furnace pressure embodiment. Detailed Implementation

[0029] To facilitate understanding of this application, a more comprehensive description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are also given. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to enable a more thorough and complete understanding of the disclosure of this application.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0031] During single crystal growth, silicon material is first placed in a quartz crucible, then the single crystal furnace is shut off and evacuated, and a protective gas is introduced into the furnace. For example, the protective gas is argon. Then, the heater is turned on, and the silicon material is heated until it is completely melted into molten silicon.

[0032] Next, the seed crystal is immersed in the silicon melt, and rotated and slowly pulled up by the seed crystal axis, so that silicon atoms grow along the seed crystal to form a single-crystal silicon rod. The seed crystal is cut or drilled from a silicon single crystal with a certain crystal orientation, and the seed crystal is generally cylindrical. The growth process of the single-crystal silicon rod includes several stages in sequence, including crystal introduction, shoulder formation, shoulder rotation, equal diameter formation, and finishing.

[0033] Specifically, the first step is the seed crystal stage. Once the silicon melt has stabilized at a certain temperature, a seed crystal is immersed in the melt and pulled at a controlled rate, causing silicon atoms to grow along the seed crystal into a narrow neck of a certain diameter until the neck reaches a predetermined length. The main purpose of this seed crystal process is to eliminate dislocation defects in single-crystal silicon caused by thermal shock. The supercooling at the crystallization front drives silicon atoms to arrange themselves sequentially on the solid silicon at the solid-liquid interface, forming single-crystal silicon.

[0034] Then, the shoulder-forming stage begins. Once the neck reaches the predetermined length, the upward pulling speed of the seed crystal is slowed down, and the temperature of the silicon melt is slightly reduced. This cooling is to promote the lateral growth of the single crystal silicon, which increases the diameter of the single crystal silicon. This process is called the shoulder-forming stage.

[0035] Next, the shoulder-turning stage begins. When the diameter of the single-crystal silicon increases to the target diameter, the heating power of the heater is increased to raise the temperature of the silicon melt. At the same time, the upward pulling speed of the seed crystal, the rotation speed, and the rotation speed of the quartz crucible are adjusted to suppress the lateral growth of the single-crystal silicon and promote its longitudinal growth, so that the single-crystal silicon grows to a near-constant diameter.

[0036] Then, the constant diameter stage begins. Once the diameter of the single-crystal silicon ingot reaches the predetermined value, the constant diameter stage begins, and the cylindrical ingot formed in this stage is the constant diameter section of the ingot. Specifically, the crucible temperature, pulling speed, crucible rotation speed, and crystal rotation speed are adjusted to stabilize the growth rate and keep the crystal diameter constant until the pulling process is complete. The constant diameter process is the main stage of single-crystal silicon growth, lasting for tens of hours.

[0037] Finally, the finishing stage begins. During this stage, the lifting rate is increased while the temperature of the molten silicon is raised, causing the crystal rod diameter to gradually decrease, forming a cone shape. When the tip of the cone is small enough, it will eventually leave the molten surface. The finished crystal rod is then lifted into the upper furnace chamber to cool for a period of time before being removed, thus completing one growth cycle.

[0038] In response to the problems raised in the background art, the technical solution adopted by the present invention is as follows:

[0039] A method for reducing the size of large-size lightly boron-doped Czochralski single-crystal silicon BMD includes the following steps: At different shoulder-growing stages, different shoulder-growing slopes, ingot pulling speeds, crucible rotation speeds, and power adjustment ranges are preset to reduce the oxygen content during the constant-diameter process. Specifically, the shoulder-growing slope is the ratio of shoulder height to shoulder diameter, and the slope range is 0-1.11 to meet the requirements of thermal field inertia, oxygen segregation efficiency, and V / G window width, thereby increasing the shoulder volume. The ingot pulling speed is 54 mm / h to 59 mm / h, the crucible rotation speed is 4 rpm to 5.5 rpm, the ingot rotation speed is 5-8 rpm, the furnace pressure is 8 kPa to 10 kPa, and the power adjustment range is -2.3 kW to -0.5 kW.

[0040] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0041] This invention provides a method for reducing the oxygen content in large-size, lightly boron-doped Czochralski single-crystal silicon BMDs. Different shoulder-growing slopes, ingot pulling speeds, crucible rotation speeds, and power adjustment ranges are preset at different shoulder-growing stages to reduce the oxygen content during the constant-diameter process. Specifically: the shoulder-growing slope is the ratio of shoulder height to shoulder diameter; the shoulder-growing slope is 0-1.11; the ingot pulling speed is 54 mm / h to 59 mm / h; the crucible rotation speed is 4 rpm to 5.5 rpm; the ingot rotation speed is 5-8 rpm; the furnace pressure is 8 kPa to 10 kPa; and the power adjustment range is -2.3 kW to -0.5 kW. This method produces a pyramidal shoulder structure with a conical upper part and a frustum-shaped lower part. This structure has a larger physical volume and mass than conventional arc-shaped or gently sloping shoulder structures, effectively creating an "oxygen impurity enrichment region" at the crystal head. During the shoulder formation process, supersaturated oxygen impurities in the melt preferentially accumulate in the thick shoulder region due to segregation effect and are effectively "locked in," thereby significantly reducing the total amount of residual oxygen that can enter the crystal interior during the constant diameter stage. Therefore, the oxygen concentration in the melt is already at a lower level at the start of constant diameter growth, and its bulk microdefect (BMD) is significantly reduced. At the same time, the spire-shaped shoulder acts as a "buffer zone" in subsequent constant diameter growth, effectively suppressing oxygen re-incorporation caused by melt convection fluctuations. Thus, actively enriching oxygen during the shoulder formation stage allows the oxygen content of the constant diameter section of the crystal rod to be stably reduced to below the target threshold, resulting in a significant decrease in bulk microdefect (BMD) density. Oxygen precipitation nucleation inside the constant diameter crystal rod is effectively suppressed, ultimately yielding a high-purity, low-defect, large-size, lightly boron-doped Czochralski single-crystal silicon product.

[0042] Furthermore, for pulling 8-inch crystal ingots, the different shoulder-forming stages include a first shoulder-forming stage and a second shoulder-forming stage, wherein the first shoulder-forming stage and the second shoulder-forming stage are continuous shoulder-forming processes;

[0043] For pulling 12-inch crystal ingots, the different shoulder-forming stages include a first shoulder-forming stage, a second shoulder-forming stage, and a third shoulder-forming stage, and the first shoulder-forming stage, the second shoulder-forming stage, and the third shoulder-forming stage are a continuous shoulder-forming process;

[0044] Wherein: the first stage of shoulder expansion refers to a shoulder expansion height from 0 to below 80mm, the second stage of shoulder expansion refers to a shoulder expansion height from above 80mm to below 200mm, and the third stage of shoulder expansion refers to a shoulder expansion height from above 200mm to below 260mm.

[0045] Furthermore, in the first stage of shoulder formation, the shoulder slope first increases and then decreases, the crystal rod pulling speed first remains stable and then gradually decreases, the power adjustment range first decreases and then increases, the crucible rotation speed remains stable, and the furnace pressure remains stable.

[0046] Furthermore, in the second stage of shoulder formation, the shoulder slope gradually decreases, the crystal rod pulling speed gradually decreases, the power adjustment range first increases and then decreases, the crucible rotation speed first remains stable and then gradually increases, and the furnace pressure first remains stable and then increases.

[0047] Furthermore, in the third stage of shoulder formation, the shoulder slope first decreases and then increases, the crystal rod pulling speed first remains stable and then increases and remains stable, the power adjustment range gradually decreases, the crucible rotation speed remains stable, and the furnace pressure remains stable.

[0048] Increasing furnace pressure in the second and third stages of the shoulder-setting process enhances the cooling efficiency of argon gas. At the same time, in conjunction with measures such as power, it buffers the thermal field fluctuations caused by crucible rotation, ensuring the microscopic stability of the solid-liquid interface and providing a stable environment for oxygen segregation and V / G control.

[0049] During the shoulder-forming process, a three-layer collaborative control architecture is used: "crate rotation adjustment V / G + furnace pressure buffering thermal disturbance + pulling speed / power linkage adjustment K". A clear adjustment strategy is implemented: when the K value deviation is small, the pulling speed is adjusted first; when the deviation is large, the pulling speed and power linkage are activated; and when there is a risk of forking, the pulling speed is temporarily suspended and the crucible rotation is adjusted instead. Multiple control objectives are decoupled and processed in layers, upgrading "constant diameter section remediation" to "shoulder-forming section prevention" to reduce BMD (Body Mass Degradation).

[0050] Furthermore, the shoulder slope of the first stage of shoulder formation is 0-1.11, the crystal rod pulling speed is 58mm / h~59mm / h, the power adjustment range is -2.3kW~-1.8kW, the crucible rotation speed is 4rpm, and the furnace pressure is 8kPa.

[0051] Furthermore, for pulling 12-inch crystal ingots, the shoulder slope of the second stage of shoulder formation is 0.77-1.07, the crystal ingot pulling speed is 54mm / h~58mm / h, the power adjustment range is -2.3kW~-1.5kW, the crucible rotation speed is 4rpm-5.2rpm, and the furnace pressure is 8kPa-9.5kPa.

[0052] Furthermore, for pulling 8-inch crystal ingots, the shoulder slope of the second stage of shoulder formation is 0.77-1.07, the crystal ingot pulling speed is 54mm / h~58mm / h, the power adjustment range is -2.3kW~-1.5kW, the crucible rotation speed is 4rpm-5rpm, and the furnace pressure is 8kPa-9kPa.

[0053] Furthermore, the shoulder slope of the third stage of shoulder formation is 0.71-0.81, the crystal rod pulling speed is 54mm / h~55mm / h, the power adjustment range is -1.5kW~-0.5kW, the crucible rotation speed is 5.2rpm-5.5rpm, and the furnace pressure is 9.5kPa-10kPa.

[0054] Furthermore, the shoulder slope is controlled through the following steps:

[0055] S1: Obtain the shoulder slope and actual shoulder diameter for different shoulder heights;

[0056] S2: Based on the actual shoulder diameter at different shoulder heights, the actual slope of different shoulder diameters is obtained through a predetermined calculation formula;

[0057] S3: Compare the actual slope of different shoulder heights with the shoulder slope to obtain the slope difference ΔK;

[0058] S4: Use the slope difference ΔK as the input of the PID to obtain the crystal pulling speed adjustment value of the PID output, so that the actual slope of different shoulder heights is the same as the shoulder slope.

[0059] S5: Adjust the pulling speed according to the pulling speed adjustment value output by the PID to obtain a spire-shaped shoulder.

[0060] Obtaining the actual shoulder diameter at different stages: In one embodiment, a CCD (Charge Coupled Device) camera can be used to acquire images of the three-phase interface between the single-crystal silicon rod and the silicon melt in the crystal growth furnace. The images are then processed by a computer to determine the diameter of the single-crystal silicon rod and fed back to the control system for crystal growth control. Specifically, during crystal growth, a bright ring is generated at the solid-liquid interface between the single-crystal silicon rod and the silicon melt due to the release of latent heat. The CCD camera acquires the image signal of the bright ring and transmits it to the computer system after analog-to-digital conversion. The image processing program in the computer system processes the single-crystal growth image to obtain the measured diameter of the single-crystal silicon rod. As an example, the method for obtaining the measured diameter of the single-crystal silicon rod based on the image signal acquired by the CCD camera includes: the image processing program extracts the bright ring at the solid-liquid interface to obtain the crystal outline; the crystal outline is fitted to obtain an elliptical boundary; the elliptical boundary is corrected to a circular boundary; three pixels are randomly selected on the circular boundary, and their coordinate values ​​are substituted into the circular coordinate formula to form an equation and solve it to calculate the center coordinates and the diameter of the crystal.

[0061] To obtain the actual shoulder height at different stages, in one embodiment, the actual shoulder height is obtained by the height raised by the seed crystal rope. The lifting head at the top of the single crystal furnace auxiliary chamber is connected to a tungsten wire rope. The motor rotates to drive the tungsten wire rope to rise, and the distance is measured at the same time to obtain the shoulder height.

[0062] Step S2: Based on the actual shoulder diameter and shoulder height obtained at different stages, the actual slope of different shoulder diameters is obtained through a predetermined calculation formula.

[0063] In one embodiment, the predetermined calculation formula is: actual slope = actual shoulder height / actual shoulder diameter.

[0064] Step S3: Compare the actual slope with the shoulder slope for different shoulder diameters to obtain the slope difference ΔK; specifically, the slope difference ΔK = actual slope - shoulder slope.

[0065] Step S4: The slope difference ΔK is used as the input of the PID controller to obtain the crystal pulling speed adjustment value output by the PID controller, so that the actual slope of different shoulder diameters is the same as the shoulder pulling slope.

[0066] In one embodiment, the slope difference ΔK is used as the input of the PID controller, and the crystal pulling speed is adjusted according to the judgment formula of the PID controller. The judgment formula is: when ΔK≤-0.1, the crystal pulling speed is reduced by 3mm / h-6mm / h.

[0067] When -0.1 < ΔK ≤ -0.05, the crystal pulling speed decreases by 1 mm / h - 3 mm / h;

[0068] When -0.05 < ΔK < 0.05, the crystal pulling speed is not adjusted;

[0069] When 0.05≤ΔK<0.1, the crystal pulling speed increases by 1mm / h-3mm / h;

[0070] When ΔK≥0.1, the crystal pulling speed increases by 3mm / h-6mm / h.

[0071] In another embodiment, in step S4, the slope difference ΔK is used as the input of the PID controller. The crystal pulling speed adjustment value is calculated according to the formula: crystal pulling speed adjustment value = ΔK × P, where P is a constant of 5 mm / h, and the unit of crystal pulling speed adjustment value is mm / h. If the slope difference ΔK > 0, the pulling speed is increased; if the slope difference ΔK < 0, the pulling speed is decreased; so as to perform real-time pulling speed adjustment.

[0072] Specifically, taking a 12-inch inch as an example, with a 5-minute acquisition cycle, the target slope, actual shoulder diameter, actual slope, and pulling speed adjustment values ​​for different shoulder heights are shown in Table 1.

[0073] Table 1

[0074] Furthermore, the rotational speed of the crystal rod is 5 rpm to 8 rpm.

[0075] The present invention will now be further described through the following embodiments.

[0076] Example 1

[0077] Using a 12-inch single crystal furnace, a quartz crucible with a diameter of 32 inches, and a charge of 500 kg, 12-inch lightly boron-doped crystal rods are drawn.

[0078] Crystal introduction and necking: Conventional process, with the neck diameter controlled at 3-5mm to ensure complete elimination of dislocations.

[0079] The shoulder slope control during the shoulder formation process is shown in Table 1, and the process is shown in Table 2 for pulling crystal rods.

[0080] Table 2

[0081] Example 2

[0082] Using an 8-inch single crystal furnace, with a quartz crucible diameter of 23-26 inches, pull crystal rods with a diameter of 205-212 mm, and a charge of 150-180 kg, pull 8-inch lightly boron-doped crystal rods.

[0083] Crystal introduction and necking: Conventional process, with the neck diameter controlled at 4.5-5mm to ensure complete elimination of dislocations.

[0084] The process of shoulder formation is shown in Table 3, which involves pulling crystal rods.

[0085] Table 3

[0086] Comparative Example 1

[0087] The shoulder-laying process is shown in Table 4. No shoulder-laying slope control is performed, and the rest is the same as in Example 1.

[0088] Table 4

[0089] The shoulder shape in Examples 1 and 2 is as follows: Figure 1 As shown, Comparative Example 1 is a shoulder shape without shoulder slope control, such as... Figure 2 As shown, oxygen content test samples were taken from the shoulder and tail of the produced crystal rod at different stages of equal diameter. After the samples were pretreated with mixed acid and polished, the oxygen value was tested using FT-IR.

[0090] It can be seen that both Examples 1 and 2 successfully produced the target shoulder shape. Comparing Example 1 and Comparative Example 1, it can be observed that in Example 1, the oxygen content at the very end of the shoulder (when the diameter is 0 mm) of the "tower-shaped" shoulder is 14.72 ppma, which is 2.44 ppma lower than the average oxygen content of Comparative Example 1. This indicates that oxygen content is concentrated in the shoulder (the trend of oxygen content in the crystal rod is high at the head and low at the tail), significantly reducing the oxygen content during the equal-diameter process. The test results are as follows... Figure 3 As shown, the average oxygen content of the comparative example refers to the average oxygen content of the process using the comparative example over one month. Therefore, by using the above method, we can avoid crystalline bifurcation after the shoulder height reaches 60mm-150mm and the shoulder diameter reaches 80mm-260mm. The crystalline will bifurcate from 4 to 8 lines, and then return to 4 lines during shoulder formation. Specifically, this avoids generating huge radial thermal stress and activates... <100> Multiple slips on the {111} plane in the crystal result in surface crystal lines (slip traces), which enable the construction of towering spires, maximize the increase in shoulder volume, and enhance oxygen storage capacity.

[0091] Corrosion pit data were obtained by testing different locations on the wafers of Example 1 and Comparative Example 1. Figure 4 Explanation of data test locations;

[0092] After acid washing, alkali washing, heat treatment, HF cleaning, dissociation, and selective etching, the sample taken from the ingot head was observed under a microscope at a high magnification greater than 500x. The number of corrosion pits was small and shallow, ranging from 1E+5 to 1E+10. The BMD results of Examples and Comparative Example 1 are as follows: Figure 5 As shown.

[0093] As can be seen from the above, by controlling the shoulder formation process, the crystal lines are prevented from splitting into 8 lines (only 4 lines) to form a tall "tower shape," increasing the physical weight and volume of the shoulder. This allows more oxygen impurities to be physically "locked" in the shoulder area, increasing the oxygen content during the shoulder formation process. Consequently, the oxygen content entering the crystal interior during the equal diameter process is reduced, thereby reducing the formation of heat-treated BMD and lowering BMD defects.

[0094] Comparative Example 2

[0095] The shoulder-laying process is shown in Table 5, and the rest is the same as in Example 1.

[0096] Table 5

[0097] The comparative examples and embodiments were obtained through calculation. Figure 6 Calculation method: Survival rate = 1 - (Number of shoulder breakages / Total number of shoulder breaks) × 100%.

[0098] Depend on Figure 6It is known that if the furnace pressure is not adjusted during the shoulder-forming process, the target shoulder shape will still be formed, but the success rate will be low. Therefore, precise matching of the furnace pressure can suppress the thermal shock caused by the crucible rotation, protecting the microscopic stability of the solid-liquid interface. This, in conjunction with the increase in power, buffers the temperature change caused by the increase in crucible rotation, ensuring the success rate of shoulder formation; it also ensures that the V / G value control will not fail due to thermal disturbance, while providing a stable thermodynamic environment for the oxygen segregation process, ultimately achieving a significant reduction in BMD density.

[0099] The above-disclosed embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the invention. Those skilled in the art will understand that implementing all or part of the above-described embodiments and making equivalent changes in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. A method for reducing BMD in large-size lightly boron-doped Czochralski single-crystal silicon, characterized in that, Includes the following steps: Different shoulder-forming slopes, ingot pulling speeds, crucible rotation speeds, and power adjustment ranges are preset at different shoulder-forming stages to reduce the oxygen content during the equal-diameter process. Specifically, the shoulder-forming slope is the ratio of shoulder height to shoulder diameter, the shoulder-forming slope is 0-1.11, the ingot pulling speed is 54mm / h~59mm / h, the crucible rotation speed is 4rpm~5.5rpm, the ingot rotation speed is 5rpm-8rpm, the furnace pressure is 8kPa-10kPa, and the power adjustment range is -2.3kW~-0.5kW.

2. The method for reducing BMD in large-size lightly boron-doped Czochralski single-crystal silicon as described in claim 1, characterized in that, For pulling 8-inch crystal ingots, the different shoulder-forming stages include a first shoulder-forming stage and a second shoulder-forming stage, and the first shoulder-forming stage and the second shoulder-forming stage are continuous shoulder-forming processes; For pulling 12-inch crystal ingots, the different shoulder-forming stages include a first shoulder-forming stage, a second shoulder-forming stage, and a third shoulder-forming stage, and the first shoulder-forming stage, the second shoulder-forming stage, and the third shoulder-forming stage are a continuous shoulder-forming process; Wherein: the first stage of shoulder expansion refers to a shoulder expansion height from 0 to below 80mm, the second stage of shoulder expansion refers to a shoulder expansion height from above 80mm to below 200mm, and the third stage of shoulder expansion refers to a shoulder expansion height from above 200mm to below 260mm.

3. The method for reducing BMD in large-size lightly boron-doped Czochralski single-crystal silicon as described in claim 2, characterized in that, The first stage of the shoulder formation has a shoulder slope of 0-1.11, the crystal rod pulling speed is 58mm / h~59mm / h, the power adjustment range is -2.3kW~-1.8kW, the crucible rotation speed is 4rpm, and the furnace pressure is 8kPa.

4. The method for reducing BMD in large-size lightly boron-doped Czochralski single-crystal silicon as described in claim 2, characterized in that, For pulling 12-inch crystal ingots, the shoulder slope of the second stage of shoulder formation is 0.77-1.07, the crystal ingot pulling speed is 54mm / h~58mm / h, the power adjustment range is -2.3kW~-1.5kW, the crucible rotation speed is 4rpm-5.2rpm, and the furnace pressure is 8kPa-9.5kPa.

5. The method for reducing BMD in large-size lightly boron-doped Czochralski single-crystal silicon as described in claim 2, characterized in that, For pulling 8-inch crystal ingots, the shoulder slope of the second stage of shoulder formation is 0.77-1.07, the crystal ingot pulling speed is 54mm / h~58mm / h, the power adjustment range is -2.3kW~-1.5kW, the crucible rotation speed is 4rpm-5rpm, and the furnace pressure is 8kPa-9kPa.

6. The method for reducing BMD in large-size lightly boron-doped Czochralski single-crystal silicon as described in claim 2, characterized in that, The shoulder slope in the third stage of shoulder formation is 0.71-0.81, the crystal rod pulling speed is 54mm / h~55mm / h, the power adjustment range is -1.5kW~-0.5kW, the crucible rotation speed is 5.2rpm-5.5rpm, and the furnace pressure is 9.5kPa-10kPa.

7. The method for reducing BMD in large-size lightly boron-doped Czochralski single-crystal silicon as described in claim 3, characterized in that, In the first stage of shoulder formation, as the shoulder height increases, the shoulder slope first increases from 0 to 1.11, and then decreases to 1.

07. The crystal rod pulling speed first remains stable at 59 mm / h and then gradually decreases to 58 mm / h. The power adjustment range first decreases from -2.3 kW to -1.8 kW and then gradually increases to -2.2 kW. The crucible rotation speed remains stable at 4 rpm, and the furnace pressure remains stable at 8 kPa.

8. The method for reducing BMD in large-size lightly boron-doped Czochralski single-crystal silicon as described in claim 4, characterized in that, For pulling 12-inch crystal ingots, in the second stage of shoulder formation, as the shoulder height increases, the shoulder slope gradually decreases from 1.07 to 0.77, the crystal ingot pulling speed gradually decreases from 58 mm / h to 54 mm / h, the power adjustment range first increases from -2.2 kW to -2.3 kW and then gradually decreases to -1.5 kW, the crucible rotation speed first remains stable at 4 rpm and then gradually increases to 5.2 rpm, and the furnace pressure first remains stable at 8 kPa and then gradually increases to 9.5 kPa.

9. The method for reducing BMD in large-size lightly boron-doped Czochralski single-crystal silicon as described in claim 5, characterized in that, For pulling 8-inch crystal ingots, in the second stage of shoulder formation, as the shoulder height increases, the shoulder slope gradually decreases from 1.07 to 0.77, the crystal ingot pulling speed gradually decreases from 58 mm / h to 54 mm / h, the power adjustment range first increases from -2.2 kW to -2.3 kW and then gradually decreases to -1.5 kW, the crucible rotation speed first remains stable at 4 rpm and then gradually increases to 5 rpm, and the furnace pressure first remains stable at 8 kPa and then gradually increases to 9 kPa.

10. The method for reducing BMD in large-size lightly boron-doped Czochralski single-crystal silicon as described in claim 6, characterized in that, In the third stage of shoulder formation, as the shoulder height increases, the shoulder slope first decreases from 0.77 to 0.71 and then gradually increases to 0.

81. The crystal rod pulling speed first remains stable at 54 mm / h, then increases to 55 mm / h and then remains constant. The power adjustment range gradually decreases from -1.5 kW to -0.5 kW. The crucible rotation speed first increases from 5.2 rpm to 5.5 rpm and then remains stable at 5.5 rpm. The furnace pressure first increases from 9.5 kPa to 10 kPa and then remains stable at 10 kPa.

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