A single crystal silicon rod containing antimony with reduced concentricity defects, a method for producing the same, and a silicon slice

Abstract

The application provides a kind of concentric circle defect reduction antimony-containing single crystal silicon rod, its preparation method and silicon wafer.The concentration of antimony element in the single crystal silicon rod is 0.5-40 ng / g, and the radial concentration variation rate RRV of antimony element on any cross section of the single crystal silicon rod is not more than 20%.The application controls the doping concentration of antimony and its radial distribution uniformity, combines with the optimized process parameters such as crystal transfer, crucible transfer, pulling speed, temperature, furnace pressure and argon flow, reduces the oxygen content of the melt by using the volatilization of antimony, and inhibits the diffusion and aggregation of oxygen by means of the "pinning effect" caused by the larger atomic radius of antimony than silicon, thereby significantly reducing the formation of concentric circle defects in the single crystal silicon rod, improving the crystal integrity, radial uniformity and electrical properties of the silicon wafer, and suitable for the preparation of TOPCon, BC and other high-efficiency solar cells.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor material preparation, in particular to a single crystal silicon rod containing antimony with reduced concentric circle defects, a preparation method thereof and a silicon wafer processed therefrom. BACKGROUND

[0002] The Czochralski method (CZ) is the mainstream method for preparing single crystal silicon. In this process, the quartz crucible dissolves oxygen into the silicon melt at high temperature, and the oxygen atoms are solid-solved in the silicon lattice in the form of interstitials. Due to the large radius of the oxygen atom, local lattice distortion will be caused. During the subsequent cooling or high-temperature process of the crystal, interstitial oxygen will diffuse and possibly nucleate in the supersaturated region, forming oxygen precipitates and associated defects (such as stacking faults, dislocation loops, etc.).

[0003] Under certain thermal history conditions, the diffusion and aggregation process of oxygen shows periodic fluctuations in the radial direction of the crystal, resulting in a pattern of alternating ring-shaped oxygen concentration distribution on the cross-section of the silicon wafer, i.e. the so-called "concentric circle" defects (also known as vortex defects). These ring-shaped structures correspond to different oxygen concentration regions, and their formation is closely related to the history of oxygen diffusion from the surface of the crystal to the interior and the fluctuations of the thermal field and flow field during the crystal growth process.

[0004] For high-efficiency solar cells such as tunnel oxide passivated contact (TOPCon), the preparation process includes multiple high-temperature steps. This secondary high-temperature process is extremely sensitive to the oxygen content and morphology of the silicon substrate. If the initial oxygen content of the silicon wafer is too high, the solid solubility of oxygen increases at high temperature, resulting in a decrease in the number of nucleation cores, but at the same time the diffusion rate of oxygen is significantly accelerated. This condition promotes the rapid aggregation and coarsening of oxygen at a small number of nucleation points, exacerbating the unevenness of oxygen distribution in the radial direction, thereby inducing or strengthening the concentric circle defects.

[0005] Such defects, as effective carrier recombination centers, can severely degrade the minority carrier lifetime of the silicon bulk material, increase the dark saturation current of the cell, and result in a decrease in the conversion efficiency of the cell. Therefore, it is crucial to suppress the formation of concentric circle defects to improve the performance and reliability of TOPCon cells.

[0006] Therefore, there is an urgent need for a new process that can synergistically regulate the behavior of oxygen from both the source and the bulk material, effectively suppress the formation of concentric circle defects, and not affect the electrical properties and production stability of the crystal. SUMMARY

[0007] The application provides a single crystal silicon rod with reduced concentric circle defects, a preparation method thereof, and a silicon wafer processed from the single crystal silicon rod, to solve the problem of concentric circle defects caused by high oxygen content and uneven radial distribution in the single crystal silicon in the prior art, and especially to meet the strict requirements of the TOPCon cell manufacturing process on the oxygen content and distribution characteristics of the silicon wafer. The preparation method introduces antimony as a dopant in the Czochralski crystal growth process, and systematically optimizes the growth parameters. The high volatility of antimony at high temperatures and the segregation characteristics of antimony itself are used to carry and remove volatile impurities that promote oxygen precipitation during the crystal pulling process, thereby reducing the relative content of related impurity elements and reducing the probability of the formation of concentric circle defects from the source. At the same time, based on the characteristic that the atomic radius of antimony is significantly larger than that of silicon, the pinning effect caused by the strain field in the crystal lattice is used to effectively inhibit the long-range diffusion of oxygen atoms in the silicon crystal and hinder the nucleation and growth of oxygen precipitation. The technical scheme provided by the application is as follows:

[0008] In a first aspect, the application provides a single crystal silicon rod with reduced concentric circle defects, wherein the antimony element concentration of the single crystal silicon rod is 0.5-40 ng / g.

[0009] Along the axial direction of the single crystal silicon rod, the radial concentration variation rate RRV of antimony element on any cross section thereof satisfies: RRV≤20%, wherein,

[0010] RRV=(C c -C e ) / C avg ×100%,

[0011] In the formula, C c , C e , and C avg are the antimony element concentrations at the center point and the edge point of the cross section and the average antimony element concentration of the cross section, respectively.

[0012] In a second aspect, the application further provides a method for preparing the single crystal silicon rod with reduced concentric circle defects, comprising:

[0013] Adding antimony element to a silicon melt;

[0014] In the isodiametric stage of the Czochralski crystal growth, the crystal rotation speed is controlled to be not lower than 10 rpm, the crucible rotation speed is controlled to be not higher than 5 rpm, and the ratio of the crystal rotation speed to the crucible rotation speed is greater than 2.

[0015] In one specific embodiment, the method further comprises: adding arsenic and / or phosphorus element to the silicon melt.

[0016] In one specific embodiment, in the isodiametric stage, the crystal pulling speed is controlled to be lower than 1.7 mm / min, and the variation rate thereof is lower than 0.2 mm / min.

[0017] In one specific embodiment, during the isodiametric phase, the fluctuation of the heating power is controlled to be less than 2 kW / h.

[0018] In one specific embodiment, during the isodiametric phase, the furnace pressure is controlled to be 10 ~ 14 Torr.

[0019] In one specific embodiment, during the isodiametric phase, the argon flow rate is controlled to be 80 ~ 120 slpm.

[0020] In one specific embodiment, during the process phase of adding antimony into the silicon melt, the following combination of process parameters is adopted: the furnace pressure is 10 ~ 14 Torr, the crucible rotation speed is 0 ~ 5 rpm, the argon flow rate is 80 ~ 95 slpm, and the melting power is 80 ~ 100 kW.

[0021] In one specific embodiment, during the antimony adding process phase, the process of adding antimony into the silicon melt comprises the following steps:

[0022] S1. Based on the reserved melt mass, the raw material feeding amount of the batch, the circulating material composition ratio, and the raw material resistivity simulation value, the theoretical doping amount of antimony is determined;

[0023] S2. Under the process conditions of the furnace pressure, the crucible rotation speed, the argon flow rate, and the melting power, after the crystal growth state is stable, the theoretical doping amount of antimony is added into the silicon melt;

[0024] S3. Based on the measured value of the antimony concentration of the obtained single crystal silicon rod after adding antimony, the amount of antimony added in the subsequent process is adjusted to compensate, so that the concentration of antimony element in the single crystal silicon rod is controlled to be 0.5 ~ 40 ng / g.

[0025] In a third aspect, the application also provides a silicon wafer, which is cut and processed from the antimony-containing single crystal silicon rod with reduced concentric circle defects.

[0026] By adopting the technical scheme, the antimony-containing single crystal silicon rod with reduced concentric circle defects, the preparation method thereof, and the silicon wafer provided by the application have the following beneficial effects:

[0027] By introducing the high-volatility dopant antimony, the application effectively promotes the volatilization and escape of SiO and other oxygen-containing impurities on the melt surface during the crystal growth process, significantly reducing the oxygen content in the silicon melt from the source; at the same time, by virtue of the "pinning effect" caused by the larger atomic radius of antimony than that of silicon, the diffusion and aggregation of oxygen atoms in the silicon lattice can be effectively bound, thereby significantly inhibiting the formation of concentric circle defects and improving the crystal structure integrity and radial uniformity of the silicon wafer.

[0028] The present application further controls the melt convection pattern and oxygen transport behavior by optimizing the crystal rotation speed and the crucible rotation speed in the isodiametric growth stage, controlling the crystal rotation speed to be above 10 rpm, reducing the crucible rotation speed to be below 5 rpm, and reasonably adjusting the ratio of the two to be greater than 2. By increasing the crystal rotation speed, the forced convection caused by the crystal rotation is enhanced, the rich-antimony melt at the solid-liquid interface is transported outward, and the low-oxygen melt in the middle is introduced to the vicinity of the interface, thereby improving the uniformity of the distribution of antimony and oxygen; and by reducing the crucible rotation speed, the natural convection driven by the crucible rotation is weakened, the oxygen input from the quartz crucible wall to the melt is effectively inhibited, and the fluctuations of temperature and flow are reduced. The above-mentioned parameters work together to stabilize the flow at the solid-liquid interface, inhibit the non-uniformity of oxygen input, promote the capture of oxygen by antimony at the interface and the formation of stable complexes, thereby significantly inhibiting the radial non-uniform diffusion and local supersaturation precipitation of oxygen, further weakening the appearance of concentric circular defects, and finally obtaining silicon wafers with more uniform oxygen distribution and more complete structure. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0030] The term "one embodiment" or "an embodiment" as used herein means that a particular feature, structure, or characteristic described can be included in at least one implementation of the present application. In the description of the application, it should be understood that the terms "first", "second", etc. are used to describe various components, but should not be construed as indicating or implying relative importance or implying the number of the indicated technical features. Therefore, the features defined with "first", "second" can be explicitly or implicitly included one or more features. Moreover, the terms "first", "second", etc. are used to distinguish similar objects, but do not necessarily describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of the application described herein can be implemented in an order other than those described herein.

[0031] When a range of values is disclosed herein, the disclosure is to be understood to encompass the explicitly stated range as well as any value within the stated range. Further, a range includes each individual number within the range, inclusive of the endpoints. In addition, a range includes each discrete value within the stated range. For example, a range of "1 to 10" is to be read to include any and all sub-ranges between, and including, the minimum value of 1 and the maximum value of 10; that is, all sub-ranges beginning with a minimum of 1 or more and ending with a maximum of 10 or less, and all sub-ranges in between, are included in the range of "1 to 10" - i.e., all sub-ranges between (and including) the minimum of 1 and the maximum of 10. An exemplary list of sub-ranges would include 1 to 6.1, 3.5 to 7.8, 5.5 to 10, and so forth; as would a list of individual numbers including 1, 4, 5.6, 10, and so forth.

[0032] The embodiment of the present application provides a single crystal silicon rod with reduced concentric circle defects, and the single crystal silicon rod has an antimony element concentration of 0.5-40 ng / g.

[0033] In the axial direction of the single crystal silicon rod, the radial concentration variation rate RRV of the antimony element in any cross section satisfies RRV≤20%, wherein,

[0034] RRV=(C c -C e ) / C avg ×100%,

[0035] In the formula, C c , C e and C avg are the antimony element concentrations at the center point, the edge point and the average antimony element concentration of the cross section, respectively.

[0036] To clarify the calculation method and the determination standard of the radial concentration variation rate (RRV), the parameters involved in the formula are defined as follows in the present application: the antimony element concentration (C c ) at the center point of the cross section is the antimony element concentration measured at the center of the cross section prepared by standardization based on the geometric center positioning by secondary ion mass spectrometry (SIMS); the antimony element concentration (C e ) at the edge point of the cross section is the arithmetic mean value of the antimony element concentrations measured at at least four equidistant positions (for example, 0°, 90°, 180°, 270°) on the same cross section circle after SIMS determination; and the average antimony element concentration (C avg ) of the cross section is the antimony element concentration measured according to a systematic radial measurement scheme (usually dots are arranged at a predetermined interval along two perpendicular diameters, and C c points and C eThe arithmetic average of the antimony concentration values of all effective measurement points on the cross section is obtained. It should be particularly pointed out that the number of measurement points, the distribution mode and the calculation scheme given above are only illustrative and are not a limitation of the present application; in actual implementation, other equivalent, comparable definition methods and measurement schemes can be used according to specific detection standards, equipment conditions or product specification requirements. All detections should be performed on standard prepared samples and follow unified instrument calibration and data processing procedures.

[0037] The present application uses antimony (Sb) as a dopant to synergistically inhibit oxygen-induced concentric ring defects in monocrystalline silicon through its dual action mechanism during high-temperature crystal pulling. First, the high volatility of antimony at high temperatures allows it to carry off volatile oxygen-containing impurities such as SiO on the melt surface and the growth interface during volatilization, thereby reducing the content of impurities that promote oxygen precipitation in the system and reducing the driving force for oxygen precipitation nucleation. Second, the antimony atom radius is much larger than that of silicon, which forms a local strain field in the silicon lattice and produces a "pinning effect" on interstitial oxygen atoms, hindering their long-range diffusion and delaying the aggregation and precipitation growth process of oxygen.

[0038] In addition, the doping timing and doping concentration of the antimony element have a key impact on this inhibition effect. Doping too late will cause a lagging effect of the antimony element, which cannot combine and carry out impurities such as SiO in time, and the antimony element should be added at the initial loading, and attention should be paid to the loading position of the antimony, which should be as close to the crucible as possible but not in contact with the crucible. During the melting process, the antimony element is used to melt and flow and evaporate to carry away oxygen elements diffused from the crucible (the main source of oxygen elements in silicon single crystals); too low a doping concentration is not enough to form an effective pinning potential barrier to inhibit oxygen diffusion; and too high a concentration will introduce significant lattice distortion due to the large radius of antimony atoms, which may induce dislocations and other crystal defects, and act as deep-level impurities to degrade carrier lifetime, resulting in a significant decrease in open-circuit voltage of the battery sheet.

[0039] Experimental verification shows that controlling the antimony doping concentration in the range of 0.5-40 ng / g and controlling the RRV within 20% can effectively reduce the concentric ring defects without significantly negatively affecting the battery efficiency. In addition, the radial distribution uniformity of the antimony element in the crystal is crucial to the battery efficiency. By controlling the RRV within 20%, the induction of dislocations and other factors that cause a significant decrease in battery efficiency due to a large difference in antimony element concentration can be prevented. The pinning effect of antimony atoms can continuously inhibit the migration of high-concentration oxygen in the center region to the edge, avoiding the formation of local aggregation and ring-shaped precipitation of oxygen, and achieving the inhibition of concentric ring defects.

[0040] The embodiment of the present application also provides a method for preparing an antimony-containing single crystal silicon rod, comprising: adding antimony element into a silicon melt; in an isodiametric stage of the Czochralski crystal growth, controlling the crystal rotation speed to be not less than 10 rpm, controlling the crucible rotation speed to be not higher than 5 rpm, and the ratio of the crystal rotation speed to the crucible rotation speed being greater than 2.

[0041] Specifically, in the isodiametric stage of the Czochralski crystal growth, the crystal rotation speed is controlled to be not less than 10 rpm, and by increasing the crystal rotation speed, the forced convection caused by the crystal rotation can be enhanced, so as to transport the antimony element enriched at the solid-liquid interface to the edge region of the melt, and at the same time, the melt with lower oxygen content in the middle of the crucible is supplied to the interface region, which is beneficial to the regulation of the solute distribution near the interface. It should be noted that the highest crystal rotation speed is preferably not higher than 20 rpm, and too high crystal rotation speed can lead to interface flow instability and induce turbulence, which in turn introduces new oxygen distribution non-uniformity. Within the rotation speed range controlled in the method, in combination with the aforementioned suitable antimony doping concentration, the oxygen diffusion can be effectively inhibited, so as to stabilize the solute distribution in the solid-liquid interface region and reduce the local enrichment of oxygen near the interface.

[0042] The crucible rotation speed is controlled to be not higher than 5 rpm, and by reducing the crucible rotation speed, the natural convection (melt flow caused by centrifugal force) driven by the crucible rotation can be weakened, so as to reduce the oxygen transport intensity from the crucible wall (SiO2 source) to the crystal growth direction. At the same time, reducing the crucible rotation speed also helps to reduce the temperature fluctuation and flow instability in the melt, and reduce the non-uniform incorporation of oxygen caused by transient transport changes.

[0043] In addition, the ratio of the crystal rotation speed to the crucible rotation speed is controlled to be greater than 2, and by increasing the ratio of the crystal rotation speed to the crucible rotation speed, in combination with the enhanced forced convection caused by increasing the crystal rotation speed, the transport of the antimony element discharged from the interface due to fractional condensation to the main body of the melt can be accelerated, and the diffusion and migration of the oxygen-containing substance at the interface are promoted; and reducing the crucible rotation speed reduces the input amount of oxygen from the crucible wall from the source. The synergistic effect of the two helps to reduce the oxygen concentration level at the solid-liquid interface, so that the antimony element is more easily combined with the residual oxygen to form a stable antimony-oxygen complex, and then the independent diffusion and precipitation of oxygen are inhibited.

[0044] The formation of the concentric ring defects (i.e. the annular high oxygen region) is usually closely related to the fluctuation of the thermal field and the radial non-uniform transport of oxygen during the crystal growth process. By increasing the crystal rotation speed to stabilize the interface flow and reducing the crucible rotation speed to reduce the transient fluctuation of oxygen input, the diffusion gradient of oxygen in the radial direction can be effectively inhibited, thereby reducing the degree of appearance of the concentric ring defects. Reducing the crucible rotation speed can also alleviate the thermal field disturbance caused by the asymmetry of the crucible rotation, and increasing the crystal rotation speed can help to compensate the symmetry of the flow on the side of the crystal. Thus, a more stable thermal field environment is obtained, which can reduce the temperature oscillation of the solid-liquid interface, avoid the supersaturation and precipitation of oxygen in the local area (such as the formation of the oxidation-induced stacking fault ring), and promote the uniform distribution of the antimony-oxygen complex in the crystal, thereby further inhibiting the formation of oxygen-induced ring defects.

[0045] In a specific embodiment, the doping process uses the antimony element as the main dopant. On this basis, arsenic and / or phosphorus elements can be selectively added to the silicon melt as co-dopants. When the above-mentioned co-doped elements are added, the doping process parameters (such as the timing and method of doping) are all based on the doping process of the antimony element.

[0046] In a specific embodiment, during the constant diameter stage, the crystal pulling speed is controlled to be lower than 1.7 mm / min, and the change rate thereof is lower than 0.2 mm / min. The change rate of the crystal pulling speed is controlled to be lower than 0.2 mm / min through an automatic program setting, so as to maintain a flat or controllable micro-convex solid-liquid interface morphology. Under this stable interface condition: the antimony forms a stable antimony-rich boundary layer with a thickness and concentration gradient on the melt side in front of the interface because its segregation coefficient is much less than 1; the effective segregation coefficient of oxygen in silicon is slightly greater than 1, and its doping behavior is highly dependent on the interface state, and the stable interface makes the axial segregation process of oxygen predictable and uniform. In this stable and predictable interface chemical environment, the antimony atoms (enriched on the melt side) can most effectively "capture" and "complex" the oxygen atoms diffused from the melt to the vicinity of the interface to form stable Sb-O complexes, thereby locking the activity of oxygen at the "entrance" of the crystal. The stable pulling speed means that the solid-liquid interface advances at a constant speed, providing a constant and predictable diffusion window for the interaction of antimony and oxygen, effectively inhibiting the radial non-uniform distribution of oxygen, and thereby reducing the formation of concentric ring oxygen defects.

[0047] In one embodiment, the fluctuation of the heating power is controlled to be less than 2 kW / h during the isodiametric stage. The fluctuation of the melt temperature directly causes the heat convection intensity and mode to change dramatically, and when the convection state is unstable, the oxygen flux entering the melt from the crucible wall will fluctuate significantly over time. The instantaneous fluctuation of the oxygen concentration is one of the most direct causes of the ring-shaped distribution (i.e., the concentric circular defects) of the radial oxygen concentration in the crystal. By stabilizing the temperature, the stability of the melt flow can be maintained, the dissolution and transport process of oxygen can be kept at a constant rate, and the radial non-uniform distribution of oxygen can be inhibited. At the same time, antimony (Sb) atoms can easily capture vacancies (V) in the crystal due to their large atomic size and unique electronic structure, and vacancies are the key channel for oxygen to rapidly diffuse and aggregate to form precipitates in the silicon lattice. Antimony atoms substantially block the diffusion path of oxygen by occupying vacancies, thereby inhibiting the migration and aggregation of oxygen; in addition, antimony can directly form a relatively stable antimony oxygen complex with oxygen, further fixing the oxygen atoms. Therefore, controlling the temperature fluctuation not only helps to stabilize the oxygen transport in the melt, but also synergistically inhibits the diffusion and precipitation of oxygen by antimony, thereby systematically reducing the risk of forming concentric circular defects.

[0048] In one embodiment, the furnace pressure is controlled to be 10-14 Torr during the isodiametric stage; the argon flow rate is controlled to be 80-120 slpm. Under this condition, the incorporation of antimony (Sb) can promote the evaporation process of oxygen from the melt surface, i.e., by forming volatile antimony oxide (Sb2O) and transporting it in the gas phase with the aid of the argon atmosphere, to actively regulate the evaporation rate of oxygen. Increasing the furnace pressure within a moderate range is beneficial to enhancing the volatilization driving of Sb oxide volatiles, thereby optimizing the escape behavior of oxygen on the melt surface and reducing the non-uniformity of the oxygen content and its radial distribution in the melt. In turn, it can effectively inhibit the local enrichment and ring-shaped distribution of oxygen during the crystal growth process, thereby reducing the tendency of concentric circular defects.

[0049] In one embodiment, the following combination of process parameters is used during the process stage of adding antimony to the silicon melt: the furnace pressure is 10-14 Torr, the lower the pressure, the stronger the volatility of antimony elements, the easier it is to carry out oxygen elements, and the lower the total amount of oxygen in the silicon single crystal, but too low a pressure will lead to an increase in cost and a decrease in equipment safety. The crucible rotation speed is 0-5 rpm, the crucible is the main source of oxygen elements in the silicon single crystal, so reducing the convection intensity (rotation) of the crucible and the silicon solution can also reduce the melting speed of oxygen in the silicon solution. The argon flow rate is 80-95 slpm, a high argon flow rate can timely carry away the volatilized oxygen elements (SiO) and antimony elements, preventing these volatiles from condensing on the crystal-melt interface and causing the failure of silicon single crystal growth. The material melting power is 80-100 kW, the lower the material melting power, the lower the heater temperature, and the lower the heat convection on the crucible surface, which is beneficial to reducing the precipitation of oxygen.

[0050] In one specific embodiment, the process of adding antimony to the silicon melt in the antimony addition process stage comprises the following steps:

[0051] S1. Based on the reserved melt mass, the raw material feeding amount of this batch, the proportion of the recycled material composition, and the raw material resistivity simulation value, the theoretical doping amount of antimony is determined;

[0052] S2. Under the process conditions of furnace pressure, crucible rotation speed, argon flow rate, and material melting power, after the crystal growth state is stable, the theoretical doping amount of antimony is added to the silicon melt;

[0053] S3. Based on the actual measured value of the antimony concentration of the obtained single crystal silicon rod after adding antimony, the addition amount of antimony in the subsequent process is adjusted to compensate, so that the concentration of antimony element in the single crystal silicon rod reaches 0.5-40 ng / g.

[0054] Specifically, in the process of adding antimony to the silicon melt, first, the theoretical doping amount of antimony is determined based on the reserved melt mass, the raw material feeding amount of this batch, the proportion of the recycled material composition, and the raw material resistivity simulation value; then, under the process conditions that the furnace pressure, the crucible rotation speed, the argon flow rate, and the material melting power are all stable, when the crystal growth enters a steady state and the breakage rate (such as 30%) remains stable, the theoretical doping amount of antimony is added to the melt; finally, according to the actual measurement results of the antimony concentration in the produced single crystal silicon rod, the addition amount of antimony in the subsequent process is dynamically adjusted to compensate, so that the average concentration of antimony element in the single crystal silicon rod is accurately controlled within the target range of 0.5-40 ng / g. Preferably, in the antimony doping stage, a specific combination of process parameters can be used, such as a furnace pressure of about 6 Torr, a crucible rotation speed of about 5 rpm, an argon flow rate of about 100 slpm, and a material melting power combination of 85 kW (main heater) and 95 kW (bottom heater). This parameter configuration reduces the gas molecular density in the furnace by reducing the furnace pressure, thereby reducing the resistance of SiO (silicon monoxide) and Sb2O (antimony oxide) to volatilize from the melt surface, increasing their saturated vapor pressure to promote volatilization; at the same time, increasing the argon flow rate to enhance the carrying capacity of the volatilized gas to prevent its back-dissolution. Although the volatilization loss of antimony increases slightly under this condition, the presence of antimony significantly enhances the co-volatilization effect of oxygen, thereby reducing the oxygen concentration in the melt from the source. Through this step-by-step control and parameter optimization, the antimony doping concentration and distribution are accurately regulated, and the volatilization of antimony and the lattice pinning effect of antimony are synergistically exerted, reducing the formation of concentric circle defects while avoiding the formation of crystal defects, providing a stable and reliable process basis for obtaining high-quality, low-oxygen defect antimony-containing single crystal silicon.

[0055] The embodiment of the present application also provides a silicon wafer cut and processed from the antimony-containing single crystal silicon rod with reduced concentric circle defects. The silicon wafer has a controlled antimony doping concentration and distribution, and a radial concentration variation rate (RRV) less than 20%. The size and density of oxygen precipitates in the silicon wafer are effectively inhibited, and the occurrence of concentric circle defects is significantly reduced, so that the silicon wafer is suitable for high-temperature processes sensitive to oxygen content, and is particularly suitable for the preparation of TOPCon solar cells.

[0056] The examples of the present application are described in detail below, which are exemplary and only used to explain the present application, and cannot be understood as a limitation of the present application.

[0057] Embodiment 1

[0058] A method for preparing an antimony-containing single crystal silicon rod with reduced concentric circle defects. 770 kg of photovoltaic-grade polycrystalline silicon raw material (400 kg of new material and 370 kg of recycled material) is used, the theoretical doping amount of antimony is determined to be 7 g based on the reserved melt mass, the composition ratio of recycled material and the simulation value of raw material resistivity, and the antimony is doped at a target concentration of 20 ng / g, and the phosphorus alloy is 85 g (the value is not fixed, and the variable factors are the phosphorus content of the recycled material, the volatilization rate of the furnace table, and the phosphorus content concentration of the mother alloy); in the adding process stage, the furnace pressure is controlled to be 6 Torr, the crucible rotation speed is set to be 5 rpm, the argon flow is adjusted to be 100 slpm, and the melting power is combined with 85 kW and 95 kW, and after the silicon material is completely melted and runs stably for 20 min, the antimony element is added to the center of the melt surface to make it completely melt within 10 min.

[0059] After entering the constant diameter stage of the Czochralski method crystal growth, the crystal rotation speed is controlled to be 15 rpm, and the crucible rotation speed is controlled to be 4 rpm, so that the rotation speed ratio reaches 3.75. The crystal pulling speed is set to be 1.5 mm / min before the constant diameter stage, and the change rate per hour is not more than 0.05 mm / min. At the same time, the heating power fluctuation is controlled to be ±0.4 kW / h, the furnace pressure is maintained at 12 Torr, and the argon flow is maintained at 85 slpm, and after the constant diameter length reaches 300 mm, the cooling is finished.

[0060] The obtained single crystal silicon rod is sampled at the head, and the measured value of the antimony concentration is 19.5 ng / g. After detection, the antimony concentration of the center point of the cross section in the middle of the crystal rod is 20.9 ng / g, the edge point concentration is 17.5 ng / g, and the average concentration is 19.5 ng / g, and the RRV value is calculated to be 17.4%. The RRV values of the three cross sections of the head, the middle and the tail are 15.8%, 17.2% and 19.1% respectively, all of which are not more than 20%. Finally, the single crystal silicon rod is processed into a photovoltaic silicon wafer, and 500,000 wafers are sent to the customer for verification, and the concentric circle ratio is 0.06% (the comparison value of the conventional process in the same period is 0.27%).

[0061] Examples 2-8 and Comparative Examples 1-4

[0062] The preparation method of Reference Example 1 was used, except that the specific process parameters of the isodiametric stage were adjusted, and the specific parameters are shown in Table 1:

[0063] Table 1

[0064]

[0065] Comparative Example 5

[0066] The preparation method of Reference Example 1 was used, except that no antimony element doping was performed.

[0067] Test Example

[0068] The antimony-containing single crystal silicon rods prepared in Examples 1-8 and Comparative Examples 1-5, the silicon wafers after slicing, and the corresponding standard photovoltaic cells were subjected to performance characterization, and the specific items included the concentric circle ratio, the theoretical maximum antimony concentration, the radial concentration variation rate (RRV), and the cell efficiency. Among them, the theoretical maximum antimony concentration was theoretically calculated based on the initial doping amount, the melt quality, the volatilization loss, and the effective segregation coefficient, providing a theoretical reference for the actual antimony concentration and a process design basis; the radial concentration variation rate (RRV) was measured by secondary ion mass spectrometry (SIMS) to measure the antimony concentration distribution of the cross sections of the head, middle, and tail of the single crystal silicon rod, and the average concentration and the radial variation coefficient were calculated to evaluate the uniformity of the distribution of the doping element in the radial direction of the crystal; the concentric circle ratio was used to evaluate the stability of the thermal field and the process conditions in the Czochralski single crystal growth process by quantifying the proportion of the ring-shaped defect pattern formed by the periodic fluctuation of the oxygen concentration in the cross section of the crystal, and was a key macroscopic index for predicting the radial distribution uniformity of the antimony dopant (significantly related to the radial concentration variation rate RRV) and the consistency of the electrical properties of the silicon wafer; the cell efficiency was measured by preparing the silicon wafer into a standard photovoltaic cell under the standard test conditions of AM1.5G, 1000 W / m², and 25°C, and comprehensively reflected the overall influence of the crystal quality, the defect control level, the doping uniformity, and the electrical properties of the material on the final device performance. The test data of the above-mentioned concentric circle ratio and cell efficiency were obtained by large-scale verification tests on 500,000 pieces of photovoltaic silicon wafers delivered to the customer, and the process consistency and product reliability of the present application under mass production conditions were systematically verified. The characterization results are shown in Tables 2 and 3.

[0069] Table 2

[0070]

[0071] Table 3

[0072]

[0073] From the analysis of the experimental data of Examples 1-8 and Comparative Examples 1-5, it can be found that in the preparation process of antimony-containing single crystal silicon rods, the process parameters in the constant diameter stage have a significant impact on the radial uniformity (RRV) of antimony doping and the proportion of concentric circle defects in the final silicon wafer. Specifically, when the pulling speed change rate of Example 1 is low (≤0.05 mm / min / h), the heating power fluctuation is small (±0.4 kW / h), the furnace pressure is moderate (about 12 Torr), and the argon flow is stable (85 slpm), the RRV values of the single crystal silicon rod head, middle and tail are all less than 20%, and the concentric circle defect proportion can be reduced to 0.06%, and the cell efficiency also shows a positive gain (+0.03%). On the contrary, when the rotation speed ratio is too low (Comparative Example 1, 1.3), the pulling speed change rate is too high (Comparative Example 2, 0.15 mm / min / h), the heating power fluctuation is large (Comparative Example 3, 1.5 kW / h) or the furnace pressure is too high (Comparative Example 4, 30 Torr), the RRV value increases significantly (up to 110%), the concentric circle proportion increases, and the cell efficiency decreases. It is particularly noteworthy that even if other parameters are optimized, the concentric circle proportion of Comparative Example 5 without antimony doping is as high as 0.25%, and the cell efficiency decreases significantly (-0.05%), further confirming the key role of antimony doping in inhibiting concentric circle defects, improving crystal uniformity and cell performance.

[0074] To verify the actual effect of the antimony doping process of the present application in inhibiting concentric circle defects, a large-scale mass production application verification was carried out in cooperation with many mainstream photovoltaic cell manufacturers downstream. By comparing the single crystal silicon wafer prepared by the method of the present application (i.e. antimony and arsenic, phosphorus element co-doping combined with a specific crystal growth process) with the corresponding batch of products produced by the industry conventional non-co-doping process at the same period or earlier, the customer concentric circle defect statistics results obtained are shown in Table 4.

[0075] Table 4

[0076]

[0077] From the data in the above table, it can be seen that the monocrystalline silicon wafer prepared by the method of the present application shows very low and stable concentric circle defect ratio on different customers and different specifications (210R / 210N) products, and the results of each batch are distributed in the excellent interval of 0.04%~0.13%. In sharp contrast to this, the silicon wafers produced by the non-co-doping conventional process in the same period or earlier in the industry have generally higher concentric circle ratio and large fluctuation range (0.08%~5.25%), and the defect rate of individual batches is abnormally high (such as the batch of Hongxixineng reaches 5.25%). The large-scale customer verification data fully prove that the present application can reduce the occurrence rate of concentric circle defects and improve the consistency and stability of the crystal quality through antimony doping and process control, meet the stringent requirements of customers for high-efficiency and high-reliability photovoltaic silicon wafers, and have outstanding industrial application value.

Claims

1. A single crystal silicon rod with reduced concentricity defects and containing antimony, characterized in that: the antimony concentration of the single crystal silicon rod is 0.5-40 ng / g; the radial concentration variation rate (RRV) of antimony along the axial direction of the single crystal silicon rod satisfies RRV≤20%, wherein, RRV = (Cmax-Cmin) / Cavg, Cmax is the maximum concentration of antimony in any cross section of the single crystal silicon rod, Cmin is the minimum concentration of antimony in any cross section of the single crystal silicon rod, and Cavg is the average concentration of antimony in any cross section of the single crystal silicon rod; and the single crystal silicon rod is prepared by a method comprising: incorporating antimony into a silicon melt; in an isodiametric stage of the Czochralski method crystal growth, controlling the crystal rotation speed to be no less than 10 rpm, controlling the crucible rotation speed to be no more than 5 rpm, and the ratio of the crystal rotation speed to the crucible rotation speed being greater than 2. The method further comprises: incorporating arsenic and / or phosphorus into the silicon melt. In the isodiametric stage, the crystal pulling speed is controlled to be lower than 1.7 mm / min, and the variation rate thereof is lower than 0.2 mm / min. RRV = (C c - C e ) / C avg x 100%, wherein: C c , C e , and C avg are the antimony element concentration at the cross-sectional center point, the edge point, and the average antimony element concentration of the cross-section, respectively.

2. A method for producing the antimony-containing single crystal silicon rod according to claim 1, characterized by, In the isodiametric stage, the fluctuation of the heating power is controlled to be less than 2 kW / h. In the isodiametric stage, the furnace pressure is controlled to be 10-14 Torr. In the isodiametric stage, the argon flow rate is controlled to be 80-120 slpm.

3. The method of claim 2, wherein, In the process stage of adding antimony to the silicon melt, the following combination of process parameters is adopted: the furnace pressure is 10-14 Torr, the crucible rotation speed is 0-5 rpm, the argon flow rate is 80-120 slpm, and the material melting power is 80-100 kW.

4. The method of claim 2, wherein, In the antimony addition process stage, the process of adding antimony to the silicon melt comprises the following steps:

5. The method of claim 2, wherein, S1. Based on the reserved melt mass, the raw material feeding amount of the batch, the circulating material composition ratio, and the raw material resistivity simulation value, the theoretical doping amount of antimony is determined; 6. The method of claim 2, wherein, S2. Under the process conditions of the furnace pressure, the crucible rotation speed, the argon flow rate, and the material melting power, the theoretical doping amount of antimony is added to the silicon melt after the crystal growth state is stable; 7. The method of claim 2, wherein, S3. Based on the measured value of the antimony concentration of the obtained single crystal silicon rod after adding antimony, the addition amount of antimony in the subsequent process is adjusted to compensate so as to control the concentration of antimony in the single crystal silicon rod to be 0.5-40 ng / g.

8. The method of claim 2, wherein, The silicon wafer is cut and processed from the single crystal silicon rod with reduced concentricity defects and containing antimony according to claim 1.

9. The method of claim 8, wherein, ​ ​ ​ ​ 10. A silicon wafer, characterized by, ​

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