Method for reducing oxygen content and improving in-plane oxygen distribution uniformity in 8-inch lightly doped czochralski silicon single crystal and single crystal ingot

Abstract

A method for reducing the silicon-oxygen content and improving the uniformity of in-plane oxygen distribution in 8-inch lightly doped Czochralski single crystals, employing a thermal field structure comprising: a heater disposed around a graphite crucible, a heat insulation cylinder disposed around the heater, and a heat shield disposed around the crystal rod and above the surface of the melt; the main structure of the heat shield has a configuration that first tapers inward and then expands outward from top to bottom, with the inward-tapering configuration occupying 2 / 3 to 3 / 4 of the overall height of the heat shield, wherein the bottom of the heat shield is located at a distance from the horizontal plane of the bottom edge of the crystal. The distance to the melt surface is 40-50 mm; it also includes the following synergistically optimized process parameters during the entire constant diameter stage of ingot growth: furnace pressure set to 1-3 Torr; argon flow rate set to 110-150 slm; pulling speed set to 0.7-0.9 mm / min; the ratio of ingot rotation speed to crucible rotation speed is 2.5:1-3:1; during ingot growth, as the melt surface decreases, the heater power decreases linearly at a rate of 0.5% per 100 mm of ingot growth.

Description

Technical Field

[0001] This invention relates to the field of monocrystalline silicon manufacturing technology, and in particular to a method and monocrystalline rod for reducing the oxygen content of 8-inch lightly doped Czochralski-grown monocrystalline silicon and improving the uniformity of in-plane oxygen distribution. Background Technology

[0002] In the Czochralski process for fabricating 8-inch lightly boron- or phosphorus-doped single-crystal silicon, a quartz crucible reacts with the high-temperature silicon melt inside, generating volatile silicon monoxide (SiO). Some of the SiO evaporates from the melt surface and is carried out of the system by argon gas, while the rest dissolves into the silicon melt and eventually enters the grown ingot, forming interstitial oxygen. The oxygen content in the ingot directly affects the electrical and mechanical properties of subsequent devices. For high-end power devices (such as fast recovery diodes), the 8-inch substrate ingot not only needs to have a low oxygen content (less than 10 ppma) but also needs to have a uniform in-plane oxygen content, meaning the oxygen radial gradient (ORG) needs to be less than 5%.

[0003] Currently, common techniques used in the industry to reduce oxygen content include: reducing crucible rotation speed to slow down the reaction rate between the crucible wall and the silicon melt, thereby reducing SiO formation; and increasing argon flow rate and reducing furnace pressure to promote SiO volatilization and discharge. However, while these methods reduce oxygen content, they also introduce other problems: excessively reducing crucible rotation speed weakens forced convection of the melt, leading to uneven temperature field and oxygen concentration distribution within the melt, which in turn worsens the uniformity of oxygen distribution within the crystal rod surface; especially under existing thermal field structures, the bottom of traditional heat shields has a flat configuration, and excessive reduction... Low furnace pressure and increased argon flow rate can cause volatile SiO to accumulate at the bottom of the hotplate, preventing timely discharge along the optimal path. This significantly increases the risk of SiO falling back into the melt, leading to increased SiO concentration within the melt and disrupting the uniformity of oxygen distribution. Ultimately, this results in increased oxygen content and decreased oxygen distribution uniformity within the crystal rod surface. Therefore, currently, 8-inch lightly boron- or phosphorus-doped single-crystal silicon crystal rods prepared using conventional methods mostly have oxygen contents higher than 10 ppma, with ORG between 5% and 10%, which cannot meet the requirements of high-end power devices for 8-inch substrate crystal rods. Therefore, achieving low oxygen content while ensuring high oxygen distribution uniformity within the crystal rod surface has become a critical technical challenge that urgently needs to be solved in the preparation of 8-inch lightly doped Czochralski-grown single-crystal silicon. Summary of the Invention

[0004] In view of this, it is necessary to provide a method and a single crystal rod for reducing the oxygen content of 8-inch lightly doped Czochralski single crystal and improving the uniformity of in-plane oxygen distribution, so as to achieve low oxygen content while ensuring the uniformity of in-plane oxygen distribution of the crystal rod, and meet the requirements of high-end power devices for oxygen content and in-plane oxygen distribution uniformity of 8-inch substrate crystal rods.

[0005] According to one aspect of the present invention, a method for reducing the silicon-oxygen content and improving the uniformity of in-plane oxygen distribution in 8-inch lightly doped Czochralski single crystals is provided. The thermal field structure includes: a heater disposed around a graphite crucible, a heat insulation cylinder disposed around the heater, and a heat shield disposed around the crystal rod and above the surface of the melt. The main structure of the heat shield has a top-to-bottom inward-contracting configuration followed by direct outward expansion. The inward-contracting configuration occupies 2 / 3-3 / 4 of the overall height of the heat shield, so that a gradually narrowing channel is first formed between the inner side of the heat shield and the crystal rod, causing the argon gas to gradually increase in velocity as it flows through this area, thereby enhancing the ability to carry and purge volatiles from the melt surface. Then, a diffusion channel is directly formed outward, allowing the gas flow to diffuse rapidly after leaving the melt surface, avoiding gas flow rebound or eddy current generation, thereby reducing SiO deposition at the lower edge of the heat shield. The distance between the bottom horizontal plane of the heat shield and the melt surface is 40-50 mm.

[0006] This also includes: employing the following synergistically optimized process parameters throughout the constant diameter stage of ingot growth:

[0007] The furnace pressure is set to 1-3 Torr;

[0008] The argon flow rate is set to 110-150 slm;

[0009] The pulling speed is set to 0.7-0.9 mm / min;

[0010] The ratio of the crystal rod rotation speed to the crucible rotation speed is 2.5:1 to 3:1;

[0011] During the growth of the crystal rod, as the surface of the melt decreases, the heater power decreases linearly at a rate of 0.5% per 100 mm of crystal rod growth, relative to the initial power at the beginning of the constant diameter phase.

[0012] Preferably, the crystal rod rotates at a speed of 12-20 rpm, and the crucible rotates at a speed of 4-8 rpm.

[0013] Preferably, the heat shield includes: an outer cover, an inner upper cover, and an inner lower cover; the outer cover, the inner upper cover, and the inner lower cover are all annular structures and interconnected; the outer cover is cylindrical; the inner upper cover has a V-shaped cross-section with an opening at the bottom; the inner lower cover has an outwardly expanding figure-eight shape in cross-section; the top of the inner lower cover is aligned with the bottom of the inner upper cover; and the bottom of the inner lower cover is aligned with the bottom of the outer cover.

[0014] Preferably, the angle α between the cross-section of the lower inner cover and the horizontal direction is 20-30 degrees, and the angle β between the cross-section of the upper inner cover and the vertical direction is 30-45 degrees.

[0015] Preferably, the outer cover, the inner upper cover, and the inner lower cover are all made of graphite.

[0016] According to another aspect of the present invention, a single crystal rod is provided, which is drawn by any of the methods described above for reducing the silicon-oxygen content of 8-inch lightly doped Czochralski single crystals and improving the uniformity of in-plane oxygen distribution.

[0017] The above-mentioned method for reducing the silicon-oxygen content and improving the in-plane oxygen distribution uniformity of 8-inch lightly doped Czochralski single crystals achieves the goal of reducing the silicon-oxygen content and improving the in-plane oxygen distribution uniformity of 8-inch lightly doped Czochralski single crystals through the following aspects: First, the main structure of the heat shield is set to a configuration that first tapers inward and then directly expands outward from top to bottom, and the inward-tapering configuration accounts for 2 / 3-3 / 4 of the overall height of the heat shield. This allows a gradually narrowing channel to be formed between the inner side of the heat shield and the crystal rod, and then a diffusion channel to be formed directly outward. This facilitates the rapid diffusion of SiO carried by argon gas and avoids the formation of a diffusion channel between the inner side of the heat shield and the crystal rod. First, a gas vortex is formed below to prevent the volatilized oxygen from being re-entrained into the melt. Second, the distance between the bottom of the heat shield and the melt surface is set to 40-50mm, increasing the space for radiative heat dissipation from the melt surface to the upper low-temperature region of the furnace. This facilitates the formation of a stronger and more stable "cold at the top, hot at the bottom" axial temperature gradient in the vertical direction of the melt. The enhanced axial temperature gradient increases the driving force for SiO to diffuse from the interior of the melt to the surface and volatilize on the surface. Third, by setting synergistically optimized furnace pressure and argon flow rate parameters, the furnace pressure is controlled within a low range while the argon flow rate is increased. This, combined with the advantages of this invention, allows for the following improvements. The supplied thermal field structure prevents airflow from accumulating below the heat shield, ensuring smooth airflow. The synergistic effect of low furnace pressure and high-velocity argon gas significantly improves the mass transport rate of SiO after it volatilizes from the melt surface. Fourth, increasing the pulling speed slightly reduces the effective segregation coefficient of oxygen at the solid-liquid interface, helping to reduce the total amount of oxygen entering the crystal and lowering the oxygen content within the crystal rod. Fifth, limiting the rotational speed ratio between the crystal rod and the crucible enhances forced convection of the melt, improving the uniformity of oxygen distribution within the melt, and thus improving the uniformity of oxygen distribution within the crystal rod. The increased SiO generation resulting from forced melt convection is achieved through the synergistic effect of the thermal field structure, furnace pressure, and argon gas flow rate. The design enhances the volatilization ability of SiO from the melt, increases the amount of SiO volatilization, and improves the carrying and diffusion ability of SiO, while simultaneously improving the uniformity of in-plane oxygen distribution and reducing oxygen content. Sixth, the linear decrease rate of heater power is limited to reduce the total heat input to the melt, compensate for the natural heating trend of the melt surface caused by the enhanced "thermal shielding effect," and keep the axial temperature gradient of the melt surface region stable. This allows the volatilization ability of SiO to remain stable throughout the entire growth process of the crystal rod, enabling the oxygen concentration in the melt to volatilize continuously and steadily, thereby improving the uniformity of in-plane oxygen distribution of the crystal rod. Attached Figure Description

[0018] Figure 1This is a schematic diagram of the existing thermal field structure.

[0019] Figure 2 This is a schematic diagram of the thermal field structure in this invention.

[0020] Figure 3 This is a schematic diagram of the airflow direction in the thermal field structure of this invention.

[0021] Figure 4 This is a further detailed structural diagram of the heat shield in this invention.

[0022] Figure 5 The oxygen content test results are shown in the lightly phosphorus-doped 8-inch single crystal rods pulled in Examples 1-3 and Comparative Examples 1-6 of this invention.

[0023] Figure 6 The ORG test results are shown in Examples 1-3 and Comparative Examples 1-6 of this invention, which are lightly phosphorus-doped 8-inch single crystal rods.

[0024] Figure 7 The oxygen content test results are shown in the lightly phosphorus-doped 8-inch single crystal rods pulled in Examples 4-6 and Comparative Examples 1-6 of the present invention.

[0025] Figure 8 The ORG test results are shown in Examples 4-6 and Comparative Examples 1-6 of this invention, which are lightly phosphorus-doped 8-inch single crystal rods.

[0026] Figure 9 The oxygen content test results are shown in the lightly phosphorus-doped 8-inch single crystal rods pulled in Examples 7-9 and Comparative Examples 1-6 of this invention.

[0027] Figure 10 The ORG test results are shown in Examples 7-9 and Comparative Examples 1-6 of this invention, which are lightly phosphorus-doped 8-inch single crystal rods.

[0028] Figure 11 The oxygen content test results are shown in the lightly phosphorus-doped 8-inch single crystal rods pulled in Examples 10-12 and Comparative Examples 1-6 of this invention.

[0029] Figure 12 The ORG test results are shown in Examples 10-12 and Comparative Examples 1-6 of this invention, which are lightly phosphorus-doped 8-inch single crystal rods.

[0030] Figure 13 The oxygen content test results are shown in Examples 13-15 and Comparative Examples 7-12 of this invention, which are lightly boron-doped 8-inch single crystal rods.

[0031] Figure 14The ORG test results are shown in Examples 13-15 and Comparative Examples 7-12 of this invention, which are lightly boron-doped 8-inch single crystal rods.

[0032] Figure 15 The oxygen content test results are shown in the lightly boron-doped 8-inch single crystal rods pulled in Examples 16-18 and Comparative Examples 7-12 of this invention.

[0033] Figure 16 The ORG test results are shown in Examples 16-18 and Comparative Examples 7-12 of this invention.

[0034] Figure 17 The oxygen content test results are shown in the lightly boron-doped 8-inch single crystal rods pulled in Examples 19-21 and Comparative Examples 7-12 of this invention.

[0035] Figure 18 The ORG test results are shown in Examples 19-21 and Comparative Examples 7-12 of this invention, which are lightly boron-doped 8-inch single crystal rods.

[0036] Figure 19 The oxygen content test results are shown in Examples 22-24 and Comparative Examples 7-12 of this invention, which are lightly boron-doped 8-inch single crystal rods.

[0037] Figure 20 The ORG test results are shown in Examples 22-24 and Comparative Examples 7-12 of this invention, which are lightly boron-doped 8-inch single crystal rods.

[0038] In the figure: Graphite crucible 1; heater 2; insulation cylinder 3; heat shield 4; outer cover 40; inner upper cover 41; inner lower cover 42; melt 5; crystal rod 6; upper heat insulation material 70; support ring 71; inner heat insulation material 72. Detailed Implementation

[0039] The technical solutions and effects of the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0040] This invention provides a method for reducing the silicon-oxygen content and improving the uniformity of in-plane oxygen distribution in 8-inch lightly doped Czochralski single crystals. Please refer to [link / reference]. Figure 1 , Figure 2 and Figure 3The adopted thermal field structure includes: a heater 2 set around the graphite crucible 1, a heat insulation cylinder 3 set around the heater 2, and a heat shield 4 set around the crystal rod 6 and above the surface of the melt 5. The main structure of the heat shield 4 is inwardly contracted and then directly outwardly expanded from top to bottom. This first forms a gradually narrowing channel between the inner side of the heat shield 4 and the crystal rod 6, which gradually increases the flow velocity of argon gas as it flows through this area, thereby enhancing the ability to carry and purge volatiles on the surface of the melt 5. Then, it directly forms an outwardly diffused channel, which allows the gas flow to diffuse rapidly after leaving the surface of the melt 5, avoiding gas flow rebound or eddy current generation, thereby reducing the deposition of SiO at the lower edge of the heat shield 4. The inwardly contracted configuration in the heat shield accounts for 2 / 3-3 / 4 of the overall height of the heat shield. The distance between the bottom horizontal plane of the heat shield 4 and the surface of the melt 5 is 40-50 mm.

[0041] This also includes: employing the following synergistically optimized process parameters throughout the constant diameter stage of ingot growth:

[0042] The furnace pressure is set to 1-3 Torr;

[0043] The argon flow rate is set to 110-150 slm;

[0044] The pulling speed is set to 0.7-0.9 mm / min;

[0045] The ratio of the crystal rod rotation speed to the crucible rotation speed is 2.5:1 to 3:1;

[0046] During the growth of the crystal rod, as the surface of the melt decreases, the heater power decreases linearly at a rate of 0.5% per 100 mm of crystal rod growth, relative to the initial power at the beginning of the constant diameter phase.

[0047] In this embodiment, the process parameters are synergistically optimized in the following aspects to achieve the goal of reducing the silicon-oxygen content of 8-inch lightly doped Czochralski single crystals while improving the uniformity of in-plane oxygen distribution:

[0048] First, coordinate the configuration of thermal field and airflow:

[0049] By configuring the main structure of the heat shield 4 in the thermal field structure as a shape that first tapers inward and then expands outward from top to bottom, with the inward-tapering configuration occupying 2 / 3-3 / 4 of the overall height of the heat shield, a gradually narrowing channel is first formed between the inner side of the heat shield 4 and the crystal rod 6, followed by an outward diffusion channel. This facilitates the rapid diffusion of SiO carried by argon gas. Compared with the traditional heat shield 4, as... Figure 1As shown, to avoid the formation of gas vortices below the heat shield 4, and to prevent the volatilized oxygen from being re-entered into the melt, causing an increase in the SiO concentration in the melt 5 and disrupting the uniformity of oxygen distribution, ultimately leading to an increase in oxygen content and a decrease in the uniformity of oxygen distribution on the surface of the crystal rod 6; on the other hand, by setting the distance between the bottom horizontal plane of the heat shield 4 and the surface of the melt 5 to 40-50mm, the radiation heat dissipation space from the surface of the melt 5 to the low-temperature region above the furnace body is increased, which is conducive to forming a stronger and more stable "cold at the top and hot at the bottom" axial temperature gradient in the vertical direction of the melt 5. The enhanced axial temperature gradient increases the driving force for SiO to diffuse from the interior of the melt to the surface of the melt 5 and volatilize on the surface, thereby reducing the oxygen content in the crystal rod 6;

[0050] On the other hand, the furnace pressure is controlled in a low range of 1-3 Torr, while the argon flow rate is increased to 110-150 slm. Due to the use of the thermal field structure provided by this invention, the airflow will not accumulate below the heat screen 4, ensuring smooth airflow. The low furnace pressure and high flow rate argon work together to greatly improve the mass transport rate of SiO after it evaporates from the surface of the melt.

[0051] Second, fine-tune the growth rate of the crystal rod:

[0052] Compared with existing technologies, slightly increasing the pulling speed can slightly reduce the effective segregation coefficient of oxygen at the solid-liquid interface, thereby helping to reduce the total amount of oxygen entering the crystal rod.

[0053] Third, adjust the dynamic parameters:

[0054] By limiting the rotational speed ratio between the crystal rod and the crucible, forced convection of the melt is enhanced, the uniformity of oxygen distribution in the melt is improved, and thus the uniformity of oxygen distribution in the crystal rod is improved.

[0055] The increased SiO generation caused by the forced convection of melt 5 enhances the volatilization ability of SiO from melt 5, increases the amount of SiO volatilization, and enhances the carrying and diffusion ability of SiO through the coordinated setting of thermal field structure, furnace pressure and argon flow rate. Thus, under the synergistic effect of thermal field structure and process parameters, the purpose of improving the uniformity of in-plane oxygen distribution and reducing oxygen content can be achieved at the same time.

[0056] Fourth, dynamic power compensation:

[0057] Limiting the linear decrease rate of heater 2 power reduces the total heat input to melt 5, compensates for the natural heating trend of melt 5 surface caused by the enhanced "thermal shielding effect", keeps the axial temperature gradient of melt 5 liquid surface region stable, and thus keeps the volatilization ability of SiO stable throughout the entire growth process of the crystal rod, allowing the oxygen concentration in melt 5 to volatilize continuously and steadily, thereby improving the uniformity of oxygen distribution in the crystal rod surface.

[0058] Furthermore, the crystal rod rotation speed is 12-20 rpm, and the crucible rotation speed is 4-8 rpm.

[0059] In this embodiment, under the limited ratio of the crystal rod rotation speed to the crucible rotation speed, the crystal rod rotation speed and the crucible rotation speed are further specifically limited, so as to facilitate specific coordination with the aforementioned furnace pressure, argon flow rate and pulling speed during the crystal pulling process, and better achieve the purpose of the present invention.

[0060] Further, please see Figure 4 The heat shield 4 includes: an outer cover 40, an inner upper cover 41, and an inner lower cover 42; the outer cover 40, the inner upper cover 41, and the inner lower cover 42 are all annular structures and are interconnected; the outer cover 40 is cylindrical; the inner upper cover 41 has a V-shaped cross-section with an opening at the bottom; the inner lower cover 42 has an outwardly expanding figure-eight cross-section; the top of the inner lower cover 42 is connected to the bottom of the inner upper cover 41; the bottom of the inner lower cover 42 is connected to the bottom of the outer cover 40.

[0061] In this embodiment, compared with the prior art, the above-mentioned arrangement guides and controls the flow rate of argon gas, and forms an optimal path for the discharge of SiO. The principle is as follows:

[0062] 1. Airflow guidance and velocity control

[0063] The upper V-shaped structure forms a gradually narrowing channel from top to bottom, which gradually increases the flow velocity of argon gas as it flows through this region (according to Bernoulli's principle, the flow velocity increases as the cross-sectional area decreases), thereby enhancing the ability of argon gas to carry and purge volatiles on the surface of the melt, namely SiO.

[0064] The lower V-shaped structure: the opening expands downward to form an outward diffusion channel, which allows the airflow to diffuse and slow down rapidly after leaving the melt surface, avoiding airflow rebound or eddy current generation, thereby preventing SiO deposition at the lower edge of the heat shield 4;

[0065] 2. Optimization of SiO discharge path

[0066] The inner wall of the lower inner cover 42, which has an outwardly expanding figure-eight structure, is inclined, which can guide the airflow to flow outward and downward, so that the airflow carrying SiO naturally moves away from the central area of ​​the melt 5, preventing SiO from falling back into the melt; it avoids the airflow stagnation area that is easily formed under the traditional heat shield 4 due to its flat bottom structure, and avoids the adhesion and accumulation of SiO at the bottom of the heat shield 4.

[0067] In this embodiment, please refer to Figure 4Furthermore, a support ring 71 is provided at the top of the heat shield 4, the heat shield 4 is installed at the bottom of the support ring 71, and an upper heat insulation material 70 is provided at the top of the support ring 71; a cavity is formed between the outer cover 40, the inner upper cover 41, and the inner lower cover 42, and the cavity is filled with the inner heat insulation material 72; both the upper heat insulation material 70 and the inner heat insulation material 72 are made of cured carbon felt; the support ring 71, the outer cover 40, the inner upper cover 41, and the inner lower cover 42 are all made of graphite;

[0068] With the above configuration, the upper thermal insulation material 70, the support ring 71, and the inner thermal insulation material 72 mainly serve as supports and heat preservation components.

[0069] Further, please see Figure 4 The angle α between the cross section of the lower inner cover and the horizontal direction is 20-30 degrees, and the angle β between the cross section of the upper inner cover and the vertical direction is 30-45 degrees.

[0070] In this embodiment, the included angle α determines the diffusion rate of the airflow after it leaves the melt surface. The larger α is, the more intense the airflow diffusion and the faster the deceleration, which is beneficial to prevent eddies. However, if the angle is too large, it will cause the airflow to lose direction and weaken the purging of the melt edge. The smaller α is, the stronger the adhesion of the airflow, which is not conducive to rapid diffusion and is easy to form a stagnation zone below the heat shield. Therefore, limiting the included angle α to 20-30 degrees ensures that the airflow can diffuse rapidly, avoids SiO falling back, and at the same time maintains the flow direction of the airflow, so as not to weaken the airflow's ability to purge and carry the SiO volatilized at the melt edge.

[0071] The included angle β determines the contraction rate of the argon gas flow through the narrowing channel between the crystal rod and the hot shield. The larger β is, the faster the narrowing channel contracts, and the more significant the increase in argon gas flow rate, which is beneficial to enhancing the purging ability of volatiles on the melt surface. However, if β is too large, it is easy to induce turbulence, resulting in poor gas flow stability. The smaller β is, the slower the increase in argon gas flow rate and the weaker the purging effect. Therefore, the included angle β is limited to 30-45 degrees so that the argon gas flow can maintain flow stability while achieving efficient purging of SiO.

[0072] The present invention also provides a single crystal rod, which is drawn by any of the methods described above for reducing the silicon-oxygen content of 8-inch lightly doped Czochralski single crystals and improving the uniformity of in-plane oxygen distribution.

[0073] The beneficial effects of the present invention will be described below with reference to specific comparative examples and embodiments.

[0074] Comparative Examples 1-3 (lightly doped with phosphorus)

[0075] Lightly phosphorus-doped crystals were pulled using a conventional flat-bottomed heatsink and the process parameters provided in this invention to pull 8-inch single-crystal rods. During the constant diameter process, the distance from the bottom horizontal plane of heatsink 4 to the melt surface, rod rotation speed, crucible rotation speed, the ratio of rod rotation speed to crucible rotation speed, furnace pressure, argon flow rate, and pulling speed are shown in Table 1. After the crystal pulling process was completed, the phosphorus-doped single-crystal sample was removed, and oxygen content and ORG were tested. The test results are as follows: Figure 5-12 As shown.

[0076] Comparative Examples 4-6 (lightly phosphorus-doped)

[0077] Lightly phosphorus-doped crystal pulling was performed using the thermal field structure provided in this invention, combined with conventional process parameters to pull 8-inch single-crystal rods. During the constant diameter process, the distance from the bottom horizontal plane of the thermal screen 4 to the melt surface, rod rotation speed, crucible rotation speed, the ratio of rod rotation speed to crucible rotation speed, furnace pressure, argon flow rate, and pulling speed are shown in Table 1. After the crystal pulling process was completed, the phosphorus-doped single-crystal sample was removed, and oxygen content and ORG were tested. The test results are as follows: Figure 5-12 As shown.

[0078] Examples 1-12 (lightly phosphorus-doped)

[0079] Lightly phosphorus-doped crystals were pulled using the thermal field structure and synergistic process parameters provided in this invention to produce 8-inch single-crystal rods. During the constant diameter process, the distance from the bottom horizontal plane of the heat shield 4 to the melt surface, the rod rotation speed, the crucible rotation speed, the ratio of rod rotation speed to crucible rotation speed, the furnace pressure, the argon flow rate, and the pulling speed are shown in Table 2. After the crystal pulling process was completed, the phosphorus-doped single-crystal sample was removed, and oxygen content and ORG were tested. The test results are as follows: Figure 5-12 As shown.

[0080] Table 1

[0081]

[0082] Table 2

[0083]

[0084] Comparative Examples 7-9 (lightly boron-doped)

[0085] Lightly boron-doped crystals were pulled using a conventional flat-bottomed hotspot and the process parameters provided in this invention to pull 8-inch single-crystal rods. During the constant diameter process, the distance from the bottom horizontal plane of the hotspot 4 to the melt surface, the rod rotation speed, the crucible rotation speed, the ratio of rod rotation speed to crucible rotation speed, the furnace pressure, the argon flow rate, and the pulling speed are shown in Table 3. After the crystal pulling process was completed, phosphorus-doped single-crystal samples were removed and tested for oxygen content and ORG. The test results are as follows: Figure 13-20 As shown.

[0086] Comparative Example 10-12 (lightly boron-doped)

[0087] Lightly boron-doped crystals were pulled using the thermal field structure provided in this invention, combined with conventional process parameters to pull 8-inch single-crystal rods. During the constant diameter process, the distance from the bottom horizontal plane of the thermal screen 4 to the melt surface, the rod rotation speed, the crucible rotation speed, the ratio of rod rotation speed to crucible rotation speed, the furnace pressure, the argon flow rate, and the pulling speed are shown in Table 3. After the crystal pulling process was completed, phosphorus-doped single-crystal samples were taken out, and oxygen content and ORG were tested. The test results are as follows: Figure 13-20 As shown.

[0088] Table 3

[0089]

[0090] Examples 13-24 (lightly boron-doped)

[0091] Lightly boron-doped crystals were pulled using the thermal field structure and synergistic process parameters provided in this invention to produce 8-inch single-crystal rods. During the constant diameter process, the distance from the bottom horizontal plane of the heat shield 4 to the melt surface, the rod rotation speed, the crucible rotation speed, the ratio of rod rotation speed to crucible rotation speed, the furnace pressure, the argon flow rate, and the pulling speed are shown in Table 4. After the crystal pulling process was completed, the boron-doped single-crystal sample was removed, and oxygen content and ORG were tested. The test results are as follows: Figure 13-20 As shown.

[0092] Table 4

[0093]

[0094] Comparative Examples 1-3 show 8-inch lightly phosphorus-doped single-crystal ingots drawn using a conventional flat-bottom design of the thermal screen and the process parameters provided by this invention. Comparative Examples 4-6 show 8-inch lightly phosphorus-doped single-crystal ingots drawn using the thermal field structure provided by this invention and conventional process parameters. Figure 5 , 7 As can be seen from Figures 9 and 11, the oxygen content of the single-crystal rods pulled in Comparative Examples 1-3 is between 10-14 ppma, all higher than 10 ppma; the oxygen content of the single-crystal rods pulled in Comparative Examples 4-6, except for a few points between 10-12 ppma, is between 12-17 ppma, all higher than 10 ppma; from Figure 6 , 8 As can be seen from 10 and 12, except for a few points in Comparative Examples 4 and 5 where the ORG is less than 5%, the ORG at the other test points in Comparative Examples 1-6 is between 5% and 11%.

[0095] Examples 1-12 are 8-inch lightly phosphorus-doped single crystal rods drawn using the thermal field structure and synergistic process parameters provided by this invention. Figure 5 , 7As can be seen from 9 and 11, in Examples 1-12, the oxygen content was higher than 10 ppma at some test points within a 200 mm crystal rod length, and lower than but close to 10 ppma at other test points. At test points with a crystal rod length greater than 200 mm, except for a few abnormal points, the oxygen content was lower than 10 ppma at other test points. However, the 200 mm section within the crystal rod head is an unstable growth section and is not included in the performance evaluation scope. Figure 6 , 8 As can be seen from 10 and 12, the ORG, which characterizes the uniformity of oxygen distribution in the surface, is above 5% at all test points except for a few abnormal points. In Examples 1-12, it is below 5% at other test points.

[0096] Comparative Examples 7-9 show 8-inch lightly boron-doped single-crystal ingots drawn using a conventional flat-bottom design and the process parameters provided by this invention. Comparative Examples 10-12 show 8-inch lightly boron-doped single-crystal ingots drawn using the thermal field structure provided by this invention and conventional process parameters. Figure 13 , 15 As can be seen from 17 and 19, the oxygen content of the single crystal rods pulled in Comparative Examples 7-9 is higher than 10 ppma; the oxygen content of the single crystal rods pulled in Comparative Examples 10-12 is higher than 10 ppma at all test points, except for a few points that are lower than but close to 10 ppma. Figure 14 , 16 As can be seen from Figures 18 and 20, the ORG of the single-crystal ingots pulled in Comparative Examples 7-9 is between 7% and 11%, all higher than 5%; the ORG of the single-crystal ingots pulled in Comparative Examples 10-12 is between 5% and 10%, all higher than 5%.

[0097] Examples 13-24 are 8-inch lightly boron-doped single crystal rods pulled using the thermal field structure and synergistic process parameters provided by this invention. Figure 13 , 15 As can be seen from 17 and 19, in Examples 13-24, except for Example 19 where the oxygen content is slightly higher than 10 ppma at the point where the crystal rod length is 0 mm, the oxygen content at other test points is lower than 10 ppma; from Figure 14 , 16 As can be seen from 18 and 20, except for a few outliers, the ORG at other test points in Examples 13-24 is below 5%;

[0098] In summary, compared with the 8-inch lightly phosphorus-doped and lightly boron-doped single crystal rods pulled using the conventional flat-bottom design of the thermal screen and the process parameters of this invention, and compared with the 8-inch lightly phosphorus-doped and lightly boron-doped single crystal rods pulled using the thermal field structure of this invention and conventional process parameters, the 8-inch lightly phosphorus-doped and lightly boron-doped single crystal rods pulled using the thermal field structure and synergistic process parameters provided by this invention simultaneously achieve the goals of reducing the oxygen content to below 10 ppma and improving the in-plane oxygen distribution (ORG) to below 5%. Therefore, by simultaneously using the thermal field structure and synergistic process parameters provided by this invention, the goals of reducing oxygen content and improving the uniformity of in-plane oxygen distribution can be achieved simultaneously, meeting the requirements of high-end power devices for 8-inch substrate rods.

[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 the silicon-oxygen content and improving the uniformity of in-plane oxygen distribution in 8-inch lightly doped Czochralski single crystals, characterized in that: The adopted thermal field structure includes: a heater surrounding the graphite crucible, a heat insulation cylinder surrounding the heater, and a heat shield surrounding the crystal rod and above the surface of the melt. The main structure of the heat shield has a top-to-bottom inward-contracting and then outward-expanding configuration. The inward-contracting configuration accounts for 2 / 3-3 / 4 of the overall height of the heat shield, forming a gradually narrowing channel between the inner side of the heat shield and the crystal rod. This allows the argon gas to gradually increase in velocity as it flows through this area, thereby enhancing its ability to carry and purge volatiles from the melt surface. Then, an outward diffusion channel is formed, allowing the gas flow to diffuse rapidly after leaving the melt surface, preventing gas flow rebound or eddy current generation, thus reducing SiO deposition at the lower edge of the heat shield. The distance between the bottom horizontal plane of the heat shield and the melt surface is 40-50 mm. This also includes: employing the following synergistically optimized process parameters throughout the constant diameter stage of ingot growth: The furnace pressure is set to 1-3 Torr; The argon flow rate is set to 110-150 slm; The pulling speed is set to 0.7-0.9 mm / min; The ratio of the crystal rod rotation speed to the crucible rotation speed is 2.5:1 to 3:1; During the growth of the crystal rod, as the surface of the melt decreases, the heater power decreases linearly at a rate of 0.5% per 100 mm of crystal rod growth, relative to the initial power at the beginning of the constant diameter phase.

2. The method for reducing oxygen content and improving in-plane oxygen distribution uniformity in 8-inch lightly doped, as-pulled, single crystal silicon of claim 1, wherein: The crystal rod rotates at a speed of 12-20 rpm, and the crucible rotates at a speed of 4-8 rpm.

3. The method for reducing the silicon-oxygen content and improving the in-plane oxygen distribution uniformity of 8-inch lightly doped Czochralski single crystals as described in claim 1, characterized in that... The heat shield includes: an outer cover, an upper inner cover, and a lower inner cover; the outer cover, the upper inner cover, and the lower inner cover are all annular structures and interconnected; the outer cover is cylindrical; the upper inner cover has a V-shaped cross-section with an opening at the bottom; the lower inner cover has an outwardly expanding V-shaped cross-section; the top of the lower inner cover is aligned with the bottom of the upper inner cover; and the bottom of the lower inner cover is aligned with the bottom of the outer cover.

4. The method for reducing the silicon-oxygen content and improving the in-plane oxygen distribution uniformity of 8-inch lightly doped Czochralski single crystals as described in claim 3, characterized in that... The angle α between the cross-section of the lower inner cover and the horizontal direction is 20-30 degrees, and the angle β between the cross-section of the upper inner cover and the vertical direction is 30-45 degrees.

5. The method for reducing the silicon-oxygen content and improving the in-plane oxygen distribution uniformity of 8-inch lightly doped Czochralski single crystals as described in claim 3, characterized in that... The outer cover, the upper inner cover, and the lower inner cover are all made of graphite.

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