A DC resistance heater and a SiC single crystal growth apparatus

Abstract

This application provides a DC resistance heater and a SiC single crystal growth apparatus. The DC resistance heater includes a bottom heating element and a middle heating element. The bottom heating element is used to heat the material at the bottom of the material filling area in the crucible, and the middle heating element is used to heat the material in the upper middle part of the material filling area in the crucible. The heat generated per unit length along the axial direction of the middle heating element of the upper middle part of the material is greater than that generated per unit length along the axial direction of the bottom heating element. In this way, an axial temperature gradient can be formed between the bottom and upper middle parts of the material, so that the temperature of the bottom material is lower than that of the upper middle part of the material. The SiC gas phase component decomposed at the bottom will not crystallize on the surface of the material with a higher temperature during the rising process, but will directly enter the growth chamber and crystallize on the seed crystal through diffusion or convection, thereby improving the crystal growth rate and contributing to the stability of the 4H-SiC crystal form.

Description

Technical Field

[0001] This invention belongs to the field of crystal growth, specifically relating to a DC resistance heater and a SiC single crystal growth apparatus. Background Technology

[0002] Silicon carbide (SiC) is a typical representative of third-generation semiconductor materials. Due to its excellent comprehensive performance and the fact that SiC-based devices can operate in extreme environments such as high temperature, high pressure, and strong radiation, silicon carbide has broad application prospects in the fields of power electronics and microwave communication.

[0003] Physical vapor transport (PVT) is currently the mainstream method for growing SiC crystals, producing n-type and semi-insulating 4H-SiC single crystals. n-type SiC single crystal substrates are primarily used for fabricating high-power power electronic devices, while semi-insulating SiC single crystal substrates are mainly used for fabricating high-power microwave devices.

[0004] With advancements in single-crystal growth technology, the diameter of SiC single-crystal substrates has been increasing year by year, from the initial 2 inches to the current 8-inch single-crystal substrates. Currently, 6 inches remains the mainstream diameter for SiC single-crystal substrates in the market, and most SiC single-crystal growth furnaces are induction heating furnaces. Due to the extremely large size of 8-inch SiC single crystals, if induction heating furnaces are still used for growth, the resulting single crystal will have very high thermal stress, and the defect density will be difficult to control. Therefore, resistance heating single-crystal furnaces should be preferred for growing 8-inch SiC single crystals.

[0005] Traditional DC resistance heaters are shaped like... Figure 1 As shown, its structure resembles a vertical fence. From Figure 1 It can be seen that when direct current is applied to the heater, the heater generates Joule heat, and the heat is transferred to the outer cylindrical surface of the crucible for SiC single crystal growth and the surfaces of the upper and lower covers through radiation. From Figure 1 It can also be seen that the Joule heat generated by the heater is relatively uniform in the vertical direction. Therefore, the axial temperature gradient of the thermal field in the crucible generated by traditional DC resistance heating is relatively small. An excessively small axial temperature gradient has the following adverse effects on SiC single crystal growth:

[0006] Because the heater extends below the bottom of the crucible, the heat radiated by the heater is transferred not only to the sides of the crucible but also to the bottom. This results in the high-temperature zone in the SiC polycrystalline material always being at the bottom, while the surface temperature remains relatively low. The SiC gaseous components that decompose at the bottom often crystallize on the surface, causing the surface to bulge upwards. This reduces the concentration of SiC gaseous components within the growth chamber, slowing down crystal growth; it also lowers the temperature of the SiC gaseous components, thereby reducing the carbon / silicon ratio in the gaseous components, which is detrimental to the crystal stability of 4H-SiC. Summary of the Invention

[0007] To address the technical problem that the small axial temperature gradient of traditional DC resistance heaters affects the growth of SiC single crystals, this application provides a DC resistance heater and a SiC single crystal growth apparatus.

[0008] The technical solution of this application is as follows:

[0009] This application provides a DC resistance heater, which includes a bottom heating element and a middle heating element along the axial direction of the DC resistance heater;

[0010] The bottom heating element is used to heat the material at the bottom of the material filling area inside the crucible, and the middle heating element is used to heat the material in the upper middle part of the material filling area inside the crucible.

[0011] Along the first direction, the amount of heat generated per unit length by the middle heating element is greater than the amount of heat generated per unit length by the bottom heating element.

[0012] In one design, along the axial direction of the DC resistance heater, the DC resistance heater includes a top heating element located at the end of the middle heating element away from the bottom heating element; the top heating element is used to heat the crystal growth region.

[0013] Along the axial direction of the DC resistance heater, the heat generated per unit length of the top heating element is less than the heat generated per unit length of the middle heating element, and less than the heat generated per unit length of the bottom heating element.

[0014] In one design, along the axial direction of the DC resistance heater, the resistance per unit length of the middle heating element is greater than that of the bottom heating element, and the resistance per unit length of the bottom heating element is greater than that of the top heating element.

[0015] In one design, the bottom heating element, the middle heating element, and the top heating element are integrated into a single structure.

[0016] Along the first direction, the DC resistance heater includes a plurality of resistance layers;

[0017] Among them, the multiple resistive layers used to heat the material at the bottom of the crucible belong to the bottom heating element, and the interlayer spacing of the multiple resistive layers of the bottom heating element is d1;

[0018] The plurality of resistive layers used for heating the material in the upper part of the crucible belong to the central heating element, and the interlayer spacing of the plurality of resistive layers of the central heating element is d2;

[0019] The multiple resistive layers used to heat the crystal growth region belong to the top heating element, and the interlayer spacing of the multiple resistive layers corresponding to the top heating element is d3;

[0020] d2 < d1 < d3.

[0021] In one design, the DC resistance heater includes n resistance units and at least one connecting resistor. The n resistance units are arranged along the circumferential direction to form a cylindrical structure capable of accommodating a crucible, where n is a natural number greater than or equal to 2.

[0022] Along the first direction, the resistor unit includes multiple stacked sub-resistor layers and multiple inter-layer resistors, and adjacent sub-resistor layers in the same resistor unit are connected in series end to end through the inter-layer resistors;

[0023] The connecting resistor is used to linearly connect n resistor units in series.

[0024] In one design, the number of resistor units is two, and the number of connecting resistors is one;

[0025] Along the first direction, the connecting resistor is located at one end of the two resistor units.

[0026] In one design, the connection resistor is a ring-shaped resistor.

[0027] In one design, the connecting resistor is located at one end of the top heating element of the resistor unit.

[0028] In one design, the connecting resistor is a notched annular resistor, with one end connected to one of the resistor units and the other end connected to another resistor unit along the direction of current flow.

[0029] In one design, the DC resistance heater includes two resistance units, a positive terminal connection resistor, and a negative terminal connection resistor. The two resistance units are arranged opposite each other to form a cylindrical structure capable of accommodating a crucible.

[0030] Along the first direction, the resistor unit includes multiple stacked sub-resistor layers and multiple inter-layer resistors, with adjacent sub-resistor layers in the same resistor unit connected in series end to end through the inter-layer resistors;

[0031] The two resistor units are connected in parallel through the positive terminal connection resistor and the negative terminal connection resistor.

[0032] In one design, along the first direction, the positive terminals of the two resistor units are located at both ends of the DC resistance heater, and the negative terminals of the two resistor units are located at both ends of the DC resistance heater.

[0033] Along the circumferential direction, the positive terminal connecting resistor and the negative terminal connecting resistor are located in different gaps between the two resistor units.

[0034] Along the first direction, one end of the positive terminal connecting resistor is connected to the positive terminal of one of the resistor units, and the other end of the positive terminal connecting resistor is connected to the positive terminal of another resistor unit; one end of the negative terminal connecting resistor is connected to the negative terminal of one of the resistor units, and the other end of the negative terminal connecting resistor is connected to the negative terminal of another resistor unit.

[0035] In one design, the DC resistance heater includes a first input electrode and a second input electrode;

[0036] The first input electrode is electrically connected to the positive terminal via a resistor, and the second input electrode is electrically connected to the negative terminal via a resistor;

[0037] The first and second input electrodes are located inside the cylindrical structure formed by the two resistive units and at the bottom end of the bottom heating element. Based on the same inventive concept, this application also provides a SiC single crystal growth apparatus, including any of the aforementioned DC resistance heaters, and further comprising:

[0038] A crucible, comprising a cavity formed by a bottom, side walls, and a top cover; the portion of the cavity near the bottom is a material filling area, and the portion of the cavity near the top cover is a crystal growth area;

[0039] A seed crystal holder, located in the crystal growth area and disposed on the inner side of the upper cover, is used to mount the seed crystal;

[0040] The bottom heating element is located on the outer periphery of the bottom of the crucible;

[0041] The central heating element is mainly located on the outer periphery of the material filling area of ​​the crucible.

[0042] Compared with the prior art, the beneficial effects of this invention are:

[0043] The DC resistance heater and SiC single crystal growth apparatus provided in this application include a bottom heating element and a middle heating element. The bottom heating element is used to heat the material at the bottom of the material filling area in the crucible, and the middle heating element is used to heat the material in the upper middle part of the material filling area in the crucible. The heat generated per unit length along the axial direction of the middle heating element of the upper middle part of the material is greater than that generated per unit length along the axial direction of the bottom heating element. In this way, an axial temperature gradient can be formed between the bottom and the upper middle part of the material, so that the temperature of the bottom material is lower than that of the upper middle part of the material. The SiC gas phase component decomposed at the bottom will not crystallize on the surface of the material with a higher temperature during the rising process, but will directly enter the growth chamber and crystallize on the seed crystal through diffusion or convection, thereby improving the crystal growth rate and contributing to the stability of the 4H-SiC crystal form.

[0044] Additional advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0045] Figure 1 The diagram shown is a structural diagram of a traditional DC resistance heater;

[0046] Figure 2 The diagram shown is a first structural schematic of a DC resistance heater provided in an embodiment of this application;

[0047] Figure 3 As shown Figure 2 The diagram shows a cross-sectional structure of a DC resistance heater.

[0048] Figure 4 The diagram shown is a structural schematic of a SiC single crystal growth apparatus provided in an embodiment of this application.

[0049] Figure 5 The diagram shown is a second structural schematic of the DC resistance heater provided in an embodiment of this application;

[0050] Figure 6 The diagram shown is a third structural schematic of the DC resistance heater provided in the embodiments of this application;

[0051] The attached figures are labeled as follows:

[0052] 1. DC resistance heater; 11. Bottom heating element; 12. Middle heating element; 13. Top heating element;

[0053] 1A, Resistor unit; 1A1, Sub-resistor layer; 1A2, Interlayer resistance; 1B, Connection resistor; 1B1, Notch; 1C, Positive connection resistor; 1D, Negative connection resistor; 1E, First input electrode; 1F, Second input electrode; 1E1, Positive interface; 1F1, Negative interface;

[0054] 2. Crucible; 21. Bottom; 22. Top cover; 23. Side wall; 2A. Material filling area; 2B. Crystal growth area; 3. Seed crystal; 4. SiC polycrystalline material. Detailed Implementation

[0055] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The implementation methods provided in this application can be combined with each other without contradiction. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0056] In the description of the embodiments of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0057] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0058] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0059] The core idea of ​​the DC resistance heater in this application is to make the material in the upper part of the material filling zone have a higher temperature than the material at the bottom. In this way, when the material at the bottom decomposes, it will not crystallize on the surface of the material in the material filling zone, thereby improving the crystal growth rate and the crystal stability of 4H-SiC.

[0060] The technical approach employed is as follows: the heat generated per unit length along the axial direction of the middle heating element is greater than that of the bottom heating element. In this way, an axial temperature gradient can be formed between the bottom and upper middle parts of the material. The temperature of the bottom material is lower than that of the upper middle material. Therefore, the SiC gas phase component decomposed at the bottom will not crystallize on the surface of the material with a higher temperature during the rising process, but will directly enter the growth chamber and crystallize on the seed crystal through diffusion or convection, thereby increasing the crystal growth rate.

[0061] It should be noted that the materials mentioned in this application refer to SiC polycrystalline material, but are not limited to SiC polycrystalline material. For example, it can also be a mixture of SiC polycrystalline material and Si particles. The DC resistance heater and SiC single crystal growth apparatus provided in the embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0062] Figure 2 The diagram shown is a first structural schematic of a DC resistance heater provided in an embodiment of this application; Figure 3 As shown Figure 2 The diagram shows a cross-sectional structure of a DC resistance heater. Figure 4 The diagram shown is a structural schematic of a SiC single crystal growth apparatus provided in an embodiment of this application. Figure 5 The diagram shown is a second structural schematic of the DC resistance heater provided in an embodiment of this application; Figure 6 The diagram shown is a third structural schematic of the DC resistance heater provided in the embodiments of this application.

[0063] Please combine Figures 2 to 6 The DC resistance heater provided in this application includes a bottom heating element 11 and a middle heating element 12 along the axial direction of the DC resistance heater. The bottom heating element 11 is used to heat the material at the bottom of the material filling area 2A in the crucible 2, and the middle heating element 12 is used to heat the material in the upper middle part of the material filling area 2A in the crucible 2. Along the axial direction of the DC resistance heater, the heat generated per unit length of the middle heating element 12 is greater than the heat generated per unit length of the bottom heating element 11.

[0064] Specifically, please combine Figures 2 to 6In this application, the heat generated per unit length of the central heating element 12 is greater than that generated per unit length of the bottom heating element 11. Therefore, when the DC resistance heater of this application is used in a SiC single crystal growth apparatus, a thermal field with an axial temperature gradient will be generated in the crucible 2. Since the heat generated per unit length of the central heating element 12 is greater than that of the bottom heating element 11, the traditional phenomenon where the high-temperature zone of a DC resistance heater is located at the bottom of the material will be changed. The temperature of the SiC polycrystalline material in the upper middle part of the crucible 2 will be greater than the temperature of the SiC polycrystalline material at the bottom of the crucible 2, particularly increasing the temperature of the material surface. As a result, the SiC gaseous components decomposed at the bottom will not crystallize on the surface of the material, causing the surface to bulge upwards. Instead, they will directly enter the growth chamber and crystallize on the seed crystal 3 through diffusion or convection, thus increasing the crystal growth rate. Please refer to [further details]. Figures 2 to 6 In some embodiments of this application, along the axial direction of the DC resistance heater, the DC resistance heater includes a top heating element 13, which is located at the end of the middle heating element 12 away from the bottom heating element 11; the top heating element 13 is used to heat the crystal growth region 2B, and the seed crystal 3 is located in the crystal growth region 2B; along the axial direction of the DC resistance heater, the heat generated per unit length of the top heating element 13 is less than the heat generated per unit length of the middle heating element 12, and less than the heat generated per unit length of the bottom heating element 11.

[0065] You might wonder if, to prevent the SiC vapor phase components from crystallizing on the material surface during the use of a traditional DC resistance heater, it's possible to increase the current of the DC resistance heater, thereby increasing its overall heat output and preventing crystallization. However, we need to consider that the traditional DC resistance heater heats not only the SiC polycrystalline material in crucible 2 but also the seed crystal 3. Increasing the heat output of the DC resistance heater would also raise the temperature of the seed crystal 3. Generally, the seed crystal 3 has a low temperature tolerance, and excessively high temperatures would damage it. Therefore, the heat output of the traditional DC resistance heater is limited by the operating temperature of the seed crystal 3. Consequently, increasing the overall heat output of the DC resistance heater to improve the crystallization of SiC vapor phase components on the material surface is not a feasible solution.

[0066] Please continue to refer to this. Figure 1 and Figure 2Comparing the DC resistance heater provided in this application with a conventional DC resistance heater, the DC resistance heater of this application has a bottom heating element 11, a middle heating element 12, and a top heating element 13. Along the axial direction of the DC resistance heater, the middle heating element 12 has the largest heat output per unit length, while the top heating element 13 has the smallest heat output per unit length. When the DC resistance heater of this application is used in a SiC single crystal growth apparatus, the middle heating element 12 is mainly used to heat the material filling area 2A of the crucible 2, the bottom heating element 11 is used to heat the bottom 21 of the crucible 2, and the top heating element 13 is used to heat the crystal growth area 2B, where the seed crystal 3 is located. Because... The heat generated per unit length of the middle heating element 12 is greater than that generated per unit length of the bottom heating element 11. Therefore, compared with traditional DC resistance heaters, the DC resistance heater of this application can achieve a higher temperature for the SiC gas phase component. Meanwhile, the heat generated per unit length of the top heating element 13 is minimal, which can meet the operating temperature requirements of the seed crystal 3. Thus, the DC resistance heater of this application can both meet the high temperature requirements of the SiC gas phase component, thereby increasing the carbon / silicon ratio in the gas phase component and improving the crystal stability of 4H-SiC, and simultaneously meet the operating temperature requirements of the seed crystal 3.

[0067] In addition, the heat generated per unit length of the top heating element 13 is the smallest, which can generate a large axial temperature difference between the middle heating element 12 and the top heating element 13. A large axial temperature difference is beneficial to crystal growth.

[0068] Please combine Figure 1 and Figure 4 In addressing the technical problem of the small axial temperature gradient in traditional DC resistance heaters affecting SiC single crystal growth, the applicant also employed three... Figure 1 The proposed scheme uses a combination of DC resistance heaters to heat the crucible, but its effectiveness is unsatisfactory. Specifically, while a large axial temperature gradient can be generated using three independent DC resistance heaters, each heater requires a separate power supply. Typically, an insulation layer is placed around the heater's periphery; supplying power to the three independent heaters necessitates damaging this layer, thus disrupting the temperature field of the crucible at the power connection points, which is detrimental to crystal growth. Therefore, this application addresses the problem of the small axial temperature gradient in traditional DC resistance heaters by integrating a bottom heating element 11, a middle heating element 12, and a top heating element 13 onto a single DC resistance heater. This allows the entire heater to be powered by a single power supply, reducing the disruption to the crystal growth temperature field at the power connection points.

[0069] Please continue to refer to this. Figures 2 to 6 In some embodiments of this application, along the axial direction of the DC resistance heater, the resistance value of the middle heating element 12 per unit length is greater than the resistance value of the bottom heating element 11 per unit length, and the resistance value of the bottom heating element 11 per unit length is greater than the resistance value of the top heating element 13 per unit length.

[0070] Specifically, as mentioned earlier, the heating principle of a DC resistance heater conforms to Joule's law. Joule's law states that the heat generated by an electric current passing through a conductor is directly proportional to the square of the current intensity, the resistance of the conductor, and the duration of the current flow. Therefore, under the condition of the same current and equal duration of the current flow, in order to make the heat generated per unit length of the middle heating element 12 greater than that generated per unit length of the bottom heating element 11, and the heat generated per unit length of the bottom heating element 11 greater than that generated per unit length of the top heating element 13, this application achieves this by structurally configuring the DC resistance heater so that the resistance value per unit length of the middle heating element 12 is greater than that of the bottom heating element 11, and the resistance value per unit length of the bottom heating element 11 is greater than that of the top heating element 13. This ensures that the heat generated per unit length of the middle heating element 12 is greater than that of the bottom heating element 11, and the heat generated per unit length of the bottom heating element 11 is greater than that of the top heating element 13.

[0071] Please continue to refer to this. Figure 2 , Figure 3 , Figure 4 , Figure 5 and Figure 6 In some embodiments of this application, the DC resistance heater includes multiple resistance layers along the axial direction of the DC resistance heater; the interlayer spacing of the multiple resistance layers corresponding to the bottom heating element 11 is d1, the interlayer spacing of the multiple resistance layers corresponding to the middle heating element 12 is d2, and the interlayer spacing of the multiple resistance layers corresponding to the top heating element 13 is d3, where d2 < d1 < d3.

[0072] Specifically, when the resistance values ​​of each resistive layer are close or the same, the heat generation per unit length of the top heating element 13, the middle heating element 12, and the bottom heating element 11 can be adjusted by adjusting the spacing between the resistive layers. Specifically, if the current and the energizing time are constant, the larger the spacing between the resistive layers, the smaller the resistance value per unit length, and the smaller the heat generation. The heat generation of the top heating element 13, the middle heating element 12, and the bottom heating element 11 can be differentiated by adjusting the spacing between the resistive layers. This structure is simple and easy to implement.

[0073] Please combine Figure 2 and Figure 5In some embodiments of this application, the DC resistance heater includes n resistance units 1A and at least one connecting resistor 1B. The n resistance units 1A are arranged along the circumferential direction to form a cylindrical structure capable of accommodating the crucible 2, where n is greater than or equal to 2. Along the first direction, the resistance unit 1A includes multiple stacked sub-resistive layers 1A1 and multiple interlayer resistors 1A2. Adjacent sub-resistive layers 1A1 in the same resistance unit 1A are connected in series end to end through interlayer resistors 1A2. The connecting resistor 1B is used to linearly connect the n resistance units 1A in series.

[0074] Specifically, in some embodiments of this application, the DC resistance heater may include a plurality of resistance units 1A arranged along the circumferential direction, the plurality of resistance units 1A being connected in series, and each resistance unit 1A including a plurality of sub-resistor layers 1A1 stacked along a first direction; based on the foregoing, the heat per unit length of the bottom heating element 11, the middle heating element 12 and the top heating element 13 can be differentiated by adjusting the interlayer spacing of the sub-resistor layers 1A1 at different axial positions in each resistance unit 1A, thereby solving the technical problem that the axial temperature gradient of the traditional DC resistance heater is small and affects the growth of SiC single crystal.

[0075] Please continue to refer to this. Figure 2 , Figure 3 and Figure 5 In some embodiments of this application, there are two resistor units 1A and one connecting resistor; along the first direction, the connecting resistor 1B is located at one end of the resistor unit 1A.

[0076] Generally, DC resistance heaters are manufactured from large graphite columns through processes such as cutting and drilling. In some embodiments of this application, the DC resistance heater includes two resistance units 1A, which are connected in series via a connecting resistor disposed at one end of each resistance unit 1A. Figure 2 , Figure 3 and Figure 5 It can be observed that, under these circumstances, the DC resistance heater has a cylindrical structure, which is relatively regular and therefore easier to manufacture.

[0077] Please continue to refer to this. Figure 2 and Figure 3 In some embodiments of this application, the connecting resistor 1B is a ring-shaped resistor.

[0078] Please combine Figure 2 and Figure 3 ,from Figure 2From the current perspective, in the left resistor unit 1A located below the connecting resistor 1B, multiple stacked sub-resistor layers 1A1 are connected in series, and a positive terminal interface 1E1 is provided at the bottom; in the right resistor unit 1A located below the connecting resistor, multiple stacked sub-resistor layers 1A1 are connected in series, and a negative terminal interface 1F1 is provided at the bottom; the left resistor unit 1A and the right resistor unit 1A are connected in series through a connecting resistor; as can be seen from the figure, the current flow path in this DC resistance heater is as follows: the current flows in from the positive terminal interface 1E1 of the left resistor unit 1A, along the stacked sub-resistor layers 1A1... Multiple sub-resistor layers 1A1 reach the connecting resistor. Since the connecting resistor 1B is a ring-shaped resistor, the current will be shunted at the inflow point and flow along the arcs on both sides of the ring-shaped resistor towards the connection point between the connecting resistor and the right-side resistor unit 1A. Then, it reaches the negative terminal interface 1F1 along the multiple sub-resistor layers 1A1 stacked on the right-side resistor unit 1A, forming a current loop. During this process, since the ring-shaped resistor has the function of shunting the current, the heat generated at the connecting resistor 1B is reduced. Moreover, the connecting resistor 1B is located at one end of the resistor unit 1A, which helps to form an axial temperature gradient.

[0079] Please continue to refer to this. Figure 2 and Figure 3 In some embodiments of this application, the connecting resistor 1B is located at one end of the top heating element 13 of the resistor unit 1A.

[0080] Specifically, as mentioned earlier, because the annular resistor has a current-shunting effect, the heat generated at the connection resistor 1B is reduced. Based on this, by placing the connection resistor 1B at one end of the top heating element 13 of the resistor unit 1A, it is easier to achieve a heat generation of less than that ... Figure 2 , Figure 3 and Figure 4 This structure has the following beneficial effects on the production of SiC single crystals:

[0081] First: The SiC polycrystalline material at the bottom of crucible 2 is within the thermal radiation range of the bottom heating element 11. Since the interlayer spacing between the neutron resistance layers 1A1 of the two resistance units 1A corresponding to the bottom heating element 11 is relatively large, the resistance value per unit length is small. Under the condition of constant current, the large interlayer spacing reduces the heat radiated per unit length by the bottom heating element 11, thereby reducing the temperature of the SiC polycrystalline material at the bottom of crucible 2 and preventing the bottom polycrystalline material temperature from being too high.

[0082] Second: The middle and upper parts of the SiC polycrystalline material are within the thermal radiation range of the central heating element 12. Because the interlayer spacing between the neutron resistance layers 1A1 of the two resistance units 1A corresponding to the central heating element 12 is relatively small, the resistance per unit length is high, increasing the heat radiated per unit length by the central heating element 12. This, in turn, increases the temperature of the SiC polycrystalline material in the upper middle part of the crucible 2, especially the surface temperature. As a result, the high-temperature SiC gaseous components do not remain on the surface of the material but directly enter the growth chamber and crystallize on the seed crystal 3 through diffusion or convection. Due to the higher average temperature in the gaseous components, the C / Si ratio in the gaseous components is increased, which is beneficial to crystal stability.

[0083] Third: The growth chamber, seed crystal 3, and top cover 22 are within the thermal radiation influence range of the top heating element 13. Since the interlayer spacing between the sub-resistor layers 1A1 in the two resistor units 1A corresponding to the top heating element 13 is relatively the largest, the resistance value per unit length is the smallest. Furthermore, since the connecting resistor is a ring-shaped resistor, which has a current shunting effect, the heat radiated per unit length by the top heating element 13 is the lowest. Thus, the axial gradient in the growth chamber from the material surface to the seed crystal 3 is relatively large. On the one hand, this is beneficial to increasing the growth rate, and on the other hand, the low temperature of the seed crystal 3 can also improve the stability of the grown 4H-SiC crystal form.

[0084] In this implementation, the typical interlayer spacing d1 of the multiple resistive layers corresponding to the bottom heating element 11 is 20-40 mm; the typical interlayer spacing d1 of the multiple resistive layers corresponding to the middle heating element 12 is 5-15 mm; and the typical interlayer spacing d1 of the multiple resistive layers corresponding to the top heating element 13 is 30-50 mm.

[0085] Of course, in some other embodiments of this application, the connecting resistor 1B may also be located at one end of the bottom heating element 11 of the resistor unit 1A, and this application does not limit this.

[0086] Figure 5 The diagram shown is a schematic diagram of a DC resistance heater provided in an embodiment of this application. In some embodiments of this application, the connecting resistor 1B is a ring-shaped resistor with a notch (1B1). Along the direction of current flow, one end of the connecting resistor 1B is connected to a resistor unit 1A, and the other end of the connecting resistor 1B is connected to another resistor unit 1A.

[0087] Please continue to refer to this. Figure 5 The part between the two dashed lines that connects resistor 1B is the gap connecting resistor 1B1.

[0088] Please continue to refer to this. Figure 5 ,from Figure 5From the current perspective, in the left resistor unit 1A located below the connecting resistor 1B, multiple stacked sub-resistor layers 1A1 are connected in series, and a positive terminal interface 1E1 is provided at the bottom; in the right resistor unit 1A located below the connecting resistor, multiple stacked sub-resistor layers 1A1 are connected in series, and a negative terminal interface 1F1 is provided at the bottom; the left resistor unit 1A and the right resistor unit 1A are connected in series through the connecting resistor; as can be seen from the figure, the current flow path in this DC resistance heater is as follows: the current flows in from the positive terminal interface 1E1 of the left resistor unit 1A, reaches one end of the connecting resistor along the multiple stacked sub-resistor layers 1A1, and since the connecting resistor is a ring-shaped resistor with a notch, the current flows from one end of the connecting resistor to the other end, and then reaches the negative terminal interface 1F1 along the multiple stacked sub-resistor layers 1A1 of the right resistor unit 1A, forming a current loop.

[0089] It is understood that the connection resistor 1B of this application can have various different shapes, such as... Figure 2 The circular shape shown can also be as follows: Figure 5 The shape shown is a ring with a notch; of course, it can also be other shapes, and this application does not limit this.

[0090] Figure 2 and Figure 5 The following describes one series structure of the DC resistance heater of this application; the DC resistance heater of this application can also be implemented through a parallel structure. Please refer to 6. In some other embodiments of this application, the DC resistance heater includes two resistance units 1A, a positive electrode connection resistor 1C, and a negative electrode connection resistor 1D. The two resistance units 1A are arranged opposite each other to form a cylindrical structure capable of accommodating the crucible 2. Along the first direction, the resistance unit 1A includes multiple stacked sub-resistive layers 1A1 and multiple interlayer resistors 1A2. Adjacent sub-resistive layers 1A1 in the same resistance unit 1A are connected in series end to end through the interlayer resistors 1A2. The two resistance units 1A are connected in parallel through the positive electrode connection resistor 1C and the negative electrode connection resistor 1D.

[0091] For details, please refer to [link / reference]. Figure 6 ,by Figure 6From the current perspective, the left resistor unit 1A forms a complete sub-DC resistance heater, and the right resistor unit 1A is also a complete sub-DC resistance heater. The two resistor units 1A are arranged opposite each other and connected in parallel through a positive terminal connected to a resistor 1C and a negative terminal connected to a resistor 1D. In this way, the left and right resistor units 1A can be powered by the same power supply to form a DC resistance heater with a large power. In the design, the heat per unit length of the bottom heating element 11, the middle heating element 12, and the top heating element 13 can be differentiated by adjusting the interlayer spacing of the sub-resistor layers 1A1 at different axial positions in each resistor unit 1A. This solves the technical problem of the small axial temperature gradient in traditional DC resistance heaters, which affects the growth of SiC single crystals.

[0092] Please continue to refer to this. Figure 6 In some embodiments of this application, along the first direction, the positive terminals of the two resistor units 1A ( Figure 6 The positions marked with a "+" are located at both ends of the DC resistance heater. The negative terminals of the two resistance units 1A (the negative terminals are located on the back of the attached diagram and are not shown) are located at both ends of the DC resistance heater. Along the circumferential direction, the positive terminal connecting resistor 1C and the negative terminal connecting resistor 1D are located in different gaps between the two resistance units 1A. Along the first direction, one end of the positive terminal connecting resistor 1C is connected to the positive terminal of one resistance unit 1A, and the other end of the positive terminal connecting resistor 1C is connected to the positive terminal of the other resistance unit 1A. One end of the negative terminal connecting resistor 1D is connected to the negative terminal of one resistance unit 1A, and the other end of the negative terminal connecting resistor 1D is connected to the negative terminal of the other resistance unit 1A.

[0093] For details, please refer to [link / reference]. Figure 6 ,exist Figure 6 In the structure shown, by placing the positive terminals of the two resistor units 1A at both ends of the DC resistance heater and the negative terminals of the two resistor units 1A at both ends of the DC resistance heater, and by placing the positive terminal connected resistor 1C and the negative terminal connected resistor 1D in the gap between the two resistor units 1A, the power supply can be made to supply power from one end of the DC resistance heater, which makes it easier to connect the power supply to the DC resistance heater.

[0094] Please continue to refer to this. Figure 6 ,by Figure 6From the current perspective, multiple stacked sub-resistor layers 1A1 in the right resistor unit 1A are connected in series, and multiple stacked sub-resistor layers 1A1 in the left resistor unit 1A are connected in series. The left resistor unit 1A and the right resistor unit 1A are connected in series via a positive terminal connection resistor 1C and a negative terminal connection resistor 1D. The positive terminal interface 1E1 and the negative terminal interface 1F1 are located at the top of the DC resistance heater. As can be seen from the figure, the current flow path in this DC resistance heater is as follows: For the left resistor unit, the current enters from the top positive terminal interface 1E1, flows along the positive terminal connection resistor 1C into the bottom layer of the left resistor unit, and then reaches the top negative terminal interface 1F1 along the multiple stacked sub-resistor layers 1A1, forming a current loop; For the right resistor unit, the current enters from the top positive terminal interface 1E1, flows along the multiple stacked sub-resistor layers 1A1 to the bottom layer of the resistor unit 1A, and then reaches the top negative terminal interface 1F1 along the negative terminal connection resistor 1D, forming a current loop.

[0095] Please continue to refer to this. Figure 6 In some embodiments of this application, the DC resistance heater further includes a first input electrode 1E and a second input electrode 1F; the first input electrode 1E is electrically connected to the positive terminal connecting resistor 1C, and the second input electrode 1F is electrically connected to the negative terminal connecting resistor 1D; the first input electrode 1E and the second input electrode 1F are located inside the cylindrical structure formed by the two resistance units 1A, and at the bottom end of the bottom heating element 11.

[0096] Specifically, please combine Figure 4 and Figure 6 The first input electrode 1E and the second input electrode 1F are disposed inside the cylindrical structure formed by the two resistance units 1A and located at the bottom end of the bottom heating element 11. In this way, when the DC resistance heater is in use, the first input electrode 1E and the second input electrode 1F can also be used as part of the bottom heating element to heat the bottom of the crucible 2, so that the material at the bottom of the crucible 2 is heated more evenly, which is beneficial to crystal growth.

[0097] In addition, to facilitate connection with an external power source, the first input electrode 1E of this application is provided with a positive terminal interface 1E1, and the second input electrode 1F is provided with a negative terminal interface 1F1. The positive terminal interface 1E1 and the negative terminal interface 1F1 are threaded holes.

[0098] Please continue to refer to this. Figure 4 Based on the same inventive concept, this application also provides a SiC single crystal growth apparatus, including any of the above-mentioned DC resistance heater 1, and further comprising:

[0099] Crucible 2 includes a cavity formed by a bottom 21, side walls 23 and a top cover 22; the part of the cavity near the bottom is the material filling area 2A, and the part of the cavity near the top cover 22 is the crystal growth area 2B.

[0100] Seed crystal holder, the seed crystal holder is set on the inside of the upper cover 22, and is used to install the seed crystal 3;

[0101] The bottom heating element 11 is located on the outer periphery of the bottom 21 of the crucible 2; the middle heating element 12 is mainly located on the outer periphery of the material filling area 2A of the crucible 2; and the top heating element 13 is mainly located on the outer periphery of the crystal growth area 2B.

[0102] Specifically, please combine Figures 2 to 6 The SiC single crystal growth apparatus provided in this application includes any of the aforementioned DC resistance heaters 1; as mentioned above, the DC resistance heater of this application includes a bottom heating element 11 and a middle heating element 12; along the axial direction of the DC resistance heater 1, the heat generated per unit length of the middle heating element 12 is greater than the heat generated per unit length of the bottom heating element 11; in some other embodiments of this application, along the axial direction of the DC resistance heater 1, the DC resistance heater includes a top heating element 13, which is located at the end of the middle heating element 12 away from the bottom heating element 11; along the axial direction of the DC resistance heater 1, the top heating element 13 is [missing information - likely a unit length] per unit length. The heat generated by the top heating element 13 is less than that generated by the middle heating element 12 per unit length and less than that generated by the bottom heating element 11 per unit length. Therefore, when the SiC single crystal growth apparatus uses the DC resistance heater 1 provided in this application, a thermal field with an axial temperature gradient will be generated in the crucible 2. Since the heat generated by the middle heating element 21 per unit length is greater than that generated by the bottom heating element 11 per unit length, the traditional phenomenon where the high-temperature zone of the DC resistance heater is located at the bottom of the material will be changed. The temperature of the SiC polycrystalline material in the upper middle part of the crucible 2 will be greater than the temperature of the SiC polycrystalline material at the bottom of the crucible 2, especially increasing the temperature of the material surface. As a result, the SiC gas phase components decomposed at the bottom will not crystallize on the surface of the material, causing the surface to bulge upwards, but will directly enter the growth chamber and crystallize on the seed crystal 3 through diffusion or convection, increasing the crystal growth rate. Furthermore, compared to traditional DC resistance heaters, the DC resistance heater of this application can achieve a higher temperature for the SiC gas phase components. At the same time, the heat generated by the top heating element 13 per unit length is minimal, which can meet the operating temperature requirements of the seed crystal 3.

[0103] The SiC single crystal growth apparatus of this application includes the DC resistance heater 1 of any of the above embodiments, and therefore also has the beneficial effects of any of the above embodiments. For details, please refer to the detailed description of the DC resistance heater 1 in the above embodiments. This embodiment will not repeat the description here.

[0104] Please continue to refer to this. Figure 4 In some embodiments of this application, the height of the DC resistance heater 1 is greater than the height of the crucible 2 to prevent an excessively large axial temperature gradient. The entire crucible 2 needs to be within the heat-affected zone of the DC resistance heater 1. If the bottom 21 of the crucible 2 is not within the DC resistance heater 1, the bottom temperature will be too low. After the material decomposes, a portion of the gaseous component will enter the growth chamber, which is beneficial for crystal growth. However, the other portion of the gaseous component will be transported to the bottom of the crucible, which is detrimental and reduces the material utilization efficiency. Therefore, the bottom temperature should not be too low. In this application, the end of the bottom heating element 11 away from the middle heating element 12 extends beyond the bottom of the crucible 2. The height of the extension is related to the height of the crucible 2 and the height of the SiC material inside the crucible 2. In addition, the end of the middle heating element 12 near the top heating element 13 extends beyond the material filling area 2A. This makes it easier for the surface of the SiC material inside the crucible 2 to have a relatively high temperature. The height of the extension is related to the height of the crucible 2 and the height of the SiC material inside the crucible 2.

[0105] It should be noted that the length of the entire current path and the dimensions of the cross-section of the DC resistance heater 1 need to be designed according to the dimensions of the crucible 2 and the power of the power supply. In addition, the radial temperature gradient in the growth chamber of the crucible 2 can be adjusted by adjusting the gap between the inner wall of the DC resistance heater 1 and the outer wall of the crucible 2, and the shape of the grown SiC crystal interface can be further controlled. The adjustable gap size is 5-30 mm.

[0106] An 8-inch 4H-SiC single crystal was grown using the SiC single crystal growth apparatus described in this application. The growth was performed using a standard SiC single crystal growth procedure, and an 8-inch 4H-SiC single crystal was obtained after furnace startup. Compared with 4H-SiC single crystals grown using conventional heaters, the 8-inch 4H-SiC single crystal grown using the DC resistance heater 1 described in this application has the characteristics of moderate growth rate and high crystal stability. The comparison results are shown in Table 1 below.

[0107] Table 1. Comparison of 8-inch 4H-SiC single crystals grown using the DC resistance heater of this application and conventional DC resistance heater.

[0108] Heater type 4H-SiC crystal structure ratio Single crystal growth rate The DC resistance heater of this application ＞90％ Approximately 200 μm / hr Traditional DC resistance heater ＜30％ Approximately 100 μm / hr

[0109] It should be noted that the structure of the DC resistance heater used in Table 1 is as follows: Figure 2 As shown in Table 1, it can be seen that after changing the axial temperature gradient of the DC resistance heater, the proportion of 4H-SiC crystal form increased by more than two times, and the single crystal growth rate increased by one time. Thus, the DC resistance heater of this application exhibits good performance. Although currently only [the application is being studied / discussed]... Figure 2The DC resistor with the structure shown was tested and achieved the above results; however, other embodiments provided in this application are different. Figure 2 The structure shown has the same inventive concept and should produce similar effects.

[0110] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A DC resistance heater, characterized in that, Along the first direction, the DC resistance heater (1) includes a bottom heating element (11) and a middle heating element (12); the first direction is the axial direction of the DC resistance heater (1); The bottom heating element (11) is used to heat the material at the bottom of the material filling area (2A) inside the crucible (2), and the middle heating element (12) is used to heat the material in the upper part of the material filling area (2A) inside the crucible (2). Along the first direction, the heat generated per unit length of the middle heating element (12) is greater than the heat generated per unit length of the bottom heating element (11); Along the first direction, the DC resistance heater includes a top heating element (13) located at the end of the middle heating element (12) away from the bottom heating element (11); the top heating element (13) is used to heat the crystal growth region (2B). Along the first direction, the heat generated per unit length of the top heating element (13) is less than the heat generated per unit length of the bottom heating element (11); Along the first direction, the resistance value per unit length of the middle heating element (12) is greater than the resistance value per unit length of the bottom heating element (11), and the resistance value per unit length of the bottom heating element (11) is greater than the resistance value per unit length of the top heating element (13). The bottom heating element (11), the middle heating element (12), and the top heating element (13) are an integral structure; Along the first direction, the DC resistance heater includes a plurality of resistance layers; Among them, the multiple resistive layers used to heat the material at the bottom of the crucible (2) belong to the bottom heating element (11), and the interlayer spacing of the multiple resistive layers of the bottom heating element (11) is d1; The multiple resistive layers used for heating the upper material in the crucible (2) belong to the central heating element (12), and the interlayer spacing of the multiple resistive layers of the central heating element (12) is d2; The multiple resistive layers used to heat the crystal growth region (2B) belong to the top heating element (13), and the interlayer spacing of the multiple resistive layers corresponding to the top heating element (13) is d3. d2 < d1 < d3.

2. The DC resistance heater according to claim 1, characterized in that, The DC resistance heater includes n resistance units (1A) and at least one connecting resistor (1B). The n resistance units (1A) are arranged in a circumferential direction to form a cylindrical structure that can accommodate the crucible. n is a natural number greater than or equal to 2. Along the first direction, the resistor unit (1A) includes a plurality of stacked sub-resistor layers (1A1) and a plurality of interlayer resistors (1A2), and adjacent sub-resistor layers (1A1) in the same resistor unit (1A) are connected in series end to end through the interlayer resistors (1A2); The connecting resistor (1B) is used to linearly connect n resistor units (1A) in series.

3. The DC resistance heater according to claim 2, characterized in that, The number of resistor units (1A) is two, and the number of connecting resistors (1B) is one; Along the first direction, the connecting resistor (1B) is located at one end of the two resistor units (1A).

4. The DC resistance heater according to claim 3, characterized in that, The connecting resistor (1B) is a ring-shaped resistor; the connecting resistor (1B) is located at one end of the top heating element (13) of the resistor unit (1A).

5. The DC resistance heater according to claim 1, characterized in that, The DC resistance heater includes two resistance units (1A), a positive terminal connected resistor (1C), and a negative terminal connected resistor (1D). The two resistance units (1A) are arranged opposite each other to form a cylindrical structure capable of accommodating a crucible. Along the first direction, the resistor unit (1A) includes a plurality of stacked sub-resistor layers (1A1) and a plurality of interlayer resistors (1A2), and adjacent sub-resistor layers (1A1) in the same resistor unit (1A) are connected in series end to end through the interlayer resistors (1A2); The two resistor units (1A) are connected in parallel through the positive terminal connecting resistor (1C) and the negative terminal connecting resistor (1D).

6. The DC resistance heater according to claim 5, characterized in that, Along the first direction, the positive terminals of the two resistor units (1A) are located at both ends of the DC resistance heater, and the negative terminals of the two resistor units (1A) are located at both ends of the DC resistance heater; Along the circumferential direction, the positive terminal connecting resistor (1C) and the negative terminal connecting resistor (1D) are respectively located in different gaps between the two resistor units (1A); Along the first direction, one end of the positive terminal connecting resistor (1C) is connected to the positive terminal of one of the resistor units (1A), and the other end of the positive terminal connecting resistor (1C) is connected to the positive terminal of another resistor unit (1A); one end of the negative terminal connecting resistor (1D) is connected to the negative terminal of one of the resistor units (1A), and the other end of the negative terminal connecting resistor (1D) is connected to the negative terminal of another resistor unit (1A).

7. A SiC single crystal growth apparatus, characterized in that, The DC resistance heater (1) according to any one of claims 1 to 6 further includes: The crucible (2) includes a cavity formed by a bottom (21), a side wall (23) and a top cover (22); the part of the cavity near the bottom is a material filling area (2A), and the part of the cavity near the top cover (22) is a crystal growth area (2B). Seed crystal holder, the seed crystal holder is located in the crystal growth area (2B) and is disposed on the inner side of the upper cover (22) for mounting seed crystal (3). The bottom heating element (11) is located on the outer periphery of the bottom of the crucible (2); The central heating element (12) is mainly located on the outer periphery of the material filling area (2A) of the crucible (2).

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