Current heating device for conductive silicon carbide wafers

Abstract

The present invention discloses a current heating device for conductive silicon carbide wafers, which includes a power control module, a temperature measurement unit, a first electrode, a second electrode and a tray structure. The tray structure is provided with a receiving groove. The first and second electrodes are respectively arranged corresponding to the center and the edge of the tray structure, and the first and second electrodes are respectively electrically connected to the positive and negative poles of the power control module. The temperature measurement unit is arranged above the tray structure and electrically connected to the power control module. When a silicon carbide wafer is accommodated in the receiving groove, the silicon carbide wafer conducts the first and second electrodes to form a heating circuit, and the internal resistance of the conductive silicon carbide wafer is used to generate heat to achieve thermal annealing. The voltage applied between the first and second electrodes is controlled according to the detection result of the temperature measurement unit to adjust the heating temperature. The heating and cooling rates of this current heating device are much faster than those of the existing furnace cavity heating devices, and it has great advantages in terms of time cost and energy consumption cost when processing conductive silicon carbide wafers in small batches.

Description

Technical Field

[0001] The present invention relates to the technical field of crystal synthesis, and particularly to a heating device applicable to the high-temperature annealing process before and after the growth of an epitaxial layer on a silicon carbide wafer by chemical vapor deposition. Background Art

[0002] Silicon carbide semiconductor materials have advantages such as high thermal conductivity, high breakdown field, high saturated electron drift rate, and high bonding energy, and can well meet the application requirements of modern electronic technologies under harsh conditions such as high temperature, high power, high voltage, high frequency, and high radiation.

[0003] All kinds of silicon carbide power electronic devices must be fabricated on high-quality epitaxial wafers. The mass production of high-quality silicon carbide epitaxial wafers requires not only epitaxial layer growth but also necessary supporting processes such as pretreatment, grinding and polishing, and cleaning. For some kilovolt-level epitaxial wafers (epitaxial layer thickness > 100 μm), additional minority carrier lifetime control processes such as carbon ion implantation and hydrogen annealing are required to ensure that carriers have sufficient diffusion distance to cope with the increased thickness. These supporting processes often involve the heat treatment process of silicon carbide substrates or epitaxial wafers. Currently, the conventional treatment method is to perform high-temperature annealing on furnace cavity heating devices such as epitaxial growth furnaces or special annealing furnaces.

[0004] The existing method of annealing treatment using an epitaxial furnace greatly occupies the production capacity of epitaxial wafers. Although a special annealing furnace can batch process epitaxial wafers through fixtures, its large cavity makes the heating and cooling times relatively long. Therefore, when dealing with a small number of wafers in the customized production process, the disadvantages of the time and energy consumption cost per wafer will be magnified. The cost issue is one of the main factors restricting the large-scale replacement of traditional silicon power electronic devices by silicon carbide power electronic devices.

[0005] Therefore, it is necessary to provide a heating device that can quickly heat and anneal silicon carbide wafers, so as to improve efficiency and have an energy-saving advantage compared with the existing heating devices when dealing with a small batch of silicon carbide wafers. Summary of the Invention

[0006] The purpose of the present invention is to provide a current heating device for conductive silicon carbide wafers, so as to improve efficiency and have an energy-saving advantage when dealing with a small batch of silicon carbide wafers.

[0007] To achieve the above object, the technical solution of the present invention is: to provide a current heating device for a conductive silicon carbide wafer, which includes a power control module, a temperature measuring unit, a first electrode, a second electrode, and a tray structure. The tray structure is provided with a receiving groove. One of the first electrode and the second electrode is arranged corresponding to the center of the tray structure, and the other of the first electrode and the second electrode is installed on the edge of the tray structure. Moreover, the first electrode and the second electrode are respectively electrically connected to the positive and negative electrodes of the power control module. The temperature measuring unit is arranged above the tray structure and electrically connected to the power control module. When the silicon carbide wafer is accommodated in the receiving groove, the silicon carbide wafer conducts the first electrode and the second electrode to form a heating circuit. The temperature measuring unit is used to detect the surface temperature of the silicon carbide wafer in the receiving groove, and the power control module is used to adjust the voltage applied between the first electrode and the second electrode according to the temperature detected by the temperature measuring unit.

[0008] Preferably, one of the first electrode and the second electrode is provided with one and is installed corresponding to the center of the tray structure, and the other of the first electrode and the second electrode is provided with multiple ones and is uniformly installed on the edge of the tray structure.

[0009] Preferably, the first electrode is arranged corresponding to the center of the tray structure and is cylindrical. A plurality of the second electrodes are uniformly arranged along the circumference of the tray structure, and each of the second electrodes has a square contact portion. The contact portion protrudes into the receiving groove. The first electrode and the contact portion are both used to abut against the silicon carbide wafer.

[0010] Preferably, the side length of the contact portion is greater than or equal to the diameter of the first electrode.

[0011] Preferably, when the first electrode is electrically connected to the positive electrode of the power control module and the second electrode is electrically connected to the negative electrode of the power control module, the heating circuit is equivalent to a resistance heating circuit in which a plurality of resistors with a resistance value of R i are connected in parallel. This way can achieve uniform heating of the silicon carbide wafer; when the first electrode is electrically connected to the negative electrode of the power control module and the second electrode is electrically connected to the positive electrode of the power control module, the heating circuit is equivalent to a plurality of resistance heating circuits with a resistance value of R i and independent of each other. This way can perform controllable non-uniform heating annealing on a specified area of the silicon carbide wafer.

[0012] Preferably, when there are n second electrodes, the resistance value R i of the equivalent resistance corresponding to the i-th second electrode = ρ·r / l i·t, where ρ is the resistivity of the silicon carbide wafer, r is the radius of the silicon carbide wafer, t is the thickness of the silicon carbide wafer, and l i is the minimum width of the projection of the first electrode and the second electrode in the connection direction between the first electrode and the i-th second electrode; where n is a positive integer greater than or equal to 1, and i is a positive integer greater than or equal to 1 and less than or equal to n.

[0013] Preferably, the power control module calculates the current and the resistance heating power of the equivalent resistance heating circuit according to the voltage applied between the first electrode and the second electrode and the resistance value R of the equivalent resistance, and adjusts the voltage applied between the first electrode and the second electrode in real time according to the relationship between the temperature detected by the temperature measurement unit and the resistance heating power, so as to adjust the resistance heating power, and further achieve the purpose of adjusting the heating temperature. i

[0014] Preferably, the tray structure includes a fused silica substrate, the thickness of the fused silica substrate is 1 cm and the silica content is more than 99.5%.

[0015] Preferably, the tray structure further includes a zone-melted single-crystal silicon layer adhered above the fused silica substrate and a polycrystalline diamond coating formed above the zone-melted single-crystal silicon layer. Among them, the thickness of the zone-melted single-crystal silicon layer is 100 μm to 500 μm, its resistivity is greater than 5000 Ω·cm, the thickness of the polycrystalline diamond coating is 10 μm to 50 μm, and the polycrystalline diamond coating has insulating and excellent heat conduction properties, mainly enabling the heat during electric heating to be quickly and evenly conducted to the entire crystal surface of the silicon carbide wafer, which is more conducive to realizing the uniform distribution of the temperature of the silicon carbide wafer.

[0016] Preferably, the diameter of the accommodation groove is 1520 mm and the depth is 0.3 mm.

[0017] Preferably, a plurality of temperature measurement units are provided, and the plurality of temperature measurement units are arranged at intervals above the accommodation groove for detecting the surface temperatures of different regions of the silicon carbide wafer, and different models of temperature measurement units can be set according to different annealing temperature ranges.

[0018] More preferably, the temperature measurement unit adopts an infrared thermometer, and when the annealing temperature is between 25°C and 450°C, a monochromatic thermometer is adopted, and when the annealing temperature is between 450°C and 1600°C, a radiation ratio thermometer is adopted.

[0019] ​Compared with the prior art, in the current heating device for conductive silicon carbide wafers of the present invention, a first electrode and a second electrode are respectively arranged corresponding to the center and the edge of the tray structure, and the first electrode and the second electrode are respectively electrically connected to the positive and negative electrodes of the power control module. Therefore, when the silicon carbide wafer is accommodated in the accommodating groove of the tray structure, the silicon carbide wafer contacts the first electrode and the second electrode to make the two conduct and form a heating circuit. First, the internal resistance of the conductive silicon carbide wafer is used to generate heat to achieve thermal annealing. Its advantage is that the heating and cooling rates are much faster than those of the existing furnace cavity heating device. When processing conductive silicon carbide wafers in small batches, it has a great advantage in terms of time cost and energy consumption cost, and can be used as a supplementary solution to the annealing process of the furnace cavity heating device in the mass production of silicon carbide epitaxial wafers. Second, the conductive circuit from the center to the edge can effectively avoid the complex electric field distribution in the conductive circuit from the edge to the edge of the circular wafer, and the two-dimensional electric field distribution model can be simplified into a one-dimensional simple circuit model, which is easier to realize the temperature control of the silicon carbide wafer by the power control module. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a top view of the current heating device according to the first embodiment of the present invention.

[0021] Figure 2 is Figure 1 a cross-sectional view of

[0022] Figure 3 is Figure 1 a cross-sectional view of the current heating device in use in

[0023] Figure 4 is Figure 3 a schematic diagram of the equivalent resistance of the current heating device in

[0024] Figure 5 is Figure 3 a schematic diagram of the equivalent circuit of the current heating device in

[0025] Figure 6 is a principle block diagram of the current heating device according to the first embodiment of the present invention.

[0026] Figure 7 is a cross-sectional view of the current heating device according to the second embodiment of the present invention.

[0027] Figure 8 is Figure 7 a cross-sectional view of the current heating device in use in

[0028] Figure 9 is Figure 8 a top view of the current heating device in DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] Reference is now made to the accompanying drawings to describe embodiments of the present invention, in which like reference numerals represent like elements. It should be noted that the orientation descriptions involved in the present invention, such as up, down, left, right, front, back, etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. This is only for the convenience of describing the technical solutions of the present application or / and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present application. The first, second, etc. described are only used to distinguish technical features and should not be construed as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features or implicitly indicating the sequence relationship of the indicated technical features.

[0030] First, in combination with Figures 1 - 9 As shown, the current heating device 100 for conductive silicon carbide wafers provided by the present invention is mainly applicable to the heating annealing of conductive silicon carbide single crystal substrate wafers and epitaxial wafers, but is not limited thereto. Of course, it can also be used for the heating annealing of other conductive wafers. For the convenience of description, the silicon carbide wafer 200 is used hereinafter to represent all conductive wafers.

[0031] In combination with Figures 1 - 9 As shown, the current heating device 100 for conductive silicon carbide wafers of the present invention includes a first electrode 110, a second electrode 120, a temperature measuring unit 130, a tray structure 140, and a power supply control module 150 (see Figures 5 - 6 ). Among them, a receiving groove 140a for accommodating the silicon carbide wafer 200 is provided on the tray structure 140. One of the first electrode 110 and the second electrode 120 is arranged corresponding to the center of the tray structure 140, and the other of the first electrode 110 and the second electrode 120 is installed on the edge of the tray structure 140. The first electrode 110 and the second electrode 120 are respectively electrically connected to the positive and negative electrodes of the power supply control module 150. The temperature measuring unit 130 is arranged above the tray structure 140 and electrically connected to the power supply control module 150. When the silicon carbide wafer 200 is accommodated in the receiving groove 140a, the first electrode 110 and the second electrode 120 are brought into contact with the silicon carbide wafer 200 so as to conduct the two. Therefore, the power supply control module 150, the first electrode 110, the silicon carbide wafer 200, and the second electrode 120 form a heating circuit, and the thermal annealing of the silicon carbide wafer 200 is realized by an electric heating method; and, the temperature measuring unit 130 is used to detect the surface temperature of the silicon carbide wafer 200 in the receiving groove 140a, and the power supply control module 150 is used to control and adjust the voltage applied between the first electrode 110 and the second electrode 120 according to the temperature detected by the temperature measuring unit 130, so that the temperature of the silicon carbide wafer 200 is maintained near the target value of the thermal annealing process.

[0032] In the present invention, one of the first electrode 110 and the second electrode 120 is provided with one and is mounted corresponding to the center of the tray structure 140, and the other of the first electrode 110 and the second electrode 120 is provided with a plurality and is uniformly mounted on the edge of the tray structure 140. In a specific embodiment, the first electrode 110 is disposed corresponding to the center of the tray structure 140 and is cylindrical, and the plurality of second electrodes 120 are uniformly arranged along the radial direction of the tray structure 140, and each second electrode 120 has a square contact portion 121, and the contact portion 121 protrudes into the accommodation groove 140a, as Figure 2 , Figure 5 shown; when the silicon carbide wafer 200 is accommodated in the accommodation groove 140a, both the first electrode 110 and the contact portion 121 can abut against the surface of the silicon carbide wafer 200, as Figure 4 , Figure 9 shown.

[0033] In the present invention, one or more temperature measuring units 130 may be provided, and the temperature measuring unit 130 is disposed above the accommodation groove 140a for detecting the surface temperature of the silicon carbide wafer 200. When there are a plurality of temperature measuring units 130, the plurality of temperature measuring units 130 are spaced apart and can respectively detect the surface temperatures of different regions of the silicon carbide wafer 200. In addition, different models of temperature measuring units 130 may be set according to different annealing temperature ranges, as will be described later.

[0034] Referring again to Figures 1 - 9 shown, different embodiments of the current heating device 100 for conductive silicon carbide wafers of the present invention will be described respectively.

[0035] First, in combination with Figures 1 - 4 shown, in the first embodiment of the present invention, the tray structure 140 includes a fused silica substrate 141, a zone-melted single-crystalline silicon layer 142 adhered above the fused silica substrate 141, and a polycrystalline diamond coating 143 formed above the zone-melted single-crystalline silicon layer 142. Among them, the thickness of the fused silica substrate 141 is 1 cm and its silica content is above 99.5%, the thickness of the zone-melted single-crystalline silicon layer 142 is 100 μm to 500 μm, the resistivity is greater than 5000 Ω·cm, and the polycrystalline diamond coating 143 is deposited on the zone-melted single-crystalline silicon layer 142 by direct current arc plasma spraying chemical vapor deposition method, and the thickness of the polycrystalline diamond coating 143 is 10 μm to 50 μm. Of course, the polycrystalline diamond coating 143 can be formed by other methods. Since the polycrystalline diamond coating 143 has insulation and excellent thermal conductivity, the heat during electric heating can be quickly and uniformly conducted to the entire crystal surface of the silicon carbide wafer 200, which is more conducive to realizing uniform distribution of the temperature of the silicon carbide wafer 200.

[0036] More specifically, the accommodating groove 140a of the tray structure 140 is provided above the polycrystalline diamond coating 143, that is, the polycrystalline diamond coating 143 forms the bottom surface of the accommodating groove 140a, as Figure 2 shown. In this embodiment, the diameter of the accommodating groove 140a is preferably 1520 mm, and the depth is preferably 0.3 mm, which is used to accommodate a silicon carbide wafer 200 with a diameter of 6 inches and a thickness of 350 μm. It can be understood that the size of the accommodating groove 140a is not limited thereto, and can be flexibly set according to the different sizes of the specific silicon carbide wafer 200 to meet the heating of silicon carbide wafers 200 of different sizes and models.

[0037] Continuing to refer to Figures 1 - 2 shown, in this embodiment, the current heating device 100 for conductive silicon carbide wafers is provided with a first electrode 110 and a plurality of second electrodes 120. Among them, the first electrode 110 is arranged corresponding to the center of the tray structure 140 and is cylindrical. The first electrode 110 is preferably made of tin-plated copper; the plurality of second electrodes 120 are uniformly arranged along the radial direction of the tray structure 140 and are grounded in parallel through wires. Each second electrode 120 has a square contact portion 121. The contact portion 121 protrudes into the accommodating groove 140a for abutting against the silicon carbide wafer 200. Each second electrode 120 is also preferably made of tin-plated copper. After the conductive silicon carbide wafer 200 is placed in the accommodating groove 140a, the first electrode 110 contacts the center of the silicon carbide wafer 200, and the contact portion 121 contacts the edge of the silicon carbide wafer 200. The silicon carbide wafer 200 contacts the first electrode 110 and the second electrode 120 to make the two conduct. In this embodiment, the setting method of the first electrode 110 and the second electrode 120 can effectively avoid the complex electric field distribution in the conductive loop from the edge to the edge of the circular wafer by using a conductive loop from the center to the edge (except for a small part of the positioning edge area, the conductive silicon carbide single crystal substrate and epitaxial wafer on the market are approximately regular circles), and the two-dimensional electric field distribution model can be simplified into a one-dimensional simple circuit model, which is easier to realize the temperature control of the silicon carbide wafer 200 by the power control module 150.

[0038] In the present invention, the side length of the contact portion 121 is greater than or equal to the diameter of the first electrode 110, as Figure 4 shown. In this embodiment, the diameter of the first electrode 110 is preferably equal to the side length of the contact portion 121, and both are preferably 6 mm. Of course, it is not limited to this value, and the sizes of the two can be flexibly set according to specific needs.

[0039] Continuing to refer to Figures 1 - 2As shown, in this embodiment, the first electrode 110 is electrically connected to the positive electrode of the power control module 150, and the second electrode 120 is electrically connected to the negative electrode of the power control module 150 and grounded in parallel through a wire. Therefore, the heating circuit of the current heating device 100 is equivalent to a resistance heating circuit formed by a plurality of silicon carbide resistors with a resistance value of R i in parallel, and rapid and uniform heating of the silicon carbide wafer 200 can be achieved in this way.

[0040] Combined with Figures 3 - 5 as shown, when there are n second electrodes 120, the heating circuit of the current heating device 100 is equivalent to a resistance heating circuit formed by silicon carbide resistors with a resistance value of R i (i = 1, 2,..., n) in parallel (see Figure 5 as shown), where n is a positive integer greater than or equal to 1. The resistance value R i of the equivalent resistance corresponding to the i-th second electrode 120 is ρ·r / l i ·t, where ρ is the resistivity of the silicon carbide wafer 200, r is the radius of the silicon carbide wafer 200, t is the thickness of the silicon carbide wafer 200, and l i is the minimum value of the width of the projection of the first electrode 110 and the second electrode 120 in the connection direction between the first electrode 110 and the i-th second electrode 120. Specifically, see Figure 4 as shown, and i is a positive integer greater than or equal to 1 and less than or equal to n.

[0041] In this embodiment, it is preferably set that there are eight second electrodes 120, and the eight second electrodes 120 are symmetrically distributed on the edge of the tray structure 140 at intervals of 40° in sequence, as Figure 1 , Figure 4 shown. Therefore, the heating circuit in this embodiment can be equivalent to a resistance heating circuit formed by eight silicon carbide resistors with a resistance value of R i (i = 1, 2,..., n) in parallel, as Figure 5 shown. For example, for one type of silicon carbide single crystal substrate, its resistivity ρ is 0.02, the radius r is 7.1.2 mm, and the wafer thickness t is 0.35 mm; for the equivalent silicon carbide resistor R i , the width l i of the equivalent silicon carbide resistor R i between the first electrode 110 and any one of the second electrodes 120 is 6 mm for all, as Figure 4 shown. According to the above formula R i = ρ·r / l i ·t, the resistance value of each equivalent silicon carbide resistor R i is calculated to be 6.78 Ω.

[0042] Combined with again Figures 1 - 5As shown, in this embodiment, after calculating the resistance value of the equivalent silicon carbide resistor R according to the above formula, the power supply control module 150 calculates the current I on the equivalent silicon carbide resistor R according to the voltage U applied thereto and Ohm's law. Then, according to the formula P = I²R, the power of each equivalent resistance heating circuit is calculated. Then, according to the correspondence between the power P and the annealing temperature, the voltage applied between the first electrode 110 and the second electrode 120 can be controlled or adjusted in real time, so as to realize the adjustment of the annealing temperature. i After calculating the resistance value of the equivalent silicon carbide resistor R, the power supply control module 150 i calculates the current I on the equivalent silicon carbide resistor R according to the voltage U applied thereto and Ohm's law. Then, according to the formula P = I²R, the power of each equivalent resistance heating circuit is calculated. Then, according to the correspondence between the power P and the annealing temperature, the voltage applied between the first electrode 110 and the second electrode 120 can be controlled or adjusted in real time, so as to realize the adjustment of the annealing temperature. i calculates the current I on the equivalent silicon carbide resistor R according to the voltage U applied thereto and Ohm's law. Then, according to the formula P = I²R, the power of each equivalent resistance heating circuit is calculated. Then, according to the correspondence between the power P and the annealing temperature, the voltage applied between the first electrode 110 and the second electrode 120 can be controlled or adjusted in real time, so as to realize the adjustment of the annealing temperature. 2 calculates the current I on the equivalent silicon carbide resistor R according to the voltage U applied thereto and Ohm's law. Then, according to the formula P = I²R, the power of each equivalent resistance heating circuit is calculated. Then, according to the correspondence between the power P and the annealing temperature, the voltage applied between the first electrode 110 and the second electrode 120 can be controlled or adjusted in real time, so as to realize the adjustment of the annealing temperature.

[0043] It should be noted that the voltage U applied to the above equivalent silicon carbide resistor R needs to consider the maximum current density passing through the silicon carbide wafer to avoid damaging the silicon carbide lattice due to excessive current density. For example, the current density of the rated power in the application of silicon carbide Schottky barrier diode (SiC - SBD) or metal - oxide - semiconductor field - effect transistor (MOSFET) devices can be referred to. Taking a 600V, 6A SiC - SBD as an example, it generally requires a die area of 2mm × 2mm, and the current density under its rated operating conditions is 1.5A / mm². From the perspective of industry experience, it shows that the long - term stable use of the device can be guaranteed at this current density without lattice damage problems. Therefore, taking the maximum current density of 1.5A / mm² as an example, when the first electrode 110 and the second electrode 120 are in contact with the silicon carbide wafer 200 and conduct, since the effective cross - sectional area S of the equivalent silicon carbide resistor R on the silicon carbide wafer 200 is S = l × t = 6mm × 0.35mm = 2.1mm². i It should be noted that the voltage U applied to the above equivalent silicon carbide resistor R needs to consider the maximum current density passing through the silicon carbide wafer to avoid damaging the silicon carbide lattice due to excessive current density. For example, the current density of the rated power in the application of silicon carbide Schottky barrier diode (SiC - SBD) or metal - oxide - semiconductor field - effect transistor (MOSFET) devices can be referred to. Taking a 600V, 6A SiC - SBD as an example, it generally requires a die area of 2mm × 2mm, and the current density under its rated operating conditions is 1.5A / mm². From the perspective of industry experience, it shows that the long - term stable use of the device can be guaranteed at this current density without lattice damage problems. Therefore, taking the maximum current density of 1.5A / mm² as an example, when the first electrode 110 and the second electrode 120 are in contact with the silicon carbide wafer 200 and conduct, since the effective cross - sectional area S of the equivalent silicon carbide resistor R on the silicon carbide wafer 200 is S = l × t = 6mm × 0.35mm = 2.1mm². 2 From the perspective of industry experience, it shows that the long - term stable use of the device can be guaranteed at this current density without lattice damage problems. Therefore, taking the maximum current density of 1.5A / mm² as an example, when the first electrode 110 and the second electrode 120 are in contact with the silicon carbide wafer 200 and conduct, since the effective cross - sectional area S of the equivalent silicon carbide resistor R on the silicon carbide wafer 200 is S = l × t = 6mm × 0.35mm = 2.1mm². 2 From the perspective of industry experience, it shows that the long - term stable use of the device can be guaranteed at this current density without lattice damage problems. Therefore, taking the maximum current density of 1.5A / mm² as an example, when the first electrode 110 and the second electrode 120 are in contact with the silicon carbide wafer 200 and conduct, since the effective cross - sectional area S of the equivalent silicon carbide resistor R on the silicon carbide wafer 200 is S = l × t = 6mm × 0.35mm = 2.1mm². i From the perspective of industry experience, it shows that the long - term stable use of the device can be guaranteed at this current density without lattice damage problems. Therefore, taking the maximum current density of 1.5A / mm² as an example, when the first electrode 110 and the second electrode 120 are in contact with the silicon carbide wafer 200 and conduct, since the effective cross - sectional area S of the equivalent silicon carbide resistor R on the silicon carbide wafer 200 is S = l × t = 6mm × 0.35mm = 2.1mm². i × t = 6mm × 0.35mm = 2.1mm². 2 From the perspective of industry experience, it shows that the long - term stable use of the device can be guaranteed at this current density without lattice damage problems. Therefore, taking the maximum current density of 1.5A / mm² as an example, when the first electrode 110 and the second electrode 120 are in contact with the silicon carbide wafer 200 and conduct, since the effective cross - sectional area S of the equivalent silicon carbide resistor R on the silicon carbide wafer 200 is S = l × t = 6mm × 0.35mm = 2.1mm². 2 From the perspective of industry experience, it shows that the long - term stable use of the device can be guaranteed at this current density without lattice damage problems. Therefore, taking the maximum current density of 1.5A / mm² as an example, when the first electrode 110 and the second electrode 120 are in contact with the silicon carbide wafer 200 and conduct, since the effective cross - sectional area S of the equivalent silicon carbide resistor R on the silicon carbide wafer 200 is S = l × t = 6mm × 0.35mm = 2.1mm². 2 × 1.5A / mm² 2 = 3.15A. According to Ohm's law, the maximum voltage U applied to each equivalent silicon carbide resistor R can be calculated as U = 3.15A × 6.78Ω = 21.357V. That is to say, by adjusting the voltage applied between the first electrode 110 and the second electrode 120 within the range not exceeding 21.357V, the adjustment of the annealing temperature can be realized on the premise of ensuring that the silicon carbide lattice is not damaged. i = 3.15A. According to Ohm's law, the maximum voltage U applied to each equivalent silicon carbide resistor R can be calculated as U = 3.15A × 6.78Ω = 21.357V. That is to say, by adjusting the voltage applied between the first electrode 110 and the second electrode 120 within the range not exceeding 21.357V, the adjustment of the annealing temperature can be realized on the premise of ensuring that the silicon carbide lattice is not damaged.

[0044] Combined with Figures 3 - 6As shown, in a specific embodiment of the present invention, to avoid damage to the silicon carbide lattice due to excessive current density, a voltage of 20.3V (less than the above maximum voltage of 21.357V) is applied between the first electrode 110 and the second electrode 120. According to Ohm's law, the current generated on each equivalent silicon carbide resistor R i is I = 20.3V / 6.78Ω ≈ 3.0A. As described above, since the current passes through the equivalent silicon carbide resistor R on the silicon carbide wafer 200 i and the effective cross-sectional area S of R is S = l i × t = 6mm × 0.35mm = 2.1mm 2 , thus, the current density passing through this cross-section can be calculated to be approximately 1.4A / mm 2 , that is, less than the current density under the rated working condition of 1.5A / mm 2 . At this time, the power P of each equivalent resistance heating circuit can be calculated, that is, P = I 2 R = (3.0A) 2 × 6.78Ω = 61w. The total power of the electric heating device 100 composed of eight resistance heating circuits is 61w × 8 = 488w, which can meet the heating of the silicon carbide wafer 200 with an annealing target temperature of 600°C. And, during the specific heating process, the temperature measuring unit 130 is used to detect the surface temperature of the silicon carbide wafer 200 in real time, and the detected temperature is fed back to the power control module 150. The power control module 150 calculates the voltage applied between the first electrode 110 and the second electrode 120 according to the corresponding relationship between the power P and the annealing temperature, and controls the temperature within the range of 600 ± 10°C through the above logical algorithm.

[0045] It can be understood that in the present invention, the number of the second electrodes 120 is not limited to eight. In other embodiments, when a higher annealing temperature is required (for example, when it exceeds 600°C), the number of the second electrodes 120 can be increased, thereby increasing the number of equivalent resistance heating circuits, and further increasing the total heating power to raise the annealing temperature.

[0046] Combined again with Figures 1 - 6 shown, in this embodiment, only one temperature measuring unit 130 is provided, and the temperature measuring unit 130 preferably uses an infrared thermometer, and different models of infrared thermometers can be equipped according to different annealing temperature ranges. For example, when the annealing temperature is between 25°C and 450°C, a monochromatic thermometer is used, and when the annealing temperature is between 450°C and 1600°C, a radiation colorimetric thermometer is used. Of course, the temperature measuring unit 130 can also be other temperature detection devices.

[0047] Next, combined again with Figures 1 - 6As shown, when the current heating device 100 in this embodiment is in use, a silicon carbide wafer 200 with a diameter of 6 inches and a thickness of 350 μm is placed in the accommodation groove 140a of the tray structure 140. At the same time, the first electrode 110 is concentrically contacted and connected to the center of the surface of the silicon carbide wafer 200. Refer to Figure 1 , Figure 4 As shown, the first electrode 110 is electrically connected to the positive electrode of the power control module 150. At the same time, eight second electrodes 120 are symmetrically arranged at intervals of 40° in sequence. The contact portion 121 of each second electrode 120 contacts the upper surface of the silicon carbide wafer 200, and each second electrode 120 is electrically connected to the negative electrode of the source control module and grounded in parallel through a wire, as Figure 6 shown.

[0048] Then, the power control module 150 applies voltages between the first electrode 110 and each second electrode 120 respectively. The conductive silicon carbide wafer 200 conducts the first electrode 110 and the second electrode 120, so as to realize resistive heating inside the silicon carbide wafer 200, and then heat the silicon carbide wafer 200. Moreover, the setting of the eight second electrodes 120 is equivalent to generating eight parallel resistive heating circuits on the silicon carbide wafer 200. When the diamond polycrystalline coating 143 of the tray structure 140 contacts the back of the silicon carbide wafer 200, it plays an insulating role, and its high thermal conductivity helps the heat to be more evenly distributed laterally on the silicon carbide wafer 200, so that the heat generated by the eight resistive heating circuits can quickly and evenly spread throughout the entire silicon carbide wafer 200, which is more conducive to realizing the uniform distribution of the temperature of the silicon carbide wafer 200.

[0049] Next, in combination with Figures 7 - 9 shown, in the second embodiment of the present invention, the main difference between the current heating device 100 and the above-mentioned first embodiment is that the electrical connection methods of the first electrode 110 and the second electrode 120 are different. In this embodiment, the first electrode 110 is electrically connected to the negative electrode of the power control module 150 and grounded, and the second electrode 120 is electrically connected to the positive electrode of the power control module 150. Therefore, the heating circuit of the current heating device 100 can be equivalent to multiple independent resistive heating circuits with a resistance value of R i And because they are multiple independent resistive heating circuits, the specified area of the silicon carbide wafer 200 can be controllably and non-uniformly heated and annealed.

[0050] In this embodiment, the resistance value R of each equivalent silicon carbide resistor i =ρ·r / l i ·t, and the equivalent and calculation methods are the same as those in the above-mentioned first embodiment, so they will not be repeated here. Therefore, the resistance value R of each equivalent silicon carbide resistor i is 6.78 Ω.

[0051] See Figures 7 - 8 As shown, in this embodiment, eight second electrodes 120 are also provided. Therefore, the heating circuit of the current heating device 100 is equivalent to eight independent resistance heating circuits with a resistance value of R i And the voltages applied between the first electrode 110 and each second electrode 120 are different, which are voltage V1, V2... V8 respectively. That is to say, the currents in the eight equivalent resistance heating circuits obtained are different, and thus different resistance heat generations are generated in each resistance heating circuit due to the inconsistent currents.

[0052] It should be noted that it does not mean that different voltages can only be applied to the eight equivalent resistance heating circuits in this embodiment. According to needs, the same voltage can of course be selected to be applied to the eight equivalent resistance heating circuits.

[0053] In this embodiment, the structures, installation methods, and other parts not described of the first electrode 110 and the second electrode 120 are the same as those in the above first embodiment, and will not be described repeatedly here.

[0054] Continue to combine with Figures 7 - 9 As shown, in this embodiment, the structure of the tray structure 140 is also slightly different from that in the above first embodiment. Specifically, the tray structure 140 only includes a quartz glass substrate 141, and the thickness of the quartz glass substrate 141 is 1 cm and its silica content is more than 99.5%. Of course, the tray structure 140 can also be formed by using other high-insulation and low-thermal-conductivity coating materials. In this embodiment, since the polycrystalline diamond coating 143 is not provided, the different heat generations generated by the eight equivalent resistance heating circuits of the current heating device 100 cannot be quickly and evenly conducted to the entire crystal surface of the silicon carbide wafer 200. Through the cooperation of the temperature measurement unit 130 and the power supply control module 150, controllable non-uniform heating annealing of the specified area of the silicon carbide wafer 200 can be achieved. The adjustment method of the heating power of each equivalent resistance heating circuit obtained specifically is the same as that in the above first embodiment, and will not be described repeatedly.

[0055] Continue to combine with Figures 7 - 8 As shown, in this embodiment, a plurality of temperature measurement units 130 are preferably provided. The plurality of temperature measurement units 130 are arranged at intervals above the accommodation groove 140a and are arranged corresponding to the specified area of the silicon carbide wafer 200, and are used to detect the surface temperature of the specified area of the silicon carbide wafer 200. The power supply control module 150 controls or adjusts the voltages between the first electrode 110 and the second electrode 120 in the corresponding area respectively according to the detection results of different temperature measurement units 130, so that the voltages of each equivalent resistance heating circuit are different, and separate heating of different areas of the silicon carbide wafer 200 is achieved.

[0056] It should be noted that for the tray structure 140 in this embodiment, it is not limited to only including the fused silica substrate 141. Of course, it can also be set as the three-layer structure in the above first embodiment, which does not affect the heating of the eight mutually independent resistance heating circuits obtained equivalently.

[0057] Combined again with Figures 7 - 9 As shown, when the current heating device 100 in this embodiment is in use, a silicon carbide wafer 200 with a diameter of 6 inches and a thickness of 350 μm is placed in the receiving groove 140a of the tray structure 140. At the same time, the first electrode 110 contacts and connects the center of the surface of the silicon carbide wafer 200 concentrically, as Figure 7 、 Figure 9 shown. At the same time, the first electrode 110 is electrically connected to the negative electrode of the power control module 150 and grounded. The eight second electrodes 120 are symmetrically arranged with a 40° interval between them. The contact portion 121 of each second electrode 120 contacts the upper surface of the silicon carbide wafer 200, and each second electrode 120 is electrically connected to the positive electrode of the power control module 150, as Figures 7 - 9 shown.

[0058] Then, the power control module 150 applies different voltages V1, V2,... V8 to the eight second electrodes 120 respectively, so that the eight resistance heating circuits obtained equivalently by the current heating device 100 generate different heat quantities. Since the diamond polycrystalline coating 143 is not provided on the tray structure 140, the different heat quantities generated by the eight resistance heating circuits are respectively transmitted to the silicon carbide wafer 200, realizing the separate heating of different regions of the silicon carbide wafer 200, and the voltages V1, V2,... V8 can be respectively controlled and adjusted to realize the controllable non-uniform heating annealing of the specified region of the silicon carbide wafer 200.

[0059] In summary, for the current heating device 100 for conductive silicon carbide wafers of the present invention, a first electrode 110 and a second electrode 120 are respectively provided corresponding to the center of the tray structure 140 and the edge of the tray structure 140, and the first electrode 110 and the second electrode 120 are respectively electrically connected to the positive and negative electrodes of the power control module 150. Therefore, when the silicon carbide wafer 200 is accommodated in the accommodation groove 140a of the tray structure 140, the silicon carbide wafer 200 comes into contact with the first electrode 110 and the second electrode 120 to make the two conduct and thus form a heating circuit. First, thermal annealing is achieved by the internal resistance heating of the conductive silicon carbide wafer 200. Its advantage is that the heating and cooling rates are much faster than those of the existing furnace cavity heating devices. When processing conductive silicon carbide wafers 200 in small batches, it has a great advantage in terms of time cost and energy consumption cost, and can be used as a supplementary solution for the annealing process of the furnace cavity heating device in the mass production of silicon carbide epitaxial wafers. Second, the conductive circuit from the center to the edge can effectively avoid the complex electric field distribution in the conductive circuit from the edge to the edge of the circular wafer, and the two-dimensional electric field distribution model can be simplified into a one-dimensional simple circuit model, which is more conducive to the power control module 150 to control the temperature of the silicon carbide wafer 200.

[0060] The foregoing disclosure is only the preferred embodiment of the present invention, and of course cannot be used to limit the scope of rights of the present invention. Therefore, equivalent changes made according to the scope of the patent application of the present invention still fall within the scope covered by the present invention.

Claims

1. A current heating device for conductive silicon carbide wafers, characterized in that, It includes a power control module, a temperature measurement unit, a first electrode, a second electrode, and a tray structure. The tray structure includes a fused silica substrate. A receiving groove is provided on the tray structure. The first electrode is arranged corresponding to the center of the tray structure. A plurality of the second electrodes are installed on the edge of the tray structure and are evenly arranged along the circumferential direction of the tray structure. And the first electrode and the second electrode are respectively electrically connected to the positive and negative electrodes of the power control module. The temperature measurement unit is arranged above the tray structure and is electrically connected to the power control module. When a silicon carbide wafer is accommodated in the receiving groove, the silicon carbide wafer conducts the first electrode and the second electrode to form a heating circuit. The temperature measurement unit is used to detect the surface temperature of the silicon carbide wafer in the receiving groove. The power control module is used to adjust the voltage applied between the first electrode and the second electrode according to the temperature detected by the temperature measurement unit; Among them, when the first electrode is electrically connected to the positive electrode of the power control module and the second electrode is electrically connected to the negative electrode of the power control module, the heating circuit is equivalent to a resistance heating circuit formed by multiple resistors with a resistance value of R i connected in parallel; when the first electrode is electrically connected to the negative electrode of the power control module and the second electrode is electrically connected to the positive electrode of the power control module, the heating circuit is equivalent to multiple resistance heating circuits with a resistance value of R i and independent of each other.

2. The current heating device for a conductive silicon carbide wafer according to claim 1, characterized in that, The first electrode is cylindrical. Each of the second electrodes has a square contact part, and the contact part protrudes into the receiving groove. The first electrode and the contact part are both used to abut against the silicon carbide wafer.

3. The current heating device for a conductive silicon carbide wafer according to claim 2, characterized in that, The side length of the contact part is greater than or equal to the diameter of the first electrode.

4. The current heating device for a conductive silicon carbide wafer according to claim 1, characterized in that, When there are n second electrodes, the resistance value of the equivalent resistance corresponding to the i-th second electrode , where ρ is the resistivity of the silicon carbide wafer, r is the radius of the silicon carbide wafer, t is the thickness of the silicon carbide wafer, l i is the minimum width of the projection of the first electrode and the second electrode in the connection direction between the first electrode and the i -th second electrode; where n is a positive integer greater than 1, and i is a positive integer greater than or equal to 1 and less than or equal to n.

5. The current heating device for a conductive silicon carbide wafer according to claim 4, wherein The power control module calculates the current and the resistance heating power of the equivalent resistance heating circuit according to the voltage applied between the first electrode and the second electrode and the resistance value R of the equivalent resistance, and adjusts the voltage applied between the first electrode and the second electrode in real time according to the relationship between the temperature detected by the temperature measurement unit and the resistance heating power. i ​ 6. The current heating device for a conductive silicon carbide wafer according to claim 1, characterized in that, The thickness of the fused silica substrate is 1 cm and the silica content thereof is above 99.5%.

7. The current heating device for a conductive silicon carbide wafer according to claim 6, characterized in that, The tray structure further includes a zone-melted monocrystalline silicon layer adhered above the fused silica substrate and a polycrystalline diamond coating formed above the zone-melted monocrystalline silicon layer. Among them, the thickness of the zone-melted monocrystalline silicon layer is 100 μm to 500 μm, the resistivity is greater than 5000 Ω·cm, and the thickness of the polycrystalline diamond coating is 10 μm to 50 μm.

8. The current heating device for a conductive silicon carbide wafer according to claim 1, characterized in that, A plurality of the temperature measurement units are provided. The plurality of temperature measurement units are spaced above the receiving groove and are used to detect the surface temperatures of different regions of the silicon carbide wafer.

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