A method for producing a high resistivity silicon carbide material and a silicon carbide material

Abstract

The application relates to the technical field of semiconductor etching materials, and provides a method for preparing high-resistivity silicon carbide material and the silicon carbide material. The method comprises the following steps: placing a substrate in a chemical vapor deposition device, vacuumizing the chemical vapor deposition device, and then introducing inert gas; silicon-carbon source gas and carrier gas are injected into the chemical vapor deposition device through a first gas inlet channel, and boron source gas is injected into the chemical vapor deposition device through a second gas inlet channel; silicon carbide is deposited on the surface of the substrate by using a chemical vapor deposition process; after gradient annealing, the substrate is removed; in step 2, the distance between the gas inlet of the first gas inlet channel and the gas inlet of the second gas inlet channel is greater than or equal to 20 cm. By the method, the boron element doping amount in the silicon carbide can be obviously increased, so that the resistivity of the silicon carbide is increased, and the etching resistance of the silicon carbide is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor etching materials, in particular to a method for preparing high-resistivity silicon carbide material and silicon carbide material. BACKGROUND

[0002] In the manufacture of semiconductor integrated circuits, etching is one of the key processes, the core of which is to transfer the pattern on the wafer to the wafer through physical and chemical methods, and the performance of the parts in the etching equipment directly affects the etching precision and efficiency. Among them, the etching ring is a key part for assisting wafer etching, and its main function is to ensure the consistency of etching quality of the wafer edge and the inside, and its material needs to have etching resistance, thermal stability and high purity to avoid contaminating the wafer and ensure the etching uniformity. The existing etching ring is mostly made of Si (silicon) material, which can meet the requirement of similar conductivity to the wafer, but has poor etching resistance in the fluorine-containing etching gas environment and is easily eroded, resulting in short service life and seriously affecting the production efficiency. In comparison, SiC (silicon carbide) bulk material has become the best choice for preparing etching ring due to its close conductivity to the wafer and excellent etching resistance.

[0003] However, the resistivity of SiC bulk material is a key factor affecting the etching rate, and high resistivity can slow down the plasma energy reaching the material surface, significantly improving the etching resistance. At present, SiC bulk material with medium and low resistivity is easy to prepare, but the preparation of SiC bulk material with high resistivity still faces challenges. The existing technology mostly improves the resistivity by improving the cleanliness of the reaction environment and the purity of the reaction gas, but the preparation of high-purity reaction gas is difficult and costly, which makes it difficult to achieve commercial mass production of SiC bulk material with high resistivity, limiting its application in key components such as etching rings. Therefore, how to obtain mass-produced high-resistance SiC bulk material to improve the etching resistance and service life of the etching ring has become a technical problem to be solved in the semiconductor etching process. SUMMARY

[0004] The present application aims to overcome the above-mentioned problems existing in the prior art, and provides a method for preparing high-resistivity silicon carbide material and silicon carbide material. The method can significantly increase the boron element doping amount in silicon carbide, thereby improving the resistivity of silicon carbide and improving the etching resistance of silicon carbide.

[0005] The first aspect of the present application provides a method for preparing high-resistivity silicon carbide material, comprising the following steps:

[0006] Step 1: placing a substrate in a chemical vapor deposition device, vacuumizing the chemical vapor deposition device, and then introducing an inert gas;

[0007] Step 2: Silicon-carbon source gas and carrier gas are injected into the chemical vapor deposition device through the first gas inlet channel, and boron source gas is injected into the chemical vapor deposition device through the second gas inlet channel, and a silicon carbide material is deposited on the surface of the substrate by a chemical vapor deposition process;

[0008] Step 3: After gradient annealing, the substrate is removed;

[0009] In step 2, the distance between the gas inlet of the first gas inlet channel and the gas inlet of the second gas inlet channel is greater than or equal to 20 cm.

[0010] The second aspect of the present application provides a silicon carbide material prepared by the method of the first aspect of the present application, wherein the boron content of the surface of the side away from the substrate is 5 at%-6 at%.

[0011] The technical scheme of the present application has the following beneficial effects:

[0012] The preparation method provided by the present application can alleviate the gas phase competitive reaction of the reaction gas in the chemical vapor deposition process, improve the boron doping efficiency, and make the boron doping amount in the silicon carbide reach a high level. The high doping amount of boron elements can optimize the carrier concentration and mobility of the silicon carbide material, and thus significantly improve the resistivity of the silicon carbide. High resistivity can enhance the sheath voltage effect of the silicon carbide material in the plasma etching environment, slow down the speed of plasma energy reaching the material surface, reduce the etching rate, and greatly improve the etching resistance of the material. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 The structure of the second gas inlet channel and the third gas inlet channel in an example of the present application is shown.

[0014] Figure 2 The positional relationship between the gas inlet channel and the graphite substrate in an example of the present application is shown.

[0015] Reference signs: 1-cyclic structure; 2-gas inlet channel; 3-gas inlet; 4-first gas inlet channel; 5-graphite substrate. DETAILED DESCRIPTION

[0016] The specific embodiments of the present application are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application.

[0017] Unless otherwise defined, all scientific and technical terms used in the present application have the same meaning as generally understood by those skilled in the art to which the present application relates.

[0018] Glossary:

[0019] Carrier: In semiconductor physics, the loss of an electron is considered a carrier. There are two carriers in a semiconductor, namely, an electron and a hole.

[0020] Hole: Hole, also known as electron hole, refers to the phenomenon that a vacancy is left on a covalent bond due to the loss of an electron on the covalent bond in solid physics. That is, some valence electrons in the covalent bond obtain some energy due to thermal motion, thereby becoming free electrons and leaving vacancies on the covalent bond, which are called holes.

[0021] Valence band: The electrons in the atomic orbit that are in a bonded state are called valence electrons. Many energy levels occupied by these valence electrons can be merged and considered as a single continuous energy range. This low-energy band formed by the energy levels of the atomic orbit filled with electrons is called the valence band (full band) of the energy level. Any energy change usually occurs within the valence band. In short, the valence band is the highest energy band in the full band occupied by valence electrons.

[0022] Acceptor energy level: When a pure semiconductor material is doped with an acceptor impurity, the migration of valence electrons will form positively charged holes and negatively charged centers. Due to the electrostatic attraction, the holes are weakly bound to the negatively charged centers to form a bound state and move around them. The holes will be released to form conductive holes after obtaining energy. The energy state of the holes bound by the acceptor impurity is called the acceptor energy level.

[0023] The first aspect of the present application provides a method for preparing high-resistivity silicon carbide material, comprising the following steps:

[0024] Step 1: placing a substrate in a chemical vapor deposition device, vacuumizing the chemical vapor deposition device, and then introducing an inert gas;

[0025] Step 2: silicon-carbon source gas and carrier gas are injected into the chemical vapor deposition device through a first gas inlet channel, and boron source gas is injected into the chemical vapor deposition device through a second gas inlet channel, and silicon carbide is deposited on the surface of the substrate by a chemical vapor deposition process;

[0026] Step 3: after gradient annealing, the substrate is removed;

[0027] In step 2, the distance between the gas inlet of the first gas inlet channel and the gas inlet of the second gas inlet channel is ≥20 cm.

[0028] In the present application, by arranging the inlet paths of the silicon-carbon source gas and the boron source gas at a certain distance, the spatial separation of the silicon-carbon source gas and the boron source gas when first introduced into the chemical vapor deposition chamber can be realized, the competitive reaction of the silicon-carbon source gas and the boron source gas in the gas phase can be effectively alleviated, the boron source gas can be prevented from being consumed too early by the silicon-carbon source gas, the boron element can efficiently participate in the deposition process of silicon carbide, and finally the boron doping amount in the silicon carbide material (SiC) can be improved. When the boron atoms in the SiC lattice are distributed at a high concentration, the dense acceptor levels will overlap with each other to form a continuous acceptor impurity band independent of the valence band. At this time, the holes need to overcome a higher activation energy to jump from the valence band to the impurity band, resulting in a significant decrease in the concentration of charge carriers (holes) that can participate in conduction, which causes the resistivity of SiC to increase significantly. At the same time, after the high-concentration boron atoms replace the SiC lattice atoms, the periodic arrangement of the lattice will be destroyed, causing significant lattice distortion and enhancing the scattering effect on charge carriers, which leads to a significant decrease in the carrier mobility, thereby further increasing the resistivity of silicon carbide and improving the etching resistance of SiC material in etching gas and the service life of SiC material. The preparation method of high-resistivity SiC material provided by the present application can realize high boron doping and high resistivity in SiC material without relying on ultra-high purity gas, and is more suitable for industrial mass production.

[0029] In some embodiments, the distance between the gas inlet of the first gas inlet channel and the gas inlet of the second gas inlet channel is ≥ 20 cm.

[0030] In some embodiments, the distance between the gas inlet of the first gas inlet channel and the gas inlet of the second gas inlet channel is 20-50 cm, for example, it can be 20 cm, 25 cm, 30 cm, 35 cm, 40 cm, 45 cm, 50 cm or any point value in the range formed by the two point values.

[0031] In the present application, by controlling the distance between the gas inlets of the first gas inlet channel and the second gas inlet channel, the gas phase pre-reaction of the silicon-carbon source gas and the boron source gas can be delayed, and the generation amount of Si-B-Cl by-products can be reduced. By further controlling the distance between the gas inlets of the first gas inlet channel and the second gas inlet channel to be in the range of 20-50 cm, the problem of boron source gas transmission loss and insufficient boron doping amount on the substrate surface caused by too large distance can be avoided.

[0032] In the present application, the distance between the air inlet of the first air passage and the air inlet of the second air passage can be explained as the straight-line distance from the center of the circumscribed circle of the air inlet shape of the first air passage to the center of the circumscribed circle of the air inlet shape of the second air passage, denoted as the distance between the air inlet of the first air passage and the air inlet of the second air passage. When the cross-sectional shape of the air inlet of the first air passage and / or the air inlet of the second air passage is circular, the straight-line distance is calculated from the center of the circle, and the distance between the air inlet of the first air passage and the air inlet of the second air passage is obtained, as shown in Figure 2 L1 in the middle.

[0033] In the present application, the first air passage and the second air passage are independent of each other and are not connected to each other.

[0034] In some embodiments, the time for the boron source gas to be injected into the chemical vapor deposition device through the second air passage is 2s-5s after the time for the silicon-carbon source gas and the carrier gas to be injected into the chemical vapor deposition device through the first air passage, for example, it can be 2s, 2.5s, 3s, 3.5s, 4s, 4.5s, 5s or any point value in the range formed by any two of the above point values.

[0035] In the present application, by delaying the injection of the boron source gas, on the one hand, it can further avoid the premature mixing of the silicon-carbon source gas and the boron source gas in the gas phase to generate Si-B-Cl byproducts, ensuring that the boron source effectively participates in lattice doping in atomic state; on the other hand, it can make the silicon-carbon source gas and the carrier gas preferentially complete the initial adsorption and nucleation on the substrate surface to form a silicon carbide initial deposition layer with certain stability, providing a uniform and suitable lattice substrate for subsequent boron atom doping, thereby improving the substitution rate of boron atoms in the silicon carbide lattice and the doping uniformity, laying a foundation for the realization of high boron doping and high resistivity of SiC materials. If the above time difference is less than 2s, i.e. the boron source gas is injected too early, the silicon-carbon source gas has not yet formed a stable initial deposition layer on the substrate surface, at this time the boron source gas is prone to pre-reaction with the silicon-carbon source gas in the gas phase to generate Si-B-Cl byproducts, resulting in the boron atoms being unable to effectively embed into the silicon carbide lattice, not only reducing the boron doping efficiency, but also introducing impurity phases, destroying the integrity of the lattice, and making it difficult to achieve high resistivity; at the same time, the doping non-uniformity increases, resulting in a lower local resistivity of the material, affecting the consistency of the etching resistance of the SiC material; if the above time difference is greater than 5s, i.e. the boron source gas is injected too late, the silicon-carbon source gas has formed a relatively thick silicon carbide deposition layer on the substrate surface, and the boron atoms need to overcome the resistance of the thick deposition layer to diffuse to the inside of the lattice, resulting in a significant reduction in deep layer doping amount, forming a gradient distribution of high boron on the surface and low boron inside, causing large fluctuations in the overall resistivity of the material; and the too thick initial deposition layer will inhibit the uniform doping of boron atoms, causing the local area to have insufficient boron content, resulting in a decrease in etching resistance, which cannot meet the requirements of the etching ring for the stability of the material performance.

[0036] In some embodiments, the vertical distance between the gas inlet of the first gas inlet channel and the substrate is 35-45 cm, for example, it can be 35 cm, 36 cm, 37 cm, 38 cm, 39 cm, 40 cm, 41 cm, 42 cm, 43 cm, 44 cm, 45 cm, or any point value in the range consisting of any two of the above point values.

[0037] In some embodiments, the vertical distance between the gas inlet of the second gas inlet channel and the substrate is 45-55 cm, for example, it can be 45 cm, 46 cm, 47 cm, 48 cm, 49 cm, 50 cm, 51 cm, 52 cm, 53 cm, 54 cm, 55 cm, or any point value in the range consisting of any two of the above point values.

[0038] In some embodiments, the vertical distance between the gas inlet of the first gas inlet channel and the graphite substrate is less than the vertical distance between the gas inlet of the second gas inlet channel and the graphite substrate. In this way, the distance of the silicon-carbon source gas to the graphite substrate is shortened, the Si / C adsorption layer is preferentially formed, the oriented bonding sites for boron atoms are provided, and the boron doping efficiency is improved.

[0039] In the present application, the "vertical distance" can be explained as the shortest straight line distance between the side surface of the graphite substrate deposited with the silicon carbide coating and the gas inlet of the first / second gas inlet channel.

[0040] In some embodiments, in step 2, the deposition temperature is 1100-1400°C, for example, it can be 1100°C, 1150°C, 1200°C, 1250°C, 1300°C, 1350°C, 1400°C, or any point value in the range consisting of any two of the above point values. This temperature range not only promotes the dense growth of silicon carbide crystals, but also matches the diffusion activity of boron atoms, while avoiding excessive volatilization of boron atoms due to thermal motion caused by excessively high temperature; a lower temperature will reduce the reactivity of the silicon-carbon source gas and the boron source gas, making it difficult for boron atoms to effectively replace Si lattice sites. Therefore, this temperature range can balance crystal growth and boron doping efficiency, and ensure the uniform embedding of boron atoms in the dense lattice.

[0041] In some embodiments, in step 2, the deposition temperature is 1200-1300°C.

[0042] In some embodiments, in step 2, the deposition pressure is 5 kPa-20 kPa, for example, it can be 5 kPa, 8 kPa, 10 kPa, 12 kPa, 14 kPa, 16 kPa, 18 kPa, 20 kPa or any point value in the range consisting of any two of the above-mentioned point values. When the deposition pressure is in the above-mentioned range, the deposition rate can be improved, the quality and uniformity of silicon carbide can be improved, and the cost can be reduced due to the excessive deposition pressure, and the density of silicon carbide and the deposition rate can be reduced due to the low deposition pressure.

[0043] In some embodiments, in step 2, the deposition time is 20-40 h, for example, it can be 20 h, 22 h, 24 h, 26 h, 28 h, 30 h, 32 h, 34 h, 36 h, 38 h, 40 h or any point value in the range consisting of any two of the above-mentioned point values, preferably 15-35 h. When the deposition time is in the above-mentioned range, it can ensure that the boron atoms have sufficient time to diffuse into the crystal lattice synchronously with the growth of the film layer during the thickening of the silicon carbide, thereby ensuring the overall uniformity of the boron doping in the silicon carbide material and ensuring the consistency of the resistivity.

[0044] In some embodiments, the thickness of the silicon carbide is 250 μm-400 μm, for example, it can be 250 μm, 270 μm, 290 μm, 300 μm, 320 μm, 340 μm, 360 μm, 380 μm, 400 μm or any point value in the range consisting of any two of the above-mentioned point values.

[0045] In some embodiments, the flow ratio of the boron source gas and the silicon-carbon source gas is (0.5-4):1, for example, it can be 0.5:1, 1:1, 2:1, 3:1, 4:1 or any ratio within the range defined in the application. Under this ratio, the reactivity and participation of the boron source gas and the silicon-carbon source gas can be balanced, and it can be ensured that the boron atoms in the boron source gas can be uniformly combined with the silicon and carbon elements provided by the silicon-carbon source gas during the reaction process and effectively embedded in the silicon carbide crystal lattice. This ratio can avoid insufficient boron doping caused by low ratio (relative shortage of boron source gas), which is difficult to achieve high resistivity, and can prevent excessive aggregation of boron atoms caused by high ratio (relative excess of boron source gas), which forms amorphous impurity phase, destroys the integrity of the crystal lattice, and causes material performance fluctuations. By adjusting the flow ratio of the boron source gas and the silicon-carbon source gas, efficient and uniform doping of boron atoms in silicon carbide can be achieved, which lays a foundation for forming a dense three-dimensional structure and stable high-resistivity characteristics, and further ensures the etching resistance and service life of the material in the etching environment.

[0046] In some embodiments, the flow rate of the silicon-carbon source gas is greater than the flow rate of the boron source gas.

[0047] In the present application, the flow rate difference between the silicon-carbon source gas and the boron source gas helps to further control the mixing time and reaction timing of the two gases in the chemical vapor deposition device, avoiding the gas phase competitive reaction of the silicon-carbon source gas and the boron source gas. The silicon-carbon source gas first reaches the Si / C adsorption layer formed on the substrate surface to provide a directional binding site for boron atoms, further improving the boron doping efficiency.

[0048] In some embodiments, the flow rate of the silicon-carbon source gas is 4 m / s-10 m / s, for example, it can be 4 m / s, 5 m / s, 6 m / s, 7 m / s, 8 m / s, 9 m / s, 10 m / s or any point value in the range composed of any two of the above point values.

[0049] In some embodiments, the flow rate of the boron source gas is 2 m / s-8 m / s, for example, it can be 2 m / s, 3 m / s, 4 m / s, 5 m / s, 6 m / s, 7 m / s, 8 m / s or any point value in the range composed of any two of the above point values.

[0050] In the present application, further controlling the different flow rate ranges of the silicon-carbon source gas and the boron source gas helps the silicon-carbon source gas to uniformly diffuse in the deposition device and form a stable gas flow field in the deposition device, so that the gas is uniformly distributed around the substrate. This can ensure uniform growth of the silicon carbide coating on the entire substrate surface and avoid problems such as uneven local coating thickness or excessive composition difference.

[0051] In some embodiments, the molar ratio of the silicon-carbon source gas to the carrier gas is 1:(1-20), for example, it can be 1:1, 1:2, 1:4, 1:6, 1:8, 1:10, 1:12, 1:14, 1:16, 1:18, 1:20 or any ratio within the range defined by the present application. In the present application, controlling the molar ratio of the silicon-carbon source gas to the carrier gas within the above range can balance the deposition rate and defect control, and a dense silicon carbide material is deposited.

[0052] In some embodiments, the flow rate of the carrier gas is 0.1 slm-1 slm, for example, it can be 0.1 slm, 0.2 slm, 0.4 slm, 0.6 slm, 0.8 slm, 1 slm or any point value in the range composed of any two of the above point values. In the present application, controlling the flow rate of the carrier gas within the above range allows the silicon-carbon source molecules to have sufficient time to adsorb on the substrate surface and grow in an orderly manner, improving the uniformity of the silicon carbide.

[0053] In some embodiments, the boron source gas is selected from boron trichloride (BCl3).

[0054] In some embodiments, the silicon-carbon source gas is selected from at least one of methyltrichlorosilane (MTS), trichlorosilane, and tetrachlorosilane.

[0055] In some embodiments, the carrier gas is selected from hydrogen.

[0056] In some embodiments, the gas system for depositing silicon carbide further includes ammonia; the ammonia is injected into the chemical vapor deposition apparatus via a third inlet channel, which is independent of the first and second inlet channels. During the silicon carbide coating deposition process, Cl is released due to the decomposition of the introduced silicon-carbon source gas (e.g., MTS) and boron source gas (e.g., BCl3). - This leads to Cl in the chemical vapor deposition equipment - The concentration increased sharply, and excess Cl - Upon recombination with the decomposition products of the boron source gas (such as BCl2), it forms gaseous BCl4. - BCl4 - The boron cannot be deposited as a solid state, leading to a decrease in boron doping efficiency. Furthermore, free Cl... - It can also be adsorbed on the silicon carbide (111) crystal plane, affecting the uniformity of boron distribution in the silicon carbide lattice.

[0057] In this invention, ammonia (NH3) is introduced through the third air inlet channel, and NH3 reacts with Cl... - Combined with the generated NH4Cl, excess free Cl in the chemical vapor deposition chamber is selectively removed. - Furthermore, the third intake channel is independent of the first and second intake channels, which physically isolates NH3 from the silicon carbide source gas, the main carrier gas path, and the boron source gas doping path. This prevents NH3 from pre-reacting with the silicon carbide source gas or the boron source gas, thereby further improving the decomposition efficiency of the boron source gas, increasing the boron doping content of silicon carbide, increasing the resistivity of silicon carbide, and thus improving the corrosion resistance and service life of silicon carbide.

[0058] In some embodiments, the molar ratio of ammonia to chloride ions in the chemical vapor deposition apparatus is (1.2-1.5):1, and the molar ratio can be, for example, 1.2:1, 1.3:1, 1.4:1, 1.5:1 or any ratio within the range defined by the present invention.

[0059] In this invention, Cl inside the chemical vapor deposition equipment is monitored in real time. - By dynamically adjusting the ammonia flow rate and concentration, and ensuring that the molar ratio of ammonia to chloride ions remains within the aforementioned range, Cl can be avoided. - Excessive residual boron improves the boron doping efficiency and the uniformity of boron distribution in the silicon carbide lattice, thereby increasing the resistivity of silicon carbide.

[0060] In some embodiments, the flow rate of ammonia is 3-8 slm, for example, it can be 3, 4, 5, 6, 7, 8 slm or any value in the range consisting of any two of the above-mentioned values.

[0061] In some embodiments, the concentration of chloride ions in the chemical vapor deposition device is controlled to be <200 ppm, for example, it can be 199, 180, 150, 100, 50 ppm or any value lower than 200 ppm. Controlling the concentration of chloride ions in the chemical vapor deposition chamber within the above range can effectively improve the decomposition efficiency of the boron source gas and reduce the cost of raw materials.

[0062] In some embodiments, the second gas inlet channel is a ring structure, and a plurality of gas inlets are uniformly arranged on the ring structure.

[0063] In some embodiments, the second gas inlet channel and the third gas inlet channel can be arranged in sequence on the ring structure. It can be understood that, in Figure 1 , one gas inlet channel 2 on the ring structure 1 is connected to the boron source gas, and the two gas inlet channels 2 adjacent to the gas inlet channel 2 are connected to ammonia.

[0064] To clarify the positional relationship between the various gas inlet channels and between the gas inlet channels and the graphite substrate in the present application, further explanation is made in combination with the schematic diagram shown in Figure 2 . In the diagram Figure 2 , the first gas inlet channel 4 is independent of and not connected to the plurality of gas inlet channels 2 on the ring structure 1. The vertical distance between the gas inlet 3 of the first gas inlet channel 4 and the graphite substrate 5 is shown as L2 in the diagram. When the gas inlet channel 2 is connected to the boron source gas, it is referred to as the second gas inlet channel. The vertical distance between the second gas inlet channel and the graphite substrate 5 is shown as L3 in the diagram, and the spacing between the second gas inlet channel and the first gas inlet channel 4 is shown as L1 in the diagram.

[0065] It should be noted that Figure 2 , it is only a schematic diagram and is intended to illustrate the spatial positional relationship between the first gas inlet channel, the second gas inlet channel, the third gas inlet channel and the graphite substrate in the present application, and does not represent the specific structure in actual application. In addition, Figure 2 , the first gas inlet channel 4 can be one or multiple. If the first gas inlet channel 4 is multiple, the vertical distance between each first gas inlet channel 4 and the graphite substrate 5 can be the same or different. The vertical distance between each of the plurality of gas inlet channels 2 on the ring structure 1 and the graphite substrate 5 can also be the same or different.

[0066] In some embodiments, the step 3 includes the following steps:

[0067] (1) in the first temperature interval of 1200℃-1600℃, holding for 1 h-4 h;

[0068] (2) reducing to the second temperature interval of 600℃-800℃ at a cooling rate of 1℃ / min-2℃ / min, holding for 1 h-2 h;

[0069] (3) reducing to the third temperature interval of 25℃-100℃ at a cooling rate of 2℃ / min-5℃ / min.

[0070] In the present application, the gradient annealing process is used to maintain high temperature (1200℃-1600℃) in the early stage of annealing, to promote the complete decomposition of residual boron source gas; in the medium temperature stage (600℃-800℃), the temperature is slowly reduced, the residence time of the decomposition products (such as BCl2) of the boron source gas on the substrate surface is prolonged, the diffusion of boron atoms into the silicon carbide lattice is promoted, and the recombination of the decomposition products of the boron source gas caused by rapid cooling is avoided, thereby reducing the boron doping efficiency. The gradient annealing process in the present application gradually releases the lattice distortion stress caused by boron doping by slowly reducing the temperature, avoids the generation of cracks, prevents the aggregation of boron atoms at defects, further improves the effective doping ratio of boron atoms, improves the resistivity of silicon carbide, and improves the etching resistance and service life of silicon carbide.

[0071] In the present application, the type of substrate is not specifically limited, for example, a graphite substrate can be selected.

[0072] In the present application, the vapor deposition equipment can be a vapor deposition chamber, a vapor deposition furnace and the like conventional equipment in the art.

[0073] The second aspect of the present application provides a silicon carbide material prepared by the method of the first aspect of the present application, wherein the boron content in the silicon carbide material is 4.5 at%-6 at%. Illustratively, the boron content in the silicon carbide material may, for example, be 4.5 at%, 4.7 at%, 4.9 at%, 5 at%, 5.2 at%, 5.4 at%, 5.6 at%, 5.8 at%, 6 at% or any value within the range of any two of the above-mentioned values.

[0074] In the present application, the boron content of silicon carbide can be tested by glow discharge mass spectrometry (GD-MS), and the testing position may, for example, be selected as the surface of the side of the silicon carbide away from the substrate.

[0075] In some embodiments, the resistivity of the silicon carbide material is 1000 Ω-cm-25000 Ω-cm. Further researches of the present application show that the higher the utilization rate of boron doping is, the more boron atoms after decomposition of the boron source gas can be effectively embedded into the silicon carbide lattice and fully replace the silicon atoms in the silicon carbide lattice to form dense and stable acceptor energy levels. These energy levels overlap to increase the activation energy of hole transition, reduce the carrier concentration, and at the same time, cause lattice distortion to enhance scattering, thereby significantly improving the resistivity. On the contrary, when the utilization rate is low, a large amount of boron source gas does not participate in lattice doping, even if the total boron doping amount in the silicon carbide bulk is high, the effective boron atoms actually playing a role may still be insufficient, resulting in limited improvement of the resistivity. For example, when the boron source gas is excessively introduced, it cannot be fully accommodated by the silicon carbide lattice, and part of the boron atoms exist in the form of free state or amorphous lattice impurities (such as interstitial boron which does not effectively replace silicon / carbon atoms). These "ineffective boron" do not participate in the formation of acceptor energy levels, but may introduce lattice defects to become the channel of carrier transport, resulting in a decrease instead of an increase in resistivity. At this time, although the total boron doping amount is high, the proportion of boron atoms effectively participating in the resistivity regulation is insufficient due to the low utilization rate of boron source gas, and finally a low resistivity is shown. Therefore, by using the vapor deposition process to prepare the silicon carbide bulk, when both the sufficient boron doping amount and the high utilization rate of boron source gas are met, the resistivity of the silicon carbide can be significantly improved, and the resistivity can be as high as 25000 Ω-cm, thereby further improving the etching resistance and service life of the silicon carbide.

[0076] In the present application, the resistivity of the silicon carbide material can be tested by a four-probe resistivity tester.

[0077] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0078] In the following examples, the materials and reagents used, unless otherwise specified, can be obtained from commercial channels.

[0079] The present application will be described in detail below with reference to specific embodiments, which are used for understanding rather than limiting the present application.

[0080] Embodiment 1

[0081] A method for preparing a high-resistivity silicon carbide material, comprising the following steps:

[0082] Step 1: cut the graphite into samples, wash the samples with deionized water for 30 min, dry the washed graphite samples, heat at 120°C for 2 h, perform nitrogen blowing, and then place the samples in a vapor deposition furnace for standby;

[0083] Step 2: Vacuumize the chemical vapor deposition furnace, and hold the pressure when the lowest vacuum value is reached; first, increase the temperature of the chemical vapor deposition furnace to a deposition temperature of 1250°C (temperature increase rate <5°C / min), and inject methyltrichlorosilane and hydrogen with a molar ratio of 1:10 into the chemical vapor deposition chamber through the first gas inlet channel; after a delay of 3s, inject boron trichloride into the chemical vapor deposition chamber through the second gas inlet channel; then inject ammonia into the chemical vapor deposition chamber through the third gas inlet channel, and monitor the content of chloride ions in the chemical vapor deposition chamber in real time using a probe to control the molar ratio of ammonia to chloride ions to be 1.3:1; deposit for 20 h at 12 kpa;

[0084] Step 3: Gradient annealing step, 1250°C, holding for 2 h; decrease to 700°C at a rate of 1.5°C / min, holding for 1.5 h; decrease to 25°C at a rate of 3°C / min, and remove the substrate by oxidizing the graphite.

[0085] wherein the flow ratio of boron trichloride to methyltrichlorosilane is 2:1; the flow rate of methyltrichlorosilane is 7 m / s; the flow rate of boron trichloride is 5 m / s; the flow rate of hydrogen is 0.5 slm; the flow rate of ammonia is 6 slm; the distance between the gas inlet of the first gas inlet channel and the gas inlet of the second gas inlet channel is 35 cm; the vertical distance between the gas inlet of the first gas inlet channel and the graphite substrate is 40 cm; and the vertical distance between the gas inlet of the second gas inlet channel and the graphite substrate is 50 cm.

[0086] Example 2 group

[0087] The method described in Example 1 is followed, except that:

[0088] In Example 2a, in Step 2, the time difference between the injection of boron trichloride and methyltrichlorosilane is 2s.

[0089] In Example 2b, in Step 2, the time difference between the injection of boron trichloride and methyltrichlorosilane is 5s.

[0090] In Example 2c, in Step 2, the time difference between the injection of boron trichloride and methyltrichlorosilane is 8s.

[0091] Example 3 group

[0092] The method described in Example 1 is followed, except that:

[0093] In Example 3a, except that the flow ratio of boron trichloride to methyltrichlorosilane is 0.5:1.

[0094] In Example 3b, except that the flow ratio of boron trichloride to methyltrichlorosilane is 4:1.

[0095] Example 4 group

[0096] The procedure described in Example 1 was followed, except that:

[0097] In Example 4a, the deposition temperature was 1100 °C.

[0098] In Example 4b, the deposition temperature was 1400 °C.

[0099] In Example 4c, the deposition temperature was 1000 °C.

[0100] In Example 4d, the deposition temperature was 1500 °C.

[0101] Example 5 group

[0102] The procedure described in Example 1 was followed, except that:

[0103] In Example 5a, there was no gradient annealing step, and the substrate was removed after the normal cool down to give the product.

[0104] In Example 5b, the annealing step was: 1250 °C for 2 h; cool down to 900 °C at a rate of 1.5 °C / min, hold for 1.5 h; cool down to 25 °C at a rate of 3 °C / min.

[0105] In Example 5c, the annealing step was: 1250 °C for 2 h; cool down to 500 °C at a rate of 1.5 °C / min, hold for 1.5 h; cool down to 25 °C at a rate of 3 °C / min.

[0106] In Example 5d, the annealing step was: 1250 °C for 2 h; cool down to 500 °C at a rate of 3 °C / min, hold for 1.5 h; cool down to 25 °C at a rate of 3 °C / min.

[0107] Example 6 group

[0108] The procedure described in Example 1 was followed, except that:

[0109] In Example 6a, no ammonia was injected into the chemical vapor deposition chamber.

[0110] In Example 6b, the molar ratio of ammonia to chloride ions was controlled to be 2:1.

[0111] In Example 6c, the molar ratio of ammonia to chloride ions was controlled to be 1:1.

[0112] Comparative Example 1

[0113] The procedure described in Example 1 was followed, except that the distance between the inlet of the first gas inlet channel and the inlet of the second gas inlet channel was 10 cm.

[0114] Comparative Example 2

[0115] The procedure described in Example 1 was followed, except that both boron trichloride and methyltrichlorosilane were injected into the chemical vapor deposition chamber through the first gas inlet channel.

[0116] Comparative Example 3

[0117] The procedure described in Example 1 was followed, except that no boron trichloride was injected into the chemical vapor deposition chamber.

[0118] Test Example 1

[0119] The boron doping amount of the semiconductor epitaxial base prepared in the examples and comparative examples was determined by the following method:

[0120] (1) A high-precision cutting device was used to cut a boron-doped SiC coating graphite substrate prepared by a CVD process to obtain a sample with appropriate size, which was generally cut into a circular sheet with a diameter of about 10-20 mm and a thickness of about 3-5 mm, and the sample surface was ensured to be flat without obvious cracks, scratches and other defects.

[0121] (2) The cut sample was sequentially placed in acetone and ethanol solutions, and ultrasonic cleaning was used, with each cleaning time being about 20 min. After cleaning, the sample was rinsed with deionized water, and then the sample was placed in a vacuum drying oven to completely dry the sample surface at a temperature of 80°C.

[0122] (3) A standard material with a composition similar to that of the SiC substrate and a known B element content was selected, and the B element content of the standard material covered the possible content range of the B element in the sample, and five standard materials with different concentration gradients were prepared.

[0123] (4) The pretreated sample was carefully installed into the sample cell of the GD-MS instrument to ensure that the sample was in close contact with the sample cell, and to avoid affecting the test results due to poor contact.

[0124] (5) The GD-MS instrument was started for testing under an environment with a vacuum degree better than 1x10 -4 Pa. The glow discharge parameters were kept consistent with the calibration stage, and the sample was deeply analyzed by adjusting the sputtering time and sputtering rate to ensure that the SiC coating could be fully analyzed, with a sputtering time of 20±5 minutes and a sputtering rate controlled at 0.5±0.1 μm / min.

[0125] During the test, the signal intensity data of the B element were collected in real time, and the signal intensity data of other related elements were also collected as references to exclude the matrix effect and the interference of other elements. Each sample was tested repeatedly for 5 times, and the average value was taken as the test result.

[0126] Test Example 2

[0127] The utilization rate of boron source gas for the semiconductor epitaxial base prepared in the examples and comparative examples was determined. The measurement principle was that the utilization rate of boron source gas (BC13) was obtained by calculating the ratio of the amount of substance of boron elements deposited in the SiC coating to the total amount of substance of input BCl3 gas (excluding the residual amount in the tail gas). The specific operation method was as follows:

[0128] (1) A mass flow controller (MFC) was used to set the BCl3 gas flow, and to ensure accuracy, the MFC was calibrated using a soap film flowmeter, so that the flow error was controlled within ±1%.

[0129] (2) According to the ideal gas state equation ninput=(QxtxtP) / (RT), wherein Q is the calibrated BCl3 flow (m / s), t is the total time of the CVD deposition process (s), P is the standard atmospheric pressure (Pa), R is the gas constant (8.314 J / (mol K)), and T is the standard temperature (273.15 K), the amount of substance of input BCl3 was calculated. 3

[0130] (3) After the CVD process, the SiC coating sample with an area of S was cut from the graphite substrate, ultrasonically cleaned with deionized water for 5 min to remove surface impurities, and then placed in a 120°C environment for drying for 30 min to constant weight.

[0131] (4) X-ray fluorescence spectroscopy (XRF) was used to determine the boron element content. When measuring, the tube voltage was set to 50 kV, the tube current was 50 mA, the measurement time was 60 s, and a SiC standard sample with known boron content was used to draw a standard curve to obtain the mass fraction of boron element WB. At the same time, the coating thickness d (accuracy ±0.1 μm) was measured by a step meter, and the porosity was analyzed by a metallographic microscope combined with ImageJ software to calculate the coating density p.

[0132] (5) The amount of boron element was calculated according to the formula mB=wBxpXdXS, and the amount of substance of deposited boron element was obtained by ndeposit=mB / MB (MB, the molar mass of boron, 10.811 g / mol).

[0133] ​(6) Build a three-stage condensing tail gas collection system. The first stage is at room temperature (25℃), condensing and collecting SiCl4 and other high-boiling-point substances; the second stage uses a dry ice / acetone bath, maintaining -77℃, to condense BCl3 with a boiling point of 12.5℃; the third stage uses a liquid nitrogen cold trap to collect H2, HCl and other low-boiling-point gases at -196℃; the collected tail gas samples are injected into a gas chromatograph-mass spectrometer (GC-MS), and the residual BCl3 in the tail gas is quantitatively analyzed using an external standard method (BCl3 standard gas) to calculate the residual boron amount nresidual.

[0134] (7) The utilization rate of boron source gas = ndeposition / (ninput-nresidual) x 100%, and the utilization rate of BCl3 gas is obtained.

[0135] Test Example 3

[0136] The resistivity of the silicon carbide material prepared in the examples and comparative examples is tested by using four probes to contact the surface of the material, and then giving a current I of 1.5 μA to obtain a corresponding voltage V of 100 mV, and calculating the resistivity of the silicon carbide material according to I and V.

[0137] Test Example 4

[0138] MTS and BCl3 delay mixing time is tested by computational fluid dynamics (CFD) simulation.

[0139] Table 1

[0140]

[0141] From the results of Table 1 above, it can be seen that the silicon carbide material prepared by the method provided by the present application can delay the pre-reaction time of the silicon-carbon source gas and the boron source gas by separating the introduction paths of the silicon-carbon source gas and the boron source gas and adjusting the flow ratio of the silicon-carbon source gas and the boron source gas, alleviate the gas phase competitive reaction, improve the uniformity of the distribution of boron atoms in the silicon carbide lattice and the boron doping efficiency, and further improve and control the boron doping amount in the silicon carbide material, improve the etching resistance and service life of the semiconductor epitaxial base.

[0142] It is to be understood that the terminology "including", "containing" or any other variation thereof does not exclude the presence of other elements or steps than those listed in the process, method, article, or apparatus. It is further understood that the steps and elements recited in any of the examples herein can be combined, removed or arranged in various ways without departing from the scope of the application. Further, the features described in relation to one example can be combined with features described in relation to other examples.

[0143] The above description is merely illustrative of the application and does not in any way delimit the scope of the application. Any modification, equivalent replacement or the like made within the spirit and principle of the application shall fall within the scope of the application.

Claims

1. A method of producing high resistivity silicon carbide material, characterized by, The method comprises the following steps: Step 1: placing a substrate in a chemical vapor deposition device, vacuumizing the chemical vapor deposition device, and then introducing an inert gas; Step 2: introducing a silicon-carbon source gas and a carrier gas into the chemical vapor deposition device through a first gas inlet channel, introducing a boron source gas into the chemical vapor deposition device through a second gas inlet channel, and depositing silicon carbide on the surface of the substrate by a chemical vapor deposition process; Step 3: removing the substrate after gradient annealing; In step 2, the distance between the gas inlet of the first gas inlet channel and the gas inlet of the second gas inlet channel is greater than or equal to 20 cm.

2. The method of claim 1, wherein, The vertical distance between the gas inlet of the first gas inlet channel and the substrate is 35-45 cm; And / or, the vertical distance between the gas inlet of the second gas inlet channel and the substrate is 45-55 cm.

3. The method of claim 1, wherein, The second gas inlet channel is in a ring structure, and a plurality of gas inlets are uniformly arranged on the ring structure.

4. The method of claim 1, wherein, The flow rate ratio of the boron source gas to the silicon-carbon source gas is (0.5-4):1; And / or, the flow rate of the silicon-carbon source gas is greater than the flow rate of the boron source gas; And / or, the time for the boron source gas to be introduced into the chemical vapor deposition device through the second gas inlet channel is 2-5 s after the time for the silicon-carbon source gas and the carrier gas to be introduced into the chemical vapor deposition device through the first gas inlet channel.

5. The method of claim 1, wherein, The flow rate of the silicon-carbon source gas is 4-10 m / s.

6. The method of claim 1, wherein, The flow rate of the boron source gas is 2-8 m / s.

7. The method of claim 1, wherein, In step 2, the deposition conditions of the silicon carbide independently include: the deposition temperature is 1100-1400℃, the deposition pressure is 5-20 kPa, and the deposition time is 20-40 h; And / or, the thickness of the silicon carbide is 250-400 μm.

8. The method of claim 1, wherein, The molar ratio of the silicon-carbon source gas to the carrier gas is 1:(1-20); And / or, the flow rate of the carrier gas is 0.1-1 slm.

9. The method of claim 1, wherein, The boron source gas is selected from boron trichloride; And / or, the silicon-carbon source gas is selected from at least one of methyltrichlorosilane, trichlorosilane and tetrachlorosilane; And / or, the carrier gas is selected from hydrogen.

10. The method of claim 9, wherein, The gas system for depositing silicon carbide further comprises ammonia; the ammonia is introduced into the chemical vapor deposition device through a third gas inlet channel, and the third gas inlet channel is independent of the first gas inlet channel and the second gas inlet channel.

11. The method of claim 10, wherein, In the chemical vapor deposition device, the molar ratio of the ammonia to the chloride ion is (1.2-1.5):

1.

12. The method of claim 11, wherein, The flow rate of the ammonia is 3-8 slm.

13. The method of claim 11, wherein, In the chemical vapor deposition device, the concentration of the chloride ion is controlled to be less than 200 ppm.

14. The method according to any one of claims 1 to 13, characterized in that, In step 3, the gradient annealing step comprises: (1) maintaining the temperature in a first temperature interval of 1200-1600℃ for 1-4 h; (2) reducing the temperature at a rate of 1-2℃ / min to a second temperature interval of 600-800℃, and maintaining the temperature for 1-2 h; (3) reducing the temperature at a rate of 2-5℃ / min to a third temperature interval of 25-100℃.

15. A silicon carbide material, characterized by, The silicon carbide material is prepared by the method of any one of claims 1-14, and the boron content in the silicon carbide material is 4.5-6 at%.

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