A method for producing an n-type semiconductor diamond material

Abstract

The application relates to the technical field of diamond materials, in particular to a preparation method of N-type semiconductor diamond material, which comprises the following steps: S1, providing a diamond substrate, and performing surface cleaning and hydrogen plasma activation pretreatment on the diamond substrate; S2, placing the pretreated diamond substrate in a reaction chamber of a chemical vapor deposition device; S3, introducing reaction gas containing a carbon source and a dopant precursor into the reaction chamber, wherein the dopant precursor comprises an aluminum source, a germanium source and a phosphorus source; and S4, performing vapor deposition growth on the diamond substrate, wherein the N-type semiconductor diamond material prepared by the Al-Ge-P ternary co-doping scheme has excellent performance and completely meets and exceeds the preset performance target.

Description

Technical Field

[0001] This invention relates to the field of diamond material technology, specifically to a method for preparing N-type semiconductor diamond material. Background Technology

[0002] The goal of researching semiconductor diamond materials is to achieve the fabrication of diamond PN junctions, which requires the preparation of P-type and N-type diamond semiconductor materials. Currently, P-type diamond materials obtained by doping diamond with boron ions through chemical vapor deposition or ion implantation meet the application requirements and have been applied in wastewater treatment, medical treatment, and science and technology.

[0003] However, the preparation of N-type diamond materials with semiconductor properties that meet application requirements still faces many challenges. Currently, the deep energy levels of impurities in N-type diamond films result in low carrier concentration, low Hall mobility, and high resistivity, making N-type diamond materials unable to meet the requirements for semiconductor electronic device fabrication and thus hindering their application. Therefore, finding a suitable method for preparing N-type semiconductor diamond materials is of great significance. Summary of the Invention

[0004] Purpose of the invention: To address the above-mentioned technical problems, this invention proposes a method for preparing N-type semiconductor diamond materials.

[0005] The technical solution adopted is as follows: A method for preparing an N-type semiconductor diamond material includes the following steps: S1: Provide a diamond substrate and perform surface cleaning and hydrogen plasma activation pretreatment on it; S2: Place the pretreated diamond substrate in the reaction chamber of the chemical vapor deposition equipment; S3: Introduce a reaction gas containing a carbon source and a dopant precursor into the reaction chamber. The dopant precursor includes an aluminum source, a germanium source, and a phosphorus source. S4: Vapor deposition growth on the diamond substrate.

[0006] Furthermore, the aluminum source is trimethylaluminum, the germanium source is tetramethylgermanium, and the phosphorus source is at least one of phosphine, dimethylphosphine, trimethylphosphine, diethylphosphine, triethylphosphine, tert-butylphosphine, triphenylphosphine, phosphorus trifluoride, phosphorus pentafluoride, phosphorus trichloride, or phosphorus pentachloride.

[0007] Preferably, the phosphorus source is phosphine (PH3).

[0008] Furthermore, the molar flow rate ratio of the aluminum source, germanium source, and phosphorus source is in the range of 1:(0.5-2):(1-5). This specific ratio range is key to achieving effective ternary synergistic doping; below or outside this range, the synergistic effect will weaken or even disappear.

[0009] Furthermore, the carbon source has a volume fraction of 0.5%-3% in the reaction gas. This range balances the growth rate and crystal quality.

[0010] Furthermore, the carbon source is a hydrocarbon compound that is gaseous at room temperature and normal pressure, such as methane, ethane, propane, or mixtures thereof, most preferably methane (CH4).

[0011] Furthermore, the reaction gas also includes a carrier gas, which is hydrogen (H2). Hydrogen, as the carrier gas, simultaneously activates the carbon source and etches the non-diamond phase.

[0012] Furthermore, the vapor deposition growth pressure is 300 mbar-400 mbar, and the substrate temperature is 1050℃-1200℃. This relatively high temperature and specific pressure window are crucial for activating the three dopant precursors and promoting their migration and incorporation at the growth interface.

[0013] Furthermore, the vapor deposition time is 1-10 hours. This time range is used to control the growth thickness of the N-type diamond material.

[0014] Furthermore, the method also includes an annealing step at a temperature of 600℃-800℃. Annealing helps to repair point defects introduced during growth and allows dopant atoms to more completely enter substitutional sites, thereby improving carrier concentration and mobility.

[0015] Furthermore, the N-type semiconductor diamond material prepared by the method has a carrier concentration of not less than 10 at room temperature. 19 cm -3 Resistivity not higher than 0.05 Ω·cm, Hall mobility not lower than 1000 cm⁻¹ 2 / (v·s).

[0016] According to another aspect of the present invention, an N-type semiconductor diamond material is also provided, specifically prepared by the preparation method described in any of the above embodiments.

[0017] The N-type semiconductor diamond material prepared by the method of this invention exhibits excellent performance in high-power electronic devices such as high-power transistors and diodes, and high-frequency microwave devices. Its applications include, but are not limited to, electric vehicle inverters, 5G base station power modules, industrial frequency converters, satellite communications, radar systems, and terahertz imaging.

[0018] The beneficial effects of this invention are: This invention provides a method for preparing N-type semiconductor diamond material, which achieves unexpected technical effects through the Al-Ge-P ternary co-doping method, mainly in the following aspects: This invention successfully increased the room-temperature carrier concentration of N-type diamond from 10 16 cm -3 The magnitude has increased to 10 19 cm -3 The resistivity decreased by an order of magnitude, from about 0.1 Ω·cm to below 0.05 Ω·cm, which is a breakthrough of an order of magnitude or even several orders of magnitude, and completely solved the core problem of insufficient performance of single phosphorus doping.

[0019] On vapor-deposited or grown surfaces, trimethylaluminum and phosphine may form a type of Al-P pre-nucleation cluster. The overall size and electronic structure of these clusters differ from individual P atoms, potentially making them more readily incorporated into the diamond lattice. Subsequent doping with germanium atoms, due to their unique valence electron structure and atomic size, may act as a "strain buffer" or "bridging center." This can partially modulate the localized lattice distortion caused by the Al-P clusters, thereby significantly reducing the formation energy of the entire doped complex.

[0020] Traditionally, it is believed that the introduction of Al would exacerbate compensation. However, under the specific proportions and process conditions of this invention, the introduction of Ge may alter the local chemical environment of Al and P, forming a stable Al-Ge-P composite donor center. This center may have shallower energy levels, and its structural characteristics suppress the generation of nearby acceptor defects (such as vacancies), thereby weakening the self-compensation effect and allowing more dopants to effectively contribute free electrons.

[0021] Despite the introduction of three heteroatoms, the diamond material prepared by this invention maintains good crystallinity through precise control of the molar flow ratio and deposition parameters. Raman spectroscopy data show that its diamond characteristic peaks remain sharp, and the full width at half maximum (FWHM) does not show significant broadening, indicating that lattice integrity is well maintained. This breaks the conventional understanding that "multi-element doping inevitably leads to high defect density."

[0022] The aluminum, germanium, and phosphorus sources used in this invention are all gaseous or easily vaporized precursors that can be used in CVD processes and are compatible with existing CVD infrastructure. By clarifying the preferred range of each parameter and their synergistic relationship, this method provides an achievable and repeatable process path. Detailed Implementation

[0023] Unless otherwise specified in the examples, the conditions were performed under standard conditions or as recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products. Techniques not mentioned in this invention refer to existing technologies. Unless otherwise specified, the following examples and comparative examples are parallel experiments, using the same processing steps and parameters.

[0024] I. General Equipment and Materials: 1. CVD equipment: All embodiments and comparative examples of this invention use a microwave plasma chemical vapor deposition (MPCVD) system.

[0025] 2. Substrate: Unless otherwise specified, Ib-type high-temperature high-pressure synthetic single crystal diamond with (100) crystal orientation is used.

[0026] 3. Gases: Hydrogen (H2, 99.999%), methane (CH4, 99.999%), phosphine (PH3, 1000ppm inH2), trimethylaluminum (Al(CH3)3, introduced by H2 carrier gas via a bubbler), tetramethylgermanium (Ge(CH3)4, introduced by H2 carrier gas via a bubbler), and high-purity argon (Ar, 99.999%).

[0027] II. General Preprocessing Steps: 1. Place the diamond substrate in acetone and anhydrous ethanol in sequence and ultrasonically clean for 15 minutes each.

[0028] 2. Transfer to deionized water and ultrasonically clean for 10 minutes, then dry with high-purity nitrogen.

[0029] 3. Place it in the MPCVD reaction chamber and evacuate to a vacuum level of ≤5×10⁻⁶. -5 mbar.

[0030] 4. Introduce hydrogen gas, adjust the pressure to 50 mbar, turn on the microwave power to 800 W, and perform hydrogen plasma treatment for 10 minutes.

[0031] Example 1: After the pretreatment is completed, the pressure in the reaction chamber is increased to 350 mbar. By adjusting the heating system and plasma power, the substrate temperature is stabilized at 1100±10℃. After stabilization, the reaction gas is introduced according to the following settings: hydrogen: 350 sccm, methane: 10 sccm (volume fraction of 2.5%), dopant precursor: 40 sccm. The dopant precursors include trimethylaluminum (concentration of 10,000 ppm) carried into the reaction chamber by hydrogen through a bubbler, tetramethylgermanium (concentration of 10,000 ppm) carried into the reaction chamber by carrier gas (hydrogen) through another bubbler, and a phosphine / hydrogen mixture (concentration of 10,000 ppm). The respective valves are adjusted to make the molar flow ratio of aluminum source, germanium source and phosphorus source range from 1:1:3.

[0032] The microwave power was maintained at 2500W, and vapor deposition was performed under these conditions for 4 hours. After growth, all carbon source and dopant gases were turned off, and the plasma was maintained in a pure hydrogen atmosphere (400 sccm) while cooling to a substrate temperature of 700±10℃. In-situ annealing was then performed for 30 minutes. Subsequently, the temperature was slowly lowered to below 200℃ in a hydrogen atmosphere. Finally, the hydrogen was turned off, a vacuum was drawn, and the sample was removed.

[0033] Example 2: After the pretreatment is completed, the pressure in the reaction chamber is increased to 350 mbar. By adjusting the heating system and plasma power, the substrate temperature is stabilized at 1060±10℃. After stabilization, the reaction gas is introduced according to the following settings: hydrogen: 350 sccm, methane: 10 sccm (volume fraction of 2.5%), dopant precursor: 40 sccm. The dopant precursors include trimethylaluminum (concentration of 10,000 ppm) carried into the reaction chamber by hydrogen through a bubbler, tetramethylgermanium (concentration of 10,000 ppm) carried into the reaction chamber by carrier gas (hydrogen) through another bubbler, and a phosphine / hydrogen mixture (concentration of 10,000 ppm). The respective valves are adjusted to make the molar flow ratio of aluminum source, germanium source and phosphorus source range from 1:0.5:1.

[0034] The microwave power was maintained at 2500W, and vapor deposition was performed under these conditions for 4 hours. After growth, all carbon source and dopant gases were turned off, and the plasma was maintained in a pure hydrogen atmosphere (400 sccm) while cooling to a substrate temperature of 610±10℃. In-situ annealing was then performed for 30 minutes. Subsequently, the temperature was slowly lowered to below 200℃ in a hydrogen atmosphere. Finally, the hydrogen atmosphere was turned off, a vacuum was drawn, and the sample was removed.

[0035] Example 3: After the pretreatment is completed, the pressure in the reaction chamber is increased to 350 mbar. By adjusting the heating system and plasma power, the substrate temperature is stabilized at 1190±10℃. After stabilization, the reaction gas is introduced according to the following settings: hydrogen: 350 sccm, methane: 10 sccm (volume fraction of 2.5%), dopant precursor: 40 sccm. The dopant precursors include trimethylaluminum (concentration of 10,000 ppm) carried into the reaction chamber by hydrogen through a bubbler, tetramethylgermanium (concentration of 10,000 ppm) carried into the reaction chamber by a carrier gas (hydrogen) through another bubbler, and a phosphine / hydrogen mixture (concentration of 10,000 ppm). The respective valves are adjusted to make the molar flow ratio of aluminum source, germanium source and phosphorus source range from 1:2:5.

[0036] Microwave power was maintained at 2500W, and vapor deposition was performed under these conditions for 4 hours. After growth, all carbon source and dopant gases were turned off, and plasma was maintained in a pure hydrogen atmosphere (400 sccm) while cooling to a substrate temperature of 790±10℃. In-situ annealing was then performed for 30 minutes. Subsequently, the temperature was slowly lowered to below 200℃ in a hydrogen atmosphere. Finally, the hydrogen atmosphere was turned off, a vacuum was drawn, and the sample was removed.

[0037] Comparative Example 1: It is basically the same as Example 1, except that only phosphorus doping is performed.

[0038] After pretreatment, the pressure in the reaction chamber was increased to 350 mbar. The substrate temperature was stabilized at 1100±10℃ by adjusting the heating system and plasma power. After stabilization, the reaction gas was introduced according to the following settings: hydrogen: 350 sccm, methane: 10 sccm (volume fraction of 2.5%), and the dopant precursor was a phosphine / hydrogen mixture with a flow rate of 40 sccm (concentration of 10000 ppm).

[0039] The microwave power was maintained at 2500W, and vapor deposition was performed under these conditions for 4 hours. After growth, all carbon source and dopant gases were turned off, and the plasma was maintained in a pure hydrogen atmosphere (400 sccm) while cooling to a substrate temperature of 700±10℃. In-situ annealing was then performed for 30 minutes. Subsequently, the temperature was slowly lowered to below 200℃ in a hydrogen atmosphere. Finally, the hydrogen was turned off, a vacuum was drawn, and the sample was removed.

[0040] Comparative Example 2: It is basically the same as Example 1, except that only aluminum doping is performed.

[0041] After pretreatment, the pressure in the reaction chamber was increased to 350 mbar. The substrate temperature was stabilized at 1100±10℃ by adjusting the heating system and plasma power. After stabilization, the reaction gases were introduced according to the following settings: hydrogen: 350 sccm, methane: 10 sccm (volume fraction of 2.5%), and the dopant precursor was trimethylaluminum (concentration of 10000 ppm) carried into the reaction chamber by hydrogen through a bubbler at a flow rate of 40 sccm.

[0042] The microwave power was maintained at 2500W, and vapor deposition was performed under these conditions for 4 hours. After growth, all carbon source and dopant gases were turned off, and the plasma was maintained in a pure hydrogen atmosphere (400 sccm) while cooling to a substrate temperature of 700±10℃. In-situ annealing was then performed for 30 minutes. Subsequently, the temperature was slowly lowered to below 200℃ in a hydrogen atmosphere. Finally, the hydrogen was turned off, a vacuum was drawn, and the sample was removed.

[0043] Comparative Example 3: It is basically the same as Example 1, except that only germanium doping is performed.

[0044] After pretreatment, the pressure in the reaction chamber is increased to 350 mbar. The substrate temperature is stabilized at 1100±10℃ by adjusting the heating system and plasma power. After stabilization, the reaction gases are introduced according to the following settings: hydrogen: 350 sccm, methane: 10 sccm (volume fraction of 2.5%), and the dopant precursor is tetramethylgermanium (concentration of 10000 ppm) carried into the reaction chamber by the carrier gas (hydrogen) through another bubbler at a flow rate of 40 sccm.

[0045] The microwave power was maintained at 2500W, and vapor deposition was performed under these conditions for 4 hours. After growth, all carbon source and dopant gases were turned off, and the plasma was maintained in a pure hydrogen atmosphere (400 sccm) while cooling to a substrate temperature of 700±10℃. In-situ annealing was then performed for 30 minutes. Subsequently, the temperature was slowly lowered to below 200℃ in a hydrogen atmosphere. Finally, the hydrogen was turned off, a vacuum was drawn, and the sample was removed.

[0046] Comparative Example 4: It is basically the same as Example 1, except that phosphorus-aluminum co-doping is performed.

[0047] After the pretreatment is completed, the pressure in the reaction chamber is increased to 350 mbar. By adjusting the heating system and plasma power, the substrate temperature is stabilized at 1100±10℃. After stabilization, the reaction gas is introduced according to the following settings: hydrogen: 350 sccm, methane: 10 sccm (volume fraction of 2.5%), dopant precursor: 40 sccm. The dopant precursors include trimethylaluminum (concentration of 10,000 ppm) carried into the reaction chamber by hydrogen gas through a bubbler, and a phosphine / hydrogen mixed gas (concentration of 10,000 ppm). The respective valves are adjusted to make the molar flow ratio of aluminum source and phosphorus source range from 1:3.

[0048] The microwave power was maintained at 2500W, and vapor deposition was performed under these conditions for 4 hours. After growth, all carbon source and dopant gases were turned off, and the plasma was maintained in a pure hydrogen atmosphere (400 sccm) while cooling to a substrate temperature of 700±10℃. In-situ annealing was then performed for 30 minutes. Subsequently, the temperature was slowly lowered to below 200℃ in a hydrogen atmosphere. Finally, the hydrogen was turned off, a vacuum was drawn, and the sample was removed.

[0049] Comparative Example 5: It is basically the same as Example 1, except that phosphorus-germanium co-doping is performed.

[0050] After the pretreatment is completed, the pressure in the reaction chamber is increased to 350 mbar. By adjusting the heating system and plasma power, the substrate temperature is stabilized at 1100±10℃. After stabilization, the reaction gas is introduced according to the following settings: hydrogen: 350 sccm, methane: 10 sccm (volume fraction of 2.5%), dopant precursor: 40 sccm. Tetramethylgermanium (concentration 10000ppm) and phosphine / hydrogen mixed gas (concentration 10000ppm) are carried into the reaction chamber by a carrier gas (hydrogen) through a bubbler. The molar flow ratio of the germanium source and the phosphorus source is adjusted to a range of 1:3 by regulating their respective valves.

[0051] The microwave power was maintained at 2500W, and vapor deposition was performed under these conditions for 4 hours. After growth, all carbon source and dopant gases were turned off, and the plasma was maintained in a pure hydrogen atmosphere (400 sccm) while cooling to a substrate temperature of 700±10℃. In-situ annealing was then performed for 30 minutes. Subsequently, the temperature was slowly lowered to below 200℃ in a hydrogen atmosphere. Finally, the hydrogen was turned off, a vacuum was drawn, and the sample was removed.

[0052] Comparative Example 6: It is basically the same as Example 1, except that aluminum-germanium co-doping is performed.

[0053] After the pretreatment is completed, the pressure in the reaction chamber is increased to 350 mbar. By adjusting the heating system and plasma power, the substrate temperature is stabilized at 1100±10℃. After stabilization, the reaction gas is introduced according to the following settings: hydrogen: 350 sccm, methane: 10 sccm (volume fraction of 2.5%), dopant precursor: 40 sccm. The dopant precursors include trimethylaluminum (concentration of 10,000 ppm) carried into the reaction chamber by hydrogen through a bubbler, and tetramethylgermanium (concentration of 10,000 ppm) carried into the reaction chamber by carrier gas (hydrogen) through another bubbler. The respective valves are adjusted to make the molar flow ratio of aluminum source and germanium source range 1:1.

[0054] The microwave power was maintained at 2500W, and vapor deposition was performed under these conditions for 4 hours. After growth, all carbon source and dopant gases were turned off, and the plasma was maintained in a pure hydrogen atmosphere (400 sccm) while cooling to a substrate temperature of 700±10℃. In-situ annealing was then performed for 30 minutes. Subsequently, the temperature was slowly lowered to below 200℃ in a hydrogen atmosphere. Finally, the hydrogen was turned off, a vacuum was drawn, and the sample was removed.

[0055] Performance testing ① The resistivity (Ω·cm) and Hall mobility (cm²) of the samples prepared in Examples 1-3 and Comparative Examples 1-6 were measured using the Hall effect. 2 / (v·s)) and carrier concentration (cm²) -3 The test results are shown in Table 1 below: As shown in Table 1 above, the N-type semiconductor diamond materials prepared by the Al-Ge-P ternary co-doping scheme (Examples 1-3) provided by this invention exhibit excellent properties, fully meeting and exceeding the preset performance targets (carrier concentration ≥10). 19 cm -3 Resistivity ≤ 0.05 Ω·cm, Hall mobility ≥ 1000 cm⁻¹ 2 Strict requirements of / (v·s)).

[0056] Compared with single doping (Comparative Examples 1-3), the performance of Examples 1-3 is significantly superior.

[0057] Compared with binary co-doping (Comparative Examples 4-6), Examples 1-3 also showed overwhelming advantages in various properties.

[0058] By comparing the results of ternary doping (Example 1) and binary doping (Comparative Example 4), the key role of germanium (Ge) in the ternary system is strongly demonstrated. It is not inert, but plays the role of a "synergistic promoter", establishing an effective "bridge" between Al and P and significantly optimizing the doping process.

[0059] ② Raman spectroscopy can be used for molecular qualitative analysis, characterization of inclusions within crystals, etc., and is an important parameter for diamond crystal materials. Generally, if diamond has no impurities, its Raman spectrum has only one intrinsic peak at 1332 cm⁻¹. -1 When functional diamond crystals are synthesized using dopants, impurity elements or inclusion defects may appear inside, causing a shift in the Raman peak position of the diamond. This can be used to characterize the crystal quality of the diamond. Table 2 shows the Raman peak positions and full width at half maximum (FWHM) of the samples prepared in Examples 1-3 and Comparative Examples 1 and 4-5.

[0060] Spectral characteristic analysis: In Example 1, the peak position was slightly shifted to the left (the standard peak position for pure single-crystal diamond is 1332.5 cm⁻¹). -1 This indicates that the film exhibits a certain degree of compressive stress. The half-width at half-maximum (FWHM) is relatively small, approaching the level of high-quality single-crystal diamond (typically 2.5-4.5 cm). -1 This indicates that the crystal has high quality and low defect density.

[0061] In Example 2, the peak position is close to the standard value, and the stress state is improved; the half-width at half-maximum has increased slightly but is still within the excellent range.

[0062] In Example 3, the peak position shifted more significantly to the left, indicating an increase in compressive stress; the increased full width at half maximum (FWHM) suggests that the higher temperature may have introduced more lattice defects.

[0063] In Comparative Example 1, the peak position is slightly higher than the standard value, which may indicate slight tensile stress or compositional changes; the half-width at half-maximum is moderate, indicating good crystal quality.

[0064] The peak position in Comparative Example 4 shifted significantly to the left, indicating the presence of strong compressive stress, which may be related to the large lattice distortion of the Al-P pair. The crystal quality was significantly lower than that of Example 1.

[0065] In Comparative Example 5, the peak position shifts to the right, indicating tensile stress characteristics; the larger half-width at half-maximum indicates a higher defect density, consistent with the results of poor electrical performance.

[0066] As shown in Table 2 above, the full width at half maximum (FWHM) of the Raman spectra of all Al-Ge-P ternary co-doped samples (Examples 1-3) remained at a low level, which was significantly better than that of all binary co-doped samples (Comparative Examples 4-6). This indicates that the ternary system has a significant advantage in maintaining high crystal quality.

[0067] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing an N-type semiconductor diamond material, characterized in that, Includes the following steps: S1: Provide a diamond substrate and perform surface cleaning and hydrogen plasma activation pretreatment on it; S2: Place the pretreated diamond substrate in the reaction chamber of the chemical vapor deposition equipment; S3: A reaction gas containing a carbon source and a dopant precursor is introduced into the reaction chamber. The dopant precursor includes an aluminum source, a germanium source, and a phosphorus source. S4: Vapor phase deposition growth on the diamond substrate; The aluminum source is trimethylaluminum, the germanium source is tetramethylgermanium, and the phosphorus source is at least one of phosphine, dimethylphosphine, trimethylphosphine, diethylphosphine, triethylphosphine, tert-butylphosphine, triphenylphosphine, phosphorus trifluoride, phosphorus pentafluoride, phosphorus trichloride, or phosphorus pentachloride. The molar flow rate ratio of the aluminum source, germanium source and phosphorus source is in the range of 1:(0.5-2):(1-5); The carbon source has a volume fraction of 0.5%-3% in the reactant gas; The carbon source is a hydrocarbon compound that is gaseous at room temperature and normal pressure; The reaction gas also includes a carrier gas, which is hydrogen. The pressure for vapor phase deposition growth is 300 mbar-400 mbar, and the substrate temperature is 1050℃-1200℃; The vapor deposition time is 1h-10h; It also includes an annealing step, with an annealing temperature of 600℃-800℃.

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