Preparation method of n-type phosphorus-doped silicon carbide crystal

Abstract

The invention belongs to the technical field of semiconductor materials, and particularly relates to a preparation method of an n-type phosphorus-doped silicon carbide crystal. According to the preparation method of the n-type phosphorus-doped silicon carbide crystal, phosphorus atoms are obtained through reaction and conversion of silicon atoms in the silicon carbide crystal and neutron capture nucleuses, and the preparation method comprises the following steps that the initial electrical property of the silicon carbide crystal to be doped is measured; calculating the target doping concentration of phosphorus atoms according to the target resistivity, and judging whether the silicon carbide crystal is subjected to phosphorus atom doping or not; carrying out neutron irradiation treatment on the silicon carbide crystal to be doped by adopting a neutron source to convert silicon atoms into phosphorus atoms so as to realize doping of the phosphorus atoms; and activating the doped phosphorus atoms to obtain the n-type phosphorus-doped silicon carbide crystal. The method has the beneficial effects that endogenous silicon in the silicon carbide is accurately regulated and controlled to be converted into phosphorus through the neutron irradiation condition, so that the method for doping phosphorus in the silicon carbide is realized; the process is simple, the cost is low, and the crystal form of the silicon carbide crystal is not changed.

Description

Technical Field

[0001] The present application belongs to the field of semiconductor material technology, and specifically relates to a method for preparing n-type phosphorus-doped silicon carbide crystals. Background Art

[0002] Silicon carbide (SiC) crystal is a third-generation wide-bandgap semiconductor material, characterized by high breakdown field strength (10 times that of silicon), high thermal conductivity (3 times that of silicon), and high electron saturation drift rate. Its excellent physical and chemical stability makes it suitable for high-temperature, high-frequency, and high-power applications, such as new energy vehicles, photovoltaic energy storage, and rail transportation.

[0003] Doping technology is commonly used to achieve conductive and semi-insulating properties in silicon carbide crystals. Doping involves introducing impurities into the crystal to improve its conductive properties. Doping of silicon carbide crystals is categorized into n-type doping and p-type doping. In n-type doping, elements with a valence electron count of 5 (such as nitrogen, phosphorus, and arsenic) are incorporated into the silicon carbide crystal. The impurity atoms become donor impurities, increasing the free electron density and altering the crystal's conductivity. Doping methods for silicon carbide semiconductors primarily include high-temperature diffusion, ion implantation, and in-situ diffusion.

[0004] Due to the high bond energy of silicon carbide and the low diffusion coefficient of dopants in the crystal, traditional high-temperature diffusion processes have difficulty in achieving effective doping in silicon carbide crystals. Ion implantation is the use of high-energy ion beams to inject impurity atoms into silicon carbide wafers. The ion implantation equipment is expensive and the process is complex. It is suitable for the semiconductor device manufacturing process after silicon carbide epitaxial preparation. At present, the doping method of the early stage of silicon carbide crystal growth process is in-situ doping, that is, impurity atoms are introduced through raw materials or atmosphere during the growth of silicon carbide crystals or epitaxial growth to achieve n-type or p-type doping in a high-temperature environment. This method relies on chemical reactions during the crystal growth process.

[0005] Theoretically, the in-situ doping of n-type silicon carbide crystals can select VA group elements nitrogen and phosphorus as dopants. However, due to the poor compatibility of the phosphorus doping system with the PVT process of crystal growth and the CVD process of epitaxial growth, it has obvious disadvantages compared with the nitrogen doping system. Therefore, nitrogen doping technology is the mainstream technology of in-situ doping process. There are relatively few studies on phosphorus doping at home and abroad. More than 90% of n-type silicon carbide substrates and epitaxial layers in the industry are doped with nitrogen. The limitations of phosphorus doping technology in existing in-situ doping processes are: (1) Phosphorus atoms occupy carbon sites, resulting in large lattice distortion. In-situ doping is carried out simultaneously with silicon carbide crystal growth at a high temperature environment above 1600℃ (2200℃ for PVT process). During the production process, phosphorus (P) atoms not only occupy the silicon sites in the lattice (P_Si), but may also occupy the carbon sites in the lattice (P_C). At this time, the introduction of phosphorus impurities brings about more serious lattice distortion; (2) The diffusion coefficient of phosphorus in silicon carbide is low, the doping process is complex, and the production cost is high. The diffusion coefficient of phosphorus atoms at 2200°C is two orders of magnitude lower than that of nitrogen atoms, which increases the difficulty and cost of controlling the doping process.

[0006] Although the nitrogen-doping system of n-type silicon carbide crystals is relatively mature, there is a problem that the ionization rate of the doping product decreases with increasing temperature (for example, the ionization rate of nitrogen-doped silicon carbide crystals is 92% at 300K and drops to 78% at 500K). The theoretical ionization energy of the phosphorus-doped system (0.053eV) is 30% lower than that of nitrogen (0.07eV), which can theoretically improve the high-temperature performance of the device. Therefore, the development of phosphorus-doping technology has potential application value. Summary of the Invention

[0007] The present application provides a method for preparing n-type phosphorus-doped silicon carbide crystals, aiming to solve the problems of the existing P atom-doped silicon carbide crystal process being complex and costly, and the doping causing lattice distortion of the silicon carbide crystals.

[0008] In a first aspect, the present application provides a method for preparing an n-type phosphorus-doped silicon carbide crystal, wherein the phosphorus atoms are converted by a neutron capture nuclear reaction between silicon atoms in the silicon carbide crystal and the silicon carbide crystal, comprising the following steps:

[0009] (1) measuring the initial electrical properties of the silicon carbide crystal to be doped; calculating the target doping concentration of phosphorus atoms based on the target resistivity, and determining whether to dope the silicon carbide crystal with phosphorus atoms;

[0010] (2) using a neutron source to perform neutron irradiation treatment on the silicon carbide crystal to be doped so as to convert silicon atoms into phosphorus atoms, thereby achieving phosphorus atom doping;

[0011] (3) Activating the doped phosphorus atoms to obtain n-type phosphorus-doped silicon carbide crystals.

[0012] The n-type phosphorus-doped silicon carbide crystal described in the present application does not change the crystal form of the silicon carbide crystal when doping with phosphorus atoms, and the doping concentration of the phosphorus atoms can be precisely controlled by nuclear reaction parameters and processes, and the operation is simple.

[0013] According to the method for preparing an n-type phosphorus-doped silicon carbide crystal described in the present application, the initial electrical properties include one or more of the initial resistivity of the silicon carbide crystal to be doped, background phosphorus impurity concentration, carrier concentration, and electron mobility;

[0014] When the initial resistivity of the silicon carbide crystal to be doped is greater than the target resistivity or when the carrier concentration of the silicon carbide crystal to be doped is less than the target doping concentration of phosphorus atoms, phosphorus atoms are doped into the silicon carbide crystal.

[0015] According to the method for preparing n-type phosphorus-doped silicon carbide crystals described in the present application, in step (1), the method for calculating the target doping concentration of phosphorus atoms is as follows:

[0016]

[0017] Among them, N D Indicates the target doping concentration of phosphorus atoms in atoms / cm 3 ;

[0018] q is the electron charge, which is 1.6×10 -19 C;

[0019] μ n is the electron mobility of the silicon carbide crystal to be doped, in cm 2 / (V·s);

[0020] ρ target is the target resistivity, in Ω·cm.

[0021] According to the method for preparing n-type phosphorus-doped silicon carbide crystals described in this application, in step (1), the target doping concentration of phosphorus atoms is 10 14 -1.5×10 21 atoms / cm 3 .

[0022] According to the method for preparing n-type phosphorus-doped silicon carbide crystals described in the present application, in step (2), the neutron source includes a reactor neutron source or an accelerator neutron source.

[0023] According to the method for preparing n-type phosphorus-doped silicon carbide crystals described in this application, the neutron flux range of the neutron irradiation is 10 12 -10 16 n / (cm 2 ·s).

[0024] According to the method for preparing n-type phosphorus-doped silicon carbide crystals described in the present application, in step (2), the doping concentration of the phosphorus atoms is calculated by the following formula:

[0025] N d =N Si ·f·λ·t

[0026] Among them, N d is the phosphorus atom doping concentration, in atoms / cm 3 ;

[0027] N si is the density of silicon atoms in the silicon carbide crystal to be doped, in atoms / cm 3 ;

[0028] f is the abundance of silicon-30 isotope in silicon carbide, which is 0.0308;

[0029] t is the time of neutron irradiation treatment, in seconds;

[0030] λ is the neutron capture rate of silicon-30, in n / s; its calculation formula is as follows:

[0031]

[0032] ψ is the neutron flux of neutron irradiation, unit is n / (cm 2 s);

[0033] σ is the neutron capture cross section of Si-30, which is 0.108×10 -24 cm 2 .

[0034] According to the method for preparing n-type phosphorus-doped silicon carbide crystal described in the present application, the activation treatment includes high-temperature activation and / or laser activation.

[0035] According to the method for preparing n-type phosphorus-doped silicon carbide crystals described in the present application, the activation treatment is high-temperature activation.

[0036] According to the method for preparing n-type phosphorus-doped silicon carbide crystals described in the present application, the temperature of the high-temperature activation is 1500-1600° C., and the time of the high-temperature activation is 20-40 minutes.

[0037] According to the method for preparing n-type phosphorus-doped silicon carbide crystals described in the present application, the method further includes measuring the resistivity of the activated silicon carbide crystals.

[0038] When the resistivity of the activated silicon carbide crystal is greater than the target resistivity or when the carrier concentration of the activated silicon carbide crystal is less than the target doping concentration of phosphorus atoms, steps (2) and (3) are repeated until the resistivity of the activated silicon carbide crystal is less than or equal to the target resistivity.

[0039] The second aspect of the present application provides an n-type phosphorus-doped silicon carbide crystal, which is prepared by the method described in the first aspect of the present application. The chemical formula of the n-type phosphorus-doped silicon carbide crystal is: Si (1-x) P x C, of ​​which 10 -8 ≤x≤0.03. DETAILED DESCRIPTION

[0040] The embodiments of the present invention are described in detail below. The examples of the embodiments are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0041] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples without contradiction.

[0042] The present invention provides a method for preparing an n-type phosphorus-doped silicon carbide crystal, comprising the following steps:

[0043] (1) measuring the initial electrical properties of the silicon carbide crystal to be doped; calculating the target doping concentration of phosphorus atoms based on the target resistivity, and determining whether to dope the silicon carbide crystal with phosphorus atoms;

[0044] (2) using a neutron source to perform neutron irradiation treatment on the silicon carbide crystal to be doped so as to convert silicon atoms into phosphorus atoms, thereby achieving phosphorus atom doping;

[0045] (3) Activating the doped phosphorus atoms to obtain n-type phosphorus-doped silicon carbide crystals.

[0046] The method for doping silicon carbide crystals with phosphorus described in the present application achieves a method for doping silicon carbide with phosphorus by precisely controlling the conversion of endogenous silicon in silicon carbide into phosphorus under neutron irradiation conditions.

[0047] When doping phosphorus atoms into silicon carbide crystals using the method described in the present application, the crystal form of the silicon carbide crystals is not changed, and the doping concentration of the phosphorus atoms can be precisely controlled by nuclear reaction parameters and processes.

[0048] The principle of the method for doping silicon carbide crystals with phosphorus atoms described in this application is as follows:

[0049] Silicon isotope 30Si (natural abundance 3.1%) absorbs thermal neutrons and undergoes a transmutation reaction:

[0050] 30 Si+n→ 31 Si→ 31 P+β ˉ +ν ˉ

[0051] Through neutron capture reactions, silicon atoms in the silicon carbide crystal are converted into phosphorus atoms.

[0052] Using the principle of neutron capture nuclear reaction to convert one atom into another is a special means to achieve doping of semiconductor materials. The purpose of semiconductor doping is to change the electrical properties of the semiconductor in a directionally controlled manner through carrier regulation. Therefore, it is also necessary to study the band structure distribution and interaction of the doping atoms and their impact on the electrical properties based on the principle of neutron irradiation doping.

[0053] Silicon carbide is a compound semiconductor composed of a periodic arrangement of carbon and silicon atoms. Compared to elemental silicon crystals, it differs significantly in terms of bond lengths, bond energies, crystal structure, and activation mechanism of phosphorus atoms after doping. Therefore, neutron irradiation doping technology for silicon carbide cannot simply be copied or replicated based on the neutron transmutation doping technology used for elemental silicon. The application of neutron irradiation technology for silicon carbide requires extensive fundamental research. Currently, there is limited systematic research on neutron irradiation of silicon carbide crystals, both domestically and internationally.

[0054] In some embodiments of the present application, the silicon carbide crystal to be doped includes one or more of a silicon carbide crystal rod, a silicon carbide wafer, a silicon carbide substrate, and a silicon carbide epitaxial layer.

[0055] In some embodiments of the present application, the crystal form of the silicon carbide crystal to be doped includes one or more of 3C-SiC, 4H-SiC and 6H-SiC.

[0056] In some embodiments of the present application, the initial electrical properties include one or more of the initial resistivity of the silicon carbide crystal to be doped, background phosphorus impurity concentration, carrier concentration, and electron mobility.

[0057] The background phosphorus impurity concentration refers to the phosphorus impurities contained in the equipment and / or the phosphorus impurities contained in the raw materials themselves.

[0058] In some embodiments of the present application, when the initial resistivity of the silicon carbide crystal to be doped is greater than the target resistivity or when the carrier concentration of the silicon carbide crystal to be doped is less than the target doping concentration of phosphorus atoms, the silicon carbide crystal is doped with phosphorus atoms.

[0059] In some embodiments of the present application, in step (1), the calculation method of the target doping concentration of phosphorus atoms is as follows:

[0060]

[0061] Among them, N D Indicates the target doping concentration of phosphorus atoms in atoms / cm 3 ;

[0062] q is the electron charge, which is 1.6×10 -19 C;

[0063] μ n is the electron mobility of the silicon carbide crystal to be doped, in cm 2 / (V·s);

[0064] ρ target is the target resistivity, in Ω·cm.

[0065] In actual operation, the target doping concentration of phosphorus atoms is calculated based on the target resistivity required by the customer, and then the doping of phosphorus atoms is implemented.

[0066] In some embodiments of the present application, in step (1), the target doping concentration of phosphorus atoms is 10 14 -1.5×10 21 atoms / cm 3 The target doping concentration of phosphorus atoms is determined according to the target resistivity required by the customer.

[0067] In some embodiments of the present application, in step (2), the neutron source includes a reactor neutron source or an accelerator neutron source.

[0068] In some embodiments of the present application, the neutron flux range of the neutron irradiation is 10 12 -10 16 n / (cm 2 s), for example, 10 12 n / (cm 2 ·s), 10 13 n / (cm 2 ·s), 10 14 n / (cm 2 ·s), 10 15 n / (cm 2 ·s), 10 16 n / (cm2 ·s) etc.

[0069] In some embodiments of the present application, in step (2), the doping concentration of the phosphorus atoms is calculated by the following formula:

[0070] N d =N Si ·f·λ·t

[0071] Among them, N d is the phosphorus atom doping concentration, in atoms / cm 3 ;

[0072] N si is the density of silicon atoms in the silicon carbide crystal to be doped, in atoms / cm 3 ;

[0073] f is the abundance of silicon-30 isotope in silicon carbide, which is 0.0308;

[0074] t is the time of neutron irradiation treatment, in seconds;

[0075] λ is the neutron capture rate of silicon-30, in n / s; its calculation formula is as follows:

[0076]

[0077] ψ is the neutron flux of neutron irradiation, unit is n / (cm 2 s);

[0078] v is the neutron capture cross section of Si-30, which is 0.108×10 -24 cm 2 .

[0079] During actual operation, the actual doping concentration of phosphorus atoms is precisely controlled by adjusting the irradiation treatment time and the neutron flux.

[0080] In some embodiments of the present application, the activation process includes high temperature activation and / or laser activation.

[0081] In some embodiments of the present application, the activation process is high-temperature activation.

[0082] In some embodiments of the present application, the high temperature activation temperature is 1500-1600°C, for example, 1500°C, 1550°C, 1600°C, etc., and the high temperature activation time is 20-40min, for example, 20min, 25min, 30min, 35min, 40min, etc.

[0083] In some embodiments of the present application, the method further includes measuring the resistivity of the activated silicon carbide crystal.

[0084] When the resistivity of the activated silicon carbide crystal is greater than the target resistivity or when the carrier concentration of the silicon carbide crystal to be doped is less than the target doping concentration of phosphorus atoms, steps (2) and (3) are repeated until the resistivity of the activated silicon carbide crystal is less than or equal to the target resistivity.

[0085] The present invention also provides an n-type phosphorus-doped silicon carbide crystal prepared by the method described in the first aspect of the present invention. The chemical formula of the n-type phosphorus-doped silicon carbide crystal is: Si (1-x) P x C, of ​​which 10 -8 ≤x≤0.03.

[0086] The technical solution of this application is further described below with reference to specific embodiments.

[0087] Example 1

[0088] A method for preparing an n-type phosphorus-doped silicon carbide wafer comprises the following steps:

[0089] (1) Preparation of silicon carbide wafer samples: A 6-inch 4H-type silicon carbide ingot processed by PVT (physical vapor transport) technology was selected, flattened, rounded, and the purple crystal surface and dome surface were removed to form a standard crystal rod; then it was cut into several thin slices with a thickness of 1 mm using a diamond wire saw, and the surface of the thin slices was polished using diamond grinding liquid. Two cut slices were randomly selected as test samples, numbered A1 and A2;

[0090] (2) Measuring the initial electrical properties and crystal form characterization of the above samples: Before the samples were neutron irradiated, the crystal form of the silicon carbide of samples A1 and A2 was characterized using an HR800 Raman spectrometer. The initial carrier concentration, electron mobility, and background phosphorus impurity concentration of the samples were measured using a mercury probe measurement instrument (CV method) and a secondary ion mass spectrometer, respectively. The crystal form characterization and electrical performance measurement results are shown in Table 1;

[0091] (3) Calculate the target doping concentration of phosphorus atoms in the sample: Based on the target resistivity index required by the customer, calculate the target doping concentration of phosphorus atoms in the above-mentioned samples A1 and A2 according to the following formula;

[0092]

[0093] Among them, N D Indicates the target doping concentration of phosphorus atoms in atoms / cm 3 ;

[0094] q is the charge of the electron, which is a physical constant with a value of 1.6×10 -19 C;

[0095] μ n The electron mobility of the silicon carbide crystal to be doped measured in the above steps is: 801.5cm 2 / (V·s),

[0096] ρ target is the target resistivity required by the customer, where ρ A1 =3.42Ω·cm; ρ A2 =1.71Ω·cm

[0097] The calculated results are shown in Table 1. The target doping concentration of phosphorus atoms in sample A1 is N D 2.28×10 15 atoms / cm 3 ; Target doping concentration of phosphorus atoms in sample A2 is N D 4.55×10 15 atoms / cm 3 .

[0098] (4) Determine whether to dope the sample with phosphorus atoms.

[0099] The judgment standard is the comparison between the calculated phosphorus target doping concentration and the initial carrier concentration. According to the measured data and calculated results (Table 1) of the above steps, the target phosphorus doping concentration of sample A1 (2.28×10 15 atoms / cm 3 ) is greater than the initial carrier concentration (7.63×10 13 toms / cm 3 ); target doping concentration of phosphorus atoms in sample A2 (4.55×10 15 atoms / cm 3 ) is greater than the initial carrier concentration (7.82×10 13 toms / cm 3 ); According to the judgment criteria, it is determined that samples A1 and A2 need to be treated with phosphorus doping.

[0100] (5) Use a reactor neutron source to irradiate the doped silicon carbide crystals with neutrons to precisely control the nuclear reaction process and phosphorus doping concentration.

[0101] The neutron flux of the reactor irradiation hole used in this example is 4.77×10 13 / (cm 2 ·s).

[0102] First, the neutron capture rate λ of the irradiation hole is calculated according to the following formula.

[0103] (Where: ψ is the neutron flux of the neutron source, the unit is n / (cm 2·s); σ is the neutron capture cross section of Si-30, which is 0.108×10 -24 cm 2 ). Calculation results: The neutron capture rate of the irradiated hole is 1.32×10 10 / s,

[0104] Secondly, based on the phosphorus atom target doping concentration of samples A1 and A2 calculated in step 3 above and the neutron capture rate calculation data of the reactor irradiation hole, the neutron irradiation treatment time is calculated according to the following formula and parameters to achieve the purpose of accurately controlling the nuclear reaction process and the phosphorus impurity doping concentration.

[0105] N d =N Si ·f·λ·t

[0106] Where: N d is the target doping concentration of phosphorus atoms, in atoms / cm 3 ;

[0107] N si is the density of silicon atoms in the silicon carbide crystal to be doped, in atoms / cm 3 ;

[0108] f is the abundance of silicon-30 isotope in silicon carbide, which is 0.0308;

[0109] t is the time of neutron irradiation treatment, in seconds.

[0110] The A1 and A2 samples were then placed in the reactor irradiation hole for irradiation. The neutron irradiation time was 172,800 seconds (48 hours) and 345,600 seconds (96 hours), respectively. Through neutron capture nuclear reactions, the silicon on the silicon carbide lattice was converted into phosphorus atoms, achieving the phosphorus doping effect.

[0111] (6) Activation treatment of doped phosphorus atoms

[0112] The neutron-irradiated A1 and A2 samples were placed in a vacuum tube furnace, and argon gas was passed into the vacuum tube furnace for 5 minutes to replace the air inside to prevent oxidation of the sample surface at high temperatures. The tube furnace was then heated to 1600°C at a heating rate of 10°C / min and kept at this temperature for 30 minutes to activate the phosphorus atoms doped in the samples.

[0113] (7) Measure the silicon carbide crystal structure and electrical properties of the activated samples

[0114] The crystal forms of samples A1 and A2 after irradiation were characterized. The carrier concentration and phosphorus doping concentration of the two activated samples were measured using a mercury probe (CV method) measuring instrument and a secondary ion mass spectrometer, respectively. The measurement results are shown in Table 1.

[0115] It can be seen from Table 1 that: (1) The actual phosphorus doping concentration of sample A1 (2.4×10 15 atoms / cm 3 ) and the carrier concentration after activation (2.12×10 15 toms / cm 3 ) is very close; the actual phosphorus doping concentration of sample A2 (4.7×10 15 atoms / cm 3 ) after activation (4.28×10 15 toms / cm 3 ) are equivalent. According to the judgment criteria, the phosphorus doping of the two samples has achieved the expected effect, and there is no need to repeat steps 5-7 for secondary neutron irradiation; (2) The crystal form of samples A1 and A2 is 4H-SiC. After neutron irradiation, the crystal form of the four samples has not changed, indicating that the neutron irradiation process does not change the silicon carbide crystal form formed by silicon carbide PVT crystal growth;

[0116] Through the above steps, an n-type phosphorus-doped silicon carbide crystal is obtained. On this basis, a silicon carbide substrate can be further prepared through subsequent mechanical processing.

[0117] Example 2

[0118] A method for preparing an n-type phosphorus-doped silicon carbide epitaxial layer and an epitaxial wafer, comprising the following steps:

[0119] (1) Preparation of silicon carbide epitaxial wafers: A chemical vapor deposition (CVD) process was used to grow a 20 μm thick silicon carbide epitaxial layer on a 6-inch silicon carbide substrate in a reaction chamber. Two epitaxial wafer samples were prepared, numbered B1 and B2.

[0120] (2) Referring to step 2 of Example 1, the silicon carbide crystal form and electrical properties of the epitaxial layers of samples B1 and B2 before irradiation were characterized; the characterization and test results are shown in Table 1;

[0121] (3) Referring to step 3 of Example 1, calculate the target doping concentration of phosphorus atoms in the epitaxial layer of samples B1 and B2, where the target resistivity required by the customer is ρ B1 =3.42Ω·cm; ρ B2 =1.71Ω·cm, the calculated results are shown in Table 1, the target doping concentration of phosphorus atoms in the epitaxial layer of sample B1 is N d 2.28×10 15 atoms / cm 3 ; Target doping concentration of phosphorus atoms in the epitaxial layer of sample B2 N d 4.55×10 15 atoms / cm 3 .

[0122] (4) Determine whether to dope the epitaxial layer of the sample with phosphorus atoms.

[0123] According to the measured data and calculated results (Table 1) of the above steps, the target phosphorus atom doping concentration of the epitaxial layer of sample B1 (2.28×10 15 atoms / cm 3 ) is greater than the initial carrier concentration before irradiation (6.42×10 13 toms / cm 3 ); target doping concentration of phosphorus atoms in sample B2 (4.55×10 15 atoms / cm 3 ) is greater than the initial carrier concentration before irradiation (7.26×10 13 toms / cm 3 ); According to the judgment criteria, it is determined that samples B1 and B2 need to be treated with phosphorus doping.

[0124] (5) Referring to step 5 of Example 1, the samples were neutron irradiated using the same neutron flux and neutron capture rate parameters as in Example 1. The neutron irradiation time was calculated to precisely control the nuclear reaction process and phosphorus doping concentration. Samples B1 and B2 were placed in the reactor irradiation hole for irradiation. The neutron irradiation time for sample B1 was 172,800 s (48 h), and the neutron irradiation time for sample B2 was 345,600 s (96 h). Phosphorus doping of the epitaxial layer was achieved through neutron capture nuclear reaction.

[0125] (6) Referring to step 6 of Example 1, the samples after neutron irradiation are activated to activate the phosphorus atoms doped in the epitaxial layers of samples B1 and B2.

[0126] (7) Referring to step 7 of Example 1, the silicon carbide crystal form and electrical properties of the epitaxial layers of samples B1 and B2 after activation were measured. The measurement results are shown in Table 1. As can be seen from Table 1: (1) The actual phosphorus atom doping concentration of sample B1 (2.3×10 15 atoms / cm 3 ) and the carrier concentration after activation (2.17×10 15 toms / cm 3 ) is very close; the actual phosphorus doping concentration of B2 sample (4.7×10 15 atoms / cm 3 ) and the carrier concentration after activation (4.28×10 15 toms / cm 3) are equivalent. According to the judgment criteria, the phosphorus doping of the two samples has achieved the expected effect, and there is no need to repeat steps 5-7 for secondary neutron irradiation; (2) The crystal form of samples B1 and B2 is 4H-SiC. After neutron irradiation, the crystal form of the four samples has not changed, indicating that the neutron irradiation process does not change the silicon carbide crystal form formed by the silicon carbide CVD epitaxial process. (3) The actual phosphorus doping concentration of B1 and B2 after irradiation is consistent with the target phosphorus doping concentration, indicating that the concentration of phosphorus impurities can be controlled by precisely controlling the neutron capture nuclear reaction rate.

[0127] Through the above operation steps, an n-type phosphorus-doped silicon carbide crystal epitaxial layer and an epitaxial wafer are prepared.

[0128] Table 1: Characterization and test results of Examples 1-2

[0129]

[0130] It can be seen from Table 1 that the preparation method described in the present application can achieve precise doping of P atoms into silicon carbide crystals without changing the crystal form of the silicon carbide crystals.

[0131] Although the above embodiments have been shown and described, it is understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. Changes, modifications, substitutions and variations of the above embodiments by those skilled in the art are all within the scope of protection of the present invention.

Claims

1. A method for preparing n-type phosphorus-doped silicon carbide crystal, characterized in that: The phosphorus atoms are obtained by converting silicon atoms in silicon carbide crystals into neutron capture nuclear reactions, comprising the following steps: (1) measuring the initial electrical properties of the silicon carbide crystal to be doped; calculating the target doping concentration of phosphorus atoms based on the target resistivity, and determining whether to dope the silicon carbide crystal with phosphorus atoms; (2) using a neutron source to perform neutron irradiation treatment on the silicon carbide crystal to be doped so as to convert silicon atoms into phosphorus atoms, thereby achieving phosphorus atom doping; (3) Activating the doped phosphorus atoms to obtain n-type phosphorus-doped silicon carbide crystals.

2. The method for preparing n-type phosphorus-doped silicon carbide crystal according to claim 1, characterized in that: The silicon carbide crystal to be doped includes one or more of a silicon carbide crystal rod, a silicon carbide wafer, a silicon carbide substrate, and a silicon carbide epitaxial layer; And / or, the crystal type of the silicon carbide crystal to be doped includes one or more of 3C-SiC, 4H-SiC and 6H-SiC.

3. The method for preparing n-type phosphorus-doped silicon carbide crystal according to claim 1, characterized in that: The initial electrical properties include one or more of the initial resistivity, background phosphorus impurity concentration, carrier concentration, and electron mobility of the silicon carbide crystal to be doped; When the initial resistivity of the silicon carbide crystal to be doped is greater than the target resistivity or when the carrier concentration of the silicon carbide crystal to be doped is less than the target doping concentration of phosphorus atoms, phosphorus atoms are doped into the silicon carbide crystal.

4. The method for preparing n-type phosphorus-doped silicon carbide crystal according to claim 3, characterized in that: In step (1), the calculation method of the target doping concentration of phosphorus atoms is as follows: Among them, N D Indicates the target doping concentration of phosphorus atoms in atoms / cm 3 ; q is the electron charge, which is 1.6×10 -19 C; μ n is the electron mobility of the silicon carbide crystal to be doped, in cm 2 / (V·s); ρ target is the target resistivity, in Ω·cm.

5. The method for preparing n-type phosphorus-doped silicon carbide crystal according to claim 1, characterized in that: In step (1), the target doping concentration of phosphorus atoms is 10 14 -1.5×10 21 atoms / cm 3 .

6. The method for preparing n-type phosphorus-doped silicon carbide crystal according to claim 1, characterized in that: In step (2), the neutron source includes a reactor neutron source or an accelerator neutron source; And / or, the neutron flux range of the neutron irradiation is 10 12 -10 16 n / (cm 2 ·s).

7. The method for preparing n-type phosphorus-doped silicon carbide crystal according to claim 1, characterized in that: In step (2), the doping concentration of the phosphorus atoms is calculated by the following formula: N d =N Si ·f·λ·t Among them, N d is the phosphorus atom doping concentration, in atoms / cm 3 ; N si is the density of silicon atoms in the silicon carbide crystal to be doped, in atoms / cm 3 ; f is the abundance of silicon-30 isotope in silicon carbide, which is 0.0308; t is the time of neutron irradiation treatment, in seconds; λ is the neutron capture rate of silicon-30, in n / s; its calculation formula is as follows: ψ is the neutron flux of neutron irradiation, unit is n / (cm 2 s); σ is the neutron capture cross section of Si-30, which is 0.108×10 -24 cm 2 .

8. The method for preparing n-type phosphorus-doped silicon carbide crystal according to claim 1, characterized in that: The activation process includes high temperature activation and / or laser activation; Preferably, the activation treatment is high-temperature activation; more preferably, the temperature of the high-temperature activation is 1500-1600° C., and the time of the high-temperature activation is 20-40 minutes.

9. The method for preparing n-type phosphorus-doped silicon carbide crystal according to claim 1, characterized in that: The method further includes measuring one or both of the resistivity and the carrier concentration of the activated silicon carbide crystal; When the resistivity of the activated silicon carbide crystal is greater than the target resistivity or when the carrier concentration of the activated silicon carbide crystal is less than the target doping concentration of phosphorus atoms, steps (2) and (3) are repeated until the resistivity of the activated silicon carbide crystal is less than or equal to the target resistivity.

10. An n-type phosphorus-doped silicon carbide crystal, characterized in that: Prepared by the method according to any one of claims 1 to 9, the chemical formula of the n-type phosphorus-doped silicon carbide crystal is: Si (1-x) P x C, of ​​which 10 -8 ≤x≤0.03.

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