A control defect silicon carbide epitaxial structure and its preparation method and application

Abstract

The application provides a control-defect silicon carbide epitaxial structure and a preparation method and application thereof, and the preparation method comprises the following steps: (1) in-situ etching a silicon carbide substrate; (2) growing a first N-type buffer layer on the surface of the silicon carbide substrate; (3) introducing oxygen atoms in-situ in an inert gas atmosphere for oxygen etching; (4) growing a second N-type buffer layer on the surface of the first N-type buffer layer; and (5) growing a drift layer on the surface of the second N-type buffer layer. The preparation method provided by the application reduces the screw dislocation and the edge dislocation in the silicon carbide epitaxial crystal, thereby improving the growth quality of the silicon carbide epitaxial structure.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor technology and relates to a silicon carbide epitaxial structure, particularly to a silicon carbide epitaxial structure for controlling defects, its preparation method, and its application. Background Technology

[0002] Third-generation wide-bandgap semiconductor materials, represented by silicon carbide, have the characteristics of wide bandgap, high critical breakdown electric field, high thermal conductivity, and high carrier saturation drift, making them particularly suitable for fabricating high-temperature, high-pressure, high-frequency, high-power, and radiation-resistant semiconductor devices.

[0003] Currently, an important topic in silicon carbide epitaxial research is defect control. Technicians mainly focus on three types of defects: morphological defects, deep-level defects, and structural defects.

[0004] Morphological defects in silicon carbide epitaxy typically include carrot defects, triangle defects, downfall, and step bunching. As the epitaxial layer thickness increases, the amount of impurities deposited on the cavity wall also increases, and these impurities are more likely to fall onto the wafer surface as epitaxy progresses, inducing epitaxial defects and making defect control in thick-film epitaxy a challenge. Currently, the combined density of typical downfall and triangle defects in a 10μm epitaxial layer can reach 0.1-1.0 cm⁻¹. -2 The level.

[0005] The deep-level defects that researchers primarily focus on include the Z1 / 2 (0.63 eV below EC) and H6 / 7 (1.55 eV below EC) centers. Among these, the Z1 / 2 defect is considered a "killer" defect for minority carrier lifetime because of its significant impact on minority carrier lifetime, and studies have found that the formation of the Z1 / 2 level is mainly related to C vacancies (VCs). Typical in-situ Z1 / 2 defect concentrations are between 10... 12 -10 13 cm -3 In thick-film epitaxial materials used in silicon carbide high-voltage bipolar devices, the density of the Z1 / 2 energy level should be controlled to reduce its concentration and enhance minority carrier lifetime. Currently, the mainstream methods are thermal oxidation and C ion implantation followed by annealing. Alternatively, the concentration of the Z1 / 2 energy level in the epitaxial material can be reduced by optimizing epitaxial growth process conditions (such as temperature, C / Si ratio, etc.).

[0006] The structural defects that engineers primarily focus on include microtubes, basal plane dislocations (BPDs), screw dislocations (TSDs), and edge dislocations (TEDs). At the beginning of silicon carbide research, microtubes were consistently considered a "killer" defect for both high-voltage and low-voltage devices. With continuous technological advancements, in single-crystal fabrication processes, by optimizing the process (such as controlling the C / Si ratio, selecting…),… or The seed crystals of the crystal planes can essentially achieve a "zero micropipe" level. During epitaxial growth, most (90%) basal plane dislocations can be converted into edge dislocations. Special epitaxial techniques, such as molten KOH etching or H2 etching before growth, can increase the conversion rate, which currently reaches 99.8%, with a BPD density approaching the level of "zero" dislocations. However, reducing screw and edge dislocations has always been a difficult problem hindering silicon carbide crystal growth.

[0007] Therefore, how to provide a silicon carbide epitaxial structure and its preparation method, reduce screw dislocations and edge dislocations in silicon carbide epitaxial crystals, and thus improve the growth quality of silicon carbide epitaxial structures, has become an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0008] The purpose of this invention is to provide a silicon carbide epitaxial structure with controlled defects, its preparation method and application. The preparation method reduces screw dislocations and edge dislocations in silicon carbide epitaxial crystals, thereby improving the growth quality of silicon carbide epitaxial structures.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a method for preparing a silicon carbide epitaxial structure with controlled defects, the method comprising the following steps:

[0011] (1) In-situ etching of silicon carbide substrate;

[0012] (2) A first N-type buffer layer is grown on the surface of a silicon carbide substrate;

[0013] (3) Introduce oxygen atoms in situ in an inert gas atmosphere for oxygen etching;

[0014] (4) Grow a second N-type buffer layer on the surface of the first N-type buffer layer;

[0015] (5) A drift layer is grown on the surface of the second N-type buffer layer.

[0016] The preparation method provided by this invention introduces oxygen atoms in situ during the silicon carbide epitaxial growth process. After the oxygen atoms are incorporated into the silicon carbide lattice, dangling bonds are increased, and surface states are introduced. Under the action of an electric field, the electrons in the oxygen atom dangling bonds recombine with positively charged screw dislocations and edge dislocations, reducing the leakage current characteristics of the device. Since the characteristic of dislocations is that they have an extra half-atom plane, and oxygen atoms are smaller than both C and N, this invention changes the direction of dislocations by introducing oxygen atoms, promoting the annihilation of screw dislocations and edge dislocations, thereby reducing the dislocation density, decreasing the probability of penetration to the drift layer, and improving the growth quality of the silicon carbide epitaxial structure.

[0017] Preferably, the silicon carbide substrate in step (1) comprises a 4H-SiC substrate, which satisfies a 4° bias in the <11-20> direction.

[0018] Preferably, the in-situ etching in step (1) includes: introducing H2 at a flow rate of 200-500 slm and etching for 5-10 min at a temperature of 1400-1650℃ and a pressure of 50-100 mbar.

[0019] The H2 flow rate is 200-500 slm, for example, it can be 200 slm, 220 slm, 240 slm, 260 slm, 280 slm, 300 slm, 320 slm, 340 slm, 360 slm, 380 slm, 400 slm, 420 slm, 440 slm, 460 slm, 480 slm, or 500 slm. The temperature is 1400-1650℃, for example, it can be 1400℃, 1420℃, 1440℃, 1460℃, 1480℃, 1500℃, 1520℃, 1540℃, 1560℃, 1580℃, 1600℃, 1620℃, or 1620℃. The temperature is 1640℃ or 1650℃, and the pressure is 50-100 mbar, for example, 50 mbar, 55 mbar, 60 mbar, 65 mbar, 70 mbar, 75 mbar, 80 mbar, 85 mbar, 90 mbar, 95 mbar or 100 mbar. The etching time is 5-10 min, for example, 5 min, 5.5 min, 6 min, 6.5 min, 7 min, 7.5 min, 8 min, 8.5 min, 9 min, 9.5 min or 10 min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] Preferably, the growth method of the first N-type buffer layer in step (2) includes: introducing carrier gas H2, chlorine-containing silicon source gas, carbon source and N-type dopant N2 at flow rates of 100-800 slm, 300-600 sccm, 200-500 sccm and 80-120 sccm respectively, and growing at a temperature of 1580-1680℃ and a pressure of 50-100 mbar.

[0021] The flow rate of the carrier gas H2 is 100-800 slm, for example, it can be 100 slm, 150 slm, 200 slm, 250 slm, 300 slm, 350 slm, 400 slm, 450 slm, 500 slm, 550 slm, 600 slm, 650 slm, 700 slm, 750 slm, or 800 slm, and the flow rate of the chlorine-containing silicon source gas is 300-6... The flow rate of the carbon source is 200-500 sccm, for example, it can be 300 sccm, 350 sccm, 400 sccm, 450 sccm, 500 sccm, 550 sccm, or 600 sccm, and the inlet flow rate of the carbon source is 200-500 sccm, for example, it can be 200 sccm, 250 sccm, 300 sccm, 350 sccm, 400 sccm, 450 sccm, or 500 sccm, and the N-type doping... The flow rate of the impurity N2 is 80-120 sccm, for example, 80 sccm, 85 sccm, 90 sccm, 95 sccm, 100 sccm, 105 sccm, 110 sccm, 115 sccm or 120 sccm; the temperature is 1580-1680℃, for example, 1580℃, 1590℃, 1600℃, 1610℃, 1620℃, 1630℃, 1640℃, 1650℃, 1660℃, 1670℃ or 1680℃; the pressure is 50-100 mbar, for example, 50 mbar, 55 mbar, 60 mbar, 65 mbar, 70 mbar, 75 mbar, 80 mbar, 85 mbar, 90 mbar, 95 mbar or 100 mbar, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0022] Preferably, the chlorine-containing silicon source gas includes any one or a combination of at least two of SiCl4, SiHCl3, SiH2Cl2, or SiH3Cl. Typical but non-limiting combinations include combinations of SiCl4 and SiHCl3, combinations of SiHCl3 and SiH2Cl2, combinations of SiH2Cl2 and SiH3Cl, combinations of SiCl4, SiHCl3, and SiH2Cl2, or combinations of SiHCl3, SiH2Cl2, and SiH3Cl.

[0023] Preferably, a first purging is performed between steps (2) and (3).

[0024] Preferably, the first purging includes: introducing carrier gas Ar at a flow rate of 100-800 slm to displace carrier gas H2 in the reaction environment.

[0025] The inlet flow rate of the carrier gas Ar is 100-800 slm, for example, it can be 100 slm, 150 slm, 200 slm, 250 slm, 300 slm, 350 slm, 400 slm, 450 slm, 500 slm, 550 slm, 600 slm, 650 slm, 700 slm, 750 slm or 800 slm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0026] In this invention, since the O2 introduced in the oxygen etching step (3) will react with the carrier gas H2, it is necessary to introduce the carrier gas Ar in advance to replace the carrier gas H2 in the reaction environment.

[0027] Preferably, the oxygen etching in step (3) includes: introducing carrier gas Ar, HCl, O2 and carbon source at flow rates of 100-800 slm, 3000-6000 sccm, 100-200 sccm and 50-100 sccm respectively, and etching for 5-10 min at a temperature of 1580-1680℃ and a pressure of 50-100 mbar.

[0028] The flow rate of the carrier gas Ar is 100-800 slm, for example, it can be 100 slm, 150 slm, 200 slm, 250 slm, 300 slm, 350 slm, 400 slm, 450 slm, 500 slm, 550 slm, 600 slm, 650 slm, 700 slm, 750 slm, or 800 slm. The flow rate of the HCl is 3000-6000 sccm, for example, it can be 3000 sccm or 3500 sccm. The flow rates are 4000 sccm, 4500 sccm, 5000 sccm, 5500 sccm, or 6000 sccm, and the O2 flow rate is 100-200 sccm, for example, 100 sccm, 110 sccm, 120 sccm, 130 sccm, 140 sccm, 150 sccm, 160 sccm, 170 sccm, 180 sccm, 190 sccm, or 200 sccm. The carbon source flow rate is 50-100 sccm, for example... The pressure can be 50 sccm, 55 sccm, 60 sccm, 65 sccm, 70 sccm, 75 sccm, 80 sccm, 85 sccm, 90 sccm, 95 sccm, or 100 sccm; the temperature is 1580-1650℃, for example, 1580℃, 1590℃, 1600℃, 1610℃, 1620℃, 1630℃, 1640℃, or 1650℃; and the pressure is 50-100 mbar, for example, 50 mbar or 55 mbar. The etching time is 5-10 min, for example, 5 min, 5.5 min, 6 min, 6.5 min, 7 min, 7 min, 7.5 min, 8 min, 8.5 min, 9 min, 9.5 min, or 10 min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0029] In this invention, since the carrier gas Ar introduced in the oxygen etching step (3) is an inert gas and will not etch silicon carbide, the flow rate of HCl introduced in the Ar atmosphere is relatively high.

[0030] Specifically, the oxygen etching process requires the introduction of a carbon source, while the silicon source is mainly obtained by etching silicon carbide. The chemical reactions that occur are as follows:

[0031] SiC(s)→Si(l)+C(s);

[0032] 2C(s) + O2 → CO2(g).

[0033] Preferably, a second purging is performed between steps (3) and (4).

[0034] Preferably, the second purging includes: introducing carrier gas H2 at a flow rate of 100-800 slm to displace carrier gas Ar in the reaction environment.

[0035] The flow rate of the carrier gas H2 is 100-800 slm, for example, it can be 100 slm, 150 slm, 200 slm, 250 slm, 300 slm, 350 slm, 400 slm, 450 slm, 500 slm, 550 slm, 600 slm, 650 slm, 700 slm, 750 slm or 800 slm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0036] Preferably, the growth method of the second N-type buffer layer in step (4) includes: introducing carrier gas H2, chlorine-containing silicon source gas, carbon source and N-type dopant N2 at flow rates of 100-800 slm, 300-600 sccm, 200-500 sccm and 80-120 sccm respectively, and growing at a temperature of 1580-1680℃ and a pressure of 50-100 mbar.

[0037] The flow rate of the carrier gas H2 is 100-800 slm, for example, it can be 100 slm, 150 slm, 200 slm, 250 slm, 300 slm, 350 slm, 400 slm, 450 slm, 500 slm, 550 slm, 600 slm, 650 slm, 700 slm, 750 slm, or 800 slm, and the flow rate of the chlorine-containing silicon source gas is 300-6... The flow rate of the carbon source is 200-500 sccm, for example, it can be 300 sccm, 350 sccm, 400 sccm, 450 sccm, 500 sccm, 550 sccm, or 600 sccm, and the inlet flow rate of the carbon source is 200-500 sccm, for example, it can be 200 sccm, 250 sccm, 300 sccm, 350 sccm, 400 sccm, 450 sccm, or 500 sccm, and the N-type doping... The flow rate of the impurity N2 is 80-120 sccm, for example, 80 sccm, 85 sccm, 90 sccm, 95 sccm, 100 sccm, 105 sccm, 110 sccm, 115 sccm or 120 sccm; the temperature is 1580-1680℃, for example, 1580℃, 1590℃, 1600℃, 1610℃, 1620℃, 1630℃, 1640℃, 1650℃, 1660℃, 1670℃ or 1680℃; the pressure is 50-100 mbar, for example, 50 mbar, 55 mbar, 60 mbar, 65 mbar, 70 mbar, 75 mbar, 80 mbar, 85 mbar, 90 mbar, 95 mbar or 100 mbar, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0038] Preferably, the chlorine-containing silicon source gas includes any one or a combination of at least two of SiCl4, SiHCl3, SiH2Cl2, or SiH3Cl. Typical but non-limiting combinations include combinations of SiCl4 and SiHCl3, combinations of SiHCl3 and SiH2Cl2, combinations of SiH2Cl2 and SiH3Cl, combinations of SiCl4, SiHCl3, and SiH2Cl2, or combinations of SiHCl3, SiH2Cl2, and SiH3Cl.

[0039] Preferably, the growth method of the drift layer in step (5) includes: introducing carrier gas H2, chlorine-containing silicon source gas, carbon source and N-type dopant N2 at flow rates of 100-800 slm, 300-600 sccm, 200-500 sccm and 20-60 sccm respectively, and growing at a temperature of 1580-1680℃ and a pressure of 50-500 mbar.

[0040] The carrier gas H2 has an inlet flow rate of 100-800 slm, for example, 100 slm, 150 slm, 200 slm, 250 slm, 300 slm, 350 slm, 400 slm, 450 slm, 500 slm, 550 slm, 600 slm, 650 slm, 700 slm, 750 slm, or 800 slm. The chlorine-containing silicon source gas has an inlet flow rate of 300-600 sccm, for example, 300 sccm, 350 sccm, 400 sccm, 450 sccm, 500 sccm, 550 sccm, or 600 sccm. The carbon source has an inlet flow rate of 200-500 sccm, for example, 200 sccm, 250 sccm, 300 sccm, 350 sccm, 400 sccm, 450 sccm, or 500 sccm. The flow rate of the N-type dopant N2 is 20-60 sccm, for example, 20 sccm, 25 sccm, 30 sccm, 35 sccm, 40 sccm, 45 sccm, 50 sccm, 55 sccm or 60 sccm; the temperature is 1580-1680℃, for example, 1580℃, 1590℃, 1600℃, 1610℃, 1620℃, 1630℃, 1640℃, 1650℃, 1660℃, 1670℃ or 1680℃; the pressure is 50-500 mbar, for example, 50 mbar, 100 mbar, 150 mbar, 200 mbar, 250 mbar, 300 mbar, 350 mbar, 400 mbar, 450 mbar or 500 mbar, but not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0041] Preferably, the chlorine-containing silicon source gas includes any one or a combination of at least two of SiCl4, SiHCl3, SiH2Cl2, or SiH3Cl. Typical but non-limiting combinations include combinations of SiCl4 and SiHCl3, combinations of SiHCl3 and SiH2Cl2, combinations of SiH2Cl2 and SiH3Cl, combinations of SiCl4, SiHCl3, and SiH2Cl2, or combinations of SiHCl3, SiH2Cl2, and SiH3Cl.

[0042] As a preferred embodiment of the first aspect of the present invention, the preparation method includes the following steps:

[0043] (1) Select a 4H-SiC substrate with a bias of 4° in the <11-20> direction, and perform in-situ etching on the silicon carbide substrate. The in-situ etching includes: introducing H2 at a flow rate of 200-500 slm and etching for 5-10 min at a temperature of 1400-1650℃ and a pressure of 50-100 mbar.

[0044] (2) A first N-type buffer layer is grown on the surface of a silicon carbide substrate. The specific growth method includes: introducing carrier gas H2, chlorine-containing silicon source gas, carbon source and N-type dopant N2 at flow rates of 100-800 slm, 300-600 sccm, 200-500 sccm and 80-120 sccm respectively, and growing at a temperature of 1580-1680℃ and a pressure of 50-100 mbar.

[0045] (3) First purging: Carrier gas Ar is introduced at a flow rate of 100-800 slm to displace carrier gas H2 in the reaction environment;

[0046] (4) In situ oxygen atoms are introduced in an argon atmosphere for oxygen etching, and the oxygen etching includes: introducing carrier gas Ar, HCl, O2 and carbon source at flow rates of 100-800 slm, 3000-6000 sccm, 100-200 sccm and 50-100 sccm respectively, and etching for 5-10 min at a temperature of 1580-1680℃ and a pressure of 50-100 mbar;

[0047] (5) Second purging: H2 is introduced at a flow rate of 100-800 slm to displace the Ar carrier gas in the reaction environment;

[0048] (6) A second N-type buffer layer is grown on the surface of the first N-type buffer layer. The specific growth method includes: introducing carrier gas H2, chlorine-containing silicon source gas, carbon source and N-type dopant N2 at flow rates of 100-800 slm, 300-600 sccm, 200-500 sccm and 80-120 sccm respectively, and growing at a temperature of 1580-1680℃ and a pressure of 50-100 mbar.

[0049] (7) A drift layer is grown on the surface of the second N-type buffer layer. The specific growth method includes: introducing carrier gas H2, chlorine-containing silicon source gas, carbon source and N-type dopant N2 at flow rates of 100-800 slm, 300-600 sccm, 200-500 sccm and 20-60 sccm respectively, and growing at a temperature of 1580-1680℃ and a pressure of 50-500 mbar.

[0050] The chlorine-containing silicon source gas includes any one or a combination of at least two of SiCl4, SiHCl3, SiH2Cl2, or SiH3Cl.

[0051] In a second aspect, the present invention provides a silicon carbide epitaxial structure prepared by the preparation method described in the first aspect, the silicon carbide epitaxial structure comprising a silicon carbide substrate, a first N-type buffer layer, a second N-type buffer layer and a drift layer stacked together.

[0052] Preferably, the thickness of the first N-type buffer layer is 0.1-0.5 μm, for example, it can be 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm or 0.5 μm, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0053] In this invention, the thickness of the first N-type buffer layer needs to be controlled within a reasonable range. When the thickness is less than 0.1 μm, it is difficult to effectively buffer lattice mismatch; when the thickness is greater than 0.5 μm, it will cause the on-resistance to increase unnecessarily.

[0054] Preferably, the doping concentration of the first N-type buffer layer is (1-5)×10⁻⁶. 18 cm -3 For example, it could be 1×10 18 cm -3 1.5×10 18 cm -3 2×10 18 cm -3 2.5×10 18 cm -3 3×10 18 cm -3 3.5×10 18 cm -3 4×10 18 cm -3 4.5×10 18 cm -3 Or 5×10 18 cm -3 However, this does not apply to all values ​​listed; other unlisted values ​​within the same range also apply.

[0055] In this invention, the doping concentration of the first N-type buffer layer needs to be controlled within a reasonable range. When the doping concentration is below 1×10⁻⁶, 18 cm -3 At that time, with substrate concentration (5×10) 18 -1×10 19 cm -3Excessive differences between the doping concentrations can lead to stacking fault defects at the interface due to large mismatch stresses; when the doping concentration exceeds 5 × 10⁻⁶, the resulting stress can cause further damage. 18 cm -3 When this happens, the on-resistance will decrease significantly, thereby reducing the device's withstand voltage performance.

[0056] Preferably, the thickness of the second N-type buffer layer is 0.9-1.1 μm, for example, it can be 0.9 μm, 0.92 μm, 0.94 μm, 0.96 μm, 0.98 μm, 1 μm, 1.02 μm, 1.04 μm, 1.06 μm, 1.08 μm or 1.1 μm, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0057] Preferably, the doping concentration of the second N-type buffer layer is (0.7-1.3)×10⁻⁶. 18 cm -3 For example, it could be 0.7 × 10 18 cm -3 0.8×10 18 cm -3 0.9×10 18 cm -3 1×10 18 cm -3 1.1×10 18 cm -3 1.2×10 18 cm -3 Or 1.3×10 18 cm -3 However, this does not apply to all values ​​listed; other unlisted values ​​within the same range also apply.

[0058] Preferably, the thickness of the drift layer is 10-200 μm, for example, it can be 10 μm, 20 μm, 40 μm, 60 μm, 80 μm, 100 μm, 120 μm, 140 μm, 160 μm, 180 μm or 200 μm, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0059] Thirdly, the present invention provides an application of the silicon carbide epitaxial structure as described in the second aspect, wherein the silicon carbide epitaxial structure is used to fabricate semiconductor devices.

[0060] Compared with the prior art, the present invention has the following beneficial effects:

[0061] The preparation method provided by this invention introduces oxygen atoms in situ during the silicon carbide epitaxial growth process. After the oxygen atoms are incorporated into the silicon carbide lattice, dangling bonds are increased, and surface states are introduced. Under the action of an electric field, the electrons in the oxygen atom dangling bonds recombine with positively charged screw dislocations and edge dislocations, reducing the leakage current characteristics of the device. Since the characteristic of dislocations is that they have an extra half-atom plane, and oxygen atoms are smaller than both C and N, this invention changes the direction of dislocations by introducing oxygen atoms, promoting the annihilation of screw dislocations and edge dislocations, thereby reducing the dislocation density, decreasing the probability of penetration to the drift layer, and improving the growth quality of the silicon carbide epitaxial structure. Attached Figure Description

[0062] Figure 1 This is a defect density diagram of the silicon carbide epitaxial structure provided in Example 1 after etching;

[0063] Figure 2 This is a defect density diagram of the silicon carbide epitaxial structure after etching, provided in Comparative Example 1. Detailed Implementation

[0064] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0065] Example 1

[0066] This embodiment provides a silicon carbide epitaxial structure with controlled defects and its preparation method, the preparation method including the following steps:

[0067] (1) Select a 4H-SiC substrate with a bias of 4° in the <11-20> direction. After standard cleaning, perform in-situ etching on the silicon carbide substrate. The in-situ etching includes: introducing H2 at a flow rate of 200 slm and etching for 10 min at a temperature of 1600℃ and a pressure of 100 mbar.

[0068] (2) A first N-type buffer layer is grown on the surface of a silicon carbide substrate. The specific growth method includes: introducing carrier gas H2, SiHCl3, carbon source and N-type dopant N2 at flow rates of 200 slm, 450 sccm, 350 sccm and 100 sccm respectively, and growing at a temperature of 1600℃ and a pressure of 100 mbar.

[0069] (3) First purging: Carrier gas Ar is introduced at a flow rate of 200 slm to displace carrier gas H2 in the reaction environment;

[0070] (4) In situ oxygen atoms are introduced in an argon atmosphere for oxygen etching, and the oxygen etching includes: introducing carrier gas Ar, HCl, O2 and carbon source at flow rates of 200 slm, 4500 sccm, 150 sccm and 75 sccm respectively, and etching for 8 min at a temperature of 1600℃ and a pressure of 100 mbar.

[0071] (5) Second purging: H2 is introduced at a flow rate of 200 slm to displace the carrier gas Ar in the reaction environment;

[0072] (6) A second N-type buffer layer is grown on the surface of the first N-type buffer layer. The specific growth method includes: passing carrier gas H2, SiHCl3, carbon source and N-type dopant N2 into the layer at flow rates of 200 slm, 450 sccm, 350 sccm and 100 sccm respectively, and growing the layer at a temperature of 1600℃ and a pressure of 100 mbar.

[0073] (7) A drift layer is grown on the surface of the second N-type buffer layer. The specific growth method includes: introducing carrier gas H2, SiHCl3, carbon source and N-type dopant N2 at flow rates of 200 slm, 450 sccm, 350 sccm and 40 sccm respectively, and growing at a temperature of 1600℃ and a pressure of 100 mbar.

[0074] In this embodiment, the carbon source is specifically ethylene.

[0075] The silicon carbide epitaxial structure prepared by the above method includes a silicon carbide substrate, a first N-type buffer layer, a second N-type buffer layer, and a drift layer stacked together. The first N-type buffer layer has a thickness of 0.3 μm and a doping concentration of 3 × 10⁻⁶. 18 cm -3 The second N-type buffer layer has a thickness of 1.0 μm and a doping concentration of 1.0 × 10⁻⁶. 18 cm -3 The thickness of the drift layer is 20 μm.

[0076] Example 2

[0077] This embodiment provides a silicon carbide epitaxial structure with controlled defects and its preparation method, the preparation method including the following steps:

[0078] (1) Select a 4H-SiC substrate with a bias of 4° in the <11-20> direction. After standard cleaning, perform in-situ etching on the silicon carbide substrate. The in-situ etching includes: introducing H2 at a flow rate of 200 slm and etching for 10 min at a temperature of 1500℃ and a pressure of 100 mbar.

[0079] (2) A first N-type buffer layer is grown on the surface of a silicon carbide substrate. The specific growth method includes: passing carrier gas H2, SiHCl3, carbon source and N-type dopant N2 into the substrate at flow rates of 200 slm, 300 sccm, 200 sccm and 80 sccm respectively, and growing the substrate at a temperature of 1580℃ and a pressure of 100 mbar.

[0080] (3) First purging: Carrier gas Ar is introduced at a flow rate of 200 slm to displace carrier gas H2 in the reaction environment;

[0081] (4) In situ oxygen atoms are introduced in an argon atmosphere for oxygen etching, and the oxygen etching includes: introducing carrier gas Ar, HCl, O2 and carbon source at flow rates of 200 slm, 3000 sccm, 100 sccm and 50 sccm respectively, and etching for 10 min at a temperature of 1580℃ and a pressure of 100 mbar.

[0082] (5) Second purging: H2 is introduced at a flow rate of 200 slm to displace the carrier gas Ar in the reaction environment;

[0083] (6) A second N-type buffer layer is grown on the surface of the first N-type buffer layer. The specific growth method includes: passing carrier gas H2, SiHCl3, carbon source and N-type dopant N2 into the layer at flow rates of 200 slm, 300 sccm, 200 sccm and 80 sccm respectively, and growing the layer at a temperature of 1580℃ and a pressure of 100 mbar.

[0084] (7) A drift layer is grown on the surface of the second N-type buffer layer. The specific growth method includes: introducing carrier gas H2, SiH2Cl2, carbon source and N-type dopant N2 at flow rates of 200slm, 300sccm, 200sccm and 20sccm respectively, and growing at a temperature of 1580℃ and a pressure of 500mbar.

[0085] In this embodiment, the carbon source is specifically ethylene.

[0086] The silicon carbide epitaxial structure prepared by the above method includes a silicon carbide substrate, a first N-type buffer layer, a second N-type buffer layer, and a drift layer stacked together. The first N-type buffer layer has a thickness of 0.1 μm and a doping concentration of 1 × 10⁻⁶. 18 cm -3 The second N-type buffer layer has a thickness of 0.9 μm and a doping concentration of 0.7 × 10⁻⁶. 18 cm -3 The thickness of the drift layer is 20 μm.

[0087] Example 3

[0088] This embodiment provides a silicon carbide epitaxial structure with controlled defects and its preparation method, the preparation method including the following steps:

[0089] (1) Select a 4H-SiC substrate with a bias of 4° in the <11-20> direction. After standard cleaning, perform in-situ etching on the silicon carbide substrate. The in-situ etching includes: introducing H2 at a flow rate of 200 slm and etching for 5 min at a temperature of 1650℃ and a pressure of 50 mbar.

[0090] (2) A first N-type buffer layer is grown on the surface of a silicon carbide substrate. The specific growth method includes: introducing carrier gas H2, SiH2Cl2, carbon source and N-type dopant N2 at flow rates of 200slm, 600sccm, 500sccm and 120sccm respectively, and growing at a temperature of 1680℃ and a pressure of 50mbar.

[0091] (3) First purging: Carrier gas Ar is introduced at a flow rate of 200 slm to displace carrier gas H2 in the reaction environment;

[0092] (4) In situ oxygen atoms are introduced in an argon atmosphere for oxygen etching, and the oxygen etching includes: introducing carrier gas Ar, HCl, O2 and carbon source at flow rates of 200 slm, 6000 sccm, 200 sccm and 100 sccm respectively, and etching for 5 min at a temperature of 1680℃ and a pressure of 50 mbar.

[0093] (5) Second purging: H2 is introduced at a flow rate of 800 slm to displace the carrier gas Ar in the reaction environment;

[0094] (6) A second N-type buffer layer is grown on the surface of the first N-type buffer layer. The specific growth method includes: introducing carrier gas H2, SiH2Cl2, carbon source and N-type dopant N2 at flow rates of 200slm, 600sccm, 500sccm and 120sccm respectively, and growing at a temperature of 1680℃ and a pressure of 50mbar.

[0095] (7) A drift layer is grown on the surface of the second N-type buffer layer. The specific growth method includes: introducing carrier gas H2, SiH3Cl, carbon source and N-type dopant N2 at flow rates of 200slm, 600sccm, 500sccm and 60sccm respectively, and growing at a temperature of 1680℃ and a pressure of 50mbar.

[0096] In this embodiment, the carbon source is specifically ethylene.

[0097] The silicon carbide epitaxial structure prepared by the above method includes a silicon carbide substrate, a first N-type buffer layer, a second N-type buffer layer, and a drift layer stacked together. The first N-type buffer layer has a thickness of 0.5 μm and a doping concentration of 5 × 10⁻⁶. 18 cm -3 The second N-type buffer layer has a thickness of 1.1 μm and a doping concentration of 1.3 × 10⁻⁶. 18 cm -3 The thickness of the drift layer is 20 μm.

[0098] Comparative Example 1

[0099] This comparative example provides a silicon carbide epitaxial structure and its preparation method, the preparation method comprising the following steps:

[0100] (1) Select a 4H-SiC substrate with a bias of 4° in the <11-20> direction. After standard cleaning, perform in-situ etching on the silicon carbide substrate. The in-situ etching includes: introducing H2 at a flow rate of 200 slm and etching for 10 min at a temperature of 1600℃ and a pressure of 100 mbar.

[0101] (2) An N-type buffer layer is grown on the surface of a silicon carbide substrate. The specific growth method includes: introducing carrier gas H2, SiHCl3, carbon source and N-type dopant N2 at flow rates of 200 slm, 450 sccm, 350 sccm and 100 sccm respectively, and growing at a temperature of 1600℃ and a pressure of 100 mbar.

[0102] (3) A drift layer is grown on the surface of the N-type buffer layer. The specific growth method includes: introducing carrier gas H2, SiHCl3, carbon source and N-type dopant N2 at flow rates of 200 slm, 450 sccm, 350 sccm and 40 sccm respectively, and growing at a temperature of 1600℃ and a pressure of 100 mbar.

[0103] In this comparative example, the carbon source is specifically ethylene.

[0104] The silicon carbide epitaxial structure prepared by the above method includes a silicon carbide substrate, an N-type buffer layer, and a drift layer stacked together. The N-type buffer layer has a thickness of 1.0 μm and a doping concentration of 1.0 × 10⁻⁶. 18 cm -3 The thickness of the drift layer is 20 μm.

[0105] Performance testing

[0106] The defect density of the silicon carbide epitaxial structures obtained in Examples 1-3 and Comparative Example 1 was measured after etching. The specific method was as follows: Molten potassium hydroxide particles were heated in a muffle furnace. After the potassium hydroxide was completely melted, the silicon carbide epitaxial wafer was placed inside. The etching temperature was set at 480℃, and the etching time was set at 15 minutes. After etching, the silicon carbide samples were washed sequentially with deionized water, dilute hydrochloric acid, and then deionized water. The etching pits in the silicon carbide were observed using an optical microscope to confirm the density of screw dislocations and edge dislocations.

[0107] Figure 1 The defect density diagram of the silicon carbide epitaxial structure provided in Example 1 after etching is shown. The defect densities of the silicon carbide epitaxial structures obtained in Examples 2 and 3 after etching are similar to those in Example 1, so they will not be described in detail here. Figure 2 Defect density diagram of the silicon carbide epitaxial structure after etching, provided for Comparative Example 1.

[0108] Depend on Figure 1 and Figure 2 It can be seen that the defect density of the silicon carbide epitaxial structure obtained in Example 1 after etching is significantly lower than that in Comparative Example 1, and based on rough estimation, the screw dislocation density in the silicon carbide epitaxial structure obtained in Example 1 is less than 10 cm⁻¹. -2 The density of edge dislocations is less than 100 cm⁻¹ -2 The density of screw dislocations in the silicon carbide epitaxial structure obtained in Comparative Example 1 is higher than 100 cm⁻¹. -2 The density of edge dislocations is higher than 500 cm⁻¹ -2 .

[0109] Therefore, the preparation method provided by this invention introduces oxygen atoms in situ during the silicon carbide epitaxial growth process. After the oxygen atoms are incorporated into the silicon carbide lattice, dangling bonds are increased, and surface states are introduced. Under the action of an electric field, the electrons in the oxygen atom dangling bonds recombine with positively charged screw dislocations and edge dislocations, reducing the leakage current characteristics of the device. Since the characteristic of a dislocation is that it has an extra half-atom plane, and oxygen atoms are smaller than both C and N, this invention changes the direction of the dislocation by introducing oxygen atoms, promoting the annihilation of screw dislocations and edge dislocations, thereby reducing the dislocation density, reducing the probability of penetration to the drift layer, and improving the growth quality of the silicon carbide epitaxial structure.

[0110] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a silicon carbide epitaxial structure with controlled defects, characterized in that, The preparation method includes the following steps: (1) In-situ etching of silicon carbide substrate, wherein the in-situ etching includes etching by introducing H2; (2) A first N-type buffer layer is grown on the surface of a silicon carbide substrate; (3) In situ oxygen atoms are introduced in an inert gas atmosphere for oxygen etching. The oxygen etching includes: introducing carrier gas Ar, HCl, O2 and carbon source at flow rates of 100-800 slm, 3000-6000 sccm, 100-200 sccm and 50-100 sccm respectively, and etching for 5-10 min at a temperature of 1580-1680℃ and a pressure of 50-100 mbar. (4) A second N-type buffer layer is grown on the surface of the first N-type buffer layer; (5) A drift layer is grown on the surface of the second N-type buffer layer; The growth method of the first N-type buffer layer, the second N-type buffer layer, and the drift layer includes introducing carrier gas H2, chlorine-containing silicon source gas, carbon source, and N-type dopant N2 for growth.

2. The preparation method according to claim 1, characterized in that, The silicon carbide substrate in step (1) includes a 4H-SiC substrate, which satisfies a 4° bias in the <11-20> direction.

3. The preparation method according to claim 1, characterized in that, Step (1) The in-situ etching includes: introducing H2 at a flow rate of 200-500 slm and etching for 5-10 min at a temperature of 1400-1650℃ and a pressure of 50-100 mbar.

4. The preparation method according to claim 1, characterized in that, Step (2) The growth method of the first N-type buffer layer includes: introducing carrier gas H2, chlorine-containing silicon source gas, carbon source and N-type dopant N2 at flow rates of 100-800 slm, 300-600 sccm, 200-500 sccm and 80-120 sccm respectively, and growing at a temperature of 1580-1680℃ and a pressure of 50-100 mbar.

5. The preparation method according to claim 4, characterized in that, The chlorine-containing silicon source gas includes any one or a combination of at least two of SiCl4, SiHCl3, SiH2Cl2, or SiH3Cl.

6. The preparation method according to claim 1, characterized in that, A first purging is also performed between steps (2) and (3).

7. The preparation method according to claim 6, characterized in that, The first purging includes: introducing carrier gas Ar at a flow rate of 100-800 slm to displace carrier gas H2 in the reaction environment.

8. The preparation method according to claim 1, characterized in that, A second purging is performed between steps (3) and (4).

9. The preparation method according to claim 8, characterized in that, The second purging includes: introducing carrier gas H2 at a flow rate of 100-800 slm to displace carrier gas Ar in the reaction environment.

10. The preparation method according to claim 1, characterized in that, Step (4) The growth method of the second N-type buffer layer includes: introducing carrier gas H2, chlorine-containing silicon source gas, carbon source and N-type dopant N2 at flow rates of 100-800 slm, 300-600 sccm, 200-500 sccm and 80-120 sccm respectively, and growing at a temperature of 1580-1680℃ and a pressure of 50-100 mbar.

11. The preparation method according to claim 10, characterized in that, The chlorine-containing silicon source gas includes any one or a combination of at least two of SiCl4, SiHCl3, SiH2Cl2, or SiH3Cl.

12. The preparation method according to claim 1, characterized in that, The growth method of the drift layer in step (5) includes: introducing carrier gas H2, chlorine-containing silicon source gas, carbon source and N-type dopant N2 at flow rates of 100-800 slm, 300-600 sccm, 200-500 sccm and 20-60 sccm respectively, and growing at a temperature of 1580-1680℃ and a pressure of 50-500 mbar.

13. The preparation method according to claim 12, characterized in that, The chlorine-containing silicon source gas includes any one or a combination of at least two of SiCl4, SiHCl3, SiH2Cl2, or SiH3Cl.

14. A method for preparing a silicon carbide epitaxial structure with controlled defects, characterized in that, The preparation method includes the following steps: (1) Select a 4H-SiC substrate biased 4° in the <11-20> direction, and perform in-situ etching on the silicon carbide substrate. The in-situ etching includes: introducing H2 at a flow rate of 200-500 slm and etching for 5-10 min at a temperature of 1400-1650℃ and a pressure of 50-100 mbar. (2) A first N-type buffer layer is grown on the surface of a silicon carbide substrate. The specific growth method includes: introducing carrier gas H2, chlorine-containing silicon source gas, carbon source and N-type dopant N2 at flow rates of 100-800 slm, 300-600 sccm, 200-500 sccm and 80-120 sccm respectively, and growing at a temperature of 1580-1680℃ and a pressure of 50-100 mbar. (3) First purging: Carrier gas Ar is introduced at a flow rate of 100-800 slm to displace carrier gas H2 in the reaction environment; (4) In situ oxygen atoms are introduced in an argon atmosphere for oxygen etching, and the oxygen etching includes: introducing carrier gas Ar, HCl, O2 and carbon source at flow rates of 100-800 slm, 3000-6000 sccm, 100-200 sccm and 50-100 sccm respectively, and etching for 5-10 min at a temperature of 1580-1680℃ and a pressure of 50-100 mbar; (5) Second purging: H2 is introduced at a flow rate of 100-800 slm to displace the Ar carrier gas in the reaction environment; (6) A second N-type buffer layer is grown on the surface of the first N-type buffer layer. The specific growth method includes: introducing carrier gas H2, chlorine-containing silicon source gas, carbon source and N-type dopant N2 at flow rates of 100-800 slm, 300-600 sccm, 200-500 sccm and 80-120 sccm respectively, and growing at a temperature of 1580-1680℃ and a pressure of 50-100 mbar. (7) A drift layer is grown on the surface of the second N-type buffer layer. The specific growth method includes: introducing carrier gas H2, chlorine-containing silicon source gas, carbon source and N-type dopant N2 at flow rates of 100-800 slm, 300-600 sccm, 200-500 sccm and 20-60 sccm respectively, and growing at a temperature of 1580-1680℃ and a pressure of 50-500 mbar. The chlorine-containing silicon source gas includes any one or a combination of at least two of SiCl4, SiHCl3, SiH2Cl2, or SiH3Cl.

15. A silicon carbide epitaxial structure prepared by the method described in claim 14, characterized in that, The silicon carbide epitaxial structure includes a silicon carbide substrate, a first N-type buffer layer, a second N-type buffer layer, and a drift layer stacked together.

16. The silicon carbide epitaxial structure according to claim 15, characterized in that, The thickness of the first N-type buffer layer is 0.1-0.5 μm.

17. The silicon carbide epitaxial structure according to claim 15, characterized in that, The doping concentration of the first N-type buffer layer is (1-5)×10 18 cm -3 .

18. The silicon carbide epitaxial structure according to claim 15, characterized in that, The thickness of the second N-type buffer layer is 0.9-1.1 μm.

19. The silicon carbide epitaxial structure according to claim 15, characterized in that, The doping concentration of the second N-type buffer layer is (0.7-1.3)×10⁻⁶. 18 cm -3 .

20. The silicon carbide epitaxial structure according to claim 15, characterized in that, The thickness of the drift layer is 10-200 μm.

21. An application of the silicon carbide epitaxial structure as described in any one of claims 15-20, characterized in that, The silicon carbide epitaxial structure is used to fabricate semiconductor devices.

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