P-type silicon carbide crystal

Abstract

A P-type silicon carbide crystal, which relates to the technical field of silicon carbide crystal growth. The maximum value of the resistivity of the P-type silicon carbide crystal is less than or equal to 3 Ω*cm, and the axial resistivity change rate at the same radial position is less than or equal to 25%. The content of impurities in a P-type element is greater than or equal to 1E17 atoms / cm 3, and the impurity change rate of the P-type element is less than or equal to 15%. The P-type silicon carbide crystal has more uniform doping, a more uniform resistivity and a higher crystal transmittance.

Description

A P-type silicon carbide crystal Technical Field

[0001] The present invention relates to the technical field of silicon carbide crystal growth, and in particular to a P-type silicon carbide crystal. Background Art

[0002] Silicon carbide (SiC) is a third-generation semiconductor material, a wide-bandgap semiconductor material following the first-generation elemental semiconductors silicon and germanium, and the second-generation compound semiconductors gallium arsenide and indium phosphide. Compared to the previous two generations of semiconductor materials, SiC exhibits superior physical and electronic properties and chemical stability. Its high thermal conductivity, strong breakdown field, and large saturated electron drift velocity make it a promising material for the fabrication and application of high-temperature, high-frequency, high-power, and corrosion-resistant radiation devices. It is widely used in defense, aerospace, communications, and other fields.

[0003] The fabrication of microelectronic devices requires crystals with high p-type or n-type doping concentrations. Doping can be achieved through raw material doping during crystal growth or through methods such as ion implantation. To achieve electronic performance, the doped ions must be activated. The activation energy of doped ions in different materials is temperature-dependent. Silicon can be activated by doped ions at room temperature, while silicon carbide has a relatively high activation energy for doped ions.

[0004] Existing PVT methods for producing P-type SiC crystals typically use boron / aluminum elements or compounds for doping. Due to their high melting and boiling points, boron / aluminum elements or compounds exist in solid form at room temperature and pressure, but can partially exist in gaseous form at room temperature and high pressure. They do not exist in gaseous form at room temperature. Therefore, solid-phase doping is currently performed using solid-phase dopants. These methods primarily involve improving process parameters such as the placement of the dopant source, the container housing the dopant source, and thermal field modifications (such as a dual-coil structure) to independently control the temperature of the dopant source region. This is done to slow dopant release during the early growth phase and increase dopant release during the later growth phase, minimizing the difference in dopant concentration between the early and late growth phases. However, these methods can only mitigate this difference to a certain extent. In the actual PVT process for producing P-type SiC crystals, due to the decreasing solid-phase dopant concentration and the uncontrollable nature of the crystal growth process, a gradual decrease in dopant concentration along the ingot growth direction is unavoidable. Summary of the Invention

[0005] The inventors have found that in the process of preparing P-type silicon carbide crystals using the PVT method, due to the reduction in the concentration of solid-phase dopants and the uncontrollability of the crystal growth process, it is inevitable that the concentration of doping substances will gradually decrease along the growth direction of the ingot as the growth progresses. In addition, due to the influence of the external environment, there will also be the presence of unintentional doping of nitrogen elements. Based on the above two influences, the resistivity of the substrate will be low in the early stage of the crystal, and the resistivity of the substrate will gradually increase in the later stage, and even the conductivity type will change, affecting the resistivity uniformity and electrical properties of the P-type substrate. Therefore, from the perspective of practical applications, it is necessary to improve the uniformity of the doping concentration of the P-type substrate, especially the axial uniformity of the doping concentration of the crystal in the early and later stages, so as to improve the uniformity of the substrate resistivity.

[0006] On the one hand, the present invention provides a P-type silicon carbide crystal, wherein the maximum resistivity of the P-type silicon carbide crystal is ≤3Ω*cm, the axial resistivity change rate at the same radial position is ≤25%; the P-type element impurity content is ≥1E 17 atoms / cm 3 , the change rate of P-type element impurities is ≤15%.

[0007] Compared with the prior art, the present invention achieves at least one of the following beneficial effects:

[0008] (1) The P-type silicon carbide crystal of the present invention has more uniform doping, more uniform resistivity, and higher and more uniform crystal transmittance.

[0009] (2) The present invention establishes the correlation between the amount of doping in the crystal and the color of the crystal.

[0010] (3) The axial resistivity change rate of the P-type silicon carbide crystal at the same radial position of the present invention is ≤25%, and the P-type element impurity content is ≥1E 17 atoms / cm 3 , the change rate of P-type element impurities is ≤15%. Preferably, the change rate of axial resistivity of the P-type silicon carbide crystal at the same radial position of the present invention is ≤10%, and the change rate of P-type element impurities is ≤10%. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0012] FIG1 shows an exemplary embodiment of a schematic structural diagram of a P-type silicon carbide crystal growth device according to the present invention;

[0013] Figure 2 shows that the Al doping amount in the crystal is greater than 1E 15 and less than or equal to 1E 16 atoms / cm 3An exemplary embodiment of an axial distribution curve diagram of Al content when

[0014] Figure 3 shows that the Al doping amount in the crystal is greater than 1E 15 and less than or equal to 1E 16 atoms / cm 3 An exemplary embodiment of a graph showing the axial resistivity variation of a crystal when φ is less than 0.05.

[0015] Figure 4 shows that the Al doping amount in the crystal is greater than 1E 18 and less than or equal to 1E 19 atoms / cm 3 An exemplary embodiment of an axial distribution curve diagram of Al content when

[0016] Figure 5 shows that the Al doping amount in the crystal is greater than 1E 18 and less than or equal to 1E 19 atoms / cm 3 An exemplary embodiment of a graph showing a change in axial resistivity of a crystal when φ is less than 0.05;

[0017] FIG6 is an enlarged view of the vapor phase doping in FIG5 ;

[0018] Figure 7 shows that the Al doping amount in the crystal is greater than 1E 20 and less than or equal to 1E 21 atoms / cm 3 An exemplary embodiment of an axial distribution curve diagram of Al content when

[0019] Figure 8 shows that the Al doping amount in the crystal is greater than 1E 20 and less than or equal to 1E 21 atoms / cm 3 An exemplary embodiment of a graph showing a change in axial resistivity of a crystal when φ is less than 0.05;

[0020] Figure 9 shows that the B doping level in the crystal is greater than 1E 18 and less than or equal to 1E 19 atoms / cm 3 An exemplary embodiment of an axial distribution curve diagram of B content in a crystal when φ=0.05;

[0021] Figure 10 shows that the B doping amount in the crystal is greater than 1E 18 and less than or equal to 1E 19 atoms / cm 3 An exemplary embodiment of a graph showing the axial resistivity variation of a crystal when φ is less than 0.05.

[0022] 1- housing; 2- induction coil; 3- quartz tube; 4- insulation cylinder; 5- crystal growth chamber; 6- seed crystal; 7- crucible; 8- evaporator; 9- doping source; 10- carrier gas source; 11- doping source switch 2#; 12- doping source switch 1#; 13- carrier gas switch 1#; 14- carrier gas switch 2#. Implementation Method

[0023] In order to more clearly illustrate the overall concept of the present invention, a detailed description is given below in an exemplary manner in conjunction with the accompanying drawings.

[0024] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0025] In addition, in the description of the present invention, it should be understood that the terms "top", "bottom", "inside", "outside", "axial", "radial", "circumferential", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0026] In the present invention, unless otherwise expressly specified or limited, terms such as "mounted," "connected," "connect," and "fixed" should be understood broadly. For example, they may refer to fixed connection, detachable connection, or integration; mechanical connection, electrical connection, or communication; direct connection or indirect connection through an intermediate medium; and internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0027] In the present invention, unless otherwise clearly specified and limited, a first feature "above" or "below" a second feature may be that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means 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 representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in an appropriate manner in any one or more embodiments or examples.

[0028] In the first exemplary embodiment of the present invention, the maximum resistivity of the P-type silicon carbide crystal is ≤3Ω*cm, the axial resistivity variation rate at the same radial position is ≤25%; the P-type element impurity content is ≥1 E 17 atoms / cm³, and the P-type element impurity change rate is ≤15%. Preferably, the axial resistivity change rate at the same radial position is ≤10%, and the P-type element impurity change rate is ≤10%. More preferably, the axial resistivity change rate at the same radial position is ≤8%, and the P-type element impurity change rate is ≤8%.

[0029] A substrate obtained by testing a P-type silicon carbide crystal using a high-resolution XRD rocking curve has a half-width (FWHM) of ≤30 arcsec, a within-chip FWHM variation of ≤30%, and a axial FWHM variation of ≤20% at the same radial position. Preferably, the within-chip FWHM variation of ≤20%, and the axial FWHM variation of ≤15% at the same radial position. More preferably, the within-chip FWHM variation of ≤15%, and the axial FWHM variation of ≤10% at the same radial position.

[0030] Specifically, the substrate obtained from the P-type silicon carbide crystal was characterized by KOH etching, and the total dislocation density was ≤3000 / cm 2 , threading dislocation density ≤ 2500 / cm 2 Preferably, the total dislocation density is ≤2000 / cm 2 , threading dislocation density ≤1000 / cm 2 .

[0031] Specifically, the hardness of the P-type silicon carbide crystal is not less than 9.5 on the Mohs hardness scale.

[0032] Specifically, the P-type silicon carbide crystal has a visible light transmittance of ≥0.6 and a refractive index of 2.6 to 2.8. Preferably, the P-type silicon carbide crystal has a visible light transmittance of ≥0.8.

[0033] Specifically, the P-type silicon carbide crystal absorbs orange light in the wavelength range of 455-490nm, and the crystal color is blue. 16 atoms / cm 3 <P-type element impurity content≤5E 16 atoms / cm 3 , the crystal color is light blue; 5E 16 atoms / cm 3 <P-type element impurity content≤1E 19 atoms / cm 3 , the crystal color is royal blue or medium blue; the P-type element impurity content in the substrate is >1E 19 atoms / cm 3 , the crystal color is dark blue.

[0034] Specifically, the method for preparing the P-type silicon carbide crystal comprises the following steps:

[0035] (1) Vacuum stage: The crystal growth furnace is evacuated to remove impurity gases in the growth chamber, and the vacuum degree is ≤1E -2 pa;

[0036] (2) Temperature and pressure increase stage: After the vacuum stage, carrier gas is introduced into the crystal growth furnace, and the temperature is increased to above 2000°C and the pressure is increased to above 10 mbar;

[0037] (3) Introducing doping sources: Introducing vaporized doping sources and carrier gas into the crystal growth furnace for gas phase doping; furthermore, the concentration of the doping source in the crystal can be controlled by controlling the carrier gas flow rate and the amount of doping source entering.

[0038] (4) Nucleation stage: Controlling the temperature near the seed crystal surface to ≥2000℃ and the pressure to ≥10mbar is beneficial to inhibit two-dimensional nucleation and improve the crystal quality;

[0039] (5) Depressurization growth stage: Control the pressure to ≤10 mbar and the temperature ≥2100°C to obtain P-type silicon carbide crystals.

[0040] The above preparation method is applicable to silicon carbide crystal types such as 4H, 6H, 15R, and 3C. The doping source can be a compound containing Al or B. For example, the doping source can be one of trimethylaluminum, trimethylboron, aluminum chloride, or boron chloride.

[0041] Furthermore, the P-type silicon carbide crystal growth device includes a gas supply unit that provides a dopant source to the crystal growth chamber of the crystal growth furnace. The gas supply unit includes at least one carrier gas channel and at least one dopant source gas channel. The carrier gas channel is provided with a carrier gas source, a carrier gas flow monitoring unit and a carrier gas switch that controls the on-off of the carrier gas channel. The dopant source gas channel is provided with a dopant source, a dopant source flow monitoring unit, a dopant source switch that controls the on-off of the dopant source gas channel, and a dopant source gasification unit.

[0042] The carrier gas source is communicated with the crystal growth chamber through the carrier gas channel, the doping source is communicated with the crystal growth chamber through the doping source gas channel, and the doping source gasification device can gasify the doping source.

[0043] The crystal growth furnace unit includes a crucible, an insulation cylinder, a furnace body and a crystal growth chamber; wherein the crucible is placed in the insulation cylinder, the bottom of the crucible is used to place silicon carbide raw materials, and the top of the crucible is used to set seed crystals; the furnace body is used to place the crucible and the insulation cylinder.

[0044] During operation, the carrier gas flow rate and the amount of doping source can be controlled by the carrier gas flow rate monitoring unit and the doping source flow rate monitoring unit to control the number of doping sources that eventually enter the crystal growth chamber, thereby controlling the concentration of the doping source in the crystal.

[0045] Specifically, the vaporization device is an evaporator or a bubbling gas. The furnace body includes an inner cavity and an outer shell. The inner cavity is provided with a quartz tube, and the outer shell is provided with an induction coil. This device ensures that the dopant source continuously enters the crystal growth chamber, maintaining a stable dopant source concentration within the chamber during crystal growth, and significantly improving the uniformity of the crystal's axial dopant concentration.

[0046] Examples 2-4

[0047] Based on the first exemplary embodiment, with reference to FIG1 , FIG1 shows a schematic structural diagram of a P-type silicon carbide crystal growth device, the P-type silicon carbide crystal growth device includes:

[0048] The crystal growth furnace unit includes a crucible 7, an insulation tube 4, a furnace body, and a crystal growth chamber 5. The crucible 7 is placed inside the insulation tube 4, with the bottom of the crucible 7 used to hold silicon carbide powder and the top of the crucible 7 used to hold seed crystals 6. The interior of the furnace body is used to hold the crucible 7 and the insulation tube 4. The furnace body includes an inner cavity and an outer shell 1. The inner cavity is provided with a quartz tube 3, and the outer shell is provided with an induction coil 2.

[0049] A gas supply unit for providing a dopant source to the crystal growth chamber of a crystal growth furnace includes a carrier gas channel and a dopant source gas channel. The carrier gas channel and the dopant source gas channel merge into one gas channel near the crystal growth chamber. The carrier gas channel is provided with a carrier gas source 10, a carrier gas flow monitoring unit, and a carrier gas switch for controlling the on / off of the carrier gas channel. The carrier gas switches include carrier gas switch 1#13 and carrier gas switch 2#14. The dopant source gas channel is provided with a dopant source 9, a dopant source flow monitoring unit, a dopant source switch for controlling the on / off of the dopant source channel, and an evaporator 8. Specifically, the dopant source switch includes dopant source switch 1#12 and dopant source switch 2#11.

[0050] Specifically, the method for preparing the P-type silicon carbide crystal comprises the following steps:

[0051] (1) Vacuum stage: The crystal growth furnace is evacuated, and the vacuum degree is ≤1E -2 pa, maintenance time ≥1h;

[0052] (2) Temperature and pressure rise stage: After the vacuum stage, open the carrier gas switch 1#13, introduce the carrier gas into the crystal growth furnace, raise the temperature to above 2000℃ and the pressure to above 10mbar, and the pressure rise time is ≥2h;

[0053] (3) Introducing the doping source: Open the carrier gas switch 2#14 and the doping source switch 1#12 to allow the doping source and the carrier gas to enter the evaporator 8, and the doping source is vaporized. Then, open the doping source switch 2#11 to allow the vaporized doping source gas and the carrier gas to enter the crystal growth furnace cavity 5. Observe the doping source flow monitoring unit and the carrier gas flow monitoring unit. By adjusting the size of the doping source switch 2#11, the doping source switch 1#12 and the carrier gas switch 2#14, the amount of the doping source entering the crystal growth furnace cavity can be controlled, thereby controlling the amount of the doping source in the crystal.

[0054] (4) Nucleation stage: control the temperature near the seed crystal surface ≥ 2000℃ and the pressure ≥ 10mbar;

[0055] (5) Depressurization growth stage: Control the pressure to ≤10 mbar and the temperature ≥2100°C to obtain P-type silicon carbide crystals.

[0056] In Examples 2-4, trimethylaluminum was used as a doping source for vapor-phase doping to prepare crystals with different doping levels. The crystal thickness was 20 mm, and the axial distribution of Al content in the prepared crystals was measured using SIMS, as shown in Figures 2, 4, and 7, respectively. The yellow curves in Figures 2, 4, and 7 are graphs showing the axial distribution of Al content in the crystals prepared in this exemplary embodiment, while the blue curves are graphs showing the axial distribution of Al content in the crystals prepared using solid-phase doping.

[0057] The axial resistivity at the same radial position in the prepared crystal was measured, as shown in Figures 3, 5, 6, and 8. The yellow curves in Figures 3, 5, 6, and 8 represent the axial resistivity variation curves for the crystal prepared in this exemplary embodiment, while the blue curves represent the axial resistivity variation curves for the crystal prepared using solid-phase doping.

[0058] The substrate of the P-type silicon carbide crystal prepared in Example 2-4 was etched with KOH to obtain a total dislocation density of ≤1000 / cm 2 , threading dislocation density ≤900 / cm 2 The substrate full width at half maximum (FWHM) was tested using high-resolution XRD rocking curves and was ≤15 arcsec, with an intra-chip FWHM variation of ≤10%, and an axial FWHM variation of ≤5% at the same radial position.

[0059] The hardness of P-type silicon carbide crystal is 9.5 on the Mohs hardness scale.

[0060] The crystal transmittance under visible light is ≥0.6, and the refractive index is between 2.64 and 2.70. Example

[0061] On the basis of Examples 2-4, in this exemplary embodiment, trimethylboron is used as the doping source for gas phase doping and solid phase doping, respectively. SIMS is used to test the axial distribution of B content in the prepared crystal, as shown in Figure 9; the axial resistivity of the prepared crystal is tested, as shown in Figure 10.

[0062] In FIG9 , the yellow curve is a graph showing the axial distribution curve of the B content in the crystals prepared in this exemplary embodiment, and the blue curve is a graph showing the axial distribution curve of the B content in the crystals prepared by solid-phase doping.

[0063] In FIG10 , the yellow curve is a graph showing a change in the axial resistivity of the crystal prepared according to this exemplary embodiment, and the blue curve is a graph showing a change in the axial resistivity of the crystal prepared by solid-phase doping.

[0064] Experimental example

[0065] On the basis of Example 2, the transmittance of the prepared crystal was tested under visible light, as shown in Table 1.

[0066] Table 1 Transmittance test table

[0067]

[0068] As shown in Table 1, the transmittance of the P-type silicon carbide crystal prepared in this embodiment is 0.63-0.65. When solid-phase doping is used, the transmittance of the prepared P-type silicon carbide crystal is 0.57-0.61. It can be seen that gas-phase doping can improve the crystal transmittance and transmittance uniformity.

[0069] The axial resistivity change rate and P-type element impurity change rate at the same radial position were calculated for the crystals prepared in Examples 2-5, and the calculation results are shown in Table 2. The crystals prepared in this application were subjected to a crystal color test at a wavelength of 455-490 nm, and the crystal color test results are shown in Table 2.

[0070] The calculation formula of the change rate in this application is: change rate = (maximum value - minimum value) / maximum value,

[0071] Where "p-type element impurity change rate" = [lg (maximum value) - lg (minimum value)] / lg (maximum value)

[0072] Table 2 Calculation of axial resistivity change rate and P-type element impurity change rate

[0073]

[0074] As shown in Examples 2-5, the maximum resistivity of the crystals prepared by vapor-phase doping in this application is ≤3Ω*cm, the axial resistivity variation at the same radial position is ≤25%, and the P-type element impurity variation is ≤10%. The maximum resistivity of the crystals prepared by solid-phase doping is >6Ω*cm, the axial resistivity variation at the same radial position is >50%, and the P-type element impurity variation is >10%. This shows that the crystals prepared by vapor-phase doping in this application have more uniform doping and axial resistivity.

[0075] The foregoing is merely an embodiment of the present invention and is not intended to limit the present invention. It will be apparent to those skilled in the art that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are intended to be included within the scope of the claims of the present invention.

Claims

1. A P-type silicon carbide crystal, characterized in that: The maximum resistivity of the P-type silicon carbide crystal is ≤3Ω*cm, and the axial resistivity change rate at the same radial position is ≤25%; the P-type element impurity content is ≥1E 17 atoms / cm 3 , the change rate of P-type element impurities is ≤15%.

2. The P-type silicon carbide crystal according to claim 1, characterized in that: The axial resistivity change rate at the same radial position is ≤10%, and the P-type element impurity change rate is ≤10%.

3. The P-type silicon carbide crystal according to claim 1, characterized in that: The half-width at half maximum in the P-type silicon carbide crystal is ≤30 arcsec, the half-width within the slice has a variation rate of ≤30%, and the axial half-width variation rate at the same radial position is ≤20%.

4. The P-type silicon carbide crystal according to claim 3, characterized in that: The half-width at half maximum of the P-type silicon carbide crystal has an intra-chip variation rate of ≤15%, and an axial half-width variation rate at the same radial position of ≤10%.

5. The P-type silicon carbide crystal according to claim 1, characterized in that: The P-type silicon carbide crystal has a thickness of ≤30 mm, a crystal transmittance of ≥0.6 under visible light, and a refractive index of 2.6-2.

8.

6. The P-type silicon carbide crystal according to claim 5, characterized in that: The P-type silicon carbide crystal has a crystal transmittance of ≥0.8 under visible light.

7. The P-type silicon carbide crystal according to claim 1, characterized in that: The total dislocation density of the P-type silicon carbide crystal is ≤3000 / cm 2 , threading dislocation density ≤2500 / cm 2 .

8. The P-type silicon carbide crystal according to claim 1, characterized in that: The hardness of the P-type silicon carbide crystal is not less than 9.5 on the Mohs hardness scale.

9. The P-type silicon carbide crystal according to claim 1, characterized in that: The P-type silicon carbide crystal absorbs orange light in the wavelength range of 455-490 nm, and the crystal color is blue.

10. The P-type silicon carbide crystal according to claim 9, characterized in that: 1E 16 atoms / cm 3 <P-type element impurity content ≤5E 16 atoms / cm 3 , the crystal color is light blue; 5E 16 atoms / cm 3 <P-type element impurity content ≤1E 18 atoms / cm 3 , the crystal color is medium blue or royal blue; the P-type element impurity content is >1E 19 atoms / cm3, the crystal color is dark blue.

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