CN116397320A - Growth method of doped silicon carbide crystal - Google Patents
Growth method of doped silicon carbide crystal Download PDFInfo
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- CN116397320A CN116397320A CN202310450107.5A CN202310450107A CN116397320A CN 116397320 A CN116397320 A CN 116397320A CN 202310450107 A CN202310450107 A CN 202310450107A CN 116397320 A CN116397320 A CN 116397320A
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- 229910010271 silicon carbide Inorganic materials 0.000 title claims abstract description 69
- 238000000034 method Methods 0.000 title claims abstract description 37
- QJGQUHMNIGDVPM-UHFFFAOYSA-N nitrogen group Chemical group [N] QJGQUHMNIGDVPM-UHFFFAOYSA-N 0.000 claims abstract description 88
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- 238000010438 heat treatment Methods 0.000 claims abstract description 36
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 27
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- 150000002500 ions Chemical class 0.000 claims description 3
- 239000000758 substrate Substances 0.000 description 14
- 238000006243 chemical reaction Methods 0.000 description 13
- 229910052786 argon Inorganic materials 0.000 description 11
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 10
- 239000010410 layer Substances 0.000 description 10
- 125000004429 atom Chemical group 0.000 description 7
- 229910052739 hydrogen Inorganic materials 0.000 description 7
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- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
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- 229910052734 helium Inorganic materials 0.000 description 1
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- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 description 1
- 238000009413 insulation Methods 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B23/00—Single-crystal growth by condensing evaporated or sublimed materials
- C30B23/002—Controlling or regulating
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B23/00—Single-crystal growth by condensing evaporated or sublimed materials
- C30B23/002—Controlling or regulating
- C30B23/005—Controlling or regulating flux or flow of depositing species or vapour
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/10—Inorganic compounds or compositions
- C30B29/36—Carbides
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B30/00—Production of single crystals or homogeneous polycrystalline material with defined structure characterised by the action of electric or magnetic fields, wave energy or other specific physical conditions
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
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Abstract
The invention discloses a growth method of doped silicon carbide crystals, which comprises the following steps: providing a growth crucible for placing a silicon carbide feedstock and a seed crystal; providing a crystal growth apparatus comprising a plurality of gas lines and a microwave plasma generating unit; heating the growth crucible to a first preset temperature at a first preset pressure; maintaining the growth crucible at a second preset pressure and heating to a second preset temperature; maintaining the temperature unchanged, reducing the pressure to a third preset pressure, and introducing nitrogen-containing gas at a first flow rate; reducing the pressure to a fourth preset pressure, continuously introducing nitrogen-containing gas at a first flow rate, heating the nitrogen-containing plasma source to a preset temperature, starting the microwave plasma generation unit, and introducing the nitrogen-containing plasma source at a second flow rate; the first specific speed adjusts the nitrogen-containing gas flow rate to a third flow rate, and the second specific speed adjusts the nitrogen-containing plasma source flow rate to a fourth flow rate. By the method for growing the doped silicon carbide crystal, the yield and the property of the doped silicon carbide crystal are improved.
Description
Technical Field
The invention relates to the field of silicon carbide synthesis, in particular to a growth method of doped silicon carbide crystals.
Background
With the demand for semiconductor device development, 6-inch silicon carbide is inevitably developed in a thicker direction. Generally, methods for growing SiC single crystals mainly include physical vapor transport (physical vapor transportmethod, PVT), high-temperature chemical vapor deposition, and solution methods. PVT method is basically the standard method for SiC single crystal growth due to higher growth rate, more stable growth process and cost advantage. The growth process of the PVT method is mainly summarized as that polycrystalline SiC sublimates under the conditions of high temperature and low pressure, and generated gas phase components reach a seed crystal at a lower temperature under the driving of a temperature gradient to generate supersaturation degree so as to continuously crystallize and grow single crystals on the seed crystal.
However, silicon carbide has different requirements in the design of semiconductor devices, and the prepared substrate can be classified into semi-insulating type and conductive type. And conductive type silicon carbide substrates can be classified into N-type and P-type according to the doping element used. The doping element commonly used in the N-type silicon carbide substrate is nitrogen, and the doping mode is to add nitrogen with a certain partial pressure into the atmosphere in the crystal growth process, and replace carbon atoms on the crystal lattice with nitrogen atoms. When the PVT method is adopted to promote the growth of the crystal, when the heating device is arranged on the periphery of the crucible, a temperature gradient is formed, wherein the inner diameter of the crucible gradually decreases from outside to inside, and when the temperature measuring hole is arranged above the crucible and used for radiating heat, a temperature gradient is formed, wherein the inner diameter of the crucible gradually decreases from top to bottom. Therefore, the nitrogen doping amount in the silicon carbide crystal is influenced by the temperature, the radial temperature gradient and the axial temperature gradient, and the quality of the formed N-type silicon carbide crystal is low.
Disclosure of Invention
In view of the above-described drawbacks of the prior art, an object of the present invention is to provide a method for growing doped silicon carbide crystals, which improves the doping uniformity of the doped silicon carbide crystals and improves the yield and quality of the doped silicon carbide crystals.
In order to achieve the above object and other related objects, the present invention adopts the following technical scheme.
The invention provides a growth method of doped silicon carbide crystals, which comprises the following steps:
providing a growth crucible, wherein a silicon carbide raw material is placed in the growth crucible, and a silicon carbide seed crystal is placed at the top of the growth crucible;
providing a crystal growth apparatus, the growth crucible being disposed within the crystal growth apparatus, the crystal growth apparatus comprising a plurality of gas lines and a microwave plasma generating unit;
setting the pressure of the growth crucible as a first preset pressure, and heating to a first preset temperature;
introducing nitrogen-free gas into the growth crucible to maintain the pressure of the growth crucible at a second preset pressure, and heating to a second preset temperature;
maintaining the temperature unchanged, and when the pressure is reduced to a third preset pressure, introducing nitrogen-containing gas into the growth crucible at a first flow rate;
maintaining the temperature unchanged, reducing the pressure by a fourth preset pressure, continuously introducing nitrogen-containing gas at a first flow rate, heating a nitrogen-containing plasma source to a preset temperature, starting a microwave plasma generation unit, and introducing the nitrogen-containing plasma source at a second flow rate;
and adjusting the flow rate of the nitrogen-containing gas to a third flow rate at a first specific speed, and adjusting the flow rate of the nitrogen-containing plasma source to a fourth flow rate at a second specific speed, so that the crystal growth interface obtains a specific doping concentration, and the silicon carbide single crystal is obtained.
In an embodiment of the present invention, the first preset pressure is 1×10 -3 mbar～1×10 -6 The second preset pressure is 300 mbar-800 mbar, the third preset pressure is 1 mbar-100 mbar, and the fourth preset pressure is 0.5 mbar-30 mbar.
In an embodiment of the present invention, the first preset temperature is 900 ℃ to 1200 ℃, and the second preset temperature is 2100 ℃ to 2400 ℃.
In one embodiment of the present invention, the predetermined temperature is 400 ℃ to 2000 ℃.
In one embodiment of the present invention, the step of increasing the temperature of the nitrogen-containing plasma source to the predetermined temperature includes:
raising the temperature from room temperature to 400-900 ℃ at a heating rate of 3-8 ℃/min; and
the temperature is increased from 400 ℃ to 900 ℃ to 2000 ℃ at a heating rate of 1 ℃ to 5 ℃ per minute.
In an embodiment of the present invention, the first flow rate is 1 ml/min-10 ml/min, the second flow rate is 0.1 ml/min-10 ml/min, the third flow rate is 0.5 ml/min-6 ml/min, and the fourth flow rate is 2 ml/min-10 ml/min.
In one embodiment of the present invention, the first specific speed is 0.01ml/min/h to 10ml/min/h, and the second specific speed is 0.01ml/min/h to 10ml/min/h. .
In an embodiment of the invention, the output power of the microwave plasma generating unit is 500 w-2500 w.
In an embodiment of the present invention, a difference between the time of introducing the nitrogen-containing gas and the time of introducing the nitrogen-containing plasma source is 0.1h to 100h.
In one embodiment of the invention, the nitrogen-containing gas and the nitrogen-containing plasma source are replaced with a gas and an ion source comprising a nitrogen-containing homogeneous element.
In summary, the present invention provides a method for growing doped silicon carbide crystals, which can perform high-quality doping by introducing nitrogen-containing gas in the initial growth stage of the silicon carbide crystals. The nitrogen-containing plasma source is introduced, the microwave plasma generation unit is started, the nitrogen-containing plasma is heated, and the heating process is controlled, so that the reaction process is prevented from being difficult to control because the heating speed of the plasma is too high, the growth quality of crystals is improved, and the doping uniformity is ensured. The flow of the nitrogen-containing gas and the nitrogen-containing plasma can be controlled, the specific nitrogen doping concentration of the crystal growth interface is ensured to be obtained, and the silicon carbide crystal with the fixed resistivity is obtained. The obtained doped silicon carbide crystal has uniform resistivity distribution, high substrate yield and better consistency.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed for the description of the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a crystal growing apparatus in one embodiment.
FIG. 2 is a schematic flow chart of a method for synthesizing doped silicon carbide according to an embodiment.
FIG. 3 is a graph showing the temperature and time variation of nitrogen-containing plasma in one embodiment.
FIG. 4 is a graph showing the flow rate versus time of nitrogen-containing gas and nitrogen-containing plasma source according to one embodiment.
FIG. 5 is a resistivity profile of a substrate prepared from the doped silicon carbide crystal obtained in example 1.
FIG. 6 is a resistivity profile of a substrate prepared from the doped silicon carbide crystal obtained in comparative example 1.
Description of the reference numerals:
10. growing a crucible; 20. a silicon carbide raw material; 30. seed crystal; 11. a heat preservation layer; 12. a heating element; 13. a microwave plasma generation chamber; 14. a first gas line; 15. a second gas line; 16. and a third gas line.
Detailed Description
Other advantages and effects of the present invention will become apparent to those skilled in the art from the following disclosure, which describes the embodiments of the present invention with reference to specific examples. The invention may be practiced or carried out in other embodiments that depart from the specific details, and the details of the present description may be modified or varied from the spirit and scope of the present invention.
It should be noted that, the illustrations provided in the present embodiment merely illustrate the basic concept of the present invention by way of illustration, and only the components related to the present invention are shown in the drawings and are not drawn according to the number, shape and size of the components in actual implementation, and the form, number and proportion of the components in actual implementation may be arbitrarily changed, and the layout of the components may be more complex.
In the present invention, it should be noted that, as terms such as "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., appear, the indicated orientation or positional relationship is based on that shown in the drawings, only for convenience of description and simplification of the description, and does not indicate or imply that the indicated apparatus or element must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present application. Furthermore, the terms "first," "second," and the like, as used herein, are used for descriptive and distinguishing purposes only and are not to be construed as indicating or implying a relative importance.
Where numerical ranges are provided in the examples, it is understood that unless otherwise stated herein, both endpoints of each numerical range and any number between the two endpoints are significant both in the numerical range. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs and to which this invention belongs, and any method, apparatus, or material of the prior art similar or equivalent to the methods, apparatus, or materials described in the examples of this invention may be used to practice the invention.
Referring to FIG. 1, a method for growing nitrogen doped N-type doped silicon carbide crystals is illustrated in one embodiment of the present invention. A growth crucible 10 is provided, and the growth crucible 10 is, for example, cylindrical, and the size of the growth crucible 10 is not limited in this respect, and may be selected according to the size of the grown crystal. Silicon carbide feedstock 20 is placed in growth crucible 10, seed crystal 30 is placed in growth crucible 10, and for example, on top of growth crucible 10, and the growth conditions of the crystal growth apparatus are set in the placement of growth crucible 10 in the crystal growth apparatus. In the present invention, the nitrogen-containing gas may permeate into the growth crucible from the interface of the growth crucible to participate in crystal growth, or may be provided with an opening (not shown) on the side wall of the growth crucible 10 corresponding to the seed crystal 30, and during crystal growth, the nitrogen-containing gas is convenient to enter the growth crucible 10 to participate in the reaction, which is not particularly limited in the present invention.
Referring to fig. 1, in an embodiment of the present invention, a crystal growth apparatus for silicon carbide crystals includes, but is not limited to, an insulating layer 11, a heating body 12, a microwave plasma generating chamber 13, and a plurality of gas lines. Wherein a growth crucible 10 is placed in an insulating layer 11. In one embodiment of the present invention, a plurality of gas lines are provided at the bottom of the crystal growing apparatus below the growth crucible 10. In this embodiment, the gas lines include, for example, a first gas line 14, a second gas line 15, and a third gas line 16, and the first gas line 14, the second gas line 15, and the third gas line 16 are disposed in parallel for introducing a nitrogen-free gas, a nitrogen-containing gas, and a nitrogen-containing plasma source, respectively. The first gas line 14, the second gas line 15 and the third gas line 16 are communicated with the microwave plasma generation chamber 13, the introduced nitrogen-free gas, nitrogen-containing gas and nitrogen-containing plasma source are collected in the microwave plasma generation chamber 13, the microwave plasma generation chamber 13 is connected with a microwave plasma generation unit (not shown in the figure), the output power of the microwave plasma generation unit is 500W to 2500W, and the plasma gas can be diffused into the growth crucible 10.
Referring to fig. 1, in an embodiment of the present invention, a heating element 12 is located around a growth crucible 10, and the heating element 12 is made of a conductive material, such as a graphene material, to convert electric energy into heat energy, and the heat energy is transferred to the growth crucible 10 for heating to reach a temperature for crystal growth. The insulating layer 11 is provided outside the heating element 12, and the material of the insulating layer 11 is, for example, a heat insulating material, specifically, a graphite heat insulating material for example, for ensuring a high temperature state in the growth crucible 10. The crystal growth apparatus further includes a heating unit (not shown) to heat the plasma. In an embodiment of the present invention, a housing (not shown) is further disposed on the outer side of the heat insulation layer 11, for example, a stainless steel double-layer water-cooled wall, a quartz tube single-layer air-cooled wall, or a quartz tube double-layer water-cooled wall, and other containers suitable for the present invention are also used.
Referring to fig. 1, in an embodiment of the present invention, a method for growing doped silicon carbide crystals is provided, which includes steps S10-S70.
Step S10, providing a growth crucible, placing silicon carbide raw materials in the growth crucible, and placing silicon carbide seed crystals on the top of the growth crucible.
Step S20, providing a crystal growing device, wherein a growing crucible is placed in the crystal growing device, and the crystal growing device comprises a plurality of gas pipelines and a microwave plasma generating unit.
Step S30, setting the pressure of the growth crucible as a first preset pressure, and heating to a first preset temperature.
And S40, introducing nitrogen-free gas into the growth crucible to maintain the pressure of the growth crucible at a second preset pressure, and heating to a second preset temperature.
And S50, maintaining the temperature unchanged, and introducing nitrogen-containing gas into the growth crucible at a first flow rate when the pressure is reduced to a third preset pressure.
Step S60, maintaining the temperature unchanged, reducing the pressure to a fourth preset pressure, continuously introducing nitrogen-containing gas at a first flow rate, heating the nitrogen-containing plasma source to a preset temperature, starting the microwave plasma generation unit, and introducing nitrogen-containing plasma into the growth crucible at a second flow rate.
Step S70, adjusting the flow rate of the nitrogen-containing gas to the third flow rate at the first specific speed, and adjusting the flow rate of the nitrogen-containing plasma source to the fourth flow rate at the second specific speed, so that the crystal growth interface obtains the specific nitrogen doping concentration.
Referring to fig. 1-2, in one embodiment of the present invention, in step S10-step S20, a silicon carbide feedstock 20 is placed in a feedstock chamber, a seed crystal 30 is placed in a growth chamber, and for example, on top of a growth crucible 10 relative to a focusing reaction chamber 20, and then the growth crucible 10 is placed in a crystal growth apparatus. The crystal growing apparatus includes a first gas line 14, a second gas line 15, a third gas line 16, and a microwave plasma generating unit 13.
Referring to fig. 1 to 2, in an embodiment of the present invention, in step S30, the pressure of the growth crucible 10 is set to a first preset pressure, for example, 1×10 -3 mbar～1×10 -6 mbar, heating to a first preset temperature, e.g. 900 DEG C～1200℃。
Referring to fig. 1 to 2, in step S40, after the temperature of the growth crucible 10 is raised to a first preset temperature, nitrogen-free gas is introduced into the growth crucible to maintain the pressure of the growth crucible at a second preset pressure. Wherein the nitrogen-free gas is other gases such as argon, hydrogen and helium, the second preset pressure is 300mbar to 800mbar, and the temperature is raised to the second preset temperature, and the second preset temperature is 2100 ℃ to 2400 ℃ for controlling the growth of silicon carbide crystals. In this embodiment, for example, a mixed gas of hydrogen and argon is introduced, and the flow rate of argon is, for example, 5ml/min to 800ml/min, and the flow rate of hydrogen is, for example, 0.1ml/min to 50ml/min.
Referring to fig. 1 to 2, in step S50, the temperature of the growth crucible 10 is maintained at a second predetermined temperature, and nitrogen-containing gas is introduced into the growth crucible at a first flow rate when the pressure is reduced to a third predetermined pressure. Wherein the third preset pressure is, for example, 1mbar to 100mbar, and the nitrogen-containing gas is, for example, N 2 Or NH 3 Or the like, and the first flow rate is, for example, 1ml/min to 10ml/min. In the early growth stage of the crystal, the nitrogen-containing gas can be doped with high quality.
Referring to fig. 1 to 2, in step S60, the temperature of the growth crucible 10 is kept at the second preset temperature, the pressure is reduced by a fourth preset pressure, and the fourth preset pressure is, for example, 0.5mbar to 30mbar, and the nitrogen-containing gas is continuously introduced into the crucible at the first flow rate. Heating the nitrogen-containing plasma source to a preset temperature, for example, 400-2000 ℃, starting a microwave plasma generation unit, plasmatizing the nitrogen-containing plasma source, and leading the generated nitrogen-containing plasma into the nitrogen-containing plasma source at a second flow rate to participate in crystal growth. In the present embodiment, the nitrogen-containing plasma source is, for example, NH 3 、SiN、(CN) 2 Or HCN, etc., and the second flow rate is, for example, 0.1ml/min to 10ml/min. The invention does not limit the activation time of the nitrogen-containing plasma, and the difference in the on-time of the nitrogen-containing gas and the nitrogen-containing plasma source is, for example, 0.And the plasma activation time can be delayed according to the change condition of the nitrogen doping concentration in the actual growth process for 1-100 h. In other embodiments of the invention, the nitrogen-containing gas and the nitrogen-containing plasma source may be replaced with plasma sources of other elements of the nitrogen-containing homolog.
Referring to fig. 3, in an embodiment of the present invention, if low temperature plasma directly flows from the plasma generating device into the growth crucible, it is difficult to control the reaction process because the temperature of the plasma is too high. In this embodiment, the plasma temperature is raised from the room temperature C0 to the first temperature C1, the first temperature C1 is, for example, 400 ℃ to 900 ℃, and then the second temperature C2 is raised from the first temperature C1, and the second temperature C2 is, for example, 1900 ℃ to 2000 ℃. The initial time T0 represents the time when the plasma starts to be introduced and the first time T1 represents the time when the plasma is raised to the first temperature C1, and at this stage, the temperature raising rate is, for example, 5 ℃/min to 8 ℃/min, and the plasma is maintained at the first temperature C1 for 0.5h to 20h to the second time T2. The third time T3 represents the time for which the plasma is raised from the first temperature C1 to the second temperature C2, and at this stage, the temperature raising rate is, for example, 1 ℃/min to 3 ℃/min, and the plasma is maintained at the second temperature C2 for 0.5h to 20h to a fourth time T4. After the crystal growth is completed, the temperature is reduced, for example, at a rate of 3 ℃ per minute to 5 ℃ per minute, until the fifth time T5 is reduced to room temperature. By heating the plasma and controlling the heating process, the problem that the reaction process is difficult to control due to the fact that the heating speed of the plasma is too high can be prevented, and therefore the growth quality of crystals and the uniformity of N-type doping are improved.
Referring to fig. 1 to 2, in step S70, the temperature of the growth crucible 10 is kept at the second preset temperature, the flow rate of the nitrogen-containing gas is adjusted to the third flow rate at the first specific speed, and the flow rate of the nitrogen-containing plasma source is adjusted to the fourth flow rate at the second specific speed. In this embodiment, the first specific speed is, for example, 0.01ml/min/h to 10ml/min/h, and the second specific speed is, for example, 0.01ml/min/h to 10ml/min/h. The third flow rate is, for example, 0.5ml/min to 6ml/min, and the fourth flow rate is, for example, 2ml/min to 10ml/min, by controlling the nitrogen-containing gas, etcThe flow of the ion source enables the crystal growth interface to obtain specific nitrogen doping concentration, and the silicon carbide crystal with fixed resistivity is obtained. In the present embodiment, the N-type silicon carbide crystal obtained has a nitrogen doping concentration of, for example, 1X 10 9 atoms/cm 3 ～1×10 25 atoms/cm 3 The resistivity is, for example, 0.01Ω·cm to 0.035 Ω·cm, and the difference between the radial and longitudinal resistivity is 0.1mΩ·cm to 25mΩ·cm.
Referring to fig. 2 and 4, in one embodiment of the present invention, the flow rate of the nitrogen-containing gas and the flow rate of the nitrogen-containing plasma source are varied during the crystal growth process as shown in fig. 4. In the process of step S50-step S70, at a third preset pressure, nitrogen-containing gas is introduced into the growth crucible at a first flow rate G1, the first flow rate G1 is maintained, and when the pressure is set to a fourth preset pressure, the time taken for the reaction is T21, and in one embodiment of the present invention, the time taken for the reaction is, for example, 10min to 20min. The introduction of the nitrogen-containing plasma is started, and the nitrogen-containing plasma reaches the second flow rate G2, for example, at time T22. In step S70, the flow rate of the nitrogen-containing gas is adjusted to the third flow rate G3 at the first specific speed, and the flow rate of the nitrogen-containing plasma source is adjusted to the fourth flow rate G4 at the second specific speed. The arrival times T23 of the third flow G3 and the fourth flow G4 may be the same or different, and in this embodiment, the arrival times T23 are the same, for example, and the arrival times T23 are 1.5h to 8h, for example. The flow of the plasma is gradually increased to the maximum of 10ml/min, the free energy of the reaction between the crystal growth interface and N element can be reduced, and simultaneously the flow of the nitrogen-containing gas is gradually reduced to the minimum of 1ml/min, so as to ensure that the nitrogen doping concentration of the interface is maintained at 1X 10 9 atoms/cm 3 ～1×10 25 atoms/cm 3 The quality and the content of N doping can be improved.
Hereinafter, the present invention will be more specifically explained by referring to examples, which should not be construed as limiting. Appropriate modifications may be made within the scope consistent with the gist of the invention, which fall within the technical scope of the invention.
Example 1
Seed crystal and silicon carbide raw materials are filled in the growth crucible, and crystal growth equipment below the growth crucibleThree gas pipelines are arranged on the upper part, and nitrogen-free gas, nitrogen-containing gas and nitrogen-containing plasma sources are respectively introduced into the growth crucible, wherein the nitrogen-free gas comprises Ar and H 2 And Ar and H 2 The flow ratio of (2) is 100:1, and the nitrogen-containing gas is N 2 The nitrogen-containing plasma source is NH 3 . The crystal growth equipment also comprises a microwave plasma generation unit, a heating element, a heat preservation layer and the like.
Placing the growth crucible into a crystal growth apparatus, maintaining the pressure at 5×10 -5 The pressure of the growth crucible is maintained at 800mbar by introducing hydrogen-argon mixed gas into the growth crucible, the flow rate of the hydrogen-argon mixed gas is maintained at 200ml/min, and the temperature is raised to 2320 ℃.
While maintaining the temperature at 2320deg.C, the pressure of the growth crucible was reduced to 35mbar, and simultaneously nitrogen gas was introduced into the growth crucible at 5 ml/min.
Maintaining the temperature at 2320deg.C, reducing the pressure of the growth crucible to 5mbar, introducing nitrogen-containing gas at a flow rate of 5ml/min, and introducing NH 3 Raising the temperature to 800 ℃ at 5 ℃/min, and adding NH at 800 DEG C 3 The flow rate of 1ml/min is led to the microwave plasma reaction cavity, the temperature in the microwave plasma reaction cavity is increased to 2000 ℃ at the same time, and the microwave plasma reaction unit provides 800W microwaves to the microwave plasma reaction cavity.
Maintaining the temperature 2320deg.C and pressure 5mbar for 100 hr, reducing the flow rate of nitrogen gas from 5ml/min to 2ml/min at a rate of 0.03 ml/min/hr, and NH at a rate of 0.01 ml/min/hr 3 The flow rate is increased from 0.3ml/min to 4ml/min, so that the concentration of N element at the crystal growth interface is 1 multiplied by 10 15 atoms/cm 3 The obtained 6 inch N-type silicon carbide crystal has the edge thickness of 25mm, the radial resistivity difference of 5mΩ & cm, the thickness of the crystal which meets the common requirements of 0.01Ω & cm-0.035 Ω & cm in industry of 25mm, the specific resistivity average value is within 0.02-0.025 Ω & cm, the resistivity of the substrate slice processed by the crystal is 0.023 Ω & cm, the radial resistivity difference is 0.2mΩ & cm,
comparative example 1
Seed crystal and silicon carbide raw material are filled in the growth crucible, and crystal below the growth crucible is grownThe long equipment is provided with two gas pipelines, nitrogen-free gas and nitrogen-containing gas are respectively introduced into the growth crucible, and the nitrogen-free gas comprises Ar and H 2 And Ar and H 2 The flow ratio of (2) is 100:1, and the nitrogen-containing gas is N 2 . The crystal growth equipment also comprises a heating body, a heat preservation layer and the like.
Placing the growth crucible into crystal growth equipment, heating to 2320deg.C, maintaining the pressure of the growth crucible at 5mbar, introducing hydrogen-argon mixed gas into the growth crucible, maintaining the flow rate of the hydrogen-argon mixed gas at 200ml/min, and introducing N at a flow rate of 5ml/min 2 Growing for 100h. Obtaining 6 inch N-type silicon carbide crystal, the thickness of the edge of the crystal is 25mm, the radial resistivity difference is 60mΩ & cm, the thickness of the crystal is 10mm which accords with the common requirement of 0.01Ω & cm-0.035 Ω & cm in industry, the resistivity of the substrate slice of crystal processing is 0.018 Ω & cm, the radial resistivity difference is 29mΩ & cm,
referring to fig. 5 to 6, in an embodiment of the present invention, fig. 5 is a resistivity distribution diagram of the doped silicon carbide crystal obtained in example 1 when processed into a substrate, and fig. 6 is a resistivity distribution diagram of the doped silicon carbide crystal obtained in comparative example 1 when processed into a substrate. For example, the resistivity of the substrate is tested by a non-contact vortex method, and the doped silicon carbide crystal obtained by the growth method has uniform resistivity distribution, high substrate yield and better consistency when being used as the substrate of an electronic power device. The silicon carbide crystal growth method provided by the invention can improve the uniformity and yield of the doped silicon carbide crystal and improve the quality of the silicon carbide crystal.
In summary, the present invention provides a method for growing doped silicon carbide crystals, which can perform high-quality doping by introducing nitrogen-containing gas in the initial growth stage of the silicon carbide crystals. After the crystal grows for a preset time, a nitrogen-containing plasma source is introduced, the nitrogen-containing plasma source is heated, and the heating process is controlled, so that the reaction process is prevented from being difficult to control because the heating speed of the plasma is too high, the growth quality of the crystal is improved, and the doping uniformity is ensured. By controlling the flow rates of the nitrogen-containing gas and the nitrogen-containing plasma source, the crystal growth boundary is formedThe surface obtains a specific nitrogen doping concentration to obtain the silicon carbide crystal with fixed resistivity. The N-type silicon carbide crystal obtained has a nitrogen doping concentration of, for example, 1X 10 9 atoms/cm 3 ～1×10 25 atoms/cm 3 The resistivity is, for example, 0.01Ω·cm to 0.035 Ω·cm, the difference between the radial and longitudinal resistivity is 0.1mΩ·cm to 25mΩ·cm, the resistivity is distributed uniformly, the substrate yield is high, and the uniformity is better.
The preferred embodiments of the invention disclosed above are intended only to assist in the explanation of the invention. The preferred embodiments are not exhaustive or to limit the invention to the precise form disclosed. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best understand and utilize the invention. The invention is limited only by the claims and the full scope and equivalents thereof.
Claims (10)
1. A method for growing doped silicon carbide crystals, comprising the steps of:
providing a growth crucible, wherein a silicon carbide raw material is placed in the growth crucible, and a silicon carbide seed crystal is placed at the top of the growth crucible;
providing a crystal growth apparatus, the growth crucible being disposed within the crystal growth apparatus, the crystal growth apparatus comprising a plurality of gas lines and a microwave plasma generating unit;
setting the pressure of the growth crucible as a first preset pressure, and heating to a first preset temperature;
introducing nitrogen-free gas into the growth crucible to maintain the pressure of the growth crucible at a second preset pressure, and heating to a second preset temperature;
maintaining the temperature unchanged, and when the pressure is reduced to a third preset pressure, introducing nitrogen-containing gas into the growth crucible at a first flow rate;
maintaining the temperature unchanged, reducing the pressure by a fourth preset pressure, continuously introducing nitrogen-containing gas at a first flow rate, heating a nitrogen-containing plasma source to a preset temperature, starting a microwave plasma generation unit, and introducing the nitrogen-containing plasma source at a second flow rate;
and adjusting the flow rate of the nitrogen-containing gas to a third flow rate at a first specific speed, and adjusting the flow rate of the nitrogen-containing plasma source to a fourth flow rate at a second specific speed, so that the crystal growth interface obtains a specific doping concentration, and the silicon carbide single crystal is obtained.
2. A method for growing doped silicon carbide crystal according to claim 1, wherein said first preset pressure is 1 x 10 -3 mbar～1×10 -6 The second preset pressure is 300 mbar-800 mbar, the third preset pressure is 1 mbar-100 mbar, and the fourth preset pressure is 0.5 mbar-30 mbar.
3. A method of growing doped silicon carbide crystals according to claim 1 wherein said first predetermined temperature is 900 ℃ to 1200 ℃ and said second predetermined temperature is 2100 ℃ to 2400 ℃.
4. A method of growing doped silicon carbide crystals according to claim 1 wherein said predetermined temperature is from 400 ℃ to 2000 ℃.
5. A method of growing doped silicon carbide crystals in accordance with claim 1 wherein said step of increasing the temperature of said nitrogen-containing plasma source to said predetermined temperature comprises:
raising the temperature from room temperature to 400-900 ℃ at a heating rate of 3-8 ℃/min; and
the temperature is increased from 400 ℃ to 900 ℃ to 2000 ℃ at a heating rate of 1 ℃ to 5 ℃ per minute.
6. The method for growing doped silicon carbide crystal according to claim 1, wherein the first flow rate is 1ml/min to 10ml/min, the second flow rate is 0.1ml/min to 10ml/min, the third flow rate is 0.5ml/min to 6ml/min, and the fourth flow rate is 2ml/min to 10ml/min.
7. A method of growing doped silicon carbide crystals according to claim 1 wherein the first specific speed is from 0.01ml/min/h to 10ml/min/h and the second specific speed is from 0.01ml/min/h to 10ml/min/h.
8. The method for growing a doped silicon carbide crystal according to claim 1, wherein the output power of the microwave plasma generating unit is 500w to 2500w.
9. The method for growing a doped silicon carbide crystal according to claim 1, wherein the time difference between the introduction of the nitrogen-containing gas and the introduction of the nitrogen-containing plasma source is 0.1h to 100h.
10. A method of growing doped silicon carbide crystals according to claim 1 wherein the nitrogen-containing gas and the nitrogen-containing plasma source are replaced with a gas and an ion source comprising a homogeneous element of nitrogen.
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| CN116926670B (en) * | 2023-07-12 | 2024-04-16 | 通威微电子有限公司 | Method for preparing silicon carbide by liquid phase method and prepared silicon carbide |
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