CN109722712B - Method for uniformly doping SiC single crystal metal impurities - Google Patents
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Abstract
The invention relates to a method for uniformly doping SiC monocrystal metal impurities, which belongs to the technical field of crystal growth and comprises the steps of uniformly mixing SiC powder and a material to be doped, heating at a constant temperature region at high temperature and normal pressure to form a polycrystal SiC block uniformly doped with metals, cutting the polycrystal SiC block into small-volume cubic blocks, uniformly mixing the polycrystal SiC block with the SiC powder, putting the polycrystal SiC block into a graphite crucible for PVT growth to carry out monocrystal growth, obtaining SiC uniformly doped with metal impurities with a set doping concentration according to a conventional monocrystal growth method, and gradually and uniformly releasing the metal impurities in the polycrystal SiC block along with the decomposition of the SiC in the PVT growth so as to achieve the purpose of uniform doping.
Description
Technical Field
The invention relates to a method for uniformly doping SiC monocrystal metal impurities, belonging to the technical field of crystal growth.
Background
As a representative of the third generation semiconductor materials, SiC is a relatively rapidly evolving semiconductor at present. The nature of the material determines the field of application of the material. The SiC material has excellent semiconductor performances of large forbidden bandwidth, high saturated electron speed, high critical breakdown electric field strength, high thermal conductivity and the like, is very suitable for preparing high-temperature, high-frequency and high-power semiconductor devices, and can be used in the fields where semiconductors such as Si and the like cannot be applied. Therefore, the SiC has great application potential in the fields of high temperature, high frequency, high power and radiation resistance. In the field of microelectronic devices, SiC-based P-i-N diodes, heterojunction bipolar transistors, high electron mobility transistors, and the like have been successfully developed, and have been widely used in the fields of aerospace, radar communication, electric vehicles, wireless communication base stations, and the like. In the field of power electronics, devices such as commercialized SiC diodes, SiC JFETs, SiC MOSFETs, and the like are taken as representatives, and great advantages are exerted in the aspects of improving the utilization efficiency of electric energy and realizing the miniaturization of power electronic devices, and SiC power electronic devices will gradually exhibit advantages in the aspects of performance and reducing the system cost in the fields of power transmission systems, power distribution systems, electric vehicles, hybrid vehicles, various industrial motors, photovoltaic inverters, and the like.
As a semiconductor, the conductivity of SiC materials can be controlled by elemental doping. There are different SiC substrate materials of N-type, P-type and semi-insulating type according to different application fields of SiC. At present, the growth technology of the N-type SiC crystal is relatively mature and is commercialized. There are 2-3 suppliers of semi-insulating SiC substrates internationally. Whereas P-type materials are difficult to obtain. The reason for this is that metal impurities such as Al and Ga are used in the growth of P-type SiC single crystal by physical vapor transport. Due to the fact that vapor pressure of the metal Al and Ga doping sources is large, the problems that the doping sources are released in a centralized mode in the crystal growth process, doping is not uniform and the like are easily caused. In order to solve the problem, part of researchers improve the physical vapor transport device to a certain extent, and a gas path pipeline is added at the bottom of the crucible and is used for introducing dopant gas components. The device mainly aims at the problems of Al component doping and high vapor pressure, and achieves the purpose of continuous doping of an Al source. However, in this method, TMAl decomposes to form H, and passivates acceptor atoms. An Al reservoir is added at the bottom of the crucible, a solid Al source is placed, and an Al component enters a growth chamber under the transportation of carrier gas to realize the doping of the crystal. The temperature of the Al reservoir layer is extremely difficult to control, and quantitative doping cannot be realized. In the earlier stage of the subject group, the doping of the transition metal V and the metal Al is realized by using a built-in crucible mode. The method of placing the crucible inside has a certain disadvantage that although the release of impurities is slowly released, the release process is not uniform.
It can be seen that there is still a need for improvements in the current state of the art for metal doping. Therefore, it is very necessary to provide a method for uniformly doping SiC single crystal metal impurities.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a method for uniformly doping SiC single crystal metal impurities.
The technical scheme of the invention is as follows:
a method for uniformly doping SiC single crystal metal impurities comprises the following steps:
(1) uniformly mixing high-purity SiC powder and a material to be doped, and taking the solid solubility of the material to be doped in SiC as the maximum doping metering value of the material to be doped; for example, table 1 lists the solid solubility of several common elements in SiC. Taking Al as an example, the solid solubility of Al is 7.0X 1020cm-3I.e., 9811 ppm. In practice, for example, 1000g of SiC is used as a raw material, and one or more of a metal, an oxide, a carbide, or a silicide containing 9.811g of Al element may be mixed.
TABLE 1 solid solubility of different elements in SiC
(2) After mixing, filling the high-purity sealed graphite crucible with the mixed powder, putting the mixed powder into heating equipment with the temperature of 2000 ℃, and placing the heated equipment in a constant temperature area; sealing the heating equipment, repeatedly pumping and filling, removing residual air in the growth cavity, particularly nitrogen and oxygen in the air, introducing inert gases such as argon and the like as background gases, and keeping the pressure at normal pressure; then heating, preserving heat and then cooling to normal temperature; taking out the formed polycrystalline block with uniform metal doping;
(3) cutting the polycrystalline blocks processed in the step (2) into block-shaped polycrystals, wherein the block-shaped polycrystals are cubic blocks or rectangular blocks and the like;
(4) uniformly mixing the blocky polycrystalline powder and the SiC high-purity powder for growth again, putting the mixture into a graphite crucible for PVT growth to carry out single crystal growth, and obtaining the SiC uniformly doped with metal impurities with the set doping concentration by a conventional single crystal growth method.
The mixing ratio is consistent with the doping target, taking Al doping as an example, the Al doping concentration is to be 7.0 × 1018cm-3Selecting 7.0X 10 Al-containing20cm-310g of polycrystalline material was mixed with 1000g of SiC powder. Through this stepThe mixing step can achieve the purpose of uniform doping and can also effectively dilute the doping amount.
Preferably, in step (1), the material to be doped is one or more of a metal, an oxide, a carbide or a silicide, so as not to introduce other impurities.
Further preferably, in the step (1), the mixing manner includes ball milling or stirring to achieve uniform mixing.
Preferably, in step (2), argon is introduced as the inert gas as the background gas.
More preferably, in the step (2), after introducing the argon gas, the temperature is raised to 1800 ℃ and 2500 ℃, and the temperature raising time is 10 minutes to 48 hours.
Preferably, in the step (2), the temperature is raised, kept for 2-48h and then cooled to the normal temperature at the cooling speed of 2-50 ℃/min.
Preferably, in step (3), the cube sizes are in the range of 1 x 1 to 10 x 10 in mm3。
The principle of the invention is as follows:
the constant temperature zone is heated at high temperature and normal pressure to ensure that metal impurities can be uniformly doped into the SiC powder and form a polycrystalline SiC block body uniformly doped with metal, the polycrystalline SiC containing metal blocks is used as a doping source to be mixed into the SiC powder for growth, and the metal impurities in the SiC polycrystalline block obtained by the method can be gradually and uniformly released along with the decomposition of SiC in the PVT growth process, so that the purpose of uniform doping is achieved.
Different crystal materials have different growth modes, for example, sapphire growth adopts a guided mode growth method, namely, a solid is changed into a solution in the growth process of raw materials, and seed crystals are contacted with the solution. In the gas phase growth method adopted by the SiC of the application, the raw material is changed from solid to gas during growth, and the seed crystal is not contacted with the raw material. The vapor pressure of the metal Al and Ga doping sources is large, so that the problems of concentrated release, uneven doping and the like of the doping sources in the crystal growth process are easily caused. Therefore, the problem of slow release of the metal elements is mainly considered in the application, and the steps of high-temperature treatment and placing the mixture into powder after cutting are needed besides the step of mixing and briquetting, so that the uniform doping is ensured.
The invention has the beneficial effects that:
1. the technical scheme of the invention can realize uniform and controllable doping of metal impurities and can carry out common doping of a plurality of metals.
2. The technical scheme of the invention has low requirements on SiC single crystal equipment and does not need to be modified. The growth can be completed on the basis of the original mature PVT growth.
3. The method does not introduce other impurities and has high repeatability.
Drawings
FIG. 1 is a schematic view showing the structure of a growth chamber for growing a SiC crystal by a Physical Vapor Transport (PVT) method in example 1;
FIG. 2 is the SIMS test results for Al doping;
FIG. 3 is the results of SIMS testing of B doping;
wherein: 1. a graphite fiber heat-insulating layer, 2, seed crystals, 3, a crucible, 4 and source material powder.
Detailed Description
The present invention will be further illustrated by the following examples, but the present invention is not limited to the following examples.
As shown in fig. 1-3.
Example 1:
a method for uniformly doping SiC single crystal metal impurities comprises the following steps:
(1) uniformly mixing high-purity SiC powder and a material to be doped, wherein the mixing mode comprises ball milling or stirring, and the solid solubility of the material to be doped in SiC is taken as the maximum doping metering value of the material to be doped; the material to be doped is one or more of metal, oxide, carbide or silicide so as to avoid introducing other impurities.
(2) After mixing, filling the high-purity sealed graphite crucible with the mixed powder, putting the mixed powder into heating equipment with the temperature of 2000 ℃, and placing the heated equipment in a constant temperature area; after the heating equipment is closed, the residual air in the growth cavity, especially nitrogen and oxygen in the air, is removed after repeated pumping and filling, inert gases such as argon are introduced as background gases, and the pressure is kept at normal pressure. Then the temperature is raised to 1800 ℃ for 10 minutes. After heating up, preserving heat for 2h, and then cooling to normal temperature at the cooling speed of 2 ℃/min; and taking out the formed polycrystalline block with uniform metal doping.
(3) And (3) cutting the polycrystalline blocks processed in the step (2) into block-shaped polycrystalline, wherein the block-shaped polycrystalline is cubic.
(4) Uniformly mixing the blocky polycrystalline powder and the SiC high-purity powder for growth again, putting the mixture into a graphite crucible for PVT growth to carry out single crystal growth, and obtaining the SiC uniformly doped with metal impurities with the set doping concentration by a conventional single crystal growth method.
Example 2:
a method for uniformly doping SiC single crystal metal impurities comprises the following steps of example 1, except that in the step (2), argon gas is introduced, and then the temperature is raised to 2500 ℃ for 48 hours.
Example 3:
a method for uniformly doping SiC single crystal metal impurities comprises the steps of example 1, wherein in the step (2), the temperature is raised, then the temperature is kept for 48 hours, and then the temperature is reduced to the normal temperature at the speed of 50 ℃/min.
Example 4:
a method for uniformly doping SiC single crystal metal impurities comprises the steps of example 1, wherein in the step (2), the temperature is raised, then the temperature is kept for 24 hours, and then the temperature is reduced to the normal temperature at the speed of 30 ℃/min.
Experimental example 1:
a method for uniformly doping SiC single crystal metal impurities comprises the following steps:
(1) selecting Al with the purity of 5N2O3As a doping source, 18.53g of Al was weighed2O3(9.811 g of Al element) and 1000g of high-purity SiC powder were mixed in a ball mill for 10 hours.
(2) And (3) after mixing, putting the powder treated in the step (1) into a high-purity sealed graphite crucible with the length of 180mm and the diameter of 300 mm. And selecting heating equipment with a constant temperature area of 20cm and capable of heating to 2000 ℃, and placing the high-purity sealed graphite crucible in the constant temperature area. And (4) sealing the heating equipment, repeatedly pumping and filling, removing residual air in the growth cavity, introducing argon as background gas, and keeping the pressure at normal pressure. Meanwhile, the temperature is raised to 2000 ℃ within 20 minutes, the temperature is kept for 2 hours, and then the temperature is rapidly reduced to the normal temperature, wherein the temperature reduction speed is more than 15 ℃/min. And taking out the formed polycrystalline block with uniform metal doping.
(3) Cutting the polycrystalline block treated in the step (2) into 5 x 5mm by using a diamond cutting line3The cubic block of (1).
(4) And (4) uniformly placing the 20g of blocky SiC polycrystalline blocks processed in the step (3) into 1000g of SiC powder, uniformly mixing again, placing into a graphite crucible for PVT growth, and performing SiC single crystal growth by adopting a PVT method. SiC uniformly doped with metal impurities at a given doping concentration is obtained.
After the growth was completed, electrical properties and SIMS measurements were performed, and the results are shown in FIG. 2. As can be seen from FIG. 2, the scheme of the present invention achieved 1.67X 1019cm-3The Al element is uniformly doped.
Experimental example 2:
a method for uniformly doping SiC single crystal metal impurities comprises the following steps:
(1) selecting B with the purity of 5N4C is used as a doping source, 0.362g (the content of B is 0.285g) and 1000g of high-purity SiC powder are weighed and put into a ball mill to be mixed for 12 hours.
(2) And (3) after mixing, putting the powder treated in the step (1) into a high-purity sealed graphite crucible with the length of 180mm and the diameter of 300 mm. And selecting heating equipment with a constant temperature area of 20cm and capable of heating to 2000 ℃, and placing the high-purity sealed graphite crucible in the constant temperature area. And (4) sealing the heating equipment, repeatedly pumping and filling, removing residual air in the growth cavity, introducing argon as background gas, and keeping the pressure at normal pressure. Meanwhile, the temperature is raised to 2300 ℃ within 2h, and is rapidly lowered to the normal temperature after being kept for 2h, wherein the cooling speed is higher than 15 ℃/min. And taking out the formed polycrystalline block with uniform metal doping.
(3) Cutting the polycrystalline block treated in the step (2) into 10 x 10mm by using a diamond cutting line3And (4) the square blocks are cleaned.
(4) And (4) uniformly placing 100g of the SiC polycrystalline blocks treated in the step (3) into 1000g of SiC powder, mixing again, placing into a graphite crucible for PVT growth, and carrying out SiC single crystal growth by adopting a PVT method. SiC uniformly doped with metal impurities at a given doping concentration is obtained. After the growth, the electrical properties and SIMS measurements were performed, and the results are shown in fig. 3, thereby achieving uniform doping of B element.
Claims (5)
1. A method for uniformly doping SiC single crystal, comprising the steps of:
(1) uniformly mixing SiC powder and a material to be doped, wherein the material to be doped is one or more of metal, oxide, carbide or silicide, and the solid solubility of the material to be doped in SiC is taken as the maximum doping metering value of the material to be doped;
(2) after mixing, filling the high-purity sealed graphite crucible with the mixed powder, putting the mixed powder into heating equipment, and placing the heated graphite crucible in a constant temperature area; sealing the heating equipment, repeatedly pumping and filling to remove residual air in the growth cavity, introducing inert gas as background gas, and keeping the pressure at normal pressure; then heating, preserving heat and then cooling to normal temperature; taking out the formed polycrystalline block with uniform metal doping;
(3) cutting the polycrystalline blocks processed in the step (2) into block-shaped polycrystals, wherein the block-shaped polycrystals are cubic blocks or rectangular blocks;
(4) uniformly mixing the blocky polycrystalline powder and the SiC high-purity powder for growth again, putting the mixture into a graphite crucible for PVT growth to carry out single crystal growth, and obtaining the SiC uniformly doped with metal impurities with the set doping concentration according to a conventional single crystal growth method.
2. The method for uniformly doping an SiC single crystal according to claim 1, wherein in the step (1), the mixing means includes ball milling or stirring.
3. The method of uniformly doping an SiC single crystal according to claim 1, wherein in the step (2), the inert gas introduced as the background gas is argon gas.
4. The method of uniformly doping an SiC single crystal as defined in claim 3, wherein in the step (2), after introducing argon gas, the temperature is raised to 1800-2500 ℃ for 10 minutes to 48 hours.
5. The method for uniformly doping the SiC single crystal according to claim 4, wherein in the step (2), the temperature is raised and then kept for 2 to 48 hours, and then the temperature is reduced to the normal temperature at a speed of 2 to 50 ℃/min.
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| CN113026093B (en) * | 2019-12-25 | 2022-08-12 | 北京天科合达半导体股份有限公司 | Semi-insulating silicon carbide wafer with uniform resistivity and preparation method thereof |
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| WO2022000997A1 (en) * | 2020-06-30 | 2022-01-06 | 山东天岳先进科技股份有限公司 | Rare earth element-doped silicon carbide powder |
| DE102021113354A1 (en) | 2021-05-21 | 2022-11-24 | TRUMPF Hüttinger GmbH + Co. KG | Inductor assembly, induction heating assembly and method of induction heating |
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