CN115074825B - Silicon carbide epitaxial structure, pulse type growth method and application thereof - Google Patents
Silicon carbide epitaxial structure, pulse type growth method and application thereof Download PDFInfo
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- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 title claims abstract description 120
- 229910010271 silicon carbide Inorganic materials 0.000 title claims abstract description 119
- 230000012010 growth Effects 0.000 title claims abstract description 77
- 238000000034 method Methods 0.000 title claims abstract description 36
- 238000006243 chemical reaction Methods 0.000 claims abstract description 64
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims abstract description 46
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 44
- 239000010703 silicon Substances 0.000 claims abstract description 43
- 239000000758 substrate Substances 0.000 claims abstract description 41
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 40
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 40
- 238000005229 chemical vapour deposition Methods 0.000 claims abstract description 26
- 238000005530 etching Methods 0.000 claims description 33
- 239000007789 gas Substances 0.000 claims description 19
- 238000011065 in-situ storage Methods 0.000 claims description 16
- BLRPTPMANUNPDV-UHFFFAOYSA-N Silane Chemical compound [SiH4] BLRPTPMANUNPDV-UHFFFAOYSA-N 0.000 claims description 13
- 239000012159 carrier gas Substances 0.000 claims description 10
- ATUOYWHBWRKTHZ-UHFFFAOYSA-N Propane Chemical compound CCC ATUOYWHBWRKTHZ-UHFFFAOYSA-N 0.000 claims description 9
- 229910000077 silane Inorganic materials 0.000 claims description 8
- 239000005046 Chlorosilane Substances 0.000 claims description 6
- KOPOQZFJUQMUML-UHFFFAOYSA-N chlorosilane Chemical compound Cl[SiH3] KOPOQZFJUQMUML-UHFFFAOYSA-N 0.000 claims description 6
- 238000010438 heat treatment Methods 0.000 claims description 4
- 239000001294 propane Substances 0.000 claims description 4
- VXEGSRKPIUDPQT-UHFFFAOYSA-N 4-[4-(4-methoxyphenyl)piperazin-1-yl]aniline Chemical compound C1=CC(OC)=CC=C1N1CCN(C=2C=CC(N)=CC=2)CC1 VXEGSRKPIUDPQT-UHFFFAOYSA-N 0.000 claims description 3
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- 239000005977 Ethylene Substances 0.000 claims description 3
- MROCJMGDEKINLD-UHFFFAOYSA-N dichlorosilane Chemical compound Cl[SiH2]Cl MROCJMGDEKINLD-UHFFFAOYSA-N 0.000 claims description 3
- 239000005049 silicon tetrachloride Substances 0.000 claims description 3
- ZDHXKXAHOVTTAH-UHFFFAOYSA-N trichlorosilane Chemical compound Cl[SiH](Cl)Cl ZDHXKXAHOVTTAH-UHFFFAOYSA-N 0.000 claims description 3
- 239000005052 trichlorosilane Substances 0.000 claims description 3
- 239000013078 crystal Substances 0.000 abstract description 3
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 17
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- 229910000041 hydrogen chloride Inorganic materials 0.000 description 15
- 235000012431 wafers Nutrition 0.000 description 12
- 238000004519 manufacturing process Methods 0.000 description 6
- 238000000231 atomic layer deposition Methods 0.000 description 5
- 239000012495 reaction gas Substances 0.000 description 5
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- 230000009286 beneficial effect Effects 0.000 description 4
- 230000000052 comparative effect Effects 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 239000004065 semiconductor Substances 0.000 description 4
- 238000001069 Raman spectroscopy Methods 0.000 description 3
- 125000004432 carbon atom Chemical group C* 0.000 description 3
- 238000004140 cleaning Methods 0.000 description 3
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 2
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 description 2
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 description 2
- 229910052786 argon Inorganic materials 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
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- 238000004943 liquid phase epitaxy Methods 0.000 description 2
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- 238000000137 annealing Methods 0.000 description 1
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- 239000011261 inert gas Substances 0.000 description 1
- 238000005468 ion implantation Methods 0.000 description 1
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- QAOWNCQODCNURD-UHFFFAOYSA-N sulfuric acid Substances OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 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
- C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
- C30B25/02—Epitaxial-layer growth
- C30B25/18—Epitaxial-layer growth characterised by the substrate
- C30B25/20—Epitaxial-layer growth characterised by the substrate the substrate being of the same materials as the epitaxial layer
-
- 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
- C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
- C30B25/02—Epitaxial-layer growth
- C30B25/16—Controlling or regulating
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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
- C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
- C30B25/02—Epitaxial-layer growth
- C30B25/18—Epitaxial-layer growth characterised by the substrate
- C30B25/186—Epitaxial-layer growth characterised by the substrate being specially pre-treated by, e.g. chemical or physical means
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- C—CHEMISTRY; METALLURGY
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- 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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- 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
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Abstract
The invention discloses a silicon carbide epitaxial structure, a pulse type growth method and application thereof, wherein a silicon carbide single crystal wafer containing a silicon carbide epitaxial layer is manufactured on a silicon carbide single crystal substrate by adopting a chemical vapor deposition method, when the growth condition of the silicon carbide epitaxial layer is reached in a growth reaction chamber, a carbon source and a silicon source are introduced into the reaction chamber, and the proportion of the carbon source and the silicon source is alternately changed every interval pulse time in a pulse mode, so that the silicon carbide epitaxial layer is epitaxially grown by adopting a CVD method in the Si-rich atmosphere and the C-rich atmosphere in the adjacent first time period and second time period respectively until the growth of the silicon carbide epitaxial layer is finished. Thereby combining the advantages of the CVD method and the ALD method, and growing the silicon carbide epitaxial structure with good thickness and concentration uniformity.
Description
Technical Field
The invention relates to the field of silicon carbide, in particular to a silicon carbide epitaxial structure, a pulse type growth method and application thereof.
Background
Silicon carbide (SiC) is used as a wide bandgap semiconductor material, has characteristics of high breakdown voltage, high electron mobility, high thermal conductivity and the like, and a semiconductor device manufactured by the silicon carbide (SiC) has the advantages of small volume, low switching loss, higher power density and the like compared with a traditional silicon (Si) base semiconductor device. With the future power system, the requirements of high voltage resistance and low power consumption of power electronic devices and the vigorous development of emerging applications such as electric automobiles, charging piles and the like, the SiC devices start to gradually replace Si-based devices, and huge market potential is shown.
In order to manufacture SiC devices that meet practical application requirements, chemical Vapor Deposition (CVD) is typically used to grow an epitaxially grown SiC film on a SiC substrate. The SiC device is not directly manufactured on the SiC substrate, on one hand, the impurity content of the substrate is higher, and the electrical property is not good enough; on the other hand, the doping difficulty is high, and even if an ion implantation mode is adopted, the subsequent high-temperature annealing is required, so that the doping effect on the epitaxial layer is far less good. Epitaxial growth is therefore critical to the fabrication of SiC devices with doping concentrations and thicknesses that meet design requirements.
Along with the growing clear application prospect of SiC devices, the cost requirements of the industry on the SiC devices are also more and more severe, and the large-diameter SiC epitaxial wafer can effectively reduce the manufacturing cost of subsequent devices, so that the 6-inch SiC epitaxial wafer and even the 8-inch SiC epitaxial wafer are expected. Meanwhile, the application of SiC has the advantages of high-voltage and ultrahigh-voltage devices, and the pressure resistance degree of the SiC devices is in direct proportion to the thickness of an epitaxial layer, so that the SiC thick epitaxial wafer is also a definite trend of industrialized development. However, the increase in the size and thickness of the epitaxial wafer tends to be accompanied by a decrease in uniformity, and how to control the uniformity of the large-sized epitaxial wafer is a key problem to be solved for improving the yield and reliability of SiC devices and further reducing the cost.
Disclosure of Invention
Aiming at the problems that the uniformity of the existing SiC epitaxial wafer is often reduced along with the increase of the size and the thickness, the embodiment of the application provides a silicon carbide epitaxial structure, a pulse growth method and application thereof, which are used for solving the problems mentioned in the background art.
In a first aspect, an embodiment of the present application provides a pulse growth method for a silicon carbide epitaxial structure, including the following steps:
1) Providing a silicon carbide substrate having an off-axis (0001) with an off-angle of several degrees pointing at <11-20 >;
2) And putting the silicon carbide substrate into a reaction chamber, and when the growth condition of the silicon carbide epitaxial layer is reached in the reaction chamber, introducing a carbon source and a silicon source into the reaction chamber, and alternately changing the proportion of the carbon source and the silicon source at intervals in a pulse mode, so that the silicon carbide epitaxial layer is epitaxially grown by adopting a CVD method in the Si-rich atmosphere and the C-rich atmosphere in the adjacent first time period and second time period respectively.
Preferably, the C/Si ratio is greater than or equal to 0.5 and less than 1 in a Si-rich atmosphere, and greater than 1 and less than or equal to 2 in a C-rich atmosphere.
Preferably, in the step 2, the ratio of the carbon source to the silicon source is changed by changing the flow rates of the carbon source and the silicon source introduced into the reaction chamber.
Preferably, the ratio of the carbon source to the silicon source is alternately changed every pulse time in the step 2 by means of pulse, and specifically includes:
maintaining the flow rate of the carbon source unchanged, and changing the flow rate of the silicon source every a period of time; or alternatively
Maintaining the flow rate of the silicon source unchanged, and changing the flow rate of the carbon source every a period of time; or alternatively
The flow rates of the silicon source and the carbon source are alternately changed every interval of time.
Preferably, the silicon source comprises silane and chlorosilane, wherein the silane comprises monosilane, and the chlorosilane comprises trichlorosilane, dichlorosilane or silicon tetrachloride; the carbon source includes ethylene and propane.
Preferably, the reaction chamber comprises the following steps before reaching the growth condition of the silicon carbide epitaxial layer:
vacuumizing the reaction chamber to 10 -4 Torr;
And introducing mixed gas of H 2 and HCl to enable the pressure in the reaction chamber to reach a certain pressure, heating to the temperature required by etching, and controlling the flow of H 2 and HCl to carry out in-situ etching on the silicon carbide substrate so as to remove subsurface loss of the silicon carbide substrate and obtain a regular surface step structure.
Preferably, the pressure in the reaction chamber is 30-150 Torr when the in-situ etching is carried out, the temperature required by the etching is 1650 ℃, the time of the in-situ etching is 30-60 min, and silane with the flow rate of 1-10 mL/min is also introduced.
Preferably, the growth conditions in the step 2 include any one or more of an epitaxial growth temperature, an epitaxial growth pressure, flow rates of a carrier gas and an etching gas, and a flow rate of a doping source, and when the growth conditions of the silicon carbide epitaxial layer are reached in the reaction chamber, the epitaxial growth temperature, the epitaxial growth pressure, the flow rates of the carrier gas and the etching gas are kept unchanged.
Preferably, the pulse time is 1 to 60 minutes.
Preferably, the reaction chamber is one of a horizontal hot wall CVD reaction chamber, a hot wall or warm wall planetary CVD reaction chamber and a vertical hot wall CVD reaction chamber.
Preferably, the silicon carbide substrate comprises a 3-8 inch conductive and semi-insulating silicon carbide substrate, and the off-angle on the silicon carbide substrate is 2-8 degrees along the <11-20> direction.
Preferably, the growth rate of the silicon carbide epitaxial layer is 60-100 mu m/h.
In a second aspect, an embodiment of the present application provides a silicon carbide epitaxial structure, where the silicon carbide epitaxial structure is manufactured by using the pulse growth method of the silicon carbide epitaxial structure.
Preferably, the thickness of the silicon carbide epitaxial layer ranges from 1 to 100 mu m, and the thickness uniformity is more than 97%.
In a third aspect, embodiments of the present application provide an application of a silicon carbide epitaxial structure according to the above in SiC devices.
Compared with the prior art, the invention has the beneficial effects that:
the invention combines the characteristics of higher growth rate of a Chemical Vapor Deposition (CVD) method and better uniformity of an Atomic Layer Deposition (ALD) method, changes the flow of an epitaxial precursor or alternately introduces the epitaxial precursor in different time intervals delta t, and approximately realizes a mode of cyclic growth of one layer of silicon atoms and one layer of carbon atoms at the step of an off-axis SiC substrate, so that the grown SiC epitaxial layer has similar effects as a film grown by utilizing an atomic layer deposition mode, namely, the thickness is precisely controlled, the uniformity is large, the yield and the reliability of SiC devices are improved, the growth speed is higher, the rapid mass production of silicon carbide epitaxial wafers is facilitated, and the production speed is improved.
Drawings
The accompanying drawings are included to provide a further understanding of the embodiments and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments and together with the description serve to explain the principles of the invention. Many of the intended advantages of other embodiments and embodiments will be readily appreciated as they become better understood by reference to the following detailed description.
FIG. 1 is a schematic illustration of a gas flow in process of a pulsed growth process for silicon carbide epitaxial structures according to an embodiment of the present application;
FIG. 2 is a schematic illustration of a gas flow-through process for the growth mode of a silicon carbide epitaxial structure of the comparative example of the present application;
Fig. 3 is a graph showing the raman results of a silicon carbide epitaxial layer of the silicon carbide epitaxial structure of example 1 of the present application.
Detailed Description
The application is described in further detail below with reference to the drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the application and are not limiting of the application. It should be noted that, for convenience of description, only the portions related to the present application are shown in the drawings.
It should be noted that, without conflict, the embodiments of the present application and features of the embodiments may be combined with each other. The application will be described in detail below with reference to the drawings in connection with embodiments.
Epitaxial growth of SiC polytypes of the same type using chemical vapor deposition has been the standard technique for fabricating SiC devices. CVD processes provide better control over the thickness, doping concentration, and uniformity within the available area of the epitaxial layer compared to Liquid Phase Epitaxy (LPE) and sublimation processes, while possessing faster growth rates compared to Molecular Beam Epitaxy (MBE) processes. At present, the main stream of SiC epitaxial growth equipment adopts a hot wall CVD reaction chamber, because compared with a cold wall CVD reaction chamber, the hot wall CVD reaction chamber requires smaller radio frequency power, and the temperature uniformity in the reaction chamber is better, and as for structural design, there are three types of horizontal, vertical and planetary.
The embodiment of the invention provides a pulse growth method of a silicon carbide epitaxial structure, which comprises the following steps of:
(1) A silicon carbide substrate is provided having an off-axis (0001) with an off-angle of several degrees pointing toward <11-20 >. Specifically, a (0001) Si-plane silicon carbide substrate having an off-angle of 2 DEG to 8 DEG along the <11-20> direction is provided, and the silicon carbide substrate includes 3 to 8 inch conductive type and semi-insulating type silicon carbide substrates. The silicon carbide substrate is then subjected to standard cleaning.
(2) The cleaned silicon carbide substrate is placed in a reaction chamber, wherein the reaction chamber is one of a horizontal hot wall CVD reaction chamber, a hot wall or warm wall planetary CVD reaction chamber and a vertical hot wall CVD reaction chamber, in a specific embodiment, the horizontal hot wall CVD reaction chamber is adopted, and the silicon carbide substrate is specifically placed on a susceptor in the hot wall CVD reaction chamber, and the susceptor can have a rotating function or not. And then adjusting the growth conditions, wherein the growth conditions comprise any one or more of epitaxial growth temperature, epitaxial growth pressure, flow rates of carrier gas and etching gas and flow rate of doping source. Firstly, vacuumizing the reaction chamber to 10 -4 Torr; h 2 and HCl mixed gas are introduced to enable the pressure in the reaction chamber to reach a certain pressure and the temperature is raised to the temperature required by etching, wherein H 2 is carrier gas, the hydrogen chloride is etching gas continuously introduced in the whole epitaxial growth process, and the hydrogen chloride and H 2 realize the effect of in-situ etching together, thereby being beneficial to obtaining a clean SiC surface without silicon drops. The flow rate of H 2 is set to be 5-100L/min, and the flow rate of HCl is set to be 5-100 mL/min. And controlling the flow rates of H 2 and HCl to carry out in-situ etching on the silicon carbide substrate so as to remove subsurface loss of the silicon carbide substrate and obtain a regular surface step structure. Specifically, the pressure in the reaction chamber is 30-150 Torr when in-situ etching, the temperature required by etching is 1650 ℃, the time of in-situ etching is 30-60 min, and monosilane with the flow rate of 1-10 mL/min is also introduced. The in-situ etching can effectively control the crystal form of SiC, realize homoepitaxial growth and simultaneously reduce the epitaxial growth temperature.
(3) When the growth conditions of the silicon carbide epitaxial layer are reached in the reaction chamber, the epitaxial growth temperature, the epitaxial growth pressure, and the flow rates of the carrier gas and the etching gas are kept unchanged. And introducing a carbon source and a silicon source into the reaction chamber, alternately changing the proportion of the carbon source and the silicon source every interval pulse time in a pulse mode, and specifically changing the proportion of the carbon source and the silicon source by changing the flow of the carbon source and the silicon source introduced into the reaction chamber, so that the silicon carbide epitaxial layer is epitaxially grown in the Si-rich atmosphere and the C-rich atmosphere in the adjacent first time period and second time period respectively. Specifically, the silicon source comprises silane and chlorosilane, wherein the silane comprises monosilane, and the chlorosilane comprises trichlorosilane, dichlorosilane or silicon tetrachloride; carbon sources include ethylene and propane. The pulse time is 1-60 min, that is, the flow rates of the carbon source and the silicon source introduced into the reaction chamber are changed every 1-60 min. The C/Si ratio is greater than or equal to 0.5 and less than 1 in the Si-rich atmosphere, and greater than 1 and less than or equal to 2 in the C-rich atmosphere.
During epitaxial growth, the silicon source and the carbon source are pulsed, i.e., the flow rates of both are time-varying. According to the general law of compound semiconductor CVD growth, when the SiC substrate surface is in a Si-rich atmosphere, the growth rate is determined by the carbon supply; also in C-rich conditions, the growth rate is mainly determined by the silicon supply. When one of the growth sources is excessive relative to the other, the excessive one is to wait for the other during the growth, and the flow rate of the growth source is controlled to change with time, which is equivalent to the cyclic appearance of the relative excessive condition, and is similar to that in each period of atomic layer deposition, the first reaction gas is chemically adsorbed on the surface of the substrate, then inert gas is purged to discharge non-adsorbed gas molecules or unreacted gas or reaction byproducts, then the second reaction gas is chemically adsorbed on the surface of the substrate, and then purging is performed again, and finally the cycle is repeated. The silicon source or the carbon source which is introduced in a pulse mode is equivalent to the first reaction gas and the second reaction gas of atomic layer deposition, and the silicon atoms and the carbon atoms generated by the decomposition of the silicon source and the carbon source at high temperature are generated through chemical adsorption; then in the case of a relative excess, either a layer of silicon atoms is grown first and then a layer of carbon atoms is grown, or vice versa; and finally, growing a silicon carbide epitaxial layer by layer on the silicon carbide substrate along with the growth time and the continuously-introduced pulse growth source.
In a specific embodiment, the ratio of the carbon source to the silicon source is alternately changed every pulse time in the step 2 in a pulse manner, which specifically includes the following 3 cases:
(1) Keeping the flow of the carbon source unchanged, and changing the flow of the silicon source every interval of time;
(2) Keeping the flow of the silicon source unchanged, and changing the flow of the carbon source every time a period of time;
(3) The flow rates of the silicon source and the carbon source are alternately changed at intervals.
By controlling the flow ratio of the silicon source and the carbon source, namely the C/Si ratio, in a reasonable range, the better surface morphology and lower defect density are obtained.
When the growth of the silicon carbide epitaxial layer is finished, stopping introducing a silicon source, a carbon source and HCl etching gas, and cooling a sample in an H 2 atmosphere; and after the reaction chamber is cooled, vacuumizing again to 10 -4 Torr or repeatedly replacing by using argon, and finally, increasing the pressure of the reaction chamber to the atmospheric pressure, and taking out the silicon carbide epitaxial wafer. In an embodiment of the application, the growth rate of the silicon carbide epitaxial layer is 60-100 μm/h.
The embodiment of the application also provides a silicon carbide epitaxial structure, which is manufactured by adopting the pulse growth method of the silicon carbide epitaxial structure. The thickness range of the silicon carbide epitaxial layer is 1-100 mu m, and the thickness uniformity is more than 97%. The silicon carbide epitaxial structure can be applied to SiC devices.
Example 1
Considering that the variables of the three cases only include the flow of the growth source, the embodiment of the application selects the case (2) as an embodiment to specifically illustrate the application, and the growth flow is shown in fig. 1; however, the present application is not limited to the following examples, but other examples can be easily obtained by changing the variables.
(1) Providing a silicon carbide substrate having an off-axis (0001) of 2-8 degrees off-angle along the <11-20> direction, comprising a 4 inch SiC substrate, performing an RCA standard cleaning process for removing contaminants, damaged layers and oxide layers from the substrate surface, using a solution comprising: concentrated sulfuric acid, ammonia water, concentrated hydrochloric acid, hydrogen peroxide, hydrofluoric acid, absolute ethyl alcohol and acetone; after the cleaning, the wafer is placed on a susceptor and placed in a horizontal hot wall CVD reaction chamber, and then the reaction chamber is evacuated to a vacuum of less than 10 -4 Torr.
(2) Setting the pressure of the reaction chamber to be 30-150 Torr, respectively introducing 5-100L/min H 2 and 5-100 mL/min HCl into the reaction chamber, and starting heating; after the growth temperature of 1650 ℃ is reached in the reaction chamber, introducing SiH 4 from the time t0 at the flow rate of 1-10 mL/min, and starting in-situ etching treatment; at this time, the ratio of SiH 4 to H 2 carrier gas was 10 -2 volume percent; the whole etching process is controlled to be 30-60 minutes.
(3) Starting from the time t1, adjusting the flow of SiH 4 to 10-100 mL/min; simultaneously, 10-100 mL/min of C 3H8 is introduced into the reaction chamber; wherein, the flows of C 3H8 in two adjacent delta t times are different, for example, the flow of C 3H8 in the time of t 1-t 1+ delta t is 20mL/min (expressed as 'high pulse'), and the flow of C 3H8 in the time of t1+ delta t-t 1+2 delta t is 5mL/min (expressed as 'low pulse'), and the flows can be reversed; the high and low pulses of C 3H8 are then repeatedly switched over the remaining growth time until the growth is completed, and the Δt time can be controlled to be within 1 minute to 1 hour.
Considering that the actual situation the switching of the flow is not done instantaneously, but rather like having a falling edge and a rising edge as in fig. 2; therefore, the C/Si ratio in the reaction chamber also varies within a certain range, and according to the flow rate value set as described above, the C/Si ratio of the present embodiment is 0.5 to 2, and the foregoing condition of relative excess can be satisfied, that is, when C 3H8 is in a high pulse, the atmosphere on the surface of the SiC substrate is C-rich, and the C/Si ratio is greater than 1 and less than or equal to 2, that is, the flow rate ratio of C 3H8 to SiH 4 is greater than 1:3 and less than or equal to 2:3, a step of; while when C 3H8 is in low pulse, the Si is rich, the ratio of C/Si is more than or equal to 0.5 and less than 1, namely the flow ratio of C 3H8 to SiH 4 is more than or equal to 1:6 and less than 1:3. Specifically, for example, the flow rate of SiH 4 is maintained at 30mL/min, the flow rate of C 3H8 at high pulse is 20mL/min, C/Si=2 at this time, and the flow rate of C 3H8 at low pulse is 5mL/min, C/Si=0.5 at this time. Meanwhile, in order to avoid graphitization of the surface of the SiC substrate in the first delta t time, a small amount of SiH 4 is introduced in the in-situ etching stage, so that the generation of large steps on the surface can be effectively inhibited, and the situation that the surface roughness and defect density of the SiC epitaxial layer are higher due to the fact that the C/Si ratio is too high can be avoided.
At time t2, the switch of SiH 4、C3H8 and HCl entering the reaction chamber is closed to stop growth. Cooling the reaction chamber in an H 2 flow atmosphere; after the reaction chamber is cooled (at time t 3), the reaction chamber is pumped to high vacuum again or replaced repeatedly by argon, and finally is filled to atmospheric pressure, and the silicon carbide epitaxial wafer is taken out, wherein the Raman results are shown in figure 3, and the Raman diagram comprises an FTA (fiber-to-the-air) mould on a peak value of 203.7cm -1, an FTO mould on a peak value of 776.6cm -1 and a FLO mould on a peak value of 964.3cm -1, and the comparison with a standard map shows that the finally obtained silicon carbide is 4H-SiC with higher purity.
Example 2
Example 2 of the present application differs from example 1 in that a6 inch silicon carbide substrate was provided in step (1).
Comparative example
The application takes a typical CVD epitaxial growth process as shown in figure 2 as a comparative example, and comprises two parts of in-situ etching and main epitaxial growth, wherein the flow rates of carrier gas, etching gas and reaction gas are fixed in the epitaxial growth process, and a silicon source and a carbon source are continuously introduced into a reaction chamber at the same time with constant flow rates, and the application specifically comprises the following steps:
(1) An off-axis (0001) SiC substrate having an off-angle of several degrees directed toward <11-20> was selected, including 2-8 inch conductivity type and semi-insulating SiC substrates, and standard cleaned and then placed on a susceptor in a hot wall CVD reactor.
(2) Vacuumizing the reaction chamber to 10 -4 Torr, then introducing mixed gas of H 2 and HCl at the time t0, and starting heating; h 2 is a carrier gas, and is continuously introduced in the whole epitaxial growth process, HCl is etching gas, and the HCl and H2 realize in-situ etching effect together, so that the clean SiC surface without silicon drops is obtained. The flow rate of H 2 is set to be 5-100L/min, and the flow rate of HCl is set to be 5-100 mL/min.
(3) When the temperature in the reaction chamber reaches the epitaxial growth temperature, the in-situ etching is carried out from t1 to t2, so as to remove subsurface damage of the substrate and obtain a regular surface step structure.
(4) Maintaining the temperature and pressure of the reaction chamber and the flow rate of the H 2/HCl mixed gas constant, and introducing a silicon source and a carbon source, such as monosilane (SiH 4) and propane (C 3H8), at the time t 2; and controlling the flow ratio of the silicon source and the carbon source, namely the ratio of C/Si, in a reasonable range, and epitaxially growing the silicon carbide epitaxial layer by using the fixed flow ratio of the silicon source and the carbon source.
The results of the growth thickness and uniformity of the silicon carbide epitaxial layers of examples 1 and 2 of the present application are shown in table 1.
TABLE 1
As can be seen from table 1, the silicon carbide epitaxial layer grown by the pulse growth method according to the embodiment of the application can achieve larger thickness and higher uniformity in different dimensions, which is beneficial to improving the yield and reliability of SiC devices.
In addition, 10 μm is the most conventional mass-produced thickness in SiC epitaxy. The time required for growing the silicon carbide epitaxial layer by the conventional method in the comparative example was 1 hour, the growth rate was 10 μm/h, and the uniformity was 95%. The growth rate of the silicon carbide epitaxial layer grown by the methods of example 1 and example 2 was 80 μm/h, and the uniformity was 97% or more. Therefore, the method not only has higher uniformity, but also has a faster growth speed, and is beneficial to the rapid mass production of the silicon carbide epitaxial wafer.
While the application has been described with reference to specific embodiments, the scope of the application is not limited thereto, and any changes or substitutions can be easily made by those skilled in the art within the scope of the application disclosed herein, and are intended to be covered by the scope of the application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.
Claims (8)
1. A method for pulsed growth of a silicon carbide epitaxial structure, comprising the steps of:
1) Providing a silicon carbide substrate having an off-axis (0001) with an off-angle of several degrees pointing at <11-20 >;
2) Putting the silicon carbide substrate into a reaction chamber, when the growth condition of the silicon carbide epitaxial layer is reached in the reaction chamber, introducing a carbon source and a silicon source into the reaction chamber, alternately changing the proportion of the carbon source and the silicon source every interval pulse time in a pulse mode, so that the silicon carbide epitaxial layer is epitaxially grown by adopting a CVD method under Si-rich and C-rich atmospheres in adjacent first time periods and second time periods respectively, wherein the C/Si ratio is more than or equal to 0.5 and less than 1 in the Si-rich atmosphere, the C/Si ratio is more than 1 and less than or equal to 2 in the C-rich atmosphere, changing the proportion of the carbon source and the silicon source by changing the flow of the carbon source and the silicon source introduced into the reaction chamber, the pulse time is 1-60 min, and the growth speed of the silicon carbide epitaxial layer is 60-100 mu m/h.
2. The method according to claim 1, wherein the ratio of the carbon source to the silicon source is alternately changed at each pulse time by pulse in the step 2, and the method specifically comprises:
maintaining the flow rate of the carbon source unchanged, and changing the flow rate of the silicon source every a period of time; or alternatively
Maintaining the flow rate of the silicon source unchanged, and changing the flow rate of the carbon source every a period of time; or alternatively
The flow rates of the silicon source and the carbon source are alternately changed every interval of time.
3. The method of claim 1, wherein the silicon source comprises silane and chlorosilane, wherein silane comprises monosilane, and chlorosilane comprises trichlorosilane, dichlorosilane, or silicon tetrachloride; the carbon source includes ethylene and propane.
4. A method of pulsed growth of silicon carbide epitaxial structures in accordance with claim 3, comprising the steps of, prior to reaching growth conditions of the silicon carbide epitaxial layer within the reaction chamber:
vacuumizing the reaction chamber to 10 -4 Torr;
And introducing mixed gas of H 2 and HCl to enable the pressure in the reaction chamber to reach a certain pressure, heating to the temperature required by etching, and controlling the flow of H 2 and HCl to carry out in-situ etching on the silicon carbide substrate so as to remove subsurface loss of the silicon carbide substrate and obtain a regular surface step structure.
5. The method according to claim 4, wherein the pressure in the reaction chamber is 30-150 Torr during the in-situ etching, the temperature required for the etching is 1650 ℃, the time for the in-situ etching is 30-60 min, and silane with a flow rate of 1-10 mL/min is also introduced.
6. The method according to claim 1, wherein the growth conditions in step 2 include at least one of an epitaxial growth temperature, an epitaxial growth pressure, a flow rate of a carrier gas and an etching gas, and a flow rate of a doping source, and the growth conditions of the silicon carbide epitaxial layer are maintained while the epitaxial growth temperature, the epitaxial growth pressure, the flow rate of the carrier gas and the etching gas are maintained.
7. The method of claim 1, wherein the reaction chamber is one of a horizontal hot wall CVD reaction chamber, a hot wall planetary CVD reaction chamber, a warm wall planetary CVD reaction chamber, and a vertical hot wall CVD reaction chamber.
8. The method of claim 1, wherein the silicon carbide substrate comprises a 3-8 inch conductive and semi-insulating silicon carbide substrate, and the off-angle on the silicon carbide substrate is 2-8 ° along the <11-20> direction.
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