US20210125826A1 - Systems and methods for growth of silicon carbide over a layer comprising graphene and/or hexagonal boron nitride and related articles - Google Patents

Systems and methods for growth of silicon carbide over a layer comprising graphene and/or hexagonal boron nitride and related articles Download PDF

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US20210125826A1
US20210125826A1 US17/254,623 US201917254623A US2021125826A1 US 20210125826 A1 US20210125826 A1 US 20210125826A1 US 201917254623 A US201917254623 A US 201917254623A US 2021125826 A1 US2021125826 A1 US 2021125826A1
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substrate
layer
sic
sic film
film
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Rachael L. Myers-Ward
Jeehwan Kim
Kuan Qiao
Wei Kong
David Kurt Gaskill
Takuji Maekawa
Noriyuki Masago
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Rohm Co Ltd
Massachusetts Institute of Technology
US Department of Navy
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Rohm Co Ltd
Massachusetts Institute of Technology
US Department of Navy
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    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
    • C23C16/30—Deposition of compounds, mixtures or solid solutions, e.g. borides, carbides, nitrides
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    • C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
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    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
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    • C30B33/00—After-treatment of single crystals or homogeneous polycrystalline material with defined structure
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Definitions

  • devices are usually fabricated from functional semiconductors, such as compound semiconductors including at least two chemical elements.
  • the lattice constants of these functional semiconductors typically do not match the lattice constants of silicon substrates.
  • lattice constant mismatch between a substrate and an epitaxial layer (epilayer) on the substrate can introduce strain into the epitaxial layer, thereby preventing epitaxial growth of thicker layers without defects. Therefore, non-silicon (non-Si) substrates are usually employed as seeds for epitaxial growth of most functional semiconductors.
  • non-Si substrates with lattice constants matching those of functional materials can be costly and therefore limit the development of non-Si electronic/photonic devices.
  • a layer-transfer technique in which functional device layers are grown on lattice-matched substrates and then removed and transferred to other substrates. The remaining lattice-matched substrates can then be reused to fabricate another device layer, thereby reducing the cost.
  • a layer-transfer method it can be desirable for a layer-transfer method to have the following properties: 1) substrate reusability; 2) a minimal substrate refurbishment step after the layer release; 3) a fast release rate; and 4) precise control of release thickness.
  • chemical lift-off still has several disadvantages.
  • the release rate is slow owing to slow penetration of chemical etchant through the sacrificial layer (e.g., typically a few days to release a single 8-inch wafer).
  • etching residues tend to become surface contamination after release.
  • chemical lift-off has limited reusability owing to the chemical mechanical planarization (CMP) performed after release to recover the roughened substrate surface into an epi-ready surface.
  • CMP chemical mechanical planarization
  • the optical lift-off technique usually uses a high-power laser to irradiate the back of the lattice-matched substrate (e.g., a transparent sapphire or SiC substrate) and selectively heat the device-substrate interface, causing decomposition of the interface and release of the device layer.
  • the lattice-matched substrate e.g., a transparent sapphire or SiC substrate
  • optical lift-off has its own limitations.
  • Controlled spalling can have a higher throughput than optical lift-off.
  • high-stress films also referred to as “stressors”
  • stressors are deposited on the epitaxial film, inducing fracture below the epilayers and resulting in the separation of active materials from the substrate.
  • a Ku shear mode can initiate a crack and a Ki opening mode can allow the propagation of the crack parallel to the interface between the epilayer and the substrate.
  • strain energy sufficient to reach the critical Ki can be provided, leading to fracture of the film/substrate interface. Because the exfoliation occurs via crack propagation, the spalling process can cause rapid release of films.
  • controlled spalling is not mature enough to be used for commercial manufacturing for at least the following reasons.
  • a method comprises forming a silicon carbide (SiC) film over a layer comprising graphene and/or hexagonal boron nitride (hBN) that is over a substrate; wherein at least a portion of the formation of the SiC film occurs in the presence of a gaseous material comprising an inert gas.
  • SiC silicon carbide
  • hBN hexagonal boron nitride
  • FIG. 1A is a schematic illustration of an exemplary article 1000 comprising a substrate 106 and a layer 104 comprising graphene and/or hexagonal boron nitride (hBN), according to one set of embodiments;
  • FIG. 1B is a schematic illustration of an exemplary system 2000 for growth of a silicon carbide (SiC) film 102 over substrate 106 , according to one set of embodiments;
  • FIG. 1C is a schematic illustration of an exemplary system 3000 depicting separation of a silicon carbide film 102 from substrate 106 , according to one set of embodiments;
  • FIG. 1D is a schematic illustration of an exemplary system 4000 comprising a free-standing silicon carbide film 102 removed from a substrate 106 (e.g., by separation as in FIG. 1C ), according to one set of embodiments;
  • FIG. 2A is a Nomarski micrograph of a SiC film grown on what was originally (graphene layer)/SiC, with a ramping to growth temperature conducted in hydrogen (H 2 ) over an on-axis substrate, according to one set of embodiments;
  • FIG. 2B is a Nomarski micrograph of a SiC film grown on what was originally (graphene layer)/SiC, with a ramping to growth temperature conducted in H 2 over a 4° off-axis substrate, according to one set of embodiments;
  • FIG. 3A is a Nomarski micrograph of a SiC film grown by remote epitaxy over an on-axis SiC substrate, with a graphene layer in between the substrate and the growing film, with the SiC film grown for 4 min, according to one set of embodiments;
  • FIG. 3B is a Nomarski micrograph of a SiC film grown by remote epitaxy over an on-axis SiC substrate, with a graphene layer in between the substrate and the growing film, with the SiC film grown for 1 hr, according to one set of embodiments;
  • FIG. 4A is a Nomarski micrograph of a sample ramped in Argon (Ar) and grown in Ar for 10 min and then 30 min in H 2 at 1450° C., according to one set of embodiments;
  • FIG. 4B is a Nomarski micrograph of a sample ramped in Ar and grown in Ar for 1 hr at 1540° C., according to one set of embodiments;
  • FIG. 4C is a Nomarski micrograph of a sample ramped in Ar and grown in Ar for 10 min at 1400° C., according to one set of embodiments;
  • FIG. 4D is a Nomarski micrograph of a sample ramped in Ar and grown in Ar for 10 min at 1540° C., according to one set of embodiments;
  • FIG. 5A is a scanning electron microscopy (SEM) image of surface morphology of a sample grown with growth conditions from FIG. 4A , according to one set of embodiments;
  • FIG. 5B is an in-plane Electron Backscatter Diffraction (EBSD) image of a sample grown with growth conditions from FIG. 4A , according to one set of embodiments;
  • EBSD Electron Backscatter Diffraction
  • FIG. 5C is an out-of-plane EBSD image of a sample grown with growth conditions from FIG. 4A , according to one set of embodiments;
  • FIG. 5D is a SEM image of an exfoliated SiC film sample grown with growth conditions from FIG. 4A , according to one set of embodiments;
  • FIG. 6 is a high resolution transmission electron microscopy (HRTEM) image (top) showing pseudo graphene (see, e.g., bottom reference figure) after SiC film growth by remote epitaxy, according to one set of embodiments;
  • HRTEM transmission electron microscopy
  • FIG. 7A is a SEM image of a sample grown at 1620° C. for 20 min in 50 slm Ar over a 4° off-axis substrate, according to one set of embodiments;
  • FIG. 7B is an EBSD image of a sample grown at 1620° C. for 20 min in 50 slm Ar over a 4° off-axis substrate, according to one set of embodiments;
  • FIG. 7C is a SEM image of a sample grown at 1620° C. for 20 min in 50 slm Ar over a 2° off-axis substrate, according to one set of embodiments;
  • FIG. 7D is an EBSD image of a sample grown at 1620° C. for 20 min in 50 slm Ar over a 2° off-axis substrate, according to one set of embodiments;
  • FIG. 7E is a SEM image of a sample grown at 1620° C. for 20 min in 50 slm Ar over an on-axis substrate, according to one set of embodiments;
  • FIG. 7F is an EBSD image of a sample grown at 1620° C. for 20 min in 50 slm Ar over an on-axis substrate, according to one set of embodiments;
  • FIG. 8A is an X-ray Diffraction (XRD) rocking curve of the (002) and (004) for SiC grown over a 4° off-axis substrate, according to one set of embodiments;
  • XRD X-ray Diffraction
  • FIG. 8B is an XRD reciprocal space map (RSM) of the (004) for SiC grown over a 4° off-axis substrate, according to one set of embodiments;
  • FIG. 8C is an XRD rocking curve of the (002) and (004) for SiC grown over a 2° off-axis substrate, according to one set of embodiments;
  • FIG. 8D is an XRD RSM of the (004) for SiC grown over a 2° off-axis substrate, according to one set of embodiments;
  • FIG. 8E is an XRD rocking curve of the (002) and (004) for SiC grown over an on-axis substrate, according to one set of embodiments;
  • FIG. 8F is an XRD RSM of the (004) for SiC grown over an on-axis substrate, according to one set of embodiments;
  • FIG. 9 is transmission electron microscopy (TEM) images (left and right), and an SEM image (center) corresponding to FIG. 7A , of an SiC film grown by remote epitaxy on a 4° off-axis substrate in Ar at 1620° C., according to one set of embodiments;
  • TEM transmission electron microscopy
  • FIG. 10A is a photograph of an exfoliated SiC film grown by remote epitaxy at 1620° C. in Ar over a 4° off-axis substrate, according to one set of embodiments;
  • FIG. 10B is an SEM image (“sub”, top) of a substrate after exfoliation and an SEM image (“tape”, bottom) of an exfoliated SiC film grown by remote epitaxy at 1620° C. in Ar over a 4° off-axis substrate, according to one set of embodiments;
  • FIG. 10C is a photograph of an exfoliated SiC film grown by remote epitaxy at 1620° C. in Ar over a 2° off-axis substrate, according to one set of embodiments;
  • FIG. 10D is an SEM image (“sub”, top) of a substrate after exfoliation and an SEM image (“tape”, bottom) of an exfoliated SiC film grown by remote epitaxy at 1620° C. in Ar over a 2° off-axis substrate, according to one set of embodiments;
  • FIG. 10E is a photograph of an exfoliated SiC film grown by remote epitaxy at 1620° C. in Ar over an on-axis substrate, according to one set of embodiments;
  • FIG. 10F is an SEM image (“sub”, top) of a substrate after exfoliation and an SEM image (“tape”, bottom) of an exfoliated SiC film grown by remote epitaxy at 1620° C. in Ar over an on-axis substrate, according to one set of embodiments;
  • FIG. 11A - FIG. 11D illustrate a method 100 of fabricating a semiconductor device using a graphene-based and/or hBN-based layer transfer process, according to one set of embodiments.
  • FIG. 12A - FIG. 12F illustrate a method 300 of graphene-based and/or hBN-based layer fabrication and transfer using a stressor layer and tape, according to one set of embodiments.
  • a method comprises forming a silicon carbide (SiC) film over a layer comprising graphene and/or hexagonal boron nitride (hBN) that is over a substrate, wherein at least a portion of the formation of the SiC film occurs in the presence of a gaseous material comprising an inert gas.
  • SiC silicon carbide
  • hBN hexagonal boron nitride
  • carrying out at least a portion of the formation of the silicon carbide film in the presence of an inert gas advantageously prevents or mitigates the etching of the layer (e.g., of the graphene and/or of the hBN) during the at least one portion of the formation of the silicon carbide film, such that the silicon carbide film is formed over the layer rather than directly on the substrate.
  • the layer may advantageously facilitate separation (e.g., mechanical separation) of the silicon carbide film from the substrate after formation of the silicon carbide film.
  • Separation of the silicon carbide film from the substrate may take place, in some embodiments, by first growing a stressor and/or attaching tape over at least a portion of (e.g., all of) an exposed surface of the silicon carbide film, and then mechanically separating the silicon carbide film from the substrate by a force applied to the stressor and/or tape to pull at least a portion of the stressor and/or tape away from the substrate.
  • the term “tape” refers to a film comprising an adhesive that adheres to silicon carbide and/or adheres to a stressor material (e.g., nickel).
  • the separated silicon carbide film may then advantageously be transferred to a second substrate (e.g., comprising a semiconductor, e.g., silicon), e.g., for fabrication of a device comprising the silicon carbide film.
  • layer-transfer processes it may be desirable for methods (e.g., layer-transfer processes) to have at least substrate reusability, minimal need for post-release treatment, a fast release rate, and/or precise control of release interfaces.
  • Conventional layer-transfer processes may exhibit some of the desired properties. For example, layer release may be much faster for mechanical lift-off than for chemical or optical lift-off, whereas the release location may be better controlled in chemical and optical lift-off.
  • conventional layer-transfer methods may suffer from rough surface formation after layer release, thereby limiting substrate reusability. In fact, the process cost to refurbish a substrate surface in conventional layer-transfer methods typically exceeds the substrate cost, so practical applications in manufacturing can be challenging.
  • a method comprises forming a SiC film over a layer comprising graphene and/or hBN, which layer in turn is disposed over a substrate that, in some embodiments, is lattice-matched to the SiC film.
  • the method comprises depositing the layer comprising graphene and/or hBN directly on the substrate (e.g., a lattice-matched substrate).
  • the method comprises transferring the layer comprising graphene and/or hBN to the substrate (e.g., lattice-matched substrate) from another substrate.
  • the method comprises removing the formed SiC film from the substrate (e.g., lattice-matched substrate) via, for example, a stressor attached to the SiC film.
  • a layer comprising graphene and/or hBN serves as a reusable platform for growing SiC films and also serves as a release layer that allows fast, precise, and repeatable release at the graphene surface.
  • a layer-transfer method may have one or more of several advantages.
  • Second, weak interaction of graphene and/or hBN with other materials may substantially relax the lattice mismatching rule for epitaxial growth, facilitating the growth of SiC films with low defect densities.
  • an SiC film grown on a layer comprising graphene and/or hBN may be easily and precisely released from the substrate over which the layer is disposed, owing at least to weak van der Waals interactions of graphene and/or hBN, which may facilitate rapid mechanical release of SiC films grown over the layer without post-release reconditioning of the released surface.
  • robustness of graphene and/or hBN may facilitate reusability of a layer for multiple growth/release cycles.
  • SiC films can be transferred from a layer comprising graphene and/or hBN, for additional flexible functions.
  • a method comprises forming a silicon carbide (SiC) film over a layer comprising graphene and/or hexagonal born nitride (hBN) that is over a substrate.
  • SiC silicon carbide
  • hBN hexagonal born nitride
  • a structure e.g., layer and/or device
  • another structure e.g., layer or substrate
  • an intervening structure e.g., a solid material, air gap, etc.
  • the inert gas comprises (e.g., in an amount of at least 10 at %, 25 at %, 50 at %, 75 at %, 90 at %, 99 at %, or more) Argon (Ar), Helium (He), and/or nitrogen (N 2 ).
  • Ar Ar
  • He Helium
  • N 2 nitrogen
  • inert gas refers to a gas or vapor comprising atoms or molecules that do not chemically react with and/or etch the graphene and/or hexagonal boron nitride.
  • this utilization of inert gas during at least a portion of the formation of the silicon carbide film decreases or prevents etching of a layer over the substrate, such that the at least one portion of the silicon carbide film is formed over the layer.
  • the inert gas consists essentially of Argon, Helium, and/or nitrogen (N 2 ).
  • the inert gas comprises (e.g., in an amount of at least 10 at %, 25 at %, 50 at %, 75 at %, 90 at %, or 99 at %) or consists essentially of Argon (Ar).
  • At least a portion of the duration of the formation of the silicon carbide film occurs in the presence of a gaseous material comprising an inert gas.
  • the gaseous material comprising the inert gas is present for at least 3 minutes, at least 5 minutes, or at least 10 minutes of the formation of the silicon carbide film.
  • the gaseous material comprising the inert gas is present for at most 90 minutes, at most 60 minutes, at most 40 minutes, or at most 20 minutes. Combinations of the above-referenced ranges are also possible (e.g., between or equal to 3 minutes and 90 minutes, between or equal to 5 minutes and 60 minutes, between or equal to 10 minutes and 20 minutes). Other ranges are also possible.
  • the gaseous material comprising the inert gas is present for 3 minutes. In certain embodiments, the gaseous material comprising the inert gas is present for 10 minutes. In certain embodiments, the gaseous material comprising the inert gas is present for 20 minutes. In certain embodiments, the gaseous material comprising the inert gas is present for 60 minutes.
  • the formation of the silicon carbide film involves the introduction of or presence of precursor gases (e.g., silane and propane) to silicon carbide in an environment of a layer comprising graphene and/or hBN over a substrate.
  • precursor gases e.g., silane and propane
  • Methods described herein may involve forming a silicon carbide film over a structure, comprising a layer over a substrate, having a certain architecture.
  • the layer comprising the graphene and/or hexagonal boron nitride is one of a plurality of layers, and forming the SiC film comprises forming the SiC film over (e.g., directly on) the plurality of layers comprising graphene and/or hexagonal boron nitride.
  • the layer comprising the graphene and/or hexagonal boron nitride is the only layer between the SiC film and the substrate.
  • a single layer of graphene is used.
  • a single layer of hexagonal boron nitride is used.
  • a method comprises growing a silicon carbide film over a structure, comprising a layer over a substrate, using a material of the structure as a seed for growth of the silicon carbide film.
  • forming the SiC film on the layer comprises using the substrate as a seed for the SiC film.
  • forming the SiC film on the layer comprises using the layer comprising the graphene and/or hexagonal boron nitride as a seed for the SiC film.
  • forming the SiC film on the layer comprises using a combination of the substrate and the layer comprising the graphene and/or hexagonal boron nitride as a seed for the SiC film.
  • the substrate is made, in whole or in part, of a compound semiconductor.
  • the substrate is made, in whole or in part, of a III-Nitride, which comprises a group III element in the periodic table (e.g., aluminum, gallium) and nitrogen.
  • substrate materials include gallium nitride (GaN), aluminum nitride (AlN), and aluminum gallium nitride (Al x Ga 1 ⁇ x N).
  • the substrate comprises silicon carbide.
  • a surface of the substrate comprises silicon carbide.
  • the surface of the substrate over which the layer is positioned during growth is an SiC surface.
  • a method comprises forming a layer comprising graphene and/or hexagonal boron nitride on a substrate.
  • forming the layer on the substrate comprises growing the layer on the substrate.
  • the substrate is a first substrate, and forming the layer on the first substrate comprises transferring the layer from a second substrate to the first substrate.
  • the layer is directly on the substrate.
  • a method comprises forming a silicon carbide film on a layer comprising graphene and/or hexagonal boron nitride that is on a substrate after forming the layer on the substrate.
  • the method comprises ramping, to a growth temperature, an environment comprising a gaseous material comprising an inert gas, wherein the environment is the environment of a layer comprising graphene and/or hBN over a substrate. In certain embodiments, the ramping occurs before formation of the silicon carbide film. In some embodiments, the method comprises ramping, to a growth temperature, an environment comprising a gaseous material comprising an inert gas, wherein the environment is the environment of a layer comprising graphene and/or hBN over a substrate, with a flow of the gaseous material at a high enough flow rate to decrease, suppress, or eliminate growth of graphene or additional graphene during the ramp.
  • the flow rate of the gaseous material comprising the inert gas during the ramp is greater than or equal to 10 standard liters per minute (slm), greater than or equal to 20 slm, greater than or equal to 30 slm, or greater than or equal to 40 slm. In some embodiments, the flow rate of the gaseous material comprising the inert gas during the ramp is less than or equal to 80 slm, less than or equal to 70 slm, less than or equal to 60 slm, or less than or equal to 50 slm.
  • slm standard liters per minute
  • the flow rate of the gaseous material comprising the inert gas during the ramp is 50 slm. In certain embodiments, the flow rate of the gaseous material comprising the inert gas during the ramp is 30 slm.
  • At least a portion of the formation of the silicon carbide film occurs at a particular growth temperature of the environment of a layer comprising graphene and/or hBN over a substrate. In some embodiments, at least a portion of the formation of the silicon carbide film occurs at a temperature of the environment of at least 1350° C., at least 1400° C., or at least 1500° C. In some embodiments, at least a portion of the formation of the silicon carbide film occurs at a temperature of the environment of at most 1800° C., at most 1620° C., or at most 1540° C. Combinations of the above-referenced ranges are also possible (e.g., between or equal to 1350° C.
  • At least a portion of the formation of the silicon carbide film occurs at a temperature of the environment of 1620° C. In certain embodiments, at least a portion of the formation of the silicon carbide film occurs at a temperature of the environment of 1400° C. In certain embodiments, at least a portion of the formation of the silicon carbide film occurs at a temperature of the environment of 1540° C.
  • a method comprises separating a SiC film from a substrate.
  • the layer comprising the graphene and/or hexagonal boron nitride is used as a release layer.
  • separating the SiC film and the substrate comprises exfoliating the SiC film.
  • the SiC film is a first SiC film, and the method further comprises forming a second SiC film on the substrate after the first SiC film and the substrate have been separated.
  • a method comprises separating a silicon carbide film from a substrate after forming a silicon carbide film on a layer comprising graphene and/or hexagonal boron nitride that is on a substrate. In certain embodiments, the method comprises forming the silicon carbide film on the layer after forming the layer on the substrate.
  • SiC films herein generally comprise at least some crystallinity.
  • the silicon carbide film is crystalline.
  • the SiC film is single-crystalline.
  • the SiC film comprises more than one polytype.
  • the SiC film comprises two polytypes.
  • the SiC film is polycrystalline.
  • a film e.g., SiC film
  • a layer of material ranging from 0.1 nm to 1000 ⁇ m in thickness.
  • the layers between the substrate and the SiC described herein generally comprise graphene and/or hBN.
  • the layer consists essentially of graphene and/or hBN.
  • the layer is a graphene layer.
  • the layer is a hBN layer.
  • the layers between the substrate and the SiC described herein generally comprise at least some crystallinity.
  • the layer is a polycrystalline layer.
  • the layer is a single-crystalline layer.
  • the substrate comprises a semiconductor.
  • the substrate is a semiconductor substrate.
  • the substrate is made, in whole or in part, of SiC.
  • the substrate is made, in whole or in part, of SiC having a certain offcut angle. In some embodiments, the substrate is made, in whole or in part, of SiC having an offcut angle of greater than or equal to 0°, greater than or equal to 2°, or greater than or equal to 4°. In some embodiments, the substrate is made, in whole or in part, of SiC having an offcut angle of less than or equal to 10°, less than or equal to 8°, or less than or equal to 6°. Combinations of the above-referenced ranges are also possible (e.g., between or equal to 0° and 10°, between or equal to 0° and 8°, between or equal to 0° and 4°).
  • the substrate is made, in whole or in part, of 4° off-axis SiC.
  • 4° off-axis silicon carbide corresponds to a 4° offcut angle.
  • the substrate is made, in whole or in part, of 2° off-axis SiC.
  • 2° off-axis silicon carbide corresponds to a 2° offcut angle.
  • the substrate is made, in whole or in part, of on-axis SiC.
  • on-axis silicon carbide corresponds to a 0° offcut angle.
  • Substrates herein generally comprise at least some crystallinity.
  • the substrate is crystalline.
  • the substrate is single-crystalline.
  • FIG. 1A is a schematic illustration of an exemplary article 1000 comprising a substrate 106 and a layer 104 comprising graphene and/or hexagonal boron nitride, according to one set of embodiments.
  • a method comprises forming layer 104 on substrate 106 .
  • a method comprises transferring layer 104 to substrate 106 .
  • FIG. 1B is a schematic illustration of an exemplary system 2000 for growth of a silicon carbide (SiC) film 102 over substrate 106 , according to one set of embodiments.
  • SiC silicon carbide
  • a method comprises forming silicon carbide film 102 over layer 104 comprising graphene and/or hexagonal boron nitride that is over substrate 106 , wherein at least a portion of the formation of silicon carbide film 102 occurs in the presence of a gaseous material 108 comprising an inert gas comprising species 112 , wherein species 112 is an atom or molecule of an inert gas (e.g., helium, argon, nitrogen (N 2 )).
  • gaseous material 108 further comprises gaseous precursors to silicon carbide.
  • substrate 106 comprises silicon carbide.
  • FIG. 1C is a schematic illustration of an exemplary system 3000 depicting separation of silicon carbide film 102 from substrate 106 , according to one set of embodiments.
  • silicon carbide film 102 was formed by a method described with respect to FIG. 1B .
  • a method comprises mechanically separating silicon carbide film 102 from substrate 106 .
  • mechanical separation of silicon carbide film 102 from substrate 106 is accomplished by first growing a stressor (not shown) and/or attaching tape (not shown) to at least a portion of (e.g., all of) an exposed surface of silicon carbide film 102 and then applying a force, directed away from substrate 106 , to at least a portion of the stressor and/or tape.
  • FIG. 1D is a schematic illustration of an exemplary system 4000 comprising a free-standing silicon carbide film 102 removed from substrate 106 (e.g., by separation as in FIG. 1C ), according to one set of embodiments.
  • Free-standing silicon carbide film 102 in some embodiments, may be disposed under a stressor and/or tape. In certain embodiments, free-standing silicon carbide film 102 may be transferred to another substrate, e.g., towards fabrication of a device comprising silicon carbide film 102 .
  • FIG. 11A - FIG. 11D illustrate a method 100 of fabricating a SiC film using graphene and/or hBN as a platform, according to some embodiments.
  • a layer 120 comprising graphene and/or hBN may be fabricated on a first substrate 110 , such as a Si substrate, SiC substrate, or copper foil.
  • layer 120 consists essentially of graphene and/or hBN.
  • Fabricated layer 120 may then be removed from first substrate 110 as shown in FIG. 11B .
  • Removed layer 120 may then be disposed on a second substrate 130 , such as a SiC substrate, as shown in FIG. 11C .
  • FIG. 11A - FIG. 11D illustrate a method 100 of fabricating a SiC film using graphene and/or hBN as a platform, according to some embodiments.
  • a first substrate 110 such as a Si substrate, SiC substrate, or copper foil.
  • layer 120 consists essentially of graphene and/or hBN.
  • a SiC film 140 (e.g., a single crystalline SiC film, advantageous for high electrical and optical device performance) may then be fabricated on layer 120 .
  • An SiC film (e.g., 140) may also be referred to as a device layer or a functional layer in this application.
  • Layer 120 may be fabricated on first substrate 110 via various methods.
  • layer 120 may include an epitaxial graphene with a single-crystalline orientation and/or an epitaxial hBN with a single-crystalline orientation and substrate 110 may include (0001) 4H—SiC (e.g., with a silicon surface) and/or (0001) 6H—SiC (e.g., with a silicon surface).
  • the fabrication of layer 120 may include multistep annealing steps. A first annealing step may be performed in H 2 gas for surface etching and vicinalization, and a second annealing step may be performed in Ar for graphitization at high temperature (e.g., about 1,575° C.).
  • layer 120 may be grown on first substrate 110 via a chemical vapor deposition (CVD) process.
  • substrate 110 may include a nickel substrate or a copper substrate.
  • substrate 110 may include an insulating substrate of SiO 2 , HfO 2 , Al 2 O 3 , Si 3 N 4 , and/or practically any other high temperature compatible planar material by CVD.
  • first substrate 110 may be any substrate that can hold layer 120 and the fabrication may include a mechanical exfoliation process.
  • first substrate 110 may function as a temporary holder for layer 120 .
  • a carrier film may be attached to layer 120 .
  • the carrier film may include a thick film of Poly(methyl methacrylate) (PMMA) or a thermal release tape and the attachment may be achieved via a spin-coating process.
  • PMMA Poly(methyl methacrylate)
  • the carrier film may be dissolved (e.g., in acetone) for further fabrication of SiC film 140 on layer 120 .
  • a stamp layer including an elastomeric material such as polydimethylsiloxane (PDMS) may be attached to layer 120 and first substrate 110 may be etched away, leaving the combination of the stamp layer and layer 120 .
  • the stamp layer may be removed by mechanical detachment, producing a clean surface of layer 120 for further processing.
  • a self-release transfer method may be used to transfer layer 120 to second substrate 130 .
  • a self-release layer may first be spun-cast over layer 120 .
  • An elastomeric stamp may then be placed in conformal contact with the self-release layer.
  • First substrate 110 may be etched away to leave the combination of the stamp layer, the self-release layer, and layer 120 .
  • the stamp layer may be removed mechanically and the self-release layer may be dissolved under mild conditions in a suitable solvent.
  • the release layer may include polystyrene (PS), poly(isobutylene) (PIB), and/or Teflon AF (poly[4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole-co-tetrafluoroethylene]).
  • PS polystyrene
  • PIB poly(isobutylene)
  • Teflon AF poly[4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole-co-tetrafluoroethylene]
  • the lattice of second substrate 130 is matched to SiC film 140 , in which case second substrate 130 functions as the seed for the growth of SiC film 140 if layer 120 is thin enough (e.g., if layer 120 is one layer thick). Sandwiching layer 120 between second substrate 130 and SiC film 140 may facilitate quick and damage-free release and transfer of SiC film 140 .
  • layer 120 may be thick enough (e.g., several layers thick) to function as a seed to grow SiC film 140 , in which case SiC film 140 may be lattice-matched to layer 120 .
  • This example may also facilitate repeated use of second substrate 130 .
  • second substrate 130 together with layer 120 may function as the seed to grow SiC film 140 .
  • Using layer 120 as the seed to fabricate SiC film 140 may also increase the tolerance over mismatch of lattice constant between the SiC film layer 120 .
  • surfaces of graphene and/or hBN typically have no dangling bonds and interact with material above them via weak van der Waals like forces. Due to the weak interaction, a SiC film may grow from the beginning with its own lattice constant forming an interface with a small amount of defects. This kind of growth may be referred to as Van Der Waals Epitaxy (VDWE).
  • VDWE Van Der Waals Epitaxy
  • the lattice matching condition may be drastically relaxed for VDWE, allowing a large variety of different heterostructures even for highly lattice mismatched systems.
  • the lattice mismatch may be about 0% to about 70% (e.g., about 0%, about 10%, about 20%, about 30%, about 40%, about 50%, about 60%, and about 70%, including any values and sub ranges in between).
  • SiC film 140 includes a 2D material system. In another example, SiC film 140 includes a 3D material system. The flexibility to fabricate both 2D and 3D material systems allows fabrication of a wide range of optical, optoelectronic, and photonic devices known in the art.
  • SiC film 140 may be carried out using semiconductor fabrication technique known in the art. For example, low-pressure Chemical Vapor Deposition (CVD) may be used to grow SiC film 140 on layer 120 , which in turn is disposed on second substrate 130 (e.g., a SiC substrate). In this example, layer 120 and second substrate 130 may be baked (e.g., under H 2 for >15 min at >1,100° C.) to clean the surface. Then the deposition of SiC film 140 may be performed.
  • CVD Chemical Vapor Deposition
  • FIG. 12A - FIG. 12F illustrate a method 300 of layer transfer.
  • FIG. 12A shows that a layer 320 comprising graphene and/or hBN is formed or disposed on a donor wafer 310 , which may be a single-crystalline wafer.
  • layer 320 may include epitaxial graphene grown on donor wafer 310 .
  • layer 320 may be exfoliated and transferred to donor wafer 310 from another wafer (not shown).
  • any of the transfer techniques described above with reference to FIG. 11A - FIG. 11D may be used here to prepare layer 320 disposed on donor wafer 310 .
  • FIG. 12B shows that a SiC film 330 may be epitaxially grown on layer 320 .
  • SiC film 330 may include an electronic layer, a photonic layer, or any other functional device layer.
  • Methods to fabricate SiC film 330 may include any methods and techniques described above with respect to FIG. 11A - FIG. 11D .
  • FIG. 12C shows that a stressor 340 may be disposed on SiC film 330 .
  • stressor 340 may include a high-stress metal film such as a Ni film.
  • the Ni stressor may be deposited in an evaporator at a vacuum level of 1 ⁇ 10 ⁇ 5 Torr.
  • FIG. 12D shows that a tape layer 350 may be disposed on stressor 340 for handling stressor 340 .
  • Using tape 350 and stressor 340 may mechanically exfoliate SiC film 330 from layer 320 at a fast release rate by applying high strain energy to the interface between SiC film 330 and layer 320 .
  • the release rate may be fast at least due to the weak van der Waals bonding between graphene and other materials such as SiC film 330 .
  • released SiC film 330 together with stressor 340 and tape layer 350 may be disposed on a host wafer 360 .
  • tape 340 and stressor 340 may be removed, leaving SiC film 330 for further processing such as forming more sophisticated devices or depositing additional materials on SiC film 330 .
  • tape layer 350 and stressor 340 may be etched away by a FeCl 3 -based solution.
  • donor wafer 310 and layer 320 may be reused for a next cycle of SiC film fabrication.
  • layer 320 may also be released.
  • a new layer may be disposed on donor wafer 310 before next cycle of SiC film fabrication.
  • layer 320 may protect donor wafer 310 from damage, thereby allowing multiple uses and reducing cost.
  • CMP chemical-mechanical planarization
  • Graphene-based and/or hBN-based layer transfer may increase reusability because layer transfer may involve an atomically smooth release surface.
  • layer release may occur precisely at the interface between SiC film 330 and layer 320 at least because graphene's and/or hBN's weak van der Waals force would not involve strong bonding to adjacent materials. This may facilitate layer 320 to be reused for multiple growth/exfoliation cycles without the need for a polishing step and without damaging the graphene, due to its mechanical robustness.
  • layer transfer may ensure a fast release rate. Because SiC film 330 may be mechanically released from a weakly bound layer 320 surface, the layer release rate in layer transfer may be high.
  • devices comprising SiC film 330 may have higher electron or hole mobility.
  • An optoelectronic device comprising SiC film 330 may also have an enhanced optical response.
  • the material of stressor 340 may be desirable for the material of stressor 340 to provide enough strain energy to the SiC film 330 /layer 320 interfaces to promote damage-free exfoliation/transfer.
  • One concern for the mechanical release process may be the bending of SiC film 330 during exfoliation and self-exfoliation during deposition of stressor 340 . If the radius of curvature is reduced during exfoliation, strain energy may increase in SiC film 330 . In some embodiments, when the strain energy reaches a critical point, cracks may form. Also, if strain energy in the stressor exceeds the SiC film 330 /layer 320 interface energy, SiC film 330 may be delaminated during stressor deposition. To address this concern, the transfer of SiC film 330 on layers 320 may be performed using feedback loop control.
  • This example generally describes the growth of SiC films, e.g., by remote epitaxy.
  • a purpose of growing SiC films by remote epitaxy was to transfer epitaxially grown SiC films from a (graphene layer)/SiC substrate to a desired substrate.
  • Growing SiC films by remote epitaxy may facilitate making electronic heterostructures which would otherwise be impractical to grow.
  • Growing SiC films by remote epitaxy may also facilitate creating devices at reduced costs by transferring to less expensive substrates or transferring to a material that may provide properties advantageous for a specific device.
  • a SiC film grown by remote epitaxy may be used to create a photonic crystal cavity for quantum sciences, e.g., by transferring a SiC film grown by remote epitaxy to a SiO 2 /Si substrate, resulting in a more easily processed cavity, at least due to working with Si instead of SiC as the substrate.
  • Growing SiC films by remote epitaxy may also facilitate processing of the material compared to SiC processing.
  • One may also use a SiC film grown by remote epitaxy to make power devices at lower cost to the consumer at least because the active region of the device may be still be SiC while the substrate may be Si for example, potentially making a significant impact on cost reduction due at least to reduced cost of the substrate.
  • a SiC film that is grown by remote epitaxy may also have a lower dislocation density and be of higher quality than the substrate, at least because the dislocations may not propagate as readily through a graphene layer (or hexagonal born nitride (hBN) layer) into the SiC film grown by remote epitaxy. Additionally, it may be difficult to grow a SiC film over an on-axis substrate. Using a graphene layer between a SiC substrate and a SiC film grown by remote epitaxy improved the surface morphology, relative to a silicon carbide film grown directly on an on-axis silicon carbide substrate, and resulted in a single crystal SiC film.
  • hBN hexagonal born nitride
  • a carrier gas typically H 2
  • a typical process began by flowing 80 slm H 2 over a substrate with a pressure at 100 mbar. Measurement in standard liters per minute (slm) assumed standard temperature and pressure (60° F. (about 15.56° C.) and 1 atm). Then, the temperature (T) was ramped to the desired growth T (e.g., 1620° C.).
  • silane was the silicon (Si) source and propane was the carbon (C) source.
  • the silane was introduced anywhere from 300 sccm to 2000 sccm with a C/Si ratio of 1.5. Measurement in standard cubic centimeters per minute (sccm) assumed standard temperature and pressure (60° F. (about 15.56° C.) and 1 atm).
  • H 2 was the carrier gas, e.g., to facilitate the propane to crack into the necessary elements for growth.
  • the flows, T, and pressure (P) were maintained during growth for a desired amount of time. After growth, the precursors were turned off and the sample was cooled in H 2 . Again, one reason to have H 2 flowing during the ramp was to prepare the surface of the substrate for growth.
  • a SiC substrate first went through Si sublimation to form a graphene layer.
  • a SiC film was grown on pseudo graphene that had been exfoliated with Ni metal to remove the top layer of graphene and leave the 6 ⁇ 3 ⁇ 6 ⁇ 3 reconstructed SiC.
  • growing on the graphene layer was preferred because this additional step (when using the pseudo graphene) of exfoliating the graphene layer to leave the 6 ⁇ 3 ⁇ 6 ⁇ 3 reconstructed SiC was not needed when growing directly on the graphene layer.
  • growth of a SiC layer was performed.
  • FIG. 2 shows Nomarski micrographs of SiC films grown on what was originally (graphene layer)/SiC, with a ramping to growth temperature conducted in H 2 ( FIG. 2A ) over an on-axis substrate and ( FIG. 2B ) over a 4° off-axis substrate. Exfoliation did not take place because the graphene was etched away during the ramp to growth temperature.
  • FIG. 2A shows the growth over an on-axis substrate (wafer) while FIG. 2B is for growth over 4° off-axis (being c-oriented with angles cut off-axis toward the [11-20] direction) substrate.
  • the morphology was improved for a SiC film grown over an off-cut substrate (e.g., FIG.
  • the on-axis grown SiC film e.g., FIG. 2A
  • the off-axis grown SiC film e.g., FIG. 2B
  • FIG. 3 shows Nomarski micrographs of SiC films grown by remote epitaxy over on-axis SiC substrates, with a graphene layer in between the substrate and the growing film, with SiC films grown ( FIG. 3A ) for 4 min and ( FIG.
  • the exfoliation yield remained between or equal to 40% and 50%.
  • the exfoliation yield advantageously increased further to between or equal to 60% and 70%.
  • SiC films were grown at significantly lower temperatures (in a range of between or equal to 1350° C. and 1500° C.) compared to temperatures (in a range of between or equal to 1500° C. and 1800° C.) for standard growth of SiC, the morphology roughened and polycrystalline material was grown for some cases instead of single crystalline material. An example of this is shown in FIG. 4 , where FIG.
  • FIG. 4A was grown at 1450° C. and FIG. 4B at 1540° C.
  • FIG. 4 shows Nomarski micrographs of samples ramped in Ar and grown in Ar for ( FIG. 4A ) 10 min and then 30 min in H 2 at 1450° C., ( FIG. 4B ) 1 hr at 1540° C. in Ar only, ( FIG. 4C ) 10 min at 1400° C. in Ar only and ( FIG. 4D ) 10 min at 1540° C. in Ar only.
  • the morphology advantageously had a low concentration of grain boundaries when grown at low temperatures for short durations and with low growth rates (1.5 microns/hour ( ⁇ m/hr)) as compared to the samples grown at higher growth rates (2.5 ⁇ m/hr).
  • a growth rate of 1.5 ⁇ m/hr typically corresponded to 312 sccm of 2% silane in H 2 , and 100% propane flowing at a rate corresponding to a typical C:Si ratio of 1.55.
  • a growth rate of 2.5 ⁇ m/hr typically corresponded to 500 sccm of 2% silane in H 2 , and 100% propane flowing at a rate corresponding to a typical C:Si ratio of 1.55.
  • SiC was grown in 50 slm Ar for 10 min and then switched to H 2 for 30 min at a growth rate of 1.5 ⁇ m/hr and temperature of 1450° C.
  • FIG. 4A SiC was grown in 50 slm Ar for 10 min and then switched to H 2 for 30 min at a growth rate of 1.5 ⁇ m/hr and temperature of 1450° C.
  • SiC was grown for 1 hr in 50 slm Ar, a growth temperature of 1540° C. and a growth rate of 2.5 ⁇ m/hr.
  • the higher growth temperature improved the morphology, where the size of the grains was significantly larger than the size of grains grown at the lower temperature.
  • FIG. 4C When samples were grown in Ar for 10 min at 1400° C.
  • FIG. 4D When samples were grown in Ar for 10 min at 1400° C.
  • FIG. 4D the nucleation of SiC was observed.
  • the stepped morphology was still present. Morphologies with an advantageously low concentration of grain boundaries were grown at the lower temperatures (see FIG. 4C and FIG. 4D ) when grown at a low growth rate (1.5 ⁇ m/hr) and for a short duration.
  • FIG. 5A SEM was taken ( FIG. 5A ) of the sample and it was clear that there were grain boundaries across the surface of the grown SiC film. While there were grain boundaries, it was found with Electron Backscatter Diffraction (EBSD) (see FIG. 5B and FIG. 5C ) that this SiC film was single polytype in both ( FIG. 5B ) in-plane and ( FIG. 5C ) out-of-plane reflections.
  • FIG. 5 shows ( FIG. 5A ) SEM image of surface morphology, ( FIG. 5B ) in-plane and ( FIG. 5C ) out-of-plane EBSD image and ( FIG. 5D ) SEM image of exfoliated SiC of a sample grown with growth conditions from FIG. 4A .
  • the material was advantageously single crystalline as determined from the EBSD.
  • Single crystalline silicon carbide films that are free of grain boundaries may be free of the different stresses and defects that would otherwise be present at the grain boundaries.
  • Devices including single crystalline silicon carbide films may have superior performance to devices comprising silicon carbide films that are polycrystalline and/or have more than one polytype.
  • a single polytype may be desirable at least because each polytype has different electrical properties, which may impact device performance. If different polytypes are present in the silicon carbide film, then the electrical performance may vary across the film, which may not be desirable.
  • This sample depicted in FIG. 5 was initially grown at 1450° C. for 10 min in 50 slm Ar and then grown for an additional 30 min in H 2 with a growth rate of 1.5 ⁇ m/hr.
  • This sample was exfoliated and there was some evidence of spalling that occurred as seen in FIG. 5D , where the image shown is the exfoliated material. The lines in the bottom left of the image are spalling evidence. However, exfoliation still took place even with spalling occurring.
  • FIG. 6 is an HRTEM image (top) showing that there was pseudo graphene present (see, e.g., bottom reference figure) after SiC film growth by remote epitaxy.
  • the bottom reference figure shows pseudo graphene, which figure is adapted from Norimatsu W., et al, “Transitional structures of the interface between graphene and 6H—SiC (0001),” Chemical Physics Letters 468 (2009) 52-56, incorporated herein by reference. As shown in FIG.
  • FIG. 7 shows SEM and EBSD of samples grown at 1620° C. for 20 min in 50 slm Ar over ( FIG. 7A - FIG. 7B ) 4° off-axis, ( FIG. 7C - FIG. 7D ) 2° off-axis and ( FIG. 7E - FIG. 7F ) on-axis substrates.
  • the morphology was roughened for the higher offcut material (e.g., FIG. 7A ) and there were mixed polytypes for the on-axis growth (e.g., FIG. 7F ).
  • the substrate off-cut was varied in these samples for a comparison of SiC film remote epitaxy growth over on-axis substrates ( FIG. 7E - FIG. 7F ), 2° off-axis substrates ( FIG. 7C - FIG. 7D ), and 4° off-axis substrates ( FIG. 7A - FIG. 7B ).
  • FIG. 7A and FIG. 7C the morphology was wavy for the two off-axis substrates, but the on-axis ( FIG. 7E ) had triangular features indicating 3C—SiC.
  • Samples depicted in FIG. 7A and FIG. 7C had a particularly favorable crystal structure; each had no grain boundaries and consisted essentially of one polytype.
  • FIG. 8 shows XRD rocking curves of the (002) and (004) for ( FIG. 8A ) 4° off-axis substrates, ( FIG. 8C ) 2° off-axis substrates, and ( FIG. 8E ) on-axis substrates and RSM of the (004) for ( FIG. 8B ) 4° off-axis substrates, ( FIG. 8D ) 2° off-axis substrates, and ( FIG. 8F ) on-axis substrates.
  • XRD X-ray diffraction
  • RSM XRD reciprocal space maps
  • FIG. 8 shows results for samples grown over 4° off-axis substrates ( FIG. 8A - FIG. 8B ), 2° off-axis substrates ( FIG. 8C - FIG. 8D ) and on-axis ( FIG. 8E - FIG. 8F ) substrates in Ar at 1620° C.
  • the narrowest FWHM (XRD rocking curve) sample was grown over the 4° off-axis substrate ( FIG. 8A ), the second narrowest was for the on-axis ( FIG. 8E ) and the widest was produced over the 2° off-axis substrate ( FIG. 8C ).
  • the RSMs for all of the samples ( FIG. 8B , FIG. 8D , FIG. 8F ) showed to have no spread in the kx (x-axis) indicating these were high quality SiC films, along with the FWHM being relatively narrow for the thicknesses that were grown, ⁇ 2 ⁇ m of SiC film.
  • FIG. 9 shows TEM images (left and right) and an SEM image (center) of an SiC film grown by remote epitaxy on a 4° off-axis substrate in Ar at 1620° C. This indicated that growing a SiC film via a remote epitaxy process reduced and/or eliminated dislocations in the SiC film, which may greatly benefit devices.
  • FIG. 10 shows photographs and SEM images of exfoliated SiC films grown by remote epitaxy at 1620° C. in Ar over ( FIG. 10A - FIG. 10B ) 4° off-axis, ( FIG. 10C - FIG.
  • FIG. 10D 2° off-axis, and ( FIG. 10E - FIG. 10F ) on-axis substrates.
  • the photograph images for each show the substrate on the left and the transferred SiC film grown by remote epitaxy on the right.
  • the SEM images ( FIG. 10B , FIG. 10D , FIG. 10F ) also show the same, where the substrate (“sub”) after exfoliation is the top SEM image and the bottom SEM image is the exfoliated SiC film grown by remote epitaxy (“tape”). Spalling did occur in these films when transferred (see, e.g., spalling marks 1022 in FIG. 10B ), but transfer was still demonstrated.
  • SiC films For the growth of SiC films by remote epitaxy, a SiC film was grown on a graphene layer that was Si sublimated from SiC, and then the SiC film was removed and/or transferred to a desired substrate.
  • the process is scalable for manufacturing purposes, as 4′′ (10.16 cm) wafers were exfoliated.
  • SiC films were grown on (graphene layer)/SiC over on-axis substrates with good morphology and single crystallinity.
  • SiC previously to this study, when growth of SiC had taken place over on-axis SiC substrates, there had generally been a combination of island and step flow growth, which did not happen with this process.
  • the SiC films had fewer dislocations than in the substrate, as the dislocations did not propagate into SiC films grown by remote epitaxy. Without wishing to be bound by theory, this was also likely the case for extended defects such as basal plane dislocations, which would favorably impact epitaxial SiC film quality for device applications.
  • a particularly useful feature to this process was ramping in Ar to reduce or eliminate etching of a graphene layer. If one were to grow a SiC film by ramping to a growth temperature and growing using H 2 as the carrier gas, there would have been no remote epitaxy as most or all of the graphene layer would have been etched away and one would just be growing a SiC film on a SiC substrate. In order to grow a SiC film by remote epitaxy, the graphene samples were ramped in a high flow rate of Ar and then SiC film growth either took place in Ar, or started in Ar flow for a short duration and then switched to H 2 . Otherwise, exfoliation of the grown SiC film did not occur.
  • exfoliation yield When samples were ramped and grown in a H 2 carrier gas, exfoliation yield was 0%. However, when ramped and grown in Ar and then switched to H 2 after a short growth duration, the exfoliation yield increased to between or equal to 40% and 50%. When a sample was ramped and grown in Ar, the exfoliation yield increased further to between or equal to 60% and 70%.
  • a reference to “A and/or B,” when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A without B (optionally including elements other than B); in another embodiment, to B without A (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.
  • the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements.
  • This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified.
  • “at least one of A and B” can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

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