WO2019023170A1 - Films cristallins obtenus à partir d'une couche de germe cristallin de silicium préparée par cristallisation induite par l'aluminium - Google Patents

Films cristallins obtenus à partir d'une couche de germe cristallin de silicium préparée par cristallisation induite par l'aluminium Download PDF

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WO2019023170A1
WO2019023170A1 PCT/US2018/043384 US2018043384W WO2019023170A1 WO 2019023170 A1 WO2019023170 A1 WO 2019023170A1 US 2018043384 W US2018043384 W US 2018043384W WO 2019023170 A1 WO2019023170 A1 WO 2019023170A1
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aluminum
group iii
crystalline
crystalline silicon
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Mel F. HAINEY
Zakaria Y. AL BALUSHI
Joan M. Redwing
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The Penn State Research Foundation
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Definitions

  • the present invention relates to preparing crystalline semiconductor group III-
  • V films e.g., group III nitride films such as gallium nitride films, from crystalline silicon seed layers, which in turn are formed by aluminum-induced crystallization.
  • Group III-V thin films are widely used for light emitting diodes and power electronics.
  • epitaxial thin film growth typically requires a single crystal substrate such as sapphire, silicon, or silicon carbide. Glass is a desirable substrate for large-scale group III-V film growth, due to its high transparency and low fabrication costs, but its amorphous crystal structure makes direct growth difficult.
  • the wide bandgap III-V material gallium nitride grown on other amorphous substrates such as oxidized Si(100) or on crystalline substrates such as polycrystalline diamond are also desirable.
  • amorphous substrates such as oxidized Si(100) or on crystalline substrates such as polycrystalline diamond.
  • crystalline substrates such as polycrystalline diamond.
  • Several approaches to produce c-plane oriented, textured GaN films on glass have been previously demonstrated, but are process-intensive and limited in scalability.
  • group III-V crystalline films e.g., group III nitride films such as gallium nitride films
  • group III nitride films such as gallium nitride films
  • An advantage of the present invention is a group III-V film.
  • Such films can be readily prepared on amorphous and non-crystalline substrates by employing a crystalline silicon seed layer, which in turn can be formed by aluminum-induced crystallization on such substrates.
  • a process of forming a crystalline group III-V film e.g., a crystalline film of a group III nitride including, for example, aluminum nitride (A1N), gallium nitride (GaN), indium nitride (InN), boron nitride (BN), and alloys thereof (e.g., InGaN, InAIN, BA1, AlGaN, etc.), a crystalline film of a group III phosphide, group III arsenide, group III antimonide, e.g., gallium, aluminum, indium or boron phosphide, gallium, aluminum, indium, boron arsenide, gallium, aluminum, indium or boron antimonide, and alloys thereof, e.g. which contain Ga, Al, In and B etc.
  • a group III nitride including, for example, aluminum nitride (A1N), gallium nitride (G
  • the process comprises forming the group III-V film from a crystalline silicon seed layer.
  • the crystalline silicon seed layer can be formed directly over an amorphous or non-crystalline surface of a substrate as well as directly over a crystalline or a polycrystalline substrate surface.
  • the crystalline silicon seed layer can be formed by annealing a layer stack composed of an amorphous silicon layer over an aluminum oxide layer over an aluminum layer over a substrate surface to form the crystalline silicon seed layer at the substrate surface.
  • the silicon seed layer displaces the aluminum layer and subsequent removal of the aluminum layer can be used to expose the crystalline silicon seed layer.
  • the process further comprises depositing a buffer layer, e.g. an aluminum nitride buffer layer, on the crystalline silicon seed layer and then forming the group III-V film over the buffer layer.
  • the process further comprises removing the formed group III-V film, e.g., a group III nitride film such as gallium nitride film, from the crystalline silicon seed layer.
  • the crystalline silicon seed layer is formed by annealing the layer stack in an inert atmosphere.
  • the layer stack is formed by depositing an aluminum layer directly on a surface of the substrate, exposing the deposited aluminum layer to oxygen to form an aluminum oxide layer thereon, and depositing an amorphous silicon (a-Si) layer directly on the aluminum oxide layer.
  • the aluminum layer can have a thickness of between about 5 nm to about 50 nm and the amorphous silicon layer can have a thickness of between 5 nm and 50 nm.
  • the crystalline silicon seed layer formed on the substrate can have greater than about 95% of an Si (111) oriented surface.
  • the process includes a substrate having a surface composed of an amorphous material or polycrystalline material such as glass, an oxide of silicon, or polycrystalline diamond.
  • Another aspect of the present disclosure includes a group III-V crystalline film, e.g., a crystalline group III nitride film such as a crystalline gallium nitride film, formed according to processes of the present disclosure including any of the forging processes individually or combined.
  • the crystalline film can be formed with a large area, such as greater than about 1 cm 2 , e.g., greater than about 10 or 100 cm 2 or more.
  • Figure 1 is a schematic illustrating an aluminum-induced crystallization process to form a highly ⁇ 111> oriented crystalline silicon seed layer in accordance with an aspect of the present disclosure.
  • Figures 2a and 2b are SEM images of gallium nitride (GaN) on aluminum- induced crystallized (AIC) silicon (Si) prepared according to an aspect of the present disclosure which shows how a grain structure of the Si film is maintained through the GaN growth. Also visible is the preferential growth of GaN on Si grains as opposed to the amorphous surface.
  • GaN gallium nitride
  • AIC aluminum- induced crystallized
  • Figure 3 is a top-down SEM image of a coalesced GaN film prepared according to processes of the present disclosure.
  • Figure 4 is a cross-section SEM image of a coalesced GaN film prepared according to processes of the present disclosure.
  • Figures 5a, 5b and 5c are images of GaN on AIC silicon prepared according to an aspect of the present disclosure.
  • Figure 5a and 5b are energy dispersive spectroscopy (EDS) maps and
  • Figure 5c is a corresponding HAADF STEM image obtained near the interface of the structure.
  • EDS energy dispersive spectroscopy
  • This disclosure is directed to a process of forming a crystalline group III-V film, e.g., crystalline films of group III nitrides including, for example, aluminum nitride (AIN), gallium nitride (GaN), indium nitride (InN), boron nitride (BN) and alloys thereof (e.g., InGaN, InAIN, BA1, AlGaN, etc.), crystalline films of group III phosphides, group III arsenides, group III antimonides, e.g., gallium, aluminum, indium or boron phosphide, gallium, aluminum, indium, or boron arsenide, gallium, aluminum, indium, or boron antimonide, and alloys thereof, e.g.
  • the crystalline films can be formed with large areas, such as greater than about 1 cm 2 , e.g., greater than about 10 or 100 cm 2 or more.
  • the process of forming a silicon thin film and subsequently a crystalline group III-V film according to the present disclosure can be advantageously scalable to the limits of metalorganic chemical vapor deposition, molecular beam epitaxy, atomic layer deposition, and liquid phase epitaxy reactor designs (typically up to about 16 inch diameter wafers).
  • the crystalline group III-V films of the present disclosure also can be formed, and/or with large grain sizes, such as greater than 10 ⁇ , e.g., greater than about 20 ⁇ , 30 ⁇ , 40 ⁇ and even greater than about 50 ⁇ .
  • the group III-V films of the present disclosure can be formed over a variety of substrates including substrates having a surface composed of an amorphous material, a single crystalline material, or polycrystalline material.
  • a crystalline group III-V film is formed from a crystalline silicon seed layer.
  • the crystalline silicon seed layer acts as a template to grow the group III-V film.
  • the crystalline silicon seed layer can, in turn, be formed from a process known as aluminum-induced crystallization (AIC).
  • AIC aluminum-induced crystallization
  • the crystalline silicon seed layer is formed by annealing a layer stack composed of an amorphous silicon (a- Si) layer over an aluminum oxide layer over an aluminum layer over a substrate surface, i.e., a-Si/Al-oxide/Al/ substrate are used as starting materials.
  • the initial Si layer displaces the aluminum layer on the substrate and crystalized resulting in a crystalline Si layer, i.e., Al/Al-oxide/poly-Si/substrate, where Si and Al atoms diffuse through the Al-oxide interface layers.
  • Removing the aluminum and Al-oxide top layers then exposes the crystalline silicon seed layer.
  • an exposed crystalline silicon seed layer with large crystal-grains can be obtained on a variety of substrates including substrates having a surface composed of non-single crystalline or amorphous materials.
  • the aluminum- induced crystallization process can form a highly ⁇ 111> oriented crystalline silicon seed layer having a greater than about 90%, e.g., 95% preferential Si ⁇ 111> oriented surface.
  • FIG. 1 schematically illustrates an aluminum-induced crystallization process to form a highly ⁇ 111> oriented crystalline silicon seed layer in accordance with an aspect of the present disclosure.
  • a thin aluminum layer (20) can be deposited on a substrate (10).
  • the substrate can have a surface composed of an amorphous material or non- single crystalline material.
  • the deposited aluminum layer can be exposed to oxygen (e.g., by exposure to air) to form a native oxide layer (22).
  • a thin amorphous silicon (a-Si) layer (30) is then deposited over the aluminum oxide to form an a-Si/Al-oxide/Al/ substrate layer stack.
  • This stack can be annealed in an inert atmosphere (e.g., nitrogen or argon) or in a vacuum and at temperatures below the Al-Si eutectic (577°C).
  • an inert atmosphere e.g., nitrogen or argon
  • the amorphous silicon diffuses across the oxide and through the aluminum grain boundaries (32) to crystallize at the Al-substrate interface.
  • large- grained crystalline silicon seed layer with a uniform ⁇ 111> surface orientation is formed (34), with the aluminum displaced upward as the layers exchange place.
  • a thin highly ⁇ 111> oriented silicon template is left on the substrate surface.
  • a crystalline group III-V film e.g., a group III nitride film such as gallium nitride film, can be grown on the crystalline silicon seed layer following recipes similar to standard recipes used for growth on Si(l ll) substrates.
  • the annealing atmosphere, temperature, time and thicknesses of the aluminum and silicon layer can influence the crystal structure of the silicon seed layer formed in the annealing step.
  • Embodiments of the present disclosure include an annealing atmosphere of an inert gas, e.g., nitrogen, argon, etc. and/or under a vacuum.
  • the annealing temperature should be below the eutectic temperature of the Al-Si system, e.g., less than 577 °C.
  • the annealing temperature should be less than the softening temperature of the substrate on which the aluminum layer is deposited such as a temperature of less than about 500 °C or less than about 350 °C and 250 °C.
  • the annealing time should be sufficient to induce the desired silicon crystal structure such as at least about 5 minutes, or at least about 30 minutes, e.g., at least 60 minutes.
  • the total thickness of the aluminum and/or amorphous silicon layer can be less than about 200 nm, e.g., no more than about 100 nm or no more than about 50 nm or within a range of between about 5 nm and about 50 nm. It is believed that a thin Al layer and thin Al oxide layer are the driving factors promoting uniform Si(l ll) orientation.
  • the silicon layer thickness is preferably less than 2x of the Al layer thickness but the extent of Si layer thickness influence is not entirely clear.
  • group III-V films including, for example, aluminum nitride (A1N), gallium nitride (GaN), indium nitride (InN), boron nitride (BN) and alloys thereof (e.g., InGaN, InAIN, BA1, AlGaN, etc.), crystalline films of group III phosphides, group III arsenides, group III antimonides, e.g., gallium, aluminum, indium or boron phosphide, gallium, aluminum, indium or boron arsenide, gallium, aluminum, indium or boron antimonide, and alloys thereof, e.g. which contain Ga, Al, In and B etc. can be prepared.
  • group III nitrides including, for example, aluminum nitride (A1N), gallium nitride (GaN), indium nitride (InN), boron nitride (BN) and alloys thereof (e.g
  • the crystalline films can be prepared by depositing group III-V precursors on a crystalline silicon seed layer formed from aluminum-induced crystallization.
  • a group III nitride film such as gallium nitride
  • the group III-V film can be prepared by growing a buffer layer, e.g., an aluminum nitride or aluminum gallium nitride buffer layer, on top of the crystalline silicon seed layer to prevent group III, e.g., gallium melt-back etching, and then the group III- V film is grown over the buffer layer.
  • Figures 2-5c illustrate GaN films prepared from a crystalline silicon seed layer which in turn was formed by aluminum-induced crystallization, according to certain aspects of the present disclosure.
  • the final film structure of a GaN film closely follows the initial grain morphology of the crystalline silicon seed layer with minimal GaN and Al-N growth directly on the substrate.
  • the substrate had an amorphous morphology.
  • Longer growth times for the Al-N and GaN layers promote coalescence of these islands into continuous films over large areas of the substrate surface, as seen in Figure 3.
  • the GaN appears to be uniformly oriented relative to the substrate surface, suggesting that the final films are growing epitaxially off of the silicon thin film.
  • Such GaN films were formed to a coalesced area of about 1 mm 2 .
  • Embodiments of the process can include forming a thin (-30 nm) Si (111) template layer with grain sizes of 30-40 ⁇ prepared by aluminum-induced crystallization (AIC) of amorphous Si at 400-500 °C.
  • the Si (111) seed layer can be formed on a variety of substrates including fused quartz, thermally oxidized Si (001), polycrystalline diamond substrates, etc.
  • MOCVD metalorganic chemical vapor deposition
  • the GaN grows epitaxially on the textured AlC-Si templates, producing textured c-axis oriented GaN films with grain sizes approaching 50 ⁇ and threading dislocation densities on the order of 8.5+1.8 x 10 9 cm "2 within regions bounded by grain boundaries, comparable to films formed on single crystal Si (111) substrates.
  • the AlC-Si template fabrication process is flexible and scalable, using well- established semiconductor processing techniques (thin film evaporation, annealing, wet etching) and can be combined with well-developed MOCVD processes for GaN-on-Si.
  • This approach can therefore offer numerous advantages for integrating group III-V films, such as GaN films, on non-single crystal substrates for display and power electronics applications.
  • the group III-V crystalline films can be formed with large areas, such as greater than about 1 cm 2 , e.g., greater than about 10 or 100 cm 2 or more.
  • the process of forming a crystalline group III-V film according to the present disclosure can be advantageously scalable to the limits of metalorganic chemical vapor deposition, molecular beam epitaxy, atomic layer deposition, and liquid phase epitaxy reactor designs. As long as controllable Al/Si deposition can be performed over a large-scale area, group III-V crystalline films can be grown over that same area.
  • forming the crystalline silicon seed layer can be carried out by depositing a layer stack composed of amorphous silicon (a-Si), over aluminum oxide over aluminum on a surface of a substrate.
  • a-Si amorphous silicon
  • the Al and a-Si film thicknesses can be in a range of between about 5 nm and about 50 nm in order to promote uniform Si(l ll) surface orientation with crystallization times on the order of 2-4 hours. (Note that crystallization times on the order of 5-10 minutes can be realized at higher annealing temperatures or with plasma surface treatments.).
  • the a-Si/Al-oxide/Al stack is then annealed in an inert atmosphere at sub-eutectic temperatures (T ⁇ 575 °C), which results in layer exchange and crystallization of the Si on the substrate surface.
  • T ⁇ 575 °C sub-eutectic temperatures
  • the substrate is placed into the MOCVD reactor for growth of a buffer layer, e.g., an A1N nucleation layer, and then an GaN epitaxial film.
  • the AIC-Si films can be formed such that the films are nearly fully coalesced and composed of crystalline Si grains roughly 30-40 ⁇ in size with a preferred (111) out-of-plane orientation and more random in-plane orientations.
  • a crystalline group III-V film e.g., a group III nitride film such as gallium nitride can be grown epitaxially on the AIC-Si template resulting in a thick coalesced crystalline group III-V film.
  • sample GaN films shows, by Inverse pole figure maps from EBSD patterns, that GaN films grow epitaxially on the Si grains with grains roughly 40-50 ⁇ in size with (0001) orientation normal to the substrate surface and random in-plane orientation. Similar to GaN growth on other textured interlayers, the GaN nucleates and grows on the AIC-Si template as large c-plane truncated islands. Consequently, the extent of film coalescence is dependent on the combination of GaN nucleation density and growth rate/time. For regions with low nucleation density, rough, pitted surfaces are formed.
  • the GaN film is more fully coalesced with a planar surface although pits are present. Further improvements in surface morphology can be made via the growth of thicker GaN layers and optimization of A1N growth conditions to reduce pit density as is typical for growth of GaN on single crystal Si (111). Cracks are observed in the coalesced films due to lattice mismatch between the GaN and AIC-Si, thermal expansion coefficient mismatch between GaN (3.76 x 10 "6 K “1 ) and fused quartz substrate (0.54 x 10 "6 K “1 ), and other factors which produce tensile stress in the GaN films.
  • Strain management approaches such as AlGaN interlayers or compositionally graded buffer layers can be implemented to reduce the extent of film cracking.
  • X-ray diffraction measurements performed in ⁇ -2 ⁇ configuration with a 5 mm lateral spot size indicate that the GaN is c-axis oriented across the entire sample area.
  • the X-ray rocking-curve full-width-at-half maximum (FWHM) of the GaN (0002) reflection is -3° similar to previous reports for GaN grown on glass using a Ti template layer.
  • TEM transmission electron microscopy
  • HAADF high-angle annular dark-field scanning TEM
  • STEM scanning TEM
  • a+c mixed-type TDs.
  • Lateral threading dislocations are also observed near grain boundaries similar to that reported for textured GaN films grown on CVD graphene and GaN grown by epitaxial lateral overgrowth.
  • the corresponding selected area diffraction pattern show that the films are highly crystalline and c- axis oriented.
  • Analysis of twenty plan-view images indicates a threading dislocation density (TD) of 8.5+1.8 x l0 9 cm "2 within regions bounded by grain boundaries which is comparable to TD densities reported for GaN films grown under similar conditions on single crystal Si (111) substrates.
  • the layer structure and the role of the AlC-Si template in GaN growth and coalescence is evident in the energy dispersive spectroscopy (EDS) map shown in Figures 5a and 5b and corresponding HAADF STEM image obtained near the interface ( Figure 5c).
  • the thin (-50 nm) AlC-Si template layer is present at the interface between the A1N and glass (S1O 2 ) substrate but exhibits discontinuities as noted by the gap visible in the EDS map (Si film marked purple).
  • the A1N nucleation layer, -230 nm thick, consists of columnar grains topped with angled facets.
  • the A1N initially grows as small disordered grains directly on the fused quartz ( Figure 5c) which are overgrown by the columnar A1N film.
  • Figure 5c fused quartz
  • This result demonstrates that a coalesced GaN film can be realized even when small gaps are present in the underlying Si seed layer, although these gaps can be reduced or eliminated through the use of thicker AlC-Si template layers.
  • the A1N overgrowth demonstrates the role of the AlC-Si layer in promoting crystalline A1N and GaN, by acting as a preferential nucleation site for columnar A1N and subsequent GaN growth.
  • Fused quartz glass Substrate A 30 nm thick aluminum layer was evaporated onto fused quartz glass using electron-beam evaporation. The aluminum was exposed to air for 5-30 min after this process to form a thin aluminum oxide layer. Amorphous silicon was subsequently deposited by electron beam evaporation over the oxide surface. The samples were then annealed in nitrogen at 450°C for 4 hours to realize full silicon crystallization. Aluminum was removed using a phosphoric acid-based aluminum etchant. The final silicon grain size is roughly 50 ⁇ . Electron backscatter diffraction is used to confirm the ⁇ 111> surface orientation of the thin films.
  • GaN growth was performed by first growing A1N at growth temperatures of 500°C and 50 Torr for 2 minutes followed by recrystallization at 1050°C and further growth at 1100°C and 100 Torr for 30 minutes. Initial GaN growth was performed at 900°C and 100 Torr for 30 minutes followed by growth at 1150°C at 100 Torr for 60 minutes. III-V ratios were roughly 1:7 during A1N growth and 1:3 and 1:5 during the two steps of the GaN growth. The final GaN samples had an area of about 1 mm 2 .
  • Oxidized Silicon and polycrystalline diamond substrates Thermal oxidation of
  • Si (100) substrates was used to fabricate oxide films of about 300 nm in thickness on the substrate surfaces. Identical cleaning and deposition processes were followed for both oxidized Si (001) substrates and T-1500 polycrystalline diamond (II- VI Inc.) substrates. That is, the substrates were sonicated in acetone/IP A/DI water for 10 minutes each before being cleaned in a buffered piranha solution at 80 °C and rinsed ten times in DI water.
  • Samples were dried and then loaded into a Lab- 18 electron beam evaporation system with base pressures below lxlO "6 Torr.
  • An Al film (30 nm thick) was deposited at 1.5 A/s, before the sample was unloaded and exposed to air for 10 minutes to form a native oxide.
  • the sample was re-introduced into the evaporator to deposit 30 nm amorphous Si (a-Si) prior to growth.
  • samples Prior to annealing, samples were diced into l x l cm 2 pieces to accommodate the pocket size of the MOCVD reactor. Note that polycrystalline diamond substrates had these dimensions as received. Samples were then stored in nitrogen prior to annealing at 450 °C for 4 hours to fully crystallize the a-Si thin films. For samples used for silicon thin film characterization, aluminum was etched from the AlC-Si film surface using aluminum etchant type A (Transene) for 5 minutes at 80 °C before the samples were rinsed in DI water and dried with a nitrogen gun.
  • aluminum etchant type A Transene
  • a low-temperature A1N layer was first deposited at 100 Torr and 550 °C for one minute, followed by a high temperature layer at 100 Torr and 1150 °C. Subsequent low-temperature GaN growth was performed at 950 °C and 100 Torr for 15 minutes, followed by a high-temperature growth at 1050 °C for 90 minutes at 50 Torr. For growth on oxidized Si (001) and polycrystalline diamond, the GaN growth was changed to 60 minutes at 100 Torr and 1050 °C to increase nucleation density, followed by 60 minutes at 50 Torr under identical growth conditions. For diamond substrates, a brief HF dip was performed to remove native oxide from the AlC-Si film on the diamond substrate surface prior to GaN growth.
  • EBSD was performed using the same FEI Helios system used for silicon thin film characterization.
  • Cross-section and plan-view samples for transmission electron microscopy (TEM) analysis were prepared using the focused ion beam equipment on the FEI Helios 660 system mentioned earlier.
  • Cross-section TEM and EDS was performed using an FEI Titan3 G2* aberration-corrected TEM at 200 KeV accelerating voltage with a SuperX EDS detector attachment.
  • Plan-view images were taken at 200 KeV on an FEI Talos F200X. Defect analysis was performed by counting dislocations in 20 different plan- view images to obtain statistically significant defect densities and distributions.
  • coalesced gallium alloy films such as GaN films on amorphous substrates such as fused quartz glass have been realized through the use of an AlC-Si template layer followed by deposition of gallium alloy precursor materials such as by MOCVD growth of an A1N buffer and GaN epilayer.
  • Such AlC-Si layer and GaN film have uniform Si (111) and GaN (0001) surface orientations, respectively, and random in-plane orientations with similar grain sizes, suggesting that the AlC-Si layer is acting as a template for subsequent GaN growth.
  • the threading dislocation density of the GaN within regions bounded by grain boundaries is comparable to previous reports of GaN grown on single crystal Si (111) substrates.
  • Improvements in film quality can be obtained via well-developed strain management techniques for GaN-on-Si.
  • the growth process was shown to be extendable to oxidized Si (001) and polycrystalline substrates such as poly crystalline diamond substrates, which also produce highly c-axis oriented GaN films, demonstrating the flexibility of the AlC-Si film as a template for growth on a variety of substrates.
  • This process is believed to be highly scalable and can also be employed to fabricate large c-axis oriented GaN island arrays through the use of patterning techniques.

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Abstract

Des films cristallins du groupe III-V peuvent être formés à partir de substrats amorphes et non cristallins en utilisant une couche germe cristallin de silicium, qui à son tour est formée par cristallisation induite par l'aluminium sur de tels substrats.
PCT/US2018/043384 2017-07-26 2018-07-24 Films cristallins obtenus à partir d'une couche de germe cristallin de silicium préparée par cristallisation induite par l'aluminium WO2019023170A1 (fr)

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WO2011105397A1 (fr) * 2010-02-25 2011-09-01 国立大学法人北海道大学 Dispositif à semi-conducteurs et procédé de fabrication de dispositif à semi-conducteurs
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CN117488408A (zh) * 2022-08-02 2024-02-02 松山湖材料实验室 单晶氮化铝材料及其制备方法
CN117488408B (zh) * 2022-08-02 2024-05-10 松山湖材料实验室 单晶氮化铝材料及其制备方法

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