III-N Material Growth Process
The described growth process for III-N materials addresses the challenges of high defect densities and high costs by using laser-altered buffer layers to separate primer and germination layers, resulting in high-quality III-N layers for vertical microelectronic devices.
Patent Information
- Application Number
- FR2023010905
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2023-10-11
- Publication Date
- 2026-01-02
- Estimated Expiration
- 2043-10-11
AI Technical Summary
Existing methods for growing III-N materials, such as GaN, on substrates like silicon or sapphire result in high defect densities and costly processes, limiting their large-scale use due to lattice mismatch, thermal expansion coefficient differences, and expensive substrates.
A growth process involving a primer layer, buffer layer, and germination layer, where the buffer layer is altered by laser radiation to separate the primer and germination layers, allowing for the growth of a III-N material with reduced structural defects and reusable primer layers.
The process achieves high-quality III-N layers with low defect densities and reduced manufacturing costs by minimizing collateral damage to the primer and germination layers, enabling cost-effective production suitable for vertical microelectronic devices.
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Abstract
Description
Title of the invention: Method for growing a material III-N technical field
[0001] The present invention relates to the growth of III-N materials, such as GaN. It advantageously enables the growth of III-N materials for the fabrication of so-called vertical microelectronic devices. Particularly advantageous applications include, for example, the fields of power electronics and microdisplays. STATE OF THE ART
[0002] Power electronic components based on a III-N material are often fabricated by epitaxy of this material, particularly by metal-organic vapor deposition, from crystalline substrates. The most commonly used substrates are GaN and silicon substrates.
[0003] GaN substrates are best suited for GaN epitaxy. Homoepitaxial fabrication of GaN layers allows for very low dislocation densities. There are no lattice mismatch or thermal expansion coefficient issues; therefore, the epitaxial layers have a crystalline quality close to that of the substrate and are subject to little stress. The document "Materials and Processing issues in vertical GaN power electronics," Materials Science in Semiconductor Processing 78, 75-84 (2018), presents the advantages of this type of substrate. However, GaN substrates are small and very expensive. Devices fabricated on these substrates are therefore generally high-performing but very costly, which is a significant obstacle to their large-scale use.
[0004] Conversely, silicon substrates are available at low cost and in large dimensions, making them very common in microelectronics. Heteroepitaxial growth of GaN on silicon substrates is possible because the (111)-oriented silicon lattice is compatible with the (001)-oriented GaN crystal lattice. However, there is a lattice mismatch of -17% between GaN and silicon. GaN layers grown by GaN epitaxy on silicon therefore exhibit high densities of crystal defects such as dislocations. Moreover, the coefficient of thermal expansion (CTE) at room temperature of Si is 2.59 × 10⁶, while that of GaN is 5.59 × 10⁶. Since GaN epitaxy is carried out at high temperature (on the order of 1000°C), high stresses are generated during the temperature drop that occurs after GaN epitaxy.For the thicknesses targeted for vertical GaN-based power components, on the order of several micrometers. Even at thicknesses of tens of micrometers, the stresses are such that the GaN layer can crack during the temperature drop. Structuring the resulting layers, and in particular faceting their surface (see, in particular, Tanaka, A., Choi, W., Chen, R. & Dayeh, SA, Si Complies with GaN to Overcome Thermal Mismatches for the Heteroepitaxy of Thick GaN on Si. Advanced Materials 29, 1702557 (2017)), can be considered to limit the number of structural defects, but this is difficult to implement and very expensive.
[0005] Furthermore, it is common practice to grow a GaN layer from a sapphire substrate and then detach it from this substrate using a laser lift-off step (see, in particular, Wong, WS, Sands, T. & Cheung, NW. Damage-free separation of GaN thin films from sapphire substrates. Appl. Phys. Lett. 72, 599-601 (1998)). However, since the laser is absorbed by the GaN, part of the GaN layer is vaporized by the radiation and damaged, which is unsatisfactory from the perspective of improving device quality. Moreover, as between GaN and silicon, there is a lattice mismatch and a CTE mismatch between GaN and sapphire. The raw layer therefore exhibits significant defect densities. It should also be noted that sapphire substrates are more expensive.
[0006] Furthermore, investigations have been made into using an ion-cutting technique to separate a GaN layer from its single-crystal substrate. However, this process has the drawback of damaging the GaN layer during ion implantation. The GaN layer exhibits high roughness after the annealing process used for detachment, which is unsatisfactory. Moreover, the detachment step following the ion implantation step requires high-temperature annealing, which limits the substrates on which the transfer can be performed. For example, with this technique, it is impossible to transfer a GaN layer onto a CMOS (Complementary Metal Oxide Semiconductor) device.
[0007] The present invention therefore aims to provide a solution for limiting, or even eliminating, at least some of the drawbacks of known solutions. Another object of the present invention is to provide a solution for growing an ILN material, preferably in a less costly way than homoepitaxy, and preferably in a way that results in fewer structural defects than existing heteroepitaxy methods. SUMMARY
[0008] To achieve this objective, according to one embodiment, a growth process for an ILN material, such as GaN, is provided, comprising the following steps: a. Providing a primer layer based on a first ILN material, the primer layer having a top face extending mainly in a a. a. To grow, by epitaxy of a buffer material, a buffer layer from the upper face of the primer layer, the buffer layer having an upper and a lower face opposite each other, the lower face of the buffer layer being opposite, and preferably in contact with, the upper face of the primer layer, c. Growing by epitaxy a germination layer, in a second III-N material, preferably identical to the first III-N material, from the upper face of the buffer layer, the germination layer having an upper face and a lower face opposite each other, the lower face of the germination layer being opposite, and preferably in contact with, the upper face of the buffer layer, d. Adhesive the upper surface of the germination layer onto a receiving substrate, e. Subject the buffer layer to laser radiation with a primary wavelength Xiaser, the primer layer being configured to transmit at least part of the laser radiation, the primer layer preferably having an absorption of less than or equal to 10%, preferably less than or equal to 5%, preferably less than or equal to 2% for the primary wavelength Xiaser, the laser radiation being configured to alter the buffer layer so as to decouple the primer layer and the germination layer, f. Grow by epitaxy of a third III-N material, preferably identical to the second III-N material, a layer of interest from the lower face of the germination layer.
[0009] In this process, the separation of the primer layer and the germination layer is achieved by altering the buffer layer through its exposure to laser radiation. The process results in minimal collateral damage to the primer and germination layers, which notably allows the growth of a layer of interest exhibiting a low density of structural defects.
[0010] Furthermore, once the germination layer and the primer layer have separated due to alteration of the buffer layer, the primer layer can be reused for further iterations of the process. Therefore, a primer layer of excellent quality can be chosen, as its cost will be offset by its reuse.
[0011] By ensuring that the primer layer is transparent to laser radiation, it can be ensured that it is not altered during the step of submitting the buffer layer to radiation. Its quality will thus be preserved for future uses during new implementations of the process.
[0012] The proposed solution thus constitutes an alternative to existing processes of growth of a III-N material has many advantages, including the fact that the layer of interest obtained has a very good crystalline quality without the process being as expensive as homoepitaxy of the same III-N material. BRIEF DESCRIPTION OF THE FIGURES
[0013] The aims, objects, features and advantages of the invention will become clearer from the detailed description of an embodiment thereof, which is illustrated by the following accompanying drawings in which:
[0014] [Fig.1A] Figures IA to II illustrate a first embodiment of the process according to the invention, in which the primer layer forms a plurality of disjoint islands.
[0015] [Fig.1B]
[0016] [Fig.1C]
[0017] [Fig.1D]
[0018] [Fig.1E]
[0019] [Fig.1F]
[0020] [Fig.1G]
[0021] [Fig.1H]
[0022] [Fig. II]
[0023] [Fig.2A] Figures 2A to 2D illustrate a second embodiment of the process according to the invention, in which the primer layer forms a single continuous layer.
[0024] [Fig.2B]
[0025] [Fig.2C]
[0026] [Fig.2D]
[0027] [Fig.3A] Figures 3A to 3C illustrate steps of a third embodiment of the process according to the invention, in which an adhesion layer surrounds the primer layer, the buffer layer and the germination layer.
[0028] [Fig.3B]
[0029] [Fig.3C]
[0030] [Fig.4A] Figures 4A to 4G illustrate an embodiment in which electrical contacts are deposited on the germination layer and on the receiving substrate before the bonding of these two elements.
[0031] [Fig.4B]
[0032] [Fig.4C]
[0033] [Fig.4D]
[0034] [Fig.4E]
[0035] [Fig.4F]
[0036] [Fig.4G]
[0037] [Fig.5A] Figures 5A to 5E illustrate an embodiment in which the receiving substrate is removed and the layer of interest is transferred onto a secondary receiving substrate.
[0038] [Fig.5B]
[0039] [Fig.5C]
[0040] [Fig.5D]
[0041] [Fig.5E]
[0042] [Fig.6A] Figures 6A to 6G illustrate an embodiment in which the receiving substrate is electrically conductive.
[0043] [Fig.6B]
[0044] [Fig.6C]
[0045] [Fig.6D]
[0046] [Fig.6E]
[0047] [Fig.6F]
[0048] [Fig.6G]
[0049] The drawings are given by way of example and are not limiting of the invention. They constitute schematic representations of principle intended to facilitate understanding of the invention and are not necessarily to scale with practical applications. In particular, the dimensions, especially the thicknesses, are not representative of reality. DETAILED DESCRIPTION
[0050] Before proceeding with a detailed review of embodiments of the invention, optional features that may be used in combination or alternatively are listed below:
[0051] According to an advantageous example, in the horizontal plane, the first IILN material has a first lattice length alu.N,i and the buffer material has a buffer lattice length atampon, with | (am.N,i - atampon ) | / aul.N,i < 0.02. This condition limits the lattice mismatch between the first IILN material and the buffer material. This improves the quality of the epitaxy of the buffer material from the first IILN material, reduces the number of defects in the buffer layer, and thus improves its crystalline quality. In this way, the crystalline quality of the nucleation layer, which is grown epitaxially from the buffer layer, is also improved, as is the layer of interest, which is grown epitaxially from the nucleation layer.
[0052] In the case where the second IILN material is distinct from the first IILN material, preferably in the horizontal plane, the second IILN material has a second mesh length a111N 2 and the buffer material has a buffer mesh length atampon, with | (aIU_N>2- atampon ) | / alu_N>2< 0.02. This condition limits the lattice mismatch between the buffer material and the second III-N material. This limits or even prevents the generation of defects during growth. This improves the quality of the epitaxy of the second III-N material from the buffer material, reduces the number of defects in the nucleation layer, and thus improves its crystalline quality compared to if this precaution were not taken. In this way, the crystalline quality of the layer of interest, which is grown epitaxially from the nucleation layer, is also improved.
[0053] According to an advantageous example, in the horizontal plane, the mesh of the first III-N material has a first angle aul.N4 and the mesh of the buffer material has an angle atampon, with | a111Nji-atampon | < 5°. In this way, the mesh mismatch between the first III-N material and the buffer material is limited. Again, this makes it possible to limit the number of defects in the buffer layer, and consequently in the germination layer and in the layer of interest.
[0054] In the case where the second III-N material is distinct from the first III-N material, preferably in the horizontal plane, the mesh of the second III-N material has a second angle alu.N,2 and the mesh of the buffer material has an angle atamPon, with I «ni N,2-atamPon | < 5°. In this way, the mesh mismatch between the buffer material and the second III-N material is limited. Again, this makes it possible to limit the number of defects in the germination layer, and consequently in the layer of interest.
[0055] According to one embodiment, the primer layer forms a supporting substrate. In this case, it does not rest on a supporting substrate different from the primer layer.
[0056] According to an advantageous example, the buffer layer has, along a third direction perpendicular to the horizontal plane, a thickness e2Oo configured such that the buffer layer has a dislocation density p of less than 1010 cm², preferably less than 10⁸ cm², and preferably less than 10⁷ cm². If the buffer layer is too thick, it relaxes and dislocations appear. Limiting the thickness of the buffer layer ensures that it is coherent with the substrate and exhibits good crystalline quality, which will also guarantee good crystalline quality of the layer of interest. It should be noted that the crystalline quality of the buffer layer is evaluated with respect to that of the substrate. Thus, limiting the thickness of the buffer layer more precisely limits the quantity of defects added relative to the defects initially present in the substrate and transferred to the buffer layer.Preferably, when the primer layer rests on a support substrate, we denote pSubStrat the dislocation density of this support substrate, and the thickness e2oo is configured so that the difference between the dislocation density p of the buffer layer and the dislocation density psubstrat of the support substrate, p-pSUbstrat, is less than or equal to . at 1010 cm², preferably 10⁹ cm², preferably 10⁸ cm². Preferably, when the primer layer is a single continuous layer and does not rest on a supporting substrate, and thus constitutes a substrate, the dislocation density of the primer layer is denoted psubstrat, and the thickness e₂O₀ is configured so that the difference between the dislocation density p of the buffer layer and the dislocation density psubstrat of the primer layer, p - pSUbStrat, is less than or equal to 10⁶ cm². In general, the thickness e₂O₀ is configured so that the dislocation density p of the buffer layer is less than or equal to 1.5 times the dislocation density pSUbStrat of the supporting substrate.For a GaN substrate, psubstrate is typically less than 10⁷ cm², for example between 10⁶ cm² and 10⁷ cm², or even on the order of 10⁴ cm² (for example, if the substrate is formed by an ammonothermal method or by oxide vapor phase epitaxy (commonly referred to as OVPE)).
[0057] Advantageously, e₂₀₀ < 100 nm, preferably e₂₀₀ < 20 nm.
[0058] Preferably, e₂₀₀ > 2 nm and advantageously e₂₀₀ > 5 nm. This ensures good absorption of the laser radiation by the buffer layer. The minimum thickness of the buffer layer required to ensure its alteration, however, depends on the buffer material and can be established on a case-by-case basis.
[0059] Preferably, the first material IIIN has a melting temperature Tfusion lll N,i, with the epitaxy of the buffer material being carried out at a growth temperature Tgrowth,buffer, where Tgrowth2buffer < Tfusion,iii-N,i*. This ensures that the primer layer is not altered during the epitaxy of the buffer material. In general, growth is carried out under conditions that limit or even prevent the degradation of the primer layer. Maintaining a good quality primer layer throughout the process allows, among other things, its reuse in subsequent implementations of the process.
[0060] Preferably, the buffer material has a melting temperature Tfusion>buffer, the epitaxy of the second material IILN being carried out at a growth temperature Tgrowth,iii-N,2, with Tgrowthîm.^N^^Tfusion,buffer*This ensures that the buffer layer is not altered during the epitaxy of the second material IILN.
[0061] According to an advantageous example, along a third direction perpendicular to the horizontal plane, the primer layer has a thickness ei00 and the layer of interest has a thickness e400, with e400 > 2*ei00, preferably e400 > 3*ei00, preferably e400^5*ei00. This is particularly desirable when the primer layer is a layer resting on a supporting substrate. According to an advantageous example, along a third direction perpendicular to the horizontal plane, the buffer layer has a thickness e200 and the layer of interest has a thickness e400, with e400 > 2*e200, preferably e400 > 3*e200, preferably e400 > 5*e200.
[0062] According to a preferred embodiment, the laser radiation is configured to pass through the primer layer before altering the buffer layer.
[0063] According to an advantageous example, after the separation of the primer layer and the germination layer, at least part of the buffer layer remains on the germination layer, and the process further comprises, after the step of subjecting the buffer layer to laser radiation and before the step of growth of the layer of interest, a step of removing said at least part of the buffer layer.
[0064] According to one embodiment, the primer layer forms a single continuous layer.
[0065] According to one embodiment, the primer layer forms germination substrates disjoint.
[0066] According to a preferred example, each of the disjoint germination substrates has, in the horizontal plane, a maximum dimension of less than 150 mm, typically less than 100 mm. In the typical case of germination substrates having, in projection in the horizontal plane, a circular shape, their maximum dimension corresponds to their diameter.
[0067] According to one embodiment, during the step of supplying the primer layer, the germination substrates are transferred onto the support substrate.
[0068] According to an advantageous example, the process further comprises, after the epitaxial step of the second material III-N and before the step of bonding the upper surface of the germination layer to the receiving substrate, the formation of an adhesion layer on the upper surface of the germination layer. In this case, the bonding of the germination layer to the receiving substrate is achieved via the adhesion layer. The presence of the adhesion layer ensures the quality of the bonding. The formation of this adhesion layer typically includes a step of planarizing this same layer. Thus, it is ensured that the bonding to the receiving substrate occurs at the level of a flat layer, which improves the quality of the bonding.
[0069] For example, the adhesion layer may be based on SiO2, SiN, Si, or any other material identified by those skilled in the art, depending on the intended application. Generally, it may be, among other things, a metal, a dielectric, a semiconductor, or a polymer. If a new epitaxial layer is to be created from the stack obtained by the process according to the invention, a dielectric will typically be chosen for its good temperature resistance. A polymer material can be used to create an adhesive bond.
[0070] When the priming layer forms a plurality of germination substrates from which islands of the buffer layer and islands of the germination layer are grown, it is advantageously provided that, in projection in the horizontal plane, the adhesion layer extends around each of the germination substrates, each of the islands of the buffer layer and each of the islands of the germination layer, preferably in contact with the flanks of the germination substrates, the flanks of the islands of the buffer layer and the sides of the islands of the germination layer. This ensures good mechanical support of the whole.
[0071] According to one example, the III-N material is based on at least one of GaN, AlN, InN and any combination of these materials.
[0072] According to one example, the buffer material is one of the following materials: HfN, ZrN, NbN, TiN.
[0073] Generally, the buffer material can be a nitride material. In the context of GaN growth, HfN is a particularly advantageous material because it exhibits a mail mismatch of only 0.2% with GaN. Furthermore, it can be deposited to a thickness of up to 100 nm without relaxing and therefore without exhibiting a detrimental dislocation rate. Moreover, a layer of approximately 100 nm of HfN has an absorption rate of 99% in the infrared, which is more than sufficient to ensure good alteration of the buffer layer when subjected to laser radiation. Typically, if the buffer material is HfN, a buffer layer thickness e2oo of approximately 5 to 20 mm is expected.
[0074] ZrN is another nitride whose properties make it a good buffer material in the context of the invention. It exhibits a very low lattice mismatch (1.3%) with GaN, can be deposited to a critical thickness of 10 nm, and, at this critical thickness, has an infrared absorption rate of 45%. It should be noted that, with regard to the buffer layer degradation condition required to allow the separation of the nucleation and seed layers, a material with an absorption rate as low as 10% or even 2% is perfectly suitable for the buffer layer. Sufficient degradation can be achieved at these absorption values.
[0075] According to an advantageous example, the method further comprises the formation of electrical contacts on the upper face of the germination layer and secondary electrical contacts on the upper face of the layer of interest.
[0076] According to an advantageous example, the receiving substrate is electrically conductive.
[0077] According to one embodiment, the receiving substrate comprises at least one integrated electronic circuit.
[0078] According to an advantageous example, the buffer material is chosen so that the buffer layer induces a polarity within the germination layer.
[0079] It is specified that, within the scope of the present invention, the terms "on", "overcomes", "covers", "underlying", "opposite", and their equivalents do not necessarily mean "in contact with". Thus, for example, the deposition, transfer, gluing, assembly, or application of a first layer on a second layer does not necessarily mean that the two layers are directly on contact with each other, but means that the first layer at least partially covers the second layer by being either directly in contact with it, or by being separated from it by at least one other layer or at least one other element.
[0080] A layer may also be composed of several sub-layers of the same material or of different materials.
[0081] A substrate, layer, or device "based on" a material M is understood to mean a substrate, layer, or device comprising only that material M or that material M and possibly other materials, for example, alloying elements, impurities, or dopant elements. Thus, a material based on a III-N material may comprise a III-N material with added dopants.
[0082] A coordinate system, preferably orthonormal, comprising the axes X, Y, Z is represented in figures IA, 2A, 3A, 4A and 5A. This coordinate system is applicable by extension to the other figures.
[0083] In this patent application, the terms thickness for a layer and height for a structure or device will be preferred. Height is measured perpendicular to the horizontal XY plane. Thickness is measured in a direction normal to the principal plane of extension of the layer. Thus, a layer typically has a thickness along Z when it extends mainly along the horizontal XY plane, and a projecting element, for example an insulation trench, has a height along Z. The relative terms "on," "under," and "below" preferentially refer to positions measured along the Z direction.
[0084] The terms "approximately", "about", "in the order of" mean "within 10%, preferably within 5%".
[0085] A first embodiment of the method according to the invention will be described with reference to Figures IA to IL
[0086] Figure 1A illustrates the provision of a support substrate 1000 that can be used in the process according to the invention. This support substrate 1000 can, for example, be a SiC substrate, a sapphire substrate, a silicon substrate, a single-crystal GaN substrate, or any other substrate based on a material IIIN. It has a top face 1001 extending mainly in a horizontal plane XY defined by a first direction X and a second direction Y.
[0087] Figure [1B] shows the formation of a primer layer 100 on the upper face 1001 of the support substrate 1000. The primer layer 100 is based on a first 1ILN material such as GaN. The primer layer is crystalline.
[0088] The primer layer 100 can be discontinuous, as illustrated in [Fig. 1B], or continuous, as will be shown in the second embodiment illustrated in Figures 2A to 2D. In the case of a discontinuous primer layer 100, it can, for example, consist of a plurality of ger substrates Disjoint germination 100a, 100b, 100c. These disjoint germination substrates 100a, 100b, 100c can also be designated as disjoint islands 100a, 100b, 100c of the primer layer 100. This set of disjoint germination substrates 100a, 100b, 100c can be described as a tiling. For example, according to an advantageous embodiment, the assembly illustrated in [Fig. 1B] is obtained by bonding a plurality of substrates smaller than the support substrate 1000 onto the substrate support 1000. These are typically single-crystal GaN-based substrates, whose diameter is currently most often between 50 mm and 150 mm, bonded to a support substrate 1000 whose dimensions allow for the support of a plurality of them. Such a support substrate 1000 could, for example, be a silicon substrate with a diameter of 200 or 300 mm.
[0089] The primer layer 100 has a lower face 102 opposite, and preferably in contact with, the upper face 1001 of the supporting substrate 1000, and an upper face 101 opposite its lower face 102.
[0090] As illustrated in [Fig.1C], a buffer layer 200 is raw from the top face 101 of the primer layer 100.
[0091] The buffer layer 200 is based on a material called buffer material whose structural properties must allow its epitaxy from the primer layer 100. In particular, it is expected that the crystalline parameters of the buffer material and the first material IIIN are close.
[0092] The buffer layer 200 can be cured by various techniques, including physical vapor deposition (PVD, “Physical Vapor Deposition”) such as pulsed laser ablation deposition (commonly referred to by the English acronym PLD, “Pulsed Laser Deposition”), sputtering deposition (reactive or non-reactive) or molecular beam epitaxy (MBE, “Molecular beam epitaxy”) or chemical vapor deposition (CVD, “Chemical Vapor Deposition”) such as metal-organic chemical vapor deposition (MOCVD, “Metal Organic Chemical Vapor Deposition”).
[0093] The buffer layer 200 has a lower face 202 opposite, and preferably in contact with, the upper face 101 of the primer layer 100, and an upper face 201 opposite its lower face 202. In the case of a primer layer 100 made up of disjoint germination substrates 100a, 100b, 100c, the buffer layer 200 is made up of islands 200a, 200b, 200c which are also disjoint.
[0094] In order not to alter the primer layer 100, the epitaxy of the buffer layer 200 is carried out at a temperature Tgrowthjbuffer lower than the melting temperature Tfusion >1UN>i of the first material IILN. This ensures the stability of the first material IILN during the growth of the buffer layer 200.
[0095] Furthermore, the thickness e2oo of the buffer layer 200 in the vertical direction Z is The buffer layer 200 is advantageously chosen to avoid the appearance of structural defects that could then propagate into the nucleation layer and the layer of interest, which will be described later. To achieve this, a critical thickness ecritic can be established for any material chosen as a buffer. This critical thickness is defined as the dislocation density p within the buffer layer 200 exceeding a given threshold ρimite when the buffer layer 200 is grown from the nucleation layer. Typically, ρimite < 1010 cm2. For example, ρimite = 108 cm2, preferably ρimite = 107 cm2. To guarantee a dislocation density below ρimite, a thickness e200 less than ecritic will be set for the buffer layer 200. These precautions ensure excellent crystalline quality in the layer of interest 400.For example, if the difference in mesh parameter between the substrate and the buffer layer is on the order of 1%, ecritique is on the order of 10 nm, if on the other hand it is on the order of 0.1%, ecritique is on the order of 100 nm.
[0096] Figure 1D then illustrates the epitaxial growth of a germination layer 300 from the upper face 201 of the buffer layer 200. Advantageously, to withstand the conditions imposed by the growth techniques of the germination layer 300, the buffer layer 200 is refractory and inert. In particular, it preferably has a melting point above 2000°C. It preferably has a chemical composition that is stable in air. Thus, a material stable under the working atmosphere and at the working temperature (typically around 1000°C) is preferably chosen for the buffer layer. The material constituting the buffer layer may be slightly modified during the process, i.e., its stoichiometry may change. However, it must not decompose during the epitaxy of the germination layer.
[0097] The germination layer 300 is based on a second IILN material, preferably identical to the first IILN material. The germination layer 300 is also crystalline. The first IILN material of the crystalline primer layer 100 is chosen, particularly in terms of lattice parameters, so that the germination layer 300 is also crystalline, without requiring the materials of the primer layer and the germination layer to be identical. If the first IILN material and the second IILN material are identical, the precautions taken regarding the feasibility of epitaxy of the buffer layer 200 from the primer layer 100 (similarity of crystalline parameters) guarantee the feasibility of epitaxy of the germination layer 300 from the buffer layer 200.If the first IILN material and the second IILN material are distinct, similar precautions can be taken regarding the similarity of the crystalline parameters of the buffer material and the second IILN material.
[0098] The germination layer 300 has a lower face 302 opposite, and preferably in contact with, the upper face 201 of the buffer layer 200, and an upper face 301 opposite its lower face 302. In the case where the primer layer 100 and the buffer layer 200 are made up of disjoint islands 100a, 100b, 100c, 200a, 200b, 200c, the germination layer 300 is also made up of disjoint islands 300a, 300b, 300c.
[0099] As illustrated in [Fig. 1E], the germination layer 300 is then bonded, its upper surface 301, to the upper surface 2001 of a receiving substrate 2000. The assembly consisting of the support substrate 1000, the priming layer 100, the buffer layer 200, and the germination layer 300 may have been inverted beforehand to perform this bonding. However, it is also possible to bond the receiving substrate 2000 to the germination layer 300 and then invert the assembly.
[0100] The concept of bonding here covers all types of transfers with adhesion. This term is not limited to the use of glue or an adhesive layer. It can, for example, refer to direct bonding, usually called "direct bonding" in English, or surface-activated bonding, designated "surface-activated bonding" (SAB) in English.
[0101] The buffer layer 200 is then subjected to laser radiation ([Fig. 1F]). This step can be described as a "laser lift-off" step. The purpose of exposing the buffer layer 200 to this laser radiation is to alter it in order to cause the separation of the primer layer 100 and the germination layer 300. More specifically, the energy of the laser radiation is absorbed by the buffer layer 200, which has the effect of heating it. Under the effect of this heating, the buffer layer 200 decomposes at least partially into liquid and gaseous forms. The gaseous portion dissipates while at least part of the liquid portion may remain in contact with the upper face 101 of the primer layer 100 and / or the lower face 302 of the germination layer 300.Potential residues, particularly liquids, from buffer layer 200 can be cleaned in a subsequent step not shown in the figures. For example, this cleaning could include at least one of the following: chemical cleaning such as soaking in a cleaning solution or chemical spray cleaning, polishing, typically chemical-mechanical polishing (CMP), or dry etching. This allows for the complete removal of buffer layer 200 residues from the surface of the primer 100 and germination layers 300, without altering their surface or structure. It is also possible to remove a very thin portion of the germination layer 300 from its lower face 302, for example, a few tens of nanometers. This portion may have been damaged by the... previous steps; removing it ensures a good quality of the germination layer 300.
[0102] Laser radiation has a principal wavelength Xiaser. In practice, laser radiation does not correspond to a single wavelength but extends over an emission range A^. Typically, the emission range Aa is between 0.8 * Xiaser and 1.2 * Xiaser. Preferably, Aa is between 0.9 * Xiaser and 1.1 * Xiaser. Xiaser is defined by the equipment that generates the laser radiation. For the same equipment, Xiaser can take several values. The user selects one of these values. Typically, the principal wavelength Xiaser is in the infrared (from about 780 nm to about 1 mm) and / or the visible range (from about 380 nm to about 780 nm). In order to ensure the separation of the primer layer 100 and the germination layer 300, as explained previously, the buffer layer 200 must absorb the laser radiation.The Aa emission range can therefore be defined in particular by the fact that the buffer layer 200 exhibits an absorption greater than or equal to 5%, preferably greater than or equal to 20%.
[0103] As illustrated in [Fig. 1F], the laser radiation typically passes through the primer layer 100 before reaching the buffer layer 200. In order to limit the degradation of the primer layer 100, an emission range A, is preferably chosen in which the primer layer 100 exhibits an absorption of less than or equal to 50%, preferably less than or equal to 20%, and preferably less than or equal to 5%. In this way, the quality of the primer layer 100 is minimally impacted, or not impacted at all, by the passage of the laser radiation, and it can be reused for a new implementation of the process according to the invention.
[0104] The laser radiation also most often passes through a support substrate 1000 as described above. An emission range Aa will then preferably be chosen in which the support substrate 1000 has an absorption of less than or equal to 90%, preferably less than or equal to 50%.
[0105] As illustrated in [Fig.1G], after subjecting the buffer layer 200 to laser radiation, on one side a stack comprising the support substrate 1000 and the primer layer 100, and on the other side a stack comprising the receiving substrate 2000 and the germination layer 300.
[0106] Figure 1H illustrates a growth step by epitaxy from the lower face 302 of the germination layer 300 of a layer of interest 400. This layer of interest 400 typically has a dimension in the vertical direction greater than its dimensions in projection onto the horizontal XY plane in order to be used in so-called vertical devices, for example, for power components. In the example illustrated in Figure 1H, each island 300a, 300b, 300c of the germination layer 300 serves as the basis for the epitaxy of an island 400a, 400b, 400c of the layer of interest 400, the islands 400a, 400b, 400c of the layer of interest 400 being disjoint.
[0107] Fig. II illustrates a variant of this same growth stage of the layer of interest 400. In this embodiment, the islands 400a, 400b, 400c of the layer of interest 400 grown from the islands 300a, 300b, 300c of the germination layer are coalesced so that the layer of interest 400 forms a single continuous layer.
[0108] It should be noted that the process may include, depending on the intended applications, one or more steps of doping the germination layer 300 and / or the layer of interest 400. The process may also include the deposition of one or more layers, possibly doped, onto the upper surface 301 of the germination layer 300 before transferring it to the receiving substrate 2000. These various optional steps may, in particular, enable the fabrication of electronic or microelectronic devices. A P / N junction may, in particular, be formed within the germination layer 300 and the layer of interest 400.
[0109] The receiving substrate 2000 is advantageously based on a material having a coefficient of thermal expansion (CTE) close to that of the second IILN material and, if the third IILN material is different from the second IILN material, close to that of the third IILN material. Advantageously, the difference between the CTEs does not exceed 20%. In this way, the occurrence of cracks due to differences in CTE is limited, particularly during the cooling of the assembly after the epitaxy of the layer of interest 400. With this in mind, and especially when the second IILN material and / or the third IILN material is GaN, a poly-AIN, poly-SiC, or silicon receiving substrate 2000 is advantageously chosen. The receiving substrate 2000 can, for example, be a silicon substrate incorporating an integrated circuit such as a CMOS circuit. This is particularly the case when the germination layer 300 and / or the layer of interest 400 are doped during the process.
[0110] Furthermore, it is noted that the stack comprising the support substrate 1000 and the starter layer 100 ([Fig. 1G]) is identical to that shown in [Fig. 1B]. It can be reused for a new implementation of the process just described with reference to Figures 1B to 1F. The same donor substrate 1000 and the same starter layer 100 can be used ten times or more for the growth of an IILN material. Thus, the present process allows for a rationalization of manufacturing costs and is therefore much less expensive than some current techniques for growing IILN materials.
[0111] A second embodiment of the process according to the invention will now be described with reference to Figures 2A to 2D. It reproduces in all respects the steps of the first embodiment but differs from it in that the primer layer 100 forms a single continuous layer, as illustrated in [Fig. 2A], and not disjointed islands. In this embodiment, the primer layer 100 can, as shown in the In the figures, the primer layer 100 rests on the support substrate 1000. According to another example, the primer layer 100 is a substrate based on the first III-N material, typically a GaN substrate. Thus, the primer layer 100 itself forms the support substrate. In this case, it typically does not rest on a separate support substrate 1000 (case not shown). In this embodiment, the primer layer 100 can, for example, have a diameter of 200 or 300 mm.
[0112] As illustrated in [Fig. 2B], the epitaxial growth of the buffer material followed by the second material III-N forms a buffer layer and a germination layer, each forming a single continuous layer. [Fig. 2C] illustrates the step of bonding the upper face 301 of the germination layer 300 to the receiving substrate 2000 and the step of exposing the buffer layer 200 to laser radiation. The characteristics of these steps presented in the first embodiment apply mutatis mutandis to this second embodiment.
[0113] The choice of a continuous or discontinuous primer layer 100 (and, consequently, of a continuous or discontinuous buffer layer 200 and germination layer 300) depends on the intended applications and in particular on the dimensions of the devices in which the layer of interest 400 will be used.
[0114] According to an example illustrated in Figures 3A to 3C, an adhesion layer 500 is deposited around the primer layer 100, the buffer layer 200 and the germination layer 300. This example is advantageously implemented in combination with the first embodiment because it allows good mechanical support between the different islands. As illustrated in [Fig.3A], the adhesion layer 500 is preferably in contact with the upper face 1001 of the support substrate 1000, the side 103A, 103B, 103C of each of the islands 100a, 100b, 100c of the priming layer 100, the side 203a, 203b, 203c of each of the islands 200a, 200b, 200c of the buffer layer 200 and the side 303a, 303b, 303c of each of the islands 300a, 300b, 300c of the germination layer 300. It can also extend above, and preferably in contact with, the upper face 301 of the germination layer 300.In the latter case, it is the upper face 501 of the adhesion layer 501 that is in direct contact with the upper face 2001 of the receiving substrate 2000.
[0115] The step of exposing the buffer layer 200 to laser radiation ([Fig. 3B]) is carried out in the same way as in the previous embodiments. The separation of the primer layer 100 and the germination layer 300 due to the alteration of the buffer layer 200 causes the adhesion layer 500 to become level with the altered buffer layer 200. The adhesion layer 500 itself eventually splits into two parts, one surrounding the germination layer 300 and the other surrounding the primer layer 100. As illustrated in [Fig. 3C], a reusable assembly is obtained, as in [Fig. 1G]. iterations of the process according to the invention, and an assembly enabling the growth of a third III-N material from the germination layer 300.
[0116] According to an advantageous example illustrated in Figures 4A to 4C, before the germination layer 300 is bonded to the receiving substrate 2000, upper electrical contacts 610 are deposited on the upper surface 301 of the germination layer 300 and / or lower electrical contacts 620 are deposited on the upper surface 2001 of the receiving substrate 2000. Figures 4A to 4C illustrate the case where contacts have been deposited on both the upper surface 301 of the germination layer 300 and on the upper surface 2001 of the substrate, and are subsequently brought into contact during bonding ([Fig. 4B]). The assembly formed by an upper electrical contact 610 and a lower electrical contact 620 will hereafter be referred to as an electrical contact 600.However, it is perfectly conceivable that only upper electrical contacts 610 are deposited and brought into contact with the upper face 2001 of the receiving substrate 2000 during the bonding step, or that only lower electrical contacts 620 are deposited and brought into contact with the upper face 301 of the germination layer 300 during the bonding step. Electrical continuity between the germination layer 300 and the receiving substrate 2000 will be ensured in each of these cases.
[0117] In the case where contacts 620 are deposited on the upper face 2001 of the receiving substrate 2000, the presence of a secondary adhesion layer 550 can be provided to ensure effective bonding of the two stacks represented in [Fig.4A] as well as good mechanical support of the assembly.
[0118] In this example, the bonding of the germination layer 300 to the receiving substrate 200 is done indirectly, more precisely at the level of the electrical contacts and possibly the upper face 501 of the adhesion layer 500.
[0119] It is also possible to provide for the presence, between the receiving substrate 2000 and the electrical contacts 610, 620, of a layer 700 comprising electrical contacts structured and configured to meet the power supply requirements of the devices that will be manufactured using the process.
[0120] Figures 4D to 4G illustrate an example of a sequence of steps that can be carried out starting from the assembly comprising the germination layer obtained in [Fig. 4C]. As in the embodiments described previously, one step consists of growing, by epitaxy, a layer of interest 400 from the lower face 302 of the germination layer. Secondary electrical contacts 650 can then be formed on the upper face 401 of the layer of interest 400. A new adhesion layer can be deposited on the adhesion layer 500, around the layer of interest 400 and the secondary electrical contacts 650, in order to complete the encapsulation of the assembly. The germination layer 300 and the layer of interest 400 can then be cut into the desired shapes and the receiving substrate 2000 can be removed ([Fig.4G]), thus forming a plurality of devices, each formed by an electrical contact 600, a portion of the germination layer 300, a portion of the layer of interest 400, and a secondary electrical contact 650.
[0121] According to another embodiment illustrated in Figures 5A to 5E, after the growth step of the layer of interest 400 ([Fig.5B]), the layer of interest 400 is transferred onto a secondary receiving substrate 3000 and the receiving substrate 2000 is removed (transition from [Fig.5C] to [Fig.5D]).
[0122] More specifically, according to this particular embodiment, the germination layer 300 was directly bonded to the receiving substrate 2000 ([Fig. 5A]) before the alteration of the buffer layer 200. As illustrated in [Fig. 5B], in the same way as in previous embodiments, the layer of interest 400 is raw from the germination layer 300. Secondary electrical contacts 650 are then formed on the upper surface 401 of the layer of interest 400, and the assembly is then transferred to the secondary receiving substrate 3000 at the level of the secondary electrical contacts 650 ([Fig. 5C]). The secondary receiving substrate 3000 can, for example, be a silicon substrate. Preferably, an additional adhesion layer is deposited on the adhesion layer 500 in order to surround the layer of interest 400 and the secondary electrical contacts 650.After the removal of the receiving substrate 2000, electrical contacts 600 are formed on the lower face 302 of the germination layer 300. The germination layer 300 and the layer of interest 400 can then be cut into the desired shapes and the secondary receiving substrate 3000 can be removed ([Fig.5E]), thus forming a plurality of devices, each formed by an electrical contact 600, a portion of the germination layer 300, a portion of the layer of interest 400, and a secondary electrical contact 650.
[0123] According to another embodiment, the receiving substrate 2000 is electrically conductive. It may, for example, be a poly-SiC substrate, possibly doped. Advantageously, electrical contacts 2010 have been formed, typically by etching, from the upper surface 2001 of the receiving substrate 2000. It is also possible to form electrical contacts on the upper surface 2001 of the receiving substrate 2000. Figures 6B to 6F illustrate steps similar to those described with reference to Figures 4B to 4F, the only difference being that the receiving substrate 2000 is electrically conductive this time. Furthermore, advantageously, as illustrated in [Fig. 6G], the receiving substrate 2000 is also cut during the device cutting step and is not removed.
[0124] The use of a conductive substrate makes it easier to inject current into the device, which is particularly advantageous in the case of a vertical device. It is possible to retain the receiving substrate 2000 in the final device, as illustrated in [Fig.6G], which saves the step of removing it.
[0125] It should be noted that the presence of the buffer layer 200 can lead to growth of the germination layer 300 under nitrogen polarity. This effect is obtained, for example, when the buffer material is HfN or TiN.
[0126] The polarization of the germination layer 300 during its formation by epitaxy is a significant advantage because it provides a polarization orientation that allows for further growth under nitrogen polarity by epitaxy after a single transfer. More precisely, the layer of interest 400 can be grown from the lower face 302 of the germination layer 300 and itself be metal-polarized. In most current approaches, it is necessary to perform a double transfer of the layer to be polarized in order to orient the polarization in the required direction, but such a double transfer is costly. The process therefore reduces the production costs of a polarized IIIN layer.
[0127] Through the different embodiments described above, it is clear that the invention offers a solution for obtaining high-quality IILN material layers while limiting manufacturing costs, thus meeting the current needs of the industry.
[0128] As mentioned in the introduction, one of the main obstacles to growing GaN on silicon lies in the very significant difference in CTE between GaN and silicon. Because of this difference, the thickness of GaN that can be grown on silicon is limited, as the thicker the layers, the more brittle the wafers become. It is therefore difficult to obtain high-quality layers, especially thick layers. By growing the layer of interest 400 on a receiving substrate 2000 with a suitable CTE, such as a poly-AIN substrate, it is possible to obtain layers with a low dislocation rate. By implementing the present invention, these high-quality layers can be transferred onto a silicon wafer, and then the active layers of a light-emitting diode (LED), for example (quantum wells, pGaN), can be epitaxially grown without going through the process of thick-layer epitaxial growth on silicon.These layers will then be available for the manufacture of micro-display devices or other components including LEDs.
[0129] The invention is not limited to the embodiments previously described and extends to all embodiments covered by the invention.
Claims
1. Demands A process for growing a III-N material, such as GaN, comprising the following steps: • Provide a primer layer (100) based on a first III-N material, the primer layer (100) having a top face (101) extending mainly in a horizontal plane (XY) defined by a first direction (X) and a second direction (Y), • To grow by epitaxy of a buffer material a buffer layer (200) from the upper face (101) of the primer layer (100), the buffer layer (200) having an upper face (201) and a lower face (202) opposite each other, the lower face (202) of the buffer layer (200) being opposite, and preferably in contact, with the upper face (101) of the primer layer (100), • Growing by epitaxy a germination layer (300), into a second III-N material, preferably identical to the first III-N material, from the upper face (201) of the buffer layer (200), the germination layer (300) having an upper face (301) and a lower face (302) opposite each other, the lower face (302) of the germination layer (300) being opposite, and preferably in contact, with the upper face (201) of the buffer layer (200), • Glue the upper surface (301) of the germination layer (300) onto a receiving substrate (2000), • Subject the buffer layer (200) to laser radiation having a main wavelength Xiaser, the primer layer (100) being configured to transmit at least part of the laser radiation, the primer layer (100) preferably having an absorption less than or equal to 10% for the main wavelength Xiaser, the laser radiation being configured to alter the buffer layer (200) so as to decouple the primer layer (100) and the germination layer (300), • Grow, by epitaxy of a third III-N material, preferably identical to the second III-N material, a layer of interest (400) from the lower face (302) of the germination layer (300).
2. A method according to the preceding claim wherein, in the horizontal plane (XY), the first material III-N has a first mesh length alu.N,i and the buffer material has a buffer mesh length a,ampOn, with | (am \4- a,ampOn ) | / am \4< 0.
02.
3. A method according to any one of the preceding claims, wherein, in the horizontal plane (XY), the mesh of the first material III-N has a first angle alu.N, and the mesh of the buffer material has an angle cttampOn, with | cttampOn — •
4. A method according to any one of the preceding claims wherein the buffer layer (200) has, along a third direction (Z) perpendicular to the horizontal plane (XY), a thickness e2Oo configured such that the buffer layer (200) has a dislocation density p less than 1010 cm2, preferably less than 108 cm2, preferably less than 107 cm2.
5. Method according to the preceding claim wherein e200<100 nm, preferably e200<20 nm.
6. A method according to any one of the preceding claims, wherein the first III-N material has a melting temperature Tmelting,ni, the epitaxy of the buffer material being carried out at a growth temperature Tgrowth,buffer, with Tgrowth,buffer = Tmelting,III-N.
7. A method according to any one of the preceding claims wherein, along a third direction (Z) perpendicular to the horizontal plane (XY), the primer layer (100) has a thickness e»» and the layer of interest (400) has a thickness e4Oo, with e4oo>2*eioo, preferably e4oo>3*eioo, preferably e4oo>5*eioo.
8. A method according to any one of the preceding claims in which, along a third direction (Z) perpendicular to the horizontal plane (XY), the buffer layer (200) has a thickness e200 and the layer of interest (400) has a thickness e400, with e4oo>2*e2oo, preferably e4oo>3*e2oo, preferably e4Oo>5*e2OO.
9. A method according to any one of the preceding claims wherein the laser radiation is configured to pass through the primer layer (100) before altering the buffer layer (200).
10. A method according to any one of the preceding claims in which, after the separation of the primer layer (100) and the germination layer (300), at least a part of the buffer layer (200) remains on the germination layer (300), and further comprising, after the step of subjecting the buffer layer (200) to laser radiation and before the step of growth of the layer of interest (400), a step of removing said at least part of the buffer layer (200).
11. A method according to any one of the preceding claims wherein the primer layer (100) forms a single continuous layer.
12. A method according to any one of claims 1 to 9 wherein the primer layer (100) forms disjoint germination substrates (100a, 100b, 100c).
13. A method according to the preceding claim in which each of the disjoint germination substrates (100a, 100b, 100c) has, in projection in the horizontal plane (XY), a maximum dimension of less than 150 mm, preferably less than 100 mm.
14. A method according to any one of the two preceding claims wherein, during the step of supplying the primer layer (100), the germination substrates (100a, 100b, 100c) are transferred onto a support substrate (1000).
15. A method according to any one of the preceding claims further comprising, after the epitaxy step of the second material III-N and before the step of bonding the upper face (301) of the germination layer (300) to the receiving substrate (2000), the formation of an adhesion layer (500) on the upper face (301) of the germination layer (300).
16. A method according to any one of the preceding claims wherein the III-N material is based on at least one of GaN, PAIN, InN and any combination of these materials.
17. A method according to any one of the preceding claims wherein the buffer material is one of the following materials: HfN, ZrN, NbN, TiN.
18. A method according to any one of the preceding claims further comprising the formation of electrical contacts (610) on the upper face (301) of the germination layer (300) and of secondary electrical contacts (650) on the upper face (401) of the layer of interest (400).
19. A method according to any one of the preceding claims wherein the receiving substrate (2000) is electrically conductive.
20. A method according to any one of the preceding claims wherein the receiving substrate (2000) comprises at least one integrated electronic circuit.
21. A method according to any one of the preceding claims wherein the buffer material is chosen so that the buffer layer (200) induces a nitrogen polarity within the germination layer (300).