Method for double transfer of layers

Abstract

The present invention relates to a method comprising the steps of supplying a heterostructure comprising a growth substrate (1), an intermediate layer of a two-dimensional material (2), and an epitaxial layer of a semiconductor material (3); supplying a rigid substrate (4) having a weakening plane (5); generating a first assembly by bonding the rigid substrate with the heterostructure, wherein the first plane (F) and the epitaxial layer (3) are present at the bonding interface; separating the first assembly in the intermediate layer of the two-dimensional material (2) to obtain a second assembly resulting from the transfer of the epitaxial layer (3) from the heterostructure to the rigid substrate (4); generating a third assembly by bonding the second assembly with a target substrate (7), wherein the epitaxial layer (3) is present at the bonding interface; and separating the third assembly along the weakening plane (5) of the rigid substrate (4).

Description

Technical Field

[0001] The field of the present invention is the field of methods for fabricating a laminated structure comprising a thin layer of semiconductor material adhering to a target substrate. More particularly, the present invention relates to a method using techniques for transferring layers based on 2D materials.

Background Art

[0002] Remote epitaxy is a method for generating a thin layer of semiconductor material, as disclosed, for example, in Kim, H., Chang, C.S., Lee, S. et al., Remote epitaxy. Nat Rev Methods Primers 2, 40 (2022), https: / / doi.org / 10.1038 / s43586-022-00122-w.

[0003] This method involves placing a layer of a two-dimensional material (also referred to as a 2D material or a van der Waals material) having strong atomic bonds in the plane but weak van der Waals interactions outside the plane between a growth substrate and a semiconductor layer grown by epitaxy. This layer of the 2D material behaves like a pseudo-transparent substrate, and the crystal structure of the epitaxial layer replicates the crystal structure of the growth substrate as if there were no intermediate layer of the 2D material. The advantage is that the epitaxial layer can be easily separated from the growth substrate due to the lack of covalent bonds between the growth substrate and the epitaxial layer. Substrates that may be expensive can thus be reused.

[0004] As described in the above article, the separation in the layer of the 2D material involves first depositing a nickel stress layer on the epitaxial layer and then placing a thermal release adhesive film on the stress layer. The laminate consisting of the adhesive film, the nickel layer, and the epitaxial layer may then be peeled off from the growth substrate after detachment induced in the layer of the 2D material by supplying mechanical energy.

[0005] As reported in the article above, this order of steps has several disadvantages.

[0006] Firstly, the deposition of a nickel layer causes contamination in both the epitaxial layer in contact with the nickel layer and the growth substrate loaded into the metal deposition apparatus. An additional protective layer may be deposited to limit contact and interaction and later removed. Therefore, several additional steps must be performed to solve this contamination problem, which is unfavorable to the cost of the method, not to mention the impact of these additional steps on the quality of the epitaxial layer and its delamination.

[0007] Next, the nickel layer is typically deposited by sputtering. The epitaxial layer is then subjected to ionic bombardment, which degrades its quality over thicknesses of several nanometers or even tens of nanometers. Consequently, the deposition of a protective layer may be necessary to protect the epitaxial layer, especially when the epitaxial layer is thin and damage over tens of nanometers must therefore be avoided. Again, an additional step must be performed, which has implications for both cost and method yield.

[0008] Furthermore, stress is applied to induce delamination in the 2D material layers. This stress must be uniform throughout the entire delamination process, from one end of the interface between the 2D material layers to the other, because even slight fluctuations in this stress can cause cracks in the epitaxial layer if it exceeds the mechanical fatigue limit of the epitaxial layer. The nickel layer helps prevent such cracks during delamination due to its thickness, but this is not a universal solution.

[0009] Finally, during this desorption process, the epitaxial layer is subjected to bending, which can cause cracks in the epitaxial layer. Subsequent handling of this layer, aimed at transferring it onto a target substrate, is further carried out using a flexible adhesive film. This also carries the risk of crack or fissure formation in the epitaxial layer. [Overview of the Initiative]

[0010] The present invention aims to propose a remote epitaxy technique that overcomes the aforementioned drawbacks and thus makes it possible to maintain the integrity of the epitaxial layer.

[0011] For this purpose, the present invention proposes a method for double transfer of layers, comprising the following steps. The step of supplying a heterostructure comprising a growth substrate, wherein an intermediate layer of a two-dimensional material and at least one epitaxial layer of a semiconductor material are formed in the intermediate layer on the growth substrate. The step of supplying a rigid substrate having a weakened plane formed by ion implantation through a first surface of the rigid substrate, wherein the weakened plane separates a thin layer from the bulk portion of the rigid substrate. A step of generating a first assembly by bonding a rigid substrate with a heterostructure, wherein the first surface of the rigid substrate and at least one epitaxial layer of the heterostructure are present at the junction interface between the rigid substrate and the heterostructure. A step of separating a first assembly in an intermediate layer of a two-dimensional material to obtain a second assembly resulting from the transfer of at least one epitaxial layer from a heterostructure to a rigid substrate, The steps include generating a third assembly by bonding a second assembly to a target substrate, wherein at least one epitaxial layer is present at the bonding interface between the second assembly and the target substrate, and A step of separating the third assembly along a weakening plane of a rigid substrate to obtain a fourth assembly resulting from the transfer of at least one epitaxial layer and thin layer of the third assembly onto a target substrate.

[0012] A preferred but non-limiting embodiment of this method is as follows: The bonding of the rigid substrate to the heterostructure for generating the first assembly is a surface-activated bond. The bonding of the rigid substrate to the heterostructure for generating the first assembly is an atomic diffusion bond. The separation of the first assembly in the intermediate layer of the two-dimensional material includes supplying mechanical and / or thermal energy. The thermal energy is supplied at a temperature lower than the temperature at which the rigid substrate separates in the weakening plane. The growth substrate and the rigid substrate have different thermal expansion coefficients of at least 0.3 ppm / K. The second assembly undergoes one or more technical steps of fabricating a semiconductor structure, each carried out at a temperature lower than the temperature at which the rigid substrate separates in the weakening plane. This further involves removing a thin layer from the fourth assembly, This further involves epitaxing a semiconductor material onto at least one epitaxial layer after the removal of a thin layer. At least one epitaxial layer of the semiconductor material comprises a layer of polar material, for example, a layer of GaN. The target substrate is a polycrystalline SiC substrate, a polycrystalline AlN substrate, a Si substrate with high electrical resistance, or a substrate supporting a semi-insulating SiC layer. The growth substrate is a silicon substrate with orientation (111). [Brief explanation of the drawing]

[0013] Other aspects, purposes, advantages, and features of the present invention will become more apparent when reading the following detailed description of preferred embodiments of the invention, which are given as non-limiting examples and illustrated with reference to the accompanying drawings. [Figure 1] This figure shows possible embodiments of the method according to the present invention. [Figure 2] A diagram showing a possible embodiment of the method according to the present invention. [Figure 3] A diagram showing a possible embodiment of the method according to the present invention. [Figure 4] A diagram showing a possible embodiment of the method according to the present invention. [Figure 5] A diagram showing a possible embodiment of the method according to the present invention. [Figure 6] A diagram showing a possible embodiment of the method according to the present invention. [Figure 7] A diagram showing a possible embodiment of the method according to the present invention. [Figure 8] A diagram showing a possible embodiment of the method according to the present invention. [Figure 9] A diagram showing a possible embodiment of the method according to the present invention. [Figure 10] A diagram showing a possible embodiment of the method according to the present invention. [Figure 11] A diagram showing a possible embodiment of the method according to the present invention. [Figure 12] A diagram showing a possible embodiment of the method according to the present invention.

Embodiments for Carrying Out the Invention

[0014] The present invention relates to a method for double transfer of layers, which combines the transfer of a semiconductor layer from a growth substrate using a transfer technology based on two-dimensional (2D) materials to a rigid substrate, and then the transfer of the semiconductor layer from the rigid substrate to a target substrate using Smart Cut (trademark) transfer technology.

[0015] In the context of this double transfer, the use of a rigid substrate makes it possible to perform a first transfer by desorption in the two-dimensional material without causing cracks in the semiconductor layer and without requiring a metal stressor layer. This use also makes it possible to handle the semiconductor layer in order to transfer the semiconductor layer onto the target substrate without cracks or cracks being formed in the semiconductor layer.

[0016] The method according to the present invention includes the step of supplying a heterostructure comprising a growth substrate, wherein an intermediate layer of a two-dimensional material and one (or more) epitaxial layers of a semiconductor material are formed on the intermediate layer on the growth substrate.

[0017] This supply may result from the fabrication of heterostructures in the context of possible embodiments of the method according to the present invention.

[0018] Referring to Figure 1, in this embodiment, the method includes the step of supplying a growth substrate 1, which is, for example, a Si substrate (particularly orientation (111)), a sapphire substrate, or a GaN substrate.

[0019] Referring to Figure 2, in this embodiment, the method then includes forming an intermediate layer of two-dimensional material 2 on the growth substrate 1. This formation may be performed after planarization of the surface of the growth substrate, for example, by mechanical or chemical polishing. The surface of the growth substrate may also be cleaned. This formation may include depositing the two-dimensional material 2 on the growth substrate 1. Purely as an example, this deposition may be carried out by MBE (Molecular Beam Epitaxy), CVD (Chemical Vapor Deposition), or ALD (Atomic Layer Deposition).

[0020] The two-dimensional material may be hexagonal boron nitride, h-BN, graphene, or more generally any van der Waals 2D material that enables remote epitaxy. The layers of the two-dimensional material thus consist of a limited number of single-atom sheets (single-atom layers) having weak interactions between them, enabling remote epitaxy of the semiconductor material layers. In possible embodiments, the number of sheets may be two or less.

[0021] Referring to Figure 3, in this embodiment, the method further includes the growth of an epitaxial layer of semiconductor material 3 on an intermediate layer 2. This growth generally occurs in two main steps: nucleation on the layer of two-dimensional material and standard growth of the epitaxial layer of semiconductor material. These two steps may be performed at different growth temperatures, with nucleation being performed at a lower temperature than standard growth.

[0022] The thickness of the epitaxial layer 3 is typically 100 nm to several microns, and in the case of a GaN epitaxial layer, it is preferably 500 nm to 2 microns. The epitaxial layer of the semiconductor material may be a layer of a polar material, such as GaN, AlN, or SiC. In the case of a GaN or AlN layer, due to its polarity, it has the characteristic of having a surface mainly composed of nitrogen atoms (N surface) on one side and a surface mainly composed of gallium atoms (Ga surface) or mainly composed of aluminum atoms (Al surface) on the other side. In this case, the Ga surface or Al surface exists at the interface with the layer of two-dimensional material 2, while the N surface forms a free surface. The same applies to a SiC layer where a Si surface exists at the interface with the layer of two-dimensional material 2, while a C surface forms a free surface.

[0023] In possible embodiments, the method involves growing multiple epitaxial layers that form a stack of crystalline layers. An example of a single epitaxial layer is discussed below, and it should be understood that the present invention is not limited to this scenario.

[0024] The method according to the present invention further includes the step of supplying a rigid substrate having a weakened plane formed by ion implantation through a first surface of the rigid substrate. This weakened plane separates a thin layer from the bulk portion of the rigid substrate.

[0025] This supply may arise from the preparation of a rigid substrate in the context of possible embodiments of the method according to the present invention.

[0026] Referring to Figure 4, in this embodiment, the method includes the step of supplying a rigid substrate 4, which is preferably an inexpensive substrate, such as a silicon substrate, and more particularly a silicon substrate with a crystal orientation (111).

[0027] Referring next to Figure 5, in this embodiment, the method includes implanting ion species through the surface F of the rigid substrate 4, thereby forming a weakening plane 5 within the rigid substrate 4 that separates the thin layer 6 from the bulk portion of the rigid substrate. The implanted species typically include hydrogen and / or helium. Those skilled in the art will be able to specify the required injection dose and energy.

[0028] After the heterostructure and the rigid substrate to be injected are supplied, the method according to the present invention, referring to Figure 6, includes the step of generating a first assembly by bonding the rigid substrate 4 with the heterostructure. This bonding is performed such that the first surface of the rigid substrate 4 and the epitaxial layer 3 of the heterostructure are present at the bonding interface between the rigid substrate and the heterostructure.

[0029] The bonding is performed to obtain a bonding energy at the junction interface between the rigid substrate and the heterostructure that is greater than the bonding energy at the van der Waals interface between the two-dimensional material and the epitaxial layer.

[0030] The bonding may be performed at ambient temperature. In possible embodiments, the bonding is performed under reduced pressure. Heat treatment to strengthen the bonding may also be performed at a temperature lower than the heat treatment temperature that would cause the rigid substrate to separate in the weakening plane.

[0031] In a preferred embodiment that enables obtaining a very strong bonding interface, the bonding of the rigid substrate to the heterostructure for generating the first assembly is surface-activated bonding (SAB), atomic diffusion bonding (ADP), or hydrophilic bonding with annealing to strengthen the bond.

[0032] Referring to Figure 7, the method then includes separating the first assembly in the intermediate layer of the two-dimensional material 2 to obtain a second assembly resulting from the transfer of the epitaxial layer 3 from the heterostructure to the rigid substrate 4, as shown in Figure 8.

[0033] This separation of the epitaxial layer 3 from the growth substrate 1 may be carried out by supplying mechanical and / or thermal energy to the layer of the two-dimensional material 2. When carried out by supplying thermal energy in conjunction with or without supplying mechanical energy, the separation utilizes stress induced during heating or subsequent cooling due to the difference in thermal expansion coefficients between the growth substrate 1 and the rigid substrate 4. For this reason, the growth substrate and the rigid substrate preferably have different thermal expansion coefficients of at least 0.3 ppm / K. The thermal energy is supplied at a temperature lower than the heat treatment temperature that causes the rigid substrate to separate in the weakening plane. As an example, it is possible to use a GaN growth substrate 1 (having a thermal expansion coefficient of 5.6 ppm / K) and a Si rigid substrate 4 (having a thermal expansion coefficient of 2.6 ppm / K), create a first assembly by bonding them at ambient temperature, and then apply heating to induce compressive stress in the GaN substrate.

[0034] It should be noted that performing injection in the rigid substrate before bonding and debonding as shown in Figures 6 and 7 is advantageous. This allows for preservation of the integrity of epitaxial layer 3 compared to solutions that perform injection in and through epitaxial layer 3 in the rigid substrate after debonding as shown in Figure 7.

[0035] In possible embodiments, after the desorption shown in Figure 7, the second assembly shown in Figure 8, more specifically the epitaxial layer 3 transferred onto the rigid substrate 4, undergoes one or more technical steps of fabricating a semiconductor structure. These steps particularly consist of cleaning, polishing, deposition, or etching. Each of these steps is performed at a temperature lower than the temperature of a heat treatment that would cause the rigid substrate to separate in a weakened plane.

[0036] After obtaining the second assembly shown in Figure 8, the method, referring to Figure 9, includes the step of generating a third assembly by bonding the second assembly to a target substrate 7, wherein the epitaxial layer 3 is present at the bonding interface between the second assembly and the target substrate. This bonding may be a hydrophilic bond, which may involve annealing to strengthen the bond.

[0037] Referring next to Figure 10, the method includes the step of separating the third assembly along the weakening plane 5 of the rigid substrate 4. As shown in Figure 11, this separation results in a fourth assembly arising from the transfer of the epitaxial layer 3 and thin layer 6 of the third assembly to the target substrate 7. This separation is typically obtained by applying a separation heat treatment at a temperature that can be 200°C to 600°C for silicon.

[0038] It should be noted that the method according to the present invention makes it possible to recycle the growth substrate and the rigid substrate for reuse in the same manner or for other purposes.

[0039] As shown in Figure 12, the method then includes removing the thin layer 6 from the fourth assembly, for example by etching, so that only the epitaxial layer 3 remains on the target substrate 7.

[0040] After the removal of the thin layer 6, the method also includes a step of restarting epitaxy on the epitaxial layer. If the epitaxial layer is a layer of polar material, the double transfer carried out by the present invention advantageously allows the surface of the epitaxial layer (e.g., Ga, Al, or Si surface) to be exposed, and thus allows the restart of epitaxy of the semiconductor material on the epitaxial layer.

[0041] The target substrate 7 may be a polycrystalline SiC substrate or a polycrystalline AlN substrate. Alternatively, the target substrate 7 may be a Si substrate having high electrical resistance. Another alternative is that the target substrate may be a substrate supporting a layer of semi-insulating SiC, for example, a Si substrate supporting such a layer of semi-insulating SiC, which optionally has high electrical resistance. The epitaxial layer 3 transferred onto the target substrate according to these examples may be a layer of GaN. "Semi-insulating material" is 10 5 This refers to materials that typically have an electrical resistance of Ω / cm or higher. "Materials with high electrical resistance" refers to materials that typically have an electrical resistance of 100 Ω / cm or higher.

Claims

1. A method for double transfer of layers, wherein the method is The step of supplying a heterostructure comprising a growth substrate (1), wherein an intermediate layer of a two-dimensional material (2) and at least one epitaxial layer of a semiconductor material (3) are formed on the intermediate layer of the growth substrate. The step of supplying a rigid substrate (4) having a weakened plane (5) formed by ion implantation through a first surface (F) of the rigid substrate (4), wherein the weakened plane separates a thin layer (6) from the bulk portion of the rigid substrate, The step of generating a first assembly by bonding the rigid substrate with the heterostructure, wherein the first surface (F) of the rigid substrate and the at least one epitaxial layer (3) of the heterostructure are present at the junction interface between the rigid substrate and the heterostructure. The steps include separating the first assembly in an intermediate layer of the two-dimensional material (2) to obtain a second assembly resulting from the transfer of the at least one epitaxial layer (3) from the heterostructure to the rigid substrate (4), The step of generating a third assembly by bonding the second assembly with a target substrate (7), wherein at least one epitaxial layer (3) is present at the bonding interface between the second assembly and the target substrate. The steps include: separating the third assembly along the weakening plane (5) of the rigid substrate (4) to obtain a fourth assembly resulting from the transfer of the at least one epitaxial layer (3) and the thin layer (6) of the third assembly onto the target substrate (7); Methods that include...

2. The method according to claim 1, wherein the bond between the rigid substrate and the heterostructure for generating the first assembly is a surface-activated bond.

3. The method according to claim 1, wherein the bond between the rigid substrate and the heterostructure for generating the first assembly is an atomic diffusion bond.

4. The method according to any one of claims 1 to 3, wherein the separation of the first assembly in the intermediate layer of the two-dimensional material includes supplying mechanical and / or thermal energy.

5. The method according to claim 4, wherein the thermal energy is supplied at a temperature lower than the temperature at which the rigid substrate separates in the weakening plane.

6. The method according to claim 5, wherein the growth substrate and the rigid substrate have different thermal expansion coefficients of at least 0.3 ppm / K.

7. The method according to any one of claims 1 to 6, wherein the second assembly undergoes one or more technical steps of fabricating a semiconductor structure, each of which is carried out at a temperature lower than the temperature at which the rigid substrate separates in the weakening plane.

8. The method according to any one of claims 1 to 7, further comprising removing the thin layer (6) from the fourth assembly.

9. The method according to claim 8, further comprising epitaxing the semiconductor material onto the at least one epitaxial layer after the removal of the thin layer.

10. The method according to any one of claims 1 to 9, wherein the at least one epitaxial layer of the semiconductor material comprises a layer of a polar material, for example, a layer of GaN.

11. The method according to any one of claims 1 to 10, wherein the target substrate is a polycrystalline SiC substrate, a polycrystalline AlN substrate, a Si substrate having high electrical resistance, or a substrate supporting a layer of semi-insulating SiC.

12. The method according to any one of claims 1 to 11, wherein the growth substrate is a silicon substrate with orientation (111).

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