Process for transferring a layer of monocrystalline SiC to a polycrystalline SiC carrier using an intermediate layer of polycrystalline SiC

Abstract

A process for manufacturing a composite structure comprising a thin layer (12) of monocrystalline SiC includes the steps of forming a polycrystalline SiC layer (11) on a donor substrate, at least a surface portion of which is made from monocrystalline SiC, implanting, before or after the forming step, ion species into said surface portion of the donor substrate so as to form a plane of weakness that defines the thin monocrystalline SiC layer (12) to be transferred, and, after the implanting and forming steps, bonding the donor substrate and a polycrystalline SiC carrier substrate (20), with the polycrystalline SiC layer (11) at the bonding interface, and separating the donor substrate along the plane of weakness so as to transfer the polycrystalline SiC layer (11) and the thin monocrystalline SiC layer (12) onto the polycrystalline SiC carrier substrate (20).

Description

[Technical field]

[0001] The field of the invention is that of semiconductor materials for microelectronic components. The invention more particularly relates to a process for manufacturing a composite structure comprising a thin layer of monocrystalline silicon carbide on a carrier substrate made of polycrystalline silicon carbide. [Background technology]

[0002] Silicon carbide (SiC) is being used more and more widely in power electronics applications, especially to meet the needs of a growing range of electronics, e.g., electric vehicles. Power devices and integrated power systems based on single crystal SiC can indeed manage much higher power densities than their conventional silicon counterparts, and do so with smaller sized active areas.

[0003] Nevertheless, monocrystalline SiC substrates for the microelectronics industry remain expensive and difficult to supply in large sizes. It is therefore preferred to use layer transfer solutions to fabricate composite structures comprising a thin layer of monocrystalline SiC on a typically lower-cost carrier substrate. One well-known thin layer transfer solution is the Smart Cut™ process, which is based on implanting light ions and bonding by direct bonding. Such a process makes it possible to manufacture composite structures comprising a thin layer made of monocrystalline SiC, taken for example from a donor substrate made of monocrystalline SiC, in direct contact with a carrier substrate made of polycrystalline SiC.

[0004] Nevertheless, achieving high-quality direct bonding by molecular adhesion between two substrates made from single-crystal and polycrystalline SiC remains challenging due to the complexity of controlling the surface finish and roughness of the substrates.

[0005] The intended application requires good thermal and electrical conduction between the thin layer made of monocrystalline SiC and the carrier substrate made of polycrystalline SiC. Moreover, the presence of bonding defects at the bonding interface is very detrimental to the quality of the structures fabricated in the thin layer made of monocrystalline SiC. For example, the lack of adhesion between the two surfaces at the bonding defect can lead to local separation of the thin layer at this location during its transfer from the monocrystalline SiC substrate to the polycrystalline SiC substrate.

[0006] Two solutions have been reported in the literature to achieve the joining of two substrates made from monocrystalline and polycrystalline SiC, but no evidence is available today regarding their effectiveness on an industrial scale. Thus, on the one hand, surface activated bonding (SAB), which consists of activating the surfaces to be joined, typically by argon bombardment, and on the other hand, atomic diffusion bonding (ADB), which involves the sputter deposition of an ultra-thin layer and bonding under ultra-high vacuum, are known. These solutions have the drawback of generating unstable layers at the joining interface that can cause joint defects and negatively affect the electrical conduction. DISCLOSURE OF THEINVENTION

[0007] The object of the present invention is to provide a technique which overcomes these drawbacks, in order to provide a composite structure comprising a thin layer made of monocrystalline SiC of very high quality, and in particular to improve the performance and reliability of power devices intended to be manufactured on said thin layer.

[0008] To this end, the invention relates to a process for manufacturing a composite structure comprising a thin layer of monocrystalline silicon carbide (SiC) arranged on a polycrystalline SiC carrier substrate, the process comprising: forming a polycrystalline SiC layer on a donor substrate, at least a surface portion of which is made of monocrystalline SiC; implanting ion species into the surface portion of the donor substrate before or after the forming step to form a plane of weakness that defines a thin monocrystalline SiC layer to be transferred; After the implanting and forming steps, bonding the donor substrate and the polycrystalline SiC carrier substrate, where the polycrystalline SiC layer is at the bonding interface, and separating the donor substrate along a plane of weakness to transfer the polycrystalline SiC layer and the thin single crystal SiC layer onto the polycrystalline SiC carrier substrate. The present invention provides a process including:

[0009] Certain preferred, but non-limiting aspects of this process are as follows. The polycrystalline SiC layer has a polytype identical to that of the carrier substrate; The step of forming the polycrystalline SiC layer includes depositing polycrystalline SiC. The deposition of polycrystalline SiC is by chemical vapor deposition. The deposition of polycrystalline SiC is carried out at temperatures below 1000 °C. The step of forming the polycrystalline SiC layer includes depositing an amorphous SiC layer and applying a recrystallization anneal to the amorphous SiC layer. The polycrystalline SiC layer deposited on the donor substrate has a thickness between 10 nm and 10 μm. This process includes thinning and / or polishing of the surface of the polycrystalline SiC layer intended to be at the bonding interface during the bonding step and / or the surface of the carrier substrate intended to be at the bonding interface during the bonding step, The process further comprises the formation of a bonding layer on each of the donor substrate and the carrier substrate, said bonding step being performed by direct bonding of the thus formed bonding layer. The bonding layer formed on each of the donor substrate and the carrier substrate is a metal layer, for example a layer of tungsten or a layer of titanium; The bonding layer formed on each of the donor substrate and the carrier substrate is a layer of silicon, carbon or silicon carbide; The bonding layer has a melting point below the annealing temperature applied during the bonding step.

[0010] Other aspects, objects, advantages and features of the present invention will become more apparent on reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example and with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is a schematic cross-sectional view of a single crystal SiC donor substrate. [Diagram 2] FIG. 1 is a schematic cross-sectional view of the deposition of a polycrystalline SiC layer on the surface of a single crystal SiC donor substrate. [Diagram 3] 2 is a schematic cross-sectional view of the formation, by implantation of ion species, of a plane of weakness in the donor substrate of FIG. 1 to define a thin monocrystalline SiC layer to be transferred. [Figure 4] 3 is a schematic cross-sectional view of the bonding of the donor substrate and carrier substrate of FIG. 2. [Diagram 5] FIG. 13 is a schematic cross-sectional view of the separation of a donor substrate along a plane of weakness for the transfer of a thin monocrystalline SiC layer to a carrier substrate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Detailed Disclosure of Specific Embodiments The invention relates to a process for manufacturing a composite structure comprising a thin layer of monocrystalline SiC arranged on a polycrystalline SiC carrier substrate, which process comprises the transfer of the thin layer of monocrystalline SiC from a donor substrate, at least a surface portion of which is made of monocrystalline SiC, to the carrier substrate according to the Smart Cut™ process.

[0013] The donor substrate can be a bulk substrate of monocrystalline SiC. In other embodiments, the donor substrate can be a composite substrate comprising a surface layer of monocrystalline SiC and at least one other layer of another material, in which case the monocrystalline SiC layer has a thickness of 0.5 μm or more.

[0014] According to the invention, a preparation is made for forming a polycrystalline SiC layer on the donor substrate before bonding with the polycrystalline SiC carrier substrate. In that way, a bonding interface is created between materials having the same morphology (i.e. two polycrystalline SiC) instead of the dissimilar crystal structures of the prior art (i.e. monocrystalline SiC added to polycrystalline SiC). Thus, the drawbacks related to the bonding of these dissimilar crystal structures are avoided. In particular, the invention makes it possible not to create a conduction barrier at the bonding interface and to have a contact area that is not reduced by the formation of cavities at this interface.

[0015] 1, the process according to the invention begins with the provision of a donor substrate 10, at least a surface portion of which is made from single crystal SiC. In the figure, a bulk substrate 10 of single crystal SiC is shown.

[0016] 2, the process includes forming a polycrystalline SiC layer 11 on a donor substrate 10. The polycrystalline SiC layer 11 formed on the donor substrate preferably has a thickness between 10 nm and 10 μm, more preferably less than 50 nm.

[0017] The size of the grains of the polycrystalline SiC layer 11 is preferably less than 30 nm, more preferably less than 10 nm, which makes it possible to limit the surface roughness of the layer 11 thus deposited. Such a reduction in grain size further provides the advantage that the conditions for forming the polycrystalline SiC layer 11 can approach those for an amorphous SiC layer, and the layer 11 thus formed can be a mixture of small grains and a high proportion of amorphous SiC, without being detrimental to the effects of the invention.

[0018] Silicon carbide comes in various crystalline forms (also called polytypes). The most common are the 4H, 6H and 3C forms. Preferably, the formation of the polycrystalline SiC layer 11 is performed to give the same polytype as that of the carrier substrate 20, typically the 3C polytype.

[0019] In one possible embodiment, the polycrystalline SiC layer is formed by deposition of polycrystalline SiC. Such deposition of the polycrystalline SiC layer can be physical vapor deposition (for example of the EBPVD [electron beam physical vapor deposition] type) or chemical vapor deposition (for example of the DLI-CVD [direct liquid injection chemical vapor deposition] type). In one possible embodiment, the deposition of the polycrystalline SiC layer is carried out at a temperature below 1000 ° C, preferably below 900 ° C, and even more preferably below 850 ° C. This embodiment has been found to be particularly suitable when the deposition of the polycrystalline SiC layer 11 is carried out after the implantation of ion species described below for forming weak planes in the donor substrate. This relatively low temperature makes it possible in particular to limit the growth of cavities present in the weak planes, which growth, in the absence of a reinforcing effect imparted to the donor substrate, would result in cavities and deformations of the layer that directly correspond to the appearance of blistering phenomena.

[0020] In one embodiment variant, which may be particularly used when the implantation of ion species described below is performed after the formation of the polycrystalline SiC layer 11, the formation of the polycrystalline SiC layer first involves the deposition of a layer of (fully or partially) amorphous SiC, followed by a recrystallization anneal, typically at a temperature above 1100° C., which converts the layer of amorphous SiC into the polycrystalline that constitutes the polycrystalline SiC layer 11.

[0021] In one possible embodiment, the formation of the polycrystalline SiC layer 11 involves the formation of a bonding layer, for example a layer of silicon, carbon or silicon carbide, or a metal layer, for example a layer of tungsten or titanium, on the polycrystalline SiC layer 11 and on the carrier substrate, respectively. The bonding layer can be formed according to a physical vapor deposition (PVD) process, using argon or an argon / nitrogen or argon / propane mixture as the gas for the ablation of the target. The bonding layer preferably has a melting point below the temperature of the annealing applied during the bonding step. Thus, for example, a bonding layer made from silicon or titanium is selected when an annealing at a temperature of the order of 1700° C. / 1800° C. is applied during the bonding step.

[0022] 3, the process further includes implanting ion species into the donor substrate 10, either before or after the formation of the polycrystalline SiC layer 11, to form a plane of weakness 13 that defines the thin monocrystalline SiC layer 12 to be transferred. In the figure, the implantation is performed after deposition of the polycrystalline SiC layer 11.

[0023] The implanted species typically include hydrogen and / or helium. A person skilled in the art can define the required implantation dose and energy.

[0024] When the donor substrate is a composite substrate, the implantation is performed so as to create a weakened surface in a surface layer of the monocrystalline SiC of said donor substrate.

[0025] Preferably, the thin layer 12 of monocrystalline SiC has a thickness of less than 1 μm. In particular, such a thickness is achievable on an industrial scale using the Smart Cut™ process. In particular, the implantation devices available on industrial production lines allow such an implantation depth to be obtained.

[0026] Referring to Figure 4, the process includes bonding of the donor substrate and the carrier substrate after said implantation and said forming. The bonding is a direct bond without an intermediate electrically insulating layer, obtained by molecular adhesion of the contacted surfaces. The bonding is typically performed at ambient temperature. The bonding is preferably performed under vacuum.

[0027] During this bonding, the polycrystalline SiC layer 11 previously formed on the donor substrate is at the bonding interface. The expression "layer at the bonding interface" is understood to mean a layer at the side of the face of the donor substrate bonded to the carrier substrate, but does not necessarily imply a direct contact between said layer and the carrier substrate. Said layer can thus be either bonded directly to the carrier substrate or covered with a bonding layer, such as the above-mentioned bonding layer, to which the bonding is performed. Bonding by direct contact of a polycrystalline layer has the advantage of physically separating the interface between the monocrystalline SiC and the polycrystalline SiC at the bonding interface.

[0028] This bonding is typically preceded by operations to prepare the surfaces to be bonded, for example here two polycrystalline SiC surfaces, for example precision polishing, wet or dry cleaning, surface activation, etc. In particular, the processes may include thinning and / or polishing of the surface of the polycrystalline SiC layer 11 that is intended to be at the bonding interface during bonding and / or of the surface of the carrier substrate 20 that is intended to be at the bonding interface during bonding.

[0029] 5, the process then involves separating the donor substrate 10 along the plane of weakness 13 so as to transfer the polycrystalline SiC layer 11 and the thin monocrystalline SiC layer 12 onto the carrier substrate 20. In a known manner, this separation can be caused by heat treatment, mechanical action, or a combination of these means. The remainder of the donor substrate 10' can preferentially be recycled for another use.

[0030] One or more finishing operations may then be applied to the transferred monocrystalline SiC layer 12. For example, smoothing, cleaning, and even polishing, e.g., chemical mechanical polishing (CMP) or grinding, may be performed to remove defects related to the implantation of ionic species and to reduce the roughness of the transferred monocrystalline SiC layer 12 (which makes it possible to obviate the need for preferential chemical etching for such and such grain orientations).

Claims

1. A process for manufacturing a composite structure comprising a thin layer (12) of single crystal silicon carbide (SiC) disposed on a polycrystalline SiC carrier substrate (20), comprising: forming a polycrystalline SiC layer (11) on a donor substrate (10) at least a surface portion of which is made of monocrystalline SiC; before or after the forming step, implanting ion species into the surface portion of the donor substrate (10) so as to form a plane of weakness (13) that defines a thin monocrystalline SiC layer (12) to be transferred; After the implanting and forming steps, bonding the donor substrate (10) and the polycrystalline SiC carrier substrate (20), with the polycrystalline SiC layer (11) at the bonding interface, and separating the donor substrate (10) along the plane of weakness (13) to transfer the polycrystalline SiC layer (11) and the thin single-crystal SiC layer (12) onto the polycrystalline SiC carrier substrate (20). The process includes:

2. The process of claim 1 , wherein the polycrystalline SiC layer (11) has the same polytype as the polytype of the carrier substrate (20).

3. The process of claim 1 or 2, wherein the step of forming the polycrystalline SiC layer (11) comprises deposition of polycrystalline SiC.

4. The process of claim 3 wherein said deposition of polycrystalline SiC is chemical vapor deposition.

5. The process of claim 3 wherein said deposition of polycrystalline SiC is carried out at a temperature below 1000°C.

6. 3. The process of claim 1 or 2, wherein the step of forming the polycrystalline SiC layer (11) comprises depositing an amorphous SiC layer and applying a recrystallization anneal to the amorphous SiC layer.

7. 3. The process of claim 1 or 2, wherein the polycrystalline SiC layer (11) formed on the donor substrate has a thickness between 10 nm and 10 μm.

8. 3. The process according to claim 1 or 2, further comprising thinning and / or polishing a surface of the polycrystalline SiC layer (11) intended to be at the bonding interface during the bonding step and / or a surface of the carrier substrate (20) intended to be at the bonding interface during the bonding step.

9. The process of claim 1 or 2, further comprising the formation of a bonding layer on each of the donor substrate and the carrier substrate, wherein the bonding step is performed by direct bonding of the bonding layer thus formed.

10. The process of claim 9 , wherein the bonding layer formed on each of the donor substrate and the carrier substrate is a metal layer, for example a layer of tungsten or a layer of titanium.

11. The process of claim 9 , wherein the bonding layer formed on each of the donor substrate and the carrier substrate is a layer of silicon, carbon, or silicon carbide.

12. The process of claim 9 , wherein the bonding layer has a melting point below the temperature of the anneal applied during the bonding step.

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