Method for transferring a layer of monocrystalline SiC onto a polycrystalline SiC support using a temporary substrate of monocrystalline SiC

Abstract

The invention relates to a method comprising the following steps: manufacturing a temporary structure comprising the formation of a polycrystalline silicon carbide, SiC, support layer (3) on a temporary monocrystalline SiC substrate (1), the temporary structure having a front face (FF) on the side of the polycrystalline SiC support layer and a rear face (BF) on the side of the temporary monocrystalline SiC substrate; transferring a thin layer of monocrystalline SiC (4) onto the front face (FF) of the temporary structure; removing the temporary monocrystalline SiC substrate (1) from the temporary structure so as to obtain a composite structure comprising the thin layer of monocrystalline SiC (4) arranged on the polycrystalline SiC support layer (3). Figure for abstract: Figure 1

Description

Title of the invention: Method for transferring a layer of monocrystalline SiC onto a polycrystalline SiC support using a temporary substrate of monocrystalline SiC Technical field

[0001] The field of the invention is that of semiconductor materials for microelectronic components. The invention relates more particularly to a method for manufacturing a composite structure comprising a thin layer of monocrystalline silicon carbide on a support substrate of polycrystalline silicon carbide. Prior art

[0002] Silicon carbide (SiC) is increasingly widely used in power electronics applications, particularly to meet the needs of emerging electronics fields such as electric vehicles. Power devices and integrated power systems based on single-crystal SiC can effectively handle much higher power density than their traditional silicon counterparts, and with smaller active area dimensions.

[0003] Monocrystalline SiC substrates intended for the microelectronics industry nevertheless remain expensive and difficult to supply in large sizes. It is therefore advantageous to use layer transfer solutions to develop composite structures typically comprising a thin layer of monocrystalline SiC on a lower-cost support substrate. A well-known thin-layer transfer solution is the Smart Cut™ process. Such a process makes it possible, for example, to manufacture a composite structure comprising a thin layer of monocrystalline SiC, taken from a donor substrate of monocrystalline SiC (mSiC), in contact with a recipient substrate of polycrystalline SiC (pSiC).

[0004] This pSiC receiving substrate is a wafer obtained from a relatively thick (for example, 0.6 to 3 mm thick) pSiC plate (generally referred to as a slab). A deposition of pSiC on a growth substrate (for example, a graphite substrate), typically a chemical vapor deposition at a temperature between 1100°C and 1400°C, makes it possible to form the pSiC plate. Following removal of the growth substrate, the pSiC plate is subjected to a process for forming one or more wafers (a so-called wafering process in English) which comprises various steps of cleaning, etching, grinding and polishing and makes it possible to obtain one or more pSiC wafers having a desired shape. (including a beveled edge) and a desired thickness. Sawing can also be performed during this process, especially when several wafers are to be manufactured from the same wafer. The target thickness of the polycrystalline SiC wafer thus manufactured is, according to the SEMI standard, 350 pm for a 150 mm diameter wafer and 500 pm for a 200 mm diameter wafer.

[0005] Reducing the thickness of the pSiC deposit proves to be complicated to achieve because a reduced thickness is a source of deformation (warp in English). This deformation cannot be corrected subsequently, except by implementing special techniques which necessarily complicate the process.

[0006] It is therefore necessary to deposit relatively thick pSiC and then thin the pSiC plate by grinding to achieve the target thickness. This thinning is however expensive and time-consuming. Statement of the invention

[0007] The objective of the invention is to propose a method for manufacturing a composite structure comprising a thin layer of mSiC on a pSiC support substrate which overcomes the aforementioned drawbacks by making it possible to reduce the thickness of pSiC to be deposited and therefore the thickness of pSiC to be thinned by grinding.

[0008] For this purpose, the invention proposes a method comprising the following steps: - manufacturing a temporary structure comprising the formation of a support layer of polycrystalline silicon carbide, SiC, on a temporary substrate of monocrystalline SiC, the temporary structure having a front face on the side of the support layer of polycrystalline SiC and a rear face on the side of the temporary substrate of monocrystalline SiC; - application of a thin layer of monocrystalline SiC to the front face of the temporary structure; - removing the temporary monocrystalline SiC substrate from the temporary structure so as to obtain a composite structure comprising the thin layer of monocrystalline SiC arranged on the support layer of polycrystalline SiC.

[0009] Some preferred but non-limiting aspects of this method are as follows: - the temporary substrate of monocrystalline SiC is covered with an intermediate layer on which the support layer of polycrystalline SiC is formed during the manufacture of the temporary structure; - removal of the temporary monocrystalline SiC substrate from the temporary structure includes laser detachment at the intermediate layer; removing the temporary monocrystalline SiC substrate from the temporary structure comprises forming a detachment plane in the temporary substrate by laser irradiation; removing the temporary monocrystalline SiC substrate from the temporary structure further comprises applying thermomechanical stresses to the detachment plane; the detachment plane is located in the polycrystalline SiC support layer; the temporary monocrystalline SiC substrate has a resistivity greater than 5 mQ.cm; it comprises, before removing the temporary monocrystalline SiC substrate from the temporary structure, bonding a handle substrate to the thin monocrystalline SiC layer and, after removing the temporary monocrystalline SiC substrate from the temporary structure, removing the handle substrate; it further comprises, after removal of the temporary monocrystalline SiC substrate from the temporary structure, thinning of the polycrystalline SiC support layer; it further comprises, after removal of the temporary monocrystalline SiC substrate from the temporary structure, metallization of a rear face of the polycrystalline SiC support layer; it further includes the fabrication of electronic component elements on the thin layer of monocrystalline SiC; the manufacturing of electronic component elements includes epitaxy of a migration layer on the thin layer of monocrystalline SiC; the formation of the polycrystalline SiC support layer on the temporary monocrystalline SiC substrate comprises chemical vapor deposition, physical vapor deposition, epitaxial growth deposition or sintering; the polycrystalline SiC support layer formed on the temporary monocrystalline SiC substrate has a thickness of between 50 pm and 200 pm, preferably between 80 pm and 180 pm; the polycrystalline SiC support layer formed on the temporary monocrystalline SiC substrate has a thickness within a target thickness range including as a central value a thickness of 350 pm or a thickness of 500 pm when the polycrystalline SiC support layer has a diameter of 150 mm or a diameter of 200 mm, respectively; - the transfer of the thin layer of monocrystalline SiC onto the front face of the temporary structure comprises bonding to the front face of the temporary structure a donor substrate of monocrystalline SiC previously subjected to an implantation of ionic species to form a weakening plane there and the supply of thermal and / or mechanical energy to separate the donor substrate of monocrystalline SiC previously subjected to an implantation of ionic species at the weakening plane. Brief description of the drawings

[0010] Other aspects, aims, advantages and characteristics of the invention will appear better on reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the appended [Fig.l] which is a diagram representing different stages of a method according to the invention.

[0011] DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0012] The invention provides a method for manufacturing a composite structure comprising a thin layer of mSiC on a pSiC support substrate.

[0013] With reference to step (A) shown in [Fig.l], this method begins by providing a temporary mSiC substrate 1. With reference to step (B) shown in [Fig.l], this method may comprise forming one or more intermediate layers 2 on the temporary mSiC substrate.

[0014] With reference to step (C) shown in [Fig.l], this method then comprises the manufacture of a temporary structure by means of the formation of a pSiC 3 support layer on the temporary mSiC 1 substrate, with, where appropriate, the intermediate layer(s) 2 present at the interface between the pSiC 3 support layer and the temporary mSiC 1 substrate. The formation of the pSiC 3 support layer may in particular comprise chemical vapor deposition, physical vapor deposition, epitaxial growth deposition or sintering.

[0015] The temporary mSiC 1 substrate has the advantage of having a coefficient of thermal expansion close to that of the pSiC 3 support layer. It is also capable of withstanding the high temperatures that may be associated with the formation of the pSiC 3 support layer.

[0016] In a possible embodiment, the pSiC support layer 3 formed in step (C) has a thickness of between 50 μm and 200 μm, preferably between 80 μm and 180 μm. Such a thickness typically complies with the requirements of a final manufacturing process, known as “Back-End”, of electronic component elements.

[0017] In another possible embodiment, the pSiC 3 support layer formed in step (C) has a pSiC thickness comprised in a target thickness range including as a central value a thickness of 350 pm or a thickness of 500 pm, for example a target thickness range of 350 pm + / - 25 pm for a pSiC 3 layer of 150 mm in diameter or 500 pm + / - 25 pm for a pSiC layer of 200 mm in diameter.

[0018] As shown in [Fig.l], the temporary structure has a front face FF on the side of the pSiC support layer 3 and a rear face BF on the side of the temporary monocrystalline mSiC substrate 1.

[0019] The pSiC 3 support layer formed in step (C) is likely to have a thickness non-uniformity (known as TTV for “Total Thickness Variation” in English). In a possible embodiment, the pSiC 3 support layer formed in step (C) may be subjected to a wafering process in order to correct this TTV. This process may in particular comprise rough grinding followed by fine grinding.

[0020] The method continues as represented by step (D) in [Fig.l] by transferring a thin layer of mSiC 4 onto the front face FF of the temporary structure. This thin layer of mSiC 4 preferably has a quality compatible with power electronics or radiofrequency electronics applications.

[0021] The transfer of the thin layer of mSiC 4 can be carried out in accordance with the Smart Cut™ process by proceeding to the bonding, on the front face of the temporary structure, of a donor substrate of mSiC previously subjected to an implantation of ionic species to form there a weakening plane and to a supply of thermal and / or mechanical energy to separate the donor substrate of mSiC at the weakening plane and thus carry out the transfer of the thin layer 4 of the donor substrate towards the temporary structure.

[0022] Prior to step (D), the pSiC support layer 3 formed in step (C) may be subjected to a surface preparation step aimed at making the front face FF compatible with the transfer of the thin layer of mSiC 4, for example with the bonding of the Smart Cut™ process. This surface preparation step may comprise polishing and / or fine grinding of the front face FF.

[0023] In a possible embodiment (not shown), the method may further comprise bonding, for example carried out using a resin or an oxide bonding layer, a handle substrate onto the thin layer of mSiC 4. The handle substrate makes it possible to mechanically stiffen and thus allow the handling of what it is attached to.

[0024] In a first case, the pSiC 3 support layer is thin (typically between 50 μm and 200 μm thick) in order to avoid the need to subsequently thin it or at least to limit the thickness of material to be removed by such thinning, it is possible to produce electronic component elements on the thin layer of mSiC 4 before proceeding with the removal of the temporary substrate of mSiC 1 during step (E) described below. The handle substrate then makes it possible to maintain the assembly constituted by the support layer of pSiC 3 and the thin layer of mSiC 4 before, during and after this removal of the temporary substrate of mSiC 1.

[0025] In another case, the first microns (1 - 5 pm up to 50 pm depending on the textures and microstructures) of formation of the pSiC 3 support layer have a microstructure that can be described as immature / changing, in the sense that the grain size / microstructure / texture has not reached the stability then present in the "core" of the material. The pSiC 3 support layer can then have a stress gradient that is likely to cause deformation of the assembly constituted by the pSiC 3 support layer and the thin mSiC 4 layer once the temporary mSiC 1 substrate has been removed. The use of the handle substrate makes it possible to limit this deformation.

[0026] In these two cases, it is possible to carry out all or part of a step of manufacturing electronic component elements on the thin layer of mSiC 4 (including for example an epitaxy of a drift layer in English) before the installation of the handle substrate.

[0027] The handle substrate is preferably made of a material having a coefficient of thermal expansion similar to that of silicon carbide. This material may be chosen so as to withstand the high temperatures (up to 1850°C) of a possible heat treatment, such as stress-relieving annealing in the pSiC 3 support layer, annealing enabling conduction to be activated at the interface between the pSiC 3 support layer and the mSiC 4 thin layer, or dopant activation annealing in an epitaxial migration layer on the mSiC 4 thin layer. This material may be mSiC, pSiC, graphite, or tungsten.

[0028] When such heat treatment is not carried out, or when it is carried out before the handle substrate is put in place, the latter may be a silicon substrate or a polymer substrate.

[0029] With reference to step (E) shown in [Fig.l], the method comprises removing the temporary mSiC substrate 1 from the temporary structure so as to obtain a composite structure comprising the thin layer of mSiC 4 arranged on the support layer of pSiC 3. This removal of the temporary mSiC substrate is, where appropriate, followed by the removal of the handle substrate. The removal of the handle substrate is for example carried out by means of a supply of thermal or mechanical energy.

[0030] The removal of the temporary mSiC substrate 1 may be preceded or followed by a step of forming electronic component elements in the thin mSiC layer 4 arranged on the pSiC support layer 3. This step typically comprises a combination of semiconductor film deposition or epitaxy operations, lithography, etching, doping, metal deposition and passivation. This step may in particular be implemented when the formation of the pSiC support layer 3 consisted of forming a layer having a thickness within a target thickness range including, for example, a thickness of 350 μm or a thickness of 500 μm as a central value. It may also be implemented when the pSiC support layer 3 formed on the temporary mSiC substrate 1 has a thin thickness of, for example, between 50 and 200 μm, then preferably using a handle substrate.

[0031] This step of forming electronic component elements may in particular comprise, before or after the removal of the temporary mSiC substrate 1 from the temporary structure, an operation of forming, typically by epitaxy, a migration layer on the thin layer of monocrystalline SiC (4).

[0032] Once these electronic component elements have been formed, the following steps are taken: (removal of the temporary mSiC 1 substrate when it has not been previously removed and) conditioning of the composite structure. This conditioning may comprise thinning of the pSiC 3 support layer. This thinning has the objective, for example, of bringing the pSiC support layer to a target thickness that meets the requirements of the final manufacturing process, known as the “Back-End”, of the electronic component elements. This target thickness is, for example, between 50 μm and 200 μm, preferably between 80 μm and 180 μm. This thinning may also have the objective of removing a damaged area or a microstructure different from that of the “core” of the pSiC 3 layer, which corresponds to the initiation of the formation of the pSiC 3 layer on the temporary mSiC 1 substrate.This thinning can be carried out in such a way as to remove a thickness of material between a few microns and around fifty microns.

[0033] The packaging of the composite structure may also comprise metallization of the rear face (i.e. the side opposite the thin layer of mSiC 4) of the support layer of pSiC 3. The possible handle substrate may be removed after all or part of this packaging.

[0034] Following removal of the temporary mSiC substrate 1, it may be subjected to various recycling operations, in particular cleaning, aimed at enabling its reuse, in particular in a process in accordance with the invention.

[0035] The following describes various possible embodiments of the removal of the temporary mSiC substrate 1 from the temporary structure.

[0036] In a first possible embodiment, this removal exploits the intermediate layer(s) 2 previously formed to be at the interface between the temporary mSiC substrate 1 and the pSiC support layer 4. In this embodiment, the removal of the temporary mSiC substrate 1 comprises laser detachment at the level of the intermediate layer(s) 2. This laser detachment, called laser lift-off (LLO) in English, consists of irradiating the intermediate layer(s), typically through the temporary mSiC substrate 1, by means of a laser whose wavelength is absorbed by the intermediate layer(s) and for which the temporary mSiC substrate is transparent.

[0037] In a possible embodiment, a pSiC 3C layer absorbing at 404nm and two Si3N4 layers sandwiching the pSiC 3C layer are used as intermediate layers. The Si3N4 layers serve as sacrificial layers in the sense that they will be sputtered due to the increase in temperature generated in them by diffusion from the pSiC 3C layer. The sandwich formed by the pSiC 3C layer and the Si3N4 layers can itself be sandwiched between layers forming a thermal barrier, for example layers of amorphous silicon.

[0038] In other embodiments not requiring the presence of intermediate layer(s), the removal of the temporary mSiC substrate 1 from the temporary structure comprises the formation of a detachment plane in the temporary substrate by laser irradiation and then the application of thermomechanical stresses to the detachment plane. This application will lead to the propagation of a crack line along the detachment plane and to the separation of the temporary mSiC substrate from the pSiC support layer.

[0039] Such removal can thus be carried out according to the process called “Cold Split” in which the application of thermomechanical constraints includes cooling or according to the process called “Kabra” in which laser irradiation leads to amorphization of the detachment plane.

[0040] In a preferred embodiment, the detachment plane is located in the pSiC support layer 3 in order not to damage the temporary mSiC substrate.

[0041] In these embodiments, in order not to negatively impact the process of removing the temporary mSiC substrate, this substrate is preferably chosen from a material not having too much doping and thus with a resistivity greater than 5 mQ.cm. Thus a resistivity of between 15 and 25 mQ.cm, or even between 102 and 103 Q.cm, or even between 104 and 105 Q.cm may be preferred.

Claims

Claims

1. Method comprising the following steps: - manufacturing a temporary structure comprising the formation of a polycrystalline silicon carbide, SiC, support layer (3) on intermediate layers (2) which cover a temporary monocrystalline SiC substrate (1), the intermediate layers comprising a 3C pSiC layer and two Si3N4 layers which sandwich the 3C pSiC layer, the temporary structure having a front face (FF) on the side of the polycrystalline SiC support layer and a rear face (BF) on the side of the temporary monocrystalline SiC substrate; - transferring a thin layer of monocrystalline SiC (4) onto the front face (FF) of the temporary structure;- removing the temporary monocrystalline SiC substrate (1) from the temporary structure so as to obtain a composite structure comprising the thin layer of monocrystalline SiC (4) arranged on the support layer of polycrystalline SiC (3), said removal comprising laser detachment at the level of the intermediate layers (2).;

2. A method according to claim 1, comprising, before removing the temporary monocrystalline SiC substrate (1) from the temporary structure, bonding a handle substrate to the thin monocrystalline SiC layer (4) and, after removing the temporary monocrystalline SiC substrate (1) from the temporary structure, removing the handle substrate.

3. Method according to one of claims 1 and 2, further comprising, after removal of the temporary monocrystalline SiC substrate (1) from the temporary structure, thinning of the polycrystalline SiC support layer (3).

4. Method according to one of claims 1 to 3, further comprising, after removal of the temporary monocrystalline SiC substrate (1) from the temporary structure, metallization of a rear face of the polycrystalline SiC support layer (3).

5. A method according to one of claims 1 to 4, further comprising fabricating electronic component elements on the thin layer of monocrystalline SiC (4).

6. The method of claim 5, wherein the manufacturing of the electronic component elements comprises epitaxy of a migration layer on the thin layer of monocrystalline SiC (4).

7. The method of one of claims 1 to 6, wherein the formation of the polycrystalline SiC support layer (3) on the temporary monocrystalline SiC substrate (1) comprises chemical vapor deposition, physical vapor deposition, epitaxial growth deposition or sintering.

8. Method according to one of claims 1 to 7, in which the polycrystalline SiC support layer (3) formed on the temporary monocrystalline SiC substrate (1) has a thickness of between 50 pm and 200 pm, preferably between 80 pm and 180 pm.

9. A method according to one of claims 1 to 7, wherein the polycrystalline SiC support layer (3) formed on the temporary monocrystalline SiC substrate (1) has a thickness within a target thickness range including as a central value a thickness of 350 pm or a thickness of 500 pm when the polycrystalline SiC support layer has a diameter of 150 mm or a diameter of 200 mm, respectively.

10. Method according to one of claims 1 to 9, in which the transfer of the thin layer of monocrystalline SiC (4) onto the front face of the temporary structure comprises bonding to the front face of the temporary structure a donor substrate of monocrystalline SiC previously subjected to an implantation of ionic species to form a weakening plane there and the supply of thermal and / or mechanical energy to separate the donor substrate of monocrystalline SiC previously subjected to an implantation of ionic species at the weakening plane.

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