Process for the manufacture of a semiconductor structure comprising a polycrystalline silicon carbide substrate and an active layer of monocrystalline silicon carbide - Patents.com

Abstract

The invention relates to a process for the manufacture of a semiconductor structure comprising a support substrate (1) of polycrystalline silicon carbide (SiC) and an active layer (2) of monocrystalline silicon carbide, comprising: - Providing a support substrate comprising a stack of a first layer (11) of polycrystalline SiC predominantly of polytype 3C and a second layer (12) of polycrystalline SiC predominantly of polytype 4H and / or 6H; Bonding a donor substrate (20) with an active layer (2) of monocrystalline SiC of polytype 4H or 6H to the polytype 4H and / or 6H face of a support substrate; Transfer of the active layer (2) onto the supporting substrate and The present invention relates to a process including the steps of:

Description

[Technical field]

[0001] The present invention relates to a process for the manufacture of a semiconductor structure comprising a support substrate of polycrystalline silicon carbide and an active layer of monocrystalline silicon carbide, and also to such a structure and to an electronic device comprising such a structure, in particular for power or radio frequency applications. [Background technology]

[0002] (prior art) Silicon carbide (SiC) is a material of choice in microelectronics, in particular in the manufacture of substrates for electronic devices intended for power applications.

[0003] These microelectronic devices comprise an active layer of single crystal SiC in or on which transistors and other electronic components suitable for performing the required functions are formed.

[0004] The active layer is disposed on a supporting substrate of doped polycrystalline SiC for good electrical conductivity, because in these devices, current applied to the transistors and other electrical components in the active layer passes through the substrate to the back side, the side opposite the active layer.

[0005] The formation of the semiconductor structure comprising the active layer and the support substrate can be performed by the Smart Cut™ process, according to which a weakened zone defining the active layer is formed by implantation of atomic species into a donor substrate of monocrystalline SiC, which is bonded to a support substrate of polycrystalline SiC, and then the donor substrate is separated along the weakened zone so as to transfer the active layer onto the support substrate. The separation can be initiated by mechanical action, heat treatment or any other suitable means, any combination of said means being possible.

[0006] SiC exhibits several polytypes, i.e. different crystal structures. The main polytypes used in the field of microelectronics are polytype 3C with a cubic crystal structure and polytypes 4H and 6H with a hexagonal crystal structure. These polytypes differ in particular in their unit cell parameters, their electronic band diagrams and their thermal expansion coefficients.

[0007] Generally, polycrystalline SiC substrates are commercially available in the 3C form, since this polytype can be obtained by chemical vapor deposition at relatively low temperatures, i.e. typically below 1400 °C, on a seed substrate generally made of graphite, making the manufacturing process relatively economical in terms of energy.

[0008] Meanwhile, single crystal SiC substrates are commercially available that have a hexagonal crystal structure of 4H or 6H type and have dimensions used in the industry, ie, typically a diameter of about 150 to 200 mm.

[0009] As a result, the assembly of an active layer of 4H type polycrystalline SiC with a supporting substrate of polycrystalline SiC involves the formation of interfaces exhibiting two types of discontinuities, namely discontinuities with respect to crystal quality (single crystal / polycrystalline) and discontinuities with respect to crystal structure (hexagonal / cubic).

[0010] These two discontinuities can cause several problems that affect the performance qualities of the structure.

[0011] On the one hand, differences in thermal expansion coefficients can cause deformation of the structure when the structure is subjected to a high thermal budget.

[0012] Such a thermal budget can be applied to the structure during an anneal intended to strengthen the bonded interface, since known processes do not allow direct bonding of the donor substrate to the support substrate, but require the use of a bonding layer, for example made of doped silicon. Bonding is then often followed by a stabilization anneal at a temperature of the order of 1700°C.

[0013] Higher thermal budgets, typically between 1500 and 2000° C., may also be applied during subsequent phases of the fabrication of the electronic device, for example when epitaxy is performed on the active layer to form other parts of the electronic device, or during heat treatments for activation of dopants.

[0014] Deformations due to differences in the thermal expansion coefficients can impair the planarity of the structure, which can impair the performance of subsequent stages in the manufacture of the electronic device and reduce the mechanical strength of the bonds.

[0015] On the other hand, differences in crystal quality that do not allow for alignment of the grains on both sides of the bonded interface can cause a loss of electrical conductivity at the interface. Summary of the Invention

[0016] BRIEF DESCRIPTION OF THE DRAWINGS One object of the present invention is to design a process for the manufacture of a semiconductor structure comprising an active layer of monocrystalline SiC on a support substrate of polycrystalline SiC, which makes it possible to minimize the drawbacks associated with differences in crystal quality and polytype at the interface between the active layer and the support substrate.

[0017] To this end, the invention relates to a process for the manufacture of a semiconductor structure comprising a support substrate of polycrystalline silicon carbide (SiC) and an active layer of monocrystalline silicon carbide, the process comprising: - Providing a support substrate comprising a stack of a first layer of polycrystalline SiC predominantly of polytype 3C and a second layer of polycrystalline SiC predominantly of polytype 4H and / or 6H; Bonding a donor substrate comprising an active layer of monocrystalline SiC of polytype 4H or 6H to the polytype 4H and / or 6H face of the support substrate; Transfer of the active layer onto the support substrate and The present invention provides a process including:

[0018] Thus, in the final structure, the interface between layers of different crystal quality (which remains at the bonded interface between the active layer and the supporting substrate) and the interface between layers of different polytypes (which are embedded in the supporting substrate at a distance from the bonded interface) are separated.

[0019] In the present text, the term "mainly of polytype 3C" means that the volume fraction of grains with 3C structure in the first layer is 60% or more, preferably 70% or more, and even 80% or more. Similarly, the expression "mainly of polytype 4H and / or 6H" means that the volume fraction of grains with 4H and / or 6H structure in the second layer is 60% or more, preferably 70% or more, and more preferably 80% or more.

[0020] In this text, the terms "first" and "second" refer to two layers of polycrystalline SiC of different polytypes on a supporting substrate, and do not imply a particular order of formation of said layers.

[0021] Thus, in some embodiments, a first layer is grown on a seed substrate and then a second layer is grown on the first layer, so that the support substrate directly presents a free surface of predominantly polytype 4H and / or 6H for bonding of a donor substrate.

[0022] In other embodiments, the second layer is grown on a seed substrate and then the first layer is grown on the second layer, in which case the seed substrate is removed to release the face of the second layer that faces the seed substrate to allow bonding of the donor substrate to the predominantly polytype 4H and / or 6H face of the support substrate.

[0023] According to other preferred but optional features, optionally combined where technically relevant, forming the support substrate includes growing a first layer on a seed substrate and then growing a second layer on the first layer; forming the support substrate sequentially includes growing a second layer on a seed substrate, growing the first layer on the second layer, and removing the seed substrate to expose a surface of the second layer for bonding of a donor substrate; The seed substrate is a monocrystalline or polycrystalline SiC substrate, mainly of polytype 4H and / or 6H, The first layer is grown to a thickness between 1 and 20 μm, the second layer is grown to a thickness between 80 and 350 μm, The first layer is grown to a thickness of between 80 and 200 μm, the second layer is grown to a thickness of between 150 and 270 μm, The growth of the first and second layers is performed by chemical vapor deposition (CVD); The growth of the first layer is carried out at a temperature between 1100 and 1500 ° C, preferably between 1200 and 1400 ° C, the growth of the second layer is carried out at a temperature between 1500 and 2600 ° C, preferably between 1700 and 1900 ° C or between 1800 and 2400 ° C, even between 2000 and 2250 ° C, The process further includes introducing a dopant during growth of the first layer and the second layer; The donor substrate is bonded directly to the polytype 4H and / or 6H side of the support substrate; The donor substrate is bonded to the polytype 4H and / or 6H surface of the support substrate via a bonding layer; the bonding layer comprises silicon or tungsten; The process further comprises the steps of implanting atomic species into the donor substrate prior to bonding to form a weakened zone defining the active layer, and separating the donor substrate along the weakened zone after bonding to transfer the active layer onto the support substrate, If the first layer is grown over a thickness between 1 and 20 μm, the first layer is removed after transfer of the active layer onto the support substrate.

[0024] Another subject of the invention is a method for manufacturing a casing comprising: a first layer of polycrystalline SiC, mainly of polytype 3C; a second layer of polycrystalline SiC predominantly of polytype 4H and / or 6H; An active layer of single crystal SiC of polytype 4H or 6H. in turn.

[0025] In this text, the term "in order" designates a spatial order of layers, but does not necessarily result in direct contact between said layers.

[0026] In some embodiments, the first layer exhibits a thickness between 80 and 350 μm and the second layer exhibits a thickness between 1 and 20 μm.

[0027] In another embodiment, the first layer exhibits a thickness between 80 and 200 μm and the second layer exhibits a thickness between 150 and 270 μm.

[0028] Another subject of the invention relates to an electronic device, in particular for power or radio frequency applications, comprising the structure described above and at least one electronic component, such as a transistor, a diode, an electronic power component and / or an electronic radio frequency component, arranged in or on the active layer.

[0029] Other features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings. [Brief description of the drawings]

[0030] [Figure 1] 1 is a cross-sectional view of a semiconductor structure according to a first embodiment. [Diagram 2] FIG. 4 is a cross-sectional view of a structure according to a second embodiment. [Figure 3A] 2A-2D are schematic diagrams illustrating different stages of a process for the manufacture of the semiconductor structure of FIG. 1. [Figure 3B] 2A-2C are schematic diagrams illustrating different stages of a process for the manufacture of the semiconductor structure of FIG. 1; [Figure 3C] 2A-2C are schematic diagrams illustrating further stages of a process for the manufacture of the semiconductor structure of FIG. 1; [Figure 3D]FIG. 2 is a schematic representation of yet another stage of a process for the manufacture of the semiconductor structure of FIG. 1. [Figure 4A] 3A-3D are schematic diagrams illustrating different stages of a process for the manufacture of the semiconductor structure of FIG. 2. [Figure 4B] 3A-3D diagrammatically represent different stages of a process for the manufacture of the semiconductor structure of FIG. 2. [Figure 4C] 3A-3D diagrammatically represent further stages of a process for the manufacture of the semiconductor structure of FIG. 2. [Figure 4D] 3 is a diagrammatic representation of yet another stage of a process for the manufacture of the semiconductor structure of FIG. 2. [Figure 5A] FIG. 5 is a schematic representation of one stage of an alternative embodiment of the process of FIGS. 3A-3D and 4A-4D. [Figure 5B] FIG. 5 is a schematic representation of another stage of an alternative embodiment of the process of FIGS. 3A-3D and 4A-4D. [Figure 5C] FIG. 5 is a schematic representation of yet another stage of an alternative embodiment of the process of FIGS. 3A-3D and 4A-4D. [Figure 5D] FIG. 5 is a schematic representation of yet another stage of an alternative embodiment of the process of FIGS. 3A-3D and 4A-4D.

[0031] For reasons of legibility, the drawings are not necessarily drawn to scale. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] Detailed Description of the Embodiments This specification relates to a semiconductor structure comprising a support substrate of polycrystalline SiC and an active layer of single crystal SiC extending over the support substrate.

[0033] The support substrate comprises two layers of polycrystalline SiC of different polytypes: a first layer of predominantly polytype 3C and a second layer of predominantly polytype 4H and / or 6H.

[0034] The first and second layers of polycrystalline SiC can be provided according to different configurations of the structure, which are described below.

[0035] The active layer is made of single crystal SiC to exhibit optimal electrical properties. The active layer exhibits a hexagonal crystal structure, mainly of polytype 4H or 6H.

[0036] The active layer is added by bonding on the polytype 4H and / or 6H side to the supporting substrate, which can be direct or indirect via a bonding layer.

[0037] It is noted that the active layer is bonded to a layer of polycrystalline SiC, also of hexagonal polytype. The material present at the bond interface therefore exhibits a structure with closer bands than in the case of a bond between a material of hexagonal and cubic structure, which may be beneficial for better electrical conductivity at the interface. Furthermore, this similarity between the hexagonal structures present at the interface makes it possible to reduce the difference in the thermal expansion coefficients on both sides of the interface. It is thus possible to avoid the risk of plastic deformation during the high-temperature manufacturing phase and also poor focusing due to the curvature of the structure during the subsequent lithography phase for the manufacture of electronic devices.

[0038] Whatever the arrangement of the first and second layers of polycrystalline SiC forming the support substrate, two interfaces of different nature are present in the structure.

[0039] The first interface is the interface between a single crystal active layer and a polycrystalline supporting substrate, which is an interface between layers of different crystalline quality but similar polytype.

[0040] The second interface is the interface between the first and second layers of polycrystalline SiC in the supporting substrate, that is, the interface between layers of different polytype but similar crystalline quality. This second interface is located in the thickness of the supporting substrate and is therefore distant from the first interface.

[0041] It should be noted that the second interface does not necessarily indicate an abrupt passage from the cubic to the hexagonal polytype, but may include a transition zone of a certain thickness, which may typically range up to 20 μm, but in view of the thickness of the second layer, the first interface is sufficiently far from the second interface, even with such a transition zone.

[0042] According to a first embodiment shown in FIG. 1 , the structure comprises, in order from back to front, a seed substrate 10, a first layer 11 of polycrystalline SiC mainly of polytype 3C, a second layer 12 of polycrystalline SiC mainly of polytype 4H and / or 6H (the seed substrate and layers 11 and 12 together form the support substrate 1), and an active layer 2 of monocrystalline SiC of polytype 4H or 6H.

[0043] As shown below, the seed substrate 10 is used for the growth of a first layer 11. The seed substrate can then be removed from the structure when its presence is no longer required.

[0044] In this first embodiment of the structure, the first layer 11 is substantially thicker than the second layer 12. For example, the first layer 11 presents a thickness between 80 and 350 μm and the second layer 12 presents a thickness between 1 and 20 μm.

[0045] Polytype 3C can be obtained at lower temperatures than polytypes 4H or 6H, making the production of this first embodiment of the structure energetically more economical.

[0046] In a subsequent manufacturing step, a back portion of the first layer 11 may optionally be removed.

[0047] The structure shows a first interface I1 between an active layer 2, which is monocrystalline, and a supporting substrate 1, which is polycrystalline.

[0048] In Figure 1, the active layer 2 is represented in direct contact with the second layer 12 of polycrystalline SiC, but it is also possible to have a bonding layer (of the type of layer referenced 3 in Figure 2) at the interface between these two layers. Such a bonding layer may typically be made from silicon or tungsten to promote the mechanical strength of the bond while ensuring electrical conduction between the active layer 2 and the supporting substrate 1.

[0049] Furthermore, the structure exhibits a second interface I2 between a first layer 11 of predominantly polytype 3C and a second layer 12 of predominantly polytype 4H and / or 6H.

[0050] Thus, interfaces I1 and I2 are separated by the thickness of the second layer 12.

[0051] According to a second embodiment shown in FIG. 2, the structure comprises, in order from back to front, a seed substrate 10, a first layer 11 of polycrystalline SiC mainly of polytype 3C, a second layer 12 of polycrystalline SiC mainly of polytype 4H and / or 6H (the seed substrate and layers 11 and 12 together form the support substrate 1), a bonding layer 3 and an active layer 2 of monocrystalline SiC of polytype 4H or 6H.

[0052] As shown below, the seed substrate 10 is used for the growth of a first layer 11. The seed substrate can then be removed from the structure when its presence is no longer required.

[0053] In this second embodiment of the structure, the first layer 11 is substantially thinner than the second layer 12. For example, the first layer 11 presents a thickness between 80 and 200 μm and the second layer 12 a thickness between 150 and 270 μm. The thinner layer of the cubic structure makes it possible to limit deformations due to the difference in thermal expansion coefficient between the 3C structure and the 4H / 6H structure.

[0054] The structure shows a first interface I1 between an active layer 2, which is monocrystalline, and a supporting substrate 1, which is polycrystalline.

[0055] 2, a bonding layer 3 is depicted between the active layer 2 and the second layer 12 of polycrystalline SiC, however this bonding layer is optional and a direct bond between layers 2 and 12 may also be made. The bonding layer 3 may typically be made from silicon or tungsten to ensure electrical conduction between the active layer 2 and the supporting substrate 1 while promoting the mechanical strength of the bond.

[0056] Furthermore, the structure exhibits a second interface I2 between a first layer 11 of predominantly polytype 3C and a second layer 12 of predominantly polytype 4H and / or 6H.

[0057] Thus, interfaces I1 and I2 are separated by the thickness of the second layer 12.

[0058] Optionally, in a subsequent step of the manufacturing process, the first layer 11 can be removed, in which case the second interface is no longer present in the final structure. However, the structure still benefits from the first interface I1 between the two layers of hexagonal structure, which is beneficial as a result of both the reduced difference in thermal expansion coefficients and the band structures being much closer, as explained above.

[0059] Next, various processes for the fabrication of these structures are described.

[0060] 3A-3D diagrammatically show process steps for the fabrication of the structure of FIG.

[0061] 3A, a first layer 11 of polycrystalline SiC, mainly of polytype 3C, is formed on a seed substrate 10. The seed substrate 10 is typically a graphite substrate, but any other material can be used whose thermal expansion coefficient is close to that of polycrystalline SiC, preferably exhibits low cost, and / or is reusable. Thus, alternative materials to graphite are single crystal SiC and sintered polycrystalline SiC (non-limiting list).

[0062] The first layer 11 may be formed by chemical vapor deposition (CVD), which may include the following precursors (non-limiting examples): For carbon, ethane, propane or acetylene; For silicon, silane, tetrachlorosilane, trichlorosilane or dichlorosilane; Alternatively, tetramethylsilane as a common source of carbon and silicon.

[0063] These precursors are carried by a carrier gas which may be selected from nitrogen, argon, helium and hydrogen.

[0064] The person skilled in the art is in a position to define the deposition parameters, in particular the temperature, depending on the precursors used and the plant used to carry out the deposition.

[0065] To obtain a cubic structure, a relatively low deposition temperature is used, typically between 1100 and 1500°C, preferably between 1200 and 1400°C. Said first layer 11 is grown over a thickness of between 80 and 350 μm. Generally, growth is performed on both sides of the seed substrate, so that on the rear side of the seed substrate also a layer of polycrystalline SiC, mainly of polytype 3C, is formed. This layer is not intended to be retained in the structure and is therefore not represented for simplicity of the drawings.

[0066] With reference to FIG. 3B, a second layer 12 of polycrystalline SiC, mainly of polytype 4H and / or 6H, is formed on the first layer 11 to obtain the support substrate 1. The second layer 12 can also be formed by chemical vapor deposition, but in order to obtain a hexagonal structure, relatively high deposition temperatures are used, typically between 1500 and 2600° C., preferably between 1700 and 1900° C. or between 1800 and 2400° C., even between 2000 and 2250° C. The growth temperatures depend in particular on the deposition technique, the precursors used and the other operating conditions and are therefore given merely as an indication, the skilled person being in a position to define a growth process suitable for the desired polytype. The precursors can be selected from the same list as those presented above for the deposition of the first layer.

[0067] Besides the chemical vapor deposition mentioned above, the second layer can also be formed by high temperature chemical vapor deposition (HTCVD), by liquid phase growth (a technique known by the acronym TSSG for "top-seeded solution growth") or by physical vapor deposition (PVD or PVT).

[0068] Carrying out the deposition at such temperatures requires extremely high energy, but the fact that the second layer is formed over a low thickness (between 1 μm and 20 μm) makes it possible to limit the overall energy consumption and cost of the process. The deposition of the second layer is preferably carried out in the same chamber as the first layer, where the deposition temperature is increased to modify the polytype of the deposited SiC.

[0069] According to an alternative which can be envisaged, the first layer 11 is formed by a sintering process before being transferred into a deposition chamber, in which the second layer 12 is then deposited on the first layer 11 by one of the deposition or growth techniques mentioned above.

[0070] The transition between the cubic structure of the first layer of polycrystalline SiC and the hexagonal structure of the second layer may not be clear, but may show a transition zone containing a mixture of 3C type grains and 4H and / or 6H type grains over a thickness that may range up to 20 μm. However, as long as this transition zone is away from the bond interface between the active layer and the support substrate, it does not harm the performance qualities of the structure.

[0071] Preferably, the first and second layers are doped during their growth by the introduction of a dopant, according to known techniques. The dopant may typically be nitrogen, boron, phosphorus or aluminum, according to the type of doping desired. The dopant content is generally between 10 18 From 10 21 at / cm 3 It is between.

[0072] 3C, a donor substrate 20 is provided in which weakened zones 21 defining the active layer 2 to be transferred are formed by implantation of atomic species (typically hydrogen and / or helium). The donor substrate 20 is a monocrystalline SiC substrate of polytype 4H or 6H, which is commercially available in suitable sizes, typically around 150-200 mm in diameter.

[0073] 3D, the donor substrate 20 is bonded to the support substrate 1. Beforehand, for the purpose of direct bonding of the two substrates, any suitable surface treatment is applied to ensure that the surfaces in contact are as smooth as possible, i.e. in particular exhibit a roughness of less than 1 nm RMS, preferably less than 0.5 nm RMS, more preferably less than 0.2 nm RMS. Furthermore, the surfaces are preferably made hydrophobic.

[0074] The donor substrate is then separated along the weakened zones 21 so as to transfer the active layer 2 onto the support substrate 1 and obtain the structure of FIG.

[0075] 4A-4D diagrammatically show process steps for the fabrication of the structure of FIG.

[0076] With reference to FIG. 4A, a first layer 11 of polycrystalline SiC, mainly of polytype 3C, is formed on a seed substrate 10. The seed substrate 10 is typically a graphite substrate. The first layer 11 is formed by chemical vapor deposition (CVD). To obtain a cubic crystal structure, a relatively low deposition temperature is used, typically between 1100 and 1500° C., preferably between 1200 and 1400° C. The first layer 11 is grown over a thickness of between 1 and 20 μm.

[0077] With reference to FIG. 4B, a second layer 12 of polycrystalline SiC, mainly of polytype 4H and / or 6H, is formed on the first layer 11 to obtain the support substrate 1. The second layer 12 is also formed by chemical vapor deposition, but in order to obtain a hexagonal structure, a relatively high deposition temperature is used, typically between 1500 and 2600° C., preferably between 1700 and 1900° C. or between 1800 and 2400° C., even between 2000 and 2250° C. As mentioned above, the skilled person is in a position to determine the growth conditions for the desired polytype depending on the technique employed and the precursors used. The second layer is formed over a thickness of between 80 and 350 μm. The deposition of the second layer is preferably carried out in the same chamber as the first layer, where the deposition temperature is increased to modify the polytype of the deposited SiC.

[0078] As noted above, the transition between the cubic crystal structure of the first layer of polycrystalline SiC and the hexagonal crystal structure of the second layer may not be sharp, but may exhibit a transition zone containing a mixture of 3C type grains and 4H and / or 6H type grains.

[0079] Preferably, the first and second layers are doped during their growth by the introduction of a dopant, according to known techniques. The dopant may typically be nitrogen, boron, phosphorus or aluminum, according to the type of doping desired. The dopant content is generally between 10 18 From 10 21 at / cm 3 It is between.

[0080] 4C, a donor substrate 20 is provided in which weakened zones 21 defining the active layer 2 to be transferred are formed by implantation of atomic species (typically hydrogen and / or helium). The donor substrate 20 is a single crystal SiC substrate of polytype 4H or 6H, which is commercially available in suitable sizes, typically around 150-200 mm in diameter.

[0081] 4D, the donor substrate 20 is bonded to the support substrate 1 via a bonding layer 3. The bonding layer 3 can be pre-deposited on either the donor substrate 20 or the second layer 12 of the support substrate 1. To promote good bonding strength, pre-treatment of the surfaces to be bonded can be performed to obtain a very low roughness, typically less than 1 nm RMS, preferably less than 0.5 nm RMS.

[0082] The donor substrate is then separated along the weakened zones 21 so as to transfer the active layer 2 onto the support substrate 1, obtaining the structure of FIG.

[0083] If the second layer (polytype 4H and / or 6H) is sufficiently thick, i.e. if it exhibits a thickness of 100 μm or more, it is possible to remove the first layer (polytype 3C), especially after the formation of the electronic components in the active layer. This removal of the first layer can be carried out by grinding or any other means. This makes it possible to expose, on the rear side of the structure, a surface of polytype 4H and / or 6H, on which the electrical contacts can then be placed if the geometry of the components requires contacts on the rear side.

[0084] This removal makes it possible to reduce the total electrical resistance of the structure, since one of the contacts is on the back surface and therefore the current has less material to pass between the components on the front surface and the contacts on the back surface. In general, it is often planned to modify the thickness of a semiconductor structure by removing a portion of the substrate, for example to adapt it to the dimensions of the tools that must be used, or to modify the structure, or to adapt the properties of the structure to its particular application.

[0085] Thus, a final structure is obtained which is entirely of polytype 4H and / or 6H and therefore exhibits greater uniformity in terms of thermal expansion coefficient and mechanical properties, but which is planned to be removed as described above and which may have a poorer crystalline quality as a result of the granular growth of the polycrystalline SiC. The initiation of the growth of the polycrystalline SiC takes place at a lower growth temperature than that of polytype 3C and is therefore more energetically economical.

[0086] The process described above is based on the successive growth of a first layer of polycrystalline SiC predominantly of polytype 3C followed by a second layer of polycrystalline SiC predominantly of polytype 4H and / or 6H on a seed substrate.

[0087] Alternatively, it is possible to first grow a second layer of polycrystalline SiC mainly of polytype 4H and / or 6H on a seed substrate and then grow a first layer of polycrystalline SiC mainly of polytype 3C on the second layer (which, as mentioned above, is more beneficial as a result of the close thermal expansion coefficients and band structures). To transfer a single-crystalline active layer of 4H or 6H type onto the surface of polytype 4H and / or 6H, it is necessary to remove the seed substrate to expose the face of the second layer of polycrystalline SiC and to flip the support substrate in order to bond a donor substrate to said second layer.

[0088] This alternative is illustrated in Figures 5A-5D. This process can be used to form the semiconductor structure of Figure 1 or the semiconductor structure of Figure 2.

[0089] With reference to FIG. 5A, a second layer 12 of polycrystalline SiC, predominantly of polytype 4H and / or 6H, is formed on a seed substrate 10. To promote the quality of the hexagonal structure of the layer 12, the seed substrate 10 is preferably a substrate of monocrystalline or polycrystalline SiC, predominantly of polytype 4H and / or 6H. The second layer 12 is formed by chemical vapor deposition at a relatively high deposition temperature, typically between 1500 and 2600° C., preferably between 1700 and 1900° C. or between 1800 and 2400° C., or even between 2000 and 2250° C. As mentioned above, the skilled person is in a position to determine the growth conditions for the desired polytype depending on the technique employed and the precursors used.

[0090] 5B, a first layer 11 of polycrystalline SiC, primarily of polytype 3C, is formed on a second layer 12. The first layer 11 is formed by chemical vapor deposition at a relatively low deposition temperature, typically between 1100 and 1500° C., preferably between 1200 and 1400° C. Deposition of the first layer is preferably performed in the same chamber as that of the second layer, and the deposition temperature is reduced to facilitate a change in polytype of the deposited SiC.

[0091] Preferably, the first and second layers are doped during their growth by the introduction of a dopant, according to known techniques. The dopant may typically be nitrogen, boron, phosphorus or aluminum, according to the type of doping desired. The dopant content is generally between 10 18 From 10 21 at / cm 3 It is between.

[0092] 5C, the seed substrate 10 is removed to expose the back side of the second layer 12, which is primarily of polytype 4H and / or 6H. The support substrate 1 thus consists only of layers 11 and 12.

[0093] As in the other embodiments of the process (see Figures 3C and 4C), a donor substrate 20 is further provided in which a weakened zone 21 defining the active layer 2 to be transferred is formed by implantation of atomic species (typically hydrogen and / or helium). The donor substrate 20 is a monocrystalline SiC substrate of polytype 4H or 6H, which is commercially available in suitable sizes, typically around 150-200 mm in diameter.

[0094] 5D, the donor substrate 20 is bonded to the support substrate 1, either directly or via the bonding layer described above. For this purpose, the support substrate is inverted so that the second layer 12, which was on the back side during the manufacture of the support substrate, is now facing the front side to receive the donor substrate 20.

[0095] The active layer 2 is then transferred onto the support substrate 1, the donor substrate being separated along the weakened zones 21 in order to obtain a semiconductor structure similar to that of FIGS. 1 and 2 in which the support substrate 1 is devoid of the seed substrate 10.

[0096] The resulting semiconductor structures may be suitably used in the manufacture of electronic devices for power and / or radio frequency applications.

[0097] To this end, it is possible to form, by epitaxial regrowth on the active layer, one or more additional semiconductor layers intended for the formation of electronic components.

[0098] For example, electronic components formed in or on the active layer may comprise one or more transistors, one or more diodes, one or more power components, or one or more radio frequency components (non-limiting list). Radio frequency components typically comprise lines for the transmission of radio frequency electrical signals and, optionally, one or more transistors. Power components are defined as components suitable for transporting currents exhibiting a power of 50 W or more.

Claims

1. A process for the manufacture of a semiconductor structure comprising a support substrate (1) of polycrystalline silicon carbide (SiC) and an active layer (2) of monocrystalline silicon carbide, comprising: - Providing a support substrate comprising a stack of a first layer (11) of polycrystalline SiC predominantly of polytype 3C and a second layer (12) of polycrystalline SiC predominantly of polytype 4H and / or 6H; bonding a donor substrate (20) comprising an active layer (2) of monocrystalline SiC of polytype 4H or 6H to the polytype 4H and / or 6H face of the support substrate; Transferring the active layer (2) onto the support substrate; The process includes:

2. 2. The process of claim 1, wherein the forming of the support substrate comprises growing the first layer (11) on a seed substrate (10) and then growing the second layer (12) on the first layer (11).

3. 2. The process of claim 1, wherein the forming of the support substrate sequentially comprises growing the second layer (12) on a seed substrate (10), growing the first layer (11) on the second layer (12), and removing the seed substrate (10) to expose a face of the second layer (12) for the bonding of the donor substrate.

4. 4. The process of claim 3, wherein the seed substrate (10) is a monocrystalline or polycrystalline SiC substrate predominantly of polytype 4H and / or 6H.

5. A process according to any one of claims 2 to 4, wherein the first layer (11) is grown over a thickness of between 1 and 20 μm and the second layer (12) is grown over a thickness of between 80 and 350 μm.

6. A process according to any one of claims 2 to 4, wherein the first layer (11) is grown over a thickness of between 80 and 200 μm and the second layer (12) is grown over a thickness of between 150 and 270 μm.

7. The process of any one of claims 2 to 4, wherein the growth of the first and second layers is performed by chemical vapor deposition (CVD).

8. A process according to any one of claims 2 to 4, wherein the growth of the first layer (11) is carried out at a temperature between 1100 and 1500°C, preferably between 1200 and 1400°C.

9. A process according to any one of claims 2 to 4, wherein the growth of the second layer (12) is carried out at a temperature between 1500 and 2600°C, preferably between 1700 and 1900°C or between 1800 and 2400°C, even between 2000 and 2250°C.

10. The process of any one of claims 2 to 4, further comprising introducing a dopant during the growth of the first and second layers.

11. The process according to any one of claims 1 to 4, wherein the donor substrate (20) is bonded directly to the face of polytype 4H and / or 6H of the support substrate.

12. The process according to any one of claims 1 to 4, wherein the donor substrate (20) is bonded to the polytype 4H and / or 6H side of the support substrate via a bonding layer (3).

13. The process of claim 12, wherein the bonding layer (3) comprises silicon or tungsten.

14. 5. The process according to claim 1, further comprising the steps of: prior to the bonding, implanting atomic species into the donor substrate (20) to form a weakened zone (21) that defines the active layer (2); and after the bonding, separating the donor substrate (20) along the weakened zone (21) to transfer the active layer (2) onto the support substrate.

15. 6. The process of claim 5, further comprising removing the first layer (11) after the transfer of the active layer onto the support substrate.

16. From back to front, a first layer (11) of polycrystalline SiC, mainly of polytype 3C; a second layer (12) of polycrystalline SiC predominantly of polytype 4H and / or 6H; an active layer (2) of single-crystal SiC of polytype 4H or 6H; in order.

17. said first layer (11) exhibiting a thickness between 80 and 350 μm; said second layer (12) exhibiting a thickness between 1 and 20 μm; 17. The structure of claim 16.

18. said first layer (11) exhibiting a thickness between 80 and 200 μm; said second layer (12) exhibiting a thickness of between 150 and 270 μm; 17. The structure of claim 16.

19. An electronic device, in particular for power or radio frequency applications, comprising a structure according to any one of claims 16 to 18 and at least one electronic component, such as a transistor, a diode, an electronic power component and / or an electronic radio frequency component, arranged in or on the active layer (2).

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