Composite structures including single crystal thin films on polycrystalline silicon carbide support substrates and related methods of manufacture

Abstract

The invention relates to a composite structure for producing microelectronic elements, said composite structure comprising a single crystal thin film located on a polycrystalline silicon carbide support substrate, said support substrate having a preferred crystal orientation on each face thereof, according to which:-a texture coefficient C422 of less than 40%; and-the sum of the texture coefficients C220 + C200 + C400 is greater than 50%, preferably greater than 80%. The invention also relates to a method for producing such a composite structure.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor materials for microelectronic components. In particular, the invention relates to a composite structure comprising a single-crystalline thin film disposed on a supporting substrate made of polycrystalline silicon carbide. The single-crystalline thin film is preferably made of silicon carbide, and the composite structure is intended for use in power electronics applications. Background Art

[0002] SiC is increasingly being used in the manufacture of innovative power devices to meet the needs of emerging electronics sectors, such as electric vehicles in particular. In fact, compared to conventional silicon power devices and integrated power systems, power devices and integrated power systems based on single-crystal silicon carbide can manage greater power density and have a lower active area size.

[0003] High-quality single-crystalline SiC substrates (c-SiC) intended for use in the microelectronics industry remain expensive and difficult to obtain on a large scale. Therefore, it is advantageous to employ a transferred layer solution to produce a composite structure, which typically comprises a thin film made of single-crystalline SiC (from a high-quality c-SiC substrate) on a less expensive support substrate, such as a support substrate made of polycrystalline SiC (p-SiC). Electronic components can then be produced on and / or in the thin film.

[0004] A well-known thin layer transfer solution is Smart Cut TM Method based on light ion implantation and direct bonding between a donor single crystal substrate and a support substrate at a bonding interface.

[0005] Currently, p-SiC substrates are available on the market that can form support substrates. However, their mechanical, electrical, or even thermal properties are not necessarily optimal for obtaining high-quality composite structures intended for power applications using thin film transfer methods.

[0006] As mentioned above, power electronics applications require that the composite structure have excellent vertical conductivity. Therefore, the single crystal film can be doped according to the requirements of the application: for example, to exhibit n-type doping or p-type doping and a resistivity of less than 30mOhm·cm, 10mOhm·cm or even less than 1mOhm·cm. The assembly interface of the composite structure must be made so as not to increase (or very slightly increase) the vertical resistance. Finally, it must be ensured that the supporting substrate of the composite structure has good conductivity. Therefore, it is necessary to strongly dope the polycrystalline substrate (n-type doping or p-type doping) to achieve a resistivity less than or equal to 15mOhm·cm, 10mOhm·cm or even less than 5mOhm·cm. However, it is known that high concentrations of dopants (such as nitrogen) in p-SiC materials may become a limiting factor in obtaining good flatness (low deformation) due to the resulting large defect density.

[0007] However, support substrates with low curvature or low deformation must be used. The curvature corresponds to the degree of bending or "warpage", which is equivalent to the algebraic difference in the deviation of the substrate relative to the reference plane. On the one hand, the curvature needs to be reduced so that these support substrates are compatible with direct assembly with good quality and high binding energy, and on the other hand, so that they are less likely to cause damage to the single crystal thin film due to significant mechanical stress during or after the transfer process. Small curvature is also important to ensure the performance of the manufacturing steps (such as lithography) of the elements on / in the film of the composite structure. The radius of curvature of the support substrate made of p-SiC (which is proportional to the inverse of the warpage) is generally targeted to be greater than about 25 μm (for a substrate with a diameter of 150 mm, the warpage is less than 100 μm, or even less than 50 μm, or ideally less than 30 μm).

[0008] Finally, thin film transfer methods based on direct bonding via molecular adhesion are highly dependent on the surface quality of the assembly substrates. In particular, both the support and donor substrates require a roughness of less than or equal to 1 nm RMS (root mean square roughness) and the presence of surface defects (particles, pores, or other protrusions that can create bonding defects). It should be noted that the hardness of SiC and the presence of grains on the surface of polycrystalline support substrates make surface preparation very complex, and achieving perfect quality has proven difficult.

[0009] Furthermore, it is often important that the supporting substrate ensures good thermal conductivity (typically greater than 200 W / (mK), or even greater than 250 W / (mK)) to effectively dissipate heat, particularly that generated by power components. However, thermal conductivity can be adversely affected by higher levels of dopants, which can hinder phonon propagation, particularly due to the creation of additional crystal defects.

[0010] Achieving all of these specifications using currently available p-SiC substrates is very complex.

[0011] Document US10934634 proposes a p-SiC substrate with a grain size variation of less than 0.43% between the two faces of the substrate, which provides it with a radius of curvature greater than 142 μm (i.e., very small deformation). In addition, at least one face of the substrate has an arithmetic mean roughness of less than 1 nm. However, this method is still expensive and consumes a lot of energy and material because most of the p-SiC initially deposited on the graphite substrate is removed and lost to obtain the proposed substrate made of p-SiC (usually 2 mm is initially deposited to form a 350 μm p-SiC substrate).

[0012] In order to reduce the manufacturing costs, it would be optimal to grow the p-SiC layer by high-speed chemical vapor deposition with a thickness as close as possible to the final thickness of the desired substrate and to stabilize the grain size very quickly after the start of the growth of the layer, in order to avoid any unnecessary thickness (which would be necessary to reduce or eliminate gradients in the grain size that would be detrimental to the flatness of the substrate); this is achieved by ensuring a very high concentration of dopants (for example n-type dopants such as nitrogen or phosphorus) (typically greater than 5×10 19 atoms / cm 3 , preferably greater than 10 20 atoms / cm 3 ) to achieve a material resistivity typically less than 15 mOhm·cm, or even less than 10 mOhm·cm, and good thermal conductivity. Summary of the Invention

[0013] Purpose of the present invention

[0014] The present invention proposes a composite structure comprising a thin film made of single-crystalline material, in particular high-quality c-SiC, arranged on a p-SiC support substrate with very low resistivity, low deformation, and good thermal conductivity. The invention also relates to a method for producing such a composite structure.

[0015] Brief Description of the Invention

[0016] The present invention relates to a composite structure for producing microelectronic components, comprising a single-crystal thin film arranged on a supporting substrate made of polycrystalline silicon carbide, the supporting substrate having a preferred crystal orientation on each of its faces, according to which:

[0017] -Texture coefficient C 422 Less than 40%, and

[0018] -Texture coefficient C 220 +C 200 +C 400The sum of is greater than 50%, preferably greater than 80%.

[0019] According to other advantageous and non-limiting features of the invention, alone or in any technically feasible combination:

[0020] The resistivity of the support substrate is less than or equal to 10 mOhm·cm, preferably less than or equal to 5 mOhm·cm, more preferably less than or equal to 3 mOhm·cm;

[0021] The supporting substrate is nitrogen-doped to a concentration greater than or equal to 5.0×10 19 atoms / cm 3 , preferably greater than or equal to 1.0×10 20 atoms / cm 3 , even more preferably greater than or equal to 1.5×10 20 atoms / cm 3 , or preferably greater than or equal to 3×10 20 atoms / cm 3 ;

[0022] Texture coefficient C 422 less than 20%, preferably less than 15%, or even preferably less than 10%;

[0023] Texture coefficient C 200 +C 400 The sum of is greater than 1%, preferably greater than 2%, even more preferably greater than 5%;

[0024] The film is composed of silicon carbide;

[0025] The film is composed of gallium nitride;

[0026] The film is composed of gallium oxide;

[0027] The film is composed of diamond;

[0028] The composite structure comprises a continuous or discontinuous intermediate layer, which is arranged between the film and the supporting substrate and consists of at least one metallic material or a semiconducting material;

[0029] The intermediate layer consists of silicon, silicon carbide, tungsten and / or titanium;

[0030] The thickness of the support substrate is between 50 μm and 650 μm;

[0031] • The composite structure includes electronic components on and / or in the film and optionally includes electrical contacts on the back side of the supporting substrate.

[0032] The present invention also relates to a method for manufacturing a composite structure comprising a single-crystal thin film arranged on a supporting substrate made of polycrystalline silicon carbide, the manufacturing method comprising the following steps:

[0033] a) providing a polycrystalline silicon carbide support substrate, said polycrystalline silicon carbide support substrate having a preferred crystal orientation on each of its faces, according to said preferred crystal orientation:

[0034] -Texture coefficient C 422 Less than 40%, and

[0035] -Texture coefficient C 220 +C 200 +C 400 The sum of is greater than 50%, preferably greater than 80%.

[0036] b) providing a donor substrate made of a single-crystalline material,

[0037] c) Transferring the thin film from the donor substrate to a supporting substrate.

[0038] According to other advantageous and non-limiting features of the invention, alone or in any technically feasible combination:

[0039] Step c) of the transfer includes:

[0040] c1) forming a buried brittle plane in the donor substrate, defining a thin film between the buried brittle plane and the front side of the donor substrate,

[0041] c2) assembling the donor substrate directly or through an intermediate layer onto the support substrate by molecular adhesion bonding,

[0042] c3) separation along the buried brittle plane, thereby transferring the film to a supporting substrate;

[0043] Before assembling the two substrates, step c2) includes:

[0044] - before or after step c1), forming an intermediate layer on the donor substrate, and / or

[0045] - forming an intermediate layer on a supporting substrate,

[0046] The intermediate layer is formed of at least one metallic material or semiconductive material selected from silicon, silicon carbide, tungsten and titanium;

[0047] The manufacturing method further comprises producing electronic components on and / or in the film of the composite structure;

[0048] The production of electronic components includes in particular steps of homoepitaxy or heteroepitaxy on thin films. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Other features and advantages of the present invention will become apparent from the following detailed description of the invention with reference to the accompanying drawings, in which:

[0050] [ Figure 1 ] Figure 1 A composite substrate according to the present invention is shown;

[0051] [ Figure 2 ] Figure 2 A table is shown, which lists 10 diffraction peaks, classified according to increasing Miller (hkl) index, considered to be 3C polytype SiC substrates and measurable by X-ray diffraction; the table also shows the positions of the peaks and their theoretical intensities;

[0052] [ Figure 3a ]

[0053] [ Figure 3b ] Figure 3a and Figure 3b shows backscattered electron images, obtained by scanning electron microscopy, of a cross section of an unprocessed p-SiC wafer and of a supporting substrate from said unprocessed wafer, said supporting substrate being implemented for producing a composite structure according to the invention;

[0054] [ Figure 4 ] Figure 4 A composite substrate according to the present invention is shown;

[0055] [ Figure 5a ]

[0056] [ Figure 5b ]

[0057] [ Figure 5c ]

[0058] [ Figure 5c' ]

[0059] [ Figure 5c ]

[0060] [ Figure 5d ] Figure 5a 、 Figure 5b 、 Figure 5c 、 Figure 5c' 、 Figure 5c and Figure 5d The steps of the manufacturing method according to the present invention are shown.

[0061] The same reference numerals may be used for like elements in the drawings. Some of the drawings are schematic and, for ease of reading, are not drawn to scale. In particular, the thickness of layers along the z-axis is not drawn to scale relative to the lateral dimensions along the x- and y-axes; and the relative thicknesses of layers between them are not necessarily considered in the drawings. DETAILED DESCRIPTION

[0062] The present invention relates to a composite structure 100 particularly suitable for manufacturing microelectronic components, comprising a single-crystal thin film 10, in particular made of silicon carbide, diamond, silicon, II-VI or III-V semiconductor compounds (such as AlN, GaN, etc.), gallium oxide (Ga2O3) or any wide-bandgap semiconductor material, and arranged on a supporting substrate 20 made of polycrystalline silicon carbide ( Figure 1 ).

[0063] In the main planes (x, y), the composite structure 100 is preferably in the form of a circular wafer with a diameter of 100 mm, 150 mm, 200 mm, or even larger. However, it may be in any other form that allows it to be processed later to produce components. In the figures, the thickness of the composite structure 100 extends along the z-axis.

[0064] The thickness of the thin film 10 of the composite structure 100 is typically between tens of nanometers and hundreds of nanometers, for example, between 50 nm and 800 nm. As will be seen below, an epitaxial growth step can be performed on the thin film 10 to increase its thickness (homoepitaxy) or to grow other materials (heteroepitaxy) to meet the requirements of the electronic component to be manufactured.

[0065] The film 10 has a resistivity suitable for the application and the intended device, for example, for power devices, in the case of n-type doping (nitrogen dopant or phosphorus dopant), its resistivity is typically less than 30 mOhm·cm, less than 10 mOhm·cm, or even less than 1 mOhm·cm.

[0066] The support substrate 20 serves as the mechanical support for the composite structure 100. The lateral dimensions of the support substrate 20 in the main plane (x, y), in particular its diameter, are identical to the lateral dimensions of the composite structure 100 in the main plane (x, y). It should be noted that, due to the transfer method, the lateral dimensions of the thin film 10 may be slightly smaller: in fact, the peripheral ring of the support substrate 20 is generally free of thin film 10, since the thinning or chamfering of the edges of the substrate 20 hinders the assembly and effective transfer of said layer 10.

[0067] In the composite structure 100, the thickness of the support substrate 20 is typically between about 50 μm and several hundred microns, for example, between 50 μm and 650 μm, or between 100 μm and 450 μm, or between 200 μm and 350 μm. Typically, the thickness of the support substrate 20 with a diameter of 150 mm is in the range of 350 μm to 450 μm, and the thickness of the support substrate 20 with a diameter of 200 mm is in the range of 500 μm to 650 μm.

[0068] As mentioned in the background, power applications require good vertical conductivity: the resistivity of the support substrate 20 is less than or equal to 10 mOhm·cm, preferably less than or equal to 5 mOhm·cm, or even more preferably less than or equal to 3 mOhm·cm. When the thin film 10 is n-type, the doping type of the support substrate 20 is usually selected to be the same, that is, it is usually doped with nitrogen or phosphorus. In order to obtain the above-mentioned low resistivity, the dopant concentration (which can be measured by secondary ion mass spectrometry) is usually greater than 5.0×10 19 atoms / cm 3 , preferably greater than or equal to 1.0×10 20 atoms / cm 3 , greater than or equal to 1.5×10 20 atoms / cm 3 , or even greater than or equal to 3×10 20 atoms / cm 3 .

[0069] The radius of curvature of the support substrate 20 is greater than 25 μm, and advantageously greater than or equal to 50 μm. For example, the curvature (or warpage) of the support substrate 20 having a diameter of 150 mm is less than or equal to 100 μm, less than or equal to 50 μm, or even less than or equal to 30 μm; and the curvature (or warpage) of the support substrate 20 having a diameter of 200 mm is less than or equal to 150 μm, less than or equal to 100 μm, less than or equal to 70 μm, or even less than or equal to 40 μm.

[0070] The range of the radius of curvature of the support substrate 20 is such that the support substrate 20 is fully compatible with the specifications of the composite structure 100 provided with the thin single-crystalline layer 10, with the method for manufacturing such a structure 100 and with the subsequent production of microelectronic components on and / or in the thin film 10. It should be noted that the curvature of the composite structure 100 remains close to the curvature of the support substrate 20.

[0071] Furthermore, the support substrate 20 made of p-SiC of the polytype 3C has a preferred crystal orientation on each of its faces, in particular on each of its two main faces (which are the faces between which the thickness of the support substrate 20 is measured). This crystal orientation is particularly advantageous for obtaining low curvature and good thermal conductivity, while having a high concentration of dopants.

[0072] Here, the preferred crystal orientation is characterized using a specific ratio of different texture coefficients. The texture coefficient can be expressed as a percentage and quantifies the average preferred orientation of the crystals of the supporting substrate 20 relative to the surface normal of the substrate 20. It will be recalled that the texture coefficient can be measured by the method described by G. Harris ("X.Quantitative measurement of preferred orientation in rolled uranium bars", Philosophical Magazine Series 7, 43:336,113-123,1952). In practice, they are measured by the θ-2θ method over an angular range of 10° to 135° (2θ scale) from diffraction peaks collected by a PANalytical X'Pert PRO MPD type X-ray diffractometer. Within this range, in the table ( Figure 2 The 10 diffraction peaks shown in FIG. 1 and classified according to the increase of the Miller (hkl) index can be considered to be a 3C-type SiC substrate.

[0073] Texture coefficient C hkl According to the peak intensity of the powder I hkl (proportional to the area under the sample peak) and the theoretical intensity I 0hkl (It can be calculated from the theoretical percentage compiled by ICDD (International Center for Diffraction Data). Texture coefficient C hkl It is expressed as follows:

[0074] C hkl =(I hkl / I 0hkl ) / (1 / N×Σ(I hkl / I 0hkl )), where N is the number of peaks considered.

[0075] The preferred crystal orientation of the support substrate 20 is characterized by the texture coefficient C 422 Less than 40%, and the texture coefficient C 220 +C 200 +C 400 The sum of is greater than 50%.

[0076] Preferably, the texture coefficient C 220 +C 200 +C 400 The sum of is greater than 60%, 70%, or even 80%. 200 +C 400 The contribution may advantageously be greater than 1%, 2%, or even 5%.

[0077] Also preferably, the texture coefficient C422 Less than 20%, less than 15%, or even less than 10%.

[0078] Figure 3b Example texture of a support substrate 20 for a composite structure 100 according to the present invention. Images were obtained in the transverse plane (y, z) (i.e., in a cross section of the support substrate 20) by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD); the white bar in the lower right corner of the image represents a scale of 100 μm. The preferred orientation (220) of the observed texture is the texture coefficient C 220 Greater than or equal to 90%, and the texture coefficient C 422 Less than 10%.

[0079] In this example, the nitrogen concentration of the supporting substrate 20 is 1.8×10 20 atoms / cm 3 , and the resistivity measured by the four-point method is 1.2 mOhm·cm. The thermal conductivity, derived from thermal diffusivity measurements using the laser flash method, is approximately 270 W / (mK). Finally, the deformation (warpage) measured on a substrate with a diameter of 150 mm and a thickness between 350 μm and 450 μm is less than 100 μm.

[0080] The preferential texturing associated with the high doping enables obtaining a support substrate 20 that meets the desired physical, mechanical and electrical specifications of the composite structure 100 , namely excellent flatness (low curvature), low resistivity and very good thermal conductivity.

[0081] According to a particular embodiment of the present invention, the composite structure 100 comprises a continuous or discontinuous intermediate layer 30, which is arranged between the film 10 and the supporting substrate 20 and is composed of at least one metallic material or semiconductor material ( Figure 4 As described below, with reference to a method for manufacturing the composite structure 100 , the intermediate layer 30 may be formed on one side of the film 10 , on one side of the support substrate 20 , or on both sides, and then assembled along the bonding interface 40 .

[0082] For example, the intermediate layer 30 may be composed of silicon, silicon carbide, tungsten and / or titanium, and has a thickness generally between several nanometers and several hundred nanometers, preferably between 2 nm and 50 nm.

[0083] The present invention also relates to a method for producing a composite structure 100 .

[0084] The method comprises a first step a) of providing a support substrate 20 made of polycrystalline silicon carbide, said support substrate 20 having a preferred crystal orientation according to which:

[0085] -Texture coefficient C 422Less than 40%, and

[0086] -Texture coefficient C 220 +C 200 +C 400 The sum of is greater than 50%.

[0087] Preferably, in order to meet the requirements of power electronic applications, the support substrate 20 has nitrogen doping or phosphorus doping, which can achieve a resistivity less than or equal to 10 mOhm·cm, 5 mOhm·cm, or even less than 3 mOhm·cm.

[0088] The radius of curvature of the support substrate 20 is greater than 25 m, advantageously greater than or equal to 50 m.

[0089] Step a) uses chemical vapor deposition (CVD) technology. This technology involves a gas mixture comprising at least one silicon precursor gas (e.g., silane or chlorosilane) and / or at least one carbon precursor gas (e.g., alkane or alkene), and / or at least one silicon precursor gas and a carbon precursor gas (e.g., methyltrichlorosilane, abbreviated as MTCS), and, if necessary, at least one dopant gas. In the case of nitrogen doping, the dopant gas may be, for example, NH3, N2H4, or N2. It should be noted that the dopant gas may also be a carbon precursor and / or a silicon precursor (e.g., an amine, such as H2NCH3). These gases may be diluted in a carrier gas, which may be a reducing gas (e.g., hydrogen) and / or an inert gas (e.g., argon). By means of this gas mixture, a polycrystalline SiC layer is formed on a so-called growth substrate.

[0090] This gas mixture enters a reactor at high temperature where the precursor gases are decomposed and react on the surface of the growth substrate (preferably fine-grained and purified isostatically pressed graphite) to form a 3C-SiC polytype whose mechanical and thermal resistance properties, thermal expansion coefficient, and purity are fully compatible with the specifications of the composite structure 100. In addition, the 3C-SiC polytype can be doped with very high levels of nitrogen, typically 10 20 atoms / cm 3 , and therefore has a resistivity of less than 10 mOhm·cm, without degrading the substrate quality (which would be detrimental to the quality of the composite structure and, consequently, the performance of the microelectronic components). Finally, it is a material capable of withstanding the high temperature processes to which the support substrate 20 is expected to be subjected during the manufacture of the composite structure 100 and the components.

[0091] The temperature of the reactor during CVD deposition of SiC must be between about 1000° C. and about 1600° C., preferably between about 1100° C. and about 1400° C., or even between about 1200° C. and about 1400° C. Within this temperature range, the deposition rate can vary over a fairly wide range (from 1 μm / hour to more than 100 μm / hour). Advantageously, the total pressure of the reactor does not exceed 350 mbar, or even 300 mbar.

[0092] By varying the parameters of the CVD process (eg, temperature, partial pressures of precursors, and percentage of potential dopant gases), the crystal orientation / texture of the deposited p-SiC layer can be altered.

[0093] For example, to obtain a support substrate 20 with a diameter of 150 mm, deposition is performed on a circular graphite cylinder with a diameter close to the nominal value of 150 mm and a thickness greater than 2 mm to ensure sufficient flatness of the substrate. The reactor can include a plurality of these discs, which can have the same or different diameters. The flatness of the two faces of the disc is preferably less than 15 μm, which is achieved by sufficient precision machining. The thermal expansion coefficient of the isostatic graphite is judiciously selected to be compatible with the p-SiC layer during the cooling process after deposition. The substrate sold by the company MERSEN under the name "grade 2303" can be used.

[0094] After deposition, the graphite growth substrate coated with the deposited p-SiC layer is machined and then air-oxidized, typically at 900°C, to remove any graphite residue. It should be noted that graphite removal can also be performed solely by machining techniques, or primarily by combustion / oxidation. Each side of the growth substrate has an unmachined p-SiC disc and a curvature due to stress relaxation of the deposited layer.

[0095] The p-SiC green wafer (optionally after release, with a material thickness of about 100 μm or more on at least its face in contact with the growth substrate) has specific crystallographic characteristics (i.e., preferred crystal orientation) characterized on each of its two faces by:

[0096] -Texture coefficient C 422 less than 40%, preferably less than 30%, and

[0097] -Texture coefficient C 220 Greater than 50%, preferably greater than 60%, or even greater than 80%.

[0098] The green disc made of p-SiC is then subjected to a heat treatment at a temperature ranging from 1800°C to 2300°C. During this heat treatment, the green disc is advantageously placed flat on a flat surface. This heat treatment results in specific changes in the size of the p-SiC grains and their crystallographic orientation, which can only be observed after deposition if the green disc has the above-mentioned specific crystallographic characteristics. This heat treatment is carried out at a temperature between 1800°C and 2300°C, preferably between 1850°C and 2200°C, more preferably between 1900°C and 2150°C, and even more preferably between 1950°C and 2150°C. Its duration is advantageously at least 10 minutes, advantageously between about 1 hour and about 12 hours, and preferably between about 2 hours and about 9 hours. A duration that is too long may lead to undesirable recrystallization, and if the duration is too short, the heat treatment may be ineffective.

[0099] The p-SiC green disc is then thinned by rough grinding and subsequent fine grinding. These grinding steps, known from the prior art, are particularly intended to remove sufficient thickness (at least 100 μm) on the side of the face of the disc in contact with the graphite to remove the initial growth zone of the crystal, thereby generating strong stresses. They also make it possible to obtain, by removing material from both faces of the green disc, an intermediate p-SiC disc having a second thickness close to the final thickness intended for supporting the substrate 20 and less deformation. This second thickness is generally less than 550 μm, preferably between 350 μm and 450 μm.

[0100] It should be noted that the above steps of thinning by grinding and heat treatment can be reversed or even nested (eg heat treatment can be performed after a first grinding sequence applied to the green wafer and before a second grinding sequence that will obtain the intermediate wafer).

[0101] By means of said heat treatment, an intermediate disc made of p-SiC is obtained, said intermediate disc having a preferred crystal orientation (which will also be the preferred crystal orientation of the supporting substrate 20 ), said preferred crystal orientation being defined as:

[0102] -Texture coefficient C 422 Less than 40%, and

[0103] -Texture coefficient C 220 +C 200 +C 400 The sum of is greater than 50%, preferably greater than 80%.

[0104] Preferably, C 200 +C 400 The contribution of C is greater than 1%, greater than 2%, or even greater than 5%. 200 +C 400This contribution to crystal orientation is characterized by a highly dominant texture C 220 , which results from a specific heat treatment to which the unprocessed disc or the intermediate disc is subjected.

[0105] Advantageously, the intermediate disc has on each of its two faces a texture coefficient C of less than 20%, preferably less than 15%, even more preferably less than 10%. 422 .

[0106] Heat treatment of the green wafer (before or after all or part of the grinding step) first leads to the rearrangement of crystal defects at the grain boundaries (which causes relaxation of residual stresses at the grain boundaries), then to recrystallization via nucleation at the grain boundaries, followed by the growth of these grains. Therefore, the initial grain size can influence the microstructure obtained at the end of heat treatment. The nature of the crystal defects is also critical: to promote effective stress-relieving recrystallization, small grains must be bounded by high-angle grain boundaries (HAGBs). These high-angle grain boundaries contain particularly large stored energy and are therefore more mobile than low-angle grain boundaries. Their internal energy is the driving force for the rearrangement of defects at the grain boundaries. The specific texture of the p-SiC of the green wafer subjected to heat treatment ensures the presence of such high-angle grain boundaries.

[0107] Without being bound by this theory, it is also assumed that the heat treatment of the wafer made of p-SiC allows for better diffusion of the dopants (especially nitrogen) and results in more efficient electronic incorporation of the dopant atoms into the crystal network. This makes it possible to obtain a density greater than 5×10 19 atoms / cm 3 , preferably greater than 1×10 20 atoms / cm 3 , even more preferably greater than 1.5×10 20 atoms / cm 3 The polycrystalline SiC wafer is doped with nitrogen concentrations of 100 nm to provide very low resistivity (less than 10 mOhm·cm, less than 5 mOhm·cm, or even less than 3 mOhm·cm).

[0108] Finally, in describing the composite structure 100 , the intermediate p-SiC wafer is subjected to conventional surface treatment by lapping and / or polishing to obtain the supporting substrate 20 made of p-SiC having the key properties described above.

[0109] Taking into account the defined preferred crystal orientation, the curvature of a green wafer made of p-SiC remains within a reasonable range, allowing the production of a support substrate 20 with low curvature from a green wafer of an economically viable thickness. This curvature can be measured by a confocal white light sensor that scans the surface of a wafer or substrate placed on a support plane of a measurement tool. The difference between the maximum and minimum heights of the surface scanned by the sensor relative to the support plane is measured. This surface can be interpolated with the median plane using the least squares method. If this median plane is parallel to the support plane, the deformation measurement is equal to the warp. In general, this method for measuring strain adds a measurement of warp.

[0110] For example, the curvature (warp) of an unprocessed p-SiC wafer with a diameter of 150 mm and a thickness of less than 1000 μm is targeted to be less than or equal to 250 μm. Thus, after grinding and polishing, a support substrate 20 with a thickness of typically less than 500 μm and a curvature of less than 100 μm, or even less than 50 μm, or even less than 30 μm can be obtained.

[0111] refer to Figure 3b The example support substrate 20 shown is a p-SiC CVD deposition with a thickness of 800 μm on a graphite growth substrate with a diameter of 150 mm at a temperature of about 1277°C, a MTCS partial pressure of 16 mbar and a NH3 mole fraction of 4%. The preferred crystal orientation of the obtained p-SiC disc has the following texture: C 220 =93%, C 422 =3%, and C 111 +C 222 +C 511 =2%, such as Figure 3a The nitrogen concentration measured by SIMS is 1.8×10 20 atoms / cm 3 , and provides a resistivity of 10 mOhm·cm (4-point method). Thermal conductivity was estimated at 240 W / m / K, which is high despite the small grain size and high doping level. The curvature of the unprocessed wafer is approximately 210 μm.

[0112] Then, a heat treatment is applied to the raw wafer made of p-SiC at 2000°C to make it flat on the flat surface. Then, a thinning step by grinding and polishing is performed to obtain Figure 3b The intermediate wafer and the supporting substrate 20 are included.

[0113] The unprocessed disc shows the main texture coefficient C 220 , with a significant component (111) near the interface with the growth substrate. The texture-rich C 111The heat treatment caused significant changes in the microstructure and grain angles ( Figure 3b ): Small grains with (220) orientation tend to merge and obtain a mixed orientation of (111)+(220)+(200). A small amount of small grains with (111) orientation are observed.

[0114] In this example, as described above, the support substrate 20 has a 1.8×10 20 atoms / cm 3 The nitrogen concentration was 0.1% and the resistivity was measured to be 1.2 mOhm·cm. The thermal conductivity was approximately 270 W / (m / K). Finally, the curvature was measured to be less than 100 μm on a substrate with a diameter of 150 mm and a thickness between 350 μm and 450 μm.

[0115] According to experience, after the above-mentioned heat treatment, in some supporting substrates 20, the average diameter of the grains (measured in a plane perpendicular to the z-axis, for example by EBSD) can be greater than or equal to 5 μm, in particular greater than or equal to 10 μm, or even 20 μm or 50 μm. In particular, the average diameter of the grains with orientations (200) and (400) is greater than or equal to 5 μm, in particular greater than or equal to 10 μm, or even 20 μm or 50 μm, which is caused by the heat treatment that causes the merging and recrystallization of some grains with a (220) orientation.

[0116] When measuring the average diameter of the grains, it is assumed that the different crystals forming one or more twins constitute the same grain, rather than separate grains.

[0117] Thus, depending on the conditions and duration of the heat treatment, the size of the grains tends to increase during the heat treatment, with their average diameter being able to increase by at least a factor of 2, typically by a factor of 5, or even by a factor of 10 or 50. This is particularly true for grains with a (220) orientation, which demonstrates that grains with a (220) orientation have a greater tendency to coalesce and recrystallize than grains with a (422) orientation. Thus, it has been demonstrated that the microstructure has a texture coefficient C of less than 40%. 422 and a texture coefficient C greater than 50% 220 +C 200 +C 400 The unprocessed wafer, which is the sum of the total mass of the wafer, is particularly sensitive to heat treatment. However, the increase in grain size during heat treatment is associated with an increase in thermal conductivity, thus enabling high thermal conductivity values ​​such as the 270 W / (mK) mentioned above to be achieved.

[0118] The merging of adjacent grains also significantly changes their morphology, because grains grown by CVD tend to be highly oriented in the thickness direction of the unprocessed wafer, while grains before heat treatment are mainly oriented along the Figure 3a The Z-axis extension can be seen in Figure 3bAs can be seen in Figure 5, the heat treatment leads to the appearance of grains with completely different morphologies.

[0119] In particular, the unprocessed wafer or support substrate 20 comprises grains having an aspect ratio, defined as the ratio between the length of the grain along the Z axis (as the numerator) and the diameter of the grain in a direction perpendicular to the Z axis (as the denominator), of less than or equal to 10, in particular less than or equal to 5, in particular less than or equal to 3. In particular, at least 5% of the grains have such an aspect ratio.

[0120] The support substrate 20 is intended to receive the face 20a ( Figure 5a ) is preferably less than or equal to 1 nm RMS (measured by atomic force microscopy over a scanning area of ​​20 μm×20 μm), even more preferably less than or equal to 0.5 nm RMS. The side of the support substrate 20 intended to form the back side of the composite structure 100 may have a greater surface roughness, for example, about 10 nm RMS.

[0121] Step a) of the method may optionally include applying a heat treatment to the support substrate 20 at a temperature greater than or equal to 1500° C. (typically between 1500° C. and 2000° C.) to stabilize its polycrystalline structure and / or eliminate defects resulting from the grinding or polishing steps (if applicable). In fact, these temperature ranges are likely to be used later in the method for manufacturing the composite structure 100.

[0122] The manufacturing method according to the present invention then comprises a step b) of providing a donor substrate 1 made of a single-crystalline material, from which a thin film 10 ( Figure 5a ). As mentioned above, with reference to the composite structure 100, the single crystal material may be silicon carbide, diamond, silicon, II-IV or III-V semiconductor compounds (particularly GaN) with a 4H, 6H or 3C polytype, etc. The donor substrate 1 is preferably in the form of a plate with a diameter of 100 mm, 150 mm, 200 mm or even larger (the same as or very close to the diameter of the support substrate 20) and a thickness typically between 300 μm and 800 μm. The donor substrate 1 has a front side 1a and a back side 1b. The surface roughness of the front side 1a measured by atomic force microscopy (AFM) over a scanning area of ​​20 μm×20 μm is advantageously selected to be less than 1 nm RMS, or even less than 0.5 nm RMS. The doping type and resistivity of the donor substrate 1 are determined according to the requirements of the components to be produced on and / or in the thin film 10 of the composite structure 100.

[0123] Finally, the method comprises a step c of transferring the thin film 10 from the donor substrate 1 onto the support substrate 20. There are different options known from the prior art for carrying out the layer transfer (mechanical thinning, chemical thinning or mechanochemical thinning, separation on a porous layer present in the donor substrate 1, etc.), which will not be described in an exhaustive manner.

[0124] According to a preferred embodiment, step c) of the method involves TM The method is based on the principle of light material injection and assembly by direct bonding.

[0125] The first stage c1) corresponds to the introduction of a light substance into the donor substrate 1 to form a buried brittle plane 11 which delimits, with the front side 1a of the donor substrate 1, the thin film 10 to be transferred ( Figure 5b ). It should be noted that, although the film 10 to be transferred is shown as a continuous layer, it may also consist of discontinuous masses (eg prepared on the surface of the donor substrate 1).

[0126] The light species is preferably hydrogen, helium, or a co-implantation of these two species, and is implanted into the donor substrate 1 at a defined depth that corresponds to the thickness of the target film 10. These light species will form microcavities around the defined depth, distributed in the film parallel to the free surface 1a of the donor substrate 1 or to the plane (x, y) in the drawing. For simplicity, this film is referred to as a buried brittle plane 11.

[0127] The implantation energy of the light species is selected to achieve a certain depth. For example, the implantation energy is between 10keV and 250keV and the implantation depth is between 5 E 16 / cm 2 to 1 E 17 / cm 2 Hydrogen ions are implanted at a dose between 100 nm and 1500 nm to define a thin film 10 having a thickness of approximately 100 nm to 1500 nm. It should be noted that prior to the ion implantation step, a protective layer may be deposited on the front side 1a of the donor substrate 1. This protective layer may be composed of a material such as silicon oxide or silicon nitride, for example. This protective layer will be removed prior to the next stage.

[0128] Then, the transfer step c) comprises assembling the donor substrate 1 (on the side of its front face 1 a) onto the support substrate 20 (on the side of its first face 20 a) by molecular adhesive bonding along the bonding interface 40 ( Figure 5c )’s second stage c2).

[0129] Optionally, before or after the introduction of the light substance in stage c1), and in any case before the assembly stage, an intermediate layer 30 can be formed on the front side 1a of the donor substrate 1. This intermediate layer 30 can be made of a semiconductor material (such as silicon or silicon carbide), or of a metallic material (such as tungsten, titanium, etc.). The thickness of the intermediate layer 30 is advantageously limited, typically ranging from a few nanometers to tens of nanometers.

[0130] In the case of forming the intermediate layer 30 before the first stage c1), the implantation energy (and potentially the dose) of the light species will be adjusted to penetrate this additional layer. In the case of forming the intermediate layer 30 after stage c1), care will be taken to form this layer by applying a thermal budget lower than the thermal budget of the bubbling that would occur on the surface of the donor substrate 1 due to the overgrowth and pressurization of the microcavities in the buried brittle plane 11.

[0131] Optionally, before the assembly stage, an intermediate layer 30 may also be deposited on the face of the support substrate 20 to be assembled; it may be chosen to have the same or different properties than the intermediate layer mentioned for the donor substrate 1. The intermediate layer 30 may optionally be deposited on both substrates 1, 20 to be assembled.

[0132] The purpose of the intermediate layer is mainly to increase the bonding energy (especially in the temperature range below 1100°C), since covalent bonds are formed at lower temperatures than in the case of two directly assembled SiC surfaces. Another advantage of this (these) intermediate layer(s) may be to improve the vertical conductivity of the bonding interface 40.

[0133] The intermediate layer 30 is intended to be embedded in the bonding component 50 after assembly ( Figure 5c' 、 Figure 5c ) and is ultimately embedded in the composite structure 100. Even if the intermediate layer 30 is continuous when it is formed on one and / or the other substrate 1, 20, it may become segmented and discontinuous during the subsequent heat treatment. This is essentially the case when the initial thickness of the layer is very small (typically less than 10 nm).

[0134] Returning to the description of the assembly stage c2), it is well known that direct bonding by molecular adhesion does not require an adhesive material, since the bond is established at the atomic scale between the assembled surfaces. There are various types of molecular adhesion bonding, which differ in particular in the temperature, pressure, atmospheric conditions, or the treatment of the surfaces before contact. Examples include bonding at room temperature (with or without prior plasma activation of the surfaces to be assembled), atomic diffusion bonding (ADB), surface activated bonding (SAB), and the like.

[0135] Before the surfaces 1a, 20a to be assembled come into contact, the assembly phase c2) may comprise a conventional chemical cleaning sequence (e.g. RCA cleaning), surface activation (e.g. oxygen plasma or nitrogen plasma) or other surface treatments (e.g. by scrubbing cleaning) that can improve the quality of the bonding interface 40 (fewer defects, stronger adhesion).

[0136] Finally, the third stage c3) consists in detaching along the buried brittle plane 11, which results in the transfer of the film 10 onto the supporting substrate 20 ( Figure 5d ).

[0137] The separation along the buried brittle plane 11 is generally carried out by applying a heat treatment at a temperature between 800° C. and 1200° C. This heat treatment causes the development of cavities and microcracks in the buried brittle plane 11 and pressurizes them by a light substance in gaseous form until the fracture propagates along said brittle plane 11. Mechanical stresses can be applied to the bonded assembly alternately or in combination, in particular at the buried brittle plane 11, in order to extend or help mechanically extend the fracture that leads to the separation. After the separation is completed, a composite structure 100 is obtained, comprising the supporting substrate 20 and the transferred thin film 10, and the remaining part 1 ' of the donor substrate. The doping level and doping type of the thin film 10 are defined by the choice of the properties of the donor substrate 1 or can be subsequently adjusted by known techniques for doping semiconductor layers.

[0138] The free surface 10a of the thin film 10 after separation is generally rough: for example, its roughness is between 5 nm RMS and 100 nm RMS. Cleaning and / or smoothing phases may be applied to restore a good surface state (roughness is generally less than a few angstroms RMS). In particular, these phases may include chemical mechanical smoothing of the free surface of the thin film 10. Removal of between 50 nm and 300 nm is effective in restoring the surface state of the layer 10. They may also include at least one thermal treatment at a temperature between 1200° C. and 1800° C. This thermal treatment is applied to expel residual light substances in the thin film 10 and promote lattice rearrangement of the thin film 10. It can also strengthen the bonding interface 40. The thermal treatment may also include or correspond to epitaxy on the thin film 10 to increase its thickness (for example, homoepitaxy of c-SiC on a thin film 10 made of c-SiC, heteroepitaxy of GaN on a thin film 10 made of c-SiC, or other).

[0139] Finally, it is noted that the transfer step c) may include a step of repairing the remaining portion 1 ′ of the donor substrate in order to reuse it as the donor substrate 1 for the new composite structure 100. Mechanical and / or chemical treatments similar to those applied to the composite structure 100 may be performed on the front side 1 ′a of the remaining substrate 1 ′.

[0140] The composite structure 100 obtained is very robust to very high temperature heat treatments that may be applied to improve the quality of the film 10 or to manufacture elements on and / or in said layer 10. The supporting substrate 20 in the composite structure 100 is stable and its curvature does not increase significantly during the high temperature heat treatments applied to the composite structure 100 for its manufacture and subsequent processing.

[0141] The composite structure 100 according to the present invention is particularly suitable for producing one (or more) high-voltage microelectronic components, such as, for example, Schottky diodes, MOSFET transistors, etc. By having excellent vertical electrical conductivity, good thermal conductivity, and by providing high-quality single-crystalline thin films 10, the present invention more broadly meets the needs of microelectronic power applications.

[0142] Of course, the invention is not limited to the embodiments and examples described, and variant embodiments thereof may be provided without departing from the scope of the invention as defined in the claims.

Claims

1. A composite structure (100) for manufacturing a microelectronic component, the composite structure (100) comprising a single-crystal thin film (10), the single-crystal thin film (10) being arranged on a support substrate (20) made of polycrystalline silicon carbide, the support substrate (20) having a preferred crystal orientation on each of its faces, according to the preferred crystal orientation: -Texture coefficient C 422 Less than 40%, and -Texture coefficient C 220 +C 200 +C 400 The sum of is greater than 50%, preferably greater than 80%.

2. The composite structure (100) according to the preceding claim, wherein The resistivity of the support substrate (20) is less than or equal to 10 mOhm·cm, preferably less than or equal to 5 mOhm·cm, more preferably less than or equal to 3 mOhm·cm.

3. The composite structure (100) according to any one of the preceding claims, wherein The support substrate (20) is nitrogen-doped, and the concentration thereof measured by secondary ion mass spectrometry is greater than or equal to 5.0×10 19 atoms / cm 3 , preferably greater than or equal to 1.0×10 20 atoms / cm 3 , even more preferably greater than or equal to 1.5×10 20 atoms / cm 3 , or preferably greater than or equal to 3×10 20 atoms / cm 3 .

4. The composite structure (100) according to any one of the preceding claims, wherein Texture coefficient C 422 Less than 20%, preferably less than 15%, or even preferably less than 10%.

5. The composite structure (100) according to any one of the preceding claims, wherein Texture coefficient C 200 +C 400 The sum of is greater than 1%, preferably greater than 2%, even more preferably greater than 5%.

6. The composite structure (100) according to any one of the preceding claims, wherein The film (10) is composed of silicon carbide.

7. The composite structure (100) according to any one of claims 1 to 5, wherein: The thin film (10) is composed of gallium nitride.

8. The composite structure (100) according to any one of claims 1 to 5, wherein: The thin film (10) consists of gallium oxide.

9. The composite structure (100) according to any one of claims 1 to 5, wherein: The film (10) is composed of diamond.

10. A composite structure (100) according to any one of the preceding claims, comprising a continuous or discontinuous intermediate layer (30), the intermediate layer (30) being arranged between the film (10) and the supporting substrate (20) and consisting of at least one metallic material or a semiconductive material.

11. Composite structure (100) according to the preceding claim, wherein The intermediate layer (30) is composed of silicon, silicon carbide, tungsten and / or titanium.

12. The composite structure (100) according to any one of the preceding claims, wherein The thickness of the support substrate (20) is between 50 microns and 650 microns.

13. A composite structure (100) according to any of the preceding claims, comprising electronic components on and / or in the film (10), and optionally comprising electrical contacts on the back side of the supporting substrate (20).

14. A method for manufacturing a composite structure (100), the composite structure (100) comprising a single-crystal thin film (10), the single-crystal thin film (10) being arranged on a supporting substrate (20) made of polycrystalline silicon carbide, the manufacturing method comprising the following steps: a) providing a support substrate (20) made of polycrystalline silicon carbide, said support substrate (20) having a preferred crystal orientation on each of its faces, according to which: -Texture coefficient C 422 Less than 40%, and -Texture coefficient C 220 +C 200 +C 400 The sum of is greater than 50%, preferably greater than 80%, b) providing a donor substrate (1) made of a single-crystalline material, c) Transferring the thin film (10) from the donor substrate (1) to a supporting substrate (20).

15. Manufacturing method according to the preceding claim, wherein The transfer step c) comprises: c1) forming a buried brittle plane (11) in the donor substrate (1), delimiting the thin film (10) between the buried brittle plane (11) and the front side (1a) of the donor substrate (1), c2) assembling the donor substrate (1) onto the support substrate (20) directly or through an intermediate layer (30) by molecular adhesion bonding, c3) separation along the buried brittle plane (11), thereby transferring the thin film (10) to a supporting substrate (20).

16. Manufacturing method according to the preceding claim, wherein Before assembling the two substrates (1, 20), step c2) comprises: - before or after step c1), forming an intermediate layer (30) on the donor substrate (1), and / or - forming an intermediate layer (30) on a supporting substrate (20), The intermediate layer (30) is formed of at least one metallic material or semiconductive material selected from silicon, silicon carbide, tungsten and titanium.

17. The manufacturing method according to any one of claims 14 to 16, further comprising producing electronic components on and / or in the film (10) of the composite structure (100).

18. Manufacturing method according to the preceding claim, wherein The production of the electronic component comprises in particular a homoepitaxial or heteroepitaxial step performed on the thin film (10).

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