Multi-step chemical-mechanical polishing process applied to materials in the semiconductor industry

Abstract

Method (100) for polishing a flat substrate (Waf) using a planarization and polishing machine comprising a support plate (Pl) provided with a polishing fabric (Pol.Pad), a head (Cond.Head) for conditioning the polishing fabric, and a head (Pol.Head) for holding the flat substrate (Waf) against the polishing fabric, the method comprising a first step (110) of a first conditioning of the polishing fabric (Pol.Pad) using the conditioning head (Cond.Head), the flat substrate (Waf) not undergoing a polishing operation; a second step (120) of a first polishing of the flat substrate (Waf), the polishing fabric not undergoing a conditioning operation; and a third step (130) in which (i) a second polishing of the flat substrate (Waf) is carried out and, simultaneously, (ii) a second conditioning of the polishing fabric (Pol.Pad). Figure to be published with the abstract: Fig. 1

Description

Title of the invention: Multi-step chemical-mechanical polishing process, applied to materials in the semiconductor industry TECHNICAL FIELD OF THE INVENTION

[0001] The invention relates to a chemical-mechanical polishing method optimized to reduce the generation of scratches on substrates such as semiconductor material substrates, called "wafers". TECHNOLOGICAL BACKGROUND

[0002] The field of semiconductor materials requires obtaining extremely flat and regular material surfaces, for example to prepare a wafer of semiconductor material for a photolithography step or a direct contact bonding step, or to work the surface of a donor wafer or a layer separated from such a wafer after a cleavage step, possibly using Smart Cut™ technology. For these purposes, mechanical or chemical-mechanical surface polishing operations, or CMP for Chemical Mechanical Polishing, are commonly used.

[0003] Chemical-mechanical polishing is a surface smoothing process combining mechanical and chemical actions. During a chemical-mechanical polishing operation of a wafer, the wafer is pressed and rubbed against a polishing cloth in the presence of a polishing solution commonly called slurry. In mechanical polishing, the slurry is chemically neutral and does not chemically attack the material to be polished.

[0004] The polishing cloth, called "polishing pad" in English terminology, generally consists of a flexible disc made of polymer or woven or non-woven fabric, of known roughness, and having a profile allowing the abrasion of the surface of the wafer. The polishing solution consists of a liquid capable of chemically attacking the wafer, for example by oxidation, and containing abrasive particles capable of mechanically attacking the material.

[0005] In parallel with the polishing of a wafer, the polishing fabric can be conditioned by friction by means of a conditioning element, consisting for example of a metal disc on the surface of which diamonds are encrusted.

[0006] A specific example where extremely fine surface preparation is required is the preparation of silicon carbide SiC wafers to provide atomically flat, damage-free substrates for high-quality epitaxy. These substrates are fundamental components in the manufacturing of high-performance semiconductor devices for high-power applications.

[0007] CMP operations involve mechanical abrasion and therefore the generation of debris that can aggravate certain surface defects, such as scratches. It may become necessary to remove this debris to ensure polishing at the desired quality level. More generally, to avoid the appearance of surface defects, or to reduce these defects, CMP operations are usually implemented by finely adjusting the polishing parameters and carefully choosing the consumables used. There remains, however, room for improvement, which it is desirable to exploit in view of the importance of the surface quality of substrates or layers in the semiconductor industry.

[0008] To this end, two-step CMP polishing processes have been developed, as discussed for example by Weilei Wang et al. in the article “Two-Step Chemical Mechanical Polishing of 4H-SiC (0001) Wafer”, 2021 ECS J. Solid State Sci. Technol. 10 074004. CMP operations involve complex interactions between the wafer surface and the CMP equipment consumables (polishing cloth, slurry, polishing cloth conditioning element). The two-step process then consists of using a first combination of consumables in a first step to achieve a first objective such as a high material removal rate from the surface of the wafer to be treated. In a second step, a second combination of consumables is used to achieve a second objective such as a high surface quality of the wafer. On the other hand, the slurry / polishing cloth pair changes between the first step and the second step. This approach complicates the choice of consumables and increases the number of operations to be carried out, in an industrial context where, on the contrary, the simplification of operations while maintaining a desired level of performance is sought. Statement of the invention

[0009] An object of the invention is to provide a method for mechanical or mechanochemical polishing of substrates used in the semiconductor industry solving the problems mentioned above.

[0010] In order to achieve these objects, one aspect of the invention is a method of polishing a planar substrate by means of a planarizing and polishing machine comprising a support plate on which an interchangeable polishing cloth is placed, an interchangeable conditioning head provided for conditioning the polishing cloth, and a polishing head provided for holding the planar substrate against the interchangeable polishing cloth, the method comprising three steps: (1) a first step in which a first conditioning of a first polishing cloth is carried out by means of a first conditioning head, the flat substrate not undergoing a polishing operation against the polishing cloth during this first step; (2) a second step following the first step, in which a first polishing of the flat substrate is carried out, the flat substrate being held against the first polishing cloth by means of the polishing head, and the first polishing cloth not undergoing a conditioning operation during this second step; and (3) a third step following the second step, in which (i) a second polishing of the flat substrate is carried out by holding the flat substrate against a second polishing cloth by means of the polishing head and, simultaneously, (ii) a second conditioning of the second polishing cloth by means of a second conditioning head.

[0011] The polishing method according to the invention makes it possible to reduce the presence of scratches on the surface of flat substrates, as well as to obtain a surface state compatible with subsequent operations requiring this surface state, such as photolithography or epitaxial growth operations for the purpose of manufacturing electronic circuits.

[0012] Furthermore, this leads to a simplification of the management of consumables (polishing cloth, conditioning head, polishing solution) used during polishing and a reduction in the number of handling operations involved by allowing the same consumables to be used throughout the polishing operation, without the obligation to change these consumables between the steps of the process.

[0013] According to additional non-limiting characteristics of the invention, considered individually or in any technically feasible combination:

[0014] - the first polishing cloth and the second polishing cloth may be the same polishing cloth;

[0015] - the same polishing solution can be brought onto the plate during the first step, second step, and third step;

[0016] - the first conditioning head and the second conditioning head can be a single conditioning head;

[0017] - a parameter representative of a force applied to the flat substrate by the head of polishing can be the same for the second stage and the third stage;

[0018] - a parameter representative of a rotation applied to the flat substrate by the head of polishing can be the same for the second stage and the third stage;

[0019] - a parameter representative of a rotation applied to the plate can be the same for the second stage and the third stage; and

[0020] - the flat substrate may consist of a silicon carbide plate or include a layer of silicon carbide on which the mechanical and chemical polishing is applied.

[0021] The invention extends to a method of manufacturing a composite substrate comprising the steps of preparing a surface of a donor substrate; preparing a surface of a receiving substrate; assembling the receiving substrate to the donor substrate by bringing the prepared surface of the donor substrate into direct contact with the prepared surface of the receiving substrate; cleaving the donor substrate so as to leave on the receiving substrate a transfer layer formed of a certain thickness of the donor substrate; and preparing a free surface of the transfer layer, in which at least one of the steps of preparing the surface of the donor substrate, preparing the surface of the receiving substrate and preparing the free surface of the transfer layer is implemented by means of the polishing method according to the invention.

[0022] According to additional non-limiting characteristics of the invention, considered individually or in any technically feasible combination:

[0023] - the donor substrate may be at least partially formed of SiC or GaN each of monocrystalline structure, and / or in which the receiving substrate may be at least partially formed of SiC or AIN each in polycrystalline form;

[0024] - the method of manufacturing a composite substrate may further comprise a step of reconditioning a free surface of the donor substrate after the cleaving step, wherein the reconditioning step is carried out by means of the polishing method according to the invention.

[0025] The invention extends to a method of manufacturing an electronic device, comprising a step chosen from a layer growth by epitaxy, a bonding step by direct contact or a photolithography operation implemented on the flat substrate having undergone the polishing method according to the invention. BRIEF DESCRIPTION OF THE FIGURES

[0026] Other characteristics and advantages of the invention will emerge from the detailed description of the invention which follows with reference to the appended figures in which:

[0027] [Fig. 1] [Fig. 1] illustrates a planarizing and polishing machine in use;

[0028] [Fig.2] [Fig.2] illustrates a chemical-mechanical polishing method according to the invention;

[0029] [Fig.3] [Fig.3] illustrates test results of a chemical-mechanical polishing process with in-situ conditioning;

[0030] [Fig.4] [Fig.4] illustrates test results of a chemical-mechanical polishing process with ex-situ conditioning;

[0031] [Fig.5] [Fig.5] illustrates test results of a three-step chemical-mechanical polishing process according to the invention;

[0032] [Fig.6] [Fig.6] illustrates the manufacture of a composite substrate implementing the polishing process of [Fig.2];

[0033] [Fig.7] [Fig.7] illustrates the process of manufacturing a composite substrate of [Fig.6]. DETAILED DESCRIPTION OF THE INVENTION Method of carrying out the invention

[0034] One embodiment of the invention is detailed below and illustrated by Figures 1 to 5.

[0035] In the remainder of this description, the invention will be described in the example of chemical-mechanical polishing. However, it should be noted that the invention is also applicable to purely mechanical polishing.

[0036] [Fig.l] illustrates a Mac chemical mechanical polishing machine in use, with a support plate PI on which an interchangeable polishing Pol.Pad cloth is placed, an interchangeable conditioning Cond.Head provided for conditioning the polishing Pad.Pol cloth, and a polishing Pol.Head provided for holding a substrate to be treated against the polishing cloth.

[0037] The polishing operation of a flat substrate Waf, such as a wafer, is carried out by holding the wafer against the polishing fabric Pol.Pad by means of the polishing head Pol.Head by applying to it a force Fl directed towards the plate PI and a rotation co2 around a vertical axis Ax2 and centered on the polishing head. The rotation co2 is transmitted to the wafer by means of a carrier element Car in contact with the wafer.

[0038] The PI plate also follows a rotation along a vertical axis Axl centered on the plate. The relative movements of the plate and the wafer allow for regular polishing.

[0039] Although not shown here, the Mac polishing machine is equipped with a system for dispensing a polishing SI solution, which plays the roles of lubrication and chemical attack of the wafer surface.

[0040] The Mac polishing machine is also equipped with a Con.Head for conditioning the Pol.Pad polishing cloth. Its role is to condition the surface of this cloth to maintain its stable characteristics. The conditioning head can consist of a rigid metal disc with a surface encrusted with diamonds. The disc is in rotation co3 around an axis Ax3 centered on the conditioning head, the latter being mounted at the end of an arm Sw.Ar in oscillating movement Sw around an axis A4 centered on the other end of the arm Sw.Ar. A vertical force F2 oriented towards the plate PI is applied to the conditioning head.

[0041] Figures 3, 4 and 5 illustrate characterization results of planar substrates having at least one silicon carbide surface having undergone, respectively, (1) polishing of the wafer with concomitant conditioning of the polishing fabric (called polishing with “in situ” conditioning), (2) polishing of the wafer following conditioning of the polishing fabric, without conditioning concomitant with the polishing (called polishing with “ex situ” conditioning), and (3) a first polishing of the wafer following conditioning of the polishing fabric, without conditioning concomitant with the polishing (therefore “ex situ” conditioning), and a second polishing of the wafer with concomitant conditioning of the polishing fabric (called polishing with “in situ” conditioning).

[0042] The relevant parameters for the polishings mentioned in the previous paragraph are as follows.

[0043] The conditioning fabric may have a hardness of between 90 and 100 Shore A, a compressibility of between 0 and 6%, a density of between 0.95 and 1.11, and be rotated at a speed of between 90 and 120 rpm.

[0044] The polishing head can impose on the wafer a pressure of between 3 and 9 psi (unit conventionally used in this field by suppliers of this type of equipment) or between 21000 and 62000 N / m2, and be driven in co2 rotation at a speed of between 70 and 160 rpm.

[0045] The conditioning head may consist of a diamond metal disc with an aggressiveness of between 20 and 30, a flatness of between 0 and 75, a rotation speed co3 of between 10 and 140 rpm, and configured to apply a force to the polishing cloth of between 4 and 8 Ibf (pound-force, a unit conventionally used by suppliers of this type of equipment), considering that the standard diameter of the conditioning head is 4.25 inches (a unit conventionally used by suppliers of this type of equipment).

[0046] The characterization illustrated here was made by a SICA88 device from the company Lasertec, which allows to combine the techniques of confocal microscopy with Nomarski prism in visible light and by photoluminescence (as described by [1] T.Kimoto et al., “Fundamentals of Silicon Carbide Technology Growth Characterization Devices and Applications”, p.126, or [2] D. Baierhofer et al, Materials Science in Semiconductor processing 140 (2022) 106414), and is commonly used to inspect the surfaces of semiconductor substrates.

[0047] In (A) of Figures 1 to 3 are shown defectivity maps, which reveal different types of defects of the analyzed surface. In (B) of Figures 1 to 3 are shown results of roughness analyses.

[0048] As shown in [Fig. 3], a conventional polishing operation involves conditioning the polishing cloth simultaneously with polishing the wafer. This procedure, however, does not satisfactorily prevent the formation of surface defects such as scratches.

[0049] The interpretations of Figures 1 to 4 are as follows. A wafer polishing step with concomitant conditioning of the polishing cloth results in a variable scratch rate (scratch-type defects in English terminology) of between 10 and 30%, meaning that 10 to 30% of the wafers have a scratch, see [Fig. 3] in (A). The associated roughness, illustrated in (B) of [Fig. 3], is in a range of 4 to 5 in arbitrary units of the SICA88 apparatus, with regions RI and R2 having roughnesses lower than 4.6 and 5.1 in arbitrary units of the SICA88 apparatus, respectively.

[0050] As illustrated by [Fig.4], a so-called "ex situ" polishing operation makes it possible to reduce the scratch rate, or scratch rate in English terminology, to a range of 0 to 8%, with a roughness in a range of 5 to 7 in arbitrary unit of the SICA88 device, with regions RI and R2 having roughnesses lower than 5.7 and 6.3 in arbitrary unit of the SICA88 device, respectively.

[0051] The mechanisms responsible for the differences in surface conditions between the types of polishing in Figures 3 and 4 are not fully explained. The lower roughness of the polishing operation with “in situ” conditioning would be due to a good surface condition of the polishing fabric, the latter being continuously reconditioned. The increased roughness of the polishing operation with “ex situ” conditioning appears to be linked to debris from the wafer, diamond particles from the conditioning head and / or abrasive particles from the polishing solution. “Ex situ” conditioning does not optimize the roughness, but seems to allow better removal of the particles or agglomerates responsible for the scratches.

[0052] Based on this observation, it is proposed to implement a method 100 for polishing a flat Waf substrate such as a wafer, in three main steps. The results of this method, illustrated by [Fig.5], will be discussed below.

[0053] In a step 110, a first polishing fabric Pol.Pad is conditioned using a conditioning head Cond.Head. A polishing solution SI is supplied to the first polishing fabric. During this first step, the flat substrate Waf does not undergo a polishing operation against the polishing fabric Pol.Pad.

[0054] In an intermediate step 115 following step 110, the conditioning head is moved away from the first polishing fabric and, conversely, the flat substrate is brought into contact with the first polishing fabric, and pressed against it by means of the polishing head Pol.Head and the carrier element Car.

[0055] In a second step 120 following the intermediate step 115, the flat substrate Waf is polished by holding it against the first polishing cloth Pad.Pol by means of the polishing head Pol.Head. A polishing solution SI is brought onto the polishing cloth. During this second step, the first polishing cloth Pad.Pol does not undergo a conditioning operation. In other words, during the second step 120 of polishing the flat substrate Waf, the conditioning head is at a distance from the polishing cloth, at least one gap being maintained between the conditioning head and the polishing cloth, i.e. the head is positioned so as not to apply any action, and in particular any mechanical action, to the polishing cloth. The head can also be completely removed from the polishing system, as illustrated in [Fig.2].

[0056] At an intermediate step 125 following step 120, the conditioning head is brought into contact with the polishing fabric and pressed against it.

[0057] In a third step 130 following the intermediate step 125, the Waf planar substrate is polished by holding the Waf planar substrate against the first or second polishing cloth Pad.Pol by means of the polishing head Pol.Head and, simultaneously, the polishing cloth Pol.Pad is conditioned by means of the conditioning head Cond.Head. A polishing SI solution is brought onto the polishing cloth.

[0058] A first polishing cloth is used during steps 110 and 120. This same first polishing cloth can be used for step 130, or it can be replaced by a second polishing cloth, of the same type or of a different type from the first polishing cloth.

[0059] A single conditioning head may be used for two or three of the three steps 110, 120 and 130, or three conditioning heads of three different types may each be used for a respective one of the three steps 110, 120 and 130.

[0060] The same polishing liquid may be used for two or three of the three steps 110, 120 and 130, or three polishing liquids of three different types may each be used for a respective one of the three steps 110, 120 and 130.

[0061] Polishing parameters such as the speeds of the rotations col, co2, co3, and co4, and quantities representative of the applied forces F1 and F2 may individually be the same for two or three of the three steps 110, 120 and 130, or may be different for each of the three steps 110, 120 and 130.

[0062] Choosing consumables - polishing cloths, conditioning heads, polishing liquid - that are distinct according to the stages allows for optimization of each of these stages and therefore optimal surface quality. On the other hand, in an industrial setting, this makes the management of consumables, the use of the polishing system (machine, stocks and handling of consumables, etc.) and its maintenance complex and a source of errors and additional costs.

[0063] Conversely, limiting variations in consumables allows for simplified management of these consumables, also simplifies the maintenance of the polishing system and limits the number of manipulations required, reducing sources of error and reducing costs.

[0064] [Fig.5] illustrates the results of three-step polishing operations in which the consumables remain the same during the three steps 110, 120 and 130.

[0065] It appears that the number of scratches is reduced compared to the polishing operations illustrated by Figures 3 and 4 and that the level of roughness is reduced compared to the polishing operations illustrated by [Fig.4], with regions RI and R2 having roughnesses lower than 5.1 and 5.7 in arbitrary unit of the SICA88 apparatus, respectively. Thus, the number of surface defects, in particular the number of scratches, as well as the roughness are compatible with subsequent operations of epitaxy, direct bonding or even photolithography. The three-step polishing process according to the invention allows a substantial reduction in the number of surface defects compared to conventional processes.

[0066] In practice, step 120 can be used to remove a relatively large thickness of the planar substrate to be treated, for example between 180 nm for substrates consisting of planar substrates comprising a layer of silicon carbide SiC, and 800 nm for monocrystalline silicon carbide wafers. This step, with “ex situ” conditioning, makes it possible to avoid the formation of scratches but leading to non-optimal roughness.

[0067] Step 130 can be considered as a finishing step, with “in situ” conditioning, removing a thickness of the flat substrate to be treated that is smaller than step 120, approximately 50 nm for example. This step makes it possible to reduce the roughness of the surface of the flat substrate without introducing scratches.

[0068] Following steps 110 to 130, the planar substrate is ready to undergo additional operations 140 for the manufacture of a semiconductor device. These operations may include one or more thin-film growth operations by epitaxy, direct contact bonding or photolithography.

[0069] Thin film growth by epitaxy makes it possible to obtain a high-quality crystalline semiconductor layer formed directly on the polished layer of the flat substrate.

[0070] Direct contact bonding makes it possible to associate a flat, homogeneous or complex structure with the flat substrate using known assembly methods such as molecular or bonding bonding or metal-metal bonding.

[0071] A photolithography operation makes it possible, on the basis of the flat substrate, to produce complex semiconductor devices.

[0072] Each of these operations benefits from the polishing quality obtained by means of the process of steps 110 to 130, which allows an increase in the production yield of the final semiconductor device.

[0073] Application example

[0074] Figures 6 and 7 illustrate a method 200, which is a particular example of application of the method described above, particularly suitable for obtaining composite semiconductor substrates comprising a thin layer of a first semiconductor material supported by a substrate of a second material. The thin layer is intended to form the active layer of a semiconductor device. The substrate is chosen for its characteristics complementary to those of the thin layer. It is thus possible to form composite substrates formed from a layer of SiC or GaN of monocrystalline structure supported by a substrate of SiC or AIN of polycrystalline structure.

[0075] The method 200 begins by providing two substrates Subi and Sub2 at two providing steps 210 and 220, respectively. In an exemplary implementation of the invention, the substrate Subi is made of SiC or GaN of monocrystalline structure, and is intended to serve as a donor substrate for forming a thin monocrystalline layer TrLay. The substrate Sub2 is made of SiC or AIN of polycrystalline structure, and is intended to serve as a support substrate for the transfer layer TrLay.

[0076] At a step 230 of implantation of at least one light species, the Subi substrate is prepared at a step of separation of the TrLay layer from a part of the thickness of the Subi substrate, according to the Smart Cut™ technology in the present example.

[0077] For this purpose, the substrate Subi must be prepared by introducing at least one light species such as hydrogen or helium into this substrate. This introduction may correspond to a hydrogen implantation, that is to say, an ion bombardment of hydrogen. In a manner known per se, and as illustrated by [Fig. 6], the hydrogen ions H+ are implanted so as to form a weakening plane Frgl delimiting the layer TrLay to be transferred, corresponding to the volume between the weakening plane Frgl and the surface Surfl of the substrate Subi through which the ions H+ have been implanted into the substrate Subi.

[0078] The nature, the dose of the implanted species and the implantation energy are chosen according to the thickness of the layer that one wishes to transfer and the physicochemical properties of the Subi substrate. In the case of a Subi substrate in SiC, one can choose to implant a dose of hydrogen between 1016 and 5.1017 at / cm2 with an energy between 30 and 300 keV to delimit a TrLay layer of the order of 200 to 2000 nm thick.

[0079] In an assembly step 250, the two substrates Subi and Sub2 are assembled to each other by placing the TrLay layer in direct contact with one face of the substrate Sub2. These two layers adhere to each other by molecular bonding. In this way, an intermediate stack IntStck is formed comprising the two substrates Subi and Sub2 with the weakening layer Frgl.

[0080] The assembly step requires that the surfaces brought into contact be as flat and smooth as possible, ideally atomically flat. To this end, the steps 210 and 220 of providing the substrates each comprise the implementation of the polishing method described above, applied at least to the faces of the substrates Subi and Sub2 intended to come into contact with each other during the assembly step 250.

[0081] In a detachment step S260 following the assembly step 250, the substrate Subi is cleaved into two parts at the level of the weakening layer Frgl, according to the Smart Cut™ method in the present example. Thus, a part of the substrate Subi is detached from the rest of its volume to isolate a layer of interest, here the layer TrLay which is detached from the rest of the substrate Subi by fracture at the level of the weakening plane Frgl. The layer TrLay is thus transferred onto the support Sub2. The assembly obtained forms the composite substrate Comp.Sub.

[0082] This detachment step may comprise the application to the stack IntStck of a heat treatment in a temperature range of the order of 800°C to 1000°C to allow the detachment of the layer TrLay and thus complete the transfer of the latter onto the substrate Sub2. As a replacement or in addition to the heat treatment, this step may comprise the application of a blade or a jet of gaseous or liquid fluid, or any other force of a mechanical nature at the level of the embrittlement plane Frgl.

[0083] In an optional step following the detachment step, a stabilizing heat treatment can be applied to the Comp.Sub composite substrate. The stabilizing heat treatment makes it possible to cure crystalline defects present in the TrLay layer. This heat treatment can be provided to bring the composite substrate to a temperature between 1500°C and 1900°C for a period of between 30 minutes and 10 hours. This heat treatment is preferably carried out by exposing the free face of the TrLay layer to a neutral gas atmosphere.

[0084] Following the detachment of the TrLay layer from the rest of the substrate Subi, its free surface Surf.Sep is irregular. In order to put it in a condition to undergo any operation conventionally used in the semiconductor industry, it is necessary to prepare this Surf.Sep surface and in particular to reduce its roughness, ideally so as to make it atomically flat and smooth.

[0085] Thus, at a surface preparation step 270, a planarization and polishing treatment is applied to the Surf.Sep surface of the TrLay layer. This may be the polishing treatment described above using [Fig.2].

[0086] After the cleavage step 260, the donor substrate Subi has a surface Surfl' formed by the cleavage of the substrate at the weakening plane. In a Refurb step of reconditioning the substrate Subi so that it can be used again as a donor substrate, the surface Surfl' can be reconditioned according to the same process as that of step 270.

[0087] In this document, the figures are not necessarily to scale. Some features and components may be shown exaggerated relative to other components or in a somewhat schematic form, and some details of conventional elements may not be shown in the interest of clarity and conciseness.

[0088] Of course, the invention is not limited to the embodiments described and variant embodiments can be made without departing from the scope of the invention as defined by the claims.

Claims

Claims

1. Method (100) for polishing a planar substrate (Waf) by means of a planarization and polishing machine comprising a support plate (PI) on which an interchangeable polishing cloth (Pol.Pad) is placed, an interchangeable conditioning head (Cond.Head) provided for conditioning the polishing cloth (Pad.Pol), and a polishing head (Pol.Head) provided for holding the planar substrate (Waf) against the interchangeable polishing cloth, the method comprising three steps: - a first step (110) in which a first conditioning of a first polishing cloth (Pol.Pad) is carried out by means of a first conditioning head (Cond.Head), the planar substrate (Waf) not undergoing a polishing operation against the polishing cloth (Pol.Pad) during this first step; - a second step (120) following the first step (110), in which a first polishing of the flat substrate (Waf) is carried out, the flat substrate (Waf) being held against the first polishing cloth (Pad.Pol) by means of the polishing head (Pol.Head), and the first polishing cloth (Pad.Pol) not undergoing a conditioning operation during this second step; and - a third step (130) following the second step (120), in which (i) a second polishing of the flat substrate (Waf) is carried out by holding the flat substrate (Waf) against a second polishing cloth (Pad.Pol) by means of the polishing head (Pol.Head) and, simultaneously, (ii) a second conditioning of the second polishing cloth (Pol.Pad) by means of a second conditioning head (Cond.Head).

2. The method (100) of claim 1, wherein the first polishing cloth and the second polishing cloth are a same polishing cloth (Pol.Pad).

3. The method (100) of claim 1 or 2, wherein the same polishing solution (SI) is supplied to the plate during the first step (110), the second step (120), and the third step (130).

4. A method (100) according to any one of claims 1 to 3, wherein the first conditioning head and the second conditioning head are the same conditioning head (Cond.Head).

5. A method (100) according to any one of claims 1 to 4, wherein a parameter representative of a force (Fl) applied to the planar substrate by the polishing head is the same for the second step (120) and the third step (130).

6. Method (100) according to any one of claims 1 to 5, in which a parameter representative of a rotation (co2) applied to the planar substrate (Waf) by the polishing head (Pol.Head) is the same for the second step and the third step.

7. Method (100) according to any one of claims 1 to 6, in which a parameter representative of a rotation (col) applied to the plate (PI) is the same for the second step and the third step.

8. The method (100) of any one of claims 1 to 7, wherein the planar substrate is made of a silicon carbide plate or comprises a layer of silicon carbide on which the chemical mechanical polishing is applied.

9. Method (200) for manufacturing a composite substrate (Comp.Sub) comprising the steps of: - preparing (210) a surface (Surfl) of a donor substrate (Subi); - preparing (220) a surface (Surf2) of a receiving substrate (Sub2); - assembling (250) the receiving substrate (Subi) to the donor substrate (Sub2) by directly contacting the prepared surface (Surfl) of the donor substrate to the prepared surface (Surf2) of the receiving substrate; - cleaving (260) the donor substrate (Subi) so as to leave on the receiving substrate (Sub2) a transfer layer (TrLay) formed of a certain thickness of the donor substrate (Subi); and - preparing (270) a surface (SurfSep) free of the transfer layer, wherein at least one of the steps of preparing the surface (Surf1) of the donor substrate, preparing the surface (Surf2) of the recipient substrate and preparing the surface (SepSurf) free of the transfer layer is carried out by means of the method of any one of claims 1 to 8.

10. The method (200) according to claim 9, wherein the donor substrate (Subi) is at least partially formed of SiC or GaN each of monocrystalline structure, and / or wherein the recipient substrate (Sub2) is at least partially formed of SiC or AIN each in polycrystalline form.

11. The method (200) according to claim 9 or 10, further comprising a step (Refurb) of reconditioning a free surface (Surfl') of the donor substrate (Subi) after the cleaving step (260), wherein the reconditioning step is carried out by means of the method of any one of claims 1 to 8.

12. A method of manufacturing an electronic device, comprising a step (140) chosen from epitaxial layer growth, a direct contact bonding step or a photolithography operation carried out on the planar substrate having undergone the method according to any one of claims 1 to 8.

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