Manufacturing process of a non-deformable p-SiC wafer

Abstract

The invention relates to a method for manufacturing a polycrystalline silicon carbide wafer, comprising the following steps: heat treatment of a plate (1) of polycrystalline silicon carbide; thinning of the polycrystalline silicon carbide plate, said thinning comprising a correction, by removal of material from the polycrystalline silicon carbide plate, of a deformation caused by the heat treatment. Figure for abstract: Fig. 3

Description

Title of the invention: Method for manufacturing a non-deformable p-SiC wafer Technical field

[0001] The field of the invention is that of the manufacture of polycrystalline silicon carbide wafers intended in particular to serve as supports for thin layers of monocrystalline silicon carbide. Prior art

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

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

[0004] These composite structures nevertheless tend to exhibit high values ​​of curvature (bow in English designating a parabolic curvature with rotational symmetry in particular with respect to the center of the plate) and of warping (warp in English designating a deformation with a positive radius of curvature in one axis and negative in the other). These high values ​​are in particular the consequence of a relaxation of stresses induced by the manufacture of the support substrate in polycrystalline SiC, relaxation likely to occur when the support substrate is subjected to a heat treatment during the Smart Cut™ process (for example during the separation annealing, generally carried out at a temperature of the order of 1300-1700°C, to effect the transfer of the thin layer from the donor substrate to the support substrate) or after the Smart Cut™ process during the formation of electronic components in the transferred thin layer (typically at temperatures of the order of 1800-2000°C).

[0005] These high curvature and strain values ​​are problematic in that they can lead to breakage of the composite structure or generate alignment problems during the lithography steps necessary to form the power components. Statement of the invention

[0006] The invention aims to propose a technique for manufacturing a polycrystalline SiC wafer which makes it possible to limit or even eliminate the risk of deformation of the wafer during subsequent heat treatments.

[0007] To this end, the invention proposes a method for manufacturing a polycrystalline silicon carbide wafer, comprising the following steps: - heat treatment of a polycrystalline silicon carbide plate; - thinning of the polycrystalline silicon carbide plate, said thinning comprising a correction, by removal of material from the polycrystalline silicon carbide plate, of a deformation caused by the heat treatment.

[0008] Some preferred but non-limiting aspects of this method are as follows: - material removal is achieved by grinding the polycrystalline silicon carbide plate; - the removal of material from the polycrystalline silicon carbide plate is carried out by electroerosion; - material removal is carried out both on the front and back faces of the polycrystalline silicon carbide plate; - the material removal is carried out so that the plate has front and rear faces that are flat and parallel to each other; - the thinning step comprises the removal, on at least one of the faces of the plate, of a thickness of material greater than or equal to 50 micrometers; - it comprises a step of manufacturing the plate by depositing material on a growth substrate, and the heat treatment step is preceded by a step of separating the plate and the growth substrate; - the heat treatment is carried out at a temperature between 1650°C and 2000°C for a period of more than 10 minutes; - the heat treatment includes a plateau at 1850°C; - heat treatment includes a step and regulation of the descent in temperature from the plateau to a target temperature; - it comprises, before the heat treatment, the formation of the polycrystalline silicon carbide plate by deposition of polycrystalline silicon carbide on a growth substrate followed by removal of the growth substrate; - the heat treatment is carried out at a temperature higher than the temperature of the deposition of the polycrystalline silicon carbide on the growth substrate.

[0009] The invention also extends to the manufacture of a composite structure by transferring a thin layer of monocrystalline silicon carbide from a monocrystalline silicon carbide substrate to a polycrystalline silicon carbide wafer manufactured in accordance with the invention. This manufacture may further comprise the formation of electronic components in the transferred thin layer at a temperature lower than the temperature of the heat treatment applied during the manufacture of the wafer. Brief description of the drawings

[0010] Other aspects, aims, advantages and characteristics of the invention will appear better on reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the appended drawings in which:

[0011] [Fig-1] [Fig. 1] is a diagram illustrating a polycrystalline silicon carbide plate after a surface smoothing step;

[0012] [Fig.2] [Fig.2] is a diagram illustrating the deformation of the polycrystalline silicon carbide plate caused by the heat treatment step;

[0013] [Fig.3] [Fig.3] is a diagram illustrating the correction, by material removal, of the deformation caused by the heat treatment;

[0014] [Fig.4] [Fig.4] is a diagram illustrating a polycrystalline silicon carbide wafer obtained by implementing the invention.

[0015] DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0016] The invention relates to a method of manufacturing a polycrystalline silicon (p-SiC) wafer from a p-SiC plate, the wafer having by definition a reduced thickness compared to that of the plate.

[0017] A deposition of p-SiC on a growth substrate (for example a graphite substrate), typically a chemical vapor deposition at a temperature between 1200°C and 1400°C, makes it possible to form a relatively thick (for example 2 to 3 mm thick) p-SiC plate (generally referred to by the English term slab). There are different crystalline forms (also called polytypes) of silicon carbide. The most widespread are the 4H, 6H and 3C forms. In a manner Preferably, the polytype of the p-SiC plate thus formed is the 3C polytype, but all polytypes are conceivable for implementing the present invention.

[0018] Following removal of the growth substrate, the p-SiC plate is subjected to a process of forming one or more wafers (so-called wafering process in English) which comprises different steps of cleaning, etching, grinding and polishing and makes it possible to obtain one or more p-SiC wafers having a desired shape (in particular a beveled edge) and a desired thickness. Sawing can also be carried out during this process, in particular when several wafers must be manufactured from the same plate.

[0019] According to the invention, a heat treatment is inserted into this wafering process in order to prepare a wafer which will not be deformed during subsequent heat treatments, for example when implementing the Smart Cut™ process or when producing electronic components. The wafering process is furthermore adapted so that the wafer thus prepared is flat and has neither curvature nor warping.

[0020] Starting from a p-SiC plate separated from its growth substrate, the method according to the invention for manufacturing a p-SiC wafer thus comprises a heat treatment of the plate and a thinning of the plate.

[0021] In a possible embodiment illustrated by [Fig. 1], the heat treatment step may be preceded by a step of smoothing the p-SiC plate 1. This surface smoothing may be carried out by grinding. It may also make it possible to remove the growth seed of the p-SiC crystal used during the formation of the plate 1.

[0022] In another possible embodiment which may or may not be combined with the previous embodiment, the heat treatment step is preceded by a step of cleaning the p-SiC plate 1.

[0023] The heat treatment is carried out at a temperature higher than a temperature of the deposition of the p-SiC on the growth substrate during the formation of the plate. This heat treatment is also carried out at a temperature higher than the highest temperature of the subsequent heat treatment(s), for example higher than the temperature of a subsequent heat treatment for manufacturing electronic components.

[0024] The heat treatment is preferably carried out at a temperature between 1650°C and 2000°C for a duration greater than 10 minutes. This heat treatment may in particular be carried out at a temperature of at least 1700°C, for example at 1850°C, at 1900°C or even at 2000°C. It may be carried out at low pressure (typically at less than 100 mbar, for example at less than 50 mbar, in particular between 10 and 30 mbar) under an argon atmosphere.

[0025] The heat treatment may include a plateau. It may also be carried out with regulation of the temperature decrease from the plateau to a target temperature. In an exemplary embodiment, the heat treatment includes a plateau at 1850°C. This plateau may have a duration of 30 minutes. The temperature increase may be carried out with a ramp of 10°C / min. The temperature decrease may be regulated, for example up to 1000°C with a ramp of 10°C / min. The temperature decrease from the target temperature to ambient temperature is then carried out by following the thermal inertia of the furnace used to carry out this heat treatment.

[0026] As shown in [Fig. 2], the heat treatment is likely to cause a deformation (curvature, warping) of the plate 1. The thinning of the plate is then adapted to include (if necessary consist of) a correction, by removal of material from the polycrystalline silicon carbide plate, of the deformation caused by the heat treatment. The removal of material is typically adapted locally so that the plate is not thinned in the same way at all points. This correction of the deformation results in a reduction in the value of curvature (bow) or warp (warp) observed after the heat treatment.

[0027] [Fig. 3] illustrates a possible embodiment of this thinning, here carried out until reaching the parallel dotted lines. [Fig. 4] illustrates the plate 2 obtained in accordance with the invention from the plate 1 of [Fig. 1].

[0028] According to one possible embodiment, the material removal intended to correct the deformation caused by the heat treatment is carried out by grinding the p-SiC plate. In another embodiment, this material removal is carried out by electroerosion. The material removal by electroerosion has the advantage over grinding of being able to be carried out without contact with the plate and without artificially correcting the deformation by elastic bending. In yet another embodiment, the material removal combines electroerosion and grinding. In the latter mode, electroerosion can carry out coarse thinning while grinding carries out finer thinning.

[0029] In an exemplary embodiment, the thinning comprises in succession very coarse thinning (by electroerosion or grinding) for example removing a thickness of the order of 150 μm or more, coarse grinding for example removing a thickness of the order of 20 μm and fine grinding for example removing a thickness of the order of 3 μm. The different grinding operations are distinguished by the size of the grains of the grinding wheel used, these grains being increasingly smaller in the succession of grinding operations.

[0030] As shown in [Fig.3], the thinning can be carried out on both the front and back faces of the p-SiC plate. And as shown in Figures 3 and 4, this thinning is preferably carried out so that the front and rear faces of the wafer obtained at the end of the process are flat and parallel to each other. These front and rear faces of the wafer 2 are not necessarily parallel to the front and rear faces of the initial plate 1.

[0031] For example, the thinning removes a thickness at least equal to the deformation value after the heat treatment minus 25 μm.

[0032] Generally, the thickness removed from each of the faces of the plate during thinning following heat treatment is, for example, greater than or equal to 50 μm, in particular greater than or equal to 100 μm or even 150 μm.

[0033] The thinning is, in particular, such that it results in a self-supporting plate, that is to say one whose thickness is such that it does not break or deform plastically under the effect of its own weight. Such a thickness is, for example, greater than or equal to 200 μm, in particular greater than or equal to 300 μm.

[0034] In particular, a thickness of between 175 μm and 200 μm can be removed from each of the faces of the plate, for a thinning of 350 to 400 μm in total. A wafer with a thickness of between 325 and 375 μm can thus be obtained from a plate having undergone a first thinning before the heat treatment bringing it to a thickness of 725 μm.

[0035] The thinning of the plate can be followed by surface finishing steps of the wafer aimed in particular at making it smoother.

[0036] The invention further extends to a method for manufacturing a composite structure, comprising the manufacturing of a p-SiC wafer as previously described and the transfer of a thin layer of monocrystalline silicon carbide from a monocrystalline silicon carbide substrate to the polycrystalline silicon carbide wafer.This transfer can be carried out using Smart Cut™ technology and thus include an implantation of ionic species in the monocrystalline silicon carbide substrate so as to form a weakening plane therein delimiting the thin layer to be transferred, the bonding of the monocrystalline silicon carbide substrate with the polycrystalline silicon carbide wafer (where appropriate by means of one or more bonding layers) then the detachment (caused by a heat treatment, a mechanical action, or a combination of these means) of the monocrystalline silicon carbide substrate along the weakening plane so as to transfer the thin active layer to the polycrystalline silicon carbide wafer. The method for manufacturing the composite structure can further include the formation of electronic components, in particular power or radiofrequency components in the transferred thin layer.

[0037] Providing heat treatment upstream of the wafering process makes it possible to avoid excessive deformation of the wafer once it has been thinned and flattened under the effect of its subsequent exposure to high temperatures.

[0038] When the heat treatment is carried out after the separation of the plate and the growth substrate, the heat treatment does not induce additional deformation of the plate which would be linked to the stresses exerted by the growth substrate on the plate during heating of the plate / substrate assembly. This further contributes to improving the flatness and stability of the final wafer.

Claims

Claims

1. A method of manufacturing a polycrystalline silicon carbide wafer (2), comprising, after forming a polycrystalline silicon carbide plate (1) by depositing polycrystalline silicon carbide on a growth substrate followed by removing the growth substrate, the following steps: - heat treatment of the polycrystalline silicon carbide plate (1); - thinning of the polycrystalline silicon carbide plate, said thinning comprising correcting, by removing material from the polycrystalline silicon carbide plate, a deformation caused by the heat treatment.

2. The method of claim 1, wherein the material removal is accomplished by grinding the polycrystalline silicon carbide plate.

3. A method according to claim 1, wherein the removal of material from the polycrystalline silicon carbide plate is carried out by electroerosion.

4. Method according to one of claims 1 to 3, in which the removal of material is carried out both on the front face and on the back face of the polycrystalline silicon carbide plate.

5. A method according to claim 4, wherein the removal of material is carried out so that the wafer has front and rear faces which are flat and parallel to each other.

6. Method according to one of claims 1 to 5, in which the thinning step comprises the removal, on at least one of the faces of the plate, of a thickness of material greater than or equal to 50 micrometers.

7. Method according to one of claims 1 to 6, in which the heat treatment is carried out at a temperature between 1650°C and 2000°C for a duration greater than 10 minutes.

8. A method according to claim 7, wherein the heat treatment comprises a hold at 1850°C.

9. The method of claim 7, wherein the heat treatment comprises a plateau and regulation of the temperature decrease from the plateau to a target temperature.

10. Method according to one of claims 1 to 9, in which the heat treatment is carried out at a temperature higher than a temperature of the deposition of the polycrystalline silicon carbide on the growth substrate.

11. A method of manufacturing a composite structure, comprising manufacturing a polycrystalline silicon carbide wafer in accordance with the method of one of claims 1 to 10 and transferring a thin layer of monocrystalline silicon carbide from a monocrystalline silicon carbide substrate to the polycrystalline silicon carbide wafer.

12. The method of claim 11, further comprising forming electronic components in the transferred thin layer at a temperature lower than the heat treatment temperature of the method of one of claims 1 to 10.

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