METHOD FOR MANUFACTURING A NON-DEFORMABLE P-SIC WAFER

Abstract

A method of manufacturing a polycrystalline silicon carbide wafer includes the following stages: heat treatment of a polycrystalline silicon carbide slab; thinning of the polycrystalline silicon carbide slab, the thinning comprising a correction, by withdrawal of material from the polycrystalline silicon carbide slab, of a deformation brought about by the heat treatment.

Claims

1. A method of manufacturing a polycrystalline silicon carbide wafer, comprising the following stages: heat treatment of a polycrystalline silicon carbide slab; and thinning of the polycrystalline silicon carbide slab, the thinning comprising a correction, by removal of material from the polycrystalline silicon carbide slab, of a deformation brought about by the heat treatment.

2. The method of claim 1, wherein the removal of material is carried out by grinding the polycrystalline silicon carbide slab.

3. The method of claim 1, wherein the removal of material from the polycrystalline silicon carbide slab is carried out by electrical discharge machining.

4. The method of claim 1, wherein the removal of material is carried out both at a front face and at a rear face of the polycrystalline silicon carbide slab.

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

6. The method of claim 1, wherein the thinning stage comprises the removal, on at least one of the faces of the slab, of a thickness of material of greater than or equal to 50 micrometers.

7. The method of claim 1, further comprising a stage of manufacture of the slab by deposition of material on a growth substrate and wherein the stage of heat treatment is preceded by a stage of separation of the slab and of the growth substrate.

8. The method of claim 1, wherein the heat treatment is carried out at a temperature of between 1650 C. and 2000 C. for a period of time of greater than 10 minutes.

9. The method of claim 8, wherein the heat treatment comprises a stationary phase at 1850 C.

10. The method of claim 8, wherein the heat treatment comprises a stationary phase in which temperature is maintained steady for a period of time and a cooling phase in which temperature is decreased in a controlled manner to a target temperature.

11. The method of claim 1, further comprising, before the heat treatment, the formation of the polycrystalline silicon carbide slab by deposition of polycrystalline silicon carbide on a growth substrate, followed by removal of the growth substrate.

12. The method of claim 11, wherein the heat treatment is carried out at a temperature greater than a temperature of the deposition of the polycrystalline silicon carbide on the growth substrate.

13. A method of manufacturing a composite structure, the method comprising manufacturing a polycrystalline silicon carbide wafer in accordance with the method according to claim 1 and transferring a thin layer made of single-crystal silicon carbide from a single-crystal silicon carbide substrate to the polycrystalline silicon carbide wafer.

14. The method of claim 13, further comprising forming electronic components in the transferred thin layer at a temperature lower than the temperature of the heat treatment of the process according to claim 1.

15. The method of claim 2, wherein the removal of material is carried out both at a front face and at a rear face of the polycrystalline silicon carbide slab.

16. The method of claim 15, wherein the removal of material is carried out so that the wafer exhibits front and rear faces that are flat and parallel to each other.

17. The method of claim 16, wherein the thinning stage comprises the removal, on at least one of the faces of the slab, of a thickness of material of greater than or equal to 50 micrometers.

18. The method of claim 3, wherein the removal of material is carried out both at a front face and at a rear face of the polycrystalline silicon carbide slab.

19. The method of claim 18, wherein the removal of material is carried out so that the wafer exhibits front and rear faces that are flat and parallel to each other.

20. The method of claim 19, wherein the thinning stage comprises the removal, on at least one of the faces of the slab, of a thickness of material of greater than or equal to 50 micrometers.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Other aspects, aims, advantages and characteristics of the present disclosure will become more clearly apparent on reading the following detailed description of preferred embodiments of the latter, given by way of nonlimiting example and made with reference to the appended drawings, in which:

[0025] FIG. 1 is a diagram illustrating a polycrystalline silicon carbide slab after a surface smoothing stage;

[0026] FIG. 2 is a diagram illustrating the deformation of the polycrystalline silicon carbide slab brought about by the stage of heat treatment;

[0027] FIG. 3 is a diagram illustrating the correction, by removal of material, of the deformation brought about by the heat treatment;

[0028] FIG. 4 is a diagram illustrating a polycrystalline silicon carbide wafer obtained by the implementation of the present disclosure.

DETAILED DESCRIPTION

[0029] The present disclosure relates to a process for the manufacture of a polycrystalline silicon carbide (p-SiC) wafer from a p-SiC slab, the wafer exhibiting, by definition, a reduced thickness with respect to that of the slab.

[0030] A deposition of p-SiC on a growth substrate (for example, a graphite substrate), typically a chemical vapor deposition at a temperature of between 1200 C. and 1400 C., makes it possible to form a p-SiC slab, which is relatively thick (for example, with a thickness of 2 to 3 mm). There exist different crystal forms (also called polytypes) of silicon carbide. The commonest are the 4H, 6H and 3C forms. Preferably, the polytype of the p-SiC slab thus formed is the 3C polytype but all the polytypes can be envisaged for implementing the present disclosure.

[0031] Following the removal of the growth substrate, the p-SiC slab is subjected to a process of formation of one or more wafers (wafering process), which comprises various cleaning, etching, grinding and polishing stages and makes it possible to obtain one or more p-SiC wafers having a desired form (in particular, a beveled edge) and a desired thickness. Sawing can also be carried out during this process, in particular, when several wafers have to be manufactured from one and the same slab.

[0032] The removal of the growth substrate, when the latter is made of graphite, is, for example, carried out by combustion of the graphite. For this, a stage of heating in the presence of oxygen, for example, at a combustion temperature of greater than or equal to 800 C., is often used. The combustion temperature is frequently less than or equal to 1000 C.

[0033] According to the present disclosure, a heat treatment is inserted in this wafering process in order to prepare a wafer that will not be deformed during subsequent heat treatments, for example, during the implementation of the SMARTCUT process or during the preparation of electronic components. The wafering process is furthermore adapted in order for the wafer thus prepared to be flat and to exhibit neither bow nor warp.

[0034] Starting from a p-SiC slab separated from its growth substrate, the process according to the present disclosure for the manufacture of a p-SiC wafer thus comprises a heat treatment of the slab and a thinning of the slab.

[0035] In a possible embodiment illustrated by FIG. 1, the stage of heat treatment can be preceded by a stage of smoothing the p-SiC slab 1. This surface smoothing can be carried out by grinding or by mechanical or chemical-mechanical polishing. It can furthermore make it possible to remove the growth seed of the p-SiC crystal used during the formation of the slab 1.

[0036] In another possible embodiment, which may or may not be combined with the preceding embodiment, the stage of heat treatment is preceded by stage of cleaning the p-SiC slab 1.

[0037] The heat treatment is carried out at a temperature greater than a temperature of the deposition of the p-SiC on the growth substrate during the formation of the slab. This heat treatment is furthermore carried out at a temperature greater than the highest temperature of the subsequent heat treatment(s), for example, greater than the temperature of a subsequent manufacturing heat treatment of electronic components.

[0038] The heat treatment is preferably carried out at a temperature of between 1650 C. and 2000 C. for a period of time of greater than 10 minutes. This heat treatment can, in particular, be carried out at a temperature of at least 1700 C., for example, at 1850 C., at 1900 C. or also at 2000 C. The heat treatment can comprise temperature rise/fall gradients of between 10 C./minute and 100 C./minute.

[0039] The heat treatment can 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), or also at a pressure of greater than 100 mbar, indeed even at atmospheric pressure.

[0040] The heat treatment is typically carried out under a neutral atmosphere, for example, under an argon or nitrogen atmosphere.

[0041] The heat treatment can comprise a stationary phase. It can also be carried out with regulation of the fall in temperature from the stationary phase down to a target temperature. In an implementational example, the heat treatment comprises a stationary phase at 1850 C. This stationary phase can exhibit a duration of 30 minutes. The rise in temperature can be carried out with a gradient of 10 C./min. The fall in temperature can be regulated, for example, down to 1000 C. with a gradient of 10 C./min. The fall in temperature from the target temperature to ambient temperature is subsequently carried out by following the thermal inertia of the furnace used to carry out this heat treatment.

[0042] As represented in FIG. 2, the heat treatment is liable to bring about a deformation (bow, warp) of the slab 1. The thinning of the slab is then adapted in order to comprise (if appropriate, to consist of) a correction, by removal of material from the polycrystalline silicon carbide slab, of the deformation brought about by the heat treatment. The removal of material is typically adapted locally so that the slab is not thinned in the same way at every point. There emerges, from this correction of the deformation, a decrease in the value of bow or of warp observed after the heat treatment.

[0043] FIG. 3 illustrates a possible implementation of this thinning, in this instance carried out until the parallel dotted lines are reached. For its part, FIG. 4 illustrates the wafer 2 obtained in accordance with the present disclosure from the slab 1 of FIG. 1.

[0044] According to a possible embodiment, the removal of material targeted at correcting the deformation brought about by the heat treatment is carried out by grinding the p-SiC slab. In another embodiment, this removal of material is carried out by electrical discharge machining. The removal of material by electrical discharge machining exhibits the advantage, in comparison with grinding, of being able to be carried out without contact with the slab and without artificially creating the deformation by elastic bending. In yet another embodiment, the removal of material combines electrical discharge machining and grinding. In this latter embodiment, the electrical discharge machining can carry out a coarse thinning, while the grinding carries out a finer thinning.

[0045] In an implementational example, the thinning comprises, in succession, a very coarse thinning (by electrical discharge machining or grinding), which will remove, for example, a thickness of the order of 150 m or more, a coarse grinding, which will remove, for example, a thickness of the order of 20 m, and a fine grinding, which will remove, for example, a thickness of the order of 3 m. The different grinding operations differ in the size of the grains of the grinding wheel used, these grains being increasingly small in the sequence of the grinding operations.

[0046] Optionally, a mechanical or chemical-mechanical polishing stage is carried out after the final grinding stage.

[0047] As represented by FIG. 3, the thinning can be carried out both at the front face and at the rear face of the p-SiC slab. And, as represented by FIGS. 3 and 4, this thinning is preferentially carried out so that the front and rear faces of the wafer obtained on conclusion of the process are flat and parallel to one another. These front and rear faces of the wafer 2 are not necessarily parallel to the front and rear faces of the starting slab 1.

[0048] By way of example, the thinning will remove a thickness at least equal to the value of deformation after the heat treatment minus 25 m.

[0049] Generally, the thickness removed from each of the faces of the slab during the thinning following the heat treatment is, for example, greater than or equal to 50 m, in particular, greater than or equal to 100 m, indeed even greater than or equal to 150 m.

[0050] The thinning is, in particular, such that it results in a self-supporting wafer, that is to say the thickness of which 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 m, in particular, greater than or equal to 300 m.

[0051] In particular, a thickness of between 175 m and 200 m can be removed from each of the faces of the slab, for a thinning of 350 to 400 m in total. A wafer with a thickness of between 325 et 375 m can thus be obtained from a slab that has been subjected to a first thinning before the heat treatment leading it to a thickness of 725 m.

[0052] The thinning of the slab can be followed by stages of surface finishing of the wafer targeted, in particular, at rendering it smoother.

[0053] The present disclosure furthermore extends to a process for the manufacture of a composite structure, comprising the manufacture of a p-SiC wafer as set out above and the transfer of a thin layer made of single-crystal silicon carbide from a single-crystal silicon carbide substrate to the polycrystalline silicon carbide wafer. This transfer can be carried out according to the SMARTCUT technology and thus comprise an implantation of ionic entities in the single-crystal silicon carbide substrate so as to form therein a weakened plane delimiting the thin layer to be transferred, the bonding of the single-crystal silicon carbide substrate with the polycrystalline silicon carbide wafer (if appropriate via one or more bonding layers), then the detachment (brought about by a heat treatment, a mechanical action or a combination of these means) of the single-crystal silicon carbide substrate along the weakened plane, so as to transfer the thin active layer to the polycrystalline silicon carbide wafer. The process for the manufacture of the composite structure can additionally comprise the formation of electronic components, in particular, of power or radiofrequency components, in the transferred thin layer.

[0054] The fact of providing a heat treatment upstream of the wafering process makes it possible to avoid an excessive deformation of the wafer once the latter has been thinned and levelled under the effect of its subsequent exposure to high temperatures.

[0055] When the heat treatment is carried out after the separation of the slab and of the growth substrate, the treatment does not bring about additional deformation of the slab, which would be linked to the stresses exerted by the growth substrate on the slab during the heating of the slab/substrate assembly. This contributes all the more to improving the flatness and the stability of the final wafer.

[0056] According to an alternative form that can be envisaged, the stage of heat treatment is shared with the stage of removal by combustion of the support substrate made of graphite. For example, during this stage, it is the assembly formed by the wafer 2 and the support substrate that is brought to a temperature of greater than or equal to 1650 C. as mentioned above, in the presence of oxygen, so as to bring about the combustion of the graphite while thermally treating the slab 1. According to another embodiment that can be envisaged, the stages of removal by combustion and of heat treatment are carried out successively, preferably in this order, in the same furnace. In this case, the furnace is first heated to 800 C. or more in the presence of oxygen, then heated above 1650 C., for example, under a neutral atmosphere after the oxygen injected has been purged from the furnace.