EP3424663B1 - Wire cutting support for bonded abrasives comprising an assembly of different materials, system comprising such a support and wire cutting methods - Google Patents

Description

TECHNICAL AREA

The present invention relates to the general field of cutting or sawing by bonded abrasive wire, in particular by diamond wire, that is to say comprising abrasive grains, in particular diamonds, fixed on the surface of the wire or wires . It particularly concerns the field of supports for wire cutting with bonded abrasives.

The invention finds applications in many fields of industry, and for example in the industry of electronic components, ferrites, quartz and/or silicas, for example when obtaining thin slices of substrates ( called "wafers" or more generally "wafers" in English) of materials such as semiconductor materials, for example crystalline silicon used in particular for the manufacture of photovoltaic cells, the cutting of sapphire, stone or silicon carbide , or even other hard and brittle materials.

The invention thus proposes a support system for cutting by bonded wire associated with a part to be cut, a method for cutting by wire with bonded abrasives of such a system, and its method of manufacture.

PRIOR ART

The document US 2013/112185 A1 discloses a system comprising a support for cutting by bonded abrasive wire at least one part to be cut, the support being produced by an assembly of different materials,

at least one part to be cut, where the part to be cut is made of a first semiconductor material, and the first material of the support is distributed inhomogeneously with the other materials of the support.

Wire cutting devices (or wire saws) conventionally comprise one or more cutting wires, present in free form or in the form of windings. Most often, they comprise a wire forming a plurality of windings around rotating members thus defining a layer of wire strands, these strands being substantially parallel to each other, the layer of wire strands being even more simply designated below. by the expression “sheet of yarn”, yarn being in the singular. This sheet of yarn is then capable of moving according to a continuous or alternating movement in support against a piece to be cut into several slices thus defining a cutting area. The cutting zone can consist of a set of pulleys or cylinders placed in parallel. These cylinders called “wire guides” can be engraved with a plurality of grooves defining the interval between the wire strands, in other words the thickness of the slices to be cut, once the thickness of the kerf has been removed. The piece to be cut can be fixed on a support table which moves perpendicularly to the sheet of wire. The travel speed defines the cutting speed. The renewal of the yarn, as well as the control of the tension, can be done in a part defining a yarn management zone, located outside the actual cutting zone.

The cutting of the part is made possible by the phenomena of abrasion caused between the wire and the part to be cut, possibly assisted by the action of a third element. Thus, as explained in more detail below, the agent which governs the cutting by wire can for example consist of an abrasive fixed to the wire (or bound to the wire), or a free abrasive brought by bubbling. In the latter case, the thread only acts as a carrier.

In addition, during wire cutting, a lubricant in fluidic form is generally used such as, for example, water, water mixed with an additive, polyethylene glycol (PEG), or even a gel, among others.

1. i) l'étape de briquetage (encore appelée « squaring » en anglais) qui correspond à la découpe des lingots en briques de section normalisée ;
2. ii) l'étape d'éboutage (encore appelée « cropping » en anglais) qui consiste à ôter les parties supérieure et inférieure de chaque brique qui contiennent des précipités d'impuretés dues à la cristallisation, et qui sont indésirables pour les étapes de fabrication ultérieures ;
3. iii) l'étape de découpe (ou encore « wafering » ou « slicing » en anglais) qui permet enfin de former les substrats ou « galettes », à partir des briques tronquées sur leurs parties supérieure et inférieure, présentant une épaisseur variant de 100 à 300 µm.

Although this is in no way limiting, the invention is particularly concerned with the cutting of crystalline silicon for applications in the field of photovoltaics and semiconductors. In this context, wire cutting devices can be used in all the silicon cutting steps implemented to move from the simple ingot stage to the stage of forming substrates (or "wafers") intended for the manufacture of photovoltaic cells. Thus, more specifically, these stages include successively:

1. i) the briquetting step (also called “squaring”) which corresponds to the cutting of the ingots into bricks of standardized section;
2. ii) the trimming step (also called "cropping") which consists of removing the upper and lower parts of each brick which contain precipitates impurities due to crystallization, which are undesirable for subsequent manufacturing steps;
3. iii) the cutting step (or "wafering" or "slicing" in English) which finally makes it possible to form the substrates or "cakes", from the bricks truncated on their upper and lower parts, having a thickness varying from 100 at 300 µm.

We have thus illustrated in perspective, respectively with reference to the figures 1A, 1B and 1C , the three operations i) bricklaying, ii) trimming and iii) cutting described above for the manufacture of silicon substrates for the production of photovoltaic cells.

Thus, as illustrated in the Figure 1A , each silicon ingot 30 is first cut in a matrix fashion during step i) of bricklaying by the strands 10 of the cutting wire to obtain a plurality of bricks 31.

Then, during step ii) of trimming illustrated on the figure 1B , each brick 31 is cut on its lower and upper parts to remove impurities resulting from crystallization.

Finally, as shown in figure 1C , step iii) of cutting makes it possible to obtain a plurality of slices of substrates 32 from each brick 31.

It should also be noted that the first two steps i) bricklaying and ii) trimming can, if necessary, be carried out without wire cutting, and then generally using a diamond blade.

Furthermore, depending on the mode of abrasion involved, wire cutting can be divided into two main categories described below.

A first type of wired cutting is indeed constituted by cutting with free abrasives. In this first type of wire cutting, abrasive grains, generally silicon carbide, are incorporated into a specific solution, containing for example polyethylene glycol (PEG), forming a cutting fluid (known as "slurry " in English). This cutting liquid is then poured between two solids sliding against each other, in this case the cutting wire, typically made of steel, on the part to be cut. The abrasive grains are set in motion by the sliding of the two bodies against each other, and thus abrade the material by multiple micro-indentations caused by the rolling of abrasive particles on the piece to be cut. This first type of wire cutting therefore corresponds to a so-called “three-body” case of abrasion, consisting of the wire, the abrasive grains and the part to be cut.

A second type of wired cutting is moreover constituted by the cutting with bonded abrasives. In this second type of wire cutting, abrasive grains, generally diamonds (hence the common name of "diamond wire cutting"), are fixed on the surface of the wire and then scratch the material of the part. to cut. This second type of wire cutting therefore corresponds to a case of so-called “two-body” abrasion, consisting of the abrasive wire and the part to be cut.

This second type of wire cutting, referred to throughout the description by the expression "cutting by bonded abrasive wire" or even "cutting by diamond wire" when the abrasive grains used are diamonds, is the technique usually favored for the cutting monocrystalline silicon. It is increasingly found in the cutting market for photovoltaic-type applications.

In fact, bonded abrasive wire cutting has many advantages in terms of cutting performance compared with the free abrasive cutting technique described above, namely in particular: a higher cutting speed, in particular two to three times faster higher than for the free abrasive cutting technique, simplification of the wire cutting devices, the possibility of integrating cutting waste recycling modules.

As indicated below, the present invention is advantageously concerned only with this bonded abrasive wire cutting technique.

Moreover, for cutting with loose abrasives, the part to be cut, for example a silicon brick, is usually glued to a cutting support in the form of a glass plate. The wire then completes the cut by crossing about 50% of the thickness of the glass plate so that the wire is completely out of the part to be cut. This glass plate is generally itself glued to a steel plate allowing the assembly to be held in the wire cutting device.

In the context of bonded abrasive wire cutting, the part to be cut, for example a silicon brick, is usually glued to a cutting support which can be of different natures, for example epoxy or graphite, among others. In this case, the glass is not used because the diamond wire cuts the glass with difficulty and the deflection of the wire, present during the cutting, cannot be absorbed correctly in the glass. Part of the material constituting the cutting support is therefore found in the cutting fluid after cutting, with the silicon powder when it is recovered.

Moreover, as for the first type of free abrasive wire cutting, during bonded abrasive wire cutting, the wire progresses in the part to be cut, in particular a block of silicon, then in a cutting support in such a way to be certain that the wire is completely out of the part, so that the wafers (or "wafers" in English) can then be detached from the support. This cutting support is also generally glued, or even assembled, for example by screwing, to a steel plate, allowing the assembly to be held in the wire cutting device.

The composition of the cutting supports is generally chosen so as to oppose less resistance to cutting in the support than in the part to be cut, in particular the silicon. This has the advantage of allowing rapid recovery of the deflection of the wire when the wire leaves the part, in particular silicon. However, this also has drawbacks, and in particular the three main ones detailed below.

First, as illustrated by figure 2 schematically according to a front view, during the last moments of the cut, when the wire 10 is mainly in contact with the material of the support to the cut 1, which opposes the least resistance to the cut compared to the material of the part, in particular the silicon 30, the vertical force exerted by the wire 10 on the short length of silicon 30 remaining to be cut tends to tear material, at the level of a zone Zp of high pressure on the silicon 30, thus creating splinters on the edge of the wafers or “wafers”. In order to avoid this phenomenon of tearing of material (also called “chipping”), a slowing down of the cutting is generally used, which reduces the productivity of the equipment.

Moreover, as illustrated by picture 3 schematically according to a longitudinal view, taking into account the fact that the new thread feeds the layer of thread at the entrance of sheet and the worn wire is located at the sheet outlet, the new and used wires do not come out of the part to be cut, in particular from the silicon block 30, at the same time. More precisely, the new wire comes out of the silicon 30 first, and the worn wire comes out later. So on this picture 3 , the reference 10a represents the ply output thread which has still only slightly penetrated the support at cut-out 1, and the reference 10b represents the input ply thread which has penetrated into the support at cut-out 1. Then, when using a material that is easier to cut than silicon 30 for the cutting support 1, which is therefore the use in wire cutting with bonded abrasives, the input wire is found therefore without an arrow, whereas the wire at the exit can present one more. It may happen, depending on the material cut, in particular the composition used, that it is no longer possible to lower the assembly formed by the silicon part 30 and the support 1 into the machine and that the output wire is not yet taken out of the silicon part 30. In this case, it is then necessary to go back and forth with the wire without moving the table supporting the assembly, at the risk of the wire shearing the thin strips created in the support by the input wire of tablecloth and patties then fall into the machine.

In addition, the composition of the cutting supports, which can be varied, can contribute to significantly increasing the contamination of the powders obtained, in particular silicon powders, which are then recovered for recycling.

DISCLOSURE OF THE INVENTION

Therefore, there is a need to provide an optimized wire-cut support solution. Such a need is particularly felt in the context of the cutting by bonded abrasive wire, in particular by diamond wire, of semiconductor materials such as silicon for obtaining substrates in "wafers"("wafers" in English) , in particular to make it possible to improve or guarantee a good surface condition of the wafers on their edge, to make it possible to detect the moment when the deflection of the wire is absorbed or even to indicate the moment when the cutting is finished, to allow to avoid the fall of wafers at the input of the ply when the recovery of the arrow lasts too long, or even to make it possible to limit the contamination of the silicon powders resulting from the cutting in order to recycle them.

The object of the invention is to remedy at least partially the needs mentioned above and the drawbacks relating to the embodiments of the prior art.

The invention is defined by all the characteristics of claim 1.

Advantageously, the support of the system according to the invention is therefore not necessarily easier to cut than the material in which the piece to be cut is made, unlike the solutions of the prior art which use a support made in a material that is easier to cut than that of the part.

The term "thread" denotes three variant embodiments of the cutting by thread, namely: either a layer of several threads, designated by the expression "layer of threads", comprising several distinct threads all substantially parallel to each other, each wire forming a winding around rotating members; either a single thread forming a single loop; or a single thread wound several times to form a plurality of windings around rotating members, thus defining a layer of thread strands, all substantially parallel to each other, this layer of thread strands being designated by the expression "thread layer », fil being in the singular. The choice then depends on the type of wire cutting device.

By virtue of the invention, it may be possible to significantly improve the surface states of the wafers on their edge, ie a reduction in the “chipping” phenomenon. It is also possible to increase the productivity of the cutting device associated with the support. In addition, as explained below, it may be possible to make it possible to detect the moment when the deflection of the thread is absorbed or to indicate the moment when the cut is finished. In addition, it may be possible to limit the contamination of silicon powders resulting from diamond wire cutting in order to recycle them. Furthermore, as also detailed below, it may be possible to achieve better cleaning of the wafers and/or to facilitate the detachment of the wafers from the support, thanks to supports in which channels are present and which allow the passage of a cleaning liquid.

The support of a wire-cutting system according to the invention may further comprise one or more of the following characteristics taken separately or in any possible technical combination.

The support can very particularly be produced by an assembly of two different materials, comprising the first material and a second material, the first material being distributed in an inhomogeneous manner relative to the second material.

Advantageously, apart from the first material, the system support may comprise a material, in particular a second material, chosen from: an epoxy resin, a ceramic material, graphite, among others. In the case of an epoxy resin, it can be selected in order to allow ease of cutting with a diamond wire and minimal contamination of the silicon powder obtained after cutting. The support may also comprise a material, in particular a second material, based on: epoxies, polyurethanes, polyesters, polystyrenes, polyethylenes, polypropylenes, polyamides, polyvinyls, among others. This or these materials may or may not be modified, for example by inserting an organic group.

According to the invention, said at least one part to be cut comprises a semiconductor material, in particular silicon.

According to the invention, the support also comprises a semiconductor material, in particular silicon, in particular at least one part made of silicon and/or based on silicon, for example a composite material containing silicon.

In particular, the support for the system can be obtained by cutting a silicon wafer from a silicon ingot, the geometry of which, namely the width and the length, depends on the cutting device used. This plate can then be glued to a steel plate allowing the assembly to be held in the wire cutting device.

The support for the system can also be obtained by molding, liquid silicon being poured into an ingot mold making it possible to obtain the support when cut to the desired geometry.

The support for the system can also be obtained by sintering, silicon powder being hot sintered in an ingot mold making it possible to obtain the support when cut to the desired geometry.

Furthermore, the support of the system may comprise an assembly of a plate made of the first material, in particular silicon, and of a plate made of the second material, the plates being assembled, in particular glued, together.

In particular, the support of the system can be formed by assembly, in particular bonding, of a plate of an existing support with a silicon plate, so that the wire passes through, at the end of cutting, practically only silicon.

In addition, according to the invention, the support of the system is made of a second material loaded with powder of the first material, the density of the first material in the second material being variable, being in particular made of epoxy loaded with silicon powder with a density variable of the silicon in the epoxy, the epoxy being in particular filled with silicon by injection.

In addition, the support of the system may comprise longitudinal channels for the passage of a cleaning liquid. Similarly, the support may comprise longitudinal channels, in particular grooves, for mechanical attachment to a plate, in particular a steel plate, in particular of an assembly intended to be integrated into a wire cutting device. Such channels are for example described in the American patent application US 2011/0100348 A1 as part of ceramic die-cut media for free-abrasive cutting technology. On the contrary, preferentially, the invention uses this type of channel for a support for epoxy cutting and for bonded abrasive wire cutting technology, in particular diamond wire cutting.

Furthermore, the support of the system may comprise one or more parts forming witnesses, made of a material different from the first material and of thickness equal to the thickness of the support, making it possible to ensure that the cutting wire is no longer at the level of the part to be cut when it is present at the level of a part forming an indicator.

In addition, the system support may have, by observation in front view, a first part made of the first material, intended to be opposite the part to be cut, and a second part made of a second different material. of the first material, the thickness of the first part decreasing from the side edges of the support towards the central zone of the support, intended to face the part to be cut, and vice versa for the thickness of the second part.

In addition, the system support may have, by observation in longitudinal view, a first part made of the first material, intended to be opposite the part to be cut, and a second part made of a second different material. of the first material, the thickness of the first part increasing from a first longitudinal edge of the support towards a second longitudinal edge of the support, and vice versa for the thickness of the second part.

The system support may comprise a first material, in particular silicon, and a second material, in particular an epoxy resin, the second material being in particular loaded with powders of the first material. The proportion of the first material relative to the second material can be between 25 and 200% by mass, and preferably of the order of 100% by mass.

Furthermore, the invention also relates, according to another of its aspects, to an assembly, characterized in that it comprises a support as defined above and a plate, in particular a steel plate, the support being glued to said plaque.

In addition, the subject of the invention is, according to one of its aspects, a system, characterized in that it comprises a support as defined above and at least one part to be cut made of a first semiconductor material, in particular silicon.

In addition, another subject of the invention, according to another of its aspects, is a process for cutting by bonded abrasive wire at least one piece to be cut, characterized in that it is implemented by means of a system as defined above, and in that it includes the step of passing the cutting wire in a support material whose cutting difficulty is identical to that of cutting said at least one part to be cut.

The invention also relates, according to another of its aspects, to a method of manufacturing a support for a system as defined previously for the cutting by wire with bonded abrasives of at least one part to be cut made in one first material, characterized in that it comprises the step of producing the support by assembling different materials comprising at least the first material distributed in an inhomogeneous manner with the other materials of the support.

The method may include the step of using recycled silicon, originating from silicon powders recovered following cutting by wire with bonded abrasives, for the manufacture of the support.

The method may also include the step of using a silicon wafer from the cutting of a silicon ingot, molding and/or sintering, for the manufacture of the support.

BRIEF DESCRIPTION OF DRAWINGS

• les figures 1A, 1B et 1C illustrent respectivement en perspective trois étapes classiques de briquetage, d'éboutage et de découpe d'un matériau en silicium pour la fabrication de substrats en silicium à des fins de réalisation de cellules photovoltaïques,
• la figure 2 illustre, selon une vue frontale partielle, le phénomène d'arrachement de matière provoqué par le fil de découpe à la jonction entre la pièce à découper et le support à la découpe,
• la figure 3 illustre, selon une vue longitudinale partielle, le cheminement de la nappe de fil dans la pièce à découper fixée au support à la découpe,
• la figure 4 représente, selon une vue frontale partielle, un exemple de support à la découpe conforme à l'invention,
• la figure 5 représente, selon une vue longitudinale partielle, un autre exemple de support à la découpe conforme à l'invention, avec présence de la pièce à découper,
• la figure 6 représente une variante de réalisation du support à la découpe de la figure 5,
• la figure 7 représente une variante de réalisation du support à la découpe de la figure 4,
• la figure 8 représente, selon une vue frontale partielle, un exemple d'ensemble comportant un support à la découpe conforme à l'invention, assemblé avec une plaque en acier pour leur positionnement dans un dispositif de découpe par fil, et
• les figures 9A et 9B sont des clichés de microscopie électronique à balayage (MEB) représentant respectivement de la poudre de silicium pure et de la poudre de silicium issue de découpe.

The invention can be better understood on reading the detailed description which follows, of non-limiting examples of implementation thereof, as well as on examining the figures, schematic and partial, of the appended drawing, on which :

• the figures 1A, 1B and 1C respectively illustrate in perspective three conventional steps of bricklaying, trimming and cutting of a silicon material for the manufacture of silicon substrates for the production of photovoltaic cells,
• the figure 2 illustrates, in a partial front view, the phenomenon of tearing of material caused by the cutting wire at the junction between the part to be cut and the cutting support,
• the picture 3 illustrates, in a partial longitudinal view, the path of the sheet of wire in the piece to be cut fixed to the cutting support,
• the figure 4 represents, according to a partial front view, an example of a support for cutting according to the invention,
• the figure 5 represents, according to a partial longitudinal view, another example of a support for cutting according to the invention, with the presence of the part to be cut,
• the figure 6 represents an alternative embodiment of the support to the cutting of the figure 5 ,
• the figure 7 represents an alternative embodiment of the support to the cutting of the figure 4 ,
• the figure 8 represents, according to a partial front view, an example of an assembly comprising a cutting support in accordance with the invention, assembled with a steel plate for their positioning in a wire cutting device, and
• the figures 9A and 9B are scanning electron microscopy (SEM) images respectively representing pure silicon powder and silicon powder resulting from cutting.

In all of these figures, identical references can designate identical or similar elements.

In addition, the various parts shown in the figures are not necessarily shown on a uniform scale, to make the figures more readable.

DETAILED DISCUSSION OF PARTICULAR EMBODIMENTS

The figures 1A to 3 have already been described previously in the part relating to the state of the prior art.

The figures 4 to 8 described below are intended to illustrate exemplary embodiments in accordance with the invention of supports 1 for cutting by bonded abrasive wire.

Preferably and applying to all the examples described below, the term “yarn” designates here a layer of yarn.

In addition, the abrasive grains attached to the wire are preferably diamond grains so that the supports of a system according to the invention can be considered as being supports 1 for cutting by diamond wire.

In addition, the part 30 to be cut comprises a fragile semiconductor material, such as crystalline silicon, and the cutting of this part 30 is carried out for the purpose of manufacturing photovoltaic modules.

Of course, all the choices mentioned above are in no way limiting of the invention as defined by the claims.

When cutting silicon bricks into wafers, a large part of the silicon is now lost. Even with a cutting process according to the prior art, notably providing for a thickness of around 180 μm for the wafers and a wire diameter of around 80 μm, it is estimated that around 36% of the silicon is lost during cutting , that is to say that the silicon chips mix with the cutting fluid, which consists mainly of water and chemical additives.

With free abrasive cutting technology, studies on silicon recycling show that this recycling is not interesting, neither economically nor environmentally. In fact, the cost of recycling is too high, the yields are too low, and it requires the use of dangerous chemicals.

On the contrary, with bonded abrasive wire cutting technology, recycling can be interesting from several points of view. In particular, the inventors noticed that it was possible to recover a silicon powder of good quality. They also found that, for example for a cutting support made of epoxy charged with alumina particles, therefore containing the chemical elements aluminum (Al), sodium (Na) and phosphorus (P), the crossing of the support by the diamond wire, consisting of a steel core containing iron (Fe) and a nickel (Ni) coating containing diamond particles, at the end of cutting generates significant contamination of the silicon powder with Al elements, Na and P. This observation could be established by making a comparison of the chemical composition of the powder collected by stopping the filtration system, in particular the centrifugation, allowing the powder to be collected before the wire does not cut into the epoxy support or by leaving the centrifugation until the end of the cut, in other words allowing the epoxy support to be cut.

However, to avoid Al, Na and P contamination of the silicon powder, stopping the centrifugation or any other filtration system to collect the powder in line just before the wire enters the support is not a very practical solution in an industrial environment. Indeed, many machines usually work at the same time, which can use a centralized coolant supply system, and the management of stopping filtration on multiple equipment and avoiding the contamination of the coolant "clean" by a "contaminated" cutting fluid would therefore be very difficult to achieve, if not practically impossible to achieve.

Also, it will now be described, with reference to the figures 4 to 8 , supports 1 of systems in accordance with the invention making it possible to meet at least in part the needs set out above.

First, with reference to the figure 4 , there is shown, in a partial front view, a first example of support 1 for cutting a system according to the invention.

The support 1 is made by assembling a first part P1 made of a first material with a second part P2 made of a second material, the first material being in an inhomogeneous configuration relative to the second material.

Preferably, the first material is silicon, as for the part to be cut 30. The second material can be a material conventionally used for a support for cutting, or a material whose cutting is easier than for silicon, for example. example an epoxy resin, graphite, a ceramic material, among others. It may also be a material based on epoxies, polyurethanes, polyesters, polystyrenes, polyethylenes, polypropylenes, polyamides, polyvinyls, among others, which may or may not be modified, for example by inserting an organic group.

Advantageously, the silicon constituting the first material can come from a recycling of silicon powder from a previous cutting by diamond wire.

In this embodiment of the figure 4 , the support 1 has, by observation in front view, a first part P1, intended to be opposite the piece to be cut 30, the thickness of which E _p1 decreases from each lateral edge Ls of the support 1 towards the central zone ZC of the support 1, intended to be opposite the piece to be cut 30. The thickness E _p2 of the second part P2 increases from each lateral edge Ls of the support 1 towards the central zone ZC of the support 1. In this way, the interface between the first and second materials forms an inverted “V”. Thus, the difficulty of cutting support 1 is adapted longitudinally, the latter being more difficult to cut at its lateral ends Ls than at its central part ZC.

Table 1 below illustrates examples of minimum, maximum or preferred thicknesses depending on the material chosen for the first part P1 and the second part P2: <i><u>Table 1</u></i> Material Minimum thickness (mm) Maximum thickness (mm) Preferred thickness (mm) P1 in silicon or in resin + silicon E _p1 2 19 10 E _p1 at a side edge Ls 2 19 12 E _p1 at the level of the central part Zc 2 12 5 P2 resin or resin + silicon Ep ₂ 2 19 10 E _p2 at the level of the central part Zc 7 18 15 E _p2 at a side edge Ls 7 18 10

In the example of the figure 5 , the support 1 comprises a first part P1' made of a first material, which may be similar to that of the example of the figure 4 , and a second part P2' made of a second material, which may be similar to that of the example of the figure 4 .

In this example, the support 1 has, by observation in longitudinal view, a first part P1' whose thickness E _p1' increases from a first longitudinal edge I _s1 of the support 1 towards a second longitudinal edge I _s2 of the support 1, while the thickness E _p2' of the second part P2' decreases from this same first longitudinal edge I _s1 of the support 1 towards this same second longitudinal edge I _s2 of the support 1.

Thus, the difficulty of cutting support 1 is first of all the lowest at the start of cutting, then it increases until it is maximum at the end of cutting.

Taking respectively for P1', P2', E _p1' and E _p2' the examples given previously in table 1 for P1, P2, E _p1 and E _p2 , table 2 below illustrates examples of minimum thicknesses, maximum or preferential obtained: <i><u>Table 2</u></i> Minimum thickness (mm) Maximum thickness (mm) Preferred thickness (mm) E _p1' at the longitudinal edge I _s2 2 19 19 E _p2' at the longitudinal edge I _s1 2 19 19

The example of realization of the figure 6 is a variant of that of figure 5 . In this example, the support 1 comprises parts forming indicators 3, made of a material different from the first material. This material can be the same as the second material, as is the case here, or even be different from the first and second materials. Advantageously, the material of the indicators 3 has a lower cutting difficulty than that of the first material, therefore silicon.

The thickness Et of the witnesses 3 is advantageously equal to the thickness Es of the support 1. As a result, at the level of a witness 3, the cutting wire can more easily come out of the part to be cut 30. In other words, the indicators 3 make it possible to ensure that the cutting wire is no longer at the level of the part to be cut 30 when it is present at the level of an indicator 3. The indicators 3 may or may not be regularly distributed longitudinally on the support 1. They are, as in this example, preferably located at the level of the longitudinal ends of the support 1 and optionally at the level of its central part.

Using the values taken for P1, P2, E _p1 , E _p2 , P1', P2', E _p1' and E _p2' in tables 1 and 2 above, the thickness Et may have a minimum thickness of 0 mm, a maximum thickness of 19 mm, and a preferred thickness of 19 mm.

Furthermore, the embodiment of the figure 7 is a variant of that of figure 4 . In this example, the support 1 comprises longitudinal channels 5 for the passage of a cleaning liquid, which are for example evenly distributed in the support 1, possibly overlapping on the first P1 and second P2 parts.

In addition, the support 1 also includes grooves 6 for mechanical fixing to a steel plate 50, corresponding to the plate carrying the support 1 in the wire cutter.

Advantageously, these fixing grooves 6 allow easy mechanical assembly of the support 1 to the plate 50, and the longitudinal channels 5 for the passage of a cleaning liquid allow effective cleaning of the silicon wafers.

The figure 8 shows, in a front view, an example of an assembly 40 comprising a steel plate 50, a support 1 according to the invention and a block of silicon 30 to be cut.

The support 1 is for example an epoxy support charged with silicon powder by injection.

In comparison with an epoxy support loaded with alumina, the support 1 made of epoxy loaded with silicon has several advantages. It can in particular make it possible to recover a silicon powder that is less contaminated than when using a conventional support, without having to stop the filtration system, for example centrifugation, before the end of the cut, while allowing better cleaning the wafers and avoiding the phenomenon of tearing of material (or "chipping"). Indeed, the support 1 as shown in figure 8 allows, once the cut is finished, to pass cleaning liquid spray nozzles inside the channels longitudinal passage 5, which allows the liquid to pass between each wafer and therefore makes it possible to obtain a better surface condition, and better cleanliness. This support 1 also makes it possible to avoid sticking and detachment of the support from the steel plate 50 due to a mechanical assembly by means of the fixing grooves 6.

Furthermore, the figures 9A and 9B are scanning electron microscopy (SEM) images respectively representing pure silicon powder and silicon powder resulting from cutting.

By comparing these negatives, it can be seen that the morphologies of the pure silicon and of the silicon resulting from cutting are different.

Also, there is a structural/morphological difference between pure silicon powder, which has a spherical morphology, and silicon powder recovered following wire cutting, which has a chip-like morphology.

Of course, the invention is not limited to the embodiments which have just been described. Various modifications can be made thereto by those skilled in the art within the scope of the invention as defined by the claims.

Claims (13)

1. A system including:

   - a support (1) for bonded-abrasive wire cutting (10) at least one workpiece to be cut (30), the support (1) being made by an assembly of different materials,

   - at least one workpiece to be cut (30), the workpiece to be cut (30) being made of a first semiconductor material, the assembly of different materials of the support comprises at least the first material of the workpiece, and the first material of the support (1) is inhomogeneously distributed with the other materials of the support (1), the support (1) being made of a second material loaded with powder of the first material, the density of the first material in the second material being variable.
2. The system according to claim 1, characterised in that the support (1) is made by an assembly of two different materials, comprising the first material and the second material, the first material being inhomogeneously distributed relative to the second material.
3. The system according to claim 1 or 2, characterised in that the support (1) includes silicon, in particular at least one silicon and/or silicon-based portion, for example a composite material containing silicon.
4. The system according to any one of the preceding claims, characterised in that the support (1) includes an assembly of a plate made of the first material, in particular silicon, and a plate made of the second material, the plates being assembled, in particular glued, to each other.
5. The system according to any one of the preceding claims, characterised in that the support (1) is made of epoxy loaded with silicon powder with a variable density of the silicon in the epoxy, the epoxy being in particular loaded with silicon by injection.
6. The system according to any one of the preceding claims, characterised in that the support (1) includes longitudinal channels (5) for the passage of a cleaning liquid.
7. The system according to any one of the preceding claims, characterised in that the support (1) includes longitudinal channels (6), in particular grooves, for mechanical fastening to a plate (50), in particular a steel plate.
8. The system according to any one of the preceding claims, characterised in that the support (1) includes one or more portions forming control portions (3), made of a material different from the first material and of a thickness (Et) equal to the thickness (Es) of the support (1), allowing ensuring that the cutting wire is no longer at the workpiece to be cut (30) when it is present at a portion forming a control portion (3).
9. The system according to any one of the preceding claims, characterised in that the support (1) has, by observation in front view, a first portion (P1) made of the first material, intended to be opposite to the workpiece to be cut (30), and a second portion (P2) made of the second material different from the first material, the thickness (E_p1) of the first portion (P1) being decreasing from the lateral edges (Ls) of the support (1) towards the central zone (ZC) of the support (1), intended to be opposite to the workpiece to be cut (30), and conversely for the thickness (E_p2) of the second portion (P2).
10. The system according to any one of the preceding claims, characterised in that the support (1) has, by observation in longitudinal view, a first portion (P1') made of the first material, intended to be opposite to the workpiece to be cut (30), and a second portion (P2') made of the second material different from the first material, the thickness (E_p1') of the first portion (P1') being increasing from a first longitudinal edge (I_s1) of the support (1) towards a second longitudinal edge (I_s2) of the support (1), and conversely for the thickness (E_p2') of the second portion (P2').
11. A method for bonded-abrasive wire cutting (10) at least one workpiece to be cut (30), characterised in that it is implemented by means of a support (1) for wire cutting (10) of a system according to any one of the preceding claims, and in that it includes the step consisting in passing the cutting wire (10) through a material of the support (1) whose cutting difficulty is identical to that of cutting said at least one workpiece to be cut (30).
12. A method for manufacturing a support (1) of a system according to any one of claims 1 to 10, for bonded-abrasive wire cutting (10) at least one workpiece to be cut (30) made of the first material, characterised in that it includes the step of making the support (1) by assembling different materials comprising at least the first material inhomogeneously distributed with the other materials of the support (1).
13. The method according to claim 12, characterised in that it includes the step of using recycled silicon, originating from silicon powders recovered following a bonded-abrasive wire cutting, for manufacturing the support (1), and/or the step of using a silicon plate originating from the cutting of a moulding and/or sintering silicon ingot for manufacturing the support (1).

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