Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B28—WORKING CEMENT, CLAY, OR STONE
  • B28D—WORKING STONE OR STONE-LIKE MATERIALS
  • B28D5/00—Fine working of gems, jewels, crystals, e.g. of semiconductor material; apparatus or devices therefor
  • B28D5/04—Fine working of gems, jewels, crystals, e.g. of semiconductor material; apparatus or devices therefor by tools other than rotary type, e.g. reciprocating tools
  • B28D5/045—Fine working of gems, jewels, crystals, e.g. of semiconductor material; apparatus or devices therefor by tools other than rotary type, e.g. reciprocating tools by cutting with wires or closed-loop blades

Definitions

• the invention relates to a method and a system for wire cutting a workpiece, in particular a part made of semiconductor material (for example silicon, germanium, or a semiconductor material III-V or II-VI ) or ceramic (for example sapphire, SiC).
• semiconductor material for example silicon, germanium, or a semiconductor material III-V or II-VI
• ceramic for example sapphire, SiC
• Wire cutting is used in many fields, particularly for slicing fragile and very hard materials such as semiconductor materials (used in the fields of microelectronics, optoelectronics or photovoltaics). or ceramics, or for cutting stones, for example marble rocks.
• wired cutting of a material it is known to use a wire that is wound multiple times (hundreds or even thousands of times) around several wire guides, typically between two and four wire guides. There is thus obtained, between the son-guides, a "sheet of son", or “sheet”, formed by a number of strands of the same cutting wire, which allow to cut the piece into several slices.
• the wire guides are rotatable and rotate the wire during cutting. Guide grooves are etched into the wire guides to ensure a predefined spacing between the "wires" of the web (i.e., between the strands of the cutting wire), which determines the thickness of the slices to cut.
• Wired wire cutting is widely used in fields making use of semiconductor materials, especially in the field of photovoltaics, to manufacture wafers or "wafers" of semiconductor material, for example in silicon.
• Wire cutting requires the use of an abrasive element to create abrasive material chips during cutting. There are two wire cutting techniques, depending on whether the abrasive element is free or bonded to the wire.
• the first cutting technique uses abrasive particles or abrasive grains, for example silicon carbide (SiC), which are integrated in a solution such as polyethylene glycol (PEG) forming a cutting liquid. or "slurry".
• This abrasive liquid mixture is poured onto a wire, for example a steel wire, and surrounds it with a liquid film containing abrasive particles. The passage of the wire surrounded by this abrasive film in a material to be cut leads to the cutting of the material.
• the second so-called “abrasive-bonded” cutting technique uses a wire on the surface of which abrasive particles, usually diamond or silicon carbide, are fixed. This type of cutting is commonly called “diamond wire cutting”.
• Figure 1 shows schematically a wire cutting system, using a cutting wire 1, a part 2 such as a silicon brick.
• the part 2 is assembled to a cutting table 4 by means of a sacrificial assembly element 3, or "beam", generally having the shape of a beam, the part 2 being secured by bonding 5 to this element 3.
• a relative translational movement of the workpiece 2 and the cutting wire 1, in a z-direction allows the wire 1 to traverse the workpiece 2 by pressing into it and to cut it into a plane (z, x).
• This relative translation movement can be obtained in two ways: - Or by maintaining the assembly of the table 4, the element 3 and the fixed part 2 and driving the wire 1 in translation along the z direction, in a first direction;
• the wire 1 is driven in a translation movement in the x direction at a speed of about 20 m / s.
• this movement is preferably oscillating: it alternates a first forward movement (from left to right in FIG. 1) and a second return movement (from right to left in FIG. 1), each displacement typically having a duration of the order of thirty seconds.
• This oscillating regime including back-and-forth feed, is commonly referred to as "back and forth". It is represented by the double arrow F2 in FIG.
• the yarn can be animated with a one-way scroll movement in the x-direction. One-way scrolling is used instead for slicing.
• Cutting with diamond wire tends to develop because it allows to increase the cutting speed and thus offers a better productivity.
• it has the major disadvantage of reducing the mechanical strength of the cut slices. This is troublesome in particular for the manufacture of wafers or wafers of semiconductor material, intended to be manipulated later.
• the mechanical strength of a wafer 6, or wafer can be characterized by a so-called "four-point" bending test.
• this test uses, for example, four parallel loading bars including two upper bars 7A, 7B (that is to say placed above the wafer 6 to be tested) and two lower bars 8A, 8B (c '). that is to say placed below the plate 6 to be tested) fixed, the spacing between the upper bars 7A, 7B being less than that between the lower bars 8A, 8B.
• the two upper bars 7A, 7B descend at a constant speed so as to cause bending of the wafer 6, the applied mechanical stress increasing until a rupture of the wafer 6 occurs. This rupture is triggered in the zone 60 of the wafer 6 which undergoes the strongest mechanical stress, constituted by the central band located between the two upper bars 7A, 7B.
• the wafer 6 may be arranged in two different configurations during the bending test.
• the loading bars are parallel to the x direction of the wire during cutting.
• the second configuration as shown in Figure 3B, the loading bars are perpendicular to the x direction of the wire during cutting.
• the four-point bending test is passed to a statistical batch of platelets containing at least twenty platelets. Tests were carried out according to the first configuration with a first batch of platelets and according to the second configuration with a second batch of platelets.
• a known solution consists in subjecting the wafers etching etching in order to reduce or to remove all or part of the surface defects of platelets.
• This solution has the disadvantage of consuming material during the chemical attack.
• the wafers remain fragile during the handling operations performed between the end of the cutting and the chemical etching operation.
• Another known solution consists in reducing the diamond size of the diamond cutting wire.
• this solution only slightly improves the mechanical strength of the wafers and significantly reduces the cutting speed.
• the invention improves the situation.
• OBJECT OF THE INVENTION the invention relates to a method of slicing a piece of semiconductor material or ceramic, using a cutting wire and abrasive particles, in which the wire is driven in translation in at least one direction and, during its displacement in translation, it enters the piece to be cut by a penetration face of said piece, characterized in that it has a damping layer opposite said penetration face of the piece to cut so that, before entering the room, the wire passes through the damping layer.
• the yarn being driven in translation in a reciprocating back-and-forth movement and penetrating into the part to be cut alternately by two opposing penetration faces, two damping layers are provided opposite the two faces of penetration respectively.
• the damping layer covers the penetration face.
• the damping layer is spaced from the penetration face by a distance less than or equal to 2 cm, advantageously less than or equal to 1 cm, and preferably less than or equal to 0.5 cm.
• the damping layer has a thickness greater than three times the average diameter of the abrasive particles, advantageously greater than five times the average diameter of the abrasive particles.
• the thickness of the damping layer may also be less than 2 cm, advantageously less than 1 cm, and preferably less than 0.5 cm.
• the damping layer may be made of at least one of the materials of the group comprising polymers having a hardness greater than 90 MPa and a modulus of elasticity greater than 2 GPa, in particular hardened epoxy resins and PMMA, materials semiconductors, advantageously silicon, ceramics having a hardness of less than 8 on the Mohs scale, in particular a silica.
• the damping layer may be a flat plate.
• the damping layer is a plate whose shape is adapted to match that of the penetration face.
• the damping layer is fixed to the penetration face of the part, for example by gluing by means of an adhesive layer having a thickness which is advantageously less than or equal to 20 m.
• the piece to be cut is secured to a cutting table by means of an assembly element, the damping layer is fixed either to the cutting table or to the assembly element.
• the damping layer can be deposited on the penetration face of the part, by a layer deposition technique, in particular by sputtering or by another deposition treatment.
• the at least one damping layer may extend over at least 40%, or even at least 60%, or even at least 80%, or even 100%, or even more. 100% of the height of the piece to be cut, this height being measured perpendicularly or substantially perpendicularly to the cutting wire.
• the invention also relates to a slicing system of a piece of semiconductor material or ceramic using a cutting wire and abrasive particles, comprising a device for driving the wire in translation in the least one direction, the wire penetrating into the workpiece by at least one penetration face of said workpiece during its movement, characterized in that it comprises at least one damping layer arranged opposite said penetration face of the piece to be cut so that, before entering the room, the wire passes through the damping layer.
• the cutting system comprises all or part of the following additional features:
• the device for driving the yarn is arranged to drive said yarn in translation in a reciprocating back-and-forth movement in which the yarn enters the piece to be cut alternately by two faces of opposite penetration, and in that it comprises two damping layers opposite the two penetration faces respectively;
• the damping layer covers the penetration face or is spaced from the penetration face by a distance less than or equal to 2 cm, advantageously less than or equal to 1 cm, and preferably less than or equal to 0.5 cm;
• the damping layer has a thickness greater than three times the average diameter of the abrasive particles, advantageously greater than five times the average diameter of the abrasive particles, advantageously still a thickness of less than 2 cm, advantageously less than 1 cm, and preferably less than 0.5 cm;
• the damping layer is made of at least one of the materials of the group comprising polymers having a hardness greater than 90 MPa and a modulus of elasticity greater than 2 GPa, in particular hardened epoxy resins and PMMA, semiconductor materials ceramics having a hardness of less than 8 on the Mohs scale, especially a silica;
• the damping layer is a flat plate or whose shape is adapted to match that of the penetration face;
• the damping layer can be fixed to the penetration face of the part, preferably by gluing by means of a glue layer advantageously still having a thickness less than or equal to 20 m;
• the damping layer is deposited on the penetration face of the part, by a layer deposition technique, in particular by sputtering or other vacuum deposition treatment;
• a first kinematic entity comprising a cutting table integral with the workpiece by means of an assembly element, and a second kinematic entity comprising the cutting wire.
• a drive device for driving in relative translation the two kinematic entities with respect to each other;
• the at least one damping layer preferably two damping layers, can extend over at least 40%, or even at least 60%, or even at least 80%, even 100%, or even more than 100% the height of the piece to be cut, this height being measured perpendicularly or substantially perpendicularly to the cutting wire.
• FIG. 1 shows a diagram of a portion of the cutting system and a workpiece, according to the prior art
• FIG. 2 represents a diagram of a silicon wafer during a bending test
• FIGS. 3A and 3B show a view from above of the silicon wafer of FIG. 2 during a bending test according to a first configuration and during a bending test according to a second configuration, respectively;
• FIG. 4 shows flexural test results of a first batch of wafers tested with the first configuration of FIG. 3A and a second batch of wafers tested with the second configuration of FIG. 3B;
• - Figure 5 shows a first embodiment of the cutting system of the invention
• FIG. 6 shows a second embodiment of the cutting system of the invention
• FIGS. 7A to 7H show other embodiments of a cutting system of the invention.
• FIG. 8 shows a diagram of a device for driving and guiding a cutting wire slices of a workpiece.
• the invention relates to the slicing of a part 2 made of brittle material (that is to say macroscopically elastic until breaking) and hard (that is to say with a hardness greater than or equal to 5 on the Mohs scale), in particular in semiconductor material (for example in silicon, germanium, III-V semiconductor, II-VI semiconductor or other) or ceramic (for example in sapphire, SiC or other) , using a cutting wire and abrasive particles. It can in particular be used for the manufacture of wafers of semiconductor material, for example silicon.
• the cutting system of a part 2 comprises the following elements:
• damping layers or damping elements, 9A, 9B.
• the workpiece 2 is a silicon brick, parallelepiped shape, to be cut into slices (or wafers or wafers).
• the assembly element 3, or "beam”, here has the shape of a beam. It is a sacrificial element intended to be at least partially cut during slicing of part 2. It may be made of hard polymer, for example from the epoxy family, or any other suitable material (ceramic , graphite). It is attached to the cutting table 4 by means of a hanging device. The piece 2 to be cut is fixed to the assembly element 3, for example by gluing, via a bonding layer or interface 10 glue. The part 2 can be secured to the assembly element 3 by all or part of one of its faces. In the example of Figure 5, the part 2 is bonded to the connecting member 3 over the entire surface of its face 20C, parallel to the plane (x, y).
• the connecting element 3 could be narrower than the component 2 in the x direction.
• the workpiece 2 is thus secured to the cutting table 4 by means of the assembly element 3.
• the assembly comprising the three integral parts, namely the table 4, the element 3 and the workpiece 2, constitutes a first entity, or a first subset, kinematic.
• the cutting wire 1 is here a bonded abrasive wire carrying abrasive particles fixed to its surface.
• the wire is for example steel.
• the particles Abrasives are here in diamond.
• Wire 1 constitutes a second kinematic entity (or kinematic subset).
• the device for driving and guiding the wire comprises in known manner a plurality of wire guides, for example three wire guides 12A-12C.
• the wire 1 is here wound many times (hundreds or even thousands of times) around these wire guides 12A-12C and thus forms a "wire web" or "web” formed by a number of strands. the same cutting wire 1.
• This sheet makes it possible to cut piece 2 simultaneously in a large number of slices.
• the wire guides are rotatable and rotate the web of threads (or yarns) 1 during cutting. They are adapted to animate the wire 1 of an oscillating movement comprising round trips, as represented by the arrow F2. Guide grooves are etched in the wire guides to ensure a predefined spacing between the wire strands of the web, which determines the thickness of the slices to be cut.
• the second displacement device or drive, (not shown) is intended to drive in relative translation the two kinematic entities with respect to each other.
• the second displacement device is arranged to move the assembly (or first kinematic entity) of the table 4, the element 3 and the part 2 in a translation movement in the z direction, downwards in FIG. 8, as represented by the arrow F3, the wire 1 (or second kinematic entity) being concomitantly maintained at the same height along z.
• the translation direction F3 is opposite to the cutting direction F1.
• the assembly of the table 4, the element 3 and the part 2 (or first kinematic entity) is held stationary (at the same height along z) and the second drive device is arranged to drive the yarn 1 (or second kinematic entity) in translation in the direction z in the direction of the cut F1.
• the two damping layers 9A, 9B are intended to attenuate the damaging effect of the diamond wire on the two opposite edges of the slices cut by which the wire 1 enters the part 2, inside the cutting groove, respectively at each move go and each move back.
• the inventors have discovered that the reduction in the mechanical strength of platelets cut by a diamond wire originates from damage at these two opposite edges of the cut wafer or wafer, and not from the surface defects thereof. .
• This damage is caused by the diamond wire, during its penetration inside the cutting groove by the two opposite faces 20A and 20B, called “penetration faces", of the part 2, respectively with each forward movement and with each return movement of the thread 1.
• the damping layers 9A, 9B are arranged, arranged opposite these opposite penetration faces 20A, 20B of the workpiece 2 so that, before entering the workpiece 2 by a penetration face 20A (or 20B), the wire 1 passes through the corresponding damping layer 9A (or 9B), each forward movement and each return movement of the wire 1, during its oscillatory movement represented by the arrow F2.
• each damping layer 9A, 9B consists of a flat plate.
• the damping layer 9A (9B) thus covers the entire corresponding penetration face 20A (20B).
• the thickness "e" of the damping layer 9A (9B), in the x direction, must be sufficient to absorb the energy of the impact between the abrasive particles (or abrasive grains) integral with the wire 1 and the cut piece 2 when the yarn 1, driven by the oscillating movement F2 along x, enters the piece 2 by the face 20A (respectively 20B). By virtue of this, it is avoided to degrade the edges in the z direction of the slices cut in the part 2.
• the thickness of each damping layer 9A, 9B is greater than three times the average diameter of the abrasive particles (or abrasive grains) of the wire 1, preferably greater than five times the average diameter of the abrasive particles of the wire 1.
• This average diameter is usually indicated by the wire manufacturer.
• the average size, or average diameter, of the abrasive particles is 10 m.
• the minimum thickness e m in damping layers 9A, 9B is therefore in this case equal to 30 ⁇ , preferably 50 m.
• the thickness e of the damping layers 9A (9B) must not be too great to avoid certain disadvantages such as fouling, heating or wear of the wire.
• the maximum thickness e max of the damping layers 9A, 9B is therefore advantageously equal to 2 cm, advantageously still equal to 1 cm, preferably equal to 0.5 cm.
• the damping layers 9A (9B) may consist of one of the following materials:
• polymers having a hardness greater than 90 MPa and a modulus of elasticity greater than 2 GPa in particular hardened epoxy resins and PMMA, semiconductor materials, for example silicon,
• ceramics having a hardness of less than 8 on the Mohs scale, in particular a silica
• the damping layer 9A (or 9B) generated by cutting with diamond wire must not adhere to the abrasive grains or abrasive particles (as this would have the effect of reducing the abrasive power of the wire), nor to the wire in the interstices between the abrasive grains (as this would have the effect of reducing the ability of the wire to extract chips from the groove dug in the cut piece 2 and to heat the system), which notably excludes soft metals and polymers or standard glasses.
• the damping layers 9A, 9B cover the penetration faces 20A and 20B to be protected from the part 2.
• the damping layers 9A, 9B are contiguous, plated against the penetration faces 20A, 20B respectively and are fixed thereto, for example by gluing by means of a layer of glue 1 1 A, 1 1 B.
• the thickness of this glue layer 1 1 A, 1 1 B is advantageously less than or equal to 20 m.
• the glue used is here analogous to that used to glue the workpiece 2 to the assembly element 3.
• a first embodiment, shown in FIG. 7A differs from the embodiment of FIG. that the damping layers 9A, 9B covering the penetration faces to be protected 20A, 20B of the part 2 are fixed to the connecting element 3, for example by gluing. More specifically, a peripheral edge of one of the faces of the damping layer 9A (or 9B) is fixed to one side facing the connecting element 3.
• a second variant embodiment, shown in FIG. 7D, differs from the embodiment of FIG. 5 in that the damping layers 9A, 9B covering the penetration faces to be protected 20A, 20B of part 2 are fixed to the cutting table 4, for example by gluing. More specifically, each damping element 9A (or 9B) is fixed by its edge to the face of the table 4 supporting the connecting element 3.
• the embodiment of Figure 6 differs from that of Figure 5 essentially by the fact that the damping layers 9A, 9B are not contiguous to the faces 20A and 20B of the part 2, but are slightly spaced from them by a distance d.
• this distance d is less than or equal to a maximum distance advantageously equal to 2 cm, advantageously still equal to at 1 cm, preferably equal to 0.5 cm.
• the damping layers 9A, 9B are fixed to the cutting table 4, by their edge. The attachment can be performed by gluing, by means of glue layers 12A, 12B.
• FIG. 7B differs from the example of FIG. 6 in that the damping layers 9A, 9B, spaced from the faces 20A, 20B, are fixed to the connecting element 3.
• FIG. 7E differs from the embodiment of FIG. 5 in that the piece to be cut 2 is cylindrical in shape.
• the damping layers 9A, 9B are in contact with the cylindrical outer surface of the part 2, only along a tangential line, parallel to the axis of the cylinder, and fixed for example by gluing to the cutting table 4 by their slice.
• the plates constituting the damping layers 9A, 9B could have a non-planar shape, adapted to match that of the protective face to be protected ( Figures 7F and 7G).
• the damping layers 9A, 9B are plates which are attached and arranged opposite each other. penetration faces to be protected from the workpiece 2, either against them or at a distance d from them.
• the damping layers 9A, 9B are layers deposited on the faces to be protected from the part 2 by a layer deposition technique, for example by sputtering or by another suitable treatment (for example vacuum deposition or coating). Note that the application of these damping layers requires no precision, finesse or purity.
• FIG. 7F shows a first exemplary implementation of this embodiment, in which the piece to be cut 2 is cylindrical.
• damping layers 9A and 9B are deposited respectively on the two half-cylinder-shaped penetration faces of the part 2.
• FIG. 7G a second exemplary embodiment is shown, in which the part at cut 2 is parallelepipedic. Two damping layers 9A and 9B are deposited respectively on the two opposite faces 20A, 20B of the part 2.
• the cutting system comprises two damping layers to protect the two penetration faces of the workpiece. This is due to the fact that, the wire being animated by an oscillating movement comprising back and forth movements, it penetrates inside the part, in the cutting groove, by two opposite penetration faces of the part.
• the wire being animated by an oscillating movement comprising back and forth movements, it penetrates inside the part, in the cutting groove, by two opposite penetration faces of the part.
• a single damping layer 9A arranged opposite the single penetration face of the piece to be cut, is necessary.
• FIG. 7H Such an exemplary embodiment is shown in FIG. 7H.
• the invention also relates to a slicing process of the part 2 with the aid of the cutting wire 1, in which the damping layers 9A, 9B are arranged facing the penetration faces to be protected from the part 2, that is to say those by which the wire 1 is intended to penetrate when it is driven in an oscillating movement back and forth.
• the damping layers 9A, 9B may be inserts or layers deposited by a layer deposition technique.
• the damping layers 9A, 9B are fixed either to the workpiece 2, to the assembly element 3, or to the cutting table 4.
• the fastening is advantageously carried out by gluing.
• the damping layers 9A, 9B are disposed at least partially against the corresponding penetration faces 20A, 20B, or at a distance strictly greater than zero from these penetration faces 20A,
• the damping layers 9A, 9B are deposited on the penetration faces 20A, 20B of the piece to be cut 2 by a layer deposition technique.
• the assembly of the table 4, of the assembly element 3 and of the workpiece 2 is translated in translation along z, here downwards, in the direction indicated by the arrow F3, relatively wire 1 which remains at the same height according to z.
• the wire 1 (or the web) is driven in translation in an oscillating movement along x, represented by the double arrow F2, comprising back and forth in the x direction.
• the wire 1 enters the part 2, that is to say into the cutting groove dug in the part 2, alternatively by the penetration face 20A and the penetration face 20B of the room 2.
• the wire 1 Before entering the room 2 by each of these penetration faces 20A (20B), the wire 1 through the corresponding cushioning layer 9A (9B), arranged nearby. Thanks to this, the damaging effect of the abrasive wire 1 at the penetration faces 20A, 20B of the part 2 is strongly attenuated, damped.
• the layers to be protected 20A, 20B of the piece 2 to be cut are deposited on the layers constituting the damping layers 9A, 9B by a known layer deposition technique.
• the yarn is driven in a one-way movement and thus enters the part 2 by a single penetration face, there is a single cushioning layer facing this penetration face, said layer covering the face penetrating or being positioned at a distance d from it.
• the damping layer is either reported or deposited by a layer deposition technique.
• the invention could also be applied to a free abrasive cutting, or slurry, using a cutting liquid containing abrasive particles and a cutting wire smooth surface or almost smooth for example steel.
• the invention also relates to a wafer, in particular a wafer, made of semiconductor material or ceramic, obtained by implementing the cutting method as just described.
• At least one damping layer 9A, 9B extend over at least 40% of the height h of the piece 2 to be cut, this height being measured parallel or substantially parallel to the axis z or in the direction of the cut F1, that is to say perpendicularly or substantially perpendicular to the cutting wire or the direction of the cutting wire; .
• At least one damping layer 9A, 9B extend over at least 60% of the height h of the piece 2 to be cut, or even at least 80 % of the height h of the workpiece 2 to be cut, or even 100% of the height h of the workpiece 2 to be cut, or even more than 100% of the height h of the workpiece 2 to be cut.
• At least the projection of a damping layer 9A, 9B, preferably each projection of the damping layers 9A, 9B, on the piece in the direction cutting wire extends over at least 40% of the height h of the piece 2 to be cut, this height being measured parallel to or substantially parallel to the z axis or to the cutting direction F1, that is to say perpendicular or substantially perpendicular to the cutting wire or the direction of the cutting wire.
• At least the projection of a damping layer 9A, 9B, preferably each projection of the damping layers 9A, 9B, on the piece in the direction of the cutting wire extends over at least 60% the height h of the piece 2 to be cut, or on minus 80% of the height h of the piece 2 to be cut, or even 100% of the height h of the piece 2 to be cut.
• At least one damping layer 9A, 9B are cut simultaneously with the piece 2, ie during the entire duration of the cutting of the part 2.

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• 2016
  • 2016-01-14 FR FR1650287A patent/FR3046737B1/fr not_active Expired - Fee Related
• 2017
  • 2017-01-16 EP EP17704395.7A patent/EP3402642B1/de not_active Not-in-force
  • 2017-01-16 WO PCT/EP2017/050821 patent/WO2017121900A1/fr not_active Ceased

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