WO2013050716A1

WO2013050716A1 - Multi-wafer holder

Info

Publication number: WO2013050716A1
Application number: PCT/FR2012/052261
Authority: WO
Inventors: Yvon Pellegrin; Jacques Morote
Original assignee: Semco Engineering
Priority date: 2011-10-07
Filing date: 2012-10-05
Publication date: 2013-04-11
Also published as: FR2980994A1; FR2980994B1

Abstract

The invention relates to a device for holding wafers (100) during the industrial use thereof. The device comprises at least one arm which is connected to a guide system and which has the general shape of a blade, said arm comprising first and second walls (2) between which a pressurised gas feed circuit (4) is arranged, in which one of said walls is provided with at least one holding member. Such a holding member comprises: i) a nozzle (6) for releasing gas at high speed, supplied by the aforementioned circuit, in which the outlet port (12) is extended by an element having a continuous curved surface which is oriented progressively in a plane that is substantially parallel to the wall (2), such that the gas flow released from the nozzle remains tangentially attached to the wall; and ii) a set of pads (7) secured to the wall close to the nozzle, said pads holding the wafer at a pre-determined distance from the wall (2). The invention also relates to a method for moving wafers (100) from a first position to a second position using such a holding device.

Description

MULTI-PLATELET PREHENSEER

The present invention belongs to the field of tools dedicated to the manipulation of objects, in particular fragile objects, and more particularly to the field of devices for handling silicon wafers during industrial processes.

It relates to a gripping device capable of handling one or more pads and move them from one place to another, thanks to an articulated arm provided with nozzles for expelling a pressurized gas and retaining pads. A method of moving platelets using this device is also an object of the invention.

A gripper is a terminal device for entering and manipulating objects. It is a tool widely used in many fields of activity, which is essential for the automation and robotization of industrial operations. The gripping member is mounted at the end of a system ensuring its displacement, such as a jack or an articulated arm, and can operate according to various principles. It can be of the mechanical type such as for example a clamp, pneumatic for example with vacuum cups or Bernouilli effect, electrostatic ... Whether they are intended for the manufacture of photovoltaic cells, semiconductors or other similar elements, the Silicon wafers have to undergo a number of operations, which are performed in several stages by specific equipment. It is therefore necessary to transport the pads from one equipment to another and place them appropriately for the intended treatment. Depending on the nature of the operation, the wafers will be either deposited on individual transport systems, or placed on trays or baskets, etc. Robots equipped with a gripper system transfer platelets from one station to another. They must grip the pads at the loading position to transport them to the unloading position where they are released.

Of course, it is desired that these manipulations be performed quickly and without damage, while the platelets are thin and very fragile. The gripping system must preserve the integrity of the parts (neither breakage, nor chipping, ...) and not bring particulate contamination or chemical pollution, in particular of metallic and / or ionic nature to the wafers. In the case of solar applications, it It is permissible for the gripper to hold the wafer by its back face or its active face, provided that it does not mark this wafer, or to introduce any chemical contamination that would be detrimental to the efficiency of the solar cell. In the case of semiconductors, it is strongly recommended to hold the plate only by its inactive backside.

In doing so, the platelet maintenance must be firm to ensure the conservation of their positioning coordinates, regardless of the directions and direction of travel speeds, otherwise during unloading the pads could be placed on the receiving station inadequately or even disconnect from the gripper being transferred.

The gripping tool must also be adapted to pre-existing industry standards that implement sophisticated equipment meeting many technological constraints, and designed to treat wafers of dimensions defined by the uses.

Faced with the multiplication of constraints of all kinds, some manufacturing steps are little or inconveniently automated. For example, it is known that during one of the manufacturing steps, the plates are arranged in baskets (also called "process boats") made of quartz or silicon carbide, for physicochemical treatment (doping, deposit of a thin layer, etching, ...). However, the spacing of the wafers in these baskets is only a few millimeters - typically less than 5 mm. To automate the manipulation of the wafers during the loading and unloading phases of the baskets, or during inspection and control operation, or for other reasons, it is desirable to have a gripper that can slide between two pads inside a basket.

It is one of the objectives of the present invention to provide a gripping device whose thickness space meets this decisive criterion of space, while meeting the other conditions imposed by the conditions of manufacture of silicon wafers, that these they are intended for a microelectronic or solar application. The aforementioned technological constraints are combined with economic imperatives, a high level of productivity being a permanent objective. This assumes a high speed of movement from one station to another and reduced waiting times between two actions, or the reduction of cases of platelet degradation. Thus, it appeared to the applicant that the decisive point for productivity gains was the possibility of simultaneous manipulation of several wafers, and in particular wafers arranged side by side. Several obstacles stand in the way, however.

The first difficulty stems from the fact that in certain manufacturing steps, the wafers to be captured may be non-coplanar because they are arranged on a support which is itself not perfectly flat. This is particularly the case when the plates are placed flat side by side on a plate. We can then have a difference in level of a wafer to another up to a millimeter. The gripper must have the ability to grab several pads simultaneously, despite their positioning in different planes.

Another problem is that the wafers themselves may not be perfectly flat. The gripping member must therefore be able to grasp and hold a fragile object whose surface has irregularities or is deformed by its internal constraints. Some systems, including vacuum cupping systems are in this case poorly adapted.

If absolute platelet retention is ensured, they can undergo very large accelerations directed parallel to the platelet holding face (that is to say perpendicular to the holding force). A system capable of moving several pads simultaneously will have to fix all of them without having the possibility to slide laterally. This requirement, already formulated in the case of a mono-wafer gripper is particularly sensitive in the case of a multi-wafer gripper, and even more so when they are arranged side by side.

It is therefore another essential objective of the present invention to provide a multi-wafer gripping device, that is to say ensuring the simultaneous gripping of several wafers during the same operation, even if these are not placed exactly in the same plane, and allowing their displacement. It is also sought to have a gripper that can adapt to different situations, in particular, which is able to handle both an individual wafer and a plurality of concomitant wafers.

Another lever to accelerate the rate of transfers from one station to another is that the gripper device can handle platelets very quickly after a high temperature treatment, without waiting for their cooling. To meet this requirement, the invention will provide a device operating at a relatively high platelet temperature (up to about 400 ° C, but typically below 350 ° C.) Many types of grippers have been proposed to perform automated operations. on silicon wafers, without, however, satisfying all these objectives, nor being entirely satisfactory, it should be noted first of all that the strictly mechanical devices, the gripper of which is generally a clamp, are to be excluded automatically because they cause frequent physical degradations: on their contact, the platelets flake or even break.

Pneumatic systems have been proposed, such as for example DE 39 23 672, in which the gripping member is provided with vacuum suction cups, or electrostatic systems such as that described in FR 2 818 050. Such systems impose an arrival in close proximity to the intimate contact of the gripper vis-à-vis platelets. Such a fine approach is not possible for a multi-wafer gripping, given the offsets of the wafers in the plane. Mechanical level compensation devices, for example using a flexible elastomer skirt, have been devised to compensate for the flatness defect. Unfortunately, these devices do not respect the temperature constraints of the processes involved and they create a bulk incompatible with the objectives of the present invention.

Other types of systems have been proposed, taking advantage of the attraction created by the depression resulting from the Bernoulli effect. For example, US Pat. No. 4,087,133 discloses a device comprising a perforated plate through which compressed air is expelled towards an object to be moved. The depression induces a suction that attracts the object by suction. The wafer is maintained at a certain equilibrium distance from the perforated plate, which avoids contact with the gripper. However, these devices have difficulty in keeping the plate in position: when the gripper will move, the plate that is not held laterally, may slip and lose its location coordinates. Certainly, this loss of location coordinates can be avoided by limiting the accelerations of the manipulator robot, that is to say by limiting the speed of the movements of the robot, but in this case it is at the cost of a loss of productivity important.)

The device for handling a substrate described in the patent application US2008 / 0267741 combines a first system acting by attraction of the upper surface of a substrate (by Bernoulli effect) and a second attraction system provided with a suction cup. empty acting on the underside. This device allows the manipulation of a single wafer, thin and very deformed, either by its upper face or its lower face, depending on the deformation it has undergone.

Thus, none of the gripping systems known to date can handle silicon wafers safely, simultaneously and quickly, responding to the constraints that are imposed during the various manufacturing steps.

The object of the present invention is to provide a gripper for handling fragile objects and of small thickness relative to their surface, such as silicon wafers, which overcomes the aforementioned drawbacks. More particularly, an object of the invention is to allow the simultaneous manipulation (gripping, holding, release) of several platelets in the same operation. Another object of the invention is to have a bulk in thickness such that the gripper can slip between two plates arranged in a storage basket or other support industry standards. Another object of the invention is to ensure good gripping platelets having an imperfectly flat surface. Another object of the invention is to ensure a good grip of a set of wafers arranged side by side in a single grip, while their position in the plane has an offset of up to one millimeter. Yet another object of the invention is to ensure effective maintenance of the parts so that they can undergo very large accelerations while maintaining their positioning coordinates, regardless of the direction and speed of movement. In particular, absolute support is sought when the accelerations are directed parallel to the holding face (that is to say perpendicular to the holding force). A further object of the invention is that the gripper device introduces the least possible inertial forces on the accelerations of the movements of the manipulator robot, in particular it must have a low mass. Finally, the gripping system must be able to handle platelets at a high temperature and the atmosphere.

In addition, it goes without saying that the gripping system must maintain the integrity of the parts (neither breaks, nor chipping, ...) and does not bring contamination or chemical pollution, in particular of a metallic and / or ionic nature. to platelets.

The invention thus relates to a device for gripping wafers during their industrial implementation, which comprises at least one arm connected to a guiding system, the arm adopting the general shape of a blade, comprising a first and a second wall between which is formed a circuit for supplying a gas under pressure, one of said walls being provided with at least one gripping element, which comprises: i) a nozzle (6) for expelling gas at high speed , fed by said circuit, whose outlet orifice (12) is extended by an element having a continuous curved surface which is gradually oriented in a plane substantially parallel to the wall (2), so that the gas flow is escaping from the nozzle remains attached tangentially to said wall, and

ii) a set of pads fixed to said wall of the blade near said nozzle, said pads holding the plate at a determined distance from the wall.

The gripping device is intended to manipulate wafers, automatically, during their industrial implementation. It is specified that the gripping carried out by the device object of the invention comprises the fact of seizing a wafer, to hold it during a phase of displacement, then to release it at the moment and at the desired place. The device can handle both a plurality of concomitant platelets. By wafers, we mean two-dimensional objects, that is to say where two dimensions predominate. These are objects with two main faces, whose thickness is small relative to the surface of these main faces. As will be seen below, thanks to the device according to the present invention, the wafers concerned here can be rigid or flexible, and of variable sizes. They may also not be completely flat and may have a smooth or rough surface.

The gripper is usually part of a robotic machine used to move objects. The machine and its accessories are driven by a guidance system, which is programmed or remotely controlled in general by an electronic operator programmable. The robotic arms are movable and usually articulated so as to make movements in all desired directions. The robot can be equipped with several arms whose movements can be coordinated or independent. However, it is important that the mass of these structural elements is as small as possible so as to minimize the additional inertia forces which counteract the movements of the robot. For the sake of clarity, the following description will cover a single arm, but expressly extends to an embodiment where the guide system controls several arms. The arm, which adopts the shape of a blade, can be for example made by joining two plates constituting a first and a second wall, between which a space is preserved to provide a circuit for supplying a gas under pressure . The gas supply means under pressure are known to those skilled in the art, which will implement them without difficulty.

A gripping element, or several preferably identical gripping elements are installed in one of the walls of the movable arm. Each element is composed of two essential organs, namely a gas expulsion nozzle and a set of pads, cooperating with each other to achieve effective, accurate and firm grip of a wafer.

Since most of the operations are initiated by approaching the movable arm above the platelets which are flat, main face horizontally, the device will be described below in the corresponding particular orientation that it adopts. at the moment of picking up the wafer, that is to say in which the wall which is provided with gripping elements is the lower wall of the movable arm. This initial orientation of the arm does not assume its orientation and the relative position of the plate in the subsequent movements of the arm. It is further noted that the gripper device according to the invention can support the platelets by their rear face or maintain them by their front face.

The nozzle is fed by the pressurized gas supply circuit so that the gas is expelled at high speed. The shape of the nozzle is such that it directs the gas flow along the wall of the blade. This high velocity jet of air draws air between the wall of the gripper arm and the wafer to grip, causing a vacuum effect. When the space between it and the wall is only a few millimeters, is created a kind of open cavity within which the pressure is lower than the atmospheric pressure, which causes an attraction of the wafer towards the nozzle. This depression and the resulting attraction effect, known as the Coanda Effect, will be maintained as long as the nozzle is supplied with compressed air.

In doing so, the wafer is kept away from the wall by the pads arranged around the nozzle. This prevents any contact of the wafer with the wall, while ensuring its lateral retention. Indeed, in the absence of pads, the plate would be in a floating position in the immediate vicinity of the wall, in equilibrium between two areas at different pressures. The skates stop the plate as a stop, so that it is continuously attracted to the wall without ever coming into contact with it. The wafer being pressed against the pads, lateral sliding (parallel to the wall of the arm) is avoided during the movements of the latter, as is the case when the wafer is levitated floating away from the nozzle. The pads thus also contribute to the lateral maintenance of the pads.

The attraction of the wafer by the effect of the depression is already manifest to a few millimeters and therefore does not impose a very strict distance from the object to be captured with respect to the gripping element. This is why it is not necessary that a wafer is perfectly flat for its grip is done correctly. It is added that, when several plates must be picked up at the same time by several gripping elements, it is not necessary either that they be arranged exactly in the same plane relative to each other so that the device according to the invention grip them all together properly. This represents an essential advantage of the present invention, which is added to that which constitutes the thin conformation of the device.

Indeed, it is noted that the movable arm is designed with a blade shape of low height and that it carries only gripping elements (one or more), which are themselves substantially integrated into the arm wall. There is thus a compact device, able to fit between close objects, and to extract one of them or to add a new one in a series.

According to an advantageous characteristic of the gripping device object of the present invention, each nozzle comprises an annular peripheral base mounted in a recess made in the wall of the blade and a central peg secured to the base by legs, the space between the base and the pin constituting a circular slot of calibrated width terminated by an outlet also circular, so that the flow of gas escapes over an angular sector of 360 °.

The base is fixed in the wall by any means available to the skilled person: crimping, gluing, or other. Preferably, it has the same thickness as the wall and thus provides no particular external roughness, likely to interfere with the process of capture and gripping.

The tabs holding the base and the central pin together are discrete, i.e. they are spaced apart and of minimal width relative to the length of the exit port. Their length defines the distance between the base and the central pin which constitutes the slot through which the pressurized gas escapes. The slot and its exit orifice are circular, insofar as their planar projection, orthogonal to the axis of the pin, is a circle. The flow of gas escapes from all sides on a 360 ° angular sector, the barrier effect that may result from the presence of the support tabs having proved insignificant. This creates a well-balanced attraction effect, perpendicular to the direction of the force of attraction.

Advantageously, according to the invention, the central pin is flared at its lower part so that the circular slot is narrower and narrower in the direction of circulation of the gas. By this conformation, it creates a narrowing through which the gas must pass, which increases its speed to its output, and accentuates the local depression in the vicinity of the nozzle.

In addition, it is known that a high rate of gas flow combined with flow over a curved surface induces a phenomenon whereby the surface layers of the gas stream tend to remain applied against the wall. The nozzle according to the invention takes advantage of this phenomenon, called "Coanda effect", to optimize the gripping of platelets. Thus, according to a preferred embodiment of the invention, the inner edge of the base adopts the shape of a rounded lip which extends beyond the exit orifice of the slot with a curved surface orienting itself. progressively in a plane substantially parallel to the wall of the blade, so that the gaseous flow escapes tangentially to the wall of the blade. The gas veins then remain glued to the surface of the base and evacuate laterally, without pushing the wafer and therefore without moving away. As a corollary, the kinetic energy of the gas molecules is transferred to the constituent molecules of the air between the wall of the arm and the wafer, which causes the entrainment of these molecules out of this space, and further accentuates the lowering the pressure in this space, while the pressure below the wafer remains unchanged (this is the atmospheric pressure). The pressure difference between the two main faces of the wafer causes a displacement thereof to the wall, the wafer being pressed against the support pads. It will be maintained there all the time that will last the expulsion of gas through the nozzle.

According to an advantageous embodiment of the invention, the lugs of the central pin to the base are integral with the lower part and the upper part thereof, defining a slit width calibrated to +/- 0,025 mm. In this way, the pin is firmly held at the base with a minimum of contact points likely to deflect the gas flow inappropriately. It is thus maintained at a well-defined and constant distance from the base, which ensures an equal distribution of the gas flow in all directions over an angular sector of 360 °. Interestingly, the base and the pin are made in one piece, so that the nozzle is formed of a single monobloc element, perfectly calibrated.

According to a particular feature of the present invention, the gripper device comprises at least three pads of heat-resistant material, non-contaminating and non-chemically polluting vis-à-vis the platelet material, and having a high coefficient of adhesion. During the movements, regardless of the direction and direction of these movements, the pads rest on the three bearing surfaces, with total stability. It goes without saying that, in microelectronic or photovoltaic applications, the material of the three pads is chosen so as not to contaminate the silicon wafers used chemically.

Thus, according to the invention, the pads are preferably made of a material chosen from polymers or ceramics. A suitable polymer may for example be a polyimide. A ceramic may also be used, for example a refractory ceramic such as an alumina (Al ₂ O ₃ ), a mullite (aluminosilicate whose composition is 3AI ₂ 03,2Si0 ₂ ), or a zirconia (common name of zirconium oxide, Zr0 ₂ ). These compounds are now mainly synthetic products.

The support surfaces offered by the pads are such that the friction forces allow the absolute maintenance of the pads during acceleration and deceleration of the robot, this without causing scratching or scratching of the surface of the pads, even when the temperature of those it is at a high value. In particular, the shape and arrangement of the pads is studied to obtain maximum adherence platelets, without disturbing the gas flow. The adhesion of the bearing surface can be quantified through roughness, denoted Ra. The roughness Ra is defined as the arithmetic mean of the absolute values of the differences between the peaks and troughs of a surface. The adhesion desired here for the bearing surface of the pads can be expressed by a value of Ra of the order 25 μηι. This result is obtained by the choice of the constituent material of the pads, but it is also possible to optimize the bearing surfaces by resorting to elongated pads placed radially at the periphery of the gas expulsion nozzle.

According to the invention, the pads fitted to the gripping device have a height sufficient to maintain the wafer away from the wall of the blade, or if the nozzle projects on the surface of the wall, above the nozzle. This difference in level can range from a few tenths of a millimeter to at most two millimeters, and in any case, it is sufficient so that the pads do not touch the nozzle or the wall of the arm, but are effectively captured and maintained. .

The pads and the lugs of the central pin to the base may be arranged radially relative to the axis of the nozzle, in alignment with each other. Each pad is the counterpart of a leg, so that if the gas flow is slightly reduced when it comes out of the nozzle at the leg, it will then meet the associated pad so that there is no of notable consequence in the regularity of the gas flow, or in the quality of the grip.

As indicated above, one of the important advantages of the device according to the invention is its ability to manipulate several objects simultaneously, without losing the advantages of a small footprint. This possibility is achieved through the establishment of several gripping elements arranged on the wall of the same arm of the gripping device. We will be able to capture as many platelets as grippers present, or even capture a large wafer using two (or more) neighboring grippers. This is why, in a preferred embodiment of the gripping device according to the invention, the wall of the arm comprises four gripping elements or eight gripping elements, arranged along a longitudinal axis of the arm.

Most often, the wafers to be supported are placed on a support and their taking is necessarily over, by their upper face. We will then use a gripping device whose lower wall is equipped with grippers. However, in some situations, it is interesting to grip the pads by their underside. The gripping device according to the invention can operate regardless of its orientation, its initial orientation and its final orientation during a displacement operation of one or more little important wafers. In this case, the gripping device must be provided with gripping elements on the upper wall. This is why, interestingly, the first and the second walls of the at least one arm are each provided with at least one gripping element.

Different configurations can be adopted for the gripping device according to the invention, depending on the workstations of the manipulator robot, without this hindering the proper operation of the device. In particular, it may comprise two arms mounted in rake on a connecting plate fixed to the guide system. For example, a U-shape is obtained if the arms are mounted parallel to the connection plate, or if they are mounted at an angle between them, one can have a V shape for two arms, W for four arms. Alternatively, the device may comprise at least two arms, single or multiple, mounted in opposition on a rotating connection plate attached to the guide system.

Thus, a system intended to grip only one light wafer may have only a single arm with a single gripping element. A heavier wafer may require a gripper system V or other. Likewise, some applications may require the transport of multiple platelets at a time, using one or more arms with multiple grippers. In doing so, one may wish to have a gripping station and / or individualized removal for each of the wafers.

The device according to the invention has been designed to be able to meet this requirement, by integrating means of ensuring the supply of gas independently for each group of gripping elements, or for each gripping element. Thus, preferably, the gas supply circuit is formed of a network of ducts arranged to separately feed each nozzle or each pair of nozzles. An appropriate control may be provided to stop or continue the gas supply to each of the nozzle supply ducts. Thus, advantageously, in the gripping device according to the invention, the gas supply circuit is connected to a control unit, said unit being able to interrupt the supply of gas in one or more ducts of said network. The control unit may for example be connected to the control means of the state of the wafers manipulated, to discard the damaged wafers of the following processing and manufacturing steps.

As indicated above, the device according to the invention has a particularly small space in the axis perpendicular to the general plane of the wafers that it has to handle, which makes it particularly useful in most silicon wafer manufacturing operations in particular. Thus said at least one arm comprising at least one gripping element, preferably has a total thickness of less than 4.75 mm so that the gripper can slip between two plates arranged in a basket or a "process boat" to the standards of the 'industry.

The device as described above is particularly suitable for use in an industrial manufacturing process using wafers, even if they are fragile. It allows a large acceleration / deceleration and therefore a high speed of movement from one station to another and reduced waiting time between two actions, or the reduction of platelet degradation cases.

Therefore, a method of moving platelets from a first position to a second position using a gripper according to the invention is also claimed, which method comprises the steps of essentially:

a) - to have a platelet gripping device comprising at least one arm connected to a guiding system, the arm adopting the general shape of a blade having a first and a second wall between which is formed a circuit of fed with a gas under pressure, one of said walls being provided with at least one gripping element, which comprises: i) a high velocity gas expulsion nozzle (6), fed by said circuit, whose outlet port (12) is extended by an element having a continuous curved surface which is progressively oriented in a substantially parallel plane at the wall (2), so that the gas flow escaping from the nozzle remains tangentially attached to said wall, and

ii) a set of pads fixed to the wall of the blade near said nozzle, said pads holding the plate at a determined distance from the wall;

b) - open the gas supply circuit for supplying gas to said at least one gripping element;

c) - approaching said arm of a wafer at said first position, until it is sensed by said at least one gripping element and immobilization in contact with said pads;

d) - moving said loaded arm of said wafer to said second position;

e) - closing the gas supply circuit to interrupt the supply of said at least one gripping element and releasing said plate at its second position,

f) - repeat steps b) to e) as long as there are platelets left to move.

The method which is the subject of the invention comprises the steps of grasping a wafer, of holding it during a phase of displacement, then of letting it go when and where it is needed. It is generally implemented using a robot comprising a gripping device, with a guidance system that is programmed or remotely controlled by an operator. The robotic arms are movable and usually articulated so as to make movements in all desired directions. With the method of the invention, the plates may not be perfectly flat, since the gripping member is capable of grasping and holding an object whose surface has irregularities or is deformed by its internal stresses.

Advantageously, the gas flow is accelerated by passing through a circular slot of calibrated width formed in said nozzle, said slot being increasingly narrow in the direction of flow of gas, before being expelled by the nozzle on a sector. angular 360 °. Preferably, the gas stream is expelled through the slot in the form of a rounded lip gradually oriented in a plane substantially parallel to the wall of the blade, so that the surface layers of the gas stream tend to remain applied against said wall, according to the Coanda effect. This accentuates the lowering of the pressure in this space, while the pressure below the wafer remains the atmospheric pressure. The pressure difference between the two main faces of the wafer causes a displacement thereof to the wall, the wafer being pressed against the support pads.

The slot of the nozzle has a width calibrated to within +/- 0.025 mm, so that we obtain a maintenance of the pawn at a well-defined and constant distance from the base, and consequently an equal distribution of the gas flow in all directions on an angular sector of 360 °.

The gripping system can handle platelets at a temperature of about 250 ° C., but higher temperatures, for example up to 350 ° C., can be encountered in the industrial processes concerned, for example at the outlet of the oven after a high-temperature treatment. temperature. Therefore, the method of moving platelets according to the invention can be performed at a platelet temperature below 350 ^< C.

Unexpectedly, it has been found that the gaseous flow flowing in the arm of the device and opening at the level of the platelets to be captured, can be usefully used to cool the atmosphere and the platelets nearby, provided that it is itself even at a moderate temperature. In other situations, it is desired to maintain a given temperature, or even increase the platelet temperature during handling. This is why, interestingly according to the invention, said at least one gripping element is fed with gas under pressure, said gas being at a predetermined temperature, to act on the temperature of the wafers. It is thus possible to cool or heat the wafer as soon as it is collected and during its movements between an initial position and a final second. The gas is sent into the circuit at a pressure of between 2 bars and 6 bars. The method of moving platelets according to the invention advantageously makes it possible to simultaneously move from said first position to said second position, at least two platelets, and preferably four platelets or eight platelets. This is made possible in particular because the gripping member has the ability to grip several plates, arranged on a support that is not perfectly flat. According to a particularly advantageous embodiment of the invention, the gas expulsion nozzles are fed by separate ducts formed in the pressurized gas supplying circuit, for example for each nozzle or for each pair of nozzles. . This arrangement allows that only some of the nozzles are in operation to capture platelets at their level without wasting gas. It also allows selective release of platelets, during a step of the method according to the invention. The same gripper arm can thus handle several plates in different positions by gripping and / or releasing them all at the same time, or sequentially one by one, or in combination.

Thus, according to the invention, the method of moving platelets may comprise a platelet selection step, during which one or more platelets are released at predetermined positions by interrupting the supply of the gas expulsion nozzles, said nozzles being fed by separate conduits of the pressurized gas supply circuit. For example, a platelet sorting step can be performed, during which the state of each platelet is controlled and the defective platelets are released by interrupting the gas supply in the corresponding conduits of said circuit. The method of moving platelets according to the invention is advantageously implemented, said displacement being effected from a first position to a second position in a translation, radial rotation or axial rotation movement, or a combination of these. this. Thus, the plates can perform movements in all directions, move from horizontal to vertical, turn in their plane, or turn completely, without losing the absolute coordinates of each of their points.

The gripping device as described above can be used for handling and for moving objects of any kind, including thin pads, flexible or rigid, possibly fragile. It is particularly suitable for automated work, taking place at high temperatures, and requiring great precision, as is the case in the silicon industry, whether for microelectronic or solar applications. Thus claimed the application of the gripping device according to the invention to the handling of silicon wafers during their industrial implementation. The present invention will be better understood, and details will arise, thanks to the description that will be made of one of its variants, in connection with the accompanying figures, in which:

- Figure 1 is a schematic sectional view of a segment of an arm comprising a gripping element belonging to a device according to the invention. In Figure 1a, the cutting plane is any, but does not go through the pads or the lugs. On fig 1b, the plane cuts a pad and a lashing tab.

FIG. 2 is a view from below of a gripping element according to the invention.

- Figure 3 is a top view of a gripping device loaded with eight plates of dimensions 150X80 mm.

- Figure 4 is a top view of a gripper loaded with four wafers of dimensions 156X156 mm.

In the present example, the platelet gripper comprises two identical arms 1, raked on the connecting plate 3, which is fixed to a guide system (not shown). The assembly has the general shape of a U. The plate 3 is the mechanical part of connection with the robot or the mechanical manipulator. It is through it that the gas supply ducts 4 located in the arms 1 will be done. Each arm 1 has the general shape of a blade having the walls 2, which are metal plates, preferably of light material such as aluminum, carbon or titanium in order to have a minimum inertia to displacements. They are assembled together in such a way as to provide the circuit for supplying a gas under pressure 4. The bottom wall 2 (in the orientation shown in the figures) of each arm 1 is provided with four gripping elements 5, aligned with each other. along the main axis of the arm 1. The arms 1 have an overall thickness of less than 4.70 mm.

Figures 1 and 2 has been shown one of the gripping elements. He understands :

i) the nozzle 6 for the expulsion of the gas at high speed, which is fed by the gas supply circuit 4, and ii) a set of three pads 7, fixed to the wall 2 near the nozzle 6. In Figure 1b, is also shown a wafer (100) of silicon during its holding by the gripper element.

The nozzle 6 is formed of the annular base 8 crimped in a recess formed in the wall 2 of the blade, and the central pin 9. The central pin 9 is secured to the base 8 by the tabs 10, spaced apart and of minimal width relative to the length of the outlet orifice. Three lashing tabs 10 are placed between the pin and the base, such as thin partitions extending from the lower part of the central pin 9 to the upper part of the central pin 9, 120 ° apart. others. They define an entirely circular slit of width calibrated to within +/- 0.025 mm, the opening of which is at most 0.2 mm, for a diameter of the order of at most 10 mm.

The space between the base 8 and the pin 9 constitutes the circular slot 1 1, which is terminated by the outlet orifice 12, also circular. The flow of gas escapes from all sides, over an angular sector of 360 °. The central pin 9 is flared at its lower part so that the circular slot 1 1 is increasingly narrow in the gas flow direction, with a ratio of the input / output surfaces of the order of 4.

The shape of the nozzle 6 is such that it directs the gas flow along the wall 2 of the blade. The inner edge 13 of the base 9 takes the form of a rounded lip which extends beyond the outlet orifice 12 of the slot 1 1 with a curved surface 14 gradually moving in a plane substantially parallel to the wall 2, so that the gas flow escapes tangentially to the wall. The gas ejected from the nozzles 6 is typically dry compressed air and filtered under a pressure of less than 6 bar. The three skates 7, of oval shape, are placed radially at 120 ° from each other, at the periphery of the gas expulsion nozzle 6, so as to obtain isostatic support of the wafer. They are arranged in the extension of the lashing legs 10. They are thermoresistant polyimide and have a roughness Ra = 25 μηι. They are fixed to the wall 2 and constitute a stop element with a height of 1 mm above the surface of the wall 2.

As represented in FIGS. 3 and 4, each arm 1 of the gripping device can manipulate several plates 100. The location of the gripping elements, not visible in this view, is indicated by the symbol φ. The wafers are here silicon wafers, such as those used for the manufacture of photovoltaic cells, small format (150X80 mm, Figure 3) or large format (156X156 mm, Figure 4). Given their thickness (150 μηι), they are objects of 12 g which are maintained by the gripping elements. The arms 1 each having four gripping elements 3, it is possible to use the same gripping device to grip eight plates 100, each using a gripping element (Figure 3), or four plates 100, each with two grippers (Figure 4).

Sorting the wafers by a selection system connected to a nozzle-differentiated gas supply shut-off system makes it possible to selectively deposit the various wafers at positions defined according to the sorting criteria. For example, defective platelets can be eliminated by an optical system connected to a system that cuts off the supply of gas to the corresponding nozzle or nozzles.

The device as described above allows high acceleration during displacements and reduced waiting time between two actions, in particular thanks to a rapid temperature setting of the wafers by the effect of the gas flow.

Claims

1. Device for gripping wafers (100) during their industrial implementation, characterized in that it comprises at least one arm (1) connected to a guiding system, said arm adopting the general shape of a blade, comprising a first and a second wall (2) between which is formed a circuit (4) for supplying a gas under pressure, one of said walls being provided with at least one gripping element (5), which comprises:

i) a high velocity gas expulsion nozzle (6), fed by said circuit, whose outlet port (12) is extended by an element having a continuous curved surface which is progressively oriented in a substantially parallel plane at the wall (2), so that the gas flow escaping from the nozzle remains tangentially attached to said wall, and

ii) a set of pads (7) fixed to said wall near said nozzle, said pads holding the plate at a determined distance from the wall (2).

2. - A gripping device according to claim 1, characterized in that each nozzle (6) comprises an annular peripheral base (8) mounted in a recess formed in said wall and a central pin (9) secured to said base by legs (10), the space between the base (8) and the pin (9) constituting a circular slot (1 1) of calibrated width terminated by an outlet orifice (12) also circular, so that the flow of gas escapes over an angular sector of 360 °.

3. - A gripping device according to claim 2, characterized in that the central pin (9) is flared at its lower part so that the circular slot (1 1) is increasingly narrow in the direction of flow of the gas .

4. - A gripping device according to one of claims 2 or 3, characterized in that the inner edge of the base (9) takes the form of a rounded lip which extends beyond the outlet orifice (12) of the slot (1 1) with a curved surface gradually moving in a plane substantially parallel to the wall (2).

5. - Gripping device according to one of claims 2 to 4, characterized in that the lashing lugs (10) of the central pin (9) to the base (8) are integral with the lower part and the upper part of said pin, defining a slot (1 1) of calibrated width within +/- 0.025 mm.

6. - gripping device according to one of the preceding claims, characterized in that it comprises at least three pads (7) of heat-resistant material, non-contaminating and not chemically polluting vis-à-vis the material of the wafers, and having a high coefficient of adhesion.

7. - gripping device according to the preceding claim, characterized in that the pads (7) are made of a material selected from polymers, ceramics.

8. - A gripping device according to one of the preceding claims, characterized in that said wall (2) comprises four or eight gripping elements (5), arranged along a longitudinal axis of the arm (1).

9- gripping device according to one of the preceding claims, characterized in that the first and second walls (2) of said at least one arm (1) are each provided with at least one gripping element (5).

10. A gripping device according to one of the preceding claims, characterized in that it comprises two arms (1) mounted in rake on a connecting plate (3) fixed to the guide system, or that it comprises at least two arms (1) single or multiple mounted in opposition on a connecting plate (3) rotating attached to the guide system.

1 1. - Gripping device according to any one of the preceding claims, characterized in that the gas supply circuit (4) is formed of a network of ducts arranged to supply separately each nozzle (6) or each pair of nozzles, said circuit being connected to a control unit able to control the supply of gas in one or more conduits of said network.

12. - A method of moving platelets (100) from a first position to a second position using a gripping device according to one of the preceding claims, characterized in that it comprises the steps consisting essentially of : a) - to have a platelet gripping device comprising at least one arm (1) connected to a guiding system, said arm adopting the general shape of a blade having a first and a second wall (2) between which a pressurized gas supply circuit (4) is provided, one of said walls being provided with at least one gripping element (5), which comprises:

b) - opening the gas supply circuit (4) for supplying gas to said at least one gripping element;

c) - approaching said arm of a wafer (100) located at said first position, until it is sensed by said at least one gripping element and immobilization in contact with said pads;

d) - moving said loaded arm of said wafer to said second position;

e) - closing the gas supply circuit (4) to interrupt feeding of said at least one gripping element and releasing said plate at its second position,

f) - repeat steps b) to e) as long as there are platelets left to move.

13. - Method of moving platelets according to the preceding claim characterized in that the gas flow is accelerated by passing through a circular slot (1 1) of calibrated width formed in the nozzle (6) in the shape of a lip rounded direction progressively in a plane substantially parallel to the wall (2), so that the gas flow escaping from the nozzle remains attached tangentially to said wall, said slot being increasingly narrow in the direction of flow of the gas, before being expelled by said nozzle over an angular sector of 360 °.

14. A method of moving platelets according to one of claims 12 or 13, characterized in that said at least one gripping element (5) is supplied with pressurized gas, said gas being sent in the circuit (4) to a pressure between 2 bars and 6 bars, at a predetermined temperature, to act on the temperature of the wafers.

15. - Method of moving platelets according to one of claims 12 to 14, characterized in that is moved simultaneously from said first position to said second position, at least two platelets, and preferably four platelets or eight platelets.

16. A method of moving platelets according to one of claims 12 to 15, characterized in that it further comprises a platelet selection step, during which one or more platelets are released at predetermined positions by interruption of the platelet. supplying gas to the gas expulsion nozzles (6), said nozzles being supplied by separate conduits of the pressurized gas supply circuit (4).

17. - A method of moving platelets according to one of claims 12 to 16, characterized in that said displacement is effected from a first position to a second position in a translational movement, radial rotation or axial rotation, or a combination thereof.

18. - Application of the gripping device according to one of claims 1 to 1 1, the handling of silicon wafers during their industrial implementation.