DE102012102239B4 - Substrate pick-up method and substrate separation system - Google Patents

Abstract

Substrate pick-up method in which a substrate (1) is picked up by a substrate stack (3) comprising a plurality of substrates (1, 2) by means of a pick-up element (4), wherein before and / or during the pick-up of the substrate (1) from the substrate stack ( 3) the substrate (1) is set into mechanical oscillation in its natural resonance by the substrate (1), several substrates (1, 2) of the substrate stack (3) or the substrate stack (3) mechanically at a natural frequency of the substrate (1) is excited, wherein for mechanical excitation: - a blowing device is used, by means of which a pulsed gas flow is directed onto the substrate (1), onto several substrates (1, 2) of the substrate stack (3) or onto the substrate stack (3) or- a sound generator is used, the mechanical excitation of the substrate (1) taking place through the substrate stack (3) by means of the sound generator.

Description

The invention relates to a substrate receiving method and a substrate separation system.

In the manufacture of modern solar cells, the production machines have to handle substrates with increasingly smaller thickness dimensions. In particular, in the case of semiconductor wafers for crystalline or multicrystalline solar cells, attempts are being made to continue to reduce the wafer thickness in order to save both wafer material and to increase the efficiency of the solar cells.

The inclusion of such thin substrates places special demands on the grippers of the automated production devices. For example, these substrates must be gripped gently without placing excessive mechanical stress on the substrates. As a rule, grippers equipped with suction devices are used here. When removing an uppermost substrate from a substrate stack, it can happen that two or more substrates adhere to one another due to forces and are picked up jointly by the gripper. In order to avoid such problems and to separate the substrates from one another before gripping, separating devices are usually used which separate the uppermost substrates of a substrate stack by means of an air flow from an air nozzle.

However, these known devices are not efficient. They usually work with constant air flows or with pulsed air flows with a low pulse frequency. In this case, substrates that adhere particularly strongly to one another cannot be separated or can only be separated with particularly high air pressures or by means of a long-lasting air flow supply. In addition, a further reduction in the mechanical stability of the wafer is foreseeable in the case of the thickness reduction aimed for in the future, so that a more efficient and gentler substrate separation will be necessary. In the case of such thin substrates, the adhesive forces between two substrates can also be increased.

DE 10 2009 039 458 A1 also describes a method for separating printing plates, each with a conductive layer. Eddy currents are excited in the conductive layers by means of a magnetic coil. These in turn generate magnetic fields that cause neighboring printing plates to repel each other.

Further describes DE 10 2005 002 499 A1 a method for picking up plate-shaped substrates from a stack by means of a movement arm. If a double or multiple pick-up is detected here, a separation process follows with the help of a vibrator unit arranged on the movement arm. Alternatively, instead of the vibrating unit, a loudspeaker can be arranged on the movement arm.

It is the object of the invention to provide a substrate pick-up method and a substrate separation system which allow a particularly efficient and nevertheless mechanically gentle separation and pick-up of individual substrates from a substrate stack.

The object is achieved according to the invention by a substrate receiving method with the features of claim 1 and by a substrate separation system with the features of claim 9. Advantageous further developments of the invention are listed in the subclaims.

The invention is based on the idea of using an excitation to achieve dynamic separation or fanning of the stacked substrates so that a single substrate can be removed from the substrate stack by means of a receiving element. In the case of a purely constant gas flow according to previous procedures or when using a pulsed air flow in which the pulse frequency is far from the natural frequency of the substrates, a purely static fanning out takes place.

The excitation takes place in such a way that the uppermost substrate or a plurality of substrates lying on top of the stack is / are set in mechanical vibrations in its natural resonance. This can be done by exciting the substrate with one of its natural frequencies. This means that the excitation itself takes place at a frequency which is very close to the natural frequency or is essentially identical to the natural frequency. In an embodiment not according to the invention, the excitation can also take place at a different frequency, as long as it is ensured, for example due to the geometry of the arrangement, that the substrate will vibrate at its natural frequency.

The natural frequencies of the substrate can be determined experimentally and / or calculated or simulated using numerical methods. Due to the low substrate thickness, the substrate can be modeled as a membrane, for example. The natural frequency is an oscillation frequency at which the substrate oscillates naturally. Since a substrate can carry out an infinite number of harmonics in addition to the basic oscillation, the possible natural frequencies accordingly include a basic frequency and upper frequencies, which are ideally in each case a multiple of the basic frequency, but can differ slightly in reality. The excitation preferably takes place at an excitation frequency of at least 5, 10, 15, 20, 50, 100 or 150 Hertz.

During or after the generation of the mechanical vibrations, preferably while the substrate is vibrating, it is picked up by means of the receiving element and separated from the stack. The receiving element is a substrate gripper which, for example, grips the substrate with the aid of a vacuum device.

The substrate separation system with which the substrate is picked up thus comprises the pickup element and an excitation device which is designed to mechanically excite the substrate, several substrates of the substrate stack or the substrate stack as a whole with a natural frequency of the substrate. The excitation can also take place with a natural frequency of the plurality of substrates, in the event that a plurality of substrates lying next to one another have different natural frequencies than a single substrate.

The substrate is preferably a semiconductor wafer, on which further layers and components are applied in a manufacturing process in order to produce a semiconductor device, in particular one or more solar cells. However, it can also be a semifinished product, that is to say a substrate on which some manufacturing steps have already been carried out, for example deposition steps, etching steps and the like, on the way to a finished semiconductor device. Furthermore, the substrate described herein can actually be a finished semiconductor device, in particular a solar cell such as a wafer solar cell, which is removed, for example, from a solar cell stack in order to equip a solar module.

The substrate is set into mechanical vibration in that the substrate, several substrates of the substrate stack or the entire substrate stack is / are mechanically excited with a natural frequency of the substrate. A blower device is used for mechanical excitation, by means of which a pulse-shaped gas stream is directed onto the substrate, onto several substrates of the substrate stack or onto the substrate stack, or a sound generator, the mechanical excitation of the substrate by means of the sound generator taking place through the substrate stack. In this case, the sound generator is thus arranged below the substrate stack. The mechanical excitation can take place not according to the invention, for example, by means of a mechanical vibration generator, such as an acoustic transducer that is mechanically or acoustically coupled to the substrate stack. In other embodiments not according to the invention, a mechanical actuator can be provided which executes translational and / or rotational movements. For example, a motor, for example an electric motor, can be provided with an imbalance that can set the stack in vibration.

The pulsed gas flow can be directed, for example, parallel to or at an angle to a substrate surface of the substrate onto a substrate edge region or a substrate edge. For example, the gas flow to the substrate surface can have an angle of less than 45 °, less than 30 ° or less than 15 °.

In an expedient embodiment it is provided that a blowing device is used for the excitation which comprises a nozzle with a switching element which is connected to a pulse generator or pulse generator. The switching element can be a solenoid valve, for example.

In particular, a loudspeaker is used as the sound generator. The mechanical excitation of the substrate by means of the sound generator takes place through the substrate stack. In this case, the sound generator is thus arranged below the substrate stack. For example, one or more sound generators can additionally be provided above and / or to the side of the substrate stack.

It is advantageously provided that the mechanical excitation runs through a frequency range. This means that the frequency of the mechanical excitation, and thus also the frequency with which the substrates vibrate in the stack, are varied over time. This procedure is advantageous when the optimal excitation frequency is not known or varies slightly from substrate to substrate. The excitation frequency can be run through in ascending or descending order. The frequency range can be traversed continuously or in discrete steps.

According to a preferred embodiment, it is provided that several mechanical natural vibrations of the substrate are excited by means of the frequency range traversed. The frequency range traversed thus has two or more natural frequencies of the substrate, two or more substrates or the substrate stack.

It is preferably provided that the frequency range comprises frequencies greater than 5, 10, 15, 20, 50, 100 or 150 Hertz. If, for example, the base frequency of the substrate is about 27 Hz and the first harmonic frequency is 63 Hz, the frequency range between 20 Hz and 70 Hz can be passed through in order to excite two natural oscillations, or the frequency range between 20 Hz and 30 Hz can be passed through in order to excite a single natural oscillation, namely the fundamental oscillation.

In an expedient development, it is provided that the substrate, after it has been set into mechanical vibration, is kept separated from the other substrates in the stack by means of a further gas flow. The further gas flow is advantageously constant, that is to say not pulsed. It is preferably a constant flow of air with which the separated substrate is kept separate. Holding the substrate separately by means of a constant gas flow has the advantage that subsequent secure gripping of the substrate by means of a gripper, for example a vacuum-based gripper, is made easier. Because with a constant gas flow, the substrate will also maintain a defined shape that is constant over time and will no longer vibrate, which makes it easier to grasp the substrate.

• 1 ein Substrattrennungssystem mit einem Aufnahmeelement und einer Anregungsvorrichtung gemäß einer Ausführungsform;
• 2 einige Schritte eines mittels des Systems aus der 1 durchgeführten Substrataufnahmeverfahrens;
• 3 errechnete Schwingungsformen bei unterschiedlichen Schwingungsfrequenzen für ein mechanisch angeregtes Substrat;
• 4 eine schematische Seitenansicht auf einen Substratstapel zur Veranschaulichung der Problematik haftender Substrate bei konstanter Anregung (sogenannte Doppelzellen);
• 5 wie das Problem aus der 4 mittels einer pulsförmigen Anregung gelöst wird;
• 6 eine schematische Seitenansicht auf einen Substratstapel zur Veranschaulichung der Prozessabfolge bei einem Wechsel zwischen pulsförmiger und konstanter Anregung;
• 7 eine schematische Seitenansicht auf einen Substratstapel zur Veranschaulichung des Trennungseffektes bei einer Gleichtaktschwingung aneinander haftender Substrate; und
• 8 eine schematische Seitenansicht auf einen Substratstapel zur Veranschaulichung des Trennungseffektes bei einer Gegentaktschwingung aneinander haftender Substrate.

The invention is explained below on the basis of exemplary embodiments with reference to the figures. Here show:

• 1 a substrate separation system with a receiving element and an excitation device according to an embodiment;
• 2 a few steps one by means of the system from the 1 substrate uptake process carried out;
• 3 Calculated waveforms at different vibration frequencies for a mechanically excited substrate;
• 4th a schematic side view of a substrate stack to illustrate the problem of adhering substrates with constant excitation (so-called double cells);
• 5 like the problem from the 4th is released by means of a pulse-shaped excitation;
• 6th a schematic side view of a substrate stack to illustrate the process sequence with a change between pulsed and constant excitation;
• 7th a schematic side view of a substrate stack to illustrate the separation effect in a common mode oscillation of adhering substrates; and
• 8th a schematic side view of a substrate stack to illustrate the separation effect in a push-pull oscillation of substrates adhering to one another.

The 1 shows schematically a substrate separation system with a stacking frame 6th in which a stack 3 from several substrates 1 , 2 is arranged. At the top of the pile 3 there is a substrate 1 , which with a receiving element 4th (also called gripper) lifted and off the stack 3 should be separated. The receiving element 4th is in the form shown here from several suction cups 41 formed, which are arranged along a plane. The suction cups 41 are each with a vacuum line 42 connected. Due to a vacuum in the vacuum line 42 is attached to the respective suction cup 41 a negative pressure is created, causing the suction cup 41 on the substrate 1 can suck up.

For lifting the substrate 1 , becomes the receiving element 4th to the pile 3 lowered down until the suction cups 41 with the substrate 1 come into contact or at least until the suction of the vacuum on the substrate 1 is big enough to lift it up and against the suction cups 41 to press. To the substrate 1 As gently as possible from the substrate stack 3 , in particular from another one below the substrate 1 lying substrate 2 to separate, in the embodiment shown here, a nozzle 5 used. Using the nozzle 5 a gas flow, in particular an air flow, is generated, which flows against the substrate 1 blows. This creates the substrate 1 mechanically stimulated and lifted, and in this way from the substrate stack 3 separated.

After the substrate 1 separated by means of the air flow and by means of the receiving element 4th from the stack 3 removed, the next substrate comes 2 your turn. For this purpose, for example, the nozzle 5 to another substrate 2 in the stack 3 be lowered. Instead, however, in the embodiment according to FIG 1 a pile lifter 7th provided on which the stack 3 rests, and which is driven up to the stack 3 to lift and thereby the further substrate 2 in position in front of the nozzle 5 to arrange.

The 2 represents schematically different states of the in the 1 substrate separation system shown in side view and serves to illustrate a substrate receiving method. In the state according to 2a) is the receiving element 4th with the suction cups 41 close to the substrate 1 in the stack 3 brought. Subsequently, or during the approach of the receiving element 4th , is by means of the nozzle 5 an air flow is generated, which leads to a separation of the substrate 1 from the stack 3 leads. This state is in 2 B) shown, whereby an embodiment is also illustrated here in which the suction cups 41 even before touching the substrate 1 withdrawn to avoid an excessively abrupt impact on the substrate 1 on the suction cups 41 to avoid damaging the substrate 1 could lead.

In the in 2c ) The state shown is the substrate 1 already with the suction cups 41 come into contact and is caused by the suction of the suction cups 41 applied vacuum on the receiving element 4th held. The substrate 1 can now be transported away, for example to a subsequent process step or to equip a solar module, if it is a finished solar cell. Then either the stack 3 raised, or the nozzle 5 is lowered to the further substrate 2 and the nozzle 5 to bring it to the same height.

In the in the 1 and 2 Embodiments shown can be the nozzle 5 be designed to be able to generate both constant and pulsed gas flows. This can be controlled by means of a switching element not shown here, for example by means of a solenoid valve. If a pulsed gas flow is generated, a pulsed mechanical excitation can thereby be generated around the substrate 1 to put into mechanical vibrations.

The substrate behaves in the case of mechanical vibration 2 similar to a membrane of the same dimensions. Calculated two-dimensional waveforms that arise at the natural frequencies of such a membrane are in the 3 reproduced. These are grid line representations of the membrane shape in each case at the moment of a maximum deflection out of the zero plane. The basic waveform is in the 3a) shown. EF1 denotes the first natural frequency, which in this case is 27 Hz (Hertz); in general, EFx denotes the xth natural frequency. The 3b) shows a harmonic oscillation at the natural frequency 63 Hz, whereby there are two different oscillation patterns, which, however, are mirror-symmetrical to one another and therefore only one of them is shown. This is why the 63 Hz are also referred to as natural frequencies two and three (EF2, EF3). The same applies to the harmonic oscillation at the two natural frequencies E7 and E8 of 200 Hz, which are shown in 3f) is shown. The 3c ), 3d) and 3e) show the harmonic oscillations at EF4 = 80 Hz, EF5 = 150 Hz and EF6 = 176 Hz.

Although these natural frequencies can be calculated, it is advantageous if the pulse-shaped excitation runs through a frequency range in order to determine the optimal excitation frequency experimentally. For example, under certain circumstances it can be advantageous if the excitation frequency does not quite match the natural frequency of the substrate 1 matches, but has a deviation from it. This can have the advantage that the substrate 1 is not damaged due to excessive swinging.

Furthermore, the substrate receiving method can be provided in such a way that the mechanical excitation passes through a specific frequency range during each separation process. Because possibly the substrates own 1 , 2 of a stack 3 Natural frequencies with a measurable frequency distribution, so that the determination of the respective natural frequencies would be too time-consuming. In this case, for example, the continuous frequency range can be a few Hertz and can be arranged around a calculated or otherwise determined natural frequency. Preferably there are even two or more natural frequencies of a single substrate in the frequency range traversed 1 .

A possible problem that occurs when the substrate is excited 1 can occur by means of a continuous air flow, or when excited by means of a pulsed air flow away from a natural frequency of the substrate 1 , for example at pulse frequencies of a few Hertz to 10 Hz, is in the 4th illustrated. Here the air flow (indicated by the arrow) does indeed raise the substrate 1 . However, it becomes the further substrate at the same time 2 with raised, the two substrates 1 , 2 stick to each other, for example due to electrostatic forces. The receiving element 4th so would two substrates 1 , 2 gripping at the same time. One usually speaks here of double substrates or, if it is the case with the substrates 1 , 2 solar cells, double cells.

The situation is different with excitation with a pulsed gas flow, as in FIG 5 indicated by the curved line above the arrow, at a pulse frequency which is close to a natural frequency of the substrate 1 or is essentially identical to this natural frequency. Here, due to an opposing oscillating movement of the two substrates adhering to one another 1 , 2 , or due to a movement in opposite directions of sections of these substrates lying on top of one another 1 , 2 , the adhesive effect can be overcome.

In a preferred, based on the 6th The illustrated embodiment of the substrate uptake process is the substrate 1 initially by means of a pulsed excitation from the stack 3 separates what is in the 6a) is shown. Then the substrate 1 by means of a low-frequency or constant or continuous excitation above the stack 3 kept what's in the 6b) is shown. When excited by means of a gas flow, the substrate floats 1 in this second phase above the pile 3 and can by means of the receiving element 4th be gripped more easily.

The 7th and 8th illustrate the operating principle by means of which the separation of substrates that adhere to one another 1 , 2 takes place on the basis of a pulsed excitation. In the 7th the case is shown that the two substrates 1 , 2 swing in unison. The 7a) , 7b) and 7c ) show three phases of an oscillation period. During the in 7a) the phase shown move the edge areas 11 of the substrates 1 , 2 up. Due to the curvature of the substrates 1 , 2 guide the originally adhering substrate surfaces to the contact area 13th of the two substrates 1 , 2 at the edge 11 a countermovement relative to each other. This countermovement along the contact surface 13th is in the 7th illustrated with arrows.

The 7b) shows the substrates 1 , 2 in a phase of oscillation in which they have no curvature.

In the 7c ) is again an oscillation phase with an opposite 7a) inverted curvature shown. Here is the counter-movements of the substrate surfaces at the edge areas 11 along the contact surface 13th correspondingly opposite to that in 7a) directed. Due to the in 7a) and 7c ) shown counter-movement along the contact surface 13th can reduce the static friction between the substrates 1 , 2 overcome and the substrates 1 , 2 so separated from each other. It can thus be seen that the two substrates 1 , 2 vibrate in unison that the substrate surfaces at the edge areas 11 however move in opposite directions to each other.

The case in which the substrates originally adhered to one another 1 , 2 due to the impulsive excitation oscillate in push-pull, is in the 8th shown. Here, in 8a) and 8b) each different phases of an oscillation period shown. While in the in 8a) the moment shown the edge areas 11 of the substrates 1 , 2 are pressed apart and the substrates 1 , 2 in the middle area 12th are pressed together, the opposite happens in the in 8b) illustrated phase. Here the substrate surfaces are in the middle area 12th pushed away from each other. Overall, this cycle leads to a separation of the substrates 1 , 2 from each other.

List of reference symbols

1

Substrate

11

Edge area

12th

Middle area

13th

Contact surface

2

another substrate

3

Substrate stack

4th

Receiving element (gripper)

41

Suction cups

42

Vacuum lines

5

jet

6th

Stacking frame

7th

Pile lifter

Claims (10)

Substrate pick-up method in which a substrate (1) is picked up by a substrate stack (3) comprising a plurality of substrates (1, 2) by means of a pick-up element (4), with the substrate (1) being picked up from the substrate stack (4) before and / or during the pick-up. 3) the substrate (1) is set into mechanical oscillation in its natural resonance by the substrate (1), several substrates (1, 2) of the substrate stack (3) or the substrate stack (3) mechanically at a natural frequency of the substrate (1) is excited, whereby for mechanical excitation: - A blowing device is used, by means of which a pulsed gas stream is directed onto the substrate (1), onto several substrates (1, 2) of the substrate stack (3) or onto the substrate stack (3) or - A sound generator is used, the mechanical excitation of the substrate (1) taking place through the substrate stack (3) by means of the sound generator. Substrate uptake process according to Claim 1 , characterized in that the pulsed gas flow is directed parallel to or at an angle to a substrate surface of the substrate (1). Substrate uptake method according to one of the Claims 1 or 2 , characterized in that a blowing device is used which comprises a nozzle (5) with a switching element. Substrate uptake method according to one of the Claims 1 to 3 , characterized in that the mechanical excitation runs through a frequency range. Substrate uptake process according to Claim 4 , characterized in that several mechanical natural vibrations of the substrate (3) are excited by means of the frequency range traversed. Substrate uptake process according to Claim 4 or 5 , characterized in that the frequency range comprises frequencies greater than 5, 10, 15, 20, 50, 100 or 150 Hertz. Substrate receiving method according to one of the preceding claims, characterized characterized in that the substrate (1), after it has been set into mechanical vibration, is kept separated from the other substrates (2) in the stack (3) by means of a further gas flow. Method according to one of the preceding claims, characterized in that the substrate is a semiconductor wafer. Substrate separation system with - A receiving element for receiving a substrate (1) from a substrate stack (3) comprising a plurality of substrates (1, 2), - An excitation device which is designed to excite the substrate (1), several substrates (1, 2) of the substrate stack (3) or the substrate stack (3) mechanically with a natural frequency of the substrate (1), the excitation device - is a blowing device which is designed to direct a pulsed gas flow onto the substrate (1), onto several substrates (1, 2) of the substrate stack (3) or onto the substrate stack (3) or - is a sound generator which is designed to allow the mechanical excitation of the substrate (1) to take place through the substrate stack (3) by means of the sound generator. Substrate separation system according to Claim 9 , characterized in that the substrate is a semiconductor wafer.

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