WO2010037559A1

WO2010037559A1 - Method and device for measuring physical parameters

Info

Publication number: WO2010037559A1
Application number: PCT/EP2009/007086
Authority: WO
Inventors: Michael Münch; Sebastian Stich; Gerhard Lindner; Roland Dechant-Wagner; Jürgen Schweckendiek; Klaus Beringer; Singer Ferdinand
Original assignee: Rena Gmbh
Priority date: 2008-10-02
Filing date: 2009-10-02
Publication date: 2010-04-08
Also published as: CN102171546A; EP2172757B1; ATE520964T1; EP2172757A1

Abstract

The present invention relates to methods and devices to measure physical parameters, such as mechanical forces acting on flat, disk-like and fragile objects during the course of their usual processing. The methods and devices are particularly useful for the manufacturing of solar cells or solar wafers. The method according to the invention provides for the processing to be applied to a test body (1) having basically the same geometrical and/or mechanical properties as said objects, and comprising at least one sensor (2) for measuring physical parameters acting on the test body (1) during the course of its processing. Preferably, the sensor (2) is placed on an elastic interlayer (9) in order to amplify the measuring signal.

Description

Method and Device for Measuring Physical Parameters

The present invention relates to methods and devices to measure physical parameters, in particular the measurement of mechanical forces or loads occurring during usual processing steps, such as the manufacturing of solar cells.

In the course of the processing of flat, disk-like and fragile objects (hereinafter ,,substrates" or ,,objects"), for example, the production of solar cells and the preliminary production of silicon wafers for solar cells, the reduction of breakage is an essential element for productivity improvement. This already applies for silicon wafers from a standard thickness of 300 μm and also for use of mono-crystalline silicon. This problem becomes more important due to the trend to use increasingly thinner substrates, e.g. 150 μm or less in the case of solar cell manufacturing. Materials currently increasingly used, such as poly or multi-crystalline silicon are much prone to break than mono-crystalline silicon. Therefore, such processes or treatments have new requirements with regard to breakage. Breakage may also occur outside of regular operation, e.g. during commissioning of newly installed or modified systems, or as a result of reduced machine availability due to the necessity for cleaning the facility and removal of debris. In the course of a production line, breakage may account for direct losses of 4 to 8% of the material used for manufacturing.

Due to the high efficiency required in industrial mass production of e. g. solar cells but also of other semiconductor products, modern production lines employ with such production plants, so called in-line systems for continuous processing. Particularly critical transfer and sorting processes (i.e. transfer from one carrier to another) shall be avoided by transporting the flat substrates (wafers) from one process station to another with the aid of especially smooth and vibration less operating roller transport systems. However, also such roller transport systems still bear breakage risks. This applies also to such systems which exert only marginal forces to single disks and employ mechanisms for the automatic centering of the disks inside the system tracks. In order to reduce the risk of breakage of fragile substrates, special transport systems have been devised, such as disclosed in e. g. PCT/EP 03/03738 or WO 03/086914.

In addition to insufficient transport systems, alignment errors may occur in the system and result in possible causes for breakage. It is often difficult to distinguish whether upstream damage of the substrate material is responsible for higher breakage rates or alignment errors of the system are to be blamed.

Although methods and devices to monitor the manufacturing process of e. g. integrated switching circuits are known in the prior art, this technology only relates to the possibility of measuring and evaluating such process-specific parameters that directly relate to the qualitative properties of the manufactured goods. For example, US 2004/0098216 Al discloses a sensor unit to measure process parameters enabling to qualitatively evaluate the changes of a disk-like substrate as a result of an upstream process step, such as e. g. the deposition of a layer by using CVD (chemical vapor deposition) . The sensors used for that purpose accordingly measure or analyze the thickness of the deposited layer and thus enable the determination, whether the product complies with the specifications or not. Although mechanical sensors

(e.g. piezo resistors and piezoelectric sensors) are disclosed, they are aswell only used for ensuring compliance with set specifications (such as compliance with a required pressure applied to the disk-like object within the scope of a CMP treatment to achieve optimal polishing results) .

State-of-the-art systems offer, if any, only limited capabilities to particularly measure mechanical parameters such as pressure forces, impulse strengths, accelerations or bending moments, that act on the substrates during processing. In particular, there are no solutions to measure such parameters outside the locations where such sensors were installed, that is, certain specified locations which are defined during the design stage. As a result, even if measurement technology is integrated in manufacturing or handling systems, only discrete, but not continuous measurement values can be detected. As the location of critical loads is often difficult to predict, either many sensors are required or sensors must be constantly relocated. Expenditure of time and/or costs are the result, and become even more an issue, if system downtime or corresponding production stoppage arise and result to even more productivity losses . The traditional approach of adapting the system is basically effected by trial-and-error with a larger data basis (due to a higher number of sensors) enabling a straight forward action. However, the experience of the user carrying out the adjustment is also an important factor. Also in this case, accordingly higher downtimes and/or breakage rates of the processed material must be considered, at least temporarily.

Finally, breakage may indeed occur as a result of sequential overload during processing. Adjustments at the location where such increased loads occur first will lower the risk, but the potential for further risk reduction by identifying other locations can not be taken into account. These issues are intensified if several loads occur in parallel, such as pressure forces and bending moments. In such cases, the identification of such loads "from the outside" is hardly - A - possible, such that under normal circumstances, no corresponding adjustments are planned for these systems since the loads are simply unknown.

On the other hand, in-line-units could be designed much more efficient if the loads acting on the substrates would be known, therefore eliminating the need for costly and unnecessary measures for the protection of the substrates (for example, especially low transport speeds or accelerations as well as extensive handling devices) . Aside from the high loads already mentioned, material defects may be responsible for breakage of the substrates, and therefore, such defects are to be detected or disproved by corresponding examination methods. This also results in additional time and cost disadvantages are the result, since such material inspection measures are always very time consuming, leading to system down times.

Successful decrease or prevention of breakage during the manufacturing process has especially high value for productivity improvement. Breakage is mainly attributable to the mechanical handling of the wafers. Even in well adjusted systems, the mechanical transport or the transfer from one station to the other is a significant factor as the cause of breakage .

It is thus an aspect of the invention to measure physical parameters such as in particular, mechanical forces and loads acting on flat objects during normal processing in a simple, inexpensive and rapid manner. Causes for increased breakage rates can then be detected reliably and remedied accordingly. The measuring of the required parameters shall be carried out without causing downtimes of the system concerned. On the one hand and for cost reasons, only a minimum number of sensors should be required. On the other hand, data should detected from as many substrate processing locations as possible. In addition, the method should be used irrespective of the experience of a given user.

The task is solved by providing the method according to claim 1 as well as the device according to claim 4. Preferred embodiments are illustrated in the dependent claims as well as in the subsequent detailed description and in the figures.

The present invention relates to a method of measuring physical parameters such as, in particular, mechanical forces and loads acting on flat, disk-like and fragile objects during the course of their processing. Examples for such objects are silicon wafers, glass or ceramic disks used as substrates for further processing.

The term "usual processing" means any state-of-the-art processes applied to flat, disk-like and fragile objects. Per definition, the "processing" is carried out in a "system". Processing may be step-wise, i.e. objects are transported to a system and undergo processing in this system and are transported afterwards from the system to another system, if required. In principle, objects do not move during processing. It is preferred, however, to effect the processing may also occur in continuous form, i.e. the objects are transported continuously. Such "in-line-units" have the distinct advantage of avoiding reloading processes, thus minimizing the risk of damages to the objects and saving time. The process according to the invention provides that the processing is applied to a test body having basically the geometrical and/or mechanical properties of the objects. The term "test body" thus defines a body which can be handled in a system suitable for the processing of the flat objects basically in the same way as the flat objects themselves. However, it is preferred that the test body has such a reduced risk of breakage, that even in the event of unusual (extreme) loads, the test body is not destroyed. Due to the similar handling properties, the test body is subject to mechanical forces and loads similar to the ones applied to flat objects during processing. The performance also relates to reaction forces exerted by the test body to the system. In other words, the test body' s performance during its "processing" in the system corresponds basically to the performance of the flat and fragile objects for whose processing the system is designed.

Any "processing" of the test body described herein shall only mean that the test body enters the system and is subjected to typical (in particular, mechanical) loads therein and is thereafter removed from the system in the way that a flat object normally to be treated. It should be noted that it is not the objective of the "processing" to change any of the characteristics or properties of the test body. If certain processing steps may be omitted as they have no significant effect on the parameters to be measured, e.g. rising or drying, it is preferred that these steps are skipped and the corresponding media, temperature increases, etc. are omitted. On the one hand this will prevent any unnecessary material wastage, and one the other hand, the test body could possibly be damaged during certain processing steps, such as e.g. tempering, which should of course be avoided.

The test body according to the invention comprises at least one sensor for measuring at least one physical parameter that actson the test body during processing, in particular, any force acting upon the test body. It can also be provided that the at least one sensor can measure several different parameters, such as e.g. forces and moments. Regarding the sensor this can be possible both ,,by design" and "by definition". The term "by definition" shall mean that the sensor' s basic design always allows for the measuring of several parameters. The term "by specification" shall mean that the sensor comprises in fact several sensing elements which are combined into one unit, for example, by arranging such elements in one common housing. Such housing shall also be considered a "sensor", if the housing is a structural unit.

Preferably, the physical parameters to be detected by the at least one sensor are mechanical parameters, selected from the group consisting of tensile forces, pressure forces, shear forces, pressures, bending moments, torsion moments, acceleration forces, and combinations thereof. By definition, rotation forces are deemed to be acceleration forces ("angular acceleration") . It is particularly preferred, that the at least one sensor can measure several of the parameters mentioned above, wherein it is most preferred that these parameters are forces and bending moments.

Alternatively or in addition, the parameter which can be measured with the at least one sensor can also be a temperature value, an electrical value or a magnetic field force, or any other physical parameter.

According to a preferred embodiment, the at least one sensor is preferably selected from the group consisting of a force sensors, pressure sensors, moment sensors and acceleration sensors. By definition, centrifugal force sensors, which are able to measure angular acceleration forces, are deemed to be included in the latter.

To ensure the compliance of the handling properties of the test body to a flat object during the "processing" and thus during the passage through the system with regard to the sensitiveness to the acting forces, the test body has basically the geometrical and/or mechanical properties of the objects. Preferably, the geometrical properties of the test body relate to its thickness, width, length, and/or outline, and the mechanical properties of the test body relate to its elasticity, bending stiffness, torsional stiffness, and/or mass. Further properties may e.g. include bulk modulus or modulus of shear. In this way, the test body's performance while passing though the system basically is the same as that of an object to be processed. This is preferred, since the acting forces and/or deformations with regard to the actual object to be processed can be measured as realistically as possible. In most cases, however, overloading of the test body should not result in its damage or destruction. Therefore, the test body should be highly resistant to breakage to allow repeated use. According relation to the invention, it is however not excluded that the test body has the identical or less resistance to breakage than the object to be processed. Therefore, the test body alternatively may also be designed for one-time use.

Preferably, the method according to the invention can be carried out to first obtain so-called standard (norm) values. These standard values service for the subsequent comparison with parameters which are also measured with the test body according to the invention. Such standard values can be obtained by having the test body pass, at a minimum, once or (preferred) repeatedly through the system, whereby the corresponding parameters are measured. If several data records are available, statistical data (e.g. average values and standard deviation) of each parameter can be calculated for every location in the system. If the flat objects are damaged during their processing in the system later on, the system can be measured once again using the test body. By comparison of the newly measured data with the standard values (being set values in this case) it can be determined at which location in the processing chain which parameter deviates from the corresponding standard value. This enables the system to be adjusted again at this particular location in order to avoid any more damages during the continuous processing.

The method according to the invention can also advantageously be use for the precise commissioning of newly installed or modified systems, when parameters such as, in particular, forces are measured with the test body according to the invention following a rough adjustment of the system. These parameters are then compared with typical or standard values which e.g. are derived from the knowledge of the mechanical

(and/or thermal, magnetic, etc.) load of the flat objects to be processed or which can be retrieved in the form of stored data, respectively. These typical values or standard values may be based on experience and/or calculations. The values may be derived also from measurements obtained by the test body which has passed through other systems. Where the measured parameters exceed the typical (allowed) values, a readjustment should be effected. This procedure ensures that the systems are commissioned very effectively, thus saving time and costs. In addition, the process provides a particularly safe and rapid possibility to determine the causes for sudden damages to the objects to be processed during their treatment. Here is an example for the method:

First, the desired physical parameters - preferably mechanical loads such as forces, moments and accelerations - are recorded using the test body according to the invention. Subsequently, the recorded parameters are compared with standard values, which were either measured or calculated at an earlier time or which are based on empirical values. Preferably, the standard values are based on several measurements which were recorded with the aid of the test body at an earlier point in time in the system and, where appropriate, have been statistically evaluated. It will then be decided, whether any of the determined deviations can be considered as a cause for the observed damages. If the decision is positive, the system is to be readjusted at the corresponding locations. If the decision is negative, it is very likely, that material defects of the objects are the cause for the damages. As a result, the material of the objects should be subjected to a thorough inspection and unnecessary readjustments of the system are not required.

According to a first embodiment of the method according to the invention, the parameter/s measured by the at least one sensor can be stored on the test body and read out after the completion of the measuring process. Another embodiment provides for the transmission of the recorded parameters, e.g. by means of a transmitter located in or allocated to the test body to a receiving and/or evaluating unit, thus enabling the recorded parameters to be analyzed almost in real time. Such a procedure can be particularly useful, if the system comprises quite extensive travel distances and/or the transport speed of the test body is comparably low. This means, that the test body must pass through the system only partly, namely up to the occurrence of a first fault, since the measurement of parameters can be terminated at that stage to enable readjustment of the system at the location of the fault.

Most preferably, the method according to the invention is used for the manufacturing or production of solar cells or solar wafers. It is irrelevant, whether mono-crystalline, poly- crystalline or multi-crystalline silicon is used in the process, or whether thin-layer solar cells with e.g. glass substrate are used.

In addition, the method according to the invention can advantageously be used in the development of transportation or handling systems, since the test body is able to determine the mechanical effect of competing of transportation or handling solutions on the flat objects to be processed.

The present invention further relates to a device for measuring physical parameters such as unparticular mechanical forces and loads acting on flat, disk-like and fragile objects during the course of their usual processing. For an explanation of the terms "parameter", "usual processing" and "flat, disk-like and fragile objects", it is referred to the above descriptions. The same shall apply to the terms "system" and "substrate".

According to the invention, the device comprises a test body having basically the geometrical and/or mechanical properties of the objects. According to a first embodiment, the test body is designed as at least one sensor for measuring at least one physical parameter that acts on the test body during the course of its processing such as, in particular, mechanical loads. In this embodiment, test body and sensor are basically identical, wherein the invention also contemplates that several sensors may be grouped together to form the test body.

In accordance with another embodiment, the test body comprises at least one sensor. The at least one sensor according to this preferred embodiment is located on or in a base body being a component of the test body. This configuration on the base body thus constitutes an add-on design, whereas a configuration in the base body corresponds to a fully or partly integrated or sandwich-like configuration. The base body according to the invention determines the geometrical and/or mechanical properties of the test body, since the at least one sensor as provided by this invention preferably has only a low impact on the geometrical and/or mechanical properties of the test body. The base body may be designed as a solid body or hollow body. Preferably, the base body includes embedded components such as built-in electronics in a chemically resistant manner, thereby enabling the measuring of measurement data even under presence of aggressive media. For this, the base body may be provided with a protective layer, at least on one side or, preferably, on all sides. Alternatively, the electronics may be unprotected, if permitted by the respective scope of application. Preferably, the base body is made metals or metallic materials; however, other materials are not excluded. Alternatively, the base body may thus also be made of synthetic material, printed circuit board materials or epoxy resin-like material.

Preferably, the base body - and therefore the entire test body - is bendable to a certain extent.

Preferably, the physical parameters to be measured are mechanical and selected from the group consisting of tensile forces, pressure forces, shear forces, pressures, bending moments, torsion moments, acceleration forces, and combinations thereof, wherein the acceleration forces also comprise rotary acceleration forces.

Preferably, the at least one sensor as provided according to the invention is selected from the group consisting of force sensors, pressure sensors, moment sensors and acceleration sensors. The latter also comprise sensors enabling the measurement of angular acceleration forces. Any state-of-the- art sensors known for mechanical loads may be used, with sensors on the basis of piezoelectric plastic films being particularly preferred. As an alternative, piezoelectric ceramics or films which are coated with piezoelectric ceramics may be used.

Alternatively or in addition, the at least one sensor is suitable to measure temperature, electrical fields, magnetic fields, or other physical parameters. In accordance with a preferred embodiment, the geometrical properties of the test body relate to its thickness, width, length, and/or outline. According to another embodiment, the mechanical properties of the test body relate to its elasticity, bending stiffness, torsion stiffness, and/or mass. With regard to the description of these properties, it is referred to the description of the method according to the invention. According to a further preferred embodiment the device according to the invention further comprises a memory unit for storing the measured at least one physical parameter and/or a transmitter unit for wireless transmission of the same. Preferably, the memory unit is installed in a cavity of the base body or allocated to the base body in another way. Alternatively or in addition, all or some of the data recorded by the at least one sensor may be transmitted wirelessly to a receiver. With regard to further explanations for storing and/or sending of data, it is referred to the above description of the method according to the invention.

For the purpose of analyzing the recorded data, in particular the measured forces, the device according to the invention may further comprise an evaluator unit for the further processing of the measured at least one physical parameter, in particular the mechanical forces. Preferably, this evaluator unit is located outside the body of the test body and only allocated to the test body and/or to the device according to the invention. Preferably, a display unit, such as e.g. a monitor, is provided, which allows the display of the recorded data.

Preferably, the device according to the invention further comprises an output unit output optical, acoustical and/or electrical signals for monitoring the status. Such signals may e.g. be warning signals to be emitted in the event of exceeding certain threshold or standard values, enabling a user to obtain certain information immediately and without the need of an additional, possibly externally arranged or allocated display device. These signals may be acoustical, optical and/or electrical signals, wherein the electrical signals are mainly suitable for the measurement by corresponding receivers, which are arranged at or comprised by the system. In this way, the system e.g. may be designed such that it switches automatically from manufacturing mode to a recording mode suitable for test operation, if a corresponding signal is received. A test body inserted in the system during running operation can thus be sorted out without difficulty.

Finally it is preferred that the device according to the invention comprises an energy supply unit. This energy supply unit can exclusively be located at or in the test body (e.g. batteries, condensers), or it can comprise include additional external components (e.g. inductive energy transfer by means of coils) . It is particularly preferred that the energy supply unit is rechargeable and or replaceable. Preferably, the test body has a rectangular form. According to a particularly preferred embodiment, the test body is quadratically designed.

For the measuring of the at least one physical parameter, the general prior art provides a multitude of different sensor types. One possible selection criterion is the type of transformation used by the sensor to transform the physical parameter into a measuring signal. According to a preferred embodiment the at least one sensor is designed such that it undergoes a change of its form due to the at least one parameter acting on the test body, and this change is used to measure the at least one parameter.

According to a simple embodiment, the sensor comprises or is designed as a plastically deformable layer. Such a layer reflects the mechanical loads acting on it in the form of permanent deformations, wherein the degree of deformation approximately corresponds to the magnitude of the mechanical load. Most preferred are materials that regain their original shape after the measurement, for example, following temporary temperature increases. Particularly those sensor types are preferred that - upon deformation - generate electrical signals and/or are able to change their electrical properties. According to a particularly preferred embodiment, the electrical signal is generated actively by the sensor. Alternatively, the parameter can be passively measured by the sensor. An example is a change of deformation induced the electrical properties which is only measurable in connection with an externally applied voltage and/or current supply. Finally, all such sensor types are preferred, which are substantially characterized by a two- dimensional planar form.

Particularly preferably are also sensor types where the measuring signal and/or the change of electrical properties approximately are proportional to the sensor's deformation.

According to a preferred embodiment the at least one sensor comprises or is designed as at least one piezoelectric plastic film. Such films consist, for example, of polyvinylidene fluoride (PVDF), or contain at least a layer of such material which has the property to react to a mechanical deformation with a charge movement.

The use of a film made of PVDF for the production of an electromechanical converter being used as a pushbutton is known from DE-OS 31 26 340 Al. The converter described therein comprises a flat piezotronic base body with the ability of unrestricted movement in the direction of its flat surfaces. An elastomer is fitted to at least one flat surface. The surface of the elastomer facing the base body features a gap, enabling the elastomer to generate force components in the direction of the base body's flat surfaces that boost the signal. Experts know that in such a configuration signals will be generated upon action of a pressure load by extension of the unfixed base body in the direction of its flat surfaces. Furthermore, it is provided that the load on the piezotronic film does not occur directly and immediately, but indirectly via the elastomer. Force components arise as a result of this indirect force action via the elastomer in the direction of the flat surfaces of the base body and cause the base body to expand in the direction of its flat surfaces. However, no significant bending takes place such that loads are substantially converted into extension forces for the base body.

As an alternative or in addition, the at least one sensor comprises at least one strain gauge (DMS) or the sensor itself is designed as a strain gauge. Other similar sensor types are, for example, designed as conducting paths, which may also be manufactured from other materials than the strain gauge. These conducting paths can be imprinted on flexible films where they react with resistance changes if deformations occur, or indicate a mechanical overload by a break in the line, as a minimum requirement.

Such sensors can be provided in a very flat and heavy-duty design and can cover a very wide measurement range depending on the design. Furthermore, forces, pressures and moments can be measured very precisely with the aid of such sensors. In addition, such sensors meet the requirement of a change in form which is approximately proportional to the change of the measuring signal. Particularly preferably are sensors on the basis of flat piezoelectric plastic films which are fixed either mechanically or in another manner, thereby enabling a signal to be generated in the event of a mechanical load as the film is bent in the direction of the mechanical load. Furthermore, it is preferred that the load acts on the sensor film directly and immediately and is substantially converted into bending forces. Such a film therefore reacts to each load or load variation with a corresponding deformation (bending) . Due to the internal charge movement, a measurable voltage is generated such that - in the ideal case - no operating power is needed to operate the sensor and to generate the electrical measuring signal. It is thus envisaged, that the voltage created by such a sensor can further be used for the energy supply of other components such as e.g. the optionally provided memory or transmitter unit.

In accordance with a particularly preferred embodiment, the at least one sensor is located parallel or diagonal to the edges of the test body. In the case of several such sensors, it is mostly preferred that these are arranged parallel and diagonal to the edges. It is further preferred that the at least one sensor has a rectangular design and is arranged in such a configuration that enables the mechanical load to be measured to act simultaneously on a maximum sensor surface in order to generate a correspondingly large measuring signal. In the case of a roller transport device with rollers arranged perpendicular to the transport direction, a configuration is thus preferred, where the sensor/s are placed parallel to the roller axis. This enables the load to act simultaneously on a maximum surface area of each rectangular sensor, resulting in the generation of a correspondingly large measuring signal.

Another preferred embodiment specifies the device according to the invention to comprise at least two sensors which are arranged on the upper and lower side of the test body.

According to a further preferred embodiment the device comprises at least one sensor being arranged at one or several edges of the test body.

Furthermore, it is preferred that the device comprising at least one sensor enables a high frame rate and/or measuring frequency to enable the measurement of short and pulse-like impacts which e.g. might occur at the edges of the test body.

For this purpose, the minimum measuring frequency must be 5

Hz. Preferably, the measuring frequency is in a range of 20 Hertz to 1 kHz or higher. Particularly preferred are measuring frequencies above 1 kHz.

According to a particularly preferred embodiment of the device according to the invention an elastic interlayer is arranged at the surface of the base body. The at least one sensor is functionally and therefore at least partly located on top of this layer, such that a load or force still immediately and directly acts on the sensor. In this context, the term "elastic" substantially serves to differentiate from the term "plastic". This means that the interlayer will take up its rest position again following a mechanical load mediated by the sensor. A (permanent) plastic deformation is not intended. Due to this interlayer, the at least one sensor can to a certain extent be mechanically decoupled from the base body and/or experience deformation, boost wherein the latter property enables an amplification of the measuring signal. In the exemplary case of a sensor that comprises a piezoelectric plastic film, this amplification is based on the extension of the deformation path in the direction of a mechanical load which the piezoelectric plastic film can travel. Without the elastic interlayer, the deformation path is limited due to the relatively low deformation ability of the plastic film, since the film is directly disposed and fixed to the usually very stiff base body. Together with the elastic interlayer, the plastic film is able to change its shape more extensively, since this is allowed by the low stiffness and/or high elasticity and/or compressibility of the elastic interlayer.

In the event, that the interlayer does not remain in its position automatically, it is advantageous that the at least one sensor is arranged such that it fixes the interlayer. This can e.g. be achieved, if the sensor protrudes sideways over the interlayer and is combined (e.g. bonded) with the base body at the sensor's free edges. Alternatively or in addition, the interlayer can be designed to have one or more passages which are e.g. filled with an adhesive substance, such that the sensor and interlayer are fixed to the base body.

As already mentioned, the at least one sensor, where appropriate together with the interlayer, can be disposed on the base body or fully or partially integrated in the base body. If desired, the latter would result in a base body hearing an even outer surface.

In the scope of the invention, the elastic interlayer can fulfill several tasks, wherein it is particularly preferred that several of the requirements described hereinafter are complied with simultaneously.

A first task of the interlayer is to enable an extended deformation path of the at least one sensor according to the invention. For this, it can be provided according to the invention, that the elastic interlayer has a certain stiffness and/or compressibility which in both cases is lower than the that of the base body and the at least one sensor.

In accordance with an alternative embodiment, the extended deformation path can also be provided in that the interlayer has indentations and/or cavities into which the sensor can deform itself by filling such indentations and/or cavities without encountering any significant resistance since no solid material has to be pushed away or compressed upon deformation into the indentations and/or cavities. In accordance with this embodiment, the interlayer can also consist of a basically non-elastic or solid material, provided that a sufficiently number of indentations and/or cavities is present. In accordance with the invention, the interlayer may consist of many flexible materials and have a homogeneous or heterogeneous structure, wherein the term "heterogeneous structure" describes the presence of flexible and non-flexible components. With a corresponding design of the elastic film, the sensitiveness of the at least one sensor may thus be adapted over a wide range to the respective task at hand.

A second task of the interlayer is to mechanically decouple the base body from the sensor' s load. Since the interlayer partly absorbs the load and elastically deforms such as e.g. the piezoelectric plastic film or the strain gauge, this load depending on the stiffness will only partly be passed on to the base body, whereby the base body and, in particular, its integrated electronic components can be protected from overloads being too high.

A third task relates to the possibility to adjust the stiffness of the test body resulting from the condition of the base body and/or the at least one sensor to an appropriate value by providing an elastic interlayer. In this way, even with a given base body having a stiffness deviating from the flat objects, the test body can achieve a certain stiffness in combination with an adapted interlayer which e.g. substantially corresponds to the stiffness of the flat objects . a fourth task of the elastic interlayer is to improve the signal-to-noise ratio of the at least one sensor by filtering any mechanical loads generated by the system or unrelated to the parameter to be measured from the signal generation as much as possible. If a type of sensor is present which is able to change its form, the thermal noise can be reduced as well, since any temperature change of the base body has a much lesser impact on the sensor. Therefore, the presence of an elastic interlayer positively affects the signal-to-noise ratio of the sensor. Depending on the task at hand or the concrete application, the interlayer according to the invention can be realized in different ways. In accordance with a first embodiment, the interlayer is designed as a homogeneous (e.g. rubber-like) layer. Such layers are flexible, yet only to a small extent compressible. They are therefore particularly suitable to dampen and/or disperse spot loads. In accordance with another embodiment, the interlayer may be designed as a sponge-like layer of foam material with open and/or enclosed cavities (pores) that are filled with a gas such as, in particular, air. Such foam materials have the benefit of a Poisson' s ratio (modulus of elasticity under tension, coefficient of contraction) near zero, being equivalent to the property of showing no substantial deformation in the other axial directions when a single-axis deformation (such as a compression force) . A layer made of such materials is therefore well compressible and as a result the deformation path of the sensor under load is extended. It may also be advantageous to design the elastic interlayer as a hermetically closed gas volume ("gas spring") which holds the malleable sensor in a certain distance from the base body if no load is applied, such that in the case of a load being applied, a corresponding deformation without significant load increase is possible. In accordance with another embodiment, the elastic interlayer is designed as a geometrical form. In this case, the elastic interlayer may have a two- or three- dimensional wave pattern on one or on both sides, or may have a honeycomb- or web-like structure, or may be designed as a supporting structure. A design as a perforated foil is also possible. In accordance with the desired performance of the layer structure, it may be useful to design the configuration with mainly solid material having smaller gaps, or a configuration with mainly bigger gaps and smaller solid material parts. The elastic interlayer in its described design shall mainly provide an additional deformation path to the sensor if a mechanical load is applied. As already mentioned above, the elastic interlayer can also be constructed from mainly stiff supporting elements such as metal webs with many and/or big gaps. It is also possible to provide filling material to the above-mentioned gaps, either in part or completely. If the filler shows a lower stiffness than the surrounding material, the stiffness of the interlayer will be insignificantly increased. The reverse case might also be conceivable with the surrounding material having a lower stiffness than the filling material, for example, if a perorated foil made of silicon is filled with epoxy resin.

Finally, it may be advantageous to provide several different interlayer areas underneath a sensor. This can be advisable if a sensor with a large surface area shall have areas of high load and areas with high sensitivity.

In accordance with a particularly preferred embodiment, the elastic interlayer is designed as a net-like silicon film. For the nonpositive joining of the interlayer with the base body on the one hand and the plastic film on the other hand, of a suitable adhesive can be used which preferable has the same mechanical properties as the silicon film. It is also particularly preferred to either completely exclude the inclusion of gas bubbles or to allow gas bubbles only in a regular pattern to ensure that the properties of the elastic interlayer remain homogeneous.

Suitable interlayers according to the invention thus relate both to homogeneous as well as to heterogeneous structures which can comprise identical or different elastic materials. In accordance with another embodiment, several sensors according to the invention, preferably having different sizes may be arranged above each other. Most preferably, a first sensor to e.g. measure a pressure acting on the entire test body is placed directly on the base body. In this case it is preferred, that the surface area of the sensor is as far as possible identical to the surface area of the test body. Onto this first sensor, one or several other sensors, which are best of smaller size and can measure "locally", are arranged. In this way, spot acting forces can be measured space- resolved.

A single elastic interlayer may be sufficient for several deformable sensors such as piezoelectric plastic films, for example, if these are arranged in successive strips and parallel to each other on the common elastic interlayer.

It is also advantageous to design the at least one sensor according to the invention as being detachable from the test body or base body, e.g. by bonding, screw or clamp connection. In this way, the placement of the at least one sensor on the test body or base body may be changed. The sensors can also quickly and cost efficiently be replaced by types with other sensitivity or if required due to defects. Preferably, the test body or base body is equipped with many electrical connections designed to be covered by detachable sensors enabling the measuring signal to be transmitted via these connections without having to provide additional cables or the like. Another preferred embodiment provides for the test body to be designed as a layered structure comprising chemically resistant exterior layers and one inside layer. The inside layer comprises the at least one sensor and, if required, further electronic components. As already described, the respective stiffnesses of the involved components affect the performance of a sensor with elastic interlayer significantly. In many cases, the interlayer preferably has a stiffness which is lower than that of the base body and the at least one sensor. Departures from this principle are possible and appropriate, depending on the application. It is particularly preferred that the stiffness of the base body is higher than the stiffness of the interlayer by a factor of 100 to 1.000, preferably around 250. Alternatively or in addition, the stiffness of the base body has a value between 100 and 3.000.000 MPa (N/mm² ) , preferably about 500 MPa (N/mm²) and/or the stiffness of the interlayer has a value between 1 and 30 MPa (N/mm²), preferably about 2 MPa (N/mm²) . Experts will realize from the present description that the methods and devices according to the invention are especially suitable for measuring loads occurring during the handling of fragile flat objects. In particular, the methods and devices are suitable for continuous measuring of loads at any place and/or anytime during handling and processing without the requirement of many sensors. The invention enables the use of a single sensor for every parameter (in particular for mechanical loads) to be measured. By using high scanning rates, short-term loads such as shocks impacting on the test body according to the invention can be measured as well. Time efforts and costs for troubleshooting following overloads or for the initial adjustment of newly commissioned or modified systems can be minimized by following the teaching according to the invention. Furthermore, the invention is suitable to minimize user influence on the result of the measurement process. Production stops and shutdown periods can be minimized as well. Finally, the invention can also be used to prevent exaggerated efforts to avoid overloads to a large extent. The method also facilitates separate, reliable and repeatable measuring of loads consisting of several individual loads. The invention may also be of use to clarify efficiently, whether sudden occurring damages during the processing of flat objects are caused by system errors or material defects of the objects. By using a device according to the invention with elastic interlayer, the sensitivity of a sensor, which is preferably designed as a piezoelectric plastic film can be increased significantly, provided the elastic interlayer due to its design and/or its lower stiffness and/or its higher compressibility as compared to the sensor and the base body facilitates a higher degree of sensor deformation than without the use of the interlayer. Furthermore, interlayer has a protective function for the base body and/or the components contained in the base body, enables the adjustment of the stiffness of the test body, and positively influences the signal-to-noise ratio.

Description of the figures

Figure 1 shows a preferred embodiment of the device according to the invention. The figure shows the device, comprising a test body 1 which comprises a base body 3 and a sensor 2. The base body 3 is designed as a hollow body. On top of the base body is the sensor 2. In accordance with the described embodiment, the sensor may e.g. be designed as a piezoelectric plastic film, being identified with the solid thick line. With the aid of the sensor 2, the physical parameters of interest such as mechanical forces are recorded. An interlayer 9 is located between sensor 2 and base body 3. The interlayer absorbs some of the mechanical and/or thermal loads that act during the usual processing onto the test body 1 and thus on the sensor 2. Furthermore, the interlayer allows the deformation path to be extended if a mechanical load is applied. Preferably, the interlayer 9 features a lower stiffness as compared with sensor 2 and base body 3. Therefore, any deformation or relocation of the sensor 2 are transferred to the base body 3, but due to the extended deformation path they are both muted and more intense. In accordance with the shown embodiment, the interlayer 9 is completely placed upon the base body 3. According to an alternative embodiment (not shown) the interlayer 9 and, where appropriate, also the sensor 2 can be partly or completely flush-mounted in the base body's 3 wall. This partly and/or fully integrated configuration achieves as far as possible an even external surface of the base body 3 and thus of the test body 1. Without doubt, the wall must be designed with a corresponding minimum thickness, preferably somewhat thicker than the thickness of the interlayer 9. Alternatively, the wall should then have a corresponding indentation for the interlayer 9 and, where appropriate, for the sensor 2 (not shown) .

Further components are located within the base body 3. These components relates an energy supply 8, a memory unit 4 which is used to save the recorded parameters, as well as a transmitter unit 5 which enables the wireless transmission of recorded parameters to an evaluator unit 6 which is located outside of the test body 1 in accordance with the shown embodiment. Finally, the base body 3 also comprises an output unit 7 which is able to generate an acoustic signal in accordance with the shown embodiment. For example, this signal can indicate to the user certain states of the test body 1 without the need for further display devices.

In the interest of clarity, electrical connections, etc., required for the operation of the device according to the invention are not shown. The figure is also not drawn to scale, in particular concerning the relation between width and thickness of the test body 1.

The figures 2A-D show a schematic cross-section of the device according to the invention with several embodiments of the elastic interlayer 9. Included in the figures are: A section of the base body 3 (displayed as a broken line) , the elastic interlayer 9 (surface shown with dotted lines), and the sensor

2 (surface shown in shades) which is designed as a piezoelectric plastic film.

Figure 2A shows the elastic interlayer 9 as a homogeneous, uniformly thick layer onto which the sensor 2 is placed. The interlayer 9 is placed upon a part of the base body 3, shown in a sectional view. The shown embodiment is suitable for one or more forces which have spot-like impact at different locations since forces impacting larger surfaces cause only a uniform compression of the interlayer 9 without significantly extending the deformation path of the sensor 2. Figure 2B shows the elastic interlayer 9 as a geometrically designed form featuring a one-sided wavelike outline in two- dimensional sectional view. If a load is applied (shown as force arrows F) , the sensor 2 changes its shape and deforms into the wavelike gaps of the elastic interlayer 9. The sensor will bend and expand in longitudinal direction L and the extent of its bending is markedly stronger as would be the case if the elastic interlayer 9 had no corresponding gaps. The stop position of the sensor 2 is indicated roughly by the dashed line, wherein the elastic interlayer 9 shows a relatively high stiffness. Unlike the embodiment shown in figure 2A, the embodiment shown here is particularly suitable for forces impacting on larger surfaces or for pressure forces . Figure 2C shows a configuration, wherein the elastic interlayer is designed as a gas spring. In this case, the sensor must be welded to the base body 3 in a continuous and hermetically fashion, or the elastic interlayer 9 should have the form of a gas bubble as indicated by the dashed outline. Finally, figure 2D shows the elastic interlayer 9 as a uniformly thick layer with perforations. By varying size, location and number of perforations, the stiffness can be easily regulated over the entire surface or in certain parts only. Alternatively, gaps can be provided, for example appearing as slots or spiral outlines in a top view (not shown here) . As required, the stiffness of the elastic interlayer 9 can be low or high. In any case, the design of the elastic interlayer 9 and/or of its gaps will ensures, that the sensor 2 has sufficient potential to deform in the direction of the base body 3, if a load is applied (not shown here) . List of References

1 Test body

2 Sensor

3 Base body 4 Memory unit

5 Transmitter unit

6 Evaluator unit

7 Output unit

8 Energy supply unit 9 Elastic interlayer

F Force arrow

L Longitudinal direction

Claims

Patent Claims

1. A method of measuring loads or load variations acting on flat, disk-like and fragile objects during the course of their usual processing, by applying the processing to a test body (1) having basically the geometrical and/or mechanical properties of said objects and comprising at least one sensor (2) for measuring at least one physical parameter that acts on the test body (1) during the course of its processing and is selected from the group consisting of tensile forces, pressure forces, shear forces, pressures, bending moments, torsion moments, acceleration forces, and combinations thereof, wherein the at least one sensor (2) comprises or is designed as a piezoelectric plastic film and is able to transform a load that directly and immediately impacts onto the sensor into bending forces .

2. The method according to claim 1, wherein the geometrical properties of the test body (1) relate to its thickness, width, length, and/or outline, and wherein the mechanical properties of the test body (1) relate to its elasticity, bending stiffness, torsional stiffness, and/or mass.

3. The method according to claim 1 or 2, wherein the processing is used for the manufacturing or production of solar cells or solar wafers.

4. A device for measuring loads or load variations acting on flat, disk-like and fragile objects during the course of their usual processing, comprising a test body (1) having basically the geometrical and/or mechanical properties of said objects and being designed as at least one sensor (2) for measuring at least one physical parameter that acts on the test body (1) during the course of its processing and is selected from the group consisting of tensile forces, pressure forces, shear forces, pressures, bending moments, torsion moments, acceleration forces, and combinations thereof, or comprising at least one such sensor (2), wherein the at least one sensor (2) comprises or is designed as a piezoelectric plastic film and is able to transform a load that directly and immediately impacts onto the sensor into bending forces .

5. The device according to claim 4, wherein the test body (1) comprises as a component a base body (3) on or in which the at least one sensor (2) is located.

6. The device according to claim 4 or 5, wherein the geometrical properties of the test body (1) relate to its thickness, width, length, and/or outline, and wherein the mechanical properties of the test body (1) relate to its elasticity, bending stiffness, torsional stiffness, and/or mass.

7. The device according to one of claims 4 to 6, further comprising:

- a memory unit (4) for storing the measured at least one physical parameter and/or a transmitter unit (5) for wireless transmission of the same;

- an evaluator unit (6) for the further processing of the measured at least one physical parameter;

- an output unit (7) to output optical, acoustical and/or electrical signals for monitoring the status; - an energy supply unit (8) .

8. The device according to one of claims 5 to 7, wherein an elastic interlayer (9) is arranged at the surface of the base body (3) and onto which the at least one sensor (2) is fitted at least partly.

9. The device according to one of claims 4 to 8, wherein the test body (1) is designed as a layered structure, wherein the layered structure comprises chemically resistant exterior layers and an inside layer having the at least one sensor (2) and, if desired, further electronic components.