PROCEDURE AND PREPARATION UNIT

Abstract

A method for preparing a workpiece for processing is provided, the method comprising the steps of providing the workpiece, applying a protective surface material comprising at least a first layer and a second layer, wherein the second layer is formed of a material having a higher glass transition temperature or melting temperature than the first layer, combining a first side of the workpiece and the first layer of the protective surface material, and applying heat to the first layer of the protective surface material through the second layer thereof. Furthermore, a preparation unit for preparing a workpiece is provided, which is configured to carry out this method.

Description

TECHNICAL FIELDThe present disclosure relates to a method for preparing a workpiece for machining and a providing unit for preparing a workpiece for machining.BACKGROUNDDevice chips are generally manufactured by forming devices on a front side of a substrate (wafer) in regions defined by dicing lines. However, the devices formed on the front surface of the substrate cause the front surface to have an uneven profile. In other words, the front surface is not flat, but has numerous grooves, depressions and projections which result in the surface of this surface having an uneven profile and which can cause difficulties in the processing of the substrate.In particular, it has been found that these asperities on the front side of the substrate are susceptible to damage or result in damage when mechanically worked, such as by grinding or dividing on the side of the substrate opposite the front side. One of the reasons determined for this is that the force applied during the processing is distributed unevenly over the surface of the front side of the substrate due to the different support, which in turn leads to stress peaks which can lead to cracks in the substrate and the components.As an approach to prevent this damage during processing, various techniques have been proposed to level the uneven surface of the front surface of the substrate that causes the uneven support.For example, US 2017 / 062278 A1 proposes to apply a protective film to one side of a wafer to cover devices on the wafer, the protective film being adhered to at least a part of the one side of the wafer with an adhesive, and provide a support to the front surface of which a curable resin has been applied. The method further includes attaching the one side of the wafer to which the protective film is attached to a front surface of a support so that the protrusions protruding from the planar surface of the wafer are embedded in the curable resin.Another technique that has been proposed (see, for example, JP 2013-021017 A) is to apply a tape to the front surface of a substrate having devices formed thereon. After the tape is applied to this uneven surface of the device on the substrate, surface changes occur on the exposed surface of the tape. These are then removed by planarizing the exposed surface by a type of milling operation using a diamond mill. This process also requires additional time and rather complex machines to be executed properly.Furthermore, US 2020 / 335 382 A1 proposes the stacking of a sheet material and a flat plate on a front side of a substrate. This process is followed by a thermo-compression bonding step. During application of a pressing force to the sheet on the substrate via a flat plate, the sheet is heated via the substrate. Thus, the planarization is performed by heating the sheet from one side and applying an external force to the sheet from the opposite side via the flat plate. Then, the flat plate is removed. However, this technique has been found to be substantially effective in cases of comparatively little unevenness of the surface profile.SUMMARY OF THE INVENTIONAccordingly, there remains a need for simplified and improved methods for planarizing an uneven surface of a workpiece, the uneven surface being caused in particular by devices formed on a front side of a substrate or wafer.To address this issue, the present disclosure provides a method of preparing a workpiece for subsequent machining. The method includes providing the workpiece and a protective surface material including at least a first layer and a second layer. The second layer is formed from a material that has a higher glass transition temperature and / or melting temperature than the first layer. The method also includes a step of combining a first side of the workpiece and the first layer of the protective sheet material and applying heat to the first layer of the protective sheet material through the second layer.This method has the advantage that it makes it possible to substantially compensate for unevenness present on the first side of the workpiece, which unevenness is caused, for example, by components arranged there.The compensation is achieved in particular by the protective sheet material by embedding the uneven surface of the first side of the workpiece in the first layer of the protective sheet material, while the second layer serves to provide a substantially planar surface that can be used to support the workpiece, in particular during a mechanical machining with forces applied to the workpiece.In addition, applying heat to the first layer via the second layer allows a uniform thermally conductive path regardless of the material and thickness of the workpiece. This enables a rapid and reaction-fast process for heating the first layer.At least when applying the heat to the first layer of the protective surface material, the first side of the workpiece preferably faces a heating means. In this way, uniform heating over the first side of the workpiece can be achieved, which has a positive effect on the leveling function of the protective surface material.The difference in the glass transition temperature and / or the melting temperature of the first and second layers makes it possible to control the moldability of the two layers. In particular, it makes it possible to heat the first layer so that it is more deformable than the second layer. More preferably, it makes it possible to control the temperature of the two layers so that the material of the first layer becomes soft enough to absorb the asperities on the first side of the workpiece. For example, the material of the first layer may plastically deform by shifting material located at a protrusion on the first side into an adjacent, less protruding region. At the same time, the second layer can substantially maintain a more rigid state that substantially prevents deformation.The first layer of the protective sheet material is preferably in contact with the first side of the workpiece. This contact of the first layer with the first side of the workpiece (i.e., in contact with or without any other intervening material) is advantageous for the first layer to accommodate asperities on the first side of the workpiece.The method may further comprise arranging the second layer of the protective sheet material on the heating means, wherein the heating means is arranged to apply heat through the second layer to the first layer of the protective sheet material.Accordingly, the heating means is arranged to apply heat to the first layer via the second layer in a controlled environment, so that it is possible to easily use a predetermined heating protocol. In other words, heat may be applied to the first layer in a predetermined manner.The second layer is preferably in contact with the heating means. In addition, the second layer of the protective sheet material can be held on the heating means under suction.When the second layer is disposed in contact with the heating medium, efficient and uniform heat transfer can be achieved. This can be further aided by using suction by an improved contact between the heating means and the second layer.The first layer and / or the second layer are preferably provided as a foil or film. This increases the adaptability to the surface of the workpiece during application and allows easy removal after machining.The first layer and the second layer are preferably formed from a polymer material (in particular polymer film(s)), wherein the polymer materials of the first and second layer are even more preferably different from one another. For example, the first layer may be formed of polyolefin or polypropylene and / or the second layer may be formed of polyethylene terephthalate (PET).Polymeric materials are easy to handle and can be easily provided as a film. By using different polymeric materials for the first and second layers, the materials or material properties can be adjusted in accordance with their function for the protective sheet material.As mentioned above, surface structures may be formed or present on the first side of the workpiece. When applying heat to the first layer of the protective surface material, the first layer is softened, so that after applying heat to the first layer of the protective surface material, the surface structures are embedded in the first layer. When applying heat to the protective sheet, it is preferred that only the first layer be softened. In other words, the first layer preferably softens (e.g., by assuming a deformable state) while the second layer remains in an undeformed, non-softened, or solid state.The first layer of the protective sheet material is preferably heated to a temperature which is above the glass transition temperature or melting temperature of the first layer, but below the glass transition temperature or melting temperature of the second layer.Accordingly, the first layer becomes deformable before the second layer, improving its embedding properties. The second layer, on the other hand, can maintain a flat surface, which, as explained above, is advantageous for supporting the workpiece during the machining. This is achieved in particular if the second layer is heated only below its glass transition temperature or melting temperature.At least the step of arranging a first side of the workpiece on the first layer of the protective sheet material and / or applying heat to the first layer of the protective sheet material may be carried out substantially under vacuum conditions, preferably in a vacuum chamber.In particular, the use of a vacuum environment during the process of applying the first layer to the workpiece prevents the entrapment of gas between the workpiece and the first layer that could otherwise form bubbles. In addition, the process of disposing, applying, or embedding the first layer can be accelerated because no gas obstructs the contact between the first layer and the workpiece.At least during or after the application of heat to the first layer of the protective surface material by its second layer, the workpiece and the protective surface material can be pressed against one another, preferably by applying a compressive load via the workpiece and / or the second layer of the protective surface material.This improves and accelerates the embedding process of the first layer, in particular in combination with a vacuum environment. In this process, in particular a displacement of the material of the first layer into depressions and around projections is assisted by mechanical pressure.This pressure can be applied via the workpiece and / or the second layer, i.e. the means for applying the pressure is arranged on this side or these sides. In either case, the pressure is applied to act on the first layer and promote the process of embedding the recesses and protrusions of the first layer-facing side of the workpiece by the first layer. Applying the pressure across the workpiece while holding the protective sheet material on a chuck table is preferable because of ease of handling.The second layer, in particular the side of the second layer opposite the side facing the first layer, may have a substantially flat shape, wherein the shape of the second layer remains substantially unchanged when heat is applied to the first layer of the protective sheet material.Before the step of heating the first layer, the side of the second layer of the protective sheet material facing away from the workpiece preferably has a planar or flat surface when placed on a planar surface, for example the surface of a chuck table or pad. Even more preferably, this also applies to the side of the first layer facing the workpiece. This state of the side(s) of the second layer remains substantially unchanged in particular even after the step of heating (and possibly of printing), wherein the side of the first layer facing the workpiece at least partially assumes the surface topography of the side of the workpiece facing the first layer.As a result, the flat side of the second layer of protective sheet material provides a planar support surface for the processing of the workpiece, with the deformed first layer enabling uniform support to be maintained on the side of the workpiece. As a result, cracks which might otherwise occur in the processing can be prevented.The present disclosure also addresses the above object by providing a preparation unit for preparing a workpiece, the preparation unit being configured to apply a protective sheet material to the workpiece. The protective sheet material includes at least a first layer disposed on the side of the workpiece and a second layer disposed on the side opposite to the workpiece side. The workpiece preparation unit includes a chuck table including a holding surface for holding the workpiece via the second layer, a heating unit, and a control unit configured to control the heating unit such that the first layer is heated via the second layer in accordance with a predetermined heating protocol.Accordingly, the preparation unit is configured to apply one of the above-described methods to a protective sheet material to attach the protective sheet material to a workpiece.Preferably, the predetermined heating protocol heats the first layer of the protective sheet material over the second layer of the protective sheet material such that the first layer softens (i.e., becomes deformable) and is capable of embedding the surface structure of the workpiece facing the first layer.Consequently, the preparation unit achieves the advantages described above for smooth support of the workpiece in subsequent machining (for example, grinding, dicing, etc.).The preparation unit includes, in particular, a pressure application means for applying a pressure load to the first layer.As described above, applying pressure assists in embedding the surface structures of the workpiece in the first layer. The pressure application means preferably has a generally planar surface to apply pressure across the workpiece side and / or the side of the second layer acting between the workpiece and the first layer during the embedding process. In other words, the pressure application means is arranged in particular on one or both sides of the pressure application.Further, the preparation unit may include a camera configured to check an exposed area of the second layer of the protective sheet material attached to the workpiece.Such a camera makes it possible to check the surface structure of the workpiece through the protective surface material and can also be used to check the result of the preparation of the workpiece for the further processing. It can in particular examine the embedding of the surface structure and / or the flatness of the exposed side of the second layer.Furthermore, the camera can be set up as a means for controlling the processing. For example, the camera may be used to adjust the position of a cutting blade or a laser beam for machining the workpiece.BRIEF DESCRIPTION OF THE DRAWINGSThe following figures schematically illustrate exemplary embodiments of a method for preparing a workpiece for machining in accordance with the present disclosure, as well as parts of a preparation unit for preparing a workpiece for machining. In these figures, like reference numerals refer to features in the drawings that have the same or an equivalent function and / or structure. It should be understood that the figures illustrate schematic examples of how the method of preparing a workpiece for machining is performed in accordance with the present invention, but do not limit the invention thereto. FIG. 1 schematically illustrates an exemplary embodiment and arrangement of a workpiece and a protective surface material used to prepare the workpiece for subsequent processing; FIG. 2 schematically illustrates the arrangement shown in FIG. 1 placed in a preparation unit for preparing the workpiece; FIG. 3 schematically illustrates an example embodiment of a method for preparing the workpiece; FIG. 4 schematically illustrates another embodiment of the process for preparing the workpiece for subsequent machining; FIG. 5 schematically illustrates inspection of the workpiece prepared in accordance with the present disclosure; FIG. 6 schematically illustrates an example of subsequent processing of a workpiece prepared in accordance with the present disclosure; and FIG. 7 schematically illustrates a workpiece formed as a wafer.DETAILED EXPLANATION OF PREFERRED EMBODIMENTSThe method for preparing a workpiece for machining and the preparation unit for preparing a workpiece for machining according to the present disclosure will be described in more detail below with reference to the accompanying drawings.In this connection, it should be mentioned that the figures schematically illustrate various embodiments of the method and parts of the preparation unit and that the dimensions of the planar materials, workpieces, machine parts are illustrated in exaggerated form (that is to say greater or smaller) for the purpose of illustration.As set forth above, the present disclosure has an object of preventing damage to a workpiece during machining thereof, particularly by mechanical machining such as grinding, dicing, and the like. During machining, forces are applied or generated that cause stresses within the workpiece. When these stresses exceed a limit of a material of the workpiece, the stresses may be released by occurrence of cracks. It is also possible that deformations of the material or residual stresses are caused by such a machining.One factor that has a significant impact and can prevent these adverse effects is proper support of the workpiece during machining. On the one hand, this support is provided by the support means of the machine which machines the workpiece. On the other hand, however, it also depends on the properties of the workpiece.As illustrated in FIG. 1, the workpiece 10 supported on a workpiece support 30 may be, for example, a wafer or an ingot. The workpiece 10 has a substrate, which can be any (semiconductor) substrate.The substrate may include, for example, a semiconductor, glass, sapphire (Al 2 O 3), ceramic, for example, alumina ceramic, quartz, zirconia, PZT (lead zirconate titanate), polycarbonate, optical crystal material, or the like. Specifically, the substrate may include silicon carbide (SiC), silicon (Si), gallium arsenide (GaAs), gallium nitride (GaN), gallium phosphide (GaP), indium arsenide (InAs), indium phosphide (InP), silicon nitride (SiN), lithium tantalate (LT), lithium niobate (LN), aluminum nitride (AlN), silicon oxide (SiO 2) or the like.The substrate may be a single crystal substrate, a glass substrate, a composite substrate such as a SiC, SiN, GaN or GaAs substrate, or a polycrystalline substrate such as a ceramic substrate.As mentioned above, the substrate may be a wafer. For example, the substrate may have a semiconductor wafer size. The term "semiconductor wafer size" here refers to a wafer having predetermined dimensions ("standardized dimensions"), in particular to the diameter (i.e. the standardized diameter, the outer diameter) of a semiconductor wafer. Such dimensions of semiconductor wafers are specified, for example, in the SEMI standards. The dimensions of polished single-crystalline silicon wafers are specified, for example, in SEMI standards M1 and M76. The semiconductor wafer may be a 3 inch, 4 inch, 5 inch, 6 inch, 8 inch, 12 inch, or 18 inch wafer.The substrate is made of a single material or a combination of different materials, for example two or more of the above materials.Functional layers or components can be formed on the substrate, in particular a wafer (see FIG. 7 ). Such functional layers or components are preferably formed on one side of the substrate. On this side, the substrate may include a central device region 15 in which devices or functional layers are formed and a peripheral edge region 16 surrounding the device region 15. In this circumferential edge region 16, preferably no components or functional layers are formed.Hereinafter, the side of the substrate or workpiece 10 having the device region 15 formed thereon will be generally referred to as the first or front side 11 of the workpiece 10. The opposite side of the substrate or workpiece 10 is referred to as the second side or back side 12 of the workpiece 10.The devices in the device region 15 may be ICs (Integrated Circuits) and LSIs (Large Area Integrations). The components can be, for example, semiconductor components, power components, optical components, medical components, electrical components, MEMS components or combinations thereof. The devices may for example comprise or be transistors such as MOSFETs, insulated gate bipolar transistors (IGBTs) or diodes such as Schottky barrier diodes.The workpiece 10 can be supported either on the front side 11 of the workpiece 10 which comprises the functional layers or components (see FIG. 3 ) or on the rear side 12 (see FIG. 4 ) opposite thereto by the workpiece support 30.The workpiece 10 is not limited to a particular shape. The workpiece 10 may be cylindrical and / or plate-shaped and include cross-sections with contours (defining a peripheral edge of the workpiece 10) that are substantially round, such as oval or circular. In other words, the workpiece 10 can have a generally round shape in plan view, in particular an oval or circular shape.However, the workpiece 10 may include at least one linear portion (not illustrated) or a notch 13 along the contours of the cross sections. In particular, in a plan view (or a cross section perpendicular to its longitudinal axis), the workpiece 10 may have a polygonal (plate) shape, for example a square or rectangular shape. Plate-shaped in this context means that the workpiece 10 comprises a thickness, i.e. a longitudinal dimension, which is significantly smaller than a transverse / lateral dimension, for example a diameter, of the workpiece 10.The front side 11 and / or the rear side 12 of the workpiece 10 is preferably substantially parallel. Moreover, the back side 12 of the workpiece 10 may be substantially flat or planar. However, the workpiece 10 has differences in height at least on its front side 11. When a device region 15 is formed on the front side 11 of the workpiece 10, the front side 11 may be formed with multiple protrusions, for example bumps, protruding from the functional layer. Accordingly, the protrusions result in an uneven front side 11 or surface of the workpiece 10.In addition, the workpiece 10 and in particular the functional layer can also comprise depressions, such as grooves, for example. These grooves can be formed, for example, in the form of separating lines between the components. Along these parting lines, the workpiece 10 is intended to be divided in order to obtain individual component chips. Furthermore, the functional layer formed on the front side 11 itself may have height differences (with or without contact bumps).Accordingly, the front side 11 of the workpiece 10 may have an uneven surface (i.e., a surface structure) due to the presence of a plurality of devices or device chips.The following example is used to describe how an uneven surface on the front side 11 of a workpiece 10 is compensated for by the application of a protective sheet material 20 in accordance with the present disclosure. Preferably, the protective surface material 20 comprises or consists of at least a first layer 21 and a second layer 22. The protective surface material 20 is configured to adapt to the shape of the workpiece 10 on one side and to provide a planar support surface on the other side opposite the one side.The first layer 21 and the second layer 22 may be provided as separate layers to be attached to each other to form the protective sheet 20, or may be provided as a prefabricated protective sheet 20 (for example, a double-layer film). The protective sheet material may include an adhesive layer with which the first layer 21 and the second layer 22 may be attached to each other. Unlike a plate, a film has substantially no bending rigidity when a force is applied perpendicularly to the film. The film is preferably formed as a sheet material or can be applied by spray coating.As illustrated in FIG. 1, the protective sheet material 20 is to be arranged on the first side 11 of the workpiece 10, wherein the first layer 21 faces the workpiece 10 and the second layer 22 faces in the opposite direction, i.e. away from the workpiece 10.The first layer 21 of the protective surface material is configured such that it can adapt to the surface structure (i.e. projections and / or depressions) present on the front side 11 of the workpiece 10. The protrusions and recesses may be defined based on an average height (arithmetic) or a median height. Alternatively, the peripheral edge portion 16 (where no devices, division lines or streets, chamfered or rounded edges are formed) may have the original height of the bare wafer and be used as a reference height.In contrast, the second layer 22 is configured such that it substantially retains its shape at least or in particular on the side facing away from the workpiece side of the protective surface material 20, while the first layer 21, as described in more detail further below, adapts its shape. For reasons which will be explained in detail further below, the second layer 22 can also be configured for improved heat transfer. In such an embodiment, the second layer 22 may provide a support surface that is substantially flat and parallel to the second side 12 of the workpiece 10.These differing properties of the first layer 21 and the second layer 22 of the protective sheet 20 allow to provide uniform support over a planar surface on the side of the second layer 22 (i.e., its exposed side with respect to the protective sheet 20) and to maintain this uniform support substantially at the interface between the first layer 21 and the front side 11 of the workpiece 10.Preferably, the protective sheet 20 is applied as a unit when a first side 11 of the workpiece 10 and the first layer 21 of the protective sheet 20 are combined. Moreover, the first layer 21 is made deformable so that it can adapt its shape (at least partially and permanently), while the second layer attached to the first layer is more preferably substantially non-deformable (i.e. it is substantially not subject to plastic deformation). It can also be configured for increased absorption of heat.For the different functions of these layers, the first layer 21 and the second layer 22 are preferably made of a polymer material and are provided in particular as polymer films. Polymeric materials have the advantage that they can be manipulated to have the material properties that fulfil the functions of the first layer 21 and the second layer 22 of the protective sheet material 20. As explained above, the films used preferably have fundamentally no appreciable bending stiffness. This is particularly advantageous for the first layer 21, which is configured such that it adapts to the surface structure of the first side 11 of the workpiece 10.In addition, the polymer materials of the first and second layers 21, 22 are preferably different from each other. The first layer 21 is formed in particular from polyolefin and / or polypropylene, while the second layer 22 is formed in particular from polyethylene terephthalate (PET).Preferably, the first layer 21 is at least partially directly attached (i.e. in physical contact) to the front side 11 of the workpiece 10. If a (central) component region 15 is present, the first layer 21 is in contact with the component region 15 in particular and can be in contact with the entire front side 11 (that is to say also with the (preferably completely) surrounding circumferential edge region 16). The extent of the contact may depend on the mounting technique of the first layer 21 on the front side 11.The first layer 21 is preferably mounted on the entire surface of the front side 11 of the workpiece 10 without an adhesive being present between the protective sheet material 20 and the workpiece 10. The assembly may be performed, for example, by the steps of bonding the first side 11 of the workpiece 10 and the first layer 21 of the protective sheet material 20 together and applying heat to the first layer 21 of the protective sheet material 20 through the second layer thereof. In other words, the first layer 21 can be attached directly to the front side 11 together with the step of embedding the surface structure of the front side 11 of the workpiece in the first layer 21 of the protective sheet material 20 without any adhesive therebetween.This prevents components or a functional layer formed on the front side 11 of the workpiece 10 from being contaminated with an adhesive. In addition, the detachment of the workpiece 10 from the protective surface material 20 and the cleaning of the workpiece 10 (if any) are facilitated.Nevertheless, and alternatively, the protective sheet 20 described above may include an adhesive. In this case, the adhesive is disposed on the side facing the workpiece 10. The adhesive is provided on a peripheral portion of the protective sheet 20, more specifically, on an entire peripheral portion of the first layer 21 facing the first side 11 of the workpiece 10. The peripheral portion provided with an adhesive preferably corresponds to a peripheral edge region 16 which surrounds the (central) component region 15 of the workpiece 10.In embodiments in which the protective sheet 20 includes an adhesive disposed on the side facing the workpiece 10, it is preferable that the adhesive comes into contact with the peripheral edge portion 16 surrounding the component portion 15 of the workpiece 10 in a state in which the front surface 11 of the workpiece 10 is disposed on the protective sheet 20. In other words, it is particularly preferred that the adhesive does not come into contact with the component region 15 of the workpiece 10.In the case that an adhesive is arranged in the peripheral edge region 16 surrounding the component region 15 of the workpiece 10, any height differences which can be caused by the adhesive or the adhesive layer are preferably likewise compensated by the first layer 21 or embedded therein.In addition, the first layer 21 and the second layer 22 are preferably attached to each other without an adhesive therebetween. Nevertheless, an adhesive layer may be used to attach the first and second layers 21, 22 to each other. Accordingly, this adhesive does not come into contact with the first side 11 of the workpiece 10. The use of such an adhesive layer facilitates the handling of the protective surface material, in particular in combination with the workpiece 10.As illustrated in FIGS. 1-6, the protective sheet material 20 may include a peripheral surplus portion that extends laterally beyond the lateral dimensions of the workpiece 10 to mount the workpiece 10 to a support frame 40. The support frame 40 is preferably a ring frame (ring frame). The ring frame may surround the workpiece 10.The support frame 40 is attached to the protective sheet 20, in particular to the first layer 21. A peripheral portion of the protective sheet 20 (layer 21) is attached to the support frame 40 such that the protective sheet 20 closes a central opening of the support frame 40, for example, the area inside the inner diameter of a ring frame.As illustrated, the ring frame 40 is preferably attached to the side of the protective sheet 20 facing the workpiece 10 (i.e., the first layer 21). However, the ring frame 40 may be provided on the opposite side of the protective sheet 20.The step of attaching the ring frame 40 to the protective sheet 20 may be performed before or during the joining of the protective sheet 20 and the workpiece 10. In this way, the handling of the protective surface material 20, in particular when attaching the protective surface material 20 to the workpiece 10, is facilitated.In addition, after disposing the protective sheet 20 on the workpiece 10, the workpiece 10 can be more easily handled by the support frame 40 via the protective sheet 20. This facilitates the handling and transport of the workpiece 10.Each of the above-described assembling steps may be performed under vacuum (i.e., in a vacuum chamber). In particular, as illustrated in FIG. 1, the application of the protective sheet material 20 is preferably carried out in a vacuum during and / or after the application or lamination of the protective sheet material 20.The use of vacuum (i.e., a vacuum) results in the protective sheet 20 following the height differences (i.e., the protrusions or depressions) on the front side 11 of the workpiece 10 in an improved manner. As a result, the protective sheet material 20 can be attached more securely since at least fewer cavities and / or air bubbles are present between the protective sheet material 20 and the first side 11 of the workpiece 10. These could otherwise cause the protective surface material 20 to unintentionally detach from the workpiece 10. This improves the attachment of the protective sheet 20 to the workpiece 10.A vacuum environment also enables, in particular, a secure attachment to the first side 11 of the workpiece 10, in particular in its central region (for example corresponding to a component region 15 on the substrate of the workpiece 10), without the use of an adhesive. When no adhesive is used, the protective sheet 20 (in particular the first layer 21) can be easily and completely removed from the front side 11 of the workpiece 10, so that substantially no post-processing of the workpiece for removing residual material may be required. In other words, the protective surface material 20 is not provided permanently (for example, it is not part of the singulated components or end products), but is removed after the workpiece 10 has been processed.The step or steps of arranging the protective sheet material 20 on the first side 11 of the workpiece 10 may be performed in a vacuum chamber, for example, as follows.After the workpiece 10 and the protective sheet 20 are loaded into the vacuum chamber, the chamber is evacuated. Optionally, air may be supplied to a rubber membrane via an air inlet port, thereby causing the rubber membrane to expand into the evacuated chamber and act as a pressure application means, which will be described in detail below (see FIGS. 3 and 4 ). In this way, the rubber diaphragm is moved in the vacuum chamber against the workpiece 10 to press the protective sheet 20 against the first side 11 of the workpiece 10.Alternatively or additionally, a pressure die 35 may be used to press the protective sheet material 20 and the first side 11 of the workpiece 10 against each other (see FIGS. 3 and 4 ). Such a printing die is substantially rigid compared to the protective sheet 20 to provide a generally planar surface on the side of the second layer 22 which contacts the printing die 35 upon application of the pressure.Subsequently, the vacuum in the vacuum chamber is released and the protective sheet 20 is held in position on the first side 11 of the workpiece 10 by the attachment force generated between the protective sheet 20 and the workpiece 10. When releasing the vacuum, the atmospheric pressure may also apply a pressing force that causes the protective sheet 20 and the workpiece 10 to be compressed. This may also relate to supporting the embedding process in the first layer 21 in connection with the present disclosure.In addition, the vacuum chamber can be used to apply the protective sheet material 20 to the first side 11 of the workpiece 10 via a vacuum (for example without applying additional pressure by the printing die 35 or a membrane). In either case, the above-described step of heating and applying pressure may be performed after the vacuum is released or after the workpiece 10, including the protective surface material, is removed from the vacuum chamber (i.e., additionally or alternatively).Further, as illustrated in FIGS. 1-6 and as described above, the protective sheet 20 is preferably applied to the workpiece 10 in a pre-assembled state (i.e., the layers 21 and 22 have already been joined prior to carrying out the present method) or may be joined as part of the present method. Accordingly, the method may comprise the step of applying a first layer 21 of the protective sheet material 20 with or without an adhesive, which substantially corresponds to a peripheral edge region 16 surrounding the (central) component region 15 of the workpiece 10, to the front side 11 of the workpiece 10. Then, the second layer 22 of the protective sheet material 20 is applied to the first layer 21 with or without an adhesive between the first and second layers 21, 22. However, it is preferable to attach the second layer 22 to the first layer 21 before applying the joined protective sheet 20 to the first side 11 of the workpiece 10.In any case, the application of one of the layers 21, 22 of the protective sheet material 20 is also preferably carried out under vacuum (i.e. by using a vacuum chamber). Moreover, the method may use heat during and / or after any or all of the application or lamination operations described above.As indicated in FIG. 2, after the first side 11 of the workpiece 10 and the first layer 21 of the protective sheet material 20 have been joined by the second layer 22 of the protective sheet material, heat is applied to the first layer 21 of the protective sheet material 20 by a heating means 32. Accordingly, the heating means is disposed on the side of the second layer 22 of the protective sheet material. The heating means 32 may be integrated into a workpiece support 30 (see FIGS. 2 and 3 ) or into a printing die (see FIG. 4 ).A heating surface 36 of the heating means 32 is preferably in contact with the second layer 22. Accordingly, the heat from the heating means 32 is transferred into and through the second layer 22 to the first layer 21 of the protective sheet material and preferably reaches the side or surface of the first layer 21 facing the first side 11 of the workpiece 10.The heat of the heating medium 32 transferred to the first layer 21 is controlled so as to cause the first layer 21 to become softer. In particular, the heat is arranged to cause the first layer 21 to transition from a solid state to a soft state in which the first layer may plastically deform or the material of the first layer may be displaced from regions of high compression to regions of lower compression. A fluid state in this context means that the material of the first layer 21 of the protective surface material can flow to an extent that a surface structure of the first side 11 of the workpiece 10 can be embedded. In other words, projections are embedded on the first side 11 and depressions are filled by the material of the first layer 21 of the protective surface material 20.This embedding process is preferably assisted by heating the first layer 21 of the protective sheet 20 to at least its glass transition temperature, but preferably below its melting temperature, to avoid first layer tackiness (i.e., the first layer has adhesive properties that cause it to adhere to the first side 11 of the workpiece 10).The first layer 21 is in particular heated to a temperature that makes the material soft enough to compensate for unevenness, but does not result in the material developing adhesive properties or adhesive properties to an extent that upon removal of the protective sheet material 20 residues remain adhered to the first side 11. Nevertheless, the first layer 21 may be heated beyond the melting temperature of its material unless this results in such adverse adhesion properties.For example, when the above-mentioned materials are used for the first layer 21 (particularly polyolefin or polypropylene), temperatures of at least 60° C. to 160° C., particularly 100° C. to 160° C., are preferred. At this temperature, the first layer 21 becomes sufficiently soft to embed the height differences on the first side 11 of the workpiece 10, while the second layer 22 can substantially maintain its original flatness.In this regard, the heat applied to the first layer 21 via the heating surface 36 preferably results in a temperature of the second layer 22 of the protective sheet material 20 that is at least 30° C., 40° C., 50° C., 60° C., or 70° C. below the melting temperature and is preferably higher than the glass transition temperature of the material of the first layer 21 of the protective sheet material 20.However, it may also be lower than the glass transition temperature by 5° C., 10° C., 15° C., 20° C. or 25° C. In such a case, in particular, the planar shape of the second layer 22 of the protective sheet 20 may remain substantially unchanged.Preferably, the second layer 22 or the side of the second layer 22 of the protective sheet material 20 is held on the heating surface 36 of the heating means 32 under suction. Accordingly, the heating surface 36 may be at least partially a porous surface or may include suction grooves to generate the negative pressure for holding the protective sheet material 20 under suction.The heating process is selected in particular such that the surface structures of the first side 11 of the workpiece 10 (i.e. the volume of the projections and / or depressions of a functional layer of the workpiece 10) are embedded by at least 80%, 85%, 90%, 95% or 98%.The temperature of the first layer 21 of the protective sheet material is preferably maintained for 15 seconds up to 180 seconds. Although a shorter time is preferred in terms of productivity, it should also be appreciated that a longer time allows the stresses acting on the first side 11 of the workpiece 10 to be reduced during heating (and in this case during the application of pressure, as explained further below). A longer time also allows better embedding and pressurization, which involves less risk of damaging the workpiece 10.The heating protocol for performing the heating of the first layer 21 over the second layer 22 of the protective sheet material is preferably a predetermined heating protocol. In other words, the heating operation may be determined in advance through experiments. This is facilitated by performing the heating operation from the side of the protective sheet 20.To determine and evaluate the parameters for the heating protocol in these experiments, the level of embedding described above may be chosen. One possibility for determining whether the embedding is sufficient or not may consist, for example, in checking the front side 11 of the workpiece 10, in particular from the side of the second layer 22, for air bubbles optically (for example by means of a microscope or a camera).Alternatively or additionally, the extent of cracks, fractures or defective components (in particular after mechanical processing) can also be used as a parameter in order to determine the heating protocol. A given heating protocol has the advantage of high productivity and less complex production control, as real-time temperature control is not required (although it may still be used).The heating operation is preferably carried out under vacuum conditions as described above with respect to the mounting of the protective sheet 20.As illustrated in FIGS. 3 and 4, a pressure application means that applies pressure may be used to improve the embedding of the first side 11 of the workpiece 10 in the first layer 21 of the protective sheet material 20. The application of pressure by the pressure application means is preferably carried out at least during and / or after the application of heat described above. Particularly in applying the pressure, the above-mentioned heating time is preferably more than 30 seconds, and more preferably more than 60 seconds, in order to reduce stress peaks during the embedding process.In contrast to applying heat to the side of the second layer 22 of the protective sheet material 20, the pressure application means may apply pressure from one (see FIGS. 3 and 4 ) or both sides 11, 12 of the workpiece 10.In FIG. 3, the pressure applying means applies pressure from the second side or the back side 12 of the workpiece 10 by using a pressure die 35. Accordingly, the heating means 32 is arranged on the side opposite thereto, i.e. the front side 11 of the workpiece 10, where the protective sheet material 20 has been arranged.In this embodiment, the protective sheet material is disposed on a workpiece support 30 (for example, a chuck table) including a heating means 32. As described above, the side of the heating means 32 having a heating surface 36 (which also serves as a holding surface 31 of the workpiece support 30 in FIG. 3 ) is preferably configured to hold the second layer 22 of the protective sheet material 20 under suction.In FIG. 4, the pressure applying means applies the pressure from the first side or front side 11 of the workpiece 10. Consequently, the pressure is applied via the protective sheet 20. Accordingly, both the pressure applying means and the heating means 32 are located on the side of the first side 11 of the workpiece 10, and in FIG. 4, they are contained in a printing die 35. In particular due to the heating means 32, the printing stamp 35 can also be configured to hold the protective surface material 20 under suction. In the exemplary embodiment of FIG. 4, the second side 12 of the workpiece 10 is placed on a holding surface 31 of a workpiece support 30 in the form of a clamping table.Instead of a pressure die 35 for applying pressure, the above-mentioned diaphragm or the like may be used. Preferably, the pressure application means comprises a rigid, flat surface. Such a rigid flat surface is advantageous in achieving an improved flat support surface on the side of the second layer 22 of the protective sheet 20, particularly in the case that the second layer 22 of the protective sheet is an arcuate film.The application of the protective sheet material 20 by using heat, in particular in combination with pressure, may result in a positive engagement of the first layer 21 with the surface structure of the first side 11 of the workpiece 10 (i.e. an interlocked relationship between the first layer 21 and the surface structure of the first side 11 of the workpiece 10). Regardless of theoretical considerations, it is assumed that this form-fit is achieved by the material of the first layer 21 flowing around the projections and depressions of the surface structure of the first side or deforming into the latter.As illustrated in FIG. 5, the preparation unit may also include a camera 50 for checking the protective surface material 20 attached to the first side 11 of the workpiece 10 and / or to the first side 11 of the workpiece 10. The camera 50 is disposed on the side of the protective sheet material 20, while the workpiece 10 is supported by an opposing workpiece support (not shown).The camera 50 may be used to detect air bubbles (e.g., to determine the degree of embedding by volume or area). In this embodiment, a visible light camera can be used if the protective sheet material is transmissive to the respective wavelengths. Otherwise, an infrared camera may be used to check the first side 11 of the workpiece 10.Another embodiment that includes a camera 150 is illustrated in FIG. 6. Here, the camera 150 may be used to assist in inspecting and / or machining the workpiece 10. As schematically shown, the workpiece 10 is supported on a workpiece support 30 on its first side 11, i.e. with the protective surface material arranged therebetween. As in the exemplary embodiment shown in FIG. 5, the camera 150 may be an infrared camera or a visible light camera. In the latter case, the workpiece support 30 (for example, made of a transparent material such as glass) and the protective sheet 20 are preferably transmissive for the wavelengths of visible light.Generally, the materials located between the camera 50, 150 and the object to be observed (in particular the first side 11 of the workpiece 10) should be transmissive to the wavelength(s) that the camera 50, 150 can capture.In FIG. 6, the camera may be used to check the result of embedding as described above. In addition, it can be used additionally or alternatively for assistance in the machining of the workpiece 10. In FIG. 6, this is schematically illustrated by the cutting blade 60. For example, the camera 150 allows intersecting parting lines or streets or cut position alignment marks formed on the first side 11 of the workpiece 10 to be detected to properly position the cutting blade 60 for dividing the workpiece 10 into individual device chips. Accordingly, FIG. 6 shows an example of the mechanical machining of the workpiece 10 with the enhanced support provided by the protective sheet material previously attached to the first side 11 of the workpiece 10.In addition, in further embodiments, the protective sheet material 20 can also have one or more additional layers. Further layers of the protective sheet material 20 may be formed of the same or a different material as the layers of the protective sheet material 20.The protective sheet 20 may have a thickness in the range of 100 to 500 μm, preferably 100 to 300 μm, and more preferably 150 to 200 μm. In particular, the first layer 21 of the protective surface material 20 has a thickness that is greater than the difference between the highest and the lowest point of a surface structure that is located on the first side 11 of the workpiece 10.REFERENCE NUMERALS1, 101 Preparation unit 10 Workpiece 11 First side or front side 12 Second side or rear side 13 Notch 14 Street 15 Component region 16 Peripheral edge region 20 Protective sheet material 21 First layer 22 Second layer 30 Workpiece support (for example, chuck table) 31 Holding surface 32 Heating means 35 Printing die 36 Heating surface 40 Supporting frame 50, 150 Camera 60 Cutting bladeReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedUS 2017 / 062278 A1

[0005] JP 2013-021017 A

[0006] US 2020 / 335 382 A1

[0007]

Claims

A method of preparing a workpiece (10) for machining, comprising: providing the workpiece (10); providing a protective sheet material (20) having at least a first layer (21) and a second layer (22), the second layer (22) being formed of a material having a higher glass transition temperature or melting temperature than the first layer (21); merging a first side (11) of the workpiece (10) and the first layer (21) of the protective sheet material (20); and applying heat to the first layer (21) of the protective sheet material (20) through the second layer (22) thereof.The method according to claim 1, wherein when applying heat to the first layer (21) of the protective sheet material (20), the first side (11) of the workpiece (10) faces a heating means (32), and the first layer (21) of the protective sheet material (20) is preferably in contact with the first side (11) of the workpiece (10).The method of claim 2, further comprising: disposing the second layer (22) of the protective sheet material (20) on the heating means (32), wherein the heating means is configured to apply heat to the first layer (21) of the protective sheet material (20) through the second layer (22) thereof, wherein the second layer (22) is preferably in contact with the heating means (32).Method according to claim 3, wherein the second layer (22) of the protective sheet material (20) is held on the heating means (32) under suction.The method of any preceding claim, wherein the first layer (21) and the second layer (22) are formed from a polymeric material, and wherein the polymeric materials of the first and second layers are different.The method according to claim 5, wherein the first layer (21) is formed from polyolefin or polypropylene, and / or wherein the second layer (22) is formed from polyethylene terephthalate.Method according to one of the preceding claims, wherein surface structures are formed on the first side (11) of the workpiece (10), and wherein, when heat is applied to the first layer (21) of the protective sheet material (20), the first layer (22) is softened such that the surface structures are embedded in the first layer (21), and wherein, when heat is applied to the protective sheet material (20), preferably only the first layer (21) is softened.The method according to any one of the preceding claims, wherein the first layer (21) of the protective sheet material (20) is heated to a temperature that is above the glass transition temperature or melting temperature of the first layer (21) but below the glass transition temperature or melting temperature of the second layer (22).Method according to any of the preceding claims, wherein the step of arranging a first side (11) of the workpiece (10) on the first layer (21) of the protective sheet material (20) and / or applying heat to the first layer (21) of the protective sheet material (20) is carried out substantially under vacuum conditions, preferably within a vacuum chamber.Method according to one of the preceding claims, in which during or after the application of heat to the first layer (21) of the protective surface material (20) by means of its second layer (22), the workpiece (10) and the protective surface material (20) are pressed against one another, preferably by application of a compressive load over the workpiece (10) and / or the second layer (22) of the protective surface material (20).Method according to any of the preceding claims, wherein the second layer (22), in particular the side of the second layer (22) opposite to the side facing the first layer (21), has a substantially flat shape, and wherein when heat is applied to the first layer (21) of the protective sheet material (20), the shape of the second layer (22) remains substantially unchanged.A preparation unit (1; 101) for preparing a workpiece (10), the preparation unit being configured to attach a protective sheet (20) to the workpiece (10), and the protective sheet (20) having at least a first layer (21) to be disposed on the side of the workpiece and a second layer (22) to be disposed on the side opposite to the side of the workpiece, the workpiece preparation unit comprising: a workpiece support (30) including a holding surface (31) for holding the workpiece (10) via the second layer (22); a heating means (32); and a control unit configured to control the heating means (32) so that the first layer (21) is heated via the second layer (22) in accordance with a predetermined heating protocol.The preparation unit (1) according to claim 12, further comprising a pressure application means arranged to apply a pressure load to the first layer (21).The preparation unit (1) according to claim 12 or 13, further comprising a camera (50) arranged to inspect an exposed area of the second layer (22) of the protective sheet material (20) attached to the workpiece (10).

Images