WO2018130278A1

WO2018130278A1 - Method and apparatus for processing a substrate

Info

Publication number: WO2018130278A1
Application number: PCT/EP2017/050494
Authority: WO
Inventors: Bernhard G. Mueller
Original assignee: Applied Materials, Inc.
Priority date: 2017-01-11
Filing date: 2017-01-11
Publication date: 2018-07-19
Also published as: TWI746739B; CN110178238A; CN110178238B; TW201837988A

Abstract

According to one aspect of the present disclosure, a method and an apparatus for processing a substrate (10), e.g. a display element, are described. The substrate has an electrically insulating back side (12) and a front side (14) opposite the electrically insulating back side. The method includes: coating the electrically insulating back side (12) with a conductive layer (20) to provide a conductive back side (22), connecting the conductive back side with ground (25) or with a reference potential, and processing of the substrate, particularly of the front side and/or of one or more electronic devices (32) formed on the front side. Further, an apparatus for processing of a substrate is described. According to a further aspect, a display element including a substrate (10) having an electrically insulating back side coated with a conductive layer (20) is described.

Description

METHOD AND APPARATUS FOR PROCESSING A SUBSTRATE

TECHNICAL FIELD

[0001] Embodiments of the present disclosure relate to the processing of substrates, particularly for the manufacture of display elements. Embodiments of the present disclosure particularly relate to methods and apparatuses for the processing of substrates having one or more electronic devices formed on a front side of the substrate. Further, a display element manufactured according to the methods described herein is provided.

BACKGROUND [0002] A current trend is the manufacture of an increasing number of electronic and particularly optoelectronic devices on substrates, e.g. in order to provide displays, circuit boards and/or solar cells. In particular, there is an increasing demand for flat display elements such as flat screens. The standards for liquid crystal displays (LCD) and other display elements, in which control elements, for example thin film transistors (TFTs), are used, increase. In addition, the increasing resolution of displays leads to decreasing structure dimensions (critical dimensions) and to a decreased layer thickness which raises the sensitivity for ESD caused defects of those display devices. These display elements typically have pixels arranged in a matrix, wherein the pixels each provide an electronic device that is to be functional. Yet, also in other fields an increasing amount of electronic devices is to be formed on a substrate. These electronic devices include for example thin film transistors, connection networks of a chip, transistors, electron emitters of an emitter array, the electrodes for pixels of a display, and/or other devices, which may distinguish themselves in particular by being present as a plurality of elements (e.g. more than 100.000 up to several 1.000.000). Each element may be electrically controllable. [0003] For thin film deposition in the field of manufacturing electronic devices on substrates, e.g. consumer electronic devices, the testing of the electronic devices on a substrate is a task that is typically to be conducted. In order to obtain, for example, a good image quality of a display element, only a few of the several million pixels are allowed to be defective. For guaranteeing a cost efficient production, it is therefore beneficial to provide high-capacity in-situ test methods.

[0004] The substrate of a flat panel display may be made of glass or of another insulating material. Charges which may accumulate on the surfaces of the substrate during handling and processing of the substrate may lead to an electrical polarization of the substrate. This may increase the risk of damage by electrostatic discharge (ESD) during handling and processing of the substrate. Accordingly, it would be beneficial to protect a substrate from damage which may be caused by electrostatic discharge.

SUMMARY

[0005] In light of the above, a method of processing a substrate, an apparatus for processing of a substrate as well as a display element including a substrate are provided.

[0006] According to one aspect of the present disclosure, a method of processing a substrate is provided, wherein the substrate has an electrically insulating back side and a front side opposite the electrically insulating back side. The method includes coating the electrically insulating back side with a conductive layer to provide a conductive back side, connecting the conductive back side with ground or with a reference potential, and processing of the substrate.

[0007] Processing of the substrate may include processing of the front side and/or of one or more electronic devices formed on the front side.

[0008] According to a further aspect, an apparatus for processing a substrate is provided, wherein the substrate has an electrically insulating back side and a front side opposite the electrically insulating back side. The apparatus includes a first coater for coating the electrically insulating back side with a conductive layer to provide a conductive back side, a substrate support configured for supporting the substrate and for connecting the conductive back side with ground or with a reference potential, and a processing device configured for processing of the front side and/or of one or more electronic devices formed on the front side.

[0009] According to yet another aspect, a display element, particularly a display element processed according to any of the methods described herein, is provided. The display element includes a substrate with an electrically insulating back side and a front side opposite the electrically insulating back side, wherein one or more electronic devices, particularly thin film transistors and/or display pixels, are formed on the front side, wherein the electrically insulating back side is coated with a conductive layer to provide a conductive back side of the substrate. [0010] Further aspects, advantages, and features of the present disclosure are apparent from the dependent claims, the description, and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments. The accompanying drawings relate to embodiments of the disclosure and are described in the following. Typical embodiments are depicted in the drawings and are detailed in the description which follows.

[0012] FIG. 1 is a schematic diagram illustrating various stages of a method of processing a substrate according to some embodiments described herein;

[0013] FIG. 2 is a schematic diagram illustrating various stages of a method of processing a substrate according to some embodiments described herein;

[0014] FIG. 3 is a schematic diagram illustrating various stages of a method of processing a substrate according to some embodiments described herein; [0015] FIG. 4 is a schematic diagram illustrating various stages of a method of processing a substrate of a comparative example; [0016] FIG. 5 is a schematic diagram illustrating optional further stages of a method of processing a substrate according to some embodiments described herein;

[0017] FIG. 6 is a schematic view of an apparatus for processing a substrate according to some embodiments described herein; and

[0018] FIG. 7 is a flow diagram illustrating a method of processing a substrate according to embodiments described herein.

DETAILED DESCRIPTION

[0019] Reference will now be made in detail to the various embodiments, one or more examples of which are illustrated in each figure. Each example is provided by way of explanation and is not meant as a limitation. For example, features illustrated or described as part of one embodiment can be used on or in conjunction with any other embodiment to yield yet a further embodiment. It is intended that the present disclosure includes such modifications and variations.

[0020] Within the following description of the drawings, the same reference numbers refer to the same or to similar components. Generally, only the differences with respect to the individual embodiments are described. Unless specified otherwise, the description of a part or aspect in one embodiment applies to a corresponding part or aspect in another embodiment as well.

[0021] The term "substrate" as used herein embraces both inflexible substrates, e.g., a glass substrate or a glass plate, and flexible substrates, such as a web or a foil. The substrate may be a coated substrate, wherein one or more thin layers of materials are coated or deposited on a front side of the substrate, for example by a physical vapor deposition (PVD) process or a chemical vapor deposition process (CVD). For example, the substrate may include one or more electronic devices deposited on the front side of the substrate, e.g. via masked deposition and/or patterning. The electronic devices may be provided on a thin transparent foil which may be attached to the front side of the substrate. In other embodiments, the substrate may be an uncoated substrate, e.g. an uncoated glass plate. [0022] Typically, flat panel displays, e.g. LCD displays, OLED displays or other flat panel displays include an insulating substrate which may be inflexible or which may have a restricted flexibility. Yet, also flexible displays may be manufactured. A cost effective manufacturing of flexible displays becomes possible when the manufacture process is done from roll to roll. For example, layers can be deposited and patterned to produce a transistor array on a flexible substrate while the substrate moves from one roll to another other roll. There are also concepts to print the transistor array on the flexible substrate, and for functional testing of the transistor array on the flexible substrate.

[0023] Embodiments described herein in particular relate to large area substrates, more particularly to large area substrates for the display market, e.g. large area glass substrates.

According to some embodiments, large area substrates may have a size of at least 1 m², e.g. 2 m² or more, 4 m² or more, or 8 m² or more. For example, the size may be from about 1.375 ni (1100 mm x 1250 mm- Gen 5) to about 9 m², more specifically from about 2 m² to about 9 m² or even up to 12 m². The substrates or substrate receiving areas, for which the structures, apparatuses, and methods according to embodiments described herein are provided, can be large area substrates as described herein. For instance, a large area substrate can be GEN 5, which corresponds to about 1.375 m² substrates (1.1 m x 1.25 m), GEN 7.5, which corresponds to about 4.39 m² substrates (1.95 m x 2.25 m), GEN 8.5, which corresponds to about 5.7m² substrates (2.2 m x 2.5 m), or even GEN 10, which corresponds to about 9 m² substrates (2.88 m x 3130 m). Even larger generations such as

GEN 11 and GEN 12 and corresponding substrate areas can similarly be implemented.

[0024] Substrates which may be used for the manufacture of electronic elements, e.g. displays, typically have an electrically insulating back side, e.g. a glass back side, and a front side opposite the electrically insulating back side. Active layers and/or active elements, e.g. pixels of a display, transistors, other electronic or optoelectronic devices, conductive layers, spacer layers and/or other layers or devices are typically formed on the front side of the substrate which is arranged opposite the electrically insulating back side. The electronic devices may be provided directly or indirectly on the front side of the substrate. For example, the electronic devices may be formed on a thin plastic foil which may be attached directly or indirectly to the front side of the substrate. [0025] An electrical polarization of the substrate, e.g. due to electrical charges on one or both of the electrically insulating back side and the front side, may increase the danger of damage by electrostatic discharge (ESD). A specifically high risk applies to substrates which have an electrically insulating back side, e.g. to glass substrates. Charges may accumulate on the electrically insulating back side, e.g. during handling and/or transport of the substrate, and the charged insulating back side cannot be completely discharged and causes polarization of the substrate. The polarization may cause extreme voltage peaks during handling, which can damage or even destroy structures on the front side of the substrate, e.g. transistors or pixels. This may result in a yield loss of several %.

[0026] The trend to thinner substrates may amplify this polarization effect and the risks associated therewith. With decreasing substrate thickness and smaller critical dimensioning, the electronic devices become more and more sensitive to ESD damage. A better ESD control is beneficial for protecting yield from ESD especially for mobile devices. A method of controlling the charges on the substrate surfaces and/or a method of reducing or eliminating an electrical field which may cause a polarization between the front side and the back side of a substrate would be beneficial. According to embodiments described herein, a method of processing a substrate with a reduced risk of ESD damage is provided.

[0027] FIG. 1 is a schematic diagram for illustrating various stages of a method of processing a substrate 10 according to embodiments described herein. The substrate 10 has an electrically insulating back side 12 and a front side 14 opposite the electrically insulating back side 12. In some embodiments, the front side 14 may be provided with one or more electrical devices and/or layers formed thereon. For example, a plurality of pixels and/or transistors may be formed on the front side 14.

[0028] Stage a) of FIG. 1 shows the substrate 10, e.g. a large area glass substrate, with the electrically insulating back side 12 and the front side 14.

[0029] In stage b) of FIG. 1, the electrically insulating back side 12 is coated with a conductive layer 20, in order to provide a conductive back side 22 of the substrate 10. The conductive layer 20 may cover the insulating back side 12 of the substrate at least partially, particularly over an area of more than 50% of the insulating back side, more particularly over an area of more than 80% of the insulating back side. More particularly, the conductive layer 20 may essentially completely cover the insulating back side of the substrate 10. Accordingly, a substrate 10 with a conductive back side 22 is provided.

[0030] For example, the insulating back side 12 of the substrate is coated with an electrically conductive coating, e.g. a metal, a transparent conductive oxide layer (TCO layer) or another layer having a conductivity higher than the conductivity of the substrate. In particular, the conductive layer may be or include an antistatic material or an electrostatic discharge material (ESD material), i.e. a material that reduces static electricity for protecting electrostatic-sensitive devices.

[0031] In some embodiments, which may be combined with other embodiments described herein, the conductive layer 20 includes a material with a low conductivity. The conductive layer may have a sheet resistance in the range of several mega ohm, e.g. a sheet resistance (Ohms per square) of lx 10⁴ or more and lx 10⁹ or less, particularly lx 10⁵ or more and 1x10 or less.

[0032] In stage c) of FIG. 1 , the conductive back side 20 is connected with ground 25 or with a reference potential, e.g. via a high resistance connection 27. Accordingly, electrical charges which may be present on the conductive back side 22 may be reduced or even eliminated and an electrically neutral back side may be provided. The risk of damage caused by ESD can be reduced.

[0033] Simultaneously and/or subsequently, the substrate may be processed. In particular, the front side 14 and/or the one or more electronic devices formed on the front side may be processed (as denoted with reference numeral 30). For example, during the processing 30, the conductive back side 20 may remain continuously connected with the ground 25 or with the reference potential. In some embodiments, the conductive back side of the substrate may be grounded at least temporarily during processing.

[0034] The term "electronic devices formed on the front side" as used herein may refer to electronic devices which are directly or indirectly formed on the front side of the substrate, e.g. with no layer or with one or more layers between the substrate and the electronic devices. It is to be noted that the electronic devices are formed on the opposite side of the substrate as compared to the conductive layer 20 which is typically directly deposited on the electrically insulating back side 12 of the substrate.

[0035] Processing 30 of the substrate, particularly of the front side 14, is not particularly limited herein and may include any handling operation and/or treatment of the substrate, e.g. a transport of the substrate such that the front side faces a treatment device, loading and/or unloading of the substrate from a substrate support or a substrate carrier, any treatment of the front side, e.g. with an ionizer, a coating of the front side, e.g. masked deposition, patterning of one or more layers deposited on the front side, etching of the front side or of layers deposited thereon, providing one or more electronic devices on the front side, e.g. by attaching a foil with electronic devices formed thereon on the front side, testing electronic devices formed on the front side, and/or similar treatments, handling operations and/or combinations thereof.

[0036] In some embodiments, which may be combined with other embodiments described herein, the processing 30 of the front side 14 may include functional testing of one or more electronic devices formed on the front side. Functional testing of the one or more electronic devices, e.g. pixels or transistors of a display, may include functional testing with an electron beam array tester and/or with a probing device configured for contacting the one or more electronic devices.

[0037] In some embodiments, the processing 30 of the front side may optionally include depositing one or more conductive layers on the front side 14, particularly depositing the one or more electronic devices 32 on the front side, e.g. by masked deposition and/or patterning. After the deposition, the electronic devices 32 formed on the front side may be tested, e.g. in a testing apparatus, particularly in an electron beam testing apparatus.

[0038] Due to the direct or indirect connection of the conductive back side 20 with the ground 25 or with the reference potential before, during and/or after the processing 30, no charges can build up on the back side of the substrate. Accordingly, as long as the front side of the substrate is not charged during the processing, the substrate may remain electrically neutral both in the near field and in the far field of the substrate. [0039] A substrate may be considered as electrically neutral in the far field, when the overall sum of charges on the outer surface of the substrate including the front side and the back side adds up to zero. However, even if the substrate is neutral in the far field, the substrate may not be neutral in the near field, e.g. when the polarity of the charges on the front face differs from the polarity of the charges on the back face. In this case, the substrate may be polarized in spite of a net amount of zero charges on the whole substrate.

[0040] The handling and/or the transport of the substrate may be critical for ESD caused defects. The conductive layer 20 may protect the front side of the substrate especially also during any handling or transporting action of the substrate, when the conductive back side 22 is connected to the ground or to the reference potential by a handling tool, e.g. by a grounded fork end effector.

[0041] In some embodiments, which may be combined with other embodiments described herein, the conductive back side 20 may be connected with the ground 25 or with the reference potential at least temporarily or continuously during handling and/or transport of the substrate, e.g. during transport of the substrate between two or more processing stages, during orientation changes of the substrate, during loading of the substrate on a substrate carrier or a substrate support, during lift-off or unloading of the substrate from a substrate carrier or a substrate support and/or during other handling actions. The ground connection of the conductive back side during the handling operations may protect the electronic devices formed on the front side of the substrate.

[0042] ESD caused defects may be based on capacitive effects, for example if the capacitance between a substrate support and a substrate placed thereon is initially high, and the capacitance becomes low during the unloading of the substrate from the substrate support, i.e. during lift-off. During unloading, the voltage may raise inversely proportional to the capacitance change. However, if the conductive back side 20 is connected to ground or to a reference potential during substrate handling, the capacitance change and thus the voltage raise can be reduced. Accordingly, the conductive back side 20 may be connected to ground or to a reference potential during some or during all substrate handling actions, in order to reduce the ESD damage. [0043] In stage d), the substrate is depicted after the processing 30. After the processing 30, the conductive back side 22 may be separated from the ground 25 or from the reference potential, without being charged. When the front side or the electronic devices formed on the front side are not charged, the substrate may be neutral both in the near field and in the far field. This may reduce or eliminate the risk of damages by electrostatic discharge ESD.

[0044] Accordingly, when processing a substrate with an electrically insulating back side according to embodiments described herein, the electrical polarization of the substrate during and after processing can be reduced or eliminated.

[0045] FIG. 2 is a schematic diagram for illustrating various stages of a method of processing a substrate 10 according to some embodiments described herein. The substrate 10 has an electrically insulating back side 12 and a front side 14 opposite the electrically insulating back side 12. In some embodiments, the front side 14 may be provided with one or more electrical devices 32 and/or layers formed thereon. For example, a plurality of pixels of a display and/or transistors may be formed on the front side 14.

[0046] Similar to the method of FIG. 1 , before processing of the front side, the insulating back side of the substrate may be coated with a conductive layer 20 to provide a conductive back side 22 of the substrate. Reference is made to the above explanations which are not repeated here.

[0047] In some embodiments, which may be combined with other embodiments described herein, the substrate 10 may be made of an electrically insulating material. The substrate may be or include at least one of a glass substrate, a display substrate, an LCD glass substrate, a wafer, a printed circuit board, a solar cell substrate, and a flexible substrate adapted for roll-to-roll processing, e.g. a foil or web substrate. The substrate may be transparent.

[0048] The substrate may be a large area substrate in some embodiments. For example, the substrate 10 may have a surface area of 1 m² or more, particularly 2 m² or more, more particularly 8 m² or more. In other words, both the front side and the back side may have a surface area of 1 m² or more, or even 8 m² or more, respectively. [0049] Alternatively or additionally, the substrate 10 may be a thin substrate, e.g. having a thickness of 1 mm or less, particularly 0.7 mm or less, more particularly 0.5 mm or less. The thickness of the substrate as used herein may be defined as the distance between the insulating back side 12 and the front side 14 of the substrate on which the one or more electronic devices and/or further layers may be deposited.

[0050] In some embodiments, which may be combined with other embodiments described herein, the one or more electronic devices 32 may include one or more of microelectronic devices, optoelectronic devices, thin film transistors, pixels of a display element, connection networks of a chip, electron emitters of an emitter array, electrodes for pixels of a display or any combination thereof. The electronic devices may be formed in an array or matrix on the front side of the substrate. For example, 1.000 or more, particularly 10.000 or more, more particularly 100.000 or more, or even 1.000.000 or more electronic devices may be provided.

[0051] In some embodiments, the one or more electronic devices may be provided on a transparent foil, e.g. on a polymer film such as a PI film, which may be attached to, e.g. laminated to, the front side of the substrate. In this case, the substrate may be a carrier for the transparent foil with the one or more electronic devices provided thereon. The substrate with the transparent foil attached thereto may allow processing of the one or more electronic devices in the same manner as electronic devices directly located on the front side of the substrate, e.g. a glass substrate.

[0052] Stage a) of FIG. 2 shows the substrate 10 having an electrically insulating back side which is coated with the conductive layer 20 to provide a conductive back side 22. Further, one or more electronic devices 32 are formed on the front side of the substrate.

[0053] As is illustrated in stage b) of FIG. 2, the conductive back side 20 of the substrate may be placed on a support surface 52 of a substrate support 50. The support surface 52 may be partially or entirely conductive. For example, the support surface 52 or the whole substrate support 50 may be made of metal. In some embodiments, the substrate support 50 is a metal stage. [0054] The substrate may be placed on the substrate support 50 such that the conductive back side 22 of the substrate is in direct electrical contact with the conductive support surface 52 of the substrate support.

[0055] The conductive support surface 52 may be directly or indirectly connected to ground 25 or to a reference potential, e.g. to a reference voltage provided by a voltage source. Accordingly, also the conductive back side 22 of the substrate is directly or indirectly connected to the ground 25 or to the reference potential.

[0056] In some embodiments, the conductive back side 22 of the substrate may be placed on the grounded conductive support surface of the substrate support 50 during the processing of the front side of the substrate or of the one or more electronic devices 32 formed thereon. For example, the substrate may be placed on the substrate support 50 during a functional test of the electric devices 32.

[0057] As is illustrated in stage c) of FIG. 2, the front side of the substrate or the one or more electronic devices 32 formed thereon may be processed, while the conductive back side 22 may be grounded, e.g. via the substrate support 50. Processing may include testing the one or more electronic devices 32 formed on the front side 14, particularly including contacting the one or more electronic devices 32 with at least one prober 42. Functional testing of the one or more electronic devices 32 may be conducted with an electron beam test apparatus.

[0058] As the conductive back side of the substrate may remain directly or indirectly connected to a reference potential during the testing, the electrical potential of the conductive back side may be defined throughout the functional testing. Accordingly, in the case of an uncharged front side, no charges may leave the front side of the substrate via the prober 42 which may contact the electrical devices 32 during the testing. Accordingly, also the front side may remain electrically neutral and a polarization of the substrate may be reduced.

[0059] In stage d) of FIG. 2, the substrate is shown after the processing. After the processing, the conductive back side 22 may be lifted off from the substrate support 50, without being charged and/or polarized. Accordingly, the substrate may be neutral both in the near field and in the far field. The risk of damage by electrostatic discharge ESD may be reduced or eliminated.

[0060] FIG. 3 is a schematic diagram for illustrating various stages of a method of processing a substrate 10 according to some embodiments described herein. The substrate 10 has an electrically insulating back side 12 and a front side 14 opposite the electrically insulating back side 12. The front side 14 may be provided with one or more electrical devices 32 and/or layers formed thereon. For example, a plurality of pixels of a display and/or transistors may be formed on the front side 14. The electrically insulating back side may be coated with a conductive layer 20 for providing a conductive back side 22.

[0061] As is illustrated in stage a) of FIG. 3, the back side of the substrate may be charged, e.g. negatively charged, from an earlier handling or processing stage of the substrate. Accordingly, there may be a potential difference between the back side and the front side of the substrate (V≠0).

[0062] In some embodiments, which may be combined with other embodiments described herein, the conductive back side 22 may be discharged, particularly before the processing. For example, the conductive back side 22 may be discharged via a high resistance connection 27, e.g. a high resistance connection to ground. In some embodiments, the conductive back side 22 is discharged before placing the conductive back side on a substrate support 50 for processing of the front side of the substrate. This is illustrated in stage b) of FIG. 3.

[0063] According to some embodiments, which may be combined with other embodiments described herein, the front side 14 and/or the one or more electronic devices 32 formed on the front side 14 may be discharged or neutralized, particularly by treating the front side 14 with an ionizer 60. During the treatment of the front side with the ionizer 60, the conductive back side 22 may be connected to the ground 25 or to the reference potential, e.g. via the high resistance connection 27. Accordingly, both the front side and the back side of the substrate may be neutralized before the processing. Thereupon, the potential difference between the back side and the front side of the substrate may be essentially zero. A measurement with a static volt meter may detect that the substrate is not charged in the near field and in the far field (V~0).

[0064] As is illustrated in stage c) of FIG. 3, the conductive back side 20 of the substrate may then be placed on a support surface 52 of a substrate support 50, e.g. on a metal stage. The support surface 52 may be partially or entirely conductive. The support surface 52 may be connected to ground 25 or to a reference potential. Reference is made to the above explanations which are not repeated here.

[0065] The electrically neutral front side and the electrically neutral back side of the substrate do not change the electric potential significantly when the substrate is placed on the substrate support. In particular, the conductive substrate support does not shield any charges on the back side of the substrate which would result in the substrate appearing more positively charged. Rather, when placed on the substrate support, the substrate remains essentially electrically neutral and/or essentially unpolarized.

[0066] As is illustrated in stage c) of FIG. 3, the front side of the substrate or the one or more electronic devices 32 formed thereon are processed, while the conductive back side 22 may be grounded, e.g. via the substrate support 50. Processing may include testing the one or more electronic devices 32 formed on the front side 14, as is described above in more detail. In particular, even when a prober 42 of a testing apparatus electrically contacts the electronic devices 32, the charge balance is not changed and no charges may be removed from the front side of the substrate upon a contact of the prober. Accordingly, during the functional test, when placed on the grounded substrate support, the substrate remains essentially electrically neutral and/or essentially unpolarized (V~0).

[0067] As is illustrated in stage d) of FIG. 3, after the lift-off of the substrate from the substrate support 50, the substrate is not charged to a high voltage, but essentially electrically neutral in the far field (V~0). The risk of damage by electrostatic discharge ESD may be reduced or eliminated.

[0068] FIG. 4 is a schematic diagram illustrating various stages of a method of processing a substrate of a comparative example. The comparative example of FIG. 4 shows the processing of a substrate 500 analogously to the processing of the substrate 10 in FIG. 3. However, in FIG. 4, the electrically insulating back side of the substrate 500 is not coated with a conductive layer.

[0069] In stage I of FIG. 4, the electrically insulating back side of the substrate may be charged, e.g. negatively charged, from an earlier handling or processing stage of the substrate. Accordingly, there may be a potential difference V between the back side and the front side of the substrate (V≠0).

[0070] In stage II of FIG. 4, the substrate may be treated with an ionizer 60 for neutralizing the charges such that the substrate is electrically neutral in the far field (V~0). However, the substrate is now polarized as the polarity of the charges on the front side may differ from the polarity of the charges on the back side.

[0071] In stage III of FIG. 4, a measurement with a static volt meter will detect that the substrate is not charged (V~0). However, the substrate is actually polarized and charged in the near field.

[0072] In stage IV of FIG. 4, the electrically insulating back side of the substrate 500 may be placed on a substrate support 50 which may be connected to ground 25.

[0073] In stage V of FIG. 4, when placed on the substrate support 50, the (negatively) charged back side of the substrate 500 may be shielded by the grounded substrate support such that the substrate, even if actually electrically neutral, may appear to be more positive in the far field (V≠0).

[0074] In stage VI of FIG. 4, the front side of the substrate 500 is processed. When a prober 42 of a testing apparatus contacts an electronic device on the front side, the capacitance to the substrate support and the contacting by the prober may change the balance. Thus, the contacting prober may remove charges from the substrate, e.g. positive charges from the front side in the example of FIG. 4. After the processing, the substrate may seem to be electrically neutral in the far field (V~0). [0075] In stage VII of FIG. 4, after the lift-off of the substrate 500 from the substrate support 50, the substrate may be charged to a high voltage (V≠0). This is because the negative charges on the back side are no longer shielded by the conductive substrate support. There may be a high risk of damage by electrostatic discharge ESD. It is noted that the decreasing capacitance by the lift-off of a substrate from the substrate support may cause a high voltage no matter where the initial charge-up comes from.

[0076] FIG. 5 is a schematic diagram illustrating optional further stages of a method of processing a substrate according to some embodiments described herein. The stages shown in FIG. 5 may be performed after the processing of the substrate, particularly after the functional testing of the electronic devices 32 and/or after the lift-off of the processed substrate from the substrate support, as is illustrated in any of the above embodiments.

[0077] In some embodiments, which may be combined with other embodiments described herein, the conductive layer 20 may be an antistatic coating or an ESD coating. In particular, the conductive layer 20 may be a removable coating, more particularly a water- removable coating.

[0078] Stage a) of FIG. 5 shows the substrate 10 with the conductive layer 20 on the back side after the processing.

[0079] Stage b) of FIG. 5 shows the removal of the conductive layer 20 after the processing with a removal device 140. For example, the conductive layer may be washed off and/or the removal device 140 may be a cleaning device which may use a fluid such as water for the removal of the conductive layer.

[0080] Alternatively, the conductive layer 20 may be removed by an abrasive process. For example, especially for thin substrate applications like mobile displays, the substrate may be thinned after the processing by an abrasive process which may also remove the conductive layer 20. [0081] Stage c) of FIG. 5 shows the processed substrate 10 after the removal of the conductive layer 20. The electronic devices 32 are arranged on the front side of the substrate 10. A display element with a plurality of pixels may be provided.

[0082] In other embodiments, the conductive layer 20 may not be removed.

[0083] FIG. 6 is a schematic view of an apparatus 100 for processing a substrate according to some embodiments described herein.

[0084] The apparatus 100 is configured for processing a substrate with an electrically insulating back side and a front side opposite the electrically insulating back side. The arrow 101 shows the path of the substrate through the apparatus in a schematic way. The apparatus may be configured for processing the substrate according to one of the methods described herein. Reference is made to the above explanations which are not repeated here.

[0085] The apparatus 100 includes a first coater 110 for coating the electrically insulating back side of the substrate with a conductive layer 20 to provide a conductive back side. The apparatus may further include a connection for connecting the conductive layer 20 with ground or with a reference potential during processing. For example, a substrate support 50 configured for supporting the substrate and for directly or indirectly connecting the conductive back side of the substrate with ground 25 or with a reference potential may be provided. Yet further, the apparatus 100 includes a processing device 120 configured for processing of the front side and/or of one or more electronic devices formed on the front side, particularly while the substrate is supported on the substrate support 50.

[0086] In some embodiments, the apparatus 100 may further include a removal device 140 configured for removing the conductive layer 20 after the processing.

[0087] In some embodiments, which may be combined with other embodiments described herein, the processing device 120 may include a second coater configured for depositing one or more layers on the front side, e.g. conductive layers and/or dielectric layers. The second coater may be configured as an evaporator, a CVD system, a PVD system, and/or as a sputter system in some embodiments. [0088] The second coater may be configured for depositing the one or more electronic devices on the front side of the substrate, e.g. by patterning a deposited layer and/or by masked deposition. For example, the second coater may be configured for forming one or more of microelectronic devices, optoelectronic devices, micromechanical devices, thin film transistors, pixels of a display element, connection networks of a chip, electron emitters of an emitter array, electrodes for pixels of a display or any combination thereof.

[0089] In some embodiments, which may be combined with other embodiments described herein, the processing device 120 may include a testing device for the functional testing of the one or more electronic devices 32 formed on the front side, particularly including at least one prober 42 configured for electrically contacting the one or more electronic devices 32.

[0090] For example, the processing device 120 may include an electron beam test system (EBT system) which may provide dynamic pixel and TFT characterization and functional tests of a flat panel matrix. The electron beam test system may be configured for generating multi e-beams for testing in parallel and for achieving high-throughput yields, especially with large area TFT-LCD displays, e.g. for flat panel displays.

[0091] In some embodiments, the apparatus 100 may further include a substrate support 50, particularly with a conductive support surface 52 which may be connected to ground 25 or to a reference potential, e.g. via a high resistance connection. The substrate support 50 may be arranged opposite the processing device 120 such that the front side of the surface can be processed with the processing device 120 while the conductive back side of the substrate may be in direct electrical contact with the support surface 52.

[0092] In some embodiments, which may be combined with other embodiments described herein, the apparatus 100 may include a static remover, also referred to herein as an ionizer 60. The ionizer may be arranged downstream from the first coater 110 and upstream from the processing device 120. The ionizer may be configured for neutralizing static electricity from the front side of the substrate or from the electronic devices formed on the front side. The ionizer 60 may be configured to produce ions. [0093] Alternatively or additionally, the apparatus 100 may include an electrical connection configured for discharging the conductive back side 20, e.g. before placing the substrate on the substrate support. The electrical connection may be configured as a high resistance connection 27. The high resistance connection 27 may be configured for connecting the conductive back side of the substrate to ground while the front side is treated with the ionizer 60 and/or while the substrate is transported or otherwise treated.

[0094] In some embodiments, the conductive layer may be an antistatic coating or an ESD coating, particularly a removable coating, more particularly a coating that can be washed off, e.g. with water.

[0095] According to a further aspect described herein, a display element is provided, as is shown in, e.g. FIG. Id), 2d), 3d), or in FIG. 5a). The display element includes a substrate with an electrically insulating back side and a front side opposite the electrically insulating back side. One or more electronic devices, particularly thin film transistors and/or pixels, are formed on the front side. The electrically insulating back side is coated with a conductive layer to provide a conductive back side of the substrate.

[0096] In some embodiments, the conductive layer may be an anti-static coating or an ESD coating, particularly a removable coating, more particularly a coating that can be washed off.

[0097] FIG. 7 is a flow diagram illustrating a method of processing a substrate according to embodiments described herein.

[0098] In box 710, a substrate 10 is provided, wherein the substrate has an electrically insulating back side 12 and a front side 14 opposite the electrically insulating back side, wherein one or more electronic devices 32 may optionally be formed on the front side 14.

[0099] In box 720, the electrically insulating back side 12 is coated with a conductive layer 20 to provide a conductive back side 22.

[00100] In (optional) box 730, the substrate is neutralized with an ionizer 60, particularly while the conductive back side is connected to ground or to a reference potential. [00101] In box 740, the conductive back side 20 is connected with ground or with a reference potential, particularly by placing the substrate on a conductive substrate support which may be grounded.

[00102] In box 750, the substrate is processed, particularly the front side and/or the one or more electronic devices 32 on the front side are processed, particularly by functional testing of the one or more electronic devices, e.g. using a prober for contacting the one or more electronic devices. During processing, the conductive back side may be directly or indirectly connected to the ground or to the reference potential.

[00103] In (optional) box 760, the substrate is lifted off from the substrate support. [00104] In (optional) box 770, the conductive layer 20 may be removed from the substrate.

[00105] While the foregoing is directed to embodiments of the disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

1. A method of processing a substrate (10), wherein the substrate has an electrically insulating back side (12) and a front side (14) opposite the electrically insulating back side (12), the method comprising: coating the electrically insulating back side (12) with a conductive layer (20) to provide a conductive back side (22); connecting the conductive back side (20) with ground (25) or with a reference potential; and processing (30) of the substrate.

2. The method of claim 1, wherein the processing of the substrate comprises processing of the front side (14) and/or of one or more electronic devices (32) formed on the front side.

3. The method of claim 2, wherein the processing (30) comprises functional testing of the one or more electronic devices (32) formed on the front side (14), particularly comprising contacting the one or more electronic devices (32) with at least one prober (42).

4. The method of any of claims 1 to 3, wherein the conductive back side (20) of the substrate is placed on a conductive support surface (52) of a substrate support (50) which is connected to the ground (25) or to the reference potential.

5. The method of any of the preceding claims, wherein the conductive back side (22) is discharged before the processing, particularly via a high resistance connection (27).

6. The method of any of the preceding claims, further comprising: treating the front side (14) and/or one or more electronic devices (32) formed on the front side (14) with an ionizer (60), particularly while the conductive back side (22) is connected to the ground (25) or to the reference potential.

7. The method of any of the preceding claims, wherein the substrate (10) comprises at least one of a glass substrate, a display substrate, an LCD glass substrate, a wafer, a printed circuit board, a solar cell substrate, and a flexible substrate adapted for roll-to-roll processing.

8. The method of any of the preceding claims, wherein one or more electronic devices (32) are formed on the front side, the one or more electronic devices comprising one or more of microelectronic devices, optoelectronic devices, thin film transistors, pixels of a display element, connection networks of a chip, electron emitters of an emitter array, and electrodes for pixels of a display.

9. The method of any of the preceding claims, wherein the substrate (10) has a thickness of 1 mm or less, particularly 0.5 mm or less, and/or a surface area of 1 m² or more, particularly 8 m² or more.

10. The method of any of the preceding claims, wherein the conductive layer (20) is an antistatic coating or an ESD coating, particularly a removable coating, more particularly a water-removable coating.

11. The method of claim 10, wherein the conductive layer (20) is removed, particularly washed off after the processing (30).

12. An apparatus (100) for processing a substrate (10), wherein the substrate has an electrically insulating back side and a front side opposite the electrically insulating back side, comprising: a first coater (110) for coating the electrically insulating back side with a conductive layer to provide a conductive back side (22); a substrate support (50) configured for supporting the substrate and for connecting the conductive back side (22) with ground (25) or with a reference potential; and a processing device (120) configured for processing of the front side and/or of one or more electronic devices (32) formed on the front side.

13. The apparatus of claim 12, further comprising: a removal device (140) configured for removing the conductive layer (20) after the processing.

14. The apparatus of claim 12 or 13, wherein the processing device (120) comprises a testing device for testing of the one or more electronic devices (32) formed on the front side, particularly comprising at least one prober (42) configured for electrically contacting the one or more electronic devices (32).

15. A display element, comprising a substrate (10) with an electrically insulating back side (12) and a front side (14) opposite the electrically insulating back side, wherein one or more electronic devices (32), particularly thin film transistors and/or display pixels, are formed on the front side, wherein the electrically insulating back side (12) is coated with a conductive layer (20) to provide a conductive back side (22) of the substrate.