WO2017035770A1 - Method for producing a bonded glass article and a bonded glass article - Google Patents

Method for producing a bonded glass article and a bonded glass article Download PDF

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Publication number
WO2017035770A1
WO2017035770A1 PCT/CN2015/088726 CN2015088726W WO2017035770A1 WO 2017035770 A1 WO2017035770 A1 WO 2017035770A1 CN 2015088726 W CN2015088726 W CN 2015088726W WO 2017035770 A1 WO2017035770 A1 WO 2017035770A1
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WIPO (PCT)
Prior art keywords
bonding
substrate
ultra
carrier substrate
bonded
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PCT/CN2015/088726
Other languages
French (fr)
Inventor
Yunfei HOU
Wentao JU
Pengxiang QIAN
Rainer Liebald
Andreas Ortner
Original Assignee
Schott Glass Technologies (Suzhou) Co., Ltd.
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Application filed by Schott Glass Technologies (Suzhou) Co., Ltd. filed Critical Schott Glass Technologies (Suzhou) Co., Ltd.
Priority to PCT/CN2015/088726 priority Critical patent/WO2017035770A1/en
Publication of WO2017035770A1 publication Critical patent/WO2017035770A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B37/00—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding
    • B32B37/0007—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding involving treatment or provisions in order to avoid deformation or air inclusion, e.g. to improve surface quality
    • B32B37/003—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding involving treatment or provisions in order to avoid deformation or air inclusion, e.g. to improve surface quality to avoid air inclusion
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B17/00—Layered products essentially comprising sheet glass, or glass, slag, or like fibres
    • B32B17/06—Layered products essentially comprising sheet glass, or glass, slag, or like fibres comprising glass as the main or only constituent of a layer, next to another layer of a specific material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B37/00—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding
    • B32B37/02—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding characterised by a sequence of laminating steps, e.g. by adding new layers at consecutive laminating stations
    • B32B37/025—Transfer laminating
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B37/00—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding
    • B32B37/14—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding characterised by the properties of the layers
    • B32B37/16—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding characterised by the properties of the layers with all layers existing as coherent layers before laminating
    • B32B37/18—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding characterised by the properties of the layers with all layers existing as coherent layers before laminating involving the assembly of discrete sheets or panels only
    • B32B37/182—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding characterised by the properties of the layers with all layers existing as coherent layers before laminating involving the assembly of discrete sheets or panels only one or more of the layers being plastic
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B37/00—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding
    • B32B37/14—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding characterised by the properties of the layers
    • B32B37/16—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding characterised by the properties of the layers with all layers existing as coherent layers before laminating
    • B32B37/18—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding characterised by the properties of the layers with all layers existing as coherent layers before laminating involving the assembly of discrete sheets or panels only
    • B32B37/187—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding characterised by the properties of the layers with all layers existing as coherent layers before laminating involving the assembly of discrete sheets or panels only the layers being placed in a carrier before going through the lamination process
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B38/00—Ancillary operations in connection with laminating processes
    • B32B38/16—Drying; Softening; Cleaning
    • B32B38/162—Cleaning
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B37/00—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding
    • B32B37/10—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding characterised by the pressing technique, e.g. using action of vacuum or fluid pressure
    • B32B2037/1063—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding characterised by the pressing technique, e.g. using action of vacuum or fluid pressure using an electrostatic force
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B38/00—Ancillary operations in connection with laminating processes
    • B32B38/16—Drying; Softening; Cleaning
    • B32B38/164—Drying
    • B32B2038/166—Removing moisture
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2310/00—Treatment by energy or chemical effects
    • B32B2310/021—Treatment by energy or chemical effects using electrical effects
    • B32B2310/025—Electrostatic charges
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2315/00—Other materials containing non-metallic inorganic compounds not provided for in groups B32B2311/00 - B32B2313/04
    • B32B2315/08—Glass

Definitions

  • the invention concerns a method for producing a bonded article, comprising an ultra-thin substrate, in particular an ultra-thin glass substrate, by bonding the ultra-thin substrate with a bonding surface to a bonding surface of a carrier substrate by an intimate bonding by direct contact of the bonding surfaces.
  • the invention also concerns a bonded article and the use of a bonded article.
  • glass and glasses generally include both glasses and glass ceramics.
  • Thin glass can be obtained by grinding a thicker glass such as e.g. a borosilicate glass to the desired thickness.
  • sheet thicknesses lower than 0.2 mm are difficult to obtain by grinding and polishing of thicker glass sheets.
  • Glass thinner than 0.3 mm, or even with a thickness of 0.1 mm or lower, such as available from can be produced by down-draw methods.
  • soda lime glass with a thickness of 0.1 mm can be produced by special float processes.
  • the handling and processing of ultrathin glass sheets is difficult since with decreasing thickness, the strength of the glass is getting lower and lower resulting in an increasing probability of breakage. It has therefore been proposed to temporarily bond thin and ultra-thin glass sheets or articles to a thicker support substrate in order to facilitate handling and processing of ultra-thin glass sheets or substrates.
  • US 2008/135175 or US 2011/0111194 e.g. propose applying an interlayer for bonding a thin glass substrate to a support substrate.
  • Adhesion promoting or adhesive interlayers can cause several problems during the processing and post-processing of the bonded system. In particular, it may be difficult to remove residual adhesives from the ultra-thin glass or from the support substrate. Moreover, the use of such interlayers generally causes comparatively high costs. In addition, outgassing of the interlayer during processing can contaminate e.g. the substrates or the processing equipment.
  • bonded articles with interlayers can best be overcome by bonding methods where the ultra-thin glass substrate and the support substrate are bonded without interlayer.
  • One such method is e.g. in-situ fabrication whereas another promising method is electrostatic bonding.
  • In-situ fabrication is described e.g. in US 2011/111194 where a bonded article is obtained joining two melt batches with different compositions for the thin glass substrate and the support substrate, respectively.
  • the support substrate can be removed by e.g. dissolution in acid or by polishing.
  • the fabrication is complicated and therefore generally not suited for mass production.
  • Electrostatic adhesion in principle, is an ideal option for bonding an ultra-thin glass substrate to a support substrate with benefits such as easy production, low cost and suitability for mass production. Such bonding methods are described e.g. in US 6,735, 982 and WO 2004/033197.
  • the ultra-thin glass substrate and the support substrate are charged with opposite charges and subsequently bonded by the electrostatic adhesion.
  • the residual electrostatic charges hold the substrates together. Due to unevenness of the ultra-thin glass sheet prior to bonding, however, air-pockets or bubbles can form between the ultra-thin glass substrate and the support substrate.
  • the ultra-thin glass substrate therefore unevenly adheres to the support substrate and the bonding is of limited quality.
  • this method already provides a viable way to establish a bonding, it also requires very clean surfaces of the glass substrates since even rather small impurities as dust or other pollution can give rise to air-pockets which generally are much larger than the impurity itself. Moreover, even at high degrees of cleanliness, air-pockets can also form without dust or impurities due to uneven establishing of the bonding.
  • TTV Total Thickness Variation
  • the objects of the invention are solved by a method for producing a bonded article and a bonded glass article according to the independent claims. Further, the objects of the invention are solved by a method for cleaning at least the bonding surface of a substrate for a bonded article and the use of such the bonded article according to a further independent claim.
  • the method is characterized in that the intimate bonding is established by electrostatic forces resulting from a weak electrostatic field potential from electrostatic charges on at least one of the bonding surfaces, wherein the weak electrostatic field potential at the bonding surfaces does not exceed 1 kV.
  • Intimate bonding herein refers to direct bonding forces between the substrates at the bonding surfaces when they are brought in to direct contact. Such forces comprise Van der Waals and/or Hydrogen bonding forces. Also strong covalent Si-O-Si or bonding by OH groups can cause the intimate bonding. Such intimate bonding can withstand processes as high temperature treatments up to 600°C or higher, vacuum processing, wet-processing, acidic treatment and also physical- (PVD) or chemical vapor deposition (CVD) processes as they may occur during flat panel display production or e.g. thin film transistor (TFT) processes. Such bonding has been proposed in the art for bonded articles, in particular for bonded glass articles.
  • adhesion promoting interlayers for establishing the bonding can be omitted.
  • adhesive layers have the potential for outgassing solvents or contamination by adsorbed materials typically at temperatures above 150°C and are therefore advantageously avoided.
  • intimate, i.e. direct bonding of the substrates such disadvantages can be overcome.
  • the direct bonding generally refers to direct contacting of the substrate material at the bonding surfaces. It is to be understood, however, that the direct contact of the intimate bonding does not withstand a coating of the bonding surface of one or both of the substrates, in particular the carrier substrate.
  • Such coatings are used for reducing the bonding force in order to prevent the bonded article from forming a permanent bonding during high temperature treatments which would prevent destruction free de-bonding at a later stage.
  • Such coatings can include e.g. Si coatings, Al coatings, Cr coatings, ITO coatings, SiO 2 coating, TiO 2 coating, Si 3 N 4 coating, BN coating or combination of them.
  • One of the remaining problems is to establish an even bonding at the bonding interface essentially without air-pockets or bubbles forming between the bonding surfaces.
  • the bonding surfaces need to be thoroughly cleaned from impurities as dust or other contaminants to a sufficient degree. Otherwise, impurities can prevent the direct contacting of the bonding surfaces and thus result in air-pockets or bubbles rendering the intimate bonding incomplete.
  • bubbles often also form without impurities. Such bubbles are a result of an uneven establishing of the intimate bonding due to the difficulty to control the bringing into direct contact of the bonding surfaces.
  • the invention has solved this problem by the surprising insight that the preparation of a bonding surface or the bonding surfaces with weak electrostatic charges allows for an even and simple establishing of the intimate bonding by the resulting weak electrostatic field potential between the bonding surfaces.
  • the weak electrostatic field potential can thereby be a byproduct of the preparation of the substrates prior to establishing the bonding, in particular of the cleaning steps of the substrates. It is therefore not necessary to have a separate charging step where the electrostatic charges are applied to the substrates e.g. by means of a charging bar. This is of particular importance since such dedicated charging steps generally do not allow for maintaining the required cleanliness of the bonding surfaces.
  • the carrier substrate and/or the ultra-thin substrate may be of any suitable material, including glass as an example (including glass-ceramics or ceramics) .
  • the substrates need not be made of glass but can essentially also include any other material that can be electrostatically charged.
  • the materials of the carrier substrate and the ultra-thin substrate can be different.
  • the invention has proven particularly advantageous with glass substrates.
  • the substrates preferably comprise an alkali containing glass composition.
  • Preferred glasses are e.g. lithium aluminosilicate glasses, soda-lime glasses, borosilicate glasses, alkali metal aluminosilicate glasses, and aluminosilicate glasses with low alkali content and also alkali-free compositions.
  • Such glasses can be produced by e.g. drawing as e.g. down-draw processes, overflow-fusion or float processes.
  • the coefficient of thermal expansion of the carrier substrate and the ultra-thin substrate should essentially match in order to prevent warping of the bonded article during processing at elevated temperatures.
  • the glass substrates comprise a lithium aluminosilicate glass with the following composition in weight-%:
  • the lithium aluminosilicate glass comprises the following glass composition in weight%:
  • the lithium aluminosilicate glass comprises the following glass composition in weight%:
  • the glass substrates comprise a soda-lime glass with the following composition in weight-%:
  • the soda-lime glass comprises the following glass composition in weight-%:
  • the soda-lime glass comprises the following glass composition in weight%:
  • the glass substrates comprise a borosilicate glass with the following composition in weight-%:
  • the borosilicate glass comprises the following composition in weight-%:
  • the borosilicate glass comprises the following composition in weight-%:
  • the glass substrates comprise an alkali metal aluminosilicate glass with the following composition in weight-%:
  • the alkali metal aluminosilicate glass comprises the following composition in weight-%:
  • the alkali metal aluminosilicate glass comprises the following composition in weight-%:
  • the glass substrates comprise an aluminosilicate glass with low or no alkali content with the following composition in weight-%:
  • the aluminosilicate glass with low or no alkali content comprises the following composition in weight-%:
  • the aluminosilicate glass with low or no alkali content comprises the following composition in weight-%:
  • the glasses used in the invention can also be modified.
  • the color can be modified by adding transition metal ions, rare earth ions as e.g. Nd 2 O 3 , Fe 2 O 3 , CoO, NiO, V 2 O 5 , MnO 2 , TiO 2 , CuO, CeO 2 , Cr 2 O 3 .
  • transition metal ions rare earth ions as e.g. Nd 2 O 3 , Fe 2 O 3 , CoO, NiO, V 2 O 5 , MnO 2 , TiO 2 , CuO, CeO 2 , Cr 2 O 3 .
  • luminescence ions, such as transition metals and rare earth ions can be added in order to endow optical functions, such as optical amplifiers, LEDs, chip lasers etc.
  • annealing to temperatures as e.g. 400°C or higher for about 5-10 hours can increase the strength of the intimate bonding to a degree that destruction-free de-bonding becomes difficult or impossible.
  • the method according to the invention can therefore also be used for producing a permanently bonded article which can e.g. be used in later applications.
  • the method of the invention preferably is executed under clean conditions in order to prevent contamination of the bonding surfaces with impurities. It is therefore preferred that all steps at least from and including the cleaning steps until the intimate bonding is established are conducted in a cleanroom environment at least according to level ISO 6 of standard ISO 14644-1, preferably at least according to level ISO 5 of standard ISO 14644-1.
  • ISO 5 thereby refers to a maximum density of particles of ⁇ 100'000 particles/m 3 having a size ⁇ 0.1 ⁇ m, ⁇ 23'700 particles/m 3 having a size ⁇ 0.2 ⁇ m, ⁇ 10'200 particles/m 3 having a size ⁇ 0.3 ⁇ m, ⁇ 3'520 particles/m 3 having a size ⁇ 0.5 ⁇ m, ⁇ 832 particles/m 3 having a size ⁇ 1 ⁇ m, and ⁇ 29 particles/m 3 having a size ⁇ 5 ⁇ m.
  • ISO 6 corresponds to a maximum density of particles of ⁇ 1'000'000 particles/m 3 having a size ⁇ 0.1 ⁇ m, ⁇ 237'000 particles/m 3 having a size ⁇ 0.2 ⁇ m, ⁇ 102'000 particles/m 3 having a size ⁇ 0.3 ⁇ m, ⁇ 35'200 particles/m 3 having a size ⁇ 0.5 ⁇ m, ⁇ 8'320 particles/m 3 having a size ⁇ 1 ⁇ m, and ⁇ 293 particles/m 3 having a size ⁇ 5 ⁇ m.
  • ISO 5 and ISO 6 correspond to cleanroom classes 100 and 1000, respectively, according to the now obsolete standard US FED STD 209E.
  • the bonded article comprises a carrier substrate, in particular a glass carrier substrate, having a bonding surface, and an ultra-thin substrate which is sheet-like and flexible, preferably an ultra-thin glass substrate, having a first and a second surface and a thickness t, where at least the first or second surface forms a bonding surface.
  • the carrier substrate and the ultra-thin substrate are intimately bonded to each other by direct contact of the bonding surface of the ultra-thin substrate with the bonding surface of the carrier substrate.
  • the bonded article is characterized in that the bonding interface formed by the intimately bonded bonding surfaces is essentially free of bubbles with surface dimensions larger than 7 mm 2 and has a density of bubbles with surface dimensions equal or smaller than 3 mm 2 which is less than 15 bubbles/0.01m 2 , preferably less than 10 bubbles/0.01m 2 and further preferably smaller than 5 bubbles/0.01m 2 .
  • the bonded article is preferably essentially electrostatically neutral, in particular its net electrostatic field potential is less than 10 V, preferably less than 1 V.
  • the electrostatic filed potential thereby refers to the overall electrostatic field potential of the bonded article with respect to ground potential.
  • Such a bonded article can e.g. be obtained by wet-washing the bonded article after establishing the intimate bonding. It is thereby important that the intimate bonding is tight enough that no washing liquid can penetrate between and de-bond the bonded substrates which can be ensured by the method according to the invention.
  • the bonded article preferably has a largest dimension of at least 0.1 m or larger, preferably 0.3 m or larger, further preferably 0.5 m or larger, or 3 inch or larger, preferably 6 inch or larger, further preferably 8 inch or larger, further preferably 12 inch or larger.
  • the bonded article according to the invention can also have a Gen 1 size or larger, e.g. Gen 2, Gen 3, Gen 4, Gen 5, Gen 8 or even larger (e.g. substrate sizes from 100 mm x 100 mm to 3 m x 3 m) .
  • Gen 1 size or larger e.g. Gen 2, Gen 3, Gen 4, Gen 5, Gen 8 or even larger
  • substrate sizes from 100 mm x 100 mm to 3 m x 3 m Generally, the larger the substrates are, the more difficult it becomes to establish an essentially bubble free bonding interface.
  • the bonded article preferably comprises the ultra-thin substrate with a thickness t of equal or less than 0.4 mm, preferably equal or less than 0.2 mm, further preferably equal or less than 0.1 mm, further preferably equal or less than 0.05 mm, further preferred equal or less than 0.01 mm.
  • Selected preferred thicknesses are 5 ⁇ m, 10 ⁇ m, 15 ⁇ m, 25 ⁇ m, 30 ⁇ m, 35 ⁇ m, 55 ⁇ m, 70 ⁇ m, 80 ⁇ m, 130 ⁇ m, 145 ⁇ m, 175 ⁇ m, 190 ⁇ m, 210 ⁇ m or 280 ⁇ m.
  • the intimate bonding of the bonded article according to the invention requires an initial de-bonding force for de-bonding the ultra-thin substrate from the carrier substrate which is larger than 0.2 N. If the bonded article is annealed after the intimate bonding has been established, the de-bonding force can be larger than 1 N and even larger than 10 N. The de-bonding force was thereby measured on a bonded article with a strip-shaped bonding interface having a width of 40 mm ⁇ 0.5mm of arbitrary length. The ultra-thin substrate was first detached at one end of the strip shaped bonded article (initial de-bonding) and then continuously peeled of along the longitudinal direction of the bonded article (continuous de-bonding) .
  • Fig. 3 block diagram of the method according to the invention.
  • Fig. 4 diagram for a cleaning step for cleaning a substrate to be bonded
  • Fig. 6a an ultra-thin substrate and a carrier substrate in an intermediate bonding state
  • Fig. 6c transition from the intermediate bonding state of Fig. 6a to the intimate bonding state according to Fig. 1 in progress;
  • Fig. 1 shows a bonded article 1 according to the invention.
  • the bonded article 1 comprises a carrier substrate 2 and an ultra-thin substrate 3 which both are made from a glass material.
  • the carrier substrate has a thickness t' and the ultra-thin substrate 3 has a thickness t.
  • the ultra-thin substrate 3 is intimately bonded with a bonding surface 3.1 to a bonding surface 2.1 of the carrier substrate 2.
  • An opposite surface 3.2 of the ultra-thin substrate is available for processing in the bonded state.
  • An opposite surface 2.2 of the carrier substrate can e.g. be used for handling as e.g. conveying the bonded article 1 during processing.
  • Fig. 3 shows a simplified flow diagram for the method for producing the bonded article 1 according to the invention.
  • the process comprises a step 10 of providing the carrier substrate 2 and the ultra-thin substrate 3, a step 20 of cleaning the substrates 2 and 3 and a step 30 of establishing the intimate bonding.
  • the ultra-thin substrate 3 can be provided as is or can already be attached to a support substrate for easier handling during the execution of the method (see e.g. Fig. 5) .
  • the ultra-thin substrate 3 with thickness t equal or larger than 0.1 mm can be processed without the support substrate.
  • the preferred cleaning step 21 and/or 22 comprises a wet-washing step 21.1 or 22.1 which includes brush cleaning by rotating brush rollers 5 (see e.g. Fig. 4) . Since such brush cleaning apparatus' can generally not be configured to process substrates of different thicknesses at the same time, it may be necessary in this case to provide two brush cleaning apparatus in parallel.
  • the preferred cleaning step 21 and/or 22 further comprise a drying step 21.2 and 22.2, respectively, during which the substrates 2 and/or 3 are dried for establishing the intimate bonding in a bonding step 30.
  • step 30 Since the electrostatic charges can quickly deplete, it is important that the bonding in step 30 follows shortly or preferably immediately after the cleaning step 20. The weak electrostatic potential thereby establishes the intimate bonding of the bonded article 1. It is to be understood that the drying step 21.2 or 22.2 can be repeated in order to achieve the desired result.
  • the bonded article 1 is provided 40.
  • at least the cleaning step 20 and the bonding step 30 are both performed in a continuous clean-room environment 50, in particular according to standard ISO 5 or ISO 6 according to standard ISO 14644-1.
  • the carrier substrate 2 is conveyed on a plurality of conveyor rollers 4 during the washing step 21.1.
  • the carrier substrate 2 thereby is supported by the conveyor rollers 4 on its surface 2.2 which is opposite to the bonding surface 2.1.
  • the conveyor rollers 4 convey the carrier substrate 2 by means of rotation in a processing direction A.
  • the conveyor rollers 4 are made or are essentially encapsulated by a polymer material, preferably IIR. Such materials can be non-sticky and thus avoid the accumulation of impurities as dust or other residual particles on the surfaces of the conveyor rollers 4 which could subsequently be transferred to the carrier substrate 2.
  • At least one brush roller 5 brushes the bonding surface 2.1 of the substrate.
  • the rotation of the brush roller 5 is thereby directed against the processing direction A of the substrate i.e. the brush bristles 5.1 brush the bonding surface 2.1 against the processing direction A.
  • the brush roller 5 is preferably stationary while the carrier substrate 2 is conveyed past the brush roller 5 in direction A.
  • Another brush roller 6 is provided for brushing the surface 2.2 of the carrier substrate 2 in the same manner.
  • the carrier substrate 2 is conveyed by further conveyer rollers 7.
  • the conveyor rollers 7 can essentially correspond to the conveyor rollers 4 of the washing step 21.1. However, it has been found that for the build-up of electrostatic charges on the bonding surface 2.1 during the drying step 21.2, a material of UPE is preferred and yields the most promising results. Also, UPE is more suitable for a dry and, as the case may be, hot environment.
  • the conveyor rollers 7 convey the carrier substrate 2 in the processing direction A by means of rotation. It is to be understood that A does not necessarily refer to a spatial direction but rather a direction in which the processing is performed.
  • the build-up of electrostatic charges on the bonding surface 2.1 is particularly well supported and can yield electrostatic field potentials of up to 1 kV.
  • Preferred parameter ranges are a relative humidity which is at or below 45%and temperatures above room temperature but which do not exceed 60°C.
  • the specific combination of the washing step 21.1 and the drying step 21.2 as described herein give an optimal environment for the activation of the bonding surfaces 2.1 and 3.1 and the build-up of the necessary weak electrostatic field potentials according to the method of the invention.
  • the electrostatic field potentials can build-up without incorporating specific equipment into the processing line and/or performing corresponding additional processing steps.
  • FIG. 4 shows a simplified schematic view and the drying assembly in an industrial application can be embodied different from the one shown.
  • several air-blade nozzles 7 or 8 can be present on either side of the carrier substrate 2 or other nozzle assemblies can be used.
  • the ultra-thin substrate 2 can be bonded to the carrier substrate 2 while the support substrate 60 is still attached or can be bonded after delamination from the support substrate 60. After the support substrate 60 has been removed, the film 61 can be peeled off from the ultrathin-substrate 3.
  • Figures 6a to 6c show the establishing of the intimate bonding in bonding step 30 where the ultra-thin substrate 3 and the carrier substrate 2 are brought into an intermediate bonding state 70 as shown in Fig. 6a (step 31 in Fig. 3) .
  • the ultra-thin substrate 3 is preferably placed on top of the carrier substrate 2 with its bonding surface 3.1 facing the bonding surface 2.1 of the carrier substrate 2. If the electrostatic potential between the bonding surfaces 2.1 and 3.1 is weak enough, neither the resulting electrostatic force nor in combination with a gravitational force may be sufficient to bring the bonding surfaces 2.1 and 3.1 in direct contact. As such, an air gap 71 persists between the bonding surfaces 2.1 and 3.1 (Fig. 6a) .
  • the weak electrostatic force field is indicated by light grey shading in Figs. 6a-6c.
  • the bonding surfaces 2.1 and 3.1 can be forced together 72 in a localized area 75 due to the flexibility of the ultra-thin substrate 3 (see Fig. 6b) .
  • the bonding surfaces 2.1 and 3.1 can thereby locally be brought into direct contact which triggers (step 32) the establishing of the intimate bonding as follows.
  • This process automatically continues as a continuous chain reaction which establishes the intimate bonding of the bonding surfaces 2.1 and 3.1 by direct contacting the bonding surfaces 2.1 and 3.1 by means of the electrostatic force resulting from the weak electrostatic potential.
  • the "front" of the increased electrostatic force thereby propagates away from the localized area 75 of the initial triggering 72. After a certain time (the propagation speed can be rather slow and last e.g. several minutes) , the intimate bonding is established across the whole bonding interface and the bonded article 1 according to Fig. 1 is obtained.
  • This method is particularly appealing since only a triggering 72 in a localized area 75 is necessary to cause the whole area of the bonding surfaces 2.1 and 3.1 to come into direct contact.
  • the process is intrinsically preventing the build-up of air-pockets or bubbles between the bonding surfaces 2.1 and 3.1 since the establishing of the intimate bonding occurs as a continuous process originating at the location of the initial trigger 72.
  • the location 75 of the triggering 72 is preferably in a central region of the bonding interface.
  • the glass composition of table 1 has a CTE (20-300) of 3.2 x 10 -6 /K , a glass transition temperature T g of 717°C and the density is 2.43 g/cm 3 .
  • the substrates were conveyed on a conveyor bed comprising conveyor rollers made from IIR.
  • a weak alkaline detergent with a pH of approx. 10 was used as washing liquid. The washing liquid was applied at a temperature of 45°C. Both substrates underwent essentially the same brush cleaning.
  • the brush cleaning and drying was performed in a clean room environment of class ISO 6 according to standard ISO 14644-1 (corresponding to class 1000 according to standard US FED STD 209E) at a temperature of 22°C.
  • the ultra-thin substrate was placed on the carrier substrate with its bonding surface facing the bonding surface of the carrier substrate with an air gap between the bonding surfaces.
  • the intimate bonding was triggered by pressing the ultra-thin substrate in a central localized area of the bonding interface against the carrier substrate. After the triggering, the intimate bonding was established automatically by a propagating increase in the electrostatic force as e.g. described in Fig. 6a-6c.
  • the initial de-bonding force amounted to approx. 10 Newton and the continuous de-bonding force was about 0.2 Newton.

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Abstract

Disclosed is a method for producing a bonded article (1), comprising providing a carrier substrate (2), having a bonding surface (2.1) and providing an ultra-thin substrate (3) which is sheet-like and flexible. The method further comprises cleaning at least the bonding surface of the ultra-thin substrate (3), cleaning at least the bonding surface of the carrier substrate (2), and establishing an intimate bonding. The method is characterized in that the intimate bonding is established by electrostatic forces resulting from a weak electrostatic field potential from electrostatic charges on at least one of the bonding surfaces, wherein the weak electrostatic field potential at the bonding surfaces does not exceed 1kV. Further disclosed are a bonded article and a use of the bonded article.

Description

Method for producing a bonded glass article and a bonded glass article
Field of invention
The invention concerns a method for producing a bonded article, comprising an ultra-thin substrate, in particular an ultra-thin glass substrate, by bonding the ultra-thin substrate with a bonding surface to a bonding surface of a carrier substrate by an intimate bonding by direct contact of the bonding surfaces. The invention also concerns a bonded article and the use of a bonded article.
Background of the invention
The market of consumer electronics often requires thinner and thinner glass articles to keep minimizing the volume and weight of the final product. Here and in the following, the terms “glass” and “glasses” generally include both glasses and glass ceramics.
Thin glass can be obtained by grinding a thicker glass such as e.g. a borosilicate glass to the desired thickness. However, sheet thicknesses lower than 0.2 mm are difficult to obtain by grinding and polishing of thicker glass sheets. Glass thinner than 0.3 mm, or even with a thickness of 0.1 mm or lower, such as
Figure PCTCN2015088726-appb-000001
available from 
Figure PCTCN2015088726-appb-000002
can be produced by down-draw methods. Also, soda lime glass with a thickness of 0.1 mm can be produced by special float processes. Unlike thicker glasses, the handling and processing of ultrathin glass sheets is difficult since with decreasing thickness, the strength of the glass is getting lower and lower resulting in an increasing probability of breakage. It has therefore been proposed to temporarily bond thin and ultra-thin glass sheets or articles to a thicker support substrate in order to facilitate handling and processing of ultra-thin glass sheets or substrates.
US 2008/135175 or US 2011/0111194 e.g. propose applying an interlayer for bonding a thin glass substrate to a support substrate. Adhesion promoting or adhesive interlayers, however, can cause several problems during the processing and post-processing of the bonded system. In particular, it may be difficult to remove residual adhesives from the ultra-thin glass or from the support substrate. Moreover, the use of such interlayers  generally causes comparatively high costs. In addition, outgassing of the interlayer during processing can contaminate e.g. the substrates or the processing equipment.
The disadvantages of bonded articles with interlayers can best be overcome by bonding methods where the ultra-thin glass substrate and the support substrate are bonded without interlayer. One such method is e.g. in-situ fabrication whereas another promising method is electrostatic bonding. In-situ fabrication is described e.g. in US 2011/111194 where a bonded article is obtained joining two melt batches with different compositions for the thin glass substrate and the support substrate, respectively. After processing the ultra-thin glass substrate, the support substrate can be removed by e.g. dissolution in acid or by polishing. However, the fabrication is complicated and therefore generally not suited for mass production.
Electrostatic adhesion, in principle, is an ideal option for bonding an ultra-thin glass substrate to a support substrate with benefits such as easy production, low cost and suitability for mass production. Such bonding methods are described e.g. in US 6,735, 982 and WO 2004/033197. The ultra-thin glass substrate and the support substrate are charged with opposite charges and subsequently bonded by the electrostatic adhesion. The residual electrostatic charges hold the substrates together. Due to unevenness of the ultra-thin glass sheet prior to bonding, however, air-pockets or bubbles can form between the ultra-thin glass substrate and the support substrate. The ultra-thin glass substrate therefore unevenly adheres to the support substrate and the bonding is of limited quality. An improved method has therefore been proposed in PCT/CN2013/077585, where a bonded article is formed by additionally applying mechanical pressure to the electrostatically charged glass substrates during the bonding process in order to avoid the formation of air-pockets and ensure a close abutment.
Whereas this method already provides a viable way to establish a bonding, it also requires very clean surfaces of the glass substrates since even rather small impurities as dust or other pollution can give rise to air-pockets which generally are much larger than the impurity itself. Moreover, even at high degrees of cleanliness, air-pockets can also form without dust or impurities due to uneven establishing of the bonding.
It is therefore an object of the invention to overcome the above mentioned disadvantages. It is a particular object of the invention to provide a method for producing a bonded article and a bonded article with an even and high quality bonding without an adhesion promoting interlayer. It is another object of the invention to provide a method for producing a bonded article and a bonded article which allow for easy and versatile handling of an ultra-thin glass substrate during its processing. It is another object of the invention to provide an easy and cost-effective method for producing a bonded article and a bonded article which can be easily and cost-effectively produced. It is another object of the invention to provide a method for producing a bonded article and a bonded article that allow for a durable bonding with good bonding strength and an electrostatically neutral bonded article, in particular for the use in semiconductor industries. It is another object of the invention to provide a method for producing a bonded article and a bonded article that allow for a wet-washing of the bonded article. It is another object of the invention to provide a method for producing a bonded article and a bonded article that allow for an essentially bubble-free or air-pocket free bonding interface.
Description of the invention
The following terminologies and abbreviations are adopted herein:
- The term “glass article” is used in its broadest sense to include any object made of glass, ceramics and/or glass ceramics. As used herein, “ultrathin glass” refers to glasses and glass sheets or articles with a thickness of equal or less than 0.4 mm, unless otherwise specified. Exemplary glass compositions optimized for thin and ultrathin forming and applications requiring ultrathin glasses are without limitation described herein or e.g. in PCT/CN2013/072695 by
Figure PCTCN2015088726-appb-000003
- Total Thickness Variation (TTV) : The maximum variation in the thickness of a substrate or of the bonded article. The Total Thickness Variation is generally determined by measuring the wafer in about 20–200 points in a cross pattern (not too close to the wafer edge) and calculating the maximum measured difference in thickness.
The objects of the invention are solved by a method for producing a bonded article and a bonded glass article according to the independent claims. Further, the objects of the  invention are solved by a method for cleaning at least the bonding surface of a substrate for a bonded article and the use of such the bonded article according to a further independent claim.
According to one aspect of the invention, a method for producing a bonded article, in particular a bonded glass article, is provided comprising:
- providing a carrier substrate, in particular a glass carrier substrate, having a bonding surface,
- providing an ultra-thin substrate which is sheet-like and flexible, in particular an ultra-thin glass substrate, having a first and a second surface and a thickness t, where at least the first or second surface forms a bonding surface to be bonded to the bonding surface of the carrier substrate,
- cleaning at least the bonding surface of the ultra-thin substrate, preferably the whole ultra-thin substrate,
- cleaning at least the bonding surface of the carrier substrate, preferably the whole carrier substrate,
- establishing an intimate bonding by direct contact of the bonding surface of the ultra-thin substrate with the bonding surface of the carrier substrate in order to form the bonded article.
The method is characterized in that the intimate bonding is established by electrostatic forces resulting from a weak electrostatic field potential from electrostatic charges on at least one of the bonding surfaces, wherein the weak electrostatic field potential at the bonding surfaces does not exceed 1 kV.
Intimate bonding herein refers to direct bonding forces between the substrates at the bonding surfaces when they are brought in to direct contact. Such forces comprise Van der Waals and/or Hydrogen bonding forces. Also strong covalent Si-O-Si or bonding by OH groups can cause the intimate bonding. Such intimate bonding can withstand processes as high temperature treatments up to 600℃ or higher, vacuum processing, wet-processing, acidic treatment and also physical- (PVD) or chemical vapor deposition (CVD) processes as they may occur during flat panel display production or e.g. thin film  transistor (TFT) processes. Such bonding has been proposed in the art for bonded articles, in particular for bonded glass articles. By utilizing the intimate bonding, adhesion promoting interlayers for establishing the bonding can be omitted. In particular, adhesive layers have the potential for outgassing solvents or contamination by adsorbed materials typically at temperatures above 150℃ and are therefore advantageously avoided. By intimate, i.e. direct bonding of the substrates such disadvantages can be overcome. The direct bonding generally refers to direct contacting of the substrate material at the bonding surfaces. It is to be understood, however, that the direct contact of the intimate bonding does not withstand a coating of the bonding surface of one or both of the substrates, in particular the carrier substrate. Such coatings are used for reducing the bonding force in order to prevent the bonded article from forming a permanent bonding during high temperature treatments which would prevent destruction free de-bonding at a later stage. Such coatings can include e.g. Si coatings, Al coatings, Cr coatings, ITO coatings, SiO2 coating, TiO2 coating, Si3N4 coating, BN coating or combination of them.
One of the remaining problems, however, is to establish an even bonding at the bonding interface essentially without air-pockets or bubbles forming between the bonding surfaces. In order to be able to establish the intimate bonding with a sufficiently high quality, the bonding surfaces need to be thoroughly cleaned from impurities as dust or other contaminants to a sufficient degree. Otherwise, impurities can prevent the direct contacting of the bonding surfaces and thus result in air-pockets or bubbles rendering the intimate bonding incomplete. However, as has been found, bubbles often also form without impurities. Such bubbles are a result of an uneven establishing of the intimate bonding due to the difficulty to control the bringing into direct contact of the bonding surfaces. The invention has solved this problem by the surprising insight that the preparation of a bonding surface or the bonding surfaces with weak electrostatic charges allows for an even and simple establishing of the intimate bonding by the resulting weak electrostatic field potential between the bonding surfaces. The weak electrostatic field potential can thereby be a byproduct of the preparation of the substrates prior to establishing the bonding, in particular of the cleaning steps of the substrates. It is therefore not necessary to have a separate charging step where the electrostatic charges are applied to the substrates e.g. by means of a charging bar. This is of particular importance since such dedicated charging steps generally do not allow  for maintaining the required cleanliness of the bonding surfaces.
The carrier substrate and/or the ultra-thin substrate may be of any suitable material, including glass as an example (including glass-ceramics or ceramics) . The substrates need not be made of glass but can essentially also include any other material that can be electrostatically charged. In particular, the materials of the carrier substrate and the ultra-thin substrate can be different. The invention, however, has proven particularly advantageous with glass substrates. If made of glass, the substrates preferably comprise an alkali containing glass composition. Preferred glasses are e.g. lithium aluminosilicate glasses, soda-lime glasses, borosilicate glasses, alkali metal aluminosilicate glasses, and aluminosilicate glasses with low alkali content and also alkali-free compositions. Such glasses can be produced by e.g. drawing as e.g. down-draw processes, overflow-fusion or float processes. The coefficient of thermal expansion of the carrier substrate and the ultra-thin substrate should essentially match in order to prevent warping of the bonded article during processing at elevated temperatures.
In a preferred embodiment, the glass substrates comprise a lithium aluminosilicate glass with the following composition in weight-％:
Composition weight-％
SiO2 55-69
Al2O3 18-25
Li2O 3-5
Na2O+K2O 0-30
MgO+CaO+SrO+BaO 0-5
ZnO 0-4
TiO2 0-5
ZrO2 0-5
TiO2+ZrO2+SnO2 2-6
P2O5 0-8
F 0-1
B2O3 0-2
Preferably, the lithium aluminosilicate glass comprises the following glass composition in weight％:
Composition weight-％
SiO2 57-66
Al2O3 18-23
Li2O 3-5
Na2O+K2O 3-25
MgO+CaO+SrO+BaO 1-4
ZnO 0-4
TiO2 0-4
ZrO2 0-5
TiO2+ZrO2+SnO2 2-6
P2O5 0-7
F 0-1
B2O3 0-2
Further preferably, the lithium aluminosilicate glass comprises the following glass composition in weight％:
Composition weight-％
SiO2 57-63
Al2O3 18-22
Li2O 3.5-5
Na2O+K2O 5-20
MgO+CaO+SrO+BaO 0-5
ZnO 0-3
TiO2 0-3
ZrO2 0-5
TiO2+ZrO2+SnO2 2-5
P2O5 0-5
F 0-1
B2O3 0-2
In another preferred embodiment, the glass substrates comprise a soda-lime glass with the following composition in weight-％:
Composition weight-％
SiO2 40-81
Al2O3 0-6
B2O3 0-5
Li2O+Na2O+K2O 5-30
MgO+CaO+SrO+BaO+ZnO 5-30
TiO2+ZrO2 0-7
P2O5 0-2
Preferably, the soda-lime glass comprises the following glass composition in weight-％:
Composition weight-％
SiO2 50-81
Al2O3 0-5
B2O3 0-5
Li2O+Na2O+K2O 5-28
MgO+CaO+SrO+BaO+ZnO 5-25
TiO2+ZrO2 0-6
P2O5 0-2
Further preferably, the soda-lime glass comprises the following glass composition in weight％:
Composition weight-％
SiO2 55-76
Al2O3 0-5
B2O3 0-5
Li2O+Na2O+K2O 5-25
MgO+CaO+SrO+BaO+ZnO 5-20
TiO2+ZrO2 0-5
P2O5 0-2
In another preferred embodiment, the glass substrates comprise a borosilicate glass with the following composition in weight-％:
Composition weight-％
SiO2 60-85
Al2O3 0-10
B2O3 5-20
Li2O+Na2O+K2O 2-16
MgO+CaO+SrO+BaO+ZnO 0-15
TiO2+ZrO2 0-5
P2O5 0-2
Preferably, the borosilicate glass comprises the following composition in weight-％:
Composition weight-％
SiO2 63-84
Al2O3 0-8
B2O3 5-18
Li2O+Na2O+K2O 3-14
MgO+CaO+SrO+BaO+ZnO 0-12
TiO2+ZrO2 0-4
P2O5 0-2
Further preferably, the borosilicate glass comprises the following composition in weight-％:
Composition weight-％
SiO2 63-83
Al2O3 0-7
B2O3 5-18
Li2O+Na2O+K2O 4-14
MgO+CaO+SrO+BaO+ZnO 0-10
TiO2+ZrO2 0-3
P2O5 0-2
In another preferred embodiment, the glass substrates comprise an alkali metal aluminosilicate glass with the following composition in weight-％:
Composition weight-％
SiO2 40-75
Al2O3 10-30
B2O3 0-20
Li2O+Na2O+K2O 4-30
MgO+CaO+SrO+BaO+ZnO 0-15
TiO2+ZrO2 0-15
P2O5 0-10
Preferably, the alkali metal aluminosilicate glass comprises the following composition in weight-％:
Composition weight-％
SiO2 50-70
Al2O3 10-27
B2O3 0-18
Li2O+Na2O+K2O 5-28
MgO+CaO+SrO+BaO+ZnO 0-13
TiO2+ZrO2 0-13
P2O5 0-9
Further preferably, the alkali metal aluminosilicate glass comprises the following composition in weight-％:
Composition weight-％
SiO2 55-68
Al2O3 10-27
B2O3 0-15
Li2O+Na2O+K2O 4-27
MgO+CaO+SrO+BaO+ZnO 0-12
TiO2+ZrO2 0-10
P2O5 0-8
In another preferred embodiment, the glass substrates comprise an aluminosilicate glass with low or no alkali content with the following composition in weight-％:
Composition weight-％
SiO2 50-75
Al2O3 7-25
B2O3 0-20
Li2O+Na2O+K2O 0-4
MgO+CaO+SrO+BaO+ZnO 5-25
TiO2+ZrO2 0-10
P2O5 0-5
Preferably, the aluminosilicate glass with low or no alkali content comprises the following composition in weight-％:
Composition weight-％
SiO2 52-73
Al2O3 7-23
B2O3 0-18
Li2O+Na2O+K2O 0-4
MgO+CaO+SrO+BaO+ZnO 5-23
TiO2+ZrO2 0-10
P2O5 0-5
Further preferably, the aluminosilicate glass with low or no alkali content comprises the following composition in weight-％:
Composition weight-％
SiO2 53-71
Al2O3 7-22
B2O3 0-18
Li2O+Na2O+K2O 0-4
MgO+CaO+SrO+BaO+ZnO 5-22
TiO2+ZrO2 0-8
P2O5 0-5
The glasses used in the invention, in particular the above mentioned glasses, can also be modified. For example, the color can be modified by adding transition metal ions, rare earth ions as e.g. Nd2O3, Fe2O3, CoO, NiO, V2O5, MnO2, TiO2, CuO, CeO2, Cr2O3. Inclusion of such modifying colorant can e.g. enrich the design of consumer electronics such as color requirements for back covers or can provide an additional function for the toughened glass article as e.g. as color filters. In addition, luminescence ions, such as transition metals and rare earth ions can be added in order to endow optical functions, such as optical amplifiers, LEDs, chip lasers etc. In particular, 0-5 weight-％of rare earth oxides can be added to introduce magnetic, photon or optical functions. Moreover, refining agents as e.g. As2O3, Sb2O3, SnO2, SO3, Cl, F, and/or CeO2 can be added into the glass compositions in amounts of 0-2 weight-％.
The glass can also be provided with an anti-microbial function by applying an ion-exchange of the glass in an Ag+-containing salt bath or a Cu2+-containing salt bath. After the ion-exchange the concentration of Ag+ or Cu2+ is higher than 1 ppm, preferably higher than 100 ppm, and more preferably higher than 1000 ppm. The ultrathin glass with anti-microbial function could be applied for medical equipment such as computers or screens used in hospitals and consumer electronics.
It is to be understood that the sum of the components of the glass compositions amounts to 100 weight-％. Further preferred variations of such glasses can be found in e.g. PCT/CN2013/072695 and are hereby incorporated by reference.
The substrates preferably have a largest dimension of at least 0.1 m or larger, preferably 0.3 m or larger, further preferably 0.5 m or larger, or at least 3 inch or larger, preferably 6 inch or larger, preferably 8 inch or larger, further preferably 12 inch or larger. In particular, the substrates can have a Gen 1 size or larger, e.g. Gen 2, Gen 3, Gen 4, Gen 5, Gen 8 or even larger (e.g. substrate sizes from 100 mm x 100 mm to  3 m x 3 m) . Generally, the ultra-thin substrate is slightly smaller than the carrier substrate in order to reduce the risk for accidental de-bonding during the further processing of the bonded article.
The ultra-thin substrate preferably has a thickness t of equal or less than 0.4 mm, preferably equal or less than 0.2 mm, further preferably equal or less than 0.1 mm, further preferably equal or less than 0.05 mm, further preferred equal or less than 0.01 mm. Selected exemplary preferred thicknesses are 5 μm, 10 μm, 15 μm, 25 μm, 30 μm, 35 μm, 55 μm, 70 μm, 80 μm, 130 μm, 145 μm, 175 μm, 190 μm, 210 μm or 280 μm.
The carrier substrate generally has a thickness of larger than 0.3 mm in order to be sufficiently rigid for supporting the ultra-thin substrate. It is to be understood that the thicknesses of the ultra-thin substrate and the carrier substrate are generally adapted to each other in order to provide favorable processing conditions according to the specific requirements. Generally, the carrier substrate has a greater thickness than the ultra-thin substrate. The substrates can have a rectangular, in particular quadratic, or elliptical, in particular circular, shape. Other shapes and dimensions can also be applied if the specific application so requires and the shapes of ultra-thin substrate and carrier substrate do not necessarily have to match. It is essentially also possible to apply several smaller ultra-thin substrates on a single large carrier substrate.
In a preferred embodiment of the method according to the invention, an intermediate bonding state is established prior to establishing the intimate bonding. In the intermediate bonding state, the ultra-thin substrate is bonded to the carrier substrate by electrostatic forces resulting from the weak electrostatic field potential with its bonding surface facing the bonding surface of the carrier substrate such that an air gap between the bonding surfaces persists. The bonding surfaces are thus brought into close proximity over the whole area of the bonding interface but do not get into direct contact in the intermediate bonding state.
According to the invention, the intermediate bonding state is established by an electrostatic field potential at the bonding surfaces which is strong enough to establish a preliminary bonding in the intermediate state but is too weak to pull the bonding surfaces together. It is surprisingly found that such an intermediate bonding can  preferably be established by comparatively weak electrostatic field potentials that do not exceed 1 kV. Such electrostatic field potentials can easily be obtained by various methods and do not require the use of electrodes or charging bars. Moreover, such weak electrostatic field potentials have the advantage that residual dust or impurities in the process atmosphere are less attracted to the bonding surfaces as it is the case with electrostatic bonding at conventional electrostatic field potentials at e.g. 15–20 kV, thus preventing further contamination of the cleaned bonding surfaces.
The intermediate bonding state can subsequently easily be established by placing e.g. the ultra-thin substrate with its bonding surface on the bonding surface of the carrier substrate. In an exemplary vertically stacked setup, gravitational pull and electrostatic force together can be weak enough that the air gap between the bonding surfaces persists i.e. the air cannot be expelled. It has to be understood that in this context "air gap" is not limited to a gap filled by air but also comprises all kinds of gas that could be advantageous in the course of producing a bonded article.
By establishing the intermediate bonding state, a semi-finished bonded article is obtained which allows for easy and controlled establishing of the intimate bonding of the bonded glass article according to the invention.
It has surprisingly been found that, once the intermediate bonding state has been established, the intimate bonding state can be established in a very simple manner and with a high degree of uniformity. Preferably, the establishing of the intimate bonding is triggered by forcing the ultra-thin substrate in the intermediate bonding state in a localized area to the carrier substrate such that the air gap between the bonding surfaces in the localized area is reduced, preferably in a manner that the bonding surfaces come into contact in the localized area, causing an increase in the electrostatic force between the bonding surfaces in the localized area which increase in the electrostatic force subsequently automatically propagates across the area of the bonding surfaces without application of any further external force and establishes the intimate bonding by bringing essentially the whole area of the bonding surfaces into direct contact.
"Localized area" herein refers to an area which is much smaller than the whole area of the bonding interface which is formed by the overlapping bonding surfaces of the ultra- thin substrate and the carrier substrate, respectively. In particular, the localized area can e.g. be line-like or point-like where, naturally, point-like or line-like includes a finite but comparatively small physical extension. It is to be understood that the dimension of the localized area generally has to be adapted to the flexibility of the ultra-thin substrate in order not to cause breakage during the application of the force e.g. mechanical force.
The thus caused increase in the electrostatic force between the bonding surfaces which is proportional to-1/r2 , causes areas of the bonding surfaces which are adjacent to the localized area to be also pulled towards each other, whereby preferably the bonding surfaces in the adjacent areas are also brought into direct contact. This, in turn, causes the further adjacent areas to be pulled towards each other and so on such that the intimate bonding is automatically established across the whole bonding interface in a manner of a continuous "chain reaction" . It has to be noted that the establishing of the intimate bonding is only triggered by forcing the bonding surfaces together in the localized area in the present case and no further force needs to be applied in other areas of the bonding surfaces. The weak electrostatic field potential ensures that the increase triggered in the localized area automatically propagates across the bonding interface and causes the bonding surfaces to come into direct contact in order to establish the intimate bonding.
A surprising advantage of this method is that the intimate bonding is automatically established in an intrinsically even manner since the electrostatic force always only increases in the next neighboring adjacent regions and, thus, expels the air in the gap in an even manner and bubble forming is prevented. The localized area is thereby preferably located in a central area of the bonding interface, preferably at a distance as large as possible from the perimeter, in order to ensure even propagation towards the perimeter.
It has surprisingly been found that the electrostatic charges causing the weak electrostatic field potential which is utilized in the course of the method according to the invention can be applied to the bonding surface or surfaces in the course of the cleaning of the carrier substrate and/or the ultra-thin substrate. The process parameters during the cleaning process can be adapted such that sufficient electrostatic charge is built-up on the bonding surface or surfaces that the necessary strength of the weak electrostatic field potential can be achieved. Thereby, it is not necessary to utilize a unit or device  that is dedicated to apply the electrostatic charges as e.g. electrodes or a charging bar. Under adequate conditions, sufficient electrostatic charges can build up during the cleaning step itself. However, it is not excluded that the method comprises a separate charging step e.g. after the cleaning step for establishing the necessary electrostatic field potential at the bonding surfaces.
Preferably, the cleaning of the at least one bonding surface of the carrier substrate and/or the cleaning of the at least one surface of the ultra-thin substrate comprise a wet-washing step and a drying step. Thereby, in particular during the drying step, electrostatic charges can be established on the bonding surface of the substrate to be cleaned, in particular the carrier substrate. The drying step is preferably performed immediately after the washing step such that contamination by impurities is prevented and charge build-up is supported.
It has to be noted that, due to the brittleness of the ultra-thin substrates, the substrate can be attached to a support substrate in case of ultra-thin substrates during the cleaning step. Currently, ultra-thin substrates with thicknesses of 0.1 mm or larger can be cleaned, in particular by brush cleaning, without utilizing a support carrier. Below such thicknesses, however, support carriers may become necessary. The support carriers in such cases are attached to a substrate surface opposite to the bonding surface.
It has been found that it is particularly advantageous if the wet-washing step comprises brush cleaning with at least one rotating brush-roller which brushes the bonding surface, preferably with at least a second rotating brush roller arranged on the opposite side of the substrate in order to simultaneously brush a surface of the substrate opposite to the bonding surface. The brush rollers preferably comprise a polymer material, in particular a soft nylon, at least as brush material. Preferably, the brush rollers rotate at approx. 100 rpm–2'000 rpm. The pressure applied by the brush rollers onto the substrate is preferably chosen as low as possible but as high as necessary to achieve the desired cleaning action without breakage of the substrate. Whereas brush cleaning is the preferred method and has yielded the most promising results, it is not excluded that other cleaning methods as e.g. ultra-sonic cleaning can also be applied during the wet-washing step.
It has proven to be particularly advantageous if the substrate is conveyed during the wet-washing step by means of conveyor rollers wherein the conveyor rollers comprise, at least on their outsides, a polymer material, in particular isobutylene isoprene (IIR) , polypropylene (PP) , polyethylene (PE) , polyethylene terephthalate (PET) , unsaturated polyethylene (UPE) , preferably isobutylene isoprene (IIR) . Other suitable materials, however, can also be considered in the wet environment of the wet-washing step. The brush roller can thereby be stationary while the substrate is conveyed past the rotating brush roller. Preferably, the rotation of the brush rollers is against the conveying direction of the substrates. The conveying speed is preferably in the range of 1 m/min–20 m/min. In a preferred embodiment, the substrate is conveyed while being supported on the conveyor rollers with a surface which is opposite to the bonding surface.
Polymeric materials for the conveyor rollers have proven to provide a non-sticky surface preventing the accumulation of dust or impurities on the roller surface which could contaminate the substrate surface. In particular, IIR has proven to be the preferable material for the conveyor rollers in a wet environment. The conveyor rollers can thereby only have an outer surface made from said materials or can be entirely formed of these materials. Preferably, the entire outer surface of the rollers is at least encapsulated by one of said materials. During the wet-washing, a washing liquid as e.g. a detergent solution is applied to the substrate where the detergent preferably has a pH value around 10.
Whereas several methods can be applied for drying the wet-washed substrate, the drying step preferably comprises blowing clean air onto the substrate, in particular onto the bonding surface. It is to be understood, however, that other gases or gas compositions can also be advantageous if the particular process conditions so require. Preferably, the clean air is also blown onto a surface opposite to the bonding surface. The clean air thereby contains at most 106 particles/m3 of size≥0.1 μm, in particular according to standard level ISO 6 of standard ISO 14644-1, and further preferably contains at most 105 particles/m3 of size≥0.1 μm, in particular according to standard level ISO 5 of standard ISO 14644-1. It has been found that such cleanroom levels are sufficient to ensure sufficient cleanliness of the bonding surfaces of the substrates for establishing a bonding with the required quality.
Preferably, the air is hot and dry and has a temperature of not more than 60℃, preferably not more than 50℃, further preferably not more than 45℃, and the relative humidity is not more than 45％, preferably not more than 25％. It has been found that the above parameter ranges result in a sufficient built-up of electrostatic charges in order to produce the necessary weak electrostatic potential. It is to be understood that the temperature of the hot and dry air is generally above room temperature since higher temperature support the drying action. However, higher temperatures reduce the electrostatic charge build-up. It is therefore necessary to adapt the process parameters during the drying step to the specific conditions. Relevant parameters comprise the temperature and humidity (dryness) of the air and the drying time during which the hot and dry air is applied. Exemplary parameter combinations yielding favorable results were air temperatures of approx. 35℃ to 45℃ and drying times of approx. 30 s–50 s to get humidity of approx. 20％to 30％or air temperatures of 55℃ to 60℃ at drying times around 10 s to get the same humidity.
Preferably, the air is blown onto the substrate by at least one air-blade assembly, preferably by two air-blade assemblies arranged on opposite sides of the substrate. An air-blade assembly thereby refers to an elongate bar with a plurality of embedded nozzles or a single elongate nozzle providing an essentially continuous curtain of air-flow. Air-blade assemblies have the advantage that the air flow can be specifically controlled and directed onto the bonding surface and, as the case may be, an opposite surface of the substrate. The air-blade assemblies are thereby preferably arranged essentially transverse, usually at a moderately oblique angle, to a processing direction of the substrate during the cleaning process and can thus process the substrate across its whole width at once. Compressed air at pipe pressures of about 0.3 MPa has proven to be sufficient to achieve the desired results by using air-blade assemblies.
During the drying step, the substrate is preferably conveyed by means of conveyor rollers where the conveyor rollers comprise, at least on their outsides, a polymer material, in particular isobutylene isoprene (IIR) , polypropylene (PP) , polyethylene (PE) , polyethylene terephthalate (PET) , unsaturated polyethylene (UPE) , preferably unsaturated polyethylene (UPE) . In the preferred embodiment, the drying step is performed stationary whereas the substrate is conveyed past e.g. an air-blade nozzle. Polymeric materials for the conveyor rollers have proven to yield excellent results  regarding an electrostatic charge build-up on the bonding surface and, at the same time, can provide a non-sticky surface preventing the build-up of dust or impurities on the roller surface which could contaminate the substrate surface. In particular, UPE has proven to be the preferable material for the conveyor rollers in the drying environment and yielded promising results regarding the build-up of electrostatic charges on the bonding surface of the substrate.
In particular, the wet-washing by brush rollers and air-drying as described in the above in combination with conveyor rollers as described surprisingly yield a clean and weakly electrostatically charged bonding surface. It is believed that the brushing of the bonding surface and wet chemical treatment by a detergent causes an activation of the bonding surface facilitating the establishment of the later intimate bonding. The drying step by blowing hot and dry air supports the build-up of electrostatic charges and allows for maintaining the activation which ultimately supports the simple and even establishment of the intimate bonding. It has to be noted that the synergetic effect in the present context of the combination of brush cleaning and hot/dry air cleaning as described in the above goes beyond what would be expected by simple stringing together the single steps. As such, the unexpected overall effect can advantageously be exploited for producing a bonded article according to the method of the present invention.
The cleaning step (s) preferably is performed in such a manner that, after the cleaning of the substrate, the density of impurities with a size in the range from 20-50 μm on the at least one bonding surface is equal or less than 5/0.01m2, preferably equal or less than 3/0.01m2, further preferably equal or less than 1/0.01m2. Such densities of impurities allow for establishing a bonding interface which is regarded as essentially bubble or air-pocket free in the present context. It is of course to be understood that the cleaner the surface the better the bonding and as such the above values are regarded as upper limits for achieving the desired results. Particles with sizes less than 20 μm do not seem to contribute to bubble or air-pocket forming.
In order to ensure sufficient cleanliness of the bonding surfaces and prevent depletion of the electrostatic charges on the bonding surfaces, it is advantageous to perform the establishing of the intimate bonding state as soon as possible after the cleaning of the substrates. It is therefore preferred to perform the cleaning of the bonding surface of the ultra-thin substrate and the cleaning of the bonding surface of the carrier substrate at  the same time such that the cleaned bonding surface of the ultra-thin substrate and the cleaned bonding surface of the carrier substrate can be provided at essentially the same time. Dependent on the cleaning process used, it can be advantageous to provide two cleaning apparatus in parallel where the carrier substrate is cleaned in one of the apparatus and the ultra-thin substrate is cleaned in the other apparatus and the both substrates are brought together immediately after the cleaning.
It has been found that in an environment with about 40％relative humidity, the bonding should usually be established at latest within about 10-15 min. whereas at higher humidity as e.g. approx. 60％, the bonding should be established within at latest 3–5 min. after the drying step i.e. after the cleaning step was completed. In order to avoid unwanted charge depletion, however, shorter times are generally preferred. It is therefore preferred to establish the intimate bonding immediately after the cleaning of the bonding surface of the carrier substrate and the bonding surface of the ultra-thin substrate. If an intermediate bonding state is established, it is preferred to establish the intermediate bonding state immediately after the cleaning and the intimate bonding is preferably immediately established after having established the intermediate bonding state. It is to be understood that "immediately" herein includes possible transfers from one processing station to another processing station in the course of the method.
The strength of the intimate bonding of the bonded article can be further increased by annealing the bonded article after the establishing of the intimate bonding to a temperature in the range from 60℃-200℃, preferably in the range from 80℃ to 160℃, for a time in the range from 1 to 10 hours. These parameter ranges have proven to ensure an excellent bonding strength and quality but still allow for later de-bonding by conventional methods which is particularly advantageous if the bonded article is used as temporarily bonded article. It has been found that a bonded article whose bonding has been strengthened by such annealing can be processed by e.g. high temperature treatments at temperatures at e.g. more than 500℃, sputtering coating as e.g. ITO coating at e.g. 150℃-300℃ and a pressure of approx. 8x10-3 Pa for about 1 to 2 hours, PVD coating as e.g. anti-reflective (AR) coating at e.g. 120℃-200℃ at pressures of approx. 2x10-2 Pa for about 0.5 to 1 hours, wet processes as brush cleaning or spin cleaning at temperatures of e.g. 25-80℃ at pH ranges of approx. 5 to 13, and further processes as e.g. high speed spinning, UV exposure etc. In particular, it  has been shown that the bonded article can endure the harsh conditions during flat panel display (FDP) processing or TFT production process without significant degeneration in the bonding quality.
The annealing also can improve the intimate bonding to render the bonding interface essentially fluid tight, in particular water tight, such that no fluid can penetrate between the carrier substrate and the ultra-thin substrate. To this end, the annealing can be applied only or primarily in border areas along the perimeter of the bonding interface in order to selectively increase the bonding strength and thus the sealing at the border.
It has also been found that annealing to temperatures as e.g. 400℃ or higher for about 5-10 hours can increase the strength of the intimate bonding to a degree that destruction-free de-bonding becomes difficult or impossible. The method according to the invention can therefore also be used for producing a permanently bonded article which can e.g. be used in later applications.
Due to the high quality of the intimate bonding that can be achieved by the method of the invention, in particular a fluid tight bonding interface, the bonded article can also be processed by a wet-processing step, in particular a wet-washing step, after having established the intimate bonding. The wet-processing is thereby preferably performed after the strength of the intimate bonding of the bonded article has been increased by annealing. Thereby, the bonded article cannot only be cleaned to a desired degree after establishing the intimate bonding, it also can essentially be electrostatically neutralized by the wet-processing. This is particularly advantageous for applications where a net electrostatic charge on the bonded article could prevent its use e.g. in semiconductor industries.
As has already been pointed out in the above, the method of the invention preferably is executed under clean conditions in order to prevent contamination of the bonding surfaces with impurities. It is therefore preferred that all steps at least from and including the cleaning steps until the intimate bonding is established are conducted in a cleanroom environment at least according to level ISO 6 of standard ISO 14644-1, preferably at least according to level ISO 5 of standard ISO 14644-1. ISO 5 thereby refers to a maximum density of particles of≤100'000 particles/m3 having a size≥0.1 μm,≤23'700 particles/m3 having a size≥0.2 μm, ≤10'200 particles/m3 having a  size≥0.3 μm, ≤3'520 particles/m3 having a size≥0.5 μm, ≤832 particles/m3 having a size≥1 μm, and≤29 particles/m3 having a size≥5 μm. ISO 6 corresponds to a maximum density of particles of≤1'000'000 particles/m3 having a size≥0.1 μm, ≤237'000 particles/m3 having a size≥0.2 μm, ≤102'000 particles/m3 having a size≥0.3 μm, ≤35'200 particles/m3 having a size≥0.5 μm, ≤8'320 particles/m3 having a size ≥1 μm, and≤293 particles/m3 having a size≥5 μm. ISO 5 and ISO 6 correspond to cleanroom classes 100 and 1000, respectively, according to the now obsolete standard US FED STD 209E.
Another aspect of the invention also concerns a bonded article, in particular a bonded glass article, preferably produced by the method for producing a bonded article described herein. The bonded article comprises a carrier substrate, in particular a glass carrier substrate, having a bonding surface, and an ultra-thin substrate which is sheet-like and flexible, preferably an ultra-thin glass substrate, having a first and a second surface and a thickness t, where at least the first or second surface forms a bonding surface. The carrier substrate and the ultra-thin substrate are intimately bonded to each other by direct contact of the bonding surface of the ultra-thin substrate with the bonding surface of the carrier substrate. The bonded article is characterized in that the bonding interface formed by the intimately bonded bonding surfaces is essentially free of bubbles with surface dimensions larger than 7 mm2 and has a density of bubbles with surface dimensions equal or smaller than 3 mm2 which is less than 15 bubbles/0.01m2, preferably less than 10 bubbles/0.01m2 and further preferably smaller than 5 bubbles/0.01m2.
The bonded article is preferably essentially electrostatically neutral, in particular its net electrostatic field potential is less than 10 V, preferably less than 1 V. The electrostatic filed potential thereby refers to the overall electrostatic field potential of the bonded article with respect to ground potential. Such a bonded article can e.g. be obtained by wet-washing the bonded article after establishing the intimate bonding. It is thereby important that the intimate bonding is tight enough that no washing liquid can penetrate between and de-bond the bonded substrates which can be ensured by the method according to the invention.
The bonded article preferably has a largest dimension of at least 0.1 m or larger, preferably 0.3 m or larger, further preferably 0.5 m or larger, or 3 inch or larger,  preferably 6 inch or larger, further preferably 8 inch or larger, further preferably 12 inch or larger. In particular, the bonded article according to the invention can also have a Gen 1 size or larger, e.g. Gen 2, Gen 3, Gen 4, Gen 5, Gen 8 or even larger (e.g. substrate sizes from 100 mm x 100 mm to 3 m x 3 m) . Generally, the larger the substrates are, the more difficult it becomes to establish an essentially bubble free bonding interface.
The bonded article preferably comprises the ultra-thin substrate with a thickness t of equal or less than 0.4 mm, preferably equal or less than 0.2 mm, further preferably equal or less than 0.1 mm, further preferably equal or less than 0.05 mm, further preferred equal or less than 0.01 mm. Selected preferred thicknesses are 5 μm, 10 μm, 15 μm, 25 μm, 30 μm, 35 μm, 55 μm, 70 μm, 80 μm, 130 μm, 145 μm, 175 μm, 190 μm, 210 μm or 280 μm.
Further preferred, the carrier substrate of the bonded article has a thickness of at least 0.3 mm. It can thereby be ensured that the carrier has sufficient rigidity in order to support the ultra-thin substrate. It is to be understood that the thicknesses of the ultra-thin substrate and the carrier substrate are generally adapted to each other in order to provide favorable processing conditions according to the specific requirements. Moreover, the total thickness of the bonded article can be adapted to the requirements as e.g. given by the processing equipment by e.g. choosing a thicker carrier in order to obtain the desired overall thickness for a given the ultra-thin substrate.
The bonded article, in particular the substrates of the bonded article, can have a rectangular, in particular quadratic, or elliptical, in particular circular, shape.
Due to the high quality of the intimate bonding of the bonded article, the Total Thickness Variation (TTV) can be essentially equal or less than the sum of the TTV of the carrier substrate and the ultra-thin substrate. In particular, the TTV of the bonded article is dominated by the TTV of the substrates whereas the bonding has only a comparatively small contribution. In particular, the TTV can be smaller than 20 μm, preferably even smaller than 10 μm.
Preferably, the intimate bonding of the bonded article according to the invention requires an initial de-bonding force for de-bonding the ultra-thin substrate from the carrier substrate which is larger than 0.2 N. If the bonded article is annealed after the  intimate bonding has been established, the de-bonding force can be larger than 1 N and even larger than 10 N. The de-bonding force was thereby measured on a bonded article with a strip-shaped bonding interface having a width of 40 mm±0.5mm of arbitrary length. The ultra-thin substrate was first detached at one end of the strip shaped bonded article (initial de-bonding) and then continuously peeled of along the longitudinal direction of the bonded article (continuous de-bonding) . The values for continuous de-bonding can lie in the range of 0.01 to 0.08 N and, after annealing even 0.1 N to 0.3 N. Preferably, the bonding interface of the bonded article is fluid tight, in particular water tight, such that no fluid can penetrate between the carrier substrate and the ultra-thin substrate. Thereby, the bonded article can e.g. be wet-processed.
The invention also concerns the use of a bonded article, in particular a bonded glass article, produced by a method for producing a bonded article or a bonded article as described herein, for applications, in particular for the production of applications, as display, display cover, in particular for cover of touch screens, preferably for LCD displays, TFT displays, OLED displays, OLED lightning, electro-luminescence (EL) lighting, sensors, in particular touch or fingerprint sensor, E-paper, optical devices, in particular optical lenses or optical filters, or MEMS/MOEMS, in particular optical switches or optical cross-connectors. MEMS hereby refer to micro-electro-mechanical systems and MOEMS to micro-opto-electro-mechanical systems.
Brief description of the drawings
The exemplary figures used for illustration of the invention schematically show:
Fig. 1: a bonded article according to the invention；
Fig. 2a: a bonded article according to the invention having circular shape；
Fig. 2b: a bonded article according to the invention having rectangular shape；
Fig. 3: block diagram of the method according to the invention；
Fig. 4: diagram for a cleaning step for cleaning a substrate to be bonded；
Fig. 5: diagram for a cleaning step for cleaning an ultra-thin substrate on a support carrier；
Fig. 6a: an ultra-thin substrate and a carrier substrate in an intermediate bonding state；
Fig. 6b: triggering a transition from the intermediate bonding state of Fig. 6a to the intimate bonding state of the bonded article according to Fig. 1；
Fig. 6c: transition from the intermediate bonding state of Fig. 6a to the intimate bonding state according to Fig. 1 in progress；
Fig. 7: exemplary force vs. distance diagram for the de-bonding of a bonded article according to the invention.
The dimensions and aspect ratios in the figures are not to scale and have been oversized in part for better visualization. Corresponding elements in the figures are generally referred to by the same reference numerals.
Detailed description of figures and examples
Fig. 1 shows a bonded article 1 according to the invention. The bonded article 1 comprises a carrier substrate 2 and an ultra-thin substrate 3 which both are made from a glass material. The carrier substrate has a thickness t' and the ultra-thin substrate 3 has a thickness t. The ultra-thin substrate 3 is intimately bonded with a bonding surface 3.1 to a bonding surface 2.1 of the carrier substrate 2. An opposite surface 3.2 of the ultra-thin substrate is available for processing in the bonded state. An opposite surface 2.2 of the carrier substrate can e.g. be used for handling as e.g. conveying the bonded article 1 during processing.
The bonding surfaces 2.1 and 3.1 are in direct contact with each other and no adhesion promoting interlayer is present. The bonding is an intimate bonding achieved by forces comprising Van der Waals and/or Hydrogen bonding forces and can also be effected by covalent Si-O-Si or bonding by OH groups. As can be seen from Fig. 2a and 2b, the bonded article 1 can have a circular or rectangular shape. The ultra-thin substrate 3 can thereby have slightly smaller dimensions as the carrier substrate 2 in order to protect  the perimeter of the bonding interface which is defined by the overlapping area of the bonding surfaces 2.1 and 3.1.
Fig. 3 shows a simplified flow diagram for the method for producing the bonded article 1 according to the invention. The process comprises a step 10 of providing the carrier substrate 2 and the ultra-thin substrate 3, a step 20 of cleaning the  substrates  2 and 3 and a step 30 of establishing the intimate bonding. In step 10, the ultra-thin substrate 3 can be provided as is or can already be attached to a support substrate for easier handling during the execution of the method (see e.g. Fig. 5) . Generally, the ultra-thin substrate 3 with thickness t equal or larger than 0.1 mm can be processed without the support substrate. For thinner ultra-thin substrates 3, however, it is generally necessary to support the ultra-thin substrate 3 in order to avoid breakage during processing. The ultra-thin substrate 3 can thereby be attached to the support substrate by known means as e.g. an electrostatic film which does not exhibit any adhesives or other materials that could contaminate the cleaning equipment as e.g. a brush roller 5.1 (see e.g. Fig. 4) and thus indirectly the bonding surface 2.1. The carrier substrate 3 is usually provided as is. Ultra-thin substrate 3 and carrier substrate 2 can have undergone preparatory steps as e.g. a pre-cleaning or other preparation before the actual cleaning step 20.
During the cleaning step 20, both the ultra-thin substrate 3 and the carrier substrate 2 are cleaned to the desired degree of cleanliness, wherein in particular the bonding surfaces 2.1 and 3.1 are cleaned. Thereby, it can be advantageous to perform a cleaning step 21 of the carrier substrate 2 and a cleaning step 22 of the ultra-thin substrate 3 at the same time i.e. in parallel such that the cleaned  substrates  2 and 3 can be provided at the same time at the end of the cleaning step 20. Dependent on the cleaning method applied, it may be necessary to provide two cleaning apparatus in parallel in a production assembly to achieve this goal.
The preferred cleaning step 21 and/or 22 comprises a wet-washing step 21.1 or 22.1 which includes brush cleaning by rotating brush rollers 5 (see e.g. Fig. 4) . Since such brush cleaning apparatus' can generally not be configured to process substrates of different thicknesses at the same time, it may be necessary in this case to provide two brush cleaning apparatus in parallel. The preferred cleaning step 21 and/or 22 further comprise a drying step 21.2 and 22.2, respectively, during which the substrates 2 and/or 3 are dried for establishing the intimate bonding in a bonding step 30.
In a preferred embodiment of the invention, the cleaning steps 21 and/or 22 are configured such that, after the drying step 21.2 and/or 22.2, the carrier substrate 2 and/or the ultra-thin substrate 3 are provided with a weak electrostatic charge on the bonding surfaces 2.1 and 3.1, respectively. The electrostatic charges, in particular the differences on the both bonding surfaces 2.1 and 3.1, cause a weak electrostatic potential between the bonding surfaces which is utilized according to the present invention to establish the intimate bonding of the bonded article 1. The weak electrostatic potential does not exceed 1 kV. This has the advantage that, in particular the ultra-thin substrate 3, remains easy to handle and contamination with impurities can be reduced due to the weak attractive forces associated with the weak electrostatic potential. Since the electrostatic charges can quickly deplete, it is important that the bonding in step 30 follows shortly or preferably immediately after the cleaning step 20. The weak electrostatic potential thereby establishes the intimate bonding of the bonded article 1. It is to be understood that the drying step 21.2 or 22.2 can be repeated in order to achieve the desired result.
The bonding step 30 can comprise establishing an intermediate bonding state in step 31 (see e.g. Fig. 6a-6c) . In the intermediate bonding state, the ultrathin-substrate 3 is arranged with its bonding surface 3.1 facing the bonding surface 2.1 of the carrier substrate 2 and is attracted by the weak electrostatic potential i.e. the corresponding forces. The intermediate state provides a starting position for establishing the intimate bonding state. The transition from the intermediate bonding state to the intimate bonding state can in this case be initiated by a trigger step 32 where a localized force is applied to the ultra-thin substrate 3 that forces the ultra-thin substrate 3 in a localized area towards the carrier substrate 2 (see Fig. 6a-6c) .
At the end of the bonding step 30, the bonded article 1 is provided 40. In a preferred embodiment, at least the cleaning step 20 and the bonding step 30 are both performed in a continuous clean-room environment 50, in particular according to standard ISO 5 or ISO 6 according to standard ISO 14644-1.
Figure 4 shows the cleaning step 21 and/or 22 with details regarding the preferred washing step 21.1/22.1 and the preferred drying step 21.2/22.2. For the sake of simplicity, the process details are described only by way of the carrier substrate 2 in the following.
The carrier substrate 2 is conveyed on a plurality of conveyor rollers 4 during the washing step 21.1. The carrier substrate 2 thereby is supported by the conveyor rollers 4 on its surface 2.2 which is opposite to the bonding surface 2.1. The conveyor rollers 4 convey the carrier substrate 2 by means of rotation in a processing direction A. It is preferred that the conveyor rollers 4 are made or are essentially encapsulated by a polymer material, preferably IIR. Such materials can be non-sticky and thus avoid the accumulation of impurities as dust or other residual particles on the surfaces of the conveyor rollers 4 which could subsequently be transferred to the carrier substrate 2.
During the washing step 21.1, at least one brush roller 5 brushes the bonding surface 2.1 of the substrate. The rotation of the brush roller 5 is thereby directed against the processing direction A of the substrate i.e. the brush bristles 5.1 brush the bonding surface 2.1 against the processing direction A. The brush roller 5 is preferably stationary while the carrier substrate 2 is conveyed past the brush roller 5 in direction A. Another brush roller 6 is provided for brushing the surface 2.2 of the carrier substrate 2 in the same manner.
It is to be understood that Fig. 4 shows a simplified schematic view and the brushing assembly can be more complicated in an industrial assembly. In particular, e.g.  several brush rollers  5 or 6 can be present on either side of the carrier substrate 2. During the washing step 21, the washing area is flooded with a washing liquid including e.g. a weakly alkaline detergent (not shown) . After the washing step 21.1, the carrier substrate 2 is further conveyed 50 to the drying area of drying step 21.2.
During the drying step 21.2, the carrier substrate 2 is conveyed by further conveyer rollers 7. The conveyor rollers 7 can essentially correspond to the conveyor rollers 4 of the washing step 21.1. However, it has been found that for the build-up of electrostatic charges on the bonding surface 2.1 during the drying step 21.2, a material of UPE is preferred and yields the most promising results. Also, UPE is more suitable for a dry and, as the case may be, hot environment. The conveyor rollers 7 convey the carrier substrate 2 in the processing direction A by means of rotation. It is to be understood that A does not necessarily refer to a spatial direction but rather a direction in which the processing is performed.
An air-blade nozzle 8 blows air onto the bonding surface 2.1. The air-blade nozzle 8 is thereby arranged essentially transversely to the processing direction of the substrate. It is to be noted, though, that an oblique arrangement can be advantageously applied for blowing off excessive liquid in a dedicated direction. The air-blade nozzle 8 removes humidity from the substrate by air-pressure forcing the residual liquid form the bonding 2.1 surface on the one hand and, on the other hand, by absorption of excess humidity by the air. It is therefore preferred that the air is dry. In addition, the air should be heated in order to improve the drying action. Moreover, the air is preferably to be cleaned in order not to introduce additional contaminants or pollutants that would render the bonding surface unusable. The air is preferably cleaned according to class ISO 6, and further preferably to class ISO 5 of standard ISO 14644-1
It has been found that for particular ranges of the humidity and temperature of the air, the build-up of electrostatic charges on the bonding surface 2.1 is particularly well supported and can yield electrostatic field potentials of up to 1 kV. Preferred parameter ranges are a relative humidity which is at or below 45％and temperatures above room temperature but which do not exceed 60℃. It has to be understood that the specific combination of the washing step 21.1 and the drying step 21.2 as described herein give an optimal environment for the activation of the bonding surfaces 2.1 and 3.1 and the build-up of the necessary weak electrostatic field potentials according to the method of the invention. In particular, the electrostatic field potentials can build-up without incorporating specific equipment into the processing line and/or performing corresponding additional processing steps. This, on the one hand, renders the production process simple and cost effective and, on the other hand, prevents further contamination of the bonding surface 2.1 by impurities: Dedicated electrostatic charging by e.g. electrodes or plasma arcs inevitable cause additional contamination with impurities and as such do not allow for achieving the desired levels of cleanliness.
Another air-blade nozzle 9 is provided for drying the surface 2.2 of the carrier substrate 2. It is to be understood that Fig. 4 shows a simplified schematic view and the drying assembly in an industrial application can be embodied different from the one shown. In particular, e.g. several air- blade nozzles  7 or 8 can be present on either side of the carrier substrate 2 or other nozzle assemblies can be used.
Figure 5 shows an exemplary washing step assembly for the ultra-thin substrate 3 which is temporarily bonded to a support substrate 60. In the present embodiment, the ultra-thin substrate 3 is bonded to the support substrate 60 by an electrostatic film 61 which is sufficient during the cleaning step according to the present invention. It has to be noted that the electrostatic film 61 is chosen since it does not contain adhesives or other materials that could compromise the clean environment. The ultra-thin substrate 3 is conveyed by means of the conveyor rollers 4 which support and convey the support substrate 60. After the cleaning step 20 is finished, the ultra-thin substrate 3 can be removed from the support substrate 60 together with the film 61 by de-bonding or cutting the film 61. The ultra-thin substrate 2 can be bonded to the carrier substrate 2 while the support substrate 60 is still attached or can be bonded after delamination from the support substrate 60. After the support substrate 60 has been removed, the film 61 can be peeled off from the ultrathin-substrate 3.
Figures 6a to 6c show the establishing of the intimate bonding in bonding step 30 where the ultra-thin substrate 3 and the carrier substrate 2 are brought into an intermediate bonding state 70 as shown in Fig. 6a (step 31 in Fig. 3) . In the intermediate bonding state 70, the ultra-thin substrate 3 is preferably placed on top of the carrier substrate 2 with its bonding surface 3.1 facing the bonding surface 2.1 of the carrier substrate 2. If the electrostatic potential between the bonding surfaces 2.1 and 3.1 is weak enough, neither the resulting electrostatic force nor in combination with a gravitational force may be sufficient to bring the bonding surfaces 2.1 and 3.1 in direct contact. As such, an air gap 71 persists between the bonding surfaces 2.1 and 3.1 (Fig. 6a) . The weak electrostatic force field is indicated by light grey shading in Figs. 6a-6c.
By applying a localized force or pressure onto the ultra-thin substrate 3 on the surface 3.2, the bonding surfaces 2.1 and 3.1 can be forced together 72 in a localized area 75 due to the flexibility of the ultra-thin substrate 3 (see Fig. 6b) . The bonding surfaces 2.1 and 3.1 can thereby locally be brought into direct contact which triggers (step 32) the establishing of the intimate bonding as follows.
By locally decreasing the distance between the bonding surfaces 2.1 and 3.1, the electrostatic force pulling the bonding surfaces 2.1 and 3.1 towards each other increases in adjacent/overlapping regions 73 due to the reduced distance in the localized area 75 (increase electrostatic force field is indicated by dark grey shading) .  Due to the increased electrostatic force, the bonding surfaces 2.1 and 3.1 are locally pulled towards each other in the regions 73. This, in turn, results in a reduction of the distance and the bonding surfaces 2.1 and 3.1 come into direct contact in the regions 73. For the same reason, the electrostatic force attracting the bonding surfaces 2.1 and 3.1 increases in regions 74, which are adjacent/overlapping to regions 73. This process automatically continues as a continuous chain reaction which establishes the intimate bonding of the bonding surfaces 2.1 and 3.1 by direct contacting the bonding surfaces 2.1 and 3.1 by means of the electrostatic force resulting from the weak electrostatic potential. The "front" of the increased electrostatic force thereby propagates away from the localized area 75 of the initial triggering 72. After a certain time (the propagation speed can be rather slow and last e.g. several minutes) , the intimate bonding is established across the whole bonding interface and the bonded article 1 according to Fig. 1 is obtained.
This method is particularly appealing since only a triggering 72 in a localized area 75 is necessary to cause the whole area of the bonding surfaces 2.1 and 3.1 to come into direct contact. In addition, the process is intrinsically preventing the build-up of air-pockets or bubbles between the bonding surfaces 2.1 and 3.1 since the establishing of the intimate bonding occurs as a continuous process originating at the location of the initial trigger 72. The location 75 of the triggering 72 is preferably in a central region of the bonding interface.
Example
Various samples comprising a carrier substrate with a thickness t' of 0.4 mm and an ultra-thin substrate with a thickness t of 0.1 mm were prepared. Both substrates were made from a glass material having the following composition:
Component Weight-％
SiO2 61
B2O3 10
Al2O3 18
MgO 2.8
CaO 4.8
BaO 3.3
Table 1: Glass composition
The glass composition of table 1 has a CTE (20-300) of 3.2 x 10-6/K , a glass transition temperature Tg of 717℃ and the density is 2.43 g/cm3.
The substrates and were cleaned by brush cleaning with stationary rotating brush rollers. During the brush cleaning, both surfaces of the substrates were brushed. The substrates were conveyed on a conveyor bed comprising conveyor rollers made from IIR. During the brush cleaning, a weak alkaline detergent with a pH of approx. 10 was used as washing liquid. The washing liquid was applied at a temperature of 45℃. Both substrates underwent essentially the same brush cleaning.
In a subsequent drying step, the substrates were dried by blowing hot and dry air onto the bonding surface and the opposite surface. The air in a first drying step had a relative humidity of 23％and a temperature of 47.6℃. In a second drying step, the relative humidity amounted to 22％and the temperature was 44.5℃.
The brush cleaning and drying was performed in a clean room environment of class ISO 6 according to standard ISO 14644-1 (corresponding to class 1000 according to standard US FED STD 209E) at a temperature of 22℃.
After the cleaning, the ultra-thin substrate was placed on the carrier substrate with its bonding surface facing the bonding surface of the carrier substrate with an air gap between the bonding surfaces. The intimate bonding was triggered by pressing the ultra-thin substrate in a central localized area of the bonding interface against the carrier substrate. After the triggering, the intimate bonding was established automatically by a propagating increase in the electrostatic force as e.g. described in Fig. 6a-6c.
The overall electrostatic charges/field potential quickly decreased after the intimate bonding was established. By applying a further wet treatment to the bonded article as e.g. a wet cleaning step, the electrostatic charges/field potential can be essentially entirely removed and the bonded article is rendered suitable even for electrostatic damage (ESD) sensible processing or applications.
The de-bonding force was measured on a bonded article with a strip-shaped bonding interface having a width of 40 mm±0.5mm. The ultra-thin substrate was first detached at one end of the strip shaped bonded article and then continuously peeled of along the longitudinal direction of the bonded article. The initial force necessary for de-bonding  the ultra-thin substrate amounted to 0.2-0.9 Newton. The continuous de-bonding force necessary for the further peeling of was in the range of 0.01 to 0.08 Newton. An exemplary force vs. longitudinal peeling distance diagram can be found in Fig. 7 showing an initial peak in the peeling force during initial de-bonding and a subsequent essentially flat force curve during continuous peeling i.e. continuous de-bonding.
After an annealing step of the bonded article at a temperature of 400℃ for about 10 hours, the initial de-bonding force amounted to approx. 10 Newton and the continuous de-bonding force was about 0.2 Newton.
The following table 3 shows exemplary measurements regarding the Total Thickness Variation (TTV) of the substrates and the bonded article for three samples of the present example:
Figure PCTCN2015088726-appb-000004
Table 3: Total Thickness Variation (TTV) measurements of 3 samples
It can be gathered that the TTV of the bonded article is dominated by the sum of the TTV of the single substrates. The intimate bonding itself contributes only comparatively little to the total TTV of the bonded article.

Claims (26)

  1. A method for producing a bonded article, in particular a bonded glass article, comprising:
    -providing a carrier substrate, in particular a glass carrier substrate, having a bonding surface,
    -providing an ultra-thin substrate which is sheet-like and flexible, in particular an ultra-thin glass substrate, having a first and a second surface and a thickness t, where at least the first or second surface forms a bonding surface to be bonded to the bonding surface of the carrier substrate,
    -cleaning at least the bonding surface of the ultra-thin substrate, preferably the whole ultra-thin substrate,
    -cleaning at least the bonding surface of the carrier substrate, preferably the whole carrier substrate,
    -establishing an intimate bonding by direct contact of the bonding surface of the ultra-thin substrate with the bonding surface of the carrier substrate in order to form the bonded article,
    characterized in that,
    the intimate bonding is established by electrostatic forces resulting from a weak electrostatic field potential from electrostatic charges on at least one of the bonding surfaces, wherein the weak electrostatic field potential at the bonding surfaces does not exceed 1 kV.
  2. Method according to claim 1, wherein prior to establishing the intimate bonding, an intermediate bonding state is established, in which the ultra-thin substrate is bonded to the carrier substrate by electrostatic forces resulting from the weak electrostatic field potential with its bonding surface facing the bonding surface of the carrier substrate such that an air gap between the bonding surfaces persists.
  3. Method according to claim 2, where the establishing of the intimate bonding is triggered by forcing the ultra-thin substrate in the intermediate bonding state in a localized area to the carrier substrate such that the air gap between the bonding surfaces in the localized area is reduced, preferably in a manner that the bonding surfaces come into contact, causing an increase in the electrostatic force between the bonding surfaces in the localized area which increase in the electrostatic force subsequently automatically propagates across the area of the bonding surfaces without application of any further external force and establishes the intimate bonding by bringing essentially the whole area of the bonding surfaces into direct contact.
  4. Method according to anyone of the preceding claims, wherein the electrostatic charges that cause the weak electrostatic field potential are applied to the bonding surface or surfaces in the course of the cleaning of the at least one bonding surface of the carrier substrate and/or the cleaning of the at least one bonding surface of the ultra-thin substrate.
  5. A method according to anyone of the preceding claims, wherein the cleaning of the at least one bonding surface of the carrier substrate and/or the cleaning of the at least one surface of the ultra-thin substrate comprise a wet-washing step and a drying step.
  6. Method according to claim 5, wherein the wet-washing step comprises brush cleaning with at least one rotating brush-roller which brushes the bonding surface, preferably with at least a second rotating brush roller arranged on the opposite side of the substrate in order to simultaneously brush a surface of the substrate opposite to the bonding surface.
  7. Method according to anyone of claims 5 to 6, wherein the drying step comprises blowing clean air onto the substrate, in particular onto the bonding surface, preferably also onto a surface opposite to the bonding surface, which contains at most 106 particles/m3 of size≥0.1 μm, in particular according to class ISO 6 of standard ISO 14644-1, and further preferably contains at most 105 particles/m3 of size≥0.1 μm, in particular according to class ISO 5 of standard ISO 14644-1.
  8. Method according claim 7, where the air is hot and dry and has a temperature of not more than 60℃, preferably not more than 50℃, further preferably not more than 45℃, and the relative humidity is not more than 45％, preferably not more than 25％.
  9. Method according to claim 7 or 8, wherein the air is blown onto the substrate by at least one air-blade assembly, preferably by two air-blade assemblies arranged on opposite sides of the substrate.
  10. Method according to anyone of claims 5 to 9, wherein the substrate is conveyed during the drying step by means of conveyor rollers where the conveyor rollers comprise, at least on their outsides, a polymer material, in particular isobutylene isoprene (IIR) , polypropylene (PP) , polyethylene (PE) , polyethylene terephthalate (PET) , unsaturated polyethylene (UPE) , preferably unsaturated polyethylene (UPE) .
  11. Method according to anyone of the preceding claims, wherein after the cleaning of the substrate, the density of impurities with a size in the range from 20 to 50 μm on the at least one bonding surface is equal or less than 5/0.01 m2, preferably equal or less than 3/0.01 m2, further preferably equal or less than 1/0.01 m2.
  12. Method according to anyone of the preceding claims, wherein the cleaning of the bonding surface of the ultra-thin substrate and the cleaning of the bonding surface of the carrier substrate are performed at the same time such that the cleaned bonding surface of the ultra-thin substrate and the cleaned bonding surface of the carrier substrate are provided at essentially the same time.
  13. Method according to anyone of the preceding claims, wherein the intimate bonding state is established immediately after the cleaning of the carrier substrate and/or the ultra-thin substrate, or, if an intermediate bonding state is established, the intermediate bonding state is immediately established after the cleaning of the carrier substrate and/or the ultra-thin substrate and the intimate bonding is preferably immediately established after the intermediate bonding state was established.
  14. Method according to anyone of the preceding claims, wherein the strength of the intimate bonding of the bonded article, in particular in border areas along the border of the bonding interface, is increased by annealing the bonded article, in particular  at least in border areas, after the establishing of the intimate bonding to a temperature in the range from 60℃-200℃, preferably in the range from 80℃ to 160℃, for a time in the range from 1 to 10 hours.
  15. Method according to anyone of the preceding claims, wherein the bonded article is processed by a wet-processing step, in particular a wet-washing step, after having established the intimate bonding, in particular after the strength of the intimate bonding of the bonded article has been increased by annealing.
  16. Method according to anyone of the preceding claims, wherein all steps at least from and including the cleaning steps until the intimate bonding is established are conducted in a cleanroom environment at least according to class ISO 6 of standard ISO 14644-1, preferably at least according to class ISO 5 of standard ISO 14644-1.
  17. Bonded article, in particular a bonded glass article, preferably produced by the method according to anyone of claims 1 to 16, comprising
    -a carrier substrate, in particular a glass carrier substrate, having a bonding surface, and
    -an ultra-thin substrate which is sheet-like and flexible, preferably an ultra-thin glass substrate, having a first and a second surface and a thickness t, where at least the first or second surface forms a bonding surface, wherein
    -the carrier substrate and the ultra-thin substrate are intimately bonded to each other by direct contact of the bonding surface of the ultra-thin substrate with the bonding surface of the carrier substrate,
    characterized in that
    the bonding interface formed by the intimately bonded bonding surfaces is essentially free of bubbles with surface dimensions larger than 7 mm2 and has a density of bubbles with surface dimensions equal or smaller than 3 mm2 which is less than 15 bubbles/0.01 m2, preferably less than 10 bubbles/0.01 m2 and further preferably smaller than 5 bubbles/0.01 m2.
  18. Bonded article according to claims 17, wherein the bonded glass article is essentially electrostatically neutral, in particular its net electrostatic potential is less than 10 V, preferably less than 1 V.
  19. Bonded article according to claim 17 or 18, wherein the bonded article has a largest dimension of at least 0.1 m or larger, preferably 0.3 m or larger, further preferably 0.5 m or larger, or 3 inch or larger, preferably 6 inch or larger, further preferably 8 inch or larger, further preferably 12 inch or larger.
  20. Bonded article according to anyone of claims 17 to 19, wherein the thickness t of the ultra-thin substrate is equal or less than 0.4 mm, preferably equal or less than 0.2 mm, further preferably equal or less than 0.1 mm, further preferably equal or less than 0.05 mm.
  21. Bonded article according to anyone of claims 17 to 20, wherein the carrier substrate has a thickness of at least 0.3 mm.
  22. Bonded article according to anyone of claims 17 to 21, wherein the bonded article has a rectangular, in particular quadratic, or elliptical, in particular circular, shape.
  23. Bonded article according to anyone of claims 17 to 22, wherein the Total Thickness Variation (TTV) is essentially equal or less than the sum of the TTV of the carrier substrate and the ultra-thin substrate.
  24. Bonded article according to anyone of claims 17 to 23, wherein the initial de-bonding force for de-bonding the ultra-thin substrate from the carrier substrate is larger than 0.2 N, further preferably larger than 1 N.
  25. Bonded article according to anyone of claims 17 to 24, wherein the bonding interface is fluid tight, in particular water tight, such that no fluid can penetrate between the carrier substrate and the ultra-thin substrate.
  26. Use of a bonded article produced by a method according to anyone of claims 1 to 16 or a toughened glass article according to anyone of claims 17 to 25, for applications, in particular for the production of applications, as display, display cover, in particular for cover of touch screens, preferably for LCD displays or OLED displays, OLED lightning, EL lighting, sensors, in particular touch or fingerprint  sensor, E-paper, optical devices, in particular optical lenses or optical filters, or MEMS/MOEMS, in particular optical switches or optical cross-connectors.
PCT/CN2015/088726 2015-09-01 2015-09-01 Method for producing a bonded glass article and a bonded glass article WO2017035770A1 (en)

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WO2021063893A1 (en) 2019-09-30 2021-04-08 Schott Ag Composite glass material and methods for producing a composite glass material

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WO2014123864A1 (en) * 2013-02-07 2014-08-14 Corning Incorporated Apparatus and methods of forming flexible glass laminates using electrostatic pinning
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WO2021063897A1 (en) 2019-09-30 2021-04-08 Schott Ag Device and method for producing a device
WO2021063893A1 (en) 2019-09-30 2021-04-08 Schott Ag Composite glass material and methods for producing a composite glass material
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