Patent Publication Number: US-2018029933-A1

Title: Methods of fabricating channels in glass articles by laser damage and etching and articles made therefrom

Description:
BACKGROUND 
     Field 
     The present specification generally relates to methods of fabricating channels in glass articles and, more particularly, methods of fabricating channels in glass articles by creating channels through laser damage and subsequently etching the laser damage regions. 
     Technical Background 
     Glass articles are used in a variety of industries, including the electronics industry where glass is used to cover displays devices. Examples of such display devices include Liquid Crystal Displays and Light Emitting Diode displays, for example, computer monitors, televisions, and handheld devices. Three-dimensional glass articles are increasingly being used for their aesthetically pleasing appearance and tactile feel. However, meeting low dimensional tolerances, particularly with shaped glass, is challenging because the glass has dimensional deformation during reforming, annealing, and chemical strengthening. Additionally, traditional computer numerical control (“CNC”) machining methods used to create features in glass articles, such as channels, if performed prior to reforming, will cause non-uniform heating during glass reforming that may lead to waviness of the surface of the glass article and undesired deformation. 
     SUMMARY 
     According to various embodiments, a method of forming a glass article is provided. The method for forming the glass article comprises providing a glass substrate sheet, and translating a pulsed laser beam on the glass substrate sheet. The pulsed laser forms a laser damage region extending from a surface of the glass substrate sheet to a mid-point of the glass substrate sheet. The method further comprises contacting the glass substrate sheet with an etchant solution, and after the contacting of the glass substrate sheet with the etchant solution, the laser damage regions form channels having width and depth dimensions of less than 150 μm. 
     According to other embodiments, a glass article is provided. The glass article comprises a first surface, a second surface, and at least one channel extending from the first surface to point between the first surface and the second surface. The at least one channel has width and height dimensions less than about 150 μm. 
     It should be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments, and are incorporated into and constitute a part of this specification. The drawings illustrate the various embodiments described herein, and together with the description serve to explain the principles and operations of the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically depicts a laser system for generating laser damage regions within a flat glass substrate sheet according to one or more embodiments described and illustrated herein; 
         FIG. 2  schematically depicts a top perspective view of a flat glass substrate sheet and a focused, pulsed laser beam according to one or more embodiments described and illustrated herein; 
         FIG. 3  schematically depicts a side view of a laser damage region within a flat glass substrate sheet according to one or more embodiments described and illustrated herein; 
         FIG. 4A  schematically depicts a separate glass wafer and an interposer according to one or more embodiments described and illustrated herein; 
         FIG. 4B  schematically depicts a combined glass wafer and an interposer according to one or more embodiments described and illustrated herein; 
         FIG. 5  schematically depicts a magnified view of an interposer according to one or more embodiments described and illustrated herein; 
         FIG. 6  graphically depicts the strength of interposers with and without channels according to one or more embodiments described and illustrated herein; and 
         FIG. 7  is a flowchart describing a method of fabricating a shaped glass article according to one or more embodiments described and illustrated herein. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to embodiments of methods of making glass articles from a flat glass substrate sheet using laser damage and chemical etching processes to form features in the glass article. Generally, laser damage regions are formed within a flat glass substrate sheet around features (e.g., channels, slots, and the like) of the desired glass article. According to embodiments, the laser damage regions are etched by subjecting the glass article or glass substrate sheet to an etchant solution, such as by immersion or spraying. Prior to etching the glass substrate sheet and after forming the laser damage regions, the flat glass substrate sheet may, in embodiments, be reformed to achieve the desired three-dimensional shape of the one or more glass articles. Thus, in some embodiments, the laser damage regions are created with an initial geometry that precompensates for the changing shape of the flat glass substrate sheet during the reforming, etching, and/or strengthening processes such that laser damage regions have a desired geometry after the reforming, etching, and/or strengthening processes. In embodiments, the glass substrate sheet is then subjected to an etchant solution to remove flakes from the features and, in embodiments, smooth edges of the features. In some embodiments, the glass articles or glass substrate sheet on which features have been formed may then be subjected to a strengthening process, such as an ion-exchange chemical strengthening process. Various methods of forming features in a flat glass substrate sheet will be described in more detail herein with specific reference to the appended drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. However, it should be understood that features may be formed in glass articles with multiple dimensions and differing geometries using the methods described below. 
     Although the methods described herein may be used to form features glass articles having a variety of compositions, in some embodiments, the flat glass substrate sheet comprises an alkali aluminosilicate glass. In one embodiment, the alkali aluminosilicate glass comprises: from about 64 mol % to about 68 mol % SiO 2 ; from about 12 mol % to about 16 mol % Na 2 O; from about 8 mol % to about 12 mol % Al 2 O 3 ; from 0 mol % to about 3 mol % B 2 O 3 ; from about 2 mol % to about 5 mol % K 2 O; from about 4 mol % to about 6 mol % MgO; and from 0 mol % to about 5 mol % CaO; wherein: 66 mol %≦SiO 2 +B 2 O 3 +CaO≦69 mol %; Na 2 O+K 2 O+B 2 O 3 +MgO+CaO+SrO&gt;10 mol %; 5 mol %≦MgO+CaO+SrO≦8 mol %; (Na 2 O+B 2 O 3 )—Al 2 O 3 ≧2 mol %; 2 mol % Na 2 O—Al 2 O 3 ≦6 mol %; and 4 mol %≦(Na 2 O+K 2 O)—Al 2 O 3 ≦10 mol %. 
     In another embodiment, the alkali aluminosilicate glass comprises: from about 60 mol % to about 70 mol % SiO 2 ; from about 6 mol % to about 14 mol % Al 2 O 3 ; from 0 mol % to about 15 mol % B 2 O 3 ; from 0 mol % to about 15 mol % Li 2 O; from 0 mol % to about 20 mol % Na 2 O; from 0 mol % to about 10 mol % K 2 O; from 0 mol % to about 8 mol % MgO; from 0 mol % to about 10 mol % CaO; from 0 mol % to about 5 mol % ZrO 2 ; from 0 mol % to about 1 mol % SnO 2 ; from 0 mol % to about 1 mol % CeO 2 ; less than about 50 ppm As 2 O 3 ; and less than about 50 ppm Sb 2 O 3 ; wherein 12 mol %≦Li 2 O+Na 2 O+K 2 O≦20 mol % and 0 mol %≦MgO+CaO≦10 mol %. 
     In another embodiment, the alkali aluminosilicate glass comprises SiO 2  and Na 2 O, wherein the glass has a temperature T 35kp  at which the glass has a viscosity of 35 kilo poise (kpoise), wherein the temperature T breakdown  at which zircon breaks down to form ZrO 2  and SiO 2  is greater than T 35kp . In some embodiments, the alkali aluminosilicate glass comprises: from about 61 mol % to about 75 mol % SiO 2 ; from about 7 mol % to about 15 mol % Al 2 O 3 ; from 0 mol % to about 12 mol % B 2 O 3 ; from about 9 mol % to about 21 mol % Na 2 O; from 0 mol % to about 4 mol % K 2 O; from 0 mol % to about 7 mol % MgO; and 0 mol % to about 3 mol % CaO. 
     In another embodiment, the alkali aluminosilicate glass comprises at least 50 mol % SiO 2  and at least one modifier selected from the group consisting of alkali metal oxides, wherein [(Al 2 O 3  (mol %)+B 2 O 3  (mol %))/(Σ alkali metal modifiers (mol %))]&gt;1. In some embodiments, the alkali aluminosilicate glass comprises: from 50 mol % to about 72 mol % SiO 2 ; from about 9 mol % to about 17 mol % Al 2 O 3 ; from about 2 mol % to about 12 mol % B 2 O 3 ; from about 8 mol % to about 16 mol % Na 2 O; and from 0 mol % to about 4 mol % K 2 O. 
     In another embodiment, the alkali aluminosilicate glass comprises SiO 2  and at least one modifier selected from the group consisting of alkaline metal oxides. In some embodiments, the alkaline metal oxide modifiers may be selected from the group consisting of MgO, CaO, SrO, BaO and mixtures thereof. Without being bound to any particular theory, it is believed that the alkaline earth metals are less soluble in the etchant (e.g., HF) than other modifiers and, thus, glasses containing alkaline earth metals have slow surface etch rates, which may lead to decreased waviness of a finished glass article. In some embodiments, the alkali aluminosilicate glass comprises from about 5 mol % to about 14 mol % alkaline metal oxides, such as from about 8 mol % to about 12 mol % alkaline earth metal oxides. In some embodiments, the alkali aluminosilicate glass comprises: from 50 mol % to about 72 mol % SiO 2 ; from about 9 mol % to about 17 mol % Al 2 O 3 ; from about 2 mol % to about 12 mol % B 2 O 3 ; from about 8 mol % to about 16 mol % Na 2 O; from 0 mol % to about 4 mol % K 2 O; and from about 5 mol % to about 14 mol % MgO+CaO+SrO. 
     In another embodiment, the alkali aluminosilicate glass comprises SiO 2 , Al 2 O 3 , P 2 O 5 , and at least one alkali metal oxide (R 2 O), wherein 0.75≦[(P 2 O 5 (mol %)+R 2 O(mol %))/M 2 O 3  (mol %)]≦1.2, where M 2 O 3 =Al 2 O 3 +B 2 O 3 . In some embodiments, the alkali aluminosilicate glass comprises: from about 40 mol % to about 70 mol % SiO 2 ; from 0 mol % to about 28 mol % B 2 O 3 ; from 0 mol % to about 28 mol % Al 2 O 3 ; from about 1 mol % to about 14 mol % P 2 O 5 ; and from about 12 mol % to about 16 mol % R 2 O; and, in certain embodiments, from about 40 to about 64 mol % SiO 2 ; from 0 mol % to about 8 mol % B 2 O 3 ; from about 16 mol % to about 28 mol % Al 2 O 3 ; from about 2 mol % to about 12% P 2 O 5 ; and from about 12 mol % to about 16 mol % R 2 O. 
     In still other embodiments, the alkali aluminosilicate glass comprises at least about 4 mol % P 2 O 5 , wherein (M 2 O 3  (mol %)/R x O (mol %))&lt;1, wherein M 2 O 3 =Al 2 O 3 +B 2 O 3 , and wherein R x O is the sum of monovalent and divalent cation oxides present in the alkali aluminosilicate glass. In some embodiments, the monovalent and divalent cation oxides are selected from the group consisting of Li 2 O, Na 2 O, K 2 O, Rb 2 O, Cs 2 O, MgO, CaO, SrO, BaO, and ZnO. In some embodiments, the glass comprises 0 mol % B 2 O 3 . 
     In still another embodiment, the alkali aluminosilicate glass comprises at least about 50 mol % SiO 2  and at least about 11 mol % Na 2 O, and the compressive stress is at least about 900 MPa. In some embodiments, the glass further comprises Al 2 O 3  and at least one of B 2 O 3 , K 2 O, MgO and ZnO, wherein −340+27.1·Al 2 O 3 −28.7·B 2 O 3 +15.6·Na 2 O−61.4·K 2 O+8.1·(MgO+ZnO)≧0 mol %. In particular embodiments, the glass comprises: from about 7 mol % to about 26 mol % Al 2 O 3 ; from 0 mol % to about 9 mol % B 2 O 3 ; from about 11 mol % to about 25 mol % Na 2 O; from 0 mol % to about 2.5 mol % K 2 O; from 0 mol % to about 8.5 mol % MgO; and from 0 mol % to about 1.5 mol % CaO. 
     In some embodiments, the alkali aluminosilicate glasses described hereinabove are substantially free of (i.e., contain 0 mol % of) at least one of lithium, boron, barium, strontium, bismuth, antimony, and arsenic. In other embodiments, the alkali aluminosilicate glass is substantially free of lithium, boron, barium, strontium, bismuth, antimony, and arsenic. 
     In some embodiments, the alkali aluminosilicate glasses described hereinabove are down-drawable by conventional processes, such as slot-drawing, fusion drawing, re-drawing, and the like, and has a liquidus viscosity of at least 130 kilopoise. 
     It should be understood that although specific glass compositions are described above, the methods and glass articles of embodiments may be made from many different types of glass and are not limited to the glass compositions described hereinabove. 
     Referring initially to  FIG. 1 , a system  120  for inducing laser damage regions into a flat glass substrate sheet  130  is schematically depicted. A laser source  122  is provided that is operable to generate a pulsed laser beam  124  that is focused by coupling optics  126  and directed toward the flat glass substrate sheet  130 . The laser source  122  may be any laser source capable of inducing the laser damage regions. As an example and not a limitation, the laser source  122  generates a pulsed ultraviolet (“UV”) pulsed laser beam  124  (e.g., about 355 nm in wavelength) that is operated in picosecond or nanosecond pulses. 
     The coupling optics  126  may be configured as one or more lenses that focus the pulsed laser beam  124  into a focused laser beam having a focal point at a desired location with respect to the flat glass substrate sheet  130 . As described in more detail below, in some embodiments, the focus of the coupling optics  126  may be controllable to form a laser damage region within the flat glass substrate sheet  130 . 
     The pulsed laser beam  124  may be configured to be scanned on the flat glass substrate sheet  130  to form the desired laser damage region. In some embodiments, the flat glass substrate sheet  130  may be coupled to a computer-controlled XYZ stage (not shown) such that the flat glass substrate sheet is translated with respect to the pulsed laser beam  124 . Additionally, in embodiments, a beam splitter (not shown) may also be provided to split a single laser beam  124  generated by the laser source  122  into a plurality of laser beams for simultaneously forming a plurality of laser damage regions within the flat glass substrate sheet  130 . 
     Referring now to  FIGS. 2 and 3 , a straight laser damage region  140  within a flat glass substrate sheet is depicted.  FIG. 2  depicts a perspective view of the flat glass substrate sheet  130  and a pulsed laser beam  124  being focused by coupling optics  126 , while  FIG. 3  depicts a side view of the flat glass substrate sheet  130 . The laser damage region  140  is defined by a plurality of individual laser damage lines  141  that are located at and between a first surface  131  and a second surface  133  at different depths within a bulk of the flat glass substrate sheet  130 . For example, in embodiments, the laser damage lines may extend from the first surface  131  to a mid-point  132  between the first surface  131  and the second surface  133 . As used herein, a mid-point refers to any position between the first surface  131  and the second surface  133  and is not limited to the geometrical middle between the first and second surfaces. As shown in  FIGS. 2 and 3 , the individual laser damage lines  141  are vertically arranged on the x-axis. Each individual laser damage line  141  may be formed by one or more passes of the pulsed laser beam  124 . For example, the first laser damage line  141  may be formed by setting the focal point of the pulsed laser beam  124  at a distance above the second surface  133  (i.e., the underside surface) that coincides with the desired depth of the feature, and near a first edge  135  of the flat glass substrate sheet  130 . The pulsed laser beam  124  may then be translated (and/or the flat glass substrate sheet  130  may be translated relative to the laser) over the flat glass substrate sheet  130  at a distance d toward a second edge  137 . Then, the position of the focal point of the pulsed laser beam  124  is incrementally moved toward the first surface  131  of the flat glass substrate sheet  130 , either by controlling the coupling optics  126 , or by moving the flat glass substrate sheet  130 . The pulsed laser beam  124  is then translated over the glass substrate sheet again (and/or the flat glass substrate sheet  130  may again be translated relative to the laser) either from the second edge  137  toward the first edge  135 , or from the first edge  135  toward the second edge  137 . The process may be repeated until pulsed laser beam  124  traverses at, or just below, first surface  131  (i.e., the upper surface), thereby completing the formation of the laser damage region  140 . 
     Microcracks formed by the individual laser damage lines  141  may extend to adjacent individual laser damage lines  141 , thereby forming a microcrack network. To prevent uncontrollable splitting of the flat glass substrate sheet  130  during the laser irradiation process, in some embodiments the individual laser damage lines  141  do not contact the edges of the glass substrate sheet (e.g., the first and second edges  135 ,  137 ). For example, the ends of the individual damage lines  141  may be offset from the edges of the flat glass substrate sheet  130  by a few millimeters or, in some embodiments, by a few hundred micrometers. Further, the pulsed laser beam  124  should be operated such that it does not form grooves within the first and second surfaces  131 ,  133  of the flat glass substrate sheet  130 . The pitch between the individual laser damage lines  141  may be set such that the flat glass substrate sheet  130  does not prematurely crack along the laser damage region  140 . In some embodiments, the pitch between the individual laser damage lines  141  may be less than or equal to about 5.0 μm, such as from about 1.0 μm to about 4.0 μm, or from about 2.0 μm to about 3.0 μm. 
     In embodiments, the laser source may be operated at a repetition rate ranging from about 60 kHz to about 200 kHz, such as from about 70 kHz to about 190 kHz. In other embodiments, the laser source may be operated at a repetition rate ranging from about 90 kHz to about 170 kHz, or from about 100 kHz to about 150 kHz. The output power of the laser source and the focusing conditions of the coupling optics should be such that the energy and intensity in the beam focus are at or slightly above damage threshold of the flat glass substrate sheet. In embodiments, the output power of the laser source may be from about 0.1 W to about 2.0 W, such as from about 0.5 W to about 2.0 W. In some embodiments, the output power of the laser source may be from about 0.75 W to about 1.5 W, such as from about 1.0 W to about 1.25 W. 
     Selective etching of the laser damage areas may be performed with glass substrate sheets having any glass thickness. It may be particularly advantageous for thinner glass substrate sheets (e.g., below 0.3 mm) of which computer numerical control (“CNC”) and other mechanical processes have very low yields, and for features having small dimensions, such as the channels described herein. 
     Embodiments of the present disclosure remove glass flakes from the features and smooth the edges of the features by subjecting the laser-written glass substrate sheet to an etching process. In embodiments, etchant solution may be provided by a spray method wherein the etchant solution is sprayed onto the shaped glass substrate sheet, or by submerging the shaped glass substrate sheet into a bath of etchant solution. It should be understood that other processes for applying an etchant to the glass substrate sheet are also included herein. 
     In embodiments where the etchant is applied by spraying, spray nozzles may oscillate at speeds from about 0 oscillations per minute to about 40 oscillations per minute, such as from about 10 oscillations per minute to about 30 oscillations per minute. In other embodiments, the nozzles may oscillate at speeds from about 15 oscillations per minute to about 25 oscillations per minute. The pressure of the spray from the nozzles may be from about 0.5 bar to about 1.7 bar, such as from about 0.75 bar to about 1.5 bar. In some embodiments, the pressure of the spray from the spray nozzles may be from about 1.0 bar to about 1.25 bar. The oscillations and pressure of the spray from the spray nozzle may be used to ensure that clean features are formed in a glass article. For example, if the oscillations are too slow and/or the pressure of the spray from the nozzles is too low, the etchant may pool and cause imprecise features. However, when the oscillations are too fast and/or the pressure of the spray from the nozzle is too high, the glass substrate sheet may be etched too quickly causing lumps and imperfections to be formed on the glass surface and within the features. 
     Without being bound to any particular theory, it is believed that the etchant solution etches the laser damage regions because of the presence of microcracks within these laser damage regions. Both the laser damage regions and the non-damaged regions are etched simultaneously, but at different etch rates. The microcracks in the laser damage regions break chemical bonds, and provide pathways for etchant to penetrate deeper into the glass substrate sheet. Therefore, the etch rate at the laser damage regions is much faster than then non-damaged regions. 
     The etchant solution may comprise hydrofluoric acid as a primary etchant. Mineral acids, such as hydrochloric acid, sulfuric acid, and nitric acid, can assist the etch process and accelerate or decelerate the etch rate, as well as improve the surface quality of the glass article and reduce the formation of sludge. In some embodiments, sulfuric acid is used in combination with hydrofluoric acid in the etchant solution. In some embodiments, the etchant solution includes from about 2 mol/L to about 5 mol/L hydrofluoric acid and from about 0.5 mol/L to about 1.2 mol/L sulfuric acid, such as about 3 mol/L hydrofluoric acid and about 0.9 mol/L sulfuric acid. 
     Further, a surfactant is believed to be beneficial to the etch process because it can improve transportation of the etchant to the laser damage regions, and to suspend the by-product produced by the etchant process. As a non-limiting example, the surfactant may be DuPont FS-10. It should be understood that other surfactants may be utilized. In embodiments, the surfactant may be present in amounts less than about 0.1 wt %, such as less than about 0.05 wt %, or less than about 0.01 wt %. 
     In embodiments using an etchant solution bath, agitation of the etchant solution bath may improve the etch rate of the laser damage region. Both the etchant solution and the byproduct need to be constantly exchanged through the narrow channels of the microcracks within the laser damage regions. Agitation may accelerate the mass transfer inside the microcracks, and refresh that laser damage region surface for a continuous etching. Ultrasonic agitation influences the etch time, surface loss, and etch ratio. An effective agitation can increase the etch ratio between the laser damage regions and the non-damaged regions, which, in turn, may reduce the surface loss of the glass substrate sheet and reduce the cost of raw material. In some embodiments, the agitation is at a frequency below about 132 kHz, such as below about 125 kHz. In other embodiments, the agitation is at a frequency below about 100 kHz, or below about 80 kHz. Because the reduction of ultrasound frequency increases the power of each individual impulsion and the scrubbing effect, lower frequencies and higher amplitudes favor the fast exchange of etchant and byproduct, and improve the etch rate at the laser damage regions. In one embodiment, the ultrasonic agitation frequency is about 40 kHz. 
     It has been found that vertical movement of the etchant solution bath in combination with ultrasonic agitation does not improve the etch rate of the laser damage regions because typically the cylindrical crack network of the laser damage regions is perpendicular to the vertical movement of the bath. In the direction parallel to the cracks, the velocity of the vertical movement is near zero. As a result, the etch ratio and the final thickness of the glass substrate sheet may be much lower when vertical agitation is applied together with ultrasound agitation. Accordingly, in embodiments, the etching process does not include vertical agitation. 
     Higher etching solution temperatures generally increase the etch rate and, thus, higher etching solution temperatures may be used to decrease the duration of the etching process or, conversely, lower etching solution temperatures may be used to slow the etch rate, thereby allowing for more control over the dimensions of the features formed from the laser-damaged region. When the temperature of the etching solution is too high during a spray etching process, the acid may evaporate out of the etching solution during the spraying. Accordingly, in embodiments the temperature of the etching solution may be about 35° C., such about 30° C., or even about 25° C. However, it should be understood that higher or lower temperatures may be used. In embodiments, the duration that the etchant solution is contacted to the glass substrate sheet may be from about 20 minutes to about 50 minutes, such as from about 25 minutes to about 45 minutes. In other embodiments, the duration that the etchant solution is contacted to the glass substrate sheet may be from about 30 minutes to about 40 minutes. In yet other embodiments, the duration that the etchant solution is contacted to the glass substrate sheet is about 50 minutes, such as about 45 minutes, or even about 40 minutes. The duration that the etchant solution is contacted to the glass is dependent on the necessary depth of the channel, etching concentrations and temperature of the etching spray. 
     To reduce surface losses of the glass substrate sheet by the etchant is to apply a coating that is resistant to the etching solution, such as pure HF or a mixture of HF and mineral acids, to one or more surface of the glass substrate sheet. In some embodiments, the acid-resistant coating is chosen so that the laser passes through the acid-resistant coating and creates laser damage in the underlying glass substrate sheet. 
     According to some embodiments, the acid-resistant coating may comprise ethylene acrylic acid and wax polymer emulsions dispersed in water. In some embodiments, the acid-resistant coating composition has from about 5 wt % to about 60 wt % solids/polymers, such as from about 15 wt % to about 46 wt % solids/polymers. The type and amount of wax polymer and ethylene acrylic acid may be modified according to the desired application. The acid-resistant coating may be applied to the glass substrate sheet by any suitable method. In some embodiments, the acid-resistant coating may be applied to the glass substrate sheet by dip coating, spray coating, spin coating, or slot coating. Once the acid-resistant coating has been applied to the glass substrate sheet, the acid-resistant coating may dried by heating. In some embodiments, the acid-resistant coating on the glass substrate sheet may be dried by heating the acid-resistant coating to temperatures of from about 150° C. to about 190° C., such as about 170° C. In some embodiments, the duration of the drying step may be from about 10 minutes to about 40 minutes, such as from about 15 minutes to about 30 minutes. In other embodiments, the duration of the drying step may be about 20 minutes. Without being bound to any particular theory, it is believed that the heating in the drying step causes the wax polymer in the acid-resistant coating to bloom thereby providing a hydrophobic surface. 
     The thickness of the acid-resistant coating may be from about 1 μm to about 15 μm, such as from about 3 μm to about 8 μm. The acid-resistant coating may be removed by a solution of 3 wt % Semi-Klean with ultrasonics. Thin layers of the acid-resistant coating, such as less than about 10 μm, may be removed in boiling water. 
     As discussed above, in embodiments, the acid-resistant coating may be selected to allow the laser to pass through the acid-resistant coating and induce damage on the underlying glass substrate sheet. Thus, in embodiments, the acid-resistant coating may be applied before or after laser damage is induced. In one embodiment, the coating may be applied to a glass substrate sheet that has been strengthened, such as by ion exchange (which is discussed in detail below), and has a transparent conductive oxide coating, such as indium tin oxide. After the acid-resistant coating has been applied, laser damage may be induced to the underlying glass substrate sheet as discussed in detail above. The glass substrate sheet may then be etched and separated, and the acid-resistant coating may subsequently be removed. It should be understood that the acid-resistant coating may be applied at virtually any step in the process disclosed herein. 
     In some embodiments, the glass articles or glass substrate sheet are strengthened by a strengthening process. In some embodiments, strengthening process may occur before the features have been formed in the glass substrate sheet. In other embodiments, the strengthening process may occur after the features have been formed in the glass substrate sheet. The glass articles or glass substrate sheet may be chemically strengthened by an ion exchange process in which ions in the surface layer of the glass are replaced by larger ions having the same valence or oxidation state. In one particular embodiment, the ions in the surface layer and the larger ions are monovalent alkali metal cations, such as Li +  (when present in the glass), Na + , K + , Rb + , and Cs + . Thus, for example, Na +  present in the glass may be replaced with the larger K +  ions. Alternatively, monovalent cations in the surface layer may be replaced with monovalent cations other than alkali metal cations, such as Ag + , Ti + , Cu + , or the like. 
     The ion-exchange process creates a compressive stress at the surfaces of the glass article or glass substrate sheet. These compressive stresses extend beneath the surface of the glass article or glass substrate sheet to a certain depth, referred to as the depth of layer (DOL). The compressive stresses are balanced by a layer of tensile stresses (referred to as central tension) such that the net stress in the glass article or glass substrate sheet is zero. The formation of compressive stresses at the surface of the shaped glass article makes the glass strong and resistant to mechanical damage and, as such, mitigates failure of the shaped glass article for flaws which do not extend through the depth of layer. 
     In one embodiment, the glass article or glass substrate sheet is chemically strengthened by ion-exchange in which smaller sodium ions near the surface of the glass are exchanged with larger potassium ions when the glass article or glass substrate sheet is placed in an ion exchange bath. Replacement of the smaller sodium ions with the larger potassium ions causes a layer of compressive stress to develop in the surfaces of the glass article or glass substrate sheet. The compressive stress extends below the surfaces of the glass article or glass substrate sheet to a specified depth of layer (compressive surface layer). A compressive surface layer extends from the upper surface and the underside surface to the depth of layer. The compressive surface layer is balanced by the development of the internal tension layer at the center of the glass article or glass substrate sheet. 
     In the embodiments described herein, the compressive stress and depth of layer developed in the shaped glass article or glass substrate sheet by strengthening are sufficient to improve the damage tolerance of the shaped glass article while also facilitating further processing (such as by edge finishing) without risk of introducing flaws into the shaped glass article. In one embodiment, the compressive stress may be from about 200 MPa to about 1000 MPa. In another embodiment, the compressive stress may be from about 500 MPa to about 800 MPa. In yet another embodiment, the compressive stress may be from about 650 MPa to about 900 MPa. In one embodiment, the depth of layer may be from about 10 microns to about 80 microns. In another embodiment, the depth of layer may be from about 30 microns to about 60 microns. In yet another embodiment, the depth of layer may be from about 40 microns to about 60 microns. 
     In embodiments, the etch process may be used as the strengthening process when other forms of chemical strengthening, such as ion exchange, is not compatible with the glass composition. 
     For example, in glass articles or glass substrate sheets that cannot be strengthened by ion exchange because the glass is too thin, such as less than about 0.4 mm thick or even less than about 0.3 mm thick, or because the glass composition does not contain elements that are suitable for ion exchange, the etch process may be used to strengthen the glass article or glass substrate sheet. Without being bound to any particular theory, it is believed that the etching process blunts the tips of surface defects and in some cases eliminates or reduces the depth of surface defects that can weaken the glass article or glass substrate sheet. In embodiments, glasses formed by the laser damage and etching method disclosed above may have a failure rate of about 50% at forces of about 5 kg, or have a failure rate of less than about 20% at forces of about 4 kg. 
     In some embodiments, the glass substrate sheet is strengthened after the laser damage and etching steps (e.g., the glass article is strengthened). However, in other embodiments the glass substrate sheet may be strengthened before the laser damage and etching step. 
     In embodiments where the glass substrate sheet is strengthened before the laser damage and etching steps, and with reference to  FIG. 1 , the laser source  122  may be operated at a repetition rate ranging from about 60 kHz to about 200 kHz. The output power of the laser source  122  and the focusing conditions of the coupling optics  126  should be such that the energy fluence and intensity in the beam focus are at or slightly above damage threshold of the flat glass substrate sheet. In embodiments, the output power of the laser source  122  may be less than or equal to about 0.6 W, such as from about 0.4 W to about 0.6 W. In some embodiments, the output power of the laser source  122  may be about 0.5 W. Without being bound to any particular theory, it is believed that edge roughness may be reduced to 1.5 μm to 2.0 μm by using laser sources having an output power at or below 0.6 W. In particular, edge roughness appears to be relatively constant in alkali aluminosilicate glasses at laser source output power from about 0.4 W to about 0.6 W. 
     In embodiments where the glass substrate sheet is strengthened after the laser damage and etching steps, and with reference again to  FIG. 1 , the laser source  122  may be operated at a repetition rate ranging from about 5 kHz to about 40 kHz, such as about 10 kHz. In embodiments, the output power of the laser source  122  may be at or below 0.6 W, such as from about 0.1 W to about 0.4 W, such as from about 0.15 W to about 0.3 W depending on the thickness and compressive stress of the glass substrate sheet. In some embodiments, the output power of the laser source  122  may be from about 0.2 W to about 0.25 W. Without being bound to any particular theory, it is believed that the laser creates multiple micro-cracks in the glass so that the glass volume increases in the laser damage region. This expansion may create laser-induced thermal effects that form additional compressive and tensile stresses superimposed in the existing stress pattern. This additional stress may be proportional to the laser power and may bring the glass closer to the frangibility limit. If the laser power is too low, it makes the laser damage too thin and it does not act as a cushion for high stresses in the surrounding glass. If the laser power is too high, it creates strong stresses that cannot be reduced by the laser damage. In both of these cases, the glass may break. 
     In either of the above embodiments (i.e., whether the glass substrate sheet is strengthened before or after the laser damage and etching), the translation speed of the pulsed laser beam may be between about 50 mm/s and about 2 m/s, in some embodiments. In other embodiments, the translation speed of the pulsed laser may be from about 50 mm/s to about 300 mm/s, such as about 250 mm/s. 
     It should be understood that laser parameters other than those described above may be used to form the laser damage regions. Laser pulse energies may vary between 5 μJ and several hundred microjoules depending on parameters such as glass properties, translation speed, laser repetition rate, and the coupling optics  126 , which may have the numerical aperture (NA) in between of 0.15 and 0.3 or more, for example. 
     In some embodiments the laser damage and etching described above are used to form channels in a glass article. Channels, as used herein, are depressions made in one surface of the glass substrate sheet that do not penetrate through to the other, opposing surface of the glass substrate sheet. The channels may be formed in any shape or geometry. For example, in various embodiments, the channels may be straight lines, circular, rectangular, triangular, etc. Forming channels in the glass article can provide many advantages, such as, for example, by providing reservoirs for fluid overflow, allowing cooling fluids to flow through the glass article, or to provide aesthetic design elements to a glass article. However, if the dimensions of the channels (both depth and width) are too large, the strength of the glass articles may be compromised. Accordingly, in embodiments, channels with small dimensions are desired. 
     Conventional methods for forming channels in glass articles, such as a CNC method, have difficulty forming channels with small dimensions because they are limited by the physical attributes of the CNC machine. For example, the width of a channel in a glass article is limited by the dimensions of the scribing mechanism in a CNC, and as the scribing mechanism wears down, such as through repeated use, the dimensions of a channel that can be formed by the CNC machine are increased. 
     In embodiments where channels are formed using the laser damage and etching methods described herein, the dimensions of the channels remain small and can be controlled within a very tight tolerance. In some embodiments, channels formed by the laser damage and etching process disclosed herein may have dimensions (width and depth) of less than about 150 μm, such as less than about 100 μm, or less than about 75 μm. In embodiments, the width of the channels may be from about 45 μm to about 125 μm, such as from about 40 μm to about 120 μm. In other embodiments, the width of the channels may be from about 45 μm to about 115 μm, such as from about 50 μm to about 110 μm. In yet other embodiments, the width of the channels may be from about 55 μm to about 105 μm, such as from about 60 μm to about 100 μm. Similarly, in embodiments, the depth of the channels may be from about 30 μm to about 100 μm, such as from about 35 μm to about 95 μm. In other embodiments, the depth of the channels may be from about 40 μm to about 90 μm, such as from about 45 μm to about 85 μm. It should be understood that the length of the channels may extend from one edge surface of the glass to another, opposite edge surface of the glass. 
     The laser damage and etch process described herein is also capable of providing the above dimensions (width and depth) within very tight tolerances. In embodiments, the width and depth of the channels have a tolerance of less than about ±35 μm, such as less than about ±30 μm. In other embodiments, the width and depth of the channels have a tolerance of less than about ±25 μm, such as less than about ±20 μm. Accordingly, in embodiments, the width and depth of the channels may have a tolerance of from about ±10 μm to about ±35 μm, such as from about ±15 μm to about ±30 μm. In other embodiments, the width and depth of the channels may have a tolerance of from about ±20 μm to about ±25 μm, such as from about ±20 μm. 
     In embodiments, the glass article may be formed as an interposer, such as for use in a microelectromechanical system (MEMS). In such embodiments, and with reference to  FIG. 4A , a glass wafer  410  may be formed by any suitable method and coated with an antireflective coating. It should be understood that although the glass wafer  410  depicted in  FIG. 4A  is circular, the glass wafer may have any shape. The antireflective coating is not particularly limited and, in embodiments, may be titanium nitride or niobium nitride, and may be applied by any suitable method, such as spray coating, dip coating, or manual application. The glass wafer  410  may also be patterned, for example, with a grid pattern  415 , as shown in  FIG. 4A . The grid pattern  415  may be formed from an adhesive, such as epoxy, urethane, and polyimides. To form an MEMS, an interposer  420  may be formed. As shown in  FIG. 4A , the interposer  420  may have patterned through holes  425  formed by a CNC method or by a laser damage and etch method as disclosed in U.S. Patent Application Publication No. 2014/0147624, which is incorporated by reference herein in its entirety. In embodiments where the through holes  425  are formed by a laser damage and etching process, the laser damage regions corresponding to the channels  427  may be formed in conjunction with forming the through holes  425 . For example, in embodiments a laser may be used to cut through holes  425  in the glass substrate sheet and the same laser may be used to form laser damage regions corresponding to channels  427  by traversing the portions of the glass substrate sheet where the channels  427  are to be formed with less passes of the laser than portions of the glass substrate sheet where the through holes  425  are to be formed. For example, if X number of laser passes are required to form laser damage regions corresponding to through holes  425 , then 0.3 X passes may be used to form damage regions corresponding to the channels  427 . Subsequently, the same etching process may be used to form the final through holes  425  and channels  427 . 
     The through holes  425  shown in  FIG. 4A  are rectangular and correspond to the grid pattern  415  formed on the glass wafer  410  so that the interposer  420  may be adhered to the glass wafer  410  by contacting the interposer  420  with the glass wafer  410 , which may comprise an adhesive to form the MEMS holder  430  shown in  FIG. 4B . With reference now to  FIG. 5 , which depicts a magnified view of cut out A from  FIG. 4A , in addition to the through holes  425 , the interposer may include channels  427 . The channels  427  are formed in a side of the interposer that is contacted to the grid pattern  415  of the glass wafer  410  so that when the interposer  420  is contacted to the glass wafer  410 , the excess adhesive that forms the grid pattern  415  of the glass wafer  410  is able to fill into the channels  427 . Thereby, uniform contact of the glass wafer  410  and the interposer  420  is facilitated while also preventing adhesive from seeping into the through holes  425  of the interposer. For example, in the embodiment shown in  FIG. 5 , each vertical elongated portion  428  of the interposer  420  has two channels  427  formed with the vertical elongated portion  428  of the interposer  420  so that a channel  427  is between each vertical column of through holes  425 . Once the glass wafer  410  and interposer  420  are adhered, as shown in  FIG. 4B , MEMS may be inserted into the through holes  425  in the interposer  420  to form a device that is suitable for use in an end product. 
     By forming channels  427  in the interposer  420  with the channel dimensions described herein, the presence of the channels does not affect the strength of the interposer. For example,  FIG. 6  graphically represents the failure rate (in percentage) of interposers with channels and the failure rate (in percentage) of interposers without channels. The channels depths and widths of the interposers shown in  FIG. 6  are all between 30 μm and 100 μm. In  FIG. 6 , percent failure is provided on the y-axis and force in MPa. Interposers without channels are represented by circles and interposers with channels are represented by squares. As can be seen from the graph of  FIG. 6 , at low forces, the interposers with channels have a lower failure rate. For example, the interposers having channels have a failure rate of about 5% at about 40 MPa, while the interposers without channels have a failure rate of about 5% at about 27 MPa. At higher forces (e.g., forces above 40 MPa) the interposers with channels and the interposers without channels have comparable failure rates. Accordingly, the strength of the interposers is improved at lower forces by having channels and is not noticeably affected at higher forces by having channels. 
     In some embodiments, the flat glass substrate sheet comprising holes and/or features formed by the above-described laser damage etching process is used in the end product without further reshaping. However, in other embodiments, discussed in detail below, the laser damage and etching process is conducted on a flat glass substrate sheet to pre-compensate for subsequent shaping of the flat glass substrate sheet into a shaped glass article. 
     Referring now to  FIG. 7 , a flowchart of a process to fabricate glass articles from a flat glass substrate sheet by laser damage and chemical etching processes. The flowchart of  FIG. 7  will first be described generally, and then each process will be described in more detail. At block  110 , a laser is utilized to induce laser damage regions in a flat glass substrate sheet. The laser damage regions extend from a mid-point of the glass substrate sheet to a second surface of the glass substrate sheet, and are defined by laser-induced microcracks, spectroscopic defects, and the like. The laser damage regions are etched compared to the non-damaged regions during the etching process of block  113 . 
     In embodiments, the laser damage regions have an initial geometry that precompensates for the deformation of the flat glass substrate sheet that occurs during the reforming process at block  111  and/or during the etching process  113 . Therefore, an initial geometry of a particular laser damage region may be different than a desired geometry of the feature of the shaped glass article. For example, the width and depth of a laser damage region before etching may be less than the width and depth of channel formed from that laser damaged region after etching. In other embodiments, a particular laser damage region intended to provide a channel in the glass article may have an initial geometry comprising a curve; however, following the reforming and/or etching process, the laser damage region changes shape to be a straight line. 
     At block  111 , the flat glass substrate sheet is optionally reformed by a reforming process. The reforming process may be any process capable of three-dimensionally reforming the flat glass substrate sheet to define one or more shaped glass articles. Such reforming processes include, but are not limited to, press molding, gravity sagging, pressure forming, and localized heating and bending. In many applications, the reforming process creates a curved perimeter area of the shaped glass article. A curved perimeter area of a cover glass may be aesthetically pleasing to end-users, for example. As stated above, the initial geometry of the laser damage regions changes to a desired geometry as the glass is reformed into the desired shape. To remove internal stresses developed during the glass substrate sheet fabrication process and/or the reforming process, the shaped glass substrate sheet may then be annealed by an annealing process at block  112 . The annealing process may be any known or yet-to-be-developed annealing process. 
     At block  113 , the reformed glass substrate sheet is subjected to an etchant solution to preferentially etch the laser damage regions, while minimally etching the non-damaged regions. The etching removes flakes and smoothes edges of the laser damaged regions without removing a significant amount of the surface layer because the etchant solution etches the laser damage regions much more efficiently than the remaining non-damaged area of the reformed glass substrate sheet. In some embodiments, hydrofluoric acid is the primary etchant of an etchant solution that also includes mineral acids, such as hydrochloric acid, sulfuric acid, and/or nitric acid. As described in more detail above, the etchant solution and etching process may be controlled to reduce the etch time, reduce surface waviness, reduce surface roughness, minimize sludge, and minimize thickness reduction. 
     Next, at block  114 , the separated shaped glass articles may optionally be strengthened by a strengthening process. In some embodiments, the shaped glass articles may be strengthened by an ion-exchange chemical strengthening process. As described in more detail above, ions in a surface layer of the shaped glass articles are replaced by larger ions having the same valence or oxidation state, thereby forming a compressive surface layer on each surface of the shaped glass articles. The compressive surface layers may resist scratching and provide additional strength to the shaped glass articles. 
     At block  115 , additional processing may be applied to the strengthened shaped glass articles, such as edge finishing, application of touch-sensitive layers (e.g., indium tin oxide layers), antireflective layers, and the like. 
     It should now be understood that embodiments described herein are directed to methods of fabricating channels in glass articles from a flat glass substrate sheet using laser damage and chemical etching processes. Laser damage regions are formed within a flat glass substrate sheet to form channels in the one or more desired glass articles. The flat glass substrate sheet may be reformed to achieve the desired three-dimensional shape of the one or more glass articles. The laser damage regions are formed with an initial geometry that precompensates for the changing shape of the flat glass substrate sheet during the reforming process such that laser damage regions have a desired geometry after the reforming process. During etching, the laser damage regions are preferentially etched over non-damaged regions when the glass substrate sheet is subjected to an etchant solution. Compared with CNC machining, selective etching of laser damage regions results in smaller and more precisely shaped channels. 
     It is noted that the terms “substantially” and “about” may be utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. These terms are also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue. 
     While particular embodiments have been illustrated and described herein, it should be understood that various other changes and modifications may be made without departing from the spirit and scope of the claimed subject matter. Moreover, although various aspects of the claimed subject matter have been described herein, such aspects need not be utilized in combination. It is therefore intended that the appended claims cover all such changes and modifications that are within the scope of the claimed subject matter.