Patent Publication Number: US-2019185373-A1

Title: Methods for etching vias in glass-based articles employing positive charge organic molecules

Description:
This application claims the benefit of priority to U.S. Provisional Application Ser. No. 62/607,638 filed on Dec. 19, 2017, the content of which is relied upon and incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Field 
     The present specification generally relates to methods for forming vias within glass-based articles and, more particularly, methods for forming vias within glass-based articles having an increased waist diameter by employing positive charge organic molecules within an etching solution. 
     Technical Background 
     Glass-based articles having vias may be used in a wide variety of applications. Glass material may be particularly desirable for electronics applications due to its electrical properties, such as low dielectric constant and low dissipation factor. Such electrical properties may be desirable in high-frequency applications, such as wireless communications applications. Glass-based articles having vias may be utilized as a redistribution layer or an interposer, for example. 
     Vias may be formed within a glass-based article by a laser-damage-and-etch process wherein damage tracks are formed through the bulk of the glass-based article by a pulsed laser beam. The glass-based article having the damage tracks is then etched using an etching solution. An etch rate of the material within the damage track is higher than a bulk etch rate of the material that was not damaged by the laser beam. Therefore, vias may be formed through the glass-based article. 
     However, laser-damage-and-etch processes may produce vias having a waist diameter that is significantly smaller than the opening diameters at the first and second surfaces of the glass-based article. This leads to vias having an hourglass shape. Vias with a narrow waist may present challenges in downstream processes, such as metallization of the vias with an electrically conductive material. 
     SUMMARY 
     In some embodiments, a method of forming a via in a glass-based article includes forming a damage track through a bulk of the glass-based article extending from a first surface of the glass-based article to a second surface of the glass-based article, and applying an etching solution to the glass-based article to form the via. The etching solution includes at least one acid and a positive charge organic molecule. An etch rate at the first surface and the second surface is lower than an etch rate at the damage track. 
     In some embodiments, a method of forming a via in a glass-based article includes applying an etching solution to a glass-based article to form the via. Prior to etching, the glass-based article has a damage track formed through a bulk of the glass-based article extending from a first surface of the glass-based article to a second surface of the glass-based article. The etching solution comprises at least one acid and a positive charge organic molecule. An etch rate at the first surface and the second surface is lower than an etch rate at the damage track. 
     In some embodiments, a method of forming a via in a glass-based article includes applying a pulsed laser beam having a line focus through a bulk of the glass-based article to form a damage track through the bulk of the glass-based article extending from a first surface of the glass-based article to a second surface of the glass-based article. The method further includes applying an etching solution to the glass-based article to form the via. The etching solution includes hydrofluoric acid and PDADMAC, and an etch rate at the first surface and the second surface is lower than an etch rate at the damage track. 
     In some embodiments, a method of forming a via in a glass-based article, the method includes applying a pulsed laser beam having a line focus through a bulk of the glass-based article to form a damage track through the bulk of the glass-based article extending from a first surface of the glass-based article to a second surface of the glass-based article. 
     The method further includes applying an etching solution to the glass-based article to form the via. The etching solution includes hydrofluoric acid and PDADMAC, and an etch rate at the first surface and the second surface is lower than an etch rate at the damage track. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing will be apparent from the following more particular description of the example embodiments, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the representative embodiments. 
         FIG. 1  schematically depicts a partial side view of a glass-based article having vias according to one or more embodiments described and illustrated herein; 
         FIG. 2A  schematically depicts a partial side view of a glass-based article having a damage track formed therethrough according to one or more embodiments described and illustrated herein; 
         FIG. 2B  schematically depicts a partial side view of the glass-based article of  FIG. 2A  being etched by an etching process according to one or more embodiments described and illustrated herein; 
         FIG. 3A  schematically depicts a partial side view of the glass-based article of  FIG. 2A  after etching wherein E 1 /E 2 =1, where E 1  is a via etch rate and E 2  is a bulk etch rate; 
         FIG. 3B  schematically depicts a partial side view of the glass-based article of  FIG. 2A  after etching wherein 1&lt;E 1 /E 2 &lt;20; 
         FIG. 3C  schematically depicts a partial side view of the glass-based article of  FIG. 2A  after etching wherein E 1 /E 2 ≥20; 
         FIG. 4  schematically depicts a glass-based article having negatively charged surfaces subjected to three different etching scenarios including, positive charge surfactant, no positive charge organic molecules, and positive charge polyelectrolyte according to one or more embodiments described and illustrated herein; 
         FIG. 5  schematically depicts a glass-based article and multiple layers of positive charge polyelectrolytes and a layer of glass by-products according to one or more embodiments described and illustrated herein; 
         FIG. 6  schematically depicts a via being etched in a glass-based article by an etching solution including hydrogen fluoride and positive charge polyelectrolyte according to one or more embodiments described and illustrated herein; 
         FIG. 7  schematically depicts a via being etched in a glass-based article by an etching solution arranged in multiple layers of positive charge polyelectrolyte, hydrogen fluoride and glass by-products according to one or more embodiments described and illustrated herein; 
         FIG. 8A  is an image of a first surface of a glass coupon having vias etched by hydrofluoric acid without positive charge organic molecules with a focus of the image on the first surface to illustrate a first diameter of the vias; 
         FIG. 8B  is an image of the first surface of the glass coupon shown in  FIG. 8A  with a focus of the image within a bulk of the glass coupon to illustrate the waist diameter of the vias; 
         FIG. 8C  is a side image of the glass coupon shown in  FIGS. 8A and 8B ; 
         FIG. 9A  is an image of a first surface of a glass coupon having vias etched by an etching solution including hydrofluoric acid and CTAB with a focus of the image on the first surface to illustrate a first diameter of the vias according to one or more embodiments described and illustrated herein; 
         FIG. 9B  is an image of the first surface of the glass coupon shown in  FIG. 9A  with a focus of the image within a bulk of the glass coupon to illustrate the waist diameter of the vias according to one or more embodiments described and illustrated herein; 
         FIG. 9C  is a side image of the glass coupon shown in  FIGS. 9A and 9B  according to one or more embodiments described and illustrated herein; 
         FIG. 10A  is an image of a first surface of a glass coupon having vias etched by an etching solution including hydrofluoric acid and PDADMAC with a focus of the image on the first surface to illustrate a first diameter of the vias according to one or more embodiments described and illustrated herein; 
         FIG. 10B  is an image of the first surface of the glass coupon shown in  FIG. 10A  with a focus of the image within a bulk of the glass coupon to illustrate the waist diameter of the vias according to one or more embodiments described and illustrated herein; 
         FIG. 10C  is a side image of the glass coupon shown in  FIGS. 10A and 10B  according to one or more embodiments described and illustrated herein; 
         FIG. 11  graphically depicts the delta via diameter for glass coupons etched by a plurality of etching solution compositions according to one or more embodiments described and illustrated herein; 
         FIG. 12  graphically depicts the delta via diameter and etch rate for glass coupons etched by a plurality of etching solution compositions having varying concentrations of PDADMAC according to one or more embodiments described and illustrated herein; 
         FIGS. 13A-13D  are images of the first surface of glass coupons etched by the etching solution compositions of  FIG. 12  according to one or more embodiments described and illustrated herein; 
         FIG. 14  graphically depicts the delta via diameter and etch rate for glass coupons etched by a plurality of etching solution compositions having varying concentrations of PDADMAC and with and without HNO 3 , according to one or more embodiments described and illustrated herein; 
         FIG. 15  schematically depicts a glass-based article in an etching solution including a positive charge polyelectrolyte and a negative charge organic molecule according to one or more embodiments described and illustrated herein; 
         FIG. 16  graphically depicts the delta via diameter and etch rate for glass coupons etched by a plurality of etching solution compositions having varying concentrations of PDADMAC and SDS according to one or more embodiments described and illustrated herein; 
         FIG. 17A  is an image of a top surface of a glass coupon etched by hydrofluoric acid without positive charge organic molecules with a focus of the image within a bulk of the glass coupon to illustrate the waist diameter of the vias; 
         FIG. 17B  is an image of a top surface of a glass coupon etched by an etching solution including hydrofluoric acid and PDADMAC with a focus of the image within a bulk of the glass coupon to illustrate the waist diameter of the vias according to one or more embodiments described and illustrated herein; 
         FIG. 17C  is an image of a top surface of a glass coupon etched by an etching solution including hydrofluoric acid, PDADMAC and SDS with a focus of the image within a bulk of the glass coupon to illustrate the waist diameter of the vias according to one or more embodiments described and illustrated herein; and 
         FIG. 17D  is an image of a top surface of a glass coupon etched by an etching solution including hydrofluoric acid and SDS with a focus of the image within a bulk of the glass coupon to illustrate the waist diameter of the vias according to one or more embodiments described and illustrated herein. 
     
    
    
     DETAILED DESCRIPTION 
     The embodiments disclosed herein relate to methods for etching vias in glass-based articles using an etching solution including positive charge organic molecules (e.g., surfactants and polyelectrolytes) that retard the bulk etch rate of the surface of the glass-based article and do not retard, or retard to a lesser extent, a via etch rate. Thus, vias etched in glass-based articles according to the methods described herein have a larger waist diameter, and therefore less of an hourglass shape, than vias etched by an etching solution not including positive charge organic molecules. Embodiments described herein improve via shape without changing glass composition or glass properties. 
     The larger waist diameter of the vias may lead to improvement in downstream processes, such as metallization of the vias. Non-limiting example metallization methods include bottom-up plating and paste filling. The glass-based articles described herein may include metalized vias and may be provided as components in electronic devices, such as a redistribution layer (e.g., in a wireless communications device) or as an interposer. 
     Various embodiments of methods for forming vias in glass-based articles are described in detail below. 
     Referring now to  FIG. 1 , a glass-based article 100 having a plurality of vias  110  (“vias”) disposed therethrough is schematically illustrated. The glass-based article  100  may be used as a product in an electronic device, for example. Non-limiting products include a redistribution layer and an interposer. It should be understood that the glass-based article  100  may be utilized as other products performing other functions. 
     The glass-based article  100  has a first surface  102  and a second surface  104 . The vias  110  extend through a bulk of the glass-based article  100  from the first surface  102  to the second surface  104 . Although the vias  110  depicted in  FIG. 1  are through-hole vias, embodiments are not limited thereto. Vias of the present disclosure may be blind vias that do not extend fully through the glass-based article. The thickness of the glass-based articles described herein is not limited by this disclosure. As an example and not a limitation, the glass-based articles  100  described herein may have a thickness after etching within a range of 200 μm to 700 μm, or within a range of 200 μm, to 500 μm, including endpoints. It should be understood that the glass-based articles  100  may have other thicknesses depending on the end application. 
     The glass-based article  100  may be fabricated from any glass-based material capable of being etched by a chemical etching process. Non-limiting example glass-based materials include aluminosilicate glass, borosilicate glass, fused silica, soda lime glass, and glass-ceramic materials. The glass-based materials described herein have transparency for at least one laser operating wavelength that is sufficient to allow the creation of damage tracks. Non-limiting examples of suitable laser operating wavelengths include 532 nm and 1064 nm. Any suitable glass-based material may be used. 
     Each via  110  has a first opening  112  at the first surface, a second opening  114  at the second surface, and a waist W. The waist W of the vias  110  is located between the first opening  112  and the second opening  114 . As described in more detail below, the diameter of the waist W of the via  110  may be less than a diameter of the first opening  112  and/or the second opening  114 . In some embodiments, the diameter of the waist W is substantially equal to the diameter of the first opening  112  and/or the second opening  114 . 
     Depending on the application of the glass-based article  100 , the vias  110  may be filled with an electrically conductive material by way of a metallization process. The type of metallization process used to fill the vias  110  is not limited by this disclosure. Generally, it may be desirable in metallization processes to have a waist W with a diameter close to the diameter of the first opening  112  and/or the second opening  114 . Vias with a high waist diameter D W  to first diameter D 1  (or second diameter D 2 ) may result in more reliable metallization of the vias  110 . Thus, it may be desirable to increase the diameter of the waist W of the vias. 
     The vias  110  of the glass-based articles  100  described herein are formed by a laser-damage-and-etch process wherein a damage track through a bulk of the glass-based article  100  is formed by a laser beam. Referring to  FIG. 2A , a glass-based article  100  having a damage track  120  formed from the first surface  102  to the second surface  104  is schematically illustrated. The damage track  120  is a damaged region within the glass-based article  100  formed by application of a laser beam. The damage track  120  has a higher etch rate than the regions of the glass-based article outside of the damage track  120 . The laser methods of forming the damage track  120  are not limited by this disclosure. Methods of forming a damage track through a glass substrate in a laser-damage-and-etch process by use of a laser beam focused into a line focus are described in U.S. Pat. Publ. No 2015/0166396, which is hereby incorporated by reference in its entirety. As an example and not a limitation, a picosecond laser may be focused into a line focus that passes through the thickness of the glass-based article  100  to damage the glass material and create a damage track  120 . To form a through-hole via, the damage track  120  extends from the first surface  102  to the second surface  104 . To form a blind via, the damage track  120  may start at the first surface  102  or the second surface  104 , but not extend fully to the opposite surface. 
     Referring now to  FIG. 2B , a glass-based article  100  having one or more damage tracks therethrough is then etched in an etching solution. As non-limiting examples, the etching solution includes hydrofluoric acid in a concentration of 0.5 to 10 wt %, including endpoints, or 2.5 wt to 10 wt %, including endpoints. The etching solutions described herein may or may not include one or more mineral acids and/or strong acids. Example mineral acids and strong acids include, but are not limited to, hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, acetic acid, and tartaric acid. In embodiments, the etching solution may include 0 to 40 wt % mineral acid, including endpoints. The etching solutions described herein may also include one or more fluoride-containing compounds, such as, without limitation, ammonium fluoride, potassium fluoride, sodium fluoride, ammonium bifluoride, potassium bifluoride, and sodium bifluoride. As an example, and not a limitation, the concentration of other fluoride compounds may be 0 to 10 wt %. 
     The etching solution etches the first surface  102  and the second surface  104  of the glass-based article  100 , as well as through the damage track  120 . The glass-based article  100  may be statically etched or with applied agitation, such as ultrasonic agitation. During the etching process, the etch rate of the damaged region of the damage track  120  is defined as E 1  and the etch rate of the bulk region (undamaged region) is defined as E 2  in  FIG. 2B . The ratio of E 1 /E 2  is defined as R herein. 
     As shown in  FIG. 3A , when R is equal to 1, the glass-based article  100  becomes thinner but a via is not formed because E 1  is equal to E 2 . However, when R is greater than 1 but less than 20, a via  110  is formed such that the first diameter D 1  of the first opening  112  and the second diameter D 2  of the second opening  114  are significantly larger than the waist diameter D W  of the waist W. When the ratio R is greater than 20, the via  110  is formed such that the waist diameter D W  is close to the first diameter D 1  and/or the second diameter D 2 , thereby forming a substantially cylindrical through via. 
     As stated above, it may be desirable to increase the ratio D W /D 1  to improve the metallization process that fills the vias  110  with electrically conductive material (e.g., copper). It is noted that the first diameter D 1  and the second diameter D 2  may be used interchangeably herein because the first diameter D 1  and the second diameter D 2  may be close in value. Thus, the ratio D W /D 1  also refers to the ratio D W /D 2  herein. 
     Embodiments of the present disclosure increase the waist diameter D W  without requiring a change in glass composition or a change in the laser damage process, as well as without significantly changing the initial glass thickness. Particularly, the laser-damage-and-etch processes described herein increase the waist diameter, and thus improve the ratio D W /D 1  by introducing positive charge organic molecules into the etching solution. 
     The positive charge organic molecules self-assemble and form an etching inhibitor layer on the first surface  102  and the second surface  104  of the glass-based article  100  that slows the rate at which the acid (e.g., hydrofluoric acid) of the etching solution reaches these surfaces. This effect reduces the bulk etch rate E 2 . When the access of the hydrofluoric acid to the glass surface is regulated (i.e., slowed down), the bulk etching rate E 2  may be reduced in a controllable manner. As non-limiting examples, the concentration of positive charge organic molecules may be within a range of 0.0035 wt % to 10 wt %, or 0.0035 wt % to 1 wt %, 0.0035 wt % to 0.1 wt %, or 0.0035 wt % to 0.05 wt %, including endpoints. 
     As shown in  FIG. 4 , the first surface  102  and the second surface  104  of the glass-based article  100  is negatively charged. Particularly, the first surface  102  and the second surface  104  are negatively charged within the etching solution when the pH of the etching solution is above the isoelectric point of the material of the glass-based article  100 . Thus, the etching solutions described herein have a pH value that is greater than the isoelectric point of the glass-based article  100  being etched to cause the surfaces to be negatively charged. The isoelectric point of the glass-based article  100  may depend on the composition of the glass-based article  100 . The isoelectric point of the glass-based articles described herein is measured by the Zetasizer Nano ZS90 sold by Malvern Instruments Ltd of the United Kingdom. First, the glass-based article is powderized to 100 μm in average diameter particles. The particles are suspended in aqueous solutions at different pH values. The particle concentration is less than  1  % by volume. Ultrasonic agitation is applied until the particles are uniformly distributed. The solution is then provided in a testing vial for zeta-potential measurement in the Zetasizer Nano ZS  90 . The zeta-potential of the sample is measured using the Zetasizer Nano ZS  90  standard operating procedure. The zeta potential may be neutral, positive or negative. The isoelectric point is the pH value where the zeta potential is neutral. 
     The etching chemistry of the embodiments described herein include positive charge organic molecules to self-assemble on the negatively-charged glass surface and therefore retard glass surface etching and improve etching selectivity between laser damaged and non-damaged areas. 
     The “positive charge molecules” described herein may be any molecule that has a positive charge that is attracted to the negatively charged first surface  102  and second surface  104  of the glass-based article  100  and provides an etching inhibitor layer for hydrofluoric acid molecules that retards the etching effect of the hydrofluoric acid on the first surface  102  and the second surface  104 . As a non-limiting example, the positive charge organic molecules may have a positive charged hydrophilic head (i.e., a hydrophilic portion) and a hydrophobic tail (i.e., a hydrophobic portion). The positive charged head is balanced with a negative charge ion, and is covalently bonded to the hydrophobic tail. Non-limiting examples of positive charge organic molecules include positive charge surfactants and positive charge polyelectrolytes. A non-limiting example of a positive charge surfactant includes cetrimonium bromide ([C 16 H 33 )N(CH 3 ) 3 ]Br) hereinafter “CTAB”). A non-limiting example of a positive charge polyelectrolyte is poly(dailydimethylammonium chloride) (hereinafter “PDADMAC”). It should be understood that the etching solutions described herein may comprise a combination of one or more positive charge surfactants and one or more positive charge polyelectrolytes. Other non-limiting examples of positive charge polyelectrolytes is amine-containing polymers having a positive charge in the etching solution, such as, without limitation, polyamine, polyethylene amine, and the like. 
     FIG,  4  illustrates three different etching scenarios in a first region  130 A, a second region  130 B and a third region  130 C. In all scenarios, the etching solution includes hydrogen fluoride molecules  132  that remove glass material of the glass-based article  100  when in contact with the first surface  102  and the second surface  104 . It is noted that the etching solution is shown as only contacting the first surface  102  in  FIGS. 4-7 and 15  for ease of illustration. It should be understood that the etching solution may contact all surfaces of the glass-based article  100 . In the scenario illustrated by the second region  130 B, the etching solution does not include positive charge organic molecules and thus the hydrofluoric acid molecules have access to the first surface  102  with no etching inhibitor layer. In such a case, the bulk etch rate E 2  is not retarded. However, in the scenario illustrated by the first region  130 A, the negative charge of the first surface  102  attracts positive charge surfactant molecules  134 . Therefore, the positive surfactant molecules form an etching inhibitor layer that inhibits access of the hydrogen fluoride molecules  132  to the first surface  102  (and the second surface  104 ) of the glass-based article  100 . The hydrogen fluoride molecules  132  need to pass through the surfactant layer formed by the positive charge surfactant molecules  134 . The positive charge surfactant molecules  134  reduce the ability for the hydrogen fluoride molecules  132  to contact and etch the surfaces of the glass-based article  100 . Accordingly the bulk etch rate E 2  of the scenario illustrated by the first region  130 A is slower than that of the scenario illustrated by the second region  130 B. 
     The third region  130 C illustrates positive charge polyelectrolyte molecules  136  attracted to the negatively charged first surface  102 , thereby forming an etching inhibitor layer in a manner similar to the positive charge surfactant molecules  134  within the first region  130 A. The positive charge polyelectrolyte molecules  136  reduce the ability for the hydrogen fluoride molecules  132  to contact and etch the first surface  102 . The hydrogen fluoride molecules  132  still access the surfaces of the class-based article but at a much slower rate than when no positive charge polyelectrolyte molecules  136  are present. It is noted that, compared to the layer formed by the positive charge surfactant molecules  134 , the layer formed by the positive charge polyelectrolyte molecules  136  may be more rigid and more effective in regulating the hydrogen fluoride molecules than the positive charge surfactant molecules  134 . Because the positive charge polyelectrolyte molecules  136  contain more than one charge per molecule, it may be more difficult to detach from the glass surface than the positive charge surfactant molecules  134 . Generally, it has been shown that the etch rate from high to low ranks as: the second region  130 B&gt;the first region  130 A&gt;the third region  130 C. Thus, if the glass-based article  100  is etched using the same etching solution and at the same etch condition, adding positive charge organic molecules can modulate glass etch rate. 
       FIG. 5  schematically illustrates a scenario similar to that of the third region  130 C illustrated by  FIG. 4  but with the addition of a graphical representation of glass by-products (e.g., CaAlF 5 , CaSiF 6 , MgSiF 6 , MgAlF 5  depending on the composition)  138  etched by the hydrofluoric acid. In some cases, the glass by-products  138  may form an additional layer that inhibits the hydrogen fluoride molecules  132  from reaching the surfaces of the glass-based article  100 . Thus, several layers formed by positive charge organic molecules and glass by-products may be formed.  FIG. 5  schematically illustrates two layers of positive charge polyelectrolyte molecules  136 A,  136 B and one layer of glass by-products  138 . It should be understood that  FIG. 5  is merely a simplified illustration of the various layers that may be formed during the etching process, and that embodiments are not limited thereto. 
     Modulation of the bulk etch rate E 2  using positive charge organic molecules may be used to increase the waist diameter D W  of vias  110  formed in glass-based articles  100 . Additionally, positive charge organic molecules may be used to form cylindrically shaped blind vias that are less tapered in shape.  FIG. 6  schematically illustrates etching of a via  110  within a glass-based article  100  using a hydrofluoric acid etching solution including positive charge organic molecules (positive charge polyelectrolyte molecules  136  in this example). During etching, a via can be classified into two areas: an opened area on the first surface  102  (and second surface  104 ) proximate and within the first opening  112  (and second opening  114 ) and a restricted area  117  within a waist W. In the opened area, positive charge polyelectrolyte molecules  136  can effectively align and slow down etching process by inhibiting the hydrogen fluoride molecules  132 . Positive charge surfactant molecules  134  perform a similar function. Both the bulk etch rate E 2  and a via widening rate within the first opening  112  is slowed down as compared to when no positive charge polyelectrolyte molecules  136  are provided in the etching solution. However, access of the positive charge polyelectrolyte molecules  136  into the restricted area  117  is restricted and thus the positive charge polyelectrolyte molecules  136  cannot as effectively inhibit etching as compared to the opened area. Accordingly, the via etch rate E 1  is not as significantly influenced by the positive charge polyelectrolyte molecules  136  as compared to the surface etch rate E 2 . Positive charge surfactant molecules  134  perform in a similar manner. 
       FIG. 7  is similar to the etching process depicted by  FIG. 6  but further includes the depiction of glass by-products  138  that, along with the positive charge polyelectrolyte molecules  136 , further inhibit the hydrogen fluoride molecules  132  from contacting the opened area of the first surface  102 . However, the positive charge polyelectrolyte molecules  136  and the glass by-products  138  do not easily enter the restricted area  117 , allowing the hydrogen fluoride molecules  132  to enter the restricted area  117  and widen the waist W of the via  110 , as described above with respect to  FIG. 6 . 
     EXAMPLE 1 
     To illustrate the effects of positive charge surfactant molecules and positive charge polyelectrolyte molecules within an etching solution in widening the waist of vias, glass coupons were subjected to a laser-and-damage-and-etch process. The 50 mm×50 mm glass coupons were fabricated from alkaline earth boro-aluminosilicate under the trade name Eagle XG® sold by Corning, Inc. of Corning, New York and had a thickness of 0.4 mm. One glass coupon was fabricated per etching condition. 10,000 damage tracks  120  were formed in each of the glass coupons using a 50 ps pulsed laser having 532 nm wavelength, a 3 mm beam diameter that entered the first surface  102 , a 30 mm working distance objective, and a 0.7 mm focus line length was present through the glass coupons. Each damage track was created using one laser burst with a burst number of 15 pulses and a burst energy of about 800. 
     Following the laser damage process, the glass coupons were statically etched at room temperature (20° C.) in an etching solution comprising a solution of 2.5 wt % HF and 3.5 wt % HNO 3  with and without positive charge organic molecules. The final thickness of the glass coupons, the waist diameter, and the first diameter of the first opening (i.e., the openings at the surface into which the laser beam enters the glass coupons) were measured using an optical microscope. The etch time was also recorded. The average top diameter D 1 , waist diameter D W , final glass coupon thickness, initial glass coupon thickness, etch time, via shape, etch rate E 1 , etch rate E 2 , etch ratio, and through time were recorded. It is noted that the via shape is quantified by a thickness of the etched glass coupon divided by two times the difference between the top diameter D 1  and the waist diameter D W . Through time is the time that the etching takes to connect the vias from the first surface to the second surface (etch time—D W /(2*E 2 ). The results are shown in Table 1 below. 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                 Delta 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                   
                   
                   
                 (Top 
                   
                   
                   
                 via 
               
               
                   
                   
                   
                 Diameter − 
                 final 
                 initial 
                 etch 
                 shape 
                 E1 
                 E2 
                 etch 
                 through 
               
               
                   
                 Top D 
                 Waist D 
                 Waist 
                 thickness 
                 thickness 
                 time 
                 (T/2)/ 
                 (Via), 
                 (bulk), 
                 ratio 
                 time 
               
               
                 etching solution 
                 (μm) 
                 (μm) 
                 Diameter) 
                 (μm) 
                 (μm) 
                 (min) 
                 (Dt − Dw) 
                 μm/min 
                 μm/min 
                 (E1/E2) 
                 (min) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 2.5 wt % HF + 3.5 wt % HNO3 
                 82.5 
                 27.6 
                 54.8 
                 305 
                 405 
                 168.3 
                 2.8 
                 1.66 
                 0.297 
                 5.60 
                 121.8 
               
               
                 2.5 wt % HF + 3.5 wt % HNO3 + 
                 81.0 
                 46.5 
                 34.5 
                 303 
                 404 
                 335 
                 4.4 
                 1.12 
                 0.151 
                 7.41 
                 180.8 
               
               
                 0.35 wt % PDAD 
               
               
                 MAC(&lt;100 K) 
               
               
                 2.5 wt % HF + 3.5 wt % HNO3 + 
                 87.1 
                 42.0 
                 45.1 
                 302 
                 402 
                 325 
                 3.3 
                 1.07 
                 0.154 
                 6.93 
                 188.5 
               
               
                 0.2 wt % PDAD 
               
               
                 MAC(100-200 K) 
               
               
                 2.5 wt % HF + 3.5 wt % HNO3 + 
                 85.6 
                 46.9 
                 38.6 
                 301 
                 402 
                 326.5 
                 3.9 
                 1.15 
                 0.155 
                 7.44 
                 174.8 
               
               
                 0.4 wt % PDAD 
               
               
                 MAC(100-200 K) 
               
               
                 2.5 wt % HF + 3.5 wt % HNO3 + 
                 91.0 
                 47.5 
                 43.6 
                 300 
                 400 
                 340 
                 3.4 
                 1.12 
                 0.147 
                 7.61 
                 178.6 
               
               
                 0.2 wt % PDAD 
               
               
                 MAC(&gt;400 K) 
               
               
                 2.5 wt % HF + 3.5 wt % HNO3 + 
                 81.3 
                 33.0 
                 48.4 
                 304 
                 403 
                 261 
                 3.1 
                 1.16 
                 0.190 
                 6.10 
                 174.1 
               
               
                 1 wt % CTAB 
               
               
                   
               
            
           
         
       
     
       FIGS. 8A-8C  depict images of vias of etched glass coupons that were etched by 2.5 wt % HF and 3.5 wt % HNO 3  (1.45M HF and 0.8M HNO 3 ). Thus, the etched glass coupons shown in  FIGS. 8A-8C  are representative of control group glass coupons because no positive charge organic molecules were included in the etching solution. The focus of the image of  FIG. 8A  is on the top surface of the glass coupon to depict the top diameter D 1  of the openings (e.g., the first openings  112  shown in  FIG. 1 ), which is represented by the diameter of the dark circles. The focus of the image of  FIG. 8B  is within the bulk of the glass coupon to depict the waist diameter D W  of the vias, which is represented by the center white circles.  FIG. 8C  is a side view of the vias of the control glass coupons depicted in  FIGS. 8A and 8B . 
     Referring to Table 1 above, the average top diameter D 1  and the average waist diameter D W  of the control glass coupons were 82.5 μm and 27.6 μm, respectively. This resulted in vias with a narrow waist and having an hourglass shape as shown in  FIG. 8C . 
       FIGS. 9A-9C  depict images of vias of etched glass coupons that were etched by 2.5 wt % HF and 3.5 wt % HNO 3  and 1 wt % CTAB (1.45M HF and 0.8M HNO 3  and 1 wt % CTAB). Similar to  FIG. 8A , the focus of the image of  FIG. 9A  is on the top surface of the glass coupon to depict the top diameter D 1  of the openings (e.g., the first openings  112  shown in  FIG. 1 ), which is represented by the diameter of the dark circles. The focus of the image of  FIG. 9B  is within the bulk of the glass coupon to depict the waist diameter D W  of the vias, which is represented by the center white circles.  FIG. 9C  is a side view of the vias of the glass coupons depicted in  FIGS. 9A and 9B . 
     Referring to Table 1 above, the average top diameter D 1  and the average waist diameter D W  for these glass coupons were 81.3 μm and 33.0 μm, respectively. Thus, the CTAB increased the average waist diameter from 27.6 μm to 33.0 μm as compared to the vias of the control glass coupons. The resulting vias as shown in  FIG. 9C  have less of an hourglass shape than those depicted in  FIG. 8C . 
       FIGS. 10A-10C  depict images of vias of etched glass coupons that were etched by 2.5 wt % HF and 3.5 wt % HNO 3  and 0.35 wt % PDADMAC as a positive charge polyelectrolyte (1.45M HF and 0.8M HNO3 and 0.35 wt % PDADMAC at 100K of molecular weight). Similar to  FIGS. 8A and 9A , the focus of the image of  FIG. 10A  is on the top surface of the glass coupon to depict the top diameter D 1  of the openings (e.g., the first openings  112  shown in  FIG. 1 ), which is represented by the diameter of the dark circles. The focus of the image of  FIG. 10B  is within the bulk of the glass coupon to depict the waist diameter D W  of the vias, which is represented by the center white circles.  FIG. 10C  is a side view of the vias of the glass coupons depicted in  FIGS. 10A and 10B . 
     Referring to Table 1 above, the average top diameter D 1  and the average waist diameter D W  for these glass coupons were 81.0 μm and 46.5 μm, respectively. Thus, the PDADMAC increased the average waist diameter from 27.6 μm to 46.5 μm as compared to the vias of the control glass coupons. The vias of  FIG. 10C  have less of an hourglass shape than those depicted in  FIGS. 8C and 9C . 
     Referring to Table 1, the glass coupons etched by an etching solution including positive charge organic molecules had a waist diameter D W  of greater than 30 μm. 
       FIG. 11  graphically depicts a chart illustrating a delta via diameter between the top diameter D 1  and the waist diameter D W  (D 1 -D W ) using the data from Table 1. The etching solutions illustrated by  FIG. 11  are as follows from left to right in the chart: 
     1) 2.5 wt % HF+3.5 wt % HNO 3 +1 wt % CTAB, 
     2) 2.5 wt % HF+3.5 wt % HNO 3 +0.2 wt % PDADMAC (100-200K), 
     3) 2.5 wt % HF+3.5 wt % HNO 3 +0.4 wt % PDADMAC (100-200K), 
     4) 2.5 wt % HF+3.5 wt % HNO 3 +0.2 wt % PDADMAC (&gt;400K), 
     5) 2.5 wt % HF+3.5 wt % HNO 3 , and 
     6) 2.5 wt % HF+3.5 wt % HNO 3 +0.35 wt % PDADMAC (&lt;100K). 
     Referring to Table 1 and the graph of  FIG. 1 , glass coupons etched by etching solutions including positive charge organic molecules had a delta via diameter of less than 50 μm. In some embodiments, the glass-based articles may have a delta via diameter of less than or equal to 50 μm for glass-based article thicknesses between 200 μm and 700 μm, including endpoints. The control glass coupons had vias with the highest delta via diameter (about 54.8 μm), while the glass coupons etched by 2.5 wt % HF and 3.5 wt % HNO 3  and 0.35 wt % PDADMAC at 100K molecular weight had the smallest delta via diameter (about 34.5 μm). Table 1 shows that the presence of positive charge organic molecules decreases the delta via diameter. The delta via diameter reflects the shape of the etch via and implicates the capability of etching solutions to generate wide opening via waist. The lower delta via diameter suggests better via waist opening, which may provide vias with a more desirable shape for metallization. 
     Generally, the example shows that positive charge PDADMAC reduced the delta via diameter more effectively than positive charge CTAB. Without being bound by theory, this may be for at least two reasons: (1) the positive charge polyelectrolyte molecule can stay on glass surface much longer (retention time) due to the stronger electrostatic interaction of multiple positive charges per molecule while the positive charge surfactant molecule contains only one positive charge per molecule and has greater potential to depart the glass surface quicker, and (2) the etching inhibitor layer of positive charge polyelectrolyte molecule may make it more difficult for the hydrogen fluoride molecules to penetrate through to reach the surfaces of the glass-based article. For at least these reasons, the positive charge polyelectrolyte molecule reduced the bulk etch rate E 2  from 0.3 um/min to 0.15 um/min in this example. The positive charge surfactant molecule reduced the bulk etch rate E 2  to 0.2 um/min. In one non-limiting embodiment, the etching solution comprises 4 wt % to 6 wt %HF and 0.0035 wt % to 0.05 wt % PDADMAC, including endpoints. 
     The size (i.e., the molecular weight) of the positive charge polyelectrolyte molecule may also play a role in restricting via opening at the surfaces, and thus etching vias with a smaller delta via diameter. Polyelectrolytes of smaller molecular weight (100K or less) may be able to access to the via area earlier than polyelectrolytes having a larger size (e.g., molecular weights of 100K-200K, and 400K or larger). Positive charge polyelectrolytes having a smaller size may reduce the via widening rate earlier, and reduce the delta via diameter more effectively. 
     Accordingly, the above-example shows that positive charge surfactants and positive charge polyelectrolytes, when included in a hydrofluoric acid etching solution, are capable of increasing the waist diameter D W  and therefore decreasing the delta via diameter between the top diameter and the waist diameter (D 1 -D W ). 
     EXAMPLE 2 
     To illustrate the impact of the concentration of positive charge polyelectrolyte in the etching solution on delta via diameter and etching rate, damage tracks were formed in glass coupons as described above with respect to Example 1. The composition and thickness of the glass coupons were the same as the glass coupons of Example 1. 
     Four sets of glass coupons were etched using an etching solution comprising hydrofluoric acid without mineral acids. A first set included control glass coupons that were etched using 3M HF (5 wt %) without positive charge organic molecules. An image of the waists of sample vias of the control glass coupons is illustrated in  FIG. 13A .  FIG. 12  is a bar graph showing delta diameter versus etchant for the glass coupons shown in  FIGS. 13A-13D . For  FIGS. 13A-13D , the focus of the images is on the waist of the vias to illustrate waist diameter D W . A second set of glass coupons was etched using 3M HF (5 wt %) with 0.35 wt % PDADMAC having a molecular weight of 100K.  FIG. 13B  shows the resulting vias. A third set of glass coupons was etched using 3M HF (5 wt %) with 0.035 wt % PDADMAC having a molecular weight of 100K.  FIG. 13C  shows the resulting vias. A fourth set of glass coupons was etched using 3M HF (5 wt %) with 0.0035 wt % PDADMAC having a molecular weight of 100K.  FIG. 13D  shows the resulting vias. 
     Referring to  FIG. 12 , low concentration of PDADMAC (0.0035 wt %) provided the smallest delta via diameter and therefore the most ideal via shapes. Thus, only a small amount of positive charge polyelectrolyte may be needed to have a large impact on via shape. Additionally, use of a lower concentration of positive charge polyelectrolytes may also reduce the etch time as compared with higher concentrations of positive charge polyelectrolytes. 
     To illustrate the effect of the concentration of positive charge polyelectrolyte in etching solutions with and without a mineral acid on delta via diameter and etching rate, damage tracks were formed in glass coupons as described above with respect to Example 1. The composition and thickness of the glass coupons were the same as the glass coupons of Example 1. 
     Nine sets of glass coupons having damage tracks were etched according to the compositions shown in the graph of  FIG. 14 . As shown in  FIG. 14 , when the etching solution includes HNO  3  (etching solution formulation 2.5 wt % HF-3.5 wt % HNO 3 ) in the example) a higher concentration (0.35 wt %) of PDADMAC yields a smaller delta via diameter than a lower concentration (0.035 wt %) of PDADMAC. When the etching solution included 2.5 wt % HF without a mineral acid, the delta via diameter and the etch time were nearly the same whether the etching solution included 0.35 wt % or 0.035 wt % PDADMAC. However, as also shown in  FIG. 13 , a lowest evaluated concentration PDADMAC (0.0035 wt %) provides the smallest delta via diameter and etch time. 
     It is noted that the presence of residue positive charge organic molecules in the etching solution tank may undesirably affect the etching results of subsequent etching processes. Thus, the etching solution tank should be cleaned to remove the positive charge organic molecules if the effects of the positive charge organic molecules are not desired. According to some embodiments, the etching solution tank may be neutralized of the positive charge organic molecules by adding negative charge organic molecules that are attracted to the positive charge organic molecules and remove the positive charge organic molecules from the surfaces of the glass-based article. Example negative charge organic molecules include, but are not limited to, anionic surfactants. Example anionic surfactants include, but are not limited to, sodium dodecyl sulfate (NaC 12 H 25 SO 4 ) (“SDS”) and fatty acid salts, such as sodium stearate. 
       FIG. 15  schematically depicts an etching solution including negative charge SDS molecules  140 , positive charge polyelectrolyte molecules  136 , and hydrogen fluoride molecules  132 . The negative charge SDS molecules  140  are attracted to the positive charge polyelectrolyte molecules  136  and remove the positive charge polyelectrolyte molecules  136  from the first surface  102  (and second surface  104 ) of the glass-based article  100 . This allows access for the hydrogen fluoride molecules  132  to contact the first surface  102  (and second surface  104 ) of the glass-based article  100 . Thus, the negative charge SDS molecules  140  counteract the positive charge polyelectrolyte molecules  136  resulting in a fast bulk etch rate E 2 . 
     EXAMPLE 3 
     To illustrate the effect of negative SDS molecules on the delta via diameter and etch time, two additional sets of glass coupons were etched by a laser-damage-and-etch process using a first etching solution comprising 5 wt % HF+0.0035 wt % PDADMAC (100K)+0.1 wt % SDS and a second etching solution comprising 5 wt % HF+0.1 wt % SDS. The composition and thickness of the glass coupons were the same as the glass coupons of Example 1. The damage tracks were formed as described above with respect to Example 1. 
       FIG. 16  is a chart that compares the etching solutions shown in  FIG. 12  with the two etching solutions including SDS as described above. As shown in  FIG. 16 , the presence of SDS increases the delta via diameter (i.e., decreases the waist diameter D W  of the vias) and decreases the etch time. This may be due to a lack of positive charge PDADMAC molecules that reduces access of the hydrogen fluoride molecules to the surfaces of the glass coupons. 
       FIGS. 17A-17D  illustrate the evolution of the change in waist diameter size as positive charge PDADMAC molecules are added to the etching solution and then negative charge SDS molecules are added to the etching solution. Particularly,  FIG. 17A  depicts a glass coupon with vias etched by 5 wt % HF,  FIG. 17B  depicts a glass coupon etched by 5 wt % HF+0.035 wt % PDADMAC (100K),  FIG. 17C  depicts a glass coupon etched by 5 wt % HF+0.035 wt % PDADMAC (100K)+0.1 wt % SDS, and  FIG. 17D  depicts a glass coupon etched by 5 wt % HF+0.1 wt % SDS. As shown in  FIGS. 17A-17D , the vias have a narrow waist when no PDADMAC is present ( FIG. 17A ), and comparatively widened vias when PDADMAC is present.  FIGS. 17C and 17D  illustrate that the vias are once again narrow when SDS is present. Thus, negative SDS molecules may be provided to the etching solution tank to remove residue positive charge organic molecules. 
     It should now be understood that embodiments of the present disclosure are directed to methods of etching vias in glass-based articles that increase the waist diameter of vias by slowing down the bulk etch rate of the open areas of the surfaces of the glass-based article while permitting etching of the waist of the via. Therefore, embodiments may result in vias having a more cylindrical and less hourglass-shaped profile which may be beneficial for downstream metallization processes. Particularly, positive charge organic molecules are added to the etching solution to provide an etching inhibitor layer at the surfaces of the glass-based article. However, hydrogen fluoride molecules are able to enter the waist such that etching of the waist of the vias is not substantially impeded. Because the bulk etch rate is reduced, less glass is etched away and less etching solution may be used, which reduces material costs. 
     While the embodiments herein are described with respect to hourglass and cylindrical shaped vias, the embodiments are equally applicable to any other via shape where it is desired to slow the bulk etch rate of the surfaces of the glass-based article relative to the etch rate of via surfaces. 
     It is noted that, in some cases, a surface haze is present in the etched glass-based articles. The surface haze may be reduced by including nitric acid in the etching solution, increasing the concentration of hydrogen fluoride, or increasing the concentration of positive charge polyelectrolyte molecules. 
     While exemplary embodiments have been described herein, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope encompassed by the appended claims.