METHODS FOR LASER PROCESSING TRANSPARENT WORKPIECES USING PULSED LASER BEAM FOCAL LINES AND CHEMICAL ETCHING SOLUTIONS

A method for processing a transparent workpiece includes forming a closed contour line having a plurality of defects in the transparent workpiece such that the closed contour line defines a closed contour. Forming the closed contour line includes directing a pulsed laser beam through an aspheric optical element and into the transparent workpiece such that a portion of the pulsed laser beam directed into the transparent workpiece generates an induced absorption within the transparent workpiece, the induced absorption producing a defect within the transparent workpiece, and translating the transparent workpiece and the pulsed laser beam relative to each other along the closed contour line. The method further includes etching the transparent workpiece with a chemical etching solution at an etching rate of about 2.5 μm/min or less to separate a portion of the transparent workpiece along the closed contour line, thereby forming an aperture extending through the transparent workpiece, the aperture comprising an aperture perimeter extending along the closed contour.

BACKGROUND

Field

The present specification generally relates to apparatuses and methods for laser processing transparent workpieces, and more particularly, to forming closed contour lines in transparent workpieces for forming apertures in transparent workpieces.

Technical Background

The area of laser processing of materials encompasses a wide variety of applications that involve cutting, drilling, milling, welding, melting, etc. of different types of materials. Among these processes, one that is of particular interest is cutting or separating different types of transparent substrates in a process that may be utilized in the production of materials such as glass, sapphire, or fused silica for thin film transistors (TFT) or display materials for electronic devices.

From process development and cost perspectives there are many opportunities for improvement in cutting and separating glass substrates. It is of great interest to have a faster, cleaner, cheaper, more repeatable, and more reliable method of separating glass substrates than what is currently practiced in the market. Accordingly, a need exists for alternative improved methods for separating glass substrates.

SUMMARY

According to some embodiments, a method for processing a transparent workpiece includes forming a closed contour line in the transparent workpiece, the closed contour line having a plurality of defects in the transparent workpiece such that the closed contour line defines a closed contour. Forming the closed contour line includes directing a pulsed laser beam oriented along a beam pathway and output by a beam source through an aspheric optical element and into the transparent workpiece such that a portion of the pulsed laser beam directed into the transparent workpiece generates an induced absorption within the transparent workpiece, the induced absorption producing a defect within the transparent workpiece, and the portion of the pulsed laser beam directed into the transparent workpiece includes a wavelength λ, a spot size w0, and a cross section that comprises a Rayleigh range ZRthat is greater than

where FDis a dimensionless divergence factor comprising a value of 10 or greater. Forming the closed contour line also includes translating the transparent workpiece and the pulsed laser beam relative to each other along the closed contour line, thereby laser forming the plurality of defects along the closed contour line within the transparent workpiece. Further, the method for processing the transparent workpiece includes etching the transparent workpiece with a chemical etching solution at an etching rate of about 10 μm/min or less to separate a portion of the transparent workpiece along the closed contour line, thereby forming an aperture extending through the transparent workpiece, the aperture comprising an aperture perimeter extending along the closed contour.

In some embodiments, for the method of any of the preceding embodiments, the etching rate is about 5 μm/min or less.

In some embodiments, for the method of any of the preceding embodiments, the etching rate is about 2.5 μm/min or less.

In some embodiments, for the method of any of the preceding embodiments, the etching rate is about 1 μm/min or less.

In some embodiments, for the method of any of the preceding embodiments, etching the transparent workpiece removes about 50% or less of a thickness of the transparent workpiece.

In some embodiments, for the method of any of the preceding embodiments, etching the transparent workpiece removes about 25% or less of a thickness of the transparent workpiece.

In some embodiments, for the method of any of the preceding embodiments, etching the transparent workpiece removes about 15% or less of a thickness of the transparent workpiece.

In some embodiments, for the method of any of the preceding embodiments, etching the transparent workpiece removes about 10% or less of a thickness of the transparent workpiece.

In some embodiments, for the method of any of the preceding embodiments, etching the transparent workpiece removes about 7.5% or less of a thickness of the transparent workpiece.

In some embodiments, for the method of any of the preceding embodiments, a spacing between adjacent defects is about 50 μm or less.

In some embodiments, for the method of any of the preceding embodiments, a spacing between adjacent defects is about 25 μm or less.

In some embodiments, for the method of any of the preceding embodiments, a spacing between adjacent defects is about 15 μm or less.

In some embodiments, for the method of any of the preceding embodiments, a spacing between adjacent defects is about 10 μm or less.

In some embodiments, for the method of any of the preceding embodiments, a spacing between adjacent defects is about 5 μm or less.

In some embodiments, for the method of any of the preceding embodiments, the transparent workpiece comprises an alkali aluminosilicate glass material.

In some embodiments, for the method of any of the preceding embodiments, the aperture perimeter comprises a diameter of from about 100 μm to about 10 mm.

In some embodiments, for the method of any of the preceding embodiments, the aperture perimeter comprises a diameter of about 3 mm or less.

In some embodiments, for the method of any of the preceding embodiments, the aperture perimeter comprises a diameter of about 800 μm or less.

In some embodiments, for the method of any of the preceding embodiments, the chemical etching solution comprises a chemical etchant and deionized water.

In some embodiments, for the method of any of the preceding embodiments, the chemical etchant of the chemical etching solution comprises hydrofluoric acid, nitric acid, hydrochloric acid, sulfuric acid, or combinations thereof.

In some embodiments, for the method of any of the preceding embodiments, the chemical etching solution comprises a chemical etchant and deionized water and the chemical etchant of the chemical etching solution comprises sodium hydroxide or potassium hydroxide.

In some embodiments, for the method of any of the preceding embodiments, the chemical etching solution comprises from about 5M to 20M Sodium Hydroxide or 5M to 20M Potassium Hydroxide.

In some embodiments, for the method of any of the preceding embodiments, the chemical etching solution is maintained at a temperature between 70° C. to about 100° C.

In some embodiments, for the method of any of the preceding embodiments, the chemical etching solution further comprises a surfactant.

In some embodiments, for the method of any of the preceding embodiments, the chemical etching solution comprises from about 0.725M to about 2.9M hydrofluoric acid and from about 0.395M to about 2.37M nitric acid.

In some embodiments, for the method of any of the preceding embodiments, the chemical etching solution comprises from about 0.725M to about 1.45M hydrofluoric acid and from about 0.395M to about 0.79M nitric acid.

In some embodiments, for the method of any of the preceding embodiments, etching the transparent workpiece with the chemical etching solution comprises immersing the transparent workpiece in a chemical etching bath comprising the chemical etching solution.

In some embodiments, for the method of any of the preceding embodiments, the resulting contour has a ratio of top diameter to waist diameter of about 1:0.9 to about 1:0.99.

In some embodiments, for the method of any of the preceding embodiments, etching the transparent workpiece with the chemical etching solution comprises spraying the transparent workpiece from either side while on a horizontal roller system.

In some embodiments, for the method of any of the preceding embodiments, the resulting contour has a ratio of top diameter to waist diameter of about less than 1:0.9.

In some embodiments, for the method of any of the preceding embodiments, the resulting contour has a ratio of top diameter to waist diameter of about 1:0.95 to about 1:1.

In some embodiments, for the method of any of the preceding embodiments, the transparent workpiece is immersed in the chemical etching bath for an etching time of 1,000 mins or greater.

In some embodiments, for the method of any of the preceding embodiments, the transparent workpiece is immersed in the chemical etching bath for an etching time of from about 60 mins to about 200 mins.

In some embodiments, for the method of any of the preceding embodiments, the transparent workpiece is immersed in the chemical etching bath for an etching time of from about 15 mins to about 30 mins.

In some embodiments, for the method of any of the preceding embodiments, the temperature of the chemical etching solution when the transparent workpiece is immersed in the chemical etching bath is from about 0° C. to about 40° C.

In some embodiments, for the method of any of the preceding embodiments, the temperature of the chemical etching solution when the transparent workpiece is immersed in the chemical etching bath is about 20° C. or less.

In some embodiments, for the method of any of the preceding embodiments, the temperature of the chemical etching solution when the transparent workpiece is immersed in the chemical etching bath is about 10° C. or less.

In some embodiments, for the method of any of the preceding embodiments, the chemical etching bath comprises about 8 L to about 10 L of the chemical etching solution.

In some embodiments, for the method of any of the preceding embodiments, etching the transparent workpiece with the chemical etching solution further comprises agitating the chemical etching solution when the transparent workpiece is immersed in the chemical etching bath by means of fluid recirculation.

In some embodiments, for the method of any of the preceding embodiments, etching the transparent workpiece with the chemical etching solution further comprises agitating the chemical etching solution when the transparent workpiece is immersed in the chemical etching bath by means of ultrasonic energy of frequencies 40 kHz, 58 kHz, 80 kHz, 120 kHz, 132 kHz, 192 kHz or a combination thereof.

In some embodiments, the method of any of the preceding embodiments further comprises rotating the transparent workpiece while chemically etching the transparent workpiece.

In some embodiments, the method of any of the preceding embodiments further comprises coupling the transparent workpiece to a workpiece fixture and immersing the transparent workpiece and the workpiece fixture in a chemical etching bath.

In some embodiments, for the method of any of the preceding embodiments, the workpiece fixture comprises a first fixture wall, a second fixture wall, and a plurality of fixture cross-bars coupled to and extending between the first fixture wall and the second fixture wall, wherein one or more grooves extend into at least one of the plurality of fixture cross-bars.

In some embodiments, for the method of any of the preceding embodiments, the dimensionless divergence factor FDcomprises a value of from about 10 to about 2000.

In some embodiments, for the method of any of the preceding embodiments, the dimensionless divergence factor FDcomprises a value of from about 50 to about 1500.

In some embodiments, for the method of any of the preceding embodiments, the dimensionless divergence factor FDcomprises a value of from about 100 to about 1000.

In some embodiments, for the method of any of the preceding embodiments, the aspheric optical element comprises a refractive axicon, a reflective axicon, negative axicon, a spatial light modulator, a diffractive optic, or a cubically shaped optical element.

In some embodiments, for the method of any of the preceding embodiments, the pulsed laser beam has a wavelength λ and wherein the transparent workpiece has combined losses due to linear absorption and scattering less than 20%/mm in the beam propagation direction.

In some embodiments, for the method of any of the preceding embodiments, the beam source comprises a pulsed beam source that produces pulse bursts with from about 1 sub-pulses per pulse burst to about 30 sub-pulses per pulse burst and a pulse burst energy is from about 50 μJ to about 600 μJ per pulse burst.

In some embodiments, a method for processing a transparent workpiece includes forming a plurality of closed contour lines in the transparent workpiece, each closed contour line including a plurality of defects in the transparent workpiece such that each closed contour line defines a closed contour. Forming each closed contour line includes directing a pulsed laser beam oriented along a beam pathway and output by a beam source through an aspheric optical element and into the transparent workpiece such that a portion of the pulsed laser beam directed into the transparent workpiece generates an induced absorption within the transparent workpiece, the induced absorption producing a defect within the transparent workpiece, and the portion of the pulsed laser beam directed into the transparent workpiece includes a wavelength λ, a spot size w0, and a cross section that comprises a Rayleigh range ZRthat is greater than

where FDis a dimensionless divergence factor comprising a value of 10 or greater. Forming each closed contour line also includes translating the transparent workpiece and the pulsed laser beam relative to each other along the closed contour line, thereby laser forming the plurality of defects along the closed contour line within the transparent workpiece. Further, the method for processing the transparent workpiece also includes etching the transparent workpiece with a chemical etching solution at an etching rate of about 10 μm/min or less to separate portions of the transparent workpiece along each closed contour line, thereby forming a plurality of apertures extending through the transparent workpiece, each aperture comprising an aperture perimeter extending along the closed contour. The plurality of apertures are positioned such that when the transparent workpiece is coupled to an electronic device having one or more speakers, the plurality of apertures are aligned with the one or more speakers, thereby providing acoustic pathways through the transparent workpiece.

In some embodiments, for the method of any of the preceding embodiments, the etching rate is about 5 μm/min or less.

In some embodiments, for the method of any of the preceding embodiments, the etching rate is about 2.5 μm/min or less.

In some embodiments, for the method of any of the preceding embodiments, etching the transparent workpiece removes about 50% or less of a thickness of the transparent workpiece.

In some embodiments, for the method of any of the preceding embodiments, etching the transparent workpiece removes about 25% or less of a thickness of the transparent workpiece.

In some embodiments, for the method of any of the preceding embodiments, etching the transparent workpiece removes about 15% or less of a thickness of the transparent workpiece.

In some embodiments, for the method of any of the preceding embodiments, etching the transparent workpiece removes about 7.5% or less of a thickness of the transparent workpiece.

In some embodiments, for the method of any of the preceding embodiments, a spacing between adjacent defects is about 50 μm or less.

In some embodiments, for the method of any of the preceding embodiments, a spacing between adjacent defects is about 15 μm or less.

In some embodiments, for the method of any of the preceding embodiments, a spacing between adjacent defects is about 10 μm or less.

In some embodiments, for the method of any of the preceding embodiments, a spacing between adjacent defects is about 5 μm or less.

In some embodiments, for the method of any of the preceding embodiments, the transparent workpiece comprises an alkali aluminosilicate glass material.

In some embodiments, for the method of any of the preceding embodiments, the aperture perimeter of each aperture comprises a diameter of from about 100 μm to about 10 mm.

In some embodiments, for the method of any of the preceding embodiments, the aperture perimeter of each aperture comprises a diameter of about 800 μm or less.

In some embodiments, for the method of any of the preceding embodiments, the chemical etching solution comprises a chemical etchant and deionized water and the chemical etchant of the chemical etching solution comprises hydrofluoric acid, nitric acid, hydrochloric acid, sulfuric acid, or combinations thereof.

In some embodiments, for the method of any of the preceding embodiments, the chemical etching solution comprises a chemical etchant and deionized water and the chemical etchant of the chemical etching solution comprises sodium hydroxide or potassium hydroxide.

In some embodiments, for the method of any of the preceding embodiments, the chemical etching solution comprises from about 5M to 20M sodium hydroxide or 5M to 20M potassium hydroxide.

In some embodiments, for the method of any of the preceding embodiments, the chemical etching solution is maintained at a temperature between 70° C. to about 100° C.

In some embodiments, the method of any of the preceding embodiments further comprises rotating the transparent workpiece while chemically etching the transparent workpiece.

In some embodiments, for the method of any of the preceding embodiments, etching the transparent workpiece with the chemical etching solution comprises immersing the transparent workpiece in a chemical etching bath comprising the chemical etching solution.

In some embodiments, for the method of any of the preceding embodiments, the resulting contour has a ratio of top diameter to waist diameter of about 1:0.9 to about 1:0.99.

In some embodiments, for the method of any of the preceding embodiments, etching the transparent workpiece with the chemical etching solution comprises spraying the transparent workpiece from either side while on a horizontal roller system.

In some embodiments, for the method of any of the preceding embodiments, the resulting contour has a ratio of top diameter to waist diameter of about less than 1:0.9.

In some embodiments, for the method of any of the preceding embodiments, the resulting contour has a ratio of top diameter to waist diameter of about 1:0.95 to about 1:1.

In some embodiments, for the method of any of the preceding embodiments, etching the transparent workpiece with the chemical etching solution further comprises agitating the chemical etching solution when the transparent workpiece is immersed in the chemical etching bath.

In some embodiments, for the method of any of the preceding embodiments, the dimensionless divergence factor FDcomprises a value of from about 10 to about 2000.

In some embodiments, for the method of any of the preceding embodiments, the aspheric optical element comprises a refractive axicon, a reflective axicon, negative axicon, a spatial light modulator, a diffractive optic, or a cubically shaped optical element.

In some embodiments, for the method of any of the preceding embodiments, the pulsed laser beam has a wavelength λ and wherein the transparent workpiece has combined losses due to linear absorption and scattering less than 20%/mm in the beam propagation direction.

Additional features and advantages of the processes and systems described herein will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments described herein, including the detailed description which follows, the claims, as well as the appended drawings.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments of processes for laser processing transparent workpieces, such as glass workpieces, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. According to one or more embodiments described herein, a transparent workpiece may be laser processed to form a closed contour line in the transparent workpiece comprising a series of defects that define a desired perimeter of one or more apertures through the transparent workpiece. According to one embodiment, a pulsed laser outputs a pulsed laser beam through an aspheric optical element such that the pulsed laser beam projects a pulsed laser beam focal line that is directed into the transparent workpiece. The pulsed laser beam focal line may be utilized to create a series of defects in the transparent workpiece thereby defining the closed contour line. These defects may be referred to, in various embodiments herein, as line defects, perforations, or nano-perforations in the workpiece. In some embodiments, the process may further include separating the transparent workpiece along the closed contour line, for example, by chemically etching, thereby forming an aperture through the transparent workpiece. Various embodiments of methods and apparatuses for processing a transparent workpiece will be described herein with specific reference to the appended drawings.

While the embodiments of processing a transparent workpiece to form one or more apertures extending through the transparent workpiece may be used in a variety of contexts, the present embodiments are particularly useful for forming apertures in transparent workpieces to create pathways for acoustic transmission through transparent workpieces. For example, a transparent workpiece may be used as a glass cover plate for a phone, tablet and other electronic devices such as computing devices, laptop electronics, televisions, or other consumer electronics, and apertures in the transparent workpiece may be positioned proximate to the speakers of these electronic device to provide an acoustic transmission pathway through the transparent workpieces and thus allow the speakers to output sound in the direction of the user (e.g., through the transparent workpiece) instead of through the sides of the electronic device, away from the user. Providing a single material cover plate having apertures for acoustic transmission provides aesthetic, cost, and design flexibility advantages over previous cover plates. Further, the transparent workpiece may be used as a backplate for a computer keyboard and the apertures may serve as key holes that allow each key of the keyboard to extend through an individual aperture.

Previous methods of forming apertures in transparent workpieces limited the achievable size and shape of these apertures. Apertures desirable for use as acoustic pathways may comprise cross-sectional dimensions (e.g., diameters) of from about 100 μm to about 10 mm, for example, less than 5 mm, less than 3 mm, less than 1 mm, or the like, which are difficult to create using previous methods. Apertures having these cross-sectional dimensions may impede external contamination of the electronics positioned underneath the transparent workpiece, i.e. under the cover plate, while allowing acoustic energy (i.e. sound) to traverse the transparent workpiece. The processing methods described herein increase the design flexibility of apertures formed in transparent workpieces and allow apertures to be formed having small cross sectional dimensions.

The phrase “transparent workpiece,” as used herein, means a workpiece formed from glass or glass-ceramic which is transparent, where the term “transparent,” as used herein, means that the material has an optical absorption of less than about 20% per mm of material depth, such as less than about 10% per mm of material depth for the specified pulsed laser wavelength, or such as less than about 1% per mm of material depth for the specified pulsed laser wavelength. According to one or more embodiments, the transparent workpiece may have a thickness of from about 50 microns (μm) to about 10 mm, such as from about 100 μm to about 5 mm, from about 0.5 mm to about 3 mm, or from about 100 μm to about 2 mm, for example, 100 μm, 250 μm, 300 μm, 500 μm, 700 μm, 1 mm, 1.2 mm, 1.5 mm, 2 mm, 5 mm, 7 mm, or the like.

According to one or more embodiments, the present disclosure provides methods for processing workpieces. As used herein, “laser processing” may include forming contour lines (e.g., closed contour lines) in transparent workpieces, separating transparent workpieces, or combinations thereof. Transparent workpieces may comprise glass workpieces formed from glass compositions, such as borosilicate glass, soda-lime glass, aluminosilicate glass, alkali aluminosilicate glass, alkaline earth aluminosilicate glass, alkaline earth boro-aluminosilicate glass, fused silica, or crystalline materials such as sapphire, silicon, gallium arsenide, or combinations thereof. In some embodiments, the glass may be ion-exchangeable, such that the glass composition can undergo ion-exchange for mechanical strengthening before or after laser processing the transparent workpiece and before or after chemical etching of the transparent workpiece. For example, the transparent workpiece may comprise ion exchanged or ion exchangeable glass, such as Corning Gorilla® Glass available from Corning Incorporated of Corning, N.Y. (e.g., code 2318, code 2319, and code 2320). Further, these ion exchanged glasses may have coefficients of thermal expansion (CTE) of from about 6 ppm/° C. to about 10 ppm/° C. In some embodiments, the glass composition of the transparent workpiece may include greater than about 1.0 mol. % boron and/or compounds containing boron, including, without limitation, B2O3. In another embodiment, the glass compositions from which the transparent workpieces are formed include less than or equal to about 1.0 mol. % of oxides of boron and/or compounds containing boron. In some embodiments, the glass compositions from which the transparent workpieces are formed include greater than or equal to about 92.5 wt % of silica. Moreover, the transparent workpiece may comprise other components which are transparent to the wavelength of the laser, for example, crystals such as sapphire or zinc selenide.

Some transparent workpieces may be utilized as display and/or TFT (thin film transistor) substrates. Some examples of such glasses or glass compositions suitable for display or TFT use are EAGLE XG®, CONTEGO, and CORNING LOTUS™ available from Corning Incorporated of Corning, N.Y. The alkaline earth boro-aluminosilicate glass compositions may be formulated to be suitable for use as substrates for electronic applications including, without limitation, substrates for TFTs. The glass compositions used in conjunction with TFTs typically have CTEs similar to that of silicon (such as less than 5×10−6/K, or even less than 4×10−6/K, for example, approximately 3×10−6/K, or about 2.5×10−6/K to about 3.5×10−6/K), and have low levels of alkali within the glass. Low levels of alkali (e.g., trace amounts of about 0 wt. % to 2 wt. %, such as less than 1 wt. %, for example, less than 0.5 wt. %) may be used in TFT applications because alkali dopants, under some conditions, leach out of glass and contaminate or “poison” the TFTs, possibly rendering the TFTs inoperable. According to embodiments, the laser cutting processes and chemical etching processes described herein may be used to form apertures within transparent workpieces in a controlled fashion with negligible debris, minimum defects, and low subsurface damage to the edges, preserving workpiece integrity and strength.

The phrase “closed contour line,” as used herein, denotes a line (e.g., a line, a curve, etc.) formed along a closed contour that extends along the surface of a transparent workpiece. The closed contour defines a desired aperture perimeter along which material of the transparent workpiece may be removed to form one or more apertures extending through the transparent workpiece upon exposure to the appropriate processing conditions. The closed contour line generally consists of one or more defects introduced into the transparent workpiece using various techniques. As used herein, a “defect” may include an area of modified material (relative to the bulk material), void space, scratch, flaw, hole, or other deformities in the transparent workpiece which enables separation of material of the transparent workpiece along the closed contour line by application of a chemical etching solution to the transparent workpiece. While not intending to be limited by theory, the chemical etching solution may remove material of the transparent workpiece at and immediately surrounding each defect, thereby enlarging each defect such that voids formed from adjacent defects overlap, ultimately leading to separation of the transparent workpiece along the closed contour line and formation of the aperture extending through the transparent workpiece.

Referring now toFIGS. 1A and 1Bby way of example, a transparent workpiece160, such as a glass workpiece or a glass-ceramic workpiece, is schematically depicted undergoing processing according to the methods described herein.FIGS. 1A and 1Bdepict the formation of a closed contour line170in the transparent workpiece160, which may be formed by translating a pulsed laser beam112and the transparent workpiece160relative to one another such that the pulsed laser beam112translates relative to the transparent workpiece160in a translation direction101.FIGS. 1A and 1Bdepict the pulsed laser beam112along a beam pathway111and oriented such that the pulsed laser beam112may be focused into a pulsed laser beam focal line113within the transparent workpiece160using an aspheric optical element120(FIG. 3), for example, an axicon and one or more lenses (e.g., a first lens130and a second lens132, as described below and depicted inFIG. 3). Further, the pulsed laser beam focal line113is a portion of a quasi non-diffracting beam, as defined in more detail below.

FIGS. 1A and 1Bdepict that the pulsed laser beam112forms a beam spot114projected onto an imaging surface162of the transparent workpiece160. As used herein the “imaging surface”162of the transparent workpiece160is the surface of the transparent workpiece160at which the pulsed laser beam112initially contacts the transparent workpiece160. As also used herein “beam spot” refers to a cross section of a laser beam (e.g., the pulsed laser beam112) at a point of first contact with a workpiece (e.g., the transparent workpiece160). In some embodiments, the pulsed laser beam focal line113may comprise an axisymmetric cross section in a direction normal the beam pathway111(e.g., an axisymmetric beam spot) and in other embodiments, the pulsed laser beam focal line113may comprise a non-axisymmetric cross section in a direction normal the beam pathway111(e.g., a non-axisymmetric beam spot). As used herein, axisymmetric refers to a shape that is symmetric, or appears the same, for any arbitrary rotation angle made about a central axis, and “non-axisymmetric” refers to a shape that is not symmetric for any arbitrary rotation angle made about a central axis. A circular beam spot is an example of an axisymmetric beam spot and an elliptical beam spot is an example of a non-axisymmetric beam spot. The rotation axis (e.g., the central axis) is most often taken as being the propagation axis of the laser beam (e.g., the beam pathway111). Example pulsed laser beams comprising a non-axisymmetric beam cross section are described in more detail in U.S. Provisional Pat. App. No. 62/402,337, titled “Apparatus and Methods for Laser Processing Transparent Workpieces Using Non-Axisymmetric Beam Spots,” herein incorporated by reference in its entirety.

Referring also toFIG. 2, the closed contour line170extends along a closed contour165which delineates a line of intended separation along which one or more apertures180(FIGS. 5C and 7) may be formed in the transparent workpiece160. The closed contour line170comprises a plurality of defects172that extend into the surface of the transparent workpiece160and establish a path for separation of material of the transparent workpiece160enclosed by the closed contour line170from the remaining transparent workpiece160thereby forming an aperture180(FIGS. 5C and 7) extending through the transparent workpiece160, for example, by applying a chemical etching solution202(FIG. 5B) to the transparent workpiece160, at least along the closed contour line170.

While the closed contour line170is depicted inFIG. 1AandFIG. 2as a circle, it should be understood that other closed configurations are contemplated and possible including, without limitation, circles, ellipses, squares, hexagons, ovals, regular geometric shapes, irregular shapes, polygonal shapes, arbitrary shapes, and the like. Further, as depicted inFIG. 2, the embodiments described herein may be used to form multiple closed contour lines170in a single transparent workpiece160and thereby form multiple apertures180, for example, arrays of apertures180(FIGS. 5C and 7). Further, these arrays of apertures180may collectively form shapes, for example, text, symbols (e.g., product indicating symbols), or the like. Moreover, these arrays of apertures180may be positioned at locations of the transparent workpiece160that correspond to the location of one or more speakers12of an electronic device10in embodiments in which the transparent workpiece160is used as cover glass for an electronic device10(FIG. 7).

Referring toFIGS. 1A, 1B, and 2, in the embodiments described herein, a pulsed laser beam112(with a beam spot114projected onto the transparent workpiece160) may be directed onto the transparent workpiece160(e.g., condensed into a high aspect ratio line focus that penetrates through at least a portion of the thickness of the transparent workpiece160). This forms the pulsed laser beam focal line113. Further, the beam spot114is an example cross section of the pulsed laser beam focal line113and when the pulsed laser beam focal line113irradiates the transparent workpiece160(forming the beam spot114), the pulsed laser beam focal line113penetrates at least a portion of the transparent workpiece160.

Further, the pulsed laser beam112may be translated relative to the transparent workpiece160(e.g., in the translation direction101) to form the plurality of defects172of the closed contour line170. Directing or localizing the pulsed laser beam112into the transparent workpiece160generates an induced absorption within the transparent workpiece160and deposits enough energy to break chemical bonds in the transparent workpiece160at spaced locations along the closed contour165to form the defects172. According to one or more embodiments, the pulsed laser beam112may be translated across the transparent workpiece160by motion of the transparent workpiece160(e.g., motion of a translation stage190coupled to the transparent workpiece160), motion of the pulsed laser beam112(e.g., motion of the pulsed laser beam focal line113), or motion of both the transparent workpiece160and the pulsed laser beam focal line113. By translating the pulsed laser beam focal line113relative to the transparent workpiece160, the plurality of defects172may be formed in the transparent workpiece160.

Referring again toFIGS. 1A-2, the pulsed laser beam112used to form the defects172further has an intensity distribution I(X,Y,Z), where Z is the beam propagation direction of the pulsed laser beam112, and X and Y are directions orthogonal to the direction of propagation, as depicted in the figures. The X-direction and Y-direction may also be referred to as cross-sectional directions and the X-Y plane may be referred to as a cross-sectional plane. The intensity distribution of the pulsed laser beam112in a cross-sectional plane may be referred to as a cross-sectional intensity distribution.

The pulsed laser beam112at the beam spot114or other cross sections may comprise a quasi-non-diffracting beam, for example, a beam having low beam divergence as mathematically defined below, by propagating the pulsed laser beam112(e.g., outputting the pulsed laser beam112, such as a Gaussian beam, using a beam source110) through an aspheric optical element120, as described in more detail below with respect to the optical assembly100depicted inFIG. 3. Beam divergence refers to the rate of enlargement of the beam cross section in the direction of beam propagation (i.e., the Z direction). As used herein, the phrase “beam cross section” refers to the cross section of the pulsed laser beam112along a plane perpendicular to the beam propagation direction of the pulsed laser beam112, for example, along the X-Y plane. One example beam cross section discussed herein is the beam spot114of the pulsed laser beam112projected onto the transparent workpiece160. Example quasi non-diffracting beams include Gauss-Bessel beams and Bessel beams.

Diffraction is one factor that leads to divergence of pulsed laser beams112. Other factors include focusing or defocusing caused by the optical systems forming the pulsed laser beams112or refraction and scattering at interfaces. Pulsed laser beams112for forming the defects172of the closed contour line170may have beam spots114with low divergence and weak diffraction. The divergence of the pulsed laser beam112is characterized by the Rayleigh range ZR, which is related to the variance σ2of the intensity distribution and beam propagation factor M2of the pulsed laser beam112. In the discussion that follows, formulas will be presented using a Cartesian coordinate system. Corresponding expressions for other coordinate systems are obtainable using mathematical techniques known to those of skill in the art. Additional information on beam divergence can be found in the articles entitled “New Developments in Laser Resonators” by A. E. Siegman in SPIE Symposium Series Vol. 1224, p. 2 (1990) and “M2factor of Bessel-Gauss beams” by R. Borghi and M. Santarsiero in Optics Letters, Vol. 22(5), 262 (1997), the disclosures of which are incorporated herein by reference in their entirety. Additional information can also be found in the international standards ISO 11146-1:2005(E) entitled “Lasers and laser-related equipment—Test methods for laser beam widths, divergence angles and beam propagation ratios—Part 1: Stigmatic and simple astigmatic beams”, ISO 11146-2:2005(E) entitled “Lasers and laser-related equipment—Test methods for laser beam widths, divergence angles and beam propagation ratios—Part 2: General astigmatic beams”, and ISO 11146-3:2004(E) entitled “Lasers and laser-related equipment—Test methods for laser beam widths, divergence angles and beam propagation ratios—Part 3: Intrinsic and geometrical laser beam classification, propagation and details of test methods”, the disclosures of which are incorporated herein by reference in their entirety.

The spatial coordinates of the centroid of the intensity profile of the pulsed laser beam112having a time-averaged intensity profile I(x,y,z) are given by the following expressions:

These are also known as the first moments of the Wigner distribution and are described in Section 3.5 of ISO 11146-2:2005(E). Their measurement is described in Section 7 of ISO 11146-2:2005(E).

Variance is a measure of the width, in the cross-sectional (X-Y) plane, of the intensity distribution of the pulsed laser beam112as a function of position z in the direction of beam propagation. For an arbitrary laser beam, variance in the X-direction may differ from variance in the Y-direction. We let σx2(z) and σy2(z) represent the variances in the X-direction and Y-direction, respectively. Of particular interest are the variances in the near field and far field limits. We let σ0x2(z) and σ0y2(z) represent variances in the X-direction and Y-direction, respectively, in the near field limit, and we let σ∞x2(z) and σ∞y2(z) represent variances in the X-direction and Y-direction, respectively, in the far field limit. For a laser beam having a time-averaged intensity profile I(x,y,z) with Fourier transform Ĩ(vx,vy) (where vxand vyare spatial frequencies in the X-direction and Y-direction, respectively), the near field and far field variances in the X-direction and Y-direction are given by the following expressions:

The variance quantities σ0x2(z), σ0y2(z), σ∞x2, and σ∞y2are also known as the diagonal elements of the Wigner distribution (see ISO 11146-2:2005(E)). These variances can be quantified for an experimental laser beam using the measurement techniques described in Section 7 of ISO 11146-2:2005(E). In brief, the measurement uses a linear unsaturated pixelated detector to measure I(x,y) over a finite spatial region that approximates the infinite integration area of the integral equations which define the variances and the centroid coordinates. The appropriate extent of the measurement area, background subtraction and the detector pixel resolution are determined by the convergence of an iterative measurement procedure described in Section 7 of ISO 11146-2:2005(E). The numerical values of the expressions given by equations 1-6 are calculated numerically from the array of intensity values as measured by the pixelated detector.

Through the Fourier transform relationship between the transverse amplitude profile ũ(x,y,z) for an arbitrary optical beam (where I(x,y,z)≡|ũ(x,y,z)|2) and the spatial-frequency distribution {tilde over (P)}(vx,vy, z) for an arbitrary optical beam (where I(vx,vy)≡|{tilde over (P)}(vx,vy, z)|2), it can be shown that:

In equations (7) and (8), σ0x2(z0x) and σ0y2(z0y) are minimum values of σ0x2(z) and σ0y2(z), which occur at waist positions z0xand z0yin the x-direction and y-direction, respectively, and λ is the wavelength of the pulsed laser beam112. Equations (7) and (8) indicate that σx2(z) and σy2(z) increase quadratically with z in either direction from the minimum values associated with the waist position of the pulsed laser beam112(e.g., the waist portion of the pulsed laser beam focal line113). Further, in the embodiments described herein comprising a beam spot114that is axisymmetric and thereby comprises an axisymmetric intensity distribution I(x,y), σx2(z)=σy2(z) and in the embodiments described herein comprising a beam spot114that is non-axisymmetric and thereby comprises a non-axisymmetric intensity distribution I(x,y), σx2(z)≠σy2(z), i.e., σx2(z)<σy2(z) or σx2(z)>σy2(z).

Equations (7) and (8) can be rewritten in terms of a beam propagation factor M2, where separate beam propagations factors Mx2and My2for the x-direction and the y-direction are defined as:

Rearrangement of Equations (9) and (10) and substitution into Equations (7) and (8) yields:

which can be rewritten as:

where the Rayleigh ranges ZRxand ZRyin the x-direction and y-direction, respectively, are given by:

The Rayleigh range corresponds to the distance (relative to the position of the beam waist as defined in Section 3.12 of ISO 11146-1:2005(E)) over which the variance of the laser beam doubles (relative to the variance at the position of the beam waist) and is a measure of the divergence of the cross sectional area of the laser beam. Further, in the embodiments described herein comprising a beam spot114that is axisymmetric and thereby comprises an axisymmetric intensity distribution I(x,y), ZRx=ZRyand in the embodiments described herein comprising a beam spot114that is non-axisymmetric and thereby comprises a non-axisymmetric intensity distribution I(x,y), ZRx≠ZRy, i.e., ZRx<ZRyor ZRx>ZRy. The Rayleigh range can also be observed as the distance along the beam axis at which the optical intensity decays to one half of its value observed at the beam waist location (location of maximum intensity). Laser beams with large Rayleigh ranges have low divergence and expand more slowly with distance in the beam propagation direction than laser beams with small Rayleigh ranges.

The formulas above can be applied to any laser beam (not just Gaussian beams) by using the intensity profile I(x,y,z) that describes the laser beam. In the case of the TEM00mode of a Gaussian beam, the intensity profile is given by:

where wois the radius (defined as the radius at which beam intensity decreases to 1/e2of the peak beam intensity of the beam at a beam waist position zo. From Equation (17) and the above formulas, we obtain the following results for a TEM00Gaussian beam:

where ZR=ZRx=ZRy. For Gaussian beams, it is further noted that M2=Mx2=My2=1.

Beam cross section is characterized by shape and dimensions. The dimensions of the beam cross section are characterized by a spot size of the beam. For a Gaussian beam, spot size is frequently defined as the radial extent at which the intensity of the beam decreases to 1/e2of its maximum value, denoted in Equation (17) as W0. The maximum intensity of a Gaussian beam occurs at the center (x=0 and y=0 (Cartesian) or r=0 (cylindrical)) of the intensity distribution and radial extent used to determine spot size is measured relative to the center.

Beams with axisymmetric (i.e. rotationally symmetric around the beam propagation axis Z) cross sections can be characterized by a single dimension or spot size that is measured at the beam waist location as specified in Section 3.12 of ISO 11146-1:2005(E). For a Gaussian beam, Equation (17) shows that spot size is equal to wo, which from Equation (18) corresponds to 2σ0xor 2σ0y. For an axisymmetric beam having an axisymmetric cross section, such as a circular cross section, σ0x=σ0y. Thus, for axisymmetric beams, the cross section dimension may be characterized with a single spot size parameter, where wo=2σ0. Spot size can be similarly defined for non-axisymmetric beam cross sections where, unlike an axisymmetric beam, σ0x≠σ0y. Thus, when the spot size of the beam is non-axisymmetric, it is necessary to characterize the cross-sectional dimensions of a non-axisymmetric beam with two spot size parameters: woxand woyin the x-direction and y-direction, respectively, where

Further, the lack of axial (i.e. arbitrary rotation angle) symmetry for a non-axisymmetric beam means that the results of a calculation of values of σ0xand σ0ywill depend on the choice of orientation of the X-axis and Y-axis. ISO 11146-1:2005(E) refers to these reference axes as the principal axes of the power density distribution (Section 3.3-3.5) and in the following discussion we will assume that the X and Y axes are aligned with these principal axes. Further, an angle ϕ about which the X-axis and Y-axis may be rotated in the cross-sectional plane (e.g., an angle of the X-axis and Y-axis relative to reference positions for the X-axis and Y-axis, respectively) may be used to define minimum (wo,min) and maximum values (wo,max) of the spot size parameters for a non-axisymmetric beam:

where 2σ0,min=2σ0x(ϕmin,x)=2σ0y(ϕmin,y) and 2σ0,max=2σ0x(ϕmax,x)=2σ0y(ϕmax,y) The magnitude of the axial asymmetry of the beam cross section can be quantified by the aspect ratio, where the aspect ratio is defined as the ratio of wo,maxto wo,min. An axisymmetric beam cross section has an aspect ratio of 1.0, while elliptical and other non-axisymmetric beam cross sections have aspect ratios greater than 1.0, for example, greater than 1.1, greater than 1.2, greater than 1.3, greater than 1.4, greater than 1.5, greater than 1.6, greater than 1.7, greater than 1.8, greater than 1.9, greater than 2.0, greater than 3.0, greater than 5.0, greater than 10.0, or the like

To promote uniformity of defects172in the beam propagation direction (e.g. depth dimension of the transparent workpiece160), a pulsed laser beam112having low divergence may be used. In one or more embodiments, pulsed laser beams112having low divergence may be utilized for forming defects172. As noted above, divergence can be characterized by the Rayleigh range. For non-axisymmetric beams, Rayleigh ranges for the principal axes X and Y are defined by Equations (15) and (16) for the X-direction and Y-direction, respectively, where it can be shown that for any real beam, Mx2>1 and My2>1 and where σ0x2, and σ0y2are determined by the intensity distribution of the laser beam. For symmetric beams, Rayleigh range is the same in the X-direction and Y-direction and is expressed by Equation (22) or Equation (23). Low divergence correlates with large values of the Rayleigh range and weak diffraction of the laser beam.

While not intending to be limited by theory, defects172with a uniform cross section along the depth dimension of the transparent workpiece160may more uniformly interact with a chemical etching solution along the depth dimension of the transparent workpiece160than defects172with a non-uniform cross section. In other words, the chemical etchant may more uniformly remove material of the transparent workpiece160surrounding the defect172, widening each defect172of the closed contour line170at a more uniform pace, thereby minimizing the etching time required to separate material of the transparent workpiece160positioned within the closed contour line170from the rest of the transparent workpiece160to form the aperture180through the depth dimension of the transparent workpiece160and also minimizing the amount of material removed from the transparent workpiece160(i.e., minimize thickness reduction).

Beams with Gaussian intensity profiles may be less preferred for laser processing to form defects172because, when focused to small enough spot sizes (such as spot sizes in the range of microns, such as about 1-5 μm or about 1-10 μm) to enable available laser pulse energies to modify materials such as glass, they are highly diffracting and diverge significantly over short propagation distances. To achieve low divergence, it is desirable to control or optimize the intensity distribution of the pulsed laser beam to reduce diffraction. Pulsed laser beams may be non-diffracting or weakly diffracting. Weakly diffracting laser beams include quasi-non-diffracting laser beams. Representative weakly diffracting laser beams include Bessel beams, Gauss-Bessel beams, Airy beams, Weber beams, and Mathieu beams.

For non-axisymmetric beams, the Rayleigh ranges ZRxand ZRyare unequal. Equations (15) and (16) indicate that ZRxand ZRydepend on σ0xand σ0y, respectively, and above we noted that the values of σ0xand σ0ydepend on the orientation of the X-axis and Y-axis. The values of ZRxand ZRywill accordingly vary, and each will have a minimum value and a maximum value that correspond to the principal axes, with the minimum value of ZRxbeing denoted as ZRx,minand the minimum value of ZRybeing denoted ZRy,minfor an arbitrary beam profile ZRx,minand ZRy,mincan be shown to be given by

Since divergence of the laser beam occurs over a shorter distance in the direction having the smallest Rayleigh range, the intensity distribution of the pulsed laser beam112used to form defects172may be controlled so that the minimum values of ZRxand ZRy(or for axisymmetric beams, the value of ZR) are as large as possible. Since the minimum value ZRx,minof ZRxand the minimum value ZRy,minof ZRydiffer for a non-axisymmetric beam, a pulsed laser beam112may be used with an intensity distribution that makes the smaller of ZRx,minand ZRy,minas large as possible when forming damage regions.

In different embodiments, the smaller of ZRx,minand ZRy,min(or for axisymmetric beams, the value of ZR) is greater than or equal to 50 μm, greater than or equal to 100 μm, greater than or equal to 200 μm, greater than or equal to 300 μm, greater than or equal to 500 μm, greater than or equal to 1 mm, greater than or equal to 2 mm, greater than or equal to 3 mm, greater than or equal to 5 mm, in the range from 50 μm to 10 mm, in the range from 100 μm to 5 mm, in the range from 200 μm to 4 mm, in the range from 300 μm to 2 mm, or the like.

The values and ranges for the smaller of ZRx,minand ZRy,min(or for axisymmetric beams, the value of ZR) specified herein are achievable for different wavelengths to which the workpiece is transparent through adjustment of the spot size parameter wo,mindefined in Equation (27). In different embodiments, the spot size parameter wo,minis greater than or equal to 0.25 μm, greater than or equal to 0.50 μm, greater than or equal to 0.75 μm, greater than or equal to 1.0 μm, greater than or equal to 2.0 μm, greater than or equal to 3.0 μm, greater than or equal to 5.0 μm, in the range from 0.25 μm to 10 μm, in the range from 0.25 μm to 5.0 μm, in the range from 0.25 μm to 2.5 μm, in the range from 0.50 μm to 10 μm, in the range from 0.50 μm to 5.0 μm, in the range from 0.50 μm to 2.5 μm, in the range from 0.75 μm to 10 μm, in the range from 0.75 μm to 5.0 μm, in the range from 0.75 μm to 2.5 μm, or the like.

Non-diffracting or quasi non-diffracting beams generally have complicated intensity profiles, such as those that decrease non-monotonically vs. radius. By analogy to a Gaussian beam, an effective spot size wo,effcan be defined for non-axisymmetric beams as the shortest radial distance, in any direction, from the radial position of the maximum intensity (r=0) at which the intensity decreases to 1/e2of the maximum intensity. Further, for axisymmetric beams wo,effis the radial distance from the radial position of the maximum intensity (r=0) at which the intensity decreases to 1/e2of the maximum intensity. A criterion for Rayleigh range based on the effective spot size wo,efffor non-axisymmetric beams or the spot size wofor axisymmetric beams can be specified as non-diffracting or quasi non-diffracting beams for forming damage regions using equation (31) for non-axisymmetric beams of equation (32) for axisymmetric beams, below:

where FDis a dimensionless divergence factor having a value of at least 10, at least 50, at least 100, at least 250, at least 500, at least 1000, in the range from 10 to 2000, in the range from 50 to 1500, in the range from 100 to 1000. By comparing Equation (31) to Equation (22) or (23), one can see that for a non-diffracting or quasi non-diffracting beam the distance, Smaller of ZRx,min,ZRy,min, in Equation (31), over which the effective beam size doubles, is FDtimes the distance expected if a typical Gaussian beam profile were used. The dimensionless divergence factor FDprovides a criterion for determining whether or not a laser beam is quasi-non-diffracting. As used herein, the pulsed laser beam112is considered quasi-non-diffracting if the characteristics of the laser beam satisfy Equation (31) or Equation (32) with a value of FD≥10. As the value of FDincreases, the pulsed laser beam112approaches a more nearly perfectly non-diffracting state. Moreover, it should be understood that Equation (32) is merely a simplification of Equation (31) and as such, Equation (31) mathematically describes the dimensionless divergence factor FDfor both axisymmetric and non-axisymmetric pulsed laser beams112.

Referring now toFIG. 3, an optical assembly100for producing a pulsed laser beam112that that is quasi-non-diffracting and forms the pulsed laser beam focal line113at the transparent workpiece160using the aspheric optical element120(e.g., an axicon122) is schematically depicted. The optical assembly100includes a beam source110that outputs the pulsed laser beam112, and a first and second lens130,132.

Further, the transparent workpiece160may be positioned such that the pulsed laser beam112output by the beam source110irradiates the transparent workpiece160, for example, after traversing the aspheric optical element120and thereafter, both the first lens130and the second lens132. An optical axis102extends between the beam source110and the transparent workpiece160along the Z-axis such that when the beam source110outputs the pulsed laser beam112, the beam pathway111of the pulsed laser beam112extends along the optical axis102. As used herein “upstream” and “downstream” refer to the relative position of two locations or components along the beam pathway111with respect to the beam source110. For example, a first component is upstream from a second component if the pulsed laser beam112traverses the first component before traversing the second component. Further, a first component is downstream from a second component if the pulsed laser beam112traverses the second component before traversing the first component.

Referring still toFIG. 3, the beam source110may comprise any known or yet to be developed beam source110configured to output pulsed laser beams112. In operation, the defects172of the closed contour line170(FIGS. 1A and 2) are produced by interaction of the transparent workpiece160with the pulsed laser beam112output by the beam source110. In some embodiments, the beam source110may output a pulsed laser beam112comprising a wavelength of for example, 1064 nm, 1030 nm, 532 nm, 530 nm, 355 nm, 343 nm, or 266 nm, or 215 nm. Further, the pulsed laser beam112used to form defects172in the transparent workpiece160may be well suited for materials that are transparent to the selected pulsed laser wavelength.

Suitable laser wavelengths for forming defects172are wavelengths at which the combined losses of linear absorption and scattering by the transparent workpiece160are sufficiently low. In embodiments, the combined losses due to linear absorption and scattering by the transparent workpiece160at the wavelength are less than 20%/mm, or less than 15%/mm, or less than 10%/mm, or less than 5%/mm, or less than 1%/mm, where the dimension “/mm” means per millimeter of distance within the transparent workpiece160in the beam propagation direction of the pulsed laser beam112(e.g., the Z direction). Representative wavelengths for many glass workpieces include fundamental and harmonic wavelengths of Nd3+(e.g. Nd3+:YAG or Nd3+:YVO4having fundamental wavelength near 1064 nm and higher order harmonic wavelengths near 532 nm, 355 nm, and 266 nm). Other wavelengths in the ultraviolet, visible, and infrared portions of the spectrum that satisfy the combined linear absorption and scattering loss requirement for a given substrate material can also be used.

In operation, the pulsed laser beam112output by the beam source110may create multi-photon absorption (MPA) in the transparent workpiece160. MPA is the simultaneous absorption of two or more photons of identical or different frequencies that excites a molecule from one state (usually the ground state) to a higher energy electronic state (i.e., ionization). The energy difference between the involved lower and upper states of the molecule is equal to the sum of the energies of the involved photons. MPA, also called induced absorption, can be a second-order or third-order process (or higher order), for example, that is several orders of magnitude weaker than linear absorption. It differs from linear absorption in that the strength of second-order induced absorption may be proportional to the square of the light intensity, for example, and thus it is a nonlinear optical process.

The perforation step that creates the closed contour line170(FIGS. 1A and 2) may utilize the beam source110(e.g., an ultra-short pulse laser) in combination with the aspheric optical element120, the first lens130, and the second lens132, to project the beam spot114on the transparent workpiece160and generate the pulsed laser beam focal line113. The pulsed laser beam focal line113comprises a quasi non-diffracting beam, such as a Gauss-Bessel beam or Bessel beam, as defined above, and may fully perforate the transparent workpiece160to form defects172in the transparent workpiece160, which may form the closed contour line170. In some embodiments, the pulse duration of the individual pulses is in a range of from about 1 femtosecond to about 200 picoseconds, such as from about 1 picosecond to about 100 picoseconds, 5 picoseconds to about 20 picoseconds, or the like, and the repetition rate of the individual pulses may be in a range from about 1 kHz to 4 MHz, such as in a range from about 10 kHz to about 3 MHz, or from about 10 kHz to about 650 kHz.

Referring also toFIGS. 4A and 4B, in addition to a single pulse operation at the aforementioned individual pulse repetition rates, the pulses may be produced in pulse bursts500of two sub-pulses500A or more (such as, for example, 3 sub-pulses, 4 sub-pulses, 5 sub-pulses, 10 sub-pulses, 15 sub-pulses, 20 sub-pulses, or more per pulse burst, such as from 2 to 30 sub-pulses per pulse burst500, or from 5 to 20 sub-pulses per pulse burst500) or a single pulse. While not intending to be limited by theory, a pulse burst is a short and fast grouping of sub-pulses that creates an optical energy interaction with the material (i.e. MPA in the material of the transparent workpiece160) on a time scale not easily accessible using a single-pulse operation. While still not intending to be limited by theory, the energy within a pulse burst (i.e. the pulse burst energy) is conserved. As an illustrative example, for a pulse burst having an energy of 100 μJ per pulse burst and 2 sub-pulses, the 100 μJ per pulse burst energy is split between the 2 sub-pulses for an average energy of 50 μJ per sub-pulse. As another illustrative example, for a pulse burst having an energy of 100 μJ per pulse burst and 10 sub-pulses, the 100 μJ per pulse burst is split amongst the 10 sub-pulses for an average energy of 10 μJ per sub-pulse. Further, the energy distribution among the sub-pulses of a pulse burst does not need to be uniform. In fact, in some instances, the energy distribution among the sub-pulses of a pulse burst is in the form of an exponential decay, where the first sub-pulse of the pulse burst contains the most energy, the second sub-pulse of the pulse burst contains slightly less energy, the third sub-pulse of the pulse burst contains even less energy, and so on. However, other energy distributions within an individual pulse burst are also possible, where the exact energy of each sub-pulse can be tailored to effect different amounts of modification to the transparent workpiece160.

While still not intending to be limited by theory, when the defects172of the closed contour line170are formed with pulse bursts having at least two sub-pulses, the force necessary to separate the transparent workpiece160along closed contour line170(i.e. the maximum break resistance) is reduced compared to the maximum break resistance of a closed contour line170of the same shape with the same spacing between adjacent defects172in an identical transparent workpiece160that is formed using a single pulse laser. For example, the maximum break resistance of a closed contour line170formed using a single pulse is at least two times greater than the maximum break resistance of a closed contour line170formed using a pulse burst having 2 or more sub-pulses. Further, the difference in maximum break resistance between a closed contour line170formed using a single pulse and a closed contour line170formed using a pulse burst having 2 sub-pulses is greater than the difference in maximum break resistance between a closed contour line170formed using a pulse burst having 2 sub-pulses and a pulse burst having 3 sub-pulses. Thus, pulse bursts may be used to form closed contour lines170that separate easier than closed contour lines170formed using a single pulse laser.

Referring still toFIGS. 4A and 4B, the sub-pulses500A within the pulse burst500may be separated by a duration that is in a range from about 1 nsec to about 50 nsec, for example, from about 10 nsec to about 30 nsec, such as about 20 nsec. In other embodiments, the sub-pulses500A within the pulse burst500may be separated by a duration of up to 100 psec (for example, 0.1 psec, 5 psec, 10 psec, 15 psec, 18 psec, 20 psec, 22 psec, 25 psec, 30 psec, 50 psec, 75 psec, or any range therebetween). For a given laser, the time separation Tp(FIG. 4B) between adjacent sub-pulses500A within a pulse burst500may be relatively uniform (e.g., within about 10% of one another). For example, in some embodiments, each sub-pulse500A within a pulse burst500is separated in time from the subsequent sub-pulse by approximately 20 nsec (50 MHz). Further, the time between each pulse burst500may be from about 0.25 microseconds to about 1000 microseconds, e.g., from about 1 microsecond to about 10 microseconds, or from about 3 microseconds to about 8 microseconds.

In some of the exemplary embodiments of the beam source110described herein, the time separation Tb(FIG. 4B) is about 5 microseconds for the beam source110outputting a pulsed laser beam112comprising a burst repetition rate of about 200 kHz. The laser burst repetition rate is related to the time Tbbetween the first pulse in a burst to the first pulse in the subsequent burst (laser burst repetition rate=1/Tb). In some embodiments, the laser burst repetition rate may be in a range of from about 1 kHz to about 4 MHz. In embodiments, the laser burst repetition rates may be, for example, in a range of from about 10 kHz to 650 kHz. The time Tbbetween the first pulse in each burst to the first pulse in the subsequent burst may be from about 0.25 microsecond (4 MHz burst repetition rate) to about 1000 microseconds (1 kHz burst repetition rate), for example from about 0.5 microseconds (2 MHz burst repetition rate) to about 40 microseconds (25 kHz burst repetition rate), or from about 2 microseconds (500 kHz burst repetition rate) to about 20 microseconds (50 k Hz burst repetition rate). The exact timing, pulse duration, and burst repetition rate may vary depending on the laser design, but short pulses (Td<20 psec and, in some embodiments, Td≤15 psec) of high intensity have been shown to work particularly well.

The burst repetition rate may be in a range of from about 1 kHz to about 2 MHz, such as from about 1 kHz to about 200 kHz. Bursting or producing pulse bursts500is a type of laser operation where the emission of sub-pulses500A is not in a uniform and steady stream but rather in tight clusters of pulse bursts500. The pulse burst laser beam may have a wavelength selected based on the material of the transparent workpiece160being operated on such that the material of the transparent workpiece160is substantially transparent at the wavelength. The average laser power per burst measured at the material may be at least about 40 μJ per mm of thickness of material. For example, in embodiments, the average laser power per burst may be from about 40 μJ/mm to about 2500 μJ/mm, or from about 500 μJ/mm to about 2250 μJ/mm. In a specific example, for 0.5 mm to 0.7 mm thick Corning EAGLE XG® transparent workpiece, pulse bursts of from about 300 μJ to about 600 μJ may cut and/or separate the workpiece, which corresponds to an exemplary range of about 428 μJ/mm to about 1200 μJ/mm (i.e., 300 μJ/0.7 mm for 0.7 mm EAGLE XG® glass and 600 μJ/0.5 mm for a 0.5 mm EAGLE XG® glass).

The energy required to modify the transparent workpiece160is the pulse energy, which may be described in terms of pules burst energy (i.e., the energy contained within a pulse burst500where each pulse burst500contains a series of sub-pulses500A), or in terms of the energy contained within a single laser pulse. The pulse energy (for example, the pulse burst energy or the energy of a single laser pulse) may be from about 25 μJ to about 750 μJ, e.g., from about 50 μJ to about 500 μJ, or from about 50 μJ to about 250 μJ. For some glass compositions, the pulse energy may be from about 100 μJ to about 250 μJ. However, for display or TFT glass compositions, the pulse energy may be higher (e.g., from about 300 μJ to about 500 μJ, or from about 400 μJ to about 600 μJ, depending on the specific glass composition of the transparent workpiece160).

While not intending to be limited by theory, the use of a pulsed laser beam112capable of generating pulse bursts is advantageous for cutting or modifying transparent materials, for example glass. In contrast with the use of single pulses spaced apart in time by the repetition rate of the single-pulsed laser, the use of a burst sequence that spreads the pulse energy over a rapid sequence of pulses within the burst allows access to larger timescales of high intensity interaction with the material than is possible with single-pulse lasers. Further, using pulse bursts is advantageous for forming closed contour lines170comprising the defects172that are separated from the transparent workpiece160using chemical etching, as described herein. In particular, pulse bursts facilitate formation of adjacent defects172that have connected or nearly connected cracks, allowing a chemical etching solution202(FIGS. 5A-5C) to rapidly penetrate through the depth of the defects172, minimizing the amount of material of the transparent workpiece160removed and the amount of byproducts formed when separating the closed contour line170and forming apertures180, as described in more detail below. The use of pulse bursts (as opposed to a single pulse operation) increases the size (e.g., the cross-sectional size) of the defects172, which facilitates the connection of adjacent defects172when separating the closed contour170to form the apertures180, thereby minimizing crack formation from the aperture180into the interior of the transparent workpiece180.

Further, using a pulse burst to form defects172increases the randomness of the orientation of cracks extending outward from each defect172into the such that individual cracks extending outward from defects172do not influence or otherwise bias the separation of the closed contour line170to form the corresponding aperture180such that separation of the defects172follows the closed contour line170. Moreover, the use of pulse bursts to form defects172of the closed contour line170facilitates separation of closed contour lines170having rounded shapes (without angled corners) via efficient connection of adjacent defects172when separating the closed contour line170. While not intending to be limited by theory, rounded corners cause less cracks to extend outward from the defects172into the transparent workpiece160during separation than angled corners.

Referring again toFIG. 3, the aspheric optical element120is positioned within the beam pathway111between the beam source110and the transparent workpiece160. In operation, propagating the pulsed laser beam112, e.g., an incoming Gaussian beam, through the aspheric optical element120may alter the pulsed laser beam112such that the portion of the pulsed laser beam112propagating beyond the aspheric optical element120is quasi-non-diffracting, as described above. The aspheric optical element120may comprise any optical element comprising an aspherical shape. In some embodiments, the aspheric optical element120may comprise a conical wavefront producing optical element, such as an axicon lens, for example, a negative refractive axicon lens, a positive refractive axicon lens, a reflective axicon lens, a diffractive axicon lens, a programmable spatial light modulator axicon lens (e.g., a phase axicon), or the like.

In some embodiments, the aspheric optical element120comprises at least one aspheric surface whose shape is mathematically described as: z′=(cr2/1)+(1−(1+k)(c2r2))1/2+(a1r+a2r2+a3r3+a4r4+a5r5+a6r6+a7r7+a8r8+a9r9+a10r10+a11r11+a12r12where z′ is the surface sag of the aspheric surface, r is the distance between the aspheric surface and the optical axis102in a radial direction (e.g., in an X-direction or a Y-direction), c is the surface curvature of the aspheric surface (i.e. ci=1/Ri, where R is the surface radius of the aspheric surface), k is the conic constant, and coefficients a1are the first through the twelfth order aspheric coefficients or higher order aspheric coefficients (polynomial aspheres) describing the aspheric surface. In one example embodiment, at least one aspheric surface of the aspheric optical element120includes the following coefficients a1−a7, respectively: −0.085274788; 0.065748845; 0.077574995; −0.054148636; 0.022077021; −0.0054987472; 0.0006682955; and the aspheric coefficients a8−a12are 0. In this embodiment, the at least one aspheric surface has the conic constant k=0. However, because the a1coefficient has a nonzero value, this is equivalent to having a conic constant k with a non-zero value. Accordingly, an equivalent surface may be described by specifying a conic constant k that is non zero, a coefficient a1that is non-zero, or a combination of a nonzero k and a non-zero coefficient a1. Further, in some embodiments, the at least one aspheric surface is described or defined by at least one higher order aspheric coefficients a2−a12with non-zero value (i.e., at least one of a2, a3. . . a12≠0). In one example embodiment, the aspheric optical element120comprises a third-order aspheric optical element such as a cubically shaped optical element, which comprises a coefficient a3that is non-zero.

In some embodiments, when the aspheric optical element120comprises an axicon122(as depicted inFIG. 3), the axicon122may have a laser output surface126(e.g., conical surface) having an angle of about 1.2°, such as from about 0.5° to about 5°, or from about 1° to about 1.5°, or even from about 0.5° to about 20°, the angle measured relative to the laser input surface124(e.g., flat surface) upon which the pulsed laser beam112enters the axicon122. Further, the laser output surface126terminates at a conical tip. Moreover, the aspheric optical element120includes a centerline axis125extending from the laser input surface124to the laser output surface126and terminating at the conical tip. In other embodiments, the aspheric optical element120may comprise a waxicon, a spatial phase modulator such as a spatial light modulator, or a diffractive optical grating. In operation, the aspheric optical element120shapes the incoming pulsed laser beam112(e.g., an incoming Gaussian beam) into a quasi-non-diffracting beam, which, in turn, is directed through the first lens130and the second lens132.

Referring still toFIG. 3, the first lens130is positioned upstream the second lens132and may collimate the pulsed laser beam112within a collimation space134between the first lens130and the second lens132. Further, the second lens132may focus the pulsed laser beam112into the transparent workpiece160, which may be positioned at an imaging plane104. In some embodiments, the first lens130and the second lens132each comprise plano-convex lenses. When the first lens130and the second lens132each comprise plano-convex lenses, the curvature of the first lens130and the second lens132may each be oriented toward the collimation space134. In other embodiments, the first lens130may comprise other collimating lenses and the second lens132may comprise a meniscus lens, an asphere, or another higher-order corrected focusing lens.

Referring again toFIGS. 1A-3, a method for forming the closed contour line170comprising defects172along the closed contour165includes directing (e.g., localizing) a pulsed laser beam112oriented along the beam pathway111and output by the beam source110into the transparent workpiece160such that the portion of the pulsed laser beam112directed into the transparent workpiece160generates an induced absorption within the transparent workpiece and the induced absorption produces a defect172within the transparent workpiece160. For example, the pulsed laser beam112may comprise a pulse energy and a pulse duration sufficient to exceed a damage threshold of the transparent workpiece160. In some embodiments, directing the pulsed laser beam112into the transparent workpiece160comprises focusing the pulsed laser beam112output by the beam source110into the pulsed laser beam focal line113oriented along the beam propagation direction (e.g., the Z axis). The transparent workpiece160is positioned in the beam pathway111to at least partially overlap the pulsed laser beam focal line113of pulsed laser beam112. The pulsed laser beam focal line113is thus directed into the transparent workpiece160. The pulsed laser beam112, e.g., the pulsed laser beam focal line113generates induced absorption within the transparent workpiece160to create the defect172in the transparent workpiece160. In some embodiments, individual defects172may be created at rates of several hundred kilohertz (i.e., several hundred thousand defects per second).

In some embodiments, the aspheric optical element120may focus the pulsed laser beam112into the pulsed laser beam focal line113. In operation, the position of the pulsed laser beam focal line113may be controlled by suitably positioning and/or aligning the pulsed laser beam112relative to the transparent workpiece160as well as by suitably selecting the parameters of the optical assembly100. For example, the position of the pulsed laser beam focal line113may be controlled along the Z-axis and about the Z-axis. Further, the pulsed laser beam focal line113may have a length in a range of from about 0.1 mm to about 100 mm or in a range of from about 0.1 mm to about 10 mm. Various embodiments may be configured to have a pulsed laser beam focal line113with a length l of about 0.1 mm, about 0.2 mm, about 0.3 mm, about 0.4 mm, about 0.5 mm, about 0.7 mm, about 1 mm, about 2 mm, about 3 mm, about 4 mm, or about 5 mm e.g., from about 0.5 mm to about 5 mm.

Referring still toFIGS. 1A-3, the method for forming the closed contour line170comprising defects172along the closed contour165may include translating the transparent workpiece160relative to the pulsed laser beam112(or the pulsed laser beam112may be translated relative to the transparent workpiece160, for example, in the translation direction101depicted inFIGS. 1A and 2) to form closed contour lines170along the closed contour165to trace out the desired perimeter of the aperture180that may be formed in the transparent workpiece160after a subsequent chemical etching step. The defects172that may penetrate the full depth of the glass. It should be understood that while sometimes described as “holes” or “hole-like,” the defects172disclosed herein may generally not be void spaces, but are rather portions of the transparent workpiece160which has been modified by laser processing as described herein.

In some embodiments, the defects172may generally be spaced apart from one another by a distance along the closed contour line170of from about 0.1 μm to about 500 μm, for example, about 1 μm to about 200 μm, about 2 μm to about 100 μm, about 5 μm to about 20 μm, or the like. For example, suitable spacing between the defects172may be from about 0.1 μm to about 50 μm, such as from about 5 μm to about 15 μm, from about 5 μm to about 12 μm, from about 7 μm to about 15 μm, or from about 7 μm to about 12 μm for the TFT/display glass compositions. In some embodiments, a spacing between adjacent defects172may be about 50 μm or less, 45 μm or less, 40 μm or less, 35 μm or less, 30 μm or less, 25 μm or less, 20 μm or less, 15 μm or less, 10 μm or less, 5 μm or less or the like. Further, the translation of the transparent workpiece160relative to the pulsed laser beam112may be performed by moving the transparent workpiece160and/or the beam source110using one or more translation stages190.

Beyond the perforation of a single transparent workpiece160, the process may also be used to perforate stacks of transparent workpieces160, such as stacks of sheets of glass, and may fully perforate glass stacks of up to a few mm total height with a single laser pass. A single glass stack may be comprised of various glass types within the stack, for example one or more layers of soda-lime glass layered with one or more layers of Corning code 2318 glass. The glass stacks additionally may have air gaps in various locations. According to another embodiment, ductile layers such as adhesives may be disposed between the glass stacks. However, the pulsed laser process described herein will still, in a single pass, fully perforate both the upper and lower glass layers of such a stack.

Referring now toFIGS. 5A-5D, following the formation of the closed contour line170in the transparent workpiece160, the transparent workpiece160may be chemically etched to separate the transparent workpiece160along the closed contour line170to form one or more apertures180extending through the transparent workpiece160. For example, the transparent workpiece160may be chemically etched by applying a chemical etching solution202comprising a chemical etchant204to the transparent workpiece160, at least along the closed contour line170. Further, when chemical etching is used to separate the transparent workpiece160along the closed contour line170to form the one or more apertures180extending through the transparent workpiece160, it may be desirable to minimize the amount of material removed from the surfaces of the transparent workpiece160(i.e. minimizing thickness removal) and to maximize the uniformity of material removal through the depth of each defect172. This may be achieved by minimizing the etching rate, as described in more detail below.

The defects172of the closed contour line170provide a pathway for the chemical etching solution202to penetrate into the depth of the transparent workpiece160and remove material of the transparent workpiece160within and surrounding the defects172. For example, the chemical etching solution202may remove material of the transparent workpiece160between adjacent defects172along the closed contour line170, thereby separating the material of the transparent workpiece160within the closed contour line170from the rest of the transparent workpiece160to form the aperture180. Moreover, because the chemical etching solution202may penetrate the thickness of the transparent workpiece160via the defects172, minimal transparent workpiece material must be removed to separate the transparent workpiece160along the closed contour line170. Thus, the amount of time the transparent workpiece160is exposed to the chemical etching solution202may be minimized, eliminating the need for a mask to be applied to the transparent workpiece160during chemical etching. While a single transparent workpiece160is depicted submerged in the chemical etching solution202inFIG. 5B, it should be understood that multiple transparent workpieces160may be simultaneously chemically etched, for example, in a batch process, which may utilize a workpiece fixture300, as depicted inFIG. 6.

While not intending to be limited by theory, chemically etching the defects172of the closed contour line170causes the defects172to form an hourglass shaped profile in which a diameter of the defect172at the major surfaces of the transparent workpiece160is greater than a waist diameter within the depth of the defect, (e.g., about halfway between each major surface of the transparent workpiece160). As used herein, “major surfaces” refers to the imaging surface162of the transparent workpiece160and the surface opposite the imaging surface162(e.g., the back surface). This hourglass shaped profile is caused by the initial restriction of the chemical etching solution202traversing the depth of the defect172(i.e., diffusing through the depth of the defect172). Thus, the portions of the defects172at and near the major surfaces will immediately undergo etching when the chemical etching solution202contacts the transparent workpiece160; while portions of the defect172within the transparent workpiece160will not undergo etching until the chemical etching solution202diffuses through the depth of the defects172(i.e., diffuses from each major surface to the waist of the defect172).

Accordingly, during chemical etching, the diameter of the defect172at the major surfaces may be larger than the waist diameter of the defect172. Further, once the chemical etching solution202traverses the defect172(i.e. reaches the waist/center of the defect172), the difference between the surface diameters and the waist diameter of each defect172will remain constant thereafter. Thus, minimizing the etching rate will minimize the thickness loss of material of the transparent workpiece160and the minimize the difference between the surface diameter and the waist diameter of the defects172because minimizing the etching rate minimizes the amount of material of the transparent workpiece160removed before the chemical etching solution202extends through the depth of the transparent workpiece160. In other words, minimizing the etching rate will maximize the uniformity of material removal through the depth of each defect172such that the difference between the diameter of the defect172at the major surfaces and the waist diameter of the defect172is minimized. Moreover, increasing the uniformity of the defect172results in more uniform walls of the aperture180formed by release of the closed contour line170(i.e. aperture walls that are nearly or fully orthogonal to the major surfaces of the transparent workpiece160)

While not intending to be limited by theory, the etching rate is a controllable variable of the Thiele modulus (φ) of a chemical etching process, which mathematically represents a ratio of etching rate to diffusion rate, as described in Thiele, E. W.Relation between catalytic activity and size of particle, Industrial and Engineering Chemistry, 31 (1939), pp. 916-920. While not intending to be limited by theory, when the etching rate is greater than the diffusion time, the Thiele modulus will be greater than 1. This means that the initial chemical etching solution202introduced into the defect172will be depleted before it reaches the waist (e.g., center) of the defect172where it can be replenished by diffusion of additional chemical etchant from the portion of the defect172at the opposite surface of the transparent workpiece160. As a result, chemical etching will begin earlier at the top and bottom of the defects172than at the center (e.g., waist), leading to an hourglass-like shape formed from the defect172. However, if the diffusion time is equal to or greater than the etching rate, then the Thiele modulus will be less than or equal to 1. Under such conditions, the chemical etchant concentration will be uniform along the entire defect172and the defect172will be etched uniformly, yielding a substantially cylindrical void along each defect172and minimizing material removal required to release the transparent workpiece160along the closed contour line170because the voids formed by the chemical etching solution202at the defects172will join adjacent voids substantially simultaneously along the entire depth of the defects172, limiting or eliminating removal of excess material at the top and bottom portions of the defects172. Such voids could be characterized by having a ratio of top diameter to waist diameter of about 1:0.9 to about 1:0.99.

As described herein, the etching rate can be controlled to control the Thiele modulus of the chemical etching process, and thereby control the ratio of the expansion of the waist diameter of the void formed along the defect172to ratio of expansion of the diameters of the top and bottom openings of the void formed from the defect172. Further, in some embodiments, the Thiele modulus for the chemical etching process described herein can be less than or equal to about 5, less than or equal to about 4.5, less than or equal to about 4, less than or equal to about 3.5, less than or equal to about 3, less than or equal to about 2.5, less than or equal to about 2, less than or equal to about 1.5, or less than or equal to about 1.

When the chemical etching solution202is applied to the transparent workpiece160to release the closed contour line170and remove material of the transparent workpieces160thereby forming the apertures180, the chemical etching solution202may remove from between about 10 μm to about 5 mm, or about 10 μm and about 90 μm of material from the thickness of the transparent workpiece160, for example, from about 35 μm to about 85 μm, 50 μm to about 80 μm, 60 μm to about 80 μm, 70 μm to about 85 μm, or the like. Further, when the chemical etching solution202is applied to the transparent workpiece160to release the closed contour line170and remove material of the transparent workpieces160thereby forming the apertures180, the chemical etching solution202may remove about 50% or less of a thickness of the transparent workpiece160, about 25% or less of a thickness of the transparent workpiece160, about 15% or less of a thickness of the transparent workpiece160, about 10% or less of a thickness of the transparent workpiece160, about 7.5% or less of a thickness of the transparent workpiece160, about 5% or less of a thickness of the transparent workpiece160, about 2.5% or less of a thickness of the transparent workpiece160, or the like.

While not intending to be limited by theory, the etching rate may be lowered by lowering the concentration of chemical etchant204of the chemical etching solution202, lowering the temperature of the chemical etching solution202, agitating the chemical etching solution202during etching, for example, using ultrasonics, physical motion, or the like. Further, the etching rate may be affected by the composition of the transparent workpiece160. While not intended to be limited by theory, increased alkali content in the transparent workpiece160increases the etching rate. For example, given a common chemical etching solution, etching rates for alikali aluminosilicate glass (e.g., Corning Code 2320) are about 2.5 times faster than etching rates of alkaline earth boro aluminosilicate (e.g., EAGLE XG®).

Referring still toFIGS. 5A-5D, the chemical etching solution202may be an aqueous solution that includes the chemical etchant204and deionized water208. In some embodiments, the chemical etchant204may comprise a primary acid and a secondary acid. The primary acid can be hydrofluoric acid and the secondary acid can be nitric acid, hydrochloric acid, or sulfuric acid. In some embodiments, the chemical etchant204may only include a primary acid. In some embodiments, the chemical etchant204may include a primary acid other than hydrofluoric acid and/or a secondary acid other than nitric acid, hydrochloric acid, or sulfuric acid. For example, in some embodiments, the primary acid chemical etchant204may comprise from about 1% by volume hydrofluoric acid to about 15% by volume hydrofluoric acid, for example, about 2.5% by volume hydrofluoric acid to about 10% by volume hydrofluoric acid, 2.5% by volume hydrofluoric acid to about 5% by volume hydrofluoric acid, and all ranges and subranges in between. Further, in some embodiments, the secondary acid may comprise may comprise from about 1% by volume hydrofluoric acid to about 20% by volume nitric acid, for example, about 2.5% by volume nitric acid to about 15% by volume nitric acid, 2.5% by volume nitric acid to about 10% by volume nitric acid, 2.5% by volume nitric acid to about 5% by volume nitric acid and all ranges and subranges in between. As additional examples, chemical etchants204can include 10% by volume hydrofluoric acid/15% by volume nitric acid, 5% by volume hydrofluoric acid/7.5% by volume nitric acid, 2.5% by volume hydrofluoric acid/3.75% by volume nitric acid, 5% by volume hydrofluoric acid/2.5% by volume nitric acid, 2.5% by volume hydrofluoric acid/5% by volume nitric acid or the like. Further, lowering the concentration of chemical etchant204in the chemical etching solution may lower the etching rate. Thus, it may be advantageous to use a minimum effective concentration of chemical etchant204in the chemical etching solution202. In some embodiments, the chemical etchant204may comprise a base, such as sodium hydroxide or potassium hydroxide. As an example, the chemical etchant204may comprise about 5M sodium hydroxide to about 20M sodium hydroxide. As an additional example, the chemical etchant204may comprise about 5M potassium hydroxide to about 20M potassium hydroxide.

In operation, the etching time required to separate the portion of the transparent workpiece160surrounded by the closed contour line170from the remaining transparent workpiece160, thereby forming the aperture180in the transparent workpiece160may be from about 2 mins to 1,000 mins or greater, for example, 5 mins to about 40 mins, 5 mins to about 30 mins, 5 mins to about 20 mins, 10 mins to about 30 mins, 10 mins to about 20 mins, 15 mins to about 30 mins, 20 mins to 60 mins, 60 mins to 200 mins, 100 mins to 1,000 mins, greater than 1,000 mins or the like. The temperature of the chemical etching solution202when etching the transparent workpiece160may be from about 0° C. to about 40° C., for example, about 30° C. or less, about 20° C. or less about 10° C. or less, about 5° C. or less, or the like. For example, about 2° C., 5° C., 7° C., 10° C., 12° C., 15° C., 18° C., 20° C., 25° C., 30° C., 35° C., or the like. Further, lowering the temperature of the chemical etching solution202when etching the transparent workpiece160lowers the etching rate. Thus, colder etching temperatures may be advantageous. In the example of a chemical etching solution202that comprises a basic etching solution, the temperature of the chemical etching solution202when etching the transparent workpiece10may be from about 70° C. to about 100° C.

As depicted inFIG. 5B, the chemical etching solution202may be housed in a chemical etching bath200, which may include from about 5 L to about 15 L of the chemical etching solution202, for example, about 8 L to about 10 L. In some embodiments, a larger chemical etching bath200and a larger volume of chemical etching solution202may be desired to allow more space for motion and agitation. In some embodiments, the chemical etching solution202may further comprise a surfactant206(FIG. 5D), which increases the wettability of the defects172when applied to the transparent workpiece160. The increased wettability lowers the diffusion time of the chemical etching solution202through the depth of each defect172, which may be desirable as described below. In some embodiments, the surfactant206can be any suitable surfactant that dissolves into the chemical etching solution202and that does not react with the chemical etchant204in the chemical etching solution202. In some embodiments, the surfactant206can be a fluorosurfactant such as Capstone® FS-50 or Capstone® FS-54. In some embodiments, the concentration of the surfactant206in terms of ml of surfactant/L of etching solution can be about 1, about 1.1, about 1.2, about 1.3, about 1.4, about 1.5, about 1.6, about 1.7, about 1.8, about 1.9, about 2 or greater.

In operation, the transparent workpiece160comprising the closed contour line170(or multiple closed contour lines170corresponding with multiple desired apertures180) may be immersed in a chemical etching bath200comprising the chemical etching solution202, as depicted inFIG. 5B. Further, while the chemical etching solution202is primarily described herein as an aqueous solution, in some embodiments, the chemical etching solution202may comprise a gaseous solution comprising, for example, a vapor HF chemical etchant. In operation, the gaseous chemical etching solution may be applied to the transparent workpiece160using a spray etching process. Using a gaseous chemical etching solution may remove the need for an agitation process in order to etch into the depth of the transparent workpiece160along the defects172, as gas may more readily diffuse into the defects172than liquid. Voids created through such a method could be characterized by having a ratio of top diameter to waist diameter of about less than 1:0.9 to about 1:1.

While not intending to be limited by theory, forming the closed contour line170comprising the plurality of defects172is a zero or near zero kerf process and thus, when the closed contour line170is formed in the transparent workpiece160, it is difficult to separate the material of the transparent workpiece160within the closed contour line170from the rest of the transparent workpiece160without damaging the transparent workpiece160. However, chemically etching the transparent workpiece160after forming the closed contour line170enlarges the defects172of the closed contour line170to release the closed contour line170and create one or more apertures180without unintended damage to the transparent workpiece160.

In some embodiments, the chemical etching solution202may be agitated when the transparent workpiece160is positioned within the chemical etching bath200. For example, the chemical etching solution202may be mechanically agitated, ultrasonically agitated, or combinations thereof. Additionally, the chemical etching solution202may be agitated by recirculation of the chemical etching solution202. Agitation may increase the diffusion rate of the chemical etching solution202through the depth of the defects172, thereby facilitating faster separation while limiting material removal and facilitating uniformly shaped defects172(any thereby uniformly shaped aperture walls). In some embodiments, the chemical etching bath200may be mechanically agitated in the X, Y, and Z directions to improve uniform etching of the defects172. The mechanical agitation in the X, Y, and Z directions may be continuous or variable. In some embodiments, the chemical etching bath200may comprise one or more ultrasonic transducers configured to generate ultrasonic agitation of the chemical etching solution202within the chemical etching bath200. For example, the ultrasonic transducers may be located at the bottom of the chemical etching bath200or one or more sides of the chemical etching bath200. Ultrasonic transducers may generate frequencies such as 40 kHz, 58 kHz, 80 kHz, 120 kHz, 132 kHz, and 192 kHz or a combination thereof.

Further, during ultrasonic agitation, the transparent workpiece160may be oriented within the chemical etching bath200such that the both ends of each defect172(e.g., the portions of the defect172located at the imaging surface162and the surface opposite the imaging surface162) receive substantially uniform exposure to ultrasonic waves such that the defects172of the closed contour line170are etched uniformly. For example, if the ultrasonic transducers are arranged at the bottom of the chemical etching bath200, the transparent workpiece160can be oriented in the chemical etching bath200so that the surfaces of the transparent workpiece160between which the defects172are perpendicular to the bottom of the chemical etching bath200(e.g., face the sides of the chemical etching bath200) rather than parallel to the bottom of the chemical etching bath200.

Referring now toFIG. 6, the one or more transparent workpieces160may be held in the chemical etching bath200using the workpiece fixture300. The workpiece fixture300may be configured to hold the transparent workpiece160with minimal contact, as contact between the workpiece fixture300and the transparent workpiece160may create marks or impressions (e.g., optical blemishes) on the transparent workpiece160because contact between the workpiece fixture300and the transparent workpiece160may prevent or impede flow of the chemical etching solution202to the portions of a surface of the transparent workpiece160that contact the workpiece fixture300. These optical blemishes are subtle but may be visible in reflected light due to a mismatch in material removal at discrete locations of the transparent workpiece160(i.e. differential local etching). While not intending to be limited by theory, optical blemishes are caused due to differing fluid flow rates and fluid contact times between the chemical etching solution202and different portions of the transparent workpiece160causing deviations in the etching rate at these different portions of the transparent workpiece160(i.e. differential local etching). Further, optical blemishes may diminish the visual quality of the transparent workpiece160. As described below, the workpiece fixture300is configured to minimize optical blemishes by minimizing contact between the workpiece fixture300and the transparent workpiece160during the etching process, minimizing the formation of etchant byproducts, and minimizing contact between portions of the transparent workpiece160that are disconnected from the remainder of the transparent workpiece160.

As depicted inFIG. 6, the workpiece fixture300comprises a first fixture wall310, a second fixture wall312and a plurality of fixture cross-bars320coupled to and extending between the first fixture wall310and the second fixture wall312. Further, the fixture cross-bars320may comprise one or more grooves322, one or more set screws324, or a combination thereof. For example, in the embodiment depicted inFIG. 6, the workpiece fixture300comprises five fixture cross-bars320, two comprising a plurality of set screws324and three comprising a plurality of grooves322. It should be understood that other arrangements of grooves322and set screws324are contemplated. In operation, one or more transparent workpieces160may be disposed within the coplanar grooves322of the fixture cross-bars320and fixed in position by engagement with corresponding coplanar set screws324of the fixture cross-bars320. The plurality of grooves322may have a depth of from about 50 μm to about 500 μm, for example, about 75 μm, 100 μm, 125 μm, 150 μm, 175 μm, 200 μm, 225 μm, 250 μm, 275 μm, 300 μm, 325 μm, 350 μm, 375 μm, 400 μm, 425 μm, 450 μm, 475 μm, or the like.

Each of the plurality of grooves322may be V-shaped to minimize contact between the transparent workpiece160and each groove322. The set screws324may also have V-shaped grooves on a contact face of the set screws324to minimize contact between the transparent workpiece160and the set screws324. Further, the set screws324may be tightened such that the transparent workpiece160sits within the grooves of the set screws324without firm contact to minimize marking effects. In some embodiments, the transparent workpiece160is held by multiple V-shaped grooves322to allow the transparent workpiece160to jostle within the grooves322, minimizing the formation of marks and impressions in the transparent workpiece160. In some embodiments, the workpiece fixture300may comprise Teflon™ or other polymers such as thermopolymers, fluoropolymers, or the like. Further, after chemically etching, the transparent workpiece160may undergo a post-etch finishing process, for example, grinding and/or polishing the transparent workpiece160to remove any marks or impressions formed on the transparent workpiece160by the workpiece fixture300.

Further, a low etching rate may reduce the formation of optical blemishes. While not intending to be limited by theory, increasing the etching rate increases the rate of formation of insoluble byproducts of the etching process, which may mask portions of the transparent workpiece160and cause differential local etching, forming optical blemishes that are visible as streaks on the transparent workpiece. In contrast, lowering the etching rate lowers the rate of formation of insoluble byproducts, allowing the agitation of the chemical etching solution202and/or the transparent workpiece160to remove the insoluble byproducts from contact with the transparent workpiece160, reducing the differential local etching caused by these byproducts. Even without agitation, the lowering the rate of formation of insoluble byproducts means a larger portion of the insoluble byproducts will diffuse away from the transparent workpiece160before causing the formation of optical blemishes.

Moreover, optical blemishes formed on the transparent workpiece160by contact between the transparent workpiece160and the workpiece fixture300may be minimized by rotating the transparent workpiece160when the transparent workpiece160is disposed (e.g., immersed) in the chemical etching bath200. While not intending to be limited by theory, directional optical blemishes are caused by gravity pulling chemical etchant byproducts over a surface of the transparent workpiece160. However, rotating the transparent workpiece160disperses optical blemishes in multiple directions, such that chemical etchant byproducts are dispersed over the surface of the transparent workpiece160in multiple directions and in any one direction for a reduced period of time, forming optical blemishes that are dispersed and less visually noticeable.

Optical blemishes may also be formed when a portion of the transparent workpiece160(e.g., a portion within the closed contour170) that is no longer connected to the remainder of the transparent workpiece160adheres to the transparent workpiece160, for example, when this “disconnected” portion of the transparent workpiece160is not yet removed to form the aperture180. In this situation, the portion of the transparent workpiece160that is covered by this disconnected portion receives differential local etching, resulting in optical blemishes. Thus, removing these disconnected portions, for example, using agitation, rotation, or the like may reduce optical blemishes.

Further, the diameter (or other cross-sectional size) of the aperture180is larger than the diameter (or other cross-sectional size) of the corresponding closed contour170used to form the aperture180, due to the removal of material caused by chemical etching. Thus, the size of the closed contour170should account for this difference to form apertures180with a desired size. Moreover, etching rates can vary spatially. For example, a 400 μm diameter closed contour170will etch differently than a 6 mm diameter closed contour170, even if the same laser parameters are used. Thus, to obtain a precisely size aperture180after chemical etching, a comprehensive size and contour dependent experiment may be executed.

In some embodiments, multiple transparent workpieces160may be simultaneously etched, for example, by simultaneous immersion in a chemical etching bath200. However, these multiple transparent workpieces160should be oriented and spaced to limit the degree of ultrasonic agitation blocked by the multiple transparent workpieces160. In other words, the multiple transparent workpieces160should be oriented and spaced to maximize the number or transparent workpieces160etched at once while retaining desirable levels of agitation.

Referring now toFIG. 7, an exploded view an electronic device10that includes a transparent workpiece160as a cover glass plate is depicted. The transparent workpiece160ofFIG. 7comprises the plurality of apertures180formed using the above described processes and the electronic device10comprises one or more speakers12aligned with the plurality of apertures180, which provide acoustic pathways through the transparent workpiece160. Further, each aperture180comprises an aperture perimeter182, which is located at the previous location of individual closed contour lines170. In some embodiments, each aperture180may comprise a cross-sectional dimension (e.g., diameter) of from about 100 μm to about 10 mm, for example, 5 mm or less, 3 mm or less, 1 mm or less, 900 μm, 800 μm or less, 700 μm, 600 μm or less, 500 μm or less, 400 μm, 300 μm or less, 250 μm or less, 200 μm or less, 100 μm or less, or the like. In some embodiments, the transparent workpiece160may comprise arrays of apertures180with individual apertures180having varying diameter.

In embodiments in which the transparent workpiece160comprising the array of apertures180comprises non-strengthened glass, edges of each aperture180along the aperture perimeter182may comprise an edge strength of from about 200 MPa to about 500 MPa, for example 250 MPa, 300 MPa, 350 MPa, 400 MPa, 450 MPa, or the like. Further, in embodiments in which the transparent workpiece160comprising the array of apertures180comprises strengthened glass, for example, ion-exchanged glass, edges of each aperture180along the aperture perimeter182may comprise an edge strength of from about 600 MPa to about 1000 MPa, for example 650 MPa, 700 MPa, 750 MPa, 800 MPa, 850 MPa, 900 MPa, 950 MPa, or the like. Further, the array of apertures180may reduce the strength of the transparent workpiece160(when compared to a similar transparent workpiece without apertures) by 30% or less, 20% or less, 10% or less, or the like.

In some embodiments, for example, embodiments in which the apertures180provide acoustic pathways, the one or more of the apertures180may extend through the transparent workpiece160at an angle such that each aperture180is not perpendicular to the surfaces of the transparent workpiece160that the aperture180extends between. For example, angular defects may be formed by directing the pulsed laser beam focal line113(FIGS. 1A and 1B) through the transparent workpiece160at an angle not perpendicular to the imaging surface162of the transparent workpiece160to form a closed contour line170comprising angular defects. These angular defects may be chemically etched to form angular apertures.

Moreover, while the apertures180are described herein as acoustic pathways, it should be understood that the processes described herein may be used to form any apertures in a transparent workpiece160, for example, slots, home buttons, or the like. For example, in some embodiments, the transparent workpiece160may be used as a backplate for a computer keyboard and the apertures180may serve as key holes that allow each key of the keyboard to extend through an individual aperture180. These apertures180may be comprise different cross-sectional sizes to accommodate keyboard keys having a variety of sizes.

In view of the foregoing description, it should be understood that formation of a closed contour line comprising defects along a closed contour corresponding with a desired aperture perimeter may be enhanced by utilizing a pulsed laser beam which is shaped by an optical assembly into a pulsed laser beam focal line such that the pulsed laser beam focal line irradiates the transparent workpiece along the closed contour. Further, it should be understood that the closed contour line comprising defects may be separated from the rest of the transparent workpiece by chemically etching the transparent workpiece to form apertures extending through the transparent workpiece. Moreover, these apertures may be used as acoustic pathways when the transparent workpiece is a cover plate of an electronics device.