Patent ID: 12186835

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments of separating a substrate, such as a coated substrate comprising a transparent workpiece and a coating layer. The coated substrate includes a primary region and a dummy region. The primary region is a portion of the coated substrate that is to be used as a resultant product, such as a screen or other substrate in a consumer electronics product, and the dummy region is a scrap region. Because the primary region is to be used as a product, it is desirable to separate the primary region from the dummy region while limiting or preventing damage to the primary region. The methods described herein include using a pulsed laser beam to form a series of defects in the coated substrate and an infrared laser beam to separate the transparent workpiece and the coating layer along the series of defects, which are formed along a boundary between the primary region and the dummy region.

In particular, the methods described herein direct thermal energy onto the dummy region of the coated substrate using techniques sufficient to both induce separation of the defects disposed in the coated substrate along the boundary between the primary region and the dummy region in a single process step. One method described herein includes translating an infrared laser beam along an oscillating pathway on the dummy region. Another method described herein includes modifying the energy distribution of an infrared laser beam into a top hat energy distribution and directing this modified laser beam onto the dummy region. Yet another method described herein includes forming the infrared laser beam into an annular shape and directing this annular infrared laser beam onto the dummy region. While the methods and systems are primarily described herein with respect to a coated substrate comprising a transparent workpiece and a coating layer, it should be understood that these methods and systems are also applicable to the separation of single substrates, such as uncoated transparent workpieces, which may benefit from the decrease in chipping and heat cracks and thus a higher release speed. Various embodiments of separating a coated substrate using laser processing techniques will be described herein with specific reference to the appended drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts.

As used herein, “laser processing” comprises directing a laser beam onto and/or into a substrate, such as a coated substrate comprising a transparent workpiece with a coating layer. In some embodiments, laser processing further comprises translating the laser beam relative to the coated substrate, for example, along a contour line or other pathway. Examples of laser processing include using a laser beam to form a contour comprising a series of defects that extend into the transparent workpiece and using an infrared laser beam to heat both the transparent workpiece and the coating layer. Laser processing may separate the coated substrate along one or more desired lines of separation.

As used herein, “beam spot” refers to a cross section of a laser beam (e.g., a beam cross section) at the impingement location of the laser beam at an impingement surface of a substrate (e.g., the coated substrate). The impingement surface is the surface of a coated substrate upon which the laser beam is first incident. The beam spot is the cross-section at the impingement location. In the embodiments described herein, the beam spot is sometimes referred to as being “axisymmetric” or “non-axisymmetric.” 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. The rotation axis (e.g., the central axis) is most often taken as being the optical axis (axis of propagation) of the laser beam, which is the axis extending in the beam propagation direction, which is referred to herein as the z-direction.

As used herein, “upstream” and “downstream” refer to the relative position of two locations or components along a beam pathway with respect to a beam source. For example, a first component is upstream from a second component if the first component is closer to the beam source along the path traversed by the laser beam than the second component.

As used herein, “pulsed laser beam focal line,” refers to a pattern of interacting (e.g., crossing) light rays of a pulsed laser beam that forms a focal region elongated in the beam propagation direction. In conventional laser processing, a pulsed laser beam is tightly focused to a focal point. The focal point is the point of maximum intensity of the pulsed laser beam and is situated at a focal plane in a substrate, such as the transparent workpiece. In the elongated focal region of a pulsed laser beam focal line, in contrast, the region of maximum intensity of the pulsed laser beam extends beyond a point to a line aligned with the beam propagation direction. A pulsed laser beam focal line is formed by converging light rays of a pulsed laser beam that intersect (e.g., cross) to form a continuous series of focal points aligned with the beam propagation direction. The pulsed laser beam focal lines described herein are formed using a quasi-non-diffracting beam, mathematically defined in detail below.

As used herein, “contour line,” corresponds to the set of intersection points of the laser beam with the incident surface of a substrate (e.g., the coated substrate) resulting from relative motion of the laser beam and the substrate. A contour line can be a linear, angled, polygonal or curved in shape. A contour line can be closed (i.e. defining an enclosed region on the surface of the substrate) or open (i.e. not defining an enclosed region on the surface of the substrate). The contour line represents a boundary along which separation of the substrate into two or more parts is facilitated. For example, in the embodiments described herein, the contour line represents a boundary between a dummy region of the coated substrate and a primary region of the coated substrate.

As used herein, “contour,” refers to a set of defects in a substrate (e.g., in the transparent workpiece of the coated substrate) formed by a laser beam through relative motion of a laser beam and the substrate along a contour line. The defects are spaced apart along the contour line and are wholly contained within the interior of the substrate or extend through one or more surfaces into the interior of the substrate. Defects may also extend through the entire thickness of the substrate. Separation of the substrate (e.g., the transparent workpiece) occurs by connecting defects, such as, for example, through propagation of a crack.

As used herein, a “defect” refers to a region of a transparent workpiece that has been modified by a laser beam. Defects include regions of a transparent workpiece having a modified refractive index relative to surrounding unmodified regions of the transparent workpiece. Common defects include structurally modified regions such as void spaces, cracks, scratches, flaws, holes, perforations, densifications, or other deformities in the transparent workpiece produced by a pulsed laser beam focal line. Defects may also be referred to, in various embodiments herein, as defect lines or damage tracks. A defect or damage track is formed through interaction of a pulsed laser beam focal line with the transparent workpiece. As described more fully below, the pulsed laser beam focal line is produced by a pulsed laser. A defect at a particular location along the contour line is formed from a pulsed laser beam focal line produced by a single laser pulse at the particular location, a pulse burst of sub-pulses at the particular location, or multiple laser pulses at the particular location. Relative motion of the laser beam and transparent workpiece along the contour line results in multiple defects that form a contour.

The phrase “transparent workpiece,” as used herein, means a workpiece formed from glass, glass-ceramic or other material which is transparent, where the term “transparent,” as used herein, means that the material has a linear optical absorption of less than 20% per mm of material depth, such as less than 10% per mm of material depth for the specified pulsed laser wavelength, or such as less than 1% per mm of material depth for the specified pulsed laser wavelength. Unless otherwise specified, the material has a linear optical absorption of less than about 20% per mm of material depth. The transparent workpiece may have a depth (e.g., thickness) of from about 50 microns (μm) to about 10 mm (such as from about 100 μm to about 5 mm, or from about 0.5 mm to about 3 mm). Transparent workpieces may comprise glass workpieces formed from glass compositions, such as borosilicate glass, soda-lime glass, aluminosilicate glass, alkali aluminosilicate, 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 glass strengthening before or after laser processing the transparent workpiece. For example, the transparent workpiece may comprise ion exchanged and ion exchangeable glass, such as Corning® Gorilla® Glass available from Corning Incorporated of Corning, NY (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. Other example transparent workpieces may comprise EAGLE XG® and CORNING LOTUS™ glass available from Corning Incorporated of Corning, NY. Moreover, the transparent workpiece may comprise other components, which are transparent to the wavelength of the laser, for example, glass ceramics or crystals such as sapphire or zinc selenide. Furthermore, in the embodiments described herein, a coating layer is disposed on the transparent workpiece forming a coated substrate.

In an ion exchange process, ions in a surface layer of the transparent workpiece are replaced by larger ions having the same valence or oxidation state, for example, by partially or fully submerging the transparent workpiece in an ion exchange bath. Replacing smaller ions with larger ions causes a layer of compressive stress to extend from one or more surfaces of the transparent workpiece to a certain depth within the transparent workpiece, referred to as the depth of layer. The compressive stresses are balanced by a layer of tensile stresses (referred to as central tension) such that the net stress in the glass sheet is zero. The formation of compressive stresses at the surface of the glass sheet makes the glass strong and resistant to mechanical damage and, as such, mitigates catastrophic failure of the glass sheet for flaws, which do not extend through the depth of layer. In some embodiments, smaller sodium ions in the surface layer of the transparent workpiece are exchanged with larger potassium ions. In some embodiments, the ions in the surface layer and the larger ions are monovalent alkali metal cations, such as Li+(when present in the glass), Na+, K+, Rb+, and Cs+. Alternatively, monovalent cations in the surface layer may be replaced with monovalent cations other than alkali metal cations, such as Ag+, Tl+, Cu+, or the like.

As used herein, the term “quasi-non-diffracting beam” is used to describe a laser beam having low beam divergence as mathematically described below. In particular, the laser beam used to form a contour of defects in the embodiments described herein. The laser beam has an intensity distribution I(X,Y,Z), where Z is the beam propagation direction of the laser beam, and X and Y are directions orthogonal to the beam propagation direction, 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 coordinates and directions X, Y, and Z are also referred to herein as x, y, and z; respectively. The intensity distribution of the laser beam in a cross-sectional plane may be referred to as a cross-sectional intensity distribution.

The quasi-non-diffracting laser beam may be formed by impinging a diffracting laser beam (such as a Gaussian beam) into, onto, and/or thorough a phase-altering optical element, such as an adaptive phase-altering optical element (e.g., a spatial light modulator, an adaptive phase plate, a deformable mirror, or the like), a static phase-altering optical element (e.g., a static phase plate, an aspheric optical element, such as an axicon, or the like), to modify the phase of the beam, to reduce beam divergence, and to increase Rayleigh range, as mathematically defined below. Example quasi-non-diffracting beams include Gauss-Bessel beams, Airy beams, Weber beams, and Bessel beams.

Referring toFIGS.1A and1B and2, the pulsed laser beam112used to form the defects further 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 element135, as described in more detail below with respect to the optical assembly100depicted inFIG.2. 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 coated substrate120.

The length of the pulsed laser beam focal line produced from a quasi-non-diffracting beam is determined by the Rayleigh range of the quasi-non-diffracting beam. Particularly, the quasi-non-diffracting beam defines a pulsed laser beam focal line113having a first end point and a second end point each defined by locations where the quasi-non-diffracting beam has propagated a distance from the beam waist equal to a Rayleigh range of the quasi-non-diffracting beam. The length of the laser beam focal line corresponds to twice the Rayleigh range of the quasi-non-diffracting beam. A detailed description of the formation of quasi-non-diffracting beams and determining their length, including a generalization of the description of such beams to asymmetric (such as non-axisymmetric) beam cross sectional profiles, is provided in U.S. Provisional Application Ser. No. 62/402,337 and Dutch Patent Application No. 2017998, which are incorporated by reference in their entireties.

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. The Rayleigh range can also be observed as the distance along the beam axis at which the peak optical intensity observed in a cross sectional profile of the beam decays to one half of its value observed in a cross sectional profile of the beam 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.

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. 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 Gaussian intensity profiles may be less preferred for laser processing to form a contour of defects because, 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 (low Rayleigh range). To achieve low divergence (high Rayleigh range), 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.

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 any beam, even 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 ZRbased on the effective spot size wo,efffor axisymmetric beams can be specified as non-diffracting or quasi-non-diffracting beams for forming damage regions in Equation (1), below:

ZR>FD⁢π⁢⁢w0,eff2λ(1)
where FDis a dimensionless divergence factor having a value of at least 10, in an embodiment at least 50, in an embodiment at least 100, in an embodiment at least 250, in particular at least 500 and in another embodiment at least 1000. In a further embodiment FDcan be in the range from 10 to 2000, in particular in the range from 50 to 1500 and furthermore in particular in the range from 100 to 1000. For a non-diffracting or quasi-non-diffracting beam the distance (Rayleigh range), ZRin Equation (1), over which the effective spot 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 (1) with a value of FD≥10. As the value of FDincreases, the pulsed laser beam112approaches a more nearly perfectly non-diffracting state. Thus, as the value of FDincreases, the length of the laser beam focal line increases, facilitating the formation of longer defects.

Additional information about Rayleigh range, beam divergence, intensity distribution, axisymmetric and non-axisymmetric beams, and spot size as used herein 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.

Referring now toFIGS.1A and1B, a coated substrate120comprising a transparent workpiece122and a coating layer121disposed on the transparent workpiece122is schematically depicted undergoing laser processing according to the methods described herein. In particular,FIGS.1A and1Bschematically depict directing a pulsed laser beam112that is output by a pulsed beam source110, such as a Gaussian pulsed beam source, and oriented along a beam pathway111into the coated substrate120to form a defect172in the coated substrate120, for example, extending into both the coating layer121and the transparent workpiece122. The pulsed laser beam112propagates along the beam pathway111and is oriented such that the pulsed laser beam112may be focused into a pulsed laser beam focal line113within the coated substrate120, for example, using an aspheric optical element135and one or more lenses (FIG.2). The pulsed laser beam focal line113generates an induced absorption within the transparent workpiece122and, in some embodiments, the coating layer121, to produce the defect172within the coated substrate120that may extend into both the coating layer121and the transparent workpiece122. Furthermore, a contour170of defects172may be formed in the coated substrate120by translating at least one of the pulsed laser beam112and the coated substrate120relative to one another such that the pulsed laser beam112translates relative to the coated substrate120in a translation direction101.

As also shown inFIG.1A, the pulsed laser beam112forms a beam spot114projected onto a first surface123of the coated substrate120. InFIG.1A, the first surface123is a surface of the coating layer121. The coating layer121may comprise any material comprising a transmission of greater than 70% per mm of material depth of the wavelength λ of the pulsed laser beam112. Without intending to be limited by theory, transmission losses are due to scattering or absorption and minimizing transmission losses minimizes disruption of the formation of the pulsed laser beam focal line113in the coating layer121and the transparent workpiece122. In some embodiments, the transmission is greater than 90% per mm of material depth, such as greater than 95% per mm of material depth. In addition, material of the coating layer121has a homogenous phase alteration (e.g., a phase alteration caused by refractive index). Without intending to be limited by theory, any step in phase alteration will result in a loss of focus on a one digit μm scale. Indeed, inhomogeneous alteration of the phase or direction of the light causes scattering, which reduces transmission. While the coating layer121may comprise any material having a transmission of greater than 70% per mm of material depth of the wavelength λ of the pulsed laser beam112, example materials include a metal oxide and a polymer.

Referring also toFIG.2, the pulsed laser beam112may be focused into the pulsed laser beam focal line113using a lens132, which is the final focusing element in an optical assembly100. While a single lens132is depicted inFIGS.1A and1B, the optical assembly100further comprises an aspheric optical element135, which modifies the pulsed laser beam112such that the pulsed laser beam112has a quasi-non-diffracting character downstream the aspheric optical element135. Thus, when the portion of the pulsed laser beam112shown inFIGS.1A and1Bimpinges the lens132, the pulsed laser beam112has a quasi-non-diffracting character. Furthermore, some embodiments may include a lens assembly130including, for example a first lens131and a second lens132, and repetitions thereof (FIG.2) to focus the pulsed laser beam112into the pulsed laser beam focal line113. Other standard optical elements (e.g. prisms, beam splitters etc.) may also be included in lens assembly130.

As depicted inFIG.1A, the pulsed laser beam112may comprise an annular shape when impinging the lens132. While the lens132is depicted focusing the pulsed laser beam112into the pulsed laser beam focal line113inFIG.1A, other embodiments may use the aspheric optical element135(FIG.2), which modifies the pulsed laser beam112such that the pulsed laser beam112has a quasi-non-diffracting character downstream the aspheric optical element135, to also focus the pulsed laser beam112into the pulsed laser beam focal line113. In other words, in some embodiments, the lens132may be the final focusing element and in other embodiments, the aspheric optical element135may be the final focusing element. 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. The length of the pulsed laser beam focal line113may be selected based on the particular laser processing goals. As one example, for thicker coated substrates120it may be advantageous to form longer pulsed laser beam focal lines113. As another example, if defects172extending into only discrete depth sections of the coated substrate120is desired, it may be advantageous to form shorter pulsed laser beam focal lines113.

Referring now toFIG.2, the optical assembly100for producing a pulsed laser beam112that is quasi-non-diffracting and forms the pulsed laser beam focal line113at the coated substrate120inclusive of the coating layer121and transparent workpiece122using the aspheric optical element135(e.g., an axicon136) is schematically depicted. The optical assembly100includes a pulsed beam source110that outputs the pulsed laser beam112, and the lens assembly130comprising the first lens131and the second lens132. The coated substrate120may be positioned such that the pulsed laser beam112output by the pulsed beam source110irradiates the coating layer121and transparent workpiece122, for example, after traversing the aspheric optical element135and thereafter, both the first lens131and the second lens132.

The aspheric optical element135is positioned within the beam pathway111between the pulsed beam source110and the coated substrate120. In operation, propagating the pulsed laser beam112, e.g., an incoming Gaussian beam, through the aspheric optical element135may alter, for example, phase alter, the pulsed laser beam112such that the portion of the pulsed laser beam112propagating beyond the aspheric optical element135is quasi-non-diffracting, as described above. The aspheric optical element135may comprise any optical element comprising an aspherical shape. In some embodiments, the aspheric optical element135may comprise a conical wavefront producing optical element, such as an axicon lens, for example, a negative refractive axicon lens (e.g., negative axicon), a positive refractive axicon lens, a reflective axicon lens, a diffractive axicon lens, a phase axicon, a diffractive optic, a cubically shaped optical element, or the like.

While the optical assembly100is primarily described as altering the pulsed laser beam112into a quasi-non-diffracting beam using the aspheric optical element135, it should be understood that a quasi-non-diffracting beam also be formed by other phase-altering optical elements, such as a spatial light modulator, an adaptive phase plate, a static phase plate, a deformable mirror, diffractive optical grating, or the like. Each of these phase-altering optical elements, including the aspheric optical element135, modify the phase of the pulsed laser beam112, to reduce beam divergence, increase Rayleigh range, and form a quasi-non-diffracting beam as mathematically defined above.

Referring still toFIG.2, the lens assembly130comprises two lenses, with the first lens131positioned upstream the second lens132. The first lens131may collimate the pulsed laser beam112within a collimation space134between the first lens131and the second lens132. Further, the most downstream positioned second lens132of the lens assembly130may focus the pulsed laser beam112into the transparent workpiece122. In some embodiments, the first lens131and the second lens132each comprise plano-convex lenses. When the first lens131and the second lens132each comprise plano-convex lenses, the curvature of the first lens131and the second lens132may each be oriented toward the collimation space134. In other embodiments, the first lens131may comprise a collimating lens and the second lens132may comprise a meniscus lens, an asphere, or another higher-order corrected focusing lens. In operation, the lens assembly130may control the position of the pulsed laser beam focal line113along the beam pathway111. In further embodiments, the lens assembly130may comprise an 8F lens assembly, a 4F lens assembly comprising a single set of first and second lenses131,132, or any other known or yet to be developed lens assembly130for focusing the pulsed laser beam112into the pulsed laser beam focal line113. Moreover, it should be understood that some embodiments may not include the lens assembly130and instead, the aspheric optical element135may focus the pulsed laser beam112into the pulsed laser beam focal line113. For example, aspheric optical element135may both transform pulsed laser beam112into a quasi-non-diffracting laser beam and focus the quasi-non-diffracting laser beam into pulsed laser beam focal line113.

Referring again toFIGS.1A-2, the pulsed beam source110is configured to output pulsed laser beam112. In operation, the defects172of the contour170are produced by interaction of the transparent workpiece122with the pulsed laser beam112output by the pulsed beam source110as modified by the aspheric optical element135and/or lens assembly130. In operation, the pulsed laser beam112output by the pulsed beam source110may create multi-photon absorption (MPA) in the transparent workpiece122. 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.

In some embodiments, the pulsed 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 workpiece122may 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 workpiece122are sufficiently low. In embodiments, the combined losses due to linear absorption and scattering by the transparent workpiece122and the coating layer121at the laser 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, such as 0.5%/mm to 20%/mm, 1%/mm to 10%/mm, or 1%/mm to 5%/mm, for example, 1%/mm, 2.5%/mm, 5%/mm, 10%/mm, 15%/mm, or any range having any two of these values as endpoints, or any open-ended range having any of these values as a lower bound. As used herein, the dimension “/mm” means per millimeter of distance within the transparent workpiece122in the beam propagation direction of the pulsed laser beam112(i.e., the Z direction). Representative laser 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 laser 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.

Referring still toFIGS.1A-2, in operation, the contour170may be formed in the coated substrate120by irradiating a contour line142with the pulsed laser beam112and translating at least one of the pulsed laser beam112and the coated substrate120relative to each other along the contour line142in the translation direction101to form the defects172of the contour170. While the contour170depicted inFIG.1Ais linear, it should be understood that the contour170may be non-linear, for example, curved. Further, in some embodiments, the contour170may be a closed contour, such as a circle, rectangles, ellipses, squares, hexagons, ovals, regular geometric shapes, irregular shapes, polygonal shapes, arbitrary shapes, and the like. The contour line142represents a boundary between a primary region124and a dummy region126of the coated substrate120. The primary region124is the region of the coated substrate120that is to be used as a resultant product and the dummy region126is a scrap region.

Directing or localizing the pulsed laser beam112into the coated substrate120generates an induced absorption (e.g., MPA) within the coating layer121, the transparent workpiece122, or both (depending on whether the pulsed laser beam focal line113extends into the coating layer121, the transparent workpiece122, or both) deposits enough energy to break chemical bonds in the coating layer121and/or the transparent workpiece122at spaced locations along the contour line142to form the defects172. According to one or more embodiments, the pulsed laser beam112may be translated across the coated substrate120by motion of the coated substrate120(e.g., motion of a translation stage190coupled to the coated substrate120), motion of the pulsed laser beam112(e.g., motion of the pulsed laser beam focal line113), or motion of both the coated substrate120and the pulsed laser beam focal line113. By translating at least one of the pulsed laser beam focal line113relative to the coated substrate120, the plurality of defects172may be formed in the coated substrate120.

In some embodiments, the defects172may generally be spaced apart from one another by a distance along the contour170of from 0.1 μm to 500 μm, such as, 1 μm to 200 μm, 2 μm to 100 μm, or 5 μm to 20 μm, 0.1 μm to 50 μm, 5 μm to 15 μm, 5 μm to 12 μm, 7 μm to 15 μm, 8 μm to 15 μm, or 8 μm to 12 μm, such as 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, such as 100 μm, 75 μm, 50 μm, 40 μm, 30 μm, 25 μm, 10 μm, 5 μm, or any range having any two of these values as endpoints, or any open-ended range having any of these values as a lower bound. While not intending to be limited by theory, increasing the spacing distance between adjacent defects172may increase the processing speed (i.e., reducing processing time) and decreasing the spacing distance between adjacent defects172may reduce the break resistance of the contour170of defects172. Further, the translation of the coated substrate120relative to the pulsed laser beam112may be performed by moving the coated substrate120and/or the pulsed beam source110using one or more translation stages190.

Referring now toFIGS.1A-3, when the defects172of the one or more contours170are formed with pulse bursts50having at least two sub-pulses51, the force necessary to separate the coated substrate120along contour170(i.e. the break resistance) is reduced compared to the break resistance of a contour170of the same shape with the same spacing between adjacent defects172in an identical coated substrate120that is formed using a single pulse laser having the same energy as the combined energies of the sub-pulses of the pulse burst50. A pulse burst (such as pulse burst50) is a short and fast grouping of sub-pulses (i.e., a tight cluster of sub-pulses, such as sub-pulses51) that are emitted by the laser and interact with the material (i.e. MPA in the material of the coating layer121and/or the transparent workpiece122). The use of pulse bursts50(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 coated substrate120along the contour170, thereby minimizing crack formation away from contour170in the separated sections of the coated substrate120.

Referring still toFIGS.1A-3, in some embodiments, pulses produced by the pulsed beam source110are produced in pulse bursts50of two sub-pulses51or more per pulse burst50, such as from 2 to 30 sub-pulses51per pulse burst50or from 5 to 20 sub-pulses51per pulse burst50. Furthermore, the energy required to modify the coating layer121and/or the transparent workpiece122is the pulse energy, which may be described in terms of pulse burst energy (i.e., the energy contained within a pulse burst50where each pulse burst50contains a series of sub-pulses51; that is, the pulse burst energy is the combined energy of all sub-pulses within the pulse burst). The pulse energy (for example, pulse burst energy) may be from 25 μJ to 1000 μJ or 25 μJ to 750 μJ, such as from 100 μJ to 600 μJ, 50 μJ to 500 μJ, or from 50 μJ to 250 μJ, for example, 25 μJ, 50 μJ, 75 μJ, 100 μJ, 200 μJ, 250 μJ, 300 μJ, 400 μJ, 500 μJ, 600 μJ, 750 μJ, or any range having any two of these values as endpoints, or any open-ended range having any of these values as a lower bound.

Referring now toFIGS.4-5B, after forming the contour170of defects172along the contour line142in the coated substrate120using, for example, one of the embodiments accordingFIGS.1-3, the coated substrate120may be further acted upon in a subsequent separating step to induce separation of the transparent workpiece122and the coating layer121along the contour line142(i.e., along the contour170of defects172). The subsequent separating step includes directing an infrared laser beam212onto the coated substrate120to apply a thermal stress to the coating layer121and the transparent workpiece122. The applied thermal stress induces separation that extends between adjacent defects172in the coated substrate120along the contour line142. In the transparent workpiece122, this separating may include propagation of a crack along the contour line142.

Without being bound by theory, the infrared laser beam212is a controlled heat source that rapidly increases the temperature of the coating layer121at or near the contour line142, modifying material of the coating layer121along or near the contour line142to induce separation of the material of the coating layer121extending between adjacent defects172. In addition, this rapid heating may build compressive stress in the transparent workpiece122on or adjacent to the contour170. Since the area of the heated surface of transparent workpiece122is relatively small and shallow when compared to the overall surface area of the transparent workpiece122, the heated area cools relatively rapidly. The resultant temperature gradient induces tensile stress in the transparent workpiece122sufficient to propagate a crack along the contour170and through the depth of the transparent workpiece122, resulting in full separation of the transparent workpiece122along the contour170. Without being bound by theory, it is believed that the tensile stress may be caused by expansion of the glass (i.e., changed density) in portions of the workpiece with higher local temperature induced by infrared laser beam212. By inducing separation of both the coating layer121and the transparent workpiece122, the infrared laser beam212induces separation of the coated substrate120along the contour line142.

FIG.4depicts an optical assembly200comprising an infrared beam source210configured to generate the infrared laser beam212. The infrared beam source210, which may comprise a carbon dioxide laser (a “CO2laser”), a carbon monoxide laser (a “CO laser”), a solid-state laser, a laser diode, or combinations thereof. The infrared laser beam212comprises a wavelength that is readily absorbed by the transparent workpiece122, for example, a wavelength ranging from 1.2 μm to 13 μm, such as, a range of 4 μm to 12 μm. The power of the infrared laser beam212may be from about 10 W to about 4000 W, for example 100 W, 250 W, 500 W, 750 W, 1000 W, or the like. Further, the infrared beam source210may comprises a continuous wave laser or a pulsed laser. The optical assembly200further comprises a lens assembly230that includes a lens232for focusing the infrared laser beam212onto the coated substrate120. In operation, the infrared laser beam212propagates along an infrared beam pathway211and is oriented such that the infrared laser beam212may be directed onto the coated substrate120, for example, focused onto the first surface123of the coated substrate120using the lens232.

Referring now toFIG.5A, a cross section of the coated substrate120with a contour170of defects172during laser processing with the infrared laser beam212is schematically depicted. InFIG.5A, the infrared laser beam212is directed onto the coated substrate120using the optical assembly200ofFIG.4and comprises a Gaussian intensity profile at the coated substrate120. In addition, inFIG.5A, the infrared laser beam212is directed onto the coated substrate120in alignment with the contour170of defects172and thus in alignment with the contour line142. Because the infrared laser beam212comprises a Gaussian energy distribution, interaction of the infrared laser beam212with the coated substrate120forms a thermal affected area140having a Gaussian shape. The thermal affected area140corresponds to the portions of coated substrate120that receive sufficient energy from the Gaussian energy distribution of infrared laser beam212to produce thermal stresses sufficient to induce separation of coated substrate120along the contour170. That is, the thermal affected area140comprises a portion of the coating layer121and a portion of the transparent workpiece122into which thermal energy sufficient to induce separation of the contour170of defects172is applied. However, when the infrared laser beam212is directed onto the coated substrate120in alignment with the contour170of defects172, as shown inFIG.5A, the thermal affected area140is formed symmetrically in both the dummy region126and the primary region124, which damages the primary region124, for example, by causing some melt and ablation by melting or ablating the coating layer121on the primary region124. Indeed,FIG.5Bshows a top view of the coated substrate120ofFIG.5Awith a series of defects172separated using the laser processing technique shown inFIG.5A. As shown inFIG.5B, the thermal affected areas140extend into the primary region124, showing that unwanted damage is generated in the primary region124using the technique ofFIG.5A. As noted above, the primary region124is the region of the coated substrate120that is to be used as a resultant product and thus any damage to the primary region124is undesired. In contrast, the dummy region126is a scrap region.

Referring now toFIG.6, one potential solution to preventing damage to the primary region124is to offset the infrared laser beam212from the defects172and direct the infrared laser beam212predominately onto the dummy region126of the coated substrate120offset from the contour170of defects172and away from the primary region124. InFIG.6, the infrared laser beam212is directed onto the coated substrate120using the optical assembly200ofFIG.4and comprises a Gaussian intensity profile at the coated substrate120. Directing the infrared laser beam212onto the dummy region126away from the primary region124modifies the coating layer121on the dummy region126adjacent and along the contour170of defects172without ablation, melting, colorization, surface alteration and/or change in conductivity, of the coating layer121on the primary region124. That is, placement of infrared laser beam212away from contour170into dummy region126reduces the thermal energy from the Gaussian energy distribution of infrared laser beam212transferred to the portion of coating layer121in primary region124to a degree sufficient to avoid damage. However, because the infrared laser beam212comprises a Gaussian intensity profile at the coated substrate120, positioning the infrared laser beam212far enough offset from the contour170of defects172to prevent damage to the primary region124may fail to induce separation of the materials of the coated substrate120between adjacent defects172since it reduce the resultant temperature gradient in proximity to the defects172. For example, positioning the infrared laser beam212far enough offset from the contour170of defects172to prevent damage to the primary region124may fail to induce tensile stress in the transparent workpiece122sufficient to propagate a crack along the contour170and through the depth of the transparent workpiece122, since it reduces the resultant temperature gradient in proximity to the defects172. Thus, alternative techniques for separating the coated substrate120(i.e., separating the primary region124from the dummy region126) while minimizing or preventing damage to the primary region124are desired.

Referring still toFIG.6, one technique to separate the coated substrate120while minimizing damage to the primary region124is to translate the infrared laser beam212offset from the contour line142along multiple passes, where each individual pass does not apply enough thermal energy to damage the primary region124. While a single pass may not be sufficient to separate the contour170of defects172, particularly the portions of the contour170of defects172that extend into the transparent workpiece122, thermal energy accumulates in the transparent workpiece122upon multiple passes, inducing separation the coated substrate120along contour170of defects172without damaging primary region124. Further, each pass may follow the same path or offset paths, each located along the dummy region126.

Referring now toFIGS.7A-9B, additional techniques to generate sufficient thermal stress to induce separation of the series of defects172of the coated substrate120along the contour line142while limiting or preventing damage to the primary region124of the coated substrate120will now be described. In particular,FIGS.7A-7Ddepict a method of laser processing the coated substrate120along an oscillating pathway150using the infrared laser beam212ofFIG.4having a Gaussian intensity profile,FIGS.8A-8Cdepict methods of laser processing the coated substrate120using an infrared laser beam212′ having a modified energy distribution, andFIGS.9A and9Bdepict a method of laser processing the coated substrate120using an infrared laser beam212″ formed into an annulus and directed onto the first surface123of the coated substrate120offset from a focal plane204of a final focusing element. Each of these techniques induce separation of the contour170of defects172in the coated substrate120in a single pass while limiting or preventing damage to the primary region124of the coated substrate120. Indeed, the techniques described herein reduce tact time, reduce debris generated during the process, and reduce the complexity of the optical system. Furthermore, while these techniques are primarily described herein with respect to the coated substrate120comprising the transparent workpiece122and the coating layer121, it should be understood that these techniques are also applicable to the separation of single substrates, such as uncoated transparent workpieces, which may benefit from the decrease in chipping and heat cracks and thus a higher release speed.

Referring now toFIGS.7A-7C, a schematic top view of the coated substrate120comprising a plurality of defects172positioned along the contour line142undergoing a separating step using the infrared laser beam212is depicted. In the method depicted inFIGS.7A-7C, the infrared laser beam212follows the oscillating pathway150. In particular, at least one of the coated substrate120and the infrared laser beam212are translated relative to each other such that an infrared beam spot214traces the oscillating pathway150. The infrared beam spot214is projected by the infrared laser beam212on the first surface123of the coated substrate120. The oscillating pathway150is disposed on the dummy region126such that infrared laser beam212generates minimal to no damage on the primary region124. Similar to the embodiment ofFIG.6, above, the infrared laser beam212comprises a Gaussian energy distribution; however, the oscillating pathway150facilitates the application of enough thermal energy to the dummy region126of the coated substrate120to induce separation of the coated substrate120along the contour line142while avoiding damage to primary region124. Traversal of infrared laser beam212along the oscillating pathway150provides a mechanism to control the amount of thermal energy transferred to primary region124. As infrared laser beam212moves closer to contour line142, more thermal energy is transferred to the vicinity of defects172and thermal energy sufficient to induce separation of transparent workpiece122is available. To prevent damage to the coating layer121in primary region124, the motion of infrared laser beam212is reversed and moved away from contour line142to prevent excess transfer of thermal energy to primary region124. By controlling the power of infrared laser beam212, the speed of traversal of infrared laser beam212along oscillating pathway150and the proximity of closest approach of infrared laser beam212to contour line142, as well as the number of times the infrared laser beam212reaches the distance of closest approach to the contour line142, transfer of thermal energy is controlled and separation of primary region124from dummy region126without damage to the coating layer121in primary region124is achievable.

As depicted inFIG.7A-7C, the oscillating pathway150follows an offset line144in a translation direction while oscillating between an inner track line146and an outer track line148. In the embodiments depicted inFIGS.7A-7C, each oscillation extends from one of the inner track line146or the outer track line148to the other. However, it should be understood that, in some embodiments, the oscillating pathway150may oscillate between the inner track line146and the outer track line148without reaching the inner track line146, the outer track line148, or both, during some or all of the oscillations. Each of the offset line144, the inner track line146, and the outer track line148are disposed on the dummy region126of the coated substrate120. In particular, each of the offset line144, the inner track line146and the outer track line148are parallel pathways on the dummy region126of the coated substrate120and are each parallel to the contour line142. For example, in the embodiment depicted inFIG.7A, the contour line142is linear along the Y axis and the transverse axis is the X axis. However, it should be understood that the contour line142and the offset line144may be curved or otherwise non-linear and thus the transverse axis may change at points along the offset line144to retain orthogonality with the offset line144.

The offset line144may be spaced a distance of 0.2 mm to 3 mm from the contour line142, such as from 0.5 mm to 2 mm from the contour line142, for example, the offset line144may be spaced from the contour line142by a distance of 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm 1 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, 2 mm, 2.25 mm, 2.5 mm, 2.75 mm, 3 mm, or any range having any two of these values as endpoints. The inner track line146may be spaced a distance of 0.25 mm to 2 mm from the contour line142, such as a distance of from 0.5 mm to 1.5 mm from the contour line142, for example, the inner track line146may be spaced from the contour line142by a distance of 0.25 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, 1.75 mm, 2 mm, or any range having any two of these values as endpoints. The outer track line148may be spaced a distance of 0.75 mm to 4 mm from the contour line142, such as a distance of from 1.5 mm to 2.5 mm from the contour line142, for example, the outer track line148may be spaced from the contour line142by a distance of 0.75 mm, 1 mm, 1.25 mm, 1.5 mm, 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, 2 mm, 2.1 mm, 2.2 mm, 2.3 mm, 2.4 mm, 2.5 mm, 2.75 mm, 3 mm, 3.25 mm, 3.5 mm, 3.75 mm, 4 mm, or any range having any two of these values as endpoints. Furthermore, the offset line144may be equally spaced from both the inner track line146and the outer track line148. In addition, the spacing distance between the offset line144and each of the inner track line146and the outer track line148may be the same as the distance between the inner track line146and the contour line142.

Furthermore, the spacing distances between the contour line142, the offset line144, the inner track line146, and the outer track line148may be a function of the 1/e2beam diameter of the infrared beam spot214. For example, the spacing distances between the contour line142, the offset line144, the inner track line146, and the outer track line148may be at least half the 1/e2beam diameter of the infrared beam spot214. The 1/e2beam diameter of the infrared beam spot214is in a range of from 350 μm to 2 mm, such as from 500 μm to 1 mm, or from 600 μm to 900 μm, for example, 500 μm, 550 μm, 600 μm, 650 μm, 700 μm, 750 μm, 800 μm, 850 μm, 900 μm, 950 μm, 1 mm, 1.5 mm, 2 mm, or any range having any two of these values as endpoints. In operation, a 1/e2beam diameter of the infrared beam spot214in the above ranges may facilitate high precision application of thermal energy to the coated substrate120and allows the infrared beam spot214to oscillate along the oscillating pathway150without impinging the primary region124.

In operation, as the infrared laser beam212is translated such that the infrared beam spot214traces the oscillating pathway150, the infrared laser beam212applies thermal energy to the coated substrate120to induce separation of the series of defects172of the coated substrate120along the contour line142while limiting or preventing damage to the primary region124of the coated substrate120. For example, as depicted inFIG.4, a scanner192is coupled to the infrared beam source210and is configured to translate the infrared beam source210and infrared laser beam212such that the infrared beam spot214traces the oscillating pathway150. In particular, the scanner192may both oscillate the infrared laser beam212while linearly translating the infrared laser beam212. The speed of motion of infrared laser beam212is preferably greater than or equal to 10 mm/s, such as between 10 mm/s and 2000 mm/s, or between 20 mm/s and 1500 mm/s, or between 30 mm/s and 1200 mm/s, or between 40 mm/s and 1000 mm/s, or between 50 mm/s and 800 mm/s, or between 60 mm/s and 500 mm/s.

Furthermore, each ofFIGS.7A-7Cdepict different embodiments of the oscillating pathway150. For example,FIG.7Adepicts an embodiment of the oscillating pathway150that is a pendulum pathway155,FIG.7Bdepicts an embodiment of the oscillating pathway150that is a wobbling pathway153, andFIG.7Cdepicts an embodiment of the oscillating pathway150that is a sawtooth pathway154.

Referring now toFIG.7A, in some embodiments the oscillating pathway150is a pendulum pathway155that follows the offset line144in a translation direction while oscillating along a transverse axis between an inner track line146and an outer track line148, where the transverse axis is orthogonal the offset line144. For example, the pendulum pathway155has a plurality of rounded portions151and a plurality of straight portions152. The plurality of rounded portions151each reach either the inner track line146or the outer track line148. Further, the straight portions152each extend between two rounded portions151and traverse the offset line144. Indeed, as depicted inFIG.7A, the straight portions152extend along the transverse axis, which is orthogonal to the offset line144. In some embodiments, the plurality of straight portions152each comprise a length of from 0.25 mm to 2 mm, such as from 0.5 mm to 1.5 mm, for example, 0.25 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, 1.75 mm, 2 mm, or any range having any two of these values as endpoints. In some embodiments, the plurality of rounded portions151each comprise a radius of curvature of from 0.25 mm to 2 mm, such as from 0.5 mm to 1.5 mm, for example, 0.25 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, 1.75 mm, 2 mm, or any range having any two of these values as endpoints.

Referring now toFIG.7B, in some embodiments the oscillating pathway150is a wobbling pathway153that rotationally oscillates between the inner track line146and the outer track line148while following the offset line144in the translation direction. In operation, the wobbling pathway153may be achieved using the scanner192. In particular, the scanner192may rotate the infrared laser beam212(e.g., rotate the infrared beam source210) in a rounded pattern around a central axis of the scanner192while linearly translating the infrared laser beam212along the translation direction to follow the offset line144. In some embodiments, the rounded pattern is a circle or ellipse and in some embodiments, the rounded pattern may be a Lissajou pattern. Referring now toFIG.7C, in some embodiments, the oscillating pathway150is a sawtooth pathway154having a plurality of straight portions connected angular turns at or between the inner track line146and the outer track line148while following the offset line144in the translation direction.

Referring now toFIGS.7A-7D, by irradiating the dummy region126of the coated substrate120with the infrared laser beam212along the oscillating pathway150ofFIGS.7A-7C, the accumulated fluence applied by the infrared laser beam212onto the dummy region126of the coated substrate120follows a top hat accumulated fluence distribution in which 20% or less of the total energy applied to the dummy region126is applied to portions of the dummy region126not located between the inner track line146and the outer track line148and that portions of the dummy region126between the inner track line146and the outer track line148are impinged by an accumulated fluence of greater than 80% of the maximum accumulated fluence applied any portion of the dummy region126. This top hat accumulated fluence distribution is graphically depicted inFIG.7D, in which line42of graph40depicts the relative accumulated fluence as a function of position along a portion of the dummy region126. The relative accumulated fluence at the peak of the accumulated fluence distribution is normalized to 1 and the balance of the accumulated fluence distribution is scaled proportionally.

Referring now toFIGS.8A-8C, another method of laser processing the coated substrate120using an infrared laser beam212′ having a modified energy distribution is schematically depicted.FIG.8schematically depicts an optical assembly200′ and lens assembly230′, which includes the optical assembly200ofFIG.4with the addition of a diffractive optical element238for modifying the intensity profile of the infrared laser beam212. In particular, the infrared laser beam212output by the infrared beam source210comprises a Gaussian energy distribution and after traversing the diffractive optical element238and reaching the coated substrate120, the infrared laser beam212(now infrared laser beam212′) comprises a modified, top hat energy distribution. Thus, an infrared beam spot214′ (FIG.8B) projected by the infrared laser beam212′ onto the first surface123of the coated substrate120comprises a top hat energy distribution. As used herein, a “top hat energy distribution” refers to an energy distribution in which 20% of the total energy of infrared beam spot (e.g., infrared beam spot214′ ofFIG.8B) has a fluence less than 80% of the maximum fluence. In the illustrative example ofFIG.8B, 80% or more of the total energy of the infrared beam spot214′ is within an inner region (e.g., inner region215) bounded at 80% of a maximum fluence of the infrared beam spot214′.

Referring now toFIG.8B, the infrared beam spot214′ formed using the optical assembly200′ ofFIG.8Ais schematically depicted in association with a graph60, which includes line62showing the relative fluence as a function of the relative radial position within the infrared beam spot214′. The relative fluence at the peak of the fluence distribution is normalized to 1 and the balance of the fluence distribution is scaled proportionally. As shown inFIG.8B, the infrared beam spot214′ includes an outer perimeter218, an inner perimeter216, and an inner region215bounded by the inner perimeter216, which is defined by a particular relative fluence, such as 80% of the maximum fluence of the infrared beam spot214′. In some embodiments, the infrared beam spot214′ comprises an energy distribution in which 10% or less of the total energy of the infrared beam spot214′ has less than 80% of the maximum fluence. In some embodiments, the infrared beam spot214′ comprises an energy distribution in which less than 5% of the total energy of the infrared beam spot214′ has a fluence less than 80% of the maximum fluence. In some embodiments, the infrared beam spot214′ comprises an energy distribution in which less than 5% of the total energy of the infrared beam spot214′ has a fluence less than 90% of the maximum fluence.

Referring now toFIG.8C, a cross section of the coated substrate120during laser processing with the infrared laser beam212′ ofFIG.8Ais schematically depicted. Because the infrared beam spot214′ comprises a top hat energy distribution, the resultant thermal affected area140formed in the coated substrate120comprises a substantially rectilinear shape. The substantially rectilinear shape means that the decrease in fluence from a relative fluence of 80% of the maximum fluence to 10%, 5%, or even 1% of the maximum fluence is steep so that, relative to a Gaussian distribution centered at the same position, a significantly reduced overlap of the wings of the distribution with the primary region124occurs. As a result, the region of high fluence of the top hat energy distribution can be placed closer to defects172to promote thermal separation without inducing damage to the coating layer121in primary region124. In operation, the infrared laser beam212′ projects the infrared beam spot214′ onto the first surface123of the coated substrate120in the dummy region126of the coated substrate120. In particular, the infrared beam spot214′ is projected onto the offset line144such that the infrared beam spot214′ is offset from the contour line142. For example, the infrared beam spot214′ may be centered onto the offset line144such that the offset line144bisects the infrared beam spot214′. In some embodiments, the inner perimeter216of the infrared beam spot214′ may be disposed at the inner track line146and the outer track line148or between the inner track line146and the outer track line148.

Forming the thermal affected area140using the infrared laser beam212′ ofFIG.8A-8Cfurther comprises translating at least one of the coated substrate120and the infrared laser beam212′ relative to each other such that the infrared beam spot214′ follows the offset line144. Without intending to be limited by theory, the infrared laser beam212′ applies thermal energy to the coated substrate120to induce separation of the series of defects172of the coated substrate120along the contour line142while limiting or preventing damage to the primary region124of the coated substrate120. Indeed, because the infrared beam spot214′ comprises a modified energy distribution that sharply drops at a particular radial location (e.g., a top hat energy distribution), the infrared laser beam212′ applies thermal energy sufficient to damage the coated substrate120to the dummy region126and not to the primary region124. Furthermore, it should be understood that in some embodiments, the infrared beam spot214′ ofFIGS.8A-8Chaving a top hat energy distribution may be traversed along the oscillating pathway150ofFIGS.7A-7C.

Referring now toFIG.9A, an optical assembly200″ for laser processing with an infrared laser beam212″ formed into an annulus using an aspheric optical element235(such as an axicon236) is schematically depicted. The aspheric optical element235may comprise any of the embodiments of the aspheric optical element135described above with respect toFIGS.1-3. Indeed, the aspheric optical element235may modify the infrared laser beam212output by the infrared beam source210into a phase modified infrared laser beam212″ having an annular shape. Without intending to be limited by theory, the infrared laser beam212″ comprises the phase characteristics that form the pulsed laser beam112ofFIGS.1-3into a quasi-non-diffracting beam. However, in the embodiment depicted inFIG.9A, the infrared laser beam212″ impinges the coated substrate120while having an annular shape (e.g., upstream a focal plane of a final focusing element).

Further, as shown inFIG.9A, the optical assembly200″ comprises a lens assembly230″, which may further comprise one or more lenses231,232, which may comprise the same lenses as lenses131,132of the lens assembly130ofFIG.2. Further, in the embodiment of the optical assembly200″ depicted inFIG.9A, the lens232operates as the final focusing element, that is, the final focusing element the infrared laser beam212″ traverses before impinging the coated substrate120. While lens232is depicted as the final focusing element, it should be understood that the aspheric optical element235may alternatively be positioned as the final focusing element. The final focusing element comprises a focal length that extends from the final focusing element to a focal plane204. As shown inFIG.9A, the final focusing element (i.e., the second lens232) and the first surface123of the coated substrate are positioned relative to one another such that the focal plane204is offset from the first surface123of the coated substrate120may an offset length OL.

Referring now toFIG.9B, a caustic217of the infrared laser beam212″ downstream the final focusing element (i.e., the second lens232). As used herein, a “caustic” refers to an envelope of light of a laser beam refracted by an optical component and thereafter directed onto and/or a substrate. For example, the caustic may comprise the envelope of light of a laser beam extending from the most downstream optical component of an optical system onto and/or into a substrate. As shown by its caustic217, the annular shaped infrared laser beam212″ impinged the coated substrate120at locations at or between the inner track line146and the outer track line148. Indeed, in some embodiments, the offset line144bisects the caustic217of the infrared laser beam212″. Furthermore, it should be understood that in some embodiments, the infrared laser beam ofFIGS.9A and9Bhaving a annular shape may be traversed along the oscillating pathway150ofFIGS.7A-7C.

Referring now toFIG.9C, because the infrared laser beam212″ impinges the first surface123offset from the focal plane204, the infrared laser beam212″ projects an infrared beam spot214″ onto the first surface of the coated substrate that comprises an annular shape.FIG.9Cschematically depicts a top view of the coated substrate120ofFIG.9Aduring laser processing using the infrared laser beam212″ ofFIG.9A. In operation, laser processing the coated substrate120using the infrared laser beam212″ comprises translating at least one of the coated substrate120and the infrared laser beam212″ relative to each other such that the infrared beam spot214″ follows the offset line144. For example, the offset line144may bisect the infrared beam spot214″. Further, the infrared beam spot214″ may projected onto the dummy region126without impinging the primary region124.

Further, in some embodiments, the infrared laser beam212″ comprises a pulsed infrared laser beam (i.e., in some embodiments, the infrared beam source210may be a pulsed infrared beam source). In embodiments in which the infrared laser beam212″ is pulsed, when translating at least one of the coated substrate120and the infrared laser beam212″ relative to each other, the infrared laser beam212″ impinges the first surface of the coating substrate at locations (i.e., impingement locations141) along the offset line spaced apart from one another by a distance of from ¼ a diameter of the infrared beam spot214″ to ½ the diameter of the infrared beam spot214″, for example, ⅓ the diameter of the infrared beam spot214″. This spacing distance between impingement locations141may be altered by altering the pulse rate of the infrared laser beam212″, the translation rate of the infrared laser beam212″ and the coated substrate120relative to one another, or both. Without intending to be limited by theory, a ¼ to ½ overlap between adjacent impingement locations141causes more continuous damage along the offset line144than fully spacing the impingement locations141apart. Similar to the embodiments, of7A-7D and the embodiments of8A-8C, the infrared laser beam212″ applies thermal energy to the coated substrate120thereby inducing crack propagation within the coated substrate120along the plurality of defects172, thereby separating the coated substrate120along the contour line142.

Indeed, by irradiating the dummy region126of the coated substrate120with the annulus of the infrared laser beam212″ along the offset line144, as depicted inFIGS.9A-9C, the accumulated fluence applied by the infrared laser beam212″ onto the dummy region126of the coated substrate120follows a top hat accumulated fluence distribution in which 20% or less of the total energy applied to the dummy region126is applied to portions of the dummy region126not located between the inner track line146and the outer track line148and that portions of the dummy region126between the inner track line146and the outer track line148are impinged by an accumulated fluence of greater than 80% of the maximum accumulated fluence applied any portion of the dummy region126. This top hat accumulated fluence distribution is graphically depicted inFIG.9D, in which line82of graph80depicts the relative accumulated fluence as a function of position along a portion of the dummy region126. The relative accumulated fluence at the peak of the accumulated fluence distribution is normalized to 1 and the balance of the accumulated fluence distribution is scaled proportionally.

In view of the foregoing description, it should be understood that a coated substrate comprising a transparent workpiece and a coating layer may be laser separated while limiting or preventing damage to a primary region of the coated substrate. The methods described herein include using a pulsed laser beam to form a series of defects in the transparent workpiece and an infrared laser beam to separate the transparent workpiece and the coating layer along the series of defects, which are formed along a boundary between the primary region and a dummy region. Methods described herein include translating an infrared laser beam along an oscillating pathway on the dummy region to separate the coated substrate, modifying the energy distribution of an infrared laser beam into a top hat energy distribution and directing this modified laser beam onto the dummy region to separate the coated substrate, and forming the infrared laser beam into an annular shape and directing this annular infrared laser beam onto the dummy region to separate the coated substrate. As described herein, these methods direct thermal energy onto the dummy region of the coated substrate using techniques sufficient to both induce crack propagation of the defects disposed in the coated substrate along the boundary between the primary region and the dummy region in a single process step.

As used herein, the term “about” means that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but may be approximate and/or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art. When the term “about” is used in describing a value or an end-point of a range, the specific value or end-point referred to is included. Whether or not a numerical value or end-point of a range in the specification recites “about,” two embodiments are described: one modified by “about,” and one not modified by “about.” It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint.

Directional terms as used herein—for example up, down, right, left, front, back, top, bottom—are made only with reference to the figures as drawn and are not intended to imply ab solute orientation.

Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order, nor that with any apparatus specific orientations be required. Accordingly, where a method claim does not actually recite an order to be followed by its steps, or that any apparatus claim does not actually recite an order or orientation to individual components, or it is not otherwise specifically stated in the claims or description that the steps are to be limited to a specific order, or that a specific order or orientation to components of an apparatus is not recited, it is in no way intended that an order or orientation be inferred, in any respect. This holds for any possible non-express basis for interpretation, including: matters of logic with respect to arrangement of steps, operational flow, order of components, or orientation of components; plain meaning derived from grammatical organization or punctuation, and; the number or type of embodiments described in the specification.

As used herein, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a” component includes aspects having two or more such components, unless the context clearly indicates otherwise.

It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Thus, it is intended that the specification cover the modifications and variations of the various embodiments described herein provided such modification and variations come within the scope of the appended claims and their equivalents.