Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/36—Removing material
  • B23K26/40—Removing material taking account of the properties of the material involved
  • B23K26/402—Removing material taking account of the properties of the material involved involving non-metallic material, e.g. isolators
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
  • B23K26/04—Automatically aligning, aiming or focusing the laser beam, e.g. using the back-scattered light
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
  • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
  • B23K26/062—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam
  • B23K26/0622—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam by shaping pulses
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
  • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
  • B23K26/062—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam
  • B23K26/0622—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam by shaping pulses
  • B23K26/0624—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam by shaping pulses using ultrashort pulses, i.e. pulses of 1 ns or less
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/36—Removing material
  • B23K26/38—Removing material by boring or cutting
  • B23K26/382—Removing material by boring or cutting by boring
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/36—Removing material
  • B23K26/40—Removing material taking account of the properties of the material involved
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K2103/00—Materials to be soldered, welded or cut
  • B23K2103/50—Inorganic materials other than metals or composite materials

Definitions

• Embodiments of the present invention relate generally to processing of substrates and, more particularly, to laser-drilling vias such as through-vias in a substrate.
• interposers As compared to presently used interposer materials such as fiber reinforced polymer or silicon, glass has a number of advantageous properties.
• Glass can be formed thin and smooth in large sheets without the need for polishing, it has higher stiffness and greater dimensional stability than organic alternatives, it is a much better electrical insulator than silicon, it has better dimensional (thermal and rigidity) stability than organic options, and it can be tailored to different coefficients of thermal expansion to control stack warp in integrated circuits.
• a variety of hole formation methods can be used to create holes in glass, such as hot pressing, lithography of photo-machinable glass, electric-discharge drilling, powder blasting, and a wide variety of laser drilling processes.
• the challenge is generally around forming a hole of sufficient quality (low cracking, appropriate size or roundness) at a high enough via-formation rate (holes/sec) which ultimately affects cost.
• hot pressing of glass has difficulty forming holes of small enough dimensions (less than or equal to about 100 microns), electrical discharge drilling can be difficult to do with a tight hole pitch (i.e., a hole to hole distance of less than about 50 microns), laser drilling of holes using beam trepanning can be slow (e.g., about 1 hole/sec), and excimer laser processing and
• photomachinable glass can have large initial capital costs.
• Conventional laser drilling processes have been developed that make particularly high quality holes.
• a UV nanosecond laser can be used in a percussion drilling process to make pilot holes (each about 10 microns in diameter) in a glass part using multiple (e.g., hundreds) of laser pulses per hole.
• the part is then etched with acid to enlarge the pilot holes and achieve the target dimensions.
• the etched holes are subsequently metalized, redistribution layers are added to fan out electrical signals, and the parts are diced into smaller pieces to create functional interposers.
• Another conventional laser drilling process involves a single-shot laser process in which a single laser pulse having a Bessel beam profile is used to modify the glass part wherever a via is desired, and the part is then etched with acid form the vias. While this process can be used to produce up to 5000 vias per second (200 ps per via), the process still requires etching which, as discussed above, can make it difficult to ensure uniform thickness of the glass parts in the finished product. Further, laser pulses having Bessel beam profiles are difficult to rapidly deflect using conventional beam-steering technologies (e.g., galvanometer mirrors, etc.). Accordingly, the time required to form a relatively sparse pattern of vias is typically much slower than 5000 vias per second.
• FIG. 1 illustrates an exemplary laser processing system for implementing a laser drilling process.
• FIGS. 2 and 3 are photographs illustrating a through-via drilled through an exemplary glass substrate using a laser drilling process according to one embodiment.
• FIG. 4 is a graph illustrating the results of experiments in which a glass substrate was subjected to laser drilling processes according to some embodiments.
• FIGS. 5 to 8 are photographs of cross-sectioned glass substrates that were processed to form though-vias according to embodiments discussed herein.
• One embodiment can be characterized as an article that includes a substrate having a plurality of laser-drilled through-holes continuously extending from a first surface of the substrate to a second surface of the substrate, opposite the first surface of the substrate, wherein: the plurality of laser-drilled through-holes have a diameter of lOpm or greater; a spacing between adjacent etched through-holes of 30pm or greater; the plurality of laser-drilled through- holes comprise an opening in the first surface, an opening in the second surface, and a waist located between the opening in the first surface and the opening in the second surface; a diameter of the waist is at least 75% of the diameter of the opening in the first surface or the opening in the second surface; and a difference between a diameter of the opening in the first surface and a diameter of the opening in the second surface is 3.5pm or less.
• Another embodiment can be characterized as a method for forming a through-via in a substrate, wherein the method includes: providing a substrate having a first surface and a second surface opposite the first surface; and directing, during a drilling period less having a duration less than lOOps, a focused beam of laser pulses into the substrate at a location through the first surface of the substrate and, subsequently, through the second surface of the substrate, wherein the focused beam of laser pulses has a wavelength to which the substrate is at least substantially transparent, wherein an optical intensity of the focused beam of laser pulses at the substrate is less than an optical breakdown intensity of the substrate, wherein the focused beam of laser pulses has a Gaussian energy distribution, wherein the focused beam of laser pulses has a pulse repetition rate greater than 5 MHz, and wherein laser pulses within the focused beam of laser pulses have a pulse width greater than 200 fs.
• Another embodiment can be characterized as a method for forming a through-via in a substrate, wherein the method includes: providing a substrate having a thickness in a range from 30 pm to 150 pm and having a first surface and a second surface opposite the first surface; and directing a focused beam of laser pulses into the substrate through the first surface of the substrate and, subsequently, through the second surface of the substrate, wherein the focused beam of laser pulses has a wavelength to which the substrate is at least substantially transparent; wherein an optical intensity of the focused beam of laser pulses at the substrate is less than an optical breakdown intensity of the substrate; wherein the focused beam of laser pulses has a Gaussian energy distribution; wherein the focused beam of laser pulses has a pulse repetition rate, a peak optical intensity at the substrate and an average power at the substrate driving a cumulative heating effect; and wherein laser pulses within the focused beam of laser pulses have a pulse width, wherein the peak optical intensity, pulse repetition rate, average power and pulse width are selected such that the through-via is formed in less than 40
• Yet another embodiment can be characterized as a method for forming a through-via in a substrate, wherein the method includes: providing a substrate having a first surface and a second surface opposite the first surface; and directing a focused beam of laser pulses into the substrate through the first surface of the substrate and, subsequently, through the second surface of the substrate, wherein the focused beam of laser pulses has a wavelength to which the substrate is at least substantially transparent and wherein a beam waist of the focused beam of laser pulses is closer to the second surface of the substrate than to the first surface of the substrate, and wherein the focused beam of laser pulses is characterized by a pulse repetition rate, a peak optical intensity at the substrate and an average power at the substrate sufficient to: melt a region of the substrate near the second surface, thereby creating a melt zone within the substrate; propagate the melt zone toward the first surface; and vaporize or boil material of the substrate and located within the melt zone.
• a range of values when recited, includes both the upper and lower limits of the range, as well as any sub-ranges therebetween.
• terms such as“first,” “second,” etc. are only used to distinguish one element from another. For example, one node could be termed a“first node” and similarly, another node could be termed a“second node”, or vice versa.
• the term“about,”“thereabout,”“approximately,” etc. 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.
• Spatially relative terms such as“below,”“beneath,”“lower,” “above,” and“upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element or feature, as illustrated in the FIGS. It should be recognized that the spatially relative terms are intended to encompass different orientations in addition to the orientation depicted in the FIGS.
• FIGS For example, if an object in the FIGS is turned over, elements described as“below” or“beneath” other elements or features would then be oriented“above” the other elements or features.
• the exemplary term “below” can encompass both an orientation of above and below.
• An object may be otherwise oriented (e.g., rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may be interpreted accordingly.
• a laser drilling process for drilling a through-via in a substrate includes directing a beam laser pulses into the substrate such that the beam of laser pulses is transmitted into the substrate through a first surface of the substrate and propagates within the substrate towards a second surface of the substrate that is opposite the first surface.
• the beam of laser pulses is focused to produce a beam waist that is located at or near the second surface (i.e., inside or outside the substrate).
• the substrate is provided as an article of glass (e.g., borosilicate glass, aluminoborosilicate glass, aluminosilicate glass, alkali-lead silicate glass, alkali alkaline earth silicate glass, germanium oxide glass, fused silica, etc.), synthetic quartz, a glass ceramic (e.g., lithium-aluminum-silicate), a ceramic, sapphire, a semiconductor material (e.g., Si, SiGe, GaAs, GaN, SiC, etc.), or the like or any combination thereof.
• borosilicate glass e.g., borosilicate glass, aluminoborosilicate glass, aluminosilicate glass, alkali-lead silicate glass, alkali alkaline earth silicate glass, germanium oxide glass, fused silica, etc.
• synthetic quartz e.g., borosilicate glass, aluminoborosilicate glass, alum
• the article may thus be provided as a glass interposer, a silicon interposer, a semiconductor wafer, a semiconductor die, a substrate (e.g., for a display screen, for wafer level packaging or other semiconductor packaging, for display panel level packaging, for a MEMS or sensor device, etc.) or the like or any combination thereof.
• the substrate is provided as an article (e.g., having a thickness in a range from 30 pm (or thereabout) to 150 pm (or thereabout)).
• the thickness of the substrate can be less than 30 pm or greater than 150 pm.
• the beam of laser pulses directed to the substrate has a wavelength to which substrate is substantially transparent.
• the substrate can be considered
• the beam of laser pulses may have a wavelength in the ultraviolet, visible or infrared regions of the
• the beam of laser pulses may have a wavelength in a range from 300 nm (or thereabout) to 1064 nm (or thereabout).
• the laser drilling process can be any laser drilling process.
• the beam of laser pulses ultimately directed to the substrate during the laser drilling process has a Gaussian energy profile.
• a beam of laser pulses having a Gaussian energy profile allows the beam of laser pulses to be rapidly deflected using conventional beam-steering technologies (e.g., galvanometer mirrors, fast-steering mirrors, rotating polygon mirrors, acousto-optical deflectors, electro-optical deflectors, etc.) to form through-vias in the substrate.
• conventional beam-steering technologies e.g., galvanometer mirrors, fast-steering mirrors, rotating polygon mirrors, acousto-optical deflectors, electro-optical deflectors, etc.
• percussion drilling can be employed (e.g., to form a via having a diameter in a range from 1 pm to 100 pm, e.g., 10 pm, 20 pm, 30 pm, 50 pm, etc.) or the beam can be deflected (e.g., as described above) to form vias having a similar or larger diameters. Since the beam can be rapidly deflected, it is also possible to form even a relatively sparse pattern of through-vias at a higher throughput than with conventional laser drilling processes. Lastly, the laser drilling process described herein does not require an acid etch process to obtain through-vias with acceptable diameters or surface morphologies.
• the laser drilling process can also be characterized by a parameter referred to herein as a “z range.”
• the z range is the range of distances between the second surface of the substrate and the beam waist of the beam of laser pulses that, during the laser drilling process is performed, produce a through- via in the substrate.
• the z range has been discovered by the inventors to be dependent upon at least some of the other aforementioned parameters of the laser drilling process. For example, at a given pulse wavelength, pulse width and pulse repetition rate, and above a threshold drilling period and average power at the substrate, the z range has been discovered to vary depending upon the drilling period and average power at the substrate during the laser drilling process.
• Identifying values for laser drilling process parameters (e.g., drilling period and average power at the substrate, for a given pulse wavelength, pulse width and pulse repetition rate) that yield a sufficiently large z range is significant because the substrate is typically not of perfectly uniform thickness (i.e., there may be thickness variability on the order of about 10 pm or more) and/or not perfectly flat when the laser drilling process is performed (i.e., there may be some waviness in the substrate, on the order of about 10 pm or more), and the thickness of one substrate may vary from the thickness of another substrate. Thus if the z range does not accommodate for variations in substrate thickness or flatness, then the laser drilling process will not reliably form through- vias.
• the substrate is typically not of perfectly uniform thickness (i.e., there may be thickness variability on the order of about 10 pm or more) and/or not perfectly flat when the laser drilling process is performed (i.e., there may be some waviness in the substrate, on the order of about 10 pm or more), and the thickness of one substrate may vary from the thickness
• the through- vias may be coated and/or filled with an electrically conductive material, or the like.
• through-vias may be formed in a substrate such as a glass interposer and coated and/or filled with an electrically conductive material (e.g., copper, aluminum, gold, silver, lead, tin, indium tin oxide, or the like or any combination or alloy thereof).
• the process used to metallize the interior of the through-vias can be, for example, electro-plating, electroless plating, physical vapor deposition, or other evaporative coating methods.
• the through-vias may also be coated with catalytic materials, such as platinum, palladium, titanium dioxide, or other materials that facilitate chemical reactions within the holes.
• the through-vias may be coated with other chemical functionalization, so as to change surface wetting properties or allow attachment of biomolecules, and used for biochemical analysis.
• chemical functionalization could be silanization of the glass surface of the through-vias, and/or additional attachment of specific proteins, antibodies, or other biologically specific molecules, designed to promote attachment of biomolecules for desired applications.
• the beam of laser pulses can be characterized by parameters such as pulse repetition rate, pulse energy and pulse width.
• the pulse energy and pulse width are selected such that, when the beam of laser pulses is focused, the beam waist is spaced apart from the second surface of the substrate by the offset distance, each laser pulse in the focused beam of laser pulses irradiates a region of the substrate (i.e., corresponding to the spot size of the laser pulse at the region of the substrate) at a peak optical intensity that is less than an optical breakdown intensity of the substrate.
• the pulse repetition rate of the beam of laser pulses is selected (e.g., in consideration of the peak optical intensity at which the region of the substrate is irradiated by each laser pulse) to be sufficiently high such that the irradiated region of the substrate can accumulate heat over an initial period of time (e.g., also referred to herein as an “incubation period”).
• the heating of the substrate during the incubation period initiates mainly due to multi-photon absorption by the substrate material.
• Absorption of laser pulses during the incubation period may also occur at point defects in the substrate that could create the defect states residing between the conduction band and the valence band for optical absorption.
• the irradiated region of the substrate (e.g., which may be at or near the second surface of the substrate, at or near the first surface of the substrate, or a combination thereof) has accumulated a sufficient amount of heat to locally increase temperature of the substrate and reduce the band gap energy thereof, enabling a transition to a regime in which the irradiated region of the substrate can melt and, eventually, evaporate. It is suspected that the bandgap of the substrate material decreases as a result of thermal ionization, i.e. the gradual overlay of the bandgap at high temperatures by electronic and vibrational states of molecules.
• the region of the substrate that becomes melted during the laser-drilling process can be characterized as a“melt zone.”
• the significant increase in the absorptivity of the laser pulses at the edge or boundary or interface of the high-temperature region within the substrate quickly causes the melt zone to progressively grow toward the first surface (i.e., in a direction opposite to the propagation direction of the beam of laser pulses from the scan lens 110).
• the focused beam of laser pulses can remain at the irradiated region of the substrate for an additional period of time (e.g., also referred to herein as a“removal period”) immediately after the incubation period to heat, melt and evaporate the irradiated region of the substrate (i.e., through the entire thickness of the substrate) to form a through-via.
• the total period of time from the beginning of the incubation period to the end of the removal period is herein referred to as the“drilling period.”
• the beam of laser pulses can be generated and focused in any manner known in the art to produce a focused beam of laser pulses, wherein each laser pulse in the focused beam of laser pulses has a peak power and peak optical intensity at the substrate sufficient to heat (but not to ablate, crack, or otherwise damage) the substrate.
• the beam of laser pulses is further generated, in any manner known in the art, to produce laser pulses having the sufficient peak power at a pulse repetition rate sufficient to prevent the substrate from substantially cooling between laser pulses (e.g., to enable the substrate to accumulate heat during the incubation period, and continue to accumulate heat during the removal period, as discussed above).
• the peak power, peak optical intensity and pulse repetition rate of the focused beam of laser pulses should also be selected to prevent the substrate from accumulating heat too quickly, which can result in undesirable phenomena such as cracking in regions of the substrate that are not irradiated by the beam of laser pulses and ejection of molten material over an undesirably large area on the exterior of the substrate.
• the beam of laser pulses as generated, focused and delivered to the substrate to implement the laser drilling process described herein, can be characterized as having a pulse repetition rate of 30 MHz and a peak power at the substrate (e.g., as determined by pulse energy and pulse width, as is known in the art) of about 78 kW to irradiate the substrate at a peak optical intensity (e.g., as determined by peak power and spot size at the substrate, as is known in the art) of 1.27 ⁇ 10 11 W/cm 2 (or thereabout).
• a peak power at the substrate e.g., as determined by pulse energy and pulse width, as is known in the art
• peak optical intensity e.g., as determined by peak power and spot size at the substrate, as is known in the art
• the beam of laser pulses may have a pulse repetition rate greater than or less than 30 MHz, and that the peak power of the beam of laser pulses at the substrate can be maintained (e.g., by adjusting the pulse width or pulse energy of laser pulses within the beam of laser pulses) or otherwise adjusted as needed to compensate for change in pulse repetition rate.
• the peak optical intensity at the substrate can, optionally, be maintained (e.g., by adjusting the pulse width, pulse energy of laser pulses within the beam of laser pulses, or spot size at the second surface of the substrate) or otherwise adjusted as needed to compensate for change in pulse repetition rate.
• the pulse repetition rate, peak power, pulse width, or pulse energy of laser pulses within the beam of laser pulses may be constant or variable.
• lasers operative to generate a beam of laser pulses having sufficiently high pulse repetition frequencies and peak powers with which the laser drilling process can be implemented are QCW lasers capable of generating laser pulses having a pulse widths in a range from 200 fs (or thereabout) to 50 ps (or thereabout).
• the laser pulses can have a pulse width of 200fs, 400fs, 800fs, lps, 2 ps, 5 ps, 10 ps, 20 ps, 25 ps, 30 ps, 40 ps, 45 ps, 50 ps, etc., or any between any of these values.
• the pulse repetition rate of the beam of laser pulses can be in a range from 5 MHz (or thereabout) to 5 GHz (or thereabout), provided that the peak power of the beam of laser pulses and, optionally, the peak optical intensity at the substrate, are adjusted as needed to compensate for change in pulse repetition rate.
• the pulse repetition rate can be in a range from 5 MHz (or thereabout) to 500 MHz (or thereabout). In other embodiments, the pulse repetition rate can be in a range from 25 MHz (or thereabout) to 40 MHz (or thereabout), in a range from 150 MHz (or thereabout) to 180 MHz (or thereabout).
• the drilling period can be in a range from 5 ps (or thereabout) to 120 ps (or thereabout). In some embodiments, the drilling period can advantageously be less than or equal to 50 ps (or thereabout), less than or equal to 30 ps (or thereabout), less than or equal to 20 ps (or thereabout), less than or equal to 15 ps (or thereabout), less than or equal to 10 ps (or thereabout), etc., or between any of these values.
• the first surface of the substrate is cleaned to remove (or reduce the amount of) contaminants on the first surface that would absorb energy within the beam of laser pulses.
• any through-vias that are formed within the substrate tend to have a relatively large opening at the first surface and a relatively small opening at the second surface.
• any through-vias that are formed within the substrate tend to have openings at the first surface and the second surface that are about the same diameter (e.g., within a range of 2 pm to 5 pm of each other).
• FIG. 1 illustrates an exemplary laser processing system for implementing the laser drilling process described in the embodiments above.
• the laser processing system 100 includes a laser 102, a beam expander 104, a beam modulator 106, a beam scanner 108, a scan lens 110 and a stage 112.
• the laser 102 can be provided as any suitable laser capable of generating the (e.g., a QCW laser capable of generating a beam of laser pulses having the characteristics noted above.
• the laser 102 may be configured to generate a beam of laser pulses at an average power of 100 W (or thereabout), a wavelength of 515 nm (or thereabout, e.g., 532 nm), a pulse width in a range from 20 ps (or thereabout) to 40 ps (or thereabout) and a pulse repetition rate in a range from 25 MHz (or thereabout) to 40MHz (or thereabout).
• the pulse width of the laser pulses is 28 ps (or thereabout), and the pulse repetition rate is 30 MHz (or thereabout).
• the beam expander 104 can be provided as any suitable device capable of expanding an incident beam from a first beam size (e.g., a diameter of 2 mm, or thereabout) to a second beam size (e.g., a diameter of 4.5 mm, or thereabout).
• the beam expander may be provided as a motorized variable beam expander.
• the beam modulator 106 can be provided as any suitable device capable of selectively attenuating (e.g., either partially, completely or not at all) the beam of laser an energy.
• the beam modulator 106 can be provided as an acousto-optic (AO) modulator (AOM) or an AO deflector (AOD).
• AO acousto-optic
• AOM acousto-optic
• AOD AO deflector
• the beam scanner 108 can be provided as any suitable device (or devices) capable of deflecting an incident beam of laser pulses (e.g., within a one-dimensional scan field, within a two-dimensional scan field, etc.). Accordingly, the beam scanner 108 can include one or more galvanometer mirrors, one or more fast-steering mirrors, one or more deformable mirrors, one or more AODs, a rotating polygon mirror, or the like or any combination thereof.
• the scan lens 110 can be provided as any suitable device (or devices) capable of focusing an incident beam of laser pulses so as to produce a focused beam of laser pulses.
• the scan lens 110 is provided as a telecentric scan lens.
• the scan lens 110 has a focal length of lOOmm (or thereabout) and a numerical aperture (NA) of about 0.5 or less.
• the scan lens 110 can be focus the beam of laser pulses to produce a beam waist (e.g., at the focal plane of the scan lens 110) that has a diameter in a range from 10 pm (or thereabout) to 13 pm (or thereabout), e.g., in a range from 11 pm to 12 pm.
• the stage 112 can be provided as any suitable device (or devices) capable of supporting and moving the aforementioned substrate (e.g., identified at 114).
• the stage 112 is configured to linearly move the substrate 114 along one axis, along two axes, or the like or any combination thereof.
• the substrate 114 can be characterized as including a first surface (e.g., which faces towards the scan lens 110) and a second surface, opposite the first surface (e.g., which faces away from the scan lens 110).
• the stage 112 is configured to support the substrate 114 such that the second surface of the substrate 114 does not contact an underlying structure, such as the stage 112.
• the first surface of the substrate 114 is also referred to as the“front surface” of the substrate 114 and the second surface of the substrate 114 is also referred to as the“back surface” of the substrate 114.
• the stage 112 supports the substrate 114 such that the focal plane of the scan lens 110 is located outside the substrate 114 (i.e., below the second surface of the substrate 114).
• the distance between the second surface of the substrate 114 and the focal plane of the scan lens 110 i.e., the aforementioned“offset distance” is set such that the focused beam of laser pulses irradiates a region of the substrate at a peak intensity that is less than the optical breakdown intensity of the substrate, while still producing a through-via in the substrate, as discussed above. It will be appreciated that the offset distance may be determined
• the system 100 may further include one or more other components to polarize, reflect, expand, focus, etc., the beam of laser pulses propagating from the laser 102 to the scan lens 110 (e.g., along the dashed lines, as exemplarily illustrated in FIG. 1).
• components include a half-wave plate 116, a pair of relay lenses 118, and a plurality of fold-mirrors (e.g., fold mirror 120).
• the pair of relay lenses are arranged and configured to magnify the beam of laser pulses as output from the beam modulator 106 (e.g., double the beam size of the beam of laser pulses as output from the beam modulator 106).
• the beam of laser pulses as output from the beam modulator 106 had the aforementioned second beam size of 4.5 mm (or thereabout), then the beam of laser pulses output from the pair of relay lenses can be characterized as having a third beam size of 9 mm (or thereabout).
• FIGS. 2 and 3 are photographs illustrating a through-via drilled through a 50pm thick glass substrate (i.e., a substrate formed of AF 32®, manufactured by SCHOTT Corporation), taken from the first and second surfaces of the glass substrate, respectively, using the
• the glass substrate was uncoated, in that it did not have any absorptive coating formed on either surface, and the average power of the beam of laser pulses at the substrate (i.e., after having been reflected, transmitted, or diffracted by the aforementioned components of the laser processing system 100) was in a range from 66 W (or thereabout) to 67 W (or thereabout).
• the diameter of the through-via at the first surface was in a range from 9.5 mih to 10.1 mih; and the diameter of the through-via at the second surface (as shown in FIG. 3) was 9 mih.
• FIG. 4 is a graph illustrating the results of experiments in which a 50pm thick glass substrate (i.e., an uncoated substrate formed of AF 32®, manufactured by SCHOTT
• the average power of the beam of laser pulses at the substrate was varied from 25W (or thereabout) to 67 W (or thereabout) and the drilling period at each location in the substrate where an attempt to form a via was made was varied from 5 ps to 120 ps in 5 ps intervals.
• the dots in the graph represent actual data points obtained from each experiment, and the boundaries of the contours were derived from the experimentally-obtained data using the statistical analysis software JPM, produced by SAS INSTITUTE, INC.
• the z range of the laser drilling process is 0.05 mm.
• the z range of the laser drilling process was found to be capable of expansion, as illustrated in FIG. 4, by increasing the average power at the substrate and/or by increasing the drilling period at each drilling location. For example, by increasing the drilling period from 40 ps to 120 ps (at an average power of 30 W), through-vias can be formed at a z offset of 0.075 mm.
• FIGS. 5 to 8 are photographs of cross-sectioned glass substrates (i.e., formed of AF 32®, manufactured by SCHOTT Corporation), that are either 50 pm thick (in the case of FIGS. 5 and 7) or 100 pm thick (in the case of FIGS. 6 and 8) that were processed (e.g., using the laser processing system 100 and the laser drilling process described above) to form though-vias, wherein each via is formed for a drilling period of l5ps.
• cross-sectioned glass substrates i.e., formed of AF 32®, manufactured by SCHOTT Corporation
• the glass substrates did not have any absorptive coating formed on either surface, and the average power of the beam of laser pulses at the substrate (i.e., after having been reflected, transmitted, or diffracted by the aforementioned components of the laser processing system 100) was in a range from 67 W (or thereabout) to 69 W (or thereabout).
• the ragged edge quality at the cross-sectioned plane is due to the fragility of glass material to the mechanical grinding method used to cross-section the substrate.
• the diameters identified in FIGS. 5 to 8 may have been smaller than those annotated thereon, prior to cross-sectioning.
• the main objective of FIGS. 5 to 8 is to illustrate how straight the sidewalls of the through-vias are, and the uniformity of the diameter of the through-vias through the entire thickness of the substrate.
• the beam of laser pulses can be scanned (e.g., by the beam scanner 108) to form a plurality of through-vias.
• the minimum via-to-via pitch i.e., the distance between nearest-neighbor vias
• the splash zone is a zone around the opening at the second surface where molten material is ejected from the substrate during formation of a through-via.
• the laser drilling process described above yields a splash zone having a diameter of about 30 pm.
• the via-to-via pitch can be at least 30 pm (or thereabout).
• the laser system 100 has been described above as including a laser 102 operative to generate a beam of laser pulses at a wavelength of 515 nm (or thereabout), it will be appreciated that the laser drilling process described in the embodiments above can be achieved using laser pulses at wavelengths other than 515 nm (or thereabout), depending on one or more other factors such as the average power at the substrate, pulse width, pulse repetition rate, the material from which the substrate is formed and the like.
• the aforementioned laser drilling process can be performed using a beam of laser pulses at wavelengths in the near-infrared region of the electromagnetic spectrum (e.g., at 1030 nm, at 1064 nm, or the like), provided that the beam of laser pulses has a pulse repetition rate as discussed above, and also provided that the average power of the beam of laser pulses at the substrate is 100 W (or thereabout) or greater (e.g., 110 W, 120 W, 130 W, or the like or between any of these values).
• laser pulses in the beam of laser pulses can have pulse widths as discussed above. However, it should be noted that the selection of the pulse width can affect the duration of the drilling period.
• a beam of laser pulses having a relatively short pulse width (e.g., 10 ps, or thereabout) will be able to form a through-via within a drilling period that is shorter than a beam of laser pulses having a relatively long pulse width (e.g., 30 ps, or thereabout).
• the laser-drilling process has been described above as eliminating need for an absorptive coating at the second surface of the substrate, it will be appreciated that the second surface of the substrate may be coated or otherwise treated with a material that is either more absorptive to the beam of laser pulses than the substrate or alters the absorptivity of the substrate (e.g., at or near the second surface thereof) to the laser pulses.
• the substrate may optionally be subjected to a thermal annealing process after the laser-drilling process has been performed to form the through-vias. In this case, the thermal annealing may act to reduce internal stresses present with the substrate due to the solidification of molten material ejected into the splash zone during the laser-drilling process.

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• Laser Beam Processing (AREA)
• Surface Treatment Of Glass (AREA)
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