Method for rapid laser drilling in glass and products made therefrom
阅读说明：本技术 在玻璃中进行快速激光钻孔的方法和由其制备的产品 (Method for rapid laser drilling in glass and products made therefrom ) 是由 S·马加诺维克 G·A·皮切 C·A·蓬西珀曼 S·尚穆加姆 S·楚达 Z·瓦尔加 R· 于 2014-12-16 设计创作，主要内容包括：本申请涉及在玻璃中进行快速激光钻孔的方法和由其制备的产品。在材料(1)中形成孔包含将脉冲激光束(2)聚焦成沿着束传播方向取向并引导进入材料的激光束聚焦线(2b),所述激光束聚焦线(2b)在材料(1)之内产生诱导吸收,该诱导吸收在材料(1)之内产生沿着激光束聚焦线(2b)的缺陷线条,以及使得材料(1)和激光束(2)相对于彼此平移,由此在材料中形成多个缺陷线条,以及在酸溶液中蚀刻材料,以通过放大材料中的缺陷线条来产生直径大于1微米的孔。玻璃制品包含玻璃基材的堆叠件,其具有形成的延伸穿过堆叠件的直径为1-100微米的孔。(The present application relates to methods of rapid laser drilling in glass and products made therefrom. Forming a hole in a material (1) comprises focusing a pulsed laser beam (2) into a laser beam focal line (2b) oriented along a beam propagation direction and directed into the material, the laser beam focal line (2b) producing an induced absorption within the material (1) that produces a defect line along the laser beam focal line (2b) within the material (1), and translating the material (1) and the laser beam (2) relative to each other, thereby forming a plurality of defect lines in the material, and etching the material in an acid solution to produce a hole having a diameter greater than 1 micron by amplifying the defect lines in the material. The glass article comprises a stack of glass substrates having pores formed extending through the stack having a diameter of 1 to 100 microns.)
1. A glass article, comprising:
a substrate having a plurality of damage tracks, wherein the damage tracks have a diameter of less than 1 micron, a spacing between adjacent damage tracks is at least 20 microns, and an aspect ratio of 20:1 or greater.
2. An article of manufacture, comprising:
a substrate having a plurality of etched vias extending continuously from a first surface of the substrate to a second surface of the substrate, wherein:
the substrate is transparent to at least one wavelength from 390nm to 700 nm;
the plurality of etched vias are 20 microns or less in diameter;
the spacing between adjacent etched vias is 10 microns or greater;
the plurality of etched vias comprise openings in the first surface, openings in the second surface, and waists between the openings in the first surface and the openings in the second surface;
the waist diameter is at least 50% of the diameter of the opening in the first surface or the opening in the second surface; and
the difference between the diameter of the opening in the first surface and the diameter of the opening in the second surface is 3 microns or less.
3. The article of claim 2, wherein the plurality of etched vias have a diameter greater than 5 microns.
4. The article of claim 2, wherein the waist diameter is at least 70% of the diameter of the opening in the first surface or the opening in the second surface.
5. The article of claim 4, wherein the waist diameter is at least 75% of the diameter of the opening in the first surface or the opening in the second surface.
6. The article of claim 5, wherein the waist diameter is at least 80% of the diameter of the opening in the first surface or the opening in the second surface.
7. The article of claim 2, wherein the substrate is fused quartz.
8. The article according to claim 2, wherein the substrate is glass.
9. The article according to claim 8, wherein the glass is a chemically strengthened glass.
10. The article of claim 2, wherein the substrate has a thickness of 1mm or less.
11. The article of claim 2, wherein the substrate has a thickness of 20 microns to 200 microns.
12. The article of claim 2, wherein the density of the plurality of etched vias is 5 vias/mm2-50 through holes/mm2。
13. The article of claim 2, wherein the plurality of etched vias have a diameter of less than or equal to 15 microns.
14. The article of claim 2, wherein the plurality of etched vias have a diameter of less than or equal to 10 microns.
15. The article of claim 2, wherein the aspect ratio of the plurality of etched vias is 5:1 to 20: 1.
16. The article of claim 2, wherein the plurality of etched vias comprise a conductive material.
17. The article of claim 2, wherein the plurality of etched vias have a roundness of less than 5 μ ι η at least one of the first surface and the second surface.
18. The article of claim 2, wherein an aspect ratio of a substrate thickness to a diameter at the first surface of at least a portion of the plurality of etched vias is 1:1 or greater.
Brief description of the drawings
The foregoing will be apparent from the following more particular description of example embodiments as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments.
FIG. 1 schematically shows an embodiment of an optical assembly for laser drilling.
FIG. 2A shows an optical assembly for laser machining according to one embodiment.
Figures 2B-1 to 2B-4 show various possibilities for processing a substrate by differently positioning the laser beam focal line relative to the substrate.
Fig. 3 shows a second embodiment of an optical assembly for laser machining.
Fig. 4A and 4B show a third embodiment of an optical assembly for laser machining.
The graph of fig. 5 shows the laser emission (intensity) of an exemplary picosecond laser as a function of time.
FIGS. 6A and 6B are scanning electron micrographs of features formed by laser drilling, taken together
Fig. 7 is a microscopic image of a typical damage track, perforation or defect line (the three terms are used interchangeably herein), which is a side view without etching. The marks made through the glass are typically not fully opened-i.e., the area material is removed, but complete vias need not be formed.
Fig. 8 is a microscopic side view without damage tracks or perforations by acid etching, at a magnification greater than that of the micrograph shown in fig. 7.
Fig. 9 is a microscopic image of a top view of a typical damage track or hole without acid etching.
Fig. 10 is a scanning electron micrograph of a hole prepared using processing conditions that form significant microcracking by using a shorter focal length objective lens (f ═ 30mm) that forms a shorter focal line (0.5 mm) and thus a high energy density in the defect line.
FIG. 11 is a scanning electron micrograph of a hole that does not penetrate the full thickness of the part, which can be used to make a blind hole.
Fig. 12A and 12B are scanning electron micrographs of an entrance aperture (laser incident side) after etching and an exit aperture (laser exit side) after acid etching, respectively.
Fig. 13 is an image after etching effected by microcracking. The microcracks have been acid etched into elongated features.
The photo of fig. 14 shows a side view of the hole after acid etching. The sample was cut into small pieces to show the cross-section. The bright areas are glass and the dark areas are holes.
The optical photograph of fig. 15 shows a side view of the holes after acid etching, but at a higher magnification than the optical photograph shown in fig. 14.
The graphs of fig. 16A-16C show the number of pores at the top (fig. 16A), bottom (fig. 16B), and at the waist (fig. 16C) as a function of diameter, which shows pore size statistics for about 10,000 pores after etching.
The graphs of fig. 17A-17C show the number of holes at the top (17A), bottom (17B), and at the waist (17C) as a function of diameter, which shows roundness statistics after etching. Roundness is the maximum diameter-minimum diameter of a given hole. The data indicates that all holes are free of significant cracks/gaps that will be etched into significant non-round shapes.
Fig. 18A-18C are optical photographs of a radial crack prior to etching (fig. 18A), and a larger magnification of the array of entrance apertures (fig. 18B and 18C).
Fig. 19A-19C are photomicrographs of the holes before etching, showing a top view (fig. 18A), a bottom view (fig. 18B), and a side view (fig. 18C).
Fig. 20A-20E are optical photographs of a top view of a hole after acid etching at 55% laser power (fig. 20A), 65% laser power (fig. 20B), 75% laser power (fig. 20C), 85% laser power (fig. 20D), and 100% laser power (fig. 20E).
Fig. 21A-21E are photomicrographs of a bottom view of the holes after acid etching at 55% laser power (fig. 21A), 65% laser power (fig. 21B), 75% laser power (fig. 21C), 85% laser power (fig. 21D), and 100% laser power (fig. 21E).
FIGS. 22A-22C are photomicrographs of a top view of the holes after acid etching-FIG. 22A: 100 micrometer holes in a 150X150 array with a pitch of 200 micrometers; 22B and
Figures 23A-23C are graphs showing the number of wells as a function of diameter for samples having a 100x100 array of wells, showing results for the top (figure 23A), bottom (figure 23B), and waist (figure 23C) of the samples.
Figures 24A-24C are graphs showing the number of wells of a sample with a 100x100 array of wells as a function of roundness, which shows results for the top (figure 24A), bottom (figure 24B), and waist (figure 24C) of the sample.
Figures 25A-25C are graphs showing the number of wells as a function of diameter for samples having a 100x100 array of wells, showing results for the top (figure 25A), bottom (figure 25B), and waist (figure 25C) of the second sample.
Figures 26A-26C are graphs showing the number of wells as a function of roundness for samples having a 100x100 array of wells, showing results for the top (figure 26A), bottom (figure 26B), and waist (figure 26C) of the second sample.
Fig. 27A-27C and 28A-28C are photomicrographs of 30 micrometer and 50 micrometer holes, respectively, made using 100% laser power after acid etching, showing top (fig. 27A,28A) side (fig. 27B,28B), and bottom (fig. 27C,28C) views.
Fig. 29A-29C and 30A-30C are photomicrographs of 75 micrometer and 100 micrometer holes, respectively, made using 100% laser power after acid etching, showing top (fig. 29A,30A) side (fig. 29B,30B), and bottom (fig. 29C,30C) views.
Fig. 31A-31C and 32A-32C are photomicrographs of 30 micrometer and 50 micrometer holes, respectively, made using 85% laser power after acid etching, showing top (fig. 31A,32A) side (fig. 31B,32B), and bottom (fig. 31C,32C) views.
Fig. 33A-33C and 34A-34C are photomicrographs of 75 micrometer and 100 micrometer holes, respectively, made using 85% laser power after acid etching, showing top (fig. 33A,34A), side (fig. 33B,34B), and bottom (fig. 33C,34C) views.
Fig. 35A-35C and 36A-36C are optical photographs of 30 micron and 50 micron holes prepared using 75% laser power, respectively, after acid etching, showing top (fig. 35A,36A), side (fig. 35B,36B), and bottom (fig. 35C,36C) views.
Fig. 37A-37C and 38A-38C are photomicrographs of 75 micrometer and 100 micrometer holes, respectively, made using 75% laser power after acid etching, showing top (fig. 37A,38A), side (fig. 37B,38B), and bottom (fig. 37C,38C) views.
Fig. 39A-39C and 40A-40C are photomicrographs of 30 micrometer and 50 micrometer holes, respectively, made using a 65% laser power after acid etching, showing top (fig. 39A,40A), side (fig. 39B,40B), and bottom (fig. 39C,40C) views.
Fig. 41A-41C and 42A-42C are photomicrographs of 75 micrometer and 100 micrometer holes, respectively, made using a 65% laser power after acid etching, showing top (fig. 41A,42A), side (fig. 41B,42B), and bottom (fig. 41C,42C) views.
Fig. 43A-43C and 44A-44C are photomicrographs of 30 micrometer and 50 micrometer holes, respectively, made using 55% laser power after acid etching, showing top (fig. 43A,44A) side (fig. 43B,44B), and bottom (fig. 43C,44C) views.
Fig. 45A-45C and 46A-46C are photomicrographs of 75 micrometer and 100 micrometer holes, respectively, made using 55% laser power after acid etching, showing top (fig. 45A,46A), side (fig. 45B,46B), and bottom (fig. 45C,46C) views.
FIG. 47 showsShowing 150 microns extending through a 3-up stack
FIG. 48 is an optical photograph prior to acid etching showing a side view of a stack of two 300 micron thick EXG glasses drilled with damage tracks.
Fig. 49 is a photomicrograph after acid etching showing a side view of the same stack as shown in fig. 48 after acid etching.
Fig. 50 is a photomicrograph after acid etching showing a top view of the same stack as shown in fig. 48 after acid etching.
Fig. 51A and 51B show the
FIG. 52 shows the Therler (Thiele) modulus of the etching system as a function of the expected waist diameter in percent relative to the top and bottom opening diameters.
FIG. 53 is a plot of Theiler modulus of an etching system as a function of radius of a damage track.
FIG. 54 is a plot of the Theiler modulus of the etching system as a function of the half thickness of the glass substrate.
FIG. 55 is a graph of the Theiler modulus versus effective diffusion coefficient (D) for an etch systemIs effective) And (3) plotting the changes.
FIG. 56 is a plot of Theiler modulus for an etching system as a function of acid concentration in volume percent and shows the combined effect of varying the effective diffusion coefficient and acid concentration on the Theiler modulus.
Fig. 57 is an optical photograph of a side view of a glass part after acid etching.
DETAILED DESCRIPTIONS
Example embodiments will be described below.
The following embodiments utilize shorter (e.g., 10) with optical systems-10-10-15Second) pulsed laser forming a line focus system to form defect lines, damage tracks or holes in a piece of material that is substantially transparent to the laser wavelength, e.g. glass, fused quartz, glass, quartz,Synthetic quartz, glass-ceramics, crystalline materials such as sapphire, or laminated layers of such materials (e.g., coated glass). Producing line focusing can be done by emitting a Gaussian laser beam into an axicon lens, in this case, forming a beam profile with what is called a Gauss-Bessel beam. Such a beam diffracts much more slowly than a Gaussian beam (e.g., it can maintain a single micron spot size in the range of hundreds of microns or millimeters as opposed to tens of microns or less for a Gaussian beam). Thus, the depth of focus or length of the strong interaction with the material will be much larger than if only a Gaussian beam were used. Other forms or slowly diffractive or non-diffractive beams, such as Airy beams, may also be used. The material or article is substantially transparent to the laser wavelength when the absorption is less than about 10%, preferably less than about 1%, per millimeter of material depth at the laser wavelength. In some embodiments, the material may also be transparent to at least one wavelength in the range of about 390nm to about 700 nm. The use of a high intensity laser and line focus allows each laser pulse to simultaneously damage, ablate, or otherwise alter (e.g., 100-. Such marks can easily extend through the entire thickness of the glass part. Thus, even a single pulse or burst (burst) can form a complete "pilot hole" or a sharp damage track without the need for percussion drilling.
The cross-sectional dimensions of the pilot holes/damage tracks are very small (a single micron or less) but rather long-i.e. they have a high aspect ratio. The part is then acid etched to obtain a final pore size-e.g., a diameter of about 30 microns or less, about 25 microns or less, about 20 microns or less, about 15 microns or less, about 10 microns or less, about 5 to about 10 microns, about 5 to about 15 microns, about 5 to about 20 microns, about 5 to about 25 microns, about 5 to about 30 microns, or up to several tens of microns, depending on the requirements of the intended application. In some embodiments, the etching may be performed such that the theler modulus of the etching process is about 3 or less, about 2.5 or less, about 2 or less, about 1.5 or less, about 1 or less, or about 0.5 or less. After etching, the glass surface is slightly textured by imperfect uniformity during etching-while the interior of the etched holes is somewhat smooth and may have some ultrafine grain texture, which is visible under a microscope or scanning electron microscope. In some embodiments, the substrate can have a plurality of through holes extending continuously from a first surface of the substrate to a second surface of the substrate, wherein the substrate is transparent to at least one wavelength in the range of 390nm to 700nm, the plurality of through holes having a diameter of 20 microns or less, the plurality of through holes comprising openings in the first surface, openings in the second surface, and a waist between the openings in the first surface and the openings in the second surface, the waist having a diameter that is at least 50% of the diameter of the openings in the first surface or the openings in the second surface, and the difference between the diameter of the openings in the first surface and the diameter of the openings in the second surface being 3 microns or less.
The holes may then be coated and/or filled with a conductive material (e.g., by metallization) to form an insert part made of a transparent material. The metal or conductive material may be, for example, copper, aluminum, gold, silver, lead, tin, indium tin oxide, or combinations or alloys thereof. The process for the metallization inside the hole may be, for example, electroplating, electroless plating, physical vapor deposition, or other vapor coating methods. The pores may also be coated with a catalytic material, such as platinum, palladium, titanium dioxide, or other materials that promote chemical reactions within the pores. Alternatively, the pores may be coated with other chemical functionalisation to alter surface wetting properties or to enable attachment of biomolecules and for biochemical analysis. Such chemical functionalization may be silanization of the glass surface of the pores and/or additional attachment of specific proteins, antibodies or other biospecific molecules designed to facilitate attachment of biomolecules for desired applications.
In one embodiment, a method of laser drilling a material includes focusing a pulsed laser beam into a laser beam focal line oriented along a beam propagation direction and directed into the material, the laser beam having an average laser pulse group energy measured at the material greater than about 50 microjoules per millimeter of thickness of the material being processed, the laser beam having a pulse group energy density of from about 25 microjoules per millimeter of line focus to about 125 microjoules per millimeter of line focus, the laser beam having a pulse duration of less than about 100 picoseconds and a repetition rate of from about 1kHz to about 4 MHz. The length of the line focus can be determined by: the intensity is the distance between two points at half the maximum intensity on the optical axis. The laser beam focal line produces an induced absorption within the material, the induced absorption forming a hole within the material along the laser beam focal line. The method also includes translating the material and the laser beam relative to each other, thereby laser drilling a plurality of holes (or damage tracks) within the material at a rate of: greater than about 50 pores/second, greater than about 100 pores/second, greater than about 500 pores/second, greater than about 1,000 pores/second, greater than about 2,000 pores/second, greater than about 3,000 pores/second, greater than about 4,000 pores/second, greater than about 5,000 pores/second, greater than about 6,000 pores/second, greater than about 7,000 pores/second, greater than about 8,000 pores/second, greater than about 9,000 pores/second, greater than about 10,000 pores/second, greater than about 25,000 pores/second, greater than about 50,000 pores/second, greater than about 75,000 pores/second, or greater than about 100,000 pores/second, depending on the desired pattern of pores/damage tracks. The method further comprises etching the material in an acid solution at a rate of less than about 5 microns/minute, for example at a rate of about 2 microns/minute, thereby enlarging pores in the material.
In some embodiments, the pulse duration may be greater than about 5 picoseconds to less than about 100 picoseconds, and the repetition rate may be between about 1kHz and 4 MHz. The pulses may be generated in bursts of at least two pulses separated by a duration of between about 1 nanosecond and about 50 nanoseconds, such as between 10 and 30 nanoseconds, for example about 20 nanoseconds ± 2 nanoseconds, and the burst repetition frequency may be between about 1kHz and about 4 MHz. The pulsed laser beam may have a wavelength selected so that the material is substantially transparent at that wavelength. This wavelength may be, for example, 1064,532,355, or 266 nanometers. In some embodiments, the burst repetition frequency can be from about 1kHz to about 4MHz, from about 10kHz to about 650kHz, about 10kHz or greater, or about 100kHz or greater.
The laser beam focal line may have a length of about 0.1mm to about 10mm, or a length of about 0.1mm to about 1mm, and an average spot diameter of about 0.1 microns to about 5 microns. The spot diameter D of a Bessel beam can be written as D ═ 2.4048 λ)/(2 π B, where λ is the laser beam wavelength and B is a function of the cone angle of the beam.
Laser and optical system:
for cutting transparent substrates, in particular glass, a method was developed which uses a 1064nm picosecond laser and optics forming a line-shaped focused beam, so that damage lines or damage tracks are formed in the substrate. This is described in detail below and is described in us patent application No. 61/752,489 filed on 15/1/2013, which is a priority application for us patent application No. 14/154,525 (us patent application publication No. 2014/0199519) filed on 14/1/2014, which is incorporated herein by reference in its entirety. In this context, a damage track formed by a laser may interchangeably refer to a hole, a pilot hole, a defective line, or a perforation. The method of cutting the transparent substrate may also be applied to form damage tracks, which are subsequently magnified by an etching process, as described below.
Fig. 1 provides a schematic diagram of one version of the concept in which light rays from a laser 3 (not shown) are focused into a
A method of laser processing a material includes focusing a
The substrate 1 (or material or glass article) is aligned perpendicular to the longitudinal beam axis and thus behind the same
Thus, microscopic (i.e., <2 microns and >100nm in diameter, and in some embodiments <0.5 microns and >100nm) elongated "holes" (also referred to as perforations, damage tracks, or defect lines, as described above) can be formed in transparent materials using a single high-energy pulse burst pulse. These individual perforations may be formed at a rate of several hundred kilohertz (e.g., several hundred thousand perforations per second). Thus, the perforations can be placed at any desired location within the workpiece by relative movement between the source and the material. In some embodiments, the defect line/damage track is a "via," which is a hole or open channel that extends from the top to the bottom of the transparent material. In some embodiments, the defect line/damage track may not be a continuous channel and may be blocked or partially blocked by portions or segments of solid material (e.g., glass). As defined herein, the internal diameter of a defect line/damage track is the internal diameter of an open channel or air hole. For example, in the embodiments described herein, the internal diameter of the defect line/damage track is <500nm, such as ≦ 400nm, or ≦ 300 nm. In the embodiments described herein, the disturbed or altered regions of material surrounding the pores (e.g., densified, fused, or otherwise altered) preferably have a diameter of <50 microns (e.g., <10 microns).
Because of the induced absorption along the
The selection of the laser source is predicted based on the ability to form multiphoton absorption (MPA) in the transparent material. MPA is the simultaneous absorption of two or more photons of the same or different frequencies, thereby exciting a molecule from one state (usually the ground state) to a higher energy electronic state (possibly leading to ionization). The energy difference between the lower and upper states of the molecule involved may be equal to the sum of the energies of the two or more photons. MPA, also known as induced absorption, can be a secondary, tertiary, or higher order process, e.g., it is orders of magnitude weaker than linear absorption. MPA differs from linear absorption in that, for example, the intensity of the induced absorption can be proportional to the square, cube, or higher power (power) of the light intensity, rather than the light intensity itself. Thus, MPA is a nonlinear optical process.
Representative
To ensure high quality drilling (involving obtaining high fracture strength, geometric accuracy, forming a strong path for the etchant, hole topography, and avoiding micro-cracking), a single focal line disposed on the substrate surface should be generated using an optical assembly as described below (hereinafter, the optical assembly is also alternatively referred to as a laser optic). In order to obtain a small spot size, e.g. 0.5-2 microns, at a given wavelength λ of the laser light 3 (interacting with the
On the other hand, to obtain the required numerical aperture, the optics must be set to the opening required for a given focal length, according to the known abbe's formula (n.a.: nsin (θ), n: the refractive index of the glass or other material being processed, θ: half of the aperture angle, and θ ═ arctan (D/2 f); D: aperture, f: focal length). On the other hand, the laser beam must illuminate optics up to the required aperture, which is typically achieved by using beam expansion of a broadening telescope between the laser and the focusing optics.
The spot size variation should not be too large for uniform interaction along the focal line. This can be ensured, for example, by the following (see the embodiments below): the focusing optics are illuminated only in a small circular area, so that the beam opening and thus the percentage of the numerical aperture changes only slightly.
According to fig. 2A (cross section perpendicular to the substrate plane and at the central beam in the laser beam cluster of the
As shown in fig. 2A, the laser beam
One potential disadvantage of such focal lines is that the conditions (spot size, laser intensity) may vary along the focal line (and along the desired depth in the material), and thus the desired type of interaction (no melting, induced absorption, thermoplastic deformation until crack formation) may occur only in selected portions of the focal line. This in turn means that it is possible that only a part of the incident laser light is absorbed by the substrate material in the desired manner. As such, the efficiency of the process (the required average laser power for the required separation speed) may be reduced, and the laser may also be transmitted into unwanted areas (parts or layers bonded to the substrate or fixtures holding the substrate) and interact with them in a disadvantageous manner (e.g., heating, diffusion, absorption, unwanted modification).
Fig. 2B-1-4 show (not only for the optical assembly in fig. 2A, but basically for any other applicable optical assembly 6) that the position of the laser beam focal line 2B can be controlled by: the
In the case shown in fig. 2B-2, a focal line 2B of length l is generated, which more or less corresponds to the substrate thickness d. Because the
It is particularly preferable to set the
Fig. 3 shows another useful
However, the layout shown is limited by: since the area of the
For this purpose it may be necessary to use an
FIG. 4B shows in detail the formation of focal lines 2B or induced
It would therefore be preferable if the focal line were formed at a distance from the laser optics, and if a larger portion of the laser radiation was focused to the desired end of the focal line. As described herein, this can be achieved by: the primary focusing element 11 (lens) is illuminated in a circular (annular) manner only on a specific outer radial area, which on the one hand serves to obtain the required numerical aperture and thus the required spot size, whereas on the other hand, after the required
If it is desired that the defect line/damage track formation continue to the back of the substrate, circular (annular) illumination still has the following advantages: (1) the laser power is optimally used because most of the laser light is still concentrated in the required length of the focal line and (2) a uniform spot size along the focal line-and thus a uniform separation of the parts from the substrate along the focal line-is obtained-which is brought about by the area of annular illumination and the required chromatic aberration set by other optical effects.
Unlike the plano-convex lens shown in fig. 4A, a focusing meniscus lens or another higher-order collimating focusing lens (aspherical, multi-lens system) may also be used.
In order to produce a very short
Thus, the
As is also shown in fig. 4A, the circular radiation SR formed by the
In the embodiment shown, a focal line length l of less than 0.5mm can be obtained using a typical laser beam diameter of 2mm, the focal length f of the focusing
It should be noted that the typical operation of such picosecond lasers forms "bursts" of pulses, sometimes referred to as "burst pulses". A burst is a laser operation in which the pulse emission is not a uniform and steady stream, but rather a tight cluster of pulses. This is shown in fig. 5. Each "pulse train" 610 can include a plurality of pulses 620 (e.g., at least 2 pulses, at least 3 pulses, at least 4 pulses, at least 5 pulses, at least 10 pulses, at least 15 pulses, at least 20 pulses, or more) having a very short duration. That is, the pulse bursts are pulse "packets," and the pulse bursts are separated from each other by a longer duration than between individual adjacent pulses within each pulse burst. Pulse duration T of
The energy required to change the material can be described by the burst energy-the energy contained within a burst (each burst 610 containing a series of pulses 620) or by the energy contained within a single laser pulse (many of which may contain a burst). For these applications, the energy/pulse train may be 25 microjoules-750 microjoules, more preferably 40 microjoules-750 microjoules, 50 microjoules-500 microjoules, 50-250 microjoules, or 100-. The energy of the individual pulses within a burst can be smaller, and the exact individual laser pulse energy will depend on the number of pulses within a burst and the decay rate (e.g., exponential decay) of the laser pulse over time, as shown in fig. 5. For example, for a constant energy/burst, if the burst contains 10 individual laser pulses, the energy of each individual laser pulse will be less than if the same burst contained only 2 individual laser pulses.
For such processing, it is preferable to use a laser that generates such a pulse train. The use of a pulse burst sequence that spreads the laser energy over a rapid sequence of sub-pulses (which make up the burst) allows for a high intensity interaction with the material over a longer time scale than can be formed using a single pulse laser, as opposed to using a single pulse separated in time by the laser repetition rate. Although a single pulse may be spread in time, in doing so the intensity within the pulse must drop by about the same factor as the pulse width increases. Thus, if the 10 picosecond pulse is extended to a 10 nanosecond pulse, the intensity will drop by about 3 orders of magnitude. This decrease may reduce the optical intensity to an extent where the nonlinear absorption is no longer significant and the optical-material interaction is no longer strong enough to effect material modification. In contrast, with a pulse burst pulsed laser, the intensity in each sub-pulse may still be very high-e.g., 3 10 picosecond pulses separated in time by about 10 nanoseconds still result in an intensity within each pulse that is within about 3 times that of a single 10 picosecond pulse, while now allowing the laser to interact with the material on a time scale that is three orders of magnitude higher than before. Thus, such modulation of the plurality of pulses within the pulse train enables manipulation of the time scale of the laser-material interaction in the following manner: the approach may facilitate more or less light interaction with the pre-existing plasma plume (plume), more or less light-material interaction and pre-excitation of atoms and molecules of the material by the initial or previous laser pulse.
When a single pulse burst of pulses impacts substantially the same location on the material, a damage track or hole is formed in the material. That is, multiple laser pulses within a single pulse burst correspond to a single defect line or hole location in the material. Of course, because the material is translated (e.g., by a constant motion stage) or the beam is moved relative to the material, the individual pulses within a pulse train cannot be precisely at the same spatial location on the material. However, a pulse must be within 1 micron of another pulse so that they impact the material at substantially the same location. For example, the pulses may impact the material at a separation sp from each other, where 0< sp ≦ 500 nanometers. For example, when a location on a material is impacted with a pulse train of 20 pulses, the individual pulses within the pulse train impact the glass within 250 nanometers of each other. Thus, in some embodiments, the spacing sp is from about 1nm to about 250nm or from about 1nm to about 100 nm.
The optical method of creating the line focus can take many forms, using a circular laser beam and a spherical lens, axicon lens, diffractive element, or other method to create a linear region of high intensity, as described above. The type (picosecond, femtosecond, etc.) and wavelength (IR, green, UV, etc.) of the laser may also be varied, provided that sufficient optical intensity is achieved to decompose the substrate material.
Hole or damage track formation:
the damage tracks formed by the laser methods described above are typically in the form of holes having an internal size of about 0.1 to 2 microns, for example 0.1 to 1.5 microns. Preferably, the size of the holes formed with the laser is very small (one micron or less) -i.e., they are narrow. In some embodiments, the pores have a diameter of 0.2 to 0.7 microns. As noted above, in some embodiments, the damage tracks are not continuous holes or channels. The damage tracks can have a diameter of 5 microns or less, 4 microns or less, 3 microns or less, 2 microns or less, or 1 micron or less. In some embodiments, the damage tracks can have a diameter of greater than 100nm to less than 2 microns, or greater than 100nm to less than 0.5 microns. Scanning electron micrographs of this feature are shown in fig. 6A and 6B. These holes are unetched holes (i.e., they have not been widened by the etching step).
The holes or defect lines/damage tracks may pass through the full thickness of the material and may be continuous openings throughout the depth of the material or not. FIG. 7 shows a through 150 micron thickness
Fig. 8 shows a larger magnification image of a similar hole or damage track, where the hole diameter can be seen more clearly, and there is also an area where the hole is blocked by the remaining glass. The diameter of the trace made through the glass was about 1 micron. The traces are not fully open-i.e., the area material is removed, but complete vias need not be formed.
Holes/damage tracks may also be punched or otherwise formed in the stack of stacked glass sheets or other substantially transparent materials. In this case, the focal line length needs to be longer than the stack height. For example, 150 microns using 3-fold stacking
This process can also be used to form holes in a sheet of transparent material other than glass. Because the optical system uses line focusing, holes can be drilled through transparent materials with large (>1 micron, up to 4mm, e.g., 10-500 microns) air gaps or other filler materials (e.g., water, transparent polymers, transparent electrodes such as indium tin oxide) between substrate sheets. It should be noted that the ability to continuously drill through multiple glass sheets is a particular advantage of this linear focused drilling method, even when the glass sheets are separated macroscopically (many microns, tens of microns, or even hundreds of microns). In contrast, when other laser methods are used, such as those that rely on Kerr effect-based self-focusing to form high aspect ratio channels, or those that use glass holes themselves to form light guides, the presence of a gap, such as an air gap, between the two glass workpieces can completely upset the process, making high quality drilling of the bottom of the sheet difficult, or completely impossible. This is because when such a non-line-shaped focused (e.g., not a Gauss-Bessel) beam enters the air, it will diffract and spread out quickly. If there are no pre-existing channels to re-define the beam or no significant Kerr effect to refocus the beam, the beam will spread to too large a diameter to modify the underlying material. In the case of self-focusing based on the Kerr effect, the critical power for self-focusing in air is up to-20 times the critical power required in glass, which makes the air gap very problematic. However, for line focus systems, the beam continues to form a high intensity nucleus regardless of the presence of glass material or polymer, or air gaps, or even vacuum there. Thus, the line-shaped focused beam can continue to drill the lower glass layer regardless of whether there is a gap between the glass layer in the material and the upper glass sheet.
Similarly, the stack substrate sheet may comprise substrates having different glass compositions in all stacks. For example, one stack may comprise two substrate sheets of EagleXG glass and Corning (Corning) glass 2320. Alternatively, the stack of transparent substrate sheets may comprise a non-glass transparent inorganic material, such as sapphire. The substrate must be substantially transparent to the laser wavelength used to form the line focus, for example, the laser wavelength is 200nm to 2000nm, e.g., 1064nm,532nm,355nm, or 266 nm. In some embodiments, the substrate may also be transparent to at least one wavelength in the range of about 390nm to about 700 nm. In some embodiments, the substrate can transmit at least 70%, at least 75%, at least 80%, at least 85%, or at least 90% of at least one wavelength in the range of about 390nm to about 700 nm. Drilling/damage tracks in glass or other transparent materials can be used to form articles comprising a stack of substrates (either spaced apart or in direct contact with each other) having a plurality of holes formed through the stack, wherein the holes extend through each of the substrates, the holes having a diameter of, for example, 1-100 microns, and a spacing of, for example, 25-1000 microns. Thus, such a method can be used to form a substantially transparent article comprising a multilayer stack, wherein the multilayer stack comprises a plurality of glass layers and at least one polymer layer located between the glass layers, or at least two glass layers having different compositions, or at least one glass layer and at least one non-glass inorganic layer.
The lateral spacing (pitch) between holes or defect lines/damage tracks is determined by the pulse or pulse group frequency of the laser as the substrate is translated under the focused laser beam. Typically, only a single picosecond laser pulse train is required to form a complete hole, but multiple pulse trains can be used if desired. To form holes at different pitches, the laser may be fired to emit at longer or shorter intervals. In some embodiments, the laser excitation may be generally synchronized with stage-driven movement of the workpiece under the beam, so laser pulse bursts are excited at fixed intervals, such as every 1 micron, every 5 microns, every 10 microns, or every 20 microns or more. When damage tracks are formed in a substrate intended for use as an interposer, the distance or periodicity between adjacent damage tracks may depend on the desired via pattern (i.e., holes formed after the etching process). For example, in some embodiments, the desired damage track pattern (and the resulting vias formed therefrom after etching) is an irregularly spaced, non-periodic pattern. The damage track pattern needs to be at the location where the traces are placed on the intermediate layer or where the special electrical connections are to be made of the chip to be placed on the intermediate layer. Thus, the cutting and damage track drilling for the interposer is different in that the through holes of the interposer are arranged in a non-periodic pattern. However, for cutting patterns, the damage tracks are prepared with a particular periodic pitch, where the pitch depends on the composition of the material being cut. In the methods described herein, the spacing between adjacent holes/defect lines/damage tracks of a hole or defect line (damage track, or perforation) may be about 10 microns or greater, about 20 microns or greater, about 30 microns or greater, about 40 microns or greater, about 50 microns or greater. In some embodiments, the spacing may be up to about 20 mm. In some embodiments, the spacing may be from 50 microns to 500 microns or from 10 microns to 50 microns.
FIG. 9 shows a similar sample, in this
Laser power and lens focal length (which determines focal line length and hence power density) are particularly important parameters to ensure complete penetration through the glass and lower microcracking. For example, fig. 10 shows the results in which significant glass microcracking occurred.
It is also possible to deliberately form perforations or damage tracks which extend only partially through the material. In this case, such traces can be used to prepare blind vias or through vias (via). An example of a laser formed blind via is shown in fig. 11. Here, the damage tracks extend through about 75% of the glass. To achieve this, the focusing of the optics is increased until the line focus only causes damage in the top portion of the glass. Other blind hole depths may be implemented, such as extending only 10%, 25%, 50% or any fractional value of the glass thickness through the glass.
The following conditions were found to be suitable for healing at 300 microns thickness
the input beam diameter to the axicon lens is about 3mm1/e2
Shaft-edge taper angle of 10 °
Initial collimator lens focal length of 125mm
Final objective focal length of 50mm
Angle of convergence of incident beam (beta) 12.75 deg
Focus was set at z 0.25mm (about 50 microns below the top surface of the part)
Laser pulse energy is about 180 microjoules)
The laser pulse repetition rate was 200 kHz.
3 pulses/pulse groups
The results of these conditions are shown in FIG. 9.
For cutting operations, the laser excitation is typically synchronized with the stage-driven movement of the part under the beam, and the laser pulses are most commonly excited at fixed intervals, for example every 1 micron or every 5 microns. The exact spacing is determined by the material properties that promote crack propagation from perforation to perforation at a given stress level in the substrate. However, instead of cutting the substrate, the same method can also be used to perforate only the material with a greater distance between holes or damage tracks. In the case of an interposer, the holes are typically spaced at a distance much greater than that required for cutting-not a pitch of about 10 microns or less, but the spacing between holes may be several hundred microns. As mentioned above, the exact location of the holes need not have regular spacing (i.e., they are non-periodic) -the location is determined only by the time the laser is fired and can be at any location within the part. The holes prepared in fig. 8 are examples of spacing and patterns for some representative interposer applications.
In general, the higher the laser power available, the faster perforations can be made in the material and/or the faster damage tracks can be made in the material using the above-described method. In the case of drilling glass for interleaf or similar applications, the processing speed is generally not directly limited by the laser power, but more by the ability to direct an already abundant laser pulse or burst to the specific location where the hole is required. As described above, in some embodiments, the desired damage track pattern (and the resulting vias formed therefrom after etching) is an irregularly spaced, non-periodic pattern. The damage track pattern needs to be at the location where the traces are placed on the intermediate layer or where the special electrical connections of the chip are to be made on the intermediate. Thus, the cutting and damage track drilling for the interposer is different in that the through holes of the interposer are arranged in a non-periodic pattern. For example, a commercially available burst mode picosecond laser can conveniently generate laser bursts of 200 microjoules per burst at a repetition rate of-100 and 200 kHz. This corresponds to a time-averaged laser power of about 20-40 watts. However, to drill an intervening layer, often most of these pulse bursts are not utilized because the beam can only be set at the desired hole location at a rate of kHz or perhaps tens of kHz, even with the very fast beam deflection method. This means that the main challenge for effective drilling using the line focus and picosecond pulsed laser methods described above is how to move and direct the beam across the substrate surface. One method may be used to segment the hole pattern into a series of one-dimensional lines, where each line contains all of the holes, e.g., holes sharing the same y-axis position. The glass or beam may then be scanned in a "raster scan" mode, in which the laser beam is moved in the x-direction, scanning across all desired aperture locations that share the same y-axis value. As the beam is scanned, the laser is fired to emit bursts only at the desired aperture locations. After scanning a given y-line, the substrate or laser beam is moved to a new y-position and the process is repeated for a new set of desired hole positions on the new y-line. This process is then continued until all of the desired pores on the substrate have been prepared.
The above process is simple but not necessarily efficient, as the speed of the stage and the required hole spacing will determine how many fractions of laser pulses/bursts can be used. For example, if the laser can generate pulses or bursts at a speed of 200,000 bursts/second, but the stage is moving at an average speed of 0.5 m/second and the holes are on average 100 microns apart, then only about 5,000 bursts/second-about 2.5% of the available laser bursts are used. While this did drill 5,000 holes (or damage tracks) per second, this was only a small fraction of the laser capacity.
A more efficient way of directing the laser beam can be used. Scanning of the glass or beam delivery optics may be combined with fast beam deflection, which may come from galvanometer mirrors (galvo) and f-theta lenses, or with piezo actuation of the optics or glass or small range, or electro-optic beam deflection (EOD) or acousto-optic beam deflection (AOD), to enable fast adjustment of the beam in a direction perpendicular to the linear "raster" scanning direction as described above. In this case, because the beam is scanned along the y-axis, small and fast adjustments can be made using a fast beam deflector, which allows pulses to be directed to any aperture within a certain range of the linear stage (x, y) coordinates in a given time. Thus, rather than directing the laser beam aperture only along a given position of the line, the system can now direct the laser beam to any aperture within the scratch (swipe) width dy of the raster scan line. This can greatly increase the number of holes per unit time that the laser beam can enter, and thus greatly increase the number of holes per second that can be drilled. Furthermore, fast beam deflectors can be used not only in the direction perpendicular to the raster scan axis, but also parallel to the scan axis. Furthermore, by flexing the beam parallel to the scan axis, a fast beam flexure assembly (e.g., galvanometer, AOD, EOD, piezo) may be used to achieve drilling of holes within dy's scribe having the same scan axis position (e.g., x-axis in the above embodiments) but having different y-axis positions, since the beam may "move" backwards relative to the stage scan without stopping the linear stage movement to drill a second hole at a given x-position. Furthermore, the rapid deflection along the scan axis also allows for more precise placement of the aperture, as it can be used to direct the beam to the desired x-axis position, regardless of any small time lag in the time that the pulsed laser can be used to fire the pulse bursts, and also compensates for velocity and acceleration artifacts (artifacts) in the linear stage movement.
Alternatively, rather than using continuous scanning in one direction and fast beam movement in coordination with the scanning, a more traditional "step and repeat" method can be used in which the linear stage is moved to a specific (x, y) position, all holes within some field of fast beam deflectors (e.g., galvanometers) are drilled, and the linear stage is stepped to a new (x, y) position and the process repeated. Then, for overall drilling speed, the above-described coordinated linear stage and fast deflector method can be preferably used, wherein the linear stage is kept almost constantly moving.
To achieve even higher system throughput (aperture/sec/system), the beam scanning methods described above can also be combined with beam splitting techniques, where a common laser source distributes its pulse bursts among multiple beam delivery heads on a single substrate or a sequence of substrates. For example, acousto-optic or electro-optic elements may be used to deflect every nth pulse to a given optical path, and N optical heads may be used. This can be achieved by: the angular deflection properties of such beam steering elements, or the polarization-varying properties of such elements, are used to direct the beam through a polarization-dependent beam splitter.
Depending on the desired pattern damage tracks (and vias formed therefrom by the etching process), the damage tracks can be formed at the following rates: greater than about 50 damage tracks/second, greater than about 100 damage tracks/second, greater than about 500 damage tracks/second, greater than about 1,000 damage tracks/second, greater than about 2,000 damage tracks/second, greater than about 3,000 damage tracks/second, greater than about 4,000 damage tracks/second, greater than about 5,000 damage tracks/second, greater than about 6,000 damage tracks/second, greater than about 7,000 damage tracks/second, greater than about 8,000 damage tracks/second, greater than about 9,000 damage tracks/second, greater than about 10,000 damage tracks/second, greater than about 25,000 damage tracks/second, greater than about 50,000 damage tracks/second, greater than about 75,000 damage tracks/second, or greater than about 100,000 damage tracks/second.
Etching:
to enlarge the hole to a size that can be used for metal/conductive material coating/filling and electrical connection, the part is acid etched. The use of acid etching to enlarge the pores to a final diameter can have several benefits 1) acid etching changes the pores from a size too small to be metallized and for the intervening layer (e.g., about 1 micron) to a more convenient size (e.g., 5 microns or higher); 2) etching may begin with a discontinuous hole or simply a damage track through the glass and etch it away to form a continuous via; 3) etching is a highly parallel process in which all holes/damage tracks in a part are simultaneously enlarged-much faster than if the laser had to contact the hole again and drill away more material to enlarge the hole; and 4) etching helps to passivate any edges or small cracks within the part, which increases the overall strength and reliability of the material.
Fig. 51A and 51B show the
In one embodiment, the acid used is 10% HF/15% HNO by volume3. The part was etched at a temperature of 24-25 c for 53 minutes to remove approximately 100 microns of material. The part was immersed in this acid bath and ultrasonically agitated using a combination of 40kHz and 80kHz frequencies to promote fluid penetration and fluid exchange in the hole/damage tracks. In addition, manual agitation (e.g., mechanical agitation) of the part is performed within the ultrasonic field to prevent standing wave patterns from the ultrasonic field from forming "hot spots" or cavitation-related damage on the part, and to provide macroscopic fluid flow across the part. The acid composition and etch rate were deliberately designed to slowly etch the part-material removal rate of only 1.9 microns/minute. An etch rate of less than, for example, about 2 microns/minute allows the acid to completely penetrate the narrow pores/damage tracks and stir to exchange fresh fluid and remove dissolved material from the very narrow pores/damage tracks from the start. This allows the holes to expand at nearly the same rate throughout the thickness of the substrate (i.e., the entire length of the hole or damage track) during the etching process. In some embodiments, the etch rate may be a rate of less than about 10 microns/minute, such as a rate of less than about 5 microns/minute, or a rate of less than about 2 microns/minute.
Fig. 12A and 12B show top and bottom views of the resulting part. The diameter of the pores was about 95 microns and very round, indicating that there was very little microcracking of the material. The pitch of the holes is 300 microns and the diameter of each hole is about 90-95 microns. The images in fig. 12A and 12B were obtained using a backlight, and the bright areas within each hole also indicate that the hole has been completely opened by acid etching. The same sample was cut into small pieces to more closely view the internal profile of the hole. Fig. 14 and 15 show the results. The holes have an "hourglass" shape, i.e. they taper towards the middle of the hole. Typically, this shape is determined by the etching environment, not by the pilot hole formation process. The bright areas are glass and the dark areas are holes. The top (laser incident) diameter of the hole is about 89 microns in diameter, the waist is about 71 microns, and the bottom (laser exit) diameter is about 85 microns.
In contrast, fig. 13 shows the results of etching a sample with significant microcracking from laser machining-the holes are etched into elongated shapes rather than circular features. Microcracking can be reduced by: decreasing the laser burst energy, increasing the number of pulses/burst, or increasing the length of the line focus, for example using a longer focal length objective lens. These variations can reduce the energy density contained within the substrate. In addition, care must be taken to ensure optimal alignment of the optical system so that chromatic aberration is not introduced into the line focus, which creates azimuthal asymmetry in the line focus. This asymmetry can introduce high energy density sites within the substrate that can lead to microcracking.
To confirm that this laser and etching process gave consistent results, a 100x100 array (10,000 total hole count) of hole patterns with a pitch of 300 microns was prepared and the etched samples were then measured using a mechanical imaging system to obtain the top and bottom diameters and waist diameter of each hole. The results are shown as histograms in FIGS. 16A-16C. The top and bottom diameters were both about 95 microns in diameter, the dimensions were very close, and the standard deviation was about 2.5 microns. Unlike the top and bottom diameters, the waist is about 70 microns with a standard deviation of about 3 microns. Thus, the waist is about 30% narrower than the top and bottom diameters. 17A-17C show histograms of roundness measurements of the top, bottom, and waist of the same wells. Roundness is defined as the maximum diameter of a hole minus the minimum diameter of the same hole and is given in microns. The distribution indicates that the pores are substantially circular to less than about 5 microns. There is no significant tail in the profile that would otherwise indicate micro-cracks or gaps etched to a non-circular shape.
After forming the acid etched substrate shown in fig. 12A-15 and having the features shown in fig. 16A-17C, it was found that the acid etching conditions can be varied to adjust the various features of the vias so that they can be used as through vias for the interposer. In some embodiments, for example, a via may have a top opening, a bottom opening, and a waist, and the ratio of the waist diameter to the top or bottom opening diameter may be controlled. As used herein, the waist refers to the narrowest portion of the aperture located between the top and bottom openings. Two factors controlling the waist diameter, top opening, and bottom opening are the etch reaction rate and diffusion rate. In order to etch away the entire thickness of the substrate to enlarge the damage tracks into through vias, the acid needs to traverse the entire length of the damage tracks. If the etch rate is too fast so that the acid does not have enough time to diffuse and reach all parts of the damage track, the acid will disproportionately etch more material away at the surface of the material than in the middle of the material. The Theiler modulus of the etching process can be controlled
wherein:
kris the reaction rate constant of the etch;
c is the bulk acid concentration;
γ is a factor based on the number of kinetic reaction steps;
r is the radius of the pores during the reaction;
Dis effectiveIs the effective diffusion coefficient of acid through water into the damage tracks or pores, which is the natural diffusion coefficient D of amplification enhanced by stirring and ultrasound; and
l is 1/2 of material thickness.
According to the above formula, the theiler modulus is greater than 1 when the etch reaction time is greater than the diffusion time. This means that the acid is depleted before it passes the entire length of the damage track or hole and can be replenished by diffusion in the center of the damage track or hole. As a result, etching proceeds faster at the top and bottom of the trace or hole and from krControlled, the etching in the center will proceed more slowly and the rate is controlled by diffusion, which results in an hourglass-like shape of the via. However, if the diffusion time is equal to or greater than the etch reaction time, the theiler modulus is less than or equal to 1. Under such conditions, the acid concentration along the entire damage tracks or holes is uniform and the damage tracks or holes will be uniformly etched to form substantially cylindrical through-holes.
In some embodiments, the diffusion time and etch reaction time can be controlled to control the theler modulus of the etching system and thereby control the ratio of the waist diameter to the top and bottom opening diameters. FIG. 52 shows the relationship between the Therler (Thiele) modulus of the etching system and the expected waist diameter in percent relative to the top and bottom opening diameters. In some embodiments, the theler modulus of the etching process may be less than or equal to about 5, less than or equal to about 4.5, less than or equal to about 4, less than or equal to about 3.5, less than or equal to about 3, less than or equal to about 2.5, less than or equal to about 2, less than or equal to about 1.5, or less than or equal to about 1. In some embodiments, the waist diameter of a through-hole is 50% -100%, 50% -95%, 50% -90%, 50% -85%, 50% -80%, 50% -75%, 50% -70%, 55% -100%, 55% -95%, 55% -90%, 55% -85%, 55% -80%, 55% -75%, 55% -70%, 60% -100%, 60% -95%, 60% -60%, 60% -85%, 60% -80%, 60% -75%, 60% -70%, 65% -100%, 65% -95%, 65% -90%, 65% -85%, 65% -80%, 65% -75%, 65% -70%, 70% -100%, 70% -95%, 70% -90%, 70% -85%, 70% -80%, 70% -75%, 75% -100%, 75% -95%, 75% -90%, 75% -85%, 75% -80%, 80% -100%, 80% -95%, 80% -90%, 80% -85%, 85% -100%, 85% -95%, 85% -90%, 90% -100%, 90% -95%, or 95% -100%. In some embodiments, the diameter of the waist of the through-hole is about 50% or greater, about 55% or greater, about 60% or greater, about 65% or greater, about 70% or greater, about 75% or greater, about 80% or greater, about 85% or greater, about 90% or greater, about 95% or greater, or about 100% of the diameter of the top opening and/or the diameter of the bottom opening of the through-hole. In some embodiments, the waist diameter of the through-hole is 50% -100%, 50% -95%, 50% -90%, 50% -85%, 50% -80%, 50% -75%, 50% -70%, 55% -100%, 55% -95%, 55% -90%, 55% -85%, 55% -80%, 55% -75%, 55% -70%, 60% -100%, 60% -95%, 60% -60%, 60% -85%, 60% -80%, 60% -75%, 60% -70%, 65% -100%, 65% -95%, 65% -90%, 65% -85%, 65% -80%, 65% -75%, 65% -70%, 70% -100%, 70% -95%, 70% -90%, 70% -85%, 70% -80%, 70% -75%, 75% -100%, 75% -95%, 75% -90%, 75% -85%, 75% -80%, 80% -100%, 80% -95%, 80% -90%, 80% -85%, 85% -100%, 85% -95%, 85% -90%, 90% -100%, 90% -95%, or 95% -100%. In some embodiments, the diameter of the waist of the through-hole is about 50% or greater, about 55% or greater, about 60% or greater, about 65% or greater, about 70% or greater, about 75% or greater, about 80% or greater, about 85% or greater, about 90% or greater, about 95% or greater, or about 100% of the average of the top opening diameter and the bottom opening diameter of the through-hole.
As can be determined from the above-mentioned theiler's modulus equation, the initial radius of the damage track and the glass thickness contribute to the theiler's modulus. Fig. 53 shows how the theler modulus decreases with the initial radius of the damage track. Fig. 54 shows how the theler modulus increases with half the thickness of the substrate. In some cases, the substrate thickness and damage track radius are factors that cannot be changed if a certain thickness or damage track radius is desired. Therefore, in this caseNext, other factors that affect the theler modulus may be adjusted. For example, FIG. 55 shows how the Theiler modulus follows the effective diffusion coefficient (D)Is effective) Is increased and decreased. In some embodiments, the effective diffusion coefficient may be increased by adding agitation and/or sonication to the etching conditions, as described in more detail below. FIG. 56 shows how the Tiler modulus decreases with decreasing acid concentration, in this example HF concentration. Figure 56 also shows how the combination of increasing the effective diffusion coefficient and decreasing the acid concentration decreases the theler modulus.
In some embodiments, the etch reaction time may be controlled by adjusting the acid concentration in the etching solution. In some embodiments, the etching solution may be an aqueous solution comprising deionized water, a primary acid, and a secondary acid. The primary acid may be hydrofluoric acid and the secondary acid may be nitric acid, hydrochloric acid or sulfuric acid. In some embodiments, the etching solution may comprise only the primary acid. In some embodiments, the etching solution may comprise a primary acid other than hydrofluoric acid and/or a secondary acid other than nitric, hydrochloric, or sulfuric acid. Exemplary etching solutions may comprise 10 volume% hydrofluoric acid/15 volume% nitric acid or 5 volume% hydrofluoric acid/7.5 volume% nitric acid, or 2.5 volume% hydrofluoric acid/3.75 volume% nitric acid.
In some embodiments, orientation of the substrate in the etch bath, mechanical agitation, and/or addition of surfactants to the etching solution are other etching conditions that may be modified to adjust the through-hole features. In some embodiments, the etching solution is ultrasonically agitated, and the substrate is oriented in an etch bath containing the etching solution such that the top and bottom openings of the damage tracks receive substantially uniform exposure to the ultrasonic waves, thereby uniformly etching the damage tracks. For example, if the ultrasonic sensor is placed at the bottom of the etch bath, the substrate may be oriented in the etch bath such that the surface of the substrate with the damage tracks is perpendicular to the bottom of the etch bath rather than parallel to the bottom of the etch bath.
In some embodiments, the etch bath may be mechanically agitated in the x, y, and z directions to improve uniform etching of damage tracks. In some embodiments, the mechanical agitation in the x, y, and z directions may be continuous.
In some embodiments, a surfactant may be added to the etching solution to increase the wetting ability of the damage tracks. Increased wetting ability reduces diffusion time and may allow for an increase in the ratio of the through-hole waist diameter to the through-hole top and bottom opening diameters. In some embodiments, the surfactant can be any suitable surfactant that dissolves in the etching solution and does not react with the acid in the etching solution. In some embodiments, the surfactant may be a fluorosurfactant such as
Speed:
one of the main advantages of using the method described above for making perforations or "pilot holes" or "damage tracks" by means of laser light is the extremely fast processing times. Each of the damage tracks shown in fig. 7 was prepared using a single burst of picosecond laser pulses. This is in essence different from percussion drilling, which requires many laser pulses to gradually remove a layer of material.
For the samples shown here, the platform speed was 12 m/min-200 mm/sec. For a 300 micron interval, this means that a burst of laser pulses is fired every 1.5 milliseconds to form a hole, with a formation rate of 667 holes/second. The stage acceleration and deceleration was calculated to produce each row of this approximately 30mmx30mm hole pattern with a hole formation rate well in excess of 300 holes/second. If the physical range of pattern preparation is larger, the frequency of plateau acceleration is lower and the average pore formation rate will be faster.
Since the laser used here can easily provide 100,000 pulses/second at full pulse energy, holes can be formed at this rate. Generally, the limit on the rate of hole formation is how fast the laser beam can be moved relative to the substrate. If the holes are 10 microns apart and the platen velocity is 1 m/sec, then 100,000 holes/sec are formed. In fact, it is often done to cut the substrate. But for actual interleaf layers, the holes are often hundreds of microns apart and the spacing is more random (i.e. there is a non-periodic pattern). Thus, the number of holes/second for the pattern shown is only about 300 holes/second as described above. To obtain higher velocities, the stage speed can be increased, for example from 200 mm/sec to 1 m/sec, which achieves a further 5-fold increase in speed. Similarly, if the average pore pitch is less than 300 microns, the rate of pore formation will increase by the same amount.
In addition to translating the substrate under the laser beam, other methods can be used to rapidly move the laser from hole to hole: the optical head itself is moved, using a galvanometer and an f-theta lens, an acousto-optic deflector, a spatial light modulator, and the like.
As mentioned above, depending on the desired pattern damage tracks (and vias formed therefrom by the etching process), the damage tracks can be formed at the following rates: greater than about 50 damage tracks/second, greater than about 100 damage tracks/second, greater than about 500 damage tracks/second, greater than about 1,000 damage tracks/second, greater than about 2,000 damage tracks/second, greater than about 3,000 damage tracks/second, greater than about 4,000 damage tracks/second, greater than about 5,000 damage tracks/second, greater than about 6,000 damage tracks/second, greater than about 7,000 damage tracks/second, greater than about 8,000 damage tracks/second, greater than about 9,000 damage tracks/second, greater than about 10,000 damage tracks/second, greater than about 25,000 damage tracks/second, greater than about 50,000 damage tracks/second, greater than about 75,000 damage tracks/second, or greater than about 100,000 damage tracks/second.
Final part:
in some embodiments, subjecting the substrate to the damage track formation and acid etching processes described above can result in a substrate having a plurality of through holes. In some embodiments, the diameter of the through-holes can be about 30 microns or less, about 25 microns or less, about 20 microns or less, about 15 microns or less, about 10 microns or less, about 5 to about 10 microns, about 5 to about 15 microns, about 5 to about 20 microns, about 5 to about 25 microns, about 5 to about 30 microns, or up to several tens of microns, depending on the requirements of the intended application. In other embodiments, the diameter of the through-hole may be greater than about 20 microns. In some embodiments, the substrate can haveThere are vias having different diameters, for example the vias may have a difference in diameter of at least 5 microns. In some embodiments, the difference in the top and bottom opening diameters of the via may be 3 microns or less, 2.5 microns or less, 2 microns or less, 1.5 microns or less, or 1 micron or less, which may be achieved by using a line-shaped focused beam to form damage tracks in the material. These damage tracks remain of very small diameter throughout the depth of the substrate, which ultimately results in uniform top and bottom diameters after etching. In some embodiments, the spacing (center-to-center distance) between adjacent vias can be about 10 microns or greater, about 20 microns or greater, about 30 microns or greater, about 40 microns or greater, about 50 microns or greater. In some embodiments, the spacing of adjacent through holes may be up to about 20 mm. In some embodiments, the via density can be about 0.01 vias/mm2Or greater, about 0.1 through holes/mm2Or greater, about 1 via/mm2Or greater, about 5 through holes/mm2Or greater, about 10 through holes/mm2Or greater, about 20 through holes/mm2Or greater, about 30 through holes/mm2Or greater, about 40 through holes/mm2Or greater, about 50 through holes/mm2Or greater, about 75 through holes/mm2Or greater, about 100 through holes/mm2Or greater, about 150 through holes/mm2Or greater, about 200 through holes/mm2Or greater, about 250 through holes/mm2Or greater, about 300 through holes/mm2Or greater, about 350 through holes/mm2Or greater, about 400 through holes/mm2Or greater, about 450 through holes/mm2Or greater, about 500 through holes/mm2Or greater, about 550 through holes/mm2Or greater, about 600 through holes/mm2Or greater, or about 650 through holes/mm2Or larger. In some embodiments, the via density can be about 0.01 vias/mm2About 650 through holes/mm2Or about 5 through holes/mm2About 50 through holes/mm2。
As noted above, in some embodiments, the waist diameter of a through-hole is 50% -100%, 50% -95%, 50% -90%, 50% -85%, 50% -80%, 50% -75%, 50% -70%, 55% -100%, 55% -95%, 55% -90%, 55% -85%, 55% -80%, 55% -75%, 55% -70%, 60% -100%, 60% -95%, 60% -60%, 60% -85%, 60% -80%, 60% -75%, 60% -70%, 65% -100%, 65% -95%, 65% -90%, 65% -85%, 65% -80%, 65% -75%, 65% -70%, 70% -100%, 70% -95%, 70% -90%, 70% -85%, 70% -80%, 70% -75%, 75% -100%, 75% -95%, 75% -90%, 75% -85%, 75% -80%, 80% -100%, 80% -95%, 80% -90%, 80% -85%, 85% -100%, 85% -95%, 85% -90%, 90% -100%, 90% -95%, or 95% -100%. In some embodiments, the diameter of the waist of the through-hole is about 50% or greater, about 55% or greater, about 60% or greater, about 65% or greater, about 70% or greater, about 75% or greater, about 80% or greater, about 85% or greater, about 90% or greater, about 95% or greater, or about 100% of the diameter of the top opening and/or the diameter of the bottom opening of the through-hole. In some embodiments, the waist diameter of the through-hole is 50% -100%, 50% -95%, 50% -90%, 50% -85%, 50% -80%, 50% -75%, 50% -70%, 55% -100%, 55% -95%, 55% -90%, 55% -85%, 55% -80%, 55% -75%, 55% -70%, 60% -100%, 60% -95%, 60% -60%, 60% -85%, 60% -80%, 60% -75%, 60% -70%, 65% -100%, 65% -95%, 65% -90%, 65% -85%, 65% -80%, 65% -75%, 65% -70%, 70% -100%, 70% -95%, 70% -90%, 70% -85%, 70% -80%, 70% -75%, 75% -100%, 75% -95%, 75% -90%, 75% -85%, 75% -80%, 80% -100%, 80% -95%, 80% -90%, 80% -85%, 85% -100%, 85% -95%, 85% -90%, 90% -100%, 90% -95%, or 95% -100%. In some embodiments, the diameter of the waist of the through-hole is about 50% or greater, about 55% or greater, about 60% or greater, about 65% or greater, about 70% or greater, about 75% or greater, about 80% or greater, about 85% or greater, about 90% or greater, about 95% or greater, or about 100% of the average diameter of the top and bottom openings of the through-hole.
In some embodiments, the aspect ratio (substrate thickness: via diameter) of the through-holes may be about 1:1 or greater, about 2:1 or greater, about 3:1 or greater, about 4:1 or greater, about 5:1 or greater, about 6:1 or greater, about 7:1 or greater, about 8:1 or greater, about 9:1 or greater, about 10:1 or greater, about 11:1 or greater, about 12:1 or greater, about 13:1 or greater, about 14:1 or greater, about 15:1 or greater, about 16:1 or greater, about 17:1 or greater, about 18:1 or greater, about 19:1 or greater, about 20:1 or greater, about 25:1 or greater, about 30:1 or greater, or about 35:1 or greater. In some embodiments, the aspect ratio of the through-holes may be from about 5:1 to about 10:1, from about 5:1 to 20:1, from about 5:1 to 30:1, or from about 10:1 to 20:1 from about 10:1 to 30: 1.
In some embodiments, the substrate has a thickness of about 20 microns to about 3mm, about 20 microns to about 1mm, or about 50 microns to 300 microns, or 100 microns to 750 microns, or about 1mm to about 3 mm. In some embodiments, the substrate may be made of a transparent material, including, but not limited to, glass, fused quartz, synthetic quartz, glass-ceramics, and crystalline materials such as sapphire. In some embodiments, the substrate can be glass, and the glass can comprise an alkali-containing glass, an alkali-free glass (e.g., an alkali-free alkali boroaluminosilicate glass), or a laminated glass piece, and the layers comprise different glass compositions. In some embodiments, the glass can be a chemically strengthened (e.g., ion exchanged) glass. In some embodiments, the substrate may be transparent to at least one wavelength in the range of about 390nm to about 700 nm. In some embodiments, the substrate can transmit at least 70%, at least 75%, at least 80%, at least 85%, or at least 90% of at least one wavelength in the range of about 390nm to about 700 nm.
The vias may then be coated and/or filled with a conductive material and used for electrical interposer applications. In some embodiments, the coating and/or filling may be performed by metallization. For example, metallization may be performed by vacuum deposition, electroless plating, filling with a conductive paste, or various other methods. After that, electrical traces can be patterned on the surface of the part, and a series of redistribution layers and contact pads can be formed, which enable routing of electrical signals from the holes to connections on the microchip or other circuitry.
For biochemical applications, such as digital polymerase chain reaction (dPCR), parts can also be functionalized with coatings that achieve control of the hydrophilic or hydrophobic properties of the surface. Other coatings may also be applied which enable the attachment of antibodies, proteins or other biomolecules. For dPCR microarrays, substrates with very dense and regular arrays of pores are particularly useful — for example, patterns of hexagonal close-packed pores with pitches less than about 100 microns. For such patterns, the speed of formation possible using the above laser method is particularly high, since the laser can be emitted extremely frequently and the full repetition rate of the laser is used efficiently. Thus, pore formation rates in excess of 10,000 pores/second (1 m/second plateau velocity and 100 micron pore spacing) can be achieved. It should be noted that hole formation may utilize only a small fraction of the laser pulse. The laser burst repetition rate can easily be several hundred kHz, but it is difficult to direct the beam to a new aperture location at a rate large enough to use all of these bursts. For example, the actual pore formation rate may be 100 pores/sec, 500 pores/sec, 999 pores/sec, 3,000 pores/sec, 5,000 pores/sec, 10,000 pores/sec, while the laser repetition rate may be 100,000 bursts/sec, 200,000 bursts/sec at the same time. In these cases, the majority of the pulse burst pulses are redirected by a device such as an electro-optic modulator into a beam dump (beam dump), rather than out of the laser and to the substrate. Thus, a smaller number of bursts/sec is used for drilling than is available from virtually the full repetition rate of the laser. Many short-pulse lasers have an electro-optical or acousto-optical modulator at their output so that they operate in this manner.
Examples
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