Methods for forming holes in substrates
Methods for forming holes in a substrate by reducing back reflections of a quasi-non-diffracting beam into the substrate are described herein. In some embodiments, a method of processing a substrate having a first surface and a second surface includes applying an exit material to the second surface of the substrate, wherein a difference between a refractive index of the exit material and a refractive index of the substrate is 0.4 or less, and focusing a pulsed laser beam into a quasi-non-diffracting beam directed into the substrate such that the quasi-non-diffracting beam enters the substrate through the first surface. The substrate is transparent to at least one wavelength of the pulsed laser beam. The quasi-non-diffracting beam generates an induced absorption within the substrate that produces a damage track within the substrate.
1. A method of processing a substrate comprising a first surface and a second surface, the method comprising:
applying an exit material to the second surface of the substrate, wherein a difference between a refractive index of the exit material and a refractive index of the substrate is 0.4 or less; and
focusing a pulsed laser beam into a quasi-non-diffracting beam directed into the substrate such that the quasi-non-diffracting beam enters the substrate through the first surface, the quasi-non-diffracting beam generating an induced absorption within the substrate, the induced absorption producing a damage track within the substrate,
wherein:
the substrate is transparent to at least one wavelength of the pulsed laser beam, and
a location that the quasi-non-diffracting beam exits the exit material is 50 μm or more away from the second surface of the substrate in a direction parallel to the quasi-non-diffracting beam.
2. The method of claim 1 , wherein the difference is 0.2 or less.
3. The method of claim 1 , wherein the substrate is selected from the group consisting of glass, glass-ceramic and ceramic.
4. The method of claim 1 , wherein a location that the quasi-non-diffracting beam exits the exit material is 50 μm or more away from the second surface of the substrate in a direction parallel to the quasi-non-diffracting beam.
5. The method of claim 1 , wherein the exit material comprises at least two layers.
6. The method of claim 1 , wherein the exit material is one or more of a polymer, an anti-reflective coating, a silicone layer, a photoresist layer, and water.
7. The method of claim 1 , wherein the exit material comprises water and a supporting substrate such that the water is disposed between the supporting substrate and the second surface of the substrate.
8. The method of claim 1 , wherein:
the exit material is a silicone layer and a polyester substrate; and
the silicone layer is disposed between the polyester substrate and the second surface of the substrate.
9. The method of claim 1 , wherein the quasi-non-diffracting beam is selected from the group consisting of a Gauss-Bessel beam and an Airy beam.
10. The method of claim 1 , wherein:
the quasi-non-diffracting beam comprises a beam waist; and
the quasi-non-diffracting beam defines a laser beam focal line having a first end point and a second end point;
the first end point and the second end point are defined as locations where the quasi-non-diffracting beam has propagated a distance from the beam waist equal to a Rayleigh range of the quasi-non-diffracting beam.
11. The method of claim 1 , wherein the exit material is applied to the second surface such that there is a reflection of 2.5% or less at a predetermined region surrounding the damage track.
12. The method of claim 11 , wherein a diameter of the predetermined region is 300 μm.
13. The method of claim 1 , wherein the pulsed laser beam comprises a burst comprising a plurality of pulses.
14. The method of claim 13 , wherein a pulse width of each pulse of the plurality of pulses is within a range of 100 fsec to 10 psec, including endpoints.
15. The method of claim 1 , wherein:
the quasi-non-diffracting beam defines a laser beam focal line having a first endpoint and a second endpoint each defined by locations where the quasi-non-diffracting beam has propagated a distance from the beam waist equal to a Rayleigh range;
the first endpoint is closer to the first surface of the substrate than the second surface;
the second endpoint is closer to the second surface of the substrate than the first surface; and
the second endpoint is outside of the substrate such that a distance between the second endpoint and the second surface is 100 μm or less.
16. The method of claim 15 , wherein the second endpoint is outside of the substrate such that a distance between the second endpoint and the second surface is 10 μm or less.
17. The method of claim 1 , further comprising etching the substrate in an etching solution to produce a hole having a diameter of 1 μm or more by enlarging the damage track in the substrate.
18. The method of claim 17 , further comprising coating interior surfaces of the hole with an electrically conductive material to provide electrical conductivity between a top and a bottom of the hole.
19. The method of claim 17 , wherein a difference between an average surface roughness of interior surfaces of the hole from a waist of the hole to the first surface and an average surface roughness of interior surfaces of the hole from the waist of the hole to the second surface is 1 μm Ra or less.
20. A method of forming a hole in a substrate comprising a first surface and a second surface, the method comprising:
focusing a pulsed laser beam into a quasi-non-diffracting beam directed into the substrate such that the quasi-non-diffracting beam enters the substrate through the first surface, the quasi-non-diffracting beam generating an induced absorption within the substrate, the induced absorption producing a damage track within the substrate, wherein:
the substrate is transparent to at least one wavelength of the pulsed laser beam;
the quasi-non-diffracting beam defines a laser beam focal line having a first endpoint and a second endpoint each defined by locations where the quasi-non-diffracting beam has propagated a distance from a beam waist equal to a Rayleigh range;
the first endpoint is closer to the first surface of the substrate than the second surface;
the second endpoint is closer to the second surface of the substrate than the first surface; and
the second endpoint is outside of the substrate such that a distance between the second endpoint and the second surface is 100 μm or less; and
etching the substrate to produce the hole by enlarging the damage track in the substrate.
21. A method of processing a substrate comprising a first surface and a second surface, the method comprising:
disposing a liquid between a first surface of a supporting substrate and the second surface of the substrate, wherein a difference between a refractive index of the supporting substrate and a refractive index of substrate is 0.4 or less, and a difference between a refractive index of the liquid and the refractive index of the substrate is 0.4 or less;
focusing a pulsed laser beam into a quasi-non-diffracting beam directed into the substrate such that the quasi-non-diffracting beam enters the substrate through the first surface, the quasi-non-diffracting beam generating an induced absorption within the substrate, the induced absorption producing a damage track within the substrate; and
etching the substrate in an etching solution to produce a hole having a diameter of 1 μm or more by enlarging the damage track in the substrate;
wherein the substrate and the supporting substrate are transparent to at least one wavelength of the pulsed laser beam.
22. The method of claim 21 , wherein a difference between an average surface roughness of interior surfaces of the hole form a waist of the hole to the first surface and an average surface roughness of interior surfaces of the hole from the waist of the hole to the second surface is 1 μm Ra or less.