阅读说明：本技术 具有轴向可变侧壁锥度的孔的含二氧化硅基材及其形成方法 (Silicon dioxide containing substrate with axially variable sidewall taper hole and method of forming the same ) 是由 R·E·达尔伯格 黄甜 金宇辉 G·A·皮切 D·O·里基茨 于 2018-05-22 设计创作，主要内容包括：揭示了包含具有窄腰的孔的含二氧化硅基材以及相关的装置和方法。在一个实施方式中,制品包括含二氧化硅基材,所述含二氧化硅基材包含大于或等于85摩尔％二氧化硅、第一表面、与第一表面相对的第二表面以及从第一表面朝向第二表面延伸穿过含二氧化硅基材的孔。孔包括：第一表面处小于或等于100μm的第一直径,第二表面处直径小于或等于100μm的第二直径,以及第一表面与第二表面之间的孔腰。孔腰具有小于第一直径和第二直径的腰直径,使得腰直径与第一直径和第二直径之比分别小于或等于75％。(Silica-containing substrates comprising pores having narrow waists and related devices and methods are disclosed. In one embodiment, an article includes a silica-containing substrate comprising greater than or equal to 85 mole percent silica, a first surface, a second surface opposite the first surface, and a pore extending through the silica-containing substrate from the first surface toward the second surface. The aperture includes: a first diameter of less than or equal to 100 μm at the first surface, a second diameter of less than or equal to 100 μm at the second surface, and a waist of pores between the first surface and the second surface. The bore waist has a waist diameter that is less than the first diameter and the second diameter such that a ratio of the waist diameter to the first diameter and the second diameter, respectively, is less than or equal to 75%.)

1. A method of processing a substrate comprising silica, a first surface, and a second surface opposite the first surface, the method comprising:

forming a damage track through the substrate from the first surface to the second surface using a laser beam, wherein a substrate modification level along the damage track decreases in a first direction from the first surface toward the substrate block and the substrate modification level decreases in a second direction from the second surface toward the substrate block, such that the damage track comprises:

a first height modification segment adjacent the first surface;

a second height-modifying segment adjacent the second surface; and

a minimum modification stage disposed between the first height modification stage and the second height modification stage; and

etching a substrate with an etching solution to form pores, the pores comprising: a first diameter at the first surface, a second diameter at the second surface, and a waist of the hole between the first surface and the second surface having a waist diameter, wherein the waist diameter is less than the first diameter and less than the second diameter.

2. The method of claim 1, wherein the minimally modified segment of the damage track is modified by a laser beam.

3. The method of any one of the preceding claims, wherein at least a portion of the substrate in the smallest modified segment of the damage track is not modified by the laser beam.

4. The method of any of claims 1-3, wherein the substrate comprises at least 75 mole% silica.

5. The method of any of claims 1-3, wherein the substrate comprises at least 90 mole% silica.

6. The method of any of claims 1-3, wherein the substrate comprises at least 99 mole% silica.

7. The method of any of claims 1-3, wherein the substrate comprises silica that has not been purposefully doped.

8. The method of any one of the preceding claims, wherein the substrate has a thickness greater than or equal to 50 μ ι η and less than or equal to 1 mm.

9. The method of any of the preceding claims, wherein the waist diameter is at least 50% of the first and second diameters, respectively.

10. The method of any one of the preceding claims, wherein the aperture has an hourglass shape.

11. The method of any one of the preceding claims, wherein the location of the aperture waist is closer to one of the first surface and the second surface relative to the other of the first surface or the second surface.

12. The method of any one of the preceding claims, wherein the first diameter and the second diameter are greater than or equal to 5 μ ι η.

13. The method of any one of the preceding claims, wherein:

a laser source that emits a laser beam with the first surface of the substrate facing downward; and

the ratio of the waist diameter to the first diameter is greater than or equal to 35% and less than or equal to 45%.

14. The method of any one of the preceding claims, wherein:

the hole comprises a longitudinal axis, an inner wall, a first tapered region between the first surface and the hole waist, and a second tapered region between the second surface and the hole waist;

the first tapered region comprises a first angle measured between an inner wall in the first tapered region and the longitudinal axis; and

the second tapered region includes a second angle measured between the inner wall in the second tapered region and the longitudinal axis.

15. The method of claim 14, wherein the first angle is equal to the second angle.

16. The method of claim 14, wherein the first angle is different from the second angle.

17. The method of any one of the preceding claims, wherein the laser beam is operated such that:

the damage track comprises an additional minimum modification stage located between the minimum modification stage and the second height modification stage; and

the modification level of the additional minimum modification stage is less than the modification levels of the first and second highly modified stages.

18. The method of any one of the preceding claims, wherein:

the aperture includes:

a longitudinal axis;

an inner wall;

a first tapered region located proximate to the first surface, the first tapered region comprising a first angle measured between an inner wall in the first tapered region and the longitudinal axis;

a second tapered region located between the first tapered region and the bore waist, the second tapered region comprising a second angle measured between an inner wall in the second tapered region and the longitudinal axis;

a third tapered region adjacent to the aperture waist, the third tapered region comprising a third angle measured between an inner wall in the third tapered region and the longitudinal axis; and

a fourth tapered region located between the third tapered region and the second surface, the fourth tapered region comprising a fourth angle measured between an inner wall in the fourth tapered region and the longitudinal axis; and

each of the second angle and the third angle is smaller than the first angle and the fourth angle.

19. The method of claim 18, wherein the first angle and the fourth angle are different.

20. The method of claim 19, wherein the first angle and the fourth angle are each less than or equal to 5 degrees.

21. The method of claim 18, wherein the second angle is different from the third angle.

22. The method of claim 18, wherein each of the first, second, third, and fourth angles is different from the others of the first, second, third, and fourth angles.

23. The method of any one of claims 18-22, wherein the aperture waist is located closer to one of the first surface and the second surface than to the other of the first surface or the second surface.

24. The method of any one of the preceding claims, wherein:

the laser beam comprises a pulsed laser beam focused into a laser beam focal line positioned through the bulk of the substrate; and

the laser beam focal line produces induced multiphoton absorption in the substrate that produces material modification within the substrate along the laser beam focal line, thereby forming a damage track.

25. The method of claim 24, wherein the pulsed laser beam comprises a plurality of laser beam sub-pulses, and individual ones of the plurality of laser beam sub-pulses are separated by a time interval.

26. The method of claim 25, wherein the plurality of laser beam groups comprises less than 10 individual laser beam sub-pulses.

27. The method of claim 25, wherein the plurality of laser beam groups comprises less than or equal to 5 individual laser beam sub-pulses.

28. The method of any of claims 24-27, wherein the laser beam focal line of the laser beam modifies the substrate more strongly near the first and second surfaces of the substrate than away from the regions at the first and second surfaces of the substrate.

29. The method of any of claims 24-28, wherein the maximum intensity of the laser beam focal line is located at a midpoint between the first surface and the second surface along a line of the desired damage trajectory.

30. The method of any of claims 24-28, wherein the maximum intensity of the laser beam focal line is closer to one of the first surface and the second surface relative to the other of the first surface or the second surface.

31. The method of any of the preceding claims, further comprising adjusting a temperature of one or more of the first surface and the second surface while forming the damage track using the laser beam.

32. The method of any preceding claim, wherein the laser beam is a quasi-undiffracted beam.

33. The method of any one of the preceding claims, wherein the energy of the laser beam is above a threshold for modification of the substrate.

34. The method of claim 33, wherein the energy of the laser beam is less than 75% above the threshold for modification of the substrate.

35. The method of claim 34, wherein the energy of the laser beam is less than 10% above the threshold for modification of the substrate.

36. The method of any of claims 24-28, further comprising manipulating the laser beam such that the intensity of the laser beam focal line at the first end of the laser beam focal line and the second end of the laser beam focal line is greater than the central region of the laser beam focal line.

37. The method of any one of the preceding claims, wherein the etching solution comprises hydrofluoric acid.

38. The method of claim 37, wherein the etching solution comprises 20 volume% hydrofluoric acid and 12 volume% hydrochloric acid.

39. The method of any one of the preceding claims, further comprising electroplating the holes after etching the substrate.

40. An article of manufacture, comprising:

a silica-containing substrate comprising greater than or equal to 75 mole percent silica, a first surface, a second surface opposite the first surface, and a hole extending through the silica-containing substrate from the first surface toward the second surface, the hole comprising:

a first diameter at the first surface;

a second diameter at the second surface; and

a waist located between the first surface and the second surface, wherein the waist has a waist diameter that is less than the first diameter and the second diameter such that a ratio of the waist diameter to the first diameter and the second diameter, respectively, is less than or equal to 75%.

41. The article of claim 40, wherein the silica-containing substrate comprises at least 90 mole percent silica.

42. The article of claim 40, wherein the silica-containing substrate comprises at least 99 mole percent silica.

43. The article of claim 40, wherein the silica-containing substrate comprises silica that has not been purposefully doped.

44. The article of any one of claims 40-43, wherein the silica-containing substrate has a thickness greater than or equal to 50 μm and less than or equal to 1 mm.

45. The article of any one of claims 40-44, wherein the waist diameter is at least 50% of the first diameter and the second diameter, respectively.

46. The article of any one of claims 40-45, wherein the aperture has an hourglass shape.

47. The article of any one of claims 40-46, wherein the aperture waist is located closer to one of the first surface and the second surface relative to the other of the first surface or the second surface.

48. The article of any one of claims 40-47, wherein the first diameter and the second diameter are each greater than or equal to 5 μm and less than or equal to 100 μm.

49. The article of any one of claims 40-48, wherein the ratio of waist diameter to first diameter is greater than or equal to 35% and less than or equal to 45%.

50. The article of any one of claims 40-49, wherein:

the hole comprises a longitudinal axis, an inner wall, a first tapered region between the first surface and the hole waist, and a second tapered region between the second surface and the hole waist;

the first tapered region comprises a first angle measured between an inner wall in the first tapered region and the longitudinal axis; and

the second tapered region includes a second angle measured between the inner wall in the second tapered region and the longitudinal axis.

51. The article of claim 50, wherein the first angle is equal to the second angle.

52. The article of claim 50, wherein the first angle is different than the second angle.

53. The article of any one of claims 40-49, wherein:

the aperture includes:

a longitudinal axis;

an inner wall;

a first tapered region located proximate to the first surface, the first tapered region comprising a first angle measured between an inner wall in the first tapered region and the longitudinal axis;

a second tapered region located between the first tapered region and the bore waist, the second tapered region comprising a second angle measured between an inner wall in the second tapered region and the longitudinal axis;

a third tapered region adjacent to the aperture waist, the third tapered region comprising a third angle measured between an inner wall in the third tapered region and the longitudinal axis; and

a fourth tapered region located between the third tapered region and the second surface, the fourth tapered region comprising a fourth angle measured between an inner wall in the fourth tapered region and the longitudinal axis; and

each of the second angle and the third angle is smaller than the first angle and the fourth angle.

54. The article of claim 53, wherein the first angle and the fourth angle are different.

55. The article of claim 54, wherein the first angle and the fourth angle are each less than or equal to 5 degrees.

56. The article of claim 53, wherein the second angle is different than the third angle.

57. The article of any one of claims 53-56, wherein the aperture waist is located closer to one of the first surface and the second surface relative to the other of the first surface or the second surface.

58. The article of any one of claims 40-57, wherein the pores are plated with a conductive material.

59. The article of any one of claims 40-58, further comprising a plurality of pores through the silica-containing substrate.

60. An electronic device, comprising:

a silica-containing substrate comprising greater than or equal to 75 mole percent silica, a first surface, a second surface opposite the first surface, and a hole extending through the silica-containing substrate from the first surface toward the second surface, the hole comprising:

a first diameter at the first surface;

a second diameter at the second surface; and

a waist located between the first surface and the second surface, wherein the waist has a waist diameter that is less than the first diameter and the second diameter such that a ratio of the waist diameter to the first diameter and the second diameter, respectively, is less than or equal to 75%; and

a semiconductor device attached to the silicon dioxide containing substrate, wherein the semiconductor device is electrically connected to the aperture.

61. The electronic device of claim 60, wherein the silica-containing substrate comprises at least 90 mole percent silica.

62. The electronic device of claim 60, wherein the silica-containing substrate comprises at least 99 mole percent silica.

63. The electronic device of claim 60, wherein the silica-containing substrate comprises silica that has not been purposefully doped.

64. The electronic device of any of claims 60-63, wherein the thickness of the silicon dioxide-containing substrate is greater than or equal to 50 μm and less than or equal to 1 mm.

65. The electronic device of any of claims 60-64, wherein the waist diameter is at least 50% of the first diameter and the second diameter, respectively.

66. The electronic device of any of claims 60-65, wherein the aperture has an hourglass shape.

67. The electronic device of any of claims 60-66, wherein the aperture waist is located closer to one of the first surface and the second surface than to the other of the first surface or the second surface.

68. The electronic device of any of claims 60-67, wherein the first diameter and the second diameter are each greater than or equal to 5 μm and less than or equal to 100 μm.

69. The electronic device of any of claims 60-68, wherein a ratio of the waist diameter to the first diameter is greater than or equal to 35% and less than or equal to 45%.

70. The electronic device of any one of claims 60-69, wherein:

the hole comprises a longitudinal axis, an inner wall, a first tapered region between the first surface and the hole waist, and a second tapered region between the second surface and the hole waist;

the first tapered region comprises a first angle measured between an inner wall in the first tapered region and the longitudinal axis; and

the second tapered region includes a second angle measured between the inner wall in the second tapered region and the longitudinal axis.

71. The electronic device of claim 70, wherein the first angle is equal to the second angle.

72. The electronic device of claim 70, wherein the first angle is different than the second angle.

73. The electronic device of any one of claims 60-69, wherein:

the aperture includes:

a longitudinal axis;

an inner wall;

a first tapered region located proximate to the first surface, the first tapered region comprising a first angle measured between an inner wall in the first tapered region and the longitudinal axis;

a second tapered region located between the first tapered region and the bore waist, the second tapered region comprising a second angle measured between an inner wall in the second tapered region and the longitudinal axis;

a third tapered region adjacent to the aperture waist, the third tapered region comprising a third angle measured between an inner wall in the third tapered region and the longitudinal axis; and

a fourth tapered region located between the third tapered region and the second surface, the fourth tapered region comprising a fourth angle measured between an inner wall in the fourth tapered region and the longitudinal axis; and

each of the second angle and the third angle is smaller than the first angle and the fourth angle.

74. The electronic device of claim 73, wherein the first angle and the fourth angle are different.

75. The electronic device of claim 74, wherein the first angle and the fourth angle are each less than or equal to 5 degrees.

76. The electronic device of claim 73, wherein the second angle is different from the third angle.

77. The electronic device of claim 73, wherein the aperture waist is located closer to one of the first surface and the second surface than to the other of the first surface or the second surface.

78. The electronic device of any of claims 60-77, wherein the holes are plated with a conductive material.

79. The electronic device of any one of claims 60-78, further comprising a plurality of pores through the silica-containing substrate.

80. A silica-containing substrate comprising greater than or equal to 75 mole% silica, a first surface, a second surface opposite the first surface, and a damage track through the silica-containing substrate from the first surface to the second surface, wherein a modification level of the silica-containing substrate along the damage track decreases in a first direction from the first surface toward a bulk of the silica-containing substrate and the modification level of the silica-containing substrate decreases in a second direction from the second surface toward the bulk of the silica-containing substrate, such that the damage track comprises:

a first height modification segment adjacent the first surface;

a second height-modifying segment adjacent the second surface; and

a minimum modification stage disposed between the first height modification stage and the second height modification stage.

81. The silica-containing substrate of claim 80, wherein the silica-containing substrate comprises at least 75 mole percent silica.

82. The silica-containing substrate of claim 80, wherein the silica-containing substrate comprises at least 90 mole percent silica.

83. The silica-containing substrate of claim 80, wherein the silica-containing substrate comprises silica that has not been purposefully doped.

84. The silica-containing substrate of any one of claims 80-83, wherein the silica-containing substrate has a thickness of greater than or equal to 50 μm and less than or equal to 1 mm.

85. An article of manufacture, comprising:

a silica-containing substrate comprising greater than or equal to 75 mole percent silica, a first surface, a second surface opposite the first surface, and a hole extending through the silica-containing substrate from the first surface toward the second surface, the hole comprising:

a first diameter at the first surface;

a second diameter at the second surface; and

a waist located between the first surface and the second surface, wherein the waist has a waist diameter that is less than the first diameter and the second diameter such that a ratio of a difference between the first diameter and the waist diameter to half the thickness of the silica-containing substrate is greater than or equal to 1/15.

86. The article of claim 85, wherein the silica-containing substrate comprises at least 90 mole percent silica.

87. The article of claim 85, wherein the silica-containing substrate comprises at least 99 mole% silica.

88. The article of claim 85, wherein the silica-containing substrate comprises silica that has not been purposefully doped.

89. The article of any one of claims 85-88, wherein the silica-containing substrate has a thickness greater than or equal to 50 μ ι η and less than or equal to 1 mm.

90. The article of any one of claims 85-89, wherein the waist diameter is at least 50% of the first diameter and the second diameter, respectively.

91. The article of any one of claims 85-90, wherein the aperture has an hourglass shape.

92. The article of any one of claims 85-91, wherein the aperture waist is located closer to one of the first surface and the second surface relative to the other of the first surface or the second surface.

93. The article of any of claims 85-92, wherein the first diameter and the second diameter are each greater than or equal to 5 μ ι η and less than or equal to 100 μ ι η.

94. The article of any one of claims 85-93, wherein the ratio of waist diameter to first diameter is greater than or equal to 35% and less than or equal to 45%.

95. The article of any one of claims 85-94, wherein:

the hole comprises a longitudinal axis, an inner wall, a first tapered region between the first surface and the hole waist, and a second tapered region between the second surface and the hole waist;

the first tapered region comprises a first angle measured between an inner wall in the first tapered region and the longitudinal axis; and

the second tapered region includes a second angle measured between the inner wall in the second tapered region and the longitudinal axis.

96. The article of claim 95, wherein the first angle is equal to the second angle.

97. The article of claim 95, wherein the first angle is different than the second angle.

98. The article of claim 85, wherein:

the aperture includes:

a longitudinal axis;

an inner wall;

a first tapered region located proximate to the first surface, the first tapered region comprising a first angle measured between an inner wall in the first tapered region and the longitudinal axis;

a second tapered region located between the first tapered region and the bore waist, the second tapered region comprising a second angle measured between an inner wall in the second tapered region and the longitudinal axis;

a third tapered region adjacent to the aperture waist, the third tapered region comprising a third angle measured between an inner wall in the third tapered region and the longitudinal axis; and

a fourth tapered region located between the third tapered region and the second surface, the fourth tapered region comprising a fourth angle measured between an inner wall in the fourth tapered region and the longitudinal axis; and

each of the second angle and the third angle is smaller than the first angle and the fourth angle.

99. The article of claim 98, wherein the first angle and the fourth angle are different.

100. The article of claim 99, wherein the first angle and the fourth angle are each less than or equal to 5 degrees.

101. The article of claim 100, wherein the second angle is different than the third angle.

102. The article of any one of claims 98-101, wherein the aperture waist is located closer to one of the first surface and the second surface relative to the other of the first surface or the second surface.

103. The article of any one of claims 98-102, wherein the pores are plated with a conductive material.

104. The article of any one of claims 98-103, further comprising a plurality of pores through the silica-containing substrate.

Technical Field

The present disclosure generally relates to silica-containing substrates having pores. In particular, the present disclosure relates to silica-containing substrates comprising at least 75 mole% silica having an axially variable sidewall taper, electronic devices incorporating the silica-containing substrates having holes, and methods for forming holes having an axially variable sidewall taper in silica-containing substrates.

Background

Disclosure of Invention

In one embodiment, a method of processing a substrate comprising silica, a first surface, and a second surface opposite the first surface comprises: forming a damage track through the substrate from the first surface to the second surface with a laser beam, wherein a substrate modification level along the damage track decreases in a first direction from the first surface towards the bulk of the substrate, and the substrate modification level decreases in a second direction from the second surface towards the bulk of the substrate. The damage track includes a first modification segment proximate the first surface, a second modification segment proximate the second surface, and a third modification segment disposed between the first and second height modification segments, wherein a level of modification of the third modification segment is less than the levels of modification of the first and second modification segments. The method further comprises the following steps: etching the substrate with an etching solution to form a hole having: a first diameter at the first surface, a second diameter at the second surface, and a waist of the hole between the first surface and the second surface having a waist diameter, wherein the waist diameter is less than the first diameter and less than the second diameter.

In another embodiment, an article includes a silica-containing substrate comprising greater than or equal to 85 mole percent silica, a first surface, a second surface opposite the first surface, and a pore extending through the silica-containing substrate from the first surface toward the second surface. The aperture includes: a first diameter of less than or equal to 100 μm at the first surface, a second diameter of less than or equal to 100 μm at the second surface, and a waist of pores between the first surface and the second surface. The bore waist has a waist diameter that is less than the first diameter and the second diameter such that a ratio of the waist diameter to the first diameter and the second diameter, respectively, is less than or equal to 75%.

In another embodiment, an electronic device includes a silica-containing substrate comprising greater than or equal to 85 mole percent silica, a first surface, a second surface opposite the first surface, and a hole extending through the silica-containing substrate from the first surface toward the second surface. The aperture includes: a first diameter at the first surface of less than or equal to 100 μm, a second diameter at the second surface of less than or equal to 100 μm, and a waist between the first surface and the second surface, wherein the waist diameter of the waist is less than the first diameter and the second diameter such that the ratio of the waist diameter to the first diameter and the second diameter, respectively, is less than or equal to 75%. The electronic device further includes a semiconductor device coupled to the silicon dioxide-containing substrate, wherein the semiconductor device is electrically coupled to the aperture.

In another embodiment, a substrate comprises greater than or equal to 85 mole percent silica, a first surface, a second surface opposite the first surface, and a damage track extending through the substrate from the first surface toward the second surface. The level of substrate modification along the trajectory of failure decreases in a first direction from the first surface toward the bulk of the substrate, and the level of substrate modification decreases in a second direction from the second surface toward the bulk of the substrate. The damage track includes a first modified segment proximate the first surface, a second modified segment proximate the second surface, and a third modified segment disposed between the first highly modified segment and the second highly modified segment.

In another embodiment, an article includes a silica-containing substrate comprising greater than or equal to 85 mole percent silica, a first surface, a second surface opposite the first surface, and a pore extending through the silica-containing substrate from the first surface toward the second surface. The aperture includes: a first diameter of less than or equal to 100 μm at the first surface, a second diameter of less than or equal to 100 μm at the second surface, and a waist of pores between the first surface and the second surface. The waist of the holes has a waist diameter that is less than the first diameter and the second diameter such that a ratio of a difference between the first diameter and the waist diameter to half the thickness of the silica-containing substrate is greater than or equal to 1/15.

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

It is to be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments described herein, and together with the description serve to explain the principles and operations of the claimed subject matter.

Drawings

The embodiments illustrated in the drawings are schematic and exemplary in nature and are not intended to limit the subject matter defined by the claims. The following detailed description of the exemplary embodiments can be understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals, and in which:

FIG. 1 schematically shows a partial perspective view of a silica-containing substrate as an insert according to one or more embodiments described and illustrated herein;

fig. 2 schematically shows an exemplary electronic device including a silica-containing substrate as an interposer disposed between electronic devices, according to one or more embodiments described and illustrated herein;

FIG. 3 schematically shows dimensional characteristics of exemplary pores through a silica-containing substrate, according to one or more embodiments described and illustrated herein;

4A-4E schematically illustrate the evolution of the formation of an exemplary hole through a silica-containing substrate according to one or more embodiments described and illustrated herein;

FIG. 5 schematically shows a method of forming a damage track in a silica-containing substrate by scanning a laser spot through a bulk of the silica-containing substrate while adjusting the laser spot intensity, according to one or more embodiments described and illustrated herein;

FIG. 6 schematically illustrates a method of forming a damage track in a silica-containing substrate by using a pulsed laser beam focused to a laser beam focal line located within a bulk of the silica-containing substrate, according to one or more embodiments described and illustrated herein;

FIGS. 7 and 8 schematically illustrate sub-pulses of the pulsed laser beam illustrated in FIG. 6, according to one or more embodiments described and illustrated herein;

9A-9C schematically illustrate the Gaussian-Bessel laser beam focal line intensity distribution of FIG. 6 having maximum intensity at various locations within a silica-containing substrate, according to one or more embodiments described and illustrated herein;

FIGS. 10A and 10B graphically illustrate two different intensity profiles of the laser beam focal line shown in FIG. 6 according to one or more embodiments described and illustrated herein;

11A-11C show digital images of a damage track within a silica-containing substrate according to one or more embodiments described and illustrated herein;

FIG. 12 shows a digital image of a hole having an hourglass shape in a silicon dioxide-containing substrate formed by a laser damage and etching process according to one or more embodiments described and illustrated herein;

13A-13C graphically display histograms showing distributions of first diameter, second diameter, and waist diameter of pores within a silica-containing substrate formed by a laser damage and etching process, according to one or more embodiments described and illustrated herein;

14A-14C graphically display histograms showing a roundness distribution of a first diameter, a second diameter, and a waist diameter of holes within a silica-containing substrate formed by a laser damage and etching process, according to one or more embodiments described and illustrated herein;

fig. 15A and 15B graphically display histograms showing waist defects and total defects for samples laser processed with 4 different burst energies and 3 different focus settings using the laser beam focal line, according to one or more embodiments described and illustrated herein.

Fig. 16A-16C graphically display histograms showing variations in aperture waist on samples laser processed with 4 different burst energies and 3 different focus settings using the laser beam focal line, according to one or more embodiments described and illustrated herein.

Detailed Description

Referring generally to the drawings, embodiments of the present disclosure generally relate to articles comprising silica-containing substrates having pores (e.g., cavities) that allow for successful downstream processing, including but not limited to: hole metallization/plating and application of redistribution layer (RDL). The articles may be used in semiconductor devices, Radio Frequency (RF) devices (e.g., antennas, electronic switches, and the like), interposer devices, microelectronic devices, optoelectronic devices, micro-electro-mechanical system (MEMS) devices, and other applications that may utilize apertures.

Embodiments of the present disclosure also generally relate to methods of creating pores in a silica-containing substrate. In some embodiments, the holes have a geometry that facilitates plating of the holes. Silica-containing substrates include glass and glass ceramics. As used herein, the term "silica-containing substrate" means the Silica (SiO) that the silica-containing substrate comprises₂) The content is greater than or equal to 75 mol%, greater than or equal to 80 mol%, greater than or equal to 85 mol%, greater than or equal to 90 mol%, greater than or equal to 91 mol%, greater than or equal to 92 mol%, greater than or equal to 93 mol%, greater than or equal to 94 mol%, greater than or equal to 95 mol%, greater than or equal to 96 mol%, greater than or equal to 97 mol%, greater than or equal to 98 mol%, greater than or equal to 99 mol%, or greater than or equal to 99.9 mol%. In some embodiments, the silica-containing substrate may be fused silica. Exemplary silica-containing substrates include, but are not limited to, those sold by corning incorporated, n.y., under glass designations 7980, 7979, and 8655

Fused silica. In one embodiment, the silica-containing substrate is a substrate comprising silica that has not been purposefully doped. The phrase "not intentionally doped" means that no additional components are intentionally added to the silica prior to melting of the silica.

The properties of silica make it a desirable substrate for interposers in electronic devices. The term "insert" generally refers to any structure that extends through or completes an electrical connection through the structure, such as, but not limited to: disposed between two or more electronic devices on opposing surfaces of the interposer. The two or more electronic devices may be co-located in a single structure or may be located adjacent to each other in different structures, such that the insert functions as part of an interconnected node, or the like. Thus, the interposer may contain one or more active areas in which vias and other interconnecting conductors (e.g., power, ground, and signal conductors) are present and formed. The insert may also include one or more active regions in which blind vias are present and formed. When the interposer is formed with other components (e.g., a die, an underfill material, and/or an encapsulation, etc.), the interposer may be referred to as an interposer assembly. Furthermore, the term "insert" may also include a plurality of inserts, e.g., an array of inserts, and the like.

The low Coefficient of Thermal Expansion (CTE) of silicon dioxide minimizes expansion and movement of the silicon dioxide-containing substrate due to the application of heat flux, such as that generated by a semiconductor device attached to the silicon dioxide-containing substrate as an interposer. Expansion of the interposer due to CTE mismatch between the interposer and the semiconductor device (or other electronic component) may cause bond failure between the interposer and the semiconductor and result in separation or other damage.

In addition, silicon dioxide containing substrates provide desirable RF properties compared to other substrates such as silicon. Desirable RF properties may be important for high frequency applications, such as high speed data communication applications.

Thus, greater than or equal to 75, 80, 85, 90, 95, or 99 mole percent silicon dioxide (SiO) is included in the interposer in a particular electronic device₂) May be a desirable material. However, when a particular geometry of the holes is desired (including but not limited to hourglass shaped holes), a silica-containing substrate is usedIt is challenging. The hourglass shaped holes facilitate metallization of the holes by an electroplating process. During the electroplating process, a conductive material (e.g., copper, silver, aluminum, titanium, gold, platinum, nickel, tungsten, magnesium, or any other suitable material) is deposited within the holes. The hourglass shaped hole has a narrow waist with a diameter smaller than the diameter of the opening at the surface of the insert. During electroplating, the deposited metal first forms metal bridges at the waist locations, and then metal is deposited onto the bridges, thereby completing the hole filling to achieve void-free hermetic filling of the holes.

Laser damage and etching techniques may be used to form holes in the silicon dioxide-containing material. However, conventional laser damage and etching techniques used to form pores in a silica substrate as defined herein result in substantially cylindrical pores (i.e., pores having substantially straight walls). Thus, due to the lack of waisting and the ability to form metal bridges, holes formed in a silicon dioxide-containing substrate may not be plated using conventional techniques. The failure to produce holes with narrow waists in the silicon dioxide containing substrate may be due to a low etch rate in hydrofluoric acid and the etching process does not result in insoluble byproducts that impede or inhibit etching in the middle of the substrate and result in different etch rates between the holes at the surface and the holes deep inside the silicon dioxide containing substrate. It is noted that the methods disclosed herein are not limited to inclusion of greater than or equal to 75 mole percent silicon dioxide (SiO)₂) A silica-containing substrate of (a). The methods disclosed herein may also be used for glass or glass-ceramic substrates having less than 75 mole percent silica. For example, the methods described herein may also be used to form a film having less than 75 mole% silicon dioxide (SiO)₂) Glass or glass ceramic substrate (e.g., Eagle sold by corning, Inc.)

Glass and

glass) to form a narrow waist hole therein.

Embodiments described herein relate to methods and articles including a silica-containing substrate having holes formed by a laser damage and etching process, the holes having a particular inner wall geometry, e.g., an inner wall having a plurality of regions, each of the plurality of regions having a different angle, thereby defining an "hourglass" shape. Embodiments provide for forming high quality hourglass shaped holes in a silica-containing substrate in a practical and reliable manner. Various embodiments of articles, semiconductor packages, and methods of forming holes with narrow waists in substrates are described in detail below.

Referring now to fig. 1, a partial perspective view of an exemplary article comprising a silica-containing substrate 100 is schematically shown. The silicon dioxide-containing substrate 100 includes a first surface 102 and a second surface 104 opposite the first surface 102. A plurality of holes 110 extend through the body of the silicon dioxide containing substrate 100 from the first surface 102 to the second surface 104. It should be understood that any number of pores 110 may extend through the silica-containing substrate 100 in any arrangement. The thickness t of the silica-containing substrate 100 can be any suitable thickness depending on the application. By way of non-limiting example, the thickness t of the silica-containing substrate is: within a range of 50 μm to 1mm (inclusive), within a range of 100 μm to 700 μm (inclusive), within a range of 100 μm to 500 μm (inclusive), or within a range of 250 μm to 500 μm (inclusive).

The pitch of the holes 110 (center-to-center spacing between adjacent holes 110) may be any size, depending on the desired application, such as, but not limited to: about 10 μm to about 2000 μm, including about 10 μm, about 50 μm, about 100 μm, about 250 μm, about 1000 μm, about 2000 μm, or any value or range between any two of these values (including endpoints). In some embodiments, the pitch between the holes 110 can vary (i.e., the pitch between the first and second holes can be different than the pitch between the first and third holes) on the same silica-containing substrate 100. In some embodiments, the pitch can be in a range, for example, from about 10 μm to about 100 μm, from about 25 μm to about 500 μm, from about 10 μm to about 1000 μm, or from about 250 μm to about 2000 μm.

As schematically shown in fig. 2, the silica-containing substrate 100 may be an interposer for an electronic device 200. The non-limiting electronic device 200 schematically shown in FIG. 2 includes: a first electronic component 201 attached to the first surface 102 of the silicon dioxide containing substrate 100 and a second electronic component 203 attached to the second surface 104 of the silicon dioxide containing substrate 100. The first electronic assembly 201 and the second electronic device 203 may be configured as any type of electronic assembly, such as, but not limited to: a semiconductor device, a substrate, an energy source, or an antenna. The silicon dioxide-containing substrate 100 includes a plurality of metallized holes 110, the metallized holes 110 electrically connecting a first electronic component 201 and a second electronic component 203 such that electrical signals and/or power can pass through.

Shown schematically in fig. 3 is an exemplary conductive via 110 having an hourglass-shaped profile through a silicon dioxide-containing substrate 100. The bore 110 has a first diameter D at the first surface 102₁And a second diameter D at the second surface 104₂. The exemplary aperture 110 also includes: a longitudinal axis LA along the length of the aperture 110, the inner wall 111, and a waist w having a waist diameter D_wIs the smallest diameter of the bore 110. Thus, the waist diameter D_wSmaller than the first diameter D₁And a second diameter D₂Both of which are described below. By way of non-limiting example, the aperture 110 is contoured such that the waist diameter d_wSmaller than the first diameter D₁And a second diameter D₂75%, 65%, 60%, 55%, 50%, 45%, 40%, 35%, 30%, 25%, 20%, 15%, 10%, or 5% of each of the above. Furthermore, if the etching time is reduced, the holes from both surfaces may not be connected, resulting in "blind" holes, which are holes that end up in the bulk of the substrate. As a non-limiting example, after etching, the first diameter D₁And a second diameter D₂The following ranges are used: 5 μm to 150 μm (inclusive), 5 μm to 100 μm (inclusive), 20 μm to 150 μm (inclusive), 30 μm to 60 μm (inclusive), or 40 μm to 50 μm (inclusive). In some embodiments, the first diameter D₁And a second diameter D₂Less than or equal to 100 μm, 90 μm, 80 μm, 70 μm, 60 μm, 50 μm, 40 μm, 30 μm, 20 μm or 10 μm. First diameter D₁And a second diameter D₂May be equal or different.

The exemplary aperture 110 of fig. 3 has 4 differencesThe tapered region of (a): a first tapered region 112, a second tapered region 113, a third tapered region 118, and a fourth tapered region 119. The exemplary bore 110 has 4 different taper angles: first angle theta₁A second angle theta₂Third angle theta₃And a fourth angle theta₄Which correspond to the first tapered region 112, the second tapered region 113, the third tapered region 118 and the fourth tapered region 119, respectively. The exemplary aperture 110 is also characterized by 4 segment lengths: a first segment length L extending from the first surface 102 to a transition to the second tapered region 113₁(ii) a A second section length L extending from the transition between the first and second conical regions 112, 113 to the waist w₂(ii) a A third segment length L extending from the waist w to the transition between the third tapered region 118 and the fourth tapered region 112₃(ii) a And a fourth section length L extending from the transition between the third tapered region 118 and the fourth tapered region 119 to the second surface 104₄。

First to fourth segment lengths L₁-L₄May be any suitable length and is not limited by this disclosure. In the example of fig. 3, the four segment lengths are respectively different from each other. However, the embodiment is not limited thereto. For example, the first section length L₁May be equal to the fourth section length L₄And/or the second segment length L₂May be equal to the third segment length L₃。

It is noted that the taper angles shown in fig. 3 are measured between respective reference lines that are parallel to the longitudinal axis LA and the inner wall 111 of the bore 110. A first angle θ is measured from the inner wall 111 of the first tapered region 112 relative to the longitudinal axis LA₁. A second angle θ is measured from the inner wall 111 of the second conical region 113 relative to the longitudinal axis LA₂. A third angle θ is measured from the inner wall 111 of the third tapered region 118 relative to the longitudinal axis LA₃. A fourth angle θ is measured from the inner wall 111 of the fourth tapered region 112 relative to the longitudinal axis LA₄。

The angle of the aperture 110 relative to the longitudinal axis LA may be determined by forming a delineation line TL matching the contour of the inner wall 111 of a particular tapered region. The trace may then be analyzed to determine the slope of one or more portions of the inner wall 111, including the respective tapered regions 112, 113, 118, 119. For example, as shown in FIG. 3, a trace TL is illustratively shown, and one or more linear regions of the trace TL are determined using the computer software described herein. The linear region is defined as follows: (1) the length of this region is not less than 5 μm and may be generally greater than 10 μm; (2) the region may be fitted to a linear function (y ═ a + bx), where y is the radius of the hole and x is the substrate depth, the absolute value of the fit residual being less than 1 μm; and (3) the slopes of the fit functions for any adjacent regions should differ by at least 0.01, which translates to a 0.57 degree difference in cone angle. A region that meets all of the above criteria is referred to as a region having a constant slope (i.e., a linear region). As shown in fig. 3, the trace TL has 4 distinct linear regions: the region between points a and B, the region between points B and C, the region between points C and D, and the region between points D and E. Thus, the slopes of the region between points a and B, the region between points B and C, the region between points C and D, and the region between points D and E are constant. However, trace TL may exist with regions of non-constant slope around points A, B, C, D and E, respectively. These regions may be transition regions between constant slope regions, as described in more detail herein. Such regions may be present when there is a gradual transition between tapered regions.

In any case where the constant slope region of the inner wall 111 terminates, there may be a transition region between the slopes of each tapered region. Referring briefly to fig. 12, as illustrated, a pore 510 is formed in a silica-containing substrate, comprising: a first tapered region 512 between points a and B, a second hammer region 513 between points C and D, a third tapered region 518 between points E and F, and a fourth tapered region 519 between points G and H. The exemplary aperture 510 has transition regions of non-constant slope, which are the regions of the trace 1415 between points B and C, points D and E, and points F and G. In some embodiments, the change in slope of the transition region relative to the slope of the constant slope region is greater than or equal to about 0.57 degrees, greater than or equal to about 1 degree, greater than or equal to about 2 degrees, greater than or equal to about 3 degrees, greater than or equal to about 4 degrees, or greater than or equal to about 5 degrees.

As noted above, the constant slope of each tapered region may be defined by an angle relative to a longitudinal axis LA of the aperture that is substantially perpendicular to the first surface 102 and/or the second surface 104. Referring again to FIG. 3, the first angle θ₁And a fourth angle theta₄Is smaller than the second angle theta₂And a third angle theta₃Due to the strong modifying materials near the first surface 102 and the second surface 104 of the silica-containing substrate 100, and the weaker modifying materials in the bulk region of the silica-containing substrate 100. By way of example, and not limitation, the first angle θ₁And a fourth angle theta₄Is less than 5 degrees, for example in the following ranges: greater than 0 and 5 degrees, greater than 0 and 4 degrees, greater than 0 and 3 degrees, greater than 0 and 2 degrees, 1 and 5 degrees, 1 and 4 degrees, 1 and 3 degrees, 1 and 2 degrees, 2 and 5 degrees, 2 and 4 degrees, 2 and 3 degrees, or 4 degrees, 3 degrees, 2 degrees, or 1 degree. In the example of fig. 3, the taper angles are respectively different from each other. However, the embodiment is not limited thereto. For example, the first angle θ₁To a fourth angle theta₄May be equal to each other, and/or the second angle theta₂And a third angle theta₄May be mutually equal.

As noted above, the waist w is the hole having the smallest diameter (D)_w) The area of (a). The through-substrate hole 111 described herein can be characterized as having a ratio of the difference between the first diameter (or second diameter) and the waist diameter to half the thickness of the silica-containing substrate greater than or equal to 1/15, as provided by the relationship:

the holes 110 may be filled with a conductive material by any known or yet to be developed process (e.g., sputtering, plating, or paste filling). The conductive material may be any suitable material, such as, but not limited to: copper, silver, aluminum, titanium, gold, platinum, nickel, tungsten, or magnesium.

Referring now to FIGS. 4A-4E, laser damage andetching process and at initial thickness t_IIn a silicon dioxide containing substrate 100, an evolution of a hole 110 having an axially variable sidewall taper is produced. Referring to fig. 4A, a laser beam is used to traverse the bulk of the silicon dioxide containing substrate 100 from the first surface 102 to the second surface 104 to form a damage track 120. By way of example and not limitation, the diameter of the damage tracks 120 is less than or equal to 1 μm. The laser beam modifies the material along the damage track 120. As used herein, the term "modifying" or "modification" with respect to a silica-containing substrate refers to a change in refractive index, a change in density of a material, melting, compressing, firing, or chemical change of a material. Modification may also include cracking of the material to create microscopic cracks or voids that may facilitate permeation of gaseous or liquid etchants. The laser beam forms the damage track 120 such that the damage track 120 has sections that provide different etching properties. The level of modification of the silica-containing substrate 100 is strongest near the first surface 102 and the second surface 104, and the level of modification decreases along the damage trajectory 120 in a direction into the bulk of the silica-containing substrate 100. The level of modification affects the etch rate of the silicon dioxide containing substrate 100. The higher the level of modification, the faster the etch rate of the silicon dioxide containing substrate 100. In the embodiments described herein, the level of modification is determined by evaluation of the damage track 120 under a microscope in the presence of a backlight. In the presence of a backlight, the darker the material along the damage track 120, the higher the level of modification. In an embodiment, the damage track 120 appears darker near the surface of the silica-containing substrate 100 (i.e., the damage track has a high level of modification in these sections) and appears brighter near the middle of the silica-containing substrate 100 (i.e., the damage track has a low level of modification in these sections as compared to near the surface sections). Fig. 11A shows the appearance of different material modification levels of damage tracks 120, 120', 120 "in a backlit silica-containing substrate 100 under a microscope (as described in more detail below).

In the example of fig. 4A, the damage track 120 includes 4 sections, each with a different level of modification to have different etching properties: a first modification stage 120A, a second modification stage 120B, a third modification stage 120C, and a fourth modification stage 120D. It is to be understood that the level of modification between the stages may not be discrete. Conversely, the level of modification may be gradually varied along the damage track 120. Thus, the level of modification may vary in a single section of the damage track 120.

As noted above, the damage track 120 is configured such that the highest level of modification is present proximate to the first surface 102 and the second surface 104 of the silica-containing substrate 100. Thus, the first modification stage 120A and the fourth modification stage 120D are highly modified stages. The second modification stage 120B and the third modification stage 120C are the minimum modification stages in which their modification levels are smaller than in the case of the first section 120A and the fourth section 120D. Although the second segment 120B and the third segment 120C are shown as individual segments (individual segments), in some embodiments, the second segment 120B and the third segment 120C are a single minimum modification segment having a modification level that is less than the modification levels of the first modification segment 120A and the fourth modification segment 120D.

Details of the nature of the laser beam used to form the damage tracks are discussed below with respect to fig. 5-8.

After the damage tracks 120 are formed, the silicon dioxide containing substrate 100 may be etched by applying an etching solution. In an example, the silicon dioxide-containing substrate 100 is disposed in an etching solution bath. Alternatively, the etching solution may be sprayed onto the silicon dioxide containing substrate 100. The present disclosure does not limit the type of etching solution. Any known or yet to be developed etching solution capable of etching a silicon dioxide-containing substrate may be used. In one example, the etching solution includes hydrofluoric acid (HF) or sodium/potassium hydroxide. As a specific example, an etching solution used to etch fused silica contains 20 vol% HF or 20 vol% HF and 12 vol% HCl, providing an etch rate of about 0.005 μm/s at about 47 degrees Celsius. Temperature adjustments (e.g., 10 to 50 degrees celsius) and acid concentration adjustments can be made to vary the etch rate. Other mineral acids may be used in place of HCl, such as nitric acid (HNO)₃). Hydroxide etchants such as sodium hydroxide (NaOH) and potassium hydroxide (KOH) may also be used.

The etching solution etches material away at the first surface 102 and the second surface 104 of the silicon dioxide-containing substrate 100, respectively, in an amount deltas as shown in figure 4B. The damaged material in the strongly modified first and fourth segments 120A, 120D of the damage track 120 is etched away at a faster rate than the undamaged regions outside of the damage track 120. This faster etch rate due to the damaged material results in opening the first guide hole 115 at the first surface 102 and extending through the bulk of the silicon dioxide-containing substrate 100 along the first segment 120A of the damage track, and opening the second guide hole 117 at the second surface 104 and extending through the bulk of the silicon dioxide-containing substrate 100 along the fourth segment 120D of the damage track 120. As shown in fig. 4C, the first guide hole 115 and the second guide hole 117 extend deeper into the bulk of the silica containing substrate 100, and the silica containing substrate 100 is further thinned by an increment Δ s.

Referring now to fig. 4D, continued etching of silicon dioxide containing substrate 100 results in the diameter of first guide hole 115 increasing and opening into first tapered region 112 and the diameter of second guide hole 117 increasing and opening into fourth tapered region 119. First surface 102 and second surface 104 of silicon dioxide-containing substrate 100 are further thinned by an increment Δ s. At this point, the etching solution reaches the second segment 120B and the third segment 120C of the damage track 120. The second segment 120B opens into the second tapered region 113 and the third segment 120C opens into the third tapered region 118. Since the modification level of the material in the second and third segments 120B and 120C is lower than that of the first and fourth segments 120A and 120D, the etching rate in the second and third segments 120B and 120C is lower than that of the first and fourth segments 120A and 120D. As shown in fig. 4D, the difference in modification level along the damage trajectory 120 results in the second conical region 113 and the third conical region 118 being at a greater angle relative to the longitudinal axis LA than the first conical region 112 and the fourth conical region 119.

The second conical region 113 and the third conical region 118 meet at the waist w. The waist w is the narrowest region of the aperture 110 and is located where metal bridges are formed during the electroplating process. Referring now to FIG. 4E, shown therein is a final thickness t_FFusing the finished exemplary aperture 110 in the substrate. As shown, the bore 110 has an axially variable sidewall taper that results in different segmentsAnd a narrow waist w providing a location for the formation of a metal bridge during the electroplating process.

The damage tracks 120 described herein with varying levels of modification of the silica-containing substrate 100 can be formed by various laser processes. In the example shown in fig. 5, the power of the laser beam is adjusted during scanning as shown in pattern 152 to produce different levels of material modification (i.e., damage) at different depths from the surface of the silica-containing substrate 100 by scanning a focused laser spot LS of the laser beam 150 in the z-direction through the thickness t of the silica-containing substrate 100 to form a damage track 120 in the silica-containing substrate 100. The laser power when the focused laser spot LS is located within the bulk (i.e., near the middle) of the silica-containing substrate 100 is lower than when the focused laser spot LS is located near the first surface 102 and the second surface 104 of the silica-containing substrate 100. However, this approach may require many successive laser exposures to form damage tracks 120 through the entire thickness of the silicon dioxide-containing substrate 100, which makes the process slow.

Referring to fig. 6, in another example, the damage track 120 is formed by a pulsed laser beam 302a, which pulsed laser beam 302a is focused to a laser beam focal line 302b that is positioned through the bulk of the silica-containing substrate 100. The laser beam focal line produces induced multiphoton absorption within the silica-containing substrate 100. The multiphoton induced absorption produces material modification along the laser beam focal line 302b in the silica-containing substrate, thereby forming the damage track 120. The laser beam focal line 302b is generated by an optic 306, which optic 306 is a cone lens (i.e., an axicon) in the non-limiting example shown in FIG. 6. Additional description of methods of generating and using laser beam focal lines for drilling holes in glass substrates is provided in U.S. patent No. 9,517,963, which is incorporated herein by reference in its entirety.

The optics 306 form the laser beam into an expanded focused (extended focus) or quasi-undiffracted beam resulting in a bessel-like or gaussian bessel beam. Due to the quasi-non-diffractive nature of the beam, the light maintains a tightly focused intensity over a much longer range than is achieved with the more commonly used gaussian beam, allowing for destruction of the entire thickness t of the glass substrate by a single pulse burst or a close-timed pulse train of laser pulses.

In order to modify the silica-containing substrate and create damage tracks, the wavelength of the pulsed laser beam should be transparent to the silica-containing substrate material. The pulse duration and intensity should be short enough to achieve the multiphoton absorption effect described above. Ultrashort pulsed lasers, such as picosecond or femtosecond laser sources, may be used. In some embodiments, a laser may be used that is pulsed for about 10 picoseconds. By way of example and not limitation, by line focusing to the extent of about 1mm to about 3mm and generating about 10 picosecond pulsed laser (250 μ J/pulse) at a 200kHz repetition rate with an output power of greater than about 50W, the optical intensity in the line region will be sufficiently high to produce nonlinear absorption in the silica-containing substrate.

It is noted that operation of such picosecond lasers described herein produces "pulse bursts" of 5 sub-pulses 5 a. Fig. 7 shows 3 sub-pulses 5a, 5 a' and 5 "(collectively" 5a "). A pulse train that produces pulses is a type of laser operation in which the emission of the pulses is not a uniform and steady stream, but rather a tight cluster of sub-pulses. Each pulse group contains a plurality of individual sub-pulses 5a (e.g., without limitation, at least 2 sub-pulses, at least 3 sub-pulses, at least 4 sub-pulses, at least 5 sub-pulses) within a very short duration. That is, pulse bursts 5 are "pockets" of sub-pulses 5a, with pulse bursts 5 being spaced from each other for a longer period of time than the spacing of adjacent pulses of cells within each pulse burst. Referring to fig. 8, which plots laser emission against time for the sub-pulse 5a of fig. 7, the sub-pulse may have a pulse duration T of up to 100 picoseconds_d(e.g., 0.1 picosecond, 5 picoseconds, 10 picoseconds, 15 picoseconds, 18 picoseconds, 20 picoseconds, 22 picoseconds, 25 picoseconds, 30 picoseconds, 50 picoseconds, 75 picoseconds, or therebetween). These individual sub-pulses (e.g., sub-pulses 5a, 5 a', and 5a ") in the single pulse train 5 are referred to herein as sub-pulses to represent the fact that they exist within the single pulse train. The energy or intensity of each individual sub-pulse 5a, 5 a', 5 "within a pulse train 5 may not be equal to the energy or intensity of the other sub-pulses within the pulse train, andthe intensity distribution of the multiple sub-pulses within a pulse burst generally conforms to the exponential decay over time governed by the laser design.

The time period t of the time interval between each sub-pulse (e.g., sub-pulse 5a, 5 a', 5a ") in the pulse train 5 of the exemplary embodiments described herein and a subsequent sub-pulse within the train_pFrom 1ns to 50ns (e.g., 10-50ns or 10-30ns, time typically governed by laser cavity design). The time interval t between each sub-pulse within a pulse burst 5 for a given laser_p(subpulse-subpulse spacing) is relatively uniform (+ -10%). For example, in some embodiments, each sub-pulse within a pulse burst is separated from a subsequent sub-pulse by approximately 20ns (50 MHz). For example, for sub-pulse intervals t yielding about 20ns_pLaser of (2), sub-pulse-sub-pulse interval t within a pulse burst_pMaintained within about + -10%, or about + -2 ns.

It has been observed that too many sub-pulses result in a cylindrically shaped hole. Specifically, a 15 sub-burst providing 80 μ J energy creates a cylindrical shaped hole, while a 5 sub-burst providing 50 μ J energy creates an hourglass shaped hole. Each sub-pulse of the former has less energy but produces a very uniform damage track through the thickness of the silica-containing substrate, while each sub-pulse of the latter has greater energy but produces a more non-uniform damage track through the thickness of the silica-containing substrate, with stronger damage being observed near the glass surface and weaker damage being observed near the middle of the silica-containing substrate.

The laser beam focal line 302b is generally of uniform intensity. However, in the embodiments described herein, the energy and number of laser beam bursts are controlled to provide a non-uniform level of modification along the desired damage track 120. In other words, the failure pattern as a function of depth within the silicon dioxide-containing substrate 100 is not uniform. A significantly different and stronger destruction of the central portion (center) of the silica-containing substrate 100 was observed near the surfaces of the silica-containing substrate 100 (specifically, within 100 μm of each surface). As observed under a backlit microscope, the area near the surface of the silica-containing substrate 100 generally appears very dark, indicating greater optical scattering and material modification, while the area near the center of the silica-containing substrate 100 appears as a bright colored or broken dark area, indicating less optical scattering and thus weaker or spatially more non-uniform material modification. In addition, the area near the surface of the silica-containing substrate 100 typically exhibits actual pores or areas where material is ejected/ablated from the substrate, which may provide a simple path for chemical etchant penetration.

This strong damaging effect near the surface is particularly pronounced when the laser energy of the laser beam focal line 302b is reduced to slightly above the threshold required to modify the silica-containing substrate 100, for example, within 60% above the threshold, within 65% above the threshold, within 55% above the threshold, within 50% above the threshold, within 45% above the threshold, within 40% above the threshold, within 35% above the threshold, within 30% above the threshold, within 25% above the threshold, within 20% above the threshold, within 15% above the threshold, or within 10% above the threshold. As used herein, the term "threshold" refers to the minimum energy required to produce surface damage on a substrate using the laser beam focal line. In such cases, the region closest to the surface may still exhibit a dark damage region, but the central portion of the silica-containing substrate may in some cases exhibit no significant damage or no modified region at all. As noted above, the differential destructive effect as a function of depth observed with such non-diffracted beams can be exploited to form tapered holes in the silica-containing substrate where such hole shapes are otherwise not possible. By way of non-limiting example, the operating range of the pulsed laser beam is 40 μ J to 55 μ J (inclusive) or 45 μ J to 50 μ J (inclusive) for 5 sub-pulses.

The position of the waist w of the aperture can be shifted by adjusting the position of the maximum intensity of the laser beam focal line. Fig. 9A plots the intensity 305 of the laser beam focal line through the silica-containing substrate 100 and shows the resulting holes 410 in an exemplary silica-containing substrate 400. As shown in fig. 9A, placing the maximum intensity 305 at the center of the silicon dioxide-containing substrate 100 results in the aperture 410 having a waist in the center of the silicon dioxide-containing substrate 400 after the etching process.

Fig. 9B graphically illustrates that the maximum intensity 305 of the laser beam focal line is shifted toward the first surface 102 of the silica-containing substrate 100. Fig. 9B also shows an exemplary silicon dioxide-containing substrate 400 'whose pores 410' have waists closer to the second surface 404 than the first surface 402 after the etching process. Fig. 9C graphically illustrates that the maximum intensity 305 of the laser beam focal line is shifted toward the second surface 104 of the silica-containing substrate 100. Fig. 9C also shows an exemplary silicon dioxide-containing substrate 400 "whose pores 410" have waists closer to the first surface 402 than the second surface 404 after the etching process. The offset of the waist w results in an asymmetric aperture relative to a plane through the middle of the silica-containing substrate 100.

It is noted that it is not necessary that the optical intensity of the quasi-undiffracted beam (e.g., the laser beam focal line 302b) be made stronger near the surface of the silica-containing substrate 100. However, optical elements (e.g., compound axicon-like elements) can be designed that produce a customized optical intensity distribution along the beam propagation direction. In such cases, it may be possible to enhance the optical intensity of the laser beam focal line 302b at the fused substrate surface while creating a lower intensity region in the middle of the silica-containing substrate. Exemplary optics for customizing the energy distribution of the laser beam focal line are described in U.S. patent application No. 62/381,345.

Fig. 10A and 10B graphically illustrate manipulation of the intensity distribution of two laser beam focal lines through a silica-containing substrate 100. In fig. 10A, the intensity distribution 305' of the laser beam focal line is a rectangular "top hat" shape. Such intensity distribution 305' may be formed, for example, by a composite axicon optic and may result in stronger modification near the surface of a silica-containing substrate than the gaussian distribution shown in fig. 9A-9C. In the intensity profile 305 "shown in fig. 10B, there are two maximum peaks near the first surface 102 and the second surface 104 of the silica-containing substrate 100, which results in stronger modification near the first surface 102 and the second surface 104 than in the middle of the silica-containing substrate. The laser beam focal line of fig. 10B has a greater intensity at a first end of the laser beam focal line and a second end of the laser beam focal line than at a central region of the laser beam focal line. Customized optics may be used to produce the intensity profile 305 "shown in fig. 10B.

Other approaches to enhancing laser damage/modification near the surface of a silica-containing substrate include heating or cooling the surface to have a temperature gradient, such as by applying a stream of hot air, thereby having a different laser/glass interaction through the thickness of the glass.