Laser segmented cutting, multi-step cutting, or both

Abstract

UV laser cutting throughput through silicon and like materials is improved by dividing a long cut path ( 112 ) into short segments ( 122 ), from about 10 μm to 1 mm. The laser output ( 32 ) is scanned within a first short segment ( 122 ) for a predetermined number of passes before being moved to and scanned within a second short segment ( 122 ) for a predetermined number of passes. The bite size, segment size ( 126 ), and segment overlap ( 136 ) can be manipulated to minimize the amount and type of trench backfill. Real-time monitoring is employed to reduce rescanning portions of the cut path 112 (112) where the cut is already completed. Polarization direction of the laser output ( 32 ) is also correlated with the cutting direction to further enhance throughput. This technique can be employed to cut a variety of materials with a variety of different lasers and wavelengths. A multi-step process can optimize the laser processes for each individual layer.

1. A method of increasing throughput in a laser cutting process, comprising:
 directing a first pass of first laser pulses to impinge along a first segment of a cutting path having that is continuous and has a cutting path length greater than 100 μm, each first laser pulse having a first spot area on a workpiece, the first spot area having a first major axis and the first segment having a first segment length that is longer than the first spot area major axis and shorter than the cutting path length; 
 directing a second pass of second laser pulses to impinge along a second segment of the cutting path, each second laser pulse having a second spot area on the workpiece, the second spot area having a second major axis and the second segment having a second segment length that is longer than the second spot area major axis and shorter than the cutting path length, the second segment overlapping the first segment by an overlap length greater than at least the first or second spot areas major axis; and 
 after directing at least the first and second passes of laser pulses, directing a third pass of third laser pulses to impinge along a third segment of the cutting path, each third laser pulse having a third spot area on the workpiece, the third spot area having a third major axis and the third segment having a third segment length that is longer than the third spot area major axis and shorter than the cutting path length, the third segment including a subsequent portion of the cutting path other than the first or second segments segment, wherein the subsequent portion of the cutting path has a nonoverlap length greater than the first, second, or third spot areas major axis. 
 
     
     
       2. The method of  claim 1  in which major portions of the first and second segments overlap. 
     
     
       3. The method of  claim 1  in which the second segment includes the first segment. 
     
     
       4. The method of  claim 3  in which the first and second segments are processed in a same direction. 
     
     
       5. The method of  claim 3  in which the first and second segments are processed in opposite directions. 
     
     
       6. The method of  claim 1  in which the first and second segments are processed in a same direction. 
     
     
       7. The method of  claim 1  in which the first and second segments are processed in opposite directions. 
     
     
       8. The method of  claim 1  in which additional sets of first and/or second laser pulses are applied to the first and/or second segments to form a through trench within the first and/or second segments prior to applying the third laser pulses. 
     
     
       9. The method of  claim 1  further comprising:
 forming a through trench in the first and/or second segments prior to applying the third laser pulses. 
 
     
     
       10. The method of  claim 1  further comprising:
 forming a through trench in the first and/or second segments with multiple passes of laser pulses prior to applying the third laser pulses; and 
 forming a through trench within the third segment. 
 
     
     
       11. The method of  claim 10  further comprising:
 forming a through trench along the entire cutting path length. 
 
     
     
       12. The method of  claim 11  in which the cutting path length is greater than 1 mm and the first, second, and third segment lengths are between about 10 μm and about 500 μm. 
     
     
       13. The method of  claim 1  in which the cutting path length is greater than 1 mm and the first, second, and third segment lengths are between about 10 μm and about 500 μm. 
     
     
       14. The method of  claim 13  in which the cutting path length is greater than 10 mm and the first, second, and third segment lengths are between about 200 μm and about 500 μm. 
     
     
       15. The method of  claim 13  in which the first, second, and third laser pulses are characterized by a UV wavelength, a pulse repetition frequency of greater than 5 kHz, pulse energies of greater than 200 μJ, and a bite size of about 0.5 to about 50 μm. 
     
     
       16. The method of  claim 1  in which the first, second, and third laser pulses are characterized by a UV wavelength, a pulse repetition frequency of greater than 5 kHz, pulse energies of greater than 200 μJ, and a bite size of about 0.5 to about 50 μm. 
     
     
       17. The method of  claim 16  in which the workpiece has a thickness greater than 50 μm. 
     
     
       18. The method of  claim 17  in which the workpiece has a thickness greater than 500 μm. 
     
     
       19. The method of  claim 12  in which the workpiece has a thickness greater than 50 μm. 
     
     
       20. The method of  claim 12  in which the workpiece has a thickness greater than 500 μm, the cutting path length is greater than 100 mm, and the throughcut along the entire length of the cutting path is made with fewer than 25 passes of laser pulses over any position along the cutting path. 
     
     
       21. The method of  claim 13  in which the workpiece has a thickness greater than 200 μm, further comprising:
 cutting through the entire thickness along the cutting path at a cutting speed of greater than 10 mm per minute. 
 
     
     
       22. The method of  claim 21  in which a major portion of the thickness of the workpiece comprises a semiconductor material, a glass material, a ceramic material, or a metallic material. 
     
     
       23. The method of  claim 21  in which a major portion of the thickness of the workpiece comprises Si, GaAs, SiC, SiN, indium phosphide, or AlTiC. 
     
     
       24. The method of  claim 22  in which the laser pulses are generated from a solid-state laser or a CO 2  laser. 
     
     
       25. The method of  claim 1  in which the laser pulses are generated from a solid-state laser or a CO 2  laser. 
     
     
       26. The method of  claim 2  in which the overlap length of the first and second portions or the first or second segment lengths are sufficiently short such that length is selected to enable the second laser pulses to impinge along the overlap length before a major portion of any debris generated by the first laser pulses cools along the overlap length to ambient temperature. 
     
     
       27. The method of  claim 1  in which the third segment excludes the first or second segments segment. 
     
     
       28. The method of  claim 1  in which the first laser pulses impinge along the cutting path in a first cutting direction and the first laser pulses have a first polarization orientation that is parallel to the first cutting direction, in which the third laser pulses impinge along the cutting path in a third cutting direction and the third laser pulses have a third polarization orientation that is parallel to the third cutting direction, and in which the first and third cutting directions are transverse. 
     
     
       29. The method of  claim 28  further comprising:
 employing a polarization control device to change from the first polarization orientation to the third polarization orientation. 
 
     
     
       30. The method of  claim 10  further comprising:
 monitoring throughcut status with a throughcut monitor to determine throughcut positions where throughcuts have been affected along the cutting path; and 
 reducing impingement of the throughcut positions during the passes of first, second, third, or subsequent laser pulses in response to information provided by the throughcut monitor. 
 
     
     
       31. The method of  claim 1  in which the laser pulses within the first pass have generally similar parameters. 
     
     
       32. The method of  claim 1  in which the laser pulses of the first, second, and third passes have generally similar parameters. 
     
     
       33. The method of  claim 1  in which the laser pulses of at least two of the first, second, and third passes have at least one generally different parameter. 
     
     
       34. The method of  claim 1  in which at least two of the laser pulses in at least one of the first, second, or third passes have at least one generally different parameter. 
     
     
       35. The method of  claim 1  in which multiple passes of laser pulses are applied to the first segment to form a throughcut within the first segment. 
     
     
       36. The method of  claim 35  in which the throughcut is formed in the first segment before the pass of second laser pulses is applied to the second segment. 
     
     
       37. The method of  claim 36  in which multiple passes of laser pulses are applied to the second segment to form a throughcut within the second segment. 
     
     
       38. The method of  claim 37  in which the throughcut is formed in the second segment before the pass of third laser pulses is applied to the third segment. 
     
     
       39. The method of  claim 38  in which multiple passes of laser pulses are applied to subsequent segments to sequentially form throughcuts within the respective subsequent segments to form a full length throughcut along the cutting path length. 
     
     
       40. The method of  claim 1  in which only minor portions of the first and second segments overlap. 
     
     
       41. The method of  claim 1  in which the first laser pulses impinge along the cutting path in a first cutting direction and the first laser pulses have a first polarization orientation that is oriented to the first cutting direction to enhance throughput or cut quality, in which the third laser pulses impinge along the cutting path in a third cutting direction and the third laser pulses have a third polarization orientation that is oriented to the third cutting direction to enhance throughput or cut quality, and in which the first and third cutting directions are transverse and the first and third polarization orientations are transverse. 
     
     
       42. The method of  claim 1  in which at least one of the segments is an arc. 
     
     
       43. The method of  claim 1  in which a purge gas is employed to facilitate blowing potential backfill debris through throughcuts along the cutting path. 
     
     
       44. The method of  claim 1  in which an elongated laser pass that includes at least three first, second, and third segments is applied to the cutting path. 
     
     
       45. The method of  claim 1  in which each spot area along a segment is in proximity to or partly overlaps the spot area of a preceding laser pulse. 
     
     
       46. A method of increasing throughput for forming a cut along a cutting path having that is continuous and has a cutting path length on a workpiece, comprising:
 selecting a segment length that is shorter than the cutting path length; 
 directing a first pass of first laser pulses having first spot areas to impinge the workpiece along a first segment of about the segment length along the cutting path, each of the first spot areas having a first major axis; 
 directing a second pass of second laser pulses having second spot areas to impinge the workpiece along a second segment of about the segment length along the cutting path, each of the second spot areas having a second major axis, and the second segment overlapping the first segment by an overlap length greater than at least the first or second spot areas major axis; and 
 after directing at least the first and second passes of laser pulses, directing a third pass of third laser pulses having third spot areas to impinge along a third segment of about the segment length along the cutting path, each of the third spot areas having a third major axis, and the third segment including a portion of the cutting path that extends beyond the first or second segments segment, wherein the portion of the cutting path has a portion length greater than the first, second, or third spot areas major axis. 
 
     
     
       47. The method of  claim 46  in which impingement of laser pulses along the cutting path generates debris and in which the overlap length or the segment length is sufficiently short such that selected to enable the second laser pulses of the second pass of second laser pulses to impinge along the overlap length before a major portion of any debris generated by the first laser pulses cools to ambient temperature along the overlap length. 
     
     
       48. A method of increasing throughput in a laser cutting process, comprising:
 directing a first pass of first laser pulses to impinge along a first segment of a cutting path having that is continuous and has a cutting path length, each first laser pulse having a first spot area on a workpiece, the first spot area having a first major axis and the first segment having a first segment length that is longer than the first spot area major axis and shorter than the cutting path length; 
 directing second passes of second laser pulses to impinge along a second segment of the cutting path, the second segment including an overlap length that overlaps at least a portion of the first segment until a throughcut is made within the overlap length, each second laser pulse having a second spot area on a workpiece, the second spot area having a second major axis and the second segment having a second segment length that is longer than the second spot area major axis and shorter than the cutting path length, the overlap length being greater than at least the first or second spot areas major axis; and 
 after directing at least the first and second passes of laser pulses, directing third passes of third laser pulses to impinge along a third segment of the cutting path until a throughcut is made within the third segment, each third laser pulse having a third spot area on a workpiece, the third spot area having a third major axis and the third segment having a third segment length that is longer than the third spot area major axis and shorter than the cutting path length, the third segment including a portion of the cutting path that extends beyond the first or second segments segment, wherein the portion of the cutting path has a portion length greater than the first, second, or third spot areas major axis. 
 
     
     
       49. The method of  claim 1  in which the overlap length of the first and second portions or the first or second segment lengths are length is in a range appropriate so as to exploit with second laser pulses persistence of a selected transient effect arising from the interaction of first pulses with the workpiece along the overlap length. 
     
     
       50. The method of  claim 46  in which the overlap length of the first and second portions or the first or second segment lengths are length is in a range appropriate so as to exploit with second laser pulses persistence of a selected transient effect arising from the interaction of first pulses with the workpiece along the overlap length. 
     
     
       51. The method of  claim 48  in which the overlap length of the first and second portions or the first or second segment lengths are length is in a range appropriate so as to exploit with second laser pulses persistence of a selected transient effect arising from the interaction of first pulses with the workpiece along the overlap length. 
     
     
       52. The method of claim 1 in which a cutting blade is employed to sever the workpiece along the cutting path. 
     
     
       53. The method of claim 1 in which the laser pulses of at least two of the first, second, and third passes have different wavelengths, including first and second wavelengths. 
     
     
       54. The method of claim 53 in which the first wavelength is a UV wavelength or a visible wavelength and the second wavelength is an IR wavelength or visible wavelength. 
     
     
       55. The method of claim 53 in which the first and second wavelengths are different UV wavelengths. 
     
     
       56. The method of claim 1 in which the laser pulses of at least two of the first, second, and third passes have different irradiances. 
     
     
       57. The method of claim 1 in which the laser pulses of at least two of the first, second, and third passes have different repetition rates. 
     
     
       58. The method of claim 1 in which the laser pulses of at least two of the first, second, and third passes have different bite sizes. 
     
     
       59. The method of claim 1 in which the laser pulses of at least two of the first, second, and third passes have different scan speeds. 
     
     
       60. The method of claim 1 in which at least two of the first, second, and third passes have different lengths. 
     
     
       61. The method of claim 1 in which the laser pulses of at least two of the first, second, and third passes have different pulse widths. 
     
     
       62. The method of claim 1 in which the laser pulses of at least two of the first, second, and third passes have different fluences. 
     
     
       63. The method of claim 1 in which the laser pulses of at least two of the first, second, and third passes have different spot areas. 
     
     
       64. The method of claim 1 in which the laser pulses of at least two of the first, second, and third passes employ a different laser, wavelength, pulse width, fluence, and/or bite size. 
     
     
       65. The method of claim 1 in which the laser pulses are generated by different lasers. 
     
     
       66. The method of claim 1 in which the work piece comprises first and second layers of different materials and in which the laser pulses applied to the first and second layers are generated by different lasers, including first and second lasers. 
     
     
       67. The method of claim 66 in which the first laser is a UV or visible laser and the second laser is an IR or visible laser. 
     
     
       68. The method of claim 66 in which the first and second lasers are both UV lasers that generate output at different wavelengths. 
     
     
       69. The method of claim 1 in which the laser pulses of at least one of the first, second, and third passes have:
 spot areas that successively overlap and impinge nonoverlapping areas, each having a spatial major axis of about 0.01 to 9.5 microns, and   a wavelength shorter than or equal to about 355 nm.   
     
     
       70. The method of claim 1 in which the laser pulses of at least one of the first, second, and third passes have a substantially Gaussian irradiance profile at a wavelength shorter than or equal to about 532 nm. 
     
     
       71. The method of claim 1 in which the workpiece has a substrate supporting a layer, the substrate having a wafer material and the layer having a material different from that of the substrate and prone to propagating cracks that initiate during a cutting technique, and in which the cutting path is a second cutting path that is addressed after a first cutting path is addressed, the method further comprising:
 applying a first technique to form a first kerf through the layer along the first cutting path, the first technique including directing a first laser output having a first set of first parameters along the first cutting path across the layer to form the first kerf through the layer, and the first parameters adapted to minimize initiation of cracks; and   applying along the second cutting path a second technique to form in the substrate a second kerf parallel to the first kerf, the second cutting path being parallel to the first cutting path, the second technique including directing the first, second and third passes, the second technique being different from the first technique, and the second technique initiating cracks in the layer that begin at the second kerf, propagate in a direction toward the first kerf, and terminate at or prior to the first kerf.   
     
     
       72. The method of claim 1 in which the workpiece has a substrate supporting a layer, the substrate having a wafer material and the layer having a material different from that of the substrate and having a tendency to delaminate from the substrate at or near a layer-substrate interface during a cutting technique, and in which the cutting path is a second cutting path that is addressed after a first cutting path is addressed, the method comprising:
 applying a first technique along the first cutting path to form a first kerf through the layer and into the substrate, the first technique including directing a first laser output having a first set of first parameters along the first cutting path across the layer to form the first kerf through the layer, and the first parameters adapted to minimize initiation of delamination of the layer from the substrate; and   applying along the second cutting path a second technique to form in the substrate a second kerf parallel to the first kerf, the second cutting path being parallel to the first cutting path, the second technique including directing the first, second and third passes, the second technique being different from the first technique, and the second technique initiating delamination of the layer from the substrate that begins at the second kerf, propagates in a direction toward the first kerf, and terminates at or prior to the first kerf.   
     
     
       73. The method of claim 1 in which the workpiece comprises an electronic device having an edge formed from the cutting path, the edge having first and second transverse surfaces, the method further comprising:
 generating first laser output having a wavelength shorter than or equal to about 355 nm;   directing the first laser output toward a first target location on the first surface in proximity to the edge of the electronic device such that a first output spot area of first laser output impinges the first surface;   generating second laser output having a second output spot area and a wavelength shorter than or equal to about 355 nm; and   directing the second laser output toward a second target location on the first surface in proximity to the edge of the electronic device, such that the second output spot area impinges the first surface and such that the second output spot area partly overlaps the first output spot area and impinges a nonoverlapping area having a spatial major axis of 0.5-9 μm, thereby converting the edge to a rounded edge in proximity to the first and second target locations.   
     
     
       74. The method of claim 1 in which the workpiece comprises a brittle, high melting temperature ceramic or glass material, having a surface; and in which the laser pulses of at least one of the first, second, or third pass have a wavelength shorter than or equal to about 355 nm and spot areas that successively overlap and impinge nonoverlapping areas each having a spatial major axis of 0.01 to 9.5 μm and generate redeposited debris that primarily comprises nonmolten materials that contact the surface and are nonpermanent and removable from the surface by conventional cleaning techniques. 
     
     
       75. The method of claim 1 in which the workpiece comprises a wafer supporting multiple electronic devices; in which the laser pulses of at least one of the first, second, or third pass have a wavelength shorter than or equal to about 355 nm and spot areas that successively overlap and impinge nonoverlapping areas each having a spatial major axis of 0.01 to 9.5 μm; and in which the cutting path is employed to separate groups of electronic devices or separate individual electronic components. 
     
     
       76. The method of claim 1 in which the laser pulses of at least one of the first, second, or third pass have a substantially Gaussian irradiance profile as generated and are subsequently propagated through an aperture to provide apertured output for the laser pulses. 
     
     
       77. The method of claim 76 in which the laser pulses of the apertured output are shaped by at least one beam shaping element before the laser pulses are propagated through the aperture to provide shaped apertured output for the laser pulses. 
     
     
       78. The method of claim 77 in which the laser pulses of the shaped apertured output have a wavelength shorter than or equal to about 532 nm. 
     
     
       79. The method of claim 1 in which the workpiece comprises a wafer supporting rows of electronic devices, the method further comprising:
 identifying a first feature on a first surface of a first row of electronic devices;   aligning with respect to the first feature on the first surface, a first target position of a laser system such that the target position is in proximity to a first intended edge of a first electronic device having surface features in a first orientation;   directing at least one of first, second, and third passes of laser pulses to impinge the first surface at the first target position and linearly therewith to form a first kerf that traverses between a first set of rows of electronic devices, one of the first set of rows including the first electronic device;   identifying a second feature on a second surface of a second row of electronic devices;   aligning with respect to the second feature on the second surface a second target position of the laser system such that the second target position is in proximity to a second intended edge of a second electronic device having surface features in a second orientation that is different from the first orientation; and   directing at least one of first, second, and third passes of laser pulses to impinge the second surface at the second target position and linearly therewith to form a second kerf that traverses between a second set of rows of electronic devices, one of the second set of rows including the second electronic device.   
     
     
       80. The method of claim 1 in which the laser pulses of at least one of the first, second, or third pass are generated by a holmium or erbium-doped laser.