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 a cutting path length greater than 100 μm, each first laser pulse having a first spot area on a workpiece, the first segment having a first segment length that is longer than the first spot area 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 segment having a second segment length that is longer than the second spot area 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; 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 segment having a third segment length that is longer than the third spot area 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, wherein the subsequent portion of the cutting path has a nonoverlap length greater than the first, second, or third spot areas.   
     
     
       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 throughout 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 the second laser pulses 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. 
     
     
       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 throughout status with a throughout monitor to determine throughout 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 throughout 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 throughout 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 throughout within the second segment. 
     
     
       38. The method of  claim 37  in which the throughout 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 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;   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, the second segment overlapping the first segment by an overlap length greater than at least the first or second spot areas; 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, the third segment including a portion of the cutting path that extends beyond the first or second segments, wherein the portion of the cutting path has a portion length greater than the first, second, or third spot areas.   
     
     
       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 the second pass of second laser pulses 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 a cutting path length, each first laser pulse having a first spot area on a workpiece, the first segment having a first segment length that is longer than the first spot area 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 segment having a second segment length that is longer than the second spot area and shorter than the cutting path length, the overlap length being greater than at least the first or second spot areas; 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 segment having a third segment length that is longer than the third spot area 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, wherein the portion of the cutting path has a portion length greater than the first, second, or third spot areas.   
     
     
       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 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 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 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. A method for laser processing, comprising:
 directing to a workpiece a primary group of passes of primary laser pulses to impinge locations along a primary segment of a cutting path that is continuous and has a cutting path length, each primary laser pulse having a primary spot area that defines a primary spatial major axis on the workpiece and impinging a location along the primary segment, the primary segment having a primary segment length that is longer than the primary spatial major axis and shorter than the cutting path length, and at least some of the locations along the primary segment length being impinged multiple times by the primary laser pulses of the primary group of passes;   directing to the workpiece a secondary group of passes of secondary laser pulses to impinge locations along a secondary segment of the cutting path, each secondary laser pulse having a secondary spot area that defines a secondary spatial major axis on the workpiece and impinging a location along the secondary segment, the secondary segment having a secondary segment length that is longer than the secondary spatial major axis and shorter than the cutting path length, and at least some of the locations along the secondary segment length being impinged multiple times by the secondary laser pulses of the secondary group of passes, the secondary segment overlapping the primary segment by an overlap length greater than at least the primary or secondary spatial major axes; and   after directing to the workpiece at least the primary and secondary groups of passes of respective primary and secondary laser pulses, directing to the workpiece a tertiary group of passes of tertiary laser pulses to impinge locations along a tertiary segment of the cutting path, each tertiary laser pulse having a tertiary spot area that defines a tertiary spatial major axis on the workpiece and impinging a location along the tertiary segment, the tertiary segment having a tertiary segment length that is longer than the tertiary spatial major axis and shorter than the cutting path length, and at least some of the locations along the tertiary segment length being impinged multiple times by the tertiary laser pulses of the tertiary group of passes, the tertiary segment including a subsequent portion of the cutting path other than the primary or secondary segments, wherein:   the subsequent portion of the cutting path has a nonoverlap length greater than any one of the primary, secondary, and tertiary spatial major axes;   the workpiece comprises a wafer substrate supporting an electronic device, the wafer substrate including a ceramic or glass target material;   at least one of the primary, secondary, and tertiary groups of passes of respective primary, secondary, and tertiary laser pulses comprises a first laser pulse of first Gaussian laser output having a substantially Gaussian irradiance profile characterized by a center of a peak irradiance amount and a peripheral region of a peripheral irradiance amount that is less than the peak irradiance amount;   a major portion of the first Gaussian laser output propagates through an aperture configured to convert the major portion of the first Gaussian laser output into a first apertured output having an irradiance profile characterized by an apertured peripheral irradiance amount that is reduced relative to the peak irradiance amount;   the first apertured output is directed to impinge a first target location in the respective primary, secondary, or tertiary segment with a first spot area defining a first respective primary, secondary, or tertiary spot area on the ceramic or glass target material, the first apertured output causing depthwise removal of an amount of target material at the first target location on the surface;   the at least one of the primary, secondary, and tertiary groups of passes of respective primary, secondary, and tertiary laser pulses comprises a second laser output pulse of second Gaussian laser output having a substantially Gaussian irradiance profile characterized by a center of a peak irradiance amount and a peripheral region of a peripheral irradiance amount that is less than the peak irradiance amount;   a major portion of the second Gaussian laser output propagates through an aperture configured to convert the major portion of the second Gaussian laser output into a second apertured output having an irradiance profile characterized by an apertured peripheral irradiance amount that is reduced relative to the peak irradiance amount; and   the second apertured output is directed to impinge a second target location in the respective primary, secondary, or tertiary segment with a second spot area defining a second respective primary, secondary, or tertiary spot area that partly overlaps the first spot area by a region of spot overlap on the target material, the second apertured output causing depthwise removal of an amount of target material at the second location and generating debris that contacts the workpiece, the region of spot overlap specifying a region of spot nonoverlap of the second and first spot areas that corresponds to a bite size of the second apertured output, the bite size being set, in cooperation with the configuration of the aperture converting the major portion of the second Gaussian laser output into the second apertured output, to facilitate laser spot irradiance profile and target material depthwise removal control of the second apertured output and thereby cause the generation of debris in a form of cleanable, nonpermanent redeposited material contacting the workpiece.   
     
     
       53. The method of claim 52, further comprising removing the nonpermanent redeposited material contacting the workpiece by a nonaggressive cleaning technique that entails mechanical scrubbing, solvent bathing, or ultrasonic vibrating. 
     
     
       54. The method of claim 52, further comprising:
 directing each of the first and second Gaussian laser outputs to propagate along an optical path through a beam-shaping component that imparts greater uniformity to the major portion of the Gaussian laser output before it propagates through the aperture.   
     
     
       55. The method of claim 54, in which the major portions of the first and second Gaussian laser outputs to which uniformity is imparted become respective first and second shaped outputs having shaped irradiance profiles, and further comprising:
 directing the first and second shaped outputs through one or more imaging lens components to form for the first and second apertured outputs imaged, shaped irradiance profiles.   
     
     
       56. The method of claim 55, in which the first and second apertured outputs formed with imaged, shaped irradiance profiles have respective first and second energy densities over the respective first and second spot areas, and the first and second energy densities are greater than a fluence below which the second apertured output generates debris in a form of permanent redeposited material contacting the workpiece. 
     
     
       57. The method of claim 52, further comprising removing the nonpermanent redeposited material contacting the workpiece by mechanical scrubbing, solvent bathing, ultrasonic vibrating, ion milling, or reaction ion etching. 
     
     
       58. The method of claim 52, in which the first and second apertured outputs comprise energy densities of greater than about 500 MW/cm 2  per pulse. 
     
     
       59. The method of claim 52, in which the region of spot nonoverlap of the second and first spot areas comprises a bite size of 1-7 μm. 
     
     
       60. The method of claim 52, in which the workpiece includes an air-bearing surface of an electronic device, the air-bearing surface has an edge, and the first and second apertured outputs are applied in proximity to the edge of the air-bearing surface to round the edge. 
     
     
       61. The method of claim 52, in which each of the first and second spot areas has a spatial major axis of about 5-15 μm. 
     
     
       62. The method of claim 52, further comprising delivering the first and second Gaussian laser outputs at repetition rates of greater than about 5 kHz. 
     
     
       63. The method of claim 52, in which the surface of target material comprises AlTiC or vacuum-deposited alumina. 
     
     
       64. The method of claim 52, in which the surface of target material comprises silicon, silicon carbide, or titanium carbide. 
     
     
       65. The method of claim 52, in which the target material forms a layer of a laser diode, an optical waveguide, or a MEMS component. 
     
     
       66. The method of claim 52, in which the beam-shaping component comprises a diffractive optical element. 
     
     
       67. The method of claim 52, in which the beam-shaping component comprises aspheric optics. 
     
     
       68. The method of claim 52, in which the first and second apertured outputs have a UV wavelength.