Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
  • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
  • B23K26/062—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam
  • B23K26/0622—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam by shaping pulses
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/352—Working by laser beam, e.g. welding, cutting or boring for surface treatment
  • B23K26/3568—Modifying rugosity
  • B23K26/3576—Diminishing rugosity, e.g. by grinding, polishing or smoothing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/08—Devices involving relative movement between laser beam and workpiece
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K2103/00—Materials to be soldered, welded or cut
  • B23K2103/50—Inorganic materials other than metals or composite materials
  • B23K2103/56—Inorganic materials other than metals or composite materials being semiconducting

Definitions

• This invention relates to laser machining and in particular to pulsed laser machining in which successive pulses do not overlap at the substrate being machined.
• Laser micro-machining with state of the art solid state lasers typically involves the use of lasers with galvanometer scanners to position a focussed laser beam on the surface of a wafer or substrate to be machined. Typically, these lasers operate at repetition rates of
• laser dicing is accomplished by scanning a laser beam across a substrate.
• successive adjacent pulses 21 are placed to have a certain overlap by scanning the laser beam at a particular scan speed to give a substantial overlap between the pulses.
• the scan is repeated in a number of passes 1 1, until the substrate is fully diced through. As shown in Figure 3, this results in dicing with a relatively smooth edge 31.
• Figures 4 and 5 if the overlap of pulses 41 is reduced the die can appear to have a 'scalloped' edge 51.
• a method of laser machining a feature in a substrate comprising: machining the substrate with a pulsed laser along a scan line with a first scan such that a centre to centre spatial distance at the substrate between successive pulses in the laser pulse train is equal to at least a sum of radii of the successive pulses so that the successive pulses at the substrate do not overlap but are either contiguous or spaced apart; and machining with succeeding scans of the laser along the scan line which are offset along the scan line with respect to the starting point of a previous scan so that multiple successive laser scans provide machining to a required depth while smoothing edges of the feature.
• successive pulses are sufficiently separated on the substrate that a plume produced by a laser pulse does not substantially absorb energy from a succeeding pulse.
• the method comprises machining with a pulse repetition rate of 200 kHz to 300 kHz.
• the method comprises complete dicing or slot cutting through the substrate.
• the machining comprises a laser dicing process for semiconductor dicing.
• the machining comprises slot drilling.
• Figure 1 is a schematic transverse cross-sectional view showing successive laser scans across a substrate to form a channel
• Figure 2 is a schematic plan view of laser pulses on a substrate according to the prior art in which a succeeding laser pulse substantially overlaps a preceding pulse.
• Figure 3 is a schematic plan view of edges of a machined channel using the laser pulse pattern of Figure 2;
• Figure 4 is a schematic plan view of pulses on a substrate in which a succeeding laser pulse overlaps a preceding pulse less than in the pulse pattern of Figure 2.
• Figure 5 is a schematic plan view of edges of a machined channel using the laser pulse pattern of Figure 4;
• Figure 6 is a transverse cross-sectional view of laser machining of a substrate using substantially overlapping laser pulses as in Figures 2 and 3;
• Figure 7 is a transverse cross-sectional view of laser machining of a substrate according to the invention using substantially non-overlapping pulses
• Figure 8 is a schematic plan view of successive offset scans of pulses on a substrate according to the invention using the substantially non-overlapping pulses of Figure 7;
• Figure 9 is a schematic successive plan views of edges of a machined channel using the successive offset scans of Figure 8;
• Figure 10 is a graph of theoretical machining speed versus pulse overlap with and without successive scans being offset as they are offset in Figure 8.
• like reference numbers denote like parts.
• Repetition rate R: The number of pulses per second emitted from the laser.
• Scan Speed Vg: The scanning velocity of the galvo.
• Kerf diameter, K Diameter of a specific trench or feature as formed by the laser pulses.
• Pulse spacing S: The centre-to-centre distance between sequential pulses of a single scan at the substrate.
• Offset dither D: The centre-to-centre distance between corresponding pulses formed by sequential scans in a multiple pass cutting process.
• Number of Scans, N The number of consecutive scans required to dice through a substrate.
• successive pulses 71, 74 are separated sufficiently such that there is substantially no interaction of a current pulse
• each successive pass 82, 83, 84 of the laser beam is offset from a previous pass 81, 82, 83 respectively. In this manner, progressively straighter edges 92, 93, 94 of the scanned feature are produced with each pass.
• the invention provides a method for laser scribing, dicing or machining of semiconductor substrates with improved edge quality, throughput and debris control using multiple pass machining with non-overlapping spatial distribution of pulses in each individual pass, but with pulses in succeeding passes offset from pulses in previous passes.
• This laser machining with zero overlap substantially prevents pulse-plume interaction, and hence substantially eliminates any loss of energy of a succeeding pulse to a plume produced by a previous pulse.
• a pulsed laser is used to scan spatially in a direction to be machined. Multiple scans of the laser are used to form a scribe or through feature.
• the scanning velocity V g and repetition rate R of the pulses is such that pulses do not overlap.
• a repetition range of 200 kHz to 300 kHz has been found to be suitable.
• Individual scans of the laser are positioned spatially to overlap with preceding scans by synchronising and use of a time delay in pulse emission from the laser.
• the laser parameters used are described in Table 1 below.
• the laser ran at 17OkHz, which gave a pulse energy at the wafer of ⁇ 60 ⁇ J.
• the scan speed was varied from 500mm/s to 3500mm/s to give overlaps in the range 80% to -50%.
• the overlap was determined from the ablated spot diameter ( ⁇ 14 ⁇ m) rather than the theoretical spot diameter ( ⁇ 8 ⁇ m).

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• Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Engineering & Computer Science (AREA)
• Plasma & Fusion (AREA)
• Mechanical Engineering (AREA)
• Dicing (AREA)
• Laser Beam Processing (AREA)

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Cited By (9)

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Citations (5)

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• 2006
  • 2006-11-27 GB GB0623642A patent/GB2444037A/en not_active Withdrawn
• 2007
  • 2007-11-27 EP EP07846853.5A patent/EP2097209B1/en not_active Not-in-force
  • 2007-11-27 WO PCT/EP2007/010291 patent/WO2008064863A1/en not_active Ceased
  • 2007-11-27 JP JP2009537562A patent/JP2010510885A/ja active Pending
  • 2007-11-27 US US12/515,926 patent/US7947575B2/en not_active Expired - Fee Related
  • 2007-11-27 KR KR1020097012900A patent/KR101260752B1/ko not_active Expired - Fee Related
  • 2007-11-27 CN CN200780049577.XA patent/CN101657292B/zh not_active Expired - Fee Related
  • 2007-11-28 TW TW096145175A patent/TWI448345B/zh not_active IP Right Cessation

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