LASER-BASED MATERIAL PROCESSING METHODS AND SYSTEMS

• US 20100197116A1
• Filed: 12/17/2009
• Published: 08/05/2010
• Est. Priority Date: 03/21/2008
• Status: Active Grant

• Current Assignee: IMRA America Incorporated (Aisin Corp.)
• Original Assignee: IMRA America Incorporated (Aisin Corp.)
• Inventors: Shah, Lawrence, Cho, Gyu Cheon, Xu, Jingzhou
• Granted Patent: US 8,158,493 B2
• Time in Patent Office: Days
• US Class Current: 438/463
• CPC Class Codes: B23K 2101/40 Semiconductor devices
• CPC Class Codes: B23K 2103/50 Inorganic material, e.g. metals, not provided for in B23K2103/02 – B23K2103/26
• CPC Class Codes: B23K 26/0624 using ultrashort pulses, i.e. pulses of 1ns or less
• CPC Class Codes: B23K 26/064 by means of optical elements, e.g. lenses, mirrors or prisms
• CPC Class Codes: B23K 26/0643 comprising mirrors
• CPC Class Codes: B23K 26/0648 comprising lenses
• CPC Class Codes: B23K 26/082 Scanning systems, i.e. devices involving movement of the laser beam relative to the laser head
• CPC Class Codes: B23K 26/083 Devices involving movement of the workpiece in at least one axial direction
• CPC Class Codes: B23K 26/364 for making a groove or trench, e.g. for scribing a break initiation groove
• CPC Class Codes: B23K 26/38 by boring or cutting
• CPC Class Codes: B23K 26/40 taking account of the properties of the material involved
• CPC Class Codes: H01L 21/268 using electromagnetic radiation, e.g. laser radiation

Abstract

Various embodiments may be used for laser-based modification of target material of a workpiece while advantageously achieving improvements in processing throughput and/or quality. Embodiments of a method of processing may include focusing and directing laser pulses to a region of the workpiece at a pulse repetition rate sufficiently high so that material is efficiently removed from the region and a quantity of unwanted material within the region, proximate to the region, or both is reduced relative to a quantity obtainable at a lower repetition rate. In at least one embodiment, an ultrashort pulse laser system may include at least one of a fiber amplifier or fiber laser. Various embodiments are suitable for at least one of dicing, cutting, scribing, and forming features on or within a semiconductor substrate. Workpiece materials may also include metals, inorganic or organic dielectrics, or any material to be micromachined with femtosecond and/or picosecond pulses, and in some embodiments with pulse widths up to a few nanoseconds.

Claims

1. A method of scribing, dicing, cutting, or processing to remove material from a region of a multi-material workpiece, said method comprising:

directing laser pulses toward at least one material of a multi-material workpiece, the laser pulses having a pulse width in a range from tens of femtoseconds to about 500 picoseconds and a pulse repetition rate of a few hundred kHz to about 10 MHz, the workpiece comprising both a pattern and a semiconductor wafer, said pattern comprising at least one of a dielectric material and a metal material;

focusing said laser pulses into laser spots having spot sizes in a range from a few microns to about 50 μ

m (1/e²); and

positioning said laser spots relative to said at least one material at a scan speed such that an overlap between adjacent focused spots for removal of material from at least a portion of the pattern is substantially greater than an overlap between adjacent focused spots for removal of material from at least a portion of the semiconductor wafer,

wherein said method controls heat accumulation within one or more materials of said workpiece, while limiting accumulation of redeposited material about the region.

2. The method of claim 1, wherein a thickness of said semiconductor wafer is less than about 100 μ

m.

3. The method of claim 1, wherein at least one laser pulse has a pulse energy in a range from about 1 μ

J to about 20 μ

J.

4. The method of claim 1, wherein said spot sizes are in a range from about 15 μ

m to about 50 μ

m, and said scan speed for removal of material from said pattern is in a range from about 0.1 msec to about 0.5 msec.

5. The method of claim 1, wherein said laser pulses are output by an ultrashort pulsed laser system.

6. The method of claim 1, wherein at least one laser pulse has a pulse energy of at least about 100 nJ, said pattern comprises said metal material and said dielectric material, and heat accumulation within said at least a portion of said pattern is sufficiently high to avoid delamination of said dielectric material from said metal material.

8. The method of claim 1, wherein a pulse width for removing at least a portion of said pattern is in a range from about 100 ps to about 500 ps, and a pulse width for removing at least a portion of said wafer is in a range from about 100 fs to about 10 ps.

9. The method of claim 1, wherein the scan speed for removal of at least a portion of said pattern is substantially less than the scan speed for removal of at least a portion of said wafer.

10. The method of claim 1, wherein said scan speed is in the range of about 0.1 msec to about 10 msec.

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17. A method of processing a multi-material workpiece, said workpiece comprising a semiconductor material and a pattern, said pattern comprising at least one of a dielectric material and metal material, said method comprising:

irradiating said workpiece with a series of laser pulses, at least two pulses of the series having different characteristics that are applied to different materials of said workpiece; and

controlling heat-affected zone (HAZ) such that at least one HAZ generated during removal of at least one of the dielectric material and the metal material is increased depthwise relative to at least one HAZ generated during removal of a portion of said semiconductor material.

18. The method of claim 17, wherein at least some laser pulses have different pulse widths, and controlling HAZ comprises applying different pulse widths to said workpiece materials, said pulse widths in a range of about 100 fs to about 500 ps.

19. The method of claim 17, wherein the different characteristics comprise at least one of:

pulse energy, peak power, and spatial overlap at said workpiece, and said controlling HAZ comprises applying pulses having at least one of the different characteristics to said different workpiece materials.

20. The method of claim 17, wherein at least one pulse of the series provides fluence in a range from about 0.25 J/cm² to about 30 J/cm².

21. A method of processing a workpiece comprising both a pattern and a semiconductor wafer region, said pattern comprising a dielectric material and a metal material, said method comprising:

modifying at least a portion of said pattern with focused laser pulses, at least one focused pulse comprising a pulse width in a range of about 100 fs to about 500 ps; and

accumulating sufficient heat in said portion of said pattern to avoid delamination of said dielectric material from said metal material.

23. The method of claim 21, wherein at least one focused laser pulse has a pulse energy at least about 1 μ

J.

24. The method of claim 21, wherein said applied fluence is at least about 0.4 J/cm².

25. The method of claim 21, wherein said pulse width is in a range from about 100 fs to about 10 ps and at least one focused laser pulse has a pulse energy in a range from about 1 μ

J to about 10 μ

J, and said method further comprises positioning said pulses relative to said pattern so that a spatial overlap between adjacent focused pulses exceeds about 95%.

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37. A laser-based system for scribing, dicing, cutting, or processing of a multi-material workpiece having a semiconductor material, the system comprising:

a source of optical pulses;

an optical amplification system configured to amplify a pulse from the source and to generate output pulses having at least one pulse width in a range from tens of femtoseconds to about 500 picoseconds;

a modulation system, including at least one optical modulator, configured to provide a repetition rate of the output optical pulses to be in a range from at least about 1 MHz to less than about 100 MHz;

a beam delivery system configured to focus and deliver pulsed laser beams to the workpiece, wherein a pulsed beam is focused into a spot size (1/e²) of at least about 5 microns; and

a positioning system configured to scan said beams at a scan rate that produces a spot overlap on or within the one or more materials of the workpiece, the spot overlap at least about 95% at said repetition rate and said spot size.

38. The laser-based system of claim 37, wherein at least some of said output pulses have a pulse energy of at least about 100 nJ.

42. The laser-based system of claim 37, wherein said amplification system comprises at least one large-mode fiber amplifier.

44. The laser-based system of claim 37, wherein said optical amplification system is configured to amplify a pulse from the source to an energy of at least about 1 μ

J and to generate ultrashort output pulses having at least one pulse width in a range of about 100 fs to about 10 ps, said optical amplification system comprising at least one large-mode fiber amplifier, said at least one large-mode fiber amplifier comprising at least one of a doped large-core leakage channel fiber amplifier, a photonic crystal fiber, and a photonic bandgap fiber, wherein at least one fiber amplifier is configured such that said laser-based system emits nearly diffraction limited pulsed output beams; and

wherein said laser-based system is configured to be adjustable to generate said pulsed output beams at a repetition rate in a range from about a few hundred kHz to about 10 MHz.

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45. A system for dicing, cutting, scribing, or forming features on or within a workpiece having a semiconductor material, said system comprising:

a pulsed laser system configured to repeatedly irradiate at least a portion of said material with focused laser pulses at a scan rate and a pulse repetition rate, wherein said repetition rate is in a range of about 100 kHz to about 5 MHz and sufficiently high to efficiently remove a substantial depthwise portion of material from a target location and to limit accumulation of unwanted material about the target location;

a beam delivery system configured to focus and deliver said laser pulses;

a positioning system configured to position said laser pulses relative to said semiconductor substrate at said scan rate, said positioning system comprising at least one of an optical scanner and a substrate positioner; and

a controller configured to be coupled to said pulsed laser system, said beam delivery system, and said positioning system, said controller configured to control a spatial overlap between adjacent focused laser pulses during processing of the workpiece at said repetition rate.

46. The system of claim 45, further comprising a beam manipulator configured to be coupled to the laser system and the controller, said beam manipulator, said laser system, and said controller operable to obtain a signal indicative of a condition of at least one of said substrate and said laser system, and to produce a control signal to alter said condition of at least one of said substrate and said laser system.

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