Laser-based material processing methods and systems

• US 8,158,493 B2
• Filed: 12/17/2009
• Issued: 04/17/2012
• 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
• Primary Examiner(s): Garber, Charles
• Assistant Examiner(s): Abdelaziez, Yasser
• Application Number:
  US12/641,256
• Publication Number:
  US 20100197116A1
• Time in Patent Office: 852 Days
• Field of Search: None
• 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. Embodiments of 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, picosecond, and/or nanosecond pulses.

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,

wherein at least one laser pulse has a pulse energy of at least about 100 nJ,

wherein said pattern comprises said metal material and said dielectric material, and

wherein 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.

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 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.

7. 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.

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

9. The method of claim 1, wherein at least one of said laser pulses provides a fluence in a range from about 0.25 J/cm² to about 30 J/cm².

10. The method of claim 1, wherein at least one of said laser pulses provides a fluence in a range from above an ablation threshold of said at least one material to about 20 times the ablation threshold of said at least one material.

11. The method of claim 1, wherein the overlap between adjacent focused spots for removal of the material from the at least a portion of the pattern exceeds about 95%.

12. The method of claim 1, wherein the overlap between adjacent focused spots for removal of the material from the at least a portion of the pattern exceeds about 99%.

13. The method of claim 1, wherein the overlap between adjacent focused spots for removal of material from the at least a portion of the pattern is in a range between about 75% to more than about 99%.

14. The method of claim 1, wherein the overlap between adjacent focused spots for removal of the material from the at least a portion of the pattern is at least about ten times greater than the overlap between adjacent focused spots for removal of the material from the at least a portion of the semiconductor wafer.

15. The method of claim 1, wherein at least a portion of said positioning is carried out with a beam deflector.

16. The method of claim 1, wherein said positioning said laser spots comprises performing multiple passes of said laser spots relative to said at least one material.