Energy efficient, laser-based method and system for processing target material
View Patent ↗An energy-efficient method and system for processing target material such as microstructures in a microscopic region without causing undesirable changes in electrical and/or physical characteristics of material surrounding the target material is provided. The system includes a controller for generating a processing control signal and a signal generator for generating a modulated drive waveform based on the processing control signal. The waveform has a sub-nanosecond rise time. The system also includes a gain-switched, pulsed semiconductor seed laser for generating a laser pulse train at a repetition rate. The drive waveform pumps the laser so that each pulse of the pulse train has a predetermined shape. Further, the system includes a laser amplifier for optically amplifying the pulse train to obtain an amplified pulse train without significantly changing the predetermined shape of the pulses. The amplified pulses have little distortion and have substantially the same relative temporal power distribution as the original pulse train from the laser. Each of the amplified pulses has a substantially square temporal power density distribution, a sharp rise time, a pulse duration and a fall time. The system further includes a beam delivery and focusing subsystem for delivering and focusing at least a portion of the amplified pulse train onto the target material.
1. A method for processing a target material in a multi-material device on a substrate, said target material having a specified dimension in a microscopic region of said multi-material device, said method comprising:
generating one or more laser pulses;
forming at least one modified laser pulse from the one or more laser pulses;
directing during continuous relative motion the at least one modified laser pulse to the target material so as to progressively heat the target material; and
timing the laser pulse generation to correlate with relative positions of the target such that the at least one modified laser pulse accurately impinges on the target material, wherein
said modified laser pulse has a sharp rise time sufficient to reduce reflectivity of the target material to minimize heat dissipation to the substrate underneath the target material and to minimize heat conduction laterally to contiguous material in a vicinity of the target material,
wherein said at least one modified laser pulse has a rapid fall time sufficient to reduce damage to said contiguous material in the vicinity of the target material, and
wherein said at least one modified laser pulse has a sufficient thermal energy to sever said target material.
2. The method of claim 1 , further comprising:
progressively heating the target material with the at least one modified laser pulse until the target material melts, thereby expanding and rupturing an insulator material over the target material.
3. The method of claim 1 , wherein forming at least one modified laser pulse comprises:
slicing a tail portion from at least one of said generated laser pulses.
4. The method of claim 1 , wherein forming at least one modified laser pulse comprises:
combining a plurality of the generated laser pulses.
5. The method of claim 1 , wherein generating comprises:
generating the laser pulses with a seed laser.
6. The method of claim 5 , wherein forming at least one modified laser pulse comprises:
optically amplifying the generated laser pulses.
7. The method of claim 1 , wherein forming at least one modified pulse comprises:
forming said least one modified pulse with a rise time is less than 1 ns, and a peak power density following said rise time of at least 10 9 W/cm 2 .
8. The method of claim 1 , wherein forming at least one modified pulse comprises:
forming said least one modified pulses with a substantially square shape.
9. The method of claim 1 , further comprising:
limited heating by the modified laser pulse to ensure that silicon for the substrate does not shift an absorption edge thereof into the infrared and enter a thermal runaway condition in which silicon damage can occur.
10. The method of claim 1 , wherein forming at least one modified laser pulse comprises:
generating a series of closely-spaced, short pulses which produce progressive heating of the target material.
11. The method of claim 1 , further comprising:
operating a laser at a pulse repetition rate exceeding the material processing rate to produce said one or more laser pulses; and
selecting processing pulses from said one or more laser pulses via a computer controlled optical switch, wherein a computer in control of the optical switch is operatively connected to a beam positioning system used to position a focused laser beam for material processing.
12. The method of claim 11 , wherein the laser comprises a seed laser and fiber amplifier, and modulation of the seed laser directly produces a desired gain-switched pulse shape which is amplified by the fiber laser amplifier.
13. The method of claim 11 , wherein forming at least one modified laser pulse comprises:
forming the one or more laser pulses having a pulse width of a few ps to 30 ns.
14. The method of claim 11 , wherein directing at least one modified laser pulse comprises:
providing a fast rising pulse to an overlying layer of an oxide on the target material for thermal shock of the oxide to facilitate target material removal.
15. The method of claim 1 , wherein forming at least one modified laser pulse comprises selecting the one or more laser pulses with an optical switch including an acousto-optic modulator or an electro-optic modulator.
16. The method of claim 1 , further comprising selectively directing the at least one modified laser pulse at a rate fast enough to process at least 10,000 structures per second.
17. The method of claim 1 , further comprising gain switching a seed laser to generate the one of more laser pulses.
18. The method of claim 1 , further comprising producing for said one or more laser pulses a short pulse having a pulse width less than 18 ns.
19. The method of claim 1 , wherein generating the one or more laser pulses comprises generating laser pulses in rapid succession, the method further comprising amplifying the one or more laser pulses in rapid succession with low distortion, and without significantly changing the shape of the one or more laser pulses.
20. The method of claim 1 , wherein forming at least one modified laser pulse comprises modulating input current to a semiconductor diode laser.
21. The method of claim 20 , wherein generating one or more laser pulses comprises generating a shaped pulse or a sequence of short pulses from a distributed Bragg reflector laser or distributed feedback laser configured for external control of at least one of gain, wavelength, and phase.
22. The method of claim 1 , further comprising gain switching a laser diode receiving a modulated drive waveform to generate said one or more laser pulses.
23. The method of claim 1 , wherein generating one or more laser pulses comprised decreasing a pulse width of a seed laser with a GaAs saturable absorber to decrease the pulse width to within the range of several picoseconds to a few nanoseconds.
24. The method of claim 1 , further comprising producing for the one or more laser pulses at least one amplified shaped pulse having an energy of at least 0.1 microjoules.
25. The method of claim 1 , wherein directing comprises directing the at least one modified laser pulse to a conductive link of a memory device.
26. The method of claim 1 , further comprising producing for the one or more laser pulses an amplified sequence of short pulses having variable width pulses.
27. The method of claim 1 , further comprising gain switching a high power laser diode or diode array to pump a laser amplifier to thereby generate said one or more laser pulses.
28. The method of claim 1 , wherein forming at least one modified laser pulse comprises modifying a portion of the one or more laser pulses.
29. The method of claim 1 , wherein generating one or more laser pulses comprises generating the one or more laser pulses with a fiber optic amplifier.
30. The method of claim 1 , wherein forming at least one modified laser pulse comprises amplifying the one or more laser pulses with multiple amplifier stages.
31. The method of claim 1 , wherein forming at least one modified laser pulse comprises amplifying the one or more laser pulses with a gain of at least 20 dB.
32. The method of claim 1 , further comprising:
delivering said thermal energy to a metal link with a predetermined non-Gaussian pulse shape waveform, the predetermined waveform comprising said sharp rise time, a duration, and said rapid fall time to prevent damage to non-target materials apart from the metal link.
33. The method of claim 1 , wherein the modified laser pulse comprises:
at least two closely spaced pulses having a wavelength within a range from the 0.4 microns to about 2 microns.
34. The method of claim 1 , wherein forming at least one modified laser pulse comprises:
producing laser seed pulses and amplifying the seed pulses.
35. The method of claim 1 , wherein the at least one modified laser pulse comprises:
at least two closely spaced pulses having similar energy density profiles.
36. The method of claim 1 , wherein directing comprises:
directing the at least one modified pulse to links having a width that is less than one micron; and
producing for the one or more laser pulses a wavelength within the infrared region.
37. The method of claim 1 , wherein directing comprises:
directing the at least one modified pulse to links having a passivation layer of a thickness of about 0.3-0.5 microns.
38. The method of claim 1 , wherein directing comprises:
directing the at least one modified pulse to links having a thickness of less than about 0.3 micron.
39. The method of claim 1 , wherein the at least one modified laser pulse comprises:
at least two closely spaced pulses having at least 0.1 microjoules of output energy and up to about 3 microjoules of energy.
40. The method of claim 1 , wherein directing comprises:
directing the at least one modified pulse to produce a laser spot on a memory link of a size in the range of about 1 micron to 4 microns.