Laser system and method for material processing with ultra fast lasers
View Patent ↗Laser system and method for material processing with ultra fast lasers are provided. One aspect of the invention features the method which removes at least a portion of a target structure such as a memory link while avoiding undesirable damage to adjacent non-target structures. The method includes applying a single ultra short laser pulse to the target structure to remove the target structure with the single pulse.
1. A method for processing target material of a microstructure while avoiding undesirable changes to adjacent non-target material having a thermal or optical property different than the target material, the target material being characterized by a relationship of fluence breakdown threshold versus laser pulse width that exhibits a rapid and distinct change in slope at a characteristic laser pulse width, the method comprising:
generating a pulsed laser beam in which a first pulse of the beam has a pulse width equal to or less than the characteristic laser pulse width;
focusing the pulsed laser beam to obtain a focused beam; and
relatively positioning the focused beam into a spot on the target material wherein the first pulse and only the first pulse removes all of the target material while avoiding undesirable change to the adjacent non-target material.
2. The method of claim 1 , wherein the microstructure is a electrically conductive, redundant memory link.
3. The method as claimed in claim 2 wherein the link is part of a semiconductor memory device having links widths pitch less than about 1.33 microns.
4. The method as claimed in claim 2 , wherein the link is supported on a silicon substrate, and wherein laser wavelength is greater than about 1 μm.
5. The method as claimed in claim 4 , wherein at least one absorbing material is located between the link and the substrate to prevent damage to at least one of the substrate and a link adjacent to the memory link.
6. The method as claimed in claim 5 , wherein the at least one absorbing material includes a sacrificial layer of material.
7. The method as claimed in claim 5 , wherein interaction of the absorbing material with the focused beam includes non-linear absorption of laser energy.
8. The method as claimed in claim 1 , wherein the micro structure is a link supported on a substrate and wherein at least one sacrificial material is located between the link and the substrate.
9. The method as claimed in claim 8 , wherein the substrate is a silicon substrate.
10. The method as claimed in claim 9 , wherein laser wavelength is less than about 500 nm.
11. The method as claimed in claim 1 , wherein the step of generating includes amplifying a seed pulse with a fiber optic amplifier.
12. The method as claimed in claim 1 , wherein energy density of the focused beam at the spot is greater than about 2 Joules/cm 2 .
13. The method as claimed in claim 12 , wherein the energy density is in a range of about 25–30 Joules/cm 2 .
14. The method as claimed in claim 1 , wherein the pulse width of the first pulse is less than about 10 ps.
15. The method as claimed in claim 1 , wherein the pulse width of the first pulse is less than about 150 fs.
16. The method as claimed in claim 1 , wherein the spot has a diameter less than about 1.6 microns.
17. A system for processing target material of a microstructure while avoiding undesirable changes to adjacent non-target material having a thermal or optical property different than the target material, the target material being characterized by a relationship of fluence breakdown threshold versus laser pulse width that exhibits a rapid and distinct change in slope at a characteristic laser pulse width, the system comprising:
means for generating a pulsed laser beam in which a first pulse of the beam has a pulse width equal to or less than the characteristic laser pulse width;
means for focusing the pulsed laser beam to obtain a focused beam; and
means for relatively positioning the focused beam into a spot on the target material wherein the first pulse and only the first pulse removes all of the target material while avoiding undesirable change to the adjacent non-target material.
18. The system as claimed in claim 17 , wherein the microstructure is an electrically conductive, redundant memory link.
19. The system as claimed in claim 18 , wherein the means for relatively positioning includes:
a positioning subsystem for relatively positioning the link and the focused beam.
20. The system as claimed in claim 18 , wherein the means for generating includes:
an oscillator to generate a source pulse;
a pulse stretcher to stretch the source pulse to obtain a stretched pulse;
an optical amplifier for amplifying the stretched pulse to obtain an amplified pulse; and
a compressor for compressing the amplified pulse so as to produce the first pulse.
21. The system as claimed in claim 20 , wherein the optical amplifier is a fiber optic amplifier.
22. The system as claimed in claim 20 , wherein the pulse stretcher and the compressor are both gratings.
23. The system as claimed in claim 20 , wherein the optical amplifier is an all-fiber parabolic pulse amplifier.
24. The system as claimed in claim 17 , wherein the means for generating includes an oscillator and an optical amplifier and wherein the oscillator and the optical amplifier are both fiber-based.
25. The system as claimed in claim 24 , wherein the means for generating uses FCPA.
26. The system as claimed in claim 17 , wherein the means for generating uses parabolic pulse amplification.
27. The system as claimed in claim 17 , wherein the means for generating uses chirped pulse amplification.