Methods and systems for laser processing of coated substrates
Examples of methods and systems for laser processing of materials are disclosed. Methods and systems for singulation of a wafer comprising a coated substrate can utilize a laser outputting light that has a wavelength that is transparent to the wafer substrate but which may not be transparent to the coating layer(s). Using techniques for managing fluence and focal condition of the laser beam, the coating layer(s) and the substrate material can be processed through ablation and internal modification, respectively. The internal modification can result in die separation.
1. A method for processing a workpiece, the workpiece comprising a substrate and at least one layer formed on the substrate, the at least one layer having an ablation threshold that is less than an ablation threshold of the substrate, the method comprising:
providing laser pulses having a pulse energy and a wavelength, wherein the substrate is substantially transparent to the laser pulses at the wavelength;
delivering the laser pulses to the workpiece; and
adjusting fluence and focal conditions of the laser pulses such that:
(1) intensity of the laser pulses in or near the at least one layer is at or above the ablation threshold of a layer in the at least one layer and below the ablation threshold of the substrate, and
(2) intensity of the laser pulses near a focal spot in the substrate is at or above the ablation threshold of the substrate,
wherein a laser pulse removes a depthwise portion of said at least one layer and controllably modifies an internal portion of said substrate.
2. The method of claim 1 , wherein the substrate is substantially transparent to the laser pulses at the wavelength.
3. The method of claim 1 , wherein said at least one layer comprises a conductive film.
4. The method of claim 3 , wherein said conductive film comprises ITO.
5. The method of claim 3 , wherein said conductive film comprises gold.
6. The method of claim 3 , further comprising at least one dielectric layer disposed between said conductive film and said substrate, said at least one dielectric layer being substantially transparent at the wavelength of said laser pulses.
7. The method of claim 6 , wherein said at least one dielectric layer comprises multiple dielectric layers.
8. The method of claim 1 , wherein said at least one layer comprises a low-k dielectric.
9. The method of claim 1 , wherein said processing with laser pulses having said intensity in or near said layer cleanly removes said at least one layer, said pulses having said intensity in said substrate modifies an internal portion of said substrate, and wherein the surface of said substrate is substantially undamaged with said processing.
10. The method of claim 1 , wherein at least a portion of said processing is carried out during relative motion of said substrate and said laser pulses, and in a single pass.
11. A laser-based method for processing a workpiece, the workpiece comprising a substrate and at least one layer formed on the substrate, wherein the substrate is substantially transparent at a laser wavelength, said method comprising:
generating a focused laser processing beam having at least one pulse, a beam diameter w 0 at an internal substrate position, and a beam diameter w 1 at or near said at least one layer on said substrate, wherein w 0 <w 1 ;
removing at least a depthwise portion of said at least one layer; and
controllably modifying an internal portion of said substrate.
12. The laser-based method of claim 11 , wherein said removing and said controllably modifying are carried out with a single laser pulse.
13. The laser-based method of claim 11 , wherein said removing and said controllably modifying are carried out with multiple laser pulses having spatial overlap between adjacent laser pulses.
14. The laser-based method of claim 13 , wherein said overlap is at least about 99%.
15. The laser-based method of claim 13 , wherein said multiple laser pulses are generated at a repetition rate of at least about 100 KHz.
16. The laser-based method of claim 11 , wherein said at least one layer is relatively opaque at a laser wavelength as compared to said substrate.
17. The laser based method of claim 11 , wherein a pulse width of at least one laser pulse is in a range from tens of femtoseconds up to tens of picoseconds.