Methods and systems for laser processing of coated substrates

Abstract

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.

What is claimed is: 
     
         1 . A system for processing a workpiece, the workpiece comprising a substrate and a layer formed on the substrate, the layer having an ablation threshold that is less than an ablation threshold of the substrate, the system comprising:
 a laser source configured to provide laser pulses having a pulse energy and a wavelength, wherein the substrate is substantially transparent to the laser pulses at the wavelength;   a beam delivery system configured to deliver the laser pulses to the workpiece;   focusing optics; and   a controller configured to adjust fluence of the laser pulses and to adjust the focusing optics to provide desired focal conditions of the laser pulses at the layer and at a focal spot inside the substrate such that:
 (1) intensity of the laser pulses in or near the layer is at or above the ablation threshold of the 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. 
   
     
     
         2 . The system of  claim 1 , wherein the substrate is substantially transparent to the laser pulses at the wavelength. 
     
     
         3 . The system of  claim 1 , wherein said layer comprises a conductive film. 
     
     
         4 . The system of  claim 3 , wherein said conductive film comprises ITO. 
     
     
         5 . The system of  claim 3 , wherein said conductive film comprises gold. 
     
     
         6 . The system 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 system of  claim 6 , wherein said at least one dielectric layer comprises multiple dielectric layers. 
     
     
         8 . The system of  claim 1 , wherein said layer comprises a low-k dielectric. 
     
     
         9 . The system of  claim 1 , wherein said system is configured such that said processing with laser pulses having said intensity in or near said layer cleanly removes said 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 system of  claim 1 , wherein said system is configured such that 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 system for processing a workpiece, the workpiece comprising a substrate and a layer disposed on the substrate, wherein the substrate is substantially transparent at a laser wavelength, said system comprising:
 a laser source configured to generate a focused laser processing beam having at least one pulse;   focusing optics to produce a beam diameter w 0  at an internal substrate position, and a beam diameter w 1  at or near said layer on said substrate, wherein w 0 <w 1 ; and   a controller configured to control said focusing optics and said laser source to remove at least a depthwise portion of said layer and to controllably modify an internal portion of said substrate.