Laser-cutting using selective polarization

Abstract

A method of cutting a semiconductor wafer by selectively controlling and utilising the polarization of incident laser beam or beams, comprising irradiating the semiconductor wafer with laser light having a first polarization state, and subsequently irradiating the semiconductor wafer with laser light having a second polarization state, the second polarization state being different from the first polarization state.

1 . A method of cutting a semiconductor wafer, comprising the steps of:
 a) providing a laser source for directing laser light to an irradiation region of a laser cutting apparatus,   b) supporting the semiconductor wafer within the laser cutting apparatus such that the irradiation region is coincident with the semiconductor wafer, and   c) irradiating the irradiation region of the semiconductor wafer with laser light having a first polarization state, and subsequently irradiating the irradiation region of the semiconductor wafer with laser light having a second polarization state, the second polarization state being different from the first polarization state.   
     
     
         2 . The method of  claim 1 , for cutting the semiconductor wafer along a cut line, wherein step b) comprises supporting the semiconductor wafer such that the irradiation region is coincident with a point on a cut line of the semiconductor wafer,
 the method further comprising the step of:   d) relatively moving the semiconductor wafer and the irradiation region in a direction parallel to the plane of the semiconductor wafer such that the irradiation region follows the cut line of the wafer, so that the semiconductor wafer is cut along the cut line.   
     
     
         3 . The method of  claim 2 , wherein the first polarization state comprises one of the group consisting of: linear polarization perpendicular to the direction of relative movement, linear polarization parallel to the direction of relative movement, circular polarization, elliptical polarization and non-polarization. 
     
     
         4 . The method of  claim 2 , wherein the second polarization state comprises one of the group consisting of: linear polarization perpendicular to the direction of relative movement, linear polarization parallel to the direction of relative movement, circular polarization, elliptical polarization and non-polarization. 
     
     
         5 . The method of  claim 2 , wherein the laser source produces a laser beam which is directed to the irradiation region,
 step d) is performed while the semiconductor wafer is irradiated with the laser beam having the first polarization state,   the laser beam is then changed to the second polarization state, and then   step d) is repeated while the semiconductor wafer is irradiated with laser beam having the second polarization state.   
     
     
         6 . The method of  claim 5 , wherein step d) is repeated at least once. 
     
     
         7 . The method of  claim 2 , wherein the laser source produces an array of laser beams, each laser beam of the array being directed to a different respective part of the irradiation region, and at least a first laser beam of the array has the first polarization state and at least one other laser beam of the array, which trails the first beam in the direction of relative movement, has the second polarization state. 
     
     
         8 . The method of  claim 2 , comprising an initial step of determining an optimum polarization state for the laser light to achieve cutting, and
 in step c), polarizing the laser light in accordance with the determined optimum polarization state.   
     
     
         9 . The method of  claim 1 , for drilling the semiconductor wafer, wherein step b) comprises supporting the semiconductor wafer such that the irradiation region is coincident with a drilling point of the semiconductor wafer, and
 wherein step c) comprises irradiating the semiconductor wafer with circularly polarized laser light, such that the polarization state of the laser light varies with time.   
     
     
         10 . Apparatus for performing the method of  claim 1 . 
     
     
         11 . Laser-cutting apparatus for cutting a semiconductor wafer, comprising:
 a laser source for emitting a laser beam;   an optical guide system for receiving the laser beam and directing laser light to an irradiation region;   a selectively actuatable optical polarizing component for switching a polarization state of the laser light directed to the irradiation region between a first polarization state and a second, different, polarization state; and   a support for supporting a semiconductor wafer in a position that is at least partially coincident with the irradiation region.   
     
     
         12 . The laser-cutting apparatus of  claim 11 , comprising a drive for relatively moving the semiconductor wafer and the irradiation region such that the irradiation region follows a cut line of the wafer. 
     
     
         13 . The laser-cutting apparatus of  claim 12 , wherein the first and second polarization states each comprise one of the group consisting of: linear polarization perpendicular to the direction of relative movement along the cut line, linear polarization parallel to the direction of relative movement along the cut line, circular polarization, elliptical polarization and non-polarization. 
     
     
         14 . The laser-cutting apparatus of  claim 12 , wherein the selectively actuatable optical polarizing component comprises a half-wave plate selectively movable for changing linear polarization of the laser beam. 
     
     
         15 . The laser-cutting apparatus of  claim 12 , wherein the selectively actuatable optical polarizing component comprises a quarter-wave plate selectively movable for changing elliptical or circular polarization of the laser beam. 
     
     
         16 . The laser-cutting apparatus of  claim 12 , wherein the optical guide system comprises a beam splitter for converting the laser beam into an array of output laser beams. 
     
     
         17 . The laser-cutting apparatus of  claim 16 , wherein the selectively actuatable optical polarizing component comprises a plurality of half-wave plates, each being selectively movable for changing linear polarization of a respective output laser beam. 
     
     
         18 . The laser-cutting apparatus of  claim 16 , wherein the selectively actuatable optical polarizing component comprises a plurality of quarter-wave plates, each being selectively movable for changing elliptical or circular polarization of a respective output laser beam.