Method and system for precisely positioning a waist of a material-processing laser beam to process microstructures within a laser-processing site

Abstract

A high-speed method and system for precisely positioning a waist of a material-processing laser beam to dynamically compensate for local variations in height of microstructures located on a plurality of objects spaced apart within a laser-processing site are provided. In the preferred embodiment, the microstructures are a plurality of conductive lines formed on a plurality of memory dice of a semiconductor wafer. The system includes a focusing lens subsystem for focusing a laser beam along an optical axis substantially orthogonal to a plane, an x-y stage for moving the wafer in the plane, and a first air bearing sled for moving the focusing lens subsystem along the optical axis.

1 - 28 . (canceled)  
   
   
       29 . A method of precisely positioning a waist of a material-processing laser beam to dynamically-compensate for local variations in height of conductive links of a semiconductive memory located on a plurality of dies formed on a wafer and spaced apart within a laser-processing site, the laser beam having a spot diameter, W(z), variable along an optical axis, and a minimum spot diameter, Wo, at a beam waist location, the method comprising: 
 controllably positioning the waist of the laser beam along the optical axis to dynamically adjust the beam waist location between first and second links to be processed within the site so that: a spot diameter, W(z), at a processing location is no more than about 5% greater than a minimum beam waist diameter over a total distance of about 1.5 microns or finer along the axis, and at a rate fast enough so that throughput is not substantially effected by the step of controllably positioning.    
   
   
       30 . The method of  claim 29  wherein the step of controllably positioning is carried out at a rate fast enough so that a link processing speed within the site which is a function of pulse generation rate and wafer velocity is not limited by the step of controllably positioning and wherein the wafer velocity is greater than about 50 mm/second.  
   
   
       31 . The method of  claim 29 , wherein the step of controllably positioning is carried out at a rate corresponding to a bandwidth greater than 100 Hz.  
   
   
       32 . The method of  claim 31 , wherein the rate corresponds to a bandwidth greater than 150 Hz.  
   
   
       33 . The method of  claim 29 , wherein the minimum beam waist diameter is about 1.7 microns or less.  
   
   
       34 . The method of  claim 33 , wherein the minimum beam waist diameter is about 1.4 microns or less.  
   
   
       35 . The method of  claim 29 , wherein the step of controllably positioning is based on a sensed position of an optical element along the optical axis.  
   
   
       36 . The method of  claim 35 , wherein sensed position is provided by a capacitive sensor.  
   
   
       37 . The method of  claim 29 , wherein the conductive links have a pitch less than about 3 um.  
   
   
       38 . The method of  claim 37 , wherein the conductive links have a pitch less than about 2 um.  
   
   
       39 . The method of  claim 29 , wherein the laser beam has a wavelength of about 1.047 microns.  
   
   
       40 . The method of  claim 29 , wherein the total distance along the optical axis is about 1 micron or finer.  
   
   
       41 . The method of  claim 29 , wherein the step of controllably positioning is within about one-tenth of the total distance.  
   
   
       42 . The method of  claim 30 , wherein the link processing speed corresponds to maximum velocity of the wafer in the range of about 50-150 mm/sec.  
   
   
       43 . The method of  claim 29 , wherein the step of controllably positioning controls time to move the beam waist between the links to within about 0.03 msec or less.  
   
   
       44 . A method for precisely positioning a waist of a material-processing laser beam to dynamically compensate for local variations in height of spaced apart conductive links of a semiconductive memory within a laser-processing site, the links lying on a surface which is substantially orthogonal to an optical axis, the method comprising: 
 controllably positioning the waist of the laser beam along the optical axis to dynamically adjust the beam waist location between first and second links to be processed within the site so that: a spot diameter W(z) at a processing location is no more than about 5% greater than the minimum beam waist diameter over a total distance of about 1.5 microns or finer along the axis and at a rate fast enough so that throughput is not substantially effected by the step of controllably positioning.    
   
   
       45 . A method of laser processing of conductive links of a semiconductive memory, the method comprising: 
 planning a trajectory to position a laser beam waist relative to the links to be processed; and    controllably positioning the beam waist along an optical axis based on the trajectory to dynamically adjust the beam waist location between first and second links to be processed so that: a spot diameter, W(z), at a processing location is no more than about 5% greater than a minimum beam waist diameter over a total distance of about 1.5 microns or finer along the axis and at a rate fast enough so that throughput is not substantially effected by the step of controllably positioning.