Laser-based material processing methods and systems

Abstract

Various embodiments may be used for laser-based modification of target material of a workpiece while advantageously achieving improvements in processing throughput and/or quality. Embodiments of a method of processing may include focusing and directing laser pulses to a region of the workpiece at a pulse repetition rate sufficiently high so that material is efficiently removed from the region and a quantity of unwanted material within the region, proximate to the region, or both is reduced relative to a quantity obtainable at a lower repetition rate. Embodiments of an ultrashort pulse laser system may include a fiber amplifier or fiber laser. Various embodiments are suitable for at least one of dicing, cutting, scribing, and forming features on or within a semiconductor substrate. Workpiece materials may include metals, inorganic or organic dielectrics, or any material to be micromachined with femtosecond, picosecond, and/or nanosecond pulses.

What is claimed is: 
     
         1 . A method for forming a trench in a workpiece having a semiconductor material, said method comprising:
 repeatedly irradiating at least a portion of said semiconductor material with focused laser pulses at a scan rate in a range from about 0.2 m/s to about 20 m/s, said laser pulses comprising a pulse width in a range from about 500 fs to about 500 ps, and sufficiently high fluence to efficiently remove a substantial depthwise portion of material from a target location to form said trench and to limit accumulation of unwanted material about the target location.   
     
     
         2 . The method of  claim 1 , wherein a pulse repetition rate is in a range of at least about 500 kHz and up to about 5 MHz. 
     
     
         3 . The method of  claim 1 , wherein said trench is characterized by having a ratio of ablated area of a feature to an area of redeposited material adjacent to said feature greater than about 0.5. 
     
     
         4 . The method of  claim 1 , wherein a quantity of the unwanted material is sufficiently low such that ultrasonic cleaning is capable of removing said unwanted material without a requirement for a substrate coating or chemical etching. 
     
     
         5 . The method of  claim 1 , wherein said trench forms a scribe and scribe line for a subsequent step of mechanical separation. 
     
     
         6 . A workpiece comprising a semiconductor material having a trench formed using the method of  claim 1 . 
     
     
         7 . A system for forming a trench in a workpiece having a semiconductor material, said system comprising:
 a pulsed laser system configured to repeatedly irradiate at least a portion of said semiconductor material with focused laser pulses at a scan rate in a range from about 0.2 m/s to about 20 m/s, said laser pulses comprising a pulse width in a range from about 500 fs to about 500 ps, and sufficiently high fluence to efficiently remove a substantial depthwise portion of material from a target location to form said trench and to limit accumulation of unwanted material about the target location;   a beam delivery system configured to focus and deliver said focused laser pulses;   a positioning system configured to position said laser pulses relative to said semiconductor material at said scan rate, said positioning system comprising at least one of an optical scanner or a substrate positioner; and   a controller configured to be coupled to said pulsed laser system, said beam delivery system, and said positioning system, said controller configured to control a spatial overlap between adjacent focused laser pulses during irradiating of the workpiece at said repetition rate.   
     
     
         8 . The system of  claim 7 , wherein the semiconductor material comprises silicon. 
     
     
         9 . The system of  claim 7 , wherein the workpiece is held in compression or tension, and a die strength of the workpiece after forming the trench is greater than 400 MPa and up to 1000 MPa. 
     
     
         10 . The system of  claim 7 , wherein one or more of scan speed, pulse energy, repetition rate at which pulses impinge a surface of the workpiece, pulse width, or spot size are adjustable over at least at least 2:1 range. 
     
     
         11 . The system of  claim 7 , wherein a pulse repetition rate is in a range of at least about 500 kHz and up to about 5 MHz. 
     
     
         12 . The system of  claim 7 , wherein at least some of the focused laser pulses have an energy in a range from about 5 μJ to about 20 μJ, with a focused 1/e 2  spot size in a range of about 15 μm to about 40 μm, and provide a fluence greater than about 0.4 J/cm 2 . 
     
     
         13 . A method of processing a multi-material workpiece, said workpiece comprising a semiconductor material and a pattern, said pattern comprising at least one of a dielectric material or a metal material, said method comprising:
 irradiating said workpiece with a series of laser pulses, at least two pulses of the series having different characteristics that are applied to different materials of said multi-material workpiece; and   controlling heat-affected zone (HAZ) such that at least one HAZ generated during removal of at least a portion of said pattern is increased depthwise relative to at least one HAZ generated during removal of a portion of said semiconductor material.   
     
     
         14 . The method of  claim 13 , wherein at least some laser pulses have different pulse widths, and controlling HAZ comprises applying different pulse widths to said workpiece materials, said pulse widths in a range of about 100 fs to about 500 ps. 
     
     
         15 . A method of processing a workpiece comprising a pattern and a semiconductor wafer, said method comprising:
 modifying at least a portion of said pattern with a laser pulse comprising a pulse width in the range from about 100 ps to about 1 ns; and   modifying at least a portion of the semiconductor wafer with a laser pulse comprising a pulse width in a range from about 100 fs to about 10 ps.   
     
     
         16 . The method of  claim 15 , wherein a depthwise portion of heat-affected zone (HAZ) produced by said modifying at least a portion of said pattern is larger than a depthwise portion of a HAZ produced by said modifying at least a portion of the semiconductor wafer. 
     
     
         17 . A method of laser processing a multi-material workpiece having a semiconductor material, the method comprising:
 focusing and directing laser pulses to a region of the workpiece at a pulse repetition rate in a range from about 100 kHz to about 10 MHz and at a repetition rate sufficiently high so that material is efficiently removed from said region and a quantity of unwanted material within or proximate to said region is limited relative to a quantity obtainable at a lower repetition rate below about 100 kHz.   
     
     
         18 . The method of  claim 17 , wherein said semiconductor material comprises a semiconductor wafer, said quantity of unwanted material comprises redeposited material, and wherein said redeposited material is limited to a thickness less than about 4 μm. 
     
     
         19 . The method of  claim 17 , wherein focusing and directing laser pulses comprises repeatedly irradiating at least one target material of the workpiece with focused laser pulses at a scan rate in a range of about 0.2 m/s to about 20 m/s. 
     
     
         20 . The method of  claim 17 , wherein at least some of said laser pulses have a non-zero spatial overlap factor with at least one other laser pulse, a pulse width less than about 1 ns, a pulse energy in a range of about 100 nJ to about 25 μJ, a focused 1/e 2  spot size in a range of about 5 μm to about 50 μm, and a fluence in a range of about 0.25 J/cm 2  to about 30 J/cm 2  at said target material. 
     
     
         21 . A system for dicing, cutting, scribing, or forming features on or within a workpiece having a semiconductor material, said system comprising:
 a pulsed laser system configured to repeatedly irradiate at least a portion of said material with focused laser pulses at a scan rate and a pulse repetition rate, wherein said repetition rate is in a range of about 100 kHz to about 5 MHz and sufficiently high to efficiently remove a substantial depthwise portion of material from a target location and to limit accumulation of unwanted material about the target location;   a beam delivery system configured to focus and deliver said laser pulses;   a positioning system configured to position said laser pulses relative to said semiconductor substrate at said scan rate, said positioning system comprising at least one of an optical scanner or a substrate positioner; and   a controller configured to be coupled to said pulsed laser system, said beam delivery system, and said positioning system, said controller configured to control a spatial overlap between adjacent focused laser pulses during processing of the workpiece at said repetition rate.