High speed, laser-based marking method and system for producing machine readable marks on workpieces and semiconductor devices with reduced subsurface damage produced thereby

Abstract

An improved method of laser marking semiconductor wafers is provided wherein undesirable subsurface damage to a silicon semiconductor wafer is avoided while providing a relative improvement in marking speed for a predetermined spot diameter. A laser pulse of a laser beam has a predetermined wavelength, pulse width, repetition rate, and energy. The method further includes irradiating a semiconductor wafer with the pulsed laser beam over a spot diameter to produce a machine readable mark on the semiconductor wafer. The mark has a mark depth. The pulse width is less than about 50 ns, and the step of irradiating irradiates over the spot diameter to produce a mark having a mark depth substantially less than about 10 microns.

1 - 14 . (canceled)  
     
     
         15 . A method of laser marking a semiconductor wafer, the method comprising: 
 generating a laser output for wafer marking, the output comprising at least one pulse having a pulse width less than about 50 nanoseconds, a wavelength, and at least one energy characteristic; and    irradiating the semiconductor wafer with the output over at least one spot having a diameter to produce a machine readable mark on the wafer, the mark having an average mark height, an average mark depth substantially less than about 10 microns, and wherein undesirable subsurface damage to the semiconductor wafer is avoided.    
     
     
         16 . The method of  claim 15  wherein the average mark depth is in the range of about 3-4.5 microns.  
     
     
         17 . The method of  claim 15  wherein the average mark depth does not exceed about 4 microns.  
     
     
         18 . The method of  claim 15  wherein the semiconductor wafer comprises a silicon wafer and wherein the step of generating is carried out using a frequency doubled Nd:YVO 4  laser having a green output wavelength.  
     
     
         19 . The method of  claim 15  wherein the undesirable subsurface damage includes microcracking.  
     
     
         20 . The method of  claim 15  wherein the at least one pulse irradiates the wafer at about 10 9  watts/cm 2  or greater over the at least one spot diameter.  
     
     
         21 . The method of  claim 20  wherein the pulse width is in the range of about 10-15 nanoseconds, a pulse energy is in the range of about 230-250 microjoules, and wherein the at least one spot diameter is in the range of about 25-40 microns.  
     
     
         22 . The method of  claim 15  wherein the output includes a plurality of pulses, at least one pulse energy incident on a surface of the wafer is in a range of about 230-250 microjoules, a pulse width is in a range of about 10-15 nanoseconds, and wherein temporal pulse spacing of at least some consecutive pulses of the output corresponds to a repetition rate in a range of about 15-30 KHz.  
     
     
         23 . The method of  claim 15  wherein a plurality of pulses irradiate the wafer over a corresponding plurality of spots, at least one spot having a spot diameter in a range of about 25-40 microns, the marking is carried out at a linear marking speed of at least 150 mm/sec, whereby the marks are substantially continuous and a dimension of the mark is substantially greater than the spot diameter.  
     
     
         24 . The method of  claim 23  wherein the spot diameter is in a range of about 30-35 microns, and the marking speed is at least 150 mm/sec.  
     
     
         25 . The method of  claim 15  wherein the diameter is in a range of about 25-40 microns.  
     
     
         26 . The method of  claim 15  wherein a plurality of pulses irradiate the wafer over a corresponding plurality of spots and wherein the steps of generating and irradiating are carried out during motion of the wafer relative to the output at a marking speed, and wherein substantial separation of the spots on the surface of the wafer is avoided with the steps of generating and irradiating.  
     
     
         27 . The method of  claim 15  wherein the output includes a plurality of pulses, and wherein temporal pulse spacing of at least some consecutive pulses corresponds to a repetition rate of at least 10 KHz.  
     
     
         28 . The method of  claim 15  wherein the output includes a plurality of pulses, and wherein temporal pulse spacing of at least some pulses of the output corresponds to a repetition rate of at least 15 KHz.