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 semiconductor device including a semiconductor substrate, circuitry formed on a first side of the substrate, and a machine readable mark formed on a second side of the substrate with a laser output, the mark having an average mark depth no greater than about 3.5 microns.  
     
     
         16 . A semiconductor device including a substrate and a machine readable mark formed on the substrate with a laser output, the mark having an average mark depth no greater than about 4 microns, wherein the mark is produced during at least one step of a process for manufacturing the device by 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 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 wafer is avoided.  
     
     
         17 . A laser marking system, including a laser for marking a semiconductor wafer, the system comprising: 
 a laser means for 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    means, including an optical system, for 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.    
     
     
         18 . The system of  claim 17  wherein the means for irradiating includes a beam positioning subsystem that includes a beam deflector, the beam deflector being operable to deflect the at least one pulse over a marking field and to position a beam corresponding to the at least one pulse of the output relative to the wafer so as to mark the wafer during motion of the wafer relative to the output at a marking speed over the marking field.  
     
     
         19 . The system of  claim 18  wherein the positioning subsystem includes at least one translator for translating the wafer and wherein the deflector is a galvanometer-based X-Y mirror system for deflecting the at least one pulse.  
     
     
         20 . The system of  claim 17  wherein the average mark depth is in the range of about 3-4.5 microns  
     
     
         21 . The system of  claim 17  wherein the average mark depth does not exceed 4 microns.  
     
     
         22 . The system of  claim 17  wherein the semiconductor wafer comprises a silicon wafer, and wherein the laser means includes a frequency doubled Nd:YVO 4  laser having a green output wavelength.  
     
     
         23 . The system of  claim 17  wherein the undesirable subsurface damage includes microcracking.  
     
     
         24 . The system of  claim 17  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.  
     
     
         25 . The system of  claim 24  wherein the pulse width is about 10-15 ns, a pulse energy is in the range of about 230-250 microjoules, and wherein the at least one spot diameter is about 25-40 microns.  
     
     
         26 . The system of  claim 17  wherein the output includes a plurality of pulses, and wherein 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.  
     
     
         27 . The system of  claim 17  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, 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.  
     
     
         28 . The system of  claim 27  wherein the spot diameter is in a range of about 30-35 microns, and the marking speed is at least 150 mm/sec.  
     
     
         29 . The system of  claim 17  wherein the diameter is in a range of about 25-40 microns  
     
     
         30 . The system of  claim 17  wherein a plurality of pulses irradiate the wafer over a corresponding plurality of spots and wherein at least one of the laser means and the means for irradiating includes means for avoiding substantial separation of the spots on a surface of the wafer.  
     
     
         31 . The system of  claim 17  wherein the 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.  
     
     
         32 . The system of  claim 17  wherein the wherein the output includes a plurality of pulses, and wherein the temporal pulse spacing of at least some consecutive pulses corresponds to a repetition rate of at least 15 KHz.  
     
     
         33 . A laser marking system for marking a semiconductor wafer, the system comprising: 
 a diode pumped solid state laser means for 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    means, including an optical system, for irradiating the semiconductor wafer with the output over at least one spot having a diameter to produce a relatively shallow mark having sufficient contrast for machine readability, the mark having an average mark height, an average mark depth no greater than about 4 microns, and wherein undesirable subsurface damage to the semiconductor wafer is avoided.    
     
     
         34 . The system of  claim 33  wherein the semiconductor wafer comprises a silicon wafer, and wherein the laser includes a frequency doubled Nd:YVO 4  laser having a green output wavelength.  
     
     
         35 . The system of  claim 33  wherein the at least one pulse irradiates the wafer at about 10 9  watts/cm 2  or greater over the diameter of the at least one spot.  
     
     
         36 . The system of  claim 33  wherein the pulse width is about 10-15 ns, a pulse energy is in the range of about 230-250 microjoules, and wherein the diameter of the at least one spot is the range of about 25-40 microns.  
     
     
         37 . The system of  claim 33  wherein the output includes a plurality of pulses, and wherein a temporal pulse spacing of at least some consecutive pulses corresponds to a repetition rate of at least 10 KHz.  
     
     
         38 . The system of  claim 33  wherein the laser means includes a fiber optic amplifier in a MOPA configuration.  
     
     
         39 . A system of laser marking a semiconductor wafer during at least one step of a semiconductor manufacturing process, the wafer having a first side with circuit features, and a second side having a rough wafer surface portion to be marked, the system comprising: 
 a q-switched diode pumped, solid state laser for generating a laser output for wafer marking, the output comprising an output wavelength less than an absorption edge of the semiconductor wafer material, laser output power of at least about 3 W at the wavelength, a plurality of pulses, each pulse having a pulse width less than about 50 ns, at least one pulse having a pulse width in the range of about 10-15 ns, the temporal spacing between at least some consecutive pulses of the plurality of pulses corresponding to a repetition rate of at least 15 Khz; and    means for irradiating the semiconductor wafer with the output over at least one spot having a diameter in the range of less than about 60 microns to produce a shallow mark having sufficient contrast for machine readability, whereby the at least one pulse irradiates at least about 10 8  W/cm 2  over the diameter while avoiding undesirable subsurface damage to the semiconductor wafer.    
     
     
         40 . The system of  claim 39  wherein the diameter is in the range of about 25-40 microns.  
     
     
         41 . The system of  claim 39  wherein the energy of the at least one pulse is in the range of about 230-250 microjoules, whereby the at least one pulse irradiates at least 10 9  W/cm 2  over the at least one spot diameter.  
     
     
         42 . The system of  claim 39  wherein the available output power is at least about 5 W at the wavelength.  
     
     
         43 . The system of  claim 39  wherein the output wavelength is a green wavelength.  
     
     
         44 . The system of  claim 39  wherein the semiconductor wafer comprises a silicon wafer and wherein the laser is a frequency doubled Nd:YVO4 laser having a green output wavelength.  
     
     
         45 . A semiconductor device including a substrate and a shallow, machine-readable mark formed on the substrate with a laser output, wherein the mark is produced during at least one step of a process for manufacturing the device by generating a q-switched laser output for wafer marking, the output comprising an output wavelength less than an absorption edge of the wafer material, a laser output power of at least about 3 W at the wavelength, a plurality of pulses, each pulse having a pulse width less than about 50 ns, at least one pulse having a pulse width in the range of about 10-15 ns, the temporal spacing between at least some consecutive pulses of the plurality of pulses corresponding to a repetition rate of at least 15 Khz: and irradiating the wafer with the output at least one spot having a diameter in the range of less than about 60 microns to produce a shallow mark having sufficient contrast for machine readability, whereby the at least one pulse irradiates at least about 10 8  W/cm 2  over the diameter while avoiding undesirable subsurface damage to the wafer.