High speed, laser-based marking method and system for producing machine readable marks on workpieces and semiconductor devices with reduced subsurface damage produced thereby
View Patent ↗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. A method 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 method comprising:
generating a q-switched laser output for wafer marking, the output comprising an output wavelength less than an absorption edge of the semiconductor wafer material, a laser output power of at least about 3W 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 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.
2. The method of claim 1 wherein the diameter is in the range of about 25–40 microns.
3. The method of claim 1 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.
4. The method of claim 1 wherein the laser output power is at least about 5 W at the wavelength.
5. The method of claim 1 wherein the output wavelength is a green wavelength.
6. The method of claim 1 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.
7. The method of claim 1 wherein the at least one spot diameter is adjustable.