Improvement of laser dicing performance II: dicing rate enhancement by multi beams and simultaneous aberration correction with phase-only spatial light modulator
2013
“Stealth Dicing” laser processing is a dry and debris-free semiconductor wafer dicing method achieved by generating
thermal micro-cracks inside a wafer with a tightly focused laser beam. This method has two practical issues: (1) the
dicing speed is limited by the repetition rate of the pulsed laser, and (2) integrated circuits on the opposite side of the
wafer from the laser light are potentially damaged by excessive laser intensity required to compensate for insufficient
beam convergence. The insufficient beam convergence is a result of spherical aberration due to a refractive index
mismatch between air and the wafer. These problems can be resolved by incorporating a phase-only spatial light
modulator (SLM) into the laser dicing system. The SLM produces two types of wavefront configurations simultaneously
for two different functions. One is for multi-beam generation with a phase grating pattern. This improves the dicing
speed by a factor equal to the number of diffracted beams. The other is for aberration correction of the multiple beams
using a pre-distorted wavefront pattern. By correcting aberrations, the focused multiple beams inside the wafer will
become sufficiently convergent to avoid undesirable laser damage. We demonstrated these improvements by dicing
sapphire wafers with a pulsed laser and a high-numerical-aperture objective lens.
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