Aplanatic solid immersion lens (SIL) microscopy is required to achieve the highest possible resolution for next generation silicon IC backside inspection and failure analysis. However, aplanatic SILs are susceptible to spherical aberration introduced by substrate thickness mismatch. We have developed a wavefront precompensation technique using a MEMS deformable mirror and demonstrate an increase in substrate thickness tolerance in aplanatic SIL imaging. Spot intensity increases by at least a factor of two to three are demonstrated for thicknesses deviating several percent from ideal.
Comparison before and after applying + 190 nm RMS first order spherical aberration correction. (a): SEM image showing the region of interest. (b): aSIL microscope image obtained before spherical aberration correction. (c): aSIL microscope image obtained afterspherical aberration correction. (d): Line cut comparison on group 318 nm. (e): Line cut comparison on group 282 nm. (f): Line cut comparison on group 252 nm.
