Adaptive Optics Compensation of Aberrations Introduced by Sample Thickness Error in aSIL Confocal Scanning Microscopy

We report on aberration compensation in an aplanatic solid immersion lens microscope used for high-resolution backside inspection of silicon integrated circuits. The imaging quality of aplanatic SIL microscope is shown to be significantly degraded by aberrations, especially when the silicon integrated circuit samples have thicknesses that are more than a few micrometers thicker or thinner than ideal. We describe and demonstrate a technique to recover near-ideal imaging quality by compensating those aberrations using a MEMS deformable mirror. The mirror, located in an optical plane conjugate to the microscope objective, is shaped in a way that counteracts spherical aberration errors associated with non-ideal sample thickness.