High Resolution Imaging of Thick Si Device Using Doublet SIL

Solid immersion lens (SILs) have been instrumental in allowing Failure Analysis (FA) microscopes to analyze increasingly smaller semiconductor features. Silicon SILs, often used with a 1300nm light source, have achieved a 3.5X improvement in resolution. The key advantage of Silicon as a SIL material is that it matches the index of refraction of Silicon devices under test (DUTs). The primary limitation of Silicon is that it has poor transmittance at shorter wavelengths of 1064nm and below. GaAs is often used as a SIL material for 1064nm imaging due to higher transmittance but has several drawbacks due to the index of refraction mismatch between the GaAs SIL material and the Silicon DUT. A new Si SIL design with high 1064nm transmittance is proposed to overcome these drawbacks, enabling higher resolution and full thickness (765um) imaging at 1064nm.