P. Scholz, U. Kerst, C. Boit, Berlin University of Technology, Berlin, Germany; T. Kujawa, T. R. Lundquist, DCG Systems, Inc, Freemont, CA

Summary: Previous works have shown that solid immersion lenses created in silicon by a focused ion beam process can significantly improve the resolution of optical backside analysis tools. The theoretical maximum of possible improvement according to SIL theory was not yet reached, mostly due to an unassisted ion beam sputtering process, which had been used. This problem is addressed by developing a chemistry-assisted FIB process,offering the ability to create larger and a greater variety of SIL shapes. An 80 µm wide SIL shape is presented that offers a lens area more than six times larger than the SIL we created so far, while still needing only 20 minutes of processing time. Larger SILs offer a larger opening angle leading to better resolution and collection efficiency. They are therefore a key aspect of the development of this technique.