Creation of Solid Immersion Lenses in Bulk Silicon Using Focused Ion Beam Backside Editing Techniques

This work describes how Solid Immersion Lenses (SILs) can be created in bulk silicon using a focused ion beam and a bitmap milling process. The optical properties are in good agreement with the expected results for the achieved lens geometries. An improvement in lateral spatial resolution by a factor of 1.8 and in image contrast by 170 % for backside analysis is demonstrated. The presented SILs are 32 mu m in diameter with a field of view of about 10 mu m. This process can be an alternative when a regular SIL placement on the chip is impossible or complex. The advantages of this method are the use of a single kind of material (no air gaps and no additional lens material with different n value), the ability to precisely position the SIL on the circuitry and the fact that a SIL may be created in less than twenty minutes of processing time.