Higher Resolution Microscopy System Based on Aplanatic Solid Immersion Lens

The solid immersion lens (SIL), invented by Mansfield and Kino in 1990 [1], attracts potential application in the field of imaging solid state devices, where the structures are buried deep into the substrate such as in integrated circuits. This is due to the ability of SIL to provide sub-surface imaging with better resolution than a conventional microscopy system. Many papers have dealt with the behavior of the fields in the focal region of the SIL microscopy system theoretically [2]. However, there has been little study on the imaging of the scattered light, i.e., the vectorial point spread function of the SIL system. Recently, the dyadic Green’s function for the aplanatic SIL was analytically derived using the far-field approximation (the radius of the SIL is much larger than the wavelength, and the source point is close to the aplanatic point, both being practical assumptions) [3]. The formulation dispenses with the need for solving complex boundary condition problems at the interface and provides closed form expressions for the dyadic Green’s function under a practical scenario. Based on the analysis of the dyadic Green’s function, we consider both the lateral and the longitudinal resolutions of SIL microscopy system of various numerical apertures. We study various interesting and important aspects of resolution provided by the SIL microscopy system by calculating the image in the CCD plane including giving a quantitative analysis of these aspects. An example of the infrequently studied longitudinal resolution is presented in Figure 1, where we see that the sources in the object region can be resolved when the distance between them is 0.19 (Figure 1 (b)), but cannot be resolved if the distance between them is further increased to 0.33  (Figure 1(c)), and then again be resolved when the distance between them is further increased (Figure 1 (d)).