High-resolution IC inspection technique

S. B. Ippolito*, A. K. Swan, B. B. Goldberg, M. S. Ünlü

*Corresponding author for this work

Research output: Contribution to journalConference articlepeer-review

2 Scopus citations


We demonstrate a through the substrate, numerical aperture increasing lens (NAIL) technique for high-resolution inspection of silicon devices. We experimentally demonstrate a resolution of 0.2 μm, with the ultimate diffraction limit of 0.14 μm. Absorption limits inspection in silicon to wavelengths greater than 1 μm, placing an ultimate limit of 0.5 μm resolution on standard subsurface microscopy techniques. Our numerical aperture increasing lens reduces this limit to 0.14 μm, a significant improvement for device visual inspection (patent pending). The NAIL technique yields a resolution improvement over standard optical microscopy of at least a factor of n, the refractive index of the substrate material, and up to a factor of n∧2. In silicon, this constitutes a resolution improvement between 3.6 and 13. This is accomplished by increasing the numerical aperture of the imaging system, without introducing any spherical aberration to the collected light. A specialized lens made of the same material as the substrate is placed on the back surface of the substrate. The convex surface of this lens is spherical with a radius of curvature, R. The vertical thickness of the lens, D, should be selected according to D = R (1 + 1/n)-X and the substrate thickness X.

Original languageEnglish (US)
Pages (from-to)126-137
Number of pages12
JournalProceedings of SPIE - The International Society for Optical Engineering
StatePublished - Jan 1 2001
EventMetrology-Based Control for Micro-Manufacturing - San Jose, CA, United States
Duration: Jan 25 2001Jan 25 2001


  • Diffraction limited through substrate imaging
  • Numerical aperture
  • Silicon
  • Visual inspection

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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