Spectral Interferometry

Optical Critical Dimension metrology has proven itself as an enabler for semiconductor device fabrication. The current workhorses in this field are the well-established normal and oblique incidence spectral reflectometry and ellipsometry (SR/SE) techniques.

Advanced process development trends introduce significant challenges for process control systems. Vertical integrations, new materials, continued scaling and increased variability are among the key contributors for increased complexity with providing robust metrology solutions – A need for better control is raised.

To accommodate that need, Nova introduced a new Optical CD technology – Spectral Interferometry (SI).

Spectral Interferometry (SI)

Using SI technology, Nova OCD systems can extract a new property of the measured sample – the complete wavefront. This property, which can be extracted at multiple AOIs and polarizations, isn’t accessible using the existing SR/SE methods. A new set of HW and algorithms had to be developed to enable that technology.

The Nova PRISM platform implements Spectral Interferometry for OCD measurements in addition to current workhorse technologies. For SI implementation, the standard optical path is replaced by an interferometric optical path, which includes a reference mirror. Light from the reference mirror is combined with light from the sample and directed to the spectrometer. The spectrometer measures every wavelength’s intensity separately and by that grabs the interference pattern of the interferometer.

The Spectral Interferometer was designed and implemented for FAB high-volume manufacturing environment and enables structural and material measurements of complex 3D structures.

Highlights and Benefits 

  • All-new platform
  • A synergy of hardware and algorithms
  • Essential information inaccessible by current solutions
  • High-end metrology enabling sensitivity to weak parameters and unique decorrelation capabilities
  • Enhanced correlation to device yield on critical steps