Super-contrast-enhanced darkfield imaging of nano objects through null ellipsometry

Area of Science:

• Materials Science
• Optical Imaging
• Nanotechnology

Background:

• Conventional darkfield imaging struggles to detect sub-20 nm non-metal nanostructures.
• Existing methods for nanoscale defect detection often require high magnification or specialized equipment.

Purpose of the Study:

• To develop a cost-effective and high-contrast imaging technique for nanoscale defect detection.
• To demonstrate the efficacy of null ellipsometry in enhancing darkfield imaging for silicon nanostructures.

Main Methods:

• Integration of polarizers, compensators, and a photodiode sensor into a standard darkfield imaging setup.
• Application of the null ellipsometry principle for image contrast enhancement.
• Utilizing low-magnification (×20) optics for imaging.

Main Results:

• Successfully distinguished 20 nm Si nano-cylinder structures (20 nm diameter, 20 nm height).
• Detected 14.6 nm gap defects and 21.9 nm bridge defects on 40 nm line/space patterns.
• Achieved visualization of nanoscale features invisible with conventional darkfield imaging.

Conclusions:

• The rediscovered null ellipsometry principle offers an outstanding contrast enhancement for darkfield imaging.
• This technique enables the detection of sub-20 nm silicon nanostructures and defects at low magnification.
• This method represents a significant advancement for identifying small non-metal nanoscale objects.