Dual low coherence scanning interferometry for rapid large step height and thickness measurements

Area of Science:

• Optical metrology
• Surface characterization
• Interferometry

Background:

• Traditional low coherence scanning interferometry faces limitations in scanning length for large topographic features.
• Accurate measurement of surface height steps and transparent material thickness is crucial in various scientific and industrial fields.

Purpose of the Study:

• To introduce a novel dual low coherence scanning interferometer for efficient measurement of large height steps and transparent optical plate thickness.
• To demonstrate the capability of reducing scanning length compared to conventional methods.

Main Methods:

• A tandem interferometric configuration utilizing dual low coherence light sources was employed.
• Spectrally-resolved interferometry was integrated to monitor gaps between correlograms.
• Dispersive plates were suggested for correlogram identification.

Main Results:

• The proposed dual low coherence scanning interferometer successfully measured 3D surface profiles of a large height step specimen.
• Accurate thickness profiles of a transparent optical plate (silicon wafer) were rapidly obtained.
• The method demonstrated a significant reduction in required scanning length.

Conclusions:

• The dual low coherence scanning interferometer is a viable and efficient technique for metrology applications involving large height steps and transparent plates.
• The integration of spectrally-resolved interferometry and dispersive plates enhances the robustness and identification capabilities of the system.
• This approach offers a promising advancement in high-speed, high-resolution surface and thickness metrology.