Non-isoplanatic lens aberration correction in dark-field digital holographic microscopy for semiconductor metrology

Abstract

In the semiconductor industry, the demand for more precise and accurate overlay metrology tools has increased because of the continued shrinking of feature sizes in integrated circuits. To achieve the required sub-nanometre precision, the current technology for overlay metrology has become complex and is reaching its limits. Herein, we present a dark-field digital holographic microscope using a simple two-element imaging lens with a high numerical aperture capable of imaging from the visible to near-infrared regions. This combination of high resolution and wavelength coverage was achieved by combining a simple imaging lens with a fast and accurate correction of non-isoplanatic aberrations. We present experimental results for overlay targets that demonstrate the capability of our computational aberration correction in the visible and near-infrared wavelength regimes. This wide-ranged-wavelength imaging system can advance semiconductor metrology.

Keywords

• lens aberrations
• non-isoplanatism
• digital holographic microscopy
• metrology
• computational imaging