AUTHOR=Agour Mostafa , Thiemicke Fabian , Müller André F. , Bergmann Ralf B. , Falldorf Claas 

TITLE=Lensless multi-spectral holographic interferometry for optical inspection

JOURNAL=Frontiers in Photonics

VOLUME=5

YEAR=2024

URL=https://www.frontiersin.org/journals/photonics/articles/10.3389/fphot.2024.1416347

DOI=10.3389/fphot.2024.1416347

ISSN=2673-6853

ABSTRACT=<p>We explore the principles, implementation details, and performance characteristics of a lensless multi-spectral digital holographic sensor and demonstrate its potential for quality assurance in semiconductor manufacturing. The method is based on capturing multi-spectral digital holograms, which are subsequently utilized to evaluate the shape of a reflective test object. It allows for a compact setup satisfying high demands regarding robustness against mechanical vibrations and thus overcomes limitations associated with conventional optical inspection setups associated with lens-based white light interferometry. Additionally, the tunable laser source enhances the versatility of the system and enables adaptation to various sample characteristics. Experimental results based on a wafer test specimen demonstrate the effectiveness of the method. The axial resolution of the sensor is <inline-formula id="inf1"><mml:math id="m1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>±</mml:mo><mml:mn>2.5</mml:mn></mml:math></inline-formula> nm, corresponding to <inline-formula id="inf2"><mml:math id="m2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mn>1</mml:mn><mml:mi>σ</mml:mi></mml:math></inline-formula>.</p>