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Dopant mapping in thin FIB prepared silicon samples by Off-Axis Electron Holography
Adi Pantzer1, Atsmon Vakahy2, Zohar Eliyahou3
1Department of Materials Engineering, Ben-Gurion University of the Negev, Israel; Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, Israel; Micron Semiconductors Israel Ltd., Qiryat-Gat 82109, Israel.
Off-Axis Electron Holography (OAEH) enables quantitative electrostatic potential mapping in semiconductor devices. New focused ion beam (FIB) preparation techniques yield thinner samples, improving OAEH accuracy for microelectronics analysis.
Area of Science:
- Materials Science
- Solid State Physics
- Nanotechnology
Background:
- Accurate dopant distribution is crucial for modern semiconductor device functionality.
- Transmission Electron Microscope (TEM) based Off-Axis Electron Holography (OAEH) offers high-resolution quantitative electrostatic potential mapping.
- Microelectronics advancements necessitate TEM sample preparation of ultra-thin (<70 nm) specimens for failure analysis and 3D device characterization.
Purpose of the Study:
- To develop and validate advanced focused ion beam (FIB) preparation methods for ultra-thin TEM samples of silicon PN junctions.
- To investigate the impact of FIB-induced damage and surface effects on OAEH measurement accuracy.
- To establish the quantitative limits of OAEH for potential mapping in thinned semiconductor samples.
Main Methods:
- Utilized focused ion beam (FIB) milling with low-energy (5 keV) ions for sample preparation, minimizing amorphization.
- Employed perpendicular FIB sectioning for precise in-situ TEM sample thickness measurement.
- Correlated OAEH measurements with secondary ion mass spectrometry (SIMS) and 1D/3D electrostatic potential simulations.
Main Results:
- Achieved silicon amorphization depths of approximately 10 nm and electrically inactive regions of about 4 nm using low-energy milling.
- Demonstrated quantitative OAEH potential mapping (~0.1 V accuracy) for TEM samples down to 100 nm thick.
- Showed qualitative OAEH potential mapping (~0.3 V accuracy) for thinner TEM samples (down to 20 nm).
Conclusions:
- Low-energy FIB milling is effective for preparing ultra-thin TEM samples of silicon PN junctions with minimal damage.
- OAEH provides quantitative electrostatic potential mapping for semiconductor analysis, with accuracy dependent on sample thickness.
- The developed methodology enables improved failure analysis and characterization of advanced microelectronic devices.
