Valery Ray Particle Beam Systems & Technology, Methuen, USA High Aspect Ratio Via Milling Endpoint Phenomena in Focused Ion Beam Modification of Integrated Circuits PBS&T

2/29/2016 ISTFA Purpose  Investigate details of secondary electron endpointing during High Aspect Ratio (HAR) via milling.  Propose a model explaining the signal distribution observed in experiment.  Enhance understanding of endpointing process.

2/29/2016 ISTFA Outline  Methodology for observation the details of spatial distribution of HAR via endpoint signal.  Models explaining spatial distribution phenomenon.  Concept for future experimental investigation of endpointing mechanism.

2/29/2016 ISTFA Observation of the Endpoint of HAR Via  Can be done on any FIB capable of imaging concurrently with GAE milling: tools running “Microsurgery”.  GAE recipe with large number of pixels and small FOV will enhance the observation.  For best results beam placement relatively to the sample should be very stable.

2/29/2016 ISTFA Distribution of Endpoint Signal Within the Via Endpoint of 0.5 μm HAR via milled on “front side” sample, FOV 1μm. Preferential distribution of the signal is apparent. Center of the via is as dark as a dielectric on the background.

2/29/2016 ISTFA Negative Charge of the Via Sidewalls: Model Proposed by Wang et. al. on ISTFA 2003 Secondary electron emission from the negatively charged sidewalls of the via could explain observations. ILD Negative charge on sidewalls Metal Line

2/29/2016 ISTFA Metal Re-Deposition on the Sidewalls of Via Alternative model of HAR via endpoint ILD Metal Line Re-deposition of metal on sidewalls Metal, sputtered from the line at the bottom of the via, re-deposits on the sidewalls.

2/29/2016 ISTFA Ion Beam Interaction with Metal Re-Deposited on Sidewalls  Re-deposited conductor creates low-resistance path along the via sidewalls.  Secondary electrons are emitted when ion beam strikes the re-deposited material.  Emission is supported by supply of electrons from the contacted conductor line.

2/29/2016 ISTFA Concept of Future Verification Experiment: Gas Assisted Etching of SiO 2 and Metals TFA Cl 2 Halogens XeF 2 GAE of Si GAE of Cu GAE of Al GAE of SiO 2 Precursor Gas

2/29/2016 ISTFA Concept of Future Verification Experiment: HAR Endpoint with Re-Deposition Model YESYESYESTFA NOYESNO Cl 2 NOYESYES XeF 2 Endpoint on Si Endpoint on Cu Endpoint on Al GAE of SiO 2 Precursor Gas

2/29/2016 ISTFA Concept of Future Verification Experiment: HAR Endpoint with Re-Deposition Model With negative wall charge model, HAR via endpoint should always be observed, regardless of GAE precursor and material of the metal line. With sidewall re-deposition model, HAR via endpoint should not be observed while using halogens (Cl 2 ) to contact aluminum line and while using XeF 2 or halogens to contact poly-silicon line.

2/29/2016 ISTFA Summary  Discovered spatial distribution of secondary electron signal advances understanding of HAR endpoint detection process.  Proposed re-deposition model of endpoint mechanism explains the observation.  Concept of experimental verification of the endpointing mechanism is proposed.

2/29/2016 ISTFA Acknowledgements Author would like to thank Mr. Nicholas Antoniou, Dr. Neil Bassom, Mr. Alex Krechmer and Mr. Andrew Saxonis from FEI Company for contributions to the abstract of this presentation.