Optimization of sample preparation procedures for quantitative Scanning Spreading Resistance Microscopy measurements

The continued scaling of semiconductor devices requires advanced characterization techniques capable of probing local electrical properties with nanoscale spatial resolution. Scanning spreading resistance microscopy (SSRM) is a unique technique by offering the ability to perform carrier density mapping of complex structures and devices with a nanometer spatial resolution. What makes it even more powerful is its ability to provide quantitative results by the use of calibration samples in conjunction with device measurements. For this, the measured resistance values of the calibration stacks are compared to measured resistance values in devices. The values measured in the devices can then be converted to carrier concentration values. Although this is a well established workflow, numerous artefacts are  known to arise when preparing cross sections for SSRM, some of which are known to alter the electrical properties. Therefore, quantification can only be accurate when the measured surfaces are defect-free or prepared in the exact same way as the calibration samples.

This project aims to explore and establish the effects of the existing sample preparation procedures used for SSRM on the obtained surfaces. These include, but are not limited to, cleaving, polishing and focused ion beam treatments. A particular focus will be placed on the impact of different polishing conditions on the electrical characteristics measured by SSRM on the prepared surfaces.

The internship student will investigate how parameters such as polishing agents and type of polishing cloths, but also temperature and ambient conditions, influence the SSRM response. Where appropriate, other complementary chemical and mechanical analysis techniques could be used to get a better understanding of the results. Measurements on well-defined reference samples will be used to establish the relationship between the different sample preparation parameters and the measured electrical resistances of the surfaces.

For this research, the student will be trained in scanning probe microscopy, with a particular emphasis on quantitative SSRM and its associated sample preparation techniques, such as cleaving and polishing. The research will also include parameter optimization and data analysis of the resulting measurements.

With the guidance of the supervisors, practical experimentation will be a major part of the thesis/internship. Complementary characterization and analysis can be performed through existing collaborations and available facilities. The project therefore provides an opportunity to combine sample preparation methods and experimental scanning probe microscopy with electrical characterization and quantitative data analysis.