Development of sample polishing procedures for application in scanning probe microscopy

Scanning Probe Microscopy (SPM) is today a very important and crucial technique for the characterization of nanoscale materials and devices. This cluster of techniques is based on the interactions between a very sharp tip scanning over the surface of interest. We focus mainly on electrical (e-SPM) techniques, which often require very smooth surfaces to create a good electrical contact between the SPM tip and the sample. Combinations of chemical and mechanical polishing can be used to acquire these ultra-smooth surfaces, both for top down and cross-sectional measurements. In mechanical polishing, material is removed by multiple consecutive steps of grinding with polishing papers which have decreasing grain sizes. The surface gets smoother and smoother by doing this. Chemical polishing is used as a final step to reach ultrasmooth surfaces.  It is often however very difficult to completely eliminate common artifacts, such as polishing lines, especially when polishing cross sections that contain different materials with varying hardnesses. These artefacts can have a detrimental effect on the quality of the e-SPM measurements.

The goal of this internship is to evaluate the current way of working for polishing cross sectional samples. A new polishing tool has been acquired recently which requires the adaptation and optimization of the existing polishing procedures. The student will start with blueprints of what is currently in use to test and learn the process. He/She will then make improvements towards better reproducibility and/or more artifact-free end results on the new tool and write a procedure summarizing the best way of working.

By performing (e-)SPM measurements on the samples, the quality of the samples can also be evaluated for the specific intended purpose.

For this topic, the student will work inside a dedicated lab environment to carry out the required experimental steps. He/She will work with a state-of-the-art polishing tool, which supports both mechanical and chemical polishing. The characterization of the samples will happen both with optical microscopes and SPM. By doing this, the student will also learn to perform the basics of SPM techniques. Since different materials often require a varying range of polishing specifications, the student will also come into contact with a variety of materials and structures used in the nanoelectronics industry. The student will be part of imec’s materials and components analysis group (MCA).