Plasma cleaning goes under the microscope

Modern microscopes working at the nanotech level need pristine surfaces. Tom Levesque, Technology Business Consulting, and Jezz Leckenby, Talking Science, discuss the use of plasma cleaning for such instruments.

With examination and fabrication nearing the atomic level, the cleanliness of specimen surfaces and the high vacuum electron microscope environments in which these surfaces are studied or processed have never been more critical than they are today. Routine manufacturing at the scale required for nanotechnology demands pristine and controlled surfaces to create the desired structures. Modern electron and ion microscopes are equipped with sophisticated vacuum systems and can provide these conditions, but maintaining cleanliness over time may be more difficult. One of the ways that scientists have been able to achieve these remarkably unadulterated surfaces has been to subject their samples and microscopes to cleaning by various plasma technologies.

Often contamination is derived from hydrocarbon molecules, which even in minute quantities can interact with the electron or ion beam, creating unwanted artefacts in images or data.

The problem of hydrocarbon contamination inside the electron microscope is well documented and has been an issue from the earliest days of electron microscopy. This artefact is the often result of the electron (or ion) beam striking unwanted contaminant molecules and promoting the growth of carbonaceous materials on the surface of the sample. Typically, in a beam-scanning instrument, this contamination layer is in the shape of the rastered pattern on the sample – a rectangle. Further, if the contaminated area is measured in an atomic force microscope (AFM), the build-up of this material has been shown to be quite pronounced.¹