The majority of failures in pattern replication processes are caused by wear of forming and forging master tools. Tribology is the science applied for lowering the wear by developing advanced (nanostructured) coatings. However, even these coatings are subject to wear that manifest itself as changes in the mechanical properties of the master tool in the form of fractures, roughness changes (adhesion) or deformation of the 3D shape. Hence a careful examination of the surface structure is essential for validating the functionality of a master tool. Ideally by applying a fast, reliable measurement, which determines the first wear before any faulty replication takes place. No such method exists at present for nanoscale structures: Scanning probe microscopy is generally slow and not suitable for the high aspect ratio structures often present in forming and forging tools. Scanning electron and helium ion microscopy offer alternatives. However both beams penetrate into the material which limits the accuracy, the beam energy can cause surface damage and there may be image distortions due to charging effects. Here we propose a new instrument based on NEUTRAL helium atoms.
The technique is strictly surface sensitive with no penetration into the bulk (the atoms interact with the outermost electronic layer on the surface). The energy of the atoms is less than 0.1 eV, 4-6 order of magnitudes less than typical electron and helium ion energies. The new technique can image down to 10 nm and has the potential of being fast and applicable over large areas. We will apply the new technique to access the tool lifetime improvement by the application of nanostructured coatings to micron and nanometer precision master tools from SME partners Kenneth Winther A/S and NILTechnology. Metrology partners DFM and KTH will evaluate the new instrument in relation to ISO-standard parameters with the aim of introducing the technique to the ISO TC213/WG16 committee for future standardization.