Nanoscale Scanning Probe Metrology for a Non-Flat World: How to measure sub-nanometer roughness on complex geometries and large samples

D. Griffin, E. Nelson, C. Newcomb
United States

Keywords: AFM, Metrology, manufacturing


As the manufacturing tolerances of parts and components trend decreasingly smaller towards the nanoscale, the need for precise, high-resolution topographical characterization of the component itself rather than a sacrificial or witness part has become a requirement. This is regardless of whether said component is a convenient size and shape (like a wafer) or big, heavy and complex (like a turbine blade). Other characterization methods like optical or stylus profilometry have been employed in the past and are significantly easier to use for non-destructive measurements on big samples or on complex shapes. As the tolerances shrink below the diffraction limit it becomes necessary to find alternative measurement technology and this leads towards a need for a scanning probe microscopy solution. Scanning Probe Microscopy (like AFM) has long been an established technique for quantifying and characterizing surface roughness of materials at the sub-nanometer vertical and nanometer lateral scale. Traditionally this has been limited to flat and/or small sample geometries, e.g. wafers or coupons. Over 30 years of design refinement and know-how exist for how to optimize AFM for automated and semi-automated analysis of silicon wafers, read-write heads in data storage, polymer samples. These are AFM solutions for the ‘flat-world’. What is needed now are AFMs that can also operate in the ‘non-flat’ world. In other words, AFMs that can measure samples like complex mirrors and optical lenses, machined parts, avionic components, artificial joints without the need to segment, cut or otherwise adulterate the sample for characterization. Samples can be big and heavy, like a convex mirror that is meters in diameter and hundreds of kilograms in mass or a sealing surface of a flange positioned on the side of larger structure. In this presentation, we will discuss what is required to build, test and deliver a characterization platform that can handle 3, 4, 5, 6 or more axis of motion control to position the region of interest and the AFM scanner allowing interrogation the component at the correct location. We will also discuss the various AFM scanner designs that can be married with the custom stage motion control to enable high-performance, low-noise roughness measurements demonstrating that AFM is a non-destructive analysis technique that extends to the Non-Flat world.