By Melbourne Centre for Nanofabrication
Scanning Electron Microscopy (SEM) is the process whereby a tightly focused electron beam is scanned onto the surface to be imaged. As the primary electrons hit the atoms in the surface, a number of secondary electrons are emitted, and collected by the instrument’s detector, which assigns a level of grey accordingly, thereby creating a pixel for a digital image. The machines can routinely image features down to about 10nm, and in some special cases down to several nm in size. SEM is a key tool for process characterisation of surface topography. Virtually every sample fabricated in the cleanroom undergoes at least one set of SEM imaging, in order to assess the quality of the fabrication and its defects. This information is fed into the process optimisation loop until a satisfying sample is produced. The tool is also used to image samples from outside, for example fixated cells and failed components. MCN has four SEMs – two Field Emission Guns (FEG-SEM), the Dual Beam FIB-SEM and the tabletop Hitachi TM3030 SEM with Oxford EDX. MCN’s FEG-SEMs are FEI Apreo 2S & FEI NovaNanoSEM-430, which features 1kv to 30kV acceleration voltage, a 5 axis stage and 100 mm stage movements. It can host up to 6 inch wafers in the chamber. The FEI Apreo 2S provides all-round nanometer or sub-nanometer resolution performance on materials ranging from nanoparticles, powders, catalysts, and nanodevices to bulk magnetic samples, even at long (10 mm) working distances. It has flexibility for handling a wide range of sample types, including insulators, sensitive materials, or magnetic samples. Elemental information is available with ChemiSEM Technology; live quantitative elemental mapping for unprecedented time to result and ease of use Advanced automation including FLASH Technology for automatic image fine tuning, undo, user guidance, maps tiling, and stitching. The FEI Helios NanoLab 600 Dual Beam FIB-SEM features an ultra-high resolution SEM and focused ion beam. The innovative Elstar Schottky thermal field emission electron gun with hot-swap capability provides outstanding resolution imaging performance of up to 1nm at low kV. Fine surface morphological detail is enhanced at very low electron beam energies and the FIB-SEM can operate from 30kV down to 200V. It has a piezo-driven high precision 5-axis motorised stage that can be tilted between -10 o and +60 o. It is also equipped with the Genesis EDX detector to analyse the chemical composition of samples as well as a STEM detector which allows the imaging of very thin samples in transmission. The Hitachi TM3030 SEM with Oxford EDX is a compact tabletop SEM with automatic operation for high resolution characterisation with minimal sample preparation. Located in the class 10,000 cleanroom space, it can hold a 70mm sample and accommodates the 5-kV, 15-kV, and EDX modes. It can image down to 100nm structures.
