Wear of ultrananocrystalline diamond AFM tips during mechanical nanomanufacturing by nanomilling

Abstract

The wear of the AFM tips has significant implications on the accuracy and throughput of the tip-based nanomanufacturing processes. Ultrananocrystalline diamond (UNCD) atomic force microscopy (AFM) tips that exhibit significantly lower wear rates compared to silicon and silicon nitride tips during the AFM application carry a strong potential to be effectively used during tip-based nanomanufacturing. In this paper, we present an experimental analysis of the wear of UNCD AFM tips during rotating tip-based mechanical nanomanufacturing (nanomilling). The diamond AFM tips are used as the nanotools to mechanically remove material from silicon and copper surfaces. The geometry of the tips is directly measured through non-contact AFM at various time points of the process. The acquired AFM images are then processed to quantify the progression of the tip wear in terms of wear volume, wear area, and change in tip radius and in tip height. The results of the analysis showed that the tips undergo two-phase wear process that consists of an early rapid break-in phase followed by a gradual steady-state phase. The wear rates experienced during nanomilling of silicon are shown to be more than an order of magnitude higher than those of copper. The analysis of the repeatability of the tip wear indicates that, for nominally identical process conditions and tip geometries, the tips could exhibit considerable variation in wear rates, particularly during the break-in phase. Without making any attempt on optimizing the process conditions, a cutting length of more than 240mm is nanomilled at a constant depth of 150nm on copper surfaces, within the life of a single nanotool.