Development of a detachable high speed miniature scanning probe microscope for large area substrates inspection

On the resolution of subsurface atomic force microscopy and its implications for subsurface feature sizing

Ultrasound atomic force microscopy (AFM) has received considerable interest due to its subsurface imaging capabilities, particularly for nanostructure imaging. The local contact stiffness variation due to the presence of a subsurface feature is the origin of the imaging contrast. Several research studies have demonstrated subsurface imaging capabilities with promising resolution. However, there is limited literature available about the definition of spatial resolution in subsurface AFM. The changes in contact stiffness and their link to the subsurface resolution are not well understood. We propose a quantitative approach to assess the resolution in subsurface AFM imaging. We have investigated the influences of several parameters of interest on the lateral resolution. The quantification of the subsurface feature size can be based on threshold criteria (full width at half maximum and Rayleigh criteria). Simulations and experimental measurements were compared, revealing that the optimal choice of parameter settings for surface topography AFM is suboptimal for subsurface AFM imaging.

Fast and reliable pre-approach for scanning probe microscopes based on tip-sample capacitance

Within the last three decades Scanning Probe Microscopy has been developed to a powerful tool for measuring surfaces and their properties on an atomic scale such that users can be found nowadays not only in academia but also in industry. This development is still pushed further by researchers, who continuously exploit new possibilities of this technique, as well as companies that focus mainly on the usability. However, although imaging has become significantly easier, the time required for a safe approach (without unwanted tip-sample contact) can be very time consuming, especially if the microscope is not equipped or suited for the observation of the tip-sample distance with an additional optical microscope. Here we show that the measurement of the absolute tip-sample capacitance provides an ideal solution for a fast and reliable pre-approach. The absolute tip-sample capacitance shows a generic behavior as a function of the distance, even though we measured it on several completely different setups. Insight into this behavior is gained via an analytical and computational analysis, from which two additional advantages arise: the capacitance measurement can be applied for observing, analyzing, and fine-tuning of the approach motor, as well as for the determination of the (effective) tip radius. The latter provides important information about the sharpness of the measured tip and can be used not only to characterize new (freshly etched) tips but also for the determination of the degradation after a tip-sample contact/crash.

High-throughput atomic force microscopes operating in parallel

Atomic force microscopy (AFM) is an essential nanoinstrument technique for several applications such as cell biology and nanoelectronics metrology and inspection. The need for statistically significant sample sizes means that data collection can be an extremely lengthy process in AFM. The use of a single AFM instrument is known for its very low speed and not being suitable for scanning large areas, resulting in a very-low-throughput measurement. We address this challenge by parallelizing AFM instruments. The parallelization is achieved by miniaturizing the AFM instrument and operating many of them simultaneously. This instrument has the advantages that each miniaturized AFM can be operated independently and that the advances in the field of AFM, both in terms of speed and imaging modalities, can be implemented more easily. Moreover, a parallel AFM instrument also allows one to measure several physical parameters simultaneously; while one instrument measures nano-scale topography, another instrument can measure mechanical, electrical, or thermal properties, making it a lab-on-an-instrument. In this paper, a proof of principle of such a parallel AFM instrument has been demonstrated by analyzing the topography of large samples such as semiconductor wafers. This nanoinstrument provides new research opportunities in the nanometrology of wafers and nanolithography masks by enabling real die-to-die and wafer-level measurements and in cell biology by measuring the nano-scale properties of a large number of cells.