Large area fast-AFM scanning with active “Quattro” cantilever arrays

Abstract

In this work, the fabrication and operation of an active parallel cantilever device integrating four self-sensing and self-actuating probes in an array is presented. The so called “Quattro” cantilever system is controlled by a multichannel field programmable gate array (FPGA) controller. The integrated cantilever devices are fabricated on the basis of a silicon-on-insulator wafer using surface micromachining and gas chopping plasma-etching processes [I. W. Rangelow, J. Vac. Sci. Technol., A 21, 1550 (2003)]. The unique design of the active cantilever probes provides both patterning and readout capabilities [Kaestner et al., J. Micro-Nanolithogr. MEMS 14, 031202 (2015)]. The thermomechanical actuation allows the individually operation of each cantilever in static and dynamic modes. This enables a simultaneous atomic force microscopy operation of all cantilevers in an array, while the piezoresistive read-out of the cantilever bending routinely ensures atomic resolution at a high imaging speed. The scanning probe lithography capabilities of the active cantilevers are based on the utilization of a Fowler–Nordheim field emission process of low-energy electrons (20–50 eV) for direct writing maskless lithography. The cantilever in the Quattro active cantilever array have a pitch of 125 μm (tip-to-tip distance), which allows an image size of 0.5 × 0.2 mm to be acquired within a single scan with 0.2 nm resolution in the vertical direction. Using parallel imaging, an effective scanning speed of 5.6 mm/s is achieved. The multichannel, scalable controller architecture allows four FPGA channels to scan and collect data simultaneously. A data buffer of 128 Mbits for a single frame of 4096 × 1024 pixels is applied. The designed data transfer system allows a packet size of 128 pixels to be transmitted within less than 10 μs, respectively. Thus, the entire image frame is transferred in less than 280 ms, which exceeds the required throughput in the practical cases like critical dimension-metrology and inspection. In this article, the authors are presenting the concept of the system, which combines imaging, metrology, and lithography capabilities with a low-cost of ownership. In this context, the authors are investigating the throughput capability, reproducibility, resolution, and positioning accuracy of the Quattro active cantilever system.