Dip-pen Nanolithography Process Control Using a Dual- Probe Afm

Dip-pen nanolithography (DPN) is a tip-based direct print technique widely used in nanofabrication applications. DPN is typically performed using Atomic force microscopes (AFM). In DPN, the nano-sized tip of the AFM is coated with a layer of ink molecules of interest, and traversed over a suitable substrate to print the desired pattern. Despite developments in recent years, DPN is still performed as an open loop process i.e. the print is neither controlled nor monitored. Since DPN is affected by many parameters including variations in ambient conditions, ink distribution on the tip, and thermal drift, obtaining a good quality print is often challenging. This paper proposes a real-time process control scheme to improve the dimensional accuracy of DPN print by controlling the print thickness and trajectory. Since closed loop control requires measurement (feedback) of the actual process, this control scheme is designed to be implemented on a dual-probe AFM (DP-AFM), which, as the name implies, has two probes; One probe is for DPN printing and the other for measuring the print. Simulation results demonstrate high quality DPN print can be obtained even in the presence of process uncertainties. Moreover, the effect of thermal drift on print thickness and print trajectory can be mitigated as much as 80 % through proper choice of process control gains.