PhD in Control for Nanotube-based profiling

Increasingly complex 3D shapes are used as Semicon devices, requiring advanced metrology techniques to monitor production and understand performance of the devices. Atomic force microscopy allows to reach the required sub-nm accuracy by using relatively blunt probes, sensing always in the same direction, but only the top of the 3D shapes can be explored. This project aims to enable the use of nanotube-based probes to scan the profile on the samples with more challenging topographies. The nanotube probe shape strongly improves how well holes or trenches in the sample can be accessed. However, the slender probes become weaker in lateral direction, while sensitivity in this direction is also needed to thoroughly scan the samples.

This PhD Position aims to provide the control techniques required to keep the probe in proximity of the sample and to ensure that the metrology objectives are achieved. Control challenges on the nanotube-based profiling include 1) navigation of the probe towards the point of interest on the sample; 2) facilitating the 2D profile sensing and selecting the correct sensing direction for this part of the sample; and 3) profile reconstruction based on measurement signals. This PhD will contribute to these challenges as follows. 1) Based on realtime-measurement data, the control should plan a path along the sample profile and optimise the sensing direction such that enough profile measurements are generated along the sample contour, minimising blind spots. 2) Two-dimensional profile information is needed at high rates to allow the real-time path planning, making the required driving signals and signal analyses a nontrivial task. Dynamical sensing methods are foreseen to achieve acceptable accuracy. 3). Estimation technique exploiting the known stage dynamics, as well as the modelled probe dynamics, will be incorporated to provide highly accurate profile information. First experiments demonstrating (elements of) these control concepts are foreseen.

The PhD Candidate will be partially located at TNO Optomechatronics, Delft and partially at the TU/e Dynamics and Control group.