Advanced observer design and over-sensing for point of interest control of ASML stages

The main goal is the development of systematic methods 1) for modeling of plant dynamics in the augmented plant setting, 2) for choosing the right number and location of sensors, and 3) for designing an effective sensor transformation (possibly a dynamic observer), aimed at an improved estimation of the point of interest in ASML stages (i.e., the die subject to exposure) and hence improved overall positioning accuracy.

PhD Candidate: Masoud Dorosti
Promoter: prof.dr. Henk Nijmeijer (TU/e)
Supervisors: Marcel Heertjes (TU/e), Rob Fey (TU/e) , Marc van de Wal (ASML RE Mechatronics)
Project Funding: This work is supported from the Pieken in de Delta 2008 program funded by SenterNovem, an agency of the Dutch Ministry of Economic Affairs and ASML Company.
Project Period: April 2013 - March 2017


ASML’s lithographic wafer scanners are subject to ever tighter demands on positioning accuracy up to 0.1 nm and throughput of 200-300 wafers per hour. The latter requiring high motion speed up to 1 m/s and acceleration up to 100 m/s2 of the wafer and reticle stages. These stages are controlled in six Degrees Of Freedom (DOF’s) x/y/Rz/z/Rx/Ry.

Problem statement

For a wafer stage, the Point Of Interest (POI) is the position of the die on the wafer which is subject to exposure. The POI is time-varying, since the wafer is subject to exposure via a meander-like pattern of the stage’s x/y setpoint. Based on geometric formulas and the assumption that the stage mainly behaves as a Rigid Body (RB), the sensor signals are transformed into estimated values of the 6-DOF position in the POI.

Research challenges

  1. Combined theoretical and experimental modeling of plant dynamics in the augmented plant setting
  2. Choosing the right number and location of sensors
  3. Designing an effective sensor transformation, possibly a dynamic observer, to improve estimation of the POI in ASML stages.