Line-to-line repetitive control of a 6-DoF hexapod stage for overlay measurements using Atomic Force Microscopy
conference paper
The overlay performance between different layers of semiconductor devices is a key parameter for correct functionality of such devices. With device features getting increasingly smaller, there is a need for novel and more accurate overlay metrology tools. This paper aims to increase the positioning accuracy of such a novel metrology machine below the nanometer by the application of repetitive control. At the heart of the machine is a large stroke 6-DoF hexapod motion stage, carrying a sub-nanometer accurate AFM head, whose positioning accuracy during scanning is a key performance driver. The sample under examination during scanning effectively forms an unknown repetitive disturbance on its feedback loop. For this reason a line-to-line repetitive controller in combination with decentralized feedback has been employed, in which the base harmonic is defined by one full line-scan. Experimental results on the machine with an emulated sample demonstrate a significant performance improvement, achieving nanometer accurate positioning while scanning. This shows that repetitive control in a line-to-line domain is a potential enabler for AFM-based overlay nanometrology.
TNO Identifier
877954
ISBN
978-1-5386-7926
Publisher
IEEE
Source title
American Control Conference, ACC 2019, Philadelphia, PA, USA, 10-12 July 2019
Collation
6 p.
Place of publication
Piscataway, NJ, USA
Pages
2464-2469
Files
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