Magnetic levitation systems compared to conventional bearing systems
Introduction
Positioning systems in semiconductor equipment determine process compatibility on the one hand, influenced by positioning uncertainty and contamination, and cost of ownership (CoO) on the other, influenced, among others, by speed and acceleration, reliability and up-time, and module costs. For next generation semiconductor equipment, about 1 nm position uncertainty is required in combination with speed and acceleration in the order of 1–5 m/s and 10–20 m/s2, respectively. In particular for next generation lithography and inspection applications based on ‘photons’ (EUV lithography) and charged particles (E-beam lithography and inspection), vacuum compatibility in the order of 10−7 mbar and sub-mGauss magnetic stray field at substrate level are additional requirements to nm-level motion performance at high throughput.
Section snippets
Isolated machine architecture
Dynamic disturbances may be self-inflicted through motion set points or transmitted from the environment. To reduce transmissibility of floor vibrations in high-end systems, dynamic isolation and direct servo control between substrate and process are essential. Here, two levels of isolation are distinguished, viz. in-plane isolation and full 6-DoF isolation.
Active magnetic bearings compared to conventional bearing systems
In addition to the opportunity for implementing an isolated architecture, a free-floating architecture has interesting advantages and additional features for substrate positioning. Table 1 shows an overview of typical characteristics of passive bearings compared to active bearings using magnetic levitation (maglev) technology. Some characteristics are discussed below in more detail.
Maglev key challenges
Although the application of maglev technology for nm-applications is not trivial, the most important key issues have been solved at this point. Unlike Lorentz actuators, variable reluctance actuators are implicitly non-linear, so an appropriate linearization scheme is required for the latter based on flux and/or gap information, and also, actuator preload is needed. Secondly, the 6-DoF free-floating architecture requires simultaneous 6-DoF motion control. To be applicable in semiconductor
Conclusions
The application of active magnetic bearing systems enables full 6-DoF active positioning with nm-level motion performance in a single stage. Magnetic levitation technology provides interesting additional features for substrate positioning, such as nm-level position uncertainty, infinite quasi-static stiffness, and ultra low contamination, in a rather simple and cost effective stage design.
It is emphasized that the result could only be attained by proper system level design. Only in combination
References (1)
- A.C.P. de Klerk, G.Z. Angelis, J. van Eijk, Design of a next generation 6-DoF stage for scanning applications in vacuum...
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