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Ultra-planar Electrostatic Chucks Based on Low CTE Materials for Lithography and Metrology |
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Novel Equipment and Processes |
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Ultra-planar electrostatic chucks based on CTE materials for lithography and metrology
Stefan Risse, Gerhard Kalkowski, Thomas Peschel, Gerd Harnisch, Sandra Müller and Ramona Eberhardt
Fraunhofer Institute for Applied Optics and Precision Engineering
Dept. of Precision Engineering
Albert-Einstein-Str. 7
07745 Jena, Germany
Abstract:
In the race for faster computing speed and shorter paths in micro-electronic circuits, the lithographic structuring process sets the limits. For future manufacturing at the 32nm node and beyond, Extreme Ultraviolet Lithography (EUVL), Electron-Beam Direct-Write (e-beam) and Mask less Lithography are promising candidates. For all these applications, the stable positioning of silicon wafers and masks in the high vacuum environment are required and attainable flatness strongly influences the result. Precision mechanics based on CTE materials like glass or glass ceramics are required to clamp and to level the substrate at the vacuum chamber.
This paper will present on the one hand the design and simulation results and on the other hand manufacturing and testing results of a central component of ultra precision assemblies for lithography and metrology tools: the electrostatic chuck. It is vacuum compatible lightweight and athermal. Using an electrostatic chuck, flattening of a bended wafer or mask is possible if chucking forces are sufficiently high and the chuck is flat and stiff. The geometry is similar to a parallel plate capacitor. The chuck surface is ultra-planar and structured with a small hexagonal pin pattern. The global flatness of chuck is better than 0.5µm (p-V) @ 12 inch for e-beam applications and better than 0.075µm @ 6inch for EUV applications. The local flatness is almost better than 10nm for the square area of (20mm)². The bending stiffness is > 30 kNm and the clamping pressure realised 15 kPa ± 10%.
For lithography, precision and stability of all tools is of the outmost importance. Dimensional variation according to temperature is difficult to control and materials with low thermal expansion are needed.
The results of simulation and experimental investigations demonstrate the ability of the Fraunhofer chuck to provide the necessary clamping pressure to flatten a Si-wafer and a reticle to the required specification of Next Generation Lithography and high precise metrology tool.
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