Techniques to measure force uniformity of electrostatic chucks for EUV mask clamping

Sathish Veeraraghavan; Jaewoong Sohn; Kevin T. Turner

doi:10.1117/12.746843

16 November 2007 Techniques to measure force uniformity of electrostatic chucks for EUV mask clamping

Sathish Veeraraghavan, Jaewoong Sohn, Kevin T. Turner

Proceedings Volume 6730, Photomask Technology 2007; 67305G (2007) https://doi.org/10.1117/12.746843
Event: SPIE Photomask Technology, 2007, Monterey, California, United States

Abstract

Extreme ultraviolet lithography (EUVL) has stringent requirements on image placement (IP) errors in order to allow for the patterning of devices with critical dimensions (CD) in the sub-32 nm regime. A major contributor to IP error in EUVL is non-flatness of the mask. Electrostatic chucks are used to support and flatten masks in EUVL scanners. Proper operation requires that the electrostatic forces generated by the chuck be of sufficient magnitude and be uniform over the entire chucking area. Hence, there is a need to measure the clamping pressure distribution to properly characterize performance of electrostatic chucks. This paper discusses two methods to measure electrostatic pressure magnitude and uniformity by examining the distortion of thin substrates (wafers) during chucking. In the first method, a wafer with lithographically defined mesas is chucked with the mesas located at the interface between the wafer and the chuck and thus results in a void near the mesa after chucking. Analytical and finite element models were used to relate the resulting void radius to the electrostatic pressure and used to assess the feasibility of the technique. Measurements of pressure on a slab chuck were conducted to demonstrate the mesa measurement approach. The second measurement method examines the deflection of a wafer between pins on a pin chuck in order to estimate the local pressure. A 3D FE model was developed to predict the deformation of the wafer between the pins as a function of applied pressure. The model was used to assess the feasibility of the approach and provide guidance on selecting appropriate substrates for use in such experiments.

Citation Download Citation

Sathish Veeraraghavan, Jaewoong Sohn, and Kevin T. Turner "Techniques to measure force uniformity of electrostatic chucks for EUV mask clamping", Proc. SPIE 6730, Photomask Technology 2007, 67305G (16 November 2007); https://doi.org/10.1117/12.746843

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