Abstract
Wafer chucks are used in advanced lithography systems to hold and flatten wafers during exposure. To minimize defocus and overlay errors, it is important that the chuck provide sufficient pressure to completely chuck the wafer and remove flatness variations across a broad range of spatial wavelengths. Analytical and finite element models of the clamping process are presented here to understand the range of wafer geometry features that can be fully chucked with different clamping pressures. The analytical model provides a simple relationship to determine the maximum feature amplitude that can be chucked as a function of spatial wavelength and chucking pressure. Three-dimensional finite element simulations are used to examine the chucking of wafers with various geometries, including cases with simulated and measured shapes. The analytical and finite element results both demonstrate that geometry variations with short spatial wavelengths (e.g., high-frequency wafer shape features) present the greatest challenge to achieving complete chucking. The models and results presented here can be used to provide guidance on wafer geometry and chuck designs for advanced exposure tools.
Highlights
Wafer chucks are used to clamp wafers in various processes during semiconductor device manufacturing
We report an analytical model to establish a basic understanding of wafer chucking and a finite element analysis-based parametric study of chucking wafers with various realistic geometries
We have established the essential mechanics of semiconductor wafer chucking
Summary
Wafer chucks are used to clamp wafers in various processes during semiconductor device manufacturing. If wafers are not chucked completely, overlay and defocus issues may arise in lithography processes.[1,2,3] While wafer chucking is not typically considered a key challenge, recent and future changes to lithography systems and processes have increased the importance of wafer chucking These changes include: (1) the development of EUV lithography systems that use electrostatic chucks with lower clamping pressures, (2) a move to smaller feature sizes with tighter requirements on defocus and overlay that make complete chucking, down to the nanometer level, critical, and (3) a transition to larger diameter, 450-mm wafers that are thicker and stiffer and more difficult to chuck. The simple analytical model and the wafer-level simulations both show that high-frequency (short spatial wavelength) features are most likely to lead to chucking problems
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