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4. Aerial Image Simulation

The two-dimensional light intensity incident on top of the wafer is commonly called aerial image. This chapter presents simulation methods to calculate the aerial image for optical projection printing systems. As outlined previously optical projection printing is predominantly used in modern IC manufacturing. The technique of image forming with a lens thereby employed is similar to that used in microscopes. Hence, the involved optical phenomena including diffraction effects have been long-studied and are well-understood [11, chs. VIII-XI]. Especially, the theory of Fourier optics--either in its scalar or vector form--provides a powerful physical framework to describe projection printing.

The chapter starts with a brief sketch of the principles of Fourier optics, whereby the application of aerial image simulation stands in the foreground of the presentation. Then lens aberrations caused by the imperfection of the optical systems are discussed. Resolution enhancement techniques like in-lens filters and advanced illumination systems are also considered. Finally, some aspects on the numerical implementation of the aerial image module are given.


Heinrich Kirchauer, Institute for Microelectronics, TU Vienna