In 193nm optical lithography, immersion technology will enable numerical apertures much greater than 1.0.
Furthermore, polarized light is likely to be applied, enhancing the imaging properties of structures with dimensions near
the resolution limit. As a result, the consequences of extreme oblique angle illumination as well as polarization effects
need to be carefully evaluated for all elements of the lithographic process. This paper explores the aberrations and
apodization induced by the pellicle film in hyper NA lithography.
In a first step, the angle and polarization-dependent phase errors of a perfectly flat pellicle are investigated and
discussed for varying thicknesses. It will be shown that for NAs greater than 1.0 the pellicle induces higher order
spherical aberrations which can be in the range of today's scanner lens specifications. Also, the impact of polarizationdependent
apodization will be discussed.
In a second step, the analysis is extended to the case of a non-flat pellicle due to a given frame bow. Under these
conditions, the phase and transmission error is not radially symmetric and, furthermore, is field dependent. It will be
discussed under which conditions this effect can lead to a significant pellicle-induced CD signature over the entire
In case drastic changes need to be made to tool configurations or blank specifications, it is important to know as early as possible under which conditions the tight image placement requirements of future lithography nodes can be achieved. Modeling, such as finite element simulations, can help predict the magnitude of structural and thermal effects before actual manufacturing issues occur, and basic experiments using current tools can readily be conducted to verify the predicted results or perform feasibility tests for future nodes. Using numerical simulations, experimental mask registration, and printing data, the effects on image placement of stressed layer patterning, pellicle attachment, blank dimensional and material tolerances, as well as charging during e-beam writing were investigated for current mask blank specifications. This provides an understanding of the areas that require more work for image placement error budgets to be met and to insure the viability of optical lithography for future nodes.