CD Control Analysis of the SCALPEL-HT/Alpha Optics

SCALPEL differs from optical lithography in its use of high-energy electron imaging, electron-scattering contrast, a segmented mask, and a sub-field stitching architecture. Imaging performance of a high-throughput SCALPEL tool is primarily determined by geometric and space-charge aberrations, which both have unique dependencies on key optics parameters. A complete understanding of the imaging point-spread function (PSF) is vital to the optimization of a high throughput SCALPEL optical subsystem and the optimum use of mask pattern data bias for proximity effect correction (PEC). Previous image modeling with an assumed Gaussian PSF model was updated to use the PSF result of Monte-Carlo analysis of electron landing distributions. We find substantially different behaviors as a result of this more rigorous analysis. A proper evaluation of the true nature of the SCALPEL electron optics PSF and its dependencies in a scanning exposure mode allows for meaningful optimization and performance prediction in the area of critical dimension (CD) control.