Image formation in layered structures: With application to X-ray and extreme ultraviolet lithographies.

摘要

Semiconductor devices are characterized by stacks of layered structures produced using microlithography. With the increasing need for devices with Ultra Large Scale Integration, the size of patterned structures must be very small. Two microlithographic techniques that can be used to fabricate structures with sizes below 100nm are X-ray lithography (XRL) and Extreme UltraViolet (EUV) lithography (EUVL). A common vein for these two lithographies is the use of radiation in the soft X-ray region where the scattering by materials is weak and the refractive indices are near unity in magnitude.; This thesis details a systematic formulation of the image formation problem in X-ray and Extreme UltraViolet Lithographies using the framework of scalar diffraction theory. For the case of X-ray lithography, the image formation modeling includes complex three dimensional masks, partial coherence effects and several physical factors. The physical modeling is then implemented as a computer program. Several illustrative examples are presented along with a comprehensive case study of printability of X-ray mask defects.; For the case of Extreme UltraViolet Lithography, this thesis addresses in detail the optics of multilayer mirrors, reflection from Extreme UltraViolet masks, the role of substrate defects, numerical aperture effects and modeling of the optical system. Several key aspects of Extreme UltraViolet lithography are pointed out that need to be addressed before it can be used for production of semiconductor devices.