Abstract
ArF lithography is approaching its limit past the 90-nm node. F 2 lithography using 157-nm light seems to be a natural extension to the next node. However, several key problems in F 2 lithography are still insurmountable. The thin-film pellicle material cannot withstand more than 10 exposures. The hard pellicle technology is far from manufacture-worthy. Ditto for the F 2 resist systems. Despite great progresses made, the CaF 2 material still suffers from quality and quantity problems. On the other hand, ArF lithography using water immersion between the front lens element and the photoresist, effectively reduces the 193-nm wavelength to 135 nm and opens up rooms for improvement in resolution and depth of focus (DOF). This paper gives a systematic examination of immersion lithography. It analyses and evaluates the diffraction DOF, required DOF, and available DOF in a dry and an immersion system. It also analyses the effects of polarization to dry and immersion imaging. These phenomena are included in simulations to study the imaging of critical layers such as Poly, Contact, and Metal layers for the 65-nm, 45-nm, and 32-nm nodes using 193-nm and 157-nm, dry and immersion systems. The imaging feasibility of 157-nm immersion to the 22-nm node is briefly studied. In additions to the imaging comparison, the impacts and challenges to employ these lithography systems will also be covered.