Christopher J. Mason

High-numerical-aperture 193-nm exposure tool

As the semiconductor industry accelerates the pace of change, a shift in exposure wavelength from 248 nm to 193 nm becomes inevitable. Correspondingly, the change to a shorter wavelength and the desire to maintain productivity, necessitates a fundamental reassessment of system design approach. Evaluation of resolution and k-factor for a lithographic tool operating at 193 nm and 0.75 numerical aperture indicates that 130 nm node production will be manageable with binary mask, and that performance consistent with 100 nm node requirements and potentially beyond will be achievable with the use of advanced lithographic techniques. This paper reviews the design, system performance analysis and early results for a full-field catadioptric lithography tool operating at numerical apertures up to 0.75 NA.

Overcoming low-alignment signal contrast induced alignment failure by alignment signal enhancement

Overlay is one of the key factors which enables optical lithography extension to 1X node DRAM manufacturing. It is natural that accurate wafer alignment is a prerequisite for good device overlay. However, alignment failures or misalignments are commonly observed in a fab. There are many factors which could induce alignment problems. Low alignment signal contrast is one of the main issues. Alignment signal contrast can be degraded by opaque stack materials or by alignment mark degradation due to processes like CMP. This issue can be compounded by mark sub-segmentation from design rules in combination with double or quadruple spacer process. Alignment signal contrast can be improved by applying new material or process optimization, which sometimes lead to the addition of another process-step with higher costs. If we can amplify the signal components containing the position information and reduce other unwanted signal and background contributions then we can improve alignment performance without process change. In this paper we use ASMLs new alignment sensor (as was introduced and released on the NXT:1980Di) and sample wafers with special stacks which can induce poor alignment signal to demonstrate alignment and overlay improvement.