The verification of not only two-dimensional feature but also three-dimensional feature, sidewall angle (SWA), has
been becoming increasingly important in NGL mask fabrication. The OMOG (Opaque MoSi on Glass) mask for ArF
immersion lithography with double patterning and the reflective type mask for EUV (Extreme Ultra- Violet) lithography
are especially in need of it.
There are several metrology tools e.g. SEM, AFM, and Scatterometry for sidewall angle (SWA) measurement. We
evaluated a new SWA measurement method using white-band width (WBW), which is equivalent to mask pattern edge
width, by CD-SEM. In general, WBW correlates with SWA. It narrows as SWA becomes steeper. However, the
correlation deteriorates when SWA is vertically near. This is due to the resolution limit of electron beam diameter used
for measurement. We analyzed the new approach to measure SWA by CD-SEM to solve this problem. And the analysis
revealed that WBW changes proportionately electron beam current value. The amount of width change depends on
In this paper, we will describe the new SWA measurement method and its evaluation results as well as SWA
measurement results of OMOG and EUV masks.