In the assessment of wafer lithography processes, normalized image log-slope (NILS) gives the % change in width for a given % change in dose [1,2]. A nominal NILS value of 2 indicates 10% change in linewidth for 10% change in dose; the % change in linewidth is inversely proportional to the NILS. In a previous article [2], it was shown… Read More
The “1.xnm” node on most roadmaps to indicate a 16-18 nm metal line pitch [1]. The center-to-center spacing may be expected to be as low as 22-26 nm (sqrt(2) times line pitch). The EXE series of EUV (13.5 nm wavelength) lithography systems from ASML feature a 0.55 “High” NA (numerical aperture), targeted… Read More
Normalized image log-slope (NILS) is probably the single most essential metric for describing lithographic image quality. It is defined as the slope of the log of intensity, multiplied by the linewidth [1], NILS = d(log I)/dx * w = w/I dI/dx. Essentially, it gives the % change in width for a given % change in dose. This is particularly… Read More
