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According to device shrinkage, pattern load, layout geometry and process induced critical dimension (CD) trend are the
most important factors deciding mask CD uniformity in a mask manufacturing process. The CD distribution is generally
divided by two categories - contribution of pattern load and process induced CD distribution. Etch bias uniformity on a
mask is one of the decisive contributors at a standpoint of pattern load. The signature of etch bias uniformity totally
depends on the pattern load in a mask. In a low pattern load, etch bias uniformity shows a radial signature which is
geometrically distributed regardless of pattern position. In a high pattern load, etch loading effect becomes dominant.
The pattern load, however, can have various definitions, which means that a criterion of low and high pattern load can be
obscure. Specific layouts which have same pattern load over mask but separated region of low and high load pattern in
one mask was designed to specify the effect of pattern load. The radial CD signature is mitigated as pattern load
increases locally. At the same time, etch loading trend grows and dominates total CD uniformity. The radial signature and
etch loading trend have inverse signs on central region which enables to compensate each signature. Therefore a specific
pattern load which can make etch bias uniformity minimized can exist. "Transition pattern load" is detected here. One
can use this specific pattern load as an indicator to specify design categories for mass production. In addition, geometry
of layout should be considered to achieve uniformity number required in 45nm node technology. In high pattern load
over transition pattern load, etch bias shows saddle shape uniformity. Since the saddle shape uniformity is uncorrectable
with conventional etch loading kernel, new correction model should be considered to meet the confined CD specification
in future device nodes.
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