Non-critical Blocking for Full Phase Masks
Publication Date: 2002-Apr-05
The IP.com Prior Art Database
Phase assignments on a phase-shift mask can require feature definition with a corresponding binary mask, particularly in non-critical areas. Critical dimensions (CDs) can be preserved, even with substantial mask misplacement, by defining multiple feature edges with the binary mask in such non-critical areas.
NON-CRITICAL BLOCKING FOR FULL PHASE MASKS
Brief Summary of the Invention:
Phase assignments on a phase-shift mask can require feature
definition with a corresponding binary mask, particularly
in non-critical areas. Critical dimensions (CDs) can be
preserved, even with substantial mask misplacement, by
defining multiple feature edges with the binary mask in
such non-critical areas.
Figure 1P illustrates a phase-shift layout, a binary
layout, and a resulting (i.e. printed) image (determined by
simulation/modeling) assuming a double exposure using masks
implementing those layouts. In this image, the following
parameters were used: a wavelength of 193 nm, a numerical
aperture (NA) of 0.7, and a partial coherence factor
(sigma) of 0.5. In this case, the binary mask is exposed
to twice the energy of the phase-shift mask (referenced as
a 1:2 exposure ratio). In other words, if the phase-shift
mask is exposed to N Joules, then the binary mask is
exposed to 2N Joules.
Note that the binary layout includes a cutout portion to
account for the proximity of the two opposite phase
shifters in the right corner of the phase-shift layout.
Specifically, two opposite phase shifters in close
proximity result in a printed line, which would create an
extraneous line in the corner. Therefore, the cutout in
the binary mask is needed to erase this extraneous line
during the double exposure. Thus, the cutout on the binary
mask actually defines the right corner of the feature.
Note further that some optical proximity correction (OPC)
features have been added to both layouts, thereby improving
the printing of the intersecting lines.
The blue portion of the printed image indicates a low
intensity, the red portion of the printed image indicates a
high intensity, and the yellow portion of the printed image
indicates an intermediate intensity. The high intensity
correlates to a high exposure, whereas the low intensity
correlates to a low exposure. As evidenced by the thin
band of yellow in the printed image, the transition from
high to low intensity is abrupt, thereby resulting in well-
defined features. Of interest, the cutout methodology can
cause the right and left corners to print slightly
differently (i.e. cause CD variations).
Figure 2P illustrates a graph that plots the CD error
versus the distance to a poly line for various
misplacements of the phase-shift and binary masks. All
measurements, i.e. the CD errors, distances, and
misplacements are in nanometers. The misplacements,
d(0,0), d(10,10), etc., refer to (x,y) misplacements of the
phase-shift and binary masks relative to each other. This
graph shows that as the distance increases (i.e. moving
away from the corner), the CD error decreases irrespective
of mask misplacements. In other words, the mask
misplacements can cause significant CD errors, particularly
near the corners.
Figure 3P illustrates a graph that plots the CD versus the
distance to the poly line (both measurements in