Computer Aided Design Tools for Phase-Shift Masks and Spatial Filtering

D.M. Newmark

EECS Department
University of California, Berkeley
Technical Report No. UCB/ERL M91/117
December 1991

http://www2.eecs.berkeley.edu/Pubs/TechRpts/1991/ERL-91-117.pdf

A computer aided design tool, Mask Analysis System by Computer (MASC), has been developed to automatically generate design graphs of user specified image quality measurements over one-dimensional cut lines and two-dimensional mask areas as a function of both optical system and mask layout variables. MASC is intended to serve as a tool to assist layout designers in determining design rules for phase-shift masks and in examining the printability of mask levels or combinations of mask levels. Several examples of analyses performed using MASC on phase-shift masks are presented. In addition, SPLAT has been extended to include lens filtering effects, and MASC is used to investigate the parameters of a spatial filter introduced by Hitachi which uses two focal points to extend the depth of focus.

The results from our analyses of phase-shift masks indicate that for dark field masks with isolated spaces and Levenson arrays of spaces, a shrink of the mask combined with a bloat of open areas shows promise as a means of designing phase-shift masks if one is willing to sacrifice the area between light regions. Results obtained by examining several typical mask patterns show that an overall shrink of the mask does not require special design rules for each type of feature, but better scaling could result by appropriately developing new rules for different patterns. A probe of phase transitions indicates that a phase transition of 0.6 lamda/NA is the optimum length to achieve the highest intensity throughout the phase transition region. A new mask pattern for contact chains is demonstrated to have a high intensity slope for a pitch of 1.2 lamda/NA and below. Examination of a phase-shift DRAM layout shows that it is not as sensitive to alignment as might be expected by examination of the mask itself. The linewidth control of the DRAM can be improved by modifying non-critical areas such as the passing Poly line. The relationship between two parameters in the Hitachi spatial filter function is determined to be theta=2pibeta, and this relationship is used to show that a 25% improvement in depth of focus requires at least a factor of 5 reduction in the clear field intensity while 100% improvement requires a factor of 10 reduction.

BibTeX citation:

@techreport{Newmark:M91/117,
    Author = {Newmark, D.M.},
    Title = {Computer Aided Design Tools for Phase-Shift Masks and Spatial Filtering},
    Institution = {EECS Department, University of California, Berkeley},
    Year = {1991},
    Month = {Dec},
    URL = {http://www2.eecs.berkeley.edu/Pubs/TechRpts/1991/1923.html},
    Number = {UCB/ERL M91/117},
    Abstract = {A computer aided design tool, Mask Analysis System by Computer
(MASC), has been developed to automatically generate design graphs
of user specified image quality measurements over one-dimensional
cut lines and two-dimensional mask areas as a function of both
optical system and mask layout variables. MASC is intended to serve
as a tool to assist layout designers in determining design rules
for phase-shift masks and in examining the printability of mask
levels or combinations of mask levels. Several examples of analyses
performed using MASC on phase-shift masks are presented. In addition,
SPLAT has been extended to include lens filtering effects, and MASC
is used to investigate the parameters of a spatial filter introduced
by Hitachi which uses two focal points to extend the depth of focus.

The results from our analyses of phase-shift masks indicate that
for dark field masks with isolated spaces and Levenson arrays of
spaces, a shrink of the mask combined with a bloat of open areas
shows promise as a means of designing phase-shift masks if one is
willing to sacrifice the area between light regions. Results obtained
by examining several typical mask patterns show that an overall
shrink of the mask does not require special design rules for each
type of feature, but better scaling could result by appropriately
developing new rules for different patterns. A probe of phase
transitions indicates that a phase transition of 0.6 lamda/NA is
the optimum length to achieve the highest intensity throughout
the phase transition region. A new mask pattern for contact chains
is demonstrated to have a high intensity slope for a pitch of 1.2
lamda/NA and below. Examination of a phase-shift DRAM layout shows
that it is not as sensitive to alignment as might be expected by
examination of the mask itself. The linewidth control of the DRAM can
be improved by modifying non-critical areas such as the passing
Poly line. The relationship between two parameters in the Hitachi
spatial filter function is determined to be theta=2pibeta, and this
relationship is used to show that a 25% improvement in depth of
focus requires at least a factor of 5 reduction in the clear field
intensity while 100% improvement requires a factor of 10 reduction.}
}

EndNote citation:

%0 Report
%A Newmark, D.M.
%T Computer Aided Design Tools for Phase-Shift Masks and Spatial Filtering
%I EECS Department, University of California, Berkeley
%D 1991
%@ UCB/ERL M91/117
%U http://www2.eecs.berkeley.edu/Pubs/TechRpts/1991/1923.html
%F Newmark:M91/117