Electrical Engineering
      and Computer Sciences

Electrical Engineering and Computer Sciences

COLLEGE OF ENGINEERING

UC Berkeley

Two-Dimensional Images with Effects of Lens Aberrations in Optical Lithography

K.K.H. Toh

EECS Department
University of California, Berkeley
Technical Report No. UCB/ERL M88/30
1988

http://www.eecs.berkeley.edu/Pubs/TechRpts/1988/ERL-88-30.pdf

A FORTRAN program associated with SAMPLE that simulates a two-dimensional optical image from a projection printer has been upgraded to include the effects of arbitrary lens aberrations. This program has been used to study general issues in projection printing, including the optical proximity effect and defect interactions with features. Basic studies of projection printed images are presented to identify the types of patterns which are most susceptible to residual lens aberrations and to establish test structures which may be used to monitor the presence of critical types of residuals. These effects are explored by including arbitrary lens optical path difference (OPD) aberration functions in the optical image simulation program. The lens aberration function is expressed either in Zernike polynomials or a series expansion. The intensity is calculated from Hopkin's transmission cross-coefficient formulation with a self-checking algorithm. A catalog of results is presented here for the dominant primary aberrations of coma and astigmatism for a fixed maximum OPD of 0.4 lamda. Contact holes are shown to be much more susceptible to astigmatism than coma and the traditional checkerboard test pattern is verified as a sensitive diagnostic pattern. An alternative structure consisting of thin lines with a short break is shown to be even more sensitive to astigmatism and useful for distinguishing it from coma. A further improvement in sensitivity is obtained through the use of small nonprintable defect-like features in proximity to regular features which coherently interact with the blurred image of the feature. A test target of this type is recommended for monitoring coma.


BibTeX citation:

@techreport{Toh:M88/30,
    Author = {Toh, K.K.H.},
    Title = {Two-Dimensional Images with Effects of Lens Aberrations in Optical Lithography},
    Institution = {EECS Department, University of California, Berkeley},
    Year = {1988},
    URL = {http://www.eecs.berkeley.edu/Pubs/TechRpts/1988/1037.html},
    Number = {UCB/ERL M88/30},
    Abstract = {A FORTRAN program associated with SAMPLE that simulates a
two-dimensional optical image from a projection printer has been
upgraded to include the effects of arbitrary lens aberrations. This
program has been used to study general issues in projection printing,
including the optical proximity effect and defect interactions with
features. Basic studies of projection printed images are presented
to identify the types of patterns which are most susceptible
to residual lens aberrations and to establish test structures
which may be used to monitor the presence of critical types of
residuals. These effects are explored by including arbitrary
lens optical path difference (OPD) aberration functions in the
optical image simulation program. The lens aberration function is
expressed either in Zernike polynomials or a series expansion. The
intensity is calculated from Hopkin's transmission cross-coefficient
formulation with a self-checking algorithm. A catalog of results
is presented here for the dominant primary aberrations of coma and
astigmatism for a fixed maximum OPD of 0.4 lamda. Contact holes are
shown to be much more susceptible to astigmatism than coma and the
traditional checkerboard test pattern is verified as a sensitive
diagnostic pattern. An alternative structure consisting of thin
lines with a short break is shown to be even more sensitive to
astigmatism and useful for distinguishing it from coma. A further
improvement in sensitivity is obtained through the use of small
nonprintable defect-like features in proximity to regular features
which coherently interact with the blurred image of the feature. A
test target of this type is recommended for monitoring coma.}
}

EndNote citation:

%0 Report
%A Toh, K.K.H.
%T Two-Dimensional Images with Effects of Lens Aberrations in Optical Lithography
%I EECS Department, University of California, Berkeley
%D 1988
%@ UCB/ERL M88/30
%U http://www.eecs.berkeley.edu/Pubs/TechRpts/1988/1037.html
%F Toh:M88/30