|
There are many IC-manufacturers over the world that use various exposure systems and
work with very high requirements in order to establish and maintain stable lithographic
processes of 65 nm, 45 nm and below. Once the process is established, manufacturer
desires to be able to run it on different tools that are available. This is why the proximity
matching plays a key role to maximize tools utilization in terms of productivity for
different types of exposure tools.
In this paper, we investigate the source of errors that cause optical proximity mismatch
and evaluate several approaches for proximity matching of different types of 193 nm
and 248 nm scanner systems such as set-get sigma calibration, contrast adjustment, and,
finally, tuning imaging parameters by optimization with Manual Scanner Matcher.
First, to monitor the proximity mismatch, we collect CD measurement data for the
reference tool and for the tool-to-be-matched. Normally, the measurement is performed
for a set of line or space through pitch structures.
Secondly, by simulation or experiment, we determine the sensitivity of the critical
structures with respect to small adjustment of exposure settings such as NA, sigma
inner, sigma outer, dose, focus scan range etc. that are called 'proximity tuning knobs'.
Then, with the help of special optimization software, we compute the proximity knob
adjustment that has to be applied to the tool-to-be-matched to match the reference tool.
Finally, we verify successful matching by exposing on the tool-to-be-matched with
tuned exposure settings.
This procedure is applicable for inter- and intra scanner type matching, but possibly
also for process transfers to the design targets.
In order to illustrate the approach we show experimental data as well as results of
imaging simulations. The set demonstrate successful matching of critical structures for
ArF scanners of different tool generations.
|
