PPF-Explorer: pointwise proximity function calibration using a new radial symmetric calibration structure
2011
Lithographic patterning encounters growing challenges to meet the requirements of current and future semiconductor
technology nodes. Even e-beam lithography is challenged due to the physical characteristic of the whole transfer process
including the e-beam blur, electron scattering, and resist effects. These effects cause an unavoidable blurring of the
exposed shapes and are often described as process proximity effect. Besides the correction of this process proximity
effect pattern contrast and process window for the lithography step have to be regarded. There are promising approaches
for contrast enhancing proximity effect correction concepts. To enable a stable patterning great efforts have to be put into
decreasing the errors of all involved technologies.
The blurring resulting from the transfer process is usually described by a so-called process proximity function (PPF) and
mostly approximated by a superposition of two or more Gaussian functions. All algorithms for proximity effect
correction use that PPF to perform their correction. Thus, an accurate determination of that PPF contributes to reducing
the error budget of the proximity effect correction scheme. Several methods for PPF calibration were introduced in the
past. Some are based on modelling the transfer process and performing Monte Carlo simulations. Another common
approach is to design and expose calibration patterns, measure the resulting CDs, and obtain the process proximity
function as the result of a simulation based parameter fitting to a model function such as a sum of Gaussian functions. In
order to respect the increased accuracy requirements an even more accurate description of the PPF is expected.
This paper describes the newly developed PPF-explorer method for the calibration of a pointwise proximity function as a
complementary technique, which is based on the exposure and evaluation of new calibration layouts. Following the
common assumption that a process proximity function is radial-symmetric, we developed radial-symmetric calibration
layouts.
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