Small feature sizes down to the current 45 nm node and precision requirements of patterning in 193 nm
lithography as well as layers where the wafer stack does not allow any BARC require - not only correction of
optical proximity (OPC) effects originating from mask topography and imaging system, but also correction of
wafer topography proximity (WTPC) effects as well. In spite of wafer planarization process steps, wafer
topography (proximity) effects induced by different optical properties of the patterned materials start playing
a significant role, and correction techniques need to be applied in order to minimize the impact.
In this paper, we study a methodology to create fast models intended for effective use in OPC and WTPC
procedures. In order to be short we use the terms "OPCWTPC modeling" and "OPCWTPC models" through
the paper although it would be more correctly to take the terms "mask synthesis modeling" and "mask
A comprehensive data set is required to build a reliable OPC model. We present a "virtual fab" concept using
extensive test pattern sets with both 1D and 2D structures to capture optical proximity effects as well as wafer
A rigorous lithography simulator taking into account exposure tool source maps, topographic mask effects as
well as wafer topography is used to generate virtual measurement data, which are used for model calibration
as well as for model validation.
For model building, we use a two step approach: in a first step, an OPC model is built using test patterns on a
planar, homogenous substrate; in a second step a WTPC model is calibrated, using results from simulated test
patterns on shallow trench isolation (STI) layer. This approach allows building models from experimental
data, including hybrid approaches where only experimental data from planar substrates is available and a
corresponding OPC model for the planar case can be retrofitted with capabilities for correcting wafer
We analyze the relevant effects and requirements for model building and validation as well as the
performance of fast WTPC models.