|
The semiconductor industry and mask shops spend great efforts in order to keep pace with the requirements on pattern
fidelity of the ITRS lithography roadmap. Even for e-beam lithography - often referred to as technology with
"unlimited" resolution - the challenges increase with shrinking feature sizes in combination with applicable resist
processes. The pattern fidelity, specifically CD control, is crucial for the application of e-beam lithography.
One aspect in CD control is the intrinsic proximity effect of the electron beam. This together with other contributions
like influences from resist process or beam generation which are summarized altogether under the term process
proximity effect have to be corrected. An accurate e-beam process proximity effect correction is therefore a key
component of e-beam lithography.
Some process proximity effect correction algorithms provide not only accurate correction for the process proximity
effect induced pattern deformation but also optimize pattern contrast by adjusting geometry and dose simultaneously.
However, the quality of the process proximity effect correction is limited by the calibration accuracy of the used model,
i.e., the accuracy of the utilized process proximity function (PPF).
In a previous paper [R. Galler et al, "PPF - Explorer: Pointwise Proximity Function calibration using a new radialsymmetric
calibration structure", BACUS 2011] the PPF-explorer - a new experimental method for pointwise process
proximity function calibration - was introduced and some first promising calibration results were shown.
This paper presents the progress of the PPFexplorer proximity function calibration. This progress, among others,
comprises automatic generation of calibration patterns, including pre-correction with respect to a rough forecast of the
process proximity function to be calibrated. This pre-correction approach significantly reduces the number of necessary
calibration structures and the number of measurement sites, without sacrificing calibration accuracy. On the contrary, the
pre-correction has positive impact on the calibration quality, since it allows unifying the pattern contrast at the
measurement sites, which reduces the SEM measurement induced error.
We present the results of a PPFexplorer calibration with special focus on minimizing the number of measurement sites.
The results show that the PPFexplorer method can help to improve the proximity effect model calibration with
controllable efforts.
|
