Linearity- and proximity effects are present on actual masks even if manufactured with current state-of-the-art
mask processes. Currently the mask writers rectify the difference on the target critical dimension generated
by these effects by changing the dose in function of the density of the pattern. However, the accuracy of this
compensation is limited resulting in a deviation dependent of the critical dimensions (CD) from the design. The
consequences of these mask imperfections on the photolithographic results on the wafer get increasingly into
focus with each shrink in the semiconductor technology. In this paper we will present a procedure for building
mask proximity simulation models. In a first part this new flow will be introduced, then one application on the
Electron beam lithography modelling is exposed.
The super-sensitivity of wafer critical dimensions (CDs) to mask CDs at low k1, known as the Mask Error Enhancement Factor (MEEF) drives the need for increasingly tighter mask CD control. In addition, the accuracy of the model based optical proximity correction (OPC) used to compensate systematic lithographic errors is partially dependent on a stable mask CD error signature that expands mask CD control requirements over multiple feature types.
This paper presents the need for improved quantification and monitoring of mask CD signatures that includes CD characteristics relevant to OPC model calibration. It also introduces and discusses a new method to characterize, quantify, and control mask signatures in a mask manufacturing environment to limit the impact of mask CD variations on the OPC model validity. Multiple approaches to implementing this "golden curve" method are discussed in terms of their advantages and disadvantages.
Linearity- and proximity effects do exist on actual masks even if manufactured with current state-of-the-art processes. The impact of these short-range mask effects on the results of the optical lithography for features sizes relevant in the 90nm-node is investigated. For this purpose, an approach is chosen which employs mask process simulations in combination with simulations of optical lithography.
Two mask models are deduced and verified from measurement data of an existing mask process. The lithographic results are simulated using parameters of current optical- and process models. Both mask models are used to evaluate the impact of the mask proximity effects on the printing results of optical lithography for critical pattern geometries. The differences in the mask proximity characteristics lead to additional pattern-dependent CD-offtargets after wafer lithography. Additionally, a mask-process dependent sensitivity of the CD-offtarget on the presence of optical sub-resolution assist features is observed.
Based on these simulation results, the efficiencies of two techniques for the correction of the mask proximity signatures are evaluated. The application of mask sub-resolution features is compared with model-based data correction on mask level. Mask sub-resolution assist features reduce the influence of the mask process significantly and provide an enhanced stability against mask process fluctuations. Data correction yields even better correction results at the cost of an increased complexity due to the susceptibility to changes of the mask processes characteristics.