Process variation-aware three-dimensional proximity effect correction for electron beam direct writing at 45nm node and beyond

The simplified electron energy flux (SEEF)model by which the backscattered energy distribution in the multilayered structure is calculated has been applied to the analysis of critical dimension (CD) variations caused by the thickness variations in copper interconnect. The SEEF model defines the reflection, downward transmission, and upward transmission of electron energy fluxes in each layer. Parameters of the SEEF model are expressed as functions of the depth from the substrate surface and are modified by the approximation in regard to the thickness variation. Using this approach, the process window for the dose and thickness variation has been analyzed quantitatively and the necessity of improving the process window has been confirmed especially at 45nm node and beyond. Moreover, a variation-aware proximity effect correction method, in which CD variations caused by process variations are reduced and dose margins for various patterns with the same linewidth are equalized, is proposed. The correction meth...