The improvement of the overlay accuracy using the reticle distortion correction for EPL technologies

Electron projection lithography (EPL) is one of the most promising candidates for the next generation lithography toward the hp 45 nm-node and beyond. EPL employs a stencil mask made from 200 mm Si wafer without a support frame, therefore chucking of an EPL tool and a metrology tool causes deformation in an EPL reticle. However. linear components of sub-field (SF) position error can be corrected by reticle alignment features of an EPL tool, whereas the non-linear components of SF position error can be corrected where each SF is measured beforehand and the corresponding reticle distortion correction (RDC) data is fed into the EPL exposure tool. The SF position error can be viewed as inter-SF IP error where it can be affected by the repeatability of measurement and by the repeatability of distortions caused by the chucking of the measurement tool and the EPL tool. The other part of inter-SF IP comes from the residual that relates to global IP. Besides inter-SF IP, intra-SF IP can be divided into "local IP" and "pattern distribution". For our studies we have investigated the measurement repeatability of the metrology tool (Nikon XY-6i), distortion repeatabilities caused by the chucking of the metrology tool and the EPL tool (NSR-EB1A), global and local IPs. and pattern distortion. Currently we find the effect of mask IP on wafer scale is less than 9 nm, and we believe that in the near future the EPL mask IP target for the hp 45 nm-node could be realized.