| Popis: |
In order to perform an optical proximity correction of memory device nodes below half-pitch 50nm, so called 3D mask effects need to be included in a model based OPC. As the mask pitch approaches wavelength of an optical system, and the angle of off-axis illumination becomes increasingly greater than normal incident beam, combined effects of transmission loss and mask induced polarization induces deviations from Kirchhoff thin mask approximation. Presently, just a handful of methods are being developed for commercial use in full-chip scale optical proximity correction: edge domain decomposition method (DDM), rim-type boundary layer and more recently, M3D model [1-6]. However, these methods currently require extensive modeling and proximity correction runtime although its methods are being continously improved for accuracy and speed. In this work, some results on an alternative approach to 3D mask modeling that is suitable for OPC are presented. Using modeling test pattern experimental data and FDTD rigorous simulation results, a thin mask approximation and alternative 3D mask approximate approaches are compared. And the results indicate improved model accuracy in terms of root mean square of 30% for a cross-pole and a dipole illumination conditions, respectively, while the OPC run-time remained similar. Furthermore, a flash memory gate-poly OPC results using the 3D mask approximate model indicates improved correlation to experimental results than a thin mask model at minimum resolution dense feature and narrow space regions. Thin mask and proposed approximate 3D mask models were calibrated for three differing illumination conditions: two X-dipole illuminations with Y-linear polarization and cross-pole quasar illumination with X&Y-linear polarization states. For each of the extreme off-axis illumination conditions, 3D mask approximate model developed for OPC indicated improved calibration results to both test pattern wafer images and rigorous simulation results. In addition, OPC layout image contours of 3D mask approximate model correlated better to wafer image than the thin mask approximation at nominal and defocus conditions. |
