Proceedings Article | 27 May 1996
Proc. SPIE. 2723, Electron-Beam, X-Ray, EUV, and Ion-Beam Submicrometer Lithographies for Manufacturing VI
KEYWORDS: Wafer-level optics, Reticles, Scattering, Fractal analysis, Photomasks, Optical proximity correction, Raster graphics, Mask making, Computer aided design, Optical calibration
Both e-beam and optical proximity effects are still a major barrier in the transfer of an ULSI design from the CAD station to the printed result on wafer. Optical proximity effect correction (OPC) is shown to be a strong tool to improve the printing latitudes for i-line lithography of 0.35 micrometers feature sizes and below, but leads to fractal geometries around 0.1 micrometers (corresponding to 0.5 micrometers on a 5x reticle). This quantum leap in required minimum linewidth on the mask may urge mask makers to apply e-beam proximity effect correction (PEC), even more than a decrease in the reticle magnification from 5x to 4x (and further) would. For raster scan e-beams, which are typically used in mask making, correction by dose variation is not practical. Hence, PEC for these systems must be tackled by modifying the geometry of the design, in a way similar to OPC techniques. Both corrections must compromise between the accuracy achieved, which is dominated by the selected (correction and exposure) grid size, and the resulting throughput loss, caused by the use of a smaller grid size. Sigma-C now introduces a new algorithm, which enables the proximity effect correction by shape variation. It is included into CAPROX and supports hierarchy in the same manner as the other postprocessing operations. The exposure of the shape corrected pattern on a raster scan machine requires only one beam pass, whereas dose variation would require one pass for each dose. Exposures were made at IMEC and at Compugraphics. The first results on Leica EBMF10.5 and MEBES III are promising. The pure shape correction increases the line width uniformity and opens the process window for critical dimensions below 1 micrometers . Performance measurements show that the 64 Mb DRAM is a job of a few hours.
