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Recent Progress in Electron-Beam Cell Projection Technology

NEC's recent progress in the development of electron-beam (EB) cell projection technology is reviewed. To make it practical, not only the development of a high-performance EB direct writing system but also the establishment of its peripheral technologies in the micro-fabrication process are pursued. In order to obtain high lithographic performance in the EB cell projection lithography system HL-800D (Hitachi), the fundamental effects in EB lithography such as the Coulomb interaction effects, the proximity effect and electron scattering by cell projection aperture (EB mask), have been studied. In addition, high-resolution and high-sensitivity resists have been developed. The Coulomb interaction effects are found to be the most critical issue in cell projection lithography because it affects resolution, linewidth accuracy and throughput. For high resolution, the beam current was reduced to suppress the Coulomb interaction. As a result, a resolution of 0.15 µ m, which is sufficient for fabricating a 1G DRAM, was obtained using the high-resolution resist. To achieve high-linewidth accuracy of less than ±5% for 0.2 µ m lines-and-lines (L/S), optimization of the EB mask structure and the development of a proximity effect correction method which includes the Coulomb interaction effect correction were carried out. Inspection technology for devices of 0.2 µ m or less was also investigated in order to accurately measure linewidth, and to detect defects, particularly those caused by shot stitching error. Finally, the cell projection technology has been applied to the device fabrication of a 1G DRAM, and was demonstrated to be feasible for the development of futuristic advanced devices.