Influence of data volume and EPC on process window in massively parallel e-beam direct write

Multiple e-beam direct write lithography (MEBDW), using >10,000 e-beams writing in parallel, proposed by MAPPER, KLA-Tencor, and IMS is a potential solution for 20-nm half-pitch and beyond. The raster scan in MEBDW makes bitmap its data format. Data handling becomes indispensable since bitmap needs a huge data volume due to the fine pixel size to keep the CD accuracy after e-beam proximity correction (EPC). In fact, in 10,000-beam MEBDW, for a 10 WPH tool of 1-nm pixel size and 1-bit gray level, the aggregated data transmission rate would be up to 1963 Tera bits per second (bps), requiring 19,630 fibers transmitting 10 Gbps in each fiber. The data rate per beam would be <20 Gbps. Hence data reduction using bigger pixel size, fewer grey levels to achieve sub-nm EPC accuracy, and data truncation have been extensively studied. In this paper, process window assessment through Exposure-Defocus (E-D) Forest to quantitatively characterize the data truncation before and after EPC is reported. REBL electron optics, electron scattering in resist, and resist acid diffusion are considered, to construct the E-D Forest and to analyze the imaging performance of the most representative layers and patterns, such as critical line/space and hole layers with minimum pitch, cutting layers, and implant layers, for the 10-nm, and 7-nm nodes.