We have improved the M-Split complementary mask pattern split program and our electron projection lithography (EPL) data conversion system to achieve a practical data processing time and data volume: The system was designed to rehierarchicalize the data, flattened after the subfield split, by extracting polygons that all have an identical shape as a cell. The M-Split stress check function was improved by using a normalized bending moment as a criterion. A clustered, computing system was used to reduce the data processing time. The processing time for a complementary mask pattern. split without rehierarchicalizing was reduced to 57 min by using the stress check function and a ten PC cluster system -3-10, times as fast as with commercially available. EPL data conversion systems. We successfully fabricated a full-size 8 in. Si stencil mask consisting of 8000 subfields using the data for an actual 70 nm design-rule system on chip device to demonstrate the effectiveness of M-Split. With a higher performance PC cluster system. and the rehierarchicalizing, we expect to further reduce the M-Split processing time to 10 min.