Comparative analysis of next generation lithography masks: PREVAIL and SCALPEL technologies

For Electron Projection Lithography (EPL) technologies to succeed in the sub-100 nm regime, it is critical to minimize the image placement (IP) errors. In order to control (or possibly eliminate) these mask-level distortions, it is important to understand and characterize the factors that contribute to the errors during mask fabrication and pattern transfer. This includes optimizing both the mask format and the thin film stresses in the critical membrane layers. To assess the thin film stress magnitudes, significant improvements were made to automate the Resonant Frequency Test (RFT). Stress profiles were then measured for the stencil and continuous mask membranes used in the finite element (FE) modeling. The fabrication process flow for two EPL technologies (SCALPEL and PREVAIL) were numerically simulated and experimentally assessed for IP. This included both continuous and stencil membranes, for 1 mm x 1 mm and 1 mm x 12 mm window sizes, on a 4-in. wafer. Direct comparisons were made between the experimentally measured IP distortions and those obtained from the FE models for both intra-membrane (i.e., within a single window) and cross-mask results. Excellent agreement was obtained between the numerical simulations and the experimental results.