Precise Delineation Characteristics of Advanced Electron Beam Mask Writer EB-X3 for Fabricating 1× X-Ray Masks

This paper discusses the delineation characteristics of a state-of-the-art variable-shaped electron-beam (e-beam) mask writer called the EB-X3, which was developed both to write 100-nm-node patterns on X-ray membrane masks and also to study the feasibility of the mask technology. For a 1-Gb dynamic random access memory (DRAM) pattern (22 mm×22 mm chip), the best image placement (IP) accuracy obtained so far is 3σ(X, Y) = (5.6 nm, 8.4 nm) and maximum Δ(X, Y) = (4.2 nm, 7.3 nm). IP values less than 15 nm are reproducible. Precise temperature control and a three-point support pallet (4-inch membrane warpage: <100 nm) are the keys to this excellent IP. A resolution of 50 nm was obtained for line-and-space patterns. Good critical dimension control of less than 10 nm and small proximity effects were obtained with ZEP resist and normal-hexyl acetate developer. A total overlay accuracy for proximity X-ray lithography of better than 40 nm was achieved at the 1-Gb-DRAM level using X-ray masks with a 19-nm overlay accuracy (gate to contact) fabricated using the EB-X3.