MASKS FOR HIGH-ASPECT-RATIO X-RAY-LITHOGRAPHY

The requirements for deep x-ray lithography (DXRL) masks are reviewed and a recently developed cost effective mask fabrication process is de scribed. The review includes a summary of tabulated properties for mat erials used in the fabrication of DXRL masks. X-ray transparency and m ask contrast are calculated for material combinations using simulation s of exposure at the Advanced Light Source (ALS) at Berkeley, and comp ared to the requirements for standard x-ray lithography (XRL) mask tec hnology. Guided by the requirements, a cost-effective fabrication proc ess for manufacturing high contrast masks for DXRL has been developed. Thick absorber patterns (10-20 mu m) on a thin silicon wafer (100-200 mu m) were made using contact printing in thick positive (Hoechst 462 0) and negative (OCG 7020) photoresist and subsequent gold electrodepo sition. Gold was deposited using a commercially available gold sulphit e bath with low current density and good agitation. The resultant gold films were fine-grained and stress-free. Replication of such masks in to 800 mu m thick acrylic sheets was performed at the ALS.