Masks for high aspect ratio x-ray lithography

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Abstract
The requirements for deep x-ray lithography (DXRL) masks are reviewed and a recently developed cost effective mask fabrication process is described. The review includes a summary of tabulated properties for materials used in the fabrication of DXRL masks. X-ray transparency and mask contrast are calculated for material combinations using simulations of exposure at the Advanced Light Source (ALS) at Berkeley, and compared to the requirements for standard x-ray lithography (XRL) mask technology. Guided by the requirements, a cost-effective fabrication process for manufacturing high contrast masks for DXRL has been developed. Thick absorber patterns () on a thin silicon wafer (m) were made using contact printing in thick positive (Hoechst 4620) and negative (OCG 7020) photoresist and subsequent gold electrodeposition. Gold was deposited using a commercially available gold sulphite bath with low current density and good agitation. The resultant gold films were fine-grained and stress-free. Replication of such masks into thick acrylic sheets was performed at the ALS.

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