High-accuracy defect-free X-ray mask technology

There are many material and processing options for building highly accurate defect-free X-ray masks that meet the 0.25-µ m and smaller lithography groundrules. IBM's path and rationale for reducing the key mask parameters of image size, image placement and defects is covered. For image size resolution and control, high voltage e-beam lithography (greater then 50 kV) is the preferred technique for X-ray masks. For tighter image placement control, special writing schemes that reduce the e-beam lithography systematic and random placement errors must be used. Special absorber electroplating conditions and thermal controls were implemented to control process-induced distortion. For tight defect control, identifying and eliminating sources of defect is key. Clearly, for IBM, most of the defect sources were process rather than foreign material related. Our defect reduction work has resulted in the fabrication of a fully functional 64-Mb DRAM (single chip) mask.