Smoother Mo films for molded FEAs by addition of N2 to Ar sputter gas

Molybdenum field emitter arrays (FEAs) fabricated by molding and a self-aligned gate process [1] have been successfully used to fabricate stacked-double-gate FEAs [2, 3], and to demonstrate high-acceleration field compatibility [4], and near infrared laser-induced field-emission [5]. For higher brightness cathodes, we are currently developing nanoscale (300nm emitters, 750 nm pitch) molded molybdenum FEAs. As emitter dimensions approach the grain size for sputtered molybdenum films, roughness in the metal grain structure, for example due to self-shadowing when coating topographic features, becomes increasingly significant for the FEA structures. Fig. 1 illustrates topographic roughening for a) coating of concave, pyramidal Si molds to make the emitters, and b) gate metallization coated over one convex emitter on a demolded FEA. During mold coating the roughness creates axial pores in the emitter tips which the subsequent evaporated and electroplated metal layers cannot fill. For gate apertures with diameter < 0.5 µm, the molybdenum grain structure distorts the aperture shape.