Patterning of dispenser cathode surfaces to a controlled porosity

A process to pattern slots approximately 1.25-μm in width into 25-μm-thick tungsten films that have been deposited onto flat or concave surfaces is discussed. These techniques are summarized as follows: a 25-μm-thick tungsten film with a high degree of (100) orientation is chemically vapor deposited (CVD) onto a flat or concave molybdenum mandrel. A 5-μm-thick aluminium film is deposited onto the CVD tungsten, followed by 2 μm of photoresist. On concave cathodes, xenon dichlorine laser ablation or X-ray lithography is used to pattern the photoresist, whereas on flat cathodes deep ultraviolet lithography can be used. The patterned photoresist serves as the mask in a chlorine ion beam assisted etching (IBAE) process to pattern the aluminum. An alternative process is to deposit aluminum oxide films onto the tungsten and pattern the aluminum oxide using laser ablation. The tungsten film is then patterned to 3-6 μm slot widths using IBAE+ClF₃ with the patterned aluminum or oxide as the mask. Finally, a sputter deposition step is required to close up to slots to approximately 1 μm. The process described is capable of patterning concave disperser cathodes to a controlled and precise porosity