Planar vias through Si3N4 fabricated by focused ion beam implantation

Previous work has demonstrated that silicon implanted into Si3N4 at doses above 1017 cm−2 can render the insulator conducting. This has been proposed as a means of making planar vias. Here we report on the use of a focused ion beam to make such planar vias in Si3N4, thus avoiding the need for resist or mask. Implants were carried out at a single energy, 160 keV, using Si++ ions or sequentially at two energies, 80 and 160 keV, using Si+ and Si++ ions, respectively. Films of 0.25‐μm‐thick Si3N4 over Al metal were implanted. Then the upper layer was deposited, patterned, and the structure was sintered at 425 °C for 30 min. The dose threshold for conduction was between 2×1017 and 5×1017 cm−2 and depended on whether the 160 keV or the two‐energy implants were carried out. Interconnects formed in areas 1.6×1.6 μm had resistances as low as 0.15 Ω, while the minimum dimension implants, made with an unscanned beam in 6–12 s, had resistances of 1.5 to 5 Ω. For vias exposed with doses below threshold permanent condu...