Planar Vias through Si3N4 Fabricated by Focused Ion Beam Implantation

摘要

Previous work has demonstrated that silicon implanted into Si3N4 at doses above 10 to the -17th power/sq. cm 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(2+) ions or sequentially at two energies, 80 and 160 keV, using Si(+) and Si(2+) ions, respectively. Films of 0.25-micrometer-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 x 10 to the 17th power/sq. cm and 5 x 10 to the 17th power/sq.cm and depended on whether the 160 keV or the two-energy implants were carried out. Interconnects formed in areas 1.6 x 1.6 micrometers had resistances as low as 0.15 Ohm, while the minimum dimension implants, made with an unscanned beam in 6-12 s, had resistances of 1.5 to 5 Ohms. For vias exposed with doses below threshold, permanent conduction could be induced by breakdown at voltages well below those needed to break down unimplanted Si3N4. Even with the present state of technology, focused ion beam implantation appears to be a useful technique for making level-to-level interconnects through Si3N4 in limited, critical areas of devices. Keywords: Reprints, Silicon nitrides, Focused ion beam implantation, Planar vias, Level-to-level interconnections. (jhd)