Fabrication of Self-Aligned Sub-100 nm Iron Wires by Selective Chemical Vapor Deposition

Abstract

We have demonstrated the ability to fabricate and self-align sub-100 nm iron wires using a combination of silicon nitride spacer technology and selective deposition of iron and tungsten by chemical vapor deposition ͑CVD͒. The discovery of selective deposition of CVD iron, from pentacarbonyl ͓Fe͑CO͒ 5 ͔ precursor, on silicon nitride surfaces over tungsten surfaces is the key factor that allows the self-alignment of iron wires. The density and conductivity of the CVD iron layers improved as the deposition temperature increased. Deposition time of 1 min was sufficient to deposit a perfectly aligned, continuous iron wire. The deposited iron layer shows 100% selectivity.In the world of microelectronics today, fabrication of fine metal lines or wires can be performed with a combination of advanced lithography and metal etching, chemical mechanical planarization ͑CMP͒, or metal lift-off. However, these techniques may not be the easiest or the most cost-effective. In lithography, there is always resolution and alignment issues such as how small a structure can be produced and how closely a structure can be aligned to another. Even when lithography issues have been solved, patterning of very fine metal lines can be a problem. Wet etching is no longer feasible when trying to produce submicrometer features because the isotropic etch produces large undercuts. Metal lift-off with sacrificial resist is one of the more common solutions to produce fine metal lines. The process has resist-imposed limitations where deposition must take place below 200°C because of resist thermal stability, preventing its use in CVD metal deposition.In this article, we demonstrate a method to produce sub -100 nm iron wires by a self-alignment process. In this process, very accurate alignment can be achieved because the alignment is not determined by the lithographic tool but by the structures and materials themselves. The fabrication of the wires can be divided into two parts. Initially, a fine silicon nitride ͑Si 3 N 4 ͒ line was formed by standard spacer technology. The spacer technique is commonly used in the fabrication of nanometer transistors and does not require the use of submicrometer lithographic tools. To produce the iron wires, we use the selective and self-aligning capability of CVD tungsten and iron. In this work, tungsten hexafluoride ͑WF 6 ͒ and iron pentacarbonyl ͓Fe͑CO͒ 5 ͔ are the respective tungsten and iron precursors.Selective CVD is an attractive process that enables the fabrication of structures not defined by the lithographic resolution. Many studies concerning the selective deposition of tungsten using a WF 6 precursor have been reported.