Tantalum metal has been deposited with Å-level control for the first time at low temperature without plasma by researchers at Wayne State University in the USA.

This opens up the prospect of using tantalum in layers just a few nanometers thick as the liner for interconnect wiring in the complex geometries of next-generation electronic chips, ultimately allowing faster and less power-hungry smartphones and computers.

The new deposition technique for tantalum was developed by Kyle Blakeney and Prof Charles Winter from Wayne State University in Detroit, alongside Daniel Löffler and Daniel Waldmann of the chemical company BASF, Ludwigshafen (Germany). This is one of a number of thin film innovations being presented at the 16th International Conference on Atomic Layer Deposition (ALD 2016), which takes place in the Convention Centre Dublin, Ireland on July 24-27.

The subject of the conference is atomic layer deposition (ALD), which is a highly precise technique for the growth of thin films. Today, ALD is primarily used for depositing thin film dielectrics that are at the heart of logic and memory devices in the semiconductor industry, and has thus enabled huge performance improvement in consumer products such as PCs, tablets and smartphones.

Now there is a need to deposit ultra-thin metal layers as part of the ever-finer mesh of three-dimensional wiring in electronic chips. It is with this in mind that Wayne State University and BASF collaborated on the tantalum ALD process.

Tantalum has previously been deposited by techniques such as sputtering or with plasma, none of which can uniformly coat complex 3D structures with the near atomic-scale tolerance that the Wayne State team report, with film thickness controlled to a fraction of an Ångstrom (10-10 m).

At the ALD2016 conference, the Wayne State researchers will also announce a new process for cobalt metal that selectively coats only certain areas, leaving other areas uncoated. This was developed by Marissa Kerrigan, Dr. Joseph Klesko, and Prof Charles Winter. Prof Winter explained that “the process selectively targets a chip’s metal surfaces but not insulating materials surrounding it. Such selectivity improves scope for further miniaturisation and has the potential to bring down the overall costs of electronics manufacturing.”

Joseph Peter Klesko from Wayne State University, said:”There exists a high demand for strongly-reducing co-reagents capable of enabling the ALD of electropositive metal films (e.g. tantalum) from metalorganic precursors. Developing new chemistry, with novel mechanistic approaches for the reduction of these precursors, is critical for the use of these metal films in next-generation devices.”

Conference chair, Dr Simon Elliott of Tyndall National Institute, said: “The Wayne State processes for tantalum and cobalt are significant steps forward in controlled growth of ultra-thin metals. Strong growth is projected for area-selective deposition: in the near future, it will allow higher-precision patterning of semiconductor chips, and in the longer term it will be an enabler for manufacturing nanostructured materials on demand. The European ALD community will be articulating this vision in a White Paper that will be launched at the ALD2016 conference.”

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