As part of the Local Control of Materials Synthesis (LoCo) program of the US Defense Advanced Research Projects Agency (DARPA), the University of Colorado, Boulder (CU) have developed the new electron-enhanced atomic layer deposition (EE-ALD) method for synthesizing ultrathin materials at room temperature (compared with existing approaches that require temperatures of 800°C or more). The advance is said to open a path to creating previously unattainable thin-film microelectronics whose production by conventional methods has been impossible because many components lose their critical functions when subjected to high temperatures.
The CU team demonstrated room-temperature deposition of silicon and gallium nitride (GaN) as well as the ability to controllably etch specific materials, leading to precise spatial control in three dimensions (critical as demand grows for ever-smaller device architectures).
After first demonstrating the process in early 2015, team members went on to perform detailed mechanistic studies to learn how best to exploit and control EE-ALD for film growth. By controlling the electron energy during the ALD cycles, they discovered that they could tune the process to favor either material deposition or removal. The ability to selectively remove (etch) deposited material with electrons under conditions as low as room temperature is said to be unprecedented and is expected to enhance film quality. The group is also exploring other methods to etch specific materials — such as aluminium nitride and hafnium oxide (key to specialized electronics applications) — showing that they can selectively etch these materials in composites, which provides an attractive alternative to traditional masking approaches.
CU has also built a custom deposition chamber to demonstrate industrial relevance and scalability of the EE-ALD process, which can deposit or etch films composed of multiple materials on industrial-scale 6-inch silicon wafers. In principle, the method could be scaled to larger substrates and parallelized to process many wafers at once. The researchers are now working to understand the vast parameter space of the EE-ALD process to better control film composition and properties in three dimensions.
"Looking forward, the EE-ALD approach could serve not just as a tool for integrating incompatible materials but also more generally to build and etch device architectures at atomic scales, an increasingly important capability as circuit geometries shrink," says DARPA program manager Tyler McQuade.
CU's work, performed in collaboration with the US Naval Research Laboratory (NRL) and National Institute of Standards and Technology (NIST), was recognized as one of six 'Highlights of 2016', selected from over 400 accepted oral presentations and posters, at the 16th International Conference on Atomic Layer Deposition (ALD 2016) in Dublin, Ireland (24-27 July).
