Researchers at the University of Colorado, Boulder (CU) have developed a new approach for synthesizing ultrathin materials at room temperature—a breakthrough over industrial approaches that have demanded temperatures of 800 degrees Celsius or more.

The advance opens 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 process, known as electron-enhanced atomic layer deposition (EE-ALD), was developed as part of the Defense Advanced Research Projects Agency’s (DARPA's) Local Control of Materials Synthesis (LoCo) program. The CU team's method demonstrated room-temperature deposition of silicon and gallium nitride—linchpin elements in many advanced microelectronics—as well as the ability to controllably etch specific materials, leading to precise spatial control in three dimensions. Such capability is critical as the demand grows for ever-smaller device architectures.

This gallium nitride film was deposited on a silicon substrate at 27 degrees Celsius using an innovative process for depositing super-thin films. Image credit: University of Colorado, Boulder.After first demonstrating the process in 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 found that they could tune the process to favor either material deposition or removal. The ability to selectively remove (etch) deposited material with electrons under room-temperature conditions is expected to enhance film quality.

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 six-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.