DARPA-supported researchers 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 a host of 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 new method, known as electron-enhanced atomic layer deposition (EE-ALD), was recently developed at the University of Colorado, Boulder (CU) as part of DARPA’s Local Control of Materials Synthesis (LoCo) program. The CU team 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 a capability is critical as the 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 unprecedented and is anticipated to enhance film quality. The group is also exploring other methods to etch specific materials—such as aluminum nitride and hafnium oxide, important in 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 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,” said Tyler McQuade, DARPA program manager.

CU’s work, which was performed in collaboration with the Naval Research Laboratory and National Institute of Standards and Technology, was recently recognized as one of six “Highlights of 2016”—selected from more than 400 accepted oral presentations and posters at the 16th International Conference on Atomic Layer Deposition in Dublin, Ireland.

Image caption: Pictured is a Gallium Nitride film deposited on a Silicon substrate at 27 degrees Celsius (80 degrees Fahrenheit) using an innovative process for depositing super thin films. Current deposition methods for these materials require temperatures around 800 degrees Celsius (1,472 degrees Fahrenheit), which is incompatible with microelectronics processing due to the damage that heat can wreak on underlying substrate materials.This new method could allow integration of previously incompatible microelectronics materials. (University of Colorado Boulder image)

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