This project investigated the connection of mechanical properties and synthesis/growth conditions of transition metal nitride thin films grown using plasma enhanced atomic layer deposition (PEALD).  The overall goal of this project was to understand how synthesis conditions, such as temperature and electrical bias, impact film structure and chemistry, and how this in turn influences friction and wear behavior.  PEALD is a thin film growth process whereby films are grown nearly one atomic layer at a time.  This technique can deposit uniform thin films with very small thicknesses of a variety of materials.  PEALD and ALD are currently used in manufacturing of electronic devices.  Importantly, prior to this project, many details of how the film growth condition affect the resulting film and the film performance (for example, wear rates) were not known.  This project sought to advance knowledge in this area.  This project was a collaboration between Lehigh University, Florida State University, Veeco-CNT, and University of Maryland.  

In this work we investigated several compositions including titanium molybdenum nitride, titanium vanadium nitride, and titanium hafnium nitride.  We examined the role of composition, deposition temperature, and radio frequency (RF) biasing.  

Thin film adhesion is an extremely important issue in a variety of materials and devices.  In finding that the nitride film studied here did not always adhere well (delaminated) from the substrate, we undertook a purposeful study on what factors influence the adhesion.  We varied the surface conditions of inorganic Si substrates including various cleaning processes and deposition of aluminum oxide before the deposition of the PEALD nitride films.  We found that using ozone based cleaning of the surface resulted in the strongest adhesion, presumably due to removal of adventitious carbon species on the surfaces.  

We investigated the effect of temperature on the friction and wear properties of titanium vanadium nitride thin films.  We found that at lower temperatures, large amounts of carbon impurities were present in the films, they had low density, and were prone to very high wear rates.  At higher temperatures, the films had less carbon, higher density, and lower wear rates.  Thus, we showed that high density and removal of carbon from the films is essential to achieving low wear rates.  

We investigated the role of substrate biasing during PEALD and its influence on film structure, chemistry, and wear behavior.  Substrate biasing can change the interaction of plasma ions with the growing film, which can modify the film in many ways.  We discovered that at low amounts of substrate electrical bias resulted in increased films compressive stress and decreases in wear rates.  At high substrate bias, we found that films failed due to cracking or the growth rate decreased, presumably due to sputtering of the growing film by high energy plasma ions.  

Broader impacts of this project include student development, tool development, and educational materials development.  Six PhD students and several undergraduate students were directly involved and benefitted from this project. Four PhD students who contributed have now graduated with positions at Sandia National Laboratories (2 students), Oak Ridge National Laboratory and Brookhaven National Laboratory. One undergraduate working on this project chose to pursue graduate school and was awarded a GRFP fellowship. New hardware in the form of a high throughput multistation tool for measuring friction and wear was developed and the instructions for their fabrication were disseminated.  Two students participated in NSF INTERN opportunities, one with Argonne National Laboratory and one with Brookhaven National Laboratory.  Results from this project have been integrated into a thin film course taught at Lehigh University.

Last Modified: 07/09/2024
Modified by: Nick Strandwitz