The quest for understanding and optimizing plasma-based deposition

The terminology “Physical Vapor Deposition” (PVD) is widely used describing a family of deposition technologies in parallel to “Chemical Vapor Deposition” (CVD). For the latter, chemical reactions on the surface of the growing film play an important role. Such classification helps us to get organized and to better understand our world where the variety of processes increases. Yet, the term “PVD” is overextended when applied to plasma-based deposition technologies because it falsely suggests that vapor is deposited. The term is correct for the original concept when thermal or electron-beam-heated vapor sources were used. As known since the 1970s, e.g. by the work of Thornton, hyperthermal kinetic energy of particles arriving on the growing film have a decisive effect on a film’s microstructure, thus its density, stress, and many resulting properties. Here, the particles may or may not be ionized (they could be energetic atoms or ions). In this talk, I’ll focus on the non-vapor components, especially the fluxes of charged particles. Exposing the growing film to plasma, and in particular to plasma with film-forming ions, such as ionized metal, offers various ways to control the energy flux by tuning the potential difference between surface and plasma (a.k.a. as “substrate bias” versus “plasma bias”). The latter was recently rediscovered when considering bipolar biasing in the context of HiPIMS. I will illustrate the effect of the various bias methods and argue that for most cases, working at an “energy sweet spot” is desirable where the kinetic energy is less than the displacement energy but the flux of charged particles is high.