Since decades, the PECVD (‘plasma enhanced chemical vapor deposition’) processes have emerged as one of the most convenient and versatile approaches to synthesize either organic or inorganic thin films on many types of substrates, including complex shapes. As a consequence, PECVD is today utilized in many fields of application ranging from microelectronic circuit fabrication to optics/photonics, biotechnology, energy, smart textiles, and many others. Nevertheless, owing to the complexity of the process including numerous gas phase and surface reactions, the fabrication of tailor-made materials for a given application is still a major challenge in the field making it obvious that mastery of the technique can only be achieved through the fundamental understanding of the chemical and physical phenomena involved in the film formation. In this context, the aim of this foundation paper is to share with the readers our perception and understanding of the basic principles behind the formation of PECVD layers considering the co-existence of different reaction pathways that can be tailored by controlling the energy dissipated in the gas phase and/or at the growing surface. We demonstrate that the key parameters controlling the functional properties of the PECVD films are similar whether they are inorganic- or organic-like (plasma polymers) in nature, thus supporting a unified description of the PECVD process. Several concrete examples of the gas phase processes and the film behavior illustrate our vision. To complete the document, we also discuss the present and future trends in the development of the PECVD processes and provide examples of important industrial applications using this powerful and versatile technology.

Advanced optical filter applications require an appropriate control of the optical constants, as well as of other suitable film properties such as mechanical performance, thermal and environmental stability, absence of refractive index inhomogeneities, and others. In the present work we studied the characteristics of two high index optical materials, namely amorphous tantalum pentoxide (Ta2O5) and niobium pentoxide (Nb2O5) prepared by plasma enhanced chemical vapor deposition, using penta-ethoxy tantalum Ta(OC2H5)5 and penta-ethoxy niobium, Nb(OC2H5)5, precursors. We particularly investigated the effect of energetic conditions on the film growth by using different modes of plasma excitation, namely rf, microwave, and dual-mode microwave/radio frequency discharges. Under sufficient ion bombardment, controlled by the rf-induced negative substrate bias, the dense Ta2O5 and Nb2O5 films exhibited a refractive index of 2.16 and 2.26 (at 550nm), respectively, while the extinction coefficient was below 10−5, as determined by spectroscopic ellipsometry, and spectrophotometry. We found that increasing ion bombardment during the film growth leads to an appreciable increase of carbon concentration, as indicated by a strong double peak at 1400 and 1500cm−1 in the Fourier transform infrared spectra. Elastic recoil detection measurements revealed an atomic concentration of 2.5% and 5.5% of carbon in the bulk of the Ta2O5 and Nb2O5 films. The presence of carbon did not appear to negatively affect the film optical and mechanical performance and stability. We discuss the relationship between the optical properties and microstructure, and the possible mechanism of carbon bonding in the form of chelate and bridging groups.

We systematically investigate the reactive behaviour of two types of high-power pulsed magnetron discharges above a Nb target using either square voltage pulses (denoted as HiPIMS) or custom-shaped pulses (denoted as MPPMS), and compare it with that of a dc magnetron sputtering (DCMS) discharge. We demonstrate that the surface metal oxides can be effectively sputter-eroded from the target during both HiPIMS and MPPMS pulses operated in reactive O₂/Ar gas mixtures, and that sputtering from a partially oxide-free target is possible even at high oxygen concentrations. This results in a hysteresis-free deposition process which allows one to prepare optically transparent high refractive index Nb₂O₅ coatings exhibiting an elevated deposition rate without the need for feedback control commonly used in reactive DCMS. The cathode voltage was identified as the principal parameter that affects the reactive discharge behaviour.

Time- and space-resolved optical emission spectroscopy and fast imaging were used for the investigation of the plasma dynamics of high-power impulse magnetron sputtering discharges. $200\mu \text{s}$ pulses with a 50 Hz repetition frequency were applied to a Cr target in Ar, ${\text{N}}_2$ , and ${\text{N}}_2/\text{Ar}$ mixtures and in a pressure range from 0.7 to 2.66 Pa. The power density peaked at $2.2–6\text{kW}{\text{cm}}^{-2}$ . Evidence of dominating self-sputtering was found for all investigated conditions. Up to four different discharge phases within each pulse were identified: (i) the ignition phase, (ii) the high-current metal-dominated phase, (iii) the transient phase, and (iv) the low-current gas-dominated phase. The emission of working gas excited by fast electrons penetrating the space in-between the electrodes during the ignition phase spread far outwards from the target at a speed of $24\text{km}{\text{s}}^{-1}$ in 1.3 Pa of Ar and at $7.5\text{km}{\text{s}}^{-1}$ in 1.3 Pa of ${\text{N}}_2$ . The dense metal plasma created next to the target propagated in the reactor at a speed ranging from 0.7 to $3.5\text{km}{\text{s}}^{-1}$ , depending on the working gas composition and the pressure. In fact, it increased with higher ${\text{N}}_2$ concentration and lower pressure. The form of the propagating plasma wave changed from a hemispherical shape in Ar, to a droplike shape extending far from the target in ${\text{N}}_2$ . An important ${\text{N}}_2$ emission rise in the latter case was detected during the transition at the end of the metal-dominated phase.