SiNx coatings deposited by reactive high power impulse magnetron sputtering: Process parameters influencing the residual coating stress

Abstract

The residual coating stress and its control is of key importance for the performance and reliability of silicon nitride (SiNx) coatings for biomedical applications. This study explores the most important deposition process parameters to tailor the residual coating stress and hence improve the adhesion of SiNx coatings deposited by reactive high power impulse magnetron sputtering (rHiPIMS). Reactive sputter deposition and plasma characterization were conducted in an industrial deposition chamber equipped with pure Si targets in N2/Ar ambient. Reactive HiPIMS processes using N2-to-Ar flow ratios of 0 and 0.28–0.3 were studied with time averaged positive ion mass spectrometry. The coatings were deposited to thicknesses of 2 μm on Si(001) and to 5 μm on polished CoCrMo disks. The residual stress of the X-ray amorphous coatings was determined from the curvature of the Si substrates as obtained by X-ray diffraction. The coatings were further characterized by X-ray photoelectron spectroscopy, scanning electron microscopy, and nanoindentation in order to study their elemental composition, morphology, and hardness, respectively. The adhesion of the 5 μm thick coatings deposited on CoCrMo disks was assessed using the Rockwell C test. The deposition of SiNx coatings by rHiPIMS using N2-to-Ar flow ratios of 0.28 yield dense and hard SiNx coatings with Si/N ratios <1. The compressive residual stress of up to 2.1 GPa can be reduced to 0.2 GPa using a comparatively high deposition pressure of 600 mPa, substrate temperatures below 200 °C, low pulse energies of <2.5 Ws, and moderate negative bias voltages of up to 100 V. These process parameters resulted in excellent coating adhesion (ISO 0, HF1) and a low surface roughness of 14 nm for coatings deposited on CoCrMo.

Si–Fe–C–N Coatings for Biomedical Applications: A Combinatorial Approach

“…A particularly promising coating material is amorphous silicon nitride [16][17][18][19][20][21][22][23][24][25] as bulk silicon nitride was shown to be biocompatible [26][27][28][29][30] and slowly dissolves in water-based solutions [19,20,[31][32][33]. Small, soluble, and biocompatible wear particles have the potential to reduce the negative immune response and prolong the implant lifetime.…”

The Effect of N, C, Cr, and Nb Content on Silicon Nitride Coatings for Joint Applications

“…As can be seen, coatings deposited with a higher target power showed lower L C2 values. This was due to higher residual stresses resulting from a higher N content and the increase in Si-N bonds [45,48]. Moreover, these coatings showed a generally denser morphology (data not shown), which in turn contributed to increased residual stresses [66], as demonstrated previously [48].…”

“…In previous studies, we reported that the addition of C altered the surface reactivity of silicon nitride and influenced the coating density and surface morphology [44,45]. In addition, we have shown that an increased N content results in a higher hardness and density [46][47][48]. In this study, we investigated the effect of N, C, Cr, and Nb content, as well as ion energy, on the properties of silicon nitride (SiN x )-based coatings for joint applications, with a focus on their wear performance in a hard-on-soft contact, since, as mentioned above, the counter surface in a joint implant is usually a polyethylene polymer.…”

“…The SiN x coatings that performed well were very dense and, thus, had low O and C contents, but also displayed more residual stresses. Likewise the coatings that did not perform well were less dense and contained more O and C (by adsorption) [48].…”

Preface to Special Topic: Reactive high power impulse magnetron sputtering

“…Ganesan et al 15 demonstrate that it is possible to tune the optical and electrical properties of hafnium oxide, tungsten oxide, and tungsten oxynitride coatings by varying the HiPIMS pulse length and therefore the duty cycle. The deposition process parameters that can be used to tailor the residual coating stress in order to improve the adhesion of SiN x coatings deposited by reactive HiPIMS are investigated by Schmidt et al 16 The angular distribution of plasma parameters and the resulting thin film characteristics were explored for Ar/O 2 HiPIMS discharge while varying the under growth angles with respect to the target surface when growing the TiO 2 film. 11 The deposition rates were found to be the largest in the forward directions and decrease towards large inclination angles and thus a pronounced anisotropy in the film deposition process and of the deposited layer structure.…”