Influence of substrate bias voltage on the properties of CNx films prepared by reactive magnetron sputtering

Abstract

In the present work, we systematically study the effect of radio frequency induced negative substrate bias voltage, Ub, on the characteristics of CNx films fabricated by direct current (dc) magnetron sputtering of a graphite target in a nitrogen plasma. CNx films, typically 1–2 μm thick, were deposited onto Si(100) substrates at a temperature of 600 °C and at a pressure of 0.5 or 5 Pa. The films’ microstructure and composition were evaluated using elastic recoil detection analysis, Fourier transform infrared spectroscopy, Raman scattering, x-ray diffraction, and atomic force microscopy. The films were found to be amorphous and partially conductive. The nitrogen concentration in the films varied between 12 and 24 at. %. Increasing the |Ub| values from 300 to 700 V resulted in increasing the N/C ratio, while the hydrogen content in the bulk decreased from 5 to 1 at. %. The latter effect clearly demonstrates the sputter-cleaning process during the ion-assisted deposition. Increasing the |Ub| values also resulted in an increase in film density from 1.5 to 2.7 g/cm3, and in a decrease in surface roughness from 13 to 2 nm. This densification was accompanied by an increased hardness (from 2 to 23 GPa), and elastic recovery (from 35% to 74%), and by higher adhesion to the silicon substrate. |Ub| values higher than 700 V lead to the degradation of the films mechanical properties. Even at its low concentration, hydrogen was found to be directly related to the film quality. We suggest that the presence of hydrogen inhibits interconnection of graphite-like planes containing carbon and nitrogen, which may hamper formation of possible fulerene-like microstructure described in recent literature.

Effect of implanted argon on hardness of novel magnetron sputtered Si–B–C–N materials: experiments andab initiosimulations

“…In the former case, the hardness is higher for the materials deposited at U b = −500 V, possibly due to a stronger bombardment by nitrogen ions which leads to ion-induced knock-on subplantation of film-forming particles, resulting in densification of the deposited materials. The same behaviour was observed also for other amorphous films, such as CN x [30], prepared in a pure N 2 . As can be seen in figure 5, the successive increase of the material hardness with an increasing Ar fraction in the gas mixture is much more pronounced at U b = −100 V. Thus films deposited with a high Ar fraction in the gas mixture have a higher hardness at U b = −100 V. Our simulations indicate that the level of Ar incorporation in the films at U b = −500 V is too high to allow substantial Si segregation.…”

Mechanical and optical properties of quaternary Si–B–C–N films prepared by reactive magnetron sputtering

“…2b), which result in densification of the deposited materials [36,37]. In our previous work dealing with sputter-deposited C-N [6,38] and Si-C-N [39] films the increased hardness was also correlated with enhanced ion-induced desorption of loosely bonded C-N species from the surface of the growing films and with a decreased residual concentration of hydrogen (observed also in this worksee Fig. 2b).…”

Growth, structure, and mechanical properties of CNxHy films deposited by dc magnetron sputtering in N2/Ar/H2 discharges

“…For example, in industrial-scale depositions there is often a high H 2 and H 2 O background pressure that could seriously affect the resulting film composition and thereby its properties. This was recently shown by Hajek et al, 21 who found that the properties of magnetron sputtered CN x films grown in a high vacuum ͑HV͒ environment could be correlated to the unintentionally added hydrogen concentration in the films. In this study we have intentionally added hydrogen during growth, in an ultrahigh vacuum ͑UHV͒ chamber, of carbon and carbon nitride films by magnetron sputtering.…”

“…9,10,13,14,21 Therefore it has been difficult to determine critical values for the hydrogen concentration at which the properties of the films start to deteriorate, e.g., with respect to hardness and elasticity. Furthermore, even if the presence of hydrogen does not seem to promote the formation of crystalline structures or increase the nitro- gen concentration, it is still important to understand how hydrogen may influence the growth and structure of CN x films.…”