For the plasma exposure time, 5 s yielded the highest mass evolution, while exposure times longer than 10 s caused a slight decrease in the growth as shown in Fig. . This decline may be attributed to the fluorine content in Cu(hfac)₂, which leads to fluorine contamination in the films, weakening adhesion and causing substrate etching. This effect could also result from increased electron exposure of the surface, potentially facilitating the desorption of certain species from the adsorbed precursor. It should also be noted that the steep drop in the mass evolution during the plasma step seen in Fig. is in line with our previous QCM studies of e-CVD, and which is attributed to momentarily heating the QCM sensor by the conduction of plasma electrons through it. This is further discussed in section SIII in the supplementary material. The increase in mass evolution after plasma exposure suggests an additional mass gain within the chamber. This could be due to the redeposition of species leaving the reactor walls and the substrate surface, entering the plasma volume, being decomposed and deposited back on to the substrate. It should here be noted that the chamber walls are not heated and that some precursor condensation on them thus is expected. To study this, we used OES to identify the excited species in the plasma volume. The plasma mainly shows emission lines from excited argon atoms, with notable spectral lines of neutral argon (Ar (I)) at wavelengths of 696. and ionized argon (Ar (II)) at wavelengths of 399.4 nm, 433.9 nm. Additionally, the observed emission spectra contain spectral lines of neutral copper (Cu (I)) at 389.30, 405.03, 448.76, 450.96, 457.45, 464.91, 467.24 and 470.91 nm, and singly ionized copper (Cu (II)) emission at 385.33, 393.15 and 459.78 nm. Doubly ionized copper (Cu 2+ , Cu (III)) exhibit emission at 435.28 and 441.41 nm. Furthermore, optical emission from fluorine radicals (F (I)) is observed at 685.6, 703.7, and 712.8 nm, alongside emission from excited oxygen (O (I)) at 777.2 nm and 844.7 nm. The OES thus suggests substantial levels of Cu(hfac)2 being decomposed in the plasma in spite of the prior purge phase, which explains the increase in the mass evolution after the plasma pulse, observed in Fig. .