Vapor- and impurity-controlled growth regimes during deposition of thin noble metal films on weakly-interacting substrates

Abstract

We study the effect of impurities on the morphological evolution of thin silver (Ag) and copper (Cu) films deposited by direct current and high-power impulse magnetron sputtering on weakly-interacting silicon dioxide and amorphous carbon substrates. We systematically vary the ratio of impurity-to-metal particle flux $\frac{J_{\mathrm{imp}}}{J_{\text{metal}}}$ arriving at the substrate in the range $\sim {10}^{-4}-10$ and assess the character of film morphological evolution and the overall growth dynamics by means of real-time in-situ diagnostic tools and ex-situ analyses. We find that both thin-film materials exhibit a three-dimensional morphological evolution, which for the case of Ag is governed by the effect of metal vapor flux magnitude on the dynamic competition among island nucleation, growth, and coalescence (vapor-controlled growth regime). At all deposition conditions, small amounts (of the order of $1\mathrm{at}.\%$) of impurities (comprising oxygen, carbon, and hydrogen) are incorporated in the Ag films, while an increase of $\frac{J_{\mathrm{imp}}}{J_{\text{metal}}}$ suppresses three-dimensional growth for layers deposited on silicon dioxide. Cu exhibits a similar (vis-à-vis Ag) behavior with respect to the overall morphology and impurity incorporation for $\frac{J_{\mathrm{imp}}}{J_{\text{metal}}}$ below a critical value of $\sim 1$. For $\frac{J_{\mathrm{imp}}}{J_{\text{metal}}}$ above $\sim 1$, the impurity content in the Cu layers increases sharply (reaching $\sim 10\mathrm{at}.\%$ for $\frac{J_{\mathrm{imp}}}{J_{\text{metal}}}\sim 10$) and film morphological evolution is seemingly determined by the effect of impurities on the fundamental structure-forming process of island nucleation, grain growth, and crystal growth (impurity-controlled growth regime).