Copper nucleation by chemical vapour deposition on organosilane treated SiO2 surfaces

Self-assembled monolayers of organosilanes deposited onto SiO2/Si substrate surfaces by either vapour-phase or wet chemical methods can act as ultrathin interfacial barriers which effectively prevent the diffusion of copper into the SiO2 dielectric, enhance its adhesion onto it and also offer the possibility of achieving selective copper chemical vapour deposition. The initial stages of copper nucleation by chemical vapour deposition on organosilane treated SiO2 surfaces at different substrate temperatures are investigated in detail by scanning electron and atomic force microscopy. The growth behaviour of copper clusters before coalescence is elucidated and analysed in detail. At temperatures below 190 °C nucleation occurs mostly on already formed copper clusters and coalescence is obtained due to an increase of the size of clusters in three dimensions. Above that temperature, secondary nucleation of smaller size clusters on the gaps among the larger clusters is observed, leading to coalescence almost in two dimensions. The stable clusters density initially increases with precursor injection time, passes through a maximum and then decreases, due to an increase at low temperatures of the size of clusters. An almost substrate temperature independent maximum clusters density which is obtained in the low temperatures region, indicates that nucleation of copper atoms occurs on surface defect sites which are assumed to be Cu(I) atoms. A low value of the apparent activation energy for nucleation, indicates higher affinity for copper chemical vapour deposition of the organosilane treated SiO2 as compared to TiN substrates used previously. At 200 °C, coalescence following the initial nucleation period, results in continuous films with low roughness and low average height, thus leading to the practical realization of a thin yet continuous film.