Comparison of Silatrane-Based Molecular Nanolayers on Si as Adhesion Promoter and Diffusion Barrier

Si on-chip Cu metallization plays a vital role in advanced integrated-circuit packaging process. Key reliability concerns of evaluating Si/SiO2/Cu heterojunctions include adhesion property and diffusion barrier performance. Molecular self-assembling is a promising method to form a bifunctional molecular nanolayer at the SiO2/Cu heterojunction as an adhesion promoter and diffusion barrier. However, the self-polymerization tendency of organosilane molecules hinders the formation of a uniform nanolayer. In this study, amine- and carboxyl-terminated silatranes are deposited on the SiO2/Si substrate to form the molecular nanolayers for subsequent Cu metallization. Due to controlled molecular assembly capability, both silatranes can form a highly ordered molecular nanolayer, as validated by X-ray photoelectron spectroscopy and ellipsometer. In comparison, the carboxyl-terminated silatrane demonstrates a superior interfacial adhesion strength of 12.26 MPa, which is notably higher than that of its amine-terminated counterpart (9.35 MPa). The carboxyl-terminated silatrane also exhibits superior diffusion barrier performance, suppressing the formation of Cu silicides up to 500 °C, which is higher than that of the amine-terminated counterpart (450 °C). The exceptional performance of carboxyl-terminated silatrane is attributed to its unique molecular structure and electronic properties, as validated by density functional theory calculations. Carboxyl-terminated silatrane enables functional and controllable silanization on SiO2 surface, paving the way for its application as a key interlayer material in next-generation integrated-circuit packaging.