Effects Of Organic Functional Groups Of Self-assembled Monolayers On Chemical Vapor-deposited Copper Films

Copper is the preferred metal for creating multilevel interconnect structures in ultra-large-scale-integrated circuits (ULSI) because of its high electrical conductivity and electromigration resistance. In Cu-interconnected sub-100 nm devices structures, <5-nm-thick interfacial layers are required to inhibit Cu diffusion into adjacent dielectrics, and to enhance interfacial adhesion. Currently used interfacial barrier materials such as Ta, TaN, and TiN, deposited by conventional methods cannot form uniform and continuous layers below 10 nm thickness, especially in high depth-to -width aspect ratio features.Self-assembled molecular layers (SAMs) have been widely studied due to their attractive properties, which can be tuned through suitable choice of chain length and terminal groups, for a number of applications such as molecular devices, lithography, and micromachines. Hence, sub-nanometer-thick SAMs can be used to enhance both diffusion barrier and adhesion properties of Cu/SiO₂ interfaces through strong local chemical interaction between interfacial Cu and the terminal groups of SAMs.This research was based on a MOCVD (metalorganic chemical vapor deposition) system, which was designed and built personally. Cu^(II)(hfac)₂ was used as precursor, and hydrogen was served as carrier gas and reactant. Copper thin films were deposited on 2-[2-(trimethoxysilyl) ethyl] pyridine (TMSEP) and n-propyltrimethoxy-silane (PTMS) modified substrates. Then, the properties of the copper films were studied and compared. There are mainly three parts as follows:First, copper films deposited on PTMS-SAMs modified substrates by chemical vapor deposition were studied. It is found that: The interaction between Cu and methyl groups is van der Waals force, which belongs to a weak interaction. So Cu aggregates on the PTMS-SAMs surface because the lack of immobilization by the functional groups. The increasing effect caused by PTMS-SAMs on inhibiting Cu ionization and transport attributes to the creation of a vacuum-like potential barrier between the Cu and the dielectric layer by the alkyl chains.Second, copper films deposited on TMSEP-SAMs modified substrates by chemical vapor deposition were studied. It is found that: the main interaction between Cu and 2-pyridyl is the conjugation provided by aromatic rings. It prevents Cu diffusion and increases adhesion effectively. The CVD process include two regimes: kinetics control regime and mass transfer control regime. The converting temperature is 350℃. The coalescence of copper films follows 'filling in'mode, which is benefit to form uniform copper films.Third, copper films deposited on different substrates were analyzed and compared. It is found that: SAMs can inhibit Cu diffusion into adjacent dielectrics and enhance interfacial adhesion through the interaction between interfacial Cu and the terminal groups of SAMs. The functional groups have a certain effect on the nucleation and growth of Cu. The location of reaction sites of the functional groups also has a certain effect on Cu CVD. If the reaction sites are covered by other atoms, the reaction between Cu and functional group would be prevented.