Properties, Preparation And Applications Of Self-assembled Monolayers On Silicon/Silica Surfaces

Self-assembled monolayers (SAMs) have experienced huge growth in recent years as a new class of functional materials in heterogeneous catalysis, biosensing, semiconductor fabrications and in other fields. SAMs about the alkylsiloxane monolayers can be bonded on the hydroxylated silica surface and used as diffusion barriers of copper connection in the ultra large scale integrated (ULSI) circuit fabrication. In this paper, we firstly optimized six models of alkylsiloxane SAMs with different terminal groups and different chain length assembled on different silica crystalline planes to analyze the influence of these elements on the SAMs' properties using molecular dynamics (MD) simulation method. Then we synthesised CN-SAM using 2-cyanoethyl triethoxysilane and transformed cyano terminal functional group to the carboxylic group to form COOH-SAM. Then chemical vapor deposited (CVD) copper films on SiO2/Si(100) substrate based on a MOCVD (metalloorganic chemical vapor deposition) system with CuⅡbis-hexafluoroacetyl acetonate [CuⅡ(hfac)2] as precursor, and hydrogen as carrier gas and reactant. At last, compared the properties of deposited copper films on the SiO2 substrate before and after modified with the SAMs.It is mainly composed of the following five parts:Chapter 1:Briefly introduced the background and the challenge of the alkylsiloxane monolayers act as the copper diffusion barriers, and the ideas and study content of this paper.Chapter 2:Studied the influence of the hydroxyl distribution on silica surface, the chain length, the terminal groups of alkylsiloxane and the interface connection styles on the self-assembling of alkylsiloxane on the hydroxylized silica surface using molecular dynamics simulation method. The results revealed that, the stabilization and the structure properties were greatly influenced by these factors. On the crystalline planes with sparse hydroxyl groups, the SAMs took the single-linking mode. When the hydroxyl groups were dense, the interface connection could take single-linking or cross-linking styles. The single-linking SAMs were ordered only when the chains were long, and the cross-linking SAMs could be ordered when the chains were short. The thickness of the SAMs shown that, only the SAMs taken cross-linking mode had the similar thickness to the experimental values. The surface morphology of the SAMs proved that, the alkylsiloxane assembled on the hydroxylized silica surface was able to form smooth and ordered monolayers, especially the long-chain SAMs in single-linking mode and the short-chain SAMs in cross-linking mode. The results also suggested that, one could use the silica surface with high dense hydroxyl groups and prolong the reaction time to get a fully hydrolyzed interface structure to obtain the high ordered and uniform thin monolayers.Chapter 3:The CN-SAM has been prepared via the adsorption of a short-chain 2-cyanoethyl triethoxysilane onto the hydroxylated surface of the SiO2/Si(100) substrates and modified into the COOH-SAM through simple hydrolysis reaction. The SAMs of cyano terminal functional group was wet chemically absorbed onto the substrate from a 5 mM solution of 2-cyanoethyl triethoxysilane in toluene for 6 h, then immersed into wake acid at 75℃for at least 90 min to form COOH-SAM. The thickness of SAMs was about 0.7 nm. The SAMs were not destroyed by the hydrolysis reaction and were uniform and ordered with head groups of alkylsiloxane connected with the hydroxylized silica surface.Chapter 4:The characterizations of copper films deposited on CN-SAM and COOH-SAM modified SiO2 substrates by chemical vapor deposition technique were investigated. The consecutive and uniform copper films were obtained at the temperature of 380℃and the roughness of the films was small when deposited above this temperature, because the films became more uniform in that cases. The chemical structures of the films were determined by X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX), which behaved the valence of zero for the copper films deposited. Then the X-ray diffraction (XRD) analysis showed that Cu(111) was the preferential growth orientation for chemical vapor deposited copper films, which was helpful to reduce the RC delay caused by electromigration.Chapter 5:The properties of copper films on OH-SiO2, CN-SAM/SiO2, COOH-SAM/Si02 substrates were compared using experiment and Quantum mechanics calculation methods. Copper films deposited on the modified substrates were much easier and the nuclei density of copper deposited on the CN-SAM was lower than that on the COOH-SAM, while in contrary, the copper grains of the former was bigger than that of the latter, which was because that the interaction energies between copper and the SAMs were bigger than that of without SAMs, and the stable states of copper and CN-SAM were less than that of copper and COOH-SAM. SAMs not only could prevent the diffusion of copper atoms, but also could enhance the interaction of copper and substrate.