Grafting low-k organic films onto copper surface by one-step electrografting method via aryldiazonium chemistry

Abstract

In the context of the continuous improvement of chip interconnection density and the further development of high-frequency communication, in order to better realize high frequency signal transmission, the interlayer dielectric insulating material between the chip interconnection layers needs to have a lower dielectric constant, so as to effectively avoid undesirable phenomena such as signal delay and crosstalk. The metal of the interconnection layer is mainly copper in the current chip Damascus Copper Interconnect Process, so it is not only limited to the preparation of insulating high performance films on the silicon surface, but also of great significance to prepare insulating films with low dielectric properties on copper. Researches have shown that the addition of polyhedral oligomeric silsesquioxane (POSS) to the polymer can make the material with higher thermal stability and mechanical toughness. Due to their desirable properties, POSS-containing polymers are expected to be further developed into high-performance electronic materials, such as interlayer dielectric materials with low-k dielectric properties. But POSS has also a major difficulty in application because of its insolubility in aqueous solution. In this experiment, we successfully covalently graft organic insulating films with POSS nanostructures on the surface of copper in an atmospheric environment by using the electrochemical grafting technology based on aryldiazonium salts. In the experiment, tetrahydrofuran and deionized water are used as mixed solvent, 4-Nitrobenzenediazonium tetrafluoroborate (NBD) as initiator, octavinylsilsesquioxane (OVS) as monomer, sodium dodecyl sulfonate (SDS) as surfactant and sulphuric acid (H2SO4) as acid regulating reagent to make the pH of the mixed solution less than 2. The initiator NBD receives the electrons provided by the cathode of the pulse power supply and reduces to nitrobenzene radical. The nitrobenzene radical further initiates the polymerization of OVS with vinyl groups, and then grows a film with POSS nano pores on the copper substrate. By means of micro infrared spectroscopy (IR), X-ray spectrometer (XPS), ellipsometer and atomic force microscope (AFM), it is further determined that the composition of the film is mainly the mixed structure of polynitrophenyl (PNP) and POSS. In addition, the content and dielectric constant of POSS in the film can be adjusted by adjusting the concentration ratio of initiator NBD and monomer OVS. The obtained insulating film has chemical bond connected with the substrate, and the film has good hydrophobic, dielectric and mechanical properties. Its dielectric constant is lower than that of traditional low k materials and some recently reported materials. This insulating film has good dielectric properties and comprehensive properties, which also means that it has potential commercial application value in the field of higher frequency communication such as 6G communication in the future.