Mechanical Properties Of Copper Interconnect Structures And Research On Resistive Memory Based On Interconnect Structures

Metallization is one of the crucial parts in modern IC technology. Nowadays, copper has been widely adopted as a substitute for aluminum in the manufacture of ultra large-scale integrated circuits (ULSI). The mechanical properties of the Cu interconnection, such as hardness and elastic modulus, also significantly influence the performance and reliability of ICs. Therefore, the characterization of nanotribological properties of Cu/Ta/SiO2/Si multilayer thin films as a system turns out to be important in the evaluation of multilevel copper interconnects and nanoscale ICs.New memory technologies must be easily integrated into standard semiconductor process. The devices should be read out non-destructively, have low power consumption and high scalability. As a promising candidate for next generation nonvolatile memories, resistive random access memory (RRAM) can provide a simple structure and outstanding performance. The interests in studying the resistance switching materials will come from both academia and industry. RRAM cells fabricated on the interconnect structures show excellent compatibility with copper/aluminum back-end-of-line (BEOL). However, the material systems of such memory cells need to be enriched; the methods of characterization remain to be improved and the switching mechanism is still a matter of debate.In this context, the nanotribological properties of Cu/Ta/SiO2/Si multilayer system as well as RRAM cells based on interconnection structure were studied respectively, the following parts were included:1. Nanoindentation was adopted to investigate the compound hardness and elastic modulus of Cu/Ta/SiO2/Si multilayer thin film system. In order to reveal the structure variance, a residual indent was cut by FIB. The cross-section of the residual indent was observed by the scanning electron microscope (SEM), as well as the scanning ion microscope (SIM). It was found that an apparent fracture occurred in Si substrate and the multilayer thin film structure delaminated. Transmission electron microscope (TEM) analysis showed that the delamination occurred at the interface between the Ta layer and SiO2 layer of the residual indent. The different strain and the ability of elastic recovery of each material under stress are supposed to be the main reason of the delamination. 2. Conductive atomic force microscopy (CAFM) analysis has been proved to be an effective method for the investigation of local conductivity of CuxO based RRAM devices. The CuxO films were grown by plasma oxidation process at room temperature. Current mapping results showed that local filaments growth and dissolution during the switching process. The scaling potential of such devices was discussed based on the density and uniformity of the filaments. The Pt/CuxO/Cu terminal memory cells did not need any forming process to activate it, however, the high resistances and the set voltages scattered in a large extent during cycling, the mechanism behind this phenomenon has been explained from microcosmic aspect.3. Copper nitride film prepared by plasma immersion ion implantation (P?) was demonstrated to exhibit reversible resistance variance character. The nitrogen ion implantation process was carried out with progressively increased negative high voltage and single voltage, so as to controll the total nitrogen concentration and distribution in the CuxN film. By forming a gradually distributed nitrogen concentration in the Cu-nitride film, the nitride based memory devices show bipolar nature with a low operation voltage, forming-free characteristics, a distinguishable resistance ratio and a dependence on electrode materials. The bipolar switching behavior is attributed to the formation and rupture of conductive filaments within a cycle, which is confirmed by spreading resistance images. From the voltage step experiment, it was found that local conducting filaments might be formed by migration of Cuz+ ions under bias voltage. The properties of the Ni/CuxN/Cu memory cell, including programming speed, temperature dependence, endurance, retention and scalability, were discussed.4. AlN thin films were fabricated on Al interconnection by using P?and Pulse Laser Deposition (PLD), respectively. And their topography, crystal structure and chemical composition were investigated. By introducing top electrode metal Cu, a capacitor consisted of insulating layer AlN, sandwiched between Cu and Al was formed. The Cu/AlN/Al memory cells showed resistive switching behavior; however, the device performance has remained quite poor up to now and needs to be improved in the next future. Finally the application prospect of the AlN based RRAM cells are discussed.