A New Generation Of Integrated Circuits Cu Interconnect Ta-based Diffusion Barrier Preparation And Characterization

With the developent of IC processing technology, Copper(Cu) hasbeen used as interconnector in advanced metallization systems to replacetraditional Aluminum(Al). Although this attractive replacement has beenachieved higher operation speed and reliability of device, contaminationof Cu diffusion is inevitable. Searching appropriate diffusion barrier hasbeen a hot research topic of Cu interconnection technology for years.At first, technological development and challenges of Cuinterconnection are reviewed, also, fabrication methods and developmenttrends of diffusion barrier are given. Then, Ta, TaN_x, Ta-Al-N and Cu/Ta,Cu/TaN_x, Cu/Ta-Al-N multilayers are deposited on p-type Si substratesby DC magnetron sputtering, rapid thermally annealed(RTA) by tungstenhalide lamp, the surface morphology and properties of the thin-films areinvestigated by four-point probe(FPP) sheet resistance measurement,AFM, SEM-EDS, Alpha-step IQ Profilers and XRD.The experimental results show that the surfaces of deposited Ta,TaN_x and Ta-Al-N nanoscale thin-films are smooth. The barrierproperties against Cu diffusion are gradually enhanced from Ta, TaN_x toTa-Al-N. N doping enhances the formation of nanocrystalline oramorphous thin-film and eliminates the interface reaction of TaN_x/Si,while Al doping increases crystallization temperature of TaN_x and keepsthe film amorphous for more severe annealing conditions, so thethermochemical stability and diffusion barrier property of thin-film areimproved. The formation of TaSi₂ resulted from interface reaction atTa/Si and Cu₃Si due to Cu diffusion along Ta grain boundaries towards Simake Ta barrier failed at low annealing temperature. The failure of TaN_xis mainly attributed to the formation of Cu₃Si on Ta/Si interface which isresult of Cu diffusion along the grain boundaries of polycrystalline TaNafter annealing. The failure mechanism of Ta-Al-N is similar to TaN_x,that is, Cu diffusion along grain boundaries which is due to crystallizedthin-film.The fabrication and diffusion barrier property of nanoscale Ta-Al-N thin-films with important prospect for application are investigated for thefirst time in this paper. Based on theoretical analysis and experimentaldata, micro- mechanism of N, Al doping and comparison of Cu diffusionbarrier property about three kinds of Ta-based thin-films are investigated.Light atoms N operating as stuffing at existing grain boundaries couldreduce the density of diffusion paths and improve diffusion barrierproperty effectively, also nanocrystalline or amorphous is favorablemicro-structure for Cu diffusion barrier.