| Summary: | 碩士 === 國立虎尾科技大學 === 材料科學與綠色能源工程研究所 === 97 === As the feature size in ultra-large scale integration (ULSI) continues to scale down, the liner resistance has dominated the performance of multilevel interconnection beyond the 45 nm technology node. The traditional tungsten contact plug is therefore facing challenges because of its high resistivity; and several works have reported on the replacement of tungsten (W) with copper (Cu) as a contact plug recently. However, Cu as a contact plug material is suffering a serious diffusion issue. Hence, an effective diffusion barrier layer must be implemented between Cu and its contact material to prevent the penetration of Cu and enhance the adhesion with Si/SiO2. Nevertheless, the current tantalum/tantalum nitride (Ta/TaN) diffusion barrier/liner for Cu interconnects encounters scaling difficulties at the 45 nm node. The Ru film allows for direct electroplating copper layer. Therefore, Ru has potential to be used as a diffusion barrier for Cu interconnection.
Part 1: This study aims at evaluating Ru barrier on NiSi/Si for Cu contact metallization. The diffusion barrier properties of the studied films were elucidated using four-point probe (FPP), x-ray diffraction (XRD), scanning electron microscopy (SEM), Energy Dispersive Spectrometer (EDS), Auger electron spectroscopy (AES) and transmission electron microscopy (TEM). The studied Cu/Ru/Ni/Si, Cu/Ru/Ni(Ru)Si/Si, Cu/NiSi/Si and Cu/Ru/NiSi/Si stacked films have the failure temperatures of 550˚C, 600˚C, 600˚C and 650˚C, respectively. Structural analysis indicated that the failure mechanism involved the Cu penetrating through Ru/NiSi stacked film at a specific temperature, inducing the accelerated dissociation of the NiSi. Interposing a Ru layer between Cu and NiSi/Si prevented the intermixing effectively, and rather improved the thermal stability in the Cu/NiSi/Si stack films.
Part 2: Ru-Ta-C films were prepared on p-type Si(100) substrate by magnetron cosputtering using Ru and TaC targets. The film properties were elucidated using a FPP, XRD, AES, and TEM. The electrical resistivity of Ru-Ta-C films is between 92~278 μΩ cm. The composition and electrical resistivity of the film can be easily controlled by adjusting sputter power ratio. Incorporation of Ta and C can drcrease the crystallinity of Ru grain.
Part 3: This part aims at developing an ultrathin Ru-Ta-C barrier for copper metallization. In a sandwiched scheme Cu/barrier(10 nm)/Si, Ru77Ta15C7 barrier exhibits a superior thermal stability up to an annealing temperature of 700˚C/30 min. The Cu/Ru(5 nm)/TaC(5 nm)/Si sample has a failure temperature of 650˚C/30 min. The results also demonstrated Cu can be direct electrochemical deposition on 5 nm Ru-Ta-C films.
Because of the high compatibility of Ta and C to IC fabrication, the Ru-Ta-C thin film is a promising diffusion barrier for Cu metallization in the sub-45-nm IC processing.
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