Showing papers by "Tomi Laurila published in 2001"

Effect of oxygen on the reactions in the Si/Ta/Cu metallization system

Abstract: The effect of oxygen on the reaction mechanisms in the Si/Ta/Cu metallization system was studied experimentally and by utilizing the thermodynamically assessed Ta–O binary system. It was presented that an interfacial tantalum oxide was formed between Cu and Ta and that it established an additional barrier layer for Cu diffusion. The formation of additional barrier layer was supported by the following observations: (i) No detectable amount of Cu was found from the Ta layer with the combined transmission electron microscopy and energy dispersive spectroscopy at temperatures as high as 650 °C. (ii) Secondary ion mass spectrometry measurements indicated that significant amount of oxygen was incorporated into the films already after the sputtering stage. (iii) 181Ta16O molecular ion signals were detected from the Ta/Cu interface, indicating that the additional layer was in fact some form of tantalum oxide. The diffusion of Cu through the Ta layer could not proceed until the interfacial oxide had been dissolved by the Ta matrix. Since the oxygen solubility in Ta matrix is high in the temperature range of interest, the interfacial oxide dissolution was kinetically controlled. It is to be noted that the threshold temperature range of the dissolution reaction was found to coincide with that of the β–Ta to the bcc-Ta transition, which was anticipated to enhance the kinetics of the dissolution.

Stability of TaC Diffusion BarrierBetween Si and Cu

Abstract: The reaction mechanisms and related microstructures in the Si/TaC/Cu metallization system have been studied experimentally and theoretically by utilizing ternary Si-Ta-C, Ta-C-Cu and Ta-C-O phase diagrams as well as calculated activity diagrams. With the help of sheet resistance measurements, Rutherford backscattering spectrometry, xray diffraction, scanning electron microscopy, and transmission electron microscopy, the metallization structure with the 70 nm thick TaC barrier layer was observed to fail completely at temperatures above 725 °C because of the formation of large Cu3Si protrusions. However, the formation of amorphous Ta layer containing significant amounts of carbon and oxygen was already observed at the TaC/Cu interface at 600 °C. This layer also constituted an additional barrier layer for Cu diffusion, which occurred only after the crystallization of the amorphous layer. The formation of Ta2O5 was observed at 725 °C with x-ray diffraction, indicating that the oxygen rich amorphous layer had started to crystallize. The formation of SiC and TaSi2 occurred almost simultaneously at 800 °C. The observed reaction structure was consistent with the thermodynamics of the ternary systems. The metallization structures with 7 nm and 35 nm TaC barrier layers failed above 550 °C and 650 °C, respectively, similarly because of the formation of Cu3Si. The high formation temperature of TaSi2 and SiC implies high stability of Si/TaC interface, thus making TaC layer a potential candidate to be used as a diffusion barrier for Cu metallization.