Cu/low-k extendability work compares Cu and Al anodes

(September 10, 2010) — Professor Joel Plawsky and student Michael Riley of Rensselaer Polytechnic Institute will be presenting a paper titled “Experimental analysis of copper diffusion into porous SiCOH” at the Techcon 2010 conference. In a podcast interview, they outline the scope of their interconnect research on copper and porous SiCOH and its significance to the industry.

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Figure 1. A comparison of the breakdown voltages using aluminum and copper anode materials. This test is similar to a traditional I-V test but testing is carried out over a range of voltage ramp rates. If the anode is inert, failure should occur due to electron and/or hole trap creation and so the breakdown field should be independent of the voltage ramp rate. If the anode is reactive and injects metal ions into the dielectric, then the breakdown field should depend upon the ramp rate since slower ramp rates allow more time for metal ion injection and drift. The data support this scenario and as the ramp rate increases, the breakdown fields for both anode materials converge to a single, asymptotic value. The process and the model developed to reproduce the behavior allows us to tie I-t and I-V testing into a single mathematical framework and to describe the results of such tests using a single breakdown mechanism.

Among the data being presented, the researchers compared breakdown voltages using aluminum and copper anode materials (Fig. 1). “This test is similar to a traditional I-V test, but testing is carried out over a range of voltage ramp rates,” notes Plawsky. “If the anode is inert, failure should occur due to electron and/or hole trap creation and so the breakdown field should be independent of the voltage ramp rate.” Additionally, if the anode is reactive and injects metal ions into the dielectric, then the breakdown field should depend upon the ramp rate since slower ramp rates allow more time for metal ion injection and drift, according to the scientists. The researchers note that the data support this scenario and as the ramp rate increases, the breakdown fields for both anode materials converge to a single, asymptotic value. “The process and the model developed to reproduce the behavior allow us to tie I-t and I-V testing into a single mathematical framework, and to describe the results of such tests using a single breakdown mechanism.”

Figure 2. A fit of RPI’s Cu ion mass transport model to the experimental data shows promising accuracy, even considering the model parameters were based on SiO2 values while the dielectric was a SiCOH-based material. The general trends in the experimental data were reproduced but more work is necessary to improve the fit. With more experimental data, we hope to be able to use the model and the variable voltage ramp procedure to extract values for the solubility and diffusivity of cu ions in SiCOH-based materials. This will help validate the mass transport mechanism and provide a valuable tool for estimating the breakdown conditions of future low-k dielectrics and tying their breakdown behavior to their materials chemistry.

In Figure 2, the researchers fit their Cu ion mass transport model to the experimental data and note that it shows promising accuracy, “Even considering the model parameters were based on SiO2 values, while the dielectric was a SiCOH-based material,” comments Plawsky. He adds that the general trends in the experimental data were reproduced but more work is necessary to improve the fit. With more experimental data, the researchers hope to be able to use the model and the variable voltage ramp procedure to extract values for the solubility and diffusivity of Cu ions in SiCOH-based materials. “This will help validate the mass transport mechanism and provide a valuable tool for estimating the breakdown conditions of future low-k dielectrics and tying their breakdown behavior to their materials chemistry.”

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