State of the art manufacturing of semiconductor devices involves the electrodeposition of copper for on-chip wiring of integrated circuits. In the Damascene process interconnects are fabricated by first patterning trenches in a dielectric medium and then filling by metal electrodeposition over the entire wafer surface. This metalization process, pioneered by IBM, depends on the use of electrolyte additives that effect the local metal deposition rate.
The additives in the electrolyte affect the local deposition rate in such a way that bottom-up filling occurs in trenches or vias. This process, known as superconformal electrodeposition or superfill, is demonstrated in the following figure. The figure shows sequential images of bottom-up superfilling of submicrometer trenches by copper deposition from an electrolyte containing PEG-SPS-Cl. Preferential metal deposition at the bottom of the trenches followed by bump formation above the filled trenches is evident.
This process has been demonstrated to depend critically on the inclusion of additives in the electrolyte. Recent publications propose Curvature Enhanced Accelerator Coverage (CEAC) as the mechanism behind the superfilling process [NIST:damascene:2001]. In this mechanism, molecules that accelerate local metal deposition displace molecules that inhibit local metal deposition on the metal/electrolyte interface. For electrolytes that yield superconformal filling of fine features, this buildup happens relatively slowly because the concentration of accelerator species is much more dilute compared to the inhibitor species in the electrolyte. The mechanism that leads to the increased rate of metal deposition along the bottom of the filling trench is the concurrent local increase of the accelerator coverage due to decreasing local surface area, which scales with the local curvature (hence the name of the mechanism). A good overview of this mechanism can be found in [moffatInterface:2004].
Example 1 provides a simple way to use FiPy to model the superfill process. The example includes a detailed description of the governing equations and feature geometry. It requires the user to import and execute a function at the python prompt. The model parameters can be passed as arguments to this function. In future all superfill examples will be provided with this type of interface. Example 2 has the same functionality as 1 but demonstrates how to write a new script in the case where the existing suite of scripts do not meet the required needs.
In general it is a good idea to obtain the Mayavi plotting package for which a specialized superfill viewer class has been created, see Installation. The other standard viewers mentioned in Installation are still adequate although they do not give such clear images that are tailored for the superfill problem. The images below demonstrate the Mayavi viewing capability. Each contour represents sequential positions of the interface and the color represents the concentration of accelerator as a surfactant. The areas of high surfactant concentration have an increased deposition rate.