Copper has been proposed as a possible replacement for aluminum as the primary microelectronics metallization material. As the feature sizes of ultralarge scale integration (ULSI) technologies reach sub-0.25 mu m in dimension, new metallization processes must be developed to properly fill the extreme topographies. This article uses GROFILMS (a thin film process simulator) to study the Cu reflow process. Comparison of simulation with experimental scanning and transmission electron micrographs show excellent agreement with regards to profile evolution and internal structure. GROFILMS is further used to study material dependent properties such as the underlayer wetting characteristics of Cu. Results show that during both the deposition and the anneal procedures, Cu’s ability to wet the underlayer can determine success or failure of the reflow process. Further, the effects of the film microstructure such as grain boundary grooving and facetting are simulated, observed in real films, and discussed in terms of process development. On the scale of ULSI features, the film texture is shown to be a significant factor in determining the success of copper reflow.