Aggregation dynamics of molybdenum-based precursors in rarefied carrier gas mixtures under sub-nucleation conditions

Precise control of fluid flow and chemical reactions under low-pressure conditions is critical for next-generation semiconductor manufacturing, where vapor-phase transport of precursor molecules governs the quality and reliability of thin-film deposition. Among emerging alternatives to conventional metals, transition metal-based compounds are gaining attention due to their favorable thermal and structural properties. In particular, molybdenum oxychloride molecules are being explored for their stability and compatibility with high-temperature processes. However, the behavior of these precursor gases in rarefied environments remains poorly understood, especially concerning spontaneous aggregation and its impact on uniformity and defect formation. This study investigates the aggregation dynamics of gas-phase molybdenum oxychloride species using atomistic simulations under varying thermodynamic conditions relevant to semiconductor processing. We explore the influence of temperature, pressure, molecular ratio, and initial density on the formation and dissociation of molecular clusters. To quantify aggregation behavior, we track the evolution of cluster size distributions and assess the likelihood and timescales of large-cluster formation. The analysis reveals that aggregation is favored at lower temperatures and higher densities, while larger clusters tend to dissociate rapidly under thermodynamically unfavorable conditions. The results indicate no persistent critical cluster size, but transient aggregation events may influence deposition outcomes. These findings provide new insights into the gas-phase behavior of transition metal precursors under low-pressure conditions and offer guidance for optimizing process parameters in vapor-phase fabrication techniques.