Surface Deposition of Diethyl Phthalate on SiO₂ and Si₃N₄ Wafers in Simulated Cleanroom Environment

The surface deposition kinetics of airborne diethyl phthalate (DEP), a representative compound for high-boiling-point organic contaminants in cleanroom environments, were investigated in this study. Between the two types of wafer surfaces evaluated, wafer surfaces with oxide (SiO₂) and wafer surfaces with nitride (Si₃N₄), DEP exhibited a stronger propensity to absorb on the SiO₂ wafers, presumably due to the greater dipole moment between DEP and SiO₂ surfaces. Under well-controlled exposure conditions, the rate parameters of a theoretical surface kinetic model were determined by employing a heuristic algorithm for numerical optimization to match the experimental profile. Subsequently, a series of time-dependent surface DEP concentrations were simulated and validated with the experimental data under various ambient concentrations. Estimation of the allowable wafer exposure durations and the maximum ambient concentrations were exemplified based on the guideline recommended by the International Technology Roadmap for Semiconductors (ITRS).¹