HF Transport Coefficients in Polymers Used for Microelectronic Applications

In order to better understand the sorption and outgassing mechanism of gases in relation to wafers containers (FOUP), we have measured HF gas transport coefficients for different FOUP polymers. Gas sorption is governed by surface adsorption, followed by diffusion and solubility. Cross contamination between FOUP and wafer occurs when polymers outgas contaminants into the surrounding environment. Diffusion is the key parameter to understanding cross contamination within the FOUP environment. In this work, we present the transport coefficients obtained for gaseous HF at cleanroom conditions (Patm, 21 ± 2°C & 40% RH) using the sorption kinetic method, based on Fick’s law, for thin films (<80μm) of polycarbonate (PC), polyetherimide (PEI) and a low absorbing polymer named Entegris Barrier Material (EBM) that constitute FOUPs. The resulting kinetic curves show Fick’s behavior, where obtained HF diffusion coefficients are between 3.7 X10-10 and 42 x10-12 cm2/s and are significantly lower than diffusion coefficients obtained for H2O using a gas permeation method. Nevertheless, the similar order of magnitude between the HF and the H2O permeability coefficients obtained by the two methods validates the sorption kinetic method. Finally, the obtained coefficients were used in numerical simulation in order to forecast polymer behavior.