Diffusivity and solubility of HF gas in polymers and nanocomposites used for automated handling containers of silicon substrates in microelectronic industry

Abstract

Thermoplastic boxes with internal clean mini-environment (ISO 14644–1:2015, class 2–3), called Front Opening Unified Pods (FOUP), are widely used in microelectronic fabrication for transport and handling of silicon substrates (named wafers) in order to minimize the negative impact of contaminants on integrated circuits. As a type of airborne molecular contaminants (AMC), hydrogen fluoride (HF) outgassed from freshly processed wafers and sorbed (adsorption and absorption) on/in FOUP's walls and then becomes a potential source for subsequent HF cross-contamination. Thin polymeric films which were comprised of available commercial FOUP materials were prepared by hot pressing. They were neat polymers (polycarbonate (PC), Entegris Barrier Materials (EBM)) and nanocomposites (polycarbonate/carbon powder (PCCP), polycarbonate/carbon nanotubes (PCCNT), and EBM/carbon nanotubes (EBMCNT)). The sorption and desorption kinetics of HF in polymers were experimentally established at ultralow HF concentration (part-per-billion-volume, ppbv) and cleanroom conditions (atmospheric pressure, 20 °C and 40%RH); such conditions mimicking fabrication process conditions. Having a polar group in polymeric chains, the PC, PCCP and PCCNT showed a higher affinity to HF rather than EBM and EBMCNT, which resulted in significantly increasing HF diffusivity (nearly two orders of magnitude, 10−10 versus 10−12 cm2.s−1) and HF solubility. The presence of embedded CNT in nanocomposites (PCCNT and EBMCNT) exhibited a significant increase of both HF diffusivity and solubility. Interestingly, based on desorption curves, it was determined that the sorbed HF in nanocomposites made with CNT was composed of two types (i) fixed-HF inside cylindrical voids of CNT and (ii) mobile-HF in polymeric bundle-chains. In addition, the obtained HF transport coefficients were applied as input data in numerical simulation model to simulate the HF concentration profiles and the evolution of HF uptake in FOUP walls in different scenarios.