Exposure assessment of process by-product nanoparticles released during the preventive maintenance of semiconductor fabrication facilities

This study characterized the process by-product particles (mostly nanoparticles) released during the preventive maintenance of semiconductor fabrication facilities, such as chemical mechanical planarization (CMP), plasma-enhanced chemical vapor deposition (PECVD), and ion implantation. Manual sampling and real-time measurements with direct reading instruments were conducted to assess the exposure levels of nanoparticles and their physical and chemical properties. Significant amount of nanoparticles were observed in the breathing zone of the workers during the maintenance of the PECVD and ion implanters with the peak number concentrations as high as 6,470,000 and 65,444 #/cm³, respectively, indicating that the deposited residual chemicals in the reaction chambers were released as airborne nanoparticles by the maintenance activities. In contrast, nanoparticles released during the maintenance of the local scrubber, CMP, and replacing CMP slurry drums were insignificant. Causes of the particle release were discussed and suggestions were made to mitigate the nanoparticle release and reduce the exposure levels.     

Functionalization of (<Emphasis Type="Italic">n</Emphasis>, 0) CNTs (<Emphasis Type="Italic">n</Emphasis> = 3–16) by uracil: DFT studies

Density functional theory (DFT) calculations were performed to investigate stabilities and properties for uracil (U)-functionalized carbon nanotubes (CNTs). To this aim, the optimized molecular properties were evaluated for (n, 0) models of CNTs (n = 3–16) in the original and U-functionalized forms. The results indicated that the dipole moments and energy gaps were independent of tubular diameters whereas the binding energies showed that the U-functionalization could be better achieved for n = 8–11 curvatures of (n, 0) CNTs. Further studies based on the evaluated atomic-scale properties, including quadrupole coupling constants (C _Q ), indicated that the electronic properties of atoms could detect the effects of diameters variations of (n, 0) CNTs, in which the effects were very much significant for the atoms around the U-functionalization regions. Finally, the achieved results of singular U, original CNTs, and CNT-U hybrids were compared to each other to demonstrate the stabilities and properties for the U-functionalized (n, 0) CNTs.     

Tunability of electronic and optical properties of the Ba–Zr–S system via dimensional reduction

Transition metal sulfide perovskites offer lower band gaps and greater tunability than oxides, along with other desirable properties for applications. Here, we explore dimensional reduction as a tuning strategy using the Ruddlesden–Popper phases in the Ba–Zr–S system as a model. The three-dimensional perovskite BaZrS₃ is a direct gap semiconductor, with a band gap of 1.5 eV suitable for solar photovoltaic application. However, the three known members of the Ruddlesden–Popper series, are all indirect gap materials, and additionally have lower fundamental band gaps. This is accompanied in the case of Ba₂ZrS₄ by a band structure that is more favorable for carrier transport for oriented samples. The layered Ruddlesden–Popper compounds show significantly anisotropic optical properties, as may be expected. The optical spectra show tails at low energy, which may complicate experimental characterization of these materials.