Aggregation and Removal of Impurity Nanoparticles via Insulator-Based Dielectrophoresis for Semiconductor Industry-Grade Material

As semiconductor dimensions continue to shrink and their structures become more complex, the requirement for ultra-high-purity chemicals in the processing stages has become more critical. During semiconductor processes, the generation of Si-based nanoparticles, especially silica (SiO₂), is prevalent. Even in trace amounts, nanoparticle contaminants can severely impact device performance and yield. The conventional purification methods for removing impurity particles, such as filtration, have reached their operational limits and no longer meet the purity standards required by the semiconductor industry. Consequently, there is a critical need to develop new purification strategies capable of removing sub-nanometer-sized impurities. Dielectrophoresis (DEP) refers to the movement of a polarizable particle in a non-uniform electric field. This method is useful for aggregating nanoparticles to region of higher electric field.
In this work, we demonstrated a novel purification approach using insulator-based dielectrophoresis (i-DEP) to effectively aggregate silica nanoparticles to interdigitated electrodes on a sapphire substrate. The factors determining the behavior of DEP include physical variables like properties of the nanoparticle in solution and particle size. Polarizability is the most critical factor of nanoparticles that influence the behavior in DEP. If the polarizability of the particle is greater than that of the solution, more charge will accumulate inside the particle than on its surface. The net dipole by charge aligns in the same direction as the external electric field, causing the particle to behave similarly to a metallic particle in the solution. Conversely, if the polarizability of the particle is smaller than that of the solution, the charge will accumulate more on the particle's surface than inside. The net dipole by charge aligns in the opposite direction to the external electric field, and the particle behaves like an insulator in the solution. The dielectric constant of silica nanoparticles is 3.9, which is much smaller than the dielectric constant of deionized water (DIW), which is 78 at room temperature. Since the dielectric constant is proportional to polarizability, silica nanoparticles in DIW exhibit insulating properties, and the weak electric field near the particle makes DEP behavior difficult to achieve. Also, DEP force is proportional to the volume of the particle. DEP behavior under 10 nm size has difficulty because DEP force of nanoparticle is 100~5000 times smaller than Brownian motion.
To overcome the difficulty of aggregating silica nanoparticles in DIW, a μm-scale interdigitated electrode was used by lithography method and optimized AC frequency for aggregation was chosen. DEP force is inversely proportional to the cube of the distance between the electrode and reduced pattern spacing allows strong DEP force to the nanoparticles. By considering the real part of the Clausius-Mossotti factor, positive DEP (p-DEP) can be achieved in a specific frequency range. I-DEP using a 20 nm Al₂O₃ as a passivation layer was used to prevent the detachment of Au atoms. We demonstrate that silica nanoparticles aggregate in regions with strong electric fields at 100 kHz frequency for p-DEP and aggregation is confirmed by using optical microscopic image, atomic force microscopy and energy dispersive X-ray spectroscopy. We observed the same phenomenon in a large-scale experiment conducted with 36 interdigitated patterns fabricated on a 2-inch sapphire substrate. After conducting 12 DEP processes by removing silica nanoparticles with buffered oxide etch at each cycle, the concentration of Si in DIW decreased by 48%. This method enabled the removal of nanoparticles that were difficult to eliminate with conventional purification systems, thereby enhancing the purity of the semiconductor solution.

This work was supported by Samsung Electronics Co., Ltd(IO231116-07926-01).