Evaluation of Sub-50 nm Colloidal Silica Detection and Non-Volatile Residue Control for Liquid Filtration through Aerosolization-Based Techniques

ZHENGYUAN PAN, Qisheng Ou, Dan Troolin, David Y. H. Pui, University of Minnesota

     Abstract Number: 90
     Working Group: Nanoparticles and Materials Synthesis

Abstract
The membrane filtration is an important technique to protect the processing liquid from contaminants, such as silica Nanoparticles (NPs), that can interfere with chip production. As semiconductor manufacturing advances toward the 1.4 nm node by around 2027, the industry demands contamination detection and control at least at the single-digit nanometer level. However, conventional optical particle counters may hit their limits at around 20 nm due to the low refractive index of silica NPs and microbubble interference. Aerosolization-based technique by aerosolizing the colloidal particles and detecting them using a Scanning Mobility Particle Sizer (SMPS) is capable of measuring a broader size range, down to 2 nm. As the liquid sample is greatly diluted after aerosolization, the Minimum Detectable Concentration Limit (MDCL) of this technique could be high. In this work, we aimed to investigate and optimize the MDCL of the aerosolization-based technique while maintaining its sensitivity to small particles. The residue control through droplet size control and dissolved Non-Volatile Residue (NVR) removal was first studied. Then, testing methods using either an aerosol generator combined with an SMPS or a Condensation Particle Counter (CPC) without a Differential Mobility Analyzer (DMA) were conducted to measure 5 to 50 nm NPs. Linear correlations between liquid-borne and air-borne particle concentrations were obtained for both methods. The results demonstrate that the DMCL can be optimized by flexibly controlling the threshold detectable size of CPC, avoiding using the DMA, especially for sub-20 nm particles.