Abstract:

As semiconductor feature sizes continue to shrink, traditional optical light-scattering tools are increasingly unable to detect sub-visible “killer” particles and particle precursors — dissolved contaminants capable of forming particles on wafer surfaces during processing — in high-purity process chemicals such as ultrapure water and isopropyl alcohol.

A method for continuous measurement of particles and particle precursor material in high-purity liquids using Aerosolization and Condensation Particle Counting (A+CPC) is presented. The technique nebulizes the liquid into a fine mist, dries the aerosol to isolate residual particles and non-volatile residues, and then grows the resulting dry particles — including species as small as 3 nm — via vapor condensation to a size detectable by laser-based counting.

To establish the relationship between liquid-phase contamination and on-wafer defectivity, a complementary validation process using Sequential Spin Coating (SSC) combined with Surface Enhanced Particle Sizing (SEPS) is described. Process chemicals are deposited onto wafer surfaces by SSC, and the resulting particle defects are quantified by SEPS, a high-sensitivity wafer inspection technique.

The integrated method was applied to monitor the effluent of an ion exchange resin column following the SEMI C93 guide. Results demonstrate a linear correlation between A+CPC liquid-phase measurements and SEPS on-wafer particle counts, enabling calculation of a deposition factor — defined as the ratio of liquid concentration to surface concentration — on the order of 1 × 10⁵ (#/mL)/(#/cm²). This deposition factor provides a practical tool for semiconductor process engineers to predict on-wafer defect levels from routine liquid purity measurements.