Investigations of Particle Hygroscopicity using High Purity Aerosolization and Condensation Particle Counting

DEREK OBERREIT, Michael Walker, Jikku Thomas, Kanomax FMT, Inc.

     Abstract Number: 495
     Working Group: Instrumentation and Methods

Abstract
The semiconductor industry is experiencing growing concern over defects formed by precipitation of particle precursor material in process chemicals, which is likely introduced to the wafer through the evaporation of droplets remaining after a spin dry process using high purity process chemicals. Nebulization of process chemicals and subsequent condensation particle of the aerosol particles formed after evaporation (Aerosolization+CPC) has been demonstrated to correlate with liquid borne wafer defects. When coupled to a process chemical source, this method also facilitates real-time monitoring of the process chemical to anticipate process disruptions.

While this method can provide insight to the concentration and threshold size of particles formed after droplet evaporation, it does not provide information about how these particles may be affected by ambient vapor. Prior research has quantitatively investigated hygroscopic growth of aerosol particles composed of various materials. For particle sizes below 10 nm, high-purity particle generation using a tube furnace is an effective method, however, it is limited to materials that do not decompose under temperatures required for sufficient evaporation/sublimation necessary to form aerosol particles.

In this work, we describe a system and method to qualitatively infer the hygroscopicity of particles formed through aerosolization of ultrapure water mixed with low concentrations of hygroscopic materials with varying water activity. The net particle concentration of these particles are measured using a water-based and butanol-based CPC where the difference between detected concentrations provides insight into the hygroscopicity of these particles. Our measurements show that for some materials, hygroscopic growth does not correlate with bulk water activity of the material.