Measurement of Particle Precursors in Ultrapure Water
Gary Van Schooneveld, Jikku Thomas - CT Associates, Inc.
Managing contamination in ultrapure water (UPW) is of critical importance to maintain a robust manufacturing process with high product yield in the semiconductor device fabrication Acceptable levels of particles in production, and consequently, allowable limits of these and other contaminants in UPW and process chemicals continue to reduce in the International Roadmap for Devices and Systems (IRDS) in anticipation of advanced devices with smaller dimensions and increasingly complex three-dimensional structures. With the critical particle sizes approaching 3.5 nm, the risk of particle formation from particle precursors is increasing.
Particle precursors are dissolved or molecular materials in a fluid smaller than a “critical size” that may form a particle of “critical size” when a droplet dries or precipitates under changing conditions. Examples of such precursors are high-molecular weight organics (HMWO) and silicates. Detecting particle precursors and particles approaching 3.5 nm in UPW is quite challenging. Conventional optical particle counting (OPC) via light scattering is unable to detect particle in these size range. Nebulization followed by aerosol-based condensation particle counting (N-CPC) has demonstrated the capability to measure both sub-10 nm particles and particle precursors (Figure 1). Our study evaluated the ability of various liquid particle measurement systems to detect and quantify concentrations of a HMWO of different molecular weights. The HMWO was selected specifically to mimic possible molecular contamination that might come from an ion exchange resin during rinse-down and operation. Instruments included in the study were 30 nm OPC, 4 nm N-CPC, 10/15/20 nm N-CPC or STPC and non-volatile residue monitor (NRM). This paper will review results of this study and discuss the implications of the results on potential metrology used for monitoring particle precursors in UPW applications
CTA publication #144: Ultrapure Micro, 2020 (Virtual)