Analysis of contaminants in IC processing chemicals at the sub-part per trillion level

As integrated circuit geometries continue to shrink, the purity of semiconductor process chemicals and de-ionized water has become a critical issue. We have developed a technique for the analysis of particulate contaminants in liquids using analytical transmission electron microscopy. The technique has an elemental detectability limit as low as 0.1 parts per trillion (ppt) and a particle concentration detectability limit as low as 1 particle/ml for particles greater than 0.2 mu m. It can provide morphological and compositional information as well as information about the contamination source. Particulates were collected by filtration through 0.2 mu m Nuclepore(R) polycarbonate filters installed in various locations in the chemical processing lines. Analytical transmission electron microscopy samples were prepared using an extraction replication method. De-ionized water and two important chemicals were studied: H2O2 (from manufacturer A) and HF (from manufacturers B and C). Spherical particles composed of light elements were observed in the de-ionized water. For H2O2 A, we identified tin and iron oxide particles which may come from the pipes used in the distillation process during H2O2 production. HF from manufacturer B contains mainly an amorphous, viscous material with Si, Sb, Cl, S, and Al identified by XEDS. Other types of as yet unidentified large particles are also observed. The HF from manufacturer C is significantly cleaner, consistent with the fact that the manufacturing yield is higher.