Measurement and control of organic contaminants in ultrapure water systems

In semiconductor manufacturing, silicon wafers are repeatedly cleaned with ultrapure water. As the wafer size increases and the line width shrinks, the ultrapure water consumption continues to increase. More stringent requirements are placed on the rinse water specification. Improvements in water purification must be brought forth to meet the needs. The total concentration of all inorganic ions subject to measurement in ultrapure water is often below 1 ppb. By comparison, the concentration of organic contaminants is often an order of magnitude higher. Organic contaminants in rinse water cause defects and decrease device yield. Removing organic contaminants is therefore very important. The present study focuses on the mechanisms and kinetics of various organic impurity removal processes, particularly, of chemical oxidation processes. A novel photocatalytic filter is developed that incorporates the feature of filtration and chemical oxidation. Organic contaminants are separated through entrapment and adsorption. They are destroyed through photocatalytic oxidation. The oxidation of organic contaminants using UV irradiation, ozone or a combination of UV and ozone is studied. For most model contaminants, UV oxidation is not a first order reaction in terms of the contaminant concentration. UV/ozone oxidation removes organic contaminants synergistically. The removal of dissolved gases and VOCs using a unique membrane degasification technology is also investigated. Another important aspect is the qualitative and quantitative analysis of impurities. In this work, organic impurities are measured using a combination of a total oxidizable organic monitor and a non-volatile residue monitor. A new method is studied using an attenuated total reflection - Fourier transform infrared spectrometer. It has the advantage of detecting the most harmful organic contaminants which adsorb on a silicon wafer. Based on the fundamental information obtained on each process unit, an overall process simulator is developed. Modeling an ultrapure water system will reveal its response characteristics to a possible contamination challenge. This makes it possible to optimize the system configuration and operation. The feasibility of rinse water recycling/reclamation is also studied