Abstract:

Organic contamination present in Ultrapure Water (UPW) poses a risk of depositing on the wafer surface during processing and cleaning. Organic contaminants include a range of chemical functionality in the form of small molecules, oligomers, and polymers. The chemistry and size of the organic contaminants influence their behavior in UPW systems, their potential for deposition, and the nature of films and particles on the wafer surface.

Last year at UPM 2023 we identified new classes of potential particle precursors from ion exchange (IX) resin extracts and proposed three chemical pathways to transform low-molecular weight (LMW) dissolved organic leachates from polishing IX mixed beds (MB) to high-molecular weight (HMW) particles on wafers. 1) “Pi-stacking” of polystyrene sulfonates exclusively from the strong acid cation (SAC) resin, 2) “Ion pairing” of polystyrene sulfonates with Triton B exclusively from the strong base anion (SBA) resin and 3) “Condensation polymerization” of organic nitrogen from the SBA. All three reactions required dry-up conditions that could be similar to conditions on wafers during and after spin rinse dry cycles.

The question for this year’s work was, can we also find HMW organics from polishing IX MB in UPW? The objectives of this study are to characterize organics from various UPW facilities, document the chemical type and size of these potential particle precursors, and compare the new results to the contaminants found in the ion exchange resin extracts last year. A correlation between aromatic and nitrogen LC-OCD responses in the HMW fraction of selected UPWs suggests a common source which is consistent with particle formation pathway #2 or namely ion-pairing of the LMW organic nitrogen (Triton B) with polystyrene sulfonate.

These findings provide basic chemical and physical property data of dissolved organics in UPW which is important because it will help enable better monitoring and improved control of potential particle formation on wafers.