High chemical purity is essential for achieving satisfactory device yield in submicron CMOS processing. Reprocessing of liquid chemicals to maintain high purity can drastically reduce both environmental impact and cost of ownership (CoO) of wafer cleaning operations. We propose the use of a novel membrane Filter technology for control of contamination spikes and reduction of liquid chemical usage in pre‐gate HF cleaning. To ensure filter effectiveness, we have developed an in‐process sensor that monitors solution cleanliness by measuring the deposition rate of reducible ions on silicon. Metals are detected through their effect on the surface recombination of photoexcited carriers. This detection method allows quantification of copper and noble metal ions down to 108 atoms/cm2 levels. We have investigated the effect of chemical purity during HF cleaning on the gate oxide integrity (GOI) of 70–200 Å gate oxides. A significant increase in the low‐field breakdown is observed for HF‐last cleaning using chemicals containing more than 10 ppt Cu. We present the results of Cu spiking experiments to evaluate our ability to quantify contamination down to the stringent levels required for an industrial scale wet‐bench. We observe a linear correlation between metal deposition rate and Cu concentration in the 1–5 ppb range.