toc (total organic carbon)

TOC (Total Organic Carbon) measures the concentration of organic contamination in ultrapure water (UPW) used in semiconductor manufacturing, quantifying all carbon-containing compounds — from simple molecules like methanol and isopropyl alcohol to complex organic acids, surfactants, and biological residues — that could deposit on wafer surfaces and cause defects. TOC is expressed in parts per billion (ppb) and is a critical water quality parameter alongside resistivity, particle count, dissolved oxygen, and metals. Modern advanced fabs (≤7nm nodes) require TOC levels below 1 ppb in UPW, with leading-edge fabs targeting < 0.5 ppb. TOC measurement works by oxidizing all organic carbon to CO₂ and measuring the resulting CO₂ concentration. Common measurement methods include: UV photooxidation with conductivity detection (UV light at 185nm and 254nm oxidizes organics, and the resulting CO₂ dissolution increases conductivity — the most common online method, capable of detecting sub-ppb levels), UV/persulfate oxidation (chemical oxidation using sodium persulfate activated by UV light — for higher concentration ranges), and heated persulfate oxidation (thermal activation of the oxidant). Organic contamination in UPW originates from multiple sources: ion exchange resin leachables (from the polishing system), membrane degradation products, biofilm formation in distribution piping, construction materials (adhesives, sealants, pipe materials), atmospheric absorption during storage or distribution, and upstream source water contamination. Impact on semiconductor manufacturing: organic residues on wafer surfaces can cause gate oxide integrity failures (even monolayer-level organic films degrade thin gate oxide quality), photoresist adhesion problems, metal contamination (organics complex with metals, carrying them to the wafer surface), particle generation during thermal processing (organic materials decompose and form particles), and reduced wetting in wet cleaning processes. TOC reduction methods include UV oxidation loops, activated carbon adsorption, and system design minimizing organic-leaching materials.