Overview and Core Principles of Semiconductor Wet Cleaning

1. Introduction: The Strategic Importance of Cleaning in Chip Manufacturing

In the semiconductor manufacturing industry, there is a widely held belief: “Three parts of a chip depend on fabrication, while seven parts depend on cleaning.” This statement is no exaggeration; it accurately reflects the current state of the industry. From a bare silicon wafer to the finished product, a single chip undergoes hundreds, or even thousands, of liquid‑cleaning steps. In advanced process nodes, the number of cleaning steps often exceeds 1,000.

The reason cleaning is so critical lies in the fact that the size of contaminants is comparable to the feature dimensions of integrated circuits. Today’s most advanced metal line widths are already below 10 nanometers—about one ten-thousandth the diameter of a human hair. At this scale, even a tiny virus, a single speck of dust, or a trace of dried pharmaceutical residue can render tens of thousands of transistors unusable. Consequently, the “bathwater” used to clean wafers is far from an ordinary liquid; it consists of highly precise chemicals with concentrations controlled down to parts per million and temperature maintained within one degree Celsius.

2. The Six Core Chemical Mechanisms of Wet Cleaning

Through an analysis of various cleaning formulations, the underlying chemical principles can be distilled into six fundamental “chemical techniques”:

• Oxidation–dissolution equilibrium: An oxidizing agent forms a thin oxide layer on the material’s surface, which is then partially dissolved by a specific chemical reagent, thereby dynamically “removing” the attachment base of particulate contaminants. Representative formulations include SC‑1 and EKC580.
• Complexation dissolution: This process involves the reaction of a complexing agent with metal ions to form stable, water-soluble complexes, effectively “putting soluble handcuffs” on the contaminants and removing them from the surface. Representative formulations include DHF, SC-2, and BOE.
• Strong oxidation mineralization: This process uses strong oxidants to completely oxidize and decompose organic pollutants into carbon dioxide and water, achieving inorganic treatment. Representative formulations include SPM and ozonated water.
• Buffered rate control: By introducing a buffering system, the etching or reaction rate is stabilized, preventing rate drift caused by changes in reactant concentrations and ensuring process uniformity and controllability. Representative formulations include BOE and ST250.
• Selective etching: Leveraging the differences in chemical properties among various materials to achieve precise etching of a specific material while leaving other materials undamaged. Representative formulations include hot phosphoric acid and EKC580.
• Swelling–dissolution: Solvents are used to swell crosslinked polymers (such as photoresists), reducing their adhesion to the substrate and thereby enabling delamination. This principle underpins the solvent matrices of all generations of resist strippers.

3. Conclusion

Wet cleaning is an indispensable and yield‑determining step in chip manufacturing. Its essence lies not in a single chemical reaction, but in the flexible integration and application of the six fundamental chemical mechanisms outlined above. A thorough understanding of these principles is essential for mastering the design and implementation of various cleaning formulations.

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