Advanced Cleaning Technologies for Specific Contaminants: SPM and Thermal Phosphoric Acid

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Process Technology

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Release time:

2026-09-24

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Specialized technologies that go beyond basic cleaning

Beyond the RCA cleaning regime, semiconductor manufacturing also employs specialized cleaning techniques tailored to specific contaminants. These methods leverage more extreme chemical conditions or greater selectivity to address challenges that conventional cleaning cannot handle.

2. SPM: An organic waste incinerator named “Piranha”

SPM cleaning solution is prepared by mixing concentrated sulfuric acid and hydrogen peroxide in a 4:1 ratio; due to its extreme corrosiveness, it is commonly referred to as “Piranha” solution. Its operating principle is as follows:

In-situ generation of a strong oxidant: Concentrated sulfuric acid and hydrogen peroxide undergo an exothermic reaction upon mixing, yielding caroic acid, which is an extremely powerful oxidizing agent, in situ.
Complete mineralization of organic compounds: At high temperatures of 120–150°C, SPM can directly oxidize and decompose nearly all organic contaminants—such as photoresist, oils, and fingerprints—into carbon dioxide and water. This represents the ultimate method for removing heavy organic contamination. Due to the vigorous nature of the reaction, SPM must be prepared fresh before use, and its handling requires extremely stringent procedures.

3. Hot Phosphoric Acid: The Selective Master Who Only Tore Down One Wall

When heated to 160–180°C, 85% phosphoric acid exhibits remarkable etching selectivity: its etch rate for silicon nitride is more than 30 times that of silicon dioxide. This property makes it an ideal choice for the precise removal of silicon nitride. In chip manufacturing, silicon nitride is often used as a “temporary stopper” in structures such as shallow trench isolation; after fulfilling its function, it must be removed with high precision without damaging the surrounding oxide layers. Hot phosphoric acid was specifically developed to meet this demanding requirement.

4. Conclusion

SPM and hot phosphoric acid represent two extremes of chemical performance in wet‑process cleaning: unparalleled oxidation capability and exceptional etch selectivity. They address, respectively, the critical challenges of complete removal of organic contaminants and selective removal of specific materials, making them indispensable specialized cleaning technologies in advanced manufacturing processes.

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SPM,RCA

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Classic RCA Cleaning Technology

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Classic RCA Cleaning Technology

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