SPM Cleaning Solution: A Strong Oxidizing Decontaminant for Semiconductor Wet Etching

In semiconductor manufacturing, contaminants such as photoresist and organic residues pose a serious threat to device performance. SPM cleaning solution, with its highly efficient and thorough capability to remove organic materials, has become a critical reagent in wet‑process cleaning steps. Its alternative name, “Piranha solution,” vividly underscores the mixture’s strong corrosivity and oxidizing power.

1. Composition and Proportioning

SPM consists of concentrated sulfuric acid (H ₂ SO ₄ ) and hydrogen peroxide (H ₂ O ₂ ) Mixed together.

• Sulfuric acid concentration: typically 98% (mass fraction)
• Hydrogen peroxide concentration: typically 30% (mass fraction)
• Typical volume ratio: H ₂ SO ₄ :H ₂ O ₂ =4:1 to 7:1

2. Physicochemical Properties

The mixing process involves an intense exothermic reaction, causing the solution temperature to rise rapidly to 120–150 °C. This high-temperature condition markedly enhances the oxidative decontamination capacity, significantly improving the removal efficiency of organic pollutants. Furthermore, the strong dehydrating nature of sulfuric acid induces dehydration and carbonization of organic macromolecules, thereby creating favorable conditions for subsequent oxidative decomposition.

3. Core Reaction Principle

The cleaning effect of SPM is primarily attributed to the highly reactive intermediate species generated during the reaction—peroxymonosulfuric acid (Caro’s Acid, H ₂ SO ₅ ), with the following reaction equation:

H ₂ SO ₄ +H ₂ O ₂ →H ₂ SO ₅ +H ₂ O

Peracetic acid possesses an extremely high oxidation potential (+2.51 V) and can directly oxidize and decompose organic pollutants into carbon dioxide and water:

Organic compound + H ₂ SO ₅ →CO ₂ +H ₂ O+ byproduct

Meanwhile, the dehydrating action of sulfuric acid proceeds in concert:

• Dehydration: Organic macromolecules → Carbonized residue
• Oxidation: Carbonization residue → CO ₂ and H ₂ O

This synergistic mechanism ensures the complete removal of organic compounds.

4. Process Advantages

• High-temperature acceleration of the oxidation rate: At 150 °C, the photoresist removal rate is increased by several orders of magnitude compared to room temperature, significantly enhancing process efficiency.
• Broad-spectrum cleaning performance: Effective against a wide range of organic contaminants, including cured photoresist, oils, and residual monomers.
• Complete mineralization: The final reaction products are harmless CO. ₂ and H ₂ O, secondary organic pollution was avoided.

5. Conclusion

SPM cleaning solution, leveraging the strong oxidizing species—peroxymonosulfuric acid—generated by the reaction of concentrated sulfuric acid with hydrogen peroxide, along with sulfuric acid’s inherent dehydrating properties, exhibits exceptional efficacy in removing organic contaminants at elevated temperatures of 120–150°C. Its synergistic “strong acid + strong oxidant” action makes it an indispensable, high‑performance cleaning agent in the field of semiconductor wet‑process cleaning.

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