Process Control and Safety Precautions for SC-2 Cleaning Solution

1. Critical Process Parameters

The cleaning performance of SC‑2 depends on the precise coordination of all process parameters; any deviation in any stage can result in reduced metal removal or secondary contamination.

1.1 Temperature Control

Temperature range: Must be strictly maintained between 65 °C and 85 °C.

Mechanism of influence:

• Below 65 °C, the reaction rate is insufficient, and the efficiency of metal complexation decreases.
• Above 85 °C, H₂O₂ decomposes rapidly, rendering the solution ineffective.
• Control accuracy: Temperature control accuracy must be within ±2 °C.

1.2 HCl Concentration Equilibrium

• Excessive risk: exacerbates equipment corrosion and increases the risk of Cl⁻ residue.
• Low risk: Insufficient complexation capacity, leading to a decline in metal removal efficiency.
• Optimization objective: Under the condition of maintaining the removal efficiency, select the lowest effective concentration to minimize corrosion and residual contamination.

1.3 H₂O₂ Stability Management

• Autocatalytic decomposition characteristics: Metal ion contamination accelerates the decomposition of H₂O₂.
• Countermeasures: Regularly monitor H₂O₂ concentration and promptly replenish or completely replace the culture medium.

1.4 Ultra-Pure Water (UPW) Requirements

• Resistivity: ≥18 MΩ·cm;
• Metal ion content: <0.1 ppb.
• Importance: If the UPW purity is insufficient, it will directly introduce secondary metal contamination.

2. Safety and Environmental Requirements

SC-2 is a strong-acid, strongly oxidizing system; its handling and waste‑liquid disposal must comply with stringent regulations.

2.1 Personnel Operational Protection

Wear acid-resistant gloves and a protective face shield.

Prevent inhalation of HCl vapor to avoid respiratory tract injury.

2.2 Waste Liquid Treatment

SC-2 waste liquid contains high concentrations of HCl and heavy metal ions.

• Treatment method: Neutralize first, then subject to heavy-metal precipitation before discharge.
• Prohibited: Discharge directly into the wastewater pipeline.

2.3 Solution Preparation Sequence and Heat Release Control

Correct order:

• First, add ultrapure water;
• Slowly add HCl;
• Finally, add H₂O₂.

Objective: To avoid excessive local heat generation and prevent solution splashing or uncontrolled decomposition.

2.4 Selection of Tank Material

Permitted materials: PFA (perfluoroalkoxy alkane) or quartz;

Prohibited materials: stainless steel, ordinary plastic.

Reason: To prevent metal leaching, which could lead to secondary contamination of the wafer.

3. Conclusion

The SC‑2 process has a narrow process window and high safety risks, making it the step that cleaning engineers must manage most rigorously. Temperature, formulation ratio, and service life management are all indispensable; moreover, safety measures such as protective safeguards, waste‑liquid disposal, and material selection must be fully implemented to ensure both cleaning performance and production safety.

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