1. Pre-treatment

Before immersing the wafer in the stripping solution, strict cleaning is required to remove surface particles, metallic contaminants, and organic residues. Common methods include:

•RCA Cleaning: Uses SC-1 (a mixture of NH₄OH, H₂O₂, and H₂O in a 1:1:5 ratio) to remove organic particles and some metallic impurities, and SC-2 (a mixture of HCl, H₂O₂, and H₂O in a 1:1:6 ratio) to eliminate metal ions.

•Ultrasonic Cleaning: Assists in removing tiny particles but requires power control to avoid damaging the wafer surface.

2. Stripping Reaction

Temperature Control

•For organic solvent-based solutions (e.g., NMP): 60–80°C (high temperatures are avoided to prevent solvent evaporation or thermal stress on the wafer).

•For strong oxidizing solutions (e.g., piranha solution): Heated to 120–150°C to accelerate the oxidation reaction.

Time Control:

Reaction time typically ranges from 5 to 15 minutes. The endpoint is determined by observing reduced bubbling or the degree of photoresist peeling. Thicker or more resistant photoresist layers may require extended processing time, but over-corrosion of underlying materials must be avoided.

3. Post-treatment

Cleaning:

The wafer is rinsed with deionized water at least 15 times to thoroughly remove residual chemicals (e.g., sulfuric acid, hydrogen peroxide) and reaction by-products. Ultrasonic cleaning (with a power of 100–300W for 1–5 minutes) may be combined to enhance cleaning efficiency.

Drying:

Vacuum drying or nitrogen purging is used to prevent water stains. Before drying, the wafer should remain submerged in deionized water to avoid surface oxidation.

4. Process Optimization and Precautions

Waste Liquid Treatment: Strong acid/oxidizing agent waste liquids must be neutralized before discharge to prevent environmental pollution.

Equipment Selection: Reaction vessels must be corrosion-resistant (e.g., PTFE or quartz materials), and heating equipment requires precise temperature control.

The wet photoresist stripping process must be adjusted based on photoresist type (positive/negative), wafer material (silicon/metal), and process requirements to ensure both efficient photoresist removal and wafer integrity.