I. Chemical Residues and Incomplete Cleaning

Residue from Photoresist Stripping Solution：Wet photoresist stripping requires organic solvents or strong oxidizers (e.g., sulfuric acid/hydrogen peroxide mixtures) to dissolve photoresist. If subsequent deionized water (DIW) cleaning is insufficient, residual chemicals may corrode the wafer surface. For example, if hydrofluoric acid (HF)—used to remove native oxide layers—is not fully cleaned, it will continuously etch the silicon substrate, leading to increased surface roughness.

Metallic Ion Contamination：Metallic impurities (e.g., Fe, Cu) may be introduced during the stripping process. If not thoroughly removed via solutions like SC-2 (HCl/H₂O₂), these impurities can impair the electrical performance of devices.

II. Challenges in Controlling Process Parameters

Temperature and Concentration Fluctuations：The efficiency of chemical reactions is highly dependent on temperature and solution concentration. For instance, in RCA cleaning, imbalanced proportions of ammonia water (NH₄OH) or hydrogen peroxide (H₂O₂) may cause particle re-adsorption or excessive oxide layer thickness.

Sensitivity to Time Windows：Excessively long stripping times may damage underlying materials (e.g., low-k dielectrics), while excessively short times result in incomplete stripping. For example, ultrasonic cleaning exceeding 30 minutes may damage the wafer surface structure.

III. Issues Related to Equipment and Process Uniformity

Uneven Spray Distribution：In the single-wafer spin spraying method, improper nozzle design (e.g., insufficient precision of flow channel notches) or poor control of rotation speed can lead to uneven distribution of chemical solutions, causing localized residue or over-etching.

Risk of Electrostatic Accumulation：Deionized water (DIW) has poor conductivity, making it prone to electrostatic adsorption of particles during cleaning. Conductivity must be enhanced by mixing with gases such as CO₂ or NH₃; otherwise, surface contamination may occur.