Following the STI liner etchback, the trench surfaces and corners are exposed to plasma, often leaving behind fluorocarbon polymers, metallic contaminants, or damaged silicon P1.Before the high-quality conformal CVD oxide is deposited to fill the trench, the surface must be meticulously cleaned to prevent trapped interfacial charge or structural defects P1.This preclean step ensures that the subsequent CVD oxide interfaces with a pristine surface, which is critical for maintaining robust electri