To understand the mechanism of noble-metal adhesion in wet processes, the behavior of Cu adhesion to the Si surface in various chemical solutions, the shape and chemical composition of Cu contaminants adhering to Si surfaces, the surface microroughness of Si surfaces, and the influence of the type of the substrates are investigated. The results show that Cu ion deposits on the Si surface in the form of metallic particles in wet chemical processing, that Cu deposition in HF solutions causes pits to be formed on the Si surface, and that, on a patterned substrate, Cu deposits on the Si surface but not on the SiO2 surface. The experimental results imply a Cu deposition mechanism. In a dilute HF solution, the Si surface beneath the Cu particles is etched away to become SiF6(2-) and a pit is made. Contamination with noble metals is critical. The mechanism for metal deposition may apply to noble metals in general. These metallic impurities must not be introduced into any wet chemical solution or ultrapure water when a bare Si surface is exposed.