In order to establish the advanced and costeffective wet cleaning technology, it is essential to reveal the mechanism of contamination adhesion and removal on Si surfaces in solutions. To reveal the mechanism of noble metal adhesion onto the Si surface in wet processes, the behavior of Cu2+ deposition onto Si surfaces in solutions was investigated. The experimental results reveal the mechanism of electrochemical metallic contamination of noble metals on Si surfaces. Moreover, it was found that, in HF solutions, Si is not directly etched in a form of SiF62- by such an oxidizing agent as Cu2+ but is first turned to oxide and then etched off. For preventing noble metal deposition on Si surfaces, it is necessary not only to keep the noble metals in the solution (i.e. to dissolve noble metals) but also to prevent oxidation/reduction reaction between Si and the noble metal ion. It is found that this oxidation/reduction reaction can be prevented by increasing the redox potential of solutions, injecting surfactants or chelating agents, and making the Si surface covered with oxide. It has been revealed that Cu deposition can be prevented by setting the redox potential of the solution at over 0.75 V vs. NHE. Cu deposition in DHF solutions can be prevented by setting the redox potential at 0.85 V vs. NHE or more. For removing Cu from the Si surface, the same conditions are found to be necessary. Moreover, it is revealed that metallic impurities included in the oxide can be removed only by etching. It is also revealed that chemicals to prevent metal deposition must be used to remove metals such as Cu which easily get redeposited on the bare Si surface. Finally, a new wet cleaning process employing ozonized ultrapure water, NH4OH/H2O2/H2O, and surfactant-injected DHF to replace the conventional RCA cleaning method is proposed.