A MODEL FOR THE ELECTROCHEMICAL DEPOSITION AND REMOVAL OF METALLIC IMPURITIES ON SI SURFACES

In order to establish the advanced and cost-effective wet cleaning tec hnology, it is essential to reveal the mechanism of contamination adhe sion and removal on Si surfaces in solutions. To reveal the mechanism of noble metal adhesion onto the Si surface in wet processes, the beha vior of Cu2+ deposition onto Si surfaces in solutions was investigated . The experimental results reveal the mechanism of electrochemical met allic contamination of noble metals on Si surfaces. Moreover, it was f ound that in HF solutions, Si is not directly etched in a form of SiF6 2- 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 oxi dation/reduction reaction can be prevented by increasing the redox pot ential of solutions, injecting surfactants or chelating agents, and ma king the Si surface covered with oxide. It has been revealed that Cu d eposition can be prevented by setting the redox potential of the solut ion at over 0.75 V vs. NHE. Cu deposition in DHF solutions can be prev ented by setting the redox potential at 0.85 V vs. NHE or more. For re moving Cu from the Si surface, the same conditions are found to be nec essary. Moreover, it is revealed that metallic impurities included in the oxide can be removed only by etching. It is also revealed that che micals to prevent metal deposition must be used to remove metals such as Cu which easily get re-deposited on the bare Si surface. Finally, a new wet cleaning process employing ozonized ultrapure water, NH4OH/H2 O2/H2O, and surfactant-injected DHF to replace the conventional RCA cl eaning method is proposed.