Increasing Dissolution Rate with Oxidizing Agents

3 Increasing Dissolution Rate with Oxidizing Agents 

Oxidizing agents such as NOj and Fe(CN)/ may be added to the NH40H-based slurries to increase the copper polish rate by increasing the dissolution rate of the abraded material. In order to form the complex ion, the NH3 complexing agent first requires the oxidation of copper to Cu (reaction (7.2)). Reaction (7.2) requires an associated reduction reaction to sink the electrons. Even if the NH3 were to complex the copper metal directly in one step  

Schematic representation of the effect of an oxidizing agent, NO, on the mixed potential. The additicxi of an oxidizing agent shifts the equilibrium to a higher (more noble) potential and a higher current density. 

One explanation for the low increase in polish rate is that the NH4NO3 salt only partially dissociates in the slurry. The dissocia- 

By adding a nitrate salt that more completely dissociates, the supply of N03 is increased. The dissociation constant for Cu(N03)2 is given by a pK = -0.6 at a Cu(N03)2 concentration of 2 M. Cu(N03)2 may be considered to completely dissociate in the slurry according to  

---

Etching of silicon in alkaline solutions occurs under evolution of hydrogen with a ratio of two molecules H2 per dissolved Si atom. This ratio is found to be reduced under positive bias [Pa6] or by addition of oxidizing agents like H202 [Sc6], If the anodic bias is increased beyond the passivation potential (PP), the dissolution rate is reduced by orders of magnitude. 

The reduction of ferricyanide increases the dissolution rate of copper. Figure 7.18 shows die polish rate of copper vs. the concentration of K3Fe(CN)g for two different pressures. Once again, a large increase in polish rate is seen with the addition of an oxidizing agent. 

The reaction of bromobenzene and styrene (points A to C) is complete within a few minutes at 140 °C (without microwave heating ) with the best supported Pd-catalysts (e.g. palladium on carbon, on metal oxides or in zeolites Fig. 10.16). The dissolution of palladium from the support (point A) starts (only ) at reaction temperature (140 C for bromobenzene) and depends on a variety of parameters (substrate, catalyst, solvent, temperature, base, additives, atmosphere). The maximum palladium concentration in solution correlates well with the highest reaction rate (turning point B of conversion curve). Palladium concentration in solution decreases with continued conversion (point C decrease of aryl halide concentration) leading to (nearly) complete re-precipitation (point D) of the originally dissolved palladium (fortunately) onto the support. Increased temperature and/or excess of a reducing agent (e.g. sodium formate) added at the end of the... 

---