Mechanistic aspects of electroless deposition

A discussion of the applicability of the MPT model to a particular electroless system ideally presumes knowledge of the kinetics and mechanisms of the anodic and cathodic partial reactions, and experimental verification of the interdependence or otherwise of these reactions. However, the study of the kinetics, catalysis, and mechanistic aspects of electroless deposition is an involved subject and is discussed separately. 

Finally, in Chapter 7 Djokic discusses the deposition of metallic powders from aqueous solutions without an external current source. Metallic powders can be successfully produced via galvanic displacement reaction or by electroless deposition from homogenous aqueous solutions or slurries. The formation of various metallic powders without an external current source e.g., Cu, Ni, Co, Ag, Pd, and Au, using appropriate reducing agents is presented. The mechanistic aspects of electroless deposition of powders are also discussed. It is shown that the hydrolysis of metallic ions is the most important factor leading to the deposition of metal powders from aqueous solutions. 

In terms of kinetics and mechanisms, electroless deposition processes have many similarities. In an attempt to analyze the electroless deposition, several mechanisms such as atomic hydrogen, hydride ion, metal hydroxide, electrochemical, and universal have been proposed.1-3 It is important to note that these mechanisms were developed for cases of nickel and copper electroless deposition, which were the most widely studied metals in this respect. Based on the proposed mechanisms, most of the features of electroless deposition can be explained. However, there are some characteristics of electroless deposition, which cannot be explained using these mechanisms. The major problems arise when attempting to generalize the proposed models explaining the mechanistic aspects. 

O Sullivan describes the fundamental theory, mechanistic aspects and practical issues associated with autocatalytic electroless metal deposition processes. Current approaches for gaining fundamental understanding of this complex process are described, along with results for copper, nickel and various alloys. Emphasis is placed on microelectronic applications that include formation of structures that are smaller than the diffusion layer thickness which influences structure formation. 

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