Metal deposits surface contamination

After formation of a primary deposit layer on foreign substrates, further layer growth will follow the laws of metal deposition on the metal itself. But when the current is interrapted even briefly, the surface of the metal already deposited will become passivated, and when the current is turned back on, difficulties will again arise in the formation of first nuclei, exactly as at the start of deposition on a foreign substrate (see Section 14.5.3). This passivation is caused by the adsorption of organic additives or contaminants from the solution. Careful prepurification of the solution can prolong the delay with which this passivation will develop. 

A critical problem with adhesion layers arises from grain boundary diffusion. Deposited films tend to be polycrystalline and granular. The electrochemistry of the adhesion film is frequently much less desirable than the electrochemistry of the primary film. Moreover, minute contamination of the primary metal film surface by adhesion components can dramatically degrade the electron transfer properties (e.g., electrochemical reversibility, as evidenced by cyclic voltammetric peak potential separation) of the film [58], Thus it is essential that the adhesion layer is not exposed to solution. While the rate of diffusion of adhesion metals through the bulk of the primary layer is quite slow, grain boundary diffusion along the surfaces of grains is much faster. In many cases, the adhesion layer can seriously compromise the performance of the electrode. This is particularly a problem for chromium underlayers. Recently a codeposited Ti/W adhesion layer has been recommended as an alternative to chromium, with reportedly better adhesion and fewer interferences than Cr. A procedure was also described to recondition these electrodes to minimize interference by adhesion layer metals [58]. 

For instance, the stripping peaks of metals deposited in a contaminated mercury film may be changed by formation of intermetallic compounds. Compounds may form between the metals and the metal of a support that has dissolved in the film, or between the metals and the surface atoms of the metal... 

Analyses of Used Catalysts. The analyses of five used catalysts tested with 50% W. Kentucky SCT SRC are given in Table 3. The coke and iron depositions appear to be strongly dependent upon catalysts Harshaw 618X and HDS-1443 are high, but Amocat 1A and IB are low in coke deposition. Since surface area measurements can include contribution by contaminants (particularly coke), these values have no clearcut meaning. Besides the coke deposition, metal deposition on the catalysts contributes to the catalyst deactivation. 

The interface of metallized polymers has been considered from the points of view of the polymer surface, reaction during metal deposition and the effect of contaminant ions. Each is discussed in terms cf the critical factors which maintain the mechanical... 

Surface contamination Surface contamination can be a major reason for premature loss of selectivity. Such contamination can be, for instance, particles from a prior wet clean step. Another high risk is if a salicide process is done before the tungsten deposition. After the silicidation of the metal the excess metal needs to be removed. This is normally done in a wet metal strip step. One can understand that if metal residues are left at the dielectric layer, these can act as a catalyst for tungsten deposition. Especially with a Pt-salicide process this is known to be a severe problem. 

The purpose of surface pretreatment is to remove contaminants, such as dust and films, from the substrate surface. The surface contamination can be extrinsic, composed of organic debris and mineral dust from the environment or preceding processes. It can also be intrinsic, such as a native oxide layer. Contaminants and films interfere with bonding, which can cause poor adhesion and even prevent deposition. Therefore, surface pretreatment is important to ensure plating quality. Most (metal) surface treatment operations have three basic steps surface cleaning, surface treatment, and rinsing. 

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