Metal slurries

The possible mechanisms which one might invoke for the activation of these transition metal slurries include (1) creation of extremely reactive dispersions, (2) improved mass transport between solution and surface,... 

The possible mechanisms which one might invoke for the activation of these transition metal slurries include (1) creation of extremely reactive dispersions, (2) improved mass transport between solution and surface, (3) generation of surface hot-spots due to cavitational micro-jets, and (4) direct trapping with CO of reactive metallic species formed during the reduction of the metal halide. The first three mechanisms can be eliminated, since complete reduction of transition metal halides by Na with ultrasonic irradiation under Ar, followed by exposure to CO in the absence or presence of ultrasound, yielded no metal carbonyl. In the case of the reduction of WClfc, sonication under CO showed the initial formation of tungsten carbonyl halides, followed by conversion of W(C0) , and finally its further reduction to W2(CO)io Thus, the reduction process appears to be sequential reactive species formed upon partial reduction are trapped by CO. 

Activated metals, generation via the reduction of metal salts, 223-225 Activation of transition metal slurries, mechanisms, 202 Addition reactions... 

Unlike oxide slurries, which use only one kind of abrasive (silica), metal slurries use various types and mixtures of abrasives. The particle size also... 

The slurry solution plays a different role between oxide (as a hydrolizer) and metal (as an oxidizer) slurries. It is more complex in metal than in oxide, because traditionally, oxide slurry is used only for polishing oxide (for ILD, for example), whereas the metal slurry (for tungsten, for example) is used to polish tungsten, titanium nitride, titanium, and oxide. Accordingly, the choice of a metal slurry oxidizer must first satisfy the requirement of the selectivities between each different deposited film. Selection of solution for oxide slurry does not have such constraints. 

As mentioned, the solution (oxidizer) plays a difficult and dominating role in the metal slurry. On one hand, the selectivity between different metal layers should be close to unity. On the other hand, the selectivity between metal and oxide should be as large as possible. Further, on one hand, the polish rate for metal needs to be higher than 3000 A/min. On the other hand, dishing or plug recession must be minimized at the metal areas on the patterned wafers. 

Generally, smaller particles are obtained with polar, more highly solvating solvents. However, these solvents do not necessarily yield the most active metal slurries. The reactivities vary, and the metal slurries can be fine tuned somewhat for use in specific types of reactions. For example, nickel particles from pentane are very active as hydrogenation catalysts, whereas nickel particles from THF are not active as hydrogenation catalysts but are very active in alkyl halide reactions. 

A recent development of work with metal vapors, which lies between atom chemistry and conventional synthetic chemistry, is the preparation of reactive metal slurries. When a metal vapor is condensed with an inert organic compound, e.g., an alkane or sometimes an ether, and the condensate is allowed to warm to room temperature, the resultant slurry contains metal in a reactive form. It is less reactive than the metal atoms because aggregation of the atoms has occurred and is comparable in reactivity to active forms of metal produced by other methods, e.g., Raney nickel. The catalytic and synthetic potential of these metal slurries is being explored (55, 60). 

Rieke obtained activation of metals by an indirect method, the reduction of salts, most of the time the chlorides, with potassium or lithium.18 The method was further improved by effecting the reduction with lithium under sonication,19 which avoids the use of potassium, prolonged heating at relatively high temperatures, and a possible deactivation of the metal slurry by annealing. 

Pad temperature influences not only pad physical properties but also the chemistry of the slurry on the pad, especially when reactive metal films are polished, since the metal slurries containing oxidizing and complexing agents are more sensitive to temperature change. Pad temperature increases because... 

Metal Slurries — Distribution — Multi-Head — Megasonic... 

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