TUngsten Slurries

Slurry Particles Surface roughness Plug recess Fe content 

H2O2 based Normal Better Slightly better  

The H202-based slurry performed the best in this evaluation. However, it has problems with plug recess and field oxide erosion. 

Plug recess and oxide erosion between the H2O2 (silica as abrasives) and the HjIOg (mixture of different abrasives) based slurries are also evaluated on patterned wafers. The same polisher (rotating), recipe, and pad (ICIOOO/ 

The plug size is 0.5 gm in diameter, and the oxide erosion measurement is 

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The distribution of the particle size must be as tight as possible, especially for hard materials such as alumina. A typical particle size distribution curve for alumina used in tungsten slurries is shown in Fig. 2a (data taken by the laser scattering method). However, from time to time the particle size distribution in a slurry may be out of control, so that a long tail will appear at the large particle end (Fig. 2b). These large particles may become a source of CMP scratches. 

Several commercially available oxide and tungsten slurries are compared in this section. 

Fig. 12. Comparison of pot life for commercial available tungsten slurries with HjOj (diamonds), Fe(N03)3 (triangles), and HjIOs (squares) oxidizers (a) linear and (b) log scales.

To summarize, for tungsten slurry, there is not yet an optimal formulation. Each kind of slurry has its strengths and weaknesses in terms of performance and ease of use. Obviously, more development work needs to be done in this area. 

FIGURE 4.26 Quality control testing of tungsten slurry (from Ref. 31). 

Different surface films affect the diffusion of reactants and products differently however. As shall be discussed in Giapter 6, tungsten slurries are tailored to form WO3 on the tungsten surface during WO3 is a dense, nonporous film and therefore a... 

Dicyclopentadiene is also polymerized with tungsten-based catalysts. Because the polymerization reaction produces heavily cross-Unked resins, the polymers are manufactured in a reaction injection mol ding (RIM) process, in which all catalyst components and resin modifiers are slurried in two batches of the monomer. The first batch contains the catalyst (a mixture of WCl and WOCl, nonylphenol, acetylacetone, additives, and fillers the second batch contains the co-catalyst (a combination of an alkyl aluminum compound and a Lewis base such as ether), antioxidants, and elastomeric fillers (qv) for better moldabihty (50). Mixing two Uquids in a mold results in a rapid polymerization reaction. Its rate is controlled by the ratio between the co-catalyst and the Lewis base. Depending on the catalyst composition, solidification time of the reaction mixture can vary from two seconds to an hour. Similar catalyst systems are used for polymerization of norbomene and for norbomene copolymerization with ethyhdenenorbomene. 

Metal polishing mechanisms appear to be considerably different from silica polishing. The critical event that determines the polishing process in metal CMP appears not only to be influenced by the crystallographic/microstructure deformation process but also to relate to more complex components of slurry [18]. To better understand the removal mechanism in metal CMP, tungsten is chosen, since both industrial and laboratory CMP data are available for this metal, and its abrasion behavior as a metal is similar to that of other ductile metals which have been studied quite extensively under two- and three-body abrasion [66]. 

Stein, D. J., Hetherington, D. L., and Cecchi, J. L., "Investigation of the Kinetics of Tungsten Chemical Polishing in Potassium lodate-Based Slurries I Role of Alumina and Potassium lodate," Journal of the Electrochemical Society, Vol. 146, 1999,pp.376-381. 

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. 

The work on the electrochemical generation of a solution of ceric sulphate from slurry of cerous sulphate in 1-2 M sulphuric acid was abandoned by BCR due to difficulties encountered in handling slurried reactants. A 6kW pilot reactor operated at 50 °C using a Ti plate anode and a tungsten wire cathode (electrolyte velocity about 2ms 1) produced 0.5 M Ce(S04)2 on the anode with a current efficiency of 60%. The usefulness of Ce(IV) has been limited by the counter anions [131,132], Problems include instability to oxidation, reactivity with organic substrates and low solubility. Grace found that use of cerium salts of methane sulfonate avoids the above problems. Walsh has summarized the process history, Scheme 6 [133],... 

H. Mizuno, Slurry Delivery System Design for Tungsten Chemical Mechanical planarization Manufacturing Site, presented at ISSM, Oct. 10, 1997. 

CMP slurries are shipped to user sites in ready-to-use strength or as a concentrate, which must be diluted to use strength or mixed with one or more chemicals to create the final CMP polishing slurry. Examples of widely used oxide and tungsten polishing slurries, which require various blending ratios, are listed in Table IV. 

Tungsten- and copper-polishing slurry Nitric acid 1-3 (% by weight)... 

J. P. Bare and B. Johl, Aging and Handling Evaluation of Tungsten CMP Slurry in Bulk Delivery System, Proceedings of Fourth Int l Chemical-Mechanical Polish Conference (CMP-MIC) (February 1999). 

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. 

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