For Oxide Slurry

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. 

Commercial oxide slurries are available with different chemistries. The most common ones are the NaOH-based, the KOH-based, and the NH40H-based slurries. The NaOH-based slurry is the best medium for OH groups because the NaOH solvent is cheap and stable. However, 

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The hquid vehicle in a slurry should have a low vapor pressure for Hquid extraction and drying be compatible with the soHds and casting mold be inexpensive and be capable of dissolving and dispersing deflocculants and other additives. Distilled or deionized water is generally used as the Hquid vehicle, however, organic Hquids must be used for such moisture sensitive oxide powders as CaO and MgO, and for oxidation sensitive nonoxide powders, eg, AIN. 

CMP of different materials needs polishing slurries with different pH value, e.g., slurry for oxide CMP has a basic pH... 

The pK of Ca2+aq (204), 12.6 at zero ionic strength, rising to over 13 as ionic strength increases, means that concentrations of CaOH+aq will be negligible in body fluids (lpolluted waters, and under all conditions of biological relevance, from the very low pHs of 0.5 (Thiobacillus thiooxidans) to 1.5 at which bacteria used for oxidative metal extraction operate (205), through acid soils and acid rain (pH 3 to 6), streams, rivers, and oceans (pH 6 to 8), soda lakes (pH 10), up to the pHs of 11 or more in Jamaican Red Mud slurry ponds (206) (cf. Section II.C.l below). 

CMP processes for oxide planarization (ILD and STI) rely on slurry chemistry to hydrolyze and soften the Si02 surface. Mechanical abrasion then controls the actual material removal. Thus, the key process output control variables (i.e., removal rate and nonuniformity) are strong functions of the mechanical properties of the system, namely, the down force and the relative velocity between the pad and the wafer. Metal CMP processes such as copper CMP rely more on chemical oxidation and dissolution of the metal than mechanical abrasion to remove the metal overburden. Consequently, careful control of the chemistry of the CMP process is more important for these CMP processes than it is for oxide CMP. Thus, CMP tools and processes optimized for ILD may not be optimal for metal CMP and vice versa. 

For oxide CMP, the purpose of the solution is two fold. First, water weakens the Si—O bond in a silicon dioxide film and softens the surface as it becomes hydrated with Si—OH bonds [6,7]. Figure 10 shows the reaction mechanism. Second, the solution is to provide a basic environment (pH > 10), which accelerates the hydration rate. An environment with high pH values will allow the polishing-induced reaction to be further accelerated because the surface Si(OH) species will be partially dissolved into water. In the meantime, the zeta potential of silica increases with increasing pH values. At high zeta potentials silica particles will repel each other, whereby a better-suspended slurry is formed. 

Fig. 11. Evaluation of particle post-CMP performance for commercial oxide slurries with fumed and colloidal silica with and without point-of-use filtration. The filter size is 0.3 /im. The bottom denotes that the slurry used is from the bottom of the drum.

About 70% of all iron oxide pigments are produced synthetically. Copperas or ferrous sulfate heptahydrate (FeS04-7H20) is the primary source of iron. It is a byproduct of the sulfate process for the manufacture of titanium dioxide as well as a by-product of pickling operations in the steel industry. Other sources of iron include ferric sulfate, ferrous chloride, ferric chloride, and the iron oxide slurry from the production of aniline by nitrobenzene reduction. 

In the design of upflow, three phase bubble column reactors, it is important that the catalyst remains well distributed throughout the bed, or reactor space time yields will suffer. The solid concentration profiles of 2.5, 50 and 100 ym silica and iron oxide particles in water and organic solutions were measured in a 12.7 cm ID bubble column to determine what conditions gave satisfactory solids suspension. These results were compared against the theoretical mean solid settling velocity and the sedimentation diffusion models. Discrepancies between the data and models are discussed. The implications for the design of the reactors for the slurry phase Fischer-Tropsch synthesis are reviewed. 

While there appears to be some agreement between the observed and theoretical iron oxide solids settling velocities, the observed silicon oxide values appear to be several times greater than expected. This difference in behavior of the silicon oxide and iron oxide slurries cannot be accounted for by density effects. Since the ratio of the density of iron oxide and silica is 2.ll+, the predicted VgT for an iron oxide would be 3.8 times greater than for silica, Further work is needed to determine the critical characteristics of a solid that are important in governing its settling velocity. 

Polishing rates with standard processing parameters are in the 100-200 nm/min region for oxide. Polishing times are therefore normally in the order of several minutes. Oxide-to-nitride selectivity depends significantly on the composition of the slurry, the deposition technique, and the thermal treatment of oxide and nitride and polishing conditions. Minimum and maximum values for commercially available slurries are several to one and several hundred to one, respectively. 

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