Oxide slurries

Fumed silica and colloidal slurry with and without filtration have been evaluated. All slurries are KOH-based. All slurries have pH values greater than 10. A same polisher was used, and a same pad was used. However, to separate the effect from post-CMP cleaning, neither scrubbing nor chemistry was applied. The oxide wafers were only water-rinsed after polishing. The results are shown in Fig. 11. The slurry with fumed silica left more particles compared to that with colloidal silica. 

Filtration can reduce the particles adhered to the wafer, but only slightly. Filtration will, however, reduce scratch defects. Slurry particles can be more effectively cleaned if more elaborate post-CMP clean chemistry is used [8]. 

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Excess NaOH is used to start the reaction and not over 35% of the chromium is added as dichromate. At the end of the reaction, the thiosulfate is removed by filtration and recovered. The hydrous oxide slurry is then acidified to pH 3—4 and washed free of sodium salts. On calcination at 1200—1300°C, a fluffy pigment oxide is obtained, which may be densifted and strengthened by grinding. The shade can be varied by changes in the chromate dichromate ratio, and by additives. 

ChemicoB-Basic A flue-gas desulfurization process using magnesium oxide slurry. 

Some work has already been done on reprocessing slurry, but to date the focus has been on oxide slurry reprocessing. Given the remarkably high contribution of slurry cost to the overall cost of ownership, one can reasonably expect that slurry reprocessing will play a greater role in the future. 

The forward reaction is favored by the alkaline slurry solutions which result in breakage of the Si—O bonds. In metal CMP, oxidizing slurries are often used, resulting in faster removal rates. Since the contributions of the chemical and mechanical components are not well known, modeling efforts have focused on empirical approaches guided by physical intuition of process mechanisms. 

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. 

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,... 

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.

Fig. 18. PECVD TEOS oxide slurry removal efficiency in ammonia-based chemistries (0.25, 6) performed at 55°C during 10 min. Diluted ammonia with megasonics gives results as good as the scrubber.

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. 

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. 

The stability of metal oxide slurries can be enhanced by the addition of surfactants [60]. The formation of a surfactant layer on the particles can modify the particle surface in two ways. It can alter the charge characteristic of the particle, which can stabilize or destabilize the particle dispersion. It can also provide steric barrier between particles, which reduces the flocculation of the particles, thereby increasing the stability of the dispersion [60]. 

As shown in Fig. 13.1, a CMP step is required in the STI process. There are two possible approaches to implementing the CMP step STI—direct and indirect. In a direct STI process, the CMP process is applied directly on a wafer right after the trench oxide deposition (Fig. 13.1). The CMP process removes the overburden oxide as well as the topography created during trench oxide deposition over the features with various pattern densities across the dies and the wafer. For some slurries, especially the conventional oxide slurries, these topographies are a challenge. To overcome this difficulty, a pre-CMP step is sometimes implemented in which a reverse mask is applied onto the film and the oxide in the raised area is preferentially etched. After the etching step, the... 

Monitoring and control of CMP slurry properties is essential for effective and uniform CMP processes. Bench-top blend sensitivity analysis helps in identification of the most sensitive blend monitoring and control parameter. Two- and three-component blends of CMP slurries can be created and monitored based on the measurements of density, wt% solids, refractive index, pH, and oxidizer level. Typical silica oxide slurry blend ratio is controlled using density as a control parameter, whereas tungsten and copper CMP slurries usually need an autotitrator for periodic monitoring of the oxidizer level. 

In US 4,386,059, a zinc hydroxyphosphite anticorrosive, is described with the theoretical formula [2 Zn(OH)2 ZnHP03] -x ZnO, wherein x = 0 to 17 [5.88]. This pigment is produced by reacting zinc oxide slurry with phosphorous acid in the presence of a zinc hydroxyphosphite complex promoter [5.88]. It is a white pigment with basic character [5.56]. 

A number of methods can be used to prepare monoliths. Extrusion is widely used for the manufacture of ceramic monoliths, whereas corrugation is used mostly for those of metallic monoliths. As to the techniques used to coat a thin layer of oxide(s) on a monolith, the sol-gel method is used the most. Other methods, e.g., surface oxidation, slurry dip-coating, or CVD and CVI techniques, can also be used. 

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