Alumina Slurries

A solution of 50 g. of j-tolylsulfonylmethyl isocyanide in 150 ml. of dichloromethane is placed on a 40 x 3 cm. column containing about 100 g. of neutral alumina slurried in dichloromethane. A nearly colorless solution (ca. 700 ml.) is collected over about 1 hour. This solution is evaporated to dryness on a rotary evaporator, providing 42—47 g. of white -tolylsulfonylmethyl isocyanide, m.p. 113-114° (dec.). 

Glass chromatography column, 1.5-cm i.d. x 45 cm with a stopcock Alumina column Place a cotton wool plug at the bottom of a glass chromatography column. Pack 15 g of alumina slurried with n-hexane-ethyl acetate (6 1, v/v) into the glass column. Make an anhydrous sodium sulfate layer of about 1 cm above and below the alumina bed... 

Alumina clarification Alumina slurry, starch, Wastewater ... 

To show the alumina effect quantitatively, a series of catalysts was made in which the amount of alumina in the matrix was varied from 25 to 100% by adding alumina sol to a 25% alumina, silica-alumina slurry. These catalysts were formulated with REY molecular sieve. The results for SO2 removal are shown in Figure 3 where SO2 removal (corrected for unit factor) increases with increasing alumina. Our conclusion that alumina was important for SO2 adsorption also confirmed the results of Blanton and Flanders at Chevron (22). The non-linearity of the relationship implies an antagonistic effect between silica and alumina. The silica-alumina antagonism will be discussed relative to deactivation subsequently. 

Fig. 16. Influence of the ionic strength in the prevention of readhesion phenomenon in the case of a positive particle on a negative substrate (alumina slurries on silicon oxide layer) a high-ionic-strength limit the double layer thickness. Particle and substrate are therefore electrically masked at a closer particle-substrate distance. (The double layer of the substrate is not represented here.)...

In the case of tungsten or copper CMP where alumina slurries are used, the pH of the solution must be greater than 9 or lower than 2 to avoid adhesion of the slurries in the porous structure of the brush (back to Fig. 13). This phenomenon, called the loading effect, increases the final particle levels on the wafers and therefore drastically reduces the brush lifetime. This effect can be greatly attenuated by injection of 0.5 to 2% ammonia, for example. 

Both silicon oxide and alumina slurries can be efficiently removed on PECVD TEOS oxide or silicon nitride substrates in a conventional SCI or in a SCI without any water peroxide in the case of outcropping tungsten (see Fig. 5). When water peroxide is not present to continuously regrow a protective oxide layer, OH species can etch the silicon. In the latter case, the backside of the wafer must therefore be protected with a nitride or oxide layer to avoid a severe silicon roughening effect. Nevertheless to achieve the same particle removal efficiency obtained with a scrubber, power mega-sonics also have to be used (see Fig. 18). 

HF-based chemistry is particularly interesting due to its compatibility with all back-end metals and barriers. Unfortunately as the absolute values of tbe zeta potential in the A area of Fig. 13 are lower than in alkaline media, the removal mechanism is even more difficult. Indeed as seen in Fig. 19, the particle removal efficiency in the HF-HCl mixture is almost zero for actual alumina slurries. Very-high-power megasonics performed in a specific HF-compatible bath are absolutely necessary to obtain the same good residual particle level as with the scrubber. 

Fig. 19. Alumina slurry removal elficiency in HF mixtures on PECVD TEOS oxide. Behavioral differences between alumina particles and slurries and efficiency of a specific HF- compatible very-high-power megasonics tank. (Direct Coupling system from SubMicron Inc.)...

Fig. 31 I3/I1 of pyrene in sodium dodecyl sulfate solutions-alumina slurries...

Fig. 51 Monomer to excimer ratio (h/Im) of DNP in SDS-alumina slurries as a function of SDS adsorption density (Am = 340 nm, Ae = 420 nm)...

Fig. 52 DNP fluorescence spectra in (A) SDS micellar solution and (B) SDS-alumina slurry [SDS]/[DNP] refers to the micellized or adsorbed SDS to added DNP...

Figure 7.19 Effect of solids content in the milling of an alumina slurry on milling rate, expressed as cumulative mass percent fines. From J. S. Reed, Principles of Ceramics Processing, 2nd ed. Copyright 1995 by John Wiley Sons, Inc. This material is used by permission of John Wiley Sons, Inc.

The pretreatment of the carbon disk UMEs (like a greater part of plane electrodes) is commonly based on mechanical procedures, i.e. polishing [118]. Initially, carbon disk UMEs are grounded down on emery paper (600 grit). Then, the electrode surface is polished with successively finer grades of alumina slurries (0.1- and 0.05-gm diameter particles) on respective cloths. Usually, that is enough to obtain a clean and adequate electroactive electrode surface. 

Allow the resin to cure for 24 h. Polish off the excess resin with sand paper to expose the gold surface. Once the surface is exposed, continue polishing with 1.0 pm alumina slurry, followed by 0.3 and 0.05 pm alumina slurry on microcloth pads (from Buehler, IL, USA) to a mirror-like finish (about 3 min each). 

Stripped alkoxides are then sent to the hydrolysis reactor. In the current ALFOL alcohol process, hydrolysis is accomplished using water instead of dilute sulfuric acid which results in a mixture of alcohols and alumina slurry being formed in the hydrolysis reactor. This mixture is phase separated. 

The alumina slurry is dried and then calcined to form a very active, high purity alumina which is marketed by Conoco Chemicals as CATAPAL alumina. Because of this unique process of manufacturing the alumina, it has a very low sodium content... 

A typical synthesis procedure involves the following steps (i) alumina is slurried in water, (ii) phosphoric acid is diluted in water, (iii) the phosphoric acid solution is added to the alumina slurry, (iv) the aluminophosphate precursor mixture is aged at ambient conditions, (v) an organic is added to the precursor mixture and aged with rapid agitation to form the final gel, which (vi) is charged into the autoclave and heated. The gel composition can be written as... 

The phosphoric acid solution is added to the alumina slurry to form a precursor mixture 3. The phosphoric acid solution is added to the aluminium slurry to form a precursor mixture ... 

Luo et al. [43] proposed an electrode prepared by intercalation of CNTs in a pyrolitic graphite electrode previously polished with emery paper and alumina slurries and sonicated with water. It was performed by grounding the dry graphite electrode on a weighing paper containing a suitable amount of CNTs powder to intercalate them on the graphite smface by mechanical force and adsorption. 

Lee BC, Wang B, Duquette DJ, Gutmann RJ. S5mthesis of model alumina slurries for damascene patterning of copper. Proc. of Materials Research S5miposia Symposium M. Spring 2001. 

Luo Q, Campbell DR, Babu SV. Stabilization of alumina slurry for chemical... 

The frictional characteristics of abrasive alumina and silica particles were investigated and are shown in Fig. 16.28. The alumina slurry was very sensitive to the slurry chemistry. The highest frictional force of 9 kgf was observed in DI water, and the lowest frictional force of 4 kgf was measured when citric acid was added into the alumina slurry. The frictional forces of silica particles (6 kgf) were about the same with or without citric acid during CMP. This is consistent with the fact that citrate has little adsorption onto silica particles. Yoon et al. [69] reported that higher adhesion force between two surfaces caused higher friction force on them. 

FIGURE 16.30 AFM images of the copper surface after polishing in (a) a DI water based alumina slurry, (b) a DI water based silica slurry, (c) a citric acid-based alumina slurry, and (d) a citric acid based silica slurry at pH 6. 

The frictional and adhesion forces between the abrasive particles and wafer surfaces were experimentally measured using alumina and silica slurries with and without citric acid. Although citric acid did not affect the zeta potential of the silica particles, it resulted in a more negative zeta potential of the alumina particles due to the adsorption of the negatively charged citrate ions onto the alumina surfaces. The highest particle adhesion force was measured in an alumina slurry without the addition of citric acid. However, the alumina slurry with the addition of citric acid had the lowest particle adhesion force due to the adsorption of citrate ions onto the alumina surfaces. Although citrate ions could easily adsorb onto alumina particles, the silica particles did not appear to benefit in terms of reduced frictional force when in citric acid solutions. 

The low copper removal rate was observed in the DI water based slurry due to the purely mechanical action of the abrasive particles. However, the highest copper removal rate was observed in alumina slurry containing citric acid,... 

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