Effect of Slurry pH

The slurry in Fig. 13.19 consists of 2wt% of L-proline and 1 wt% of ceria with pH adjusted to the desired value with either HCl or KOH. The nitride rate is relatively constant from pH 6-8 while the oxide rate gradually increases with pH. The nitride removal rate drops dramatically to a rate of roughly 1 nm/min as the pH increases from 8 to just below 10. The nitride rate rapidly increases from pH 10 to its highest value (with proline additive) at pH 11. Fig. 13.20 shows the selectivity of oxide to nitride in the proline-ceria slurry that has a linear behavior over the pH range of 6-8, has a very large rise from pH 8 to just below pH 10, and then falls quickly from pH 10 to pH 11. 

The pH of a slurry has a profound influence on its colloidal stability and CMP performance. Strong correlations have been established between the particle isoelectric point (lEP) and the optimal pH for slurry stability. The general rule is that the slurry is more stable at a pH that is away from the lEP, so the zeta potential of the particles is greater than 20 mV. The focus of this section is on the influence of pH on the slurry performances such as material removal rate and defectivity. In order to examine the impact of slurry pH on these two important performance features, we first take a closer look at the interaction between abrasive particles and the surface to be polished. There is a vast amount of literature on the interaction between abrasive particles and silicon dioxide surface [26]. The discussion below will focus on the interaction between ceria abrasive particles and the silicon dioxide surface to be polished. The basic principles and conclusions can be easily extended to other pairs of abrasive particles and surfaces. 

Interactions between the ceria abrasives and the oxide surface have been investigated using both the chemical and the instrumental approaches. Suphantharida and Osseo-Asare [27] used zeta-potential measurements, silicate adsorption, and polishing experiment to investigate the role of ceria abrasives-Si02 surface interaction. T o determine the effect of pH on the surface charges, the zeta potentials of abrasive particles were measured (Fig. 13.21). The points of zero charge (pzc) or isoelectric point is at pH 6.0 for ceria and pH 1.5 for silica. These values are consistent with those reported by others [28,29]. 

Silicate ions of varying concentrations were added to ceria dispersions in order to study the electrostatic interaction between ceria particles and silicate ions. It was observed that the zeta potential of ceria becomes less positive or more negative. With an increase in Na2Si03 concentration, the isoelectric point shifts to lower pH values. At high silicate concentration, the zeta potential of ceria particles follows a trend similar to that of silica. This is a clear indication that the silicate ions adsorb onto the ceria particles [30,31]. 

The adsorption isotherms for the silicate-ceria system were obtained for slurries with pH ranges from 2 to 12 (Fig. 13.22). With an increase in silicate concentration, the total amount of adsorption onto ceria also increases. The adsorption curves reach a maximum at a pH of about 9. 

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Figure 5. Polishing rate of TEOS for sub-arrays of varying width of line and spaces and the effect of slurry pH.

Kang et al. [6] studied the effect of slurry pH during polishing of silicon wafer and polycrystalline silicon films using abrasive-free and silica slurries to understand and compare the polishing mechanism of sUicon. They noticed that the poly-Si CMP process was strongly influenced by mechanical factors however, bare silicon wafer polishing was influenced more by chemical effects. 

Y-J. Kang, B-K. Kang, J-G. Park, Y-K. Hong, S-Y. Han, S-K. Yun, B-U. Yoon, C-K. Hong, Effect of Slurry PH on Poly Silicon CMP, International Conference on Planarization/CMP Technology, Dresden, Germany (2007). 

C. K. Hong, Effect of slurry pH on poly silicon cmp, in Proceedings of the International Conference on Planarization/CMP Technology, Dresden, Germany, 2007. 

The effect of slurry pH on the formation of active component of MoVTeNbO catalyst for selective (atnm)oxidation of ethane and propane has been studied. pH affects the nature and composition of the cmde and dry precnrsors as well as chemical and phase composition of the final catalyst. The most effective catalyst is prepared at pH=3.0, which is characterized by a maximum content of Ml phase. 

The goal of the present work is to study the effect of slurry pH on the phase formation of MoVTeNbO catalyst. 

It is instructive to plot Equation (7.6) graphically to show the dependence of the NH3 concentration (and thus the complexing power of the slurry) upon pH. Figure 7.12 shows the fraction of the total dissolved ammonia occurring as NH3 vs. pH. At a pH of approximately 10, a sharp drop in the concentration of NH3 occurs. Below pH 8, the ability of the slurry to complex the copper declines, as with NH4NO3. The next section further discusses the effect of lowering pH on the ability of ammonia-based slurries to complex the copper. 

The effect of the pH of slurry containing ceria particles (average diameter 440 nm and lEP 8.5), on the removal rates of TEOS oxide and silicon nitride was found to be weak, Figure 3. Polishing with a different ceria slurry (average particle diameter 140 nm and lEP 6.5) also shows a weak pH dependence for TEOS oxide removal rate but the silicon nitride polish rate decreases with pH, as seen in Figure 4. The dependence of the polish rate for both the ceria slurries on pH... 

Effect of pH. In another work> Joshi et al. (64) investigated the effect of acidic, alkaline as well as nautral pH conditions on the removal of pyritic sulfur in oxydesulfurization. The pH was varied by adding sulfuric acid or sodium carbonate to a coal-water slurry. The effect of neutral pH determined... 

Samples that contain suspended matter are among the most difficult types from which to obtain accurate pH readings because of the so-called suspension effect, ie, the suspended particles produce abnormal Hquid-junction potentials at the reference electrode (16). This effect is especially noticeable with soil slurries, pastes, and other types of colloidal suspensions. In the case of a slurry that separates into two layers, pH differences of several units may result, depending on the placement of the electrodes in the layers. Internal consistency is achieved by pH measurement using carefully prescribed measurement protocols, as has been used in the determination of soil pH (17). 

Fig. 34 —Effect of the particle size on (a) surface waviness Wa, (b) surface roughness Ra, and (c) material removal rate. The slurry contains 5 wt % SIO2 particles, 1.5 wt % oxidizer, and 1 wt % lubricant In Dl water at pH 1.8.

Fig. 38—Effect of pH value of the slurry on (a) Wa, (b) Ra, and (c) material removal amount. The slurry contains 6 wt % Si02 particles with a diameter of 30 nm, 1 wt % oxidizer and 2 wt % lubricant in Dl water.

A total of 81 tests were conducted, 44 without magnesia addition, and 37 with magnesia. The tests were designed to evaluate the effects of magnesia addition, slurry flow rate to the scrubber, scrubber inlet liquor pH, and total height of spheres on SO2 removal. Gas velocity has no significant effect on SO2 removal for the range tested. 

Soils of lower pH (high H " molar concentration) have mobilized the Ca and therefore the soil slurry will be relatively unbuffered. The addition of HCI to the solution will immediately drop the pH in these samples where calcite has been removed, but will have little effect where calcite been precipitated. These buffered soils should be on the edge of the low pH (high H" ). The pattern from an oxidizing sulfide should therefore be an H" high and surrounded by a small or no change in H" concentration when HCI has been added. 

This product was among the top three effective performers in all systems. This product s main advantage over the others tested is that it effectively controlled the Methylobacterium sp. in all slurry samples. This is also a combination biocide that provides beneficial synergy and enables the use of lower dosages. The result is a safe biocide that decreases exposure to the handler and the end-user. The product is FDA-approved under the specified clearances. It is very effective over a pH range of 8.3-9.S and unlike the 1,5-pentanedial, it produced no offensive odour. 

Fleming et al. (18) did not examine the effect of pH on water absorption, but these researchers examined the effect of "pH activation" on water absorption of sunflower and soy products. For pH activation, 1.25 N NaOH was added to slurries to achieve pH 12.2 and then 6.0 N HGl was added to return to pH 6.0 in 10 min. The pH activation process improved the water absorption properties for most products but did not increase water absorption of the soy flour. Processes similar to pH activation may be encountered in the processing of vegetable protein additives. 

In considering an organic-rich slurry wall additive, the governing sorption mechanism is often considered to be hydrophobic partitioning and the effects of solution chemistry (pH, ionic strength, etc.) are considered secondary. The specification ofthe appropriate sorption model requires several choices ... 

The DM content of the steam-pretreated SFF was adjusted to 5% and the pH set to 5.0 with NaOH. Enzymatic hydrolysis was performed using a Celluclast + Ultraflo mixture (1 1) at a ratio of 2 g of enzyme/100 g of slurry (10). Hydrolysis was carried out for 72 h in 100-mL shake flasks maintained at 50°C and shaken at 200 rpm in a laboratory rotary shaker-incubator (LSR/L-V Adolf Kiihner AG) for 72 h. Samples were withdrawn after 0,2, 4.5, 7.5,11,14, 24,31, 38,48, 60, and 72 h for analysis of monosaccharides. Direct enzymatic hydrolysis of a 5% DM SFF slurry was also performed as a reference to evaluate the effect of steam pretreatment on the yield. 

We believe the effect of alumina additives on catalyst slurry viscosity is associated with the surface reactivity of the additive. OH" is a catalyst for polymerization and Si-O-Si bonding of uncondensed silanols higher pH promotes conversion to a solid phase consisting of discrete silica particles (19). Ostermaier and Elliott (15) suggest that pH be carefully controlled at a value less than 3.5, or thickening occurs in the alumina-free reference formula. 

The quantity of acid used is usually in the neighborhood of 16 lbs of hydrogen chloride per 2,500 gallons (0.77 g per liter) of starch slurry, producing a pH of 1.80 for the suspension. The time required to attain a desired, exact degree of conversion depends on the pH attained in the converter, which, in turn, is affected by small variations in the impurities in the starch. It is difficult to judge this effect precisely by measurement of the pH of the starch-acid mixture before it enters the converters. 

DMA tests were eondueted with the specimens soaked in various environments for 0, 24, 72, 168, and 320 h. Pads exposed to slurry showed the lowest storage modulus G (especially at the temperatures below 0 °C) and the highest chain mobility reflected by the highest peak of the damping curve. The effect of time for which pads were soaked in pH 4 buffer solution on the reduction of the pad s dynamic storage modulus (i.e., pad softening) is shown in Fig. 2.14. The pad softening due to the increase in the chain mobility can be... 

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