Alumina zeta potential

The work of Larson et al. (62) represented the first detailed study to show agreement between AFM-derived diffuse layer potentials and ((-potentials obtained from traditional electrokinetic techniques. The AFM experimental data was satisfactorily fitted to the theory of McCormack et al. (46). The fitting parameters used, silica and alumina zeta-potentials, were independently determined for the same surfaces used in the AFM study using electrophoretic and streaming-potential measurements, respectively. This same system was later used by another research group (63). Hartley and coworkers 63 also compared dissimilar surface interactions with electrokinetic measurements, namely between a silica probe interacting with a polylysine coated mica flat (see Section III.B.). It is also possible to conduct measurements between a colloid probe and a metal or semiconductor surface whose electrochemical properties are controlled by the experimenter 164-66). In Ref. 64 Raiteri et al. studied the interactions between... 

Fig. 14.3 Zeta-potential of halloysite, and silica and alumina nanoparticles (for comparison).

Shimizu, Y., K. Yokosawa, K. Matsushita, I. Miura, T. Yazawa, H. Yanagisawa and K. Eguchi. 1989. Zeta potential of alumina membrane. Nippon Seramikkusu Kyokai Gakujutsu Ronbunshi 97(4) 498-501. 

As the charge of the particles is in equilibrium with the other species in solution, the zeta potential depends on the pH as well. Figure 13 shows the zeta potential of some materials concerned by the CMP process, where SiOj stands for both the substrate and the fumed glass slurries PVA is the material used for the scrubber brushes (poly vinyl alcohol) SijN. is used as a polish stop layer and AI2O3 and CeOj represent the alumina and ceria slurries, respectively. 

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. 28 Zeta potential of alumina as a function of equilibrium concentration of SDS (designation based on the shape of isotherm in Fig. 31)...

Fig. 32 Schematic representation of the correlation of surface charge and growth of the aggregates for the various regions of the adsorption isotherm of SDS on alumina based on fluorescence data and zeta potential measurement...

Figure 3. Variation of the zeta potential of silica and alumina (gibbsite) as a function of pH.

Sprycha, R., Electrical double layer at alumina/electrolyte interface I. Surface charge and zeta potential, J. Colloid Interface Sci., 127, 1, 1989. 

In brush cleaning, an alkaline chemistry such as NH4OH is often used to remove the particles such as particles of silica, alumina, glass, polystyrene latex (PSL), and silicon nitride from various wafers in the first brush. The basic chemistry is used mainly to increase the repulsive charge by the zeta potential between the particle and the substrate. 

The largest adhesion force of alumina particles in DI water was attributed to a stronger electrostatic attraction between alumina particles and copper surface in DI water owing to their opposite signs of zeta potentials. The smallest adhesion force of alumina particles in the citric acid slurry was attributed to the... 

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. 

Thus alumina membranes surface modified with silanes and sulfone [Shimizu et al. 1987] and with trimethyl chlorosilane TMS [Shimizu et al. 1989] and glass membranes adsorbed with surfactants [Busscher et al. 1987] have been studied this way. The results show that surface treatments alter the zeta potentials. Shimizu et al. [1989] have also demonstrated that under normal operating conditions the zeta potentials of alumina membranes do not change over time even for a period of two to three years. The isoelectric point for alumina particles thus determined is close to 4.00 as determined by direct measurement of membranes. 

FIGURE 11.6 Zeta potential as a function of pH for alumina (AI2O3). where... 

FIGURE 11.14 Viscosity and separation barrier vs. the pH. The calculation is done with the use of Equation 11.34 for alumina particles of radius 100 imi and 10" M salt concentration. The maximum of the barrier and the minimum of the viscosity are at pH = 9.1. The data about the zeta potential as a function of pH are obtained from Figure 11.6. 

The purpose of this study was to explore the interaction between slurry particles and wafer surfaces by the measurements of their zeta potentials. The zeta potentials of slurry particles such as fumed and colloidal silica, alumina, ceria and MnOj and substrates such as silicon, TEGS, W, and A1 have been measured by electrophoretic and electroosmosis method to evaluate the electrical properties of surfaces, respectively. The zeta potential of oxide and metal surfaces showed similar values to those of particles as a function of pH. The interaction energy between alumina and silica particles and TEOS, W and A1 substrate were calculated based on DLVO theory. No deposition of silica particles on TEOS and the heavy deposition of alumina particles on metal substrates were observed in the particle deposition test. Experimental results were well agreed with the theoretical calculation. 

The selection of slurry abrasives is one of the most important task in CMP process development. It will determine the removal rate and the level of defects such as particles and scratches. In this study various slurry particles and surfaces to be polished were chosen to measure their electrical properties in aqueous solutions. The harder particles, the greater the removal rates. Table 1 shows the hardness of materials of interest to CMP process. Among particles in Table 1, y-alumina, Ce02, Mn02, fumed and colloidal silica particles were used to measure their zeta potentials as a function of solution pH. 

The zeta potential of slurry particles was measured as shown in Figure 1. Fumed silica showed a higher isoelectric point (lEP) at which the net charge and electrophoretic mobility is zero, than that of colloidal silica as shown in Figure 1 (a). Also zeta potentials of colloidal silica were around 20mV lower than that of fumed silica. Figure 1 (b) shows the zeta potentials of alumina, ceria and Mn02 particles. Due to their lower hardness than alumina, ceria has been... 

Figure 1. Zeta potentials of (a) fumed and colloidal silica and (b) alumina, ceria and MnO particles as a function of solution pH.

Figure 2 shows the zeta potentials of wafer surfaces of interest to oxide and metal CMP. Aluminum surface showed its lEP at around pH 8.5 which was lower than that of alumina as shown in Figure 2(a). However, zeta potential of Al was very similar to that of alumina particles as a function of pH. TEOS wafer also showed a very similar zeta potentials to those of colloidal silica even though there was a slight shift to lower negative potentials. Also the zeta potential of bare silicon surface was measured at different pHs and the lEP was slightly larger than 3. Silicon surface has a zeta potential lower than -80 mV above pH 9. 

Zeta potentials of slun particles and wafer surfaces were measured to calculate the DLVO total interaction energy between them at various pHs. Instead of the Debye-Huckel low potential approximation, Overbeek s approximate was applied to the calculation. The repulsive energy was calculated between silica and TEOS wafers. Particle dip test also showed no deposition of particles on TEOS wafer. Due to the low cell constant of conductive W plate, it was not possible to measure the zeta potentials of W. The Hamaker constants of A1 and W were calculated and applied to the calculation of total interaction energy. The theoretical calculation was agreed well with the experimental results. The strong attractive interaction between metal surfaces and alumina particles were observed in both the calculation and experiments. 

Figure 9.30. (a) Adsorption isotherm of sodium dodecyl sulfate (SDS) on alumina at pH 6.5 in 0.1 M NaCl. (b) Zeta potential of alumina as a function of equilibrium concentration of SDS (designation of regions based on isotherm shape). (From Chandar et al., 1987 based on the data of Somasundaran and Fuerstenau, 1966.) Chandar et al. (1987) have shown with the aid of fluorescent probe studies that in region II and above adsorption occurs through the formation of surfactant aggregates of limited size. 

Figure 1 Zeta potential measurements showing surface charge dependence with pH for different spores and alumina...

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