Polishing Agents

The polishing of glass is of fundamental importance in many industries, including the jewelry industry. But it goes beyond aesthetic reasons: precision optics, technical glass, laser technology, electronics and cell phones also require polished surfaces. Together with iron oxide (polishing red), cerium oxide is one of the most effective glass polishing agents and ensures high-quality polished surfaces. The special polishing efficiency of cerium oxide is due to its chemical properties. The polishing of glass and other surfaces is not just a purely mechanical process. A series of complex chemical interactions between the polishing agent, the surface and the polishing medium also contribute to the result. Although mechanical factors, such as pressure or the movement of the polishing tool, dominate the removal of material, the chemical interactions must also be taken into account during polishing to achieve optimum results. This process is known as chemical-mechanical polishing or planarization (CMP). In recent years, the factors that influence the efficiency of CMP have been increasingly studied, as the demand for high-quality surfaces is constantly increasing due to ever more sophisticated modern electronic devices.

Cerium oxide-based polishing powders are usually produced by the thermal decomposition of carbonates, cerium oxalates, acetates or hydroxides. However, the cerium oxide content in the final polishing powders varies in a relatively wide range from approx. 50 to 100 %. Rare earth metals are often additional components in the polishing powders; they are not considered a critical factor, as cerium oxide forms solid solutions with the oxides of other lanthanide elements and incorporates them into its crystal structure without changing its crystalline structure. The composition can therefore be easily adapted to the respective requirements and modified with additives. Conventional polishing powders, on the other hand, often consist of 100% cerium oxide.

For optimum results in chemical-mechanical polishing, the polishing agent should have suitable mechanical properties. For example, high mechanical resistance, a homogeneous particle size distribution and crystallinity. At the same time, it should have sufficient chemical reactivity to interact with the polished surface under the given conditions and support the polishing process.

One example is near-surface trench isolation during chemical-mechanical polishing. A certain polishing selectivity is required here, namely the ability to remove silicon dioxide and not silicon nitride. Polishing agents with such a high selectivity must be of high quality. Thus, the properties of cerium oxide are primarily determined by the conditions to which the material is exposed during its thermal treatment in the manufacturing process, especially the calcination temperature. IBU-tec has extensive experience in calcining a wide variety of materials - excellent prerequisites for developing and producing high-quality cerium oxide.

Polishing agents produced from carbonate precursors exhibit increasing polishing efficiency (expressed in terms of removal rate) as the calcination temperature of the polishing agent increases. The most dramatic effects can be observed in a temperature range of approx. 300 - 700 °C. University studies have shown that the efficiency of the polishing agents did not increase any further with a further increase in the calcination temperature up to 1000 °C, whereas in our earlier work we still observed a certain increase in polishing agents that were annealed at temperatures just above 1000 °C. In the temperature range of approx. 300 - 700 °C, not only the essential physical properties of cerium oxide change dramatically, but also its sorption capacity and reactivity. It is therefore not possible to make general statements. If polishing is a critical step for value creation, it may be necessary to test different manufacturing processes for the polishing agent and find the optimum solution for your particular application.

Another issue that needs to be addressed in the development of polishing agents is the influence of particle size and morphology of the polishing agent on the polishing process and the workpiece, as well as the effect of different concentrations of the polishing agent in the polishing slurry. Scientific progress in understanding the chemical aspects of the polishing process has increased over the years to such an extent that it is now possible to better utilize this knowledge for polish selection and to use chemical and other additives to improve polishing selectivity, particularly in shallow trench isolation in chemical mechanical polishing.

IBU-tec has produced a range of cerium oxides by calcining the cerium carbonate precursor at various temperatures between 200 and 1200°C. The glass polishing efficiency was then measured in a simple set-up without further treatment (e.g. grinding) of the polishing agents and without chemical modification of the polishing paste, confirming that the thermal process does indeed have a significant influence on the performance of the polishing agent. We can advise you and support you in the selection or development of a polishing agent specifically for your requirements. IBU-tec has extensive experience in the development of thermal processes, which you can take advantage of.