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As flash technologies face scaling issues at 32 nm and beyond, phase change memory (PCM) emerges as the best performing candidate for scaled non-volatile memories of next generation. To fabricate PCM device with high volume and low power consumption, the structure of PCM has evolved from planar structure to confined cells, which pose challenges for chemical mechanical polishing (CMP) of the phase change material Ge 2 Sb 2 Te 5 (GST).In this study, we discuss the properties, polishing mechanisms and slurry formulations for amorphous GST. Static etching characteristics and zeta potentials of GST powders are first explored to evaluate the chemical properties of GST. Then the polishing mechanisms of GST at pH 2 and pH 11 are discussed by means of static etching experiments, polishing performance, GST film hardness measurement, GST solubility and open circuit potential test. Finally, our efforts for GST slurry development are described. By a combination effect of inhibitors, in which one can form adsorption layer on GST by carbonyl O and the other one can further protect GST surface by forming hydrogen bond through multiple OH groups, we have overcome the corrosion issue of GST. Meanwhile, by the adsorption of the inhibitor layers on GST surface and extremely low removal rate of oxide film (<0.05 nm/min), we have achieved a self-stop GST CMP process with over-polish dishing <8 nm and oxide loss <6 nm for 60 nm GST vias. We have also resolved the issue of particle residue by using our self-formulated post-cleaning solution. [ABSTRACT FROM AUTHOR]

Abstract: We report the exploration of Ge2Sb2Te5 (GST) chemical mechanical polishing (CMP) mechanism. Static etching experiments of GST film were first conducted in two typical silica-based slurries (pH 2 and pH 11). To investigate the chemical nature of GST in different chemical environments, solubility of GST in slurries and also the zeta potentials of GST powders vs pH were measured. We further compared the polishing performance to the removal rate (RR), surface roughness, polishing selectivity of GST over oxide, and influence on the phase change property by using the two typical slurries. Then measurements were done for the hardness of GST films before and after polishing, particle size of the slurry during polishing, and also the open circuit potential (OCP) of GST in the two slurries. On the basis of the aforementioned results, we proposed a possible mechanism for GST CMP including reaction formulas, removal of GST as molecules instead of as a lump, surface hydration in alkaline region and electrochemical process, which was partially supported by residue analysis for 8″ patterned wafers using energy dispersive spectroscopy (EDS) under transmission electron microscope (TEM). [Copyright &y& Elsevier]

We report about the effect of acids and surfactants on the chemical mechanical polishing (CMP) of Ge2Sb2Te5 (GST). A scanning electronic microscope was used to measure the material removal rate. An atomic force microscope was adopted to characterize the surface quality. On the basis of the polishing results, the GST CMP process was promoted by the additives with an increase in the molecular chain length and the O/OH number. A possible reaction mechanism was presented. Furthermore, the comparison of the electrical property of GST films before and after CMP revealed that the polished GST film possessed a higher resistivity due to the surface oxidation, which would be beneficial for reducing the high reset current of the phase-change memory cells. [ABSTRACT FROM AUTHOR]