Chemical mechanical planarization mechanism of epitaxially grown Ge-film for sequential integrating 3D-structured transistor cells

Abstract

Recently, three-dimensional (3D) integration technology has been actively pursued as an alternative solution to overcome the significant issues such as the increase in resistance capacitance (RC) delay and power consumption in fabricating two-dimensional complementary metal oxide semiconductor field emission transistor of less than 10 nm node. To integrate the 3D structure of a transistor cell, a high Ge-film polishing rate is required to polish the facet crystalline Ge while fabricating the Ge channel or germanium on insulator (GOI) substrate through recrystallization and epitaxial growth processes in the sequential 3D integration technology. The analysis of the chemical composition of the Ge surface and Ge-film CMP in the neutral and alkaline regions from pH 7 to 11 using a slurry containing colloidal silica abrasive and H2O2 revealed that the formation of oxidation layer (GeO and GeO2) in the polished Ge-film surface linearly increased when the pH of the slurry was between 7 and 10 and slightly decreased when it was higher than 10. These results indicate that the main CMP mechanism is based on the formation of GeO and GeO2 owing to the oxidation reaction between dissolved oxygen and the Ge-film surface in the neutral and alkaline pH regions, rather than the dissolution mechanism associated with the Ge-film CMP mechanism. Significantly, a very high Ge-film polishing rate of 623.9 nm/min was achieved at a pH of 10, at which maximum number of layers of GeO and GeO2 were formed on the Ge-film surface.