Ge-nanocluster formation in Ge-doped polysilicon films under oxidation and heat treatment

• Published in: Russian microelectronics 2009-03, Vol.38 (2), p.118-129
• Main Authors: Kovalevsky, A. A., Strogova, A. S., Plyakin, D. V.
• Format: Article
• Language: English
• Subjects: Electrical Engineering; Engineering; Thin Films
• ISSN: 1063-7397; 1608-3415
• DOI: 10.1134/S106373970902005X

An experimental investigation is conducted into the formation Ge nanoclusters by heat treatment of germanosilicate-glass (Si x Ge y O z ) films that are produced by oxidation of Ge-doped nanostructured polysilicon. It employs Auger and IR spectroscopy, high-resolution electron microscopy, and x-ray diffraction. The process by which Ge atoms in the films are transported toward the substrate is found to include the following stages: (1) the formation of a GeO 2 and a SiO 2 phase, (2) the reduction of GeO 2 to Ge by Si, (3) Ge-crystallite nucleation, and (4) Ge-crystallite growth. Heat treatment in humid oxygen at ≥ 800°C is found to increase Ge-nanocluster size, the point of crystallization being 500°C. It is established that heat treatment at a temperature close to the Ge melting point results in complete aggregation of the germanium into clusters, with a twofold increase in both the mean size and the number of clusters. Germanium is found to accumulate at the interface between oxidized and unoxidized polysilicon.