TEM sample preparation and analysis of single-crystalline Si spheres

Abstract

In parallel with the technological advancements in the field of Transmission Electron Microscopy (TEM), numerous innovations in TEM sample preparation have also transpired. Innovations in polishing techniques, ion etching, and ultramicrotomy have not only expanded the types of materials that are being investigated with TEM, but have also improved the quality of the thin sections that are examined. Described in this paper is a sample preparation procedure that was developed in order to prepare small Si spheres for TEM analysis. Metallurgical-grade Si is the starting material used in the productionof the spheres. The Si spheres are the main components in the Spheral Solar Cell technology developed by Texas Instruments. The solar cell configuration is shown schematically in Fig. 1. The spheresaresubjected to a number of refinement steps, for example: denuding, gettering, and annealing in order to achieve a purity that is suitable for solar cell fabrication. TEM characterization of the Si spheres was performed at various stages in the refinement process. The spherical shape and size (ave. dia.=0.75 mm) of the Si pose a challenge for TEM sample preparation.