CHEMICAL AND ELECTRICAL CHARACTERIZATION OF POLYCRYSTALLINE SEMICONDUCTORS

Abstract

The chemistry and composition of inter- and intragrain regions in polycrystalline semiconductors can be related to, as well as dominate, the electrical characteristics of the materials, and devices fabricated from them. In this paper, high-resolution, complementary surface analysis techniques, including Auger electron spectroscopy (AES), secondary ion mass spectroscopy (SIMS), X-ray photoelectron spectroscopy (XPS) and low-energy electron loss spectroscopy (EELS), are used to investigate the compositional properties of grains and grain boundaries in Si and GaAs. Segregated impurities localized at grain boundaries and other defects are mapped using scanning AES with better than 500 A lateral resolution, in conjunction with an in-situ fracture technique. Comparisons between grain and grain boundary regions are presented. The electrical activity of these impurities is evaluated within the grain boundary plane using a modified AES measurement to determine surface potential. The effects of illumination on the barrier potential and minority-carrier lifetimes of clean and intentionallydoped (Al, Te, Cu) silicon grain boundaries are presented. The effects of annealing on grain boundaries containing various impurities are discussed. Evidence is presented to show that oxygen segregation to silicon grain boundaries strongly influences grain boundary electrical activity. AES, EELS, SIMS and ion microscopy are used to investigate grain boundary chemistry - indicating that oxygen moves to the intergrain regions during high-temperature heat-treatments. Direct ion mapping data (~ 1 µm resolution) are presented as functions of time and temperature to show the grain boundary oxygen segregation. Complementary minority carrier lifetime data and electron beam induced current (EBIC) measurements support the oxygen segregation model and identifies this mechanism as the probable source for electrical activation of such grain boundaries.