ELECTRICAL AND STRUCTURAL STUDIES OF COPPER AND NICKEL PRECIPITATES IN A SIGMA=25 SILICON BICRYSTAL

Deep-level transient spectroscopy measurements of electronic defect st ates in a coincidence SIGMA = 25 grain boundary (GB) in silicon have b een performed after quenching of heat-treated samples (900-degrees-C, 2 h) containing copper and/or nickel. These elements are usually suspe cted to be nonintentionally contaminating impurities. The special care supplied to get processed samples free from transition-metal impuriti es (particularly copper) has led to the measurement of a continuous di stribution of boundary levels between E(c) - 0.20 eV and E(c) - 0.38 e V which shift toward deeper energies (between E(c)-0.25 eV and E(c)-0. 42 eV) with a gradual increase of the copper content. The heavily cont aminated samples with Cu or with both Cu and Ni exhibit a single inter face trap at E(c) - 0.54 eV. According to transmission electron micros copy (TEM) and energy-dispersive x-ray (EDX) analyses, as well as comp arable data reported earlier, this interface state seems characteristi c of copper precipitates obtained by quenching from 900-degrees-C; how ever, the incorporation of nickel in a '' copper-free '' bicrystal has been found to result in an almost discrete boundary level at E(c) - 0 .50 eV. From TEM, EDX, and electron-diffraction investigations, the co rresponding precipitates were geometrically shaped, intersecting the G B plane, and identified as two types (A and B) of NiSi2 silicide.