The electrical activity of interfacial misfit dislocations in silicon has been examined using the electron beam induced current technique in a scanning electron microscope. Clean dislocations formed during high-temperature Si(Ge) chemical vapor epitaxy were studied. These defects were subsequently decorated with known metallic impurities (Au and Ni) by diffusion at different temperatures from a backside evaporated layer. Differences in electrical activity are discussed in relation to the detection limits of electron beam induced current technique and energy levels anticipated for the clean or decorated dislocations.
Electron beam induced current variations in images of strain relaxed epitaxial Si/Si(Ge)/Si wafers deliberately contaminated with nickel from the backside are reported for different contamination levels. Strong recombination contrast due to NiSi2 precipitates was observed both at the top Si surface and along buried interfacial misfit dislocations. A surface conductivity inversion from n to p type was obtained for the high level Ni contaminated sample. A theoretical analysis based on the presence of a surface potential due either to a metal-silicon Schottky contact, or to the accumulation of charged traps is used to explain the observed effects.
A study of gettering and electrical activity of metallic impurities Ni, Au and Cu has been carried out on epitaxial Si/Si(2%Ge)/Si wafers containing interfacial misfit dislocations. The impurities were intentionally introduced from a backside deposited thin metal followed by rapid thermal annealing (RTA). Transmission Electron Microscopy (TEM) results indicate that the impurities were gettered along the misfit dislocations in near-surface regions either as Au precipitate colonies, or as NiSi2 and CuSi silicide precipitates. Data from Scanning Electron Microscopy (SEM) in the Electron Beam Induced Current (EBIC) mode revealed that these precipitates dominate the recombination properties of the initially inactive misfit dislocation.
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