Ion Beam Induced Charge Microscopy of Integrated Circuits

The ion beam induced charge (IBIC) microscopy technique has recently been developed as a means of imaging the depletion regions of working microelectronic devices beneath their thick metallisation and passivation layers. IBIC microscopy is analogous to electron beam induced current microscopy but has the advantages of a larger analytical depth, lower lateral scattering of the incident focused MeV ion beam and negligible charging effects. These characteristics enable IBIC to image small, buried active device regions without the need to remove the surface layers prior to analysis. The basis of this new technique is outlined and the applications for integrated circuit analysis, characterising upset mechanisms, and for imaging dislocation networks in semiconductor wafers are reviewed

Cationic vacancy induced room-temperature ferromagnetism in transparent conducting anatase Ti_{1-x}Ta_xO_2 (x~0.05) thin films

We report room-temperature ferromagnetism in highly conducting transparent anatase Ti1-xTaxO2 (x~0.05) thin films grown by pulsed laser deposition on LaAlO3 substrates. Rutherford backscattering spectrometry (RBS), x-ray diffraction (XRD), proton induced x-ray emission (PIXE), x-ray absorption spectroscopy (XAS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) indicated negligible magnetic contaminants in the films. The presence of ferromagnetism with concomitant large carrier densities was determined by a combination of superconducting quantum interference device (SQUID) magnetometry, electrical transport measurements, soft x-ray magnetic circular dichroism (SXMCD), XAS, and optical magnetic circular dichroism (OMCD) and was supported by first-principle calculations. SXMCD and XAS measurements revealed a 90% contribution to ferromagnetism from the Ti ions and a 10% contribution from the O ions. RBS/channelling measurements show complete Ta substitution in the Ti sites though carrier activation was only 50% at 5% Ta concentration implying compensation by cationic defects. The role of Ti vacancy and Ti3+ was studied via XAS and x-ray photoemission spectroscopy (XPS) respectively. It was found that in films with strong ferromagnetism, the Ti vacancy signal was strong while Ti3+ signal was absent. We propose (in the absence of any obvious exchange mechanisms) that the localised magnetic moments, Ti vacancy sites, are ferromagnetically ordered by itinerant carriers. Cationic-defect-induced magnetism is an alternative route to ferromagnetism in wide-band-gap semiconducting oxides without any magnetic elements.Comment: 21 pages, 10 figures, to appear in Philosophical Transaction - Royal Soc.