Radiation Induced Subsurface Charging in the Buried Oxide Layer in SIMOX
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Radiation Induced Subsurface Charging in the Buried Oxide Layer in SIMOX M. A. Stevens-Kalceff 1,2 and S. Mickle1 1 2
School of Physics, University of New South Wales, Sydney, 2052, NSW, Australia. Electron Microscope Unit, University of New South Wales, Sydney, 2052, NSW, Australia.
ABSTRACT Kelvin Probe Microscopy has been used to characterize the magnitude and spatial distribution of reproducible characteristic residual potential in electron beam irradiated silicon on insulator specimens (SIMOX). Focussed electron beam irradiation produces trapped charge within the insulating buried oxide layer which produces highly localized electric fields. The charging processes are dynamic, localized, and dependent on pre-existing and irradiation induced defect concentrations. The characteristic experimental surface potential distributions are compared with calculated model surface potential distributions. This work demonstrates that proximal probe methods which are usually considered to be surface analysis techniques, can be used to investigate subsurface properties and give insight into subsurface charging processes. INTRODUCTION Charged beam irradiation of electrically insulating materials may result in the trapping of charge within an irradiated specimen. Electron beam irradiation induced charging in a scanning electron microscope (SEM) has been shown to result in localized (micro-) modification of insulating bulk specimens [1-3]. The electron irradiation induced subsurface charging effects in SIMOX have been investigated using advanced Scanning Probe Microscopy (SPM) techniques. Scanning Probe Microscopy (SPM) techniques enable non-destructive three dimensional high resolution real space images of surfaces via detection of local interactions between the specimen surface and a sharp probe [4]. Kelvin Probe Microscopy (KPM) or (Scanning) Surface Potential Microscopy (SSPM) is a specialized Atomic Force Microscopy (AFM) technique in which longrange Coulomb forces between a conductive atomic force probe and a specimen enable the electrical potential at the specimen surface to be imaged with high spatial resolution. Charge trapping resulting from charged beam irradiation can occur at either pre-existing or irradiation induced defects, thereby inducing a localized electric field within the irradiated specimen. The reproducible characteristic observed surface potentials associated with the trapped charge are compared with calculated potential profiles. This gives insight into charging processes during irradiation and the resultant spatial distributions of the residual trapped charge. Electrically insulating silicon dioxide strongly charges when irradiated with an electron beam in a scanning electron microscope (SEM).[3] Irradiation of semiconducting silicon under identical conditions results in negligible charging at 295K. A combined silicon-silicon dioxidesilicon layered structure can be fabricated using the process known as Separation by IMplantation of OXygen (SIMOX): Oxygen ions are implanted into the silicon subs
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