Electron Energy Loss Microspectroscopy: Small Particles in Silicon
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ELECTRON ENERGY LOSS MICROSPECTROSCOPY: SMALL PARTICLES IN SILICON W.M. SKIFF, H.L. TSAI* AND R.W. CARPENTER Center for Solid State Science, Arizona State University, Tempe, AZ 85287. *Now at Texas Instruments, Dallas, TX 75265. ABSTRACT The method of electron energy loss spectroscopy in a transmission electron microscope is applied to the analysis of small particles in silicon. Elemental and chemical microanalysis is demonstrated on nitrogen and oxygen-associated defects in silicon, using silicon-based standards. INTRODUCTION Electron energy loss microspectroscopy [1] in a transmission electron microscope (TEM) is a direct method for obtaining both elemental and chemical microanalyses on small carbon, nitrogen and oxygen-containing particles in silicon [2,3]. For optimum results the method requires thin specimen materials, a high brightness field emission gun with probe forming lenses, a cooling stage to prevent specimen contamination, convergent beam diffraction capability to control probe position, and a tilting stage to control diffracting conditions. Coupled with the microdiffraction and imaging capabilities of standard TEM, this technique can be used to characterize particles and defect structures that are as small as the probe diameter itself, about 30A in the present work. We first describe the experimental techniques used to obtain energy loss spectra (ELS) from small particles and small regions of single crystals. The Si L core shell absorption edges from single crystal regions of silicon and silicon carbide, nitride, and oxide are then used to demonstrate the elemental and chemical information that is available in core shell edges. The application of this information to quantitative elemental and chemical microanalysis is discussed. Finally, these methods are demonstrated on small particles in silicon. The examples shown here include amorphous and defect regions in silicon, obtained by nitrogen ion implantation in silicon wafers, and the plate-type oxygen related precipitates in thermally annealed Czochralski grown silicon. EXPERIMENTAL
METHODOLOGY
Specimens of thicknesses less than -. 500A are necessary for energy loss analysis, to avoid multiple scattering. This allows for ELS interpretation using single scattering theory. Samples were prepared using mechanical thinning and/or chemical dissolution, usually followed by ion beam thinning. Often, more than one thinning method is used in order to assess the importance of artifacts created by the thinning method. The microspectroscopy was done with a Philips EM400 TEM
Mat. Res- Soc. Symp. Proc. Vol. 59. ' 1986 Materials Research Society
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A coupled to a Gatan 607 magnetic sector spectrometer. liquid-nitrogen cooled sample stage was used to eliminate which is essential for specimen-borne carbon contamination, The field looking at features that may contain carbon. 100A diameter probe, with a emission gun produces a lOOkeV, and a beam convergence half-angle of 10 current of 50namps, mrad. The microscope was used in diffraction mode so that the entrance
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