Detection of Point Defect Chains in Ion Irradiated Silicon by High Resolution Electron Microscopy
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DETECTION OF POINT DEFECT CHAINS IN ION IRRADIATED SILICON BY HIGH RESOLUTION ELECTRON MICROSCOPY
W. Krakow, T.Y. Tan and H. Foell IBM T.J. Watson Research Center, Yorktown Heights, N.Y. 10598 U.S.A.
ABSTRACT
In a lattice imaging study of As+ ion damaged Si, we have detected chain type defects which are not associated with any significant strain or configurational changes. By image matching of the experimental and calculated micrographs of vacancies and interstitials, it is established that about 100% more interstitial atoms may incorporate into a defective chain. A structure model of this defect is proposed wherein a di-interstitial, occupying the split position, is incorporated into every available site along a chain.
INTRODUCTION For the past twenty years defect creation in semiconductors due to radiation damage has been extensively studied using electron paramagnetic resonance where defect complexes consisting of a few point defects and impurity atoms have been considered[l]. Alternatively, transmission electron microscopy (TEM) has been used primarily to observe extended defects strain fields which are a minimum of a few hundred A in extent by diffraction contrast. For smaller defect configurations there has been a minimal effort, since it constitutes a more difficult problem to obtain and interpret the data. It is for this reason the manner by which point defects condense into extended defects has not been discussed extensively in the literature. In this paper we demonstrate that the proper use of high resolution electron microscopy, at the atomic resolution level constitutes a suitable method for studying point defect chains where diffraction contrast would not be sufficient. Whereas dislocation dipoles and other intermediate defect configurations in Si, when viewed along a , are easily identified because of significant configurational changes in the lattice images, an interstitial or vacancy chain has almost no lattice distortion and hence requires the precise adjustment of electron microscope imaging conditions to optimize image contrast.
EXPERIMENTAL METHODS AND RESULTS 2 For our experiments, P-typef 12 cm, oriented silicon wafers were implanted with As+ ions at 80keV to a dose of 8xl05/cm2 at 1IOOAA ion current. From these samples oriented cross-sectioned thin foils, about 200A thick were prepared and examined in a Siemens 102 microscope at 125keV. Defects were then studied by bright-field axial illumination imaging with the foil oriented in a and with seven Bragg beams, (000), _(11l),_(lll)and +(002), included in the objective lens apperture. Fig. la shows a micrograph containing a linear defect which was image processed to eliminate photographic noise. The micrograph was taken in an underfocussed setting of the objective lens, for which the white dots are interpreted as a chain of two unresolved columns of Si atoms lying approximately 1.36A apart. Fig. lb shows the power spectrum of the image demonstrating the presence of the seven beams. It is seen in Fig. I a that the white dots exhib
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