Ion Implantation Damage in Aluminum Studied by Quantitative Electron Chanelling and Tem.
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ION IMPLANTATION DAMAGE IN ALUMINUM STUDIED BY QUANTITATIVE ELECTRON CHANELLING AND TEM. RONALD G. VARDIMAN U. S. Naval Research Laboratory, 4555 Overlook Ave., S.W., Washington, DC 20375-5000 ABSTRACT Electron chanelling linewidth changes in aluminum have been measured as a function of dose for boron and aluminum ion implantation. Weak beam TEM observations assist interpretation of the results by showing the nature and degree of the damage. For self implantation, a linear relationship between dose, linewidth, and dislocation density has been found up to 1 7 3xlO ions/cm2 . For boron implantation, a new point-like defect appears at the higher boron concentrations, giving a16much slower increase of chanelling linewidth with dose above lx10 ions/cm2 . Boron interaction with the damage stabilizes higher damage acumilations than for sel f-i mpl antati on. INTRODUCTION The study of ion implantation damage in metals has been chiefly conducted by means of transmission electron microscopy aid ion chanelling. Recently the technique of quantitative electron chanelling has been applied to this problem (1-3). The chanelling linewidth is sensitive to intermediate to high damage levels and has the advantage of speed and ease of use, although presently lacking the theoretical basis of ion chanelling. Implantation damage 2 in aluminum has been well studied by TEM at low doses (1011-1015 ions/cm ) (4-8) and by ion chanelling at high doses (1015-1017 ions/cm2 ) (9-11). These studies have demonstrated that damage begins as small dislocation loops with an average size about 3nm. The number of loops was observed to increase linearly with dose (8). At higher doses the2 loops grow to form dislocation networks with densities as high as loll cm- (9,10). At these densities, standard TEM imaging is difficult and density measurements uncertain. In earlier work (1) it was shown that the width of the (220) backscattered electron chanelling line in self impanted aluminum increased linearly with dose up to 3x10 17 ions/cm2 , showing some flattening at higher doses. The present work extends the chanelling measurements to boron implantation. Boron was chosen because of its interstitial nature and the absence of intermediate phases in the concentration range of interest. Although an amorphous layer was found for boron concentrations above about 20 at. pct., a wide range of damage effects could be studied below this 1evel. It is desirable to have a second method of observing the implantation damage to aid in the interpretation of the chanelling results. Although the dislocation structure can be seen by bright and dark field TEM imaging, much detail is obscured by strain contrast bands. These can be largely eliminated and superior resolution obtained by using weak beam imaging. This technique has been used here to correlate the chanelling measurements with the nature and density of the damage for both aluminum and boron impl antati on.
Mat. Res. Soc. Symp. Proc. Vol. 100. 01988 Materials Research Society
164
EXPERIMENTAL METHODS Details of the cha
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