Divacancy control of the balance between ion-beam-induced epitaxial cyrstallization and amorphization in silicon
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zation and amorphization.
I. INTRODUCTION Solid phase epitaxial crystallization of amorphous layers in silicon occurs at measurable rates at temperatures > 450 °C. The regrowth velocity is strongly temperature dependent and is characterized by an activation energy of ~ 2.7 eV.l Recent studies have also shown that solid phase epitaxial crystallization can be induced by ion irradiation at temperatures as low as 150 °C (see, e.g., Refs. 2-9 and Ref. 10 for a review). In this case the extent of crystallization, which is linearly dependent on ion dose, has been shown to be proportional to the energy deposited by the ions into atomic collision processes at, or near, the amorphous/crystalline interface. Furthermore, a relatively weak temperature dependence of ion-induced crystallization is observed, being characterized by an activation energy of ~0.2-0.3 eV.6'8 Ionbeam-induced epitaxy has been suggested to result from the interaction of beam-induced point defects with the amorphous/crystalline interface.6-8 The low thermal activation energy is then a consequence of the fact that most of the 2.7 eV activation energy for thermal epitaxy has been provided in the ion-beam-induced case by the athermal generation of defects by the ions as a result of displacements of silicon atoms in collision cascades. Recently, it has been shown that at high ion dose rates and/or low temperatures, epitaxial crystallization can be reversed, resulting in planar, layer by layer, amorphization. n>12 The present paper reports on the conditions of dose rate and temperature that characterize this reversal of the interface movement and the variations in those conditions for irradiations with different ion species. An activation energy for the ion dose rate resulting in zero interface movement is deduced and a scaling law reduces data for different bombarding ions to a general condition for the balance between crystalli-
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P e r m a n e n t address: Swedish Institute of Microelectronics, P . O . Box 1084, S-16421 Kista, Sweden. Permanent address: Royal Melbourne Institute of Technology, G P O Box 2476V, Melbourne, Victoria 3001, Australia.
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J. Mater. Res. 3 (6), Nov/Dec 1988
http://journals.cambridge.org
II. EXPERIMENTAL PROCEDURES Experiments were performed on (100) silicon samples having an amorphous surface layer that was formed by implanting 29Si ions (70 keV, 6 x 1014 ions/cm 2 ) at liquid-nitrogen temperature. The layer was partly recrystallized by a thermal anneal at 500 °C for 100 min. This resulted in an amorphous layer extending from the surface to a depth of 750 A with an abrupt amorphous/ crystalline interface that was stable at the temperatures used during subsequent ion-beam irradiations. Beam-induced epitaxial crystallization or planar, layer-by-layer amorphization was induced by irradiation with 1.5 MeV 129Xe, 84Kr, 40Ar, or 20Ne ions in a nonchanneled direction. Ion doses were chosen in the range 5 x l 0 1 5 - 3 X l 0 1 7 ions/cm 2 to promote a few hundred A of interface movement. During irradiation the target was mount
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