Explosive Recrystallization of Ion Implantation Amorphous Silicon Layers
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Symp. Proc. Vol. 13 (1983) Published by Elsevier Science Publishing Co., Inc.
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EXPERIMENTAL Silicon single crystals (having orientations, resistivity 2-6 a-cm, 0.5 mmVhickN were amorphized by 75As+ ion implantation (100 keV, dose = 5.0 x 10l' cm- ). This leads to the formation of 1300 A thick amorphous layer followed by a "200 A wide band containing dislocation loops. These specimens were treated with CWAr+ laser operating in mu3timode. The diameter of the Gaussian shaped laser spot was 60-70 pm at 1/e . The power of the laser beam varied from 15 to 20 watts and the scanning velocity from 150 to 300 cms" 1 . The electron beam irradiation was performed with a 8 Pm (at 1/e 2 ) diameter beam, which was scanned at 150 to 200 cms- 1 . The maximum power of the electron beam was 6 watts. RESULTS AND DISCUSSION The nature of explosive crystallization induced by electron or laser beams is basically similar, although the power and scanning velocity required to induce XCR are different in the two cases due to differences in the heat deposition. The absorption of laser light depends upon the optical properties of near surface layers, but usually the energy is deposited in -100 A thick surface region. The energy deposition in the case of electron beams is determined by electronic stopping power. The width of e--beam recrystallized region in Fig. 1 is considerably smaller than that due to the laser beam because of corresponding differences in the beam diameter. Figure 1 contains explosively recrystallized crescents with average periodicity of 3.0 pm. It is interesting to note that the next explosive event starts immediately after the end of the preceding one. The surface morphology of recrystallized areas was found to be smooth. Figure 2 shows ending and beginning of an explosive event or explosion at a higher magnification. At the beginning of an explosion, the region is dominated by high number density of nuclei, as shown at n. It is envisaged that a highly undercooled state of molten silicon in the region provides a large driving force for nucleation. Some of these nuclei can develop a crystallization front and sustain the growth which is derived by the release of heat of crystallization. The top left corner of the micrograph contains termination of an explosive event, where the average grain size is considerably smaller than that between the source and the termination point. Figure 3 shows termination or quenching of explosive recrystallization in the amorphous region. The boundary between the recrystallized and amorphous regions is sharp. Although the regions near the end have finer grains but contain no amorphous zones. This point was confirmed by detailed STEMomicrodiffraction studies where diffraction information from the areas < 400 A diameter could be obtained. The texture which is characterized by orientation normals to the recrystallized layers and the crystallizing interface, is of particular interest during XCR because it provides information on unseeded crystallization. Figure 4(b) shows a microdiffraction pa
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