Micro-Raman analysis of residual stresses and phase transformations in crystalline silicon under microindentation
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Micro-Raman analysis of residual stresses and phase transformations in crystalline silicon under microindentation G. Lucazeau and L. Abello Laboratoire d’Ionique et d’Electrochimie du Solide de Grenoble, ENSEEG-B.P. 75, 38402 Saint Martin d’H`eres Cedex, France (Received 12 June 1995; accepted 12 July 1996)
Vickers microindentations obtained with loads between 0.05 N and 2 N were performed on crystalline (100) silicon. The residual stress field and the different structural states induced by loading were studied by mapping the indented zones by their micro-Raman response. A Raman signature of amorphous silicon is found in the center of the impression. The energy of the G25 zone center phonon is found to vary from 522 cm21 when probing the silicon at a distance of 80 mm from the center of the indentation up to 527 cm21 when probing the pileup region of the impression. When probing cracked zones in the vicinity of the pileup region, wave numbers as high as 536 cm21 are measured. The stress components induced by a point indentation (1 N) have been calculated from analytical expressions given in the literature. For an average conversion factor of 3.2 cm21yGPa, the residual local stresses after unloading are found of the same order of magnitude or even larger than the calculated stresses that are generated during loading. A tentative explanation is proposed. Finally a systematic laser-induced thermal treatment of the central area and of the pileup region of indentations was performed. It is shown that the amorphous silicon in the center can partly recrystallize but that the residual stress state in the pileup region cannot be completely relaxed by local laser heating.
I. INTRODUCTION
Phase transitions in semiconductors induced by high pressure have been extensively studied.1–3 The formation of hexagonal polymorph (Si IV), when submitting crystalline silicon to hot indentations, was reported by several authors.4,5 Also the high pressure polymorphs of silicon and germanium were analyzed by Gridnova and co-workers6 from indentation results. A semiconducting to metallic transition on amorphous silicon and germanium when submitted to high pressures was reported by Shimomura and co-workers.7 Consistent with these experimental results, Gerk and Tabor8 suggested that a semiconducting-metallic transition activated by critical indentation loads takes place in crystalline silicon, germanium, and diamond. Indeed, on single crystals of silicon Gupta and Ruoff,9 using a spherical indentation technique, have detected such a transition and have studied its dependence on both the stress level and direction: these authors have shown that in the (111) direction, the transition was activated at a lower compressive stress than along the (100) direction. More recently, using nanoindentation technique, Pharr et al.10–12 have analyzed the same transition in silicon. The plots of loads versus displacement were found to follow the changes in electrical resistivity and were interpreted in terms of me
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