Crystallization of Isolated Amorphous Zones in Semiconductor Materials
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Crystallization of Isolated Amorphous Zones in Semiconductor Materials Eric P. Hollar, Ian M. Robertson, and Igor JenþLþ* University of Illinois, Dept. of Materials Science and Engineering, 1304 W. Green Street, Urbana, IL 61801, U.S.A. * -RåHI6WHIDQ,QVWitute, Jamova 39, 1000 Ljubljana, SLOVENIA.
ABSTRACT Crystallization of spatially isolated amorphous zones in Si, Ge, GaP, InP and GaAs was stimulated thermally and by irradiation with electrons and photons. The amorphous zones were created by a 50 keV Xe+ implantation. Significant thermal crystallization occurred at temperatures greater than 425 K, 375 K and 200 K in Si, Ge and GaAs, respectively. Electrons with energies between 25 and 300 keV stimulated crystallization in all materials at temperatures between 90 K and room temperature. For electron energies above the displacement threshold, the crystallization rate decreased as the electron energy decreased. As the electron energy was decreased below approximately 100 keV, the crystallization rate unexpectedly increased. The crystallization rate was independent of temperature for all electron irradiations. Irradiation with a 532 nm green laser (K = 2.33 eV) caused crystallization in Si (Eg = 1.11 eV) and Ge (Eg = 0.67 eV) at a rate comparable to a thermal anneal at 425 K and 375 K, respectively, and caused minimal crystallization in GaP (Eg = 2.26 eV). The electron and photon irradiation results are consistent with the model that crystallization is controlled by defects (dangling bonds and kinks) created by electronic excitation at the amorphous-crystalline interface.
INTRODUCTION Phase transformations in semiconductors are both scientifically interesting and technologically important. For example, understanding the crystalline to amorphous and the amorphous to crystalline transformations became an industrial priority with the widespread implementation of ion-implantation in integrated circuit fabrication. Collisions from impinging energetic ions and lattice atoms produce structural damage (extended defects and amorphous material) and cause undesired changes of electrical properties. For most applications, the damage produced by ion implantation must be removed before the device can be made operational, e.g., the amorphous material has to be crystallized. The amorphous to crystalline transition in semiconductor materials can be stimulated either thermally [1] or by irradiation with energetic particles [2-4]. While thermal crystallization seems well-characterized [1,5,6], there exists some questions about the mechanism(s) responsible when crystallization is induced by energetic particle bombardment. Also, the extent and geometry of the amorphous damage is important. Continuous amorphous layers are more resistant to crystallization than isolated amorphous zones created by low dose, heavy ion irradiations. For example, in silicon amorphous zones produced by a 30 keV Bi ion implantation begin to recrystallize at 425 K [7] compared to / 740 K for a continuous amorphous layer [1,8]. Similarly, electrons with energy b
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