Crystallization and Regrowth of Amorphous Si

During ion implantation, each ion produces a region of disorder around the ion track. As the implantation dose increases, the disorder increases until all the atoms have been displaced and an amorphous layer is produced over a depth Rp. The buildup and saturation of disorder are shown in Fig. 10.1 for 40 keV phosphorus ions incident on Si. In this example, about 4 x 1014 phosphorus ions cnT2 are required to form an amorphous layer. Except for low doses or implantation with light ions, we can anticipate that an amorphous layer is formed during the implantation process. This assumes that no recovery of lattice order occurs around the ion track. 

This figure shows, for ions of various mass implanted at different temperatures, the energy density that must be deposited per unit volume through nuclear collision processes to produce a continuous amorphous layer. At low temperatures 

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Current research interest is in the solid phase epitaxial regrowth of amorphous Si using laser processing. RBS has been used to follow the melting and recrystallization of the crystal-amorphous interface (12). This is accomplished by monitoring the backscattered spectrum+with the substrate oriented in a direction that will allow the He to channel along the crystal planes. 

Channeling measurements have been used to study the epitaxial regrowth of Ge and Si crystals amorphized by ion implantation for a variety of crystal orientations (Csepregi et al. 1977). These studies have shown that, with the exception of (111) orientated Si crystals and samples cut within 16° of the (111) direction, the amorphous/crystal interface moves with a constant velocity toward the surface (at a fixed annealing temperature) and maintains a laterally uniform front. 

The effects of damage by ion implantation on the low-temperature diffusion of dopant can also be studied by implanting Si+ or Ge+ ions into predeposited layers in Si. Recently, Servidori et al. (58) studied the influence of lattice defects induced by Si+ implantation. Using triple crystal X-ray diffraction and TEM, they confirmed (1) that below the original amorphous surface-crystal interface, interstitial dislocation loops and interstitial clusters exist and (2) that epitaxial regrowth leaves a vacancy-rich region in the surface. 

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