Abstract
This thesis mainly discusses some factors that have the influence on the formation of the nickel disilicide. The factors investigated here include (1) the surface cleanness, (2) the very thin Ge layer, and (3) the Ge overlayer. The abstract of the individual topic is listed in sequence. The amount of the oxide on the surface is controlled by the surface cleaning temperature or by flowing condition of the oxygen gas on the cleaned surface. Here, three types of structures of NiSi2 phase, which include the inverted-hut structure containing only the A-type NiSi2/Si interfaces, the parallel-epipedal structure, and the nanowire structure containing the B-type NiSi2/Si interfaces, can be observed. The formation of these three kinds of structures is affected by the surface thermal cleaning process, the growth temperature, the deposition rate of Ni, the deposited thickness of Ni, the amount of oxide on the surface, and the post-annealing process. As the inverted-hut structures nucleate first and continue to grow until reaching areas with the oxide, the B-type interfaces related structures form. The appearance of the B-type interfaces related structure accompanies the shrinkage of the aspect ratio in the inverted-hut structure. Atomic model is proposed to explain that the existence of the oxygen on the metastable adsorption site of the Si surface can lead to the formation of B-type NiSi2(111)/Si(111) interface. The effect of a very thin Ge layer on the growth of the epitaxial NiSi2 islands using reactive deposition epitaxy is investigated. It was found that the prescence of a 0.2 nm-thick Ge on Si(001) substrate increases the surface diffusion length of Ni adatoms. Therefore, the density and the size of NiSi2 islands is lower and greater, respectively. Compared with the NiSi2 islands grown on the Si without the thin Ge layer, the aspect ratio of the NiSi2 islands, formed on Si substrate with the 0.2 nm Ge interlayer, is distributed close to 1. In addition, it was observed that the NiGe phase forms near the surface and surrounds the top part of silicide. The effects of Ge overlayers on the reaction of one monolayer of Ni on Si(001) substrate using solid state reaction were investigated. After the deposition of Ni and Ge, the samples were then ex-situ annealed at 400-800 oC. The reaction process began with dissolution of the Ni atoms into the amorphous Ge layer. Then, solid phase epitaxy of the amorphous layer was observed. The Ni atoms were expelled from the crystallized region and redistributed in the amorphous region. Until the concentration of Ni in the amorphous Ge layer exceeded the solubility limit, the Ni atoms diffused through the crystallized Ge layer and reacted with the substrate to form NiSi2. The NiSi2 phase formation was kinetically controlled by the rate of solid phase epitaxy of the Ge overlayers for the reaction system.