The effect of implantation conditions on microstructural evolution in oxygen implanted silicon

Ion implantation is used for the fabrication of SIMOX (separation by implanted oxygen). SIMOX is a silicon on insulator structure used for microelectronic devices, where a buried oxide layer insulates a silicon overlayer from the substrate. High energy, high dose oxygen ions are implanted into a heated single crystalline silicon wafer, followed by high temperature annealing to create a uniform buried oxide and eliminate implantation damage.; The final quality of SIMOX material depends on the properties of the silicon overlayer and the buried oxide. The dominant defects are threading dislocations in the silicon overlayer and silicon inclusions (silicon islands) within the buried oxide, both of which are detrimental. The objectives of this dissertation were to evaluate the effect of implantation conditions on the formation of these defects, and to understand the underlying physical mechanisms which govern microstructural evolution in this system.; The effects of implant dose, energy, substrate temperature and beam current variations on microstructural evolution were investigated, primarily, by transmission electron microscopy and x-ray diffraction. Only specific dose ranges yielded low defect density SIMOX. Threading dislocation densities were low for intermediate doses and were high for very low and very high doses. However, low silicon island densities in the buried oxide were obtained at only one specific low dose and at high doses. These dose windows were affected to different extents by the other implantation parameters.; The physical mechanisms for these effects were established. Threading dislocations in the annealed state evolved from dislocation half loops present in the as-implanted state at high doses. The presence of dislocation half loops was a result of strain relief processes in the near surface region during implantation. Threading dislocations at low doses were the result of defect pinning by a bilayer oxide structure.; The precipitate distribution in the as-implanted state controlled the coarsening process during annealing, and thus determined the final morphology of the buried oxide. Severe inhomogeneities in precipitate sizes after implantation led to the formation of silicon islands during annealing. A roadmap for manipulating the implantation parameters to improve SIMOX has been developed based on this mechanistic understanding.