| Diffusional processes play an integral role in a wide range of microelectronics fabrication steps. Understanding diffusional processes helps to predict the effects of processing conditions as well as guide in the appropriate selection of these conditions. For bulk diffusion, serious shortcomings associated with the widely used thermal budget concept for modeling rapid thermal processing have been highlighted. A replacement framework accounting for rate selectivity is presented. Experimental and theoretical demonstrations illustrate how this framework will always give the appropriate processing conditions so as to minimize the extent of any undesired process.; For surface diffusion, second ham-ionic microscopy has been utilized to quantify the Arrhenius parameters for diffusion of germanium on silicon at high temperatures. Molecular dynamics simulations provide insight on a picosecond timescale into the complex nature of the mass transfer diffusive process. Two methods of nonthermally modifying surface diffusivities are presented: photon illumination and low-energy ion bombardment. The first direct experimental evidence for photoninfluenced surface diffusion shows a light beam of modest intensity having an energy greater than the silicon bandgap can either increase or decrease both the activation energy and preexponential factor depending on the substrate doping type. The direction of the effect remains independent of adsorbate type (In, Ge or Sb), suggesting that surface vacancy charging controls the behavior. The first quantitative evidence for ion-influenced surface diffusion is presented. Both ion energy and ion mass, along with substrate temperature, play a crucial role in the magnitude of the effect. Experiments show two-regimes to exist: low temperature, where a 65 eV argon beam can provide order-of-magnitude enhancement, and high temperature. Molecular dynamics simulations help confirm the notion that momentum transfer effects control the behavior. In the low-temperature regime, the impinging ion helps to push the germanium adatom along the surface, thereby increasing the average diffusion length. In the high-temperature regime, the impinging ion increases the number of adatom-vacancy pairs on the surface. The increase in vacancy concentration means more sinks exist for germanium adatoms, thus reducing the fraction of mobile germanium adatoms and consequently lowering the diffusivity. |
