Diffusional Phenomena in Microelectronics Processing
Ditchfield, Roderick
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Permalink
https://hdl.handle.net/2142/82459
Description
Title
Diffusional Phenomena in Microelectronics Processing
Author(s)
Ditchfield, Roderick
Issue Date
1998
Doctoral Committee Chair(s)
Seebauer, Edmund G.
Department of Study
Chemical Engineering
Discipline
Chemical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Electronics and Electrical
Language
eng
Abstract
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.
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