Atomic-Step-Networks For Nanopatterning On Si Surfaces

Abstract

Nonlithographic methods of nanofabrication and nanopatterning will be needed for integration of future devices that will be based on new concepts such as quantum effects and single electron charging effects. In nonlithographic techniques, nanostructures are fabricated by self-organization processes. In order to apply these techniques to integrated devices, a template is needed for the nanostructure formation. Because crystal growth and chemical reactions are often initiated at atomic steps, they are the basic surface structure that can be used for a template. One example is quantum-dots grown at the steps during the Stranski-Krastanow growth mode. If the atomic step arrangement on the initial surface can be artificially designed, a quantum dot network can be organized in an orderly manner. Therefore, step arrangement control is one of the key technologies in non lit hog rap hic patterning. Step arrangement on S i ( l l 1 ) surfaces in equilibrium state is determined by the misorientation direction of the substrate and its angle: various types of step arrangement can be obtained.',') For application to integrated devices, the steps must be controlled on a wafer scale. For this purpose, we have developed step rearrangement techniques in which the step motion is controlled by etched patterns fabricated by the conventional lithography and e t~h ing .~ .~) This technique can provide us with atomic-step networks for the templates of self-organized nanostructures. The step motions to be controlled in order to fabricate step networks are divided into two categories: step retreat due to detachment of adatoms at the step edges and step advance due to the attachment. When Si surfaces are heated, the adatoms on the terraces evaporate and the shortage of the adatoms is compensated by the detachment of Si atoms at the step edges, resulting in the step retreat. When Si atoms are deposited on the surface, excess adatoms are preferentially incorporated at step edges unless the diffusion length is too short. During this process, step arrangement is modulated to form a specific att tern.^) In this talk, we will show local and wafer-scale step networks formed by step motion controls on patterned and non-patterned Si(l11) surfaces. Although an ultrahigh vacuum is often used to study the fundamental behaviors of the steps, furnace annealing is more suitable when conventional Si technology is used. We will show step networks fabricated by furnace annealing as well as by heating in ultrahigh vacuum.