Measurement of phosphorus segregation in silicon at the atomic scale using scanning tunneling microscopy

In order to fabricate precise atomic-scale devices in silicon using a combination of scanning tunneling microscopy (STM) to position dopant atoms and molecular beam epitaxy to encapsulate the dopants it is necessary to minimize the segregation/diffusion of dopant atoms during silicon encapsulation. We characterize the surface segregation/diffusion of phosphorus atoms from a delta-doped layer in silicon after encapsulation at 250 degreesC and room temperature using secondary ion mass spectrometry (SIMS) and STM. We show that the surface phosphorus density can be reduced to a few percent of the initial delta-doped density if the phosphorus atoms are encapsulated with 5 monolayers of epitaxial silicon at room temperature. We highlight the limitations of SIMS to determine phosphorus segregation at the atomic scale and the advantage of using STM directly. (C) 2004 American Institute of Physics.