Measurement of phosphorus segregation in silicon at the atomic-scale using STM

TL;DR

This study investigates phosphorus atom segregation in silicon at the atomic scale, demonstrating that encapsulation with epitaxial silicon at room temperature significantly reduces surface phosphorus density, with STM providing atomic-scale insights.

Contribution

It introduces a method to minimize phosphorus segregation during silicon encapsulation and highlights STM's advantage over SIMS and AES for atomic-scale analysis.

Findings

Phosphorus surface density can be reduced to a few percent of initial levels.

Encapsulation with 5 or 10 monolayers at room temperature is effective.

STM provides atomic-scale characterization of phosphorus segregation.

Abstract

In order to fabricate precise atomic-scale devices in silicon using a combination of scanning tunnelling microscopy (STM) and molecular beam epitaxy 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$^{\circ}$C and room temperature using secondary ion mass spectrometry (SIMS), Auger electron spectroscopy (AES), 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 or 10 monolayers of epitaxial silicon at room temperature. We highlight the limitations of SIMS and AES to determine phosphorus segregation at the atomic-scale and the advantage of using STM directly.