Spatial Metrology of Dopants in Silicon with Exact Lattice Site Precision

TL;DR

This paper introduces a precise metrology combining low-temperature STM imaging and quantum modeling to determine the exact lattice site positions of subsurface dopants in silicon, crucial for nanoelectronics and quantum computing.

Contribution

It develops a novel method to pinpoint subsurface dopant locations in silicon with atomic precision using combined experimental and theoretical techniques.

Findings

Successfully identified lattice sites of dopants up to 36 atomic layers deep.

Achieved high accuracy in dopant positioning for both phosphorus and arsenic in silicon.

Demonstrated the technique's potential for nanoscale device optimization.

Abstract

The aggressive scaling of silicon-based nanoelectronics has reached the regime where device function is affected not only by the presence of individual dopants, but more critically their position in the structure. The quantitative determination of the positions of subsurface dopant atoms is an important issue in a range of applications from channel doping in ultra-scaled transistors to quantum information processing, and hence poses a significant challenge. Here, we establish a metrology combining low-temperature scanning tunnelling microscopy (STM) imaging and a comprehensive quantum treatment of the dopant-STM system to pin-point the exact lattice-site location of sub-surface dopants in silicon. The technique is underpinned by the observation that STM images of sub surface dopants typically contain many atomic-sized features in ordered patterns, which are highly sensitive to the details of the STM tip orbital and the absolute lattice-site position of the dopant atom itself. We demonstrate the technique on two types of dopant samples in silicon -- the first where phosphorus dopants are placed with high precision, and a second containing randomly placed arsenic dopants. Based on the quantitative agreement between STM measurements and multi-million-atom calculations, the precise lattice site of these dopants is determined, demonstrating that the metrology works to depths of about 36 lattice planes. The ability to uniquely determine the exact positions of sub-surface dopants down to depths of 5 nm will provide critical knowledge in the design and optimisation of nanoscale devices for both classical and quantum computing applications.