Dopant profiling based on scanning electron and helium ion microscopy

In this paper, we evaluate and compare doping contrast generated inside the scanning electron microscope (SEM) and scanning helium ion microscope (SHIM). Specialised energy-filtering techniques are often required to produce strong doping contrast to map donor distributions using the secondary electron (SE) signal in the SEM. However, strong doping contrast can be obtained from n-type regions in the SHIM, even without energy-filtering. This SHIM technique is more sensitive than the SEM to donor density changes above its sensitivity threshold, i.e. 10¹⁶ or 10¹⁷ donors cm^-3 respectively on specimens with or without a p-n junction; its sensitivity limit is well above 2×10¹⁷ acceptors cm^-3 on specimens with or without a p-n junction. Good correlation is found between the widths and slopes of experimentally measured doping contrast profiles of thin p-layers and the calculated widths and slopes of the potential energy distributions across these layers, at a depth of 1–3 nm and 5–10 nm below the surface in the SHIM and the SEM respectively. This is consistent with the mean escape depth of SEs in Si being about 1.8 nm and 7 nm in the SHIM and SEM respectively, and we conclude that short escape depth, low energy SE signals are most suitable for donor profiling.

doping contrast, secondary electron energy filtering, sensitivity limit, electric potentials, escape depth, p-n junction

10.1016/j.ultramic.2015.10.003

0304-3991

1-18

Chee, Augustus K.W.

58d02d5b-9a0b-4c2c-aa4c-d17037f350d1

Boden, Stuart A.

83976b65-e90f-42d1-9a01-fe9cfc571bf8

19 October 2015

Chee, Augustus K.W.

58d02d5b-9a0b-4c2c-aa4c-d17037f350d1

Boden, Stuart A.

83976b65-e90f-42d1-9a01-fe9cfc571bf8

Chee, Augustus K.W. and Boden, Stuart A. (2015) Dopant profiling based on scanning electron and helium ion microscopy. Ultramicroscopy, 1-18. (doi:10.1016/j.ultramic.2015.10.003).