Sub-Microscopic Precipitation of Dopants in Nanoscale Electronic Devices

The different electronic devices in computer chips have more or less the same architecture since about four decades. However, decreasing their size makes them smaller (in a simple explanation, the speed-up comes from the fact that electrons have to travel a shorter distance at constant velocity). At the currently very small dimensions of what has now become nanoelectronics devices, previously spurious effects can become large and domination.

Example: Boron Clustering in Silicon*

One such problem is the nucleation of B-Si precipitates. B atoms are introduced into Si to make it conducting in well defined areas. Miniaturization forces to pack more B into smaller regions, which currently pushes the B concentration above its solubility limit. The accurate prediction of the amount and form of precipitates is important to predict the electrical performance of the device.
Starting from the B-Si phase diagram, we have suggested B icosahedra as the smallest nanocrsytal formed before macroscopic phase separation begins. In a physical multiscale modeling formalism, we have determined the initial nucleation path with ab-initio calculations. Implementation of the resulting continuum model into a partial differential equation solver shows that the formation and dissolution of small clusters – long before Si_1.8B_5.2 macroscopic precipitates start to form – dominate the activation and deactivation of B in Si. Good agreement with experiment confirms our general concept and its application to the nucleation of nanoparticles (Fig. 2).

*X. Y. Liu, W. Windl, and M. P. Masquelier, Appl. Phys. Lett. 77, 2018 (2000).