What is it about?

The relentless scaling of semiconductor devices pushes the doping level far above the equilibrium solubility, yet the doped material must be sufficiently stable for subsequent device fabrication and operation. We use microwave annealing to selectively activate metastable phosphorus-vacancy clusters by interacting with their dipole moments, while keeping lattice heating below 700 °C. Compared with conventional rapid thermal annealing, microwave annealing can result in 25% lower sheet resistance and three times higher stability at 700 °C.

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Why is it important?

Microwave dopant activation may enable the silicon CMOS technology to scale from 3 nm to 2 nm and from FinFETs to gate-all-around 3D-stacked nanosheet FETs.

Perspectives

When a lattice is doped above the solubility limit, it is only natural for the excess dopants to be compensated by point defects in order to reduce the overall lattice strain. To cheat nature, we can use microwave to force apart the dopant-defect clusters without lattice heating or diffusion-induced junction broadening. This unique feature of microwave dopant activation may allow us to achieve extreme doping levels not only with different dopants but also in different semiconductors. Beyond semiconductors, there may be many other ways to take advantage of this unique feature of microwave annealing. For example, we are currently investigating the use of microwave in stopping the yeast action in wine making without an off taste such as after conventional pasteurization.

James Hwang
Cornell University

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This page is a summary of: Efficient and stable activation by microwave annealing of nanosheet silicon doped with phosphorus above its solubility limit, Applied Physics Letters, August 2022, American Institute of Physics, DOI: 10.1063/5.0099083.
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