Ion Implantation Profile Optimization in Piezoresistive Diaphragms
Implantation energy and post-anneal thermal budgets set piezoresistive sensitivity and offset stability in silicon pressure sensor diaphragms.
Oxide Screen
Barrier Layer
Protective dielectric films on a silicon substrate prevent physical damage and contamination during high-energy processes. During manufacturing, an oxide screen serves to protect the silicon crystal surface from metal contamination and ion implantation damage. This thin layer of silicon dioxide is grown or deposited before the implantation step begins.
Implant Control
The thickness of the protective layer is designed to slow down incoming dopant ions and randomize their direction. When ions pass through the oxide screen, they lose energy and their paths scatter, which helps to prevent the ion channeling effect in the silicon crystal. This scattering ensures a more predictable dopant distribution in the substrate.
Removal Step
After the implantation is complete, the protective layer is removed using a chemical etch. This wet chemical process uses buffered hydrofluoric acid to strip the oxide screen without damaging the silicon substrate.
Thickness Metrology
Spectroscopic ellipsometry is used to measure the thickness and uniformity of the dielectric film. Because even a small deviation in thickness can alter the final junction depth of the implanted dopants, the oxide screen must be measured with sub-nanometer precision. Wafers with oxide thickness outside the allowed range are stripped and re-oxidized before they can proceed to the implantation chamber.