The ability of silicon dioxide to act as a dopant mask in high temperature diffusion is widely used in MEMS device fabrication. The diffusivity of dopants like Boron and Phosphorus is much smaller in silicon dioxide compared to silicon. So silicon dioxide is widely used as a mask to selectively protect areas of silicon that require no doping.
This design interface can be used to calculate the oxide thickness required to mask the high temperature pre-deposition of either Boron or Phosphorus for a given time and temperature. Phosphorous diffuses faster through silicon dioxide and hence a thicker layer of oxide is required to mask Phosphorus. Arsenic diffuses slower than Phosphorus and hence a mask suitable for Phosphorus diffusion will be effective against Arsenic
The plot shows the oxide mask thickness over diffusion time in a log-log plot. This plot is for the selected temperature and the selected dopant. Using the crosshair, the mask thickness for any diffusion time can be found out.