Silicon dioxide mask for high temperature diffusion

temp      diffusion temperature in °C
time       diffusion time in min
dop         type of the dopant, select Boron or Phosphorus


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. 


-Doping is in the absence of hydrogen, fluorine or other impurities..
-The dopants diffuse uniformly through the oxide.
-The concentration of the dopant on the surface of the oxide is constant.
-The source of the dopant is vapor based with an ambient nitrogen atmosphere.
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Process > Diffusion > Diffusion mask

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