In the ion implantation process, positively charged ions impact on the semiconductor surface. Normally these ions are neutralized by capturing an electron from the conducting substrate.

However, when the mask is an insulator like SiO₂, the charge on the ions may not be neutralized as easily.

Consider the case where a dose Q is implanted into the surface of an SiO₂ layer (assume all the charge re-sides at the oxide surface).

Further assume that the oxide can withstand an electric field of 10⁷ Vcm^-1 before it breaks down.

What implant dose Q is required to cause electrical failure of the mask?

That is, what dose will cause a field of 10⁷ Vcm^-1 across the oxide?