Discussion
Distribution of implanted impurity ions by Ion implantation method is :
Answer: B
The implanted ions are distributed in a Gaussian profile.
Each ion loses energy through random collisions, so the depths at which they stop are spread around a mean, the projected range Rp, with a standard deviation called the straggle \(\Delta R_{p}\). To a first approximation the concentration is
\[ \begin{aligned} N(x) &= N_{p}\, e^{-(x - R_{p})^{2}/2\Delta R_{p}^{2}} \\ N_{p} &= \frac{Q}{\sqrt{2\pi}\,\Delta R_{p}} \end{aligned} \]
where Q is the implanted dose. It is not constant, because the peak is below the surface; not parabolic; and, although each stopping event is random, the resulting distribution is not described as random but as Gaussian.
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