= Solution
Read the straight-line extrapolation on the logarithmic dose axis, rather than the rounded shoulder of the measured curve. The retention and clearing intercepts are approximately $D_0=10$ and $D_{100}=50\,\mathrm{mJ\,cm^{-2}}$. Thus the <photoresist contrast> is
$$
\boxed{\gamma=\frac{1}{\log_{10}(50/10)}=1.43.}
$$
Here the subscripts denote the two dose thresholds used in the supplied definition. The physical positive-resist curve decreases with exposure; $D_{100}$ is the higher clearing dose in that definition, not a statement that the film retains its full thickness there. Graphical intercepts justify roughly two significant figures.
Back to article page
