Diode edge effect on doping-profile measurements

Diode edge effects can be a source of error in doping profile measurements made by the capacity versus voltage technique or CIP technique. A numerical calculation indicates that for uniform doping the apparent doping will be higher than the actual doping by a factor of
(1 +bx/r)^{3}
where
b=1.5
and
x/r
is the ratio of depth
x
to diode radius
r
. Comparison with other sources of error shows that edge-effect error will be the largest error when the diode diameter is greater than 10 mils (250 µm) because this error decreases at the slowest rate as the diameter increases (as the reciprocal of the diameter rather than the reciprocal of the diameter squared).